JPH05241131A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the temp. rise by the generation of heat in the active matrix type liquid crystal display device. CONSTITUTION:An active matrix substrate 1 and a counter substrate 2 are disposed to face each other via a prescribed spacing and a liquid crystal layer 3 is held in this spacing. A horizontal driving circuit part and a vertical driving circuit part are also formed in addition to a display part on the active matrix substrate 1 to constitute a monolithic structure. The display part includes picture element electrodes arranged in a matrix form and thin-film transistors (TFTs) driving these picture element electrodes. On the other hand, the driving circuit parts are constituted of the TFTs integrated at a high density and include, for example, N channel TRs4 P channel TRs 5, etc. The heat is generated by the operation of these TRs 4, 5. A heat conduction member 17 facing the heat generating region is provided on the side of the active matrix substrate 1 opposite from the side in contact with the liquid crystal layer. This heat conduction member 17 is brought into pressurized contact with the above- mentioned region by a supporting member 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic type active matrix type liquid crystal display device in which a display section or a pixel section and a drive section are formed on the same substrate.
More specifically, the present invention relates to a heat radiation structure for heat generated from thin film transistors that are densely integrated in a driving unit.

[0002]

2. Description of the Related Art In order to clarify the background of the present invention, a general structure of a monolithic active matrix type liquid crystal display device will be briefly described with reference to FIG. This type of display device has a structure in which an active matrix substrate 101 and a counter substrate 102 are bonded together by a spacer 103,
Liquid crystal is filled in the gap between the substrates 101 and 102. A pixel portion or a display portion 104 is formed on the inner surface of the active matrix substrate 101. The display unit 104 includes pixel electrodes arranged in a matrix and switching elements for individually driving the pixel electrodes.
As the switching element, a thin film transistor made of polycrystalline silicon is usually used. The active matrix substrate 101 is also provided with a drive section or a peripheral section,
This includes a horizontal drive circuit 105 and a vertical drive circuit 106. These drive circuits drive the switching elements, for example, dot-sequentially to display an image. These drive circuits 105 and 106 include logic elements that are integrated and formed with high density. This logic element is also composed of a thin film transistor made of polycrystalline silicon. The peripheral portion is connected to an external circuit via the extraction electrode 107.

[0003]

The problem to be solved by the invention will be briefly described with reference to FIG. The active matrix substrate 101 is generally made of a quartz glass material and its thermal conductivity is not so high. The drive circuits 105 and 106 are formed on the inner surface of the substrate as described above. Since the thin film transistors included in these driving circuits are integrated with high density and operate at high speed, heat is generated. However, since the heat dissipation function of the active matrix substrate 101 is insufficient, the heat generated tends to be accumulated in the display device. Cooling capacity is not sufficient only by radiation of heat from the substrate surface. In particular, when the temperature of the environment in which the liquid crystal display device is used is high, cooling is not performed, and heat is further accumulated inside the device. Generally, unlike a MOS transistor formed on a silicon wafer, a thin film transistor has a characteristic that thermal runaway easily occurs due to increase in on-current and off-current accompanying heat generation. Once thermal runaway occurs, the amount of heat generated further increases, causing damage to the device and thermal deformation of accessory parts such as color filters and polarizing plates, which is a reliability problem.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems or problems of the prior art, it is an object of the present invention to impart an effective heat dissipation function to a monolithic active matrix type liquid crystal display device. The measures taken to achieve such an object will be briefly described. The liquid crystal display device to which the present invention is directed has, as a general configuration, a display section including pixel electrodes arranged in a matrix and thin film transistors for driving the pixel electrodes, a horizontal drive circuit section connected to the display section, and An active matrix substrate on which a vertical drive circuit section is formed; a counter substrate having a counter electrode and arranged to face the active matrix substrate; and a liquid crystal layer held between the active matrix substrate and the counter substrate. I have it. In the liquid crystal display device having such a structure, a heat conducting member is provided in the heat generating region on the side opposite to the side of the active matrix substrate which is in contact with the liquid crystal layer, and the heat conducting member is held in pressure contact with a support material.

[0005]

According to the present invention, the heat conducting member is attached to the outer surface side of the active matrix substrate. Since the drive circuit portion formed on the inner surface of the active matrix substrate is integrated with high density and operates at high speed, it generates a large amount of heat and serves as a heat generation region. The heat generated in this region moves in the thickness direction of the active matrix substrate, is transferred to the heat conducting member, and is effectively diffused. The diffused heat is radiated to the outside through the support member that is in pressure contact with the heat conducting member, and an excellent cooling function is obtained. Therefore, heat accumulation inside the display device can be suppressed and the temperature rise is prevented, so that thermal runaway of the thin film transistor or the like can be prevented.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial sectional view showing an embodiment of a monolithic active matrix type liquid crystal display device according to the present invention. In particular, the portion provided with the drive circuit portion forming the heat generating region is cut out and shown. This liquid crystal display device has a liquid crystal panel structure or a liquid crystal cell structure in which an active matrix substrate 1 and a counter substrate 2 are stacked with a predetermined gap therebetween and a liquid crystal layer 3 is enclosed and filled in the gap. The active matrix substrate 1 and the counter substrate 2 are made of, for example, a quartz glass material, and the liquid crystal layer 3 is made of, for example, a twisted nematic aligned liquid crystal material.

A vertical drive circuit section and a horizontal drive circuit section are formed on the inner surface of the active matrix substrate 1 in addition to the pixel section (not shown). In the illustrated example, the CMOS structures included in these drive circuit units are cut out and illustrated. The CMOS structure has a pair of N-channel transistors 4
And a P-channel transistor 5. Each of the transistors is a so-called thin film transistor or TFT, which is formed by using the polycrystalline silicon thin film 6. A source region, a drain region, and a channel region are formed in each patterned polycrystalline silicon thin film 6, and a gate electrode 8 is formed above the channel region via a gate insulating film 7. Further, a metal wiring 10 such as aluminum is connected to the source / drain region of each transistor through a contact hole provided in the interlayer insulating film 9. The transistor having such a structure is covered with a passivation film 11 made of PSG or the like. A silicon nitride protective film 12 is formed thereon, and an alignment film 13 made of polyimide or the like is further stacked thereon. In the example shown in FIG. 1, since the peripheral portion such as the drive circuit portion is also included in the liquid crystal cell, the area of the alignment film 13 extends.

The N-channel transistor 4 and the P-channel transistor 5 forming the drive circuit portion are integrated and formed at a higher density than the pixel portion and operate at a high speed, so a large amount of heat is generated. Therefore, these portions mainly serve as heat generating regions.

On the other hand, on the inner surface of the counter substrate 2, a color filter 14, a counter electrode or a common electrode 15, and an alignment film 16 are sequentially laminated. A polarizing plate (not shown) is generally attached to the outer surface of the counter substrate 2.

On the outer surface of the active matrix substrate 1, a heat conducting member 17 is provided so as to cover at least the above-mentioned heat generating area. The heat conducting member 17 has a function of effectively guiding and dispersing the heat transferred from the heat generating region along the thickness direction of the active matrix substrate 1. In this way, it is possible to prevent a local temperature rise in the heat generation region. The material of the heat conducting member 17 is preferably one having a higher heat conductivity than the silica glass constituting the active matrix substrate, such as aluminum, copper,
A metal material such as gold or stainless steel is used. Alternatively,
It is also possible to use ceramics having excellent thermal conductivity or transparent organic materials having particularly high thermal conductivity. Heat conduction member 17
Is attached to the back surface side of the active matrix substrate 1 via an adhesive having a small heat resistance, for example. A supporting member 18 is pressed against the heat conducting member 17. The support member 18 is also made of a material having excellent thermal conductivity, such as metal, and functions as a heat dissipation plate. That is, the heat conducted from the heat generating area of the liquid crystal panel through the heat conducting member 17 is radiated to the outside by the supporting member 18. It is preferable to press the support member 18 against the heat conducting member 17 in order to enhance the heat conducting efficiency.

FIG. 2 is an external perspective view of the liquid crystal display device shown in FIG. Active matrix substrate 1 and counter substrate 2
Is a spacer 1 having a predetermined thickness and formed in a window frame shape.
They are bonded together via 9 to form a liquid crystal cell. The liquid crystal is filled and sealed inside the cell as described above. A display unit 20 is provided on the inner surface of the active matrix substrate 1, and pixel electrodes arranged in a matrix and thin film transistors for individually driving the pixel electrodes are formed. Further, peripheral parts such as the horizontal drive circuit part 21 and the vertical drive circuit part 22 are also provided. These drive circuit units are connected to the display unit 20 and drive the thin film transistors. The drive circuit portions 21 and 22 include a thin film transistor element group integrated at high density and are the main heat generating regions. Further, a lead electrode 23 for external connection is formed on the exposed surface of the active matrix substrate 1.

A heat conducting member 17 is laminated on the outer surface of the active matrix substrate 1. In the illustrated example, the heat conducting member 17 is overlaid on the entire surface of the liquid crystal cell, but may be any member that can cover at least the heat generating regions of the driving units 21, 22 and the like. A support member 18 is further laminated on the heat conduction member 17. This supporting member 18 also has an outer shape that matches the liquid crystal cell, but at least the heat conducting member 1
It should be compatible with 7.

The liquid crystal cell may be either a transmissive type or a reflective type. In the case of a transmissive type, the active matrix substrate 1 and the counter substrate 2 are made of a transparent material such as quartz glass. In this case, at least the display unit 20 should not be shielded so that light can be transmitted. On the other hand, the heat conduction member 17 and the support member 18 are made of, for example, a metal material. Since the metal material is opaque, the display unit 20 is shielded as it is. Therefore, when applied to a transmissive liquid crystal cell, the heat conducting member 17 and the supporting member 1
It is necessary to provide a window frame portion 8 or a cutout portion 8 which is aligned with the display portion 20. If the heat conducting member 17 and the supporting member 18 are made of a transparent material, it is not necessary to take such measures.

Next, a method of assembling the liquid crystal display device according to the present invention will be described with reference to FIGS. Here, a liquid crystal display device used in a viewfinder mounted on a video camera or the like is taken as an example. First, FIG. 3 shows a state before assembly. The liquid crystal panel 24 is housed in a fixture 25. The liquid crystal panel 24 is attached to the housing 26 of the viewfinder using the fixture 25. Screw holes 2 are provided in the receiving portion of the housing 26.
7 is provided. A flexible tape lead 28 for external connection is adhered to the liquid crystal panel 24. Usually, polarizing plates made of an organic material are attached to both surfaces of the liquid crystal panel 24. Separately, the heat conducting member 17 and the supporting member 18 are prepared separately.

FIG. 4 shows an assembling process. The heat conducting member 17 and the supporting member 18 are set on the receiving portion of the housing 26 in an overlapping manner. Also, a fixing screw 29 is prepared.

FIG. 5 is a completed assembly drawing. The fixing member 25 is fixed to the receiving portion of the housing 26 in a state where the support member 18 and the liquid crystal panel 24 are overlapped with each other with the heat conducting member 17 interposed therebetween. For this fixing, insert the flange portion of the fixture 25,
A screw 29 that engages with a screw hole 27 provided in the receiving portion of the housing 26 is used. With such a fixing structure, the liquid crystal panel 24, the heat conducting member 17 and the supporting member 18 are pressed against each other to obtain a heat radiating structure. That is, the liquid crystal panel 24
The heat generated inside the heat conduction member 17 and the support member 18
Heat is radiated to the housing 26 via the.

Finally, a high temperature operation test was conducted in order to confirm the effect of the present invention. The results are shown in the graph of FIG.
The high temperature operation test was carried out for each of 10 invention samples having a heat dissipation structure and 10 conventional samples having no heat dissipation mechanism. The high temperature operation test was performed by applying a drive voltage of 14 V while the sample was held at 85 ° C. The horizontal axis of the graph represents the high temperature drive time, and the vertical axis represents the cumulative failure rate.
Failure was judged when the polarizing plate attached to each sample was deformed. The deformation of the polarizing plate occurs when the temperature of the liquid crystal panel exceeds 100 ° C. As is clear from the graph, no failure occurred for the invention product. On the other hand, with the conventional product, a failure occurs as the operation test time elapses. In other words, it was found that in the conventional product, the heat generated is accumulated inside the liquid crystal panel and the panel temperature rises. On the other hand, in the case of the invention product, the effect of the heat dissipation mechanism is remarkably exhibited and the panel temperature does not rise.

The liquid crystal material filled in the liquid crystal panel has temperature dependency and is affected by the ambient temperature. Generally, the upper limit guaranteed temperature of 55 ° C. is standard. Since a backlight is actually used for illumination, it is necessary to expect a heating amount of 15 ° C. and guarantee a normal operation up to 70 ° C.
However, if no heat dissipation mechanism is provided, the panel temperature easily rises to 100 ° C. due to the heat from the heat generating region. If thermal runaway is added to this, the panel temperature will rise further. The polarizing plate and the color filter provided in the liquid crystal panel are made of an organic material and have a softening point of about 120 ° C. Therefore, if the panel temperature rises, the film may be easily damaged and the film may peel off or change color. The heat dissipation mechanism according to the present invention is practically effective for preventing the occurrence of such a failure.

[0019]

As described above, according to the present invention, in a liquid crystal display device in which a drive circuit composed of thin film transistors is formed on an insulating substrate, the insulation is performed by facing a region in the drive circuit where the thin film transistor integration density is high. The structure is such that the heat conducting member is provided via the substrate and the supporting member having excellent heat conductivity is pressed and held. Therefore, it is possible to suppress a local temperature rise and prevent thermal damage to the liquid crystal display device. Further, thermal runaway of the drive circuit included in the liquid crystal display device is suppressed, so that the reliability is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing a basic configuration of a liquid crystal display device according to the present invention.

FIG. 2 is an external perspective view of the liquid crystal display device shown in FIG.

FIG. 3 is an explanatory diagram showing a process of assembling the liquid crystal display device according to the present invention.

FIG. 4 is an explanatory view showing the same assembling step.

FIG. 5 is an explanatory view showing the same assembling step.

FIG. 6 is a graph showing the results of a high temperature operation test of a liquid crystal display device.

FIG. 7 is an external perspective view of a conventional liquid crystal display device.

[Explanation of symbols]

 1 Active Matrix Substrate 2 Counter Substrate 3 Liquid Crystal Layer 4 N-Channel Transistor 5 P-Channel Transistor 6 Polycrystalline Silicon Thin Film 14 Color Filter 17 Thermal Conductive Member 18 Supporting Member 20 Display 21 Horizontal Drive Circuit 22 Vertical Drive Circuit 24 Liquid Crystal Panel

Claims (2)

[Claims] 1. An active matrix in which a display section including pixel electrodes arranged in a matrix and thin film transistors for driving the pixel electrodes and a horizontal drive circuit section and a vertical drive circuit section connected to the display section are formed. A substrate, a counter substrate having a counter electrode and facing the active matrix substrate, a liquid crystal layer held between the active matrix substrate and the counter substrate, and a side of the active matrix substrate in contact with the liquid crystal layer. A liquid crystal display device, comprising: a heat conducting member provided in a heat generating region on the opposite side; and a supporting member supporting the heat conducting member. 2. The liquid crystal display device according to claim 1, wherein each of the active matrix substrate and the counter substrate is made of quartz glass.