JPH0862616A - Reflection type liquid crystal element and projection type display device using this element - Google Patents

Abstract

PURPOSE: To reduce the size of a silicon chip which is a reflection substrate, etc., and to improve the yield at the time of production by having connecting terminals to external circuits on a surface opposite to a surface having the active elements and reflection pixel electrodes of a reflection substrate. CONSTITUTION: This reflection type liquid crystal element consists of a transparent substrate 1 having transparent electrodes 2, liquid crystals 3, a sealant 11 and the reflection substrate 7 and is provided with the connecting terminal parts 8 to the external circuits on the surface opposite to the surface provided with the reflection pixel electrodes 4 from wiring parts 10 for power source supply, control signals, etc., via through-holes 9 on the reflection substrate 7 formed with the active elements 5 and the reflection pixel electrodes 4 on the silicon substrate 6, etc. Then, the connecting terminal parts 8 are arranged without being restricted by the pixel parts, peripheral circuits, etc., and since wire bonding is executable on the surface opposite to a surface facing dichroic prisms, the reliability at the time of packaging is improved. The positions of wire bonding pads are no longer restricted to the outer side of the positions of the reflection pixel electrodes 4 and, therefore, the size reduction of the silicon substrate 6 is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of mounting a reflection type display element using liquid crystal, and a projection type display device using the same.

[0002]

2. Description of the Related Art A projection type display device using a reflection type liquid crystal element is disclosed in, for example, Japanese Patent Laid-Open No. 4-194921. FIG. 2 shows the configuration of the projection type display device in this conventional example. here,
The reflective liquid crystal elements 19R, 19G, and 19B use, for example, polymer dispersed liquid crystal that changes from a scattering state to a transmissive state when a voltage is applied. By configuring this liquid crystal between the reflective pixel electrode connected to the active element and the transparent electrode to which a constant voltage is applied, the reflective liquid crystal element can be scattered according to the voltage applied to the pixel electrode. ，
It functions as an element that displays an image depending on the state of reflection.
In the voltage main projection display device, the light flux from the light source 12 is converted into substantially parallel light by the mirror 13 and condensed near the folding mirror 10 by the condenser lens 14, and then converted again into parallel light by the lens 17. The cross dichroic prism 18 separates each color into red, green, and blue and irradiates the reflective liquid crystal elements 19R, 19G, and 19B. Here, in the reflective liquid crystal element, the scattering and reflecting states are set for each pixel in accordance with a desired image as described above. Therefore, the light flux applied to the pixel in the reflective state is specularly reflected by the reflective pixel electrode and reflected as substantially parallel light, and then the red, green, and blue colors are combined by the cross dichroic mirror 18, and again by the lens 17, After being focused,
It is projected as a projection image on the screen 22 by the projection lens 21. On the other hand, the light flux applied to the pixels in the scattered state is not condensed by the lens 17 because it is reflected by the scattered light, and most of the light flux is blocked by the blocking mask 20 and the folding mirror 1.
It is blocked by 0 and the light shielding portion 15 and does not reach the screen 22.

On the other hand, a more specific structure of the reflection type liquid crystal element having an active driving element is, for example, Japan Disp.
lay '83, pp. 408-411. As shown in FIG. 3, the structure is such that a liquid crystal 25 is sandwiched between a transparent substrate 23 having a transparent electrode 24 formed on its surface and a reflective substrate 28, and the periphery thereof is sealed with a sealant 31. The whole is mounted on a ceramic substrate 29. Here, the reflective substrate 28 is composed of a reflective pixel electrode 27 and a silicon substrate 26 on which a MOS transistor is formed as an active element for controlling the applied voltage. Supply of power supply voltage and image signal from the outside of the device to the active device on the reflective substrate and the transparent electrode on the transparent substrate is done to the connection terminals on the ceramic substrate (not shown), and the wire bonding pad on the ceramic substrate. 32, the wires 34, and the wire bonding pads 33 on the silicon substrate are used to electrically connect to the reflective substrate by wire bonding. A voltage is further supplied to the transparent electrode via the conductive paste 30.

[0004]

However, the conventional method has the following problems. That is, when the reflection type liquid crystal element is mounted in the projection type display device, in order to prevent the reflection type liquid crystal element from tilting with respect to the optical axis, it is effective to bring it into close contact with a cross dichroic prism manufactured with high mechanical accuracy. In addition, it is desirable that the distance between the reflective liquid crystal element and the cross dichroic prism is short in order to reduce the size of the entire device. Further, in the structure using the reflective liquid crystal element, extra reflected light from other than the liquid crystal lowers the contrast of the projected image, and therefore must be reduced as much as possible.
As a countermeasure, by interposing a medium such as an ethylene glycol aqueous solution between the reflective liquid crystal element and the cross dichroic prism, the refractive index matching is performed between the cross dichroic prism and the transparent substrate having the transparent electrode to prevent reflection at the interface. The method of reducing is effective. In order to take such measures, it is necessary for the reflective liquid crystal element to have a structure in which it is almost in close contact with the cross dichroic prism.

However, in the conventional reflection type liquid crystal element, the height of the loop of the wire bonding of the connection between the reflective substrate and the transparent substrate and the ceramic substrate is close to the upper surface of the transparent electrode, which causes a cross. When the wires are in close contact with the dichroic prism, the wires are likely to come into contact with each other and receive stress, resulting in breakage at the bonding portion. That is, the height of the loop of the wire needs to be about 1.5 mm from the surface of the ceramic substrate in order to secure good bonding strength, and the thickness of the general transparent substrate and the thickness of the silicon substrate are 1 mm and 0.8 m, respectively.
m, 1.8 mm in total, so there is almost no margin. This is the same even if it is covered with resin to protect the wire bonding part, and the substantial height increases by the thickness of the resin.If a hard resin is used, the transparent substrate becomes a dichroic substrate. There was also a risk of hindering close contact. To prevent this, it is possible to increase the thickness of the transparent substrate, but it is necessary to separate the position of the bonding pad on the silicon substrate from the end face of the transparent substrate due to restrictions during bonding work. Of the number of substrates that can be obtained from the wafer, resulting in an increase in cost.

Further, the provision of the wire bonding pad itself causes the size of the silicon substrate to become larger than the size required for display.

As described above, in the prior art, the mounting of the reflection type liquid crystal element has not been considered for application to the projection type display device.

[0008]

In order to solve the above problems, the means according to the present invention comprises, as shown in FIG. 1, a transparent substrate 1 having a transparent electrode 1, a liquid crystal 3, a sealant 11 and a reflective substrate 7. Is a reflective liquid crystal element, and is reflected from a wiring portion 10 for supplying power and control signals through a through hole 9 to a reflective substrate 7 in which an active element 5 and a reflective pixel electrode 4 are formed on a silicon substrate 6 or the like. A connection terminal portion 8 for connecting to an external circuit is provided on the surface opposite to the surface on which the pixel electrode 4 is provided.

[0009]

By the above means, the wire bonding can be performed on the surface opposite to the surface facing the dichroic prism, so that the above-mentioned problem is solved and the reliability at the time of mounting is improved. Also,
Since the position of the wire bonding pad is not limited to the outside of the position of the reflective electrode, the size of the silicon substrate can be reduced.

For the same reason, since the area of the connecting portion can be increased, not only wire bonding but also other connecting means such as a flexible cable using an anisotropic conductive film can be used.

[0011]

EXAMPLES The present invention will be described in more detail by way of examples.

(Embodiment 1) FIG. 4 is a circuit diagram of an active element on a reflective substrate. This circuit has a configuration in which peripheral circuits are built in, and more specifically, the pixel circuit 35 and the sample circuit 3
6, a horizontal scanning circuit 37, a vertical scanning circuit 38, and an AND gate 38. The pixel circuit 35 includes a plurality of scanning signal lines 4
2. A plurality of video signal lines 43 and a plurality of substrate power supply lines 44 intersecting with this, a MOS transistor 45 provided at the intersection of the scanning signal line and the video signal line, and a storage capacitor 47, and a liquid crystal as an equivalent circuit of the liquid crystal. The capacity 46 is shown.
One set of MOS transistor 45, storage capacitor 47, and liquid crystal capacitor 46 forms one pixel, and as a whole, M is arranged in the horizontal direction.
, N in the vertical direction are arranged in a matrix.
The scanning signals Vg1 to VgN are applied to the gate electrode of the MOS transistor 45 via the scanning signal line 42, and the luminance signals Vd1 to VdM are applied to the drain electrode via the video signal line.
Further, one electrode of the storage capacitor 47 and one electrode (reflection pixel electrode) of the liquid crystal capacitor 46 are connected to the source electrode. Further, the other electrode of the storage capacitor 47 is connected to the substrate feeding line 4
4 to a substrate power supply terminal 44 for supplying the substrate voltage VSS. The liquid crystal capacitor 46 is the pixel circuit 3
5 is an equivalent circuit of a liquid crystal sandwiched between a reflective substrate forming 5 and a transparent substrate with a transparent electrode facing the reflective substrate.

The horizontal scanning circuit 37 outputs M-phase multiphase signals PH1 to PHM based on the horizontal scanning timing signal HTIM externally applied to the horizontal scanning timing signal terminal 43. The sample circuit 36 is composed of a MOS switch, and the gate electrode of the MOS switch has an output signal PH.
1 to PHM, and the drain electrode of the MOS switch is supplied with video signals VI1 or VI2 having different polarities from the outside via two video signal terminals 65a and 65b.
Luminance signals Vd1 to Vd are applied to the source electrodes of the MOS switches.
Output M. The horizontal scanning circuit 37 and the sample circuit 36 are covered with a light shielding layer 40, the vertical scanning circuit 38 and the AND gate 39 are covered with a light shielding layer 41, and both the light shielding layers 40 and 41 are connected to a common voltage supply terminal 66 together with a transparent electrode. ing. The video signals VI1 and VI2 are signals that change with the common voltage COM as a reference, and flicker is reduced by making their polarities opposite.

The vertical scanning circuit 38 outputs multi-phase signals PV1 to PVN according to the vertical scanning timing signal externally applied to the vertical scanning timing signal terminal 67. AN
The D gate 39 receives the vertical scanning signal Vg of the pixel circuit based on the multi-phase signals PV1 to PVN and the vertical scanning control signal CNT supplied from the outside through the vertical scanning control signal terminal 48.
1 to VgN is output.

The brightness signals Vd1 to VdM are input to the pixel circuits 35 arranged in a matrix for each column. At this time, only the MOS transistors of the pixel circuit 35 selected by the vertical scanning signals Vg1 to VgN are turned on, and the luminance signals Vd1 to VdM are written in the holding capacitors 47 and the liquid crystal capacitors 46 of the pixel circuits in the selected row, A voltage corresponding to the luminance signal is applied to the liquid crystal, and an image corresponding to the image signal is displayed. The logic voltage VCC supply terminal is omitted in FIG.

FIG. 5 shows a cross-sectional view of a pixel portion of a reflective liquid crystal element using a reflective substrate having this circuit formed on a single crystal silicon substrate. Basically, a transparent substrate 1 having a transparent electrode 2
And a source region 53 which is an n + region on the silicon substrate 6.
In this embodiment, a polymer dispersed liquid crystal is sandwiched as the liquid crystal 3 between the MOS transistor 45 including the drain region 55 and the polysilicon gate 54 and the reflective substrate 7 having the reflective pixel electrode 4. Although not shown in the figure, a silicon oxide layer is interposed between the polysilicon gate 54 and the p-type semiconductor layer 52. In addition, a silicon oxide layer is interposed between the polysilicon layer 58 and the p-type semiconductor layer 52 to form the storage capacitor 47. Drain region 55
Are connected to the reflective pixel electrode 4 through the contact hole 56 in the first interlayer insulating layer 57, the aluminum wiring layer 51, the through hole 49 in the second interlayer insulating layer 50, and the like.

The sectional structure of the connection terminal portion of the reflective substrate is shown in FIG. The wiring portions 10 from various signal terminals, voltage supply terminals, etc. in FIG. 4 are respectively drawn out through the through holes 9 on the surface opposite to the reflective pixel electrode to form the connection terminal portion 8. This through hole is disclosed in, for example, Japanese Patent Laid-Open No. 5-2
As described in Japanese Patent No. 67469, a gallium ion beam is applied to a predetermined place and etching is performed in order from the surface. Next, an insulating film is formed by atmospheric pressure CVD method or laser CVD method on the surface on which the wiring portion 10 and the connection terminal portion 8 are formed and the wall surface of the through hole. Then, a gallium ion beam is irradiated in W (CO2) gas to deposit tungsten formed by gas decomposition in the through hole 9, and the wiring portion 10 is formed.
And the connection terminal portions 8 are connected.

FIG. 6 shows a method of connecting to an external circuit. The connection terminal portion 8 drawn out on the back surface of the reflective substrate and the transparent electrode terminal portion 61 formed on the surface of the transparent substrate 1 facing the liquid crystal are connected by a flexible cable 59 having an anisotropic conductive film. Then, the transparent electrode terminal portion on the transparent substrate is further connected to an external circuit by the flexible film 60 having an anisotropic conductive film. The transparent electrode terminal portion 61 also includes a lead line from the transparent electrode 2 facing the reflective pixel electrode on the transparent substrate.

The three reflective liquid crystal elements 19R, 19G,
19B is arranged in close contact with the three surfaces of the cross dichroic prism 18 with an ethylene glycol aqueous solution for optical coupling or the like interposed therebetween as shown in FIG. The jig for fixing the reflective liquid crystal elements 19R, 19G, and 19B has a structure in which the peripheral portions of the transparent substrates 8R, 8G, and 8B are pressed against the cross dichroic prism, so that single crystal silicon having poor mechanical strength is used. It is possible to prevent damage to the reflective substrate made of. Then, a projection optical device as shown in FIG. 2 can be constructed.

(Embodiment 2) As another embodiment, FIG. 9 shows a sectional view of a connection portion of a reflection type liquid crystal element using a supporting substrate 64 made of ceramics. The connection terminal portion 8 of the reflective substrate 7 having the same structure as in the first embodiment and the connection terminal portion 63 on the support substrate 64 are opposed to each other, and the both are connected by the conductive paste 62. This conductive paste is, for example, silver-
Lead-based conductive paste can be used. Similar to the first embodiment, the connection terminal portion 63 on the support substrate 64 is connected to an external circuit by flexing with an anisotropic conductive film or the like. The transparent electrode 2 on the transparent substrate 1 is also connected to the connection terminal portion 63 on the support substrate 64 by a conductive paste at a location not shown in the figure, and is connected to an external circuit together with other connection terminals. There is.

The reflective substrate in the present invention is not limited to the one using the single crystal silicon substrate in the embodiment, and may be, for example, a structure in which a thin film transistor and a reflective pixel electrode are formed on glass or quartz. It may be a thing.

[0022]

According to the present invention, since the electric signal and voltage supply connection portion of the reflective substrate having the active element is arranged on the side opposite to the optical mounting surface, the connection terminal portion is not restricted by the pixel portion, the peripheral circuit portion or the like. , The size of the silicon substrate or the like, which is a reflective substrate, can be reduced, and the yield in manufacturing is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a connection portion of a reflective liquid crystal element according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a projection display device.

FIG. 3 is a cross-sectional view showing a conventional example of a reflective liquid crystal element.

FIG. 4 is a circuit diagram of a reflective substrate according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a pixel portion of a reflective liquid crystal element according to an example of the present invention.

FIG. 6 is an explanatory diagram showing a method for connecting reflective liquid crystal elements in an example of the present invention.

FIG. 7 is an explanatory diagram showing a method of mounting a reflective liquid crystal element on a cross dichroic prism according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view of a connection portion of a reflective liquid crystal element according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... Transparent electrode, 3 ... Liquid crystal, 4 ... Reflection pixel electrode, 5 ... Active element, 6 ... Silicon substrate, 7 ... Reflection substrate, 8 ... Connection terminal part, 9 ... Through hole, 10 ... Wiring part , 11 ... Sealing agent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Sato Inventor Hide 1-1 Satoshi Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Minoru Hoshino 7-chome Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Tsunenori Yamamoto 7-1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Shoichi Hirota Hitachi City, Ibaraki Prefecture 7-1, Omika-cho, Hitachi, Ltd., Hitachi Research Laboratory, Inc. (72) Inventor, Youji Miyahara, 5-2-1 Omika-cho, Hitachi, Hitachi, Ibaraki Prefecture, Ltd., Omika, Hitachi, Ltd. (72) Inventor, Katsuyama Ichiro 52-1 Omika-cho, Hitachi-shi, Ibaraki Hiritsu Process Computer Engineering Co., Ltd.

Claims (8)

[Claims] 1. A reflective liquid crystal device comprising a transparent substrate, liquid crystal, and a reflective substrate having an active element and a reflective electrode, wherein the reflective substrate has a surface opposite to a surface having the active element and the reflective electrode. A reflection type liquid crystal device having a connection terminal to an external circuit. 2. A reflective liquid crystal device comprising a transparent substrate, liquid crystal, and a reflective substrate having an active element and a reflective electrode, wherein the reflective substrate has wiring regions on both sides, and the wiring route is electrically connected. A reflective liquid crystal device characterized by being provided. 3. A reflection type liquid crystal element comprising a transparent substrate, a liquid crystal, a reflection substrate having an active element and a reflection electrode, and a holding substrate having a wiring layer on the surface and on which the reflection substrate is mounted. 2. The reflective liquid crystal element, wherein the active element and the support substrate are electrically connected to each other through a through hole extending from a surface having the active element and the reflective electrode to an opposite surface. 4. A reflection type liquid crystal element comprising a transparent substrate, a liquid crystal, a reflection substrate having an active element and a reflection electrode, and a holding substrate having a wiring layer on its surface and on which the reflection substrate is mounted. A reflective liquid crystal device, wherein the reflective substrate and the reflective substrate are electrically connected. 5. A reflection type liquid crystal element comprising a transparent substrate, a liquid crystal, a reflection substrate having an active element and a reflection electrode, and a holding substrate having a wiring layer on the surface and on which the reflection substrate is mounted. 2. A reflective liquid crystal device, wherein the connection terminal is formed on the transparent substrate. 6. The method according to claim 1, 2, 3, 4 or 5.
A reflective liquid crystal device in which the active element is a MOS transistor and the reflective substrate is a silicon substrate. 7. A projection type display device using the reflection type liquid crystal element according to claim 1, 2, 3, 4 or 5. 8. A projection type display device comprising the reflection type liquid crystal element according to claim 1, 2, 3, 4 or 5, a dichroic prism, a light source, and a projection lens.