JPH06230350A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make up the degradation in the strength of a bored part without fluctuation in image display by a temp. change. CONSTITUTION:The liquid crystal display device which is constituted by sealing a liquid crystal 3 between a non-light transparent circuit board 1 provided with light transparency by forming the bored part 4 in a display part region and a light transparent counter substrate 2 is provided with a light transparent sealing substrate 6 via a sealing material 5 on the bored part 4 side existing on the counter liquid crystal sealing side. A flowable and light transparent potting material 7 is sealed between the circuit board 1 and the sealing substrate 6. The volumetric change of the potting material 7 by a temp. change and the volumetric change between the circuit board 1 and the sealing substrate 6 according to the volumetric change of the sealing material 7 by the temp. change are made nearly equal to each other. As a result, a membrane part 10 left by the formation of the bored part 4 is pressed by the pressure generated by the expansion of the potting material 7. This membrane part 10 is thus reinforced by the potting material 7 while the change in the thickness of the liquid crystal 3 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, liquid crystal is sealed between a translucent circuit board on which a drive circuit is formed and a translucent counter substrate, and an image is displayed by driving the sealed liquid crystal. Liquid crystal display devices are widely used.

In order to improve the image quality of such a liquid crystal display device, it is necessary to reduce the area of one pixel, which is several tens of microns square, and arrange a larger number of pixels.

Therefore, as the number of pixel electrodes and transistors arranged in the display area increases and the screen becomes larger, the wiring length per vertical and horizontal shift register drive wiring becomes longer, resulting in vertical and horizontal shift. The register requires a larger driving force. In addition, since the transistor used in the display region needs to hold the potential of the pixel electrode for a longer time, it is necessary that the leakage current be small.

As a technique meeting the above requirements, it is conceivable to use single crystal Si for forming a drive circuit on a circuit board.

The formation of single crystal Si on an insulator is widely known as the Silicon on Insulator (SOI) technology,
Much research has been done because devices utilizing SOI technology have a number of advantages that cannot be reached with bulk Si substrates for producing ordinary Si integrated circuits.

That is, by using the SOI technology, 1. 1. Dielectric isolation is easy and high integration is possible. 2. It has excellent radiation resistance. 3. The floating capacity is reduced and the speed can be increased. 4. The well process can be omitted, Latch-up can be prevented, 6. Advantages such as a fully depleted field effect transistor can be obtained by thinning the film.

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

In the meantime, in constructing a projection type liquid crystal display device, it is important to form a high performance semiconductor element or the like on a circuit substrate transparent to visible light.

In this regard, in the method using the Si single crystal substrate described above, the circuit board becomes non-translucent,
It does not meet the purpose of obtaining a good quality single crystal Si layer on a transparent circuit board. In general, on a transparent circuit board typified by glass, the disorder of the crystal structure is reflected, and only amorphous or good polycrystal is formed. However, it is difficult to create a driving element having desired performance.

For this reason, the conventional liquid crystal display device has amorphous or polycrystalline S on the glass circuit board.
An i semiconductor layer is formed and is used to form a transistor (T
A drive circuit such as ET) is used.

[0012]

On the other hand, in view of the above background, the present inventors have previously made the single crystal S whose surface is made porous.
After epitaxially growing single crystal Si on the surface of the i substrate, another single crystal Si substrate having an insulating layer formed by oxidizing the surface is bonded to this surface to form a single crystal Si substrate having the surface made porous. By removing it, a technique of forming a single crystal Si layer on a single crystal Si substrate with an insulating layer interposed was developed.

By the way, the above-mentioned technique is also applicable to the conventional SOI.
Similar to the technique, since a single crystal Si substrate is used, when this is used in a liquid crystal display device, the circuit board becomes non-translucent.

Therefore, the inventors of the present invention have proposed that these single crystal Si
In order to use the SOI structure using a substrate in a liquid crystal display device, a hollow portion is formed in a single crystal Si substrate portion on the side opposite to the liquid crystal enclosing side in a region to be a display portion, thereby obtaining translucency. Devised.

However, when the hollow portion is formed in the single crystal Si substrate portion, there is a problem that the hollow portion has a membrane portion including the insulating layer and the drive circuit formed thereon, resulting in a decrease in strength. is there. In addition, there is a problem that the membrane portion is subjected to mechanical and chemical stress with respect to changes in temperature, humidity and atmospheric pressure in the actual use state, and the display state is deteriorated.

The present invention has been made in view of the above problems, and a non-translucent circuit board having a translucent property by forming a cutout portion in a region serving as a display portion and a translucent material. It is an object of the present invention to make it possible to compensate for the decrease in strength of the cutout portion in a liquid crystal display device in which liquid crystal is sealed between opposed substrates, without causing image display fluctuations due to temperature changes and the like.

[0017]

Means for solving the problems will be described with reference to FIG. 1 corresponding to one embodiment. In the present invention, a non-translucent circuit board having a drive circuit is formed. 1, a liquid crystal 3 is sealed between the transparent substrate 1 and a transparent substrate 2, and a hollow portion 4 is formed on the side opposite to the liquid crystal sealed side of the circuit board 1 to provide a light-transmitting property. On the side of the hollowed-out portion 4 of No. 1, a fluid and translucent potting material 7 is sealed between the translucent sealing substrate 6 attached via a seal material 5, and the temperature-dependent potting material 7 This is a liquid crystal display device in which the volume change of the potting material 7 and the volume change between the circuit board 1 and the sealing substrate 6 due to the expansion and contraction of the sealing material 5 due to the temperature change are adjusted to be substantially equal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view showing a first embodiment, in which a circuit board 1 is non-translucent, and TFTs and other driving circuits are formed on its surface through an insulating layer. There is. On the side of the circuit board 1 on which the drive circuit is formed, a translucent counter substrate 2 such as glass is attached by a sealing material 8 and a liquid crystal 3 is sealed between the two.

The term "translucency" as used herein means that visible light is transmitted.

On the other hand, a cut-out portion 4 is formed on the side opposite to the liquid crystal sealed side of the circuit board 1, so that the area of the circuit board 1 corresponding to the display area is provided with translucency.

A translucent sealing substrate 6 such as glass is attached to the hollowed-out portion 4 side through a sealing material 5, and a potting material 7 is enclosed between the circuit board 1 and the sealing substrate 6. Has been done. The potting material 7 has a fluidity that does not solidify in the temperature range where the liquid crystal display device is actually used and is a translucent material.

As the sealing material 5, for example, silicone resin, epoxy resin or the like can be used, and as the potting material 7, for example, polyethylene glycol, transparent liquid crystal material, silicone gel or the like can be used.

FIG. 2 is a perspective view showing a state in which the sealing substrate 6 is removed and the potting material 7 is not enclosed.

As shown in the figure, a sealing material 5 for adhering the sealing substrate 6 and the circuit board 1 is provided so as to surround the outside of the hollow portion 4. An injection port 9 for injecting the potting material 7 is formed on one side of the area surrounded by the sealing material 5.

As will be described later, the potting material 7 is injected between the circuit board 1 and the sealing board 6 through the injection port 9 after the sealing board 6 is bonded to the circuit board 1 via the sealing material 5. After that, the injection port 9 is sealed with a sealing material.

By encapsulating the potting material 7, the membrane portion 10 left by the formation of the hollow portion 4 is covered with the potting material 7 and the sealing substrate 6,
Protected from changes in humidity and atmospheric pressure.

By the way, the actual use of the liquid crystal display device is usually carried out in a temperature range of about -20 to + 60 ° C. Therefore,
In this temperature range, it is necessary that the pressure applied to the membrane portion 10 left by the formation of the hollow portion 4 does not become excessively large.

For this reason, according to the present invention, the volume change of the potting material 7 due to the temperature change changes the volume of the seal material 5 and the space between the circuit board 1 and the sealing board 6 changes. The volume change between the sealing substrates 6 is set to be almost equal.

That is, as shown in FIG. 1, d ₁ and d ₂ are determined, the length of one side of the display area corresponding to the width of the cutout portion 4 is L, and the distance from the side edge of the cutout portion 4 to the sealing material 5 is set. Is defined as 1 and the coefficient of linear expansion of the sealing material 5 in the longitudinal direction is
(K ⁻¹ ), the body expansion coefficient of the potting material 7 is α (K ⁻¹ ),
Assuming that the temperature change is T (K) and l << L, d ₁ ρL ² T ≈ (d ₁ + d ₂ ) αL ² T (A).

In the above formula (A), the left side is the sealing material 5.
Is the volume change of the potting material 7 enclosed area due to the bulge (contraction), and the right side is the volume change of the potting material 7.

The above equation (A) becomes d ₁ ρ≈ (d ₁ + d ₂ ) α (B).

An example of satisfying the above expression (B) is a case where ethylene glycol is used for the potting material 7 and a silicone resin is used for the sealing material 5.

For example, d ₂ = 600 μm and d ₁ = 5 mm. Body expansion coefficient α of ethylene glycol is 0.64 × 1
It is 0 ^-3 (K ^-1 ). Various types of silicone resin are made, and the linear expansion coefficient ρ in the longitudinal direction is 0.1 to 10 × 1.
It can be selected in the range of 0 ^-3 (K ^-1 ). Here, the above expression (B) can be established by selecting the one having ρ = 0.7 × 10 ⁻³ (K ⁻¹ ).

Actually, ρ and α are slightly different depending on the temperature, but as the design value, the average value in the temperature range in actual use may be adopted.

Next, a method for manufacturing the present liquid crystal display device will be described.

First, the counter substrate 2 and the circuit board 1 are bonded together via the sealing material 8, the liquid crystal 3 is injected between them to seal them, and then the hollow portion 4 is formed on the circuit board 1 to form the membrane portion. Leave 10

Next, the potting material 7 is injected and sealed. This is divided into three steps, that is, the step of attaching the sealing material 5, the step of injecting the potting material 7, and the step of sealing the injection port 9 (see FIG. 2). To be

(1) Attaching Step of Sealing Material 5 First, the sealing material 5 is applied around the hollow portion 4. This application can be performed by tracing the shape discharged from the tip of the injection needle with a dispenser or by squeegee printing. At the time of this application, the injection port 9 shown in FIG. 2 is formed.

A sealing substrate 6 made of glass or the like is placed on the applied sealing material 5, and the circuit substrate 1 and the sealing substrate 6 are pressed with a desired gap so as to overlap each other and baked (for example, 80 ° C.).
(2 hours in the oven) to form the filling area of the potting material 7.

The gap between the circuit board 1 and the sealing substrate 6 is
It can be controlled by sandwiching a gap material having a desired thickness such as glass or an injection needle between the circuit board 1 and the sealing board 2. Further, when a very narrow gap (for example, about 10 μm) is required, a desired gap can be obtained by mixing and applying beads having a diameter corresponding to this gap into the sealing material 5.

(2) Potting material 7 injecting step The potting material 7 can be filled by a conventionally known vacuum injecting method.

The potting material 7 is vacuum degassed (for example, at 10 ⁻³ Torr for 12 hours) before injection so that no air bubbles are mixed.

Liquid crystal display device (liquid crystal cell) in which a potting material 7 filling region is formed between the circuit board 1 and the sealing substrate 2.
Then, the potting material 7 placed in a petri dish or the like is set in a vacuum device, and vacuumed to a vacuum degree of about 10 ⁻³ . The evacuation time is 1 to 24 after reaching 10 ^-3 Torr
It's about time.

After that, the liquid crystal display device is immersed in a petri dish or the like containing the potting material 7 in a vacuum state.
Then, due to the capillary phenomenon, the potting material 7 penetrates into the filling area to some extent.

After the equilibrium state of the injection due to the capillary phenomenon is reached, the potting material 7 can be sufficiently injected into the filling region by slowly leaking the vacuum device over 20 minutes to 1 hour.

Since it is easy to inject the potting material 7 by such a vacuum injection method, the potting material 7
Is preferably a material having a low vapor pressure.

(3) Sealing Step for Filling Port 9 The liquid crystal display device is taken out from the vacuum device, and after thoroughly filling the filling port 9 with acetone or the like to degrease it, a filling material is put on the filling port 9 for sealing. As the sealing material, an epoxy resin can be used when polyethylene glycol is used as the potting material 7.

After that, the injection sealing of the potting material 7 is completed by sufficiently curing the sealing material.

FIG. 3 is a sectional view showing the second embodiment, in which a groove 11 is formed at a position where the sealing material 5 is attached to the circuit board 1, and the sealing material 5 is attached to fill the groove 11. The sealing material 5 is substantially thickly coated without increasing the distance between the circuit board 1 and the sealing substrate 6, and is similar to the first embodiment.

That is, the volume change of the sealing material 5 can be made larger than that of the first embodiment, and can be followed even when the volume change of the potting material 7 is large.

Further, the groove 11 is formed by the cutout portion 4
If it is performed at the same time as the formation (usually performed by etching), an increase in the number of steps can be prevented.

The depth of the groove 11 in this embodiment is equal to the depth of the hollow portion 4, but the depth of the groove 11 depends on the material of the potting material 7 and the sealing material 5. It may be selected according to the material and the like.

In the present embodiment, the conditions under which the volume change of the potting material 7 due to the temperature change and the volume change between the circuit board 1 and the sealing substrate 6 due to the volume change of the sealing material 5 due to the temperature change are substantially equal to each other. Is set to l << L, and then (d ₁ + d ₂ ) ρL ² T≈ (d ₁ + d ₂ ) αL ² T ... (C), then ρ≈α ... (D).

FIG. 4 is a cross-sectional view showing a third embodiment, in which a wide region including the range where the sealing material 5 is attached is cut out.
By so doing, it is possible to obtain the same effect as that of the second embodiment.

In this case, the outside of the display area also includes the circuit board 1.
Since it has a light-transmitting property, it transmits light (visible light), but the adverse effect of this can be prevented by providing the light-shielding layer 12 on the circuit board 1. The light-shielding layer 12 is provided on the surface of the circuit board 1 on the side opposite to the illustrated position and the sealing substrate 6.
Can also be provided.

In the present embodiment, the volume change of the potting material 7 due to the temperature change and the volume change between the circuit board 1 and the sealing substrate 6 due to the volume change of the sealing material 5 due to the temperature change are substantially equal. Even if the value of l is a value that cannot be ignored with respect to L, the condition of is the condition represented by the equation (D).

FIG. 5 is a sectional view showing a fourth embodiment. The sealing substrate 6 has a sectional shape of a convex shape with its central portion projecting in the direction of the hollow portion 4 and is thick in the display area, and a seal around it. The third embodiment is similar to the third embodiment except that the area is thin.

In the case of the present embodiment, since the sealing substrate 6 is thick in the display area, the volume of the potting material 7 can be reduced and the selection range of the sealing material 5 can be widened.

In the present embodiment, the conditions under which the volume change of the potting material 7 due to the temperature change and the volume change between the circuit board 1 and the sealing substrate 6 due to the volume change of the sealing material 5 due to the temperature change are substantially equal to each other. Is (d ₁ + d ₂ ) ρ≈ (d ₁ −d ₂ ) α with l << L using d ₁ and d ₂ shown in FIG. Ρ can be set smaller than that in the embodiment.

FIG. 6 is a cross-sectional view showing the fifth embodiment.
As the sealing substrate 6 in this embodiment, the sealing substrate 6 having a convex cross section shown in the fourth embodiment is used.

In the case of this embodiment, the body expansion coefficient of the potting material 7 needs to be smaller than that of the fourth embodiment, but there is an advantage that the attachment state of the sealing material 5 is easier to stabilize than in the fourth embodiment. .

In the present embodiment, the conditions under which the volume change of the potting material 7 due to the temperature change and the volume change between the circuit board 1 and the sealing substrate 6 due to the volume change of the sealing material 5 due to the temperature change are substantially equal to each other. uses the d ₁ and d ₂ shown in Figure 6, as L«L, a d ₂ [rho ≒ d ₁ alpha.

[0063]

The present invention is as described above, and the non-translucent circuit board 1 having the translucent property by forming the cutout portion 4 in the region serving as the display portion and the translucent material. Counter substrate 2
In the liquid crystal display device in which the liquid crystal 3 is sealed in between, the cutout portion 4 is provided without causing image display fluctuation due to temperature change or the like.
It is possible to make up for the decrease in strength.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a perspective view showing a state before the potting material 7 is enclosed, with the sealing substrate removed.

FIG. 3 is a sectional view showing a second embodiment of the present invention.

FIG. 4 is a sectional view showing a third embodiment of the present invention.

FIG. 5 is a sectional view showing a fourth embodiment of the present invention.

FIG. 6 is a sectional view showing a fifth embodiment of the present invention.

[Explanation of symbols]

 1 Circuit board 2 Counter substrate 3 Liquid crystal 4 Cutout part 5 Sealing material 6 Sealing board 7 Potting material 8 Sealing material 9 Injection port 10 Membrane part 11 Groove 12 Light-shielding layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Genji 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A liquid crystal is sealed between a non-translucent circuit board on which a drive circuit is formed and a translucent counter substrate, and a hollow portion is formed on the side opposite to the liquid crystal sealed side of the circuit board. Translucency is imparted to the circuit board, and a fluid and translucent potting material is enclosed between the hollowed-out side of this circuit board and the translucent sealing board that is attached via a sealing material. The liquid crystal display is characterized in that the volume change of the potting material due to temperature change and the volume change between the circuit board and the sealing substrate due to the volume change of the seal material due to temperature change are adjusted to be substantially equal. apparatus. 2. The liquid crystal display device according to claim 1, wherein the sealing material is provided so as to fill a groove provided in the circuit board. 3. The liquid crystal display device according to claim 1, wherein a sealing material is provided in the hollow portion. 4. The liquid crystal display device according to claim 1, wherein the sealing substrate has a convex cross-sectional shape in which a central portion thereof projects toward the hollow portion.