JP2011027822A - Flexible display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a flexible display device of high reliability, which is prevented from cracking in a TFT layer even when being bent with a small curvature radius. <P>SOLUTION: A TFT layer 40 is formed on a glass substrate and is separated from the glass substrate and is transferred to a plastic substrate 10. Adhesion between the TFT layer 40 and the plastic substrate 10 has a two-layered structure of an adhesive layer 12 having glass fibers and an ordinary adhesive layer 11. The adhesive layer 12 having glass fibers is disposed on the side of the TFT layer 40 to relax bending stress and stress due to thermal expansion to the TFT layer 40, and thus the flexible display device of high reliability is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a display device, and more particularly to a display device that can be flexibly bent by using a plastic substrate.

  In order to increase the added value of small and medium-sized displays, flexible display devices that are lightweight, do not break even when dropped, and can be bent are being developed. One of the main problems is a technique for forming pixel driving TFTs (Thin Film Transistors) on a plastic substrate in an array. The plastic substrate has much lower heat resistance than the glass substrate, so it is impossible to apply the normal TFT fabrication process. For this reason, two types of solutions have been studied.

  One is a method of directly forming a TFT array on a plastic substrate by using a low temperature process. However, since the heat resistance temperature of the plastic substrate is low, it is impossible to form a polysilicon TFT. Therefore, this type of flexible display device has been studied with an oxide semiconductor TFT array such as amorphous silicon (a-Si) or ZnO.

The other is called a transfer method, in which a TFT layer is produced on a supporting substrate such as a glass substrate, the glass substrate is removed from the TFT layer by some method, and then bonded to a plastic substrate. Here, the TFT layer collectively represents everything from a base insulating film such as SiO ₂ to an island-shaped polysilicon, an interlayer insulating film, an electrode, an organic planarizing film, and an ITO electrode. This transfer method is disadvantageous in terms of cost because a transfer process is required in addition to the TFT layer fabrication. However, if a thermally stable support substrate is used, a flexible TFT substrate that is impossible by the direct method, such as a high-definition TFT array with a small pixel pitch or a polysilicon TFT array that requires a high temperature of 400 ° C. or higher, can be produced. There is a possibility. The process of the transfer method will be described as follows, taking as an example a method of removing the glass substrate by etching.

    (1) An etching stop layer and a TFT layer are sequentially formed on a glass substrate. The etching stop layer is made of a material that does not dissolve in the hydrofluoric acid glass etchant. For example, Mo, W, a-Si, diamond, diamond-like carbon, etc.

    (2) A protective film is bonded to the TFT layer side so that the TFT layer is not dissolved by the glass etching solution.

    (3) The glass is removed with a hydrofluoric acid-based etchant. At this point, a TFT layer having a thickness of several μm is attached to the protective film.

    (4) A plastic substrate is attached to the glass removal surface side of the TFT layer from which the glass has been removed. An adhesive or an adhesive is used for pasting.

    (5) The protective film is peeled off. As a protective film that can be easily peeled off, a type using an organic solvent-meltable adhesive, a type that can be peeled off by heating or ultraviolet irradiation, and the like can be used.

  The production of the flexible transfer TFT substrate is completed by removing the protective film in the step (5). When a liquid crystal panel is produced using this substrate, it undergoes steps of coating an alignment film, baking, alignment by rubbing or ultraviolet irradiation, bonding with a flexible, counter substrate having a color filter, liquid crystal injection, and sealing. A panel is made.

  Configurations for forming a flexible image device by a transfer method are described in “Patent Document 1,” “Patent Document 2,” “Patent Document 3,” and the like. On the other hand, “Patent Document 4” describes a configuration in which a heat-resistant resin is coated on a glass substrate and a thin film device is formed thereon.

JP-A-2005-85830 JP 2003-316281 A JP 2004-165679 A JP 2009-21322 A

  In the following, the problem in the case of the liquid crystal display device will be described as an example, but the same applies to the case of the organic EL display device.

  It is expected that the plastic substrate onto which the TFT array is transferred can be bent freely. However, when the film is actually bent with a curvature radius of 150 mm or less, there is a problem that the TFT layer is easily cracked.

Considering the cause of cracks from the material of the TFT layer and the structure of the transfer TFT substrate, the following explanation can be made. The structure of the transfer TFT substrate is roughly composed of three layers. When the bottom is a flexible plastic substrate, the second from the bottom is an adhesive, and the TFT layer is on top. Here, the TFT layer refers to all layers from the base insulating film above the glass to the ITO, specifically, the base insulating film made of SiO ₂ and SiN, island-like polysilicon, interlayer insulation. A film, an electrode, an organic flattening film, and ITO.

The entire TFT layer is as thin as about 2 μm, and it is brittle material such as SiO ₂ and SiN that easily breaks and occupies about 1 μm. That is, a soft and fluid adhesive material is placed on a soft plastic substrate having a thickness of 100 μm, and a thin and brittle TFT layer having a thickness of about 2 μm is floating on the adhesive material. That is, since the strength of the TFT layer itself is weak and the fixing is insufficient, when the TFT layer is bent outward, the TFT layer cannot withstand the tensile stress and cracks. Also, since the entire transfer TFT substrate is soft, unintended bending occurs due to weak force or impact, and stress concentrates on a part of the TFT layer, causing cracks in the TFT layer.

  The use of an adhesive instead of an adhesive as a material for bonding a plastic substrate and a TFT layer is also known as a transfer method. The adhesive is a hard material having a large elastic modulus. When it is used, it becomes strong against impact and pressure from the surface. However, since there is no stress relaxation function as in the case of the adhesive material, the TFT layer becomes weaker against bending and is not flexible, as in the case of using the adhesive material.

  In the following, problems of the known technique in the process of attaching the TFT layer to the plastic substrate in the transfer process described in the background art will be described. When considering bonding in the process of actually bonding the TFT layer to the plastic substrate, there are various options. For example, the main component is either inorganic or organic as the type of adhesive, and the curing method is either evaporation of the solvent, adhesion by heating, thermal curing, photocuring by irradiating UV light, or just pressing There are non-curing types such as pressure-sensitive adhesives that are bonded together, so-called adhesive materials.

  In particular, regarding the curing method, the sample may be damaged by heating or UV light irradiation, so it is considered that the process conditions are greatly affected. In addition, the hardness of the adhesive, that is, the elastic modulus and viscosity, is considered to affect the properties of the flexible substrate. As described above, there are many technical problems in bonding in the process of bonding the TFT layer to the plastic substrate.

  As an example of a publicly known example related to a process of attaching a TFT layer to a plastic substrate, there is “Patent Document 1”. The problem described in “Patent Document 1” is that in a transfer TFT substrate, there is a difference in coefficient of thermal expansion between the TFT layer and the plastic substrate. Content.

  As a solution to this problem, two layers of an adhesive material and an adhesive material are used in an overlapping manner in the process of attaching the TFT layer to the plastic substrate. The bonding on the TFT layer side uses an adhesive to reinforce the TFT layer. An adhesive material is used on the plastic substrate side to form a stress relaxation layer to solve the problem of thermal expansion.

  On the other hand, most of the other known examples do not regard the process of attaching the TFT layer to the plastic substrate as in “Patent Document 2” or “Patent Document 3” as a technical problem. In the bonding of the TFT layer and the plastic substrate described in the examples, what kind of adhesives are used such as reactive curing type, thermosetting type and ultraviolet curing type, and pressure sensitive adhesive called adhesive material, etc. In addition, the composition of the epoxy type, silicone type, and acrylic type is not particularly limited.

  The plastic substrate to which the TFT array is transferred is cracked in the TFT layer not only when the radius of curvature is bent with a curvature of 150 mm or less but also when the temperature rises. For example, in the liquid crystal panel manufacturing process, the alignment film is baked, and the temperature rise due to the backlight may be considered after the panel manufacturing. That is, the transfer TFT substrate has a problem that it is pulled or cracked by bending or temperature rise.

The cause of the crack can be explained below from the structure of the transfer TFT substrate and the material of the TFT layer. The structure of the transfer TFT substrate is roughly composed of three layers. When the bottom is a flexible plastic substrate, the second from the bottom is an adhesive or adhesive, and the TFT layer is on top. The cause of the crack is basically that the entire TFT layer is as thin as about 2 μm, and that it is about 1 μm with brittle materials such as SiO ₂ and SiN that are easily broken.

  However, in the case of using an adhesive material and an adhesive material, or in the case of a laminated structure of an adhesive material and an adhesive material as in "Patent Document 1," a phenomenon that is partially different in terms of stress generation and crack generation. become.

  FIG. 9 shows a transfer TFT substrate in which the TFT layer 40 and the plastic substrate 10 are bonded together with a UV curable adhesive 25. FIG. 10 shows the sample bent with the TFT layer 40 facing outward. A tensile stress acts on the outer TFT layer 40, and a positive strain is generated. In other words, it is growing. On the other hand, in the portion inside the plastic substrate 10, compressive stress works and negative strain is generated. A center line RC indicated by a dotted line is a portion where the strain is zero, a portion where the outside is extended by tensile stress, and a portion where the inside is contracted by compressive stress.

  The outermost TFT layer 40 is where the maximum tensile stress is applied. Since the adhesive material 25 is hard without viscoelasticity like an adhesive material, the distance between the TFT layer 40 and the center line is increased, and the elongation amount of the TFT layer 40 is also large. Therefore, when the transfer TFT substrate is bent, the TFT layer 40 is easily cracked because the critical value of the tensile stress of the TFT layer 40 is exceeded.

Next, consider the case where the temperature of the entire transfer TFT substrate rises. The thermal expansion coefficient of the TFT layer 40 is considered to be 5 ppm / ° C. or less even when estimated from its main components SiO ₂ , SiN, etc., but the thermal expansion coefficient of the adhesive 25 and the plastic substrate 10 is The thermal expansion coefficient is usually 10 times or more, and even a flexible substrate currently under development has several times the thermal expansion coefficient. Therefore, when the temperature of the entire transfer TFT substrate rises, the TFT layer 40 tries to suppress the expansion of the plastic substrate 10 and the adhesive 25, and thermal stress is generated.

  However, in the TFT layer 40 having a thickness of about several μm, the thermal expansion of the adhesive 25 and the plastic substrate 10 cannot be suppressed, so that the TFT layer 40 is easily cracked. That is, in the transfer TFT substrate using the adhesive material 25 of FIG. 9 or FIG. 10, tensile stress is generated in the TFT layer 40 even if it is bent or the temperature rises, but there is nothing that reinforces the TFT layer 40 or becomes a stress relaxation layer. For this reason, cracks are likely to occur.

  FIG. 11 shows a transfer TFT substrate using the adhesive material 11, and FIG. 12 shows the TFT layer 40 bent outward. The difference from the case of the adhesive 25 in FIG. 9 or FIG. 10 is that since the adhesive 11 has viscoelasticity, it becomes a stress relaxation layer, and the position of the center line RC cannot be specified depending on the bending speed. However, since the adhesive material 11 is easily stretched, the center line RC when bent at a certain radius of curvature is located more inside than the adhesive material 25 in FIG. 10 and the tensile stress generated in the TFT layer 40 is reduced. I can expect.

  However, since the TFT layer 40 is thin and has a low critical value, the TFT layer 40 is easily cracked in the same manner as in FIG. 9 or FIG. On the other hand, in the case of a temperature rise, generally, the rate of temperature change is often slow, and the viscosity of the adhesive material 11 is reduced, so that the effect as a stress relaxation layer is high. That is, in the transfer TFT substrate using the adhesive material 11 of FIG. 10 or FIG. 11, the adhesive material 11 becomes a stress relaxation layer, so that it is more resistant to temperature rise than the adhesive material 25.

  However, the effect on bending is small and cracks are likely to occur. Further, the structure is such that a soft and fluid adhesive material 11 is placed on a soft plastic substrate 10, and a thin and brittle TFT layer 40 having a film thickness of about several μm is floated thereon. . Therefore, there is a drawback that it becomes extremely weak when a local pressure is applied to the surface of the transfer TFT substrate or when an unintended bending occurs due to carrying.

  FIG. 13 shows a transfer TFT substrate disclosed in “Patent Document 1” in which an adhesive 25 and an adhesive 11 are stacked. In FIG. 14, the TFT layer 40 is bent outward. The adhesive material 11 in this case also functions as a stress relaxation layer to some extent, but a positive strain is generated in the outer adhesive material 25 and the TFT layer 40 and tensile stress is generated. However, if the adhesive 25 having a high elastic modulus is used, the TFT layer will be reinforced, and the effect of preventing cracking in the TFT layer will be obtained.

  Next, in the case of a temperature rise, the adhesive material 25, the adhesive material 11, and the plastic substrate 10 all have a thermal expansion coefficient that is 10 times or more that of the TFT layer 40 having a low thermal expansion coefficient. Therefore, when the temperature of the transfer TFT substrate rises, it is necessary to suppress the thermal expansion of the three layers of the adhesive material 26, the adhesive material 11 and the plastic substrate 10 with only the thin TFT layer 40. However, this is not possible except when the viscosity of the adhesive 11 is extremely small and has fluidity like a liquid, and the TFT layer 40 is cracked immediately.

  As described above, in any of the structures shown in FIGS. 9 to 14, cracks are easily generated in the TFT layer 40 due to bending or temperature rise, so that a crack preventing means is necessary. In order to prevent cracking of the TFT layer 40, it is naturally effective to make the TFT layer itself resistant to pulling. However, since the material constituting the TFT layer 40 is limited by characteristics, processes, etc., effective means cannot be taken immediately.

  Accordingly, an object of the present invention is to provide a highly reliable flexible display device in which the TFT layer 40 is hardly cracked by a novel structure in which the TFT layer 40 and the plastic substrate 10 are bonded without changing the constituent material of the TFT layer 40. Is to realize.

  The present invention solves the problems as described above, and specific means are as follows.

  (1) A display device having a TFT substrate in which an adhesive layer is formed on a plastic substrate and a TFT layer is formed on the adhesive layer, wherein the TFT layer includes a semiconductor layer, a gate insulating film, and a gate electrode Including an interlayer insulating film, a drain electrode, and a source electrode, and the adhesive layer is composed of an adhesive material layer and an adhesive material layer containing glass fiber, and the adhesive material layer exists on the plastic substrate side, and the glass fiber is The display device characterized in that the adhesive material layer is present on the TFT layer side.

  (2) The display device according to (1), wherein a refractive index of the glass fiber is the same as that of the adhesive material.

  (3) The display device according to (1), wherein the glass fibers are randomly present in a direction parallel to a main surface of the plastic substrate.

  (4) The display device according to (1), wherein the glass fiber exists in a mesh shape parallel to the main surface of the plastic substrate.

  (5) The display device according to (1), wherein the semiconductor in the TFT layer is made of poly-Si.

  (6) A display device having a TFT substrate in which an adhesive layer is formed on a plastic substrate, a plastic film is formed on the adhesive layer, and a TFT layer is formed on the plastic film, the TFT The layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode, and the adhesive layer includes an adhesive material layer and an adhesive material layer including a glass fiber, and the adhesive material layer includes The display device according to claim 1, wherein the pressure-sensitive adhesive layer including the glass fiber is present on the plastic substrate side.

  According to the present invention, since the transfer TFT layer and the plastic substrate are bonded with a plurality of layers of a normal adhesive layer and an adhesive layer containing glass fibers, the formed flexible display device is bent with a curvature radius of 150 mm or less. However, since the transfer TFT layer does not crack, a flexible display device resistant to bending can be realized.

  Moreover, since the stress due to thermal expansion on the TFT layer is suppressed by the adhesive layer containing glass fiber, the TFT layer can be prevented from cracking even with respect to temperature change, and a highly reliable flexible display device can be realized. .

It is sectional drawing of the TFT substrate using a transfer system. It is process drawing which forms the TFT substrate by a transfer system. 2 is a cross-sectional view of a TFT substrate according to Example 1. FIG. FIG. 3 is a cross-sectional view of a TFT substrate according to Example 1 curved. It is a schematic diagram of the adhesive material layer which disperse | distributed the glass fiber. It is a schematic diagram of the adhesive material layer which has the glass fiber formed in mesh shape. 6 is a cross-sectional view of a TFT substrate according to Example 2. FIG. It is sectional drawing of the TFT substrate in the state of the middle process of transcription | transfer. It is sectional drawing of the TFT substrate by a prior art example. It is sectional drawing which shows the state which curved FIG. It is sectional drawing of the TFT substrate by another prior art example. It is sectional drawing which shows the state which curved FIG. It is sectional drawing of the TFT substrate by another prior art example. It is sectional drawing which shows the state which curved FIG.

  Before explaining the specific configuration of the present invention, the background to the present invention will be described with reference to FIG. FIG. 8 shows the structure of the plastic substrate 10, the adhesive 11, the TFT layer 40, and the protective film 80 from the bottom before the protective film 80 is peeled off, that is, with the protective film attached to the transfer TFT 40. . This structure was strong against cracks. Here, the protective film 80 is attached at the beginning of the transfer process in order to protect the TFT layer 40 from the hydrofluoric acid-based etching solution.

  When the sample is bent with the protective film 40 on the outside, the adhesive 11 serves as a stress relaxation layer and serves to weaken the tensile stress. On the other hand, the protective film 80 served to reinforce the TFT layer 40 so as not to crack. That is, it is effective to have two layers, a stress relaxation layer for relaxing the tension of the TFT layer 40 and a reinforcing layer against tension. However, since an actual transfer TFT substrate is used with the protective film 80 removed, the same structure cannot be obtained.

  Furthermore, actually, it is necessary to take measures against the temperature rise of the transfer TFT substrate. Accordingly, by introducing two mechanisms of stress relaxation and reinforcement, a transfer TFT substrate that is resistant to bending and temperature rise can be manufactured. In the present invention, the adhesive layer 13 for bonding the plastic substrate 10 and the TFT layer 40 is formed by two layers of a normal adhesive material layer 11 and an adhesive material layer 12 in which glass fibers are dispersed. Thus, two effects of stress relaxation and reinforcement are obtained. The contents of the present invention will be described in detail below using examples.

  Hereinafter, a liquid crystal display device will be described as an example, but the present invention can also be applied to an organic EL display device. FIG. 1 is a cross-sectional view showing an example of a TFT substrate in a liquid crystal display device to which the present invention is applied. In FIG. 1, a TFT layer is disposed on a plastic substrate via an adhesive layer 13. The adhesive layer 13 is formed of an adhesive material layer 11 and an adhesive material layer 12 containing glass fiber. The glass fiber-containing adhesive material layer 12 is formed on the TFT layer 40 side, and the normal adhesive material 11 is formed on the plastic substrate side. The glass fiber-containing adhesive layer 12 has a role of stress relaxation and reinforcement for the TFT layer 40.

An etching stop layer 101 is formed on the glass fiber-containing adhesive layer 12, and a base insulating film 102 is formed on the etching stop layer 101. The base insulating film is often formed of two layers, a SiN layer and a SiO ₂ layer. A semiconductor layer 103 made of poly-Si is formed on the base insulating film 102. The semiconductor layer 103 forms a channel layer of the TFT below the gate electrode 105. The source region S and the drain region D are formed by performing ion implantation using the gate electrode 105 as a mask.

A gate insulating film 104 is formed on the semiconductor layer 103, and a gate electrode 105 is formed on the gate insulating film 104. An interlayer insulating film 106 is formed on the gate electrode 105, and a drain electrode 107 and a source electrode 108 are formed on the interlayer insulating film 106. In order to protect the TFT thus formed, an inorganic passivation film 109 made of SiO ₂ or SiN is formed.

  On the inorganic passivation film 109, an organic passivation film 110 that also serves as a planarization film is formed. Since the organic passivation film 110 also serves as a planarizing film, the organic passivation film 110 is formed as thick as about 2 microns. A pixel electrode 111 is formed of ITO on the organic passivation film 110, and an alignment film 112 is formed to cover the pixel electrode 111.

  A liquid crystal display device is completed by disposing a counter substrate on which a color filter or the like is formed facing the TFT substrate shown in FIG. 1 at a predetermined interval and enclosing liquid crystal between the TFT substrate and the counter substrate. .

  In the organic EL display device, a TFT substrate is completed by disposing a lower electrode, an organic EL light emitting layer, and an upper electrode instead of the pixel electrode 111 and the alignment film 112 in FIG. Thereafter, in order to protect the organic EL light emitting layer from moisture, the counter substrate is disposed to face the TFT substrate, and the inside is kept airtight to complete the organic EL display device. A TFT as shown in FIG. 1 is formed for each pixel. Therefore, the TFTs are formed in an array on the TFT substrate.

The TFT substrate manufacturing method by the transfer method is as shown in FIG. In FIG. 2A, an etching stop layer 101 and a TFT layer 40 are formed in order on a glass substrate 30. Here, the TFT layer 40 refers to the base insulating film 102 such as SiO ₂ , the island-shaped polysilicon 103, the interlayer insulating film 106, the gate electrode 105, the drain electrode 107, the source electrode 108, the inorganic passivation film 109, and the organic planarization. The film 110, the ITO electrode 111, and the like are all represented together.

  The etching stop layer 101 is provided so that the TFT layer 40 is not etched during glass etching in a later process, and a material that does not dissolve in a hydrofluoric acid glass etchant is used. For example, Mo, W, a-Si, diamond, diamond-like carbon, and the like can be used. However, in the case of an opaque material, it is necessary to selectively remove it with another etching solution after glass etching.

  As shown in FIG. 2B, in order to protect the TFT in preparation for glass etching, a protective film 80 on which a protective film adhesive 90 is formed is prepared and attached to the TFT layer 40. As the protective film adhesive 90, for example, a material that does not have adhesive strength in a low temperature environment and can be peeled off is used.

  As shown in FIG. 2C, after the TFT layer 40 is protected by the protective film 80, the glass 30 is removed with a glass etching solution. For example, a hydrofluoric acid-based etching solution is used as the etching solution for the glass 30. The TFT layer 40 is protected from the etching solution by the etching stop layer 101 and the protective film 80. In the state of FIG. 2C, the TFT layer 40 having a thickness of several μm is stuck to the protective film 80.

  Next, as shown in FIG. 2D, the plastic substrate 10 is attached to the TFT layer 40 on the etching stop layer 101 side, that is, on the side where the glass substrate is present, with the adhesive layer 13 interposed. The adhesive layer 13 is formed of two layers of adhesive material. A layer close to the TFT layer is an adhesive material layer 12 containing glass fiber, and a layer close to the plastic substrate is a normal adhesive material layer 11.

  Next, as shown in FIG. 2E, the protective film 80 is peeled off. In this embodiment, the protective film 80 is fixed with a material whose adhesive strength decreases at a low temperature, and therefore can be peeled off by cooling. In addition, as a protective film that can be easily peeled, a type using an organic solvent-meltable adhesive, a type that can be peeled off by heating or ultraviolet irradiation, or the like can be used.

  When the protective film 80 is peeled off, the TFT layer 40 including the organic passivation film 110 and the pixel electrode 111 is transferred to the plastic substrate 40. Thereafter, an alignment film 112 or the like is applied. The alignment film 112 is baked at about 180 ° C. and is aligned by rubbing or photo-alignment. Note that the alignment film 112 may be applied and baked after the step of FIG. 2A and before the step of FIG. This is because the alignment film 112 is baked at about 180 ° C., so that there is a risk that the TFT layer 40 may crack.

  FIG. 3 is a cross-sectional view of a typical transfer TFT substrate of the present invention, and FIG. 4 is bent with the TFT layer 40 facing outward. The adhesive layer 13 is used to bond the TFT layer 40 and the plastic substrate 10 together. The adhesive layer 13 is divided into two layers, an adhesive layer 12 in which glass fibers are dispersed and a normal adhesive layer 11. Since the glass fiber-containing adhesive material layer 12 is disposed on the TFT layer side and the adhesive material is fixed to the glass fiber, the in-plane elongation and thermal expansion are limited to the glass fiber. The glass fiber 15 is not mixed in the adhesive material 11 in contact with the plastic substrate.

  The pressure-sensitive adhesive is also called a pressure-sensitive adhesive, and refers to an adhesive having the characteristics of a highly viscous liquid or a gel-like solid that is used in an uncured state. It is desirable to use a silicone material that has high heat and cold resistance, supports a wide range of temperatures, and has high chemical resistance.

  The thickness of the TFT layer 40 in FIGS. 3 and 4 is 3 μm or less, and the plastic substrate is in the range of 50 μm to 200 μm. The thickness of the adhesive layer is 5 μm to 30 μm for each of the adhesive layer 12 containing glass fibers and the normal adhesive layer 11.

When producing a liquid crystal panel from the transfer TFT substrate of FIG. 3, the adhesive layers 11 and 12 and the plastic substrate 10 are materials that transmit visible light. When other image display elements do not require transmitted light, there is no problem even if they are colored. Although the plastic substrate 10 may have a SiO ₂ or SiN barrier film, it does not affect the effects of the present invention. The configuration of FIG. 3 is the same even when a metal substrate is used as the substrate 10 instead of a plastic substrate.

  The manufacturing method of the transfer TFT substrate of FIG. 3 is the same process as the technical contents described in FIG. That is, (1) formation of the TFT layer 40, (2) attachment of the protective film 80, (3) removal of the support substrate 30 (for example, glass etching), (4) attachment of the TFT layer 40 and the plastic substrate 10 ( 5) Peeling of the protective film 80. In the bonding of the plastic substrate of (4), it is a feature of the present invention that both the glass fiber-containing adhesive material layer 12 and the normal adhesive material layer 11 are used.

  The adhesive layer 13 is formed by laminating an adhesive material layer 12 with glass fiber and a normal adhesive material layer 11 without glass fiber. Alternatively, use an adhesive that is premixed with glass fiber biased on one side. Any method may be used.

  The effect of the typical transfer TFT substrate of FIG. 3 is that cracking of the TFT layer can be prevented when bent at a radius of curvature of 150 mm or less and when the temperature rises. In the part where the glass fiber of the adhesive material is mixed, the glass fiber and the adhesive material are integrated, so the strain and thermal expansion in the in-plane direction are limited by the glass fiber. Therefore, when the TFT layer 40 of the transfer TFT substrate is bent outward or when the substrate expands due to a temperature rise, the portion of the adhesive layer 12 containing glass fibers becomes a reinforcing material, and the TFT layer 40 Reduces stress due to thermal expansion.

  Further, the adhesive layer 11 without glass fiber on the plastic substrate 10 side also serves as a stress relaxation layer and serves to weaken the tensile stress. That is, the strength against bending of the TFT layer 40 is increased by two effects, and the strength against stress due to thermal expansion is increased. In the liquid crystal panel manufacturing process, local pressure may be applied to the surface of the TFT layer in processes such as color filter bonding and terminal connection. Even in such a case, since the glass fiber-containing adhesive material layer 12 reinforces the TFT layer 40, the strength does not become extremely insufficient as in the case where the adhesive material layer 11 is used alone.

  Since the glass fiber 15 functions to suppress pulling and thermal expansion in the in-plane direction of the transfer TFT substrate, the fiber needs to extend in the in-plane direction. FIG. 5 shows the shape of the glass fiber 15 in which fibers with a submicron diameter are kneaded randomly. The glass fibers 15 are arranged in the same direction as the main surface of the plastic substrate. Although the glass fiber 15 in FIG. 5 is short and not bent, it is more effective that a long bent fiber is entangled. The diameter of the glass fiber 15 is from submicron to several tens of μm, and the longer the length is 1 mm or more, the better. The glass fibers 15 may be bundled. Moreover, as shown in FIG. 6, it may be woven in a mesh shape. The glass fiber preferably has the same refractive index as that of the adhesive material in order to prevent light scattering.

  The glass of the glass fiber 15 is transparent to visible light and has a refractive index equal to that of the adhesive material. Therefore, a glass mainly composed of silicon oxide is optimal. However, if it is an application other than a liquid crystal display panel, it may be glassy with a large Young's modulus and a low thermal expansion coefficient, and carbon fiber, ceramic fiber, boron fiber, metal fiber, etc. used for fiber reinforced plastics are used. You can also

  While the basic structure of the present invention has been described above, changes in the structure are allowed within the scope of the present invention. For example, in the case of a soft adhesive material having a Young's modulus of 200 MPa or less, since it expands and contracts with a weak force, the same effect as an adhesive material can be expected. That is, in this case, the glass fiber is mixed into the soft adhesive.

  For example, when the substrate is soft such that the Young's modulus is 500 Mpa, glass fibers may be mixed in the entire adhesive material.

  FIG. 7 is a cross-sectional view showing a second embodiment of the present invention, which is an embodiment of a transfer TFT substrate having a form different from that of the first embodiment. A plastic coating layer 20 having a thickness of 30 μm or less is formed under the TFT layer 40, and the bonding with the plastic substrate 10 is an adhesive material mixed with glass fibers as in the typical transfer TFT substrate of FIG. It is formed of a layer 12 and a layer 11 made of only an adhesive material.

  As a method for manufacturing the transfer TFT substrate of FIG. 7, two transfer methods are conceivable. First, before producing the TFT layer on the supporting substrate, a thin plastic layer of several tens of μm is placed on the supporting substrate in advance, and then the TFT layer is produced, and the TFT layer and the plastic layer are simultaneously transferred to the plastic substrate. Is the method.

  For example, in “Patent Document 4”, in the transfer TFT substrate manufacturing process, a plastic coating layer having a thickness of 30 μm or less is formed before the TFT layer is formed, and the TFT layer is formed thereon. The support substrate is removed by a method of peeling the plastic coating layer from the support substrate by light irradiation.

  The purpose of the plastic coating layer in this first fabrication method is to easily remove the support substrate from the TFT layer. However, since the heat resistant temperature is low, the TFT layer 40 cannot be manufactured at a high temperature of 400 ° C. or higher. Therefore, the TFT of the transfer TFT substrate uses a material other than polysilicon, for example, amorphous silicon.

  In the structure of the transfer TFT substrate of FIG. 7, thermal stress is generated in the plastic coating layer 20 when the temperature rises. However, by using the glass fiber-containing adhesive layer 12, the TFT layer 40 and the glass fiber-containing adhesive material 12 are suppressed on both sides of the plastic coating layer 20, so that expansion can be suppressed.

  Another method for producing the transfer TFT substrate of FIG. 7 is a method of producing the plastic layer 20 on the TFT layer 40 after producing the TFT layer 40 on the support substrate and further removing the support substrate from the TFT layer 40. It is. That is, in the TFT substrate transfer process shown in FIG. 2, a plastic coating layer is prepared between the removal of the support substrate in FIG. 2C and the plastic substrate bonding in FIG.

  The purpose of the plastic coating layer of the second manufacturing method is to make the reinforcement of the TFT layer 40 stronger. Considering the tensile stress of the TFT layer 40 when bent, the plastic coating layer 20 is preferably made of a thin, hard material that does not stretch. For example, it is desirable that the thickness is 5 μm or less and the Young's modulus is at least 1 GPa.

  Thermal stress is generated in the plastic coating layer 20 of the second manufacturing method due to the temperature rise of the transfer TFT substrate. The effect of suppressing the expansion of the TFT layer 40 and the glass fiber-containing adhesive material on both sides is the same as in the case of the first manufacturing method.

  The plastic coating layer 20 of the second manufacturing method may be any type of plastic coating layer 20 as long as it has hardness to reinforce the TFT layer 40. For example, an adhesive that cures by heat or chemical reaction can be used. However, in consideration of damage caused by heating, the UV curable adhesive is the most functional and cost effective.

  There are two types of UV curable adhesives: an acrylic oligomer that cures by radical polymerization and an epoxy oligomer that cures by cationic polymerization. In addition to the base oligomer, a reactive diluent, a photopolymerization initiator, a sensitizer, and a filler are added and used. In general, epoxy systems are preferable for use in the present invention because they have less volume shrinkage during curing and higher heat resistance.

  A production method of the plastic coating layer 20 of the second production method will be described using a UV curable adhesive as an example. A liquid UV curable adhesive is applied to the TFT layer with protective film 40 from which the support substrate has been removed in the step of FIG. For coating, use a bar coater or spinner to make the film thickness uniform. Curing by UV light irradiation. Here, when it is difficult to proceed with the curing of the surface, there is a method of covering a peelable sheet even after the UV curable adhesive is cured. A glass fiber-containing adhesive material 12, a normal adhesive material 11, and a plastic substrate 10 are bonded together in order to the cured UV curable adhesive material. Alternatively, the adhesive layer 11 and the glass fiber-containing adhesive layer 12 may be bonded to the plastic substrate 10 in advance, and then bonded to the UV curable adhesive.

  DESCRIPTION OF SYMBOLS 10 ... Plastic substrate, 11 ... Adhesive material layer, 12 ... Adhesive material layer containing glass fiber, 13 ... Adhesive layer, 15 ... Glass fiber, 20 ... Plastic coating layer, 25 ... UV cured adhesive material layer, 12 ... Adhesion containing glass fiber Material layer, 30 ... Glass substrate, 40 ... TFT layer, 80 ... Protective film, 90 ... Adhesive material for protective film, 101 ... Etching stop layer, 102 ... Gate electrode, 103 ... Semiconductor layer, 104 ... Gate insulating film, 105 ... Base insulating film 106 ... Interlayer insulating film 107 ... Drain electrode 108 ... Source electrode 109 ... Inorganic passivation film 110 ... Organic passivation film 111 ... Pixel electrode 112 ... Alignment film D ... Drain region RC ... Bent Center line, S ... Source region.

Claims (10)

A display device having a TFT substrate in which an adhesive layer is formed on a plastic substrate, and a TFT layer is formed on the adhesive layer,
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer including glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer including glass fiber is present on the TFT layer side. A display device.   The display device according to claim 1, wherein a refractive index of the glass fiber is the same as that of the adhesive material.   The display device according to claim 1, wherein the glass fibers are randomly present in a direction parallel to a main surface of the plastic substrate.   The display device according to claim 1, wherein the glass fiber exists in a mesh shape in a direction parallel to a main surface of the plastic substrate.   The display device according to claim 1, wherein the semiconductor in the TFT layer is made of poly-Si. A display device having a TFT substrate in which an adhesive layer is formed on a plastic substrate, a plastic film is formed on the adhesive layer, and a TFT layer is formed on the plastic film,
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer containing glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer containing the glass fiber is present on the plastic film side. A display device. An adhesive layer is formed on a plastic substrate, a TFT substrate having a TFT layer formed on the adhesive layer is provided, and an opposing substrate is disposed opposite the TFT substrate, and the TFT substrate, the opposing substrate, A liquid crystal display device in which a liquid crystal is sandwiched between
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer including glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer including glass fiber is present on the TFT layer side. A liquid crystal display device. An adhesive layer is formed on a plastic substrate, a plastic film is formed on the adhesive layer, a TFT substrate having a TFT layer formed on the plastic film, and a counter substrate facing the TFT substrate Is a liquid crystal display device in which liquid crystal is sandwiched between the TFT substrate and the counter substrate,
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer containing glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer containing the glass fiber is present on the plastic film side. A liquid crystal display device. An organic EL display device having a TFT substrate in which an adhesive layer is formed on a plastic substrate, a TFT layer is formed on the adhesive layer, and an organic EL light emitting layer is formed on the TFT layer,
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer including glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer including glass fiber is present on the TFT layer side. An organic EL display device. A TFT in which an adhesive layer is formed on a plastic substrate, a plastic film is formed on the adhesive layer, a TFT layer is formed on the plastic film, and an organic EL light emitting layer is formed on the TFT layer An organic EL display device having a substrate,
The TFT layer includes a semiconductor layer, a gate insulating film, a gate electrode, an interlayer insulating film, a drain electrode, and a source electrode,
The adhesive layer is composed of an adhesive material layer and an adhesive material layer containing glass fiber, the adhesive material layer is present on the plastic substrate side, and the adhesive material layer containing the glass fiber is present on the plastic film side. An organic EL display device.

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