JPH0467020A - Thin film transistor array - Google Patents

Abstract

PURPOSE:To maintain the liquid crystal function of a liquid crystal display device for a long period and to improve the display quality by forming an electrode for auxiliary capacity of the same metal with a signal scanning electrode and also forming at least part of a dielectric layer of the oxide of the same metal with the signal scanning electrode. CONSTITUTION:The electrode 3 for auxiliary capacity is formed of the same metal with the signal scanning electrode 2 and the dielectric layer 4 is a metal oxide film formed by oxidizing the surface of the electrode 3 for auxiliary capacity. The electrode 3 for auxiliary capacity is formed of the material which hardly transmits light, so an aperture rate is preferably secured by reducing an area which overlaps with a picture element electrode 5 as much as possible and the electrode 3 is formed normally along the edge part of the picture element electrode 5. Consequently, the liquid crystal function of the liquid crystal display device can be maintained for a long period and the isplay uality can be improve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film transistor array constituting an active matrix liquid crystal display.

[Prior Art] In general, it is considered desirable for liquid crystal display devices to be driven with pure alternating current in order to avoid deterioration in the functionality of the liquid crystal. However, in active matrix liquid crystal displays,
The parasitic capacitance generated in the thin film transistors hinders pure AC drive, and tends to gradually degrade the functionality of the liquid crystal. When the LCD function deteriorates, flickering may occur,
When a still image is displayed as "black" for a long period of time and then reversed to "white", a phenomenon in which an afterimage of the "black" display remains (generally called burn-in) occurs, resulting in a decrease in display quality. was there. Therefore, it has been proposed that the thin film transistor array be provided with an auxiliary capacitor for display.

FIG. 2 is a diagram showing an example of the configuration of a conventional thin film transistor array equipped with the above-mentioned auxiliary capacitance. FIG. 2(a) is a partial plan view thereof, and FIG. It is a partial cross-sectional view taken along the line II.

A conventional thin film transistor array is shown in FIGS. 2(a) and (
As shown in b), scanning signal electrodes 2 are formed on the glass substrate 21.
2 and an auxiliary capacitance electrode 23. The scanning signal electrode 22 is formed in a stripe shape from a metal such as tantalum (Ta), and a gate insulating film 22b is formed by partially oxidizing the above metal in a region where a thin film transistor is to be formed, such as the gate electrode 22a. There is. The auxiliary capacitance electrode 23 is provided in a region that substantially overlaps with the pixel electrode 24, and is formed from a transparent electrode such as ITO so as not to impair the display quality of the liquid crystal display device. A dielectric layer 25 is provided on the signal scanning electrode 22 and the auxiliary capacitance electrode 23 so as to cover the entire substrate. The dielectric layer 25 is generally made of silicon nitride (SiN), and the portion covering the gate electrode 22a also functions as a second gate insulating layer. Further, the dielectric layer 25 is made of silicon oxide (
It may be composed of two layers: a Sin, ) layer and a SiN0 layer.

A semiconductor layer 26 made of aSi is provided on the dielectric layer 25 in a region where a thin film transistor is formed (a region overlapping with the gate electrode 22a), and a drain electrode 2 made of aluminum, chromium, nichrome, etc. is provided on the semiconductor layer 26.
7a and a source electrode 27b. The drain electrode 27a is formed integrally with the data line electrode 27, and the data line electrode 27 is formed in a stripe shape on the dielectric layer 25 perpendicular to the signal scanning electrode 22. Note that the data line electrode 27, drain electrode 27a, and source electrode 27b are formed from the same material in a single process.

In the above device, the gate electrode 22a1 the gate insulating film 22b
1 dielectric layer (second gate insulating film) 25, semiconductor layer 26,
By the drain electrode 27a1 and the source electrode 27b,
A thin film transistor is configured.

A pixel electrode 24 is provided in a region surrounded by the signal scanning electrode 22 and the data line electrode 27. Pixel electrode 2
4 is made of a transparent electrode material such as ITO, and the source electrode 2
7b.

On the thin film transistor and pixel electrode 24, Si
An insulating film 28 made of N, etc. is formed over the entire surface of the substrate, and an alignment film 29 made of a rubbed polyimide film or the like is further formed on the insulating film 28.

A thin film transistor array is constituted by each of the above-mentioned components.

FIG. 3 is a partial cross-sectional view showing an example in which the thin film transistor array described above is incorporated into a liquid crystal display device.

In FIG. 3, the same components as in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in Figure 3,
The thin film transistor array 31 having the above configuration is arranged to face a front glass substrate 35 provided with a common electrode 33 made of ITO or the like and an alignment film 34 made of a rubbed polyimide film or the like, with a liquid crystal layer 32 in between. By doing so, a liquid crystal display device is constructed.

In the liquid crystal display device, the selected pixel is driven by the thin film transistor to perform display.
A parasitic capacitance is generated between the capacitor and the capacitor 2a. This is because it is technically difficult to define the positions of the drain electrode 27a, the source electrode 27b, and the gate electrode 22a by self-alignment, and they are formed so as to overlap slightly.

Therefore, in the above-described liquid crystal display device, in addition to the original capacitance for display constituted by the pixel electrode 24, the liquid crystal layer 32, and the common electrode 33, the auxiliary capacitance electrode 23, the dielectric layer 25, and the pixel It has an auxiliary capacitance formed by the electrode 24. As shown in FIG. 2(a), the auxiliary capacitor is supplied with charge from the adjacent signal scanning electrode through the connecting portion 23a, and when the relevant pixel is selected, the charge is supplied to the auxiliary capacitor along with the original capacitor for display. Functions as a capacity. If the above-mentioned original capacitance and auxiliary capacitance are combined, the parasitic capacitance generated in the thin film transistor becomes negligible, so pure AC drive becomes possible, and the liquid crystal function is maintained over a long period of time, resulting in excellent display quality. It is expected that liquid crystal display devices will be obtained.

There is also a method of supplying charges to the auxiliary capacitance all at once by wiring from a dedicated electrode to the auxiliary capacitance electrode of each pixel.

[Problems to be Solved by the Invention] However, in the conventional thin film transistor array having an auxiliary capacitor, the area of the dielectric layer must be increased due to the low dielectric constant of the dielectric of the auxiliary capacitor. There was a problem that the probability of forming defects such as pinholes was high. If a pinhole occurs in the dielectric layer, a short circuit will occur between the pixel electrode and the auxiliary capacitor electrode, which is undesirable.

In order to solve the above problem, a technique has been proposed in which an insulating film is formed over the thin film transistor over almost the entire surface of the substrate, and a pixel electrode is formed on the insulating film. A partial cross-sectional view of a thin film transistor array according to the above proposal is shown in FIG. In FIG. 4, the same components as in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the thin film transistor array shown in FIG.
is formed over the entire surface of the substrate, leaving a region (contact hole) 28a for connection to the pixel electrode 24 on the source electrode 27b. Then, the signal scanning electrode 2 on the insulating film 28
A pixel electrode 24 is provided in a region surrounded by a contact hole 28 and a data line electrode 26.
a to the source electrode 27b. Alignment film 2
9 is provided on the pixel electrode 24 and is formed on the entire surface of the substrate.

According to the above configuration, since there are two dielectric layers, short-circuiting between the pixel electrode and the auxiliary capacitor electrode can be avoided unless pinholes occur at the same location in each layer. Since the dielectric layer is also made of SiN and the area of the dielectric layer is the same as before, it does not reduce the probability of pinholes occurring, and cannot be said to be an essential improvement over the prior art.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and its purpose is to provide a thin film transistor array that can maintain the liquid crystal function of a liquid crystal display device over a long period of time and improve display quality. It's about doing.

[Means for Solving the Problems] The thin film transistor array of the present invention includes an insulating substrate, signal scanning electrodes provided in stripes on the insulating substrate, and signal scanning electrodes provided in stripes perpendicular to the signal scanning electrodes on the insulating substrate. a thin film transistor provided at the intersection of the signal scanning electrode and the data line electrode, an auxiliary capacitor electrode provided on the insulating substrate, and a auxiliary capacitor electrode provided to cover the auxiliary capacitor electrode. and a pixel electrode provided on the insulating substrate and connected to the thin film transistor, and laminated with the auxiliary capacitor electrode and at least part of the dielectric layer to form an auxiliary capacitor. The auxiliary capacitance electrode is made of the same metal as the signal scanning electrode, and at least a part of the dielectric layer is made of an oxide of the same metal as the signal scanning electrode. There is.

[Function] In the thin film transistor array of the present invention, the auxiliary capacitance electrode is formed of the same metal material as the signal scanning electrode, and the oxide film of the metal formed by oxidizing the surface of the auxiliary capacitance electrode forms a dielectric forming layers. That is, the dielectric layer is made of the same metal oxide as the gate insulating film. Since the metal oxide has a higher dielectric constant than S i N I+, the area of the dielectric layer is required to be smaller than the required charge, and the probability of film defects such as pinholes is reduced. Therefore, a short circuit between the signal scanning electrode and the pixel electrode can be avoided, and the auxiliary capacitance can effectively function in liquid crystal display.

Furthermore, although the material used for the auxiliary capacitor electrode of the present invention is a material that does not easily transmit light, since the area of the dielectric layer is small, the auxiliary capacitor electrode itself can be made small, and the aperture ratio can be reduced. can avoid.

[Example 2] A thin film transistor array according to the present invention will be described below based on an illustrated example.

Figure 1 is a diagram showing an example of a thin film transistor array according to the present invention. - It is a partial sectional view taken along the I line.

As shown in FIGS. 1(a) and 1(b), the thin film transistor array of this embodiment includes a signal scanning electrode 2 and an auxiliary capacitance electrode 3 on a glass substrate 1. The signal scanning electrode 2 is formed in a stripe shape from one metal of tantalum, aluminum, tungsten, zirconium, niobium, etc. or a combination of these metals, and forms a thin film transistor such as a gate electrode 2a on the signal scanning electrode 2. A first gate insulating film 2b is formed in the region where the metal oxide is partially oxidized.

In the thin film transistor array of the present invention, the auxiliary capacitor electrode 3 is made of the same metal as the signal scanning electrode 2, and the dielectric layer 4 is made of a metal oxide formed by oxidizing the surface of the auxiliary capacitor electrode 3. It is characterized by being a film. Since the auxiliary capacitance electrode 3 is made of a material that does not easily transmit light, it is preferable to minimize the area overlapping with the pixel electrode 5 in order to secure the aperture ratio. Form along the In this embodiment, the auxiliary capacitance electrode 3 is formed all around the edge of the pixel electrode 5, but it is only necessary to obtain sufficient charge and a sufficient aperture ratio for the auxiliary capacitance, There are no particular limitations on the region or area. In addition, the auxiliary capacitance electrode 3
is connected to an adjacent signal scanning electrode by a connecting portion 3a, and charge is supplied from the connecting portion 3a to the auxiliary capacitor.

Charges may be supplied to the auxiliary capacitance all at once by wiring from a dedicated electrode to the auxiliary capacitance electrode of each pixel.

In the thin film transistor array of the present invention, the auxiliary capacitance electrode 3, the connecting portion 3a, and the signal scanning electrode 2 are formed of the same material, which is advantageous because they can be formed simultaneously in a single step. Furthermore, it is advantageous that the dielectric layer 4 and the first gate insulating film 2b can be formed simultaneously in a single process.

SiN is deposited on the glass substrate 1 so as to cover the area on the signal scanning electrode 2 where the thin film transistor is to be formed.

A second gate insulating film 6 made of A-8i is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8i is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8I is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8i is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8i is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8i is provided on the second gate insulating film 6, and a semiconductor layer 7 made of A-8i is provided on the second gate insulating film 6. Drain electrode 8a and source electrode 8b
is provided. The drain electrode 8a is formed integrally with the data line electrode 8, and the data line electrode 8 is formed in a stripe shape orthogonal to the signal scanning electrode 2.

Note that the data line electrode 8, drain electrode 8a, and source electrode 8b are formed from the same material in a single process.

In the above device, the gate electrode 2a, the first gate insulating film 2
b, the second gate insulating film 6, the semiconductor layer 7, the drain electrode 8a, and the source electrode 8b constitute a thin film transistor.

A pixel electrode 5 is provided in a region surrounded by the signal scanning electrode 2 and the data line electrode 8 on the glass substrate 1 .

The pixel electrode 5 is made of a transparent electrode material such as ITO, and is connected to the source electrode 8b.

On the thin film transistor and pixel electrode 5, an insulating film 9 made of SiN or the like is formed on the entire surface of the substrate in order to protect the surfaces thereof, and on the insulating film 9, a polyimide film that has been subjected to a rubbing process is further formed. Alignment film 10 consisting of etc.
is formed.

A thin film transistor array is constituted by each of the above-mentioned components.

When the thin film transistor array of this example constitutes a liquid crystal display device, the auxiliary capacitance electrode 3, the dielectric layer 4, and the
Since the portion consisting of the pixel electrode 5 acts as an auxiliary capacitor, the parasitic capacitance generated in the thin film transistor can be ignored, and the liquid crystal layer can be driven substantially with pure alternating current. Further, since the dielectric of the auxiliary capacitor is an oxide of the metal forming the auxiliary capacitor electrode, the dielectric constant is high, and a sufficient effect can be obtained even with a small area of the dielectric layer. Therefore, the probability of film defects such as pinholes occurring in the dielectric layer is low, and short circuits between the auxiliary capacitor electrode and the pixel electrode are less likely to occur.

FIG. 5 is a partial cross-sectional view showing the structure of the thin film transistor array of this example. In FIG. 5, the same components as in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the thin film transistor array of this embodiment, the dielectric layer includes a metal oxide film 4 obtained by oxidizing the surface of the auxiliary capacitance electrode 3, and a SiN layer 6 that also serves as a second gate insulating film.
This example is the same as Example 1 except that it consists of two layers.

The thin film transistor array of this example has an S of the region sandwiched between the auxiliary capacitance electrode 3, the dielectric (oxide film) layer 4, the auxiliary capacitance electrode 3, and the pixel electrode 5 when configuring a liquid crystal display device. Since the portion consisting of the iN x layer 6 and the pixel electrode 5 acts as an auxiliary capacitor, the parasitic capacitance generated in the thin film transistor can be ignored, and the liquid crystal layer can be driven substantially with pure alternating current. In addition to the effects described in Example 1, the dielectric layer is made of metal oxide film layer and Si.
By forming a two-layer structure with the Nx layer, it is possible to further reduce the probability that film defects will occur.

Figure 6 is a partial cross-sectional view showing the structure of the thin film transistor array of this embodiment. In FIG. 6, the same components as in FIG. 1 are given the same reference numerals and detailed explanations are omitted.

In the thin film transistor array of this example, the layer that also serves as the second gate insulating film of the dielectric layer is further made of Sin, and the layer 6
The second embodiment is the same as the second embodiment except that it consists of two layers: a, SiN, and layer 6b.

The thin film transistor array of the present example has a region sandwiched between the auxiliary capacitor electrode 3, the dielectric (metal oxide film) layer 4, the auxiliary capacitor electrode 3, and the pixel electrode 5 when configuring a liquid crystal display device. Sin, layer 6a5 SiN8 layer 6 in the above region
b. Since the portion consisting of the pixel electrode 5 acts as an auxiliary capacitor, the parasitic capacitance generated in the thin film transistor can be ignored, and the liquid crystal layer can be driven substantially with pure alternating current. In addition to the effects described in Example 1, the dielectric layer may be a metal oxide film layer, a Si layer, or a SiN layer.
By forming a three-layer structure with three layers, it is possible to further reduce the probability of film defects occurring.

Convoluted plane 1 FIG. 7 is a partial cross-sectional view showing the structure of the thin film transistor array of this example. In FIG. 7, the same components as in FIG. 1 are given the same reference numerals, and detailed explanations are omitted.

In the thin film transistor array of this embodiment, an insulating film 9 is formed over the entire surface of the substrate except for a contact hole 9a above a source electrode 8b, and an area on the insulating film 9 surrounded by a signal scanning electrode 2 and a data line electrode 8 is formed. Embodiment 2 is different from Embodiment 2 except that a pixel electrode 5 is provided in the second embodiment, and the pixel electrode 5 is connected to a source electrode 8b through a contact hole 9a.
It is similar to

The thin film transistor array of the present example has a region sandwiched between the auxiliary capacitor electrode 3, the dielectric (metal oxide film) layer 4, the auxiliary capacitor electrode 3, and the pixel electrode 5 when configuring a liquid crystal display device. S i N x layer 6, insulating film 9 in the above region
, and the pixel electrode 5 act as an auxiliary capacitance, so that the parasitic capacitance generated in the thin film transistor can be ignored, and the liquid crystal layer can be driven substantially with pure alternating current.

In addition to the effects described in Example 1, the dielectric layer is a metal oxide film layer, an insulating film (SiN) layer, and a SiN layer.
By forming a three-layer structure with the x layer, it is possible to further reduce the probability of film defects occurring.

[Effects of the Invention] According to the thin film transistor array of the present invention, by reducing the area of the dielectric layer, it is possible to avoid short-circuiting between the auxiliary capacitor electrode and the pixel electrode, so that the auxiliary capacitor can work effectively. Therefore, it is possible to avoid deterioration in the function of the liquid crystal and deterioration in the display quality of the liquid crystal display device due to the parasitic capacitance of the thin film transistor.

The effect of preventing short circuit between the auxiliary capacitance electrode and the pixel electrode is that the S
It can be further increased by laminating layers of iOx, SiN, etc. The above-mentioned 5iO8, SiN, etc. layer is advantageous because it not only makes it difficult to short-circuit the auxiliary capacitance electrode and the pixel electrode, but also functions as a dielectric.

Further, since the area of the dielectric layer may be small, the auxiliary capacitor electrode itself may also be small, and a high aperture ratio can be obtained even though the auxiliary capacitor electrode is made of a material that does not easily transmit light.

Therefore, according to the present invention, it is possible to provide a thin film transistor array that can maintain the liquid crystal function of a liquid crystal display device over a long period of time and improve display quality.

[Brief explanation of the drawing]

FIG. 1(a) is a partial plan view showing the configuration of an embodiment of a thin film transistor array according to the present invention, and FIG. 1(b) is a partial sectional view taken along the line II in FIG. 1(a). , FIG. 2(a) is a partial plan view showing an example of the configuration of a conventional thin film transistor array, and FIG. 1(b) is a partial plan view showing an example of the configuration of a conventional thin film transistor array.
3 is a partial sectional view showing an example in which the thin film transistor array shown in FIG. 2 is incorporated into a liquid crystal display device; FIG. 4 is a partial sectional view taken along a single line; FIG. 4 is a partial sectional view showing another configuration example of the conventional thin film transistor array FIG. 5 to FIG. 7 are partial cross-sectional views showing the configuration of other embodiments of the thin film transistor array according to the present invention. 3... Electrode for auxiliary capacitance, 4... Dielectric (metal oxide) layer, 5... Pixel electrode. , 5-A row of body parts, g 10,000 \ [2 pieces Fig. 2 / 7a 22゜7b 4 Coming East Akicho refuses the pot basket 3 Teiwei゛ mouth Fig. 3 22t) 2a 8a In (Otsu.a [I Figure 4. Procedural amendment words and deeds) 1. Indication of the case 1990 Patent Application No. 178317 2. Name of the invention Thin film transistor array 3. Person making the amendment Relationship to the case Patent applicant Address 1-7-12 Toranomon, Minato-ku, Tokyo Name (0
29) Oki Electric Industry Co., Ltd. Representative Nobuko Kosugi 4 Agent Address (〒160) 7-6-2-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo
The "Brief Description of Drawings" in the Description of Contents of the Amendment is amended as follows. 1. On page 20 of the specification, lines 7 and 8, it is stated that “Figure 1 (b
) is shown in Figure 1 (a)'', while 'Figure 2 (b) is shown in Figure 2
Figure (a)” is corrected.

Claims (1)

[Scope of Claims] An insulating substrate; signal scanning electrodes provided in stripes on the insulating substrate; data line electrodes provided in stripes on the insulating substrate orthogonal to the signal scanning electrodes; a thin film transistor provided at the intersection of the signal scanning electrode and the data line electrode; an auxiliary capacitor electrode provided on the insulating substrate; a dielectric layer provided to cover the auxiliary capacitor electrode; A thin film transistor array comprising a pixel electrode provided on a substrate, connected to the thin film transistor, and laminated with the auxiliary capacitor electrode and at least a portion of the dielectric layer to form an auxiliary capacitor, A thin film transistor array, wherein the capacitor electrode is made of the same metal as the signal scan electrode, and at least a part of the dielectric layer is made of an oxide of the same metal as the signal scan electrode.