JPS6247623A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain an image having a high saturation and contrast, notwithstanding an unevenness of the substrate by orientating a liquid crystal vertically on an array substrate of a thin film transistor having a display picture element electrode, and by orientating the liquid crystal horizontally on an transparent substrate which has a counter electrode. CONSTITUTION:The display picture element electrode 35 contg. the thin film transistor array is formed on the glass substrate 32 followed by forming the vertically orientating film 38 on the prescribed electrode 35. While, the counter electrode 36 and the horizontally orienting film 37 composed of a polyimide are formed on the glass substrate 31 followed by rubbing it. And then, the liquid crystal 42 is enclosed between the substrates 31 and 32. The surroundings of the prescribed liquid crystal is sealed with an epoxy adhesives 39. And, polarizing plates 33 and 34 are stuck on the outside of the substrates 31 and 32 respectively such that the polarizing axis makes an angle of 45 deg. to a direction of rubbing of the orienting films. A conductor 40 is connected with a contact 41. Thus, if the substrate the unevenness, the uniform hybrid arrangement makes possible, and the display having the high saturation and contrast is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a hybrid array type electric field controlled birefringence effect type liquid crystal display device.

[Technical background of the invention and its problems] Liquid crystal display devices that display arbitrary figures and characters in color use active elements such as thin film transistor (hereinafter referred to as TPT) arrays, guest-host type, color filter type, or electrolytically controlled birefringence. It has been proposed in the past to drive an effect (hereinafter referred to as EC8) type liquid crystal display.

However, in the guest-host type and color filter type, each pixel can only display one color, so when displaying multiple colors, the resolution may decrease, or the guest dye itself or color filter itself may absorb light of a specific wavelength. This caused problems such as the display screen becoming dark and colors changing over time due to fading of the dye itself or the color filter itself.

On the other hand, color display using the ECB effect does not have these problems and is therefore advantageous when performing multicolor display in combination with TPT.

In general, liquid crystal display devices using the EC8 effect are roughly classified into the following four types from the viewpoint of liquid crystal alignment when no voltage is applied.

That is, (a) horizontal arrangement, (b) vertical arrangement, (c) tilted arrangement, and (d) hybrid arrangement (hereinafter referred to as HAN).
(S,) latsumoto etal; J, Ap
pl, Phys, 47-9.3842 (1976).

Among these methods, methods (a) and (b) have the problem that the color changes rapidly with respect to voltage, making color control difficult. Further, in the method (c), since the tilted arrangement method uses tilted deposition of SiQ, etc., manufacturing is complicated and expensive.

On the other hand, vertical alignment (usually achieved by forming a vertical alignment film) on one substrate, and horizontal alignment (usually achieved by rubbing after forming a horizontal alignment film) on the other substrate.
In the (2) HAN type array type CB effect liquid crystal display device, it is easy to form an oriented thin film and the color change with respect to voltage is gradual, so color control is easy and color separation is clear. There are advantages.

However, when realizing this AN array type ECB effect liquid crystal display using a TFT array substrate, the following problems occur.

In other words, there is a height difference between the transistors, wiring, etc. of the TPT substrate and the surface of the transparent substrate (usually transistors and wiring are higher than the display area by several micrometers), and unevenness occurs on the TFTI board surface. When horizontal alignment is induced on a TPT substrate, it becomes difficult to uniformly apply rubbing to the entire display pixel, resulting in a problem of poor alignment, resulting in a decrease in the saturation of displayed colors.

[Object of the Invention] The present invention has been made to solve the above problems, and is an I-
Uniform HA in IAN type ECB effect liquid crystal display device
The purpose of the present invention is to obtain a liquid crystal display element having an N arrangement, high saturation of display colors, and high contrast.

[Summary of the Invention] In order to achieve the above object, the liquid crystal display device of the present invention has a transparent substrate having a display pixel electrode and a transparent substrate having a counter electrode, which are disposed facing each other with their electrode surfaces facing inside. A haoblid array liquid crystal cell is configured such that a liquid crystal is sandwiched between substrates, and the liquid crystal is vertically aligned on one transparent substrate and horizontally aligned on the other transparent substrate, and In an electric field controlled birefringence effect type liquid crystal display device with two polarizing plates,
The vertical alignment is induced on a transparent substrate having the display pixel electrode, and the horizontal alignment is induced on a transparent substrate having the counter electrode.

In the present invention, when performing vertical alignment treatment on the surface of a transparent substrate having display pixel electrodes, a TPT array can be used as the display pixel electrode since rubbing is not required. Even if the horizontal alignment process by rubbing is performed, since there are no irregularities on the surface, a uniform horizontal alignment can be obtained. Therefore, the display pixel portion has a uniform HAN-shaped arrangement, and a uniform display color can be obtained.

FIGS. 2 and 3 are circuits and schematic cross-sectional views of an active matrix liquid crystal display device equipped with a TFT array that is effective when the present invention is applied.

In FIG. 2, 11 is a TPT as a switch element;
12 is a display pixel electrode connected to the source of TFTll. The gates of TPTll are commonly connected in each row to provide gate bus lines Y1, Y2, . . . Yn, and the drains are commonly connected in each column to provide train bus lines X+ N X2,
..., Xn are provided.

13 is a counter electrode, and 14 is a liquid crystal layer. Further, in FIG. 3, reference numeral 15 denotes a first electrode substrate, on which a TFT array (not shown in the figure) and display pixel electrodes 12 selectively driven by the TFT array are integrated and formed on a transparent insulating substrate 16 made of glass or the like. 17 is a second electrode substrate, and a counter electrode 13 made of a transparent conductive film is formed on a transparent insulating substrate 18 made of glass or the like.

The liquid crystal layer 14 is sandwiched between these first and second electrode substrates 15 and 17. 19 is a spacer and a sealing part.

4 and 5 show the specific structure of one pixel. FIG. 4 is a planar pattern of the first electrode substrate 15, and FIG. 5 is a detailed cross-sectional view thereof. That is, the first electrode substrate 15 has a drain electrode 20 made of a transparent conductive film and a source electrode 21 integrated with the display pixel electrode 12 formed on a transparent insulating substrate 16, a semiconductor thin film 22 deposited thereon, and a SiO2 film etc. A gate electrode 24 made of an Aβ film or the like is formed via a gate insulating film 23, and a surface protection film 25 made of a SiO2 film or the like is formed. .

In the above configuration, the liquid crystal display device operates as follows. That is, gate bus lines Y1, Y2,...Y
, are sequentially scanned and driven by a scanning signal, and the TFT11 is sequentially turned on for a period of TF/n for each gate bus line. Here, the bottom is the frame scanning period. For example, when parallel image signal voltages are supplied to the drain bus lines X1, X2, . . .
The liquid crystal layer 14, which is sandwiched between the two terminals 4 and 4, is excited in accordance with the signal voltage, and an image is displayed.

In such display devices, the TPT is susceptible to light effects. In particular, when amorphous silicon (a-8i:H) is used as a semiconductor film, the electrical conductivity increases by more than three orders of magnitude when irradiated with light, and the leakage current in the OFF state of TPT increases significantly. This has the disadvantage of degrading the performance of the display device. To guarantee this, it is necessary to provide a light shielding tank in the TFT section.

Further, in the above display device, the signal voltage transmitted through the TFT II is held by a capacitor formed by the display pixel electrode 12, the counter electrode 13, and the liquid crystal layer 14, but in many application examples, the signal voltage transmitted through the TFT II is A leakage current flows, and the signal voltage is attenuated by the time TFTll is driven next.

To avoid this, an auxiliary capacitor is often provided in parallel with the liquid crystal capacitor. In this case, as shown in FIG. 5, a capacitor electrode 26 made of a transparent conductive film is first formed on the transparent insulating substrate 16, and then an insulating film 26 such as a SiO2 film is formed on the transparent insulating substrate 16.
7, a TFT array and display pixel electrodes are formed in the same manner as in FIG.

[Embodiments of the invention] Next, examples of the present invention will be described.

FIG. 1 is a partial sectional view of a liquid crystal display device according to an embodiment of the present invention.

In the figure, 31.32 is a glass substrate, 33.3
4 is a deflection plate attached to these glass substrates 31 and 32, and 35 and 36 are display pixel electrodes (including TPT), respectively.
The counter electrodes 36 and 37 are a horizontal alignment film and a vertical alignment film, respectively, and the horizontal alignment films are subjected to a rubbing treatment.

Reference numeral 39 indicates an adhesive, 40 a conductor, and 41 a contact.

The liquid crystal display device of this example is manufactured as follows.

That is, first, TPT is formed on the glass substrate 32, and a vertical alignment agent FC8 (trade name of 3M Company) is dip-coated thereon to form the vertical alignment film 38. On the other hand, a counter electrode 36 is formed on the glass substrate 31, a horizontal alignment film 37 made of polyimide is formed thereon, and rubbing is performed on this in a usual manner. Next, these two glass substrates 31 and 32 are held with a distance of 25 μm between the substrates by scattering glass spacers on the opposing surfaces, and a nematic liquid crystal E8 (trade name of B, D, To1 Company) 42 is sealed, Seal around the area with three epoxy adhesives. Roughly, two polarizing plates 33 and 34 are pasted on the outside of both glass substrates 31 and 32 so that one optical axis is at an angle of 45 degrees with the rubbing direction, and the conductor 40 is connected to the contact 41 to create a liquid crystal display. The device is completed. Note that the difference in height between TPT and display pixel electrode is approximately 3 μm.
It is.

Further, as a comparative example, a horizontal alignment film 3 is provided on the display pixel electrode 35 side.
A liquid crystal display device having the same structure as the example except that a vertical alignment film 38 was formed on the opposite electrode 36 side was fabricated. FIGS. 7 and 8 are cross-sectional views showing the arrangement states of the liquid crystal display devices of the example and the comparative example during driving, respectively, and the arrows indicate the direction of rubbing.

In each of these liquid crystal display devices, the example showed a uniform color, whereas the comparative example showed areas of different display colors around the convex portion of the TPT. This is because in the embodiment of the present invention, the glass substrate with unevenness on the TPT side shows a uniform HAN arrangement because it is not rubbed.
This is because in the comparative example, rubbing was not performed sufficiently around the convex portion on the TFT side, and a uniform HAN arrangement could not be obtained.

In addition, the chromaticity of the entire screen when various identical signals are applied to all display pixels and various identical colors are displayed on the entire screen is that in the comparative example, sufficient saturation is achieved in the shaded area in Figure 10. On the other hand, in the example, as shown by the solid line in FIG. 9, the saturation was significantly increased and a vivid display was obtained.

[Effects of the Invention] According to the present invention, a uniform HAN arrangement can be obtained even when a transparent substrate having an uneven surface due to TPT or the like is used.
This results in HA with high display color saturation and high contrast.
An N-type ECB effect liquid crystal display device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view explaining the present invention in detail, FIG. 2 is an equivalent circuit diagram of an active matrix liquid crystal display device, FIG. 3 is a schematic sectional view showing its overall structure, and FIG. 4 is a sectional view of one pixel. A diagram showing the first electrode substrate pattern, FIG. 5 is a cross-sectional view of one pixel, FIG. 6 is a cross-sectional view corresponding to FIG. 5 of an active matrix liquid crystal display device provided with auxiliary capacitance, and FIG. FIG. 8 is a cross-sectional view for explaining the state of the liquid crystal during operation in the example and comparative example, respectively, and FIG. 9 is a partially enlarged plan view for explaining the display state of the display pixel section in the example of the present invention. FIG. 10 is a partially enlarged plan view illustrating the display state of the display pixel section of the comparative example. 31.32... Glass substrate 33.34... Polarizing plate 35... Display pixel electrode (including TPT) 36.
...Counter electrode layer 37...Horizontal alignment film 38...Vertical alignment film Applicant: Toshiba Corporation Patent attorney Satoshi Suyama - Figure 3, Figure 4, Figure 9 Figure 10 Procedural amendment (voluntary) October 4, 1985 2, Title of invention: Liquid crystal display device 3, Person making the amendment Relationship with the case Patent applicant: Toshiba Corporation 4, Agent: 101 Tokyo 2-1, Kandatamachi, Chiyoda-ku (1) The claims, detailed description of the invention, and brief description of the drawings in Book 1 (1) (2) "Drawings" are corrected. ■ On page 5, line 4, "have" was corrected to "have unevenness on the surface." ■ On page 5, line 20, "Iwo" was corrected to "a board with uneven backside like A." ■ On page 9, line 2, "Figure 5" was corrected to "Figure 6." ■ On page 9, line 14, "Counter electrode 36.37" was corrected to "Counter electrode, 37.38." ■ On page 10, line 2, rFc8J was corrected to rFc805. ■ After the 11th line of page 11, it says, ``When we investigated the color of each pixel when actually driven, it was found that in the example, as shown in Figure 9, the color was uniform throughout the display pixels. On the other hand, in the comparative example, the shaded area in Figure 10 was different in color from the other areas.'' was added. ■ On page 11, line 14, "as shown by diagonal lines in Figure 10" was corrected to "as shown in dashed lines in Figure 11". ■ On page 11, line 16, "Figure 9" was corrected to "Figure 11." (3) Correct the brief description of the drawing as follows. ■ "De" in line 16 of page 12 was corrected to "Figure 11 is a chromaticity diagram showing the display colors of the example and comparative example." (4) Add Figure 11 of the drawing. [Attachment F] Claims (1) A transparent substrate having a display pixel electrode and an uneven surface and a transparent substrate having a counter electrode are arranged facing each other with the electrode surfaces inside, and the space between these transparent substrates is a hybrid array liquid crystal cell configured to sandwich a liquid crystal between the two transparent substrates, vertically align the liquid crystal on one transparent substrate, and horizontally align the liquid crystal on the other transparent substrate; In the field-controlled birefringence effect type liquid crystal display device, the vertical alignment is induced on a transparent substrate having the display pixel electrode, and the horizontal alignment is induced on the transparent substrate having the counter electrode. A liquid crystal display device characterized in that: (2) The liquid crystal display device according to claim 1, characterized in that the bulge having the display pixel electrode and having an uneven surface is a thin film transistor array.

Claims (3)

[Claims] (1) A transparent substrate having a display pixel electrode and a transparent substrate having a counter electrode are arranged facing each other with the electrode surfaces facing inside, a liquid crystal is sandwiched between these transparent substrates, and this liquid crystal is placed on one of the transparent substrates. An electric field controlled birefringence effect type liquid crystal cell comprising a hybrid array liquid crystal cell configured to be vertically aligned on one transparent substrate and horizontally aligned on the other transparent substrate, and two polarizing plates arranged on the outside of both the transparent substrates. A liquid crystal display device, wherein the vertical alignment is induced on a transparent substrate having the display pixel electrode, and the horizontal alignment is induced on a transparent substrate having the counter electrode. (2) The liquid crystal display device according to claim 1, wherein the display pixel electrode is a thin film transistor array. (3) The liquid crystal display device according to claim 1 or 2, wherein the horizontal alignment is performed by a horizontal alignment film and irregularities formed thereon and oriented in a certain direction.