Patent Publication Number: US-2023137029-A1

Title: Photosensitive device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110140624, filed on Nov. 1, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a photosensitive device, and more particularly, to a photosensitive device including multiple photosensitive elements. 
     Description of Related Art 
     At present, in order to increase the security of products, many manufacturers install fingerprint recognition sensing devices in their products. In the existing fingerprint recognition technology, the sensing device detects the light reflected by the fingerprint of the finger, and the uneven surfaces of the fingerprint cause reflected light of different intensities, so the different fingerprint appearances are distinguished by the sensing device. Generally speaking, a sensing device for fingerprint recognition includes photosensitive elements arranged in an array. The uneven surfaces of the fingerprint at different positions are detected by the photosensitive elements arranged in an array to obtain the overall appearance of the fingerprint. 
     SUMMARY 
     The disclosure provides a photosensitive device which has an anti-counterfeiting function and can improve the reliability of fingerprint recognition. 
     At least an embodiment of the disclosure provides a photosensitive device. The photosensitive device includes a substrate, an active element layer, a first photosensitive element, and a second photosensitive element. The active element layer is located above the substrate. Each first photosensitive element includes a first lower conductive structure, a first photosensitive layer, and a first upper conductive structure stacked in sequence. The first lower conductive structure is electrically connected to the active element layer. Each second photosensitive element includes a second lower conductive structure, a second photosensitive layer, and a second upper conductive structure stacked in sequence. The second lower conductive structure is electrically connected to the active element layer. The first upper conductive structure includes an opaque electrode or a semi-transparent electrode. The second upper conductive structure includes a transparent electrode. The first upper conductive structure is configured so that a signal difference between a photocurrent signal and a dark current signal of the at least one first photosensitive element is smaller than a signal difference between a photocurrent signal and a dark current signal of the at least one second photosensitive element. 
     At least an embodiment of the disclosure provides a photosensitive device. The photosensitive device includes a substrate, an active element layer, a first photosensitive element, and a second photosensitive element. The active element layer is located above the substrate. Each first photosensitive element includes a first lower conductive structure, a first photosensitive layer, and a first upper conductive structure stacked in sequence. The first lower conductive structure is electrically connected to the active element layer. Each second photosensitive element includes a second lower conductive structure, a second photosensitive layer, and a second upper conductive structure stacked in sequence. The second lower conductive structure is electrically connected to the active element layer. The first lower conductive structure includes a transparent electrode. The second lower conductive structure includes an opaque electrode. The first lower conductive structure is configured so that a signal difference between a photocurrent signal and a dark current signal of the at least one first photosensitive element is smaller than a signal difference between a photocurrent signal and a dark current signal of the at least one second photosensitive element. 
     At least an embodiment of the disclosure provides a photosensitive device. The photosensitive device includes a substrate, an active element layer, a first photosensitive element, and a second photosensitive element. The active element layer is located above the substrate. Each first photosensitive element includes a first lower conductive structure, a first photosensitive layer, and a first upper conductive structure stacked in sequence. The first lower conductive structure is electrically connected to the active element layer. Each second photosensitive element includes a second lower conductive structure, a second photosensitive layer, and a second upper conductive structure stacked in sequence. The second lower conductive structure is electrically connected to the active element layer. A first shielding structure is an opaque structure or a semi-transparent structure, and the first shielding structure overlaps the first photosensitive element and does not overlap the second photosensitive element. The first shielding structure is configured so that a signal difference between a photocurrent signal and a dark current signal of the at least one first photosensitive element is smaller than a signal difference between a photocurrent signal and a dark current signal of the at least one second photosensitive element. 
     Based on the above, by reducing the difference between the photocurrent signal and the dark current signal of the first photosensitive element, the photosensitive device has an anti-counterfeiting function, thereby improving the reliability of fingerprint recognition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  2    is a schematic top view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  3    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  4    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  5    is a voltage-current graph of the photosensitive device of  FIG.  4   . 
         FIG.  6    is an output voltage-time graph of the photosensitive device of  FIG.  4   . 
         FIG.  7    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  8    is a voltage-current graph of the photosensitive device of  FIG.  7   . 
         FIG.  9    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  10    is a voltage-current graph of the photosensitive device of  FIG.  9   . 
         FIG.  11    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  12    is a voltage-current graph of the photosensitive device of  FIG.  11   . 
         FIG.  13    is a schematic top view of a photosensitive device according to an embodiment of the disclosure. 
         FIG.  14    is a schematic cross-sectional view taken along line a-a′ of  FIG.  13   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the disclosure, relative terms such as “below” or “bottom” and “above” or “top” may serve to describe the relation between one element and another element in the text according to the illustration of the drawings. It should also be understood that the relative terms are intended to include different orientations of a device in addition to the orientation shown in the drawings. For example, if a device in the accompanying drawings is flipped, an element described as being on the “lower” side of other elements shall be re-orientated to be on the “upper” side of other elements. Thus, the exemplary term “lower” may cover the orientations of “upper” and “lower”, depending on the specific orientations of the accompanying drawings. Similarly, if a device in the accompanying drawings is flipped, an element described as being “below” other elements shall be re-orientated to be “above” other elements. Thus, the exemplary term “above” or “below” may cover the orientations of above and below. 
       FIG.  1    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. 
     Please refer to  FIG.  1   . A photosensitive device  10  includes a substrate  100 , an active element layer  110 , at least one first photosensitive element PD 1  and at least one second photosensitive element PD 2 . In this embodiment, the photosensitive device  10  further includes a first collimating structure  230 , a second collimating structure  260 , a third collimating structure  290  and a lens element  300 . It should be noted that, in  FIG.  1   , the number of photosensitive elements and the number of active elements are only used for illustration, but not for limiting the disclosure. In other words, the number of photosensitive elements and the number of active elements may be adjusted according to actual needs. 
     The material of the substrate  100  includes glass, quartz, organic polymers, or opaque/reflective materials (for example, conductive materials, metals, wafers, ceramics, or other applicable materials) or other applicable materials. If a conductive material or metal is used, an insulating layer (not shown) is coated on the substrate  100  to avoid the short circuit problem. 
     The active element layer  110  is located above the substrate  100 . In this embodiment, a buffer layer  102  is optionally included between the active element layer  110  and the substrate  100 . The active element layer  110  includes multiple active elements. For example, the active element layer  110  includes multiple first active elements T 1  and multiple second active elements T 2 . The first active element T 1  and the second active element T 2  are bottom gate type thin film transistors, top gate type thin film transistors, double gate type thin film transistors or other types of thin film transistors. In this embodiment, the first active element T 1  and the second active element T 2  are top gate type thin film transistors. 
     In this embodiment, the first active element T 1  and the second active element T 2  each include a gate G, a channel CH, a source S, and a drain D. The channel CH overlaps the gate G, and a gate insulating layer  112  is sandwiched between the channel CH and the gate G. An interlayer dielectric layer  114  is located on the gate G and the gate insulating layer  112 . The source S and the drain D are located on the interlayer dielectric layer  114  and are electrically connected to the channel CH through a conductive hole penetrating the gate insulating layer  112  and the interlayer dielectric layer  114 . 
     In some embodiments, the material of the channel CH includes amorphous silicon, polycrystalline silicon, microcrystalline silicon, monocrystalline silicon, organic semiconductor materials, oxide semiconductor materials (for example, indium zinc oxide, indium gallium zinc oxide or other suitable materials or combinations of the above) or other suitable materials or combinations of the above. The materials of the gate G, the source S and the drain D include chromium, gold, silver, copper, tin, lead, hafnium, tungsten, molybdenum, neodymium, titanium, tantalum, aluminum, zinc and other metals, alloys of the above metals, oxides of the above metals, nitride of the above metals, or combinations of the above or other conductive materials. 
     In this embodiment, the first active element T 1  and the second active element T 2  include the same structure, but the disclosure is not limited thereto. In other embodiments, the first active element T 1  and the second active element T 2  include different structures. For example, the first active element T 1  and the second active element T 2  include different types of thin film transistors or include thin film transistors made of different materials. 
     The first photosensitive element PD 1  and the second photosensitive element PD 2  are electrically connected to the active element layer  110 . Each first photosensitive element PD 1  includes a first lower conductive structure LC 1 , a first photosensitive layer PS 1 , and a first upper conductive structure UC 1  stacked in sequence. Each second photosensitive element PD 2  includes a second lower conductive structure LC 2 , a second photosensitive layer PS 2 , and a second upper conductive structure UC 2  stacked in sequence. 
     In this embodiment, each photosensitive element is electrically connected to a corresponding active element. Specifically, each first photosensitive element PD 1  is electrically connected to a corresponding one of the first active elements T 1  in the active element layer  110 , and each second photosensitive element PD 2  is electrically connected to a corresponding one of the second active elements T 2  in the active element layer  110 . 
     In this embodiment, the first lower conductive structure LC 1  of the first photosensitive element PD 1  and the second lower conductive structure LC 2  of the second photosensitive element PD 2  are electrically connected to the active element layer  110 . In this embodiment, the first lower conductive structure LC 1  is integrated with the drain D of the corresponding first active element T 1 , and the second lower conductive structure LC 2  is integrated with the drain D of the corresponding second active element T 2 . In this embodiment, the source S and drain D of the first active element T 1 , the source S and drain D of the second active element T 2 , the first lower conductive structure LC 1  and the second lower conductive structure LC 2  belong to the same conductive layers, and include the same materials, but the disclosure is not limited thereto. In other embodiments, the first lower conductive structure LC 1  and the second lower conductive structure LC 2  may belong to different conductive layers from the source S and drain D of the first active element T 1  and the source S and drain D of the second active element T 2 . In other words, in other embodiments, the first lower conductive structure LC 1  and the second lower conductive structure LC 2  may include materials different from the source S and the drain D. In this embodiment, the first lower conductive structure LC 1  and the second lower conductive structure LC 2  are opaque metal electrodes. 
     The first photosensitive layer PS 1  is located on the first lower conductive structure LC 1 , and the second photosensitive layer PS 2  is located on the second lower conductive structure LC 2 . In some embodiments, the respective materials of the first photosensitive layer PS 1  and the second photosensitive layer PS 2  include, for example, silicon-rich nitride, silicon-rich oxynitride, silicon-rich carbide, silicon-rich oxycarbide, hydrogenated silicon-rich oxide, hydrogenated silicon-rich nitride, hydrogenated silicon-rich carbide, or a combination thereof, but the disclosure is not limited thereto. In other embodiments, the first photosensitive layer PS 1  and the second photosensitive layer PS 2  each include a stacked layer of a P-type semiconductor, an intrinsic semiconductor, and an N-type semiconductor. In this embodiment, the first photosensitive layer PS 1  and the second photosensitive layer PS 2  include the same material, but the disclosure is not limited thereto. 
     In some embodiments, a protective layer BF 1  and a protective layer BF 2  for suppressing dark current signals are formed between the first lower conductive structure LC 1  and the first photosensitive layer PS 1  and between the metal material of the second lower conductive structure LC 2  and the second photosensitive layer PS 2 , respectively. The protective layer BF 1  and the protective layer BF 2  are, for example, metal oxides. For example, in some embodiments, the first lower conductive structure LC 1  and the second lower conductive structure LC 2  each include a stacked structure of titanium, aluminum and titanium. The titanium in the outer layer is oxidized during the manufacturing process, and the protective layer BF 1  and the protective layer BF 2  including titanium oxide are formed. In other embodiments, the material of the protective layer BF 1  and the protective layer BF 2  includes molybdenum oxide, and the method for forming the protective layer BF 1  and the protective layer BF 2  includes a sputtering or water oxidation process. 
     A first insulating layer  200  is located on the active element layer  110 , the first photosensitive layer PS 1  and the second photosensitive layer PS 2 , and has multiple openings overlapping the first photosensitive layer PS 1  and the second photosensitive layer PS 2 . In some embodiments, the first insulating layer  200  includes a single-layer or multi-layer structure, and the material of the first insulating layer  200  includes an organic material or an inorganic material. 
     The first upper conductive structure UC 1  and the second upper conductive structure UC 2  are located on the first insulating layer  200  and fill the openings in the first insulating layer  200  to contact the first photosensitive layer PS 1  and the second photosensitive layer PS 2  respectively. In this embodiment, the material of the first upper conductive structure UC 1  is different from the material of the second upper conductive structure UC 2 , and the first upper conductive structure UC 1  includes an opaque electrode or a semi-transparent electrode, and the second upper conductive structure UC 2  includes a transparent electrode. 
     In some embodiments, the first upper conductive structure UC 1  includes a semi-transparent or opaque metal. In this embodiment, the first upper conductive structure UC 1  includes a semi-transparent metal, such as molybdenum or aluminum with a thickness of less than 500 nm. 
     In some embodiments, the second upper conductive structure UC 2  includes a transparent conductive material, such as indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium gallium zinc oxide, or a stacked layer of at least two of the above or other materials. In this embodiment, the thickness of the second upper conductive structure UC 2  is greater than the thickness of the first upper conductive structure UC 1 . 
     A second insulating layer  210  is located on the first photosensitive element PD 1  and the second photosensitive element PD 2 . In some embodiments, the second insulating layer  210  includes a single-layer or multi-layer structure, and the material of the second insulating layer  210  includes an organic material or an inorganic material. 
     A first buffer layer  220  is located on the second insulating layer  210 . In some embodiments, the first buffer layer  220  includes a single-layer or multi-layer structure, and the material of the first buffer layer  220  includes an organic material or an inorganic material. 
     The first collimating structure  230  is located on the first buffer layer  220 . In this embodiment, the first collimating structure  230  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 . The first collimating structure  230  has multiple openings  236  overlapping the first photosensitive element PD 1  and the second photosensitive element PD 2 . 
     The first collimating structure  230  includes a single-layer or multi-layer structure. In this embodiment, the first collimating structure  230  includes a first light shielding layer  232  and a first anti-reflection layer  234  on the first light shielding layer  232 . In some embodiments, the first light shielding layer  232  includes a metal (for example, molybdenum), and the first anti-reflection layer  234  includes a metal oxide (for example, molybdenum oxide), but the disclosure is not limited thereto. 
     A third insulating layer  240  is located on the first collimating structure  230 . In some embodiments, the third insulating layer  240  includes a single-layer or multi-layer structure, and the material of the third insulating layer  240  includes an organic material or an inorganic material. 
     A second buffer layer  250  is located on the third insulating layer  240 . In some embodiments, the second buffer layer  250  includes a single-layer or multi-layer structure, and the material of the second buffer layer  250  includes an organic material or an inorganic material. 
     The second collimating structure  260  is located on the second buffer layer  250 . In this embodiment, the second collimating structure  260  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 . The second collimating structure  260  has multiple openings  266  overlapping the first photosensitive element PD 1  and the second photosensitive element PD 2 . In this embodiment, the openings  266  of the second collimating structure  260  overlap the openings  236  of the first collimating structure  230 , and the width of the openings  266  is greater than or equal to the width of the openings  236 . 
     The second collimating structure  260  includes a single-layer or multi-layer structure. In this embodiment, the second collimating structure  260  includes a second light shielding layer  262  and a second anti-reflection layer  264  on the second light shielding layer  262 . In some embodiments, the second light shielding layer  262  includes a metal (for example, molybdenum), and the second anti-reflection layer  264  includes a metal oxide (for example, molybdenum oxide), but the disclosure is not limited thereto. 
     A fourth insulating layer  270  is located on the second collimating structure  260 . In some embodiments, the fourth insulating layer  270  includes a single-layer or multi-layer structure, and the material of the fourth insulating layer  270  includes an organic material or an inorganic material. 
     A third buffer layer  280  is located on the fourth insulating layer  270 . In some embodiments, the third buffer layer  280  includes a single-layer or multi-layer structure, and the material of the third buffer layer  280  includes an organic material or an inorganic material. 
     The third collimating structure  290  is located on the third buffer layer  280 . In this embodiment, the third collimating structure  290  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 . The third collimating structure  290  has multiple openings  296  overlapping the first photosensitive element PD 1  and the second photosensitive element PD 2 . In this embodiment, the openings  296  of the third collimating structure  290  overlap the openings  236  of the first collimating structure  230  and the openings  266  of the second collimating structure  260 , and the width of the openings  296  is greater than or equal to the width of the openings  266 . 
     The third collimating structure  290  includes a single-layer or multi-layer structure. In this embodiment, the third collimating structure  290  includes a third light shielding layer  292  and a third anti-reflection layer  294  on the third light shielding layer  292 . In some embodiments, the third light shielding layer  292  includes a metal (for example, molybdenum), and the third anti-reflection layer  294  includes a metal oxide (for example, molybdenum oxide), but the disclosure is not limited thereto. 
     Multiple lens elements  300  are located on the third buffer layer  280 . In this embodiment, the lens elements  300  are located in the openings  296  of the third collimating structure  290 . The lens elements  300  are located above the first photosensitive element PD 1  and the second photosensitive element PD 2  and overlap the openings  236 , the openings  266  and the openings  296 . In some embodiments, the lens elements  300  include an organic material or an inorganic material. 
     In this embodiment, the first photosensitive element PD 1  and the second photosensitive element PD 2  are adapted for receiving light reflected by a finger. When the light is received, the first photosensitive element PD 1  and the second photosensitive element PD 2  each generate a corresponding photocurrent signal. When no light is received, the first photosensitive element PD 1  and the second photosensitive element PD 2  each generate a corresponding dark current signal. 
     Table 1 compares the differences in the photocurrent signals generated by the first photosensitive element PD 1  when different materials and thicknesses of the first upper conductive structure UC 1  are used. In Table 1, the comparison is made based on the photocurrent signal being 100% when the first upper conductive structure UC 1  is made of transparent indium tin oxide. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 First upper 
                   
                 Molybdenum 
                 Molybdenum 
                 Aluminum 
               
               
                 conductive 
                 Indium 
                 (150 
                 (300 
                 (150 
               
               
                 structure 
                 tin oxide 
                 angstroms) 
                 angstroms) 
                 angstroms) 
               
               
                   
               
             
            
               
                 Photocurrent 
                 100% 
                 15.8% 
                 6.1% 
                 12.1% 
               
               
                 signal 
               
               
                   
               
            
           
         
       
     
     As may be seen from Table 1, when the first upper conductive structure is made of molybdenum or aluminum with poor light transmittance, the intensity of the photocurrent signal generated by the first photosensitive element PD 1  decreases. 
     Based on the above, under the same amount of light, since the first upper conductive structure UC 1  includes an opaque electrode or a semi-transparent electrode, and the second upper conductive structure UC 2  includes a transparent electrode, the intensity of the photocurrent signal generated by the first photosensitive element PD 1  is smaller than the intensity of the photocurrent signal generated by the second photosensitive element PD 2 . Therefore, a signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than a signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . In other words, the first upper conductive structure UC 1  is configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . 
     In this embodiment, the difference between the signal difference I 1  and the signal difference I 2  may be used to identify the authenticity of the fingerprint. For example, the first photosensitive element PD 1  and the second photosensitive element PD 2  respectively generate the signal difference I 1  between the photocurrent signal and the dark current signal and the signal difference I 2  between the photocurrent signal and the dark current signal after receiving the light reflected by the finger, and the first photosensitive element PD 1  and the second photosensitive element PD 2  respectively generate a signal difference I 1 ′ between the photocurrent signal and the dark current signal and a signal difference I 2 ′ between the photocurrent signal and the dark current signal after receiving light reflected from other materials. Since a difference between the signal difference I 1  and the signal difference I 2  is different from a difference between the signal difference IF and the signal difference I 2 ′, it may be identified whether the light received by the first photosensitive element PD 1  and the second photosensitive element PD 2  is reflected by the finger or reflected by other materials. Based on the above, the photosensitive device  10  has an anti-counterfeiting function, and the reliability of fingerprint recognition may be improved by the first photosensitive element PD 1  and the second photosensitive element PD 2 . 
       FIG.  2    is a schematic top view of a photosensitive device according to an embodiment of the disclosure.  FIG.  2    is used to illustrate the distribution positions of the first photosensitive element PD 1  and the second photosensitive element PD 2 , and  FIG.  2    omits the illustration of other structures of the photosensitive device. For the structure of the photosensitive device, please refer to  FIG.  1    and the related description of  FIG.  1   , and details are not repeated here. 
     Please refer to  FIG.  2   . In this embodiment, each first photosensitive element PD 1  is adjacent to four or more second photosensitive elements PD 2 . It should be noted that  FIG.  2    is only used to illustrate one distribution pattern of the first photosensitive element PD 1  and the second photosensitive element PD 2 . In other embodiments, the first photosensitive element PD 1  and the second photosensitive element PD 2  may have other distribution patterns. 
       FIG.  3    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. It is noted that the embodiment of  FIG.  3    uses the reference numerals and a part of the contents of the embodiment of  FIG.  1   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiment, and details are not described herein. 
     The difference between a photosensitive device  20  of  FIG.  3    and the photosensitive device  10  of  FIG.  1    is that in the photosensitive device  20 , the material of the first lower conductive structure LC 1 ′ of the first photosensitive element PD 1  is different from the material of the second lower conductive structure LC 2  of the second photosensitive element PD 2 . 
     In this embodiment, the first lower conductive structure LC 1 ′ of the first photosensitive element PD 1  includes a transparent electrode, such as a metal oxide. In this embodiment, the second lower conductive structure LC 2  of the second photosensitive element PD 2  includes an opaque electrode, such as an opaque metal. In this embodiment, the first lower conductive structure LC 1 ′ is integrated with the drain D′ of the first active element T 1 , and the materials of the first lower conductive structure LC 1 ′ and the drain D′ of the first active element T 1  both Include metal oxides; therefore, the material of the drain D′ of the first active element T 1  is different from the material (for example, metal material) of the drain D of the second active element T 2 , but the disclosure is not limited thereto. In other embodiments, the first lower conductive structure LC 1 ′ is not integrally formed with the drain D′ of the first active element T 1 , and the material of the first lower conductive structure LC 1 ′ includes metal oxide, and the material of the drain D′ of the first active element T 1  includes metal. 
     In this embodiment, the material of the second lower conductive structure LC 2  includes metal, and the material of the first lower conductive structure LC 1 ′ includes metal oxide. Therefore, in the process, the protective layer BF 2  is formed between the second lower conductive structure LC 2  and the second photosensitive layer PS 2 , and no protective layer is formed between the first lower conductive structure LC 1 ′ and the first photosensitive layer PS 1 . The protective layer BF 2  is located between the second photosensitive layer PS 2  and the second lower conductive structure LC 2 . 
     In this embodiment, the first lower conductive structure LC 1 ′ and the first upper conductive structure UC 1  are both configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . In this embodiment, the protective layer BF 2  helps to suppress the dark current signal of the second photosensitive element PD 2 , thereby increasing the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . In addition, since the first photosensitive element PD 1  does not have a protective layer, the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  may be reduced, thereby increasing the difference between the signal difference I 1  and the signal difference I 2 . In this embodiment, the dark current signal of the first photosensitive element PD 1  is greater than the dark current signal of the second photosensitive element PD 2 . 
     Based on the above, the photosensitive device  20  has an anti-counterfeiting function, and the reliability of fingerprint recognition may be improved by the first photosensitive element PD 1  and the second photosensitive element PD 2 . 
       FIG.  4    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. It is noted that the embodiment of  FIG.  4    uses the reference numerals and a part of the contents of the embodiment of  FIG.  3   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiment, and details are not described herein. 
     The difference between a photosensitive device  30  of  FIG.  4    and the photosensitive device  20  of  FIG.  3    is that in the photosensitive device  30 , the material of the first upper conductive structure UC 1 ′ of the first photosensitive element PD 1  is the same as the material of the second upper conductive structure UC 2  of the second photosensitive element PD 2 . 
     Please refer to  FIG.  4   . The photosensitive device  30  includes a substrate  100 , an active element layer  110 , a first photosensitive element PD 1  and a second photosensitive element PD 2 . The active element layer  110  is located above the substrate  100 . The active element layer  110  includes multiple first active elements T 1  and multiple second active elements T 2 . 
     Each first photosensitive element PD 1  includes a first lower conductive structure LC 1 ′, a first photosensitive layer PS 1 , and a first upper conductive structure UC 1 ′ stacked in sequence. The first lower conductive structure LC 1 ′ is electrically connected to the active element layer  110 . The first active element T 1  of the active element layer  110  is electrically connected to the first lower conductive structure LC 1 ′. Each second photosensitive element PD 2  includes a second lower conductive structure LC 2 , a second photosensitive layer PS 2 , and a second upper conductive structure UC 2  stacked in sequence. The second lower conductive structure LC 2  is electrically connected to the active element layer  110 . The second active element T 2  of the active element layer  110  is electrically connected to the second lower conductive structure LC 2 . 
     In this embodiment, the first upper conductive structure UC 1 ′ and the second upper conductive structure UC 2  include the same material. In this embodiment, both the first upper conductive structure UC 1 ′ and the second upper conductive structure UC 2  include a transparent conductive material, such as indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium gallium zinc oxide, or a stacked layer of at least two of the above or other materials. In this embodiment, the thickness of the second upper conductive structure UC 2  is equal to the thickness of the first upper conductive structure UC 1 . 
     In this embodiment, the first lower conductive structure LC 1 ′ of the first photosensitive element PD 1  includes a transparent electrode, such as a metal oxide (for example, indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium gallium zinc oxide, or a stacked layer of at least two of the above or other materials). In this embodiment, the second lower conductive structure LC 2  of the second photosensitive element PD 2  includes an opaque electrode, such as an opaque metal. 
     In this embodiment, the second lower conductive structure LC 2  includes metal, and the first lower conductive structure LC 1 ′ includes metal oxide. Therefore, in the process, the protective layer BF 2  is formed between the second lower conductive structure LC 2  and the second photosensitive layer PS 2 , and no protective layer is formed between the first lower conductive structure LC 1 ′ and the first photosensitive layer PS 1 . 
     In this embodiment, the first lower conductive structure LC 1 ′ is configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . In this embodiment, the protective layer BF 2  helps to suppress the dark current signal of the second photosensitive element PD 2 , thereby increasing the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 . In addition, since the first photosensitive element PD 1  does not have a protective layer, the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  may be reduced, thereby increasing the difference between the signal difference I 1  and the signal difference I 2 . In this embodiment, the dark current signal of the first photosensitive element PD 1  is greater than the dark current signal of the second photosensitive element PD 2 . 
       FIG.  5    is a voltage-current graph of the photosensitive device of  FIG.  4   .  FIG.  6    is an output voltage-time graph of the photosensitive device of  FIG.  4   . 
     In the embodiments of  FIG.  4    to  FIG.  6   , the first lower conductive structure LC 1 ′ and the first upper conductive structure UC 1 ′ of the first photosensitive element PD 1  both include transparent electrodes. The second lower conductive structure LC 2  of the second photosensitive element PD 2  includes an opaque electrode, and the second upper conductive structure UC 2  includes a transparent electrode. 
     It may be seen from  FIG.  5    and  FIG.  6    that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 , and the output voltage of the first photosensitive element PD 1  is lower than the output voltage of the second photosensitive element PD 2 . 
       FIG.  7    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. It is noted that the embodiment of  FIG.  7    uses the reference numerals and a part of the contents of the embodiment of  FIG.  1   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiments, and details are not described herein. 
     The difference between a photosensitive device  40  of  FIG.  7    and the photosensitive device  10  of  FIG.  1    is that in the photosensitive device  40 , the material of the first upper conductive structure UC 1 ′ of the first photosensitive element PD 1  is the same as the material of the second upper conductive structure UC 2  of the second photosensitive element PD 2 . 
     Please refer to  FIG.  7   . The photosensitive device  40  includes a substrate  100 , an active element layer  110 , a first photosensitive element PD 1  and a second photosensitive element PD 2 . The active element layer  110  is located above the substrate  100 . 
     Each first photosensitive element PD 1  includes a first lower conductive structure LC 1 , a first photosensitive layer SR 1 , and a first upper conductive structure UC 1 ′ stacked in sequence. Each second photosensitive element PD 2  includes a second lower conductive structure LC 2 , a second photosensitive layer SR 2 , and a second upper conductive structure UC 2  stacked in sequence. The first lower conductive structure LC 1  and the second lower conductive structure LC 2  are electrically connected to the active element layer  110 . 
     In this embodiment, the material of the first upper conductive structure UC 1 ′ of the first photosensitive element PD 1  is the same as the material of the second upper conductive structure UC 2  of the second photosensitive element PD 2 , and the material of the first lower conductive structure LC 1  of the first photosensitive element PD 1  is the same as the material of the second lower conductive structure LC 2  of the second photosensitive element PD 2 . 
     In this embodiment, the first upper conductive structure UC 1 ′ and the second upper conductive structure UC 2  include a transparent conductive material, such as indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium gallium zinc oxide, or a stacked layer of at least two of the above or other materials. The first lower conductive structure LC 1  and the second lower conductive structure LC 2  include opaque metal electrodes. 
     A first shielding structure  238  overlaps the first photosensitive element PD 1 , and does not overlap the second photosensitive element PD 2 . The first shielding structure  238  is an opaque structure or a semi-transparent structure. In this embodiment, the first shielding structure  238  is a semi-transparent structure and includes molybdenum, aluminum or other materials. The thickness of the first shielding structure  238  is less than 500 nm. 
     In this embodiment, the first collimating structure  230  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 , and the first collimating structure  230  and the first shielding structure  238  include the same metal material. For example, the first collimating structure  230  includes a first light shielding layer  232  and a first anti-reflection layer  234  on the first light shielding layer  232 . The first light shielding layer  232  and the first shielding structure  238  include the same metal material, and the first light shielding layer  232  and the first shielding structure  238  are directly connected, and the thickness of the first shielding structure  238  is less than the thickness of the first light shielding layer  232 . In this embodiment, the first anti-reflection layer  234  does not overlap the first shielding structure  238 . In some embodiments, the first light shielding layer  232  is formed together with the first shielding structure  238 , thereby reducing the manufacturing cost of the photosensitive device  40 . 
     Based on the above, the intensity of the photocurrent signal generated by the first photosensitive element PD 1  is smaller than the intensity of the photocurrent signal generated by the second photosensitive element PD 2 , and the dark current signals of the first photosensitive element PD 1  and the second photosensitive element PD 2  have the same intensity. The first shielding structure  238  is configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 , as shown in  FIG.  8   . 
     In this embodiment, the difference between the signal difference I 1  and the signal difference I 2  may be used to identify the authenticity of the fingerprint, so that the photosensitive device  40  has an anti-counterfeiting function, and the reliability of fingerprint recognition may be improved by the first photosensitive element PD 1  and the second photosensitive element PD 2 . 
       FIG.  9    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. It is noted that the embodiment of  FIG.  9    uses the reference numerals and a part of the contents of the embodiment of  FIG.  7   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiments, and details are not described herein. 
     The difference between a photosensitive device  50  of  FIG.  9    and the photosensitive device  40  of  FIG.  7    is that the photosensitive device  50  further includes a second shielding structure  268 . 
     Please refer to  FIG.  9   . The second shielding structure  268  overlaps the first photosensitive element PD 1  and the first shielding structure  238 , and does not overlap the second photosensitive element PD 2 . The second shielding structure  268  is an opaque structure or a semi-transparent structure. In this embodiment, the second shielding structure  268  is a semi-transparent structure and includes molybdenum, aluminum or other materials. The thickness of the second shielding structure  268  is less than 500 nm. In this embodiment, the second shielding structure  268  is farther away from the first photosensitive element PD 1  than the first shielding structure  238 , and the width of the second shielding structure  268  is greater than the width of the first shielding structure  238 . 
     In this embodiment, the second collimating structure  260  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 , and the second collimating structure  260  and the second shielding structure  268  include the same metal material. For example, the second collimating structure  260  includes a second light shielding layer  262  and a second anti-reflection layer  264  on the second light shielding layer  262 . The second light shielding layer  262  and the second shielding structure  268  include the same metal material, and the second light shielding layer  262  and the second shielding structure  268  are directly connected, and the thickness of the second shielding structure  268  is less than the thickness of the second light shielding layer  262 . In this embodiment, the second anti-reflection layer  264  does not overlap the second shielding structure  268 . In some embodiments, the second light shielding layer  262  is formed together with the second shielding structure  268 , thereby reducing the manufacturing cost of the photosensitive device  50 . 
     Based on the above, the intensity of the photocurrent signal generated by the first photosensitive element PD 1  is smaller than the intensity of the photocurrent signal generated by the second photosensitive element PD 2 , and the dark current signals of the first photosensitive element PD 1  and the second photosensitive element PD 2  have the same intensity. The first shielding structure  238  and the second shielding structure  268  are configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 , as shown in  FIG.  10   . 
       FIG.  11    is a schematic cross-sectional view of a photosensitive device according to an embodiment of the disclosure. It is noted that the embodiment of  FIG.  11    uses the reference numerals and a part of the contents of the embodiment of  FIG.  9   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiments, and details are not described herein. 
     The difference between a photosensitive device  60  of  FIG.  11    and the photosensitive device  50  of  FIG.  9    is that the photosensitive device  60  further includes a third shielding structure  298 . 
     Please refer to  FIG.  11   . The third shielding structure  298  overlaps the first photosensitive element PD 1 , the first shielding structure  238  and the second shielding structure  268 , and does not overlap the second photosensitive element PD 2 . The third shielding structure  298  is an opaque structure or a semi-transparent structure. In this embodiment, the third shielding structure  298  is a semi-transparent structure and includes molybdenum, aluminum or other materials. The thickness of the third shielding structure  298  is less than 500 nm. In this embodiment, the third shielding structure  298  is farther away from the first photosensitive element PD 1  than the second shielding structure  268 , and the width of the third shielding structure  298  is greater than or equal to the width of the second shielding structure  268 . 
     In this embodiment, the third collimating structure  290  is located above the first photosensitive element PD 1  and above the second photosensitive element PD 2 , and the third collimating structure  290  and the third shielding structure  298  include the same metal material. For example, the third collimating structure  290  includes a third light shielding layer  292  and a third anti-reflection layer  294  on the third light shielding layer  292 . The third light shielding layer  292  and the third shielding structure  298  include the same metal material, and the third light shielding layer  292  and the third shielding structure  298  are directly connected, and the thickness of the third shielding structure  298  is less than the thickness of the third light shielding layer  292 . In this embodiment, the third anti-reflection layer  294  does not overlap the third shielding structure  298 . In some embodiments, the third light shielding layer  292  is formed together with the third shielding structure  298 , thereby reducing the manufacturing cost of the photosensitive device  60 . 
     Based on the above, the intensity of the photocurrent signal generated by the first photosensitive element PD 1  is smaller than the intensity of the photocurrent signal generated by the second photosensitive element PD 2 , and the dark current signals of the first photosensitive element PD 1  and the second photosensitive element PD 2  have the same intensity. The first shielding structure  238 , the second shielding structure  268  and the third shielding structure  298  are configured to reduce the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1 , so that the signal difference I 1  between the photocurrent signal and the dark current signal of the first photosensitive element PD 1  is smaller than the signal difference I 2  between the photocurrent signal and the dark current signal of the second photosensitive element PD 2 , as shown in  FIG.  12   . 
       FIG.  13    is a schematic top view of a photosensitive device according to an embodiment of the disclosure.  FIG.  14    is a schematic cross-sectional view taken along line a-a′ of  FIG.  13   . It is noted that the embodiment of  FIG.  13    and  FIG.  14    uses the reference numerals and a part of the contents of the embodiment of  FIG.  1   , and the same or similar reference numerals are used to denote the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, reference may be made to the foregoing embodiments, and details are not described herein. 
     In this embodiment, two or more photosensitive elements PD are connected to each other, and one active element Ta and one active element Tb in the active element layer  110  are electrically connected to the two or more photosensitive elements PD. In some embodiments, the photosensitive element PD is the first photosensitive element of the foregoing embodiments, and the active element Ta is the first active element of the foregoing embodiments. In some embodiments, the photosensitive element PD is the second photosensitive element of the foregoing embodiments, and the active element Ta is the second active element of the foregoing embodiments. 
     The active element layer  110  includes multiple first signal lines SL 1 , multiple second signal lines SL 2 , multiple third signal lines SL 3 , a gate line GL, a common electrode line CL, the active element Ta and the active element Tb. The first signal lines SL 1 , the second signal lines SL 2 , and the third signal lines SL 3  extend along a first direction E 1 , and the gate line GL and the common electrode line CL extend along a second direction E 2 . 
     The active element Ta includes a gate Ga, a channel CHa, a source Sa, and a drain Da. The channel CHa overlaps the gate Ga, and a gate insulating layer  112  is sandwiched between the channel CHa and the gate Ga. An interlayer dielectric layer  114  is located on the gate Ga and the gate insulating layer  112 . The source Sa and the drain Da are located on the interlayer dielectric layer  114  and are electrically connected to the channel CHa through a conductive hole penetrating the gate insulating layer  112  and the interlayer dielectric layer  114 . The gate Ga is electrically connected to the gate line GL. The source Sa is electrically connected to the first signal line SL 1 , and the drain Da is electrically connected to the lower conductive structures LC of the photosensitive elements PD. In this embodiment, the lower conductive structures LC of the photosensitive elements PD are connected to each other. In this embodiment, the lower conductive structure LC of the photosensitive element PD is integrated with the drain Da, but the disclosure is not limited thereto. 
     The active element Tb includes a gate Gb, a channel CHb, a source Sb, and a drain Db. The channel CHb overlaps the gate Gb, and the gate insulating layer  112  is sandwiched between the channel CHb and the gate Gb. The interlayer dielectric layer  114  is located on the gate Gb and the gate insulating layer  112 . The source Sb and the drain Db are located on the interlayer dielectric layer  114  and are electrically connected to the channel CHb through a conductive hole penetrating the gate insulating layer  112  and the interlayer dielectric layer  114 . The gate Gb is electrically connected to the lower conductive structures LC of the photosensitive elements PD. The source Sb is electrically connected to the second signal line SL 2 , and the drain Db is electrically connected to the third signal line SL 3 . 
     In this embodiment, the photosensitive layers PS of the photosensitive elements PD are separated from each other. The upper conductive structures UC of the photosensitive elements PD are connected to each other and electrically connected to the common electrode line CL. In addition, a protective layer (not shown) is optionally included between the lower conductive structure LC of the photosensitive element PD and the photosensitive layer PS, and for example, the protective layer is adapted for suppressing the generation of dark current. 
     To sum up, the embodiments of the disclosure may reduce the difference between the photocurrent signal and the dark current signal of the first photosensitive element without disposing a color filter overlapping the photosensitive element in the photosensitive device. Therefore, the photosensitive device has low manufacturing cost and high reliability.