Light detection device

Abstract

To provide a photodetector in which a leakage current is reduced.SOLUTION: A light detection device (100) includes a photodiode (20) that converts light into electric charges, and a TFT (10) that detects the electric charges, in which the TFT includes a gate electrode (18), a source electrode (14), a drain electrode (16), and an oxide semiconductor film (12) extending between the source electrode and the drain electrode, and a width of the oxide semiconductor film is smaller than widths of the source electrode and the drain electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a photodetector device having a photodiode and a thin film transistor. [Background technology]

[0002] Flat panel type photodetectors, in which photodiodes that convert light into electric charges and thin film transistors (TFTs) that function as switching elements are arranged in a matrix, are widely used as image sensors, photosensors, etc. An example of a radiation imaging device equipped with such a photodetector is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-156119 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that the semiconductor film of a TFT may be made of an oxide semiconductor such as indium gallium zinc oxide (InGaZnO) or zinc oxide (ZnO). Compared to other semiconductors, oxide semiconductors have the advantage of low leakage current.

[0005] However, in a photodetector device, the TFT is damaged during the process of forming the photodiode after the TFT is formed, resulting in a problem of increased leakage current.

[0006] An object of one aspect of the present disclosure is to provide a photodetector with reduced leakage current. [Means for solving the problem]

[0007] In order to solve the above problem, a photodetector according to one embodiment of the present disclosure includes a photodiode that converts light into electric charges and a TFT (Thin Film Transistor) that detects the electric charges, wherein the TFT includes a gate electrode, a source electrode, a drain electrode, and an oxide semiconductor film that spans between the source electrode and the drain electrode, wherein the oxide semiconductor film includes a first region that overlaps with the source electrode in a planar view, a second region that overlaps with the drain electrode in a planar view, and a third region that is between the first region and the second region and overlaps only with the gate electrode in a planar view, and wherein a width of the oxide semiconductor film in a second direction that is perpendicular to a first direction that is a direction that passes through each of the first region, the second region, and the third region in a shortest distance and is perpendicular to the oxide semiconductor film in a planar view is smaller than a width of the source electrode and the drain electrode. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, a photodetector with reduced leakage current can be realized. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are a schematic cross-sectional view and a plan view of a photodetector according to a first embodiment. [Figure 2] 1 is a schematic plan view of a TFT included in the photodetector according to the first embodiment. [Figure 3] FIG. 1 is a cross-sectional view showing a schematic structure of a conventional photodetector. [Figure 4] FIG. 2 is a plan view showing a schematic structure of a TFT. [Figure 5] 1 is a graph showing the relationship between the thickness of a gate insulating film and the amount of variation in threshold voltage in a TFT. [Figure 6] 1 is a graph showing the relationship between gate voltage and drain current in a TFT. [Figure 7] 1 is a graph showing the change in the relationship between the gate voltage and the drain current in a TFT due to X-ray irradiation. [Figure 8]FIG. 10 is a plan view schematically illustrating an example of a TFT according to a second embodiment. [Figure 9] 9 is a plan view schematically showing another example of the TFT according to the second embodiment, different from that shown in FIG. 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] An embodiment of the present disclosure will be described in detail below. In the following description, "A to B" indicating a numerical range means "greater than or equal to A and less than or equal to B" unless otherwise specified.

[0011] (Configuration of the photodetector) 1 is a schematic cross-sectional view and a plan view of a photodetector 100 according to embodiment 1. In Fig. 1, reference numeral 101 denotes a cross-sectional view, and reference numeral 102 denotes a plan view. In particular, reference numeral 101 denotes a cross-sectional view of reference numeral 102 taken along line 1A-1A.

[0012] The photodetector 100 is, for example, a flat panel type, and may be, for example, a photosensor, an image sensor, or a radiation detection device (X-ray imaging display device), but is not limited to these. As shown in Fig. 1, the photodetector 100 includes a TFT (Thin Film Transistor) 10 and a photodiode 20. The TFT 10 and the photodiode 20 are formed on a substrate (not shown).

[0013] The TFT 10 detects the charge converted by the photodiode 20. Specifically, the TFT 10 is a switching element that is switched in response to the charge converted by the photodiode 20. The TFT 10 has an oxide semiconductor film 12, a source electrode 14, a drain electrode 16, and a gate electrode 18. The TFT 10 further includes a gate insulating film 13. The TFT 10 is a so-called bottom-gate TFT.

[0014] The oxide semiconductor film 12 may be an oxide semiconductor film containing at least one element selected from In, Ga, and Zn. This allows the photodetector 100 to have higher sensitivity and be smaller in size than when the oxide semiconductor film 12 is formed of other oxide semiconductors. However, in the photodetector 100, the oxide semiconductor film 12 may be an oxide semiconductor film containing none of In, Ga, and Zn.

[0015] The photodiode 20 converts light into an electric charge. The photodiode 20 includes a lower electrode 21 electrically connected to the drain electrode 16 of the TFT 10, an n-type semiconductor layer 22, an i-type semiconductor layer 24, a p-type semiconductor layer 26, and an upper electrode 27. In the example shown in FIG. 1 , the lower electrode 21 is formed integrally with the drain electrode 16. However, the lower electrode 21 may be an electrode separate from the drain electrode 16 and connected to the drain electrode 16 by wiring or the like. The photodiode 20 also includes a wiring layer 28 for applying a bias. For visibility reasons, the wiring layer 28 is positioned further away from the source electrode 14 in the photodiode 20 shown at 101 than in the photodiode 20 shown at 102.

[0016] The photodetector 100 further includes a first passivation film 61 that covers the TFT 10. The first passivation film 61 has a contact hole 61a for electrically connecting the lower electrode 21 and the n-type semiconductor layer 22.

[0017] The photodetector 100 further includes a second passivation film 62 that covers the first passivation film 61 and a portion of the photodiode 20. The second passivation film 62 has an opening 62a for exposing the photodiode 20.

[0018] Furthermore, the photodetector 100 further includes a planarization film 64 that covers the second passivation film 62. The photodetector 100 has an opening 64a for exposing the photodiode 20.

[0019] The material and thickness of each component will be described later along with an example of a method for manufacturing the photodetector 100.

[0020] Fig. 2 is a schematic plan view of the TFT 10. Fig. 2 shows the oxide semiconductor film 12, source electrode 14, drain electrode 16, and gate electrode 18 included in the TFT 10, viewed from the oxide semiconductor film 12 side relative to the gate electrode 18 in a direction perpendicular to the oxide semiconductor film 12. The gate insulating film 13 is omitted from Fig. 2.

[0021] 2, the oxide semiconductor film 12 includes a first region R1, a second region R2, and a third region R3 in the above-mentioned plan view. The first region R1 is a region where the oxide semiconductor film 12 overlaps with the source electrode 14. The second region R2 is a region where the oxide semiconductor film 12 overlaps with the drain electrode 16. The oxide semiconductor film 12 further overlaps with the gate electrode 18 in both the first region R1 and the second region R2. The third region R3 is a region between the first region R1 and the second region R2 that overlaps only with the gate electrode 18.

[0022] In the above-described plan view, the direction passing through the first region R1, the second region R2, and the third region R3 in the shortest distance is referred to as the first direction. Furthermore, in the above-described plan view, the direction perpendicular to the first direction is referred to as the second direction. In other words, the second direction is perpendicular to the first direction and perpendicular to the oxide semiconductor film 12. In FIG. 2 , width W1 is the width of the oxide semiconductor film 12 in the second direction. Width W2 is the width of the source electrode 14 and the drain electrode 16 in the second direction. Note that if the width of the source electrode 14 and the width of the drain electrode 16 are different from each other, width W2 is the smaller of the widths of the source electrode 14 and the drain electrode 16. In the TFT 10, width W1 of the oxide semiconductor film 12 in the second direction is smaller than width W2 of the source electrode 14 and the drain electrode 16. For example, W1 = 4 μm and W2 = 8 μm, but W1 and W2 are not limited thereto.

[0023] (Compared to conventional photodetectors) Fig. 3 is a cross-sectional view showing a schematic structure of a conventional photodetector 200. As shown in Fig. 3, the photodetector 200 includes a TFT 30 instead of a TFT 10. The TFT 30 includes an a-Si semiconductor film 32 instead of an oxide semiconductor film 12. The a-Si semiconductor film 32 is formed of amorphous silicon (a-Si) instead of an oxide semiconductor.

[0024] Generally, oxide semiconductors have higher charge mobility and smaller leakage current than a-Si. The photodetector 100 of this embodiment is a photodetector that has improved sensitivity compared to the photodetector 200 by including a TFT 10 having an oxide semiconductor film 12 instead of a TFT 30 having an a-Si semiconductor film 32.

[0025] 4 is a plan view showing the schematic structures of TFT30 and TFT40. TFT40 is a comparative example TFT manufactured during the development process of a TFT including an oxide semiconductor film 12. In FIG. 4, reference numeral 401 indicates the schematic structure of TFT30. Reference numeral 402 indicates the schematic structure of TFT40. Like TFT10, TFT40 includes an oxide semiconductor film 12. However, TFT40 differs from TFT10 in that the width W1 of TFT40 is larger than the width W2.

[0026] When manufacturing the photodetector 100, the photodiode 20 is formed after the TFT 10 is formed. At this time, process damage, particularly damage due to dry etching, occurs to the TFT 10 in the process of forming the photodiode 20. The magnitude of the damage depends on the size of the TFT 10, specifically the size of the oxide semiconductor film 12.

[0027] 4, the TFT 40 is formed smaller than the TFT 30. Similarly, the TFT 10 is formed smaller than the TFT 30. As a result, in the photodetector 100, damage to the TFT 10 during the process of forming the photodiode 20 is reduced compared to when the TFT 10 is manufactured to the same size as the TFT 30.

[0028] 5 is a graph showing the relationship between the thickness of the gate insulating film 13 in the TFT 10 and the variation ΔVth of the threshold voltage. In FIG. 5, the horizontal axis represents the thickness (nm) of the gate insulating film 13, and the vertical axis represents ΔVth (V). ΔVth represents the variation of the threshold voltage Vth in the TFT 10. The threshold voltage Vth is the gate voltage Vg when the drain current Id reaches a predetermined value. The predetermined value for the drain current Id is, for example, 1 nA.

[0029] During the development of a TFT including an oxide semiconductor film 12, the inventors of the present application discovered that irradiating the TFT with X-rays changes the relationship between Vg and Id and Vth. Specifically, irradiating a TFT 10 including an oxide semiconductor film 12 and at least a portion of whose gate insulating film 13 is made of silicon dioxide (SiO2) with X-rays causes a change in Vth. As shown in FIG. 5, ΔVth varies linearly with the thickness of the SiO2, with a negative slope. Therefore, ΔVth can be reduced by thinning the SiO2 in the gate insulating film 13.

[0030] When the thickness of SiO2 in the gate insulating film 13 is about 10 nm, ΔVth in the TFT 10 is approximately the same as ΔVth in the TFT 30. However, the thickness of the gate insulating film 13 may vary.

[0031] FIG. 6 is a graph showing the relationship between gate voltage Vg and drain current Id for TFT 30 and TFT 10. In FIG. 6, reference numeral 601 indicates the relationship between Vg and Id for TFT 30, in which W1 is set to 6 μm. Reference numeral 602 indicates the relationship between Vg and Id for TFT 10, in which W1 is set to 6 μm and the SiO2 thickness of the gate insulating film 13 is approximately 10 nm. In both reference numerals 601 and 602, the horizontal axis represents Vg (V) and the vertical axis represents Id (A). In both reference numerals 601 and 602, the relationship between Vg and Id before X-ray irradiation is shown by a dashed line, and the relationship between Vg and Id after X-ray irradiation is shown by a solid line.

[0032] In the example shown by reference numeral 601, ΔVth of TFT30 was +0.3 V. On the other hand, in the example shown by reference numeral 602, ΔVth of TFT10 was +0.2 V, which was similar to the example shown by reference numeral 601. Furthermore, TFT30 had a smaller Id at which it entered the on state than TFT10. This difference in Id at which it entered the on state is a general difference in characteristics between a TFT having an oxide semiconductor film and a TFT having an a-Si semiconductor film.

[0033] In TFT 30, there was no particular restriction on the relationship between the width of the a-Si semiconductor film 32 and the widths of the source electrode 14 and the drain electrode 16. For this reason, in the development process of TFT 10 including oxide semiconductor film 12, TFTs in which W1 is larger than W2, such as TFT 40, were also manufactured. The inventors of the present application found that there is a difference in the change in the relationship between Vg and Id due to X-ray irradiation between a case in which W1 is larger than W2, such as TFT 40, and a case in which W1 is smaller than W2, such as TFT 10.

[0034] FIG. 7 is a graph illustrating the change in the relationship between gate voltage Vg and drain current Id in TFTs 40 and 10 due to X-ray irradiation. In FIG. 7, reference numeral 701 denotes a graph illustrating the relationship between Vg and Id in TFT 40 where W1 = 8 μm and W2 = 4 μm. Reference numeral 702 denotes a graph illustrating the relationship between Vg and Id in TFT 10 where W1 = 4 μm and W2 = 8 μm. In both reference numerals 701 and 702, the horizontal axis is Vg (V) and the vertical axis is Id (A). In both reference numerals 701 and 702, the graphs for TFTs 40 and 10 before X-ray irradiation are indicated by dashed lines, and the graphs for TFTs 40 and 10 after X-ray irradiation are indicated by solid lines.

[0035] In the example shown by reference numeral 701, the threshold voltage Vth for Vg of the TFT 40 was +1.09 V before X-ray irradiation, but was −3.89 V after X-ray irradiation. On the other hand, in the example shown by reference numeral 702, the threshold voltage Vth for Vg of the TFT 10 was +1.05 V before X-ray irradiation, but was −0.06 V after X-ray irradiation. That is, in the TFT including the oxide semiconductor film 12, when W1 was smaller than W2, the change in Vth due to X-ray irradiation was smaller than when W1 was larger than W2.

[0036] When the TFTs 10 and 40 are irradiated with ionizing radiation including X-rays, electron-hole pairs are generated in the gate insulating film 13. Of these, the electrons are released from the gate insulating film 13 in a short time. On the other hand, the holes have lower mobility than the electrons. Therefore, some of the holes in the gate insulating film 13 are trapped near the interface with the oxide semiconductor film 12 and become fixed positive charges. It is believed that these fixed positive charges in the gate insulating film 13 cause a change in Vth.

[0037] The amount of trapped fixed positive charges in the gate insulating film 13 is proportional to the 0.5 to 2 power of the thickness of the SiO2 in the gate insulating film 13. Therefore, ΔVth tends to decrease rapidly as the SiO2 becomes thinner. This is thought to be because the thinner SiO2 makes it easier for holes injected into the oxide semiconductor film 12 to pass through the gate insulating film 13 and move to the gate electrode 18 due to the tunneling effect, thereby suppressing an increase in the electric field strength in the gate insulating film 13.

[0038] Furthermore, when W1 is smaller than W2, the area of ​​the interface between SiO2 and the oxide semiconductor film 12 is smaller than when W1 is larger than W2. As the area decreases, the influence of the fixed positive charges in the gate insulating film 13 decreases, and ΔVth decreases.

[0039] As described above, in the TFT 10, W1 is formed to be smaller than W2, which reduces the change in Vth due to X-ray irradiation compared to when W1 is formed to be equal to or larger than W2.

[0040] (Manufacturing method) The following describes a method for manufacturing the photodetector 100. First, a conductive film that will become the gate electrode 18 is formed on a substrate to a thickness of 50 nm to 500 nm.

[0041] Examples of the substrate include a glass substrate, a silicon substrate, and a heat-resistant plastic substrate. In particular, the plastic substrate may be made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), acrylic, polyimide, or the like.

[0042] The conductive film may be a film of a metal such as aluminum (Al), tungsten (W), molybdenum (Mo), tantalum (Ta), chromium (Cr), titanium (Ti), or copper (Cu), or an alloy or metal nitride thereof. The conductive film may also be a laminate of two or more of these. For example, a W film is formed on a substrate to a thickness of 370 nm, followed by a TaN film to a thickness of 50 nm, to form a gate electrode 18 having a laminated structure of W and TaN (W / TaN=370 nm / 50 nm). Specifically, W and TaN are vapor-deposited on the substrate by sputtering, and then the gate electrode 18 is formed into a desired shape by photolithography using dry etching.

[0043] Next, the gate insulating film 13 is formed on the gate electrode 18. The gate insulating film 13 may have a two-layer structure. The gate insulating film 13 may be made of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ) (x>y), silicon oxynitride (SiN x O y ) (x>y) or the like can be used as appropriate. When the gate insulating film 13 has a two-layer structure, the lower gate insulating film located on the gate electrode 18 side is made of SiN to prevent the diffusion of impurities and the like from the substrate. x or SiNx O y (x>y), etc. The upper gate insulating film located on the opposite side to the gate electrode 18 may be formed of SiO x or silicon oxynitride SiO x N y (x>y) and so on.

[0044] A dense insulating film can be formed at a relatively low temperature by mixing a rare gas such as argon into the reactive gas used to form the gate insulating film 13 and mixing the rare gas into the gate insulating film 13. By making the gate insulating film 13 a dense insulating film, leakage current can be reduced.

[0045] For example, a CVD (Chemical Vapor Deposition) device is used to deposit a 325 nm thick SiN film as a lower layer, and then a 10 nm thick SiO2 film is continuously deposited thereon as an upper layer, thereby forming a gate insulating film 13 having a two-layer structure.

[0046] On the gate insulating film 13, the oxide semiconductor film 12 is formed to a thickness of 30 nm to 100 nm. As described above, the oxide semiconductor film 12 may be an oxide semiconductor film containing at least one element selected from In, Ga, and Zn. Specifically, the material of the oxide semiconductor film 12 may be InGaO3(ZnO)5, magnesium zinc oxide (Mg x Zn 1-x O), cadmium zinc oxide (Cd x Zn 1-xThe oxide semiconductor film 12 may be made of ZnO doped with one or more impurity elements selected from the group 1, 13, 14, 15, and 17 elements. In this case, the ZnO may be in an amorphous state, a polycrystalline state, or a microcrystalline state in which the amorphous and polycrystalline states are mixed. Furthermore, the oxide semiconductor film 12 may be made of ZnO doped with no impurity elements.

[0047] For example, an oxide semiconductor film that will become the oxide semiconductor film 12 is formed by a sputtering method, and then the oxide semiconductor film 12 is formed into a desired shape by a photolithography method using dry etching.

[0048] A source electrode 14, a drain electrode 16, and a lower electrode 21 integral with the drain electrode 16 are formed on the oxide semiconductor film 12. Specifically, a conductive film is formed on the gate insulating film 13 and the oxide semiconductor film 12. Furthermore, the conductive film is processed into a desired shape using a resist mask in a photolithography process to form the source electrode 14, the drain electrode 16, and the lower electrode 21. The conductive film may be made of a metal such as aluminum (Al), tungsten (W), molybdenum (Mo), tantalum (Ta), copper (Cu), chromium (Cr), or titanium (Ti), or an alloy or nitride thereof. Here, Ti / Al / Ti films with thicknesses of 100 nm / 300 nm / 30 nm are formed by sputtering, and then the source electrode 14, the drain electrode 16, and the lower electrode 21 are formed into the desired shapes by photolithography using dry etching. This completes the TFT 10. The lower electrode 21 of the photodiode 20 is also formed.

[0049] A first passivation film 61 is formed to a thickness of 200 nm to 300 nm so as to cover the TFT 10 and the lower electrode 21. The first passivation film 61 may be formed using a thin film formation method such as plasma CVD or sputtering. The first passivation film 61 may be made of an insulating material such as silicon nitride, silicon oxide, silicon nitride oxide, or silicon oxynitride. The first passivation film 61 is not limited to a single layer, but may be two or more layers. A resist mask is formed on the first passivation film 61, and a contact hole 61a is formed by photolithography using dry etching so that the lower electrode 21 is exposed from the first passivation film 61. After the first passivation film 61 is formed, a process of heating the entire surface of the substrate may be further performed. The heating is performed until the substrate reaches, for example, 350°C.

[0050] On the lower electrode 21, an n-type semiconductor layer 22, an i-type semiconductor layer 24, and a p-type semiconductor layer 26 are formed in this order, for example, by CVD. The n-type semiconductor layer 22 is made of, for example, amorphous silicon (a-Si) and forms an n+ region. The thickness of the n-type semiconductor layer 22 is, for example, approximately 10 nm to 50 nm. The i-type semiconductor layer 24 is a semiconductor layer having lower conductivity than the n-type semiconductor layer 22 and the p-type semiconductor layer 26, for example, a non-doped intrinsic semiconductor layer, and is made of, for example, amorphous silicon (a-Si). The thickness of the i-type semiconductor layer 24 is, for example, approximately 400 nm to 1000 nm. The thicker the i-type semiconductor layer 24, the higher the photosensitivity of the photodiode 20. The p-type semiconductor layer 26 is made of, for example, amorphous silicon (a-Si) and forms a p+ region. The thickness of the p-type semiconductor layer 26 is, for example, approximately 40 nm to 50 nm. The p-type semiconductor layer 26 may be formed by implanting B into the upper layer portion of the i-type semiconductor layer 24 by ion shower doping or ion implantation.

[0051] An upper electrode 27 is formed on the p-type semiconductor layer 26. The upper electrode 27 is made of, for example, IZO (indium zinc oxide) or ITO (indium tin oxide). The upper electrode 27 is formed in the region above the p-type semiconductor layer 26 by sputtering and photolithography.

[0052] Next, a second passivation film 62 is formed. The second passivation film 62 covers the entire first passivation film 61, the side surfaces of the photodiode 20, and part of the upper electrode 27 of the photodiode 20. The second passivation film 62 is formed of, for example, the same material as the first passivation film 61. Specifically, a film of an insulating material is formed by, for example, a CVD method so as to cover the first passivation film 61 and the photodiode 20. Thereafter, an opening 62a is formed in part of the upper surface of the photodiode 20 by photolithography, thereby forming the second passivation film 62.

[0053] A planarization film 64 is formed on the second passivation film 62. The planarization film 64 is made of an inorganic insulating material or an organic insulating material. Examples of inorganic insulating materials include silicon dioxide, silicon nitride, silicon oxynitride, silicon nitride oxide, and TEOS (Tetraethyl orthosilicate). Specifically, a film of an inorganic insulating material or an organic insulating material is formed over the entire second passivation film 62 by a CVD method or the like. Thereafter, an opening 64a is formed in a portion of the upper surface of the photodiode 20 by a photolithography method, thereby forming the planarization film 64.

[0054] The wiring layer 28 is formed by, for example, sputtering or photolithography on the upper electrode 27 of the photodiode 20 exposed from the opening 64a of the planarization film 64. The wiring layer 28 is made of, for example, Mo or Ti.

[0055] The photodetector 100 can be manufactured through the above steps. Furthermore, a wavelength conversion layer (not shown), such as a scintillator that converts radiation into light, can be formed on the upper side of the photodiode 20 to manufacture a radiation imaging device including the photodetector 100. The scintillator is made of, for example, cesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S).

[0056] [Embodiment 2] Other embodiments of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0057] Fig. 8 is a plan view schematically illustrating an example of a TFT 10A according to embodiment 2. Fig. 9 is a plan view schematically illustrating another example of the TFT 10A different from that shown in Fig. 8. The gate electrode 18 is omitted in Figs. 8 and 9. The TFT 10A differs from the TFT 10 in that it includes an oxide semiconductor film 12A instead of the oxide semiconductor film 12.

[0058] 8, the oxide semiconductor film 12A has a first portion 121 and a second portion 122. The first portion 121 and the second portion 122 are arranged in parallel to each other in the second direction. In other words, the oxide semiconductor film 12A is divided into two portions, the first portion 121 and the second portion 122, along the second direction.

[0059] 8, width W11 is the width in the second direction of first portion 121. Width W12 is the width in the second direction of second portion 122. In TFT 10A, the sum of width W11 and width W12 in oxide semiconductor film 12A is smaller than width W2.

[0060] 9, the oxide semiconductor film 12A may further include a third portion 123 in addition to the first portion 121 and the second portion 122. In this example, the first portion 121, the second portion 122, and the third portion 123 are arranged in parallel with one another in the second direction. In other words, the oxide semiconductor film 12A is divided into three portions, the first portion 121, the second portion 122, and the third portion 123, along the second direction.

[0061] 9, width W13 is the width in the second direction of the third portion 123. In the example shown in FIG 9, the sum of widths W11, W12, and W13 in the oxide semiconductor film 12A is smaller than width W2.

[0062] Furthermore, the oxide semiconductor film 12A may be divided into four or more parts along the second direction. In this case, the total width of the divided oxide semiconductor film 12A in the second direction should be smaller than the width W2 of the source electrode 14 and the drain electrode 16. This allows the photo-detector 100 including the TFT 10A to reduce a change in Vth due to X-ray irradiation, as in the case where the photo-detector 100 includes the TFT 10.

[0063] Furthermore, in the TFT 10A, since the oxide semiconductor film 12A is divided into multiple pieces, even if the conductivity of one of the multiple divided oxide semiconductor films 12A deteriorates, a current can flow through the other oxide semiconductor films 12A, thereby reducing the impact of the deterioration of conductivity.

[0064] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Explanation of symbols]

[0065] 10 TFT 12 Oxide semiconductor film 14 Source electrode 16 Drain electrode 18 gate electrode 20 Photodiode R1 1st area R2 2nd area R3 3rd area

Claims

1. a photodiode that converts light into an electric charge; a TFT (Thin Film Transistor) that detects the charge; the TFT includes a gate electrode, a source electrode, a drain electrode, and an oxide semiconductor film extending between the source electrode and the drain electrode; the oxide semiconductor film includes a first region overlapping with the source electrode in a plan view, a second region overlapping with the drain electrode in a plan view, and a third region between the first region and the second region and overlapping only with the gate electrode in a plan view; a width of the oxide semiconductor film in a second direction perpendicular to a first direction that is a direction passing through the first region, the second region, and the third region at the shortest distance and perpendicular to the oxide semiconductor film in a plan view is smaller than a width of the source electrode and the drain electrode.

2. the oxide semiconductor film is divided into a plurality of parts in the second direction, The photodetector according to claim 1 , wherein a total width of the divided oxide semiconductor film in the second direction is smaller than a width of the source electrode and the drain electrode in the second direction.

3. The photodetector according to claim 1 , wherein the oxide semiconductor film contains at least one element selected from the group consisting of In, Ga, and Zn.

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