JPH02211428A - Active matrix substrate for liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the active matrix substrate which allows good liquid crystal display at a high yield by providing a transparent insulating flat film over the entire surface of the substrate. CONSTITUTION:Active elements consisting of P-Si semiconductor layers 104 and display electrodes 110 thereof as well as matrix wirings, etc., are formed on a glass substrate 101. For example, a coating material film of 1 to 2mum thickness consisting of a silicon dioxide system is applied by spin coating over the entire surface of the substrate and is calcined to form a flattening film 111; thereafter, the surface is rubbed to form an oriented film 112. Steep steps by the wirings, etc., are, therefore, made into the flat surface and the good liquid crystal display is enabled by the smooth oriented film 112. Since the need for strong rubbing is eliminated, the substrate of the high yield having no defects is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix substrate for a liquid crystal display device having an active element using a thin film semiconductor.

[Conventional technology]

In recent years, thin film transistors (TPT) and thin film diodes (
2. Description of the Related Art Active matrix liquid crystal display devices, in which each pixel is provided with an active element using a thin film semiconductor such as TFD, are being actively developed with the aim of achieving high image quality. Such a liquid crystal display device has a structure in which a liquid crystal is sandwiched between two substrates, one of which is an active matrix substrate in which the active elements are formed in a matrix, and the other is an opposing substrate made of, for example, a glass substrate with transparent electrodes formed on the entire surface. It consists of a substrate.

Since TN type liquid crystals, which usually have high contrast, are often used as liquid crystals, transmission type liquid crystal display devices have been developed in which transparent substrates such as glass are used as substrates for forming active elements.

Amorphous silicon (a-St) and polysilicon (p-Si) are mainly used as thin film semiconductor materials that form channel regions of active elements. Since a-5i can be formed into a film at a low temperature, an inexpensive glass substrate can be used, and it has been applied to many recent pocket-type liquid crystal televisions. P-Si has higher mobility than a-3i and is single crystal silicon.

Compared to a-St, it has extremely low photosensitivity, that is, it is possible to realize a high-performance active element that is extremely stable against light. For this reason, it is expected that it will be applied to the next generation of high-definition liquid crystal display devices, but the current state is that the technology that can easily form large areas at low enough temperatures to use inexpensive glass substrates has not yet matured. .

Is there a way to form an active element using such p-5i using a normal silicon IC'? There is a method that utilizes a high-temperature p-Si process during the LSI process. However, the substrate material must be quartz or single crystal silicon that can withstand such high-temperature processes. Among these, the latter single-crystal silicon substrate is used, and the peripheral drive circuit, which requires no light incidence and high speed and high performance, is constructed with a single-crystal silicon transistor circuit, and the active element portion with light incidence is p -5.
A method of forming an active matrix substrate using TFTs is described, for example, in the specification of Japanese Patent Application No. 61-246653 "Active Matrix Liquid Crystal Display Device and Manufacturing Method Therefor". According to this invention, as shown in FIG. 2, a device layer in which active elements are formed is adhered to a transparent glass substrate 201 using a transparent adhesive layer 202 such as epoxy or polyimide to form an active matrix substrate. There is. Details of this device layer are as follows. Although not shown in FIG. 2, a normal silicon IC is mounted on a single crystal silicon substrate.

A thermally oxidized insulating film 203 made of, for example, silicon dioxide is formed using an LSI process, and island-shaped p-
After forming the Si semiconductor layers 204 in a matrix,
Gate insulating film 205. The gate electrode 206 is sequentially made of p-St
After forming a pattern on the semiconductor layer 204, source and drain regions are formed in the p-5i semiconductor layer 204 by, for example, ion implantation, and then an insulating film 207 for wiring isolation is formed. Drill a contact hole in the drain wiring 208. for signal wiring using aluminum wiring, for example. Pattern source contact 209 and T
The 0 display electrode 210, which is PT, is a transparent electrode made of, for example, ITO, and is connected to the source contact 209 and formed on the wiring isolation insulating film. In this case, there may be no need for a source contact, but if the display electrode 210 is only about 500 thick, the depth is usually 3000 Å.
The reliability of the connection with the source region through the above contact hole is lost. Finally, this single-crystal silicon substrate was selectively polished from the back side down to the thermal oxide insulating film 203, and FIG. 3 shows a schematic plan view of the active matrix substrate including the zero peripheral drive circuit, which is used as a thin-film device layer. 0 For example, matrix wiring in which the gate electrode 206 is a horizontal wiring and the drain wiring 208 is a vertical wiring and p
-5i TFT 303 and pixels separated from each other by display electrodes 210. Around the active matrix element section formed from pixels separated by the display electrodes 210, a scanning drive circuit 301. A liquid crystal alignment film 211 is formed on the entire surface of at least the display electrodes 210 on an active matrix substrate formed in the manner shown in FIG.
A transparent counter electrode 212 consisting of a transparent glass substrate 201
For example, the TN type liquid crystal 21
By sandwiching 3, the liquid crystal display device is completed.

[Problem to be solved by the invention]

By the way, there are several methods that can be considered for forming the liquid crystal alignment film 211, but recently, the Lavigre method, which is very easy to manufacture, has been used. This is a method in which, for example, an organic film such as polyimide is patterned by printing or the like, and then the organic film is rubbed with flocking on the surface of cloth or the like so that liquid crystal molecules are aligned in one direction. When using this method to form a liquid crystal alignment film 211 by rubbing an organic film formed on an active matrix substrate as shown in FIG. 2, uniform alignment cannot be obtained over the entire area due to steps such as aluminum wiring. This is noticeable in the step portion, that is, in the periphery of the display electrode 210.

For example, if the level difference due to the film thickness of aluminum wiring is usually 1 μm or more and is significant, most of the rubbing will be done on the aluminum wiring, and the display electrode 210 to be rubbed will be non-oriented. If the frictional force is increased to form an alignment film, it may damage the TPT. It was a structure with poor yield that could cause damage. The above problem is to directly produce p-5iT on a quartz substrate.
The same applies to an active matrix substrate on which FTs are formed.

An object of the present invention is to eliminate such conventional drawbacks and provide a high-yield, high-performance active matrix substrate for a liquid crystal display device.

[Means to solve the problem]

In order to achieve the above object, the active matrix substrate for a liquid crystal display device of the present invention includes thin film semiconductor active elements formed in a matrix on an insulating substrate, and display devices connected one-to-one to the active elements. In an active matrix substrate for a liquid crystal display device comprising at least an electrode and a matrix wiring for controlling and applying a signal to the display electrode through the active element, the active matrix substrate for a liquid crystal display device is flattened with a transparent insulating material on the entire surface. A membrane is installed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an active matrix substrate for a liquid crystal display device for explaining one embodiment of the present invention. In FIG. 1, for example, a thin film device layer having active elements made of p-5ET F T arranged in a matrix is installed on an inexpensive transparent glass substrate 101 as a holding substrate via an adhesive layer 102. is the same as the conventional example described above. Further, the adhesive layer 102 is also made of a transparent adhesive material such as epoxy or polyimide, as in the conventional example.

The device layer will be described in detail below. Although not shown, an insulating film 103 of silicon dioxide, for example, is formed on a single crystal silicon substrate by a thermal oxidation method, a CVD method, or the like. The thickness is not particularly limited, but is preferably 1000 Å or more from the viewpoint of polishing accuracy for forming a device layer, which will be described later. A p-5i semiconductor layer 104 is deposited on this insulating film 103 by, for example, the CVD method, and a TPT layer is formed for each pixel in a matrix.
Patterned into an island shape to form a channel region. Subsequently, a gate insulating film 105 made of, for example, silicon dioxide by thermal oxidation and a p-St gate electrode 106 are sequentially formed and patterned on the p-8t semiconductor layer 104 by a process similar to that of a MOSFET of a normal silicon IC. The p-St gate electrode 106 forms a matrix wiring, for example, a horizontal wiring, and controls opening and closing of the p-SiT F T. After performing, for example, ion implantation to form source and drain regions in the p-9i semiconductor layer 104, the gate electrode 1
Insulating film 10 for wiring separation that separates 06 and subsequent aluminum wiring
A contact hole is formed in a portion corresponding to the source and train regions. 1μ thick on the insulating film 107
After depositing an aluminum film of about m thickness over the entire surface, a drain wiring 108 and a source contact 109, which will serve as signal application wiring, are patterned. Thereafter, a transparent display electrode 110 made of, for example, ITO is formed and connected to the aluminum of the source contact 109, and pattern separation is performed for each pixel. At this time, the display electrode 110 may be formed before the drain wiring 108 and the source contact 109 are deposited with aluminum. Also, as stated in the conventional example, aluminum for the source contact 109 is not particularly required.
At least on the entire surface of the pixels formed in a matrix, for example, a silicon dioxide-based coating film material (trade name: Tokyo Ohka Co., Ltd.
A flattening film 111 is formed by applying a coating material such as CD) or an alical resin coating material (trade name JSS-451 manufactured by Nippon Synthetic Rubber Co., Ltd.) to a thickness of about 1 μm to 2 μm using a spin cord and baking it. Finally, as described in the conventional example, selective polishing is used to polish the single crystal silicon substrate from the back side until the insulating film 103 is exposed, thereby completing the device layer. The planarizing film 111 can be formed on the active matrix substrate after polishing the single crystal silicon substrate. For example, a level difference of about 1 μm due to
It is reduced to about m. In addition, the level difference due to matrix wiring etc. is steep due to photolithography, but the flattening film 1
11 has a smooth stepped structure.

As a liquid crystal display device, as shown in FIG. 1, a liquid crystal alignment film 1 is used.
After forming 12, as shown in the figure, a structure is formed in which the liquid crystal is sandwiched between a counter substrate having a counter electrode. Therefore, in the active matrix substrate of this embodiment, the signal voltage applied between the display electrode 110 and the counter electrode is applied between the liquid crystal and the flattening film 110.
The signal voltage to be applied to the liquid crystal substantially decreases. This partial pressure ratio depends on the capacitance connected in series between the liquid crystal and the flattening film 111. Therefore, it is sufficient to reduce the capacitance of the liquid crystal and increase that of the flattening film 111. Although the capacitance depends on the film thickness and dielectric constant, the film thickness cannot be changed so much depending on contrast and flattening properties.

The dielectric constant is 3 to 5 for both the SiO % or more signal voltage is applied. Therefore, no particular problem arises, but it is preferable to select a material with a high dielectric constant for the planarization film 111 if possible. Such materials include, for example, ferroelectric PL.
ZT-based coating material (product name: Kojundo Kagaku Alcolade)
etc. are valid.

In this embodiment, the peripheral drive circuit is constructed on a single-crystal silicon substrate in the same manner as in the conventional example shown in FIG. 3, and the planarization process can also be shared. Further, in this embodiment, an active matrix substrate in which p-5i TFTs are formed on a single crystal silicon substrate has been described, but even in the case where p-5i TFTs are directly formed on a quartz substrate as described in the conventional example, the a- The same applies to active matrix substrates such as 3iTFT and TFD.

〔Effect of the invention〕

As explained above, according to the active matrix substrate for a liquid crystal display device of the present invention, a steep and high step caused by aluminum wiring etc. can be made into a smooth and flat surface by a simple process of spin-coding the flattening film 11. is possible,
By rubbing, a good liquid crystal alignment film 112 with no unevenness is formed even on the display electrode portion, thereby enabling good liquid crystal display. Also, rubbing with strong frictional force is unnecessary,
It has a high-yield structure with no defects and little damage to the aluminum wiring and TFT parts during rubbing.

Insulating film, 106,206...Gate electrode, 107°207...Insulating film for wiring separation, 108,208...
Drain wiring, 109,209... Source contact, 110,210... Display electrode, 111... Flattening film, 112.211... Liquid crystal alignment film, 212... Counter electrode, 213... Liquid crystal, 301...Scanning drive circuit, 302...Signal drive circuit.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an active matrix substrate for a liquid crystal display device for explaining an embodiment of the present invention, FIG. 2 is a cross-sectional view of an active matrix liquid crystal display device for explaining a conventional example, and FIG. 1 is a schematic plan view of an active matrix substrate for a liquid crystal display device for explaining the present invention and a conventional example. 101.201...Glass substrate, 102.202...
・Adhesive layer, 103,203...Insulating film, 104°20
4... p-Si semiconductor layer, 105,205... Game agent patent attorney Susumu Uchihara

Claims (1)

[Claims] Thin film semiconductor active elements formed in a matrix on an insulating substrate, display electrodes connected one-to-one to the active elements, and matrix wiring for controlling and applying signals to the display electrodes through the active elements. 1. An active matrix substrate for a liquid crystal display device comprising at least an active matrix substrate for a liquid crystal display device, characterized in that a transparent insulating flattening film is provided on the entire surface of the active matrix substrate for a liquid crystal display device.