JPH0561057A - Active matrix type liquid crystal display - Google Patents

Abstract

PURPOSE:To an active matrix type liquid crystal display having a bright screen by making an area opposed to a transference electrode small and also making capacity large, and securing the substantial area for receiving light of the transference electrode as much as possible when additional capacity is formed between the transference electrode constituting a liquid crystal element and an electrode opposed to this transference electrode. CONSTITUTION:The additional capacity Cs is constituted by arranging the transference electrode 17 constituting the liquid crystal element 1, a grand line electrode 6 whose one part is opposed to the transference electrode 17, and a TaOx layer 16 between the two electrodes 6 and 17, and the grand line electrode 6 is constituted of a tantalic member and is grounded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called active matrix type liquid crystal display in which a thin film transistor as a switching element is integrally formed with a liquid crystal element on the same substrate, and more particularly to an additional capacitor for accumulating charges for driving the liquid crystal element. Related to those provided.

[0002]

2. Description of the Related Art Recently, in order to solve problems such as crosstalk in a conventional matrix type liquid crystal display,
Various so-called active matrix type liquid crystal displays in which, for example, thin film transistors are provided as switching elements at the intersections of the XY matrix electrode structure have been proposed. 6 to 8 show an example of such an active matrix type liquid crystal display, and a schematic configuration thereof will be described below with reference to the same drawings. 6 is a plan view of a conventional active matrix type liquid crystal display, FIG. 7 is a sectional view taken along the line BB of FIG. 6, and FIG. 8 is an equivalent circuit diagram of the conventional active matrix type liquid crystal display. In the figure, the active matrix type liquid crystal display is one in which a thin film transistor (hereinafter referred to as “TFT”) 20 and a liquid crystal element 21 are integrally formed on an insulating substrate 22 made of glass or the like. TFT2
Reference numeral 0 denotes a so-called planar structure, in which, for example, a polysilicon layer 23 and a gate insulating layer 24 are formed in this order on the insulating substrate 22 to have a thickness of about 500 angstroms, respectively. The gate electrode 2 is provided on the gate insulating layer 24 and on the portion facing the polysilicon layer 23.
5 is formed. Then, before forming the interlayer insulating film 26 on the gate electrode 25, impurities are implanted into the polysilicon layer 23 by an ion implantation method using the gate electrode 25 as a mask. Impurity diffusion layers 23a and 23b are partially formed. And
After that, an interlayer insulating film 26 and an aluminum wiring 27 are sequentially formed, and one end of the aluminum wiring 27 has impurity diffusion layers 23 a, 23 via contact holes formed in the gate insulating layer 24.
connected to b. Further, a protective film 28 is formed on the interlayer insulating layer 26 and the aluminum wiring 27. Liquid crystal element 2
1 is a gate insulating layer 2 which constitutes a part of the TFT 20.
The gate line electrode 29 is formed between the interlayer insulating layer 26 and the interlayer insulating layer 26, and the transparent electrode 30 is further formed on the interlayer insulating layer 26. The other end of the aluminum wiring 27 described above is connected to the transparent electrode 30. Although not shown, a liquid crystal and a transparent electrode are sequentially laminated on the protective layer 28 to form a liquid crystal element 21. Further, the plurality of gate line electrodes 29 described above are provided in parallel, and are arranged so as to be orthogonal to the data line electrodes 31 similarly provided in parallel to form a so-called XY matrix. (Fig. 8)
reference). In such a structure, the gate line electrode 2
9 and the transparent electrode 30 are provided so that a part thereof faces each other, and together with a part of the interlayer insulating layer 26 located between these electrodes 29 and 30, an additional capacitance Cs is formed, and The charge corresponding to the voltage applied from the tareline electrode 31 is accumulated (see FIG. 8). In this way, the additional capacitance Cs is not provided to obtain a sufficient storage capacitance only with the capacitance CLs of the liquid crystal cell, and the TFT 2
This is to prevent the accumulated charge from being reduced by the leak current of 0, the liquid crystal element 21 not being maintained in a sufficiently driven state, and the screen brightness of the entire display from being lowered.

[0003]

However, in the above-mentioned structure, the additional capacitance Cs is connected between the drain of the TFT 20 and the gate line electrode 29 (see FIG. 8), so that the gate is connected. When the try line electrode 29 is long, that is, when the number of elements in the X direction (left and right direction of the paper surface in FIG. 8) increases, many additional capacitors Cs are connected to the gate line electrode 29. Therefore, since the above-mentioned additional capacitance Cs acts as a load with respect to the gate voltage applied to the gate line electrode 29, the vicinity of the end of the gate line electrode 29 distant from the point where the gate voltage is applied. In the area of, the gate voltage decreases and the TFT
There was a problem that 20 could not be driven sufficiently. In order to solve such a problem, for example, instead of the gate line electrode 29 which has been provided so as to partially face the transparent electrode 30, the grounded linear electrode is made to face the transparent electrode 30. It is conceivable that the problem of attenuation of the gate voltage as described above can be avoided by providing the additional capacitance Cs and not connecting the additional capacitance Cs to the gate line electrode. In the latter structure, although the problem of gate voltage attenuation, which is the drawback of the former, is solved, the former can also be said that the ground line forming the additional capacitance Cs is connected to the liquid crystal element. Since the light-incident side of the liquid crystal element is provided so as to face the transparent electrode that constitutes the liquid crystal element, the light receiving area of the transparent electrode is reduced by the amount of overlapping with the ground line, and the entire screen of the liquid crystal display becomes dark. was there. In particular, silicon oxide (SiO ₂ ) that is often used as a member for forming an interlayer insulating layer that becomes a dielectric between the transparent electrode and the ground line is
Since the dielectric constant is relatively low (about 3.5), it is necessary to have a certain area to face the newly provided linear electrode and transparent electrode in order to obtain the additional capacitance Cs having a sufficient capacitance. Therefore, it was unavoidable that the screen became darker. The present invention has been made in view of the above circumstances, and an object thereof is to provide an active matrix type liquid crystal display having a bright screen by securing a light receiving area of a transparent electrode.

[0004]

In order to solve the above problems, an active matrix type liquid crystal display according to the present invention is provided with an electrode made of a tantalum member so as to face a transparent electrode forming a liquid crystal element, The electrode is grounded and tantalum oxide is filled between the electrode and the transparent electrode.

[0005]

According to the present invention, the tantalum oxide filled between the transparent electrode and the electrode provided so as to face the transparent electrode has a dielectric constant of silicon nitride (Si).
Since it is much higher than O ₂ ) etc., the facing area between the transparent electrode and the electrode facing the transparent electrode is made small, while an additional capacitance having a large capacitance value is formed between these two electrodes. As a result, it is possible to secure a larger light receiving area of the transparent electrode and obtain an active matrix type liquid crystal display having a brighter screen than ever before.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Here, FIG. 1 is a plan view of one pixel corresponding to the active matrix liquid crystal display according to the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a main view of the active matrix liquid crystal display in the present embodiment. FIG. 4 is a plan view showing the arrangement of the gate line electrodes and the ground line electrodes in this embodiment, and FIG. 5 is an equivalent circuit diagram of the active matrix type liquid crystal display in this embodiment. is there.

The active matrix type liquid crystal display in the present embodiment is basically different from the conventional one in that it is an active matrix type liquid crystal display having a well-known n × m pixel number (bit). Although not mentioned, it has a feature in the structure of the additional capacitance Cs as described later. First, an electrical equivalent circuit of the active matrix type liquid crystal display of this embodiment will be described with reference to FIG. The configuration per pixel is
Liquid crystal element 1 represented by element capacitance CLs, and this liquid crystal element 1
A thin film transistor whose drain is connected to (hereinafter referred to as "T
2) and an additional capacitance Cs described later. Then, an active matrix type device having such a configuration is arranged by n (bits) in the X direction (horizontal direction of the paper in FIG. 5) and m (bits) in the Y direction (vertical direction of the paper in FIG. 5). A liquid crystal display is configured. Further, the gates of the TFTs 2 arranged in the same row (left and right direction on the paper surface in FIG. 5) are connected to the same gate line electrode 4 provided in the X direction, and the TFTs 2 are simultaneously connected through the electrodes 4. A gate signal is applied to the gate. Further, the sources of the TFTs 2 arranged in the same column (vertical direction on the paper in FIG. 5) are connected to the data line electrodes 5 provided in the Y direction, and the device capacitance CLs, that is, the voltage applied to the liquid crystal device 1 is applied. The signals are simultaneously applied to the source side of the m TFTs 2 in the same column. Further, the additional capacitor Cs is T
It is connected between the drain of FT2 and the ground line electrode 6 which is provided in the X direction and has one end grounded.

When a gate signal is applied to the gate line electrode 4 and a predetermined voltage is applied to the data line electrode 5, the gate line electrode 4 to which the gate signal is applied and the data are applied. The TFT 2 at the intersection with the data line electrode 5 becomes conductive, and the voltage applied to the data line electrode 5 is applied to the device capacitance CLs and the additional capacitance Cs as the liquid crystal device 1 during this time, The element 1 is in a driving state. Here, the gate signal becomes zero after a lapse of a predetermined time, and the TFT 2 becomes non-conducting, but the liquid crystal element 1 is kept in the operating state by the electric charge accumulated in the additional capacitance Cs.

FIGS. 1 and 2 show the structure of one pixel constituting the active matrix type liquid crystal display of this embodiment in cross section and plan view, and the structure will be described below with reference to the same drawing. To do. Note that FIG. 1 is a plan view of one pixel as viewed from the insulating substrate side, that is, from the light incident direction. The active matrix type liquid crystal display of the present embodiment is one in which a liquid crystal element 1 and a TFT 2 which controls the driving of the liquid crystal element 1 are integrally formed on an insulating substrate 7. As shown in FIG. 1, the TFT 2 has impurity diffusion regions 8a and 8b partially formed on an insulating substrate 7 made of a translucent insulating member such as glass (see the method for forming the impurity diffusion regions 8a and 8b). A polysilicon film to be a polysilicon layer 8, a silicon nitride (SiNx) film to be a gate insulating layer 9, a tantalum (Ta) layer to be a gate electrode 10, and an interlayer insulating layer 11 will be described later. Nitride (SiNx) film as a source and source / drain wiring 1
It has a so-called planar structure in which an aluminum film to be 2a and 12b and a protective layer 13 are sequentially laminated.

On the other hand, the liquid crystal element 1 of this embodiment is basically the same as that conventionally used for this type of liquid crystal display, and the insulating layer 14 is formed on the insulating substrate 7. And a tantalum (Ta) film serving as the ground line electrode 6 which constitutes the additional capacitance Cs,
A TaOx film 16 serving as a dielectric of the additional capacitance Cs, an indium tin oxide (ITO) film serving as a transparent electrode 17, and a silicon nitride (SiNx) film serving as an interlayer insulating layer 11.
The protective film 13 is sequentially laminated. The insulating layer 14 described above is a common layer with the gate insulating layer 9 of the TFT 2 described above. Further, the interlayer protective layer 11 and the protective layer 13 are also common to both the TFT 2 and the liquid crystal element 1. Then, the additional capacitance Cs is configured by a part of the ground line electrode 6, the TaOx layer 16 and a part of the transparent electrode 17 described above. Note that the liquid crystal element 1 shown in FIG. 2 shows only a main part, and a liquid crystal film, a transparent electrode, and the like sequentially stacked on the protective layer 13 are omitted because they are not directly related to the gist of the present invention. I am doing it.

Next, the manufacturing process of the active matrix type liquid crystal display of the present embodiment will be described with reference to FIG. 3 focusing on the manufacturing process of the additional capacitor Cs. First, on the insulating substrate 7 made of a translucent insulating member such as glass, the polysilicon layer 8 and the TF forming the TFT 2 are formed.
At the same time as forming a part of T2, the insulating layer 14 of the liquid crystal element 1 is formed.
The gate insulating layer 9 is formed in order. After that, the gate line electrode 4 and the ground line electrode 6 forming a part of the additional capacitance Cs are formed at predetermined positions. The portion of the gate line electrode 4 that projects laterally from the longitudinal axis direction becomes the gate electrode 10. In the longitudinal axis direction of the gate line electrode 4,
It is provided discretely. Further, both the gate line electrode 4 and the ground line electrode 6 of this embodiment are made of Ta alloy. The gate line electrode 4 is formed of another member such as chrome (C
r) or the like, the ground line electrode 6 may be a Ta alloy or a T alloy for convenience of use as an anode when the TaOx layer 16 is formed by an anodic oxidation method as described later.
It must be formed by using a itself. From the viewpoint that the manufacturing process can be simplified, it is preferable to use Ta alloy of the same material for both the gate line electrode 4 and the ground line electrode 6. Further, as shown in FIG. 4, a plurality of gate line electrodes 4 and ground line electrodes 6 are provided on substantially the same plane. In particular, the ground line electrodes 6 are base electrodes 6 a formed on the insulating substrate 7. (See FIG. 4). This base electrode 6
The symbol a is formed simultaneously with the ground line electrode 6, and is finally fixed to a certain potential when the display is used.

Next, the entire insulating substrate 7 on which the polysilicon layer 8 and the like are formed as described above is dipped in a 0.1% nitric acid solution, and a counter electrode (not shown) arranged in this nitric acid solution. ) And the base electrode 6a described above, a DC voltage of 100 V is applied. This is a connection for forming an oxide film, which is generally called an anodic oxidation method, whereby the surface of the ground line electrode 6 (the insulating substrate 7 in FIG. 3B) is formed.
The TaOx layer 16 is formed in a film thickness of about 1500 angstroms on the surface not bonded to.
The above-mentioned DC applied voltage and the concentration of the nitric acid solution are merely examples, and the values are not limited to the above-mentioned values. It can be arbitrarily changed within a range where a thick TaOx layer can be obtained. Further, as a means for simply depositing the TaOx layer, there are methods other than the anodic oxidation method. However, in the case of the anodic oxidation method, pinholes are generated extremely less than other methods, and the method is very uniform. Since it is excellent in that a TaOx layer is obtained, it is most desirable to form the TaOx layer 16 by the anodic oxidation method as in this embodiment.

After the TaOx layer 16 is formed, the insulating substrate 7 is taken out from the nitric acid solution and an impurity diffusion region is formed in the polysilicon layer 8 as described below. That is, from the gate electrode 10 side, by ion implantation, for example, phosphorus (P) is about 150 KeV and boron (B) is 100K.
The impurity diffusion layers 8a and 8b are formed in a self-aligned manner by accelerating at about eV and implanting into the polysilicon layer 8. Since the formation of the impurity diffusion layer by such an ion implantation method is a known and well-known technique, a detailed description thereof will be omitted here.

As described above, after the impurity diffusion layers 8a and 8b are formed, indium tin oxide (IT) which becomes the transparent electrode 17 is formed.
O), silicon nitride (SiN
x) and aluminum to be the source / drain wirings 12a and 12b are sequentially deposited. The formation of the transparent electrodes 17 and the like is not particularly peculiar to the present invention, and is a known and well-known technique for this type of device, and therefore detailed description thereof will be omitted here.

Finally, with reference to FIG. 5, the operation of the active matrix type liquid crystal display having the above structure will be briefly described. FIG. 5 shows an equivalent circuit for four pixels of the active matrix type liquid crystal display. Of these, for example, in FIG.
Taking the case of driving the pixel shown by as an example, in order to apply a voltage to the liquid crystal element 1 of n1, first, the gate line electrode 4 shown by G1 in the figure is selected,
A predetermined pulse gate voltage is applied to the gate line electrode 4. Simultaneously with the application of the pulse gate voltage, the data line electrode 5 indicated by D1 is selected and the voltage is applied,
The TFT 2 in n1 becomes conductive while the gate voltage is applied, and the voltage signal applied to the data line electrode 5 is applied to the element capacitance CLs and the additional capacitance Cs of the liquid crystal element 1. This means that the liquid crystal element 1 is in a driving state. Then, charges corresponding to the applied voltage are accumulated in each of the capacitors CLs and Cs, and the charges remain substantially unchanged even after the gate voltage is zero, that is, the TFT 2 is in a non-conducting state. The liquid crystal element 1 is maintained in the driven state by being held in the capacitors CLs and Cs.

Here, TaOx, which is a dielectric material of the additional capacitance Cs according to the present invention, has a low dielectric constant of 3.5, which is conventionally used, for example, silicon oxide (SiO ₂ ). It has a high dielectric constant of 25. Therefore, the additional capacitance Cs naturally has a larger capacitance value than the conventional additional capacitance,
Even if the TFT 2 becomes non-conductive, the liquid crystal element 1 can be maintained in a sufficiently driven state. Moreover, since the dielectric constant of TaOx is sufficiently high, the area product of the facing area of the transparent electrode 17 and the ground line electrode 6 is smaller than that of the conventional one, and even if the facing area is smaller than that of the conventional one, the capacitance value is small. Since it is larger than the conventional one, the additional capacitor Cs retains sufficient electric charge to maintain the liquid crystal element 1 in the driven state even after the TFT 2 is turned off as described above. At the same time, the decrease in the facing area between the transparent electrode 17 and the ground line electrode 6 increases the light receiving area of the transparent electrode 17, resulting in a bright screen for the active matrix liquid crystal display as a whole.

[0017]

According to the present invention, one of the electrodes forming the additional capacitance is made of tantalum, and a tantalum oxide film having a high dielectric constant is formed on the surface of the electrode to form a dielectric between the electrode and the transparent electrode. As the body, by configuring the additional capacitance, the facing area between the transparent electrode and the ground line electrode facing the transparent electrode can be extremely small, and the light receiving area of the transparent electrode can be secured. It is possible to provide an active matrix type liquid crystal display having a bright screen.

[Brief description of drawings]

FIG. 1 is a plan view of a portion corresponding to one pixel of an active matrix type liquid crystal display according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram for explaining a manufacturing process of main parts of the active matrix type liquid crystal display according to the present invention.

FIG. 4 is a plan view showing the arrangement of gate line electrodes and ground line electrodes that constitute the active matrix type liquid crystal display according to the present invention.

FIG. 5 is an equivalent circuit diagram of an active matrix type liquid crystal display according to the present invention.

FIG. 6 is a plan view of one pixel of a conventional active matrix type liquid crystal display.

7 is a cross-sectional view taken along the line BB of FIG.

8 is an equivalent circuit diagram of the conventional active matrix type liquid crystal display shown in FIGS. 6 and 7. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal element, 2 ... Thin film transistor, 4 ... Gate line electrode, 5 ... Data line electrode, 6 ... Ground line electrode, 6a ... Base electrode, 7 ... Insulating substrate, 1.
6 ... TaOx layer, 17 ... Transparent electrode

Claims (1)

[Claims] 1. A liquid crystal element, a thin film transistor electrically connected to the liquid crystal element to control driving of the liquid crystal element, and a wiring group connecting the thin film transistor to an external circuit are integrally formed on a substrate. In the active matrix type liquid crystal display, the active matrix type liquid crystal is characterized in that an electrode made of a tantalum member facing the transparent electrode constituting the liquid crystal element is provided via a tantalum oxide layer and the electrode is grounded. display.