JPH01155320A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To increase an aperture rate and to make a high-resolution or high- contrast display by forming a metal-insulating film-metal element which has a common electrode as one electrode directly at a fine-pattern position of the common electrode. CONSTITUTION:Part of the common electrode 12 is formed in a pattern which is narrow to constant line width at the position of each picture element electrode 11 and the MIM element which has the common electrode as its one electrode is formed directly at the narrow pattern position of the common electrode. Consequently, the aperture rate of picture elements is increased and the high- resolution or high-contrast display is made; even if there is a mask position shift, the area of the MIM element is caused to vary and variance in its characteristics is eliminated, so that the characteristics of the liquid crystal display are made stable.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an active matrix liquid crystal display device using a metal-insulating film-metal element (MIM element).

Prior art liquid crystal display devices have been put into practical use as lightweight and thin flat panel displays, and are now also used as displays for portable computers and pocket televisions. It is also expected to be used as a high-resolution display for personal computers and word processors, and as a large-sized display for home use or high-definition televisions.
'Here, a simple matrix method is generally used as a driving method for a liquid crystal display.

However, when display performance such as contrast ratio, number of pixels, and response are considered in order to increase resolution, the simple matrix drive method has a limit in display performance and is unsuitable for high-resolution displays.

Therefore, an active matrix method using a three-terminal element such as a thin film transistor (TPT) or a two-terminal element such as an MIM element is considered to be a promising driving method. These are, for example, JP-A No. 61-295529, rN
IKKEI ELECTRONICS 1987.
1.12 “5iNx2 terminal element aimed at reducing manufacturing cost of active matrix liquid crystal panels”
And rNIKKEI ICRODEVICES
The company is known for its articles such as ``MIM diode liquid crystal panel J that aims to improve TPT image quality by improving drive technology'' in the July 1987 issue.

However, in the case of active matrix method.

Those using TPT have the drawbacks that the number of masks is large, resulting in poor yield, and the area of the element is large, resulting in a high defect rate, and the surface has a small aperture ratio.

On the other hand, devices using MIM elements are two-terminal devices and require fewer masks, increasing yield, but current mask patterns cannot increase the aperture ratio, and when the number of pixels increases, high resolution and high Contrast displays are difficult to create. For example, Figure 6 shows MI
This shows a conventional liquid crystal display device using M elements,
The MIM element 1 is formed by laminating an insulating film 4 and an upper electrode 5 on a protruding electrode 3 formed protruding from a common electrode 2, and this upper electrode 5 is connected to a pixel electrode 6.
The MIM element 1 performs this switching.

In other words, as can be seen from the diagram, a part of the pixel electrode 6 is cut out as a notch 7 in order to prevent changes in the element area due to mask position shift of the MIM element 1, and the aperture ratio is reduced accordingly. be. Since the driving element is incorporated into the pixel in this way, the pixel area becomes small, which has the drawback of reducing the so-called aperture ratio. or,
The size of the element is several μm×several μm to several tens of μm×
Since it is small, on the order of several tens of micrometers, variations in characteristics occur due to errors in mask alignment.

OBJECTS The present invention has been made in view of the above points, and an object of the present invention is to obtain a liquid crystal display device that can increase the aperture ratio and achieve a display with high resolution or high contrast.

Structure In order to achieve the above object, the present invention provides a liquid crystal display device using a metal-insulating film-metal element in which an insulating film is interposed between the electrodes, in which a part of the common electrode is fixed at a constant position for each pixel electrode. It is characterized by forming a pattern with a narrow line width, and directly forming a metal-insulating film-metal element with the common electrode as one electrode at the narrow pattern position of the common electrode.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 and 2. First, a common electrode 12 is provided adjacent to the pixel electrodes 11, which is patterned along the direction in which the plurality of pixel electrodes 11 are arranged. Here, the MIM element 13 is connected in series between the pixel electrode 11 and the common electrode 12 for switching, but in this embodiment, this MIM element 13 is placed at the position of the common electrode 12. It is formed directly. First, the pixel electrode 11 itself is formed in a rectangular shape, and a portion thereof is formed as a protruding electrode (one electrode) 11a up to a position where it can intersect with the common electrode 12.

Then, an insulating film 14 is formed in a predetermined pattern on this protruding electrode 11a, and a common electrode 14 is formed so as to pass over these.
2, and a part of this common electrode 12 is directly used as the other electrode (metal) of the MIM element 13. Here,
A portion of the common electrode 12 where the MIM element 13 is to be formed
The thin pattern part 1 has a constant line width thinner than other parts.
It is considered to be 2a. Such a thin pattern portion 12a is formed at a position for each pixel electrode 11.

According to such a configuration, first, since the MIM element 13 is directly formed on the common electrode 12 portion, it is not necessary to extend and form the protruding electrode 3 from the common electrode 2 side to the pixel electrode 6 side as in the conventional case. Therefore, the aperture ratio of the pixel can be improved. That is, the common electrode 12 portion is at least a portion that cannot become a pixel, and the MIM element 13 is placed in this portion.
This is because forming the area does not affect the pixel and is the most effective area for improving the aperture ratio. In this way, the pixel electrode 11 does not require the conventional notch 7,
It can be fully formed into a rectangular shape and has a high aperture ratio. Furthermore, in this embodiment, the common electrode 12 portion forming the MIM element 13 is made into the thin pattern portion 12a in order to prevent the area change of the MIM element 13 due to mask positional deviation.
Moreover, the overall wiring resistance can be reduced. In other words, if the common electrode 12 in the area where the MIM element 13 is formed remains wide and there is mask misalignment, the area of the MIM element itself will change and its characteristics may vary, but even if there is mask misalignment, The MIM element 13 has a constant area regulated by the thin pattern portion 12a. Furthermore, if the wiring resistance of the common electrode 12 is high, it becomes difficult to control pixel display, so it is necessary to lower the wiring resistance, and the common electrode 12 is formed in the MIM element 1 or with a conventional line width.

By the way, the method for creating the structure of this example will be explained.

The first method will be explained with reference to FIG.

First, a transparent substrate such as glass, plastic, or flexible plastic is used as the substrate. A common electrode 12 is formed on such a substrate.

The common electrode 12 is made of Afi, Ni-Cr. Mo. Cr, Ni
% Ti, Zr, Nb, Au, As, Pt, or other highly conductive material, and is deposited to a thickness of several hundred to several thousand layers by sputtering, vapor deposition, CVD, or the like. This is patterned into a predetermined pattern using a photolithography and etching process. Furthermore, such a common electrode 1
2 or on the substrate by depositing an insulating film 14 made of SiNx, 1-C (hard carbon), etc. by CVD, sputtering, vapor deposition, etc., and then photolithography or
It is patterned into a predetermined pattern by an etching process or a lift-off method. However, the insulating film 14 may be formed by oxidizing the common electrode 12 by anodic oxidation to form an insulating film on a portion of the surface of the common electrode 12 instead of being deposited in this manner. Next, a transparent electrode that will become the pixel electrode 11 is deposited on these. Materials include ITO, ZnO:A
fi.

Zn○:Si, SnO, :Sb is used, and CVD
Several hundred to 1 μm by method, sputtering method, vapor deposition method, etc.
It is deposited to a film thickness of about Then, it may be patterned into a predetermined pattern (protruding electrode 11a+pixel electrode 11 body) by a photolithography/etching process.

The second production method will be explained with reference to FIG. 1 or 3. First, a transparent electrode as the pixel electrode 11 is deposited on a transparent substrate and patterned. Next, an insulating film 14 such as iC or SiNx is deposited and patterned by CVD, sputtering, vapor deposition, or the like. At this time, as shown in FIG. 3, the auxiliary electrode 15 may be patterned only on the protruding electrode 11a portion of the transparent electrode 11 before the insulating film 14 is deposited. This auxiliary electrode 15 is made of AQ, Ni,
Cr, Ni-Cr, Mo, Ta, Ti%Nb. Au%A
It is made of a highly conductive material such as S, Pt, etc. and,
The common electrode 12 may be formed by depositing a highly conductive material on the insulating film 14 and patterning it.

The third production method will be explained with reference to FIG. The manufacturing method is basically the same as that described above, but here the pixel electrode 11 is made into an isolated rectangular shape that does not include the protruding electrode 11a, and the MIM element 13 is made independent of the common electrode 12 and the insulating film 14. It is configured by an upper electrode 16 provided at the top.

In other words, this upper electrode 16 makes contact between the MIM element 13 and the pixel electrode 11.

MI of this embodiment method created based on such a method
FIG. 5 shows the IV characteristics of the M element 13.

Further, more specific production examples in this example will be sequentially described as specific examples 1 to 3.

Specific Example 1 ITO is deposited to a thickness of 600 mm as the pixel electrode 11 and patterned. Next, 5 Ao was used as the auxiliary electrode 15.
Af is deposited to a film thickness of 0.00 mm only on the protruding electrode 11a.
Perform patterning to leave i. After applying a resist thereon and patterning it, a hard carbon film is deposited on the resist film using a plasma CVD method to form an insulating film 14.
form. The film forming conditions at this time were a pressure of 0.0 I Torr.
r, CH4/H, = 515, RF power was 50 W, and the film thickness was 800.

Incidentally, the method for creating the hard carbon film that will become the insulating film 14 will be further explained. Although this hard carbon film can also be formed by an ion beam method, an example using a plasma CVD method will be explained here. First, as the apparatus, for example, a parallel plate type plasma CVD apparatus is used. First, the substrate on which the film is to be formed is attached to the RF power supply side where positive ion bombardment is promoted due to self-bias. and hydrocarbons (e.g. CH4, C,H,, C,H,, C4H,.

, C, H, etc.) and hydrogen is introduced into the device, and a 13.56 MHz high-frequency electric field is applied between parallel plate electrodes to generate a glow discharge.

Due to this glow discharge, the raw material gas is decomposed into radicals and ions and reacts, thereby forming an amorphous (amorphous) consisting of carbon atoms C and hydrogen atoms H or a hard carbon film partially containing microcrystalline substances on the substrate. is deposited. This hard carbon film is generally called a diamond-like carbon film, an i-C film, an amorphous diamond film, or a diamond thin film. The deposition conditions for such a hard carbon film are as follows: RF power: 10 to 200 W; pressure: 10'' to 10 Torr; deposition temperature: room temperature to 150°C.

The physical properties of the film created under these deposition conditions and the MIM
The nonlinear characteristics of the element are as follows: Specific resistance (ρ) +lO'~10''' Ω Vickers hardness (H): ~10000 kg-mm-'' Refractive index (
n): 1.9 to 2.25 nonlinear characteristic β
:2-9 Physical properties and characteristics. However, the specific resistance was measured by IV characteristics using a coplanar cell, the Vickers hardness was measured by a micro Vickers meter, and the refractive index was measured by an ellipsometer.

That is, according to X-ray and electron diffraction analysis, it is in an amorphous state (a-C:H) or an amorphous state containing about 50 to 100 microcrystalline grains.

As a result of analysis by IR absorption method and Raman spectroscopy, it has been revealed that interatomic bonds in which the carbon atoms form SP'' hybrid orbitals and SP'' hybrid orbitals coexist.

It should be noted that such a hard carbon film mainly consists of SP' and SP'.
There are two types of films, one containing SPl as the main component and the other containing SF3 mainly consisting of SPl.In addition, in film formation, the smaller the RF specific output and the lower the pressure, the higher the resistivity and hardness of the film, and the higher the hydrogen mixing ratio. As the refractive index increases, the defect density decreases, which means that a film of good quality can be obtained6.Furthermore, even when hard carbon films are manufactured at relatively low temperatures, such as room temperature to about 150°C, the film quality deteriorates. As the MIM element By forming the insulating film from a hard carbon film, variations in device characteristics are reduced, and an MIM device that can withstand mechanical damage can be obtained.In other words, damage caused by the rubbing process during encapsulation of liquid crystal material is reduced, and yield is improved. Become something.Also,
Since such a hard carbon film can be formed at a temperature as low as room temperature, the substrate is not limited to being heat resistant.
The degree of freedom in selection is increased, and the dielectric constant ε of the hard carbon film is
Since r is as small as about εr#4, it can be formed with high precision without requiring as much microfabrication as on the left, and from this point of view as well, the yield is improved.

After the insulating film 14 is formed of a hard carbon film in this way, the resist film is peeled off or the hard carbon film is patterned by a lift-off method. Further, a common electrode 12 is deposited using PT to a thickness of 1000 mm by EB evaporation, and patterned by lift-off. In this way, the MIM element 13 of the type shown in FIG. 3 is created. Patterning of the hard carbon film is not limited to the beam lift-off method. After patterning the upper electrode, the hard carbon film may be deposited on the entire surface and then patterned by dry etching.

Specific Example 2 First, a common electrode 12 is formed by depositing Cr as a material to a thickness of 1,000 yen by a vapor deposition method, and this is patterned. Next, plasma C was applied on top of this using SiNx as a material.
The insulating film 14 is formed by depositing 500 gases using the VD method using SiH4 and NH and patterning. Furthermore, the pixel electrode 11 is formed by depositing and patterning 100 layers by magnetron sputtering using IT○.

In this way, the MIM element 13 of the type shown in FIG. 2 is created.

Specific Example 3 First, a pixel electrode 11 is formed by depositing I'T 2 O as a material by sputtering to a thickness of 1000 mm, and this is patterned. Next, a common electrode 12 is formed by depositing and patterning Ta to a thickness of 3000 nm by sputtering. Then, the Ta film serving as the common electrode 12 is anodized to form an insulating film 14 made of Ta and O to a thickness of 500 mm. Thereafter, 2000 Cr is deposited as the upper electrode 16 and contact electrode and patterned. In this way, the MIM element 13 of the form shown in FIG.
is created.

Effects As described above, the present invention forms a thin pattern on a part of the common electrode to have a constant line width at the position of each pixel electrode, and forms an MI in which the common electrode is used as one electrode at the thin pattern position of the common electrode.
Since the M element is directly formed, the aperture ratio of the pixel can be increased, making it easy to create a high-resolution display or high contrast, and the area of the MIM element does not change even if the mask position shifts. Therefore, the characteristics of the liquid crystal display can be stabilized, and the characteristics of the liquid crystal display can be stabilized.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view showing one embodiment of the present invention, Figs. 2 to 4 are schematic plan views for explaining various production methods, Fig. 5 is an I-V characteristic diagram, and Fig. 6 is a schematic plan view showing an embodiment of the present invention. FIG. 2 is a schematic plan view showing a conventional example. 11... Pixel electrode, 12... Common electrode, 12a...
・Fine pattern part, 13...MIM element, 14...Insulating film, 16...Top electrode Applicant: Ricoh Co., Ltd.

Claims (1)

[Claims] In a liquid crystal display device using a metal-insulating film-metal element in which an insulating film is interposed between electrodes, a part of the common electrode is formed into a thin pattern with a constant line width at the position of each pixel electrode. A liquid crystal display device characterized in that a metal-insulating film-metal element with a common electrode as one electrode is directly formed at a narrow pattern position.