Photodetector for imaging applications

Abstract

A photodetector (100) for medical imaging applications, in particular for computed tomography applications, is provided. The photodetector (100) comprises a photodiode array (100a) having a plurality of photodiodes (110). Each has a bulk sensitive area (111) comprising amorphous material and a periphery (112) at a lithographically defined edge (112) of the photodiode (110). The photodetector (100) further comprises a metal bias line (132) directly at the periphery (112) of the bulk sensitive area (111) of the photodiode (110). A charge trapping suppression unit (130, 140) is provided configured to suppress trapping of charges at the edge (112) of the photodiode.

Description

Technical Field

[0001] This invention relates to a photodetector for imaging applications and a method for manufacturing a photodetector for imaging applications. Background Technology

[0002] In medical imaging applications such as computed tomography, photodetectors are required to detect incident photons. To reduce the cost of detectors for image acquisition applications, photodetectors with photodiodes based on amorphous materials have been proposed. However, due to defects along the bulk layer thickness and impurities present during deposition, trapping sites for charge carriers are generated in amorphous materials. Unlike their crystalline counterparts, photodetectors with amorphous materials are affected by charge trapping at defect sites at the material level, which degrades the performance of the photodetector.

[0003] US 2005 / 0111612 A1 discloses a computed tomography detector with an optical mask layer to reduce crosstalk artifacts.

[0004] US 2013 / 075591 A1 discloses a photodetector with a photodiode array. Each photodiode in the photodiode array has a main sensitive region and a periphery.

[0005] US 2011 / 0133060 A1 discloses a photodetector having a photodiode array having a plurality of photodiodes having a main sensitive region made of crystalline silicon.

[0006] WO 2012 / 120653 A1 also discloses a photodetector with a photodiode having a main sensitive region made of crystalline silicon.

[0007] WO 2018 / 0153591 discloses a photodetector having a plurality of photodiodes, each of which has a main sensitive region made of crystalline silicon resin.

[0008] US 2017 / 018588A1 discloses an X-ray imaging system that uses a photodiode as a photodetector. Summary of the Invention

[0009] One object of the present invention is to provide a photodetector for imaging applications with improved efficiency. Specifically, one object of the present invention is to provide a photodetector for medical applications that is cost-effective and allows for very rapid image acquisition.

[0010] This objective is achieved through a photodetector for imaging applications, particularly high-speed imaging applications. The photodetector comprises a photodiode array having multiple photodiodes. Each photodiode has a primary (light)-sensitive region and a periphery at a photolithographically defined edge of the primary sensitive region. The primary sensitive region comprises an amorphous material. The edge of the primary sensitive material can also comprise an amorphous material. The photodetector further includes a charge trapping suppression unit configured to suppress charge trapping at the edges of the photodetector. This is particularly advantageous because the negative impact of charge trapping at the edges of the photodetector on the performance of the photodetector is reduced.

[0011] The charge trapping suppression unit includes a metal bias line at the periphery of the body photosensitive material of the photodiode. The metal bias line can be connected to a voltage source to bias the metal bias line, thereby repelling charge carriers of the same polarity as the bias line. Thus, charges or charge carriers are repelled by electromagnetic force. The photodiode includes a bottom metal electrode, a body photosensitive material at a photolithographically defined edge, and a top metal electrode. The top metal electrode faces the incident light, and the bottom electrode faces away from the incident light.

[0012] The metal bias line does not contact the bottom and top metal electrodes. This is advantageous because it avoids short circuits between the bottom and top electrodes.

[0013] It should be noted that amorphous materials, specifically amorphous silicon, are cheaper than crystalline silicon.

[0014] According to an embodiment, the charge trapping suppression unit includes a shadow mask covering the photodiode array. The shadow mask has multiple openings smaller than the body sensitive region of the photodiode, such that the edges of the photodiode are covered by the shadow mask.

[0015] During the photolithography process, photodiodes are patterned, creating edges around their perimeter. This patterning of the photodiodes is performed to avoid lateral charge migration caused by potential bias differences between adjacent pixels, which can lead to crosstalk and degrade image quality. Pixels can be defined by pixelating the top or bottom of the photodiode or both metal electrodes.

[0016] According to an embodiment, each photodiode can be biased by a bias voltage, wherein the bias voltage is zero.

[0017] According to an embodiment, the photodiode has a bottom metal electrode, a host sensitive organic material, and a top metal electrode.

[0018] According to an embodiment, a method is provided for manufacturing a photodetector for imaging applications, specifically for computed tomography applications. A photodiode array having a plurality of photodiodes is fabricated using photolithography. Each photodiode has a main sensitive region and a periphery at a photolithographically defined edge of the photodiode. The main sensitive material comprises an amorphous material. A metal bias line is applied at the periphery of the main sensitive material of the photodiode, wherein the metal bias line can be connected to a voltage source to bias the metal bias line, repelling charges from trap sites at the edge of the photodiode. Additionally or alternatively, a shadow mask covering the region of the photodiode is provided. The shadow mask has a plurality of openings smaller than the main sensitive region of the photodiode, such that the edge of the photodiode is covered by the shadow mask.

[0019] According to an embodiment, a method for detecting photons using a photodetector is provided. A bias voltage is applied to a metal bias line and / or a shadow mask is provided over a photodiode. Photons are detected by an array of photodiodes. The photodiodes are biased to zero.

[0020] According to an embodiment, an imaging system is provided, which includes at least one photodetector as described above. The imaging system can be implemented as a computed tomography system or alternatively as an X-ray system. Specifically, the imaging system is a medical imaging system.

[0021] The shadow mask can be implemented as a photomask element that can be placed at the edge of the photodiode. Alternatively, the shadow mask can be patterned during photolithography, for example, in the form of a metallic element.

[0022] According to embodiments, photodetectors for imaging applications, specifically for computed tomography or X-ray applications, can reduce the high residual signal in amorphous photodiodes, thereby enabling faster image acquisition. This is achieved by providing a photodiode array having multiple photodiodes. A photodiode has a main photosensitive region and a periphery due to the lithographically defined edges surrounding the photosensitive region. A metal bias line, biased with appropriate voltage and polarity, is provided around the light rays or the periphery of the photodiode's photosensitive region, depending on which charge carriers are read from the photodiode to an external electronic device. As an alternative or addition to the metal bias line, a shadow mask is provided over the photodiode array having an opening smaller than the photosensitive region of the photodiode. Thus, the edges of the photosensitive array of photodiodes are covered by the shadow mask.

[0023] By using photodetectors, the occurrence rate of generated charge carriers (falling into the incident light absorptivity at defect sites typically concentrated at the edges of photodiodes) can be significantly suppressed. These sites exist at the edges of photodiodes and are a result of dangling bonds. They are dominant in smaller photodiodes. Therefore, the higher residual signal that produces hysteresis is caused by the slow release of charge carriers from the trap sites present at the edges of the photodiode. Due to the slow release of charge carriers from the charge trap sites (specifically at the edges of the photodiode), image hysteresis in photodetectors is detrimental to rapid image acquisition in medical imaging applications such as computed tomography (CT).

[0024] According to an embodiment, the imaging system with a photodetector is implemented as a computed tomography system or X-ray application. Here, a photodetector with a very fast response time and a very low residual signal is required. Preferably, for such an imaging system, specifically for computed tomography applications, the residual signal specification is below 1500–2000 ppm (parts per million) for a low light intensity level of approximately 10 nA from the photodiode output signal. Here, the photodetector is measured at a 0V bias, a 450 ms light pulse time, and a light signal level of 10 nanoamps. The response time of the photodiode in the photodetector according to the embodiment can be 10 μs for both rise and fall times.

[0025] If the size of the main sensitive region of a photodiode increases, the amount of main defects in the silicon of the photodiode also increases. This increase in defects leads to increased image hysteresis. Conversely, reducing the size of the main sensitive region will also reduce the amount of main defects. However, for smaller main sensitive regions, the effect of defects at the edges of the photodiode becomes more pronounced. In other words, the smaller the size of the main sensitive region, the more prominent the effect of its edges. Due to charge trapping at the edges of the photodiode, the effect of defects at the edges can become the dominant defect. A very high surface area to volume ratio in a photodiode will tend to exhibit the adverse effects of charge trapping in amorphous photodiodes. This will lead to a shorter response time for the photodiode. The width and / or length of the photodiode can be approximately 150 μm.

[0026] The silicon in the main sensitive region of a photodiode can be amorphous silicon or crystalline silicon. However, amorphous silicon is preferred to reduce the cost of the photodetector. Alternatively, the photodiode can also be made of organic semiconductors to further reduce the cost of the photodetector.

[0027] According to an embodiment, the photodetector includes a bottom metal electrode (e.g., indium tin oxide, ITO), a body (light)-sensitive material of the photodiode surrounding a photolithographically defined edge, and a top metal layer. A metal bias line is provided at the photolithographically defined edge of the photodiode. Preferably, this is implemented to avoid any connection to the two metal contacts to prevent short circuits. Connection to either the top or bottom electrode should also be avoided to achieve good efficiency in suppressing charge trapping at the edge of the photodiode. The metal bias line does not touch the bottom or top electrodes of the photodiode.

[0028] According to an embodiment, a computed tomography (CT) image having at least one photodetector as described above is provided.

[0029] Photolithography is used to manufacture photodiodes and photodetectors. Photodiodes are patterned with pixelated structures. Photolithography is a process used in microfabrication to pattern portions of thin films or the bulk of a substrate. Specifically, light is used to transfer a geometric pattern from a photomask to a photosensitive resist. The photoresist is exposed and developed. Alternatively, etching can be used to create the desired structure. Thus, photodiodes have edges created during the photolithography process. Depending on the properties of the amorphous material, etching can be performed using either dry or wet etching processes. Amorphous silicon can be readily dry-etched.

[0030] According to an embodiment, a medical imaging system in the form of an X-ray computed tomography system is provided. The imaging system includes at least a photodetector and a continuous X-ray source as described above. The photodiode of the photodetector is not reverse-biased but has a zero-bias voltage. Therefore, a medical imaging system is provided having a low-cost photodetector with a photodiode of amorphous material, wherein the photodetector is still capable of performing high-speed imaging at low cost. This is achieved by using a photodiode of amorphous material and providing a bias metal line around the body sensitive material of the photodiode.

[0031] Other aspects of the invention are defined in the dependent claims.

[0032] The advantages and embodiments of the present invention are illustrated with reference to the accompanying drawings.

[0033] It should be understood that the preferred embodiments of the present invention can also be any combination of the dependent claims or the above embodiments and the independent claims.

[0034] These and other aspects of the invention will become apparent and will be illustrated with reference to the embodiments described below. Attached Figure Description

[0035] In the attached diagram:

[0036] Figure 1 A schematic top view of a photodetector according to an embodiment is shown.

[0037] Figure 2 A schematic top view of a photodetector according to another embodiment is shown.

[0038] Figure 3 It shows according to Figure 1 A schematic cross-section of a photodetector.

[0039] Figure 4 It shows Figure 2 A schematic cross-section of the photodetector, and

[0040] Figure 5 A schematic block diagram of an imaging system according to an embodiment is shown. Detailed Implementation

[0041] Figure 1 A schematic top view of a photodetector according to an embodiment is shown. The photodetector 100 includes a photodiode array 100a having a plurality of photodiodes 110. Each photodiode 110 specifically has a photosensitive region 111 and a periphery 112 at a photolithographically defined edge. A spacing 120 exists between adjacent photodiodes 110 in the photodiode array 100a.

[0042] To reduce or suppress charge trapping in photodiode 110, a charge trapping suppression unit is provided. The charge trapping suppression unit can be implemented as a (metal) bias line 132 directly at the edge 112 of each photodiode 110. The (metal) bias lines 132 of each photodiode 110 are interconnected via a connecting line 131 and connected to a voltage source via a line 133, such that the metal bias lines 132 can be biased as needed.

[0043] Therefore, the photodetector 100 includes a plurality of photodiodes 110 spaced apart from each other by a spacing 120. Each photodiode 110 has a bias line 132 disposed directly at the periphery of the photosensitive region 111 of the photodiode 110. The bias line unit 130 can be coupled to a voltage source via a line 133 to bias the bias lines 132, 130, 133. As an example, the photodiodes 110 can be segmented and pixelated photodiodes and can have a size of, for example, 2 mm x 2 mm with a perimeter of 8 mm. However, it should be noted that other sizes of the photodiode array are also possible.

[0044] The distance between adjacent photodiodes 110 can be selected according to the application of the photodiode array 100a as a photodetector.

[0045] By using bias lines 130-133 that are biased by voltage, the charge carrier concentration around the edge of the photodiode can be suppressed. Therefore, specifically for photodetectors utilizing photodiodes with amorphous materials, the signal rise and fall trajectories of the photodetector are significantly increased. Thus, a cheaper and faster photodetector is obtained, specifically for computed tomography applications.

[0046] By providing a bias line 132 (directly) around the edge 112 of the photodetector 110, the influence of higher defect states at the edge of the photodiode, which can generate trap sites for photoinduced charge carriers, is reduced. The presence of photoinduced charge carriers at the trap sites causes a decrease in the speed of the photodetector when the photoinduced charge carriers are released in subsequent frames or during subsequent integration times. Therefore, according to Figure 1 By utilizing bias lines, charge trapping is significantly reduced.

[0047] Due to the bias line 132 at the edge of the photodiode, charge carriers of the same polarity are repelled, thus preventing them from falling into trap sites caused by the higher defect density at the edge of the photodiode. The electric field effect generated by the bias applied via the bias line 132 at the edge 112 of the photodiode 110 can be considered analogous to the operating principle of a thin-film transistor (MOSFET) TFT. Here, the MOSFET TFT can be turned on and off by providing a high polarity voltage biased to the gate electrode of the device. By correspondingly biasing the bias line, charge carriers of the same polarity around the edge of the photodiode are repelled. Therefore, charge trapping occurring at the edge of the photodiode is significantly reduced. This is particularly advantageous for smaller photodiode sizes because the effect of the edge is increased.

[0048] In other words, compared to the guard ring, a metal bias line (with an appropriately applied bias) covering at least a portion of the photolithographically defined edge of the photodiode's main sensitive region generates an electric field that repels charges of the same polarity as the photodiode's edge. The metal bias line at the edge of the photodiode (the main sensitive region) functions similarly to the gate electrode of a MOSFET, enabling the conversion of depletion modes in the semiconductor into inversion modes.

[0049] Therefore, according to Figure 1 The photodetector is particularly advantageous for computed tomography applications because it results in lower residual signal in the photodiode and allows for faster switching.

[0050] The host sensitive material can include amorphous materials.

[0051] Figure 2A schematic top view of a photodetector according to another embodiment is shown. The photodetector 100 includes a photodiode array 100a having a plurality of photodiodes 110, which can be made of an amorphous material. Each photodiode 110 includes a photosensitive region 111 and an edge 112.

[0052] To reduce or suppress charge trapping in the photodiode 110, a charge trapping suppression unit is provided. The charge trapping suppression unit can be implemented as a cover 140 having a plurality of openings 141 on the top of the photodiode 110. The openings 141 are arranged above the photosensitive array 110 of the photodiode 110. The size of the openings 141 is chosen such that the cover 140 covers the edge 112 of the photodiode 110.

[0053] The cover 140 can be implemented as a metal shadow mask. Due to the size of the opening 141 in the cover 140, the effective photosensitive area 111 of the photodetector is reduced as the edge 112 of the photodetector is covered.

[0054] Therefore, according to Figure 2 The photodetector mitigates high residual signal by placing a shadow mask on top of the photodiode array. By covering the edge 112 of the photodiode 110 with the shadow mask 140, the edge of the photodiode 110 is covered and therefore unresponsive to light conditions. This is particularly advantageous because it prevents the generation of any photoinduced charge carriers at the edge of the photodiode. Thus, charge carrier trapping at the light edge is prevented or at least significantly reduced. It should be noted that although the effective photosensitive array of the photodiode is reduced, the contribution of photoinduced charge carriers generated in the body region of the photodiode at the trap sites at the edge of the photodiode is small. Due to the vertical electric field between the anode and cathode of the applied photodiode, the vertical drift motion of charge carriers is induced and the lateral diffusion towards the edge of the photodiode is minimized.

[0055] Using according to Figure 2 The photodetector thus minimizes the concentration of charge carriers trapped at the edge of the photodiode, and thus achieves a faster photodetector with lower residual signal.

[0056] According to other embodiments, Figure 1 and Figure 2 The features can be combined such that the edge 112 of the photodiode is provided with a bias line 132, which is biased with an appropriate voltage via bias lines 130-133. At the top of the photodiode, a shadow mask 140 can be provided with an opening 141 smaller than the photosensitive array of the photodiode 100a covering the edge 112 of the photodiode 110.

[0057] The shadow mask 140 can be a photomask element that is placed on top of the photodiode to cover at least a portion of the edge of the photodiode. The shadow mask should be aligned relative to the photodiode to ensure that the edge of the photodiode is covered.

[0058] Alternatively, the shadow mask can also be implemented as a metal element that can be patterned during photolithography. The metal element is disposed at the edge of the photodiode and covers at least a portion of the edge of the photodiode. This can suppress light interaction at the edge of the photodiode.

[0059] The edge of the photodiode 110 is covered by the shadow mask 140. Specifically, the overlap can be between 0.5 μm and 5 μm, preferably 1 μm.

[0060] The host sensitive material can include amorphous materials.

[0061] Figure 3 It shows according to Figure 1 A schematic cross-section of a photodetector. Figure 3 In the middle, it was made public Figure 1 The cross-section of the photodetector. In Figure 3 The image depicts an optional first layer 110a made of Si3N4, an optional second layer 110b made of SiO2, a third layer 110c made of indium tin oxide (ITO) serving as the bottom metal electrode, and a fourth layer 110d made of p+Si. On top of the fourth layer 110d, the photodiode 110's main (photo)sensitive material 111 is shown, with its periphery 112 at a photolithographically defined edge. On top of the main sensitive region 110, a fifth layer 110e made of n+Si and a sixth layer 110f made of tantalum / aluminum / tantalum Ta / Al / Ta are provided. At the photolithographically defined edge 112 of the photodiode 110, a metal bias line 132 is provided to directly contact the main sensitive region 111.

[0062] Preferably, the metal bias line 132 does not contact the bottom and top electrodes of the photodiode 110.

[0063] The top metal electrode 110f points towards the light source or photon source. The bottom metal electrode 110c faces away from the light source or photon source.

[0064] The main region 111 is made of or includes amorphous materials.

[0065] Figure 4 It shows Figure 2 A schematic cross-section of a photodetector. Figure 4 The cross-section essentially corresponds to the one with an additional 140° shading. Figure 3The cross-section is shown. Additionally, an interlayer dielectric layer 100g and electrical contacts 100h are provided. The dielectric layer 100g is used to passivate the edges and the remainder of the photodiode. The electrical contacts 100g are used to contact the bottom and top electrodes of the photodiode.

[0066] According to one aspect, the n+Si layer 110e and the p+Si layer 110d are amorphous silicon layers. The main body region 111 can also be made of amorphous silicon. This bulk amorphous silicon is used for light absorption and the generation of charge carriers. The n+amorphous silicon layer 110e and the p+amorphous silicon layer 110d are used to block one of the polarities of the charge carriers.

[0067] Organic photodiodes can also be used as an alternative to amorphous silicon photodiodes. Organic photodiodes can be supplied at low cost because organic materials are cheaper than crystalline silicon.

[0068] When these charges approach the trapping sites at the edge of the photodiode, the bias metal lines surrounding the edge of the photodiode repel charges of the same polarity. Therefore, the charge trapping rate at the edge of the photodiode decreases. This effect is even smaller when the photodiode is biased at 0V, by using the bias lines, compared to any reverse bias case. At 0V, the lateral diffusion of charge carriers towards the outer edge is higher, resulting in more charge trapping.

[0069] It can replace the bias metal line or be used outside the bias metal line. The shadow mask covering the edge of the photodiode can be used additionally to prevent photoinduced charge carriers at the edge of the body sensitive region 111.

[0070] According to an embodiment, the photodetector 100 includes a bottom metal electrode 110c (e.g., indium tin oxide (ITO), a p+Si layer 110d, a body photosensitive material 111 of a photodiode 110 with its periphery 112 at a photolithographically defined edge, an n+Si layer 110e, and a top metal layer (e.g., made of tantalum / aluminum / tantalum Ta / Al / Ta). A metal bias line 132 is provided at the photolithographically defined edge 112 of the photodiode. The metal bias line 132 does not contact the bottom and top electrodes of the photodiode.

[0071] According to other embodiments, the photodiode is implemented as an organic photodiode. In this case, the photodiode includes a bottom metal electrode, a host sensitive organic material, and a top metal electrode.

[0072] Figure 5A schematic block diagram of an imaging system according to an embodiment is shown. The imaging system 10 includes an X-ray source 200 and at least one photodetector 100. The photodetector 100 includes a photodiode array having a plurality of photodiodes 110. Each photodiode 110 can be biased by a bias voltage 100b. The photodetector 100 may correspond to the embodiment described above. Figures 1 to 3 The photodetector. Furthermore, the bias voltage 100b of each photodiode 110 is zero. In other words, the photodiodes are not reverse biased.

[0073] The X-ray source 200 is preferably a continuous X-ray source 200.

[0074] Low dark leakage current can be achieved by avoiding reverse biasing of the photodiode 110, which contains amorphous material. Therefore, by not biasing the photodiode, the dark leakage current is reduced compared to a photodetector with a reverse-biased photodiode. On the other hand, by avoiding reverse biasing the diode, the possibility of charge carriers laterally diffusing to the edge of the photodiode increases compared to a photodetector with a reverse-biased photodiode. Therefore, for photodetectors using photodiodes with amorphous material and no reverse bias, the need to focus on charge trapping at the periphery of the main sensitive region becomes more important. However, according to the embodiment, this problem is solved by providing a metal bias line at the periphery of the main sensitive material, which in turn includes amorphous material. For a reverse-biased photodiode in a photodetector, the vertical drift motion of charge carriers in the electric field of the reverse-biased photodiode leads to reduced lateral diffusion. Since this is no longer applicable to photodetectors with photodiodes without any reverse bias, a charge trapping suppression step must be provided.

[0075] According to an embodiment, a computed tomography system having at least one photodetector as described above is provided.

[0076] According to an embodiment, an imaging system with a photodetector is provided in the form of an X-ray system for medical imaging applications.

[0077] The imaging system can also be implemented as a security scanning system.

[0078] Imaging systems with photodetectors as described above have a residual signal specification of approximately 1500–2000 ppm (parts per million). The photodetector measures at a 0V bias with a 450ms optical pulse time and a 10 nanoampere optical signal level.

[0079] According to one aspect, an X-ray computed tomography system is provided, wherein a continuous X-ray source, unlike other systems, is present when pulsed X-rays are provided. Computed tomography applications require very fast imaging, and therefore, combined with a low X-ray dose that causes low light signals from the scintillator to be absorbed by the photodiode, it is possible to see the signal rise trajectory and signal attenuation more clearly. Under low light conditions, charge trapping in amorphous silicon is very high.

[0080] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention.

[0081] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0082] A single unit or device can perform the functions of multiple items recounted in the claims. The fact that certain measures are described in mutually different dependent claims does not mean that a combination of these measures cannot be used advantageously.

[0083] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A photodetector (100) for imaging applications, comprising: A photodiode array (100a) having multiple photodiodes (110), Each photodiode (110) has a main sensitive region (111) and a periphery (112) at the photolithographically defined edge of the main sensitive region (111) of the photodiode (110), and A charge trapping suppression unit is configured to suppress charge trapping at the edge of the photodiode (110), wherein The charge trapping suppression unit includes a metal bias line (132) at the periphery (112) of the main sensitive region (111) of the photodiode (110) that is in direct contact with the main sensitive region (111). The metal bias line (132) can be connected to a voltage source to bias the bias line (132), thereby repelling charge carriers of the same polarity as the bias line from the trap sites at the edge of the photodiode (110). The main sensitive region (111) comprises an amorphous material. Each of the photodiodes (110) includes a bottom metal electrode (110c), a main sensitive region (111) at a photolithographically defined edge of its periphery (112), and a top metal electrode (110f). The top metal electrode (110f) faces the incident light, while the bottom metal electrode (110c) faces away from the incident light. The metal bias line (132) does not contact the bottom metal electrode (110c) and the top metal electrode (110f) of the photodiode (110).

2. The photodetector (100) for imaging applications according to claim 1, wherein, The imaging application is a high-speed imaging application.

3. The photodetector for imaging applications according to claim 1, wherein... The charge trapping suppression unit includes a shadow mask (140) covering the photodiode array (100a), the shadow mask (140) having a plurality of openings (141) smaller than the main sensitive region (111) of the photodiode (110), such that the edge of the photodiode (110) is covered by the shadow mask (140).

4. The photodetector according to any one of claims 1 to 3, wherein Each photodiode (110) can be biased by a bias voltage (100b), wherein, The bias voltage (100b) of the photodiode (110) is zero.

5. The photodetector according to any one of claims 1 to 3, wherein, The material of the main sensitive region (111) is a main photosensitive organic semiconductor material.

6. A method for manufacturing a photodetector (100) for medical imaging applications, comprising the following steps: A photodiode array (100a) having multiple photodiodes (110) is fabricated using photolithography, wherein each photodiode (110) has a main sensitive region (111) of amorphous material and a periphery (112) at the photolithographically defined edge of the main sensitive region of the photodiode (110). A metal bias line (132) is applied directly to the main sensitive region (111) of the photodiode (110) at the periphery (112). The metal bias line (132) can be connected to a voltage source to bias the bias line (132), thereby repelling charge carriers of the same polarity as the bias line from trap sites at the edge of the photodiode (110). Each of the photodiodes (110) includes a bottom metal electrode (110c), a main sensitive region (111) at a photolithographically defined edge of its periphery (112), and a top metal electrode (110f). The top metal electrode (110f) faces the incident light, while the bottom metal electrode (110c) faces away from the incident light. The metal bias line (132) does not contact the bottom metal electrode (110c) and the top metal electrode (110f) of the photodiode (110).

7. The method according to claim 6, further comprising the following step: A shadow mask (140) is applied to cover the photodiode array (100a), the shadow mask (140) having a plurality of openings (141) smaller than the main sensitive region (111) of the photodiode (110), such that the edge of the photodiode (110) is covered by the shadow mask (140).

8. A method for detecting photons using a photodetector according to any one of claims 1 to 4, comprising the following steps: A bias voltage is applied to the metal bias line, and photons are detected using the photodiode array. Each photodiode (110) can be biased by a zero bias voltage (100b).

9. An imaging system, comprising At least one photodetector (100) according to any one of claims 1 to 5.

10. The imaging system according to claim 9, wherein, The imaging system is a medical imaging system in the form of an X-ray computed tomography system.

11. The imaging system according to claim 9, wherein The imaging system is a security scanning system.

12. The imaging system according to any one of claims 9-11, further comprising: X-ray source (200), in, Each photodiode (110) can be biased by a bias voltage (100b), wherein the bias voltage (100b) is zero.

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