Patent Publication Number: US-2023162527-A1

Title: Optical fingerprint imaging device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. provisional application Ser. No. 63/281,092, filed on Nov. 19, 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 sensing device, and more particularly to an optical fingerprint imaging device. 
     Description of Related Art 
     Nowadays, the biometric device is closely related to our daily life, replaces the cumbersome process of password input and the inconvenience of passwords being easily forgotten, and provides preferred security and convenience in fields such as security, confidentiality protection, and cash payment. 
     Many optical biometric devices have been developed. For example, uniform light diffusion is achieved through a periodic structure and a diffusion layer under a characteristic pressing surface, so that the fingerprint can receive uniform brightness on the pressing surface. Alternatively, light is transmitted from a bottom light source to the characteristic pressing surface using an annular light guiding structure. Alternatively, secondary excitation light is generated by a light color conversion element, and the wavelength of the light source and the wavelength of the secondary excitation light are further distinguished using a light filter element, so as to obtain a biometric image with preferred contrast. 
     However, the above-mentioned methods are often limited by the limited size of the mechanism, resulting in the inability to obtain biometric images with both high uniformity and high contrast. Therefore, how to reduce the occurrence of stray light spots through the arrangement of a light shielding element and a light emitting element such that a device can have a wide imaging area range in a small-sized mechanism while having high uniform brightness and high contrast is a topic to be pursued in the art. 
     SUMMARY 
     The disclosure provides an optical fingerprint imaging device, which can reduce the occurrence of stray light spots, so that the device can obtain a wide imaging area range in a small-sized mechanism while having high uniform brightness and high contrast. 
     The disclosure provides an optical fingerprint imaging device, which includes a substrate, an imaging module, at least one light emitting element, a light shielding element, a case, and a pressing substrate. The imaging module is disposed on the substrate. The at least one light emitting element is disposed on the substrate and surrounds the imaging module. The light shielding element is disposed on the substrate and is located between the imaging module and the at least one light emitting element. The case is disposed on an edge of the substrate and surrounds the imaging module. The pressing substrate is disposed on the case and covers the imaging module, the at least one light emitting element, and the light shielding element. The optical fingerprint imaging device satisfies conditional expressions of h≤H≤h+(R/tan(θ/2)) and Ravg&lt;S&lt;5Ravg, where h is a height from a field angle origin of the imaging module to the substrate, H is a height of the light shielding element at a measurement position, R is a distance from a center of the imaging module to the measurement position of the light shielding element in a horizontal direction, θ is an angle of a field angle of the imaging module, Ravg is an average value of distances from the center of the imaging module to measurement positions of the light shielding element in the horizontal direction, and S is a distance from the center of the imaging module to a center of the at least one light emitting element in the horizontal direction. 
     In an embodiment of the disclosure, the at least one light emitting element is a light emitting diode, a laser diode, or a vertical-cavity surface-emitting laser. 
     In an embodiment of the disclosure, a haze of the pressing substrate is less than 5%. 
     In an embodiment of the disclosure, the pressing substrate includes a color conversion layer including a medium layer and multiple color conversion materials. 
     In an embodiment of the disclosure, the medium layer is glass, acrylic, epoxy resin, polycarbonate, polyvinyl alcohol, polyethylene terephthalate, polyolefin, silicon, or any combination thereof. 
     In an embodiment of the disclosure, the color conversion materials are quantum dot materials, inorganic fluorescent powders, organic fluorescent dyes, or any combination thereof. 
     In an embodiment of the disclosure, the pressing substrate further includes a base layer connected to the color conversion layer, and the color conversion layer is located between the imaging module and the base layer. 
     In an embodiment of the disclosure, the base layer is glass, polymethyl methacrylate, polycarbonate, polyvinyl alcohol, polyethylene terephthalate, polyolefin, or any combination thereof. 
     In an embodiment of the disclosure, the pressing substrate further includes a filter layer connected between the color conversion layer and the base layer. 
     In an embodiment of the disclosure, the filter layer is a low-pass filter, a high-pass filter, or a band-pass filter. 
     In an embodiment of the disclosure, the light shielding element is plastic or metal, and the light shielding element is non-transparent. 
     In an embodiment of the disclosure, distances from a top surface of the light shielding element to the substrate are all the same. 
     In an embodiment of the disclosure, distances from a top surface of the light shielding element to the substrate gradually increase from adjacent to the imaging module to away from the imaging module. 
     In an embodiment of the disclosure, an appearance of the light shielding element in the horizontal direction is a circle, a square, or a polygon. 
     In an embodiment of the disclosure, the imaging module includes a sensing element, at least one optical lens, a lens barrel, and a lens holder. 
     In an embodiment of the disclosure, the light shielding element and the lens holder are integrally formed. 
     In an embodiment of the disclosure, the light shielding element, the lens barrel, and the lens holder are integrally formed. 
     In an embodiment of the disclosure, the case is plastic or metal. 
     In an embodiment of the disclosure, the case is metal, the case and the substrate have a capacitance value, and the optical fingerprint imaging device changes an activation state according to the capacitance value. 
     Based on the above, in the optical fingerprint imaging device of the disclosure, the light shielding element is disposed between the imaging module and the at least one light emitting element to reduce stray light spots entering the sensing element. In addition, the optical fingerprint imaging device satisfies the conditional expressions of h≤H≤h+(R/tan(θ/2)) and Ravg&lt;S&lt;5Ravg, where h is the height from the field angle origin of the imaging module to the substrate, H is the height of the light shielding element at the measurement position, R is the distance from the center of the imaging module to the measurement position of the light shielding element in the horizontal direction, θ is the angle of the field angle of the imaging module, Ravg is the average value of the distances from the center of the imaging module to the measurement positions of the light shielding element in the horizontal direction, and S is the distance from the center of the imaging module to the center of the light emitting element in the horizontal direction. In this way, through the arrangement of the light shielding element and the light emitting element, the occurrence of stray light spots can be reduced, so that the device can have a wide imaging area range in a small-sized mechanism while having high uniform brightness and high contrast, thereby obtaining preferable optical sensing. 
     In order for the features and advantages of the disclosure to be more comprehensible, the following specific embodiments are described in detail in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional schematic view of an optical fingerprint imaging device according to an embodiment of the disclosure. 
         FIG.  2    is a top schematic view of the optical fingerprint imaging device of  FIG.  1   . 
         FIG.  3    is an exploded schematic view of the optical fingerprint imaging device of  FIG.  1   . 
         FIG.  4 A  and  FIG.  4 B  are respectively schematic views of a light shielding element according to different embodiments of the disclosure. 
         FIG.  5 A  to  FIG.  5 C  are respectively schematic views of a pressing substrate according to different embodiments of the disclosure. 
         FIG.  6    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure. 
         FIG.  7 A  and  FIG.  7 B  are respectively schematic views of a light shielding element according to different embodiments of the disclosure. 
         FIG.  8    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure. 
         FIG.  9    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG.  1    is a cross-sectional schematic view of an optical fingerprint imaging device according to an embodiment of the disclosure.  FIG.  2    is a top schematic view of the optical fingerprint imaging device of  FIG.  1   .  FIG.  3    is an exploded schematic view of the optical fingerprint imaging device of  FIG.  1   . Please refer to  FIG.  1    to  FIG.  3   . The embodiment provides an optical fingerprint imaging device  100  for sensing a finger  10  to obtain fingerprint information. The optical fingerprint imaging device  100  includes a substrate  110 , an imaging module  120 , at least one light emitting element  130 , a light shielding element  140 , a case  150 , and a pressing substrate  160 . The imaging module  120 , the at least one light emitting element  130 , the light shielding element  140 , and the case  150  are all disposed on the substrate  110 . 
     The substrate  110  is, for example, a printed circuit board (PCB), a flexible printed circuit board (FPCB), a glass carrier having a circuit, or a ceramic substrate having a circuit, but not limited thereto. 
     The imaging module  120  is used to capture an image of the finger  10  and has a field angle, and an angle A of the field angle is between 90 degrees and 150 degrees. Specifically, in the embodiment, the imaging module  120  includes a sensing element  122 , at least one optical lens  124 , a lens barrel  126 , and a lens holder  128 . The sensing element  122  is, for example, a charge coupled device (CCD), a complementary metal-oxide semiconductor (CMOS), or other suitable image sensing elements, but the disclosure is not limited thereto. The at least one optical lens  124  includes, for example, a combination of one or more optical lens elements having dioptric powers, such as various combinations of non-planar lens elements including bi-concave lenses, bi-convex lenses, concave-convex lenses, convex-concave lenses, plano-convex lenses, plano-concave lenses, etc., but the disclosure is not limited thereto. The lens barrel  126  is used to carry the at least one optical lens  124 , and the lens barrel  126  may be fixed to the lens holder  128  by threads or other types of fixing structures. The materials of the lens barrel  126  and the lens holder  128  may be metal or plastic, but the disclosure is not limited thereto. 
     The at least one light emitting element  130  is disposed on the substrate  110  and surrounds the imaging module  120 . The at least one light emitting element  130  is used to provide a sensing light beam to the finger  10 , and the finger  10  reflects a light beam with the fingerprint information back to the imaging module  120 . For example, in the embodiment, there are, for example, four light emitting elements  130 , which are evenly distributed on the periphery of the imaging module  120 , as shown in  FIG.  2   . The at least one light emitting element  130  is, for example, a light emitting diode (LED), a laser diode (LD), or a vertical-cavity surface-emitting laser (VCSEL). In addition, the provided light beam may include visible light, non-visible light, or a combination of the two, but the disclosure is not limited thereto. The non-visible light may be infrared light, but the disclosure is not limited thereto. 
       FIG.  4 A  and  FIG.  4 B  are respectively schematic views of a light shielding element according to different embodiments of the disclosure. Please refer to  FIG.  1    to  FIG.  4 A  first. The light shielding element  140  shown in  FIG.  4 A  may at least be applied to the optical fingerprint imaging device  100  of  FIG.  1   , so the following description takes the application of the light shielding element  140  shown in  FIG.  4 A  to the optical fingerprint imaging device  100  of  FIG.  1    as an example. The light shielding element  140  is disposed on the substrate  110  and is located between the imaging module  120  and the at least one light emitting element  130 . The light shielding element  140  is used to reduce the occurrence of stray light spots, thereby improving the quality of fingerprint imaging. The light shielding element  140  is plastic or metal, and the light emitting wavelength of the light shielding element  140  to the light emitting element  130  is non-transparent. In the embodiment, distances from a top surface S 1  of the light shielding element  140  to the substrate  110  are all the same, but the disclosure is not limited thereto. That is, the light shielding element  140  has the top surface S 1  parallel to a horizontal direction. In addition, in the embodiment, the appearance of the light shielding element  140  in the horizontal direction is a circle. However, in different embodiments, the appearance of the light shielding element  140 A in the horizontal direction is a square or another type of polygon, as shown in  FIG.  4 B , but the disclosure is not limited thereto. 
     Please continue to refer to  FIG.  1    to  FIG.  3   . The case  150  is disposed on the edge of the substrate  110  and surrounds the imaging module  120 , wherein the light emitting element  130  is located between the imaging module  120  and the case  150 . The case  150  is, for example, plastic or metal, and is used to support the pressing substrate  160  disposed thereon and dustproof internal components. In an embodiment, the material of the case  150  is metal, so that the case  150  and the substrate  110  have a capacitance value, such that the optical fingerprint imaging device  110  may change an activation state according to the magnitude of or changes in the capacitance value. 
       FIG.  5 A  to  FIG.  5 C  are respectively schematic views of a pressing substrate according to different embodiments of the disclosure. Please refer to  FIG.  1    to  FIG.  3    and  FIG.  5 A  to  FIG.  5 C  first. The pressing substrate  160  is disposed on the case  150  and covers the imaging module  120 , the at least one light emitting element  130 , and the light shielding element  140 . The pressing substrate  160  is used to allow the finger  10  to be pressed against, so that the distance from the finger  10  to the imaging module  120  is fixed. In the embodiment, the haze of the pressing substrate  160  is less than 5%. In an embodiment, a pressing substrate  160 A includes a color conversion layer  162  for changing the wavelength of the light emitting element  130  beam. In detail, the color conversion layer  162  includes a medium layer (not shown) and multiple color conversion materials (not shown) evenly dispersed in the medium layer. The medium layer is glass, acrylic, epoxy resin, polycarbonate, polyvinyl alcohol, polyethylene terephthalate, polyolefin, silicon, or any combination thereof, and the color conversion materials are quantum dot materials, inorganic fluorescent powders, organic fluorescent dyes, or any combination thereof. In another embodiment, the pressing substrate  160 A may also directly replace the color conversion layer  162  with the medium layer to form a transparent plate, but the disclosure is not limited thereto. 
     In the embodiment, the pressing substrate  160  includes the color conversion layer  162  and a base layer  164  connected to the color conversion layer  162 , and the base layer  164  is used to improve the reliability of the pressing substrate  160 . The color conversion layer  162  is located between the imaging module  120  and the base layer  164 . For example, the base layer  164  is glass, polymethyl methacrylate, polycarbonate, polyvinyl alcohol, polyethylene terephthalate, polyolefin, or any combination thereof, but the disclosure is not limited thereto. In yet another embodiment, a pressing substrate  160 B may further include a filter layer  166  connected between the color conversion layer  162  and the base layer  164 . The filter layer  166  is used to filter out light rays with a specific wavelength, thereby improving the fingerprint imaging quality of the optical fingerprint imaging device  100 . For example, the filter layer  166  is a low-pass filter, a high-pass filter, or a band-pass filter and may be made into a different type of filter such as a reflection filter or an absorption filter, but the disclosure is not limited thereto. 
     Please continue to refer to  FIG.  1    to  FIG.  3   . It is worth mentioning that in the embodiment, the optical fingerprint imaging device  100  satisfies conditional expressions of h≤H≤h+(R/tan(θ/2)) and Ravg&lt;S&lt;5Ravg, where h is a height D 1  from a field angle origin B of the imaging module  120  to the substrate  110 , H is the height of the light shielding element  140  at a measurement position (that is, in the light shielding element  140 , a distance D 2  from the top surface S 1  to the substrate  110 ), R is a distance D 3  from a center C 1  of the imaging module  120  to the measurement position of the light shielding element  140  in the horizontal direction, θ is the angle A of the field angle of the imaging module  120 , Ravg is the average value of the distances D 3  from the center C 1  of the imaging module  120  to the measurement positions of the light shielding element  140  in the horizontal direction, and S is a distance D 4  from the center C 1  of the imaging module  120  to a center C 2  of the light emitting element  130  in the horizontal direction, wherein the measurement positions in the different parameter definitions are the same position. In this way, through the arrangement of the light shielding element  140  and the light emitting element  130 , the occurrence of stray light spots can be reduced, so that the device can have a wide imaging area range in a small-sized mechanism while having high uniform brightness and high contrast, thereby obtaining preferable optical sensing. 
       FIG.  6    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure.  FIG.  7 A  and  FIG.  7 B  are respectively schematic views of a light shielding element according to different embodiments of the disclosure. Please refer to  FIG.  6    to  FIG.  7 B . An optical fingerprint imaging device  100 A of the embodiment is similar to the optical fingerprint imaging device  100  shown in  FIG.  1   . The difference between the two is that in the embodiment, the distances D 2  from a top surface S 2  of a light shielding element  140 B to the substrate  110  gradually increase from adjacent to the imaging module  120  to away from the imaging module  120 . In this way, the material can be further saved and the fingerprint imaging quality of the optical fingerprint imaging device  100  can be improved. Similar to the embodiment shown in  FIG.  4 A  and  FIG.  4 B , the appearance of the light shielding element  140 B of the embodiment in the horizontal direction is a circle, as shown in  FIG.  7 A . However, in different embodiments, the appearance of a light shielding element  140 C in the horizontal direction is a square or another type of polygon, as shown in  FIG.  7 B , but the disclosure is not limited thereto. 
       FIG.  8    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure. Please refer to  FIG.  8   . An optical fingerprint imaging device  100 B of the embodiment is similar to the optical fingerprint imaging device  100  shown in  FIG.  1   . The difference between the two is that in the embodiment, a light shielding element  140 D and a lens holder  128 A in an imaging module  120 A are integrally formed. Besides, similar to the light shielding element  140  shown in  FIG.  1   , the light shielding element  140 D has the top surface S 1  parallel to the horizontal direction. In this way, the material can be further saved and the reliability of the optical fingerprint imaging device  100 B can be increased. 
       FIG.  9    is a cross-sectional schematic view of an optical fingerprint imaging device according to another embodiment of the disclosure. Please refer to  FIG.  9   . An optical fingerprint imaging device  100 C of the embodiment is similar to the optical fingerprint imaging device  100  shown in  FIG.  1   . The difference between the two is that in the embodiment, a light shielding element  140 E and the lens holder  128 A in the imaging module  120 A are integrally formed. Besides, similar to the light shielding element  140 B shown in  FIG.  6   , distances from the top surface S 2  of the light shielding element  140 E to the substrate  110  gradually increase from adjacent to the imaging module  120 A to away from the imaging module  120 A. In this way, the material can be further saved and the fingerprint imaging quality of the optical fingerprint imaging device  100 C can be improved. In addition, the material can be further saved and the reliability of the optical fingerprint imaging device  100 C can be increased. 
     In summary, in the optical fingerprint imaging device of the disclosure, the light shielding element is disposed between the imaging module and the at least one light emitting element to reduce stray light spots entering the sensing element. In addition, the optical fingerprint imaging device satisfies the conditional expressions of h≤H≤h+(R/tan(θ/2)) and Ravg&lt;S&lt;5Ravg, where h is the height from the field angle origin of the imaging module to the substrate, H is the height of the light shielding element at the measurement position, R is the distance from the center of the imaging module to the measurement position of the light shielding element in the horizontal direction, θ is the angle of the field angle of the imaging module, Ravg is the average value of the distances from the center of the imaging module to the measurement positions of the light shielding element in the horizontal direction, and S is the distance from the center of the imaging module to the center of the light emitting element in the horizontal direction. In this way, through the arrangement of the light shielding element and the light emitting element, the occurrence of stray light spots can be reduced, so that the device can have a wide imaging area range in a small-sized mechanism while having high uniform brightness and high contrast, thereby obtaining preferable optical sensing. 
     Although the disclosure has been disclosed in the above embodiments, the embodiments are not intended to limit the disclosure. Persons skilled in the art may make some changes and modifications without departing from the spirit and scope of the disclosure. Therefore, the protection scope of the disclosure shall be defined by the appended claims.