A display device

Abstract: A display device that includes a substrate, a display means disposed on the substrate, a driving circuit arranged along the periphery of the substrate, wherein the driving circuit (36) is covered with a light-shielding heat releaser (38) on the surface thereof in opposition to the substrate.

Description: The present invention relates generally to a display device such as a thin-film transistor (TFT) liquid crystal display device, and more particularly to a device for protecting a display device against the detrimental build-up of heat and the irradiation of light. In recent years liquid crystal display devices of an active matrix type, which have a thin film transistors (TFT) with pixels of liquid crystal, have become popular. This type of display device exhibits a higher gradation than a duty-drive type liquid crystal display, and the resulting image quality is almost equal to that reproduced by conventional CRT displays. When the image quality is the same, the active matrix crystal display is more advantageous than the conventional CRT displays in that the thickness and size of the active matrix crystal display devices can be easily reduced, thus saving electricity. These merits stimulate the industry's interest in the active matrix crystal display device. Referring to Figure 7 of the accompanying drawings, a typical example of the IC drivers used in a conventional TFT display devices will be described: An IC driver 2 is supported by a tape carrier 1 which is coupled by an anisotropic conductive film (not shown) to the terminal electrodes of a liquid crystal panel 3 . This arrangement is not applicable to a high precision display device having a liquid crystal panel 3 which requires terminal electrodes to be arranged with pitches of 100 µm or less, because of the difficulty of accurately arranging the terminal electrodes of the tape carrier 1 , and the low resolution of the anisotropic conductive film. Figure 8 shows an improved display device which has a liquid display section having substrates 12 , and 13 with a liquid crystal 11 interposed therebetween. The substrate 12 includes wiring electrodes 14 disposed on an edge area thereof on which a IC driver 15 is provided by the Chip-on-Glass System (COG System). Electric welding is carried out by wire bonding or alternatively soldering, each of which requires that the wiring is made of metal capable of wire bonding or having good affinity with solder. The selected material is costly, thereby increasing the production costs of liquid crystal display devices. The wiring electrodes 14 are joined to the electrodes of the IC driver 15 with an electrically conductive adhesive. However, the build-up of heat in the display device impairs the constant resistivity of the joined electrodes, particularly at such a relatively high temperature such as when analog signals are treated. The build-up of heat also causes the malfunction of the IC driver 15 . The IC driver 15 includes a circuit as shown in Figure 9. The image signal applied to a terminal 21 is stored in a sampling capacitor 23 in response to the input of a sampling pulse supplied to a gate transistor 22 . When a transfer (TRF) signal applied to another gate transistor 24 is amplified to a higher level, the signal stored in the sampling capacitor 23 is transferred to a hold capacitor 25 , and then is delivered to a signal electrode through an output circuit including a differential amplifier 26 and an output transistor 27 . In the circuit described above, when light is irradiated upon the IC driver 15 , (1) the transistor 22 of the sampling pulse input section whose potential becomes high, and (2) the transistor 24 of the TRF signal input section becomes leaky owing to photoelectric effect. The leak causes a false display on the liquid crystal display device. The false display provides a problem particularly for liquid crystal display devices for projection TV where an intensified light is irradiated. It is known from GB-A-1418520 to incorporate a cooling member, in the form of a strip of metal, over a semi-conductor body on the side of the semi-conductor body remote from a supporting substrate. This cooling member is provided for the purpose of enabling the semi-conductor body to handle larger amounts of electrical power than would otherwise be the case. It is also known from DE-A-3025784 to dispose a dark layer on the opposite side of a substrate to that carrying an opto-electronic control element for the purpose of increasing the light contrast in the region of that opto-electronic control element. It is an object of the present invention to provide a display device which overcomes the above discussed and other disadvantages and deficiencies of the prior art. In accordance with the present invention, a display device comprises a substrate, a display means disposed on the substrate and a driving circuit which is arranged along the periphery of the substrate and is covered with a light-shielding, heat dissipation means on the surface thereof remote from the substrate, the light-shielding heat dissipation means comprising a single layer which covers said surface of the driving circuit in its entirety and a light-shielding member being attached to that bottom surface portion of the substrate that corresponds to the driver circuit. According to another aspect of the invention, the display device comprises a smaller substrate and a larger substrate, a display means interposed between the two substrates, a driving circuit arranged on the rim portions of the larger substrate, a third substrate butt joined to the larger substrate, the third substrate carrying a control circuit thereon, and a light-shielding, heat dissipating means extending from a bottom surface portion of the larger substrate that corresponds to the driving circuit to the smaller substrate by way of the third substrate, the control circuit and the driving circuit so that the driving circuit and the control circuit are enclosed by the light-shielding, heat dissipating means, wherein the driving circuit is in contact with the light-shielding heat dissipating means. According to further aspects of the present invention, the display device is as claimed in claim 3 or 9. In a preferred embodiment, the case comprises two half portions, one of which is fitted in the other. In another preferred embodiment, the electrical connected between the light-shielding, heat dissipation means and the case is effected by means of a spring of electrically conductive material. In a further embodiment, the electrical connection between the light-shielding, heat dissipating means and the case is effected by direct contact of a part of the heat dissipating means with the case. In a preferred embodiment, the driving circuit comprises a sampling capacitor for applying a driving voltage to the display means, which includes a liquid crystal, and a hold capacitor. Thus, the invention described herein makes possible the provision of (1) a display device having a high-precision large screen, capable of economical fabrication without the use of expensive components, (2) a display device safe from high temperatures generated in the driving elements because of the effective dissipation of heat by the heat dissipation means, and (3) a display device free from malfunction which would otherwise be caused by light, thereby enabling the display device to be used under intensified light irradiation. The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view showing a display device not in accordance with the present invention; Figure 2 is a cross-sectional view taken along the line II-II of Figure 1; Figures 3 to 6 are cross-sectional views each showing examples of the display devices according to the present invention. Figure 7 is a perspective view showing a prior art liquid crystal display device employing a taper carrier; Figure 8 is a cross-sectional view showing another prior art display device employing a COG system; and Figure 9 is a circuit diagram showing a driver circuit included in a TFT liquid crystal display device. Referring to Figures 1 and 2, which illustrates an example of a TFT liquid crystal display which is not according to the present invention, the display includes a display section which comprises a smaller substrate 31 and a larger substrate 32 with a liquid crystal 33 sandwiched therebetween. The substrate 32 includes wiring electrodes 34 around the periphery thereof that has no portion of the smaller substrate 31 as shown in Figure 2. The reference numeral 36 denotes an IC driver for activating a liquid crystal display panel. The IC drivers 36 include the liquid crystal driver circuit shown in Figure 9, and are provided with projecting electrodes 35 joined to the wiring electrodes 34 with an adhesive 37 of electrically conductive material so as to effect an electrical connection between the IC drivers 36 and the wiring electrodes 34 . In general, the sampling capacitor 23 and the hold capacitor 25 , especially the latter, are likely to cause electrical leaks upon exposure to light. Thus liquid crystal panels including such ICs must be shielded from exposure to light. The substrate 32 and a light-shielding and heat-dissipating member 38 are connected to each other by way of the IC driver 36 . Hereinafter, the light-shielding and heat- dissipating member 38 will be referred to merely as "light-shielding member". The light-shielding member 38 is made of a foil or a sheet which can shield light and is electrically conductive. For example, aluminum or copper foil can be used. In order to join the light-shielding member 38 to the surface the substrate 32 opposed to the IC driver 36 , a surface of the metal foil is coated with an adhesive, and the adhesive-coated surface is overlaid on the top surface of the IC drivers 36 . In the illustrated example a single light-shielding member 38 is used to cover all the IC drivers 36 , especially to protect the sampling capacitor 23 and the hold capacitor 25 in the IC drivers against exposure to light, but a number of light-shielding members 38 corresponding to that of the IC drivers can be used to cover the IC drivers 36 individually. The embodiment illustrated in Figures 1 and 2 releases heat directly from the IC drivers 36 into the atmosphere because of the direct joint between the light shielding member 38 and the IC drivers 36 . This favorable effect is obtainable if the adhesive is electrically conductive, thereby maintaining the reliability of connection resistance throughout in the entire display device. As a result, the wiring electrodes 34 (i.e. terminal electrodes) can be made of relatively cheap material, thereby reducing the production cost of the display device. The light irradiated upon the top surfaces of the IC drivers 36 is interrupted by the light-shielding member 38 , thereby avoiding the occurrence of leaks which would otherwise occur because of the irradiated light. Thus, sampling pulses corresponding to an image signal supplied to the input terminal 21 are sure to be applied to the liquid crystal layer 33 , thereby displaying images without the interruptions of noise and error. Referring to Fig. 3, there is now described an embodiment in accordance with the present invention in which like reference numerals denote like elements and components to those in Figures 1 and 2, and their description will be omitted for simplicity: The display device of Fig. 3 differs from the one described above with reference to Figures 1 and 2, in that a light-shielding tape 39 is adhered to the bottom surface of the substrate 32 . More specifically, the tapes 39 are bonded to those areas which correspond to the IC drivers 36 . The tape 39 protects the IC drivers 36 against light passing through the substrate 32 which often happens when a high voltage source such as that used for projecting TV systems is used. In this way, this embodiment can reduce the possibility of leaks owing to the photo-electric effect. The tape 39 can be made of the same material for the light-shielding member 38 or may be made of a different material. It is also possible that the light-shielding member 38 and the tape 39 are connected to each other at one side of the substrate 32 . Figure 4 shows a further example in accordance with the invention characterized in that another substrate 41 is butt joined to the substrate 32 so as to constitute an integer, in that IC controllers 40 are disposed on the second substrate 41 , the IC controllers 41 having control circuits. The light-shielding member 38 extends from a part of the bottom surface of the substrate 32 through the whole bottom surface of the substrate 41 and the IC drivers 36 , and reaches a part of the top surface of the substrate 31 . In this way, the light-shielding member 38 covers the IC drivers 36 and the IC controllers 40 . When the light-shielding member 38 is made of an electrically conductive material, the member 38 shields electro-magnetism. This example has advantages in that it protects the IC drivers 36 against light passing through the substrate 32 , and also light irradiated from the backs of the IC drivers 36 . Fig. 5 shows a still further example in accordance with the present invention, which is also provided with the substrate 41 butt joined to the substrate 32 . The second substrate 41 carries the IC controllers 40 . This example is characterized in that the IC drivers 36 and the IC controllers 40 are encased in a shield case 44 of tin plate or stainless steel plate which comprises an upper half member 45 fitted in a lower half member 46 . The upper half member 45 is connected to the light-shielding member 38 by means of a spring 47 of electrically conductive metal so that the case 44 is electrically connected to the light-shielding member 38 . The spring 47 is also effective to press the light-shielding member 38 against the IC drivers 36 so as to place the light-shielding member 38 into close contact with the IC drivers 36 , thereby eliminating the necessity of using adhesive. The non-use of adhesive facilitates the replacement of any deficient IC driver 36 by a fresh one. In addition, the electrical connection of the spring 47 to the case 44 strengthens the protection of the IC drivers 36 and the IC controllers 40 against electro-magnetism. Figure 6 shows a modification to the example illustrated in Figure 5, from which this modified version is different in that the spring 47 is not used; more specifically, instead of using the spring 47 , the light-shielding member 38 is bonded to the top surfaces of the IC drivers 36 with its inner end portion attached to the inside surface of the case 44 . The IC driver 36 includes many heat-generating elements such as transistors, and as the operation continues, the generated heat builds up, thereby causing malfunction of the IC drivers. Advantageously, the light-shielding member 38 and the case 44 can dissipate heat generated by the IC driver 36 . The illustrated embodiments of Figures 3 to 6 are examples obtained which the present invention is applied to TFT liquid crystal display devices, but the present invention can be of course applied to duty-type liquid crystal display devices, electro-luminescence display devices and plasma display devices. The present invention is particularly adapted for display devices using driving elements requiring a large capacitance and large volumes of electric power. It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope of this invention as defined by the appended claims.

Claims: A display device comprising a substrate (32), a display means (33) disposed on the substrate (32), and a driving circuit (36) arranged along the periphery of the substrate (32), characterised in that the driving circuit (36) is covered with a light-shielding heat dissipation means (38) on the surface thereof remote from the substrate (32), the light-shielding heat dissipation means (38) comprising a single layer which covers said surface of the driving circuit (36) in its entirety (36), and in that a light-shielding member is attached to that bottom surface portion of the substrate that corresponds to the driver circuit (36). A display device comprising a smaller substrate (31) and a larger substrate (32), a display means (33) interposed between the two substrates, a driving circuit (36) arranged on the rim portions of the larger substrate, and a third substrate (41) butt jointed to the larger substrate (32), the third substrate (41) carrying a control circuit (40) thereon, characterised by a light-shielding heat dissipating means (38) extending from a bottom surface portion of the larger substrate (32) that corresponds to the driving circuit (36) to the smaller substrate (31) by way of the third substrate (41), the control circuit (40) and the driving circuit (36) so that the driving circuit and the control circuit are enclosed by the light-shielding heat dissipating means, wherein the driving circuit (36) is in contact with the light-shielding heat dissipating means (38). A display device comprising a smaller substrate (31) and a larger substrate (32), a display means (33) interposed between the two substrates, a driving circuit (36) arranged on the rim portions of the larger substrate (32), and a third substrate (41) butt joined to the larger substrate (32), the third substrate (41) carrying a control circuit (40) thereon, characterised by an electrically conductive, light shielding case (44) for enclosing a bottom surface portion of the larger substrate that corresponds to the driving circuit to the smaller substrate by way of the third substrate, the driving circuit being covered with a light-shielding heat dissipating means (38) disposed on the surface remote from the substrate (32) and electrically connected to the case. A display device as claimed in claim 3, in which the case (44) acts as a further heat dissipating means. A display device according to claim 3 or 4, wherein the case comprises two half portions (45,46), one of which is fitted in the other. A display device according to any of claims 3 to 5, wherein the electrical connection between the light-shielding heat dissipating means and the case is effected by means of a spring (47) of electrically conductive material. A display device according to any of claims 3 to 5, wherein the electrical connection between the light-shielding heat dissipating means and the case is effected by direct contact of a part of the heat dissipating means with the case. A display device according to any of claims 3 to 7, wherein the driving circuit comprises a sampling capacitor for applying a driving voltage to the display means, which includes a liquid crystal, and a hold capacitor. A display device comprising a smaller substrate (31) and a larger substrate (32), a display means (33) interposed between the two substrates (31,32), a driving circuit (36) arranged on the rim portions of the larger substrate (32), a third substrate (41) butt joined to the larger substrate (32), the third substrate (41) carrying a control circuit (40) thereon, the driving circuit (36) being covered by a light-shielding, heat dissipation means (38) on the surface remote from the substrate (32), and a light shielding case (44) made of metal which encloses a bottom surface portion of the larger substrate (32) that corresponds to the driving circuit (36) and extends to the smaller substrate (31) by way of the third substrate (41), the case (44) acting as a heat dissipation means and being electrically connected to the light-shielding, heat dissipation means (38).

Inventors: KAWAGUCHI HISAO, NAKABU SHIGEO, KAWAGUCHI, HISAO, NAKABU, SHIGEO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G02F1
IPC codes: G09F9, G02F1