JPH0772778B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a micro computer by connecting a thin film type insulated gate field effect semiconductor device and a ferroelectric liquid crystal to form one pixel and arranging these pixels in a matrix. The present invention relates to a liquid crystal display device for reducing the thickness of a display unit such as a personal computer, a personal computer, a word processor, or a television.

[0002]

2. Description of the Related Art In a solid-state display panel, a method of independently controlling each pixel is effective for a large area. Conventionally, such a panel uses a dual-frequency liquid crystal, for example, a twisty nematic liquid crystal, and a display device using a multiplexing drive system in an A4 size simple matrix configuration with 400 elements in the horizontal direction and 200 elements in the vertical direction. It has been known.

[0003]

However, it has been found that it is impossible to use a twisty nematic liquid crystal in order to manufacture a large-area display device having a larger number of pixels due to the limit of frequency characteristics. did. In addition, even if the respective pixels are arranged in a matrix with a predetermined distance therebetween, a crosstalk (a phenomenon in which they are electrically weakly conducted) is likely to occur between adjacent pixels. Therefore, even if one function is turned on and the other function is turned off, each pixel cannot be turned on or off sufficiently, resulting in insufficient contrast.

In addition, it is necessary to rub the alignment layer of the liquid crystal in order to provide it with alignment characteristics. However, when the alignment layer is rubbed, the friction of 1000V or 2
High static electricity of 000V is generated. Therefore, the active element has a problem that it may be destroyed by the high static electricity. A method using a non-linear element is known as a means for preventing crosstalk between adjacent pixels. Further, in the passive type configuration (simple matrix system), it has been attempted to use a ferroelectric liquid crystal as a liquid crystal instead of a conventionally known Twistick nematic liquid crystal, but there is a cross talk. But not the best.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device capable of preventing cross talk and increasing frequency characteristics and viewing angle. . An object of the present invention is to provide a liquid crystal display device capable of preventing the active element from being destroyed by the alignment treatment.

[0006]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises an active element 2 formed of a thin film type insulated gate field effect semiconductor device formed on a substrate, and a ferroelectric liquid crystal. 3 is connected to form one pixel,
These pixels are arranged in a matrix, and of the pair of electrodes 23, 24 sandwiching the ferroelectric liquid crystal 3, inside the electrode 23 on the active element 2 side,
A liquid crystal display device comprising an insulating film which is not subjected to alignment treatment.

[0007]

[Operation] The Applicant paid attention to the combination of the ferroelectric liquid crystal + TFT, and investigated its characteristics in various directions.
Then, the following results were obtained. TWISTIC / ferroelectric liquid crystal + TFT Nematic liquid crystal + TFT memory function ◎ ◎ Cross talk prevention ◎ ◎ Simple process × × High-speed frequency response △ ○ Wide range of operating temperature ○ △ Wide aperture ratio × × Ease of peripheral circuit △ △ Field of view Large angle Δ ○ Small amount of liquid crystal used △ ○ Gradation is possible ○ △ However, ◎ is very good, ○ is good, Δ is slightly bad, and × is bad.

Considering the above two methods, the ferroelectric liquid crystal + TFT is the twistic nematic liquid crystal + T
It is superior to FT in terms of high-speed frequency response, viewing angle, amount of liquid crystal used, and inferior in operating temperature and gradation. When the ferroelectric liquid crystal and the thin film type insulated gate field effect semiconductor device are combined, the alignment treatment for improving the alignment characteristic of the ferroelectric liquid crystal may be omitted even if the thin film type insulated gate field effect semiconductor device side is omitted. I found it good. Further, the present invention is
Since a thin film type insulated gate field effect semiconductor device and a ferroelectric liquid crystal are used, they both operate synergistically and cross
It has been found that the structure is very close to the ideal type because it does not have any trouble, the process is not so complicated, and the viewing angle can be improved because the ferroelectric liquid crystal is used.

Thus, by connecting the thin film type insulated gate field effect semiconductor device and the ferroelectric liquid crystal in series to form each pixel, for example, a liquid crystal display device having a large area of A4 size or larger is manufactured. Even so, the crosstalk between the respective pixels could be minimized. Further, according to the present invention, color display is also possible by passing red (called R), green (called G), and blue (called B) filters corresponding to the other X wiring of the ferroelectric liquid crystal. It has the feature.

[0010]

[Examples] In this example, a thin film type insulated gate field effect semiconductor device and a ferroelectric liquid crystal were connected in series to form one pixel, but this operating temperature range is such that a plurality of different ferroelectric liquid crystals are used. It can be used in combination at 0 ° C to 50 ° C. Therefore, in practical use, there is no problem. As for gradation, if the color is limited to 8 colors, gradation is unnecessary. Therefore, it has been proved that it is sufficiently practical as a display for a micro computer or the like. Therefore, in particular, as described in the present embodiment, it has been found that a large-sized large-area liquid crystal display can be manufactured only by a pixel provided by connecting a thin film type insulated gate field effect semiconductor device and a ferroelectric liquid crystal in series. did.

Further, in this embodiment, a composite diode using space charge limited current (hereinafter referred to as "SCLAD" in the present specification) is used as the non-linear element. And the pixel are more integrated. That is, the non-linear element used in this example has an N-type semiconductor-I-type semiconductor-N-type semiconductor structure,
Alternatively, a P-type semiconductor-I-type semiconductor-P-type semiconductor structure is mainly used. Further, in this embodiment, since the SCLAD and the pixels forming the matrix can be of the self-alignment type, the process can be performed with only two masks. A representative example of the structure of the present invention is shown in FIG. 4 and its manufacturing process is shown in FIG. Furthermore, in this embodiment,
When a ferroelectric liquid crystal is used as the liquid crystal, the distance between opposing electrodes can be 3 μm or less, typically 1.5 ± 0.5 μm.

An embodiment of the present invention will be described below. Example 1 FIG. 1 is a circuit diagram for explaining the liquid crystal display device of this example. In FIG. 1, the pixel is SCLAD (2).
Of the ferroelectric liquid crystal (3) from the electrode (21) (first electrode) of the ferroelectric liquid crystal (3)
3) (third electrode). SCLAD is Y wiring
It is connected to (4) and (5) by the second electrode (22). On the other hand, the fourth electrode (24) of the ferroelectric liquid crystal (3) (counter electrode)
Is connected to X wirings (6) and (7). The X wiring corresponds to the third electrode (23) of the ferroelectric liquid crystal (3) and corresponds to another transparent insulating substrate, typically a glass substrate (see FIG. 4C).
It is provided closely to the (20 ') side ((6) or (24) in Fig. 1 and Fig. 4 (C)).

FIG. 2 is a diagram for explaining a manufacturing process in the case where a composite diode and a ferroelectric liquid crystal are connected in series to form one pixel in this embodiment. FIG. 3 is a diagram for explaining the characteristics in the case where a composite diode and a ferroelectric liquid crystal are connected in series to form one pixel in this embodiment. FIG. 4 is a configuration diagram of an embodiment of the present invention, which is a plan view (A), a vertical sectional view (B) and (C) in a region surrounded by a broken line in FIG.
, (D) are shown. And Fig. 2 (A), (B), (C)
, (D) correspond to FIG. 4 (D). In FIG. 2A, Corning 7059 glass (20) was used as the translucent insulating substrate. Molybdenum, which is a conductive film, is deposited on the upper surface by sputtering or electron beam evaporation to a thickness of 0.1 μm to 0.5 μm.
It was formed to a thickness of μm. After this, light CV over these entire surfaces
A non-single crystal semiconductor film was formed by using the D method or the plasma CVD method. Its thickness is N type semiconductor (13) (0.1 μm)
-I type semiconductor (14) (0.3μm) -N type semiconductor (15) (500Å)
SCLAD with NIN junction. After that, chromium is deposited on this upper surface by electron beam evaporation or sputtering.
It was laminated to a thickness of 0.1 μm to 0.2 μm.

Further, as shown in FIG. 2B, anisotropic plasma etching was performed by the first photomask so that the peripheral portion was vertical, and a laminate (50) was provided. Next, a photosensitive polyimide resin (27) was formed on the entire surface of these by a coating method to a thickness of about 1 μm. Thus, the upper surface of the electrode (21) of the laminate (50) and the upper surface of the polyimide resin (27) (3
The term 9) means that the surface of the insulator and the surface of the laminate were smoothly and continuously formed after curing, except for the convex portions of the laminate. That is, ultraviolet light was exposed from the back surface side of the glass substrate (20) side using a known mask aligner from the glass surface side without using a mask. For example, a Cobilt aligner exposed for about 2 minutes. For ultraviolet light (10 mW / cm ² ) having an intensity of 300 nm to 400 nm, 15 seconds to 30 seconds is sufficient.

Then, with respect to the laminated body (thickness: about 1 μm) (50) having the side surface (26), the convex area above the shaded area is not exposed, and only the periphery of that side is exposed. Further, after developing, the non-photosensitive protrusions were removed by rinsing. Next, all of these are 180 ℃ 30 minutes + 300 ℃ 30 minutes + 400 ℃
It was heated for 30 minutes in nitrogen and cured. Thus,
In addition to exposing the second electrode of the non-linear element, which is the upper surface of the laminated body, without using a photomask, the upper surface and the peripheral surface of the polyimide resin insulator are smoothly connected to each other. It became possible to obtain C). Next, the electrode of the ferroelectric liquid crystal (3) is formed on the entire upper surface of FIG. 2 (C).
(23) (3rd electrode) ITO 0.1 μm to 0.3 μm
Was formed by a sputtering method or an electron beam evaporation method. Further, this electrode is formed into a predetermined shape, for example,
The electrode of one pixel of 120 μm × 420 μm was selectively etched by the second photomask ().

Further, an inorganic material such as alumina, silicon oxide or magnesium fluoride is used as one of the non-rubbing layers (layers not subjected to rubbing treatment) (25) of the asymmetric alignment layer on the upper surface, and 50 Å to 300 Å Was formed by the electron beam vapor deposition method. Thus, the second electrode (22) connected to the lead (6) in the Y direction, the SCLAD (2) on the second electrode (22) and the laminated body (50) of the upper first electrode (21) are provided, A third electrode (23) of the ferroelectric liquid crystal (3) may be provided in close contact with this first electrode. For this purpose, two photomasks, that is, active elements corresponding to each pixel can be provided by one mask alignment. The symbol of this SCLAD structure is described as symbol (2) in FIG. As a result, the nonlinear characteristics (electrode area 12
0 μm × 420 μm) is shown in Fig. 2 (the vertical axis is the absolute value in the log scale.
(Shown in le).

In order to form a pixel as a liquid crystal display element, as shown in FIGS. 4C and 4D, a rubbing alignment treatment is performed on the inside of the substrates facing each other in the X direction, and the counter electrode and counter electrode. (24) is provided. Then, inside the pair of electrodes (23) and the counter electrode (24), the asymmetric alignment film (2
5) and (25 ') are provided to sandwich the ferroelectric liquid crystal (thickness 2 μm). The counter electrode (24) is made of polyacrylonitrile (PAN) and polyvinyl alcohol (PVA).
It was provided by a spin method to a thickness of 1 μm and subjected to a known rubbing treatment. As an example of the rubbing treatment, nylon was rotated in a rubbing device at 900 PPM, and the surface was formed by moving the substrate at a speed of 2 m / min.

That is, an alignment film is formed on one electrode (23) without forming a rubbing treatment by forming a film of an inorganic compound. On the other electrode (24 '), an alignment film is formed by forming a film of an organic compound and rubbing the film. A ferroelectric liquid crystal, for example, octyl oxybenzylidene aminomethyl benzoate (S8) was filled between these alignment films. Other than this BOBA
It may be filled with a ferroelectric liquid crystal such as MBC, or a ferroelectric liquid crystal in which a plurality of ferroelectric liquid crystals are bent. An example of the threshold characteristic of this pixel is shown in FIG. Also in the drawing, curves (29) and (29 ') were obtained by applying ± 5V. Further, it was found that the threshold value characteristic example of the pixel shown in FIG. 3 (B) is capable of transmitting and non-transmitting, sufficiently inverting, and obtaining a hysteresis showing a memory effect. In FIG. 3B, the vertical axis represents the transmittance.

[Example 2] This example is a modification of the alignment treatment of Example 1. That is, the electrodes connected to the active element are made of inorganic material of 100 Å to 20
Formed to a thickness of 0Å. In addition, the counter electrode is made of ITO or tin oxide on top of alumina, magnesium oxide,
Alternatively, silicon oxide is formed to a thickness of about 100 Å by the electron beam evaporation method. Further, PAN or PVA was laminated thereon by a spin method to a thickness of about 0.1 μm. Then, the organic material was subjected to a rubbing treatment and an asymmetric orientation treatment. Then, it is possible to obtain curves (30) and (30 ') that further widen the hysteresis width peculiar to the ferroelectric liquid crystal, which is the characteristic of Fig. 2.
We were able to widen the width of (32) and eventually increase the contrast ratio.

[Embodiment 3] FIG. 4 is a block diagram of an embodiment of the present invention. FIG. 4 is a plan view (A) and vertical sectional views (B), (C), (D) in a region surrounded by a broken line in FIG. ) It is shown. Furthermore, FIGS. 4 (B), (C), and (D) are respectively A- in FIG.
The longitudinal cross-sectional view in A ', BB', and CC 'is shown. In addition, FIG. 4 (C)
, (D) is the ferroelectric liquid crystal (3) Alignment treatment layer (25 '), (2
5), the counter electrode (24) and the substrate (20 ') are also shown. The other (A) and (B) show only the side having the non-linear element (2) for simplicity. As the non-linear element (2), for example, a thin film type insulated gate field effect semiconductor device is used. The manufacturing method of this element is the same as that of the first embodiment. That is, two masks are used to form a rectangular first electrode (21) and a third electrode (23), and a semiconductor having the same shape as the first electrode, a second electrode (22), and a lead (4) between them. ) Is configured.

The shape of the translucent conductive film forming the third electrode (23) was 420 μm × 420 μm. Third electrode
Since (23) is provided above the rectangular first and third electrodes, if its position is set to the center of the initial position, it will not be offset even if ± 200 μm (maximum) above and below it. The electrode area of the linear element does not change, and it is possible to make a pattern without affecting the electrical characteristics (current value) at all. That is,
In a 640 × 400 device, for example, a glass substrate (30
The upper right edge and the lower left edge (cm x 20 cm) cause the mask to shift by a factor of 10 compared to the conventional one, for example, one side is 200 on the + side.
It is possible to align the mask even with poor accuracy in which the other side shifts to the negative side by 200 μm. In the drawing, ferroelectric liquid crystal
(3) is a pair of substrates (20), a counter substrate (20 '), a pair of electrodes
It is filled between (23), the counter electrode (24), and the asymmetric alignment layers (25) and (25 ').

After that, as the display panel, a light source of a transmissive type was provided on the back side, and this power source was selected by the shutter function of the ferroelectric liquid crystal to be used as a display. In order to make it a reflective type, the third electrode (23) should be in close contact with the first electrode (21) and an aluminum electrode (thickness 0.3 μm) should be formed on top of it.
ITO (thickness 0.1 μm) was provided. Then, since the reflectance of this aluminum is particularly 100%, incident light from the left side in FIG. 4 (D) can be reflected only by the electrode portion, and the ferroelectric liquid crystal (3) is turned on or off. , Reflected light can be emitted to the right. That is, the reflected light can be reflected into the incident light regardless of the thin film type insulated gate field effect semiconductor device as the active element (2) and the resin (20) around the side thereof. Since the liquid crystal material is a ferroelectric liquid crystal, this is possible for the first time as a result of providing an asymmetric alignment film on the electrode, and in particular, providing an alignment layer not subjected to rubbing treatment on the reflective electrode. .

In the conventional Twistic nematic liquid crystal type, the glass substrate (see FIG.
If it is compared with (D), the (20) side must be further deflected and the light reflected by the reflector must be emitted again to the incident light side. Therefore, the light source becomes long and the light loss becomes large. Therefore, if the ferroelectric liquid crystal is used as the reflective liquid crystal, the contrast can be improved. Furthermore, FIG.
The peripheral circuits (8) and (9) shown in (1) were arranged on a printed circuit board, and the leads of this printed circuit board and the respective leads of the display element were connected so as to correspond to each other. Thus, it becomes possible to pattern an active element type panel with only three masks.

The aperture ratio was 86.7% in the case of the pattern shown in the drawing, and could be reduced to 4.5% as compared with 91.2% in the passive system which does not use any element. This is sufficient to satisfy the specifications that if the aperture ratio is 80% or more, there is no annoyance. Also, the viewing angle is
Since a ferroelectric liquid crystal is used, not only one light shield plate,
In particular, because it uses ferroelectricity, it does not have the narrow viewing angle found in Twistick nematic liquid crystals. The examples of the present invention showed a 2 × 2 matrix. However, the experiment was done by creating a 100 × 100 matrix. It was confirmed that the characters and the like were sufficiently displayed. If frequency characteristics are taken into consideration, 8-bit parallel processing is applied and full color of 1920 (640 × 3) × 400
It is also possible to create the display device of.

Further, according to the present invention, the number of photomasks required for manufacturing the substrate may be two in order to form the pixel composed of the non-linear element and the ferroelectric liquid crystal. In addition, the electrode area of the non-linear element (current value when a given voltage is applied) may change up or down by up to ± 200 μm from the center of the rectangular electrode, or even a few mm left or right. It has a certain non-linear characteristic and can prevent the variation in the electric characteristic of the active drive over the entire matrix. In the embodiment of the present invention, SCLAD
The structure is mainly shown. But this interactive dio-
The mode may have a MIM (metal-insulating film-metal) structure. In this case, the conductor (M) was metallic tantalum or chromium. However, other metals such as aluminum, titanium and copper may be used. Alternatively, a semiconductor to which impurities are added at a sufficiently high concentration, that is, a P ⁺ or N ⁺ type non-single-crystal semiconductor may be used.

On the other hand, according to the embodiment of the present invention, as another non-linear element, one diode having a PIN structure or a diode having a tandem structure is provided as a ring ring,
It is also possible to provide a PIN structure with back-to-back bonding. However, the former has the drawback that it requires four photomasks, but it is presumed that the frequency characteristics are superior to the MIM structure and a large area of 640 × 400 is possible. On the other hand, in the latter, the process is NIP-based instead of the MIM laminate of the present invention.
Only the electrode-PIN structure can be used, and the exact same process can be used, and it can be processed with two photomasks. However, there are drawbacks that the reverse withstand voltage is too large, and the voltage easily varies in a large area.

[0027]

As described above in detail, the present invention is a combination of an active element, particularly a thin film type insulated gate field effect semiconductor device and a ferroelectric liquid crystal. Then, the electrode on the active element side is subjected to the asymmetric alignment treatment in which the rubbing treatment is not performed, so that the active element is not damaged by the rubbing treatment. As a result, the liquid crystal display device of the present invention was able to produce a large area display. For example, 2 × as in the embodiment
Even in the matrix structure of 2, when the active element and (1, 1) shown in FIG. 1 are turned on, (1, 2), (2, 2),
For non-linear elements, the voltage applied simultaneously via (2, 1)
No current flows because the OV current value is low enough. As a result, when (1, 1) was turned on, it was possible for the first time to turn off other addresses at the same time with a non-linear element, and it was possible to completely prevent crosstalk. The manufacturing process was also extremely simple in the structure shown in the embodiment.

[Brief description of drawings]

FIG. 1 shows a circuit diagram for explaining a liquid crystal display device of this embodiment.

FIG. 2 is a drawing for explaining a manufacturing process in the case where a composite diode and a ferroelectric liquid crystal are connected in series to form one pixel in the present embodiment.

FIG. 3 is a diagram for explaining characteristics in the case where a composite diode and a ferroelectric liquid crystal are connected in series to form one pixel in the present embodiment. It is one longitudinal cross-sectional view showing a manufacturing process of the space charge limited current type composite diode of the present invention.

FIG. 4 is a configuration diagram of an embodiment of the present invention, and is a plan view (A) and vertical sectional views (B) and (C) in a region surrounded by a broken line in FIG.
, (D) are shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Area 2 ... Composite type diode using space charge limiting current 3 ... Ferroelectric liquid crystal 4, 5 ... Y wiring 6, 7 ... X wiring 8, 9 ... Periphery Circuits 21, 22, 23, 24 ... Electrodes

Front page continuation (72) Inventor Toshimitsu Onuma 7-21-21 Kitakarasuyama, Setagaya-ku, Tokyo Inside the Semiconductor Energy Laboratory Co., Ltd. (72) Inventor Mitsunori Sakama 7-21-21 Kitakarasyama, Setagaya-ku, Tokyo (72) Inventor, Toshiji Hamaya 7-21-21 Kitakarasyama, Setagaya-ku, Tokyo Incorporated, Semiconductor Energy Laboratory (72) Minoru Miyazaki, Inventor 7-21 21 Kitakarasyama, Setagaya-ku, Tokyo No. 21 Inside Semiconductor Energy Laboratory Co., Ltd. (72) Kohei Okitsu 7-21 Kitakarasyama, Setagaya-ku, Tokyo No. 21-21 Inside Semiconductor Energy Laboratory Co., Ltd. (72) Toshiharu Yamaguchi 7-chome Kitakarasyama, Setagaya-ku, Tokyo 21-21 No. 21 Semiconductor Energy Laboratory Co., Ltd. (56) References JP-A-59-137925 (JP, A)

Claims (2)

[Claims] 1. A pixel is formed by connecting an active element composed of a thin film type insulated gate field effect semiconductor device formed on a substrate and a ferroelectric liquid crystal, and these pixels are arranged in a matrix. In the liquid crystal display device, an insulating film which is not subjected to alignment treatment is provided inside the electrode on the active element side of the pair of electrodes sandwiching the ferroelectric liquid crystal. . 2. An active element composed of a thin film type insulated gate field effect semiconductor device formed on a substrate and a ferroelectric liquid crystal are connected to form one pixel, and these pixels are arranged in a matrix. Liquid crystal display device.