JP4809540B2 - Driving method of liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device typified by a liquid crystal display device and an electronic apparatus in which such a display device is mounted as a component.
[0002]
[Prior art]
In recent years, active matrix liquid crystal display devices using TFTs (Thin Film Transistors) have been widely used in display devices in which a semiconductor thin film is formed over an insulator, particularly a glass substrate. In an active matrix liquid crystal display device, pixels are arranged in a matrix, TFTs are arranged in each of these pixels, the luminance of each pixel is controlled using these TFTs, and an image is displayed.
[0003]
In the active matrix liquid crystal display device, since pixels are individually switched by active elements such as transistors and diodes, high-definition display can be realized without problems such as crosstalk between pixels. Furthermore, it is widely used for personal computers, AV equipment, in-vehicle navigation systems, and portable information terminal applications by taking advantage of its thin and lightweight features.
[0004]
FIG. 14 shows a circuit configuration of an active liquid crystal display device. As an example, an example of a liquid crystal display device using a TFT in which polycrystalline silicon is applied to a semiconductor film is shown. The liquid crystal display device includes a pixel portion and a driver circuit portion arranged around the pixel portion on the same substrate.
[0005]
In the pixel portion, a storage capacitor 204, a pixel TFT 202, and a liquid crystal cell 203 are arranged for each pixel 201. The gate electrode of the pixel TFT of each pixel is G ₁ ~ G _n Are connected to any one of the scanning lines 205 having the address of ₁ ~ S _m The drain is connected to the liquid crystal cell and the storage capacitor. The analog signal input to the signal line is input to the liquid crystal cell and the storage capacitor via the source and drain of the pixel TFT that is turned on by the signal input to the scanning line. Depending on the voltage of the analog signal, the transmittance of the liquid crystal cell changes, and the luminance of each pixel is realized. In this specification, inputting an analog signal to a liquid crystal cell and a storage capacitor through a pixel TFT which is in a conductive state is referred to as “inputting a signal to a pixel”. The address is S _x Signal line and G _y A pixel having a pixel TFT connected to the scanning line is called a pixel having an address (x, y).
[0006]
The drive circuit portion includes a scan side drive circuit 207 that inputs a signal for switching the pixel TFT to a conductive state or a nonconductive state on the scan line, and a signal side drive circuit 208 that inputs an analog signal to the signal line. In order to control these signals, the drive circuit section has a configuration in which a CMOS circuit composed of an n-channel TFT and a p-channel TFT is a basic circuit.
[0007]
Note that in this specification, the element substrate is a substrate provided with TFTs, and the counter substrate is a substrate provided facing the element substrate so as to sandwich the liquid crystal layer.
[0008]
In this specification, a liquid crystal cell refers to a cell having a structure in which a liquid crystal layer is sandwiched between two electrodes with an alignment film interposed therebetween, and the amount of transmitted light is controlled by an electric field. In the case of an active matrix liquid crystal display device, one of two electrodes of a liquid crystal cell is a pixel electrode connected to a pixel TFT, and the other is a counter electrode provided on an element substrate or a counter substrate.
[0009]
The liquid crystal material is burned when a DC voltage is applied for a long time. Burn-in is a phenomenon in which the previous image appears to remain even after switching images. The liquid crystal material is AC driven to change the polarity of the voltage at regular intervals in order to prevent burn-in.
[0010]
In recent years, driving using a field sequential method in which color display is performed using color mixture by time division has been proposed. The field sequential method is a method that performs color display using afterimages that remain in human eyes by switching between red, blue, and green images at high speed in response to blinking of red, blue, and green light sources. is there. Since there is no light absorption by the color filter, a brighter display is possible compared to the color filter method. Furthermore, since the field sequential method has better color purity than the color filter method, it can display with better color reproducibility than the color filter method. In addition, since one pixel can perform color display, it is possible to realize a display that is three times higher than the color filter method (Monthly FPD Intelligence 1999.2. P66 to p69 Press Journal).
[0011]
As described above, the liquid crystal display device is being developed in order to realize a display with high definition, high luminance, and good color reproducibility. In particular, when an active matrix liquid crystal display device is driven by a field sequential method, bright display can be realized with high-definition pixels.
[0012]
[Problems to be solved by the invention]
However, an active matrix liquid crystal display device is expensive because it has many processes, as represented by a semiconductor thin film patterning process, a wiring patterning process, a doping process process, and the like. For this reason, the cost reduction of the transistor manufacturing process is required. As a method of employing a low-cost transistor, it has been proposed to use a transistor with a low breakdown voltage.
[0013]
A driving method that is widely used in liquid crystal display devices maintains the counter electrode at a constant potential as shown in the waveform diagram of FIG. _COM The signal voltage V with reference to (209) _S The polarity of (210) is inverted for each frame to drive the active matrix type liquid crystal display device.
[0014]
However, in such a driving method, it is necessary to increase the withstand voltage of the signal side drive circuit because the range in which the voltage of the signal side drive circuit changes is more than twice the maximum value of the voltage applied to the liquid crystal cell. The process cost was increased.
[0015]
For example, in a liquid crystal display device in which amorphous silicon is used as an active layer of a pixel TFT, in order to increase the amplitude of the signal voltage, it is necessary to increase the breakdown voltage of the transistor in the drive circuit section, and the drive circuit is mainly provided externally. The process cost of the part increased.
[0016]
In a liquid crystal display device using single crystal silicon or polycrystalline silicon as an active body layer, a pixel portion and a drive circuit portion are integrally formed on an element substrate. In order to increase the amplitude of the signal voltage, it is required to increase the breakdown voltage of the transistor in the driver circuit portion, and the process cost for manufacturing the element substrate has increased.
[0017]
As an example of another driving method, as shown in the waveform diagram of FIG. _COM (211) and the potential V of the signal voltage _S There is a method of driving an active matrix liquid crystal display device by alternately inverting (212) in units of one frame. Since the range in which the signal voltage changes can be reduced to less than half that of the driving method shown in FIG. 15, a signal-side driving circuit with a low withstand voltage can be used. In addition, the withstand voltage required for the scanning side drive circuit section decreases as the amplitude of the signal voltage decreases. For this reason, the cost can be reduced regardless of the material of the active layer used for the pixel TFT, such as amorphous silicon, polycrystalline silicon, or single crystal silicon.
[0018]
However, when the potential of the counter electrode is inverted, the luminance of each pixel differs before and after the inversion. The change of this image is demonstrated using FIG. 16 (A)-FIG. 16 (E). FIG. 16 illustrates a signal input to a pixel in a first frame 600 that displays one image and a second frame 601 that is continuous with the first frame.
[0019]
FIG. 16A is a chart showing timing for inputting an analog signal to a pixel. After one line period 602 in which the scanning line is selected, there is a liquid crystal response period 603. The horizontal axis represents time, and the vertical axis represents the scanning line address. Scan line is G ₁ ~ G _n Address. Signals are input to the pixels from the smallest scanning line address to the largest scanning line address.
[0020]
FIG. 16B to FIG. 16C show waveform diagrams for driving each pixel. The horizontal axis represents time, and the vertical axis represents voltage. The potential 604 of the counter electrode is inverted at the boundary between the first frame and the second frame. FIG. 16 (B) shows G ₁ The voltage applied to the pixel connected to the scanning line having the address is shown. In the period 607 from when the potential of the counter electrode is inverted in the second frame to when a signal is input to the pixel, the potential difference between the potential 605 of the pixel electrode and the potential 604 of the counter electrode is in the liquid crystal layer in the image to be displayed. It is determined independently of the applied voltage. FIG. 16C shows the voltage applied to the pixel at the center of the screen. Even in the pixel at the center of the screen, an image unrelated to the image to be displayed is formed in the period 608.
[0021]
FIG. 16D illustrates a lighting period of the light source. The horizontal axis represents time, and the vertical axis represents backlight luminance. Since an illuminating device such as a backlight is always lit, an image different from the display image formed with the reversal of the potential of the counter electrode is recognized by the user as it is and appears to be distorted on the screen.
[0022]
If the image is disturbed each time the potential of the counter electrode is reversed, it will flicker to the human eye when displaying a moving image. However, if the period for reversing the potential of the counter electrode is lengthened, liquid crystal burns and afterimages are generated, and display quality is impaired.
[0023]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a technology for realizing a high-definition and high-luminance display, which is a low-cost liquid crystal display device. .
[0024]
[Means for Solving the Problems]
The present invention combines a field sequential method in which red, green, and blue light sources of a lighting device such as a backlight are intermittently turned on and a driving method that inverts the potential of the counter electrode and applies an AC voltage to the liquid crystal. It is characterized by. According to the present invention, the potential of the counter electrode is inverted during the period when the light source is turned off, and the flicker that occurs at the moment when the potential of the counter electrode is inverted can be prevented from being visually recognized by the user.
[0025]
The field sequential method performs color display by intermittently turning on the light source of the backlight. For this reason, the light source can be turned off when the display image is disturbed as the potential of the counter electrode is reversed. Combining the driving that inverts the potential of the counter electrode and the field sequential method can realize a low-cost liquid crystal display device that does not disturb the image and has good color reproducibility and high image quality. In particular, the field sequential method is suitable for the present invention in which the potential of the counter electrode is inverted at a high frequency because the light source is switched on and off at high speed in an illumination device such as a backlight.
[0026]
Note that in this specification, a frame is a period for forming one color-displayed image, and is composed of a plurality of subframe periods in a field sequential method in which a monochrome image is displayed in a time division manner. A subframe refers to a period in which all the scanning lines in the display area are sequentially scanned from above to display one image.
[0027]
An example of the present invention will be described with reference to FIG. FIG. 1 shows a field sequential driving method. A chart showing the timing of inputting a signal to the pixel and a waveform diagram for driving each pixel are shown.
[0028]
One frame 144 includes a first subframe 145, a second subframe 146, and a third subframe 147. In the chart of FIG. 1A, a scanning line selection period (one line period: 148) and a liquid crystal response period 149 are shown. The horizontal axis is time, and the vertical axis is G ₁ ~ G _n Each address of the scanning line having the address is shown.
[0029]
1 (B) shows G ₁ FIG. 1C shows a signal input to a pixel at the center of the screen, FIG. 1D shows a signal input to an arbitrary pixel connected to the scanning line having the address of FIG. _n A signal input to an arbitrary pixel connected to a scanning line having a predetermined address. A change in the potential of the pixel electrode indicates that a signal is newly input to the pixel.
[0030]
In the present invention, the potential 113 of the counter electrode can be reversed at any time from the start of the selection of the first scanning line to the end of the selection of the nth scanning line in the first subframe. .
[0031]
The pixel electrode potential 112 is adjusted so that an AC voltage is applied to the liquid crystal layer with reference to the inverted potential of the counter electrode. In this way, an AC voltage is applied to the liquid crystal layer for each frame 144, so that liquid crystal burn-in can be suppressed.
[0032]
FIG. 1E shows the lighting timing of the light source. The horizontal axis is time, and the vertical axis is the luminance of the light source. Turn on the red, blue, and green light sources in any order. For example, red is turned on during the period 150 when the light source of the first emission color is turned on, green is turned on during the period 151 when the light source of the second emission color is turned on, and blue is turned on during the period 152 of the light source of the third emission color is turned on. . During the period when all the light sources are turned off, a signal is input to the pixel and the potential of the counter electrode is inverted.
[0033]
In the example shown in FIG. 1, the light source is turned off and the scanning line of the first row is selected at the same time as the first subframe starts, and the potential of the counter electrode is set at the same time as the signal is input to the center pixel of the screen. The light source is turned on after a lapse of time after the selection of the scanning line of the nth row is completed.
[0034]
The driving method of FIG. 1 is characterized in that the potential of the counter electrode is inverted during the period when the light source is turned off in the field sequential driving method using a light source that periodically turns on and off. As a result, inversion of the potential of the counter electrode and image disturbance due to signal input to the pixel are not visually recognized.
[0035]
Further, in the driving method shown in FIG. 1, since the inversion of the counter electrode is performed once per frame, the current consumption due to the inversion of the potential of the counter electrode is not so much. In addition, since the amplitude of the potential of the pixel electrode (signal voltage potential) is less than half that of the conventional driving of FIG. 15, driving with low power consumption can be realized.
[0036]
According to the present invention, one frame has a second period in which the light source is turned on following the first period in which the light source is turned off, and the potential of the counter electrode is inverted in the first period, Applicable to a driving method of a liquid crystal display device, wherein the potential of the pixel electrode is adjusted with reference to the potential of the counter electrode, and the polarity of the voltage applied to the liquid crystal layer changes before and after the potential of the counter electrode is reversed. be able to. This is a method that can be used without being limited to the field sequential method, and is characterized in that the light source is turned off so as to hide the disturbance of the image before and after inversion in the frame in which the potential of the counter electrode is inverted.
[0037]
According to the present invention, one frame includes at least three subframes, and each of the subframes has a second period in which the light source is turned on following the first period in which the light source is turned off. The potential of the counter electrode is inverted during the first period in at least one of the sub-frames, the potential of the pixel electrode is adjusted based on the potential of the counter electrode, and the potential of the counter electrode is inverted. The present invention can be applied to a driving method of a liquid crystal display device in which the polarity of a voltage applied to the liquid crystal layer changes before and after.
[0038]
According to the present invention, one frame includes a first subframe, a second subframe, and a third subframe, and the first subframe, the second subframe, and the third subframe. The frame has a period in which the light source is turned on following the period in which the light source is turned off, and from the start of the selection of the first row scanning line to the end of the selection of the nth scanning line in the first subframe. And the potential of the counter electrode is inverted during the first sub-frame, and the light source is turned on after at least the selection of the n-th scanning line is completed in the first sub-frame. Can do. At this time, the potential of the pixel electrode may be adjusted based on the potential of the counter electrode, and the polarity of the voltage applied to the liquid crystal layer may be changed before and after the potential of the counter electrode is inverted.
[0039]
According to the present invention, one frame includes a first subframe, a second subframe, and a third subframe, and the first subframe, the second subframe, and the third subframe. The sub-frame has a first period and a second period, the light source is turned off during the first period, the light source is turned on during the second period, the first sub-frame, In the second subframe and the third subframe, the potential of the counter electrode is inverted during the first period, and the potential of the pixel electrode is adjusted based on the potential of the counter electrode, so that the voltage applied to the liquid crystal layer The polarity is the same in the first subframe and the third subframe, and the polarity is different in the first subframe and the second subframe. can do.
[0040]
According to the present invention, one frame includes a first subframe, a second subframe, and a third subframe, and the first subframe, the second subframe, and the third subframe. In the period from the selection of the first scanning line to the selection of the nth scanning line, the potential of the counter electrode is inverted,
The light source is turned off at least from the start of selection of the first scanning line to the end of selection of the nth scanning line, and at least after selection of the nth scanning line is completed. The light source starts to light,
The potential of the pixel electrode is adjusted with reference to the potential of the counter electrode, and the polarity of the voltage applied to the liquid crystal layer is the same in the first subframe and the third subframe, and the first subframe And the second sub-frame can be applied to a driving method of a liquid crystal display device.
[0041]
The present invention also provides 2n-1 (n = 1, 2, 3) sub-frames in which one frame displays gradation, and 2n (n = 1, 2, 3) in which the light source is turned off. Consisting of subframes,
In the second n-1 (n = 1, 2, 3) subframe and the second n (n = 1, 2, 3) subframe, the selection of the scanning line of the first row starts, and then the nth row Until the selection of the scanning line is completed, the potential of the counter electrode is reversed,
In the 2n-1 (n = 1, 2, 3) subframe, the light source is turned on after selection of at least the nth scanning line is finished, and the polarity of the voltage applied to the liquid crystal layer is the second n−. The present invention can be applied to driving of a liquid crystal display device characterized in that 1 (n = 1, 2, 3) subframes and 2n (n = 1, 2, 3) subframes are different from each other.
[0042]
The present invention also provides a first subframe and a second subframe for displaying an image, and a third subframe in which a light source sandwiched between the first subframe and the second subframe is turned off. And the potential of the counter electrode is inverted in the third subframe, the potential of the pixel electrode is adjusted with reference to the potential of the counter electrode, and the potential of the pixel electrode is adjusted in the first subframe and the second subframe. The present invention can be applied to a driving method of a liquid crystal display device characterized in that polarities of voltages applied to the liquid crystal layer are different.
[0043]
In the present invention, each of the first frame and the second frame includes a first subframe, a second subframe, a third subframe, and a fourth subframe, and the first subframe is all The second sub-frame has a period during which the first light-emitting color light source is lit, and the third sub-frame has a second light-emitting color light source. The fourth sub-frame has a period in which the light source of the third emission color is lit,
In the first subframe, the potential of the counter electrode is inverted, the potential of the pixel electrode is adjusted with reference to the potential of the counter electrode, and the first frame and the second frame have a voltage applied to the liquid crystal layer. The present invention can be applied to a driving method of a liquid crystal display device having different polarities.
[0044]
In the present invention, known means are used as means for periodically inverting the potential of the counter electrode and means for adjusting the potential of the pixel electrode with reference to the potential of the counter electrode and applying an AC voltage to the liquid crystal layer. be able to. For example, the technique disclosed in JP-A-9-73065 can be used. This technology uses two types of common voltage V _{COM +} And V _COM Are supplied to the selection circuit and one of the common voltages is output in accordance with a control signal input from the control circuit. This publication also discloses a technique for changing the signal voltage input from the signal side drive circuit to the signal line in accordance with the potential of the common voltage.
[0045]
Further, the present invention requires means for turning off the light source of the illumination device before the potential of the counter electrode is reversed. This can be done by changing the timing at which the light source is turned on in accordance with the driving of the present invention in a known technique such as a field sequential backlight. For example, the control circuit is provided in connection with an illumination device such as a backlight and a liquid crystal electro-optical device. The light source is turned on in accordance with a control signal input from the control circuit, and an image is displayed.
[0046]
An illumination device such as a backlight includes a light source that emits red, blue, and green light. A plurality of light sources may be arranged in order to make the luminance distribution in the display area uniform. As the light source, it is preferable to use a cold cathode fluorescent tube, a light emitting diode, or the like that switches on and off at high speed.
[0047]
A method for inputting a signal to a pixel of a liquid crystal display device includes a driving method called dot sequential driving for inputting a signal for each pixel, a driving method called line sequential driving for inputting a signal for each scanning line, and a signal for each image. There is a driving method called “frame sequential driving”. The present invention can be used for any driving method, but it is particularly preferable to apply the method to dot sequential driving or line sequential driving. This is because if the potential of the counter electrode is inverted during the sequential writing of signals to each pixel, display discontinuity occurs before and after the inversion.
[0048]
As the liquid crystal material, ferroelectric liquid crystal, antiferroelectric liquid crystal, nematic liquid crystal, or the like may be used. As an alignment method of the nematic liquid crystal, an IPS method, a TN method, a vertical alignment method, or the like may be used. Any liquid crystal material or liquid crystal alignment method capable of high-speed response can be freely applied to the present invention.
[0049]
Note that the present invention can be applied to both a simple matrix liquid crystal display device and an active matrix liquid crystal display device. Some active matrix liquid crystal display devices use amorphous silicon, polycrystalline silicon, or single crystal silicon for the active layer in the display region, but the present invention can be freely applied regardless of the material of the active layer. Can do.
[0050]
According to the present invention, the amplitude of the signal voltage required for gradation display is reduced by alternating-current driving the counter electrode, and the burden on the signal side drive circuit is reduced. Further, when the amplitude of the signal voltage is reduced, the amplitude of the scanning voltage that determines conduction or non-conduction of the transistor can be reduced, and the burden on the scanning side driving circuit is reduced. For this reason, if the present invention is applied, the transistor of the driver circuit portion and the like can be manufactured with a simple structure, and the process cost of the liquid crystal display device can be reduced.
[0051]
The transistor of the present invention includes a semiconductor film, a gate electrode that overlaps the channel region of the semiconductor film with an insulating film interposed therebetween, and a high-concentration impurity region (source, drain) formed across the channel region of the semiconductor film. This is a simple configuration. Conventionally, a low-concentration impurity region is required between a high-concentration impurity region and a channel region in order to increase the breakdown voltage of a transistor, and a doping process using a resist as a mask has been added, resulting in an increase in process cost. However, the process can be simplified by the driving method of the present invention.
[0052]
According to the present invention, a high-quality display can be performed in a liquid crystal display device manufactured at low cost.
[0053]
The present invention will be described in the following embodiments and examples. Embodiments and examples can be combined with features as appropriate.
[0054]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
This embodiment will be described with reference to FIG. FIG. 1 is a timing chart showing a field sequential driving method.
[0055]
A frame 144 that forms an image for displaying one color includes a first subframe 145, a second subframe 146 that follows the first subframe, and a third subframe 147 that follows the second subframe. It consists of.
[0056]
FIG. 1A is a chart for explaining timing for inputting a signal to a pixel. The horizontal axis represents time, and the vertical axis represents the scanning line address. Scan line is G ₁ ~ G _n Address. G in the first subframe 145 ₁ When a scan line having an address of ₁ The pixel TFT connected to the scanning line having the address becomes conductive. After this, S ₁ ~ S _m A signal is input from the signal line having the address. Here, a period in which one scanning line is selected is referred to as one horizontal period (one line period 148). G ₁ A period during which the scanning line having the address is selected is defined as a first line period. G ₁ When the signal has been input to the pixel having the pixel TFT connected to the scanning line having the address of ₂ All of the pixel TFTs connected to the scanning line having the address are turned on. Thus, signal input from the signal line is started in the second line period.
[0057]
When the above operation is repeated for all the scanning lines and is completed until the nth line period, the input of signals to the pixels in the first subframe 145 is completed.
[0058]
The liquid crystal response period 149 follows the one line period 148. When the response of the liquid crystal starts according to the signal input to the liquid crystal cell and the response of the liquid crystal is completed, the luminance of each pixel is realized.
[0059]
Next, the second sub-frame 146 starts, and a signal is input through the pixel TFT which is in a conductive state by selecting a scanning line every line period, and the liquid crystal responds according to the input signal. When the second subframe ends, a third subframe 147 begins.
[0060]
The third subframe begins and G ₁ When the scanning line having the address is selected, the pixel TFT connected to the scanning line is turned on, and a signal is input from the signal line to the pixel. When this operation is repeated for all the scanning lines and is finished until the nth line period, the input of signals to the pixels in the third subframe is finished.
[0061]
Such an operation is repeated in the next frame, and an image displayed in color is formed for each frame.
[0062]
1 (B) shows G ₁ FIG. 1C shows a pixel at the center of the screen, and FIG. _n For an arbitrary pixel connected to a scanning line having the address, the potential of the electrode sandwiching the liquid crystal layer is shown. In FIG. 1B to FIG. 1D, the potential 112 of the pixel electrode is indicated by a solid line, and the potential 113 of the counter electrode is indicated by a dotted line. In any pixel, an image different from an image to be displayed is formed 153 between when the potential of the counter electrode is inverted and when a signal is input to the pixel and the potential of the pixel electrode is switched.
[0063]
For this reason, as shown in the chart of FIG. 1E showing the timing when the light source is turned on, the light source is turned off simultaneously with the start of the first subframe, and signals are transmitted to all pixels at least in the first subframe. The light source is turned on after input.
[0064]
As an example of another timing of turning on and off the light source, the light source is turned off when the first subframe starts, and at least 90 to 100% of the gradation that the liquid crystal of all the pixels wants to display in the first subframe. It is also possible to start lighting the light source after responding to the brightness of. Thereby, it is possible to ensure good display performance in which gradation display is made accurate.
[0065]
The color temperature of white display of the liquid crystal display device is determined by the time during which the light sources of each color are turned on and the luminance of the light emitted from the light sources. Therefore, the length of the period 151 in which the light source of the second emission color is turned on, the length of the period 152 in which the light source of the third emission color is turned on, and the length of the period 150 in which the light source of the first emission color is turned on. And adjusting the luminance of the light emitted from the light sources of the respective colors to ensure a desired color temperature.
[0066]
When displaying a moving image at 60 Hz, the frame period may be 16.6 msec as usual, and the subframe period may be 5.5 msec. The frame period is determined according to the frequency of the moving image display.
[0067]
Since the potential of the counter electrode is switched during the period when the light source is turned off, image disturbance due to a change in the potential of the counter electrode is not visually recognized by the user, and good display quality can be ensured.
[0068]
[Embodiment 2]
This embodiment will be described with reference to FIG. FIG. 2 shows a field sequential driving method. The difference between Embodiment 1 and Embodiment 2 is that the polarity of the voltage applied to the liquid crystal layer differs for each subframe.
[0069]
One frame 118 includes a first subframe 120, a second subframe 121, and a third subframe 122. Each of the first to third subframes is a subframe that displays a monochrome image. Each of the first to third subframes has a first period 123 in which the light source is turned off and a second period 124 in which the light source is turned on.
[0070]
FIG. 2A shows the timing at which a signal is input to the pixel. The horizontal axis represents time, and the vertical axis represents the scanning line address. In the present embodiment, either a dot sequential drive or a line sequential drive can be used, but a description will be given assuming that a signal is input to the pixel by the dot sequential drive. Since signals are input by dot sequential driving, signals are input in order from the pixel having the smallest address of the signal line to the pixel having the larger address even when the scanning line is selected. When the pixel TFT connected to the scanning line in the first row becomes conductive, S ₁ An analog signal is input from the signal line having the address (1) to the (1, 1) pixel. And sequentially S ₂ Signal line having the address of S _Three Signal line having the address of S _Four A signal is input to the pixel from the signal line having the address. And S _m When a signal is input from the signal line having the address (m, 1) to the pixel (m, 1), the pixel TFT connected to the second scanning line is turned on. Then, an analog signal is input from the signal line to the (m, 2) pixels sequentially from the (1, 2) pixels connected to the scanning line. The same operation is repeated for each scanning line, and when the pixel TFT connected to the n-th scanning line is finally turned on, the pixel having the address (1, n) has the address (m, n) sequentially. A signal is input from the signal line to the pixel, and the input of the signal in the subframe is completed.
[0071]
A liquid crystal response period 148 after one line period 147 in which one scanning line is selected responds according to a signal to which liquid crystal is input.
[0072]
2B is a pixel having an address of (1, 1), FIG. 2C is a pixel at the center of the screen, and FIG. 2D is a pixel having an address of (m, n). The voltage applied to the electrodes sandwiching the liquid crystal layer is shown. The horizontal axis represents time, and the vertical axis represents voltage.
[0073]
AC driving is performed by reversing the potential of the counter electrode. The counter electrode potential 113 is inverted at the beginning of the first period, and the pixel electrode potential 112 is adjusted with reference to the counter electrode potential. The polarity of the voltage applied to the liquid crystal layer after signals are input to all the pixels changes for each subframe, and is the same in the first subframe and the third subframe. 3 sub-frames differ from the second sub-frame.
[0074]
The image is disturbed until the signal input to at least all the pixels is finished after the potential of the counter electrode is inverted. In FIG. 2D, the first subframe 120 is described as an example. T ₀ At the time of (119), the first subframe starts, and at the same time, the potential 113 of the counter electrode is inverted. The disturbance of the image due to the reversal of the potential of the counter electrode is the time T when the signal is input to the (m, n) pixel at the right end of the bottom end of the screen. ₁ Continue to (128). When a signal is input to the pixel (m, n), a potential corresponding to an image to be displayed on all the pixel electrodes is applied with the potential of the counter electrode after inversion as a reference.
[0075]
For this reason, at least the light source is turned off until a signal is input to the pixel (m, n) at the right end of the lowermost end of the display area after the potential of the counter electrode is reversed and an image to be displayed on the entire screen is formed. Need to be.
[0076]
However, since the transmittance of the liquid crystal gradually changes in accordance with the change in voltage, just because a signal is input to the (m, n) pixel does not mean that the image to be displayed is completed. Therefore, in this embodiment, the period 123 during which the light source is turned off is further lengthened, and the light source is kept turned off until the response of all the liquid crystals on the screen is completed after the first subframe starts. Thus, the light source can be turned on after the response of the liquid crystal is completed and one image is formed. FIG. 2E shows a period during which the light source is turned on. The light sources include a light source 125 having a first emission color, a light source 126 having a second emission color, and a light source 127 having a third emission color. The light source is turned on after a signal is input to the pixel connected to the n-th scanning line.
[0077]
That is, when the timings of turning off and turning on the light source and reversing the potential of the counter electrode are summarized, in this embodiment, at the same time as the first subframe starts, the potential of the counter electrode is reversed and the light source is turned off. The light source is turned on after a lapse of time from the selection of the scanning line.
[0078]
The light source turned on in the first subframe is turned off when the second subframe starts. The same lighting and extinguishing operations are repeated in the second subframe and the third subframe.
[0079]
In the present embodiment, one frame has a period of 16.6 msec, and the first to third subframes have a period of 5.5 msec.
[0080]
According to this embodiment, an image irrelevant to the display formed when the potential of the counter electrode is inverted can be prevented from being visually recognized by turning off the light source, and a high-quality display can be realized. In addition, since the polarity of the voltage applied to the liquid crystal layer changes from subframe to subframe, high-frequency AC driving is possible, and flicker caused by feedthrough and asymmetric optical characteristics of the liquid crystal material can be made inconspicuous.
[0081]
Further, not only the potential of the counter electrode is inverted every subframe, but the potential of the counter electrode may be inverted once every two subframes. A cycle in which the potential of the counter electrode is inverted can be appropriately designed in consideration of power consumption, display quality, and the like.
[0082]
[Embodiment 3]
This embodiment will be described with reference to FIG. FIG. 3 shows a field sequential driving method.
[0083]
In a frame 129 that forms one image, a first subframe to a sixth subframe are sequentially formed. The 2n-1 (n = 1, 2, 3) subframes are subframes for displaying gradation, and the first subframe 130, the third subframe 132, and the fifth subframe 134 are included in this. Equivalent to. The second n (n = 1, 2, 3) subframes are subframes in which the light source is turned off and black display is performed, and the second subframe 131, the fourth subframe 133, and the sixth subframe 135 are the subframes. It corresponds to.
[0084]
FIG. 3A shows timing for writing a signal to a pixel. A one-line period 149 and a liquid crystal response period 150 are shown. The horizontal axis represents time, and the vertical axis represents the scanning line address. The driving method of the liquid crystal display device of this embodiment can be point-sequential driving or line-sequential driving. In this embodiment, the driving method of dot-sequential driving is adopted.
[0085]
3B to 3D show signals applied to each pixel. The horizontal axis represents time, and the vertical axis represents voltage. The potential 113 of the counter electrode is indicated by a dotted line, and the potential 112 of the pixel electrode is indicated by a solid line. The potential of the counter electrode needs to be inverted in the period from the selection of the first row scanning line to the selection of the nth scanning line in each of the first to sixth subframes. . In the present embodiment, the potential of the counter electrode is inverted simultaneously with the start of the first subframe. The potential of the pixel electrode is adjusted with reference to the potential of the counter electrode after inversion.
[0086]
3B is a pixel having an address of (1, 1), FIG. 3C is a pixel in the center of the screen, and FIG. 3D is a liquid crystal in a pixel having an address of (m, n). The potential applied to the electrodes sandwiching the layers is shown. The horizontal axis represents time, and the vertical axis represents voltage.
[0087]
In the present embodiment, high-frequency driving is performed in which burn-in is less likely to occur than in the first and second embodiments. This will be described with reference to FIG. The first subframe 130 and the second subframe 131 are taken as an example. T ₀ At the time of (136), the first subframe starts and T ₁ At time (137), the second subframe starts and T ₂ The third subframe starts at (138). Since the potential of the counter electrode is reversed at the same time as the subframe starts, the potential of the counter electrode is T ₀ (136) and T ₁ (At time 137), T ₂ Inverted at time (138).
[0088]
T _Three In the first subframe at the time of (154), T _Four At the time of (155), input of signals to all the pixels is completed in the second subframe. The period from when the signal is input to the pixel until the potential of the counter electrode is inverted (T _Three ~ T ₁ , T _Four ~ T ₂ ), The voltage applied to the liquid crystal layer has the same absolute value and different polarities in the first subframe and the second subframe. For example, the potential difference between the pixel electrode and the counter electrode with reference to the potential of the counter electrode after inversion is an absolute difference between the first potential difference 139 in the first subframe and the second potential difference 140 in the second subframe. The values are the same and the polarities are different.
[0089]
Thus, the 2n-1 (n = 1, 2, 3) sub-frames that are odd frames and the 2n (n = 1, 2, 3) sub-frames that are even frames consecutive to the sub-frames. AC driving is performed to equalize the absolute value of the voltage applied to the liquid crystal layer. In the first subframe and the second subframe, voltages having the same absolute value and different polarities are applied to the liquid crystal layer. The relationship between the third subframe and the fourth subframe and the relationship between the fifth subframe and the sixth subframe are the same.
[0090]
In the present embodiment, the frame period is 16.6 msec, and the period from the first subframe to the sixth subframe is 2.8 msec.
[0091]
FIG. 3E shows a period during which the light source is turned on. In the first subframe, the third subframe, and the fifth subframe, the light source is turned on after selection of the scanning line of at least the n-th column is completed. The display discontinuity that occurs before and after the potential of the counter electrode is reversed is not recognized until the normal image is displayed because the light source is turned off.
[0092]
When the liquid crystal display device employs a liquid crystal that displays black with a voltage of one polarity and whose transmittance is determined according to the voltage of one polarity, like the liquid crystal having voltage-transmittance characteristics shown in FIG. In addition, the driving method according to the present embodiment is a driving method that should be employed in order to prevent burn-in and display with good display quality. The driving according to the present embodiment not only can prevent burn-in by performing high-frequency AC driving, but also the brightness in the first subframe and the second subframe appears to be averaged. This is because the key can be displayed. Of course, the liquid crystal material used in the present embodiment is not limited to the liquid crystal material having the voltage-transmittance characteristics shown in FIG. 5 and can be appropriately selected.
[0093]
The liquid crystal material having the voltage-transmittance characteristics shown in FIG. 5 is a polymer stabilization that eliminates the hysteresis of the smectic liquid crystal by polymerizing the ferroelectric liquid crystal CDR2402 manufactured by Clariant and the liquid crystalline polymer mixed in the smectic liquid crystal. A typical example is liquid crystal (monthly FPD Intelligence 1999.2. P78-p80 Press Journal).
[0094]
In the liquid crystal material having the voltage-transmittance characteristics shown in FIG. 5, the light source such as the backlight is turned on only in an odd frame in which the transmittance is determined according to the voltage. That is, the light source 141 of the first emission color is turned on in the first subframe, the light source 142 of the second emission color is turned on in the third subframe, and the third emission color light source 142 is turned on in the fifth subframe. The light source 143 may be turned on.
[0095]
In order to perform color display using light sources of red, blue, and green which are additive primary colors, in this embodiment, the light source of the first emission color is red, the light source of the second emission color is green, and the third light emission. The color light source is blue.
[0096]
In the present embodiment, since the first voltage 139 is applied to the liquid crystal layer in the odd-numbered subframe and then the second voltage 140 having the same absolute value and the same polarity as the first voltage is applied in the even-numbered subframe, Can be effectively canceled out. For this reason, image sticking can be suppressed in a liquid crystal having spontaneous polarization such as a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal.
[0097]
[Embodiment 4]
This embodiment will be described with reference to FIG. FIG. 4 is a timing chart showing a field sequential driving method.
[0098]
The first frame 100 and the second frame 101 display one color-displayed image. In the present embodiment, it is preferable that the first frame and the second frame have a period of 16.6 msec to 33.3 msec in order to display a moving image of 30 to 60 Hz. In the present embodiment, one frame has a period of 16.6 msec.
[0099]
Since the display is performed by the field sequential method, a monochrome image is displayed in the subframe, and a color display image is formed in one frame from the monochrome image displayed in time division. In the present embodiment, a subframe (first subframe) in which all light sources are turned off is provided before a subframe (second subframe to fourth subframe) for displaying a monochrome image. .
[0100]
The first frame is subsequent to the first subframe 102, the second subframe 103 subsequent to the first subframe, the third subframe 104 subsequent to the second subframe, and the third subframe. And the fourth subframe 105. Similarly, the second frame includes a first subframe 106, a second subframe 107 subsequent to the first subframe, a third subframe 108 subsequent to the second subframe, and a third subframe. It consists of a fourth subframe 109 following the subframe.
[0101]
In the first subframe, the subframe period can be freely determined. However, in consideration of the speed at which a signal is input from the driver circuit to the pixel and the response time of the liquid crystal, the first subframe is preferably set to a period of 1 msec to 8.3 msec. In the present embodiment, the first subframe has a period of 4.15 msec.
[0102]
The second subframe, the third subframe, and the fourth subframe preferably have the same subframe period. In order to display a moving image of 30 to 60 Hz, the period from the second subframe to the fourth subframe is preferably 2.7 msec to 7.3 msec. In the present embodiment, the second subframe, the third subframe, and the fourth subframe have a period of 4.15 msec.
[0103]
In the present embodiment, the periods of the second subframe, the third subframe, and the fourth subframe are equal to the period of the first subframe. However, the present invention is not necessarily limited to this. Absent.
[0104]
FIG. 4A shows timing for inputting a signal to a pixel. The horizontal axis represents time, and the vertical axis represents the scanning line address. Following the one-line period 110 for selecting the scanning line, there is a liquid crystal response period 111 in which the liquid crystal responds according to the voltage of the analog signal input from the signal line.
[0105]
4B to 4D show waveform diagrams for driving each pixel. The horizontal axis indicates time, and the vertical axis indicates voltage. 4 (B) shows G ₁ FIG. 4C shows a pixel at the center of the screen, and FIG. 4D shows G for an arbitrary pixel connected to the scanning line having the address of FIG. _n For an arbitrary pixel connected to a scanning line having the address, the potential of the electrode sandwiching the liquid crystal layer is shown. 4B to 4D, the potential 112 of the pixel electrode is indicated by a solid line, and the potential 113 of the counter electrode is indicated by a dotted line.
[0106]
In the first subframe 106 of the second frame, the potential 113 of the counter electrode is inverted. The potential of the pixel electrode 112 is adjusted with reference to the potential of the counter electrode after inversion in the first frame before inversion and in the second frame. In order to prevent liquid crystal burn-in, voltages having different polarities are applied to the liquid crystal layer in the first frame and the second frame. Since the voltage applied to the liquid crystal layer is the difference between the potential 112 of the pixel electrode and the potential 113 of the counter electrode, a negative voltage is applied to the liquid crystal layer in the first frame 100 and a positive voltage is applied to the liquid crystal layer in the second frame 101. AC drive is performed.
[0107]
The signal input to the pixel in the first subframe 102 in which all the light sources are turned off is preferably the same signal as the signal input to the pixel in the second subframe 103 that forms a monochrome image. In a liquid crystal whose alignment state is determined according to a potential difference such as a nematic liquid crystal, the potential difference of the voltage applied to the liquid crystal in the second subframe is made equal to the potential difference 114 of the voltage applied to the liquid crystal in the first subframe. Thus, the alignment state in the second subframe is determined soon.
[0108]
FIG. 4E shows the timing of turning on the light source in an illumination device such as a backlight having a plurality of light sources having different emission colors. The light source is preferably one that can be switched on and off at high speed. For example, a cold cathode fluorescent tube or a light emitting diode can be used.
[0109]
In the second subframe, red is emitted during the period 115 when the first emission color is lit, green is emitted during the period 116 when the second emission color is lit during the third subframe, and third emission is performed during the fourth subframe. Blue is lit during the period 117 during which the color is lit. In the first subframe, the voltage applied to the liquid crystal changes discontinuously before and after the potential of the counter electrode is inverted. Since an image irrelevant to the image to be displayed is formed, the screen is disturbed. Therefore, the turbulent image is prevented from being visually recognized by keeping the light source off in the first subframe. This operation of turning on and off is repeated periodically.
[0110]
By combining the color sequential display method using the field sequential method and driving for inverting the potential of the counter electrode, discontinuous image display before and after the potential of the counter electrode is inverted cannot be recognized. This is because all the light sources are turned off in the first subframe where the potential of the counter electrode is inverted.
[0111]
This embodiment is different from the first to third embodiments in that all light sources are turned off in the first subframe. In the case where it takes time until the liquid crystal responds to the gradation to be displayed by reversing the potential of the counter electrode, inputting a signal to the pixel, and changing the voltage applied to the liquid crystal twice in a short period of time. A driving method should be adopted. Since the light source is turned on after the response of the liquid crystal is completed, the gradation display is accurate and more colors can be displayed in the color display image.
[0112]
In addition, if the number of times of inputting a signal is reduced, input of a signal to a pixel may be omitted in the second subframe. Since the liquid crystal cell of each pixel already has a potential difference corresponding to the image displayed in the second subframe in the first subframe, an image to be displayed without newly inputting a signal to the pixel in the second subframe A potential difference corresponding to is already applied to the liquid crystal layer. In this way, the power consumption can be reduced by omitting the input of the analog signal to the signal line and the input of the pulse signal to the scanning line.
[0113]
[Embodiment 5]
An embodiment of the present invention will be described with reference to FIGS. Here, a method for simultaneously manufacturing the pixel TFT and the storage capacitor of the pixel portion and the TFT of the driver circuit portion provided around the display region will be described in detail according to the process. However, in order to simplify the description, a CMOS circuit which is a basic configuration circuit is illustrated in the drive circuit portion, and an n-channel TFT is illustrated in a cross section along a certain path in the pixel TFT of the pixel portion. To do.
[0114]
First, as shown in FIG. 6A, a silicon oxide film is formed on a substrate 400 made of glass such as barium borosilicate glass represented by Corning # 7059 glass or # 1737 glass, or aluminoborosilicate glass. A base film 401 made of an insulating film such as a silicon nitride film or a silicon oxynitride film is formed. For example, SiH by plasma CVD method _Four , NH _Three , N ₂ A silicon oxynitride film 401a made of O is formed to 10 to 200 nm (preferably 50 to 100 nm) and similarly SiH _Four , N ₂ A silicon oxynitride silicon film 401b formed from O is stacked to a thickness of 50 to 200 nm (preferably 100 to 150 nm). Although the base film 401 is shown as a two-layer structure in this embodiment, it may be formed as a single-layer film of the insulating film or a structure in which two or more layers are stacked.
[0115]
The island-shaped semiconductor films 402 to 406 are formed using a crystalline semiconductor film formed by using a laser crystallization method or a known thermal crystallization method from a semiconductor film having an amorphous structure. The island-shaped semiconductor films 402 to 406 are formed to a thickness of 25 to 80 nm (preferably 30 to 60 nm). There is no limitation on the material of the crystalline semiconductor film, but the crystalline semiconductor film is preferably formed of silicon or a silicon germanium (SiGe) alloy.
[0116]
In order to fabricate a crystalline semiconductor film by laser crystallization, a pulse oscillation type or continuous emission type excimer laser, YAG laser, YVO _Four Use a laser. When these lasers are used, it is preferable to use a method in which laser light emitted from a laser oscillator is linearly collected by an optical system and irradiated onto a semiconductor film. Crystallization conditions are appropriately selected by the practitioner. When an excimer laser is used, the pulse oscillation frequency is 30 Hz and the laser energy density is 100 to 400 mJ / cm. ² (Typically 200-300mJ / cm ² ). When a YAG laser is used, the second harmonic is used and the pulse oscillation frequency is 1 to 10 kHz, and the laser energy density is 300 to 600 mJ / cm. ² (Typically 350-500mJ / cm ² ) Then, laser light condensed linearly with a width of 100 to 1000 μm, for example, 400 μm, is irradiated over the entire surface of the substrate, and the superposition ratio (overlap ratio) of the linear laser light at this time is 80 to 98%.
[0117]
Next, a gate insulating film 407 that covers the island-shaped semiconductor films 402 to 406 is formed. The gate insulating film 407 is formed of an insulating film containing silicon with a thickness of 40 to 150 nm by using a plasma CVD method or a sputtering method. In this embodiment, a silicon oxynitride film having a thickness of 120 nm is formed. Needless to say, the gate insulating film is not limited to such a silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure. For example, when a silicon oxide film is used, TEOS (Tetraethyl Ortho Silicate) and O ₂ The reaction pressure is 40 Pa, the substrate temperature is 300 to 400 ° C., and the high frequency (13.56 MHz) power density is 0.5 to 0.8 W / cm. ² And can be formed by discharging. The silicon oxide film thus manufactured can obtain good characteristics as a gate insulating film by subsequent thermal annealing at 400 to 500 ° C.
[0118]
Then, a first conductive film 408 and a second conductive film 409 for forming a gate electrode are formed over the gate insulating film 407. In this embodiment, the first conductive film 408 is formed with TaN to a thickness of 50 to 100 nm, and the second conductive film 409 is formed with W to a thickness of 100 to 300 nm.
[0119]
When forming a W film, it is formed by sputtering using W as a target. In addition, tungsten hexafluoride (WF ₆ It can also be formed by a thermal CVD method using In any case, in order to use as a gate electrode, it is necessary to reduce the resistance, and the resistivity of the W film is desirably 20 μΩcm or less. The resistivity of the W film can be reduced by increasing the crystal grains. However, when there are many impurity elements such as oxygen in W, crystallization is hindered and the resistance is increased. Therefore, in the case of sputtering, the resistivity is obtained by using a W target with a purity of 99.9999% and forming a W film with sufficient consideration so that impurities are not mixed in the gas phase during film formation. 9-20 μΩcm can be realized.
[0120]
In the present embodiment, the first conductive film 408 is TaN and the second conductive film 409 is W. However, any of the elements selected from Ta, W, Ti, Mo, Al, and Cu, or the element You may form with the alloy material or compound material which has as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. As a combination other than the present embodiment, the first conductive film is formed of tantalum (Ta), the second conductive film is formed of W, the first conductive film is formed of tantalum nitride (TaN), There are combinations in which the second conductive film is made of Al, the first conductive film is made of tantalum nitride (TaN), and the second conductive film is made of Cu.
[0121]
Next, resist masks 410 to 415 are formed, and a first etching process for forming electrodes and wirings is performed. In this embodiment, an ICP (Inductively Coupled Plasma) etching method is used, an etching gas is mixed, and 500 W of RF (13.56 MHz) power is applied to a coil-type electrode at a pressure of 1 Pa to generate plasma. Generate and do. 100 W RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied. By appropriately selecting the etching gas, the W film and the TaN film are etched to the same extent.
[0122]
Then, a first doping process is performed, and an impurity element imparting n-type conductivity is added. (FIG. 6B) The doping method may be an ion doping method or an ion implantation method. The condition of the ion doping method is a dose of 1 × 10 ¹³ ~ 5x10 ¹⁴ atoms / cm ² The acceleration voltage is set to 60 to 100 keV. As an impurity element imparting n-type, an element belonging to Group 15, typically phosphorus (P) or arsenic (As), is used here, but phosphorus (P) is used. In this case, the first shape conductive layers 416 to 421 serve as a mask for the impurity element imparting n-type, and the first impurity regions 422 to 425 and 443 are formed in a self-aligning manner. The first impurity regions 422 to 425 and 443 have 1 × 10 ²⁰ ~ 1x10 ^{twenty one} atomic / cm ^Three An impurity element imparting n-type is added in a concentration range of.
[0123]
Then, resist masks 426 to 427 are formed as shown in FIG. 6C, and a second doping process is performed to add an impurity element imparting p-type conductivity. Second impurity regions 428 to 429 having a conductivity type opposite to the one conductivity type are formed in the island-shaped semiconductor films 404 and 406. At this time, the island-like semiconductor films 403, 405, and 402 that form the n-channel TFT are covered with resist masks 426 to 427 over the entire surface. Diborane (B ₂ H ₆ The impurity concentration is 2 × 10 2 by ion doping using ²⁰ ~ 2x10 ^{twenty one} atoms / cm ^Three To be.
[0124]
Through the above steps, an impurity region is formed in each island-like semiconductor film. The first shape conductive layers 417 to 419 overlapping with the island-shaped semiconductor film function as TFT gate electrodes. In the first shape conductive layer 421, a region overlapping with the island-shaped semiconductor film 402 functions as a gate electrode, and a region overlapping with the island-shaped semiconductor film 406 functions as a capacitor electrode. Reference numeral 420 denotes a signal wiring, and 416 functions as a wiring in the driving circuit.
[0125]
Thus, for the purpose of controlling the conductivity type, as shown in FIG. 7, a step of activating the impurity element added to each island-like semiconductor film is performed. This step is performed by a thermal annealing method using a furnace annealing furnace. In addition, a laser annealing method or a rapid thermal annealing method (RTA method) can be applied. In the thermal annealing method, the oxygen concentration is 1 ppm or less, preferably 0.1 ppm or less in a nitrogen atmosphere at 400 to 700 ° C., typically 500 to 600 ° C. In this embodiment, the temperature is 500 ° C. for 4 hours. Heat treatment is performed. However, when the wiring material used for 416 to 421 is weak against heat, activation is preferably performed after an interlayer insulating film (mainly composed of silicon) is formed in order to protect the wiring and the like.
[0126]
Further, a heat treatment is performed at 300 to 450 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% hydrogen to perform a step of hydrogenating the island-shaped semiconductor film. This step is a step of terminating dangling bonds in the semiconductor film with thermally excited hydrogen. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.
[0127]
Then, as shown in FIG. 8, the first interlayer insulating film 430 is formed of a silicon oxynitride film with a thickness of 100 to 200 nm. An acrylic resin film or polyimide resin film is formed thereon with a thickness of 1.8 μm as a second interlayer insulating film 431 made of an organic insulating material. Next, an etching process for forming a contact hole is performed.
[0128]
Next, a conductive metal film is formed by sputtering or vacuum deposition. In this method, a Ti film is formed to a thickness of 50 to 150 nm, a contact is formed with a semiconductor film that forms a source or drain region of the island-shaped semiconductor film, and aluminum (Al) 300 to 300 is stacked on the Ti film. The film was formed to a thickness of 400 nm, and a Ti film or a titanium nitride (TiN) film was formed to a thickness of 100 to 200 nm to form a three-layer structure.
[0129]
Then, source wirings 432 to 434 that form contacts with the source region of the island-shaped semiconductor film and drain wirings 435 to 437 that form contacts with the drain region are formed in the driver circuit portion.
[0130]
In the pixel portion, a connection electrode 441, a scanning line 440, a drain electrode 439, and an electrode 438 are formed.
[0131]
The connection electrode 441 is electrically connected to the signal line 420 and the source region of the island-shaped semiconductor film 406. Although not shown, the scanning line 440 is electrically connected to the gate electrode 421 through a contact hole. The drain electrode 439 is electrically connected to the drain region of the island-shaped semiconductor film 406. The electrode 438 is electrically connected to the island-shaped semiconductor film 402 so that the island-shaped semiconductor film 402 functions as an electrode of the storage capacitor 505.
[0132]
Thereafter, a transparent conductive film is formed over the entire surface, and a pixel electrode 442 is formed by patterning processing and etching processing using a photomask. The pixel electrode is formed on the second interlayer insulating film 431, and a portion overlapping with the drain electrode 439 and part of the electrode 438 of the pixel TFT is provided to form a connection structure.
[0133]
The material of the transparent conductive film is indium oxide (In ₂ O _Three ) Or indium tin oxide alloy (In ₂ O _Three -SnO ₂ ; ITO) or the like can be formed using a sputtering method, a vacuum deposition method, or the like. Etching treatment of such a material is performed with a hydrochloric acid based solution. However, in particular, etching of ITO is likely to generate a residue, so in order to improve etching processability, an indium oxide-zinc oxide alloy (In ₂ O _Three —ZnO) may also be used. Since the indium oxide-zinc oxide alloy has excellent surface smoothness and excellent thermal stability with respect to ITO, it can prevent a corrosion reaction with Al coming into contact with the end surfaces of the drain electrode 439 and the electrode 438. Similarly, zinc oxide (ZnO) is also a suitable material, and zinc oxide (ZnO: Ga) to which gallium (Ga) is added to further increase the transmittance and conductivity of visible light can be used.
[0134]
In this way, an active matrix substrate corresponding to a transmissive liquid crystal electro-optical device can be completed.
[0135]
As described above, the driver circuit portion 506 including the n-channel TFT 501, the p-channel TFT 502, and the n-channel TFT 503, and the pixel portion 507 including the pixel TFT 504 and the storage capacitor 505 can be formed over the same substrate. . In this specification, such a substrate is referred to as an active matrix substrate for convenience.
[0136]
9 corresponds to the cross section cut along the chain lines AA ′ and BB ′ in FIG. 8. The cross section taken along the chain lines AA ′ and BB ′ in FIG. The same elements as those in FIG. 8 are denoted by the same reference numerals in FIG. In the top view of FIG. 9, reference numerals 301 to 305 denote contact holes.
[0137]
An active matrix substrate of a reflective liquid crystal electro-optical device can also be manufactured by providing the drain electrode of this embodiment as a conductive film having reflectivity and a function as a pixel electrode.
[0138]
According to the process shown in this embodiment, the doping process for adding the impurity element to the island-shaped semiconductor film may be performed twice, that is, the first doping process and the second doping process. As a result, the process time is shortened, which can contribute to reduction in manufacturing cost and improvement in yield. Furthermore, since the active matrix substrate is manufactured using two wiring layers, the process time can be further reduced as compared with the conventional substrate.
[0139]
[Embodiment 5]
In this embodiment, a method for manufacturing a liquid crystal display device used for a field sequential method is illustrated with reference to cross-sectional views in FIGS. FIG. 10A is a cross-sectional view of an active liquid crystal electro-optical device, and FIG. 10B is a cross-sectional view of a liquid crystal display device including an active liquid crystal electro-optical device and an illumination device.
[0140]
A light shielding film is formed on the substrate 508 of the counter substrate. Chrome (Cr) or the like can be used for the light shielding film. The thickness of the light shielding film is desirably 100 nm to 200 nm.
[0141]
A transparent conductive film 509 is formed as a counter electrode on the light shielding film. As the transparent conductive film, an indium tin oxide (ITO) film can be used. In order to keep the visible light transmittance high, the thickness of the transparent conductive film is preferably 100 nm to 120 nm.
[0142]
Alignment films 510 to 511 are formed on the active matrix substrate and the counter substrate. The thickness of the alignment film is preferably 30 nm to 80 nm. SE7792 made by Nissan Chemical Co., Ltd. can be used for the alignment film. The pretilt value is preferably 5 ° to 8 °.
[0143]
The alignment films 510 to 511 are rubbed. The rubbing direction is set to be orthogonal to each other when the counter substrate and the active matrix substrate are provided so that the surfaces on which the alignment films are formed face each other.
[0144]
Although not shown, the spacer is preferably provided by patterning a photosensitive resin. In order to obtain a good response speed, the spacer is preferably formed at a height of 1.5 to 1.8 μm. In this embodiment, the spacer is formed to a height of 1.5 μm.
[0145]
The counter substrate and the active matrix substrate are bonded together by the sealant 512. The sealing agent is a UV curable sealing agent and XNR5610-1H1 manufactured by Mitsui Toatsu Co., Ltd. is used. After the sealant is cured, the counter substrate and the active matrix substrate are separated.
[0146]
Liquid crystal material 513 is injected. As the liquid crystal material, a low-viscosity material is desirable in terms of high-speed response. In this embodiment, nematic liquid crystal is used as the liquid crystal material. Since the distance between the counter electrode and the pixel electrode is narrow and the electric field strength is strong, even a nematic liquid crystal can sufficiently respond.
[0147]
After confirming that the liquid crystal material has been injected, the injection port of the liquid crystal display device is sealed with a UV curable sealant.
[0148]
Next, a polarizing plate (not shown) is attached by a known technique. The liquid crystal electro-optical device is completed through the above steps. (Fig. 10 (A))
[0149]
The backlight includes a light source, a light guide plate, and a reflection plate. Although not shown, a diffusion plate may be provided between the light guide plate and the liquid crystal electro-optical device to improve the uniformity of the luminance distribution on the light exit surface of the light guide plate. In addition, a prism sheet may be provided between the light guide plate and the liquid crystal electro-optical device to provide directivity in the light emission direction.
[0150]
The light source is composed of a plurality of light sources having different emission colors. A light source that emits red light, a light source that emits green light, and a light source that emits blue light are provided and lighted intermittently. Only the light source 514 that emits red light is shown in the drawing. A light source that emits red light, a light source that emits green light, and a light source that emits blue light use light emitting diodes.
[0151]
The light guide plate 516 is disposed below the liquid crystal electro-optical device. The light guide plate has a wedge shape in cross section, and the width in the thickness direction becomes narrower as the distance from the light source increases. When the cross-sectional shape is wedge-shaped, the light emitted to the liquid crystal electro-optical device side can realize a uniform luminance distribution on the light incident surface of the liquid crystal electro-optical device.
[0152]
The reflector 515 is made of a metal having light reflectivity. When light emitted from the light source is emitted to the side opposite to the light guide plate, or when light leaks from the light guide plate to the side opposite to the liquid crystal electro-optical device, it is reflected by the reflecting plate and returned to the light guide plate side. This increases the utilization rate of light.
[0153]
A liquid crystal display device is completed by attaching a backlight as a lighting device to the liquid crystal electro-optical device by a known method. (Fig. 10 (B))
[0154]
【Example】
The liquid crystal display device formed by implementing each of the first to sixth embodiments can be applied to all electronic devices in which the liquid crystal display device is incorporated in a display unit.
[0155]
Such electronic devices include video cameras, digital cameras, head mounted displays (goggles type displays), car navigation systems, car stereos, personal computers, personal digital assistants (mobile computers, mobile phones, electronic books, etc.) and the like. . Examples of these are shown in FIGS.
[0156]
FIG. 12A illustrates a personal computer, which includes a main body 2001, an image input portion 2002, a display portion 2003, a keyboard 2004, and the like. The present invention can be applied to the display portion 2003.
[0157]
FIG. 12B illustrates a video camera, which includes a main body 2101, a display portion 2102, an audio input portion 2103, operation switches 2104, a battery 2105, an image receiving portion 2106, and the like. The present invention can be applied to the display portion 2102.
[0158]
FIG. 12C illustrates a mobile computer, which includes a main body 2201, a camera unit 2202, an image receiving unit 2203, operation switches 2204, a display unit 2205, and the like. The present invention can be applied to the display portion 2205.
[0159]
FIG. 12D shows a goggle type display, which includes a main body 2301, a display portion 2302, an arm portion 2303, and the like. The present invention can be applied to the display portion 2302.
[0160]
FIG. 12E shows a player using a recording medium (hereinafter referred to as a recording medium) on which a program is recorded, which includes a main body 2401, a display portion 2402, a speaker portion 2403, a recording medium 2404, an operation switch 2405, and the like. This player uses a DVD (Digital Versatile Disc), CD, or the like as a recording medium, and can perform music appreciation, movie appreciation, games, and the Internet. The present invention can be applied to the display portion 2402.
[0161]
FIG. 12F illustrates a digital camera, which includes a main body 2501, a display portion 2502, an eyepiece portion 2503, an operation switch 2504, an image receiving portion (not shown), and the like. The present invention can be applied to the display portion 2502.
[0162]
FIG. 14A shows a cellular phone, which includes a main body 2901, an audio output portion 2902, an audio input portion 2903, a display portion 2904, operation switches 2905, an antenna 2906, and the like. The present invention can be applied to the display portion 2904.
[0163]
FIG. 14B illustrates a portable book (electronic book) which includes a main body 3001, display portions 3002 and 3003, a storage medium 3004, operation switches 3005, an antenna 3006, and the like. The present invention can be applied to the display portions 3002 and 3003.
[0164]
FIG. 14C illustrates a display, which includes a main body 3101, a support base 3102, a display portion 3103, and the like. The present invention can be applied to the display portion 3103.
[0165]
As described above, the application range of the present invention is extremely wide and can be applied to electronic devices in various fields. Further, the electronic apparatus of this example can be realized by using a configuration including any combination of the embodiments.
[0166]
【The invention's effect】
Since the counter electrode is AC driven, it is possible to use a transistor having a low withstand voltage and a reduced burden on the signal side driving circuit, the scanning side driving circuit, and the pixel TFT. For this reason, a liquid crystal display device is manufactured inexpensively by a simple process. In addition, since the manufacturing process time is shortened, mass productivity is improved.
[0167]
In addition, when driving the liquid crystal display device using the field sequential method, the red, blue, and green light sources are all turned off before the counter electrode potential is inverted. Is not visible. Furthermore, since no color filter is required, a display with high luminance and high definition and good color reproducibility can be realized.
[0168]
According to the present invention, both the display with good image quality, which is a characteristic of the field sequential driving, and the reduction of the breakdown voltage of the transistor, which is the characteristic of the method of alternating driving the counter electrode, are combined. Accordingly, it is possible to provide a liquid crystal display device that has an effect that the disturbance of the image accompanying it is not visually recognized, is low in price, and has high image quality.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a field sequential driving method according to a first embodiment.
FIG. 2 is a diagram illustrating a field sequential driving method according to a second embodiment.
FIG. 3 is a diagram showing a field sequential driving method according to a third embodiment.
FIG. 4 is a diagram illustrating a field sequential driving method according to a fourth embodiment.
5 is a graph showing voltage-transmittance characteristics of the liquid crystal material of Embodiment 3. FIG.
6 is a cross-sectional view showing a process of manufacturing an active matrix substrate of Embodiment 5. FIG.
7 is a cross-sectional view showing a process for manufacturing the active matrix substrate of Embodiment 5. FIG.
FIG. 8 is a cross-sectional view showing a process of manufacturing an active matrix substrate of Embodiment 5.
9 is a top view showing a pixel portion of an active matrix substrate of Embodiment 5. FIG.
10 is a cross-sectional view showing a liquid crystal electro-optical device and a liquid crystal display device of Embodiment 6. FIG.
FIG. 11 is a perspective view illustrating an example of an electronic apparatus according to an embodiment.
FIG. 12 is a perspective view illustrating an example of an electronic apparatus according to an embodiment.
FIG. 13 is a circuit diagram showing a configuration of a conventional liquid crystal display device.
FIG. 14 is a waveform diagram showing a driving method of a liquid crystal display device of a conventional example.
FIG. 15 is a waveform diagram showing a driving method of a liquid crystal display device of a conventional example.
FIG. 16 is a diagram showing a driving method of a liquid crystal display device of a conventional example.
[Explanation of symbols]
144: Frame
145: First subframe
146: Second subframe
147: Third subframe
150: Period in which the first emission color is emitted
151: Period in which the first emission color is emitted
152: period in which the first emission color is emitted

Claims (7)

A driving method of a liquid crystal display device having n scanning lines,
One frame has first to sixth subframes,
The first subframe, the third subframe, and the fifth subframe are periods in which gradation is displayed,
The second subframe, the fourth subframe, and the sixth subframe are periods in which black display is performed with the light source turned off,
In each of the first to sixth subframes, the potential of the counter electrode is inverted from the start of the selection of the first row scanning line to the end of the selection of the nth scanning line,
The first subframe, the third subframe, and the fifth subframe, and the second subframe, the fourth subframe, and the sixth subframe are formed on a liquid crystal layer. The applied voltages have different polarities,
In the first sub-frame, at least after the selection of the scanning line of the n-th row, the lighting of the light source of the first emission color starts,
In the third subframe, at least after the selection of the scanning line of the nth row is finished, the lighting of the light source of the second emission color starts,
A driving method of a liquid crystal display device, wherein in the fifth sub-frame, the light source of the third emission color starts to be turned on after selection of at least the n-th scanning line is completed. In claim 1,
The voltage applied to the liquid crystal layer in the first subframe has the same absolute value as the voltage applied to the liquid crystal layer in the second subframe,
The voltage applied to the liquid crystal layer in the third subframe has the same absolute value as the voltage applied to the liquid crystal layer in the fourth subframe,
A driving method of a liquid crystal display device, wherein the voltage applied to the liquid crystal layer in the fifth subframe has the same absolute value as the voltage applied to the liquid crystal layer in the sixth subframe. In claim 1 or claim 2,
The light transmittance is zero at one polarity voltage applied to the liquid crystal layer, and the light transmittance varies according to the voltage at the other polarity voltage applied to the liquid crystal layer. A method for driving a liquid crystal display device, comprising using a liquid crystal material having the liquid crystal layer for the liquid crystal layer. A driving method of a liquid crystal display device having n scanning lines,
One frame has first to fourth subframes,
The first sub-frame is a period in which all light sources are turned off,
The second sub-frame has a period during which the light source of the first emission color is lit.
The third sub-frame has a period during which the light source of the second emission color is on,
The fourth sub-frame has a period during which the light source of the third emission color is lit,
In the first subframe, the potential of the counter electrode is inverted, and the potential of the pixel electrode is adjusted based on the potential of the counter electrode .
In the second to fourth subframes, the potential of the counter electrode is not inverted,
In the second sub-frame, the light source of the first emission color starts to be turned on after selection of at least the n-th scanning line ends.
In the third subframe, at least after the selection of the scanning line of the nth row, the lighting of the light source of the second emission color starts,
A driving method of a liquid crystal display device, wherein in the fourth sub-frame, lighting of the light source of the third emission color starts after selection of at least the n-th scanning line is finished . In claim 4,
A method for driving a liquid crystal display device, wherein a signal input to the pixel electrode in the first subframe is the same as a signal input to the pixel electrode in the second subframe. In claim 4 or claim 5 ,
The method of driving a liquid crystal display device, wherein the second to fourth subframes have the same subframe period. In claim 4 or claim 5 ,
The method for driving a liquid crystal display device, wherein the first to fourth subframes have the same subframe period.

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