Patent Publication Number: US-2022214215-A1

Title: Optical sensor and display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application No. PCT/JP2020/035042, filed on Sep. 16, 2020, which claims priority to Japanese Patent Application No. 2019-181626, filed on Oct. 1, 2019, the disclosures of which are incorporated herein by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An embodiment of the present invention relates to an optical sensor that can control the wavelength of incident light on a photoelectric conversion element. An embodiment of the present invention relates to an optical sensor including, for example, a Fabry-Perot interferometer and a photoelectric conversion element. An embodiment of the present invention relates to a display device including this type of optical sensor. 
     2. Description of Related Art 
     As a display device with an optical sensor that can scan an image or the like, Japanese Unexamined Patent Publication No. 2009-294315 discloses a liquid crystal display device including an array substrate provided with a plurality of switching elements and a plurality of optical sensors, a counter substrate, a liquid crystal layer, and an alignment control unit, wherein the alignment control unit is provided on at least one of the array substrate and the counter substrate, and the plurality of optical sensors overlap on the alignment control unit. 
     The optical sensor is applicable to various applications, but the appropriate wavelength differs depending on the object to be sensed. For example, when the optical sensor is utilized for fingerprint authentication, a visible light band (for example, 550 nm) is utilized, and when it is utilized for vein authentication, a near infrared light band (for example, 900 nm) is utilized. 
     SUMMARY OF THE INVENTION 
     An optical sensor in an embodiment according to the present invention includes at least one interferometer having a pair of semi-transparent mirrors spaced apart and oppositely arranged, and at least one position of the pair of semi-transparent mirrors can be displaced, at least one collimating element overlapping the at least one interferometer, and at least one photoelectric conversion element having sensitivity in the visible and near infrared light bands and receiving light passing through the interferometer and the collimating element. 
     A display device in an embodiment according to the present invention includes an optical sensor, and a display panel overlapping the optical sensor. The optical sensor including at least one interferometer having a pair of semi-transparent mirrors spaced apart and oppositely arranged, and at least one position of the pair of semi-transparent mirrors can be displaced, at least one collimating element overlapping the at least one interferometer, and at least one photoelectric conversion element having sensitivity in the visible and near light infrared bands and receiving light passing through the interferometer and the collimating element. The display panel is located on the side of the at least one interferometer of the optical sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a schematic plan view of an optical sensor according to an embodiment of the present invention; 
         FIG. 1B  is a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention, and shows a cross-sectional structure corresponding to A 1 -A 2  shown in  FIG. 1A ; 
         FIG. 2A  shows a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention; 
         FIG. 2B  shows a method of performing authentication using an optical sensor according to an embodiment of the present invention; 
         FIG. 3  shows a schematic cross-sectional view of a pixel in an optical sensor according to an embodiment of the present invention; 
         FIG. 4A  shows a schematic plan view of a collimating element utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 4B  is a schematic cross-sectional view of a collimating element of the present invention, and shows an example of a cross-sectional structure corresponding to B 1 -B 2  shown in  FIG. 2A ; 
         FIG. 4C  is a schematic cross-sectional view of a collimating element utilized in an optical sensor according to an embodiment of the present invention, and shows another example of a cross-sectional structure corresponding to B 1 -B 2  shown in  FIG. 2A ; 
         FIG. 5A  shows a schematic plan view of an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 5B  is a schematic cross-sectional view of an interferometer utilized in an optical sensor according to an embodiment of the present invention, and shows a cross-sectional structure corresponding to C 1 -C 2  shown in  FIG. 5A ; 
         FIG. 5C  is a schematic cross-sectional view of an interferometer utilized in an optical sensor according to an embodiment of the present invention, and shows a cross-sectional structure corresponding to D 1 -D 2  shown in  FIG. 5A ; 
         FIG. 6A  is a diagram for explaining the operation of an interferometer utilized in an optical sensor according to an embodiment of the present invention, and shows a state in which a gap between two semi-transparent mirrors is Z 1 , 
         FIG. 6B  is a diagram for explaining an operation of an interferometer utilized in an optical sensor according to an embodiment of the present invention, and shows a state in which a gap between a set of semi-transparent mirrors is Z 2  (&lt;Z 1 ); 
         FIG. 7A  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 7B  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 7C  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 7D  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 8A  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 8B  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 8C  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 8D  shows an example of a method of manufacturing an interferometer utilized in an optical sensor according to an embodiment of the present invention; 
         FIG. 9A  shows an example of a pixel circuit in an optical sensor according to an embodiment of the present invention; 
         FIG. 9B  shows an example of a control circuit of an interferometer in an optical sensor according to an embodiment of the present invention; 
         FIG. 10  shows an example of a method of driving an optical sensor according to an embodiment of the present invention; 
         FIG. 11A  shows a schematic plan view of an optical sensor according to an embodiment of the present invention; 
         FIG. 11B  is a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention, and shows a cross-sectional structure corresponding to E 1 -E 2  shown in  FIG. 11A ; 
         FIG. 12A  shows a schematic plan view of an optical sensor according to an embodiment of the present invention; 
         FIG. 12B  is a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention, and shows a cross-sectional structure corresponding to F 1 -F 2  shown in  FIG. 12A ; 
         FIG. 13  shows a configuration of a display device according to an embodiment of the present invention; 
         FIG. 14A  shows a display mode that is one of the operation modes of a display device according to an embodiment of the present invention; 
         FIG. 14B  shows a sensing mode that is one of the operation modes of the display device according to an embodiment of the present invention; and 
         FIG. 14C  shows a hybrid mode that is one of the operation modes of a display device according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The present invention may be carried out in various forms without departing from the gist thereof, and is not to be construed as being limited to any of the following embodiments. Although the drawings may schematically represent the width, thickness, shape, and the like of each part in comparison with the actual embodiment in order to clarify the description, they are merely examples and do not limit the interpretation of the present invention. In the present specification and each of the figures, elements similar to those described previously with respect to the figures already mentioned are designated by the same reference numerals (or numbers followed by a, b, etc.), and a detailed description thereof may be omitted as appropriate. Furthermore, the characters “first” and “second” appended to each element are convenient signs used to distinguish each element, and have no further meaning unless specifically described. 
     As used herein, where a member or region is “on” (or “below”) another member or region, this includes cases where it is not only directly on (or just under) the other member or region but also above (or below) the other member or region, unless otherwise specified. That is, it includes the case where another component is included in between above (or below) other members or regions. 
     First Embodiment 
     An optical sensor according to an embodiment of the present invention has a function of dispersing incident light in a visible light band to a near infrared light band and detecting the spectroscopic light. The optical sensor according to the present embodiment will be described below with reference to the drawings. 
     1. Optical Sensor 
       FIG. 1A  shows a schematic plan view of the optical sensor  100   a  according to the present embodiment, and  FIG. 1B  shows a schematic cross-sectional view A 1 -A 2  shown in the schematic plan view. As shown in  FIG. 1A , the optical sensor  100   a  has a light receiving part  104 . A plurality of pixels  106  are arranged in a first direction and a second direction intersecting the first direction in the light receiving part  104 . The pixel  106  includes an interferometer  108 , a collimating element  110 , and a photoelectric conversion element  114 . 
     As shown in  FIG. 1B , the pixel  106  has a structure in which the interferometer  108 , the collimating element  110 , and a photo sensor  112  overlap from the light incident side. The photo sensor  112  is composed of a photoelectric conversion element  114  arranged corresponding to the pixel  106 . The photoelectric conversion element  114  is arranged on a base plate  102 . A glass substrate, a plastic substrate (including a flexible plastic film) or the like is used as the base plate  102 . The optical sensor  100   a  has a structure in which light passing through the interferometer  108  and the collimating element  110  enters the photoelectric conversion element  114  composing the photo sensor  112 . 
     The interferometer  108  has a structure in which a first semi-transparent mirror  116  and a second semi-transparent mirror  118  are oppositely arranged with a gap. In the interferometer  108 , the position of at least one of the first semi-transparent mirror  116  and the second semi-transparent mirror  118  can be displaced, and has the function of spectrally dispersing the transmitted light by adjusting a gap between the pair of semi-transparent mirrors. 
     The collimating element  110  has a light guide path  120 , and an absorption part  122  is arranged to surround the light guide path  120 . The light guide path  120  is transparent to light in the visible light band to the near infrared light band, and an aperture of the light guide path  120  is preferably large enough to expose the light receiving surface of at least one photoelectric conversion element  114 . The collimating element  110  has a function for adjusting the incident light beam into a parallel light beam by having a structure in which the light guide path  120  is surrounded by the absorption part  122 . The collimating element  110  is preferably arranged so that the light guide path  120  corresponds to the photoelectric conversion element  114 . The collimating element  110  makes it possible to make collimated light beams incident on the photoelectric conversion element  114 , and it is possible to prevent light from being incident on the adjacent photoelectric conversion element (also called crosstalk). The collimating element  110  may be omitted, and in that case, the photo sensor  112  is arranged under the interferometer  108 . 
     The photoelectric conversion element  114  converts light energy of incident light to electric energy, and has sensitivity to light in a visible light band to a near infrared light band. The photoelectric conversion element  114  is, for example, a semiconductor element such as a photodiode or a phototransistor. The optical sensor  100   a  according to the present embodiment can image an object since the pixels  106  including the photoelectric conversion element  114  are arranged in the first direction and the second direction in the light receiving part  104 . Since the light incident on the photoelectric conversion element  114  is the light spectrally dispersed by the interferometer  108 , the optical sensor  100   a  can selectively receive light of a specific wavelength transmitted through the object, reflected from the object, or emitted by the object, and can acquire information about the object as two-dimensional data. 
     The optical sensor  100   a  is not limited to the configuration shown in  FIG. 1A  and  FIG. 1B , and the photo sensor  112  may have a configuration in which the photoelectric conversion elements  114  are arrayed one-dimensionally. In this configuration, the photo sensor  112  can be regarded as a detection head in which the photoelectric conversion elements  114  are arrayed one-dimensionally, and two-dimensional data on an object can be acquired by scanning the detection head in one direction. Although not shown in  FIG. 1A  and  FIG. 1B , the optical sensor  100   a  may be arranged with a driving circuit for driving the pixel  106  and a reading circuit for reading the output signal of the photo sensor  112  outside the light receiving part  104 . 
     The optical sensor  100   a  may further include a lighting unit  126  on the light incident side of the interferometer  108 , as shown in  FIG. 2A . The lighting unit  126  is composed of a light emitting diode and a light guide plate, and the light guide plate may be provided with a through hole  128 . The lighting unit  126  may be configured to illuminate the object  200  and cause reflected light to enter the interferometer  108  through the through hole  128 . The optical sensor  100   a  shown in  FIG. 2A  allows the light reflected by the object  200  to be injected into the through holes  128  when the object  200  is irradiated with white light including near-infrared light from the lighting unit  126 , so that the light spectrally dispersed by the interferometer  108  can be detected by the photoelectric conversion element  114 . A plurality of kinds of information attributable to the optical characteristics of the object  200  can be obtained by spectroscopy of the reflected light by the interferometer  108 . 
     The lighting unit  126  may be disposed on the opposite side of the object  200 . 
     That is, the lighting unit  126  and the optical sensor  100   a  may be arranged across the object  200 . According to this arrangement, the light emitted from the lighting unit  126  and transmitted through the object  200  enters the optical sensor  100   a.    
     2. Pixel 
       FIG. 3  shows a cross-sectional structure of the pixel  106 . The pixel  106  has a structure in which the interferometer  108 , the collimating element  110 , and the photoelectric conversion element  114  overlap from the light incident side. The pixel  106  is configured to optically adjust the light spectrally dispersed by the interferometer  108  to parallel light by the collimating element  110  and enter the photoelectric conversion element  114 . It is possible to obtain a two-dimensional image having a high resolution, since each pixel  106  of the optical sensor  100   a  has such a configuration. 
     The interferometer  108  includes the first semi-transparent mirror  116 , a window  134  formed of an insulating material that transmits light in at least the visible and near-infrared bands, a beam  132  having elasticity and supporting the window  134 , a pillar  130  supporting the beam  132 , the second semi-transparent mirror  118 , and a substrate  140  formed of an insulating material that transmits light in at least the visible and near-infrared bands. The pillar  130  supports the beam  132  and has a function as a spacer separating the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . 
     The first semi-transparent mirror  116  and the second semi-transparent mirror  118  are formed of a film having a high refractive index (high refractive index film). A semiconductor material such as silicon (Si) or germanium (Ge) is used as the high refractive index film. Also, the first semi-transparent mirror  116  and the second semi-transparent mirror  118  may be formed of a semi-transparent film made of a metal such as aluminum. The first semi-transparent mirror  116  and the second semi-transparent mirror  118  can be formed of a metal oxide material used for a transparent conductive film such as indium tin oxide (ITO) or indium zinc oxide (IZO). The beam  132  is bent to change the size of a gap  138  when an electrostatic force is applied between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . The interferometer  108  has a function of displacing at least one position of the first semi-transparent mirror  116  and the second semi-transparent mirror  118  to change the size of the gap  138 , thereby interfering with the incident light and emitting the light whose wavelength is changed from the side of the second semi-transparent mirror  118 . 
     The light guide path  120  of the collimating element  110  is arranged to overlap the photoelectric conversion element  114 . The absorption part  122  is arranged around the light guide path  120 . Even when the photoelectric conversion elements  114  are arranged in a matrix, it is possible to prevent stray light from entering the adjacent photoelectric conversion elements by arranging the collimating elements  110 . In other words, crosstalk between pixels can be prevented. The collimating element  110  has a function of adjusting the light output from the interferometer  108  so that it becomes a parallel light beam, and has a thickness of 10 μm to 200 μm, for example, about 100 μm. 
     The photoelectric conversion element  114  is irradiated with light passing through the collimating element  110 . The photoelectric conversion element  114  has a function of converting light energy to electric energy by a photovoltaic effect when the light receiving surface is irradiated with light. The photovoltaic power generated in the photoelectric conversion element  114  is read out as an electric signal. The optical sensor  100   a  has pixels  106  arranged in a matrix in the light receiving part  104 , and can obtain information based on the optical characteristics of an object as two-dimensional information (image information) by obtaining signals from each pixel. 
     3. Photoelectric Conversion Element 
     The photoelectric conversion element  114  includes a photoelectric conversion layer  152 , a first electrode  156 , and a second electrode  158 , as shown in  FIG. 3 . The photoelectric conversion layer  152  is arranged on the base plate  102 . The photoelectric conversion layer  152  is formed of an inorganic semiconductor material or an organic semiconductor material that exhibits a photovoltaic effect on light in the visible and near-infrared bands. The photoelectric conversion layer  152  is connected to the first electrode  156  and the second electrode  158 . One of the first electrode  156  and the second electrode  158  is a positive electrode and the other is a negative electrode. An insulating layer  154  may be disposed on the photoelectric conversion layer  152 , and the first electrode  156  and the second electrode  158  may be connected to the photoelectric conversion layer  152  through contact holes formed in the insulating layer  154 . Further, a planarizing layer  160  formed of an insulating material may be disposed on the upper layers of the first electrode  156  and the second electrode  158 . Although the photoelectric conversion element  114  shown in  FIG. 3  shows an example in which the electrode is a planar type, as another embodiment, the first electrode  156  and the second electrode  158  may be a sandwich type sandwiching the photoelectric conversion layer  152 . The photoelectric conversion element  114  has a light receiving surface in a region inside the first electrode  156  and the second electrode  158 . 
     For example, the photoelectric conversion element  114  is formed of crystalline silicon. It is possible to obtain the photoelectric effect by light in the visible to near-infrared light band by forming a photodiode with such a silicon semiconductor, since the band gap of single-crystal silicon is 1.1 eV and that of poly-crystalline silicon is roughly 1.2 to 1.4 eV. The photoelectric conversion element  114  may be formed of an organic semiconductor that is sensitive to light in the visible to near-infrared light bands. A π-conjugated polymer material can be used as the organic semiconductor. The photoelectric conversion element  114  can be made thinner by forming the photoelectric conversion layer  152  as a thin film. Although not shown, a photodiode formed on a semiconductor substrate may be used as the photoelectric conversion element  114 . 
     4. Collimating Element 
       FIG. 4A  shows a plan view of the collimating element  110 . The collimating element  110  shown in  FIG. 4A  is an example, and has a structure in which the light guide path  120  is arranged in the absorption part  122 . The light guide path  120  has a configuration arranged in a first direction and a second direction intersecting the first direction. The light guide path  120  is formed of a member which transmits light in the visible and near infrared light bands, and the absorption part  122  is formed of a member which absorbs light. The structures of the light guide path  120  and the absorption part  122  can vary and an example thereof will be described with reference to  FIG. 4B  and  FIG. 4C . 
       FIG. 4B  shows an example of a cross-sectional structure of the collimating element  110  corresponding to B 1 -B 2  shown in a plan view. The collimating element  110  shown in  FIG. 4B  has a structure in which a plurality of light shielding layers  142  are arranged across a transparent resin layer  146 . The light shielding layer  142  is formed of a through hole  144 , and a light guide path  120  is formed by arranging the through hole  144  to overlap. The collimating element  110  shown in  FIG. 4B  can be simply manufactured by alternately laminating the light shielding layer  142  and the transparent resin layer  146 . A resin material containing titanium black, carbon black or the like as a black pigment is used for the light shielding layer  142 , and an acrylic resin, an epoxy resin or the like can be used for the transparent resin layer  146 . The collimating element  110  shown in  FIG. 4B  has absorption parts  122  formed by overlapping light shielding layers  142 , and light guide paths  120  formed by overlapping regions of through holes  144 . 
     The collimating element  110  shown in  FIG. 4C  is arranged with a light guide pillar  150  to pass through the light shielding layer  148 . The light shielding layer  148  is arranged to surround the light guide pillar  150  along the longitudinal direction thereof. A resin material containing titanium black, carbon black or the like as a black pigment is used as the light shielding layer  148 . The light shielding layer  148  may be formed of an organic material or an inorganic material, and the surface of the light shielding layer may be blackened to suppress reflection, for example, by black plating. The light guide pillar  150  is formed of a rod made of a transparent resin material, glass or plastic. In the collimating element  110  shown in  FIG. 4C , the light guide pillar  150  corresponds to the light guide path  120 , and the light shielding layer  148  corresponds to the absorption part  122 . The optical sensor  100   a  according to the present embodiment may have both the configurations shown in  FIG. 4B  and  FIG. 4C . 
     5. Interferometer 
       FIG. 5A ,  FIG. 5B , and  FIG. 5C  show a structure of interferometer  108 .  FIG. 5A  shows a plan view of interferometer  108 ,  FIG. 5B  shows a cross sectional view corresponding to C 1 -C 2  shown in a plan view, and  FIG. 5C  shows a cross sectional view corresponding to D 1 -D 2  shown in a plan view. 
     The interferometer  108  has a fine structure including a movable part and a gap. As shown in  FIG. 5  A, the interferometer  108  includes the pillar  130  arranged at four corners, a window  134  arranged surrounded by the pillar  130 , and the beam  132  arranged to bridge between the pillar  130  and the window  134 . The window  134  is connected to the beam  132  at four locations, thereby maintaining a horizontal state and maintaining a stable state. The periphery of the window  134  is separated from the pillar  130  by providing the gap  138  except for the portion of the beam  132 . The first semi-transparent mirror  116  and the second semi-transparent mirror  118  are arranged to have overlapping portions in a plan view. For example, it is possible to ensure that interfere the incident light is interfered with and perform spectroscopy by arranging the first semi-transparent mirror  116  arranged on the light incident side so that the area of the second semi-transparent mirror  118  arranged on the light emitting side is increased with respect to the first semi-transparent mirror  116  arranged on the light incident side. 
     As shown in  FIG. 5B , the first semi-transparent mirror  116  is arranged on the side of the window  134 , and the second semi-transparent mirror  118  is arranged on the side of the substrate  140 . The gap  136  is formed between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . The gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  is set by the height of the pillar  130 . The gap  138  is formed between the window  134  and the pillar  130 . The window  134  can be displaced vertically without interference (without sliding) with the pillar  130  by the gap  138 . 
     As shown in  FIG. 5C , since both ends of the window  134  are supported by the beam  132  (four portions), the window  134  is maintained in a substantially horizontal state to prevent twisting and tilting, and the first semi-transparent mirror  1165  and the second semi-transparent mirror  118  are maintained in parallel. The window  134  is a movable part and is displaced vertically in the cross-sectional view of  FIG. 5C . The first semi-transparent mirror  116  is arranged in the window  134 , and the second semi-transparent mirror  118  is arranged on the substrate  140 . The gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  is set to be approximately the same range as the wavelength band of the light to be spectrally dispersed, and is arranged to have a gap of, for example, 1000 nm to 1500 nm. 
     The interferometer  108  has a function of causing interference of light between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  and outputting light of a specific wavelength as transmitted light. These interferometers are also referred to as Fabry-Perot interferometers. Thus, the interferometer  108  may also be referred to as a Fabry-Perot interferometer. 
     The interferometer  108  can change the wavelength of transmitted light by adjusting the gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . It is possible to change the gap between the two semi-transparent mirrors and select the wavelength of the interfering light by applying an electrostatic force between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . In other words, the wavelength of the transmitted light can be changed by the potential difference between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . The interferometer  108  having such a structure and function can be manufactured by microelectromechanical system (MEMS) technology. The interferometer  108  includes a micro-mechanical element, such as the semi-transmissive mirror, formed by a MEMS structure in which the micro-mechanical element operates by electrical action. 
       FIG. 6A  shows a state of not applying a voltage between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . That is, the gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  is Z 1 , indicating the initial state. In this state, the incident light interferes between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  when white light enters from the side of the first semi-transparent mirror  116 , and the light of the wavelength λ 1  intensified by the interference is emitted from the second semi-transparent mirror  118  as transmitted light. 
       FIG. 6B  shows a state of applying a predetermined voltage between the first semi-transparent mirror  116  and the second semi-transparent mirror  118 . The electrostatic force works by the applied voltage, and the gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  changes to Z 2 . 
     It is assumed that when applied with the voltage, the gap Z 2  is smaller than the gap Z 1  in the initial state (Z 2 &lt;Z 1 ). In this case, the wavelength λ 2  of the light emitted from the side of the second semi-transparent mirror  118  is shorter than the wavelength λ 1  of the initial state, and light having a shorter wavelength is emitted from the interferometer  108 . In this way, the interferometer  108  has a function of dispersing the incident light, and the wavelength of the spectroscopic light can be changed by electrically controlling the gap between the two semi-transmissive mirrors. 
     6. Method for Fabricating Interferometer 
     Referring to  FIG. 7A ,  FIG. 7B ,  FIG. 7C , and  FIG. 7D , and  FIG. 8A ,  FIG. 8B ,  FIG. 8C , and  FIG. 8D , a method of manufacturing the interferometer  108  will be described. As shown below, the interferometer  108  is manufactured by MEMS technology. 
       FIG. 7A  shows a step of forming a semiconductor film  164  and an insulating film  166  on a substrate  162 . A glass substrate is utilized as the substrate  162 , for example. A polycrystalline silicon film or an amorphous silicon film is utilized as the semiconductor film  164 . The polycrystalline silicon and the amorphous silicon are prepared by a low-pressure CVD method (vapor phase growth method) or a plasma CVD method. A thickness of the semiconductor film  164  is 1 μm to 10 μm, for example, 4 μm. The insulating film  166  is formed on the semiconductor film  164 . For example, a silicon oxide film is utilized as the insulating film  166 . A thickness of the silicon oxide film is 1 μm to 5 μm, for example, 2 μm by a low-pressure CVD method or a plasma CVD method. 
       FIG. 7B  shows a step of forming the pillars  130 . The pillars  130  are formed of a semiconductor film. As described above, a polycrystalline silicon film or an amorphous silicon film is utilized as the semiconductor film. At first, a semiconductor film is formed on top of the insulating film  166  with a thickness of μm to 1.5 μm, then, a mask is formed by photolithography, and the semiconductor film in the part that serves as the window is removed by etching to form the pillar  130 . 
       FIG. 7C  shows a step of forming the first semi-transparent mirror  116 . The first semi-transparent mirror  116  is formed on the surface of the insulating film  166  exposed between the pillars  130 . The first semi-transparent mirror  116  is formed of a high refractive index film such as silicon (Si) or germanium (Ge). The first semi-transparent mirror  116  is formed of a semi-transparent film made of a metal such as aluminum or a transparent conductive film such as ITO. 
       FIG. 7D  shows a step of processing the insulating film  166  that forms the window  134 . Since the window  134  becomes a free member from the pillar  130 , as shown in the figure, the insulating film  166  between the first semi-transparent mirror  116  and the pillar  130  are removed by etching to form the gap  138 . 
       FIG. 8A  shows a step of forming a second semi-transparent mirror  118  on the substrate  140 . A glass substrate, a plastic substrate (or a flexible plastic film) is used as the substrate  140 . The second semi-transparent mirror  118  is formed of a high refractive index film such as silicon (Si) or germanium (Ge), a semi-transparent film such as aluminum, or a transparent conductive film such as ITO. 
       FIG. 8B  shows a step of integrating the substrate  140  and the structure including the semiconductor film  164 , the window  134 , the first semi-transparent mirror  116 , and the pillars  130  fabricated in the steps up to  FIG. 7D . Specifically, the pillars  130  and the substrate  140  are brought into contact with each other and bonded by direct bonding or anodic bonding. The pillars  130  and the substrate  140  may be bonded together using an adhesive. 
       FIG. 8C  shows a step of removing the substrate  162  to expose the semiconductor film  164 . Since the substrate  162  is a glass substrate, it can be removed by etching using hydrofluoric acid or the like. The substrate  162  may be thinned by chemical mechanical polishing (CMP) and then removed by chemical etching using hydrofluoric acid or the like to expose the surface of the semiconductor film  164 . 
       FIG. 8D  shows the step of forming the beam  132 . The beam  132  is formed of a semiconductor film  164 . The semiconductor film  164  is etched so that the window  134  is connected to the beam  132  and the beam  132  is supported by the pillars  130 . 
     As described above, the interferometer  108  shown in  FIG. 5A ,  FIG. 5B , and  FIG. 5C  is fabricated. The interferometer  108  according to the present embodiment can be fabricated by using a thin film deposition technique and a processing technique used for fabricating a semiconductor device or a display panel, and has an advantage that it is not necessary to introduce much new equipment. The methods of fabricating the interferometer  108  are shown in  FIG. 7A ,  FIG. 7B ,  FIG. 7C , and  FIG. 7D , and  FIG. 8A ,  FIG. 8B ,  FIG. 8C , and  FIG. 8D  are examples. 
     7. Circuit and Drive Method for Optical Sensor 
       FIG. 9A  shows an example of a pixel circuit of the photo sensor  112 . The read circuit  300  includes a first transistor  302  connected to a power supply line (VDD)  312 , a second transistor  304  connected between the first transistor  302  and the photoelectric conversion element  114 , a first capacitor  310  connected in parallel between the first transistor  302  and the second transistor  304 , a third transistor  306  in which a voltage applied in the first capacitor  310  is applied to a gate and connected to the power supply line  312 , and a fourth transistor  308  connected between the third transistor  306  and a data output line  314 . The read circuit outputs a current corresponding to the quantity of light received by the photoelectric conversion element  114  from the third transistor  306  to the data output line  314 . The first to fourth transistors are formed on the base plate  102  by thin film transistors. 
       FIG. 9B  shows an example of a control circuit of the interferometer  108 . The control circuit  316  includes a fifth transistor  320  connected to a control signal line  318 , a second capacitor  322  connected to the output terminal of the fifth transistor  320 , and a sixth transistor  324  for resetting the voltage of the second capacitor  322 . The first semi-transparent mirror  116  is connected to the fifth transistor  320 , and the second semi-transparent mirror  118  is held at a ground potential, in the interferometer  108 . The voltage applied to the first semi-transparent mirror  116  is held by the second capacitor  322 . The voltage applied to the first semi-transparent mirror  116  is held for a certain period of time. When the fifth transistor  320  is turned off and the sixth transistor  324  is turned on, the second capacitor  322  is discharged and reset to the initial state. Thus, the voltage applied to the first semi-transparent mirror  116  also changes to the ground voltage. 
     The reading circuit  300  shown in  FIG. 9A  and the control circuit  316  shown in  FIG. 9B  are examples, and the circuit configuration of the optical sensor  100   a  according to the present embodiment is not limited thereto. As for the circuit for driving the optical sensor  100   a , as long as the circuit has the same function, a circuit having another configuration may be applied. 
       FIG. 10  shows an example of a driving method of the optical sensor  100   a . The optical sensor  100   a  operates in conjunction with the interferometer  108  and the photo sensor  112 . Hereinafter, the pixel  106  of the optical sensor  100   a  will be described as having the circuits shown in  FIG. 9A  and  FIG. 9B . 
     The optical sensor  100   a  receives one image data in one frame. As shown in  FIG. 10 , the photo sensor  112  includes a reset period, a reading period, and a readout period in one frame. In the reset period, the first transistor  302  is turned on, the second transistor  304  and the fourth transistor  308  are turned off, and the first capacitor  310  is charged to the power supply voltage (VDD) and initialized. In the reading period, the first transistor  302  is turned off, the second transistor  304  is turned on, and the fourth transistor  308  is turned off, and the photoelectric conversion element  114  is irradiated with light. Thus, the first capacitor  310  is charged to a voltage corresponding to the photovoltaic power of the photoelectric conversion element  114 . In the readout period, the first transistor  302  and the second transistor  304  are turned off, the fourth transistor  308  is turned on, and a current corresponding to the gate voltage of the third transistor  306  flows from the power supply line  312  to the data output line  314 . As for the gate voltage of the third transistor  306 , a charging voltage is applied to the first capacitor  310 . With this operation, a signal corresponding to the photovoltaic power of the photoelectric conversion element  114  can be read from the data output line  314 . 
     The interferometer  108  includes a setting period, a holding period, and a reset period in one frame. The setting period corresponds to the reset period of the photo sensor  112 , the holding period corresponds to the reading period, and the reset period corresponds to the readout period, in the interferometer  108 , respectively. In the setting period, the fifth transistor  320  is turned on and the sixth transistor is turned off, and a voltage signal for controlling the gap between the two semi-transparent mirrors is input from the control signal line  318 . The voltage signal input from the control signal line  318  is a charging voltage of the second capacitor  322 . In the holding period, the fifth transistor  320  and the sixth transistor  324  are turned off, and the charged voltage of the second capacitor  322  is applied to the first semi-transparent mirror  116 . The second semi-transparent mirror  118  is grounded, and an electrostatic force works on the two semi-transparent mirrors. That is, the displacement of the first semi-transparent mirror  116  is controlled by the charged voltage of the second capacitor  322 . In the reset period, the fifth transistor  320  is turned off, the sixth transistor  324  is turned on, and the second capacitor  322  is discharged to return to the initial state. As a result, the first semi-transparent mirror  116  is set to the ground potential and returned to the initial state. 
     As shown in  FIG. 10 , it is possible to irradiate the photoelectric conversion element  114  with light of different wavelengths for each frame by operating the photo sensor  112  and the interferometer  108  in synchronization, and to obtain information corresponding to the exposure wavelength. It is possible to obtain a color image of an object by controlling the interference wavelength of the interferometer  108  for each frame and each pixel. The driving method shown in  FIG. 10  is an example, and the optical sensor  100   a  according to the present embodiment is not limited to this driving method. 
     The optical sensor  100   a  according to the present embodiment can be used for biometric authentication, for example. Fingerprint authentication, vein authentication, and the like have been proposed as types of biometric authentication. 
     Biometric authentication is performed optically, but visible light (for example, light having a wavelength of 550 nm) is suitable for fingerprint authentication, and near-infrared light (for example, light having a wavelength of 900 nm) is suitable for vein authentication. In this case, in the conventional biometric sensor, to detect these plural wavelengths by one sensor, it is necessary to arrange a sensor for visible light detection and a sensor for near infrared light detection in the plane of the light receiving part, or arrange a visible light filter and a near infrared light filter. However, in such a conventional configuration, resolution is reduced which is a problem. 
     On the other hand, since the optical sensor  100   a  according to the present embodiment can control the light to be received by the photo sensor  112  by the interferometer  108 , the image based on the light of different wavelengths can be obtained by the light receiving part  104  having the same resolution. For example, as shown in  FIG. 2B , fingerprint authentication and vein authentication can be performed continuously just by putting a finger on the optical sensor  100   a  and irradiating the light of the lighting unit  126 . In this case, as described above, the optical sensor  100   a  can perform fingerprint authentication and vein authentication substantially simultaneously without imposing a burden on the subject (or without being noticed by the subject) by changing the wavelength of the light received by the photo sensor  112  for each frame. Thus, the optical sensor  100   a  can be used as a biometric authentication device. 
     As described above, the optical sensor according to the present embodiment can select the wavelength of light detected by the optical sensor with the interferometer. It is possible to sense a plurality of information of an object without lowering resolution, by using an optical sensor having light sensitivity in a wide wavelength band. 
     Second Embodiment 
     This embodiment shows a configuration of the interferometer  108  different from that of the first embodiment. In the following description, parts different from the first embodiment will be mainly described. 
       FIG. 11A  shows a schematic plan view of an optical sensor  100   b  according to the present embodiment, and  FIG. 11B  shows a schematic cross-sectional view corresponding to E 1 -E 2  shown in the schematic plan view. The optical sensor  100   b  has a configuration in which the photoelectric conversion element  114  is arranged for each pixel  106  and an interferometer  108  common to a plurality of pixels  106  is provided. The size of the interferometer is different from that of the first embodiment, and the structure of the interferometer  108  is the same. 
     The driving method of the photoelectric conversion element  114  and the interferometer  108  is the same as that of the first embodiment. The driving method can detect light of different wavelengths by changing the gap between the first semi-transparent mirror  116  and the second semi-transparent mirror  118  in the interferometer  108  for each frame, and can obtain a color image by superposing images of a plurality of frames. 
     According to the present embodiment, the structure of the optical sensor  100   b  can be simplified by commonly providing the interferometer  108  to the plurality of pixels  106 . The configuration other than the interferometer  108  is the same as that of the first embodiment, and the same advantageous effects and effects can be obtained. 
     Third Embodiment 
     This embodiment shows an optical sensor in which the arrangement of the collimating elements is different from that of the second embodiment. In the following description, parts different from the second embodiment will be described. 
       FIG. 12A  shows a schematic plan view of an optical sensor  100   c  according to the present embodiment, and  FIG. 12B  shows a schematic cross-sectional view corresponding to F 1 -F 2  shown in the schematic plan view. The optical sensor  100   c  has a configuration in which the collimating element  110 , the interferometer  108 , and the photoelectric conversion element  114  are arranged from the light incident side. According to such an arrangement, since the incident light is adjusted to parallel beams by the collimating element  110  and incident on the interferometer  108 , the color purity of the spectrally dispersed light can be enhanced, and an image with higher accuracy can be obtained. 
     The optical sensor  100   c  is similar to that of the second embodiment except that the collimating element  110  is arranged differently, and the same advantageous effect can be obtained. The configuration of this embodiment can be appropriately combined with the optical sensor  100   a  of the first embodiment. 
     Fourth Embodiment 
     The optical sensors shown in the first to third embodiments can be combined with or incorporated into various devices. This embodiment shows an example of a display device in which an optical sensor and a display panel are combined. 
       FIG. 13  shows an example of a display device  400  according to the present embodiment. The display device  400  includes a display panel  402 , the lighting unit  126 , and the optical sensor  100   a . The display panel  402  is arranged on a front side (visual recognition side) and the optical sensor  100   a  is arranged on a rear side of the display device  400 . The lighting unit  126  is arranged between the display panel  402  and the optical sensor  100   a.    
     The display panel  402  has a configuration in which a first substrate  404  disposed with a pixel electrode  408  and a second substrate  406  disposed with a counter electrode  410  are oppositely arranged with a gap, and a liquid crystal layer  412  is disposed between them. The first substrate  404  and the second substrate  406  are fixed by a sealing material  414 . The display panel  402  having such a configuration is also referred to as a so called liquid crystal display panel, and has a function in which the lighting unit  126  is disposed on the back side and an image is displayed by using the electro-optical effect of the liquid crystal. 
     The optical sensor  100   a  has the same configuration as that shown in the first embodiment. That is, the optical sensor  100   a  has the structure in which the interferometer  108 , the collimating element  110 , and the photo sensor  112  overlap. The optical sensor  100   a  has a configuration similar to that shown in the first embodiment. That is, the optical sensor  100   a  has a configuration in which the interferometer  108 , the collimating element  110 , and the photo sensor  112  are superposed on each other. The optical sensor  100   a  obtains information of the object  200  through the display panel  402 . 
       FIG. 14A ,  FIG. 14B , and  FIG. 14C  are schematic views for explaining the operation state of the display device  400  according to the present embodiment.  FIG. 14A ,  FIG. 14B , and  FIG. 14C  are simplified diagrams showing a structure in which the display panel  402 , the lighting unit  126 , and the optical sensor  100   a  overlap as described with reference to  FIG. 13 . 
     The display device  400  has at least two operation modes: a display mode ( FIG. 14A ) in which an image is displayed by the display panel  402 , and a sensing mode ( FIG. 14B ) in which the object  200  is sensed by the optical sensor  100   a . The display mode shown in  FIG. 14A  displays an image by the display panel  402  and the lighting unit  126  as described above. Since only an image is displayed in the display mode, the operation of the optical sensor  100   a  may be stopped. 
     The sensing mode shown in  FIG. 14B  operates the optical sensor  100   a  so that the reflected light from the object  200  of the light emitted from the lighting unit  126  is incident through the through hole  128 , the incident light is spectrally dispersed by the interferometer  108 , adjusted to parallel light by the collimating element  110 , and changed to an electric signal by the photo sensor  112 . In this case, since the light emitted from the lighting unit  126  and the light reflected from the object need to be transmitted through the display panel  402 , the display panel  402  is controlled in the transmission mode (white display state). 
     Thus, the display device  400  can display an image and function as a sensor by having two operation modes. The display device  400  can control the operation of the interferometer  108  individually corresponding to the pixels  106  in the configuration of the optical sensor  100   a . As a result, as shown in  FIG. 14C , the hybrid mode can be realized by displaying an image on a part of the display panel (operation as a display mode) and using the other part for sensing the object  200  (operation in the sensing mode). According to such a hybrid mode, biometric authentication can be integrated in a tablet computer. 
     As shown in  FIG. 13 , the display device  400  may have a configuration in which substantially the entire surface of the display panel  402  and substantially the entire surface of the optical sensor  100   a  overlap, and the optical sensor  100   a  may be arranged so as to overlap a part of the display panel  402  (in other words, in a plan view, the size of the optical sensor  100   a  may be smaller than that of the display panel  402 ). 
     The display device according to the present embodiment has the sensing function for detecting the information of the object in addition to the display function, and the sensing function can select the wavelength of the light detected by the optical sensor by the interferometer, and it is possible to sense a plurality of information of an object without lowering resolution by using the photo sensor having light sensitivity in a wide wavelength band. 
     Although this embodiment shows a configuration in which the optical sensor  100   a  according to the first embodiment is used as the optical sensor, the display device  400  is not limited thereto, and the optical sensor according to the second and third embodiments may be used. The display panel  402  is not limited to a liquid crystal panel, and can be replaced with an LED display panel having LED chips arranged in pixels or an organic EL display panel.