JPH0311318A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enlarge a picture element electrode to raise the aperture rate of the picture element electrode by producing a nonlinear resistance layer on or under a lead electrode and providing a picture element connection electrode on the face opposite to the lead electrode of the nonlinear resistance layer and connecting the picture element connection electrode and the picture element electrode. CONSTITUTION:A thin film two-terminal element is arranged on a lead electrode 2. With respect to the structure of the thin film two-terminal element, the lead electrode 2 is used as the lower electrode and a nonlinear resistance layer 3 is so formed that the lead electrode 2 is covered with it. A picture element connection electrode 4 is formed as the upper electrode so as to intersect orthogonally with the lead electrode and connected to a picture element elec trode 5. Since the thin film two-terminal element and the picture element elec trode are connected in series and the thin film two-terminal element is provided on the lead electrode 2, the part where the thin film two-terminal element con ventionally occupies can be used for the picture element electrode, as well and the picture element electrode 5 is enlarged. Thus, the numerical aperture of the picture element electrode is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thin film two-terminal element type active matrix liquid crystal display element using a nonlinear resistance element.

(Prior Art) In recent years, applications of liquid crystal display devices (LCDs), mainly twisted nematic type (TN type), have been developed and are being used in large quantities in the fields of wristwatches and calculators. In addition, in recent years,
Matrix types, which can display arbitrary characters, figures, etc., are also beginning to be used. In order to expand the field of application of this matrix type LCD in which pixels are arranged in a matrix, it is necessary to increase the display capacity. However, since the rise of the voltage-transmittance change characteristic of conventional LCDs is not very steep, when the number of scans in multiplex drive is increased to increase the display capacity, the The effective voltage ratio decreases, resulting in a cross-reaction between a decrease in the transmittance of the selected pixel and an increase in the transmittance of the non-selected pixels. (
(In case of Normanoplac with polarizing plates arranged in parallel)
. As a result, the display contrast is significantly reduced and the viewing angle at which a certain degree of contrast can be obtained is narrowed, and in conventional LCDs, the limit for high image quality is about 60 scanning lines. Recently, super twisted nematic type (
There is a type called STN type), but the contrast is T.
Although it is superior to the N type, it has a major drawback of slow response.

In order to significantly increase the display capacity of this matrix type LCD, an active matrix LCD has been proposed in which a switching element is arranged in series in each pixel of the LCD.

The switching elements of the 7 active matrix LCD prototypes announced so far are thin film transistor elements (TP) using amorphous Si or polySi as semiconductor materials.
T) is often used.

On the other hand, because the manufacturing and structure are relatively simple,
Active matrix LCDs using thin film two-terminal devices (hereinafter abbreviated as TFDs) are also attracting attention because they can simplify the manufacturing process and are expected to have high yields and low costs. This TFD
is a nonlinear resistance element in circuit terms.

Such a thin film two-terminal element type active matrix LC
In D (hereinafter abbreviated as TFD-LCD), an LCD that is considered to be close to the one used for fragrances uses a TFD with a metal-nonlinear resistance-metal structure element (hereinafter referred to as MIM element or MI
This is an LCD (hereinafter abbreviated as MIM-LCD) using MIM-LCD (abbreviated as MIM-LCD). By connecting a TFD such as MIM in series with a liquid crystal, due to the highly nonlinear voltage characteristics of the TFD,
The voltage-transmittance change characteristic of the TFD-liquid crystal becomes steeper, making it possible to greatly increase the number of scans of the liquid crystal display. FIG. 3 shows an equivalent circuit of this TFD-LCD.

In an MIM device, the most important material is the material of the insulator layer. Tantalum oxide is the most well-known insulator material. LC using such MIM
Conventional examples of D are, for example, D, R, Baraf in the paper.
f,et al,,The Opimization
of Metal-Insulator-Metal
Mon-1inear Devices for Us
e inMultiplexed Liquid Cr
ystal Displays “IEEE Tran
s.

Electron Devices, vol, ED-2
8, pp736-739 (1981) and Shinji Morikaku et al. 250 x 240 pixel lateral MIM-L
CD Television Society Technical Report (IPD83-8), p.
39-44. Published December 1983) is shown as a representative.

The characteristics required when applying such an MIM element to a large-capacity display are as follows, when the current (I) flowing through the element and the applied voltage (V) are expressed as I=A・Va (A is a constant). The nonlinear coefficient a is large, the voltage characteristics are symmetrical in positive and negative directions regardless of the polarity of the applied voltage, and the capacitance of the MIM element is small. However, MIM elements using tantalum oxide as a nonlinear resistor have good symmetry, but the nonlinear coefficient is not very large at 5 to 6, and the dielectric constant is high, so the element capacitance is large. Drink.

Therefore, silicon nitride, which has a low dielectric constant, has been developed as a nonlinear resistor for MIM elements. For example, M.
5uzuki et al “A New Activ
e DiodeMatrix LCD using O
ff-stoichiometric SiNx La
yer”Proceedings of the SI
D, Vol. 28 plol-104, 1987.

The structure of the conventional MIM-LCD shown in these documents is shown below. FIG. 4 shows a cross-sectional view of a structure using silicon nitride-based MIM elements, FIG. 5 shows a plan view of the substrate on which the MIM elements are formed, and FIG. It is shown in Figure 6.

FIG. 4 shows an example in which silicon nitride is used for the nonlinear resistance layer 3. After the silicon nitride is formed, it is patterned into a predetermined shape by etching. As shown in FIG. 6, the lead electrode 2 is led out of the liquid crystal cell and connected to a drive circuit. The counter transparent electrode 8 is perpendicular to the lead electrode 2, is patterned into a stripe shape with a width approximately corresponding to the pixel electrode, and is connected to a drive circuit. Lead electrode 2 corresponds to either data electrode 10 or scan electrode 13 shown in FIG. 3, and opposing transparent electrode 8 corresponds to the rest of data electrode 8 or scan electrode 13. Details are given in the above-mentioned document.

(Problems to be Solved by the Invention) Thin-film two-terminal active matrix liquid crystal display devices, which are the field of the present invention, have a simpler structure than TFT active matrix liquid crystal display devices and are easier to manufacture. It is attracting attention because it can display a larger capacity than display elements.

However, since a thin film two-terminal element must be fabricated in the pixel portion, the aperture ratio of the pixel electrode is lower than that of a simple matrix liquid crystal display element.

An object of the present invention is to provide a thin-film two-terminal element type liquid crystal display element that minimizes the decrease in aperture ratio due to the thin-film two-terminal element.

(Means for Solving the Problems) According to the present invention, there is provided a lower substrate in which a lead electrode and a pixel electrode are connected via a nonlinear resistance element, and an upper substrate in which a counter transparent electrode is provided in correspondence with the pixel electrode. In a liquid crystal display element consisting of a substrate and a liquid crystal sandwiched between the upper and lower substrates, a nonlinear resistance layer is formed above or below the lead electrode, and a pixel connection electrode is formed on the surface of the nonlinear resistance layer opposite to the lead electrode. A liquid crystal display element is obtained by connecting this pixel connection electrode and the pixel electrode.

(Function) FIG. 1 shows an example of one pixel of a thin film two-terminal active matrix liquid crystal device according to the present invention.

In this example, a thin film two-terminal element is placed on the lead electrode 2 .

The structure of the thin film two-terminal element is that the lead electrode 2 is used as the lower electrode.
is used. Next, a nonlinear resistance layer 3 is formed to cover the straight electrode 2. Next, a pixel connection electrode 4 as an upper electrode is formed perpendicular to the lead electrode and connected to the pixel electrode 5.

This results in a structure in which the thin film two-terminal element and the pixel electrode are connected in series, similar to the conventional example shown in FIG. Moreover, unlike the conventional example, since there is a thin film two-terminal element on the lead electrode, the part where the thin film two-terminal element was conventionally used can also be used as a pixel electrode, and the pixel electrode can be made larger.

In this way, the present thin film two-terminal active matrix liquid crystal device allows the pixel electrode to be made larger, and therefore the aperture ratio of the pixel electrode to be increased.

(Example 1) Examples of the present invention are shown below.

FIG. 1 shows a plan view of a representative example of one pixel of an active matrix LCD using a thin film two-terminal device obtained by this example, and FIG. 2 shows a cross-sectional view.

The lower glass substrate 1 is often coated with a glass protective layer such as 5i02, but since it is not essential, the coating can be omitted, and is omitted in this embodiment. First, a Cr film having a thickness of about 300 to 600 A is formed as a lower electrode, and then a lead electrode 2 which also serves as a lower electrode of a thin film two-terminal element is formed by ordinary photolithography.

Next, as the nonlinear resistance layer 3, a silicon nitride layer of 1.2
A thickness of about 00A to 2000A is formed and patterned by photolithography.

Subsequently, 100 OA of Cr is formed as an upper electrode, and patterned by photolithography to become the pixel connection electrode 4.

Furthermore, indium-tin oxide (generally called ITO) is patterned and formed as the pixel electrode 5.

An ITO film was formed and patterned on the upper glass substrate to serve as a counter transparent electrode. This is similar to the conventional thin film two-terminal element type active matrix liquid crystal panel shown in FIG. 4, and is also almost the same as a normal simple matrix LCD. After the lower glass substrate and the upper glass substrate were subjected to orientation treatment, they were pasted together with a spacer such as a glass fiber interposed therebetween, and sealed with a common epoxy adhesive. The cell thickness was 5 μm.

Thereafter, TN type liquid crystal was injected to form a liquid crystal layer. By sealing this, a thin film two-terminal active matrix liquid crystal device was completed.

(Example 2) As shown in the cross-sectional view of FIG.
A prototype was produced in the same manner as in Example 1, except that after forming the nonlinear resistor N3, the lead electrode 2 was formed.

As a result, a thin film two-terminal element could be fabricated under the lead electrode 2.

(Example 3) As shown in the plan view of FIG. 8, a prototype was produced in the same manner as in Example 1, except that the lead electrode 2 was made of tantalum and the nonlinear resistance layer was made of tantalum oxide by anodization. Anodization was carried out as usual with 0.1 wt% citric acid, and 75n
m tantalum oxide was grown.

(Example 4) As shown in the plan view of FIG. 9, the lead electrode 2 in the thin film two-terminal element part was made thinner, and the part of the pixel electrode next to the thin film two-terminal element part was recessed. A prototype was produced in the same manner as Example 1. This made it possible to reduce the probability of a defect occurring due to a short circuit between the adjacent pixel electrode 5 and the pixel connection electrode 4.

(Effects of the Invention) As described above, according to the present invention, the pixel electrode can be made large and the aperture ratio of the pixel electrode can be increased.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a first embodiment of a thin film two-terminal active matrix liquid crystal device according to the present invention, and FIG. 2 is a cross-sectional view. FIG. 3 shows a general isochoric circuit of a TFD-LCD. FIGS. 4, 5, and 6 show examples of conventional thin film two-terminal active matrix liquid crystal devices. FIG. 7 is a sectional view of a second embodiment of the invention, FIG. 8 is a plan view of a third embodiment of the invention, and FIG. 9 is a plan view of a fourth embodiment of the invention. 1... Lower glass substrate, 2... Lead electrode, 3...
- Nonlinear resistance layer, 4... Pixel connection electrode, 5... Pixel electrode, 6... Alignment film, 7... Liquid crystal layer, 8... Opposing transparent electrode, 9... Upper glass electrode, DESCRIPTION OF SYMBOLS 10... Data electrode, 11... Nonlinear resistance element, 12... Liquid crystal element, 13... Scanning electrode, 14... Terminal part.

Claims (1)

[Claims] A liquid crystal comprising a lower substrate in which a lead electrode and a pixel electrode are connected via a nonlinear resistance element, an upper substrate in which a counter transparent electrode is provided corresponding to the pixel electrode, and a liquid crystal sandwiched between the upper and lower substrates. In the display element, a nonlinear resistance layer is formed above or below the lead electrode, a pixel connection electrode is provided on the surface of the nonlinear resistance layer opposite to the lead electrode, and the pixel connection electrode and the pixel electrode are connected. A liquid crystal display element featuring: