Photodiode array and image sensor

Abstract

Disclosed is a photodiode array and an image sensor. The photodiode array includes a plurality of elementary elements arranged on a substrate. Each of the plurality of elementary elements includes an upper electrode, a lower electrode, a photoelectric conversion region between the upper electrode and the lower electrode, a lower conductive portion below the lower electrode, and an insulating layer between the lower electrode and the lower conductive portion. The lower conductive portion at least partially overlaps the lower electrode with the insulating layer interposed therebetween when viewed in plan.

Description

Technical Field

[0001] This invention relates to photodiode arrays. Background Technology

[0002] Flat panel detectors (FPDs) used in image sensors, such as X-ray sensors, have been improved for higher accuracy. FPDs used in X-ray sensors are generally classified into direct conversion type and indirect conversion type. Indirect conversion type FPDs consist of a light-emitting material (scintillator) that converts X-rays into light (such as visible light or ultraviolet light) and a photodiode array that converts the light into an electrical signal in its X-ray detection panel. Summary of the Invention

[0003] The increased accuracy of FPDs has created a demand for technologies that utilize photodiode arrays to detect light efficiently and accurately.

[0004] One aspect of the present invention is a photodiode array comprising a plurality of basic elements arranged on a substrate. Each of the plurality of basic elements includes: an upper electrode; a lower electrode; a photoelectric conversion region located between the upper electrode and the lower electrode; a lower conductive portion located below the lower electrode; and an insulating layer located between the lower electrode and the lower conductive portion. When viewed in a plan view, the lower conductive portion at least partially overlaps the lower electrode across the insulating layer.

[0005] One aspect of the present invention improves the characteristics of photodiode arrays.

[0006] It should be understood that the foregoing overview and the following detailed description are exemplary and illustrative, and do not limit the invention. Attached Figure Description

[0007] Figure 1 This is a block diagram illustrating the structure of the image sensor in the embodiment;

[0008] Figure 2 This is a circuit diagram of the equivalent circuit of the pixels of the image sensor in the implementation method.

[0009] Figure 3A It is a plan view that schematically illustrates an example of the structure of pixels, gate lines, and signal lines;

[0010] Figure 3B It is along Figure 3A The cross-sectional view taken by section line IIIB-IIIB' in the diagram;

[0011] Figure 3C It is along Figure 3A The cross-sectional view taken by section line IIIC-IIIC' in the diagram;

[0012] Figure 4 References are shown Figures 3A to 3C The pixel capacitor in the described structure;

[0013] Figure 5A This is a plan view schematically illustrating another example of the structure of pixels, gate lines, and signal lines;

[0014] Figure 5B It is along Figure 5A The cross-sectional view taken by the section line VB-VB' in the diagram;

[0015] Figure 5C It is along Figure 5A The cross-sectional view taken by the section line VC-VC' in the diagram;

[0016] Figure 6A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0017] Figure 6B It is along Figure 6A The cross-sectional view taken by section line VIB-VIB' in the diagram;

[0018] Figure 7A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0019] Figure 7B It is along Figure 7A The cross-sectional view taken by section line VIIB-VIIB' in the diagram;

[0020] Figure 8A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0021] Figure 8B It is along Figure 8A The cross-sectional view taken by section line VIIIB-VIIIB' in the diagram;

[0022] Figure 9A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0023] Figure 9B It is along Figure 9A The cross-sectional view taken by section line IXB-IXB' in the diagram;

[0024] Figure 10A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0025] Figure 10B It is along Figure 10A The cross-sectional view taken by the section line XB-XB' in the diagram;

[0026] Figure 11A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0027] Figure 11B It is along Figure 11A The cross-sectional view taken by the section line XIB-XIB' in the diagram;

[0028] Figure 12A This is a plan view that schematically illustrates yet another example of the structure of pixels, gate lines, and signal lines;

[0029] Figure 12B It is along Figure 12A The cross-sectional view taken by the section line XIIB-XIIB' in the diagram;

[0030] Figure 13A This is a plan view schematically illustrating yet another example of the structure of pixels, gate lines, and signal lines; and

[0031] Figure 13B It is along Figure 13A The cross-sectional view taken by section line XIIIB-XIIIB' in the diagram. Detailed Implementation

[0032] In the following description, photodiode arrays related to embodiments of this specification will be specifically described with reference to the accompanying drawings. These photodiode arrays are suitable for image sensors. However, the structure of the photodiode arrays of the present invention is also suitable for devices other than image sensors.

[0033] The dimensions or scale of the components in each accompanying figure may vary depending on the context to ensure good identification within the figure. Shaded lines in the figures are used to distinguish components, not to represent cross-sections. Nonlinear components used as switching or amplifying elements are called transistors. Transistors include thin-film transistors (TFTs).

[0034] The photodiode array in the embodiments of this specification includes a plurality of pixels arranged on a substrate. Each pixel includes a lower conductive portion and a photodiode sandwiched between a lower electrode and an upper electrode. The lower conductive portion is located below the lower electrode, and an insulating layer is inserted between the lower conductive portion and the lower electrode. In addition to the junction capacitor included between the lower electrode and the upper electrode, the pixel capacitor also includes an additional capacitor between the lower electrode and the lower conductive portion. Therefore, the pixel capacitor can have a larger capacitance to improve pixel characteristics.

[0035] The image sensor of this invention is applicable to X-ray imaging equipment in the fields of medical and industrial non-destructive testing. The light to be detected is electromagnetic radiation of any frequency, which can be infrared, visible light, or X-rays.

[0036] Structure of an image sensor

[0037] Figure 1 This is a block diagram illustrating an example structure of an image sensor according to an embodiment of this specification. The image sensor 10 includes a sensor substrate 11 and a control circuit. The control circuit includes a driver circuit 14, a signal detector circuit 16, and a main control circuit 18.

[0038] The sensor substrate 11 includes an insulating substrate (e.g., a glass substrate) and pixel regions 12 on the insulating substrate. Within the pixel regions 12, pixels 13 are arranged horizontally and vertically (as in a matrix). Pixels 13 are examples of basic elements on the insulating substrate, including photodiodes. The layout of the pixels 13 is not limited to... Figure 1 The matrix layout is shown. Pixel region 12 may include a scintillator that fluoresces in response to the radiation to be detected.

[0039] Pixel 13 is positioned at the intersection of multiple signal lines 106 and multiple gate lines (scan lines) 105. Figure 1 In this configuration, signal lines 106 are arranged to extend vertically and are spaced apart horizontally. Gate lines 105 are arranged to extend horizontally and are spaced apart vertically. Each pixel 13 is connected to a bias line 107. Figure 1 In this configuration, the offset lines are arranged to extend vertically and are spaced apart from each other in the horizontal direction. Figure 1 In the figure, only one pixel, one signal line, one gate line and one bias line are respectively labeled 13, 106, 105 and 107.

[0040] Each signal line 106 is connected to a different pixel column. Each gate line 105 is connected to a different pixel row. Signal lines 106 are connected to signal detector circuit 16, and gate lines 105 are connected to driver circuit 14. Each bias line 107 is connected to a common bias line 108. The pad 109 of the common bias line 108 is provided with a bias potential. Driver circuit 14 drives the gate lines 105 of pixel 13 for light detection of pixel 13. Signal detector circuit 16 detects signals from each signal line. Main control circuit 18 controls driver circuit 14 and signal detector circuit 16.

[0041] Pixel circuit structure

[0042] Figure 2This is a circuit diagram showing the equivalent circuit of a pixel 13. Pixel 13 includes a photodiode 121 as a photoelectric conversion element and a thin-film transistor (TFT) 122 as a switching element. The gate terminal of the TFT 122 is connected to the gate line 105, one of the source and drain terminals is connected to the signal line 106, and the other of the source and drain terminals is connected to the cathode terminal of the photodiode 121. Figure 2 In the example, the anode terminal of photodiode 121 is connected to bias line 107.

[0043] Thin-film transistor 122 can be an amorphous silicon (a-Si) thin-film transistor, a polycrystalline silicon thin-film transistor, or an oxide semiconductor thin-film transistor. Thin-film transistor 122 can be of n-conductivity type.

[0044] Pixel 13 also includes a junction capacitor 125 for the photodiode 121 and a capacitor element 126. The junction capacitor 125 and the capacitor element 126 are connected in parallel with the photodiode 121 between the switching TFT 122 and the bias line 107.

[0045] The image sensor 10, used as an X-ray imaging device, stores a signal charge corresponding to the amount of light incident on the photodiode 121 in the junction capacitor 125 and the capacitor element 126. The pixel 13, which includes not only the junction capacitor 125 of the photodiode 121 but also the capacitor element 126, obtains a greater amount of saturated signal without changing the manufacturing conditions of the photodiode 121.

[0046] The main control circuit 18 reads signals by turning on the thin-film transistor 122 in the pixel 13 to extract the charge stored in the junction capacitor 125 and the capacitor element 126 to the outside.

[0047] Specifically, the driver circuit 14 selects each gate line 105 sequentially and applies pulses to turn on the thin-film transistor 122. The anode terminal of the photodiode 121 is connected to the bias line 107, and a reference potential is provided to the signal line 106 by the signal detector circuit 16. Therefore, the photodiode 121 is charged to the differential voltage between the bias potential of the bias line 107 and the reference potential. Typically, this differential voltage is set as a reverse bias voltage where the cathode potential is higher than the anode potential.

[0048] The charge required to recharge photodiode 121 to the reverse bias voltage depends on the amount of light incident on photodiode 121. Signal detector circuit 16 reads the signal charge by integrating the flowing current during the process of recharging photodiode 121 to the reverse bias state.

[0049] When reading signal charge, the voltage at the terminal of thin-film transistor 122 connected to signal line 106 is higher than the voltage at the terminal connected to photodiode 121. Therefore, in signal charge detection, the terminal connected to signal line 106 is the drain, and the terminal connected to photodiode 121 is the source. Pixel 13 may include... Figure 2 Additional components not shown, such as additional thin-film transistors.

[0050] Example of pixel structure

[0051] The following describes some examples of the component structure of pixel 13. The photodiode 121, thin-film transistor 122 and capacitor element 126 included in pixel 13 each have a stacked structure on an insulating substrate.

[0052] Figure 3A This is a plan view schematically showing the structure of pixel 13, gate line 105, and signal line 106. Figure 3A In the diagram, signal line 106 extends vertically, gate line 105 extends horizontally, and thin-film transistor 122 is arranged at the intersection of signal line 106 and gate line 105.

[0053] Pixel 13 includes a lower electrode 201 and an upper electrode 205. Figure 3A In the structural example, when viewed in a plan view, the entire upper electrode 205 overlaps with the lower electrode 201. In other words, when viewed in a plan view, the entire area of ​​the upper electrode 205 is included within the area of ​​the lower electrode 201. As described below, the photodiode 121 is sandwiched between the lower electrode 201 and the upper electrode 205.

[0054] Pixel 13 also includes a thin-film transistor 122, a lower conductive portion 210, and a bias electrode 221. The thin-film transistor 122 includes a gate electrode 251, a semiconductor portion 252, a source electrode 253, and a drain electrode 254.

[0055] As described below, the lower conductive portion 210 is located below the lower electrode 201. Figure 3A In the diagram, the portion of the lower conductive portion 210 covered by the lower electrode 201 is outlined by a dashed line. The lower conductive portion 210 includes an electrode region 211 and connector regions 212 and 213. The electrode region 211 is a wide region, and the width (horizontal length) of the connector regions 212 and 213 is smaller than the width of the electrode region 211. The connector regions 212 and 213 extend upward and downward from the electrode region 211, respectively.

[0056] The entire area of ​​electrode region 211 is covered by lower electrode 201. In other words, the entire electrode region 211 is opposite to lower electrode 201. Each of connector regions 212 and 213 is partially opposite to lower electrode 201, and the remainders extend outside lower electrode 201. Lower conductive portion 210 includes capacitor electrodes, which are the areas opposite to lower electrode 201.

[0057] Figure 3A The capacitor electrode in the example includes the entire area of ​​electrode region 211, a portion of connector region 212, and a portion of connector region 213. Figure 3A In the structural example, the capacitor electrode essentially corresponds to electrode region 211. The capacitor electrode, the portion of the lower electrode 201 opposite to the capacitor electrode, and the insulating portion between this portion and the capacitor electrode constitute the capacitor element 126. Figure 3A In the structural example, when viewed in a plan view, the entire area of ​​electrode region 211 lies within the area of ​​lower electrode 201 and upper electrode 205.

[0058] Bias electrode 221 interconnects the lower conductive portion 210 and the upper electrode 205. Specifically, contact area (interconnection area) 225 interconnects the connector area 212 of the lower conductive portion 210 and the bias electrode 221. Another contact area 226 interconnects the upper electrode 205 and the bias electrode 221.

[0059] exist Figure 3A In the structural example, multiple lower conductive parts 210 arranged along the signal line are connected to transmit a bias potential. Figure 3A In the structural example, the lower conductive portion 210 is connected to its vertically adjacent lower conductive portion 210 via connector regions 212 and 213. The lower conductive portions 210 are not connected to their horizontally adjacent lower conductive portions 210, but are spaced apart from each other. Each bias line 107 includes a group of lower conductive portions 210 connected in a line. A bias potential is supplied from the lower conductive portion 210 of pixel 13 to the upper electrode 205 via bias electrode 221.

[0060] The bias electrode 221 is connected to the lower conductive portion 210 at contact region 225 and to the upper electrode 205 at contact region 226. The bias electrode 221 does not extend through the region of the upper electrode 205. When viewed in plan view, the distal end of the bias electrode 221 in the direction from contact region 225 to contact region 226 is located above the upper electrode 205. In other words, the bias electrode 221... Figure 3A The end drawn below the contact area 226 is located above the upper electrode 205.

[0061] Contact area 225 is located outside the upper electrode 205 and the lower electrode 201. Each of the upper electrode 205 and the lower electrode 201 has a groove. Contact area 225 is located in the groove region of the lower electrode 201. The distance from the center of contact area 226 to the end of the upper electrode 205 (where a virtual straight line starting from the center of contact area 225 and passing through the center of contact area 226 first intersects the end) is shorter than the distance between the two ends of the upper electrode 205 (where the same virtual line intersects the two ends), for example, less than half the distance between the two ends of the upper electrode 205.

[0062] Furthermore, when viewed in a plan view, the ends of the bias electrode 221 on the left and right sides of the contact area 226 are located above the upper electrode 205. This small overlap between the bias electrode 221 and the upper electrode 205, as described above, increases the light-receiving area of ​​the photodiode 121.

[0063] exist Figure 3A In the structural example, when viewed in plan view, the lower conductive portion 210 is away from both the gate line 105 and the signal line 106, and does not overlap with them. Similarly, when viewed in plan view, the lower electrode 201 and the upper electrode 205 are also away from both the gate line 105 and the signal line 106, and do not overlap with them. Furthermore, when viewed in plan view, the lower conductive portion 210 is away from the semiconductor portion 252, and does not overlap with it. Likewise, when viewed in plan view, the lower electrode 201 and the upper electrode 205 are also away from the semiconductor portion 252, and do not overlap with it.

[0064] Next, the description Figure 3A The cross-sectional structure of pixel 13 shown. Figure 3B It is along Figure 3A The cross-sectional view taken by section line IIIB-IIIB' in the diagram. Figure 3C It is along Figure 3A The cross-sectional view is taken by section line IIIC-IIIC'. For the following description, some component reference numerals may be omitted from the accompanying drawings.

[0065] refer to Figure 3B and Figure 3C Thin-film transistor 122 (see Figure 3A It includes a gate electrode 251 disposed on an insulating substrate 271, a gate insulating layer 272 above the gate electrode 251, and a semiconductor portion 252 above the gate insulating layer 272.

[0066] like Figure 3AAs shown, gate electrode 251 is an upwardly projecting portion from the horizontally extending gate line 105; gate electrode 251 extends from gate line 105. Gate electrode 251 and gate line 105 are formed on insulating substrate (insulating layer) 271 and are included in the same conductive layer. A silicon insulating layer may be disposed between insulating substrate 271 and the conductive layer of gate electrode 251 and gate line 105.

[0067] Unseparated or separated conductive components included in the same conductive layer are made of the same material and are located above and in direct contact with the same insulating layer. During manufacturing, conductive components in the same conductive layer are produced in the same manufacturing step. The conductive layer can have a single-layer or multi-layer structure.

[0068] In this structural example, the thin-film transistor 122 has a bottom gate structure, and the gate electrode 251 is located below the semiconductor portion 252. The thin-film transistor 122 also includes electrodes 253 and 254 located above the gate insulating layer 272. Electrodes 253 and 254 are included in the same conductive layer.

[0069] Depending on the flow of charge carriers, one of electrodes 253 and 254 is the source electrode, and the other is the drain electrode. When detecting the charge of photodiode 121, electrode 253 is the source electrode, and electrode 254 is the drain electrode. Therefore, electrode 253 will be referred to as the source electrode and electrode 254 as the drain electrode in the following text.

[0070] The source electrode 253 and the drain electrode 254 are in direct contact with the semiconductor section 252. The source electrode 253 and the drain electrode 254 are formed to contact a portion of the top surface and the side surface of the island-shaped semiconductor section 252.

[0071] The gate insulating layer 272 is formed to completely cover the gate electrode 251. The gate insulating layer 272 is disposed between the gate electrode 251 and the semiconductor portion 252. The first interlayer insulating layer 273 covers the entire thin-film transistor 122. Specifically, the first interlayer insulating layer 273 covers the top surface of the semiconductor portion 252, the top surface of the source electrode 253, and the top surface of the drain electrode 254.

[0072] The substrate 271 can be made of glass or resin. The gate electrode 251 is a conductor and can be made of a metal or silicon doped with impurities. The gate insulating layer 272 can be made of thermally oxidized silicon. The semiconductor of the semiconductor portion 252 can be an oxide semiconductor or amorphous silicon. The oxide semiconductor includes at least one of In, Ga, and Zn, and examples of oxide semiconductors include amorphous InGaZnO (a-InGaZnO) and microcrystalline InGaZnO.

[0073] The source electrode 253 and drain electrode 254 are conductors and may be, for example, metal layers or laminates of Mo, Ti, Al, or Cr or their alloys. The first interlayer insulating layer 273 is made of an inorganic or organic insulator. Although Figure 3A and Figure 3B The thin-film transistor 122 shown has a bottom gate structure, but the thin-film transistor 122 may have a top gate structure or include both a top gate electrode and a bottom gate electrode.

[0074] A lower conductive portion 210 is disposed above the first interlayer insulating layer 273. The lower conductive portion 210 is in direct contact with the first interlayer insulating layer 273. The lower conductive portion 210 is located above the gate electrode 251 and the gate line 105, and below the lower electrode 201. The first interlayer insulating layer 273 is located between the lower conductive portion 210 and the conductive layers of the gate electrode 251 and the gate line 105. A second interlayer insulating layer 274 is disposed between the lower conductive portion 210 and the lower electrode 201. The second interlayer insulating layer 274 is made of an inorganic or organic insulator. In this example, the second interlayer insulating layer 274 is in direct contact with the lower electrode 201 and the lower conductive portion 210.

[0075] When viewed from a floor plan, as Figures 3A to 3C As shown, the lower electrode 201 at least partially overlaps with the lower conductive portion 210, wherein a second interlayer insulating layer 274 is inserted between the lower electrode 201 and the lower conductive portion 210. In other words, when viewed in a plan view, at least a portion of the lower electrode 201 covers at least a portion of the lower conductive portion 210. In this structural example, a portion of the lower electrode 201 is located above a portion of the lower conductive portion 210.

[0076] like Figure 3B As shown, the lower electrode 201 is connected to the source electrode 253 of the thin-film transistor 122 through a contact region 227 in a through-hole formed through the second interlayer insulating layer 274 and the first interlayer insulating layer 273. The lower electrode 201 is a conductor and may be a metal layer or a laminate of these materials, such as Cr, Mo, or Al or alloys thereof.

[0077] The photodiode 121 consists of a photoelectric conversion region sandwiched between the lower electrode 201 and the upper electrode 205, and portions of the lower electrode 201 and the upper electrode 205 that are in contact with the photoelectric conversion region. Figure 3B and Figure 3C The example of photodiode 121 shown is a PIN diode. PIN diodes have a thick depletion layer in terms of film thickness to efficiently detect light. The upper electrode 205 is a transparent electrode for light from the scintillator, and it can be made of ITO.

[0078] The photoelectric conversion region of photodiode 121 includes an n-type amorphous silicon layer (film) 202 located above the lower electrode 201, an intrinsic amorphous silicon layer (film) 203 located above the n-type amorphous silicon layer 202, and a p-type amorphous silicon layer (film) 204 located above the intrinsic amorphous silicon layer 203. In this structural example, the n-type amorphous silicon layer 202 is in direct contact with the lower electrode 201.

[0079] The upper electrode 205 is disposed above the p-type amorphous silicon layer 204. In this structural example, the upper electrode 205 is in direct contact with the p-type amorphous silicon layer 204. The light to be detected enters the photodiode 121 through the upper electrode 205. The positions of the n-type amorphous silicon layer 202 and the p-type amorphous silicon layer 204 can be reversed, and the intrinsic amorphous silicon layer 203 can be removed.

[0080] The third interlayer insulating layer 275 is configured to cover the lower electrode 201, silicon layers 202 to 204, and the upper electrode 205. The third interlayer insulating layer 275 is made of an inorganic or organic insulator. The bias electrode 221 and the signal line 106 are disposed above the third interlayer insulating layer 275. In this example, the bias electrode 221 and the signal line 106 are in direct contact with the third interlayer insulating layer 275. The signal line 106 is connected to the drain electrode 254 of the thin-film transistor 122 through a contact region 228 in a via formed through the third interlayer insulating layer 275, the second interlayer insulating layer 274, and the first interlayer insulating layer 273.

[0081] The bias electrode 221 is connected to the upper electrode 205 via a contact area 226 provided in a through-hole formed through the third interlayer insulating layer 275. The bias electrode 221 is also connected to the lower conductive portion 210 via contact areas 225 provided in through-holes formed through the third interlayer insulating layer 275 and the second interlayer insulating layer 274. The bias electrode 221 is a conductor and may be, for example, a metal layer of Mo, Ti, or Al or an alloy thereof, or a laminate of these materials.

[0082] A passivation layer (film) 276 is provided to cover the signal line 106, the bias electrode 221, and the third interlayer insulating layer 275. The passivation layer 276 covers the entire area of ​​the pixel region 12. The passivation layer 276 is made of an inorganic or organic insulator. A scintillator (not shown) is disposed above the passivation layer 276.

[0083] The scintillator covers the entire pixel area 12. The scintillator emits light upon excitation by radioactive radiation. Specifically, the scintillator converts received X-rays into light with a wavelength detectable by the photodiode 121. The photodiode 121 generates a signal charge of the same amount as the light from the scintillator and stores this signal charge in the junction capacitor 125 and the capacitor element 126 (see [link to documentation]). Figure 2 ).

[0084] In the above structural example, the photodiode 121 is positioned above the thin-film transistor 122. This arrangement is advantageous because the insulating layer causes less attenuation of the received light, and the fabrication of the thin-film transistor and photodiode in semiconductor processes is easier.

[0085] Reference Figures 3A to 3C In the described structure, a bias potential is supplied to the upper electrode 205 from the lower conductive portion 210 located below the upper electrode 205 via the bias electrode 221. For example... Figure 3A As shown, the bias electrode 221 covers only a portion of the end of the upper electrode 205. Compared to a structure where the bias line extends end-to-end above the upper electrode 205, this structure allows the upper electrode 205 to have a small area covered by a conductor, enabling the photodiode 121 to have a large light-receiving area.

[0086] Photodiode arrays require higher resolution and accuracy. These requirements are met by reducing pixel size. However, reducing pixel size reduces the area of ​​the photodiode. The junction capacitance of the photodiode also becomes smaller to reduce saturation signal.

[0087] The saturation semaphore is one of the factors determining the dynamic range. The upper limit of the dynamic range is determined by the saturation semaphore, which is determined by the pixel capacitance and bias potential. The dynamic range depends not only on the saturation semaphore but also on the magnitude of noise generated by various factors, such as the dark current of the photodiode. The lower limit of the dynamic range is determined by the magnitude of the noise.

[0088] Dark current depends on the bias potential, so it can be reduced by decreasing the bias potential. However, decreasing the bias potential also reduces the saturation signal intensity without increasing the dynamic range. If the saturation signal intensity decreases, the photodiode cannot output a signal corresponding to the intensity of light (X-rays) when it receives light with an intensity higher than the saturation signal intensity.

[0089] Therefore, it is necessary to increase the saturation signal intensity while limiting the pixel size. As mentioned above, the saturation signal intensity depends on the pixel capacitance and bias potential, and can be increased by increasing the pixel capacitance.

[0090] Figure 4 References are shown Figures 3A to 3C The pixel capacitor in the described structure. Pixel 13 includes the junction capacitor Cpd of the photodiode 121 and the capacitor Cadd between the lower electrode 201 and the lower conductive portion 210. That is, the lower electrode 201 and the lower conductive portion 210 together with the insulating layer between them (part of the interlayer insulating layer 274) form an additional capacitor element.

[0091] As described above, a lower conductive portion 210, similar to an electrode, is provided below the lower electrode 201, generating a capacitor between the lower electrode 201 and the lower conductive portion 210. The generated capacitor corresponds to an additional capacitor element 126 connected in parallel with the junction capacitor 125 of the photodiode 121 (see [link to documentation]). Figure 2 Therefore, the pixel capacitance is increased to improve the saturation signal of the pixel.

[0092] Especially for products with small-sized pixels, it is difficult to change the junction capacitance according to manufacturing conditions because it affects other characteristics such as quantum efficiency and dark current. However, this structure includes a capacitive element using a conductive layer located below the lower electrode 201, thus increasing the saturation signal intensity with almost no change to the manufacturing conditions of the photodiode 121. Furthermore, depending on the application or purpose, the additional capacitance Cadd can be changed as desired by altering the size of the lower conductive portion 210 or its distance from the lower electrode 201.

[0093] This structure avoids reducing the saturation signal strength, but dark current can be reduced by adding a capacitor 126 in parallel with the photodiode 121 and using a low bias potential. Therefore, this structure can increase the aforementioned dynamic range.

[0094] Since the lower conductive portion 210 is located below the lower electrode 201, its area can be increased without affecting the light receiving area. Therefore, this structure reduces the possibility of open circuits and further effectively reduces the noise caused by the gate line 105.

[0095] Reference Figure 3B and Figure 3C In the described structure, the layer located between the gate line 105 and the lower electrode 201 includes a lower conductive portion 210. This structure results in a small parasitic capacitance generated by the pixel electrode and the gate line 105 (due to the electrostatic shielding effect of the electrode with a fixed potential). When the parasitic capacitance is small, the noise added to the lower electrode 201 by the gate line 105 is reduced.

[0096] A more detailed explanation is provided below. When the lower electrode 201 is connected to the gate line 105 via a parasitic capacitor, the gate line 105 becomes a noise source with a noise voltage Vn. Therefore, a noise current flows through the parasitic capacitor to the lower electrode 201, and noise is generated at the lower electrode 201 through electrostatic induction. The magnitude of this noise is proportional to the parasitic capacitance.

[0097] The lower conductive portion 210, located midway between the gate line 105 and the lower electrode 201, divides the parasitic capacitance between the gate line 105 and the lower electrode 201 into three capacitors: a capacitor between the gate line 105 and the lower electrode 201, a capacitor between the gate line 105 and the lower conductive portion 210, and a capacitor between the lower conductive portion 210 and the lower electrode 201. The lower conductive portion 210 is always fixed at a bias potential. Therefore, the noise current originating from the gate line 105 mainly flows between the gate line 105 and the lower conductive portion 210, thus reducing the noise current flowing into the lower electrode 201.

[0098] The arrangement of the lower conductive portion 210 for transmitting bias potential located below the lower electrode 201 increases the saturation signal amount of the pixel 13 and reduces the noise originating from the gate line 105.

[0099] As described above, the switching transistor of the pixel can be a semiconductor with desired characteristics. In one embodiment of this specification, the switching transistor has a mobility greater than 5 cm⁻¹. 2 / Vs Semiconductor Division.

[0100] Because the addition of capacitor element 126 increases the pixel capacitance, the write rate decreases after the transistor is turned on. Therefore, the signal charge of pixel 13 cannot be fully read, resulting in increased image hysteresis. Therefore, a switching element with the aforementioned mobility characteristic is used for more suitable and accurate signal reading. A thin-film transistor with this characteristic can be a switching transistor using a high-mobility semiconductor (e.g., oxide semiconductor or low-temperature polycrystalline silicon).

[0101] Other structural examples of pixels

[0102] The following text describes other structural examples of pixels. Figure 5A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 5B It is along Figure 5A The cross-sectional view taken by section line VB-VB' in the diagram. Figure 5C It is along Figure 5A The cross-sectional view is taken by the section line VC-VC'. The following is a main description and reference. Figures 3A to 3C The differences in the described structures.

[0103] This structural example includes a bias line 321 instead. Figures 3A to 3C The bias electrode 221 is in the bias line 321. Figure 5A The bias line 321 extends vertically along the middle and is connected to the upper electrode 305 of the plurality of pixels 13 through its contact area 323. The bias line 321 extends from one end of the upper electrode 305 to the opposite end. The bias line 321 may be made of the same material as the bias electrode 221.

[0104] Figure 5A The upper electrode 305 and lower electrode 301 in the structure are not like Figure 3A The upper electrode 205 and lower electrode 201 have grooves, as in the example. Figure 5B and Figure 5C As shown, the bias line 321 is disposed above the third interlayer insulating layer 275 and in direct contact with the third interlayer insulating layer 275. The bias line 321 is connected to the upper electrode 205 through the contact area 323 provided by the third interlayer insulating layer 275.

[0105] In pixel 13, the lower conductive portion 310 is not interconnected with the upper electrode 305 and is electrically isolated from the upper electrode 305. The lower conductive portion 310 includes an electrode region 311 and connector regions 312 and 313 extending vertically from the electrode region 311, such as... Figure 5C As shown. In this structural example, the widths of connector regions 312 and 313 are equal to or less than the width of bias line 321. The lower conductive portion 310 is connected to the lower conductive portion 310 of the vertically adjacent pixel 13 via connector regions 312 and 313. The lower conductive portion 310 can interconnect with the bias line 321 outside the pixel region 12.

[0106] In this structural example, for instance, a bias potential or constant potential different from the bias potential from the signal detector circuit 16 is provided to the lower conductive portion 310 of each column. The lower conductive portion 310, together with the lower electrode 301 and the second interlayer insulating layer 274, forms an additional capacitor element 126. The lower conductive portion 310 also serves to reduce noise from the gate line 105 to the lower electrode 301.

[0107] Figure 6A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 6B It is along Figure 6A The cross-sectional view is taken by section line VIB-VIB'. The following text mainly describes and references... Figures 3A to 3C The structures described differ. In this example structure, the lower conductive portion is included in the same conductive layer as the source and drain electrodes. This structure simplifies the manufacturing process.

[0108] like Figure 6B As shown, the lower conductive portion 400 is disposed above and in direct contact with the gate insulating layer 272. The lower conductive portion 400 is made of the same material as the source electrode 253 and drain electrode 254 of the thin-film transistor. The lower conductive portion 400 is included in the same layer as the source electrode 253 and drain electrode 254. The lower conductive portion 400 may have the same... Figure 3A The lower conductive part 210 has the same planar shape.

[0109] Figure 7A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 7B It is along Figure 7A The cross-sectional view taken by section lines VIIB-VIIB' in the diagram. The following is a main description and reference. Figures 3A to 3C The structures described are different. For example... Figure 7A As shown, in addition to the electrode region for the additional capacitor element 126, the lower conductive portion 410 in this structural example also includes a top gate electrode region 413.

[0110] The top gate electrode region 413 extends from the electrode region 211 toward the thin-film transistor 122. When viewed in plan view, the top gate electrode region 413 covers the channel region between the source electrode 253 and the drain electrode 254. The top gate electrode region 413 may cover only a portion of the channel region.

[0111] like Figure 7B As shown, a portion of the first interlayer insulating layer 273 is located between the top gate electrode region 413 and the semiconductor portion 252. The top gate electrode region 413 controls the threshold of the thin-film transistor 122. The top gate electrode region 413 also reduces the amount of light incident on the semiconductor portion 252.

[0112] As described above, oxide semiconductor TFTs with high mobility can be used as thin-film transistors 122. The threshold of an oxide semiconductor TFT readily changes in response to external stimuli such as light, voltage, and stress. Therefore, as... Figure 7A As shown, the thin-film transistor 122 has a dual-gate structure including a lower bottom gate electrode 251 and an upper top gate electrode 413, so that the threshold can be controlled by the top gate potential.

[0113] Each photodiode 121 in the photodiode array is typically fixed in reverse bias mode. When a negative potential is provided to the top gate electrode region 413, the threshold is shifted in the positive direction compared to the threshold in a single-gate structure due to the top gate potential. Therefore, if the threshold shifts in the negative direction due to external stimuli, the top gate has a compensating effect for the negative shift.

[0114] Figure 8A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 8B It is along Figure 8A The cross-sectional view is taken by section lines VIIIB-VIIIB'. The following is a main description and reference. Figures 3A to 3C The differences in the described structures.

[0115] like Figure 8AAs shown, the lower conductive portion 420 is connected not only to the lower conductive portions of the vertically adjacent pixels 13, but also to the lower conductive portions of the horizontally adjacent pixels 13. The lower conductive portion 420 is connected to the lower conductive portions of the horizontally adjacent pixels 13 via connector regions 214 and 215. Connector regions 214 and 215 are part of the lower conductive portion 420. This structure more effectively avoids the breakage of the bias line transmitting the bias potential.

[0116] Figure 9A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 9B It is along Figure 9A The cross-sectional view is taken by section line IXB-IXB'. The following mainly describes the cross-section. Figure 7A and Figure 7B The structures shown are different.

[0117] like Figure 9A As shown, the bias electrode 435 is connected to the top gate electrode region 433 of the lower conductive portion 430 via a contact region (first contact region) 437. The bias electrode 435 is also connected to the upper electrode 439 via a contact region (second contact region) 436. The bias electrode 435 may have the same characteristics as... Figure 7A The bias electrodes in it have the same shape.

[0118] like Figure 9B As shown, contact region 436 is configured to pass through the third interlayer insulating layer 275 to interconnect bias electrode 435 and upper electrode 439. Contact region 437 is configured to pass through the third interlayer insulating layer 275 and the second interlayer insulating layer 274 to interconnect bias electrode 435 and top gate electrode region 433 (lower conductive portion 430).

[0119] and Figure 7A Compared to the structural examples, Figure 9A The lower electrode 438 and upper electrode 439 in the thin-film transistor 122 do not have grooves on the other side. Therefore, this structure achieves a larger light-receiving area (aperture ratio) for the photodiode 121. Figure 9A As shown, the lower conductive portion 430 is connected to the lower conductive portion of the vertically adjacent pixel through connector region 432 and connector region 213.

[0120] Figure 10A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 10B It is along Figure 10A The cross-sectional view is taken by section line XB-XB'. The following mainly describes the cross-section. Figure 7A and Figure 7BThe structures shown differ. In this example, a photodiode is provided to cover all or part of the thin-film transistor when viewed in a plan view. A portion of the photodiode is located directly above the thin-film transistor. This structure increases the light-receiving area (aperture ratio) of the photodiode.

[0121] like Figure 10A As shown, the lower electrode 446 and the upper electrode 445 cover a portion of the thin-film transistor 122. In this example, the semiconductor portion 252 is completely covered by the lower electrode 446 and the upper electrode 445. Figure 10B As shown, the photoelectric conversion region 443 also covers a portion of the thin-film transistor 122. In this example, the photoelectric conversion region 443 is a PIN silicon laminate, and when viewed from a plan view, it covers the same area as the upper electrode 445.

[0122] Figure 11A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 11B It is along Figure 11A The cross-sectional view is taken by section line XIB-XIB'. The following mainly describes the cross-section. Figures 3A to 3C The structures shown are different.

[0123] In this structural example, the lower conductive portion 440 has an opening 444 in the electrode region 441. When viewed from a plan view, the opening 444 is located in the region covered by the lower electrode 201. Therefore, an additional capacitor with a desired capacitance can be obtained by adjusting the size of the opening 444.

[0124] exist Figure 11A In the structural example, when viewed from a plan view, electrode region 441 partially extends outside the upper electrode 205. When viewed from a plan view, the entire electrode region 441 is located within the region of the lower electrode 201. The lower conductive portion 440 is connected to the lower conductive portion of the vertically adjacent pixel 13 via connector regions 442 and 443.

[0125] Figure 12A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 12B It is along Figure 12A The cross-sectional view is taken by section line XIIB-XIIB'. The following mainly describes the cross-section. Figures 3A to 3C The structures shown are different.

[0126] exist Figure 12A and Figure 12BIn the structural example, when viewed from a plan view, the electrode region 451 of the lower conductive portion 450 partially extends outside the upper electrode 205 and the lower electrode 201. The portion of the electrode region 451 located outside the lower electrode 201 partially overlaps with the gate line 105. This structure can more effectively reduce noise from the gate line.

[0127] Figure 13A This is a plan view schematically showing another structure of pixel 13, gate line 105 and signal line 106. Figure 13B It is along Figure 13A The cross-sectional view taken by section lines XIIIB-XIIIB' in the diagram. The following mainly describes the cross-section. Figure 12A and Figure 12B The structures shown are different.

[0128] A portion of the lower electrode 461 is located directly above the gate line 105, and a portion of the electrode region 451 of the lower conductive portion 450 is inserted between this portion of the lower electrode 461 and the gate line 105. A portion of the upper electrode 465 and a portion of the photoelectric conversion region 467 are also located directly above the gate line 105, and a portion of the lower electrode 461 is inserted between this portion of the upper electrode 465 and this portion of the photoelectric conversion region 467 and the gate line 105. When viewed in plan view, the lower electrode 461, the upper electrode 465, and the photoelectric conversion region 467 extend to cover a portion of the gate line 105. Therefore, this structure further increases the light-receiving area (aperture ratio) of the photoelectric conversion region.

[0129] As described above, embodiments of the present invention have been presented; however, the present invention is not limited to the foregoing embodiments. Those skilled in the art can readily modify, add to, or transform each element of the foregoing embodiments within the scope of the present invention. A portion of the structure of one embodiment may be replaced by the structure of another embodiment, or the structure of one embodiment may be incorporated into the structure of another embodiment.

Claims

1. A photodiode array comprising a plurality of basic elements arranged on a substrate, each of the plurality of basic elements comprising: Upper electrode; Lower electrode; A photoelectric conversion region is located between the upper electrode and the lower electrode; A lower conductive portion, the lower conductive portion being located below the lower electrode; A first insulating layer is located between the lower electrode and the lower conductive portion; A switching transistor configured to switch whether the basic element is electrically connected to a signal line; Bias electrode; A first contact region is configured to overlap with a portion of the switching transistor when viewed in a plan view, and to electrically connect at least a portion of the bias electrode and the lower conductive portion of the channel covering the switching transistor when viewed in a plan view. and A second contact region is configured to electrically connect the bias electrode and the upper electrode. The switching transistor includes a source electrode and a drain electrode located below the lower electrode, and a gate electrode located below the source electrode and the drain electrode. Each of the plurality of basic elements includes a second insulating layer located between the lower conductive portion and the source electrode and the drain electrode. When viewed in a plan view, the lower conductive portion at least partially overlaps with the lower electrode through the first insulating layer, and The lower conductive portion is electrically insulated from the lower electrode, the source electrode, and the drain electrode.

2. The photodiode array according to claim 1, in, The plurality of basic elements are arranged in a matrix, and The lower conductive part is connected to other lower conductive parts that are horizontally and vertically adjacent to it.

3. The photodiode array according to claim 1, wherein, The source / drain electrodes of the switching transistor and the lower conductive portion are located on the same insulating layer and are made of the same material.

4. The photodiode array according to claim 1, wherein, When viewed from a plan view, the lower conductive portion has an opening in the region opposite to the lower electrode.

5. The photodiode array according to claim 1, wherein, When viewed in a plan view, a portion of the lower conductive portion covers at least a portion of the gate line, which is configured to transmit a signal to the gate electrode.

6. The photodiode array according to claim 5, wherein, When viewed in a plan view, a portion of the photoelectric conversion region covers at least a portion of the gate line.

7. An image sensor, comprising: The photodiode array according to claim 1; and A circuit configured to drive and control the photodiode array.

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