JP2592382B2 - Image display method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of displaying an image in a liquid crystal display device using a thin film transistor (hereinafter referred to as a TFT) as a driving switching element, and in particular, to a gradation display method for obtaining an intermediate color tone or shade. It is about. The present invention particularly relates to a so-called perfect digital gradation display that performs gradation display without externally applying any analog signal to an active element, and a liquid crystal material used is a strong liquid crystal material having excellent high-speed response. A display method for a liquid crystal display device, which is limited to a dielectric liquid crystal or an antiferroelectric liquid crystal, or a so-called polymer liquid crystal (also referred to as a dispersion liquid crystal) in which they are dispersed in a polymer compound (polymer). About.

[0002]

2. Description of the Related Art Liquid crystal compositions have different dielectric constants in a horizontal direction and a vertical direction with respect to a molecular axis due to their material properties. Therefore, liquid crystal compositions can be horizontally or vertically aligned with an external electric field. Can be easily done. The liquid crystal electro-optical device displays ON / OFF, that is, displays light and dark by controlling the amount of transmitted light or the amount of scattering of light using the anisotropy of the dielectric constant. Liquid crystal materials include TN (twinstead nematic) liquid crystal, STN (super twinstead nematic) liquid crystal, ferroelectric or antiferroelectric liquid crystal, and recently, nematic liquid crystal or ferroelectric or antiferroelectric. A material called a polymer liquid crystal (also referred to as a dispersion type liquid crystal) in which a crystalline liquid crystal is dispersed in a polymer material is known. It is known that a liquid crystal does not respond to an external voltage in an infinitely short time, but takes a certain time to respond. The value is specific to each liquid crystal material.
0 msec, several hundred msec for STN liquid crystal,
In the case of a ferroelectric liquid crystal, it takes several tens of microseconds, and in the case of a dispersion type or polymer liquid crystal using a nematic liquid crystal, it takes several tens of milliseconds.

[0003] Among electro-optical devices using liquid crystals, the one that can obtain the best image quality is the one using the active matrix system. In a conventional active matrix type liquid crystal electro-optical device, a thin film transistor (TFT) is used as an active element, an amorphous or polycrystalline semiconductor is used for the TFT, and P
In this case, a TFT of only one of the N-type and the N-type was used. That is, in general, an N-channel TFT
(Referred to as NTFT) is connected in series to the pixel. Then, a signal voltage is applied to the signal lines of the matrix, and when signals are applied from both sides to the TFTs provided at the orthogonal portions of the respective signal lines, the ON / OFF state of the liquid crystal pixels is utilized by utilizing the fact that the TFTs are turned ON. OFF was individually controlled. By controlling the pixels by such a method, a liquid crystal electro-optical device having a high contrast can be realized.

[0004]

However, in such an active matrix system, it is extremely difficult to perform gradation display such as light and dark and color tone. Conventionally, for gray scale display, a method has been studied which utilizes the fact that the light transmittance of a liquid crystal changes depending on the magnitude of an applied voltage. This is, for example, the source of the TFT in the matrix.
By supplying an appropriate voltage from the peripheral circuit between the drains and applying a signal voltage to the gate electrode in that state,
It is intended to apply a voltage of that magnitude to the liquid crystal pixels.

However, in such a method, for example, due to the inhomogeneity of the TFT and the inhomogeneity of the matrix wiring, the voltage actually applied to the liquid crystal pixels differs by at least several% depending on each pixel. Oops. On the other hand, for example, the voltage dependence of the light transmittance of the liquid crystal is extremely non-linear, and the light transmittance changes rapidly at a specific voltage. In some cases it was significantly different. Therefore, in practice, achieving 16 gradations has been the limit. For example, in a TN liquid crystal material, a so-called transition region in which light transmittance changes,
In order to achieve 16 gradations, which has a width of only 1.2 V, it is necessary to control a voltage as small as 75 mV, so that the production yield has been significantly reduced.

[0006] As described above, the difficulty of gradation display is extremely disadvantageous in that the liquid crystal display device competes with a conventional general display device such as a cathode ray tube (CRT). An object of the present invention is to propose a completely new method for realizing a gray scale display which has been difficult in the past.

[0007]

[Means for Solving the Problem] As mentioned above, it is possible to control the light transmittance of the liquid crystal by controlling the voltage applied to the liquid crystal in an analog manner. It has been found that gradation can be visually obtained by controlling the time during which voltage is applied to the liquid crystal.

For example, when a TN (twisted nematic) liquid crystal, which is a typical liquid crystal material, is used,
For example, although various pulse waveforms are shown in FIG. 1, it has been found that the brightness can be changed by applying such a waveform voltage to the liquid crystal pixels. That is, “1”, “2”,.
Brightness can be gradually increased in the order of “15”. That is, in the example of FIG. 1, display of 16 gradations is possible. At this time, at "1", a pulse having a length of one unit is applied. In the case of "2", a pulse having a length of 2 units is applied. At “3”, one unit pulse and two unit pulses are applied, and as a result, a pulse having a length of three units is applied. At “4”, a pulse having a length of 4 units is applied. At "5", one unit pulse and four unit pulses are applied, and at "6", two unit pulses and four unit pulses are applied. Further, by providing a pulse of 8 units in length, a pulse of 15 units in length can be obtained as a result.

That is, by appropriately combining four types of pulses of 1 unit, 2 units, 4 units, and 8 units, it is possible to display 2 ⁴ = 16 gradations. In addition, 1
By preparing as many pulses as 6 units, 32 units, 64 units, and 128 units,
Advanced gray scale display of 32 gray scales, 64 gray scales, 128 gray scales, and 256 gray scales becomes possible. For example, in order to obtain 256 gradation display, eight types of pulses may be prepared.

In the example of FIG. 1, the duration of the voltage applied to the pixel, that is, the pulse interval is T _{1 at first} and 2 at the next.
An example in which T ₁ is arranged so as to increase in a geometric progression such as T ₁ and 4T ₁ is shown in FIG.
, First T ₁ , then 8T ₁ , then 2T ₁ ,
Finally it may be 4T _1. That is, i and N are finite
Natural numbers, when the the _{T 1} constant, i-th and (i + 1) th
The interval of the eye pulse is T ₁ , the (i + 1) th pulse,
(I + 2) -th interval of the pulse is ^{_{2 N T 1, (i +}} 2)
The interval between the (i + 3) th pulse and the 2nd pulse is 2
T ₁ , (i + 3) th pulse and (i + 4) th pulse
By spacing of the scan is allowed to sequence such that 2 ^_N-1 T ^1, it is possible to reduce the burden of the apparatus for transmitting data to the display device.

However, when the TN liquid crystal is used, as a result, the applied voltage is required to have the same accuracy as that of the conventional analog gradation display system. That is, when 5 V is applied to the pixel as an ON voltage and “10” in FIG.
The display looks darker by about 2% than when the same “10” is displayed by applying a voltage of 1V. That is, in such a digital gray scale display system, it is required that there is no variation in TFT as in the conventional analog gray scale display system.

This drawback is due to the fact that the TN liquid crystal changes its light transmittance according to the effective voltage. The same applies to the STN liquid crystal or the dispersion type liquid crystal using the nematic liquid crystal which is the basic material. On the other hand, a ferroelectric liquid crystal or an antiferroelectric liquid crystal shows a very high-speed response, and does not substantially respond to an effective value voltage. Therefore, when digital gradation display as described above is performed, T
It has been clarified that uniform gradation display is possible regardless of the characteristics of the FT. That is, when a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal is applied with a voltage of 1 msec or more as an ON voltage, the same light transmittance is exhibited at 5 V and 5.1 V.

A similar effect was observed in a material in which a ferroelectric liquid crystal or an antiferroelectric liquid crystal was dispersed in a polymer.

In order to carry out the present invention, for example, a matrix circuit using thin film transistors as shown in FIG. 4 may be assembled. The circuit shown in FIG. 4 is the same as the circuit used in a conventional active matrix display device using a TFT.

Since the ferroelectric liquid crystal or the antiferroelectric liquid crystal itself has a memory property, an auxiliary capacitance (capacity inserted in parallel with the pixel capacitance) as required in the conventional active matrix is provided. In other words, the ON state can be maintained even when the pixel electrode is discharged. However, such a material having strong ferroelectricity (or antiferroelectricity) tends to cause a so-called "burn" phenomenon and has a lack of reliability. On the other hand, a material having low ferroelectricity (or antiferroelectricity) has few defects relating to display such as "burn", but the pixel capacitance is severely discharged, and a voltage sufficient to maintain display cannot be maintained. In this case, it is difficult to maintain the ON state (or the OFF state). Therefore, a storage capacitor is required as in the related art.

Of course, if the discharge of the pixel is sufficiently small, such an artificial capacitor is not required. In particular, the presence of an excessive storage capacitor takes a long time for the charging or discharging operation, which is not desirable in practicing the present invention. In order to reduce the discharge of the pixel, for example, it is necessary to sufficiently increase the OFF resistance of the thin film transistor to reduce the leak current and to sufficiently increase the resistance between the electrodes of the pixel itself such as liquid crystal. Especially for the latter purpose, it is effective to cover the pixel electrode with an insulating material such as tantalum oxide or aluminum oxide such as silicon nitride or silicon oxide.

In such a circuit, by controlling the gate voltage and the source-drain voltage of each thin film transistor, the ON / OFF of the voltage applied to the pixel is controlled.
It is possible to control OFF. In this example, the matrix is 640 × 480 dots, but for the sake of simplicity, only the vicinity of n rows and m columns is shown. If you expand the same thing up, down, left and right, you will get a complete one. FIG. 2 shows an operation example using this circuit.

The signal lines X _1, X _2,... X _n, X _{n + 1,...} X ₄₈₀ (hereinafter collectively referred to as X-rays) are connected to the gate electrodes of the respective TFTs. Then, as shown in FIG. 2, rectangular pulse signals are sequentially applied. On the other hand, the signal lines Y1 _, Y2 _{, ..} Y
_m, Y _{m + 1, ..} Y ₆₄₀ (hereinafter collectively referred to as Y line)
It is connected to the source (or drain electrode) of T, to which a signal consisting of a plurality of pulses is also applied. This pulse train, in a unit of time T _1, which contains 640 information.

In the following, four pixels Z _{n, m} , Z _{n + 1, m} ,
Pay attention to _{Zn, m + 1} and Zn _{+ 1, m + 1} , but the leak current of the pixel is sufficiently small and the voltage of the pixel does not change unless a signal comes to both the gate electrode and the source electrode. Therefore, regarding these four pixels, attention should be paid to the signal lines X _{n and} X _{n + 1} and Y _{m and} Y _{m + 1} .

Consider the case where a rectangular pulse is applied to X _n as shown in the figure. Now, four pixels Z _{n, m} ,
Assuming that attention is paid to _{Zn, m + 1} , Zn _{+ 1, m} , and Zn _{+ 1, m + 1} , it is sufficient to pay attention to the current states of _Ym and Ym _{+ 1} . At this time, since there is a signal at Y _m and no signal at Y _{m + 1} , the pixel Zn _{, m} is in a voltage state and the pixel Zn _{, m + 1} is in a non-voltage state. By cutting off the pulse of the X-ray earlier than the voltage applied to the Y-line, the voltage state of the pixel is maintained by the capacitor of the pixel.
_{n and m} maintain the voltage state. Thereafter, until the next signal X _n is applied, it is basically the state of each pixel lasting.

Next, a pulse is applied to X _{n + 1} . As shown in the figure, at that time, Y _m is in a non-voltage state, and Y _{m + 1} is in a voltage state, so that pixel Zn _{+ 1, m} is in a non-voltage state, and pixel Zn _{+ 1, m + 1.} Becomes a voltage state, and keeps maintaining each state in the same manner as described above.

Next, when after the pulse is applied to the X _n above, second pulse to a signal line X _n is applied after a time T ₁ is Y _m and Y _{m + 1,} respectively, the non-voltage state, since the voltage state, the pixel Z _{n, m} in the non-voltage state, the pixel Z _{n, m + 1} is the voltage state, respectively, state changes. Further, a pulse is applied to X _{n + 1} . As shown, since at that time Y _m be Y _{m + 1} is also a voltage state, the pixel Z _{n + 1, m} be Z _{n + 1, m + 1} is the voltage state. At this time, the pixel Zn _{+ 1, m + 1} continues the voltage state.

[0023] Then, after a time 2T _1, the signal for the third time is applied to the X _n. At that time, since Y _m may Y _{m + 1} is also a voltage state, the pixel Z _{n, m} varies from a non-voltage state to the voltage state, the pixel Z _{n, m + 1} becomes possible to continue the voltage state. Further, a pulse is applied to X _{n + 1} . At that time, since both Y _m and Y _{m + 1} are in a non-voltage state, the pixel Zn _{+ 1, m}
Also, Zn _{+ 1 and m + 1} are in the non-voltage state, and the voltage state ends in both cases.

[0024] Then, after a time 4T _1, 4 th signal is applied to the X _n. At that time, Y _m be Y for _{m + 1} also is a non-voltage state, changes the pixel Z _{n, m} also pixel Z _{n, m + 1} from the voltage state to the non-voltage state. Further, the pulse is applied to the X n _{+ 1,} also Y for _m even Y _{m + 1} also is a non-voltage state, the pixel Z _{n + 1, m} be Z _{n + 1, m + 1} is non-voltage state Remains.

Thus, one frame is completed.
During this time, four pulses are applied to each X-ray, and 3 × 480 = 1440 information signals are applied to each Y-ray. The time of one frame is 7T ₁ , and T ₁
For example, 10 nsec to 10 msec is appropriate. Then, paying attention to each pixel, the pixel Zn _{, m}
, A pulse of time T _{1 and} a pulse of 4T ₁ are applied, and visually the same effect as that obtained by applying a pulse of 5T ₁ is obtained. That is, a brightness of “5” is obtained. Similarly, the brightness of “2”, “6”, and “3” is obtained for the pixels Zn _{, m + 1} , Zn _{+ 1, m} , and Zn _{+ 1, m + 1} .

In the above example, eight gradations can be displayed, but higher gradations can be achieved by adding more pulse signals. For example, by applying five pulses to each X-ray and applying 3840 information signals to each Y-line during one frame, a high gray scale display of 256 gray scales can be achieved.

Further, if a high gradation display is to be performed, an extremely high-speed switching is required, as is apparent from FIG. For example, in order to realize 256 gradations, it is necessary to feed out 30 or more moving images per second, so that 256T ₁ <30 msec. Therefore, T ₁ <1
00 μsec. Therefore, for example, when the number of X-rays (connected to the gate electrode) is 480, the width 20
It is necessary to apply a pulse of 0 nsec or less. FIG.
In the above example, only the NMOS TFT is used, but a circuit having a CMOS circuit may be connected to the pixel for the purpose of increasing the operation speed. For example, when a CMOS transfer gate circuit or the like is used, the speed can be increased.

In the above description, the signals are clearly distinguished from the non-voltage state to the voltage state for easy understanding. , Or more, and need not be absolutely zero.

Further, it is possible to change the substantial voltage applied to the pixel material by applying an appropriate bias voltage to the counter electrode of the pixel. For example, by applying an appropriate voltage to the counter electrode of the pixel, the direction of the voltage applied to the pixel material can be both positive and negative.

[0030]

【Example】

Example 1 In this example, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. The TFT at that time was made of polycrystalline silicon using laser annealing.

First, a method for manufacturing a liquid crystal panel used in this embodiment will be described with reference to FIG. In FIG. 6A, a silicon oxide film as a blocking layer 2 is formed on a glass 1 capable of withstanding a heat treatment at 700 ° C. or less, for example, about 600 ° C. by using a magnetron RF (high frequency) sputtering method.
It is made to a thickness of 0 to 3000 mm. The process conditions are an oxygen 100% atmosphere, a deposition temperature of 15 ° C., and an output of 400 to 800.
W, pressure 0.5 Pa. Synthetic quartz was used as a target to reduce impurities. The deposition rate is 30 to 10
0 ° / min.

A silicon film 3 was formed thereon by a plasma CVD method. The deposition temperature is 250 ° C to 350
° C, and in this example, the temperature was set to 320 ° C.
(SiH ₄ ) was used. Not only monosilane (SiH ₄ ) but also disilane
(Si ₂ H ₆ ) Alternatively, trisilane (Si ₃ H ₈ ) may be used. These were introduced into the PCVD apparatus at a pressure of 3 Pa, and 13.5
A film was formed by applying a high frequency power of 6 MHz. At this time, the appropriate high frequency power is 0.02 to 0.10 W / cm ² ,
In this embodiment, 0.055 W / cm ² is used. The flow rate of monosilane (SiH ₄ ) was set to 20 SCCM, and the deposition rate at that time was about 120 ° / min. The silicon film may be a pure intrinsic semiconductor, or boron may be added at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane during the film formation. In addition, not only the plasma CVD but also a sputtering method and a low pressure CVD method may be used for forming the silicon layer to be a channel region of the TFT, and the method will be briefly described below.

When the sputtering method is used, the back pressure before the sputtering is set to 1 × 10 ⁻⁵ Pa or less, and single crystal silicon is used as a target in an atmosphere in which hydrogen is mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%.
The film formation temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

In the case of forming by a reduced pressure gas phase method, 450 to 550 ° C. lower by 100 to 200 ° C. than the crystallization temperature, for example, 5 to 50 ° C.
Disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) was supplied to the CVD apparatus at 30 ° C. to form a film. The reactor pressure is 30 ~
It was set to 300 Pa. The deposition rate was 50-250 ° / min.

The coatings formed by these methods are:
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. In order to promote crystallization, the oxygen concentration should be 7 × 10 ¹⁹ cm ⁻³ or less,
Preferably, it is desirable to be 1 × 10 ¹⁹ cm ⁻³ or less,
If the amount is too small, the leakage current in the off state increases due to the backlight, so this concentration was selected. If the oxygen concentration is high, crystallization is difficult, and the laser annealing temperature must be increased or the laser annealing time must be increased. Hydrogen is 4 × 10 ²⁰ cm ⁻³ and silicon 4 × 10 ²²
When compared with cm ^-3 , it was 1 atomic%.

In order to promote crystallization of the source and the drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less,
Oxygen may be added only to the T channel formation region by ion implantation so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .
According to the above method, the amorphous silicon film is
The film was formed to have a thickness of 5000 to 5000 Å, and 1000 Å in this embodiment.

Thereafter, a pattern in which only the source / drain regions were opened using the photoresist 4 as a mask was formed. A silicon film 5 serving as an n-type active layer was formed thereon by a plasma CVD method. The film formation temperature is from 250 ° C to 35
In this example, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) were 3%.
Concentrations were used. These were introduced into the PCVD apparatus at a pressure of 5 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is 0.05 to 0.20.
W / cm ² is appropriate, and in this embodiment, it is 0.120 W / cm ^2.
cm ² was used.

The specific conductivity of the n-type silicon layer completed by this method was about 2 × 10 ⁻¹ [Ωcm ⁻¹ ]. The film thickness was 50 °. In this way, FIG.
I got Thereafter, the resist 4 was removed by a lift-off method to form source / drain regions 6 and 7. Thus, FIG. 6B was obtained.

Thereafter, as shown in FIG.
Using an excimer laser, laser doping was performed on the active layer at the same time as laser annealing of the source, drain, and channel regions. At this time, the threshold energy of the laser energy is 130 mJ / cm ² , and 220 mJ / cm ² is required to crystallize the entire film thickness.
However, when an energy of 220 mJ / cm ² or more is irradiated from the beginning, hydrogen contained in the film is rapidly released, and the film is destroyed. For this purpose, it is necessary to first displace hydrogen and then melt it with low energy. After performing the flush hydrogen in the first 150 mJ / cm ² in the present embodiment was subjected to crystallization at 230 mJ / cm ^2.

Thereafter, the silicon film 3 was removed by etching using a mask to form an N-channel type thin film transistor island region 10. Further, a silicon oxide film 8 is formed thereon as a gate insulating film at 500 to 2000 .ANG.
It was formed to a thickness of 000 mm. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix the sodium ions.

Thereafter, 1 to 5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned using a third photomask to obtain a gate electrode 9 for NTFT (FIG. 6D). The size of the gate electrode was, for example, 7 μm in channel length, and the thickness of the gate electrode was 0.2 μm of silicon doped with phosphorus and 0.3 μm of molybdenum thereon.

As the gate electrode material, for example, aluminum (Al) can be used in addition to the above materials. When aluminum is used, it is patterned by a third photomask and then anodized on its surface, so that the self-alignment method can be applied.
Since the source / drain contact hole can be formed at a position closer to the gate, the characteristics of the TFT can be further improved in terms of reduction in mobility and threshold voltage.

Thus, a C / TFT can be manufactured without applying a temperature to 400 ° C. or more in all steps. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and it can be said that the process is very suitable for the large-screen liquid crystal display device of the present invention.

Further, a silicon oxide film was formed on the interlayer insulator 11 by the above-mentioned sputtering method. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, it was formed to a thickness of 0.2 to 0.6 μm, and then a window 13 for an electrode was formed using a fourth photomask. Thereafter, aluminum was further formed on the entire surface to a thickness of 0.3 μm by sputtering, and leads 12 and contacts 14 were formed using a fifth photomask. Thus, FIG. 6E was obtained.

Thereafter, an organic resin 15 for flattening, for example, a translucent polyimide resin was applied on the surface, and an electrode hole was formed again using a sixth photomask. Further, ITO (indium tin oxide) was formed on the whole by sputtering to a thickness of 0.1 μm, and a pixel electrode 16 was formed using a seventh photomask. This ITO is between room temperature and 15
Films were formed at 0 ° C. and achieved with oxygen at 200-400 ° C. or in air. Thus, FIG. 6F was obtained.

The electrical characteristics of the TFT obtained as described above have a mobility of 80 (cm ² / Vs) and a Vth of 5.0 (V).
Met. One substrate for a liquid crystal electro-optical device manufactured according to the above method was obtained. By repeating such a structure left, right, up and down, 640 × 48
A liquid crystal display device having a large pixel size of 0, 1280 × 960 can be obtained. In this embodiment, the size is set to 1920 × 400. Thus, a first substrate was obtained.

FIG. 5 shows a method for manufacturing the other substrate. A polyimide resin obtained by mixing a black pigment with polyimide is formed on a glass substrate to a thickness of 1 μm using a spin coating method,
Using an eighth photomask, a black stripe 41 is formed.
Was prepared. Thereafter, a polyimide resin mixed with a red pigment was formed into a film having a thickness of 1 μm by spin coating, and a red filter 82 was manufactured using a ninth photomask. Similarly, a green filter 43 and a blue filter 44 were manufactured using masks (circled numbers 10 and 11). After these preparations, each filter was fired at 350 ° C. in nitrogen for 60 minutes. After that, the leveling layer 45 was manufactured using a transparent polyimide, also using the spin coating method.

Thereafter, ITO (indium tin oxide) was formed on the entire surface to a thickness of 0.1 μm by sputtering to form a common electrode 46. This ITO is between room temperature and 150 ℃
The film was formed by oxygen at 200 to 300 ° C. or annealed in air to obtain a second substrate.

A polyimide precursor was printed on the substrate by an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere, for example, nitrogen. Thereafter, a known rubbing method was used to modify the surface of the polyimide, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided.

Thereafter, a liquid crystal display device is constituted by the first substrate and the second substrate, and T leads are formed on the leads on the substrate.
PC having AB-shaped drive IC, common signal and potential wiring
B was connected, and a polarizing plate was attached on the outside to obtain a transmission type liquid crystal electro-optical device. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves to complete a wall-mounted TV. Compared to a conventional CRT system television, the device has a flat shape, so that it can be installed on a wall or the like. It has been confirmed that the operation of this liquid crystal television can display eight gradations by applying a signal substantially equivalent to that shown in FIG. 2 to the liquid crystal pixels. At this time, T ₁ = 4 msec, X-ray and Y
The pulse width (or minimum pulse width) of the line is
5 μsec and 8 μsec.

Example 2 In this example, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. 4, and a description thereof will be given. Also T at that time
FT was polycrystalline silicon using laser annealing.

Hereinafter, a method of manufacturing the TFT portion will be described with reference to FIG. In FIG. 7A, 70
Using a magnetron RF (high frequency) sputtering method, a silicon oxide film as a blocking layer 21 is formed on a glass 20 capable of withstanding a heat treatment of 0 ° C. or less, for example, about 600 ° C.
It is made to a thickness of 3000 mm. Process condition is oxygen 10
0% atmosphere, film formation temperature 15 ° C, output 400-800W,
The pressure was 0.5 Pa. The deposition rate using quartz as the target was 30 to 100 ° / min.

The silicon film 2 is formed thereon by a plasma CVD method.
2 was produced. The film formation temperature is 250 ° C. to 350 ° C.,
In this example, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) was used. Not only the monosilane (SiH _4), may be used disilane (Si ₂ H ₆₎ The trisilane (Si ₃ H _8). These are PCVD
The film was introduced into the apparatus at a pressure of 3 Pa, and a high frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is set to 0.
An appropriate value is from 02 to 0.10 W / cm ² , and in this example, 0.055 W / cm ² was used. In addition, monosilane (SiH
₄ ) The flow rate was 20 SCCM, and the film formation rate at that time was about 1
It was 20Å / min. This silicon film is an intrinsic semiconductor, and boron is used as diborane to form 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ^−3.
May be added during the film formation.

In order to further promote crystallization of the source and the drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less,
Oxygen may be added only to the T channel formation region by ion implantation so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .
According to the above method, the amorphous silicon film is
The film was formed to have a thickness of 5000 to 5000 Å, and 1000 Å in this embodiment.

Thereafter, a pattern was formed by using the photoresist 23 as a mask to form holes only in the regions to be the source / drain regions of the NTFT. And resist 2
3 is used as a mask, and phosphorus ions are ion-implanted.
2 × 10 ^{14 to} 5 × 10 ¹⁶ cm ⁻² , preferably 2 × 10 ¹⁶
By implanting only cm ⁻² , an n-type impurity region 24 was formed.
After that, the resist 103 was removed.

Thereafter, as shown in FIG. 7B, a thickness of 50 to 300 nm, for example, 100 nm is formed on the silicon film 22.
Was formed by the RF sputtering method described above. Then, using a XeCl excimer laser, the source, drain and channel regions were crystallized and activated by laser annealing. After the completion of the laser annealing, the silicon oxide film 25 was removed.

This crystallization can also be performed by a thermal annealing method. In that case, 45
0-700 ° C, preferably 550-600 ° C
The heat treatment may be performed at a temperature of 12 to 70 hours, for example, 24 hours in a non-oxidizing atmosphere, for example, a hydrogen or nitrogen atmosphere.

Thereafter, an island-like NTFT region 28 was formed using a photomask. On this, a silicon oxide film 26 was formed as a gate insulating film to a thickness of 500 to 2000 {for example, 1000}. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer.

Thereafter, 1 to 5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This is patterned using a third photomask, and as shown in FIG.
A gate electrode 27 for FT was formed. For example, the channel length is 7 μm, and the gate electrode is 0.2 μm of phosphorus silicon.
m, and molybdenum was formed thereon to a thickness of 0.3 μm.

Further, in FIG. 7E, an interlayer insulator 29 was formed as a silicon oxide film by the above-mentioned sputtering method. This silicon oxide film is formed by an LPCVD method
A VD method or a normal pressure CVD method may be used. For example, 0.2 ~
A thickness of 0.6 μm was formed, and then a window 31 for an electrode was formed using a fourth photomask. After that, further, aluminum is formed on the whole by sputtering to a thickness of 0.3 μm, and a lead 30 and a contact 32 are manufactured using a fifth photomask. A translucent polyimide resin was applied and formed, and an electrode hole was formed again using a sixth photomask. Further, ITO (indium tin oxide) was formed to a thickness of 0.1 μm on all of them by a sputtering method, and a pixel electrode 33 was formed using a seventh photomask.
This ITO is formed at room temperature to 150 ° C.
Fulfilled by oxygen at 0 ° C or atmospheric annealing. As for the electrical characteristics of the TFT obtained as described above, the mobility was 90 (cm ² / Vs) and the Vth was 4.8 (V).

One substrate for a liquid crystal electro-optical device manufactured according to the above method was obtained. The method for fabricating the other substrate is the same as that in the first embodiment, and will not be described.
Then, a liquid crystal display device is constituted by the first substrate and the second substrate, and a drive IC having a TAB shape, a common signal, and a PCB having a potential wiring are connected to leads on the substrate,
A polarizing plate was attached on the outside to obtain a transmission type liquid crystal electro-optical device. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves to complete a wall-mounted TV. Compared to a conventional CRT television,
Since the device has a planar shape, it can be installed on a wall or the like. The operation of this liquid crystal television was confirmed to be capable of displaying 128 gradations by applying signals substantially equivalent to those shown in FIG. 2 to the liquid crystal pixels.

[0062]

According to the present invention, in contrast to the conventional analog gradation display using a nematic liquid crystal, a digital gradation display using a ferroelectric or antiferroelectric liquid crystal material or a polymer liquid crystal material thereof is used. It is characterized by performing. As an effect, assuming a liquid crystal electro-optical device having a number of pixels of 640 × 400 dots, for example, it is very difficult to manufacture all the 256,000 TFTs without variation in characteristics. In consideration of mass productivity and yield, 16-gradation display is considered to be the limit. However, as in the present invention, gradation display is performed purely by digital control without adding analog signals at all. By doing so, gray scale display of 256 gray scale display or more is possible. Since it is a complete digital display,
The ambiguity of the gradation due to the variation in the characteristics of the FT was completely eliminated. Therefore, even if the variation in the TFT was slight, a very uniform gradation display was possible. Therefore, while the yield was extremely low in the past in order to obtain a TFT having a small variation, the present invention has reduced the yield of the TFT so much that the yield of the TFT is improved and the manufacturing cost is significantly reduced. did it.

For example, 256,0 of 640 × 400 dots
When a normal analog gradation display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square,
Since there is about ± 10% variation in TFT characteristics,
Six gradation display was the limit. However, when the digital gradation display according to the present invention is performed, the display is hardly affected by the variation in the characteristics of the TFT elements, so that it is possible to display up to 256 gradations.
A variety of 16 colors can be displayed in subtle colors. In the case of displaying software such as television images, for example, even a “rock” made of the same color has a slightly different color due to its minute dents and the like. If you try to display something close to the colors of nature,
Difficulty is required for 16 gradations. With the gradation display according to the present invention, it is possible to impart these minute color changes.

[Brief description of the drawings]

FIG. 1 shows an example of a driving waveform according to the present invention.

FIG. 2 shows an example of a driving waveform according to the present invention.

FIG. 3 shows an example of a driving waveform according to the present invention.

FIG. 4 shows an example of a matrix configuration according to the invention.

FIG. 5 shows a process of a color filter according to an example.

FIG. 6 shows a TFT process according to an embodiment.

FIG. 7 illustrates a TFT process according to an embodiment.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-107381 (JP, A) JP-A-61-69036 (JP, A) JP-A 1-267619 (JP, A)

Claims (1)

(57) [Claims] 1. A N signal lines _{X 1, X 2,.} . _Xn,. .
X _N and, M the signal lines _Y 1 of which is perpendicular _{thereto, Y 2,.} .
Y _m,. . Y a wiring formed in a matrix by the _M, the intersection area of each matrix, at least one N-channel type thin film transistor or, P-channel type thin film transistor and a pixel Z ₁₁ provided in the intersection region of the signal _lines, Z ₁₂ ,. . . Z _mn,. . . Z _MN
One of the source or the drain of each thin film transistor is connected to one of the electrodes constituting each pixel, and the gate electrode of the thin film transistor is connected to the signal line X.
_{1, X} 2,. . _Xn,. . To X _N, the signal lines _Y 1 other one of the source or _{drain, Y 2,.} . Y _m,. . Y
Forming a first substrate connected to _M and a transparent conductive film
A second substrate, wherein the first and second substrates are opposed to each other at an interval of 10 μm or less, and a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or a polymer compound thereof is interposed therebetween. In a liquid crystal display device in which a fine mixture is sandwiched, in a pulse applied to an arbitrary signal line _Xn , an interval between a _first pulse and a second pulse is 1T ₁ ,
The interval between the second pulse and the third pulse is 8T ₁ ,
The interval between the third pulse and the fourth pulse is 2T ₁ ,
The interval between the fourth pulse and the fifth pulse is 4T
An image display method for an electro-optical device, wherein the image display method is represented by ₁ (T ₁ is a constant).