JPS5893031A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active matrix type liquid crystal display device in which sufficient contrast can be obtained.

In recent years, there has been a growing demand for image display devices that are smaller and consume less power than cathode ray tubes, etc., and in response to this demand, image display devices that use liquid crystal display devices that have features such as thinness, low voltage drive, and low power consumption have been developed. Nowadays, various methods of driving image display devices using liquid crystal display devices have been put into practical use.At present, there are two driving methods for image display devices using liquid crystal display devices: a time-division driving method (also called a simple matrix method) and an active matrix method. Some methods are known, but among these, in the time division driving method, there is a limit of 4 in increasing the number of pixels, making it difficult to increase the resolution. However, in the active matrix method, each pixel has a switching element, so in principle there is no limit to the number of pixels, and sufficient resolution can be obtained, so it is widely adopted as a liquid crystal display device for displaying images. Therefore, we will introduce an example of a liquid crystal display device using this active matrix method as the first example.
IIK shows 0 1 II is a side view of the entire structure with water included, 1
2 is a semiconductor substrate such as a transistor for switching devices arranged in a tube matrix, 2 is a liquid crystal, 3 is a glass plate provided with transparent electrode tubes, and 4 is a spacer.

As is clear from FIG. 1, this active matrix type liquid crystal display device differs from the conventional type using two glass substrates in that one substrate is an opaque semiconductor substrate. The format cannot be made into a transmission type, and is limited to a reflection type.

Therefore, the liquid crystal that can be used in this active matrix liquid crystal display device is dynamic switching (dynamic switching).
# Akira Kato and guest host (guest-heat)y
# There are 02 types of tansho, but among them, those with a wide viewing angle,
In terms of low power consumption, etc., a device using a guest-host type housing is superior.

An example of an active matrix type guest-host liquid crystal display device suitable for such image display will be explained with reference to Figs. 2 to 4. First, Fig. 2 shows its equivalent circuit, and 5 is a switching MO8) 6 is a storage capacitor, 7 is a liquid crystal cell, 8 is a scanning electrode, and 9 is a signal electrode.

A unit pixel of a liquid crystal display device is composed of a transistor 5, a capacitor 6, and a liquid crystal self, and is driven line-sequentially.
Or it is done point-sequentially.

Now, when a pulse is applied to the selected scanning electrode 8, the transistors in the horizontal direction are turned on, and in synchronization with this, the amplitude is modulated by the video signal and the pulse is selected from the signal electrode 9. The voltage is applied to the capacitor 6 and the liquid crystal cell through the transistor 5, and a display is performed.

At this time, the scanning pulse disappears and the MOS) transistor 5
Even if the LCD is turned OFF, as long as the photocharge accumulated in the capacitor 6 continues to apply voltage to the liquid crystal display, the liquid crystal display can continue displaying according to the voltage. The photocharge accumulated in the capacitor 6 is discharged through the OFF resistance of the MOS transistor 5 and the resistance of the liquid crystal self until the next scanning pulse is applied.

Therefore, as shown in Fig. 2, if a large number of unit pixels are arranged in a matrix, the horizontal MOS transistors are turned on as described above, a video signal is written to the capacitor, and the image signal is sequentially scanned in the vertical direction. Images can be displayed from K.

FIG. 3 is a cross-sectional structural diagram of a semiconductor substrate 1 constructed by integrating the unit pixels shown in FIG. 2 on a silicon substrate, and is a MOS
) The transistor 5 includes a source diffusion layer 10, a drain diffusion layer 11, a gate oxide film 12, and a gate electrode 13.
(polysilicon electrode), capacitor 6Fi
It is composed of a capacitor diffusion layer 14, a capacitor oxide film 15, and a capacitor electrode 16 (polysilicon electrode). In addition, the gate electrode 13 also serves as the scanning electrode 8. 17 is the first layer aluminum wiring,
It is used for wiring between the drain diffusion layer 11 and the capacitor electrode 1-, and for the signal electrode 9. 18t! The second layer of aluminum wiring forms one pixel electrode of the liquid crystal cell. Also, 19 is 810. 20 is a silicon substrate, and 21#i is an alignment control film for aligning liquid crystal molecules.

Next, a silicon substrate 2 on which such an integrated circuit is formed
01 As shown in FIG. 4, the pixel electrode 18 and the transparent electrode 22 are placed facing each other with a glass plate 23 with a transparent electrode 22 attached thereon, and a guest-host type liquid crystal is sealed between them.
The liquid crystal self is composed of:

Here, FIGS. 4(a) and 4(b) show the principle of success of the guest-host type liquid crystal cell.

First, in the so-called OFF state in which no voltage is applied to the liquid crystal cell shown in FIG. They are oriented in parallel, and the dye molecules 25 also point in the same direction as the liquid crystal molecules 24, so these molecules 24 and 25 are both parallel to the silicon substrate 20 and the glass plate 23. On the other hand, when the light enters from above the glass plate 23, Since the nine lights 27 pass through the polarizing plate 26' and are polarized in the long axis direction of the dye molecules 25, they are absorbed by the dye molecules 25, and therefore, at this time, the liquid crystal cell appears colored.

Next, in the so-called ON state where the voltage shown in FIG. Since it is facing the direction, the incident light 27 is the dye molecule f
In the end, K does not color the liquid crystal cell.

Therefore, in the active matrix guest-host type liquid crystal display device, when a voltage is applied, the surface of the silicon substrate 20 (mainly the surface of the pixel electrode 180) is visible, and therefore, the surface of the pixel electrode 18 is visible. If the brightness and contrast are determined by the reflection characteristics of the surface and the absorption characteristics of the dye, then it becomes K.

Therefore, such an activity invasion itrix method guest
In a host type liquid crystal display device, in order to obtain high contrast and a wide viewing angle, the surface of the pixel electrode 18 of the silicon substrate 20 is required to have a bright white color like a diffuse reflection surface.

Conventionally, as a method for obtaining such diffuse reflection Wi, the formation conditions of 1 g of pixel electrode (second layer aluminum wiring) (
For example, by controlling the substrate temperature, deposition rate, degree of vacuum, etc.), or by controlling the subsequent heat treatment, the surface of the pixel electrode 18 can be made uneven (
The idea was to make it so-called milky.

However, the diffuse reflection characteristics of such an uneven surface are related to the depth h1 pitch p of the unevenness; when h<p, it becomes a mirror surface, and when h>p, it becomes black due to absorption due to multiple reflections. Therefore, in order to obtain a bright white color, h
and pt - Strict and strict control is required to obtain the optimum value. However, with the above-described method of controlling the formation conditions and heat treatment of the pixel electrode 18 to obtain an uneven surface, it is very difficult to set h and p to optimal values, and bright white color 11 cannot be obtained. However, the disadvantage was that sufficient contrast could not be seen.

As is clear from FIG. 3, there are many steps on the surface of the semiconductor substrate 1O due to circuit formation (turn formation, etc.), but in the conventional method described above, these steps remain. Therefore, there is a disadvantage that there is a lot of multiple reflection at these stepped portions, and the contrast is also reduced.An object of the present invention is to eliminate the disadvantages of the above-mentioned prior art and to easily improve the surface mt of a semiconductor substrate. It can be made to exhibit a bright white color,
An object of the present invention is to provide an active matrix guest-host type liquid crystal display tube that can obtain sufficient contrast improvement.

In order to achieve this object, the present invention uses a heat-resistant organic insulating film such as polyide as an interlayer insulating film of a semiconductor substrate on which a pixel electrode is formed, and absorbs steps caused by circuit patterns, etc. In addition, in order to easily control the surface shape, the point t41 is set as 0. Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described with reference to the drawings.

FIG. 115 shows an embodiment of a semiconductor substrate in a liquid crystal display device of the present invention, in which the same or equivalent parts as in the conventional example of FIG. 3 are given the same reference numerals, and detailed explanation thereof will be omitted.

In the embodiment shown in FIG. 5, 28 is a heat-resistant organic insulating film made of polyimide or the like, and 810 in the conventional example shown in FIG.
It is provided in place of the two-layer insulating film 19, and the rest is the same as the conventional example shown in FIG.

In this embodiment as well, the overall structure, equivalent circuit, and operating principle of the liquid crystal display device will be described.
Since they are the same as the conventional examples shown in FIGS. 2 and 4, detailed explanations thereof will be omitted.

Now, in the embodiment shown in FIG.
are formed after the formation of the first layer of aluminum wiring 17 is completed.

First, a polyimide coating liquid made of predetermined components is prepared, and this is applied relatively thickly to the silicon substrate 20 on which the formation of aluminum wiring 17 has been completed using a spinning method, and then hardened by a predetermined heat treatment. In this way, 28 tubes of heat-resistant organic insulating film are formed.

Next, the surface 28't of this heat-resistant organic insulating film 280 is photo-etched to form a number of recesses 29 having a predetermined pitch p' and depth h', and then, as in the conventional example, an aluminum wiring that will become the pixel electrode 18 is formed. and orientation control film 21? By providing this, it is possible to obtain a semiconductor substrate it which has a large number of recesses 18' with a predetermined pitch p and depth h on the surface of the pixel electrode 18.

According to this embodiment, a heat-resistant insulating film 28 made of polyimide or the like is applied relatively thickly on the surface of the first layer of aluminum wiring 17, and then steps on the surface of the silicon substrate 2o caused by circuit patterns etc. are absorbed. Since the surface area of the film 28 is averaged and curved, the surface w2' of this film 28 becomes almost flat.

In addition, the formation of the recess 29 on the surface 2''8' requires the following steps:
Since the photo-etching technique can be applied, this O recess 29
It becomes extremely easy to control dimensions such as the pitch p' and depth h' of the pixel electrode 18 (second layer aluminum) formed on the surface. Concave portion 18 to be formed on the surface of the ζ nium matrix Im)
Since the dimensional accuracy of the pitch p and depth h of ' is kept sufficiently high, the semiconductor substrate 10 surface can be made into a bright white diffuse reflection surface, and the contrast of the liquid crystal display device can be sufficiently improved. can.

Next, FIG. 1 shows another embodiment of the present invention.

In FIG. 6, 30 is the second layer aluminum wiring 18
30' is an aluminum wiring provided directly on the surface of the heat-resistant organic insulating film 28.
This is a convex portion formed by separating the two by etching or the like.

That is, in this embodiment, the first layer aluminum wiring 17
A heat-resistant organic insulator 1128 such as polyimide is provided on top of the aluminum wiring 30, and then K is immediately provided on the surface of the aluminum wiring 30 without etching its surface shape to shape it.
Then, a large number of convex portions 30' are separated and formed by photo-etching or the like.

Then, a second layer of aluminum wiring 18 is provided thereon, and due to the presence of the convex portion 30', a recess [118'] having a predetermined pitch p and depth ht- is formed on the surface of this aluminum wiring 18.
K is formed so that .

Therefore, according to this embodiment as well, the aluminum wiring 3
Since the photo-etching technique can be applied to form the convex portions 30' apart from the convex portion 30', the dimensional accuracy of the pitch p and depth h of the concave portions 18' can be easily controlled, and a bright white diffuse reflection surface can be formed. In addition, according to this embodiment, the surface shape of the heat-resistant organic insulating film 280 remains flat, which makes it difficult to obtain a liquid crystal display device with improved contrast. It is inevitable that the aluminum wiring 17 and the double-layer aluminum wiring 18 will cause an unnecessary short circuit in the thinned part of the heat-resistant organic insulating film 28, and the liquid crystal display device will have excellent reliability. can be obtained.

As explained above, according to the present invention, with a simple structure in which a heat-resistant organic insulating film is used as an interlayer insulating film of a semiconductor substrate, it is possible to eliminate the level difference on the pixel electrode surface of the semiconductor substrate, and to produce bright white diffuse reflection. Since it can be shown that the present invention provides characteristics, it is possible to eliminate the drawbacks of the prior art, sufficiently improve image contrast, and provide a highly reliable active matrix type liquid crystal display device.

[Brief explanation of drawings]

Figure 1 is a side view showing an outline of an active matrix type liquid crystal display device, and Figures 2 and 3 are equivalent circuit diagrams.
The figure is a partially enlarged cross-sectional view showing a conventional example of a semiconductor substrate in an active matrix type liquid crystal display device;
), (b) are explanatory diagrams of the operation of a guest-host type liquid crystal display device, FIG. 5 is a cross-sectional view showing one embodiment of a semiconductor substrate in the liquid crystal display device of the present invention, and FIG. 6 is another embodiment of the same. FIG. 10... Source diffusion layer, 11... Drain diffusion layer, 12...-gate oxide film, 13...
... Gate electrode, 14 ... Diffusion layer for capacitor, 16 ... Capacitor electrode, 17 ...
...First layer aluminum wiring, 18...Second layer aluminum wiring, 18'...Concavity, 20
... Silicon substrate, 21 ... Orientation control film, 28 ... Heat-resistant organic insulating film, 28' ...
...Surface, 29...Concavity, 30...
Al1=Um wiring, 30'...Protrusion. Figure 2 Figure 3 Figure 4 U Figure 6

Claims (1)

[Claims] (1) The switching element for each pixel is
In an active matrix liquid crystal display device in which one electrode surface is a semiconductor substrate arranged in a J-square shape, the electrode surface of the semiconductor substrate is formed by forming the glabella insulating film of the semiconductor substrate with a heat-resistant organic insulating film. A liquid crystal display device characterized in that it is configured to enable control of light reflection characteristics. (2. A liquid crystal display device according to claim 1, characterized in that the image shape of the heat-resistant organic insulating film is shaped to give the electrode surface a diffuse reflection characteristic. (3. ) Patent Claim 01 [8] A liquid crystal display device according to item 1, wherein the heat-resistant organic insulating film is provided with a large number of protrusions at midsummer, thereby imparting a diffuse reflection characteristic to the electrode surface. .