Patent Publication Number: US-2020285827-A1

Title: Under-display sensing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Invention Patent Application No. 108107736, filed on Mar. 8, 2019. 
     FIELD 
     The disclosure relates to a sensing device, and more particularly to an under-display sensing device. 
     BACKGROUND 
     Fingerprint is commonly used in electronic devices for verification or authentication of personal identity. It is desirable to have quick and accurate recognition of the fingerprint. Among many sensing techniques that have been widely developed, under-display sensing is one of the promising techniques used in fingerprint recognition. Sensing device utilizing such technique includes a fingerprint sensing module that is disposed under a touch screen. However, the position of the fingerprint sensing module in this type of sensing device makes the sensing light easily interfered or influenced by the touch screen, resulting in low sensitivity, low resolution and slow recognizing speed. 
     Referring to  FIG. 1 , a conventional under-display sensing device for generating three dimensional fingerprinting data is disclosed in U.S. Invention Patent Application Publication No. 2018/0225498 A1. The sensing device includes an array of pixels  13  serving as a light source, an optical image sensor  12  disposed under the pixels  13 , a first optically clear adhesive (OCA) layer  14  disposed above the optical image sensor  12 , a transparent support member  15  disposed above the first OCA layer  14 , a pin hole array mask layer  16  spaced from the optical image sensor  12  by the transparent support member  15  and disposed under the pixels  13 , a display encapsulation layer  17  covering the pixels  13 , a second OCA layer  18  disposed over the display encapsulation layer  17 , a transparent cover layer  19  disposed over the second OCA layer  18  and defining a finger placement surface, and optionally a light source  101  for directing light into a user&#39;s finger  10  or directing light to the optical image sensor  12 . In particular, the pin hole array mask layer  16  has a plurality of openings  161  to permit light passing therethrough. Upon the user&#39;s finger  10  contacting the finger placement surface, a light from the pixels  13  is reflected by the finger  10 , then passes through the openings  161  of the pin hole array mask layer  16 , and finally is captured by the optical image sensor  12  for sensing. The image resolution may be controlled by adjusting the spacing between the openings  161 , the diameter of each opening  161 , and the thickness of the transparent support member  15  and the transparent cover layer  19 , thereby increasing the resolution of the fingerprinting data. Moreover, the pin hole array mask layer  16  may further include lenses (not shown in  FIG. 1 ) in the openings  161  to improve image quality and signal-to-noise ratio (SNR). 
     Despite the rapid development of fingerprint recognition, there is still a need for further improvement of the sensitivity of fingerprint sensing device. 
     SUMMARY 
     Therefore, an object of the disclosure is to provide an under-display sensing device that can alleviate at least one of the drawbacks of the prior art. 
     The under-display sensing device of this disclosure includes a liquid crystal display (LCD) module which includes an LCD unit, an optical filter unit and an optical sensing unit. The LCD unit has a display surface and a backlight unit disposed at a side opposite to the display surface for emitting a light. The optical filter unit is disposed on the backlight unit at a side opposite to the LCD unit for filtering the light to obtain a filtered light having predetermined wavelengths. The optical sensing unit is disposed on the optical filter unit at a side opposite to the backlight unit for detecting the filtered light from the optical filter unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic cross sectional view illustrating a conventional under-display sensing device; 
         FIG. 2  is a schematic cross sectional view illustrating a first embodiment of an under-display sensing device according to the disclosure; 
         FIG. 3  is a schematic cross sectional view illustrating a second embodiment of the under-display sensing device according to the disclosure; 
         FIG. 4  is a schematic cross sectional view illustrating a third embodiment of the under-display sensing device according to the disclosure; and 
         FIG. 5  is a schematic cross sectional view illustrating a fourth embodiment of the under-display sensing device according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Before the disclosure is described in greater detail, it should be noted that where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
     Referring to  FIG. 2 , a first embodiment of the under-display sensing device  1  according to the disclosure is provided for sensing a biometric object  100  (such as a finger), and includes a liquid crystal display (LCD) module  2 , an optical filter unit  31 , an optical sensing unit  32  and a circuit control module  4 . The LCD module  2 , the optical filter unit  31 , the optical sensing unit  32  and the circuit control module  4  of the under-display sensing device  1  are integrated into a housing (not shown in the figure). 
     The LCD module  2  includes an LCD unit  21  having a display surface  211 , and a backlight unit  22  disposed at a side opposite to the display surface  211  for emitting a light. The display surface  211  of the LCD unit  21  has a sensing region  212  for recognizing the biometric object  100 . Taking mobile phone as an example, the sensing region  212  maybe a region of the home button for fingerprint recognition of the biometric object  100 . It should be noted that the LCD module  2  may be a conventional LCD and is well known to a person skilled in the art, and thus a detailed description of the structure thereof is omitted herein for brevity. 
     The optical filter unit  31  is disposed on the backlight unit  22  at a side opposite to the LCD unit  21  for filtering the light to obtain a filtered light having predetermined wavelengths. The optical sensing unit  32  is disposed on the optical filter unit  31  at a side opposite to the backlight unit  22  for detecting the filtered light from the optical filter unit  31 . 
     In this embodiment, the optical filter unit  31  includes a transparent substrate  311  disposed under the backlight unit  22 , and an optical filter  312  disposed between the backlight unit  22  and the optical sensing unit  32  for filtering the light. Alternatively, the transparent substrate  311  may be omitted in the optical filter unit  31 , and the optical filter  312  is formed on a surface of the backlight unit  22  opposite to the LCD unit  21 . To have more light reaching the optical sensing unit  32 , the optical filter unit  31  has a transmittance of not lower than 60%. 
     In one example, the transparent substrate  311  is a transparent plate or a transparent circuit board. In one example, the optical filter  312  is a band-pass filter which transmits light having wavelengths within a specific range and blocks light having wavelengths outside the specific range. The optical filter  312  may be made of any suitable material capable of absorbing light having specific wavelengths, and may include stacked optical films having different refractive indices and thicknesses depending on the passband, stopband and spectrum of the light to be filtered. Since the design of the optical films of the band-pass filter is well known to those skilled in this art, a detailed description thereof is omitted herein for brevity. 
     In certain embodiments, for better control of the sensitivity of the optical sensing unit  32 , the optical filter  312  is designed to permit green light (i.e., having a wavelength ranging from 480 nm to 570 nm) to pass therethrough. 
     In certain embodiments, a projection of the optical filter unit  31  on the backlight unit  22  completely or partially covers the backlight unit  22 . That is, the projection of the optical filter unit  31  may have the same size as the backlight unit  22 , or may be located at a portion of the backlight unit  22  that corresponds in position to a particular region such as the sensing region  212  on the LCD unit  21 . In this embodiment, the projection of the optical filter unit  31  completely covers the backlight unit  22 , but is not limited thereto. 
     In certain embodiments, the optical sensing unit  32  includes a circuit board  322 , a plurality of optical sensing chips  321  disposed on the circuit board  322 , and a plurality of film transistors (not shown) electrically connected to the optical sensing chips  321 . The optical sensing chips  321  may be one of a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS). The film transistors are communicatively connected to the circuit control module  4  via the circuit board  322  and may control the signal transmission of the optical sensing chips  321  via the circuit control module  4 . 
     In certain embodiments, a projection of the optical sensing unit  32  on the optical filter unit  31  completely or partially covers the optical filter unit  31 . That is, the projection of optical sensing unit  32  on the optical filter unit  31  may have the same size as the optical filter unit  31  or may be located at a portion of the optical filter unit  31  that corresponds in position to a particular region such as the sensing region  212  on the LCD unit  21 . 
     In certain embodiments, a projection of the optical sensing unit  32  on the backlight unit  22  falls within the backlight unit  22 . That is, the projection of the optical sensing unit  32  on the backlight unit  22  is smaller in size than the backlight unit  22 . 
     The circuit control module  4  is communicatively connected to the optical sensing unit  32  and may include a first control circuit (not shown) for controlling the signal transmission of the optical sensing unit  32 . The circuit control module  4  may be further communicatively connected to the backlight unit  22  through a second control circuit (not shown) for controlling the signal transmission of the backlight unit  22 . 
     In use, when the user&#39;s finger  100  approaches or touches the sensing region  212  on the LCD unit  21 , the light emitted from the backlight unit  22  toward the finger  100  will be reflected by the finger  100  and reaches the optical filter unit  31 . The reflected light passes through the optical filter unit  31  to filter out undesirable wavelengths of light and generate a filtered light having predetermined wavelengths, which is then captured and sensitively detected by the optical sensing unit  32 . Therefore, the sensitivity of the optical sensing chips  321  of the optical sensing unit  32  can be greatly improved. 
     Referring to  FIG. 3 , a second embodiment of the under-display sensing device  1  is similar to the first embodiment except for the optical filter unit  31 . To be specific, in the second embodiment, the optical filter unit  31  is free of the transparent substrate  311 , and the optical filter  312  is formed on and covers the optical sensing chips  321  of the optical sensing unit  32 . In this way, the light lost in traveling from the optical filter unit  31  to the optical sensing chips  321  can be effectively reduced. 
     Referring to  FIG. 4 , a third embodiment of the under-display sensing device  1  is similar to the first embodiment except that the third embodiment further includes a light converging film  313  disposed on the optical filter  312  opposite to the backlight unit  22 . The light converging film  313  has an optical structure that can make the light entering therein refract and converge to a predetermined region so as to be accurately detected by the optical sensing unit  3 . For example, the light converging film  313  may be constructed with stacked optical films having different refractive indices, thicknesses and position angles. Using the stacked optical films having different properties, the light incident on the light converging film  313  may refract and converge to the region where the optical sensing chips  321  is positioned, and thus more light may reach to the optical sensing unit  32 . Since the structure of the light converging film  313  is well known to a person skilled in the art, a detailed description thereof is omitted herein for brevity. 
     It should be noted that the position of the light converging film  313  may be varied according to practical requirements, and is not limited to that disclosed in  FIG. 4 . For example, in certain embodiments, the optical filter  312  and the light converging film  313  may be disposed on opposite surfaces of the transparent substrate  311 . In other embodiments, the light converging film  313  is disposed between the transparent substrate  311  and the optical filter  312 . In other words, the light first converges and then is filtered. Alternatively, the transparent substrate  311  may be omitted, and the optical filter  312  and the light converging film  313  disposed thereon are formed between the backlight unit  22  and the optical sensing unit  32 . 
     In yet other embodiments, the light converging film  313  is disposed on the transparent substrate  311 , and the optical filter  312  is formed on and covers the optical sensing chips  321  of the optical sensing unit  32 , which is similar to the second embodiment (see  FIG. 3 ). 
     Referring to  FIG. 5 , a fourth embodiment of the under-display sensing device  1  is similar to the first embodiment except that the fourth embodiment further includes an auxiliary light source  5  for providing auxiliary light in a range of full wavelengths or specific wavelengths. As such, the auxiliary light source  5  and the backlight unit  22  both provide light for sensing such that more light may reach to the optical sensing unit  32 . The sensitivity of the under-display sensing device  1  is thus improved. 
     To sum up, with the optical filter unit  31  disposed in front of the optical sensing unit  32 , only filtered light with predetermined wavelengths from the optical filter unit  31  reaches to the optical sensing unit  32  for sensing, and thus the under-display sensing device  1  of this disclosure may have an improved sensitivity. 
     In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. It should also be appreciated that reference throughout this specification to “one embodiment,” “an embodiment,” an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects, and that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure. 
     While the disclosure has been described in connection with what are considered the exemplary embodiments, it is understood that this disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.