JPH09275202A - Photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both satisfactory shielding and a satisfactory aperture rate, by providing a shielding layer that shields a switch TFT and further has an aperture region the area of which is larger than the light receiving area of a photoelectric conversion element. SOLUTION: A SiN film is formed as a passivation film 33 by plasma CVD, and then a red filter is formed as a shielding film 28 in a specified pattern. Polyimide resin is simultaneously placed as a protective film 29 in a specified pattern, and unnecessary parts, such as wire lead-out sections, are etched by RIE using the polyimide resin as a mask. It allows a switch TFT to be sufficiently shielded to use for the shielding member a material that selectively blocks the wavelength of incident light or a wavelength to which the switch TFT is sensitive, as mentioned above. This makes it possible to place a shielding layer having an aperture region the area of which is larger than the light receiving area of a photoelectric conversion element. Thus, it is possible to obtain a photodetector with reduced TFT leakage current and cross talk.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-dimensional and two-dimensional image reading apparatus used for a facsimile, a digital copying machine, a scanner, etc., and further, a radiation such as X-rays and γ-rays by using a fluorescent plate for visible light. The present invention relates to a photodetection device that converts light into light and reads the converted light.

[0002]

2. Description of the Related Art Conventionally, a reading system using a reduction optical system and a CCD type sensor has been used as a reading system for a facsimile, a digital copying machine, a radiation detecting device, or the like. However, in recent years, amorphous silicon (hereinafter,
a photoelectric conversion semiconductor material represented by abbreviated as a-Si film) to form a photoelectric conversion element on a large area substrate,
A contact sensor that reads with an optical system of the same size as the information source is being developed and put into practical use. As an example, TFT (Th
FIG. 18A shows a schematic cross-sectional view of a one-dimensional photodetector using an in Film Transistor) type photoelectric conversion element. In the figure, 101 is a TFT type sensor section, 102 is a switch TFT section, and 103 is a charge storage section. Also, in the figure, 2
01 is a glass substrate, 202 is a Cr gate electrode, 203 is a SiN gate insulating film, 204 is i-type amorphous Si, 205
Is n ⁺ type amorphous Si, 206 is an Al SD electrode, 20
7 is a SiN channel protective film. In addition, a 1-bit equivalent circuit of this example is shown in FIG. In the figure, incident light on the inverted stagger type TFT sensor 101 is photoelectrically converted, and the generated charges are stored in the charge storage unit 103. After that, the charge is distributed and transferred by the switch TFT 102 to the capacitor portion 104 formed between wirings, and the voltage is read as an electric signal. In this example, in particular, aS
i film is not only a photoelectric conversion material but also a switch TFT
Since it can be used also as a semiconductor material of 102,
As described above, the photoelectric conversion semiconductor layer of the photoelectric conversion element and the TFT
There is also an advantage that it can be formed simultaneously with the semiconductor layer. Also, a
Since the -Si film can easily have a large area, it is also advantageous for two-dimensionalization. As an example, an outline of a two-dimensional photodetector using a PIN photodiode will be described.
FIG. 19A shows a schematic equivalent circuit diagram of a part of the area sensor. In the figure, 301 is a PIN type sensor section, 302 is a switch TFT section, 303 is a data line, 304 is a gate line, and 305 is a bias line. Each pixel has a sensor unit 301 and a switch TFT unit 3.
02, the PIN sensor 301 is connected to the switch TFT 302, and the switch TFT 302 is connected to the data line. Further, FIG. 19B shows a schematic sectional view of one pixel shown in FIG. In the figure, 401 is a glass substrate, 402 is a Cr gate electrode, 4
03 is a SiN gate insulating film, 404 is i-type amorphous Si,
405 is n + type amorphous Si, 406 is an Al SD electrode, 407 is a SiN channel protective film, 411 is p type,
i-type and n-type amorphous Si, 412 Cr electrode, 410 I
TO transparent electrode, 414 and 415 are SiN and PI, respectively
Etc. is a protective film.

Incidentally, the radiation detecting apparatus has a structure in which the above-mentioned photo-converting element and TFT are set as one pixel, uniformly or individually on a one-dimensionally or two-dimensionally arranged photo-detector. A structure in which a phosphor is arranged for each pixel is generally used, and a sensor reads an image emitted by the phosphor upon irradiation with radiation.

In any of the above-mentioned configurations, incident light converted into image information, for example, reflected light from a document or converted light converted by a phosphor enters a photodetector, and a photoelectric converter is formed. The photoelectrically converted electric charges are transferred by the TFT and the image information is obtained by the TFT. At the same time, the incident light also enters the portion other than the sensor portion, that is, the TFT portion. As a result, there is a problem that the leak current of the TFT portion increases and the S / N ratio of the sensor is indirectly reduced. As a specific example, FIG. 20 shows the relationship between the amount of incident light and the PIN sensor output and the TFT leakage current. If the sensor output is Is and the incident light quantity is F,
The sensor output increases according to the amount of incident light as follows.

Is = αF ↑ γ1 However, in “↑ γ1”, [↑] represents an exponent, and [γ1]
Represents the number in the index.

On the other hand, if the TFT leakage current is It, it can be expressed as follows, like the sensor.

It = βF ↑ γ2 where γ1 and γ2 are real numbers, and among "↑ γ2",
[↑] represents an index, and [γ2] represents a number within the index.

However, in the present example, since γ1> γ2, the TFT leak current becomes about the same as the sensor output in the low light amount region, which affects the image. On the other hand, since the TFT is connected to the sensor, the sensor output increases in the high light amount region, so that the voltage between the source and drain of the TFT increases. Therefore, the relationship between the incident light amount and the leak current is not constant as shown in FIG. As a result, a sufficient S / N ratio of the sensor cannot be obtained in the low light amount region and the high light amount region. That is, the usable light amount range is limited.

Further, the incident light is simultaneously incident on the region intersecting with the gate line and the data line. As a result, the capacitance formed in that region changes, and a phenomenon such as crosstalk occurs, which causes a problem of deteriorating the photodetector characteristics. Therefore, attempts have conventionally been made to reduce the incidence of light on the TFT section, but there are drawbacks as described below in terms of realization, and the reality is that they have not been completed in reality.

For example, as the light-shielding material, a metal thin film can be generally used, and there is a structure in which the metal thin film is arranged directly on the TFT. However, since it is a conductive material, it acts as a back gate of the TFT channel portion to affect the TFT operation. There is a drawback in that the switching speed is lowered because of giving or forming a new capacitance. Furthermore, when the size of the TFT is increased in order to compensate for this drawback, it has a large effect on the entire photodetector, such as a reduction in the aperture ratio, and it is difficult to dispose the light shielding member directly on the TFT. Also, since the reflectance is large,
The reflected light enters again and the MTF (Modulation Transfer Fu
nction) will also be reduced. Here, in this conventional example, in consideration of MTF and incident light efficiency, the light shielding member is laminated at a distance equal to or less than the pixel pitch and only via a protective film such as a SiN film. On the other hand, the pigment-dispersed light-shielding material, which is an insulating material, has no electrical influence, and
Although it can be directly arranged on T and has a lot of advantages because it has a low reflectance, a film thickness of about several μm is required to carry out the same light shielding as the metal thin film described above. But,
With the miniaturization of the TFT, it is necessary to realize a fine light-shielding pattern for shielding the wiring cross portion and the like.

FIG. 21 shows the correlation between the film thickness of the conventional pigment-dispersed black light-shielding film and the pattern accuracy. Specifically, the light shielding film needs to have a film thickness of 2 to 3 μm at an OD value (2.5 to 3.0) capable of sufficiently shielding light, and the pattern accuracy at that time is 2
It is 0 μ to 30 μ. In other words, at present, only a rough light-shielding pattern is possible to perform sufficient light-shielding. Therefore, a pattern arrangement that reduces the sensor aperture ratio is used, or the light-shielding film overlaps the sensor aperture, As a result, the aperture ratio is reduced.

FIG. 22 is a schematic plan view of the photodetector. Practically, as shown in FIG. 22, the pixels 311 are arranged at a constant pitch, and the distance e between the pixels is about several μ to several tens μ. The region between the pixels is the region where the pattern accuracy is most required, and the region including the wiring cross portion is effective in reducing crosstalk. Also,
It is also possible to prevent a decrease in MTF due to transmitted light reaching the back surface of the photodetector.

However, if the pattern accuracy is about 20 μ to 30 μ, the light shielding film overlaps the pixel portion and the aperture ratio is reduced. Conversely, setting the inter-pixel distance according to the pattern accuracy also causes a decrease in the aperture ratio.

[0014]

In order to shield the light without lowering the aperture ratio of the photodetector, pattern accuracy of at least about 10 μ, preferably about several μ is required. However, if the light blocking is performed sufficiently, the aperture ratio of the photodetector decreases, and conversely, there is a problem that sufficient light blocking cannot be achieved if the aperture ratio is maintained, and it is necessary to satisfy both the light blocking and the aperture ratio at the same time.

[0015]

In the photodetector according to the present invention, the light-shielding member is arranged directly at least on the switch TFT by optimizing the light-shielding wavelength and the film thickness of the light-shielding member, and the photoelectric conversion element portion is provided. By forming and arranging the opening region larger than the light receiving area of (1), it is possible to secure the yield of the photodetector and provide the photodetector with a high S / N ratio and a high aperture ratio. In order to specifically explain the operation of the present invention, among the photodetectors using the a-Si thin film taken up in the conventional example, a radiation detector using a phosphor will be described below as an example.

Specifically, in a photodetector having at least a photoelectric conversion element and a switch TFT, at least the switch TFT is shielded from light and an opening region larger than the light receiving area of the photoelectric conversion element is formed. It is characterized in that the layers are arranged. The photoelectric conversion element is an inverted stagger type TFT, and a drive wiring for driving the photoelectric conversion element, a gate wiring for driving the switch TFT, and a signal wiring connected to the switch TFT. It is characterized by being composed of. Further, the photoelectric conversion element is a PIN photodiode, and is composed of a drive wiring for driving the photoelectric conversion element, a gate wiring for driving the switch TFT, and a signal wiring connected to the switch TFT. It is characterized by being configured. Further, the photoelectric conversion element is a MIS type photoelectric conversion element composed of a first electrode layer, an insulating layer, a semiconductor layer, a carrier injection blocking layer to the semiconductor layer, and a second electrode layer. It is characterized in that it is composed of a drive wiring for driving the photoelectric conversion element, a gate wiring for driving the switch TFT, and a signal wiring connected to the switch element. Further, the semiconductor layer is an amorphous silicon thin film.

[0017]

1 is a diagram showing the wavelength dependence of the relative sensitivity of a PIN photodiode as the photosensitivity of an a-Si film. In addition, FIG. 2 shows CsI: Tl as a phosphor.
It is a figure which shows the wavelength dependence of the relative luminescence intensity of. The leak current of the TFT is approximately proportional to the product of the photosensitivity of the a-Si film and the emission intensity of the phosphor. Here, the wavelength dependence of the sensitivity of the a-Si film is represented by fs (λ), and the ratio Qs of the sensitivity to light of wavelengths λ1 to λ2 to the total sensitivity is expressed as wavelengths λ1 to λ.
2 is [λ1 to λ2] ∫, and integration at all wavelengths is [all wavelength] ∫, Qs = [λ1 to λ2] ∫fs (λ) dλ / [all wavelength] ∫
Assuming that fs (λ) dλ, for example, Qs> 0.99, that is, 99%
The wavelengths λ1 and λ2 that can obtain the above sensitivity can be set, in other words, if a material that can completely shield light from λ1 to λ2 is used, suppose that incident light with uniform intensity at all wavelengths is used. However, by using this light-shielding film, the leak current can be reduced to 1%.

Further, the wavelength dependence of the emission intensity of the phosphor is
The ratio Qf of the emission intensity to light of wavelengths λ1 to λ2 with respect to the total emission intensity is represented by (λ), and the integration at wavelengths λ1 to λ2 is [λ1 to λ2] ∫, and the integration at all wavelengths is [total wavelength] ∫, Qf = [λ1 to λ2] ∫ff (λ) dλ / [all wavelengths] ∫
Assuming ff (λ) dλ, similarly, Qf> 0.99, that is, 99%
The wavelengths λ1 and λ2 at which the above emission intensity is obtained can be set,
If the light-shielding film can completely shield light from λ1 to λ2, even if the material has uniform sensitivity at all wavelengths, the light-shielding film can be used to reduce the leak current to 1%. it can.

However, in practice, the wavelength to be shielded is a-
It is determined by the product of the sensitivity of the Si film and the emission intensity of the phosphor. The product Qsf of this ratio Qf is considered to be proportional to the magnitude of the leakage current itself of the TFT after all, and this is considered as the total sensitivity. Further, Qsf = [λ1 to λ2] ∫fs (λ) ff (λ ) Dλ /
[All wavelengths] ∫ fs (λ) ff (λ) dλ Assuming that Qsf> 0.99, λ1 and λ2 can be set, and the light shielding film can completely shield light from λ1 to λ2. If so, the TFT leakage current can be reduced to approximately 1%. Of course, the light-shielding film also has wavelength dispersion, and the transmittance differs depending on the film thickness. The transmittance is expressed as T (λ), and Qsft = [λ1 to λ2] ∫fs (λ) ff (λ) T
Assuming that (λ) dλ / [total wavelength] ∫fs (λ) ff (λ) dλ, the sensor material, the phosphor, the light-shielding film material, and the film thickness for which Qsft> 0.99 are satisfied for all wavelengths. By making a selection, the target leak current can be reduced.
FIG. 3 shows the product of the sensitivity of the a-Si film and the emission intensity of the phosphor using CsI: Tl, that is, the total sensitivity and the transmittance of the light shielding film. It is sufficient to use a light-shielding film having maximum absorption or reflection at 550 nm, which has the highest overall sensitivity.
It can be confirmed that the film thickness should be set so as to satisfy the above Qsft> 0.99. With such a design, it is possible to select a light shielding material, reduce the film thickness as much as possible, and secure a film thickness capable of forming a detailed pattern.

[0020]

【Example】

[Embodiment 1] In this embodiment, a photodetector using a MIS type photoelectric conversion element will be described. First, a method for producing the photodetector will be described with reference to FIGS.

First, as shown in FIG. 4, the glass substrate 21
On top (OA-2 made by Nippon Electric Glass Co., Ltd.), a Cr thin film of 1000 Å is formed as the gate electrode 22 by a sputtering method. Then, a predetermined pattern is formed by the photolithography method.

Second, as shown in FIG. 5, plasma CVD
A SiN film as the gate insulating film 23 by the method of 3000 angstroms, the photoelectric conversion layer 24 and the TFT semiconductor layer 2
4, an a-Si film of 5000 angstrom and an ohmic contact layer 25 of n ⁺ film 1000 angstrom are continuously formed.

Thirdly, as shown in FIG. 6, a contact hole 27 is formed. A predetermined pattern is formed by the photolithography method and processed by the CDE method.

Fourth, as shown in FIG. 7, an Al thin film of 1 μm is formed as a source / drain electrode 26 by a sputtering method. Then, a predetermined pattern is formed by the photolithography method.

Fifth, as shown in FIG. 8, a predetermined pattern is formed by the photolithography method, the n ⁺ film 25 is etched by about 1000 angstroms and the a-Si film 24 is etched by about 200 angstroms by the RIE method.
The FT channel portion 34 is formed.

Sixth, as shown in FIG. 9, a predetermined pattern is formed by the photolithography method, and the n ⁺ film 25, the a-Si film 24 and the SiN film 23 are simultaneously etched by the RIE method to separate the elements. .

Seventh, as shown in FIG. 10, a SiN film is formed as a passivation film 33 by a plasma CVD method, and then a red filter is formed in a predetermined pattern as a light shielding film 28. Similarly, a polyimide resin is formed in a predetermined pattern as the protective film 29, and unnecessary portions such as wiring lead-out portions (not shown) are etched by the RIE method using the polyimide resin as a mask.

The light source in this embodiment uses a green LED having a wavelength of 550 nm, so that the light is selectively shielded.
Using a red filter with transmittance as shown in FIG. 11, 1
Sufficient light shielding is possible with a film thickness of about μm.

FIG. 12 shows a schematic plan view of the photodetector thus manufactured. In the figure, 11 is a MIS type sensor section, 12 is a switch TFT section, 13 is a signal wiring,
Reference numeral 14 is a gate wiring, and 15 is a sensor driving refresh wiring.

The shaded area in the figure is the light-shielding pattern in this embodiment. The pattern accuracy is improved to about several μ, and as a result, it is arranged directly on the switch TFT as in this embodiment.
It is possible to shield the inter-pixel region and form / arrange an opening region larger than the light receiving area of the photoelectric conversion element portion.

Here, the relationship between the size of the opening of the light shielding layer and the size of the light receiving portion will be described. Usually, for example, M
The pattern shift processed by the photolithography method using a PA exposure apparatus is about 3 μ at maximum. Therefore, a margin of about 3 μ is required for the size of the opening of the light shielding layer and the size of the light receiving portion. This is basically to prevent a reduction in the aperture ratio of the light receiving portion due to the pattern shift. That is, the MTF obtained as a result of repeating addition of a margin matched to the capability of the process of the photolithography method to the size of the opening of the light-shielding layer, transmission and reflection of the photodetector to the back surface of the substrate, and reflection on the front surface of the substrate again. It is necessary to minimize the deterioration of FIG. 13 shows an example. The shaded area in the figure is the light-shielding layer. Further, at this time, the gate film 16 of the pixel portion is provided with the above-mentioned margin in the size of the opening 17 of the light shielding layer, so that it is possible to prevent reflection in the substrate and prevent a decrease in MTF.

[Embodiment 2] As a second embodiment, a photodetector or the like using the MIS type photoelectric conversion element in Embodiment 1 and X
An X-ray detector using a phosphor or the like that converts radiation such as rays and γ rays into visible light will be described. FIG. 14 shows a schematic cross-sectional view of this embodiment. In the figure, 21 to 26 are the same as those in the first embodiment, and are composed of a glass substrate 21, a gate electrode 22, a gate insulating film 23, a photoelectric conversion layer and a TFT semiconductor layer 24, an ohmic contact layer 25, and source / drain electrodes 26. It Further, 30 is a magenta filter,
The magenta filter 30 is formed on the N protective film 33. In addition, 32 is a phosphor, which is an adhesive agent 3 such as epoxy.
Bonded by 1.

In this embodiment, radiation is emitted from the upper part of FIG. 14, the phosphor 32 is converted into visible light having the emission intensity as shown in FIG. 15, and the converted light is selectively shielded. In addition, the magenta filter 30 having the transmittance as shown in FIG. 16 is used as a light shielding film. At this time, sufficient light shielding is possible with a film thickness of about 1 μm.

In this way, by selecting a light-shielding film corresponding to the emission wavelength of the phosphor and enabling thinning, it can be directly arranged on the switch TFT as in the first embodiment, and the photoelectric conversion element part It is possible to form and arrange an opening region larger than the light receiving area.

[Embodiment 3] As another embodiment, a light shielding method for a color photodetector will be described. In this embodiment, R, G and B pixels are respectively assigned to R, G and B pixels.
When forming a filter, the TFT of each pixel is simultaneously
It is also formed in a light-shielding portion such as a portion. FIG. 17 shows a schematic sectional view according to this embodiment. In the figure, 21 is a glass substrate, 501, 502 and 503 respectively correspond to R, G and B pixels, and each pixel is composed of a TFT section 504 and a photodetection section 505. Further, 33 is a SiN protective film, 51 is a red filter, 52 is a green filter, 53 is a blue filter, and 29 is a PI protective film. Since each layer can have a sufficient filter function with a film thickness of about 1 μm, sufficient pattern accuracy can be obtained. Furthermore, R, G,
Since B is stacked, it is possible to block light on each TFT portion 504.

Further, each filter is sequentially formed in a predetermined area, and the area where all the R, G, B filters are laminated covers the TFT section 504, and the photodetection section 50 is formed.
The pattern has an opening area larger than 5. In this way, it is possible to form the light shielding film at the same time when the color filter is formed.

[0037]

As described above, according to the present invention,
The light-shielding member in the photodetector is a member that selectively shields the incident light wavelength or the wavelength having sensitivity to the switch TFT, thereby reducing the thickness of the light-shielding film that has been conventionally required. It becomes possible. as a result,
A fine pattern can be realized, and at least a switch TFT can be sufficiently shielded from light without reducing the sensor aperture ratio, and a light shielding layer forming an aperture region larger than the light receiving area of the photoelectric conversion element can be arranged. This makes it possible to realize a photodetector with a high S / N ratio, which reduces TFT leakage current and crosstalk.

[Brief description of drawings]

FIG. 1 is a graph showing the relative sensitivity of an a-Si film for explaining the present invention.

FIG. 2 is a graph showing the relative emission intensity of CsI: Tl of the fluorescent material for explaining the present invention.

FIG. 3 is a graph showing the overall sensitivity and the transmittance of a light-shielding film by an a-Si film and CsI: Tl for explaining the present invention.

FIG. 4 is a schematic cross-sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 5 is a schematic sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 6 is a schematic cross-sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 7 is a schematic sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 8 is a schematic cross-sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 9 is a schematic cross-sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 10 is a schematic cross-sectional view showing formation of the photodetector of the first embodiment according to the present invention.

FIG. 11 is a graph of wavelength dispersion of the transmittance of the red filter in the light shielding film used in the first example according to the present invention.

FIG. 12 is a schematic plan view of the photodetector of the first embodiment according to the present invention.

FIG. 13 is a schematic plan view of the photodetector of the first embodiment according to the present invention.

FIG. 14 is a schematic sectional view of an X-ray detector according to a second embodiment of the present invention.

FIG. 15 is a graph showing emission intensity dispersion of the phosphor of Example 2 according to the present invention.

FIG. 16 is a graph of wavelength dispersion of the light shielding film of the second embodiment according to the present invention.

FIG. 17 is a schematic sectional view of a photodetector according to a third embodiment of the present invention.

FIG. 18 is a schematic cross-sectional view of a conventional one-dimensional photodetector and a 1-bit equivalent circuit.

FIG. 19 is a schematic plan view and a schematic sectional view of a conventional two-dimensional photodetector.

FIG. 20 is a graph showing a relationship between a conventional incident light amount, a sensor output, and a TFT leak current.

FIG. 21 is a graph showing the relationship between the film thickness of a conventional light-shielding film and the pattern accuracy.

FIG. 22 is a schematic layout diagram showing a pixel array of a conventional photodetector.

[Explanation of symbols]

101 TFT type sensor section 102 Switch TFT section 103 Charge storage section 21, 201, 401 Glass substrate 22, 202, 402 Cr gate electrode 23, 203, 403 SiN gate insulating film 24, 204, 404 i-type amorphous Si 25, 205, 405 n ⁺ type amorphous Si 26, 206, 406 Al SD electrode 27, 207, 407 SiN protective film 28, 30 light-shielding film 29 protective film 31 adhesive layer 32 phosphor 51, 52, 53 R, G, B filter 410, 411, 412 p-type, i-type, n-type amorphous Si 413 Cr electrode 414 ITO transparent electrode 501, 502, 503, 504 R, G, B pixel part and TFT part 11 MIS type sensor part 12 switch TFT section 13 signal wiring 14 gate wiring 15 sensor drive wiring

Claims (5)

[Claims] 1. At least a photoelectric conversion element and a switch TF
In the photodetector device having T, a photodetector device is provided, which shields at least the switch TFT and forms an opening region larger than the light receiving area of the photoelectric conversion element. . 2. The inverted stagger type TF is used for the photoelectric conversion element.
T, which is composed of a drive wiring for driving the photoelectric conversion element, a gate wiring for driving the switch TFT, and a signal wiring connected to the switch TFT. The photodetector according to item 1. 3. The photoelectric conversion element is a PIN type photodiode, a drive wiring for driving the photoelectric conversion element, a gate wiring for driving the switch TFT, and a signal connected to the switch TFT. The photodetector according to claim 1, wherein the photodetector comprises a wiring. 4. The photoelectric conversion element is a MIS-type photoelectric conversion element composed of a first electrode layer, an insulating layer, a semiconductor layer, a carrier injection blocking layer into the semiconductor layer, and a second electrode layer. 2. A drive line for driving the photoelectric conversion element, a gate line for driving the switch TFT, and a signal line connected to the switch element. The photodetector according to. 5. The photodetector according to claim 1, wherein the semiconductor layer is an amorphous silicon thin film.