JP2011199192A - Thin-film transistor substrate, and display device and electromagnetic sensor with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film transistor substrate configured such that a thin-film transistor formed on a resin film is unlikely to crack, and to provide a display device and electromagnetic sensor with the same.SOLUTION: The thin-film transistor substrate 100 includes the resin film 10, a buffer layer 16 provided on the resin film and having a multilayer structure in which at least three layers, i.e., layers 12A and 12B with a compressive stress and a layer 14 with a tensile stress, are laminated alternately and a top layer and a bottom layer are layers with the compressive stress, and the thin film transistor 21 provided on the buffer layer.

Description

  The present invention relates to a thin film transistor substrate, a display device including the same, and an electromagnetic wave sensor.

In the manufacture of display devices such as liquid crystal displays and organic electroluminescence (organic EL) displays, glass substrates are mainly used as substrates for forming thin transistors (TFTs), but they meet the demands for weight reduction and thickness reduction. Therefore, the development of products in which the thickness of the glass substrate is reduced is in progress. For example, a technique for reducing the thickness of a substrate by etching a glass substrate with hydrofluoric acid has been disclosed (see Patent Document 1).
However, there is a limit to reducing the thickness of a glass substrate, and there is a movement to use a resin film as a substrate in order to realize further reduction in weight and thickness. By using a resin film, it is possible not only to reduce the weight and thickness, but also to make the product flexible and resistant to impacts, and to reduce the weight of the outer case at the same time. There are also advantages.

On the other hand, when a resin film is used, various problems that cannot occur in a glass substrate occur. This is because the resin film has the following physical properties different from glass.
(1) The coefficient of thermal expansion is larger than that of glass.
(2) Irreversible heat shrinkage occurs.
(3) The film expands and contracts due to water absorption, moisture absorption, and drying.
(4) The heat resistant temperature is low.
(5) Unevenness on the surface is large.

  Various methods have been proposed to solve the problems caused by these physical properties. For example, with respect to the above (1) and (2), element designs and manufacturing processes in which the expansion and contraction of the film are considered in advance have been proposed (see, for example, Patent Documents 2 to 4). Further, regarding (5), it has been proposed that a resin layer is formed by applying a resin to the surface of a resin film, and that a TFT is formed on the resin layer (see Patent Document 5).

  In addition, cracks are likely to occur in the electrodes and semiconductor layers constituting the TFTs produced on the resin film due to the above (1) and (2). In order to prevent the occurrence of such cracks, it has been proposed to form an inorganic film having a compressive stress on a resin film (see Patent Document 6).

Japanese Patent No. 3974749 JP 2002-151522 A Japanese Patent No. 4280736 JP 2006-165555 A Japanese Patent No. 2900229 JP 2008-147207 A

  An object of the present invention is to provide a thin film transistor substrate in which cracks are unlikely to occur in a thin film transistor formed on a resin film, a display device including the same, and an electromagnetic wave sensor.

In order to achieve the above object, the present invention provides the following thin film transistor substrate, a display device and an electromagnetic wave sensor including the same.
<1> Provided on the resin film and the resin film, the compressive stress layer and the tensile stress layer are alternately laminated at least three layers, and the lowermost layer and the uppermost layer are the compressive stress layer. A thin film transistor substrate comprising: a buffer layer having a stacked structure of: and a thin film transistor provided on the buffer layer.
<2> The thin film transistor substrate according to <1>, wherein all layers constituting the buffer layer are made of an inorganic material.
<3> The layer constituting the buffer layer is made of at least one material selected from the group consisting of SixOy, SixNy, SixOyNz, AlxOy, TixOy, ZrxOy, and HfxOy. <1> or <2> The thin film transistor substrate according to 1.
<4> The thin film transistor substrate according to any one of <1> to <3>, wherein all layers constituting the buffer layer are made of the same kind of material.
<5> The thin film transistor substrate according to any one of <1> to <4>, wherein the resin film has a Young's modulus of 4 GPa or less.
<6> A display device comprising the thin film transistor substrate according to any one of <1> to <5>.
<7> An electromagnetic wave sensor comprising the thin film transistor substrate according to any one of <1> to <5>.

  ADVANTAGE OF THE INVENTION According to this invention, a thin-film transistor substrate with which a crack is hard to generate | occur | produce in the thin-film transistor formed on the resin film, a display apparatus provided with the same, and an electromagnetic wave sensor are provided.

It is the schematic which shows an example of a structure of the thin-film transistor substrate which concerns on 1st Embodiment. It is the schematic which shows an example of a structure of the thin-film transistor substrate which concerns on 2nd Embodiment. It is a figure which shows the relationship between the thickness of each layer which comprises a buffer layer, and stress intensity | strength. It is the schematic which shows an example of a structure of the organic electroluminescent display using the thin-film transistor substrate which concerns on 1st Embodiment. It is the schematic which shows an example of a structure of the X-ray flat panel detector using the thin-film transistor substrate which concerns on 1st Embodiment.

  Hereinafter, an organic EL display and an X-ray detector will be described as a thin film transistor substrate according to the present invention, a display device including the same, and an electromagnetic wave sensor, respectively, with reference to the accompanying drawings. Note that the display device and the electromagnetic wave sensor including the thin film transistor substrate according to the present invention are not limited thereto, and can be applied to other electronic devices including TFTs. In addition, the materials, thicknesses, film formation methods, and the like of each component are described as appropriate, but the present invention is not limited to these, and may be appropriately selected according to the configuration of the target electronic device.

  In many cases, tensile stress is inherent in the electrode layer and the semiconductor layer constituting the TFT. In general, a substance is strong against compressive stress but weak against tensile stress and easily breaks. Therefore, when forming TFT on a resin film, the resin film used as a board | substrate needs high rigidity which can endure expansion-contraction, and it is possible to provide the buffer layer by an inorganic layer as the means.

However, according to the experiments of the present inventor, even if a compressive stress inorganic layer (for example, SiO _{2 having a} thickness of 200 nm) is formed on the surface of the resin film and a TFT is formed on this inorganic layer, the structure of the TFT It was confirmed that cracks would occur in the electrode layer or the like depending on (material and layer configuration). For example, when a material having a strong tensile stress such as molybdenum is used as the electrode material, cracks are likely to occur after film formation or in the process of temperature increase or decrease during the manufacturing process. If a crack occurs in the electrode layer or semiconductor layer constituting the TFT, it greatly affects the electrical characteristics such as deterioration of transistor performance and disconnection.
For example, if the compressive-stress inorganic layer is formed as thick as about 5 μm, the generation of cracks in the TFT can be more reliably suppressed. However, when such an extremely thick inorganic layer is formed, the film formation time becomes long, the manufacturing cost increases remarkably, and the original flexibility (flexibility) of the resin film is impaired.

  Furthermore, when the present inventor repeated research, the following knowledge was obtained. The reason why cracks occur in the electrode layer, the semiconductor layer, and the like in which tensile stress is inherent is considered to be mainly due to the fact that the resin film is not expanded but is softer than a glass substrate or the like. Specifically, it is considered that a crack occurs as a result of the resin film as the substrate being easily deformed where the electrode layer or the semiconductor layer is shrinking due to the inherent tensile stress. In other words, the expansion of the resin film has a small effect on the occurrence of cracks, and the resin film has a lower Young's modulus than glass and silicon and is more likely to be deformed. It is thought to be the main cause.

  As a result of repeated research to suppress the occurrence of cracks in the TFT formed on the resin film, the present inventor provided a buffer layer having a specific laminated structure having strength and rigidity on the resin film. It has been found that if a TFT is formed on a buffer layer, it is possible to effectively suppress the generation of cracks in the electrode layer and semiconductor layer constituting the TFT.

<Thin film transistor substrate>
The thin film transistor substrate according to the present invention is provided on a resin film and the resin film, and at least three layers of compressive stress layers and tensile stress layers are alternately laminated. A buffer layer having a stacked structure which is a compressive stress layer; and a thin film transistor provided on the buffer layer. If it is a buffer layer which has the above laminated structures, it can give rigidity even if it does not make it 5 micrometers or more thick film. When the thickness of the resin film used as a board | substrate is thin or it is comprised with soft resin, a film becomes easier to deform | transform. Therefore, for example, the influence of the tensile stress of the semiconductor layer becomes stronger and cracks are likely to occur, but even in such a case, the occurrence of cracks in the TFT is effectively suppressed by having a high rigidity of the buffer layer. Can do.

  FIG. 1 is a schematic view showing an example of the configuration of the thin film transistor substrate according to the first embodiment. The thin film transistor substrate 100 according to the present embodiment is provided with a buffer layer 16 having a three-layer structure in which compressive stress layers 12A and 12B and tensile stress layers 14 are alternately formed on a resin film 10, and the buffer layer A thin film transistor 21 is provided on 16.

(Resin film)
The resin film 10 is not particularly limited as long as it can form the buffer layer 16 and the TFT 21 and can support other members constituting the electronic device. Examples of the material constituting the resin film 10 include polyesters such as polyethylene terephthalate (PET), polybutylene phthalate, and polyethylene naphthalate (PEN), polystyrene, polycarbonate, polyethersulfone, polyarylate, aramid, polyamide, acrylic, Examples include organic materials such as polyimide, polycycloolefin, norbornene resin, and poly (chlorotrifluoroethylene).

  As the resin film 10 is softer, the TFT 21 is more likely to be cracked. However, since the buffer layer 16 according to the present invention is thin and can impart relatively high rigidity to the resin film 10, if the Young's modulus of the resin film 10 is small. The smaller the value is, the more effective the effect of the present invention is. The Young's modulus of a typical resin film is as follows.

PET 5GPa
PEN 6GPa
Aramid 10GPa
Polyamide 10GPa
Polyimide 2-3GPa
Polyester 6GPa
Polyethersulfone 2-3GPa
Acrylic 0.5-2GPa
Polycarbonate 2GPa
Polyarylate 3-4GPa

  When a relatively soft resin film such as polyimide, polyethersulfone, acrylic, polycarbonate, or polyarylate is used, cracks are generated in the TFT 21 compared to a case where a relatively hard substrate such as PET or PEN is used. However, providing the buffer layer 16 between the resin film 10 and the TFT 21 provides rigidity and makes it difficult for the substrate to be bent or deformed. Therefore, the occurrence of cracks in the TFT 21 can be effectively suppressed. . When the resin film has a small Young's modulus and is soft, particularly when a resin film having a Young's modulus of 4 GPa or less is used, the effect of the present invention is more effectively exhibited.

  The thickness of the resin film 10 has strength as a support, and effectively suppresses the film 10 from being greatly deformed or broken after the process of manufacturing the TFT 21 or the like on the film 10 or the electronic device is manufactured. On the other hand, it is preferable to set the thickness to maintain flexibility and light transmission. From such a viewpoint, the thickness of the resin film 10 is preferably 3 μm or more and 500 μm or less, and more preferably 10 μm or more and 50 μm or less.

(Buffer layer)
The buffer layer 16 has a stacked structure in which compressive stress layers 12A and 12B and tensile stress layers 14 are alternately stacked, and the lowermost layer 12A and the uppermost layer 12B are compressive stress layers. That is, the buffer layer 16 having a laminated structure in which a tensile stress layer (abbreviated as “tensile stress layer” as appropriate) is sandwiched between compressive stress layers (abbreviated as “compressive stress layer” as appropriate) is a resin film. By providing on the buffer layer 16, the rigidity can be improved. By forming the TFT 21 on the buffer layer 16, the generation of cracks in the electrode layer, the semiconductor layer, etc. can be effectively suppressed.

-Compressive stress layer-
The compressive stress layers 12 </ b> A and 12 </ b> B constituting the buffer layer 16 are layers in which a force that the formed layer tends to extend in the surface direction is inherent. The material constituting the compressive stress layers 12A and 12B may be an organic material or an inorganic material. However, the organic material is preferably an inorganic film from the viewpoint that it generally has a small Young's modulus and is easily deformed, so that it is difficult to contribute to improvement in rigidity. .
Specific examples of the material constituting the compressive stress layers 12A and 12B include SixOy, SixNy, SixOyNz, AlxOy, TixOy, ZrxOy, HfxOy, and the like, and can be formed by a sputtering method, a CVD method, or the like.
The total thickness of the compressive stress layers 12A and 12B depends on the material, the number of layers constituting the buffer layer 16, the thickness of the tensile stress layer 14, and the like. From the viewpoint of ensuring the rigidity of the entire buffer layer, 250 nm or more. It is preferably 5 μm or less.

-Layer of tensile stress-
The tensile stress layer 14 constituting the buffer layer 16 is a layer in which a force that causes the formed layer to shrink in the plane direction is inherent. The material constituting the tensile stress layer 14 may be either an organic material or an inorganic material. However, since the organic material generally has a small Young's modulus and is easily deformed, it is preferably an inorganic film from the viewpoint of hardly contributing to improvement in rigidity. Specific examples of the material constituting the tensile stress layer 14 include SixOy, SixNy, SixOyNz, AlxOy, TixOy, ZrxOy, and HfxOy, and can be formed by sputtering, CVD, or the like.
The total thickness of the tensile stress layer 14 depends on the material, the number of layers constituting the buffer layer 16, the thickness of the compressive stress layers 12A and 12B, and the like, but from the viewpoint of ensuring the rigidity of the entire buffer layer, 250 nm or more. It is preferably 5 μm or less.

The total thickness of the buffer layer including the compressive stress layer and the tensile stress layer depends on the material, the number of layers constituting the buffer layer 16, and the stress and thickness of each layer, but from the viewpoint of ensuring the rigidity of the entire buffer layer, 500 nm The thickness is preferably 5 μm or less.
It is preferable that all layers constituting the buffer layer 16 are made of the same kind of material. Here, the same kind of material means that the elements of the material constituting each of the layers 12A, 14 and 12B are the same. For example, when the compressive stress layers 12A and 12B and the tensile stress layer 14 are each composed of SixNy, the compressive stress layers 12A and 12B and the tensile stress layer 14 have different x and y (composition ratios are different). included.
When all the layers constituting the buffer layer 16 are made of the same kind of material and each layer is formed by sputtering, all the films can be formed by using only one target. When forming a film by sputtering using one target, the compressive stress layers 12A and 12B and the tensile stress layer 14 can be formed by adjusting the film forming conditions. Specifically, assuming that the film is formed by sputtering, a dense film is formed by increasing the voltage applied to the target to a highly excited state, increasing the degree of vacuum, raising the substrate temperature, etc. As a result, the compressive stress layers 12A and 12B can be formed.
On the other hand, a porous film quality can be obtained by lowering the voltage applied to the target, lowering the degree of vacuum, lowering the substrate temperature, and the like. As a result, the tensile stress layer 14 can be formed.

  Note that the stress of each layer constituting the buffer layer 16 can be quantified by deflection measurement using an optical technique. For example, assuming that a film is formed on a flat substrate (for example, silicon), the substrate is warped when an internal stress is inherent in the formed material. If this curvature can be accurately measured using a laser to obtain the radius of curvature, the internal stress σ can be obtained from the Stoney equation as follows.

ここで、E_s：基板のヤング率、v_s：基板のポアソン比、t_s：基板の厚さ、t_F：薄膜の厚さ、R：基板の反りの曲率半径、を示す。

Here, E _{s is} the Young's modulus of the substrate, v _{s is} the Poisson's ratio of the substrate, t _{s is} the thickness of the substrate, t _{F is} the thickness of the thin film, and R is the curvature radius of the warp of the substrate.

  If each layer constituting the buffer layer 16 is formed of the same kind of material, the apparatus cost can be reduced and the film formation time can be shortened compared to the case where the compressive stress layers 12A and 12B and the tensile stress layer 14 are formed of different materials. Can do. For example, liquid crystal displays have recently become larger and the substrate size has also increased. Then, as the size of the substrate increases, the manufacturing apparatus also increases in size, and the capital investment increases. If the buffer layer 16 can be formed with one apparatus, the equipment cost can be reduced.

The buffer layer 16 is composed of three or more layers. However, if the number of layers is too large, it may take time to form the buffer layer 16 and the productivity may decrease. In addition, if the thickness of the entire buffer layer is too large, it takes time to form the buffer layer 16, and the rigidity becomes too high, so that the flexibility inherent in the resin film 10 is reduced, and the flexible electronic device There is also a possibility that it may become unsuitable when producing the product. From such a viewpoint, the total number of layers constituting the buffer layer 16 is preferably about 3 to 9 layers.
For example, when the buffer layer 16 has a five-layer structure, from the resin film side, a compressive stress layer (lowermost layer), a tensile stress layer, a compressive stress layer, a tensile stress layer, and a compressive stress The structure may be a layered structure in the order of the sex layers (uppermost layer).

(Thin film transistor)
The thin film transistor 21 includes a gate electrode 18, a gate insulating layer 20, an active layer 26, and source / drain electrodes 22 and 24, and is provided on the buffer layer 16. In the present embodiment, the bottom gate type TFT 21 is provided, but the form of the TFT is not particularly limited. Hereinafter, the material, thickness, forming method, and the like of the members constituting the TFT will be specifically described, but the present invention is not limited to these.

-Gate electrode-
A molybdenum (Mo) film having a thickness of 0.05 μm is formed on the buffer layer 16 by sputtering, for example, and then patterned by photolithography and etching to form the gate electrode 18.
The material of the gate electrode 18 is not limited to Mo, and other known conductive materials can be used. For example, metals such as Al, Cr, Ta, Ti, Au, Ag, alloys such as Al-Nd, APC, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Examples thereof include metal conductive films, organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, or mixtures thereof.

The film formation method and patterning method of the gate electrode 18 may be appropriately selected according to the material to be used. As the film formation method, in addition to the sputtering method, for example, a vacuum deposition method, an ion plating method, etc. Examples include physical methods, chemical methods such as CVD and plasma CVD methods, and wet methods such as printing methods and coating methods.
As a patterning method, patterning may be performed by a lift-off method, or a metal mask (shadow mask) having an opening corresponding to the pattern of the gate electrode 18 to be formed may be used.

-Gate insulation layer-
After the gate electrode 18 is formed, a SiO ₂ layer (thickness: 0.2 μm) as the gate insulating layer 20, an InGaZnO ₄ layer (thickness: 0.05 μm) as the active layer 26, and a protective layer (not shown) that protects the active layer 26 ) Ga ₂ O ₃ layers (thickness: 0.1 μm) are sequentially formed. Similar to the formation of the gate electrode, these layers are sequentially formed by sputtering or the like, and patterned according to the shape of each layer.
In addition, what is necessary is just to select the material of each layer suitably. For example, the gate insulating layer 20 is composed of an insulator such as SiN _x , SiON, Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , HfO _{2, and the} like as an insulating layer containing two or more of these compounds. Also good. Alternatively, a polymer insulator such as polyimide may be used.

-Active layer-
The active layer 26 is preferably an amorphous oxide semiconductor that can be formed at a low temperature. Specifically, an oxide containing at least one of In, Ga, and Zn, for example, an oxide containing In, and In and Zn are used. And an oxide containing In, Ga, and Zn. The composition structure is preferably InGaO ₃ (ZnO) _m (m is a natural number of less than 6). These are n-type semiconductors whose carriers are electrons. Note that a p-type oxide semiconductor such as ZnO.Rh ₂ O ₃ , CuGaO ₂ , or SrCu ₂ O ₂ may be used for the active layer, or an oxide semiconductor disclosed in Japanese Patent Application Laid-Open No. 2006-165529. It may be used.

-Source / drain electrodes-
For example, after patterning the active layer by photolithography and etching, AlNd (thickness: 0.1 μm) to be the source / drain electrodes 22, 24 is formed by sputtering and patterned on the source / drain electrodes 22, 24. To do. It should be noted that the source / drain electrodes 22 and 24 can be appropriately formed from the materials exemplified in the formation of the gate electrode 18, the film forming method, the patterning method, and the like.

  As a result, the bottom contact type TFT 21 having the active layer 26 formed before the source / drain electrodes 22 and 24 is formed on the buffer layer 16. Note that the structure of the TFT is not limited to the above structure, and may be selected as appropriate. For example, a bottom contact type TFT in which an active layer 26 is formed after the source / drain electrodes 22, 24 may be used, or a top gate type TFT in which the source / drain electrodes 22, 24 are formed before the gate electrode 18 may be used. .

FIG. 2 schematically shows a thin film transistor substrate according to the second embodiment. Since the TFT 21 is the same as that of the first embodiment, the description thereof is omitted.
The thin film transistor substrate 200 according to the present embodiment has a laminated structure in which the buffer layer 17 includes five layers, and the compressive stress layers 12A, 12B, and 12C and the tensile stress layers 14A and 14B are alternately stacked in this order from the resin film side. is doing. Since the compressibility and the tensile property can be controlled by changing the film forming conditions, all the layers 12A, 14A, 12B, 14B, and 12C constituting the buffer layer 17 can be formed of, for example, SiN.

  FIG. 3 shows the relationship between the thickness of each layer constituting the buffer layer 17 and the stress intensity (internal stress). By designing so as to cancel each other's stress based on the magnitude and thickness of each of compressive stress and tensile stress, the stress in the entire buffer layer can be made substantially zero (stress free). Moreover, the effect of further improving the rigidity of the buffer layer 17 is obtained by designing the compressive stress layers 12A, 12B, 12C and the tensile stress layers 14A, 14B constituting the buffer layer 17 to cancel each other's stresses. It is done. Thereby, generation | occurrence | production of the crack to TFT21 formed on the buffer layer 17 can be suppressed further.

<Organic EL display>
FIG. 4 schematically shows a configuration of an organic EL display 300 using the thin film transistor substrate according to the first embodiment. A flattening layer 28 and a through hole (not shown) exposing a part of the source electrode 22 are formed on the flattening layer 28 on the TFT 21, and then connected to a part of the source electrode 22 through the through hole. Alternatively, a pixel electrode 30 to be a cathode is formed, an organic EL layer 32 (for example, a hole injection layer, a light emitting layer, an electron transport layer) and an upper electrode 34 are formed thereon, and finally a sealing film 36 is pasted. It has a configuration. Hereinafter, a method for forming an organic EL element using the thin film transistor substrate according to the first embodiment will be described.

-Flattening layer-
After the source / drain electrodes 22 and 24 are formed, a flattening layer (interlayer insulating layer) 28 is formed on the entire surface of the substrate on which the TFT 21 is formed and flattened. For example, the planarization layer 28 (thickness: 1.5 μm) is formed by spin coating using an acrylic resin.

-Pixel electrode-
Next, a through hole (not shown) that exposes a part of the source electrode 22 is formed in the planarization layer 28, and then connected to a part of the source electrode 22 through the through hole to be a pixel electrode 30 serving as an anode or a cathode. Form. As the pixel electrode 30, for example, a conductive film such as Al, Mo, IZO, or ITO is formed by sputtering, and then patterned by photolithography and etching. Further, the pixel electrode 30 may be formed using a metal mask corresponding to the pattern of the pixel electrode 30 to be formed.

-Organic EL layer-
After the pixel electrode 30 is formed, the organic EL layer 32 is formed. The organic EL layer 32 is a layer including at least a light emitting layer, and a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, a block layer, and the like are formed as necessary. As the configuration of the organic EL element including the anode and the cathode, for example, the following layer configuration can be adopted, but is not limited to these layer configurations and may be appropriately determined according to the purpose and the like.

Anode / light-emitting layer / cathode Anode / hole transport layer / light-emitting layer / electron transport layer / cathode Anode / hole transport layer / light-emitting layer / block layer / electron transport layer / cathode Anode / hole transport layer / Light emitting layer / block layer / electron transport layer / electron injection layer / cathode ・ Anode / hole injection layer / hole transport layer / light emission layer / block layer / electron transport layer / cathode ・ Anode / hole injection layer / hole transport Layer / light-emitting layer / block layer / electron transport layer / electron injection layer / cathode • anode / hole transport layer / block layer / light-emitting layer / electron transport layer / cathode • anode / hole transport layer / block layer / light-emitting layer / Electron transport layer / electron injection layer / cathode ・ Anode / hole injection layer / hole transport layer / block layer / light emitting layer / electron transport layer / cathode ・ Anode / hole injection layer / hole transport layer / block layer / light emission Layer / electron transport layer / electron injection layer / cathode

  For example, when manufacturing an organic EL display for full color display, organic light emitting materials corresponding to red, blue, and green are used, and each color pixel is arranged by regular deposition using a metal mask. A light emitting layer is formed by film formation.

-Common electrode-
Following the formation of the organic EL layer 32, ITO is formed on the entire surface as an electrode on the light extraction side to form a common electrode 34 having optical transparency. The light extraction side electrode 34 does not need to be divided for each pixel, and may be formed on the entire surface of the organic EL layer 32 by a sputtering method to form the common electrode 34.

After forming the common electrode 34, a transparent sealing film 36 having a barrier property is attached via an adhesive or the like for sealing. Examples of the material constituting the sealing film 36 include polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, polycycloolefin, norbornene resin, and poly (chlorotrifluoro). And organic materials such as ethylene).
Examples of the barrier layer for preventing permeation of moisture and oxygen include inorganic substances such as silicon nitride, silicon oxide, silicon oxynitride, and aluminum oxide.

<X-ray flat panel detector>
FIG. 5 is a schematic view showing an example of the configuration of an X-ray flat panel detector 400 (referred to as “FPD” as appropriate) using the thin film transistor substrate according to the first embodiment.
In this embodiment, the buffer layer 16 and the TFT 21 are formed on the PET film 10. On the TFT 21, a planarizing layer 28 and a through hole (not shown) for exposing a part of the source electrode 22 are formed in the planarizing layer 28, and then connected to a part of the source electrode 22 through the through hole. A pixel electrode 40 to be an anode or a cathode is formed, a photodetector layer 42 made of silicon or an organic material, and an ITO transparent electrode 44 are formed thereon, a scintillator film 46 is pasted through an adhesive, and finally, sealing is performed. The film 48 is attached.

In the case of manufacturing the FPD 400 having such a configuration, after forming the buffer layer 16 on the PET film 10 as in the first embodiment, the gate electrode (Mo) 18, the gate insulating layer (SiO ₂ ) 20, the active layer ( An InGaZnO ₄ ) 26, a protective layer (Ga ₂ O ₃ ), and source / drain electrodes (AlNd) 22 and 24 are formed in this order to manufacture the TFT 21.

Next, a SiO ₂ insulating layer 38 is formed on the entire surface by sputtering. Further, after a through hole (not shown) for taking out the source electrode 22 is formed in the SiO ₂ insulating layer 38 by photolithography and etching, the Ti / Au electrode 40, mainly a charge transport material layer and a charge generation material layer. An organic photoreceptor layer 42 and an ITO transparent electrode 44 are formed and patterned.
Next, a sheet-like scintillator 46 is attached via an adhesive or the like, and a sealing film 48 is further attached. The material constituting the scintillator 46 is not limited to Gd ₂ O ₂ S, and CaWO ₄ , CsI, and the like can be selected.
Thereby, the X-ray flat panel detector 400 is obtained.

  Also in this embodiment, since the TFT 21 is formed on the buffer layer 16, the occurrence of cracks in the gate electrode 18 and the like is effectively suppressed. Moreover, since the thickness of the buffer layer 16 can be suppressed and rigidity can be imparted, the X-ray flat panel detector 400 having the inherent flexibility of the resin film and having high reliability can be manufactured with high productivity. .

In the FPD according to the present embodiment, an example in which an organic material is used as a photodetector has been described. However, the present invention is not limited to this. For example, a commonly used detector using Si may be employed.
The FPD according to this embodiment is (a) lightweight, (b) not easily broken because of its high flexibility (strong against bending and impact), and (c) high compared to those using a glass plate as a support. It has advantages such as sensitivity (reduction of X-ray absorption loss by using a resin film). In particular, the higher sensitivity of (c) ultimately reduces the X-ray dose irradiated to the patient, which is an important effect of reducing invasiveness.

  Hereinafter, examples will be described, but the present invention is not limited thereto.

<Example 1>
A thin film transistor substrate having the configuration shown in FIG. 1 was manufactured.
Polyimide (thickness: 25 μm) was used as a resin film to be a support, and the following buffer layer and TFT were sequentially formed on this film.

-Buffer layer-
The buffer layer is configured by laminating three layers of a compressive stress layer, a tensile stress layer, and a compressive stress layer in order. As the compressive stress layer, SiN was formed with a thickness of 150 nm, and as the tensile stress layer, SiO ₂ was formed with a thickness of 200 nm.
The stress absolute value of each of the compressive stress layer and the tensile stress layer was 0.5 GPa. The stress of each layer was controlled by changing the conditions during film formation (target applied voltage, degree of vacuum, substrate temperature, etc. in the sputtering method).
The film formation of SiN as the compressive stress layer was performed under the following conditions.
Applied voltage: 1 kV
Pressure: 0.1Pa
Substrate temperature: 120 ° C
The film formation of SiO _{2 as} the tensile stress layer was performed under the following conditions.
Applied voltage: 0.5 kV
Pressure: 1Pa
Substrate temperature: 25 ° C

-Thin film transistor-
A bottom gate thin film transistor (TFT) was formed on the buffer layer.
Specifically, a gate electrode made of molybdenum (thickness 50 nm), an insulating film made of SiO ₂ (thickness 200 nm), a channel layer made of amorphous InGaZnO (thickness 30 nm), a channel protective layer made of GaO (thickness 100 nm). ) And source / drain electrodes (thickness 80 nm) made of molybdenum were sequentially formed by sputtering and patterning by photolithography.

<Comparative Example 1>
A thin film transistor was formed on the resin film in the same manner as in Example 1 except that the buffer layer was not formed.

<Comparative example 2>
A thin film transistor was formed in the same manner as in Example 1 except that a compressive stress layer was formed instead of the buffer layer formed in Example 1.

<Comparative Example 3>
A thin film transistor was formed in the same manner as in Example 1 except that a tensile stress layer was formed instead of the buffer layer formed in Example 1.

<Example 2>
Compared with the buffer layer formed in Example 1, a thin film transistor was formed in the same manner as in Example 1 except that each of the compressive stress layer was 50 nm and the tensile stress layer was 100 nm.

<Example 3>
Compared with the buffer layer formed in Example 1, a thin film transistor was formed in the same manner as in Example 1 except that each of the compressive stress layers was 100 nm and the tensile stress layer was 150 nm.

-Evaluation of crack occurrence-
The TFTs produced in Examples 1 to 3 and Comparative Examples 1 to 3 were examined for occurrence of cracks by the following method.
After making the TFT, the density was evaluated by observing with a microscope and counting the number of cracks present in the field of view (500 μmφ circle).
The results are shown in Table 1 below.

No crack was observed in the gate electrode of the TFT formed on the buffer layer in Example 1. In addition, no cracks were observed in the semiconductor layer and the source / drain electrodes.
On the other hand, the TFTs manufactured in Comparative Examples 1 to 3 all had minute cracks in the gate or source / drain electrodes. It is considered that cracks occurred during the formation of the molybdenum used for the electrodes or in the resist baking process during patterning.

<Comparative Experimental Example 1>
A thin film transistor substrate having the configuration shown in FIG. 1 was produced.
Acrylic, polycarbonate (PC), polyimide (PI), polyarylate (PAR), PET, PEN, and aramid were used for the resin film to be the support, and films having a thickness of 25 μm were all used. The following buffer layer and TFT were formed in this order on this film.

-Buffer layer-
The buffer layer is formed by stacking a total of five layers in the order of the SiN compressive stress layer, the SiO ₂ tensile stress layer, the SiN compressive stress layer, the SiO ₂ tensile stress layer, and the SiN compressive stress layer, and the thickness (t) of all buffer layers. As a comparative example, a sample without a buffer layer was also manufactured. The stress absolute value of each of the compressive stress layer and the tensile stress layer was 0.5 GPa.
-TFT-
The TFT had the same structure as in Example 1. About the produced TFT, the crack density was evaluated by microscopic observation. The results are shown in Table 2 below.

  According to the above results, a crack-free TFT can be manufactured on most resin films by setting the buffer layer thickness to 500 nm or more. In particular, the insertion effect of the buffer layer is effective when the Young's modulus of the film is small, and is particularly effective when a soft resin having a Young's modulus of 4 GPa or less is used.

<Examples 4-6, Comparative Examples 4-6>
A thin film transistor substrate having the configuration shown in FIG. 1 was produced.
Polyimide (PI) was used for the resin film to be the support, the thickness was 25 μm, and the following buffer layer and TFT were formed in this order on this film.

-Buffer layer-
The buffer layer was constituted by laminating three layers of a compressive stress layer of 150 nm, a tensile stress layer of 200 nm, and a compressive stress layer of 150 nm in this order, and six types of samples were prepared by changing the internal stress of each layer. The total thickness is 500 nm. Regarding the stress, the compressibility is indicated by plus (+), and the tensile property is indicated by minus (−). The thickness of each layer is obtained by a step meter (for example, alpha step) or a cross-sectional photograph by an electron microscope (for example, Hitachi field emission scanning electron microscope S-4800), etc. Technology).
The internal stress value remaining in the entire buffer layer was converted by adding the product of the thickness and stress of each layer, and the relationship with the crack density was investigated. About the produced TFT, the crack density was evaluated by microscopic observation similarly to the previous Example. The results are shown in Table 3 below.

  As shown in this result, if the buffer layer is formed so that the first layer and the third layer become the compressive stress layer and the second layer becomes the tensile stress layer, and the TFT is formed on the buffer layer, the TFT is formed. Although no crack was generated, if one of the internal stresses of the compressive stress layer (first layer and third layer) or the tensile stress layer (second layer) is zero, that is, a stress-free layer, the TFT formed thereon It was found that cracks occurred. It was also found that the crack density tends to increase as the value of the residual internal stress in the entire buffer layer increases. This result suggests that cracks are less likely to occur by making the residual internal stress in the entire buffer layer as small as possible.

The case where the organic EL display and the X-ray detector are manufactured using the thin film transistor substrate according to the present invention has been described above, but the present invention is not limited to the above embodiment. What is necessary is just to select the electronic device manufactured using the thin-film transistor substrate which concerns on this invention according to the objective. For example, the present invention can be suitably applied to the manufacture of electronic paper and liquid crystal displays.
The X-ray detector may also be a direct conversion system that converts X-rays directly into electric charges, or an indirect conversion system that converts X-rays once into visible light and converts the converted light into electric charges.

DESCRIPTION OF SYMBOLS 10 Resin film 12A, 12B, 12C Compressive stress layer 14, 14A, 14B Tensile stress layer 16, 17 Buffer layer 18 Gate electrode 20 Gate insulating layer 21 Thin-film transistor (TFT)
22, 24 Source / drain electrode 26 Active layer 28 Planarizing layer 30 Pixel electrode 32 Organic EL layer 34 Upper electrode (common electrode)
36 sealing film 38 insulating layer 40 pixel electrode 42 light absorption layer 44 transparent electrode (common electrode)
46 Scintillator 48 Films 100 and 200 for sealing Thin-film transistor substrate 300 Organic EL display 400 X-ray flat panel detector

Claims (8)

A resin film;
A buffer provided on the resin film and having a laminated structure in which at least three layers of compressive stress and layers of tensile stress are alternately laminated, and the lowermost layer and the uppermost layer are the layers of compressive stress. Layers,
A thin film transistor provided on the buffer layer;
A thin film transistor substrate.   The thin film transistor substrate according to claim 1, wherein all layers constituting the buffer layer are made of an inorganic material.   The layer constituting the buffer layer is composed of at least one material selected from the group consisting of SixOy, SixNy, SixOyNz, AlxOy, TixOy, ZrxOy, and HfxOy. Thin film transistor substrate.   4. The thin film transistor substrate according to claim 1, wherein all the layers constituting the buffer layer are made of the same material. 5.   The thin film transistor substrate according to any one of claims 1 to 4, wherein the buffer layer has a thickness of 500 nm or more.   The thin film transistor substrate according to claim 1, wherein the resin film has a Young's modulus of 4 GPa or less.   The display apparatus provided with the thin-film transistor substrate as described in any one of Claims 1-6.   The electromagnetic wave sensor provided with the thin-film transistor substrate as described in any one of Claims 1-6.

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