JPH06230432A - Liquid crystal image display device - Google Patents

Abstract

PURPOSE:To lessen the generation of leak current by incident light from a bored surface part and to intensify the strength of the bored surface part by providing a light shieldable material as discrete light shielding areas to cover at least the channel regions of thin-film transistors(TFTs). CONSTITUTION:The part of a non-light transmittable substrate 7 below a liquid crystal display part A is removed as the bored surface part 16 so that light can be transmitted through the liquid crystal display part A by the bored surface part 16. The light shieldable material as the discrete light shielding areas 18 to cover at least the channel regions of the TFTs constituting pixel switches 10 is provided within the bored surface part 16. The light from the back light source, etc., of the liquid crystal image display device enters the liquid crystal display part A through the bored surface part 16. The TFTs constituting the pixel switches 10 are, however, not affected by this incident light as at least the channel regions of the TFTs are covered by the light shieldable material 17 within the bored surface part 16. Then, the generation of the leak current by light excitation is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal image display device useful as a viewfinder or the like.

[0002]

2. Description of the Related Art The formation of a single crystal Si semiconductor layer on an insulator is widely known as a silicon-on-insulator (SOI) technique, and is a bulk Si for manufacturing a normal Si integrated circuit.
Much research has been done because devices using SOI technology have numerous advantages that cannot be reached with a substrate. That is, by using the SOI technology, (1) dielectric isolation is easy and high integration is possible, (2) excellent radiation resistance, (3) floating capacitance is reduced and high speed is possible,
Advantages such as (4) the well process can be omitted, (5) latch-up can be prevented, and (6) a fully depleted field effect transistor by thinning are possible.

In recent years, attempts have been made to realize an SOI structure without using a sapphire substrate. To this end, (1) after the surface of the Si single crystal substrate is oxidized, a window is opened to partially expose the Si substrate, and the portion is used as a seed for lateral epitaxial growth.
Technology for forming a single crystal Si layer on iO ₂ , and (2) Si
There is a technique in which the surface of the single crystal substrate itself is used as an active layer and SiO ₂ is formed thereunder.

By the way, in constructing a contact sensor which is a light receiving element or a projection type liquid crystal image display device, a substrate which is transparent to visible light is handled and a high performance semiconductor element or the like is mounted thereon. It is important to form.
In this regard, the method using the Si single crystal substrate described above does not meet the purpose of obtaining a good quality single crystal layer on the light transmissive substrate because the substrate is non-translucent. Further, on a transparent substrate typified by glass, in general, amorphous or good polycrystal is formed, reflecting the disorder of the crystal structure, and the crystal structure having many defects is It is difficult to create a drive element having desired performance. Therefore,
A conventional liquid crystal display device uses a TFT (thin film transistor) by forming an amorphous or polycrystalline Si semiconductor layer on a glass substrate.

FIG. 1 shows the structure of a conventional active matrix type liquid crystal display device in a viewfinder. A large number of liquid crystal pixel portions 5 are arranged in a matrix on the transparent substrate 6 to form a liquid crystal display portion A having a desired size. Further, a pixel switch 1 is formed small by a TFT at a corner of each liquid crystal pixel unit 5, and selectively driven by a buffer unit 2, a horizontal shift register unit 3, and a vertical shift register unit 4 arranged around the liquid crystal display unit A. It has a possible structure.

The luminance signal and the audio signal of the television are compressed into a certain band and sent to the buffer section 2 driven by the horizontal shift register section 3 having a driving capability capable of following the frequency. Next, a signal is transferred to the liquid crystal by the vertical shift register unit 4 while the pixel switch 1 is ON.

The pixel switch 1 and the vertical shift register section 4 may have relatively small driving capabilities, but the horizontal shift register section 3 and the buffer section 2 are required to be driven at high speed. Therefore, in the current liquid crystal display element, the pixel switch 1 and the vertical Soshift register section 4 are formed monolithically with the liquid crystal by polycrystalline Si or amorphous SiTFT deposited on the glass substrate, and other peripheral circuits are I
This is achieved by mounting the C chip from the outside.

[0008]

On the other hand, under the above background, the inventors of the present invention, as the invention of the prior application, bond two semiconductor substrates with an insulating layer interposed therebetween, and one substrate is a thin layer. To obtain a silicon-on-insulator (SOI) type substrate structure in which a single crystal Si semiconductor layer is formed on an insulator, and to remove a portion below the liquid crystal pixel portion in the non-light transmissive substrate. , A liquid crystal image display device in which light can be transmitted to the liquid crystal pixel portion is proposed. This achieves the purpose of obtaining a good quality single crystal layer on the light transmissive substrate.

However, in the technique according to the invention of the above-mentioned prior application,
The thin film portion of the non-light-transmissive substrate below the liquid crystal pixel portion from which silicon has been removed, that is, the TFT (thin film transistor) portion that constitutes the pixel switch is vulnerable to light that enters from the back side through the "cutout surface portion", A leak current flows through the pixel TFT. This is, for example, the pixel TF
When N is composed of N-channel MOSFET,
It is generated by the fact that holes are excited in the N channel by the incident light and recombine in the P region forming the source or the drain. That is, the leak current due to this recombination is superimposed on the normal video signal, which deteriorates the image reproducibility.

Particularly, in the viewfinder shown in FIG. 6, for example, when the backlight b is placed on the panel a of the liquid crystal image display device, the temperature of the panel operation is room temperature + 30 ° C. due to being heated by the backlight or the like. Since it rises to the maximum, the leak current generated in the pixel TFT is large, and heat dissipation measures are required.

Further, a thin layer (a single crystal Si layer or a single crystal Si layer and a single crystal Si layer and a single crystal Si layer, in which the electronic device on the surface of the "membrane (Membrane) portion", that is, the surface of the light projecting area is incorporated above the hollow surface portion. The thickness of the insulation layer is ~
Since it is less than μm, it is necessary to increase its strength. This becomes necessary especially as the cut-out area increases.

The present invention has been made in view of the above problems, and provides a liquid crystal image display device capable of reducing the occurrence of a leak current due to incident light from the hollow surface portion and reinforcing the strength of the hollow surface portion. To do.

[0013]

In order to achieve the above object, a liquid crystal image display device according to the present invention includes a large number of liquid crystal pixels and their pixel switches on a substrate that is impermeable to light in the visible light region. And a thin film surface part is formed by removing a portion of the non-light-transmitting substrate below the liquid crystal display part. The thin film surface part allows light to be transmitted to the liquid crystal display part. A light-shielding material is provided as an individual light-shielding area that covers at least the channel region of the thin film transistor forming the pixel switch (claim 1).

In the present invention, the light-shielding material may be provided in a form in which light-shielding areas are connected in a mesh shape, and further, as a conductive material, the potential may be fixed. ).

[0015]

The light from the backlight light source of the liquid crystal image display device enters the liquid crystal display unit through the cut-out surface. But,
For the thin film transistor that constitutes the pixel switch,
Since at least the channel region is covered with the light-shielding material in the hollowed-out surface portion, it is not affected by this incident light. Therefore, the generation of leak current due to photoexcitation is also suppressed (Claim 1).

In this case, if the individual light-shielding areas are connected in a mesh shape, not only the light-shielding portions but also the membrane portion can be reinforced and the strength thereof can be improved (claim 2). Furthermore, if the light-shielding material is a conductive material and the potential is fixed, the thermal influence on the transistor of the pixel switch can be eliminated, the threshold control and the element breakdown voltage can be improved, and the leakage current can be improved. Possible (Claim 3).

[0017]

The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 schematically shows an example of a manufacturing process of a liquid crystal image display device according to an embodiment of the present invention.

In FIG. 1A, 7 is a non-translucent substrate such as Si single crystal, 8 is a translucent insulating layer, and 9 is a semiconductor single crystal layer such as single crystal Si semiconductor layer. This substrate structure is S
It is widely known as an OI structure and is one in which two semiconductor substrates are bonded together via an insulating layer to thin one substrate, which is suitable in that the insulating layer can be freely selected.

A known integrated circuit process technology is applied to the SOI substrate shown in FIG.
As shown in FIG. 3, the pixel switching element 10 which is a semiconductor active element required for the liquid crystal image display device, the driving circuit 11, and the peripheral circuit 12 are formed. After that, as shown in FIG. 1C, using the cover glass 15 and the sealing material 13,
The liquid crystal 14 is enclosed to form the liquid crystal display section A. Needless to say, the liquid crystal display portion A requires an alignment film, a counter electrode, a filter, a polarizing plate, etc., but since these are known technical matters, they are omitted here.

As it is, the substrate 7 is not transparent to visible light and therefore cannot be used as a projection type liquid crystal image display device in which a light source for backlight is arranged on the back side of the substrate. Therefore, as shown in FIG. 1D, the portion 16 of the non-translucent substrate 7 located below the liquid crystal display portion A is removed by etching from the back surface to the translucent insulating layer 8. The hollowed-out surface portion 16 makes the substrate 7 substantially light-transmissive. When this hollowed-out surface portion 16 is formed, the pixel TFT portion that constitutes the pixel switching element 10 becomes unprotected against the incidence of light from this portion, which causes leakage current. Therefore, in the present invention, as shown at the end in FIG.
MO constituting the T section (pixel switching element 10)
A light-shielding material 17 is provided in the region of the cut-out surface portion 16 as an individual light-shielding area 18 that covers at least the channel region of the SFET.

In FIG. 1, in the area of the hollow surface portion 16,
The pixel switching element 10 is a backlight 1 on the back surface of the substrate
As a partial small area (light-shielding area) 18 to be hidden from 8, the number of pixel switching elements 10 is formed so as to suppress the generation of leak current in each pixel switching element 10. That is, first, a resist (organic material) containing a material (black pigment or the like) that does not transmit light is applied as the light-shielding material 17 in the area of the hollow surface portion 16 so that the portion corresponding to each pixel switching element 10 is left. Pattern. At this time, after using a photomask to align each pixel switching element 10 in the cut-out surface portion 16, the pixel switching element 10 is removed from the front side by a normal photolithography technique to leave a desired portion of the resist.

When the light-shielding area 18 is provided in this manner, the light 20 from the backlight light source emits light 20 from the pixel switching element 1.
Since the light does not enter 0, it is possible to suppress the generation of the leak current in the pixel switching element 10 while securing the required light amount of the backlight as the image display device.

FIG. 2 shows another embodiment. This is the “Membrane” on the upper side of the hollow surface portion 16.
Part, that is, a thin layer (single crystal Si layer or single crystal S layer) in which an electronic device on the surface of the light-transmitting region is incorporated.
Considering that the i layer and the insulating layer) have a thickness of ˜μm or less and the strength thereof is relatively low, the light shielding material 17 described above is used.
Each of the light-shielding areas 18 composed of is connected by a wiring portion 19 in a mesh shape. With such a mesh structure, not only light can be shielded but also the strength of the membrane portion above the cut-out surface portion can be improved. For patterning in this case, a photomask is used as in the embodiment of FIG. However, as a maskless method, a method of performing self-alignment exposure using poly-Si or Al of a signal line or a gate line as a mask can also be adopted.

FIG. 3 shows another embodiment. Here, as in the case of the second embodiment, the light shielding material 17 including the light shielding areas 18 and the wiring portions 19 connecting the light shielding areas 18 to the mesh is provided. However, in the case of this embodiment, the light shielding material 17 is made of a conductive material,
As a result, it is electrically connected to the substrate 7 and is applied with a constant potential 21. As the conductive material that also functions as the light-shielding material 17, metals such as Al, Cr, ..., Poly Si, a
-Si (those doped with low resistance) and the like.

With this structure, the charge characteristics and the leak current in the threshold V _th control of the pixel TFT which constitutes the pixel switching element 10 can be improved,
The breakdown voltage of the device can be improved. Further, similar to the embodiment of FIG. 2, it is possible to obtain the effects of preventing the generation of leak current in the pixel TFT section and improving the strength of the membrane section.

In the above-mentioned embodiment, the non-translucent substrate 7 is removed from the rear surface up to the translucent insulating layer 8 to make it substantially light-transmissive. However, depending on the circumstances, the cut-out surface portion where the semiconductor single crystal layer 9 is removed. The present invention can be applied to. In addition, in order to improve mechanical strength or reliability, it is possible to fill the region of the cut-out surface portion 16 before or after providing the light shielding material 17 with a transparent resin, spin-on glass or the like.

Further, in the above embodiment, it was explained that two semiconductor substrates were simply bonded together with an insulating layer interposed therebetween, and one substrate was thinned to obtain a substrate having an SOI structure. However, it is uniform over a large area. A flat Si single crystal substrate having extremely excellent crystallinity can be manufactured, for example, by the following method shown in FIG.

First, a P-type (100) single crystal Si substrate having a thickness of 300 μm is anodized in an HF solution to form a porous Si substrate 101 (FIG. 4).
(A)).

The anodizing conditions were as follows.

Applied voltage: 2.6 V, current density: 30 (mA · cm ⁻² ), anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1:
1: 1, time: 2.4 (hour), thickness of porous Si: 300 (μm), Porosity: 56 (%) P-type (100) porous Si substrate 101 thus obtained
Then, the Si epitaxial layer 102 is grown to a thickness of 1.0 micron by the low pressure CVD method. The deposition conditions are as follows.

Source gas: SiH ₄ , carrier gas: H ₂ , temperature: 850 ° C., pressure: 1 × 10 ^-2 Torr, growth rate: 3.3 nm / sec. An oxide layer 103 is formed, and an oxide layer 104 having a surface of 5000 angstroms is formed on the oxide surface 103.
The other Si substrate 107 on which the nitride layer 105 having a thickness of 000 angstroms has been formed is superposed on the other Si substrate 107, and the substrate 8
The two Si substrates are firmly bonded together by heating at 00 ° C. for 0.5 hours (FIG. 4B).

After that, the bonded substrates are mixed with each other by a mixed solution of 49% hydrofluoric acid, alcohol and 30% hydrogen peroxide (10:
The selective etching was performed in 5:50) without stirring.
After 65 minutes, only the non-porous Si layer remained without being etched, and the porous Si substrate 101 was selectively etched by using the single crystal Si as an etching stop material and completely removed (FIG. 4C). . The etching rate of the non-porous Si single crystal with respect to the etching solution is extremely low.
Even after 5 minutes, the etching layer was 50 angstroms or less, and the selection ratio to the etching rate of the porous layer reached 10 5 or less, and the etching amount in the non-porous layer (tens of angstroms) was practically negligible. belongs to. As a result, the porous Si substrate 101 having a thickness of 200 μm is removed and SiO ₂ 103
A single crystal Si layer 102 having a thickness of 1.0 μm can be formed thereon. When SiH ₂ Cl is used as the source gas, it is necessary to raise the growth temperature by several tens of degrees, but the enhanced etching characteristic peculiar to the porous substrate is maintained.

A TFT is formed on the single crystal silicon thin film 102, and thereafter, the Si substrate side is covered with a hydrofluoric acid resistant rubber except under the liquid crystal pixel portion, and insulation is performed using a mixed solution of hydrofluoric acid, acetic acid and nitric acid. The silicon substrate is partially removed up to the layer to form a hollow surface portion 110 as a light transmitting portion (FIG. 4).
(D)).

With respect to the substrate with TFT thus obtained,
As a measure for suppressing the leak current caused by the incident light from the cut-out surface portion 110, the light-shielding material 17 is provided in the form of the light-shielding area 18, or the light-shielding areas 18 are connected to each other with a mesh, as described above. Is the same. However, the Si substrate manufactured by the method shown in FIG. 4 is a highly economical Si single crystal substrate having extremely excellent crystallinity that is uniform and flat over a large area. Since it is formed on a small number of Si single crystal layers, the stray capacitance of the semiconductor element is reduced, high-speed operation is possible, and elements and circuits excellent in radiation resistance without latch-up phenomenon are displayed on the liquid crystal image. It is possible to provide a high-performance liquid crystal display body by integrating the display pixels on the same substrate.

[0036]

As described above, according to the present invention, the following excellent effects can be obtained.

1) According to the first aspect, the light from the rear of the panel of the liquid crystal image display device is blocked by the light blocking material of the cut-out surface portion and does not enter the thin film transistor which constitutes the pixel switch in the liquid crystal display portion. . Therefore, it is not affected by the light incident on the rear side, and the generation of leak current is suppressed.

2) According to the second aspect, the individual light shielding areas are connected in a mesh shape, and the strength of the membrane portion as well as the light shielding portion can be improved.

3) According to claim 3, the potential of the light-shielding material is fixed, the stability of the threshold control in the transistor of the pixel switch and the element breakdown voltage can be improved, and the leakage current is improved. Can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a manufacturing process of a liquid crystal image display device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a hollow surface portion showing another embodiment of the present invention.

FIG. 3 is a schematic sectional view of a crystal image display device showing another embodiment of the present invention.

FIG. 4 is a diagram showing an example of a method for manufacturing a Si substrate.

FIG. 5 is a schematic view of a conventional active matrix type liquid crystal image display device.

FIG. 6 is a diagram showing a relationship with a backlight light source in the viewfinder.

[Explanation of symbols]

 1 Pixel Switch 2 Buffer Section 3 Horizontal Shift Register Section 4 Vertical Shift Register Section 5 Liquid Crystal Pixel Section 6 Transparent Substrate 7 Non-Translucent Substrate 8 Translucent Insulating Layer 9 Semiconductor Single Crystal Layer 10 Pixel Switching Element 11 Driving Circuit 12 Peripheral Circuit 13 Sealing Material 14 Liquid Crystal 15 Cover Glass 16 Cutout Surface 17 Light-shielding Material 18 Light-shielding Area 19 Wiring 20 Light from Backlight Light Source 21 Potential A Liquid Crystal Display

Claims (3)

[Claims] 1. A liquid crystal display unit including a large number of liquid crystal pixels and pixel switches for the liquid crystal display unit is formed on a substrate that is opaque to light in the visible light region, and the non-light permeable substrate below the liquid crystal display unit. Is removed to form a thin film surface portion, and the thin film surface portion allows light to be transmitted to the liquid crystal display portion, and in the thin film surface portion, an individual light shield that covers at least the channel region of the thin film transistor forming the pixel switch is provided. A liquid crystal image display device, characterized in that a light-shielding material is provided as an area. 2. The liquid crystal image display device according to claim 1, wherein the light-shielding material is provided in a form of meshing light-shielding areas. 3. The liquid crystal image display device according to claim 2, wherein the light-shielding material is a conductive material and the electric potential is fixed.