Patent Publication Number: US-2022223802-A1

Title: Photoelectric conversion element and imaging device

Description:
TECHNICAL FIELD 
     The present disclosure relates to, for example, a photoelectric conversion element using an organic material and an imaging device including the same. 
     BACKGROUND ART 
     For example, PTL 1 and NPTL 1 have reported that, for example, a combination of a coumarin dye and fullerene is used as a material of a photoelectric conversion layer that absorbs blue light and performs photoelectric conversion of the blue light. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2012-129276 
     Non-Patent Literature 
     NPTL 1: Jpn. J. Appl. Phys., Vol. 49, No. 11, pp. 111601.1-11601.4 (2010) 
     SUMMARY OF THE INVENTION 
     Incidentally, development of a photoelectric conversion element having high external quantum efficiency and high optical responsivity is desired. 
     It is desirable to provide a photoelectric conversion element and an imaging device that make it possible to improve external quantum efficiency and optical responsivity. 
     A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode; a second electrode that is opposed to the first electrode; and an organic photoelectric conversion layer that is provided between the first electrode and the second electrode, and includes, as a first organic semiconductor material, a benzothienobenzothiophene-based compound represented by the following general formula (1). 
     
       
         
         
             
             
         
       
         
         (R1 to R4 are each independently a phenyl group, a biphenyl group, a terphenyl group, a naphthalene group, a phenylnaphthalene group, a biphenylnaphthalene group, a binaphthalene group, a thiophene group, a bithiophene group, a terthiophene group, a benzothiophene group, a phenyl benzothiophene group, a biphenyl benzothiophene benzofuran group, a phenyl benzofuran group, a biphenyl benzothiophene group, an alkane group, a cycloalkane group, a fluorene group, a phenylfluorene group, or any of derivatives thereof.) 
       
    
     An imaging device according to an embodiment of the present disclosure includes a plurality of pixels each including one or a plurality of organic photoelectric converters, and includes the photoelectric conversion element according to the embodiment described above as the organic photoelectric converters. 
     In the photoelectric conversion element according to the embodiment of the present disclosure and the imaging device according to the embodiment of the present disclosure, the organic photoelectric conversion layer is formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above. This leads to an improvement in carrier mobility to the first electrode and the second electrode that are opposed to each other with the organic photoelectric conversion layer interposed therebetween. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of an example of a configuration of an imaging element according to a first embodiment of the present disclosure. 
         FIG. 2  is a diagram illustrating an entire configuration of the imaging element illustrated in  FIG. 1 . 
         FIG. 3  is an equivalent circuit diagram of the imaging element illustrated in  FIG. 1 . 
         FIG. 4  is a schematic view of a layout of a lower electrode and transistors included in a controller in the imaging element illustrated in  FIG. 1 . 
         FIG. 5  is a schematic cross-sectional view of another example of the configuration of the imaging element according to the first embodiment of the present disclosure. 
         FIG. 6  is a cross-sectional view for describing a method of manufacturing the imaging element illustrated in  FIG. 1 . 
         FIG. 7  is a cross-sectional view of a process subsequent to  FIG. 6 . 
         FIG. 8  is a cross-sectional view of a process subsequent to  FIG. 7 . 
         FIG. 9  is a cross-sectional view of a process subsequent to  FIG. 8 . 
         FIG. 10  is a cross-sectional view of a process subsequent to  FIG. 9 . 
         FIG. 11  is a timing chart illustrating an operation example of the imaging element illustrated in  FIG. 1 . 
         FIG. 12  is a schematic cross-sectional view of an example of a configuration of an imaging element according to a second embodiment of the present disclosure. 
         FIG. 13  is a schematic cross-sectional view of an example of a configuration of an imaging element according to a third embodiment of the present disclosure. 
         FIG. 14  is a schematic cross-sectional view of an example of a configuration of an imaging element according to a fourth embodiment of the present disclosure. 
         FIG. 15  is a block diagram illustrating a configuration of an imaging device using the imaging element illustrated in  FIG. 1  and the like for a pixel. 
         FIG. 16  is a functional block diagram illustrating an electronic apparatus (camera) using the imaging device illustrated in  FIG. 15 . 
         FIG. 17  is a block diagram depicting an example of a schematic configuration of an in-vivo information acquisition system. 
         FIG. 18  is a view depicting an example of a schematic configuration of an endoscopic surgery system. 
         FIG. 19  is a block diagram depicting an example of a functional configuration of a camera head and a camera control unit (CCU). 
         FIG. 20  is a block diagram depicting an example of schematic configuration of a vehicle control system. 
         FIG. 21  is a diagram of assistance in explaining an example of installation positions of an outside-vehicle information detecting section and an imaging section. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, some embodiments of the present disclosure are described in detail with reference to the drawings. The following description is given of specific examples of the present disclosure, and the present disclosure is not limited to the following embodiments. Moreover, the present disclosure is not limited to positions, dimensions, dimension ratios, and the like of respective components illustrated in the respective drawings. It is to be noted that description is given in the following order. 
     1. First Embodiment
     (An example of a photoelectric conversion element including a photoelectric conversion layer that includes a benzothienobenzothiophene-based compound)   

     1-1. Configuration of Imaging Element 
     1-2. Method of Manufacturing Imaging Element 
     1-3. Workings and Effects 
     2. Second Embodiment (An example in which two organic photoelectric converters are stacked on a semiconductor substrate) 
     3. Third Embodiment (An example in which a lower electrode includes an organic photoelectric converter formed with a solid film) 
     4. Fourth Embodiment (An example in which three organic photoelectric converters are stacked on a semiconductor substrate) 
     5. Application Examples 
     6. Practical Application Examples 
     7. Examples 
     1. First Embodiment 
       FIG. 1  illustrates an example of a cross-sectional configuration of an imaging element (an imaging element  10 A) according to a first embodiment of the present disclosure.  FIG. 2  illustrates a planar configuration of the imaging element  10 A illustrated in  FIG. 1 .  FIG. 3  is an equivalent circuit diagram of the imaging element  10 A illustrated in  FIG. 1 , and corresponds to a region  100  illustrated in  FIG. 2 .  FIG. 4  schematically illustrates a layout of a lower electrode  21  and transistors included in a controller in the imaging element  10 A illustrated in  FIG. 1 . The imaging element  10 A is included, for example, in one pixel (a unit pixel P) of an imaging device (an imaging device  1 ; see  FIG. 17 ) such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor used for an electronic apparatus such as a digital still camera and a video camera. The imaging element  10 A according to the present embodiment includes an organic photoelectric converter  20  in which the lower electrode  21 , a photoelectric conversion layer  24 , and an upper electrode  25  are stacked in this order. The photoelectric conversion layer  24  is formed by using a benzothienobenzothiophene-based compound represented by a general formula (1) to be described later. The organic photoelectric converter  20  corresponds to a specific example of a “photoelectric conversion element” of the present disclosure. 
     (1-1. Configuration of Imaging Element) 
     The imaging element  10 A is of a so-called longitudinal spectral type in which one organic photoelectric converter  20  and two inorganic photoelectric converters  32 G and  32 R are stacked in a longitudinal direction. The organic photoelectric converter  20  is provided on a first surface (a back surface; a surface  30 S 1 ) side of a semiconductor substrate  30 . The inorganic photoelectric converters  32 G and  32 R are formed to be embedded in the semiconductor substrate  30 , and are stacked in a thickness direction of the semiconductor substrate  30 . The organic photoelectric converter  20  includes a photoelectric conversion layer  24  between the lower electrode  21  and the upper electrode  25  that are opposed to each other, as described above. The photoelectric conversion layer  24  is formed by using an organic material. The photoelectric conversion layer  24  includes a p-type semiconductor and an n-type semiconductor, and has a bulk heterojunction structure in a layer. The bulk heterojunction structure is a p/n junction surface that is formed by mixing the p-type semiconductor and the n-type semiconductor. 
     The organic photoelectric converter  20  and the inorganic photoelectric converters  32 G and  32 R each selectively detect light in a corresponding one of wavelength bands different from each other, and perform photoelectric conversion of the thus-detected light. For example, the organic photoelectric converter  20  acquires a blue (B) color signal. The inorganic photoelectric converters  32 G and  32 R respectively acquire a green (G) color signal and a red (R) color signal by a difference in absorption coefficient. This allows the imaging element  10 A to acquire a plurality of kinds of color signals in one pixel without using a color filter. 
     It is to be noted that, in the present embodiment, description is given of a case where electrons of pairs of electrons and holes (electron-hole pairs) generated by photoelectric conversion are read as signal electric charges (in a case where an n-type semiconductor region serves as a photoelectric conversion layer). In addition, in the drawings, “+ (plus)” attached to “p” or “n” indicates that p-type or n-type impurity concentration is high. 
     For example, floating diffusions (floating diffusion layers) FD 1  (a region  36 B in the semiconductor substrate  30 ), FD 2  (a region  37 C in the semiconductor substrate  30 ), and FD 3  (a region  38 C in the semiconductor substrate  30 ), transfer transistors Tr 2  and Tr 3 , an amplifier transistor (a modulation element) AMP, a reset transistor RST, a selection transistor SEL, and multilayer wiring  40  are provided on a second surface (a front surface;  30 S 2 ) of the semiconductor substrate  30 . The multilayer wiring  40  has, for example, a configuration in which wiring layers  41 ,  42 , and  43  are stacked in an insulating layer  44 . 
     It is to be noted that in the drawing, the first surface (the surface  30 S 1 ) side of the semiconductor substrate  30  is represented as a light incident side S 1  and the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  is represented as a wiring layer side S 2 . 
     The organic photoelectric converter  20  includes the lower electrode  21 , the semiconductor layer  23 , the photoelectric conversion layer  24 , and the upper electrode  25  that are stacked in this order from the first surface (the surface  30 S 1 ) side of the semiconductor substrate  30 . In addition, an insulating layer  22  is provided between the lower electrode  21  and the semiconductor layer  23 . The lower electrode  21  is formed separately for each imaging element  10 A, for example, and includes a readout electrode  21 A and an accumulation electrode  21 B that are separated from each other with the insulating layer  22  interposed therebetween as described in detail later. The readout electrode  21 A of the lower electrode  21  is electrically coupled to the semiconductor layer  23  via an opening  22 H provided in the insulating layer  22 .  FIG. 1  illustrates an example in which the semiconductor layer  23 , the photoelectric conversion layer  24 , and the upper electrode  25  are provided as common continuous layers for a plurality of imaging elements  10 A, but the semiconductor layer  23 , the photoelectric conversion layer  24 , and the upper electrode  25  may be formed separately for each imaging element  10 A, for example. For example, a dielectric film  26 , an insulating film  27 , and an interlayer insulating layer  28  are provided between the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and the lower electrode  21 . A protective layer  51  is provided on the upper electrode  25 . A light-shielding film  52  is provided, for example, at a position corresponding to the readout electrode  21 A in the protective layer  51 . It is sufficient if the light-shielding film  52 A is provided to cover at least a region of the readout electrode  21 A directly in contact with the semiconductor layer  23  without covering at least the accumulation electrode  21 B. Optical members such a planarization layer (not illustrated) and an on-chip lens  53  are provided above the protective layer  51 . 
     A through electrode  34  is provided between the first surface (the surface  30 S 1 ) and the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 . The through electrode  34  is electrically coupled to the readout electrode  21  of the organic photoelectric converter  20 , and the organic photoelectric converter  20  is coupled to a gate Gamp of the amplifier transistor AMP and one source/drain region  36 B, which also serves as the floating diffusion FD 1 , of the reset transistor RST (a reset transistor Tr 1 rst) via the through electrode  34 . This makes it possible to favorably transfer electric charges generated in the organic photoelectric converter  20  on the first surface (the surface  30 S 21 ) side of the semiconductor substrate  30  to the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  and enhance characteristics in the imaging element  10 A. 
     A lower end of the through electrode  34  is coupled to a coupling section  41 A in the wiring layer  41 , and the coupling section  41 A and the gate Gamp of the amplifier transistor AMP are coupled to each other via a first lower contact  45 . The coupling section  41 A and the floating diffusion FD 1  (the region  36 B) are coupled to each other via a second lower contact  46 , for example. An upper end of the through electrode  34  is coupled to the readout electrode  21 A via a first upper contact  29 A, a pad section  39 A, and a second upper contact  29 B, for example. 
     The through electrode  34  is provided for each organic photoelectric converter  20  in each of the imaging elements  10 A, for example. The through electrode  34  has a function as a connector between the organic photoelectric converter  20  and both the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 1 , and serves as a transmission path of electric charges generated in the organic photoelectric converter  20 . 
     A reset gate Grst of the reset transistor RST is disposed adjacent to the floating diffusion FD 1  (the one source/drain region  36 B of the reset transistor RST). This makes it possible to reset electric charges accumulated in the floating diffusion FD 1  by the reset transistor RST. 
     In the imaging element  10 A according to the present embodiment, light having entered the organic photoelectric converter  20  from the upper electrode  25  side is absorbed by the photoelectric conversion layer  24 . Excitons thereby generated move to an interface between an electron donor and an electron acceptor included in the photoelectric conversion layer  24 , and the excitons are dissociated, that is, the excitons are dissociated into electrons and holes. Electric charges generated herein (electrons and holes) are each carried to different electrodes by diffusion resulting from a difference in concentration between carriers or an internal electric field resulting from a difference in work function between an anode (for example, the upper electrode  25 ) and a cathode (for example, the lower electrode  21 ), and detected as a photocurrent. Moreover, it is also possible to control transport directions of the electrons and the holes by application of a potential between the lower electrode  21  and the upper electrode  25 . 
     In the following, description is given of the configurations, materials, and the like of respective components. 
     The organic photoelectric converter  20  is an organic photoelectric conversion element that absorbs light corresponding to a wavelength band of a portion or the entirety of a selective wavelength band (for example, from 400 nm to 700 nm both inclusive) to generate electron-hole pairs. 
     The lower electrode  21  includes the readout electrode  21 A and the accumulation electrode  21 B that are separately formed as described above. The readout electrode  21 A transfers electric charges generated in the photoelectric conversion layer  24  to the floating diffusion FD 1 , and is coupled to the floating diffusion FD 1  via the second upper contact  29 B, the pad section  39 A, the first upper contact  29 A, the through electrode  34 , the coupling section  41 A, and the second lower contact  46 , for example. The accumulation electrode  21 B accumulates, in the semiconductor layer  23 , electrons as signal electric charges of the electric charges generated in the photoelectric conversion layer  24 . The accumulation electrode  21 B is directly opposed to light reception surfaces of the inorganic photoelectric converters  32 G and  32 R formed in the semiconductor substrate  30 , and is provided in a region that covers these light reception surfaces. The accumulation electrode  21 B is preferably larger than the readout electrode  21 A, which makes it possible to accumulate many electric charges. A voltage application circuit  60  is coupled to the accumulation electrode  21 B via wiring as illustrated in  FIG. 4 . 
     The lower electrode  21  includes an electrically conductive film having light transmissivity. Examples of a constituent material of the lower electrode  21  include ITO, In 2 O 3  to which tin (Sn) is added as a dopant, and indium tin oxide including crystalline ITO and amorphous ITO. In addition to the materials described above, a tin oxide (SnO 2 )-based material to which a dopant is added or a zinc oxide-based material prepared by adding a dopant may be used as the constituent material of the lower electrode  21 . Examples of the zinc oxide-based material include aluminum zinc oxide (AZO) to which aluminum (Al) is added as a dopant, gallium zinc oxide (GZO) to which gallium (Ga) is added, boron zinc oxide to which boron (B) is added, and indium zinc oxide (IZO) to which indium (In) is added. In addition, CuI, InSbO 4 , ZnMgO, CuInO 2 , MgIN 2 O 4 , CdO, ZnSnO 3 , TiO 2 , or the like may be used as the constituent material of the lower electrode  21 . Further, a spinel oxide or an oxide having a YbFe 2 O 4  structure may be used. It is to be noted that the lower electrode  21  formed by using the material as described above generally has a high work function, and functions as an anode electrode. 
     The semiconductor layer  23  is provided below the photoelectric conversion layer  24 , specifically between the insulating layer  22  and the photoelectric conversion layer  24 , and accumulate signal electric charges generated in the photoelectric conversion layer  24 . The semiconductor layer  23  is preferably formed by using a material having higher electric charge mobility than that of the photoelectric conversion layer  24  and having a large band gap. For example, the band gap of the constituent material of the semiconductor layer  23  is preferably 3.0 eV or greater. Examples of such a material include a oxide semiconductor material such as IGZO, an organic semiconductor material, and the like. Examples of the organic semiconductor material include transition metal dichalcogenide, silicon carbide, diamond, graphene, carbon nanotubes, a condensed polycyclic hydrocarbon compound, a condensed heterocyclic compound, and the like. The semiconductor layer  23  has, for example, a thickness of 10 nm to 300 nm both inclusive. Providing the semiconductor layer  23  including the material described above below the photoelectric conversion layer  24  makes it possible to prevent recombination of electric charges during electric charge accumulation and improve transfer efficiency. 
     The photoelectric conversion layer  24  converts optical energy into electric energy. The photoelectric conversion layer  24  according to the present embodiment absorbs, for example, light of some or all of wavelengths within a range from 400 nm to 700 nm both inclusive. The photoelectric conversion layer  24  includes, for example, two or more kinds of organic materials (p-type semiconductor materials or n-type semiconductor materials) that each function as a p-type semiconductor or an n-type semiconductor. The photoelectric conversion layer  24  has a junction surface (a p/n junction surface) of the p-type semiconductor material and the n-type semiconductor material in a layer. The p-type semiconductor relatively functions as an electron donor (a donor), and the n-type semiconductor relatively functions as an electron acceptor (an acceptor). The photoelectric conversion layer  24  provides a field where excitons generated upon absorption of light are dissociated into electrons and holes. Specifically, the excitons are dissociated into the electrons and the holes at an interface (the p/n junction surface) between the electron donor and the electron acceptor. 
     The photoelectric conversion layer  24  may include, in addition to the p-type semiconductor material and the n-type semiconductor material, an organic material, i.e., a so-called dye material, that photoelectrically converts light in a predetermined wavelength band and allows light in another wavelength band to pass therethrough. In a case where the photoelectric conversion layer  24  is formed by using three kinds of organic materials, that is, the p-type semiconductor material, the n-type semiconductor material, and the dye material, the p-type semiconductor material and the n-type semiconductor material are preferably materials having light transmissivity in a visible region (for example, from 400 nm to 700 nm). The thickness of the photoelectric conversion layer  24  is, for example, from 25 nm to 400 nm both inclusive, preferably from 50 nm to 350 nm both inclusive, and more preferably from 150 nm to 300 nm both inclusive. 
     In the present embodiment, the photoelectric conversion layer  24  is formed by including, for example, a benzothienobenzothiophene-based compound represented by the following general formula (1) that absorbs light of 400 nm to 500 nm both inclusive. The benzothienobenzothiophene-based compound corresponds to a specific example of a “first organic semiconductor material” of the present disclosure. 
     
       
         
         
             
             
         
       
     
     (R1 to R4 are each independently a phenyl group, a biphenyl group, a terphenyl group, a naphthalene group, a phenylnaphthalene group, a biphenylnaphthalene group, a binaphthalene group, a thiophene group, a bithiophene group, a terthiophene group, a benzothiophene group, a phenyl benzothiophene group, a biphenyl benzothiophene benzofuran group, a phenyl benzofuran group, a biphenyl benzothiophene group, an alkane group, a cycloalkane group, a fluorene group, a phenylfluorene group, or any of derivatives thereof.) 
     Examples of other organic materials included in the photoelectric conversion layer  24  include fullerene or a fullerene derivative. Fullerene or a fullerene derivative corresponds to a specific example of a “second organic semiconductor material” of the present disclosure. 
     Furthermore, the photoelectric conversion layer  24  may include, for example, an organic semiconductor material that absorbs any of wavelengths from 400 nm to 700 nm both inclusive. Examples of such a material include a coumarin derivative, a perylene derivative, a porphyrin derivative, a merocyanine derivative, an anthraquinone derivative, and the like. The organic semiconductor material described above corresponds to a specific example of a “third organic semiconductor material” of the present disclosure. 
     A combination of the organic materials described above function as a p-type semiconductor or an n-type semiconductor depending on the combination. 
     It is to be noted that the photoelectric conversion layer  24  may include an organic material other than the organic semiconductor materials described above. As the organic material other than the organic semiconductor materials described above, for example, one kind of quinacridone, boron subphthalocyanine chloride, pentacene, benzothienobenzothiophene, naphthalene, anthracene, phenanthrene, tetracene, pyrene, perylene, fluoranthene, and derivatives thereof is preferably used. Alternatively, a polymer such as phenylenevinylene, fluorene, carbazole, indole, pyrene, pyrrole, picoline, thiophene, acetylene, diacetylene or a derivative thereof may be used. Additionally, it is possible to preferably use a metal complex dye, a cyanine-based dye, a merocyanine-based dye, a phenylxanthene-based dye, a triphenylmethane-based dye, a rhodacyanine-based dye, a xanthene-based dye, a macrocyclic azaannulene-based dye, an azulene-based dye, naphthaquinone, an anthraquinone-based dye, a chain compound in which a condensed polycyclic aromatic group such as anthracene and pyrene and an aromatic ring or a heterocyclic compound are condensed, a cyanine-like dye bonded by two nitrogen-containing hetero rings such as quinoline, benzothiazole, and benzoxazole that have a squarylium group and a croconic methine group as a bonded chain, or by a squarylium group or a croconic methine group, or the like. It is to be noted that as the metal complex dye described above, a dithiol metal complex-based dye, a metallophthalocyanine dye, a metalloporphyrine dye, or a ruthenium complex dye is preferable, but the metal complex dye is not limited thereto. 
     The upper electrode  25  includes an electrically conductive film having light transmissivity similarly to the lower electrode  21 . In the imaging device  1  using the imaging element  10 A as one pixel, the upper electrode  25  may be provided separately for each of the pixels, or may be formed as a common electrode for the respective pixels. The upper electrode  25  has a thickness of 10 nm to 200 nm, for example. 
     Any other layer may be provided each between the semiconductor layer  23  and the photoelectric conversion layer  24  and between the photoelectric conversion layer  24  and the upper electrode  25 . For example, as with an imaging element  10 B illustrated in  FIG. 5 , for example, the semiconductor layer  23 , an electron blocking layer  24 A (a first electric charge blocking layer), the photoelectric conversion layer  24 , and a hole blocking layer  24 B (a second electric charge blocking layer) may be stacked in order from the lower electrode  21  side. Furthermore, a undercoat layer and a hole transport layer may be provided between the lower electrode  21  and the photoelectric conversion layer  24 , or a work function adjustment layer, a buffer layer, or an electron transport layer may be provided between the photoelectric conversion layer  24  and the upper electrode  25 . 
     The insulating layer  22  electrically separates the accumulation electrode  21 B and the semiconductor layer  23  from each other. The insulating layer  22  is provided, for example, on the interlayer insulating layer  28  to cover the lower electrode  21 . In addition, the insulating layer  22  has the opening  22 H above the readout electrode  21 A of the lower electrode  21 , and the readout electrode  21 A and the semiconductor layer  23  are electrically coupled to each other via the opening  22 H. The insulating layer  22  includes, for example, a single-layer film including one kind of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiON), and the like, or a stacked film including two or more kinds thereof. The insulating layer  22  has a thickness of 20 nm to 500 nm, for example. 
     The dielectric film  26  prevents reflection of light generated by a difference in refractive index between the semiconductor substrate  30  and the insulating film  27 . As a material of the dielectric film  26 , a material having a refractive index that falls between the refractive index of the semiconductor substrate  30  and the refractive index of the insulating film  27  is preferable. Further, as the material of the dielectric film  26 , for example, a material that is able to form a film having negative fixed electric charges is preferably used. Alternatively, as the material of the dielectric film  26 , a semiconductor material or an electrically conductive material having a wider band gap than that of the semiconductor substrate  30  is preferably used. This makes it possible to suppress generation of a dark current at an interface of the semiconductor substrate  30 . Such materials include hafnium oxide (HfO x ), aluminum oxide (AlO x ), zirconium oxide (ZrO x ), tantalum oxide (TaO x ), titanium oxide (TiO x ), lanthanum oxide (LaO x ), praseodymium oxide (PrO x ), cerium oxide (CeO x ), neodymium oxide (NdO x ), promethium oxide (PmO x ), samarium oxide (SmO x ), europium oxide (EuO x ), gadolinium oxide (GdO x ), terbium oxide (TbO x ), dysprosium oxide (DyO x ), holmium oxide (HoO x ), thulium oxide (TmO x ), ytterbium oxide (YbO x ), lutetium oxide (LuO x ), yttrium oxide (YO x ), hafnium nitride (HfN x ), aluminum nitride (AlN x ), hafnium oxynitride (HfO x N y ), aluminum oxynitride (AlO x N y ), and the like. 
     The insulating film  27  is provided on the dielectric film  26  that is formed on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and a side surface of the through hole  30 H, and electrically insulates the through electrode  34  and the semiconductor substrate  30  from each other. Examples of a material of the insulating film  27  include silicon oxide (SiO x ), TEOS, silicon nitride (SiN x ), silicon oxynitride (SiON), and the like. 
     The interlayer insulation layer  28  includes, for example, a single-layer film including one kind of silicon oxide (SiO x ), TEOS, silicon nitride (SiN x ), silicon oxynitride (SiON), and the like, or a stacked film including two or more kinds thereof. 
     The protective layer  51  includes a material having light transmissivity, and includes, for example, a single-layer film including one of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiON), and the like, or a stacked film including two or more kinds thereof. The protective layer  51  has a thickness of 100 nm to 30000 nm, for example. 
     The semiconductor substrate  30  includes an n-type silicon (Si) substrate, for example, and has a p-well  31  in a predetermined region (for example, a pixel section  1   a ). The transfer transistors Tr 2  and Tr 3 , the amplifier transistor AMP, the reset transistor RST, the selection transistor SEL, and the like described above are provided on the second surface (the surface  30 S 2 ) of the p-well  31 . In addition, as illustrated in  FIG. 2 , for example, a pixel readout circuit  110  and a pixel drive circuit  120  that include a logic circuit and the like are provided in a peripheral section (a peripheral section  1   b ) of the semiconductor substrate  30 . 
     The reset transistor RST (the reset transistor Tr 1 rst) resets electric charges transferred from the organic photoelectric converter  20  to the floating diffusion FD 1 , and includes, for example, a MOS transistor. Specifically, the reset transistor Tr 1 rst includes the reset gate Grst, a channel formation region  36 A, and source/drain regions  36 B and  36 C. The reset gate Grst is coupled to a reset line RST 1 , and the one source/drain region  36 B of the reset transistor Tr 1 rst also serves as the floating diffusion FD 1 . The other source/drain region  36 C included in the reset transistor Tr 1 rst is coupled to a power source VDD. 
     The amplifier transistor AMP is a modulation element that modulates an amount of electric charges generated in the organic photoelectric converter  20  into voltage, and includes, for example, a MOS transistor. Specifically, the amplifier transistor AMP includes a gate Gamp, a channel formation region  35 A, and source/drain regions  35 B and  35 C. The gate Gamp is coupled to the readout electrode  21 A and the one source/drain region  36 B (the floating diffusion FD 1 ) o the reset transistor Tr 1 rst via the first lower contact  45 , the coupling section  41 A, the second lower contact  46 , the through electrode  34 , and the like. In addition, one source/drain region  35 B shares a region with the other source drain region  36 C included in the reset transistor Tr 1 rst, and is coupled to the power source VDD. 
     The selection transistor SEL (a selection transistor TR 1 sel) includes a gate Gsel, a channel formation region  34 A, and source/drain regions  34 B and  34 C. The gate Gsel is coupled to a selection line SEL 1 . In addition, one source/drain region  34 B shares a region with the other source/drain region  35 C included in the amplifier transistor AMP, and the other source/drain region  34 C is coupled to a signal line (a data output line) VSL 1 . 
     The inorganic photoelectric converters  32 G and  32 R each have a pn junction in a predetermined region of the semiconductor substrate  30 . The inorganic photoelectric converters  32 G and  32 R enable dispersion of light in the longitudinal direction with use of a difference in wavelength of absorbed light depending on a depth of light incidence in the silicon substrate. The inorganic photoelectric converter  32 G selectively detects green light to accumulate signal electric charges corresponding to green, and is disposed at a depth that allows for efficient photoelectric conversion of the green light. The inorganic photoelectric converter  32 R selectively detects red light to accumulate signal electric charges corresponding to red, and is disposed at a depth that allows for efficient photoelectric conversion of the red light. It is to be noted that green (G) and red (R) are colors respectively corresponding to a wavelength band from 495 nm to 620 nm, for example, and a wavelength band from 620 nm to 750 nm, for example. It is sufficient if each of the inorganic photoelectric converters  32 G and  32 R is allowed to detect light in a portion or the entirety of a corresponding one of the wavelength bands. 
     The inorganic photoelectric converter  32 G includes, for example, a p+ region serving as a hole accumulation layer, and an n region serving as an electron accumulation layer. The inorganic photoelectric converter  32 R includes, for example, a p+ region serving as a hole accumulation layer, and an n region serving as an electron accumulation layer (has a p-n-p stacking structure). The n region of the inorganic photoelectric converter  32 G is coupled to the vertical transfer transistor Tr 2 . The p+ region of the inorganic photoelectric converter  32 G bends along the transfer transistor Tr 2  and is coupled to the p+ region of the inorganic photoelectric converter  32 R. 
     The transfer transistor Tr 2  (a transfer transistor TR 2 trs) transfers, to the floating diffusion FD 2 , signal electric charges corresponding to green generated and accumulated in the inorganic photoelectric converter  32 G. The inorganic photoelectric converter  32 G is formed at a position deep from the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 ; therefore, the transfer transistor TR 2 trs of the inorganic photoelectric converter  32 G preferably includes a vertical transistor. In addition, the transfer transistor TR 2 trs is coupled to a transfer gate line TG 2 . Further, the floating diffusion FD 2  is provided in a region  37 C in proximity to the gate Gtrs 2  of the transfer transistor TR 2 trs. Electric charges accumulated in the inorganic photoelectric converter  32 G are read by the floating diffusion FD 2  via a transfer channel formed along the gate Gtrs 2 . 
     The transfer transistor Tr 3  (a transfer transistor TR 3 trs) transfers, to the floating diffusion FD 3 , signal electric charges corresponding to red generated and accumulated in the inorganic photoelectric converter  32 R, and includes, for example, a MOS transistor. In addition, the transfer transistor TR 3 trs is coupled to a transfer gate line TG 3 . Further, the floating diffusion FD 3  is provided in a region  38 C in proximity to the gate Gtrs 3  of the transfer transistor TR 3 trs. Electric charges accumulated in the inorganic photoelectric converter  32 R are read by the floating diffusion FD 3  via a transfer channel formed along the gate Gtrs 3 . 
     A reset transistor TR 2 rst, an amplifier transistor TR 2 amp, and a selection transistor TR 2 sel that are included in a controller of the inorganic photoelectric converter  32 G are further provided on the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30 . In addition, a reset transistor TR 3 rst, an amplifier transistor TR 3 amp, and a selection transistor TR 3 sel that are included in a controller of the inorganic photoelectric converter  32 R are provided. 
     The reset transistor TR 2 rst includes a gate, a channel formation region, and source/drain regions. The gate of the reset transistor TR 2 rst is coupled to a reset line RST 2 , and one source drain region of the reset transistor TR 2 rst is coupled to the power source VDD. Another source/drain region of the reset transistor TR 2 rst also serves as the floating diffusion FD 2 . 
     The amplifier transistor TR 2 amp includes a gate, a channel formation region, and source/drain regions. The gate is coupled to the other source/drain region (the floating diffusion FD 2 ) of the reset transistor TR 2 rst. In addition, one source/drain region included in the amplifier transistor TR 2 amp shares a region with the one source/drain region included in the reset transistor TR 2 rst, and is coupled to the power source VDD. 
     The selection transistor TR 2 sel includes a gate, a channel formation region, and source/drain regions The gate is coupled to a selection line SEL 2 . In addition, one source/drain region included in the selection transistor TR 2 sel shares a region with another source /drain region included in the amplifier transistor TR 2 amp. Another source/drain region included in the selection transistor TR 2 sel is coupled t a signal line (a data output line) VSL 2 . 
     The reset transistor TR 3 rst includes a gate, a channel formation region, and source/drain regions. The gate of the reset transistor TR 3 rst is coupled to a reset line RST 3 , and one source/drain region included in the reset transistor TR 3 rst is coupled to the power source VDD. Another source/drain region included in the reset transistor TR 3 rst also serves as the floating diffusion FD 3 . 
     The amplifier transistor TR 3 amp includes a gate, a channel formation region, and source/drain regions. The gate is coupled to the other source/drain region (the floating diffusion FD 3 ) included in the reset transistor TR 3 rst. In addition, one source/drain region included in the amplifier transistor TR 3 amp shares a region with the one source/drain region included in the reset transistor TR 3 rst, and is coupled to the power source VDD. 
     The selection transistor TR 3 sel includes a gate, a channel formation region, and source/drain regions. The gate is coupled to a selection line SEL 3 . One source/drain region included in the selection transistor TR 3 sel shares a region with another source/drain region included in the amplifier transistor TR 3 amp. Another source/drain region included in the selection transistor TR 3 sel is coupled to a signal line (a data output line) VSL 3 . 
     The reset lines RST 1 , RST 2 , and RST 3 , the selection lines SEL 1 , SEL 2 , and SEL 3 , and the transfer gate lines TG 2  and TG 3  are each coupled to a vertical drive circuit  112  included in a drive circuit. The signal lines (data output lines) VSL 1 , VSL 2 , and VSL 3  are coupled to a column signal processing circuit  113  included in the drive circuit. 
     The first lower contact  45 , the second lower contact  46 , the first upper contact  29 A, the second upper contact  29 B, and a third upper contact  29 C each include, for example, a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon) or a metal material such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (Hf), and tantalum (Ta). 
     (1-2. Method of Manufacturing Imaging Element) 
     It is possible to manufacture the imaging element  10 A according to the present embodiment as follows, for example. 
       FIGS. 6 to 10  illustrate a method of manufacturing the imaging element  10 A in process order. First, as illustrated in  FIG. 6 , for example, the p-well  31  is formed as a well of a first conductivity type in the semiconductor substrate  30 , and the inorganic photoelectric converters  32 G and  32 R of a second conductivity type (for example, an n type) are formed in this p-well  31 . A p+ region is formed in proximity to the first surface (the surface  30 S 1 ) of the semiconductor substrate  30 . 
     Similarly, as illustrated in  FIG. 6 , on the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 , for example, n+ regions serving as the floating diffusions FD 1  to FD 3  are formed, and thereafter, a gate insulating layer  33  and a gate wiring layer  47  including respective gates of the transfer transistor Tr 2 , the transfer transistor Tr 3 , the selection transistor SEL, the amplifier transistor AMP, and the reset transistor RST are formed. Thus, the transfer transistor Tr 2 , the transfer transistor Tr 3 , the selection transistor SEL, the amplifier transistor AMP, and the reset transistor RST are formed. Further, the multilayer wiring  40  including the wiring layers  41  to  43  and the insulating layer  44  is formed on the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 . The wiring layers  41  to  43  include the first lower contact  45 , the second lower contact  46 , and the coupling section  41 A. 
     As a base substrate of the semiconductor substrate  30 , an SOI (Silicon on Insulator) substrate is used in which the semiconductor substrate  30 , an embedded oxide film (not illustrated), and a retaining substrate (not illustrated) are stacked. The embedded oxide film and the retaining substrate are not illustrated in  FIG. 6 , but are joined to the first surface (the surface  30 S 1 ) of the semiconductor substrate  30 . Annealing treatment is performed after ion implantation. 
     Next, a supporting substrate (not illustrated), another semiconductor substrate, or the like is joined to the second surface (the surface  30 S 2 ) side (the multilayer wiring  40  side) of the semiconductor substrate  30  and flipped from top to bottom. Subsequently, the semiconductor substrate  30  is separated from the embedded oxide film and the retaining substrate of the SOI substrate to expose the first surface (the surface  30 S 1 ) of the semiconductor substrate  30 . It is possible to perform the above processes with technologies used in a normal CMOS process such as ion implantation and CVD (Chemical Vapor Deposition). 
     Next, as illustrated in  FIG. 7 , the semiconductor substrate  30  is processed from the first surface (the surface  30 S 1 ) side, for example, by dry etching to form, for example, an annular through hole  30 H. As illustrated in  FIG. 7 , a depth of the through hole  30 H preferably penetrates from the first surface (the surface  30 S 1 ) to the second surface (the surface  30 S 2 ) of the semiconductor substrate  30  and reaches the coupling section  41 A, for example. 
     Subsequently, as illustrated in  FIG. 8 , the dielectric film  26  is formed on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and the side surface of the through hole  30 H with use of an atomic layer deposition (Atomic Layer Deposition; ALD) method, for example. Thus, the dielectric film  26  is continuously formed on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and the side surface and a bottom surface of the through hole  30 H. Next, the insulating film  27  is formed on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and in the through hole 30 H, and thereafter the insulating film  27  and the dielectric film  26  formed on the bottom surface of the through hole  30 H are removed by dry etching, for example, to expose the coupling section  41 A. It is to be noted that at this time, the insulating film  27  on the first surface (the surface  30 S 1 ) is also thinned. Subsequently, an electrically conductive film is formed on the insulating film  27  and in the through hole  30 H, and thereafter a photoresist PR is formed at a predetermined position on the electrically conductive film. Next, etching and removal of the photoresist PR are performed to form the through electrode  34  having an overhang portion on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30 . 
     Next, as illustrated in  FIG. 9 , an insulating film that forms the interlayer insulating layer  28  is formed on the insulating film  27  and the through electrode  34 , and thereafter, the first upper contact  29 A, pad sections  39 A and  39 B, the second upper contact  29 B, and the third upper contact  29 C are formed on the through electrode  34 , and the like. Thereafter, a surface of the interlayer insulating layer  28  is planarized with use of a CMP (Chemical Mechanical Polishing) method. Next, an electrically conductive film  21   x  is formed on the interlayer insulating layer  28 , and thereafter a photoresist is formed at a predetermined position of the electrically conductive film  21   x.    
     Subsequently, as illustrated in  FIG. 10 , etching and removal of the photoresist are performed to form the readout electrode  21 A and the accumulation electrode  21 B. 
     Thereafter, the insulating layer  22  is formed on the interlayer insulating layer  28 , the readout electrode  21 A, and the accumulation electrode  21 B, and thereafter, the opening  22 H is provided on the readout electrode  21 A. Next, the semiconductor layer  23 , the photoelectric conversion layer  24 , and the upper electrode  25  are formed in order on the insulating layer  22 . Finally, the protective layer  51 , the light-shielding film  52 , and the on-chip lens  53  are provided on the upper electrode  25 . Thus, the imaging element  10 A illustrated in  FIG. 1  is completed. 
     It is to be noted that in a case where the semiconductor layer  23  and other organic layers are formed with use of an organic material, it is desirable to form the semiconductor layer  23  and the organic layers continuously (by an in-situ vacuum process) in a vacuum process. In addition, a method of forming the organic photoelectric conversion layer  16  is not necessarily limited to a method using a vacuum evaporation method, and, other methods, for example, spin coating technology, printing technology, and the like may be used. Further, methods of forming transparent electrodes (the lower electrode  21  and the upper electrode  25 ) may include, depending on materials included in transparent electrodes, a physical vapor deposition method (PVD method) such as a vacuum evaporation method, a reactive evaporation method, various kinds of sputtering methods, an electron beam evaporation method, and an ion plating method, a pyrosol method, a method of pyrolyzing an organic metal component, a spraying method, a dip method, various kinds of chemical vapor deposition methods (CVD methods) including a MOCVD method, an electroless plating method, and an electroplating method. 
     In the imaging element  10 A, in a case where light enters the organic photoelectric converter  20  via the on-chip lenses  53 , the light passes through the organic photoelectric converter  20  and the inorganic photoelectric converters  32 G and  32 R in order, and each of green light, blue light, and red light is photoelectrically converted in the course of passing. Signal acquisition operations of the respective colors are described below. 
     (Acquisition of Blue Signal by Organic Photoelectric Converter  20 ) 
     Of light having entered the imaging element  10 A, first, blue light is selectively detected (absorbed) and photoelectrically converted in the organic photoelectric converter  20 . 
     The organic photoelectric converter  20  is coupled to the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 1  via the through electrode  34 . Thus, electrons of electron-hole pairs generated in the organic photoelectric converter  20  are extracted from the lower electrode  21  side, transferred to the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  via the through electrode  34 , and accumulated in the floating diffusion FD 1 . Simultaneously with this, the amount of electric charges generated in the organic photoelectric converter  20  is modulated into voltage by the amplifier transistor AMP. 
     In addition, the reset gate Grst of the reset transistor RST is disposed adjacent to the floating diffusion FD 1 . Accordingly, the electric charges accumulated in the floating diffusion FD 1  are reset by the reset transistor RST. 
     Herein, the organic photoelectric converter  20  is coupled not only to the amplifier transistor AMP but also to the floating diffusion FD 1  via the through electrode  34 , thus making it possible for the reset transistor RST to easily reset the electric charges accumulated in the floating diffusion FD 1 . 
     In contrast to this, in a case where the through electrode  34  is not coupled to the floating diffusion FD 1 , it is difficult to reset the electric charges accumulated in the floating diffusion FD 1 , causing the electric charges to be drawn to the upper electrode  25  side by application of a large voltage. This may damage the photoelectric conversion layer  24 . In addition, a configuration that enables resetting in a short period of time causes an increase in dark time noise, thereby resulting in a trade-off; therefore, this configuration is difficult. 
       FIG. 11  illustrates an operation example of the imaging element  10 A, where (A) indicates a potential at the accumulation electrode  21 B, (B) indicates a potential at the floating diffusion FD 1  (the readout electrode  21 A), and (C) indicates a potential at the gate (Gsel) of the reset transistor TR 1 rst. In the imaging element  10 A, a voltage is individually applied to each of the readout electrode  21 A and the accumulation electrode  21 B. 
     In the imaging element  10 A, in an accumulation period, a drive circuit applies a potential V 1  to the readout electrode  21 A, and applies a potential V 2  to the accumulation electrode  21 B. Here, it is assumed that the potentials V 1  and V 2  satisfy V 2 &gt;V 1 . This causes electric charges (signal electric charges; electrons) generated by photoelectric conversion to be drawn to the accumulation electrode  21 B and accumulated in a region of the semiconductor layer  23  opposed to the accumulation electrode  21 B (the accumulation period). Additionally, the value of the potential in the region of the semiconductor layer  23  opposed to the accumulation electrode  21 B becomes more negative with the passage of time of photoelectric conversion. It is to be noted that holes are sent from the upper electrode  25  to the drive circuit. 
     In the imaging element  10 A, a reset operation is performed in a later period of the accumulation period. Specifically, at a timing t 1 , a scanner changes the voltage of a reset signal RST from a low level to a high level. This turns on the reset transistor TR 1 rst in the unit pixel P, and as a result, the voltage of the floating diffusion FD 1  is set to a power source voltage VDD, and the voltage of the floating diffusion FD 1  is reset (a reset period). 
     After completion of the reset operation, electric charges are read out. Specifically, at a timing t 2 , the drive circuit applies a potential V 3  to the readout electrode  21 A, and applies a potential V 4  to the accumulation electrode  21 B. Here, it is assumed that the potentials V 3  and V 4  satisfy V 3 &lt;V 4 . This causes electric charges accumulated in a region corresponding to the accumulation electrode  21 B to be read out from the readout electrode  21 A to the floating diffusion FD 1 . That is, electric charges accumulated in the semiconductor layer  23  are read out by a controller (a transfer period). 
     After completion of a readout operation, the drive circuit applies the potential V 1  to the readout electrode  21 A again, and applies the potential V 2  to the accumulation electrode  21 B again. This causes electric charges generated by photoelectric conversion to be drawn to the accumulation electrode  21 B and accumulated in the region of the photoelectric conversion layer  24  opposed to the accumulation electrode  21 B (the accumulation period). 
     (Acquisition of Green Signal and Red Signal by Inorganic Photoelectric Converters  32 G and  32 R) 
     Subsequently, green light and red light of the light having passed through the organic photoelectric converter  20  are absorbed and photoelectrically converted in sequence respectively in the inorganic photoelectric converter  32 G and the inorganic photoelectric converter  32 R. In the inorganic photoelectric converter  32 G, electrons corresponding to the incident green light are accumulated in the n region of the inorganic photoelectric converter  32 G, and the accumulated electrons are transferred to the floating diffusion FD 2  by the transfer transistor Tr 2 . Similarly, in the inorganic photoelectric converter  32 R, electrons corresponding to the incident red light are accumulated in the n region of the inorganic photoelectric converter  32 R, and the accumulated electrons are transferred to the floating diffusion FD 3  by the transfer transistor Tr 3 . 
     (1-3. Workings and Effects) 
     As described above, development of a photoelectric conversion element for blue light having high external quantum efficiency is desired. For example, a blue organic photoelectric conversion element using a porphyrin dye has been reported; however, external quantum efficiency thereof is about 20% at 80 V. In addition, a photoelectric conversion element using a combination of fullerene and a coumarin dye as materials of a blue organic photoelectric conversion film has been reported; however, external quantum efficiency thereof is about 23% at 5 V. 
     In contrast, in the present embodiment, as the material of the photoelectric conversion layer  24 , the benzothienobenzothiophene-based compound represented by the general formula (1) described above is used. 
     In the benzothienobenzothiophene-based compound represented by the general formula (1) described above, a major axis of a molecule takes face-on orientation horizontal to a substrate surface. In addition, the benzothienobenzothiophene-based compound represented by the general formula (1) described above may become herringbone-type crystal that is advantageous in carrier transport by strong intermolecular interaction by a benzothienobenzothiophene skeleton. Accordingly, the benzothienobenzothiophene-based compound represented by the general formula (1) in the photoelectric conversion layer  24  exhibits high carrier mobility with respect to a vertical direction of each of electrode surfaces of the lower electrode  21  and the upper electrode  25 . In addition, the benzothienobenzothiophene-based compound represented by the general formula (1) exhibits superior optical response current at a low voltage. 
     As described above, the photoelectric conversion layer  24  is formed that absorbs light of 400 nm to 500 nm both inclusive and has high carrier mobility to the lower electrode  21  and the upper electrode  25 . This makes it possible to provide the imaging element  10 A for blue light having high external quantum efficiency. 
     In addition, the benzothienobenzothiophene-based compound represented by the general formula (1) exhibits high carrier mobility with respect to the vertical direction of each of the electrode surfaces of the lower electrode  21  and the upper electrode  25  that are opposed to each other with the photoelectric conversion layer  24  interposed therebetween. This makes it possible to improve photocurrent on-off response characteristics depending on presence or absence of light irradiation. 
     Additionally, the benzothienobenzothiophene-based compound represented by the general formula (1) has a transition dipole moment horizontal to a light incident direction, which makes it possible to strongly absorb light of 400 nm to 500 nm both inclusive. Accordingly, an on-chip color filter is not necessary, and it is possible to configure a so-called longitudinal spectral type imaging element in which photoelectric converters absorbing light of wavelengths different from each other are stacked in the longitudinal direction, similarly to the imaging element  10 A according to the present embodiment. 
     Next, description is given of second to fifth embodiments of the present disclosure. In the following, components similar to those in the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted. 
     2. Second Embodiment 
       FIG. 12  illustrates a cross-sectional configuration of an imaging element (an imaging element  10 C) according to the second embodiment of the present disclosure. The imaging element  10 C is included, for example, in one pixel (a unit pixel P) in an imaging device (the imaging device  1 ) such as a CMOS image sensor used for an electronic apparatus such as a digital still camera and a video camera. The imaging element  10 C according to the present embodiment includes two organic photoelectric converters  20  and  70  and one inorganic photoelectric converter  32  that are stacked in the longitudinal direction. 
     The organic photoelectric converters  20  and  70  and the inorganic photoelectric converter  32  each selectively detect light in a corresponding one of wavelength bands different from each other, and perform photoelectric conversion of the thus-detected light. Specifically, for example, the organic photoelectric converter  20  acquires a blue (B) color signal similarly to the first embodiment described above. The organic photoelectric converter  70  acquires, for example, a green (G) color signal. The inorganic photoelectric converter  32  acquires, for example, a red (R) color signal. This allows the imaging element  10 C to acquire a plurality of kinds of color signals in one pixel without using a color filter. 
     The organic photoelectric converter  70  is stacked above the organic photoelectric converter  20 , for example, and has a configuration in which a lower electrode  71 , a semiconductor layer  73 , a photoelectric conversion layer  74 , and an upper electrode  75  are stacked in this order from the first surface (the surface  30 S 1 ) side of the semiconductor substrate  30 , similarly to the organic photoelectric converter  20 . In addition, an insulating layer  72  is provided between the lower electrode  71  and the semiconductor layer  73 . The lower electrode  71  is formed separately for each imaging element  10 C, for example, and includes a readout electrode  71 A and an accumulation electrode  71 B that are separated from each other with the insulating layer  72  interposed therebetween as described in detail later. The readout electrode  71 A of the lower electrode  71  is electrically coupled to the photoelectric conversion layer  74  via an opening  72 H provided in the insulating layer  72 .  FIG. 12  illustrates an example in which the semiconductor layer  73 , the photoelectric conversion layer  74 , and the upper electrode  75  are formed separately for each imaging element  10 C; however, the semiconductor layer  73 , the photoelectric conversion layer  74 , and the upper electrode  75  may be formed as common continuous layers for a plurality of imaging elements  10 C, for example. 
     The photoelectric conversion layer  74  converts optical energy into electric energy, and includes, for example, two or more kinds of organic materials (p-type semiconductor materials or n-type semiconductor materials) that each function as a p-type semiconductor or an n-type semiconductor, similarly to the photoelectric conversion layer  24 . The photoelectric conversion layer  74  may include, in addition to the p-type semiconductor material and the n-type semiconductor material, an organic material, i.e., a so-called dye material, that photoelectrically converts light in a predetermined wavelength band and allows light in another wavelength band to pass therethrough. In a case where the photoelectric conversion layer  74  is formed by using three kinds of organic materials, that is, the p-type semiconductor material, the n-type semiconductor material, and the dye material, the p-type semiconductor material and the n-type semiconductor material are preferably materials having light transmissivity in a visible region (for example, from 400 nm to 700 nm). The thickness of the photoelectric conversion layer  74  is, for example, from 25 nm to 400 nm both inclusive, preferably from 50 nm to 350 nm both inclusive, and more preferably from 150 nm to 300 nm both inclusive. Examples of the dye material used for the photoelectric conversion layer  74  include subphthalocyanine, phthalocyanine, coumarin, porphyrin, a derivative thereof, a derivative thereof, or the like. 
     Two through electrodes  34 X and  34 Y are provided between the first surface (the surface  30 S 1 ) and the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 . 
     Similarly to the first embodiment described above, the through electrode  34 X is electrically coupled to the readout electrode  21 A of the organic photoelectric converter  20 , and the organic photoelectric converter  20  is coupled to the gate Gamp of the amplifier transistor AMP and one source/drain region  36 B 1  of the reset transistor RST (the reset transistor Tr 1 rst) also serving as the floating diffusion FD 1  via the through electrode  34 X. An upper end of the through electrode  34 X is coupled to the readout electrode  21 A via the first upper contact  29 A, the pad section  39 A, and the second upper contact  29 B, for example. 
     The through electrode  34 Y is electrically coupled to the readout electrode  71 A of the organic photoelectric converter  70 , and the organic photoelectric converter  70  is coupled to the gate Gamp of the amplifier transistor AMP and one source/drain region  36 B 2  of the reset transistor RST (a reset transistor Tr 2 rst) also serving as the floating diffusion FD 2  via the through electrode  34 Y. An upper end of the through electrode  34 Y is coupled to the readout electrode  71 A via a fourth upper contact  79 A, a pad section  69 A, a fifth upper contact  79 B, a pad section  69 B, and a sixth upper contact  79 C, for example. In addition, a pad  69 C is coupled to the accumulation electrode  71 B of the lower electrode  71  included in the organic photoelectric converter  70  via a seventh upper contact  79 D. 
     As described above, the imaging element  10 B according to the present embodiment has a configuration in which two organic photoelectric converters  20  and  70  and one inorganic photoelectric converter  32  are stacked, and similarly to the first embodiment described above, for example, the photoelectric conversion layer  24  included in the organic photoelectric converter  20  that acquires the blue (B) color signal is formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above. This makes it possible to achieve effects similar to those in the first embodiment described above. 
     3. Third Embodiment 
       FIG. 13  schematically illustrates a cross-sectional configuration of an imaging element (an imaging element  10 D) according to the third embodiment of the present disclosure. The imaging element  10 D is included, for example, in one pixel (a unit pixel P) of an imaging device (the imaging device  1 ) such as a CMOS image sensor used for an electronic apparatus such as a digital still camera and a video camera. An organic photoelectric converter  80  according to the present embodiment differs from the first and second embodiments described above in that the organic photoelectric converter  80  has a configuration in which a lower electrode  81 , the photoelectric conversion layer  24 , and the upper electrode  25  are stacked in this order and the lower electrode  81  is formed as a solid film in a pixel. 
     The imaging element  10 D includes, for each unit pixel P, one organic photoelectric converter  80  and two inorganic photoelectric converters  32 G and  32 R that are stacked in the longitudinal direction. The organic photoelectric converter  80  and the inorganic photoelectric converters  32 G and  32 R each selectively detect light in a corresponding one of wavelength bands different from each other, and perform photoelectric conversion of the thus-detected light. Specifically, for example, the organic photoelectric converter  80  acquires a blue (B) color signal similarly to the first embodiment described above. A multilayer wiring layer  40  is provided on the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 . The multilayer wiring layer  40  has, for example, a configuration in which the wiring layers  41 ,  42 , and  43  are stacked in the insulating layer  44 . 
     The organic photoelectric converter  80  is an organic photoelectric conversion element that absorbs light corresponding to a wavelength band of a portion or the entirety of a selective wavelength band (for example, from 400 nm to 700 nm both inclusive) to generate electron-hole pairs. The organic photoelectric converter  80  includes, for example, the lower electrode  81  and the upper electrode  25  that are opposed to each other, and the photoelectric conversion layer  24  that is provided between the lower electrode  81  and the upper electrode  25 , as described above. As illustrated in  FIG. 13 , in the organic photoelectric converter  80  according to the present embodiment, the lower electrode  81 , the photoelectric conversion layer  24 , and the upper electrode  25  each have a configuration similar to that in the organic photoelectric converter  20  according to the first embodiment described above, except that the lower electrode  81  is formed as a solid film in each pixel. 
     For example, the floating diffusions (floating diffusion layers) FD 1 , FD 2 , and FD 3 , the vertical transistor (transfer transistor) Tr 1 , the transfer transistor Tr 2 , the amplifier transistor (modulation element) AMP, and the reset transistor RST are provided on the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 . 
     The vertical transistor Tr 1  is a transfer transistor that transfers, to the floating diffusion FD 1 , signal electric charges corresponding to green generated and accumulated in the inorganic photoelectric converter  32 G. The inorganic photoelectric converter  32 G is formed at a position deep from the second surface (the surface  30 S 2 ) of the semiconductor substrate  30 ; therefore, the transfer transistor of the inorganic photoelectric converter  32 G preferably includes the vertical transistor Tr 1 . The transfer transistor Tr 2  transfers, to the floating diffusion FD 2 , signal electric charges corresponding to red generated and accumulated in the inorganic photoelectric converter  32 R, and includes, for example, a MOS transistor. The amplifier transistor AMP is a modulation element that modulates an amount of electric charges generated in the organic photoelectric converter  80  into voltage, and includes, for example, a MOS transistor. The reset transistor RST resets electric charges transferred from the organic photoelectric converter  80  to the floating diffusion FD 3 , and includes, for example, a MOS transistor. 
     The first lower contact  45  and the second lower contact  46  each include, for example, a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon) or a metal material such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (Hf), and tantalum (Ta). 
     In the imaging element  10 D, each color signal is acquired as follows. 
     (Acquisition of Blue Signal by Organic Photoelectric Converter  80 ) 
     Of light having entered the imaging element  10 D, first, blue light is selectively detected (absorbed) and photoelectrically converted in the organic photoelectric converter  80 . 
     The organic photoelectric converter  80  is coupled to the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 3  via the through electrode  34 . Thus, electrons of electron-hole pairs generated in the organic photoelectric converter  80  are extracted from the lower electrode  81  side, transferred to the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  via the through electrode  34 , and accumulated in the floating diffusion FD 3 . Simultaneously with this, the amount of electric charges generated in the organic photoelectric converter  80  is modulated into voltage by the amplifier transistor AMP. 
     In addition, the reset gate Grst of the reset transistor RST is disposed adjacent to the floating diffusion FD 3 . Accordingly, the electric charges accumulated in the floating diffusion FD 3  are reset by the reset transistor RST. 
     Herein, the organic photoelectric converter  80  is coupled not only to the amplifier transistor AMP but also to the floating diffusion FD 3  via the through electrode  34 , thus making it possible for the reset transistor RST to easily reset the electric charges accumulated in the floating diffusion FD 3 . 
     In contrast to this, in a case where the through electrode  34  is not coupled to the floating diffusion FD 3 , it is difficult to reset the electric charges accumulated in the floating diffusion FD 3 , causing the electric charges to be drawn to the upper electrode  25  side by application of a large voltage. This may damage the photoelectric conversion layer  24 . In addition, a configuration that enables resetting in a short period of time causes an increase in dark time noise, thereby resulting in a trade-off; therefore, this configuration is difficult. 
     (Acquisition of Green Signal and Red Signal by Inorganic Photoelectric Converters  32 G and  32 R) 
     Subsequently, green light and red light of the light having passed through the organic photoelectric converter  80  are absorbed and photoelectrically converted in sequence respectively in the inorganic photoelectric converter  32 G and the inorganic photoelectric converter  32 R. In the inorganic photoelectric converter  32 G, electrons corresponding to the incident green light are accumulated in the n region of the inorganic photoelectric converter  32 G, and the accumulated electrons are transferred to the floating diffusion FD 1  by the vertical transistor Tr 1 . Similarly, in the inorganic photoelectric converter  32 R, electrons corresponding to the incident red light are accumulated in the n region of the inorganic photoelectric converter  32 R, and the accumulated electrons are transferred to the floating diffusion FD 2  by the transfer transistor Tr 2 . 
     As described above, in the imaging element  10 D according to the present embodiment, the lower electrode  81  included in the organic photoelectric converter  80  is formed as a solid film, and similarly to the first embodiment described above, for example, the photoelectric conversion layer  24  included in the organic photoelectric converter  80  that acquires the blue (B) color signal is formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above. This makes it possible to achieve effects similar to those in the first embodiment described above. 
     4. Fourth Embodiment 
       FIG. 14  schematically illustrates a cross-sectional configuration of an imaging element (an imaging element  10 E) according to the fourth embodiment of the present disclosure. The imaging element  10 E is included, for example, in one pixel (a unit pixel P) in an imaging device (the imaging device  1 ) such as a CMOS image sensor used for an electronic apparatus such as a digital still camera and a video camera. The imaging element  10 E according to the present embodiment has a configuration in which a red photoelectric converter  90 R, a green photoelectric converter  90 G, and a blue photoelectric converter  90 B are stacked in this order on the semiconductor substrate  30  with an insulating layer  96  interposed therebetween. 
     The red photoelectric converter  90 R, the green photoelectric converter  90 G, and the blue photoelectric converter  90 B respectively include organic photoelectric conversion layers  92 R,  92 G, and  92 B between a pair of electrodes, specifically between a first electrode  91 R and a second electrode  93 R, between a first electrode  91 G and a second electrode  93 G, and between a first electrode  91 B and a second electrode  93 B. The organic photoelectric conversion layer  92 B is formed, for example, by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above, similarly to the first embodiment described above. 
     An on-chip lens  98 L is provided on the blue photoelectric converter  90 B with a protective layer  97  and an on-chip lens layer  98  interposed therebetween. A red accumulation layer  310 R, a green accumulation layer  310 G, and a blue accumulation layer  310 B are provided in the semiconductor substrate  30 . Light having entered the on-chip lens  98 L is photoelectrically converted by the red photoelectric converter  90 R, the green photoelectric converter  90 G, and the blue photoelectric converter  90 B, and signal electric charges are transmitted from the red photoelectric converter  90 R to the red accumulation layer  310 R, from the green photoelectric converter  90 G to the green accumulation layer  310 G, and from the blue photoelectric converter  90 B to the blue accumulation layer  310 B. The signal electric charges may be electrons or holes generated by photoelectric conversion, but a case where electrons are read out as signal electric charges is described as an example below. 
     The semiconductor substrate  30  includes, for example, a p-type silicon substrate. The red accumulation layer  310 R, the green accumulation layer  310 G, and the blue accumulation layer  310 B provided in the semiconductor substrate  30  each include an n-type semiconductor region, and signal electric charges (electrons) supplied from the red photoelectric converter  90 R, the green photoelectric converter  90 G, and the blue photoelectric converter  90 B are accumulated in the n-type semiconductor regions. The n-type semiconductor regions of the red accumulation layer  310 R, the green accumulation layer  310 G, and the blue accumulation layer  310 B are formed by doping the semiconductor substrate  30  with an n-type impurity such as phosphorus (P) or arsenic (As), for example. It is to be noted that the semiconductor substrate  30  may be provided on a supporting substrate (not illustrated) including glass or the like. 
     In the semiconductor substrate  30 , a pixel transistor is provided. The pixel transfer is used to read electrons from each of the red accumulation layer  310 R, the green accumulation layer  310 G, and the blue accumulation layer  310 B and transfer the electrons to a vertical signal line (for example, a vertical signal line Lsig in  FIG. 15  to be described later), for example. A floating diffusion of the pixel transistor is provided in the semiconductor substrate  30 , and the floating diffusion is coupled to the red accumulation layer  310 R, the green accumulation layer  310 G, and the blue accumulation layer  310 B. The floating diffusion includes an n-type semiconductor region. 
     The insulating layer  96  includes, for example, a single-layer film including one kind of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiON), hafnium oxide (HfO x ), and the like, or a stacked film including two or more kinds thereof. In addition, the insulating layer  96  may be formed by using an organic insulating material. Although not illustrated, the insulating layer  96  includes respective plugs for coupling between the red accumulation layer  310 R and the red photoelectric converter  90 R, between the green accumulation layer  310 G and the green photoelectric converter  90 G, and between the blue accumulation layer  310 B and the blue photoelectric converter  90 B, and electrodes. 
     The red photoelectric converter  90 R includes the first electrode  91 R, the organic photoelectric conversion layer  92 R, and the second electrode  93 R in this order from a position close to the semiconductor substrate  30 . The green photoelectric converter  90 G includes the first electrode  91 G, the organic photoelectric conversion layer  92 G, and the second electrode  93 G in this order from a position close to the red photoelectric converter  90 R. The blue photoelectric converter  90 B includes the first electrode  91 B, the organic photoelectric conversion layer  92 B, and the second electrode  93 B in this order from a position close to the green photoelectric converter  90 G. An insulating layer  94  is provided between the red photoelectric converter  90 R and the green photoelectric converter  90 G, and an insulating layer  95  is provided between the green photoelectric converter  90 G and the blue photoelectric converter  90 B. The red photoelectric converter  90 R, the green photoelectric converter  90 G, and the blue photoelectric converter  90 B respectively selectively absorb red (for example, a wavelength of 600 nm or greater and less than 700 nm) light, green (for example, a wavelength of 500 nm or greater and less than 600 nm) light, and blue (for example, a wavelength of 400 or greater and less than 500 nm) light to generate electron-hole pairs. 
     The first electrode  91 R, the first electrode  91 G, and the first electrode  91 B respectively extract signal electric charges generated in the organic photoelectric conversion layer  92 R, signal electric charges generated in the organic photoelectric conversion layer  92 G, and signal electric charges generated in the organic photoelectric conversion layer  92 B. The first electrodes  91 R,  91 G, and  91 B are provided for each pixel, for example. The first electrodes  91 R,  91 G, and  91 B include, for example, an electrically conductive material having light transmissivity, specifically ITO. The first electrodes  91 R,  91 G, and  91 B may include, for example, a tin oxide-based material or a zinc oxide-based material. The tin oxide-based material is tin oxide to which a dopant is added, and examples of the zinc oxide-based material include aluminum zinc oxide prepared by adding aluminum as a dopant to zinc oxide, gallium zinc oxide prepared by adding gallium as a dopant to zinc oxide, indium zinc oxide prepared by adding indium as a dopant to zinc oxide, and the like. Other than these materials, it is possible to use IGZO, CuI, InSbO 4 , ZnMgO, CuInO 2 , MgIn 2 O 4 , CdO, ZnSnO 3 , and the like. Each of the first electrodes  91 R,  91 G, and  91 B has, for example, a thickness of 50 nm to 500 nm. 
     For example, an electron transport layer may be provided each between the first electrode  91 R and the organic photoelectric conversion layer  92 R, between the first electrode  91 G and the organic photoelectric conversion layer  92 G, and between the first electrode  91 B and the organic photoelectric conversion layer  92 B. The electron transport layer promotes supplying of electrons generated in the organic photoelectric conversion layers  92 R,  92 G, and  92 B to the first electrodes  91 R,  91 G, and  91 B, and includes, for example, titanium oxide, zinc oxide, or the like. The electron transport layer may be configured by stacking a titanium oxide film and a zinc oxide film. A thickness of the electron transport layer is, for example, from 0.1 nm to 1000 nm, and preferably from 0.5 nm to 300 nm. 
     The organic photoelectric conversion layer  92 R,  92 G, and  92 B each absorb light in a selective wavelength band for photoelectric conversion, and allow light in another wavelength band to pass therethrough. Herein, the light in the selective wavelength band is, for example, light in a wavelength band of a wavelength of 600 nm or greater and less than 700 nm for the organic photoelectric conversion layer  92 R, light in a wavelength band of a wavelength of 500 nm or greater and less than 600 nm for the organic photoelectric conversion layer  92 G, and light in a wavelength band of a wavelength of 400 nm or greater and less than 500 nm for the organic photoelectric conversion layer  92 B. A thickness of each of the organic photoelectric conversion layers  92 R,  92 G, and  92 B is, for example, from 25 nm to 400 nm both inclusive, preferably from 50 nm to 350 nm both inclusive, and more preferably from 150 nm to 300 nm both inclusive. 
     The organic photoelectric conversion layers  92 R,  92 G, and  92 B each convert optical energy into electric energy, and each include two or more kinds of organic materials (p-type semiconductor materials or n-type semiconductor materials) that each function as a p-type semiconductor or an n-type semiconductor similarly to the photoelectric conversion layer  24 . The organic photoelectric conversion layers  92 R,  92 G, and  92 B may include, in addition to the p-type semiconductor material and the n-type semiconductor material, an organic material, i.e., a so-called dye material, that photoelectrically converts light in the predetermined wavelength band described above and allows light in another wavelength band to pass therethrough. Examples of such a material include rhodamine, merocyanine, and derivatives thereof for the organic photoelectric conversion layer  92 R. The examples include subphthalocyanine, phthalocyanine, coumarin, porphyrin, and derivatives thereof for the organic photoelectric conversion layer  92 G. The examples include the benzothienobenzothiophene-based compound represented by the general formula (1) described above for the organic photoelectric conversion layer  92 B. 
     Examples of the organic materials included in the organic photoelectric conversion layers  92 R,  92 G, and  92 B include fullerene or a fullerene derivative. The organic photoelectric conversion layers  92 R,  92 G, and  92 B may further include an organic material other than the organic materials described above. 
     For example, a hole transport layer may be provided each between the organic photoelectric conversion layer  92 R and the second electrode  93 R, between the organic photoelectric conversion layer  92 G and the second electrode  93 G, and between the organic photoelectric conversion layer  92 B and the second electrode  93 B. The hole transport layer promotes supplying of holes generated in the organic photoelectric conversion layers  92 R,  92 G, and  92 B to the second electrodes  93 R,  93 G, and  93 B, and includes, for example, molybdenum oxide, nickel oxide, vanadium oxide, or the like. The hole transport layer may include an organic material such as PEDOT (Poly(3,4-ethylenedioxythiophene)) and TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine). The hole transport layer has, for example, a thickness of 0.5 nm to 100 nm both inclusive. 
     The second electrode  93 R, the second electrode  93 G, and the second electrode  93 B respectively extract holes generated in the organic photoelectric conversion layer  92 R, holes generated in the organic photoelectric conversion layer  92 G, and holes generated in the organic photoelectric conversion layer  92 B. The holes extracted from each of the second electrodes  93 R,  93 G, and  93 B are discharged to, for example, a p-type semiconductor region (not illustrated) in the semiconductor substrate  30  via each transmission path (not illustrated). The second electrodes  93 R,  93 G, and  93 B include, for example, an electrically conductive material such as gold (Au), silver (Ag), copper (Cu), and aluminum (Al). Similarly to first electrodes  91 R,  91 G, and  91 B, the second electrodes  93 R,  93 G, and  93 B may include a transparent electrically conductive material. In the imaging element  10 E, the holes extracted from the second electrodes  93 R,  93 G, and  93 B are discharged; therefore, for example, in a case where a plurality of imaging elements  10 E is disposed in the imaging device  1  to be described later, the second electrodes  93 R,  93 G, and  93 B may be provided common to each of the imaging elements  10 E (unit pixels P). Each of the second electrodes  93 R,  93 G, and  93 B has, for example, a thickness of 0.5 nm to 100 nm both inclusive. 
     The insulating layer  94  insulates the second electrode  93 R and the first electrode  91 G from each other. The insulating layer  95  insulates the second electrode  93 G and the first electrode  91 B from each other. The insulating layers  94  and  95  include, for example, a metal oxide, a metal sulfide, or an organic substance. Examples of the metal oxide include silicon oxide (SiO x ), aluminum oxide (AlO x ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), zinc oxide (ZnO x ), tungsten oxide (WO x ), magnesium oxide (MgO x ), niobium oxide (NbO x ), tin oxide (SnO x ), gallium oxide (GaO x ), and the like. Examples of the metal sulfide include zinc sulfide (ZnS), magnesium sulfide (MgS), and the like. A band gap of a constituent material of each of the insulating layers  94  and  95  is preferably 3.0 eV or greater. Each of the insulating layers  94  and  95  has, for example, a thickness of 2 nm to 100 nm both inclusive. 
     As described above, the organic photoelectric conversion layer  92 B is formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above, which makes it possible to achieve effects similar to those in the first embodiment described above. 
     5. APPLICATION EXAMPLES 
     Application Example 1 
       FIG. 15  illustrates an overall configuration of an imaging device (the imaging device  1 ) using, for each of the pixels, the imaging element  10 A (or any of the imaging elements  10 B to  10 E) described in the first to fourth embodiments described above. The imaging device  1  is a CMOS image sensor, and includes, on the semiconductor substrate  30 , the pixel section  1   a  as an imaging region and a peripheral circuit section  130  including, for example, a row scanner  131 , a horizontal selector  133 , a column scanner  134 , and a system controller  132  in a peripheral region of the pixel section  1   a.    
     The pixel section  1   a  has a plurality of unit pixels P (each corresponding to an imaging element  10 ) two-dimensionally arranged in a matrix, for example. The unit pixels P are wired with pixel drive lines Lread (specifically, row selection lines and reset control lines) for respective pixel rows, and vertical signal lines Lsig for respective pixel columns, for example. The pixel drive lines Lread transmit drive signals for signal reading from the pixels. The pixel drive lines Lread each have one end coupled to a corresponding one of output terminals, corresponding to the respective rows, of the row scanner  131 . 
     The row scanner  131  includes a shift register, an address decoder, and the like, and is a pixel driver, for example, that drives the respective unit pixels P in the pixel section  1   a  on a row-by-row basis. A signal outputted from each of the unit pixels P of a pixel row selectively scanned by the row scanner  131  is supplied to the horizontal selector  133  through each of the vertical signal lines Lsig. The horizontal selector  133  includes an amplifier, a horizontal selection switch, and the like provided for each of the vertical signal lines Lsig. 
     The column scanner  134  includes a shift register, an address decoder, and the like, and drives respective horizontal selection switches of the horizontal selector  133  in sequence while scanning the horizontal selection switches. Such selective scanning by the column scanner  134  causes the signals of the respective pixels transmitted through the respective vertical signal lines Lsig to be outputted in sequence to a horizontal signal line  135  and thereafter transmitted to outside of the semiconductor substrate  30  through the horizontal signal line  135 . 
     Circuit components including the row scanner  131 , the horizontal selector  133 , the column scanner  134 , and the horizontal signal line  135  may be formed directly on the semiconductor substrate  30  or disposed in an external control IC. Alternatively, these circuit components may be formed in any other substrate coupled by a cable, or the like. 
     The system controller  132  receives a clock given from the outside of the semiconductor substrate  30 , or data or the like on instructions of operation modes, and also outputs data such as internal information of the imaging device  1 . The system controller  132  further has a timing generator that generates various timing signals, and performs drive control of the peripheral circuits such as the row scanner  131 , the horizontal selector  133 , and the column scanner  134 , on the basis of the various timing signals generated by the timing generator. 
     Application Example 2 
     The imaging device  1  described above is applicable to, for example, various kinds of electronic apparatuses having imaging functions. Examples of the electronic apparatuses include camera systems such as digital still cameras and video cameras and mobile phones having the imaging functions.  FIG. 16  illustrates, for purpose of an example, a schematic configuration of an electronic apparatus  2  (a camera). The electronic apparatus  2  is a video camera that enables shooting of a still image or a moving image, for example, and includes the imaging device  1 , an optical system (optical lens)  310 , a shutter device  311 , a driver  313  that drives the imaging device  1  and the shutter device  311 , and a signal processor  312 . 
     The optical system  310  guides image light (incident light) from a subject to the pixel section  1   a  of the imaging device  1 . The optical system  310  may include a plurality of optical lenses. The shutter device  311  controls a period in which the imaging device  1  is irradiated with the light and a period in which the light is blocked. The driver  313  controls a transfer operation of the imaging device  1  and a shutter operation of the shutter device  311 . The signal processor  312  performs various kinds of signal processing on signals outputted from the imaging device  1 . An image signal Dout having been subjected to the signal processing is stored in a storage medium such as a memory or outputted to a monitor, or the like. 
     Application Example 3 
     Further, the imaging device  1  described above is applicable to the following electronic apparatuses (a capsule type endoscope  10100  and a mobile body such as a vehicle). 
     6. PRACTICAL APPLICATION EXAMPLE 
     Practical Application Example to In-Vivo Information Acquisition System) 
     Further, the technology (present technology) according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 17  is a block diagram depicting an example of a schematic configuration of an in-vivo information acquisition system of a patient using a capsule type endoscope, to which the technology according to an embodiment of the present disclosure (present technology) can be applied. 
     The in-vivo information acquisition system  10001  includes a capsule type endoscope  10100  and an external controlling apparatus  10200 . 
     The capsule type endoscope  10100  is swallowed by a patient at the time of inspection. The capsule type endoscope  10100  has an image pickup function and a wireless communication function and successively picks up an image of the inside of an organ such as the stomach or an intestine (hereinafter referred to as in-vivo image) at predetermined intervals while it moves inside of the organ by peristaltic motion for a period of time until it is naturally discharged from the patient. Then, the capsule type endoscope  10100  successively transmits information of the in-vivo image to the external controlling apparatus  10200  outside the body by wireless transmission. 
     The external controlling apparatus  10200  integrally controls operation of the in-vivo information acquisition system  10001 . Further, the external controlling apparatus  10200  receives information of an in-vivo image transmitted thereto from the capsule type endoscope  10100  and generates image data for displaying the in-vivo image on a display apparatus (not depicted) on the basis of the received information of the in-vivo image. 
     In the in-vivo information acquisition system  10001 , an in-vivo image imaged a state of the inside of the body of a patient can be acquired at any time in this manner for a period of time until the capsule type endoscope  10100  is discharged after it is swallowed. 
     A configuration and functions of the capsule type endoscope  10100  and the external controlling apparatus  10200  are described in more detail below. 
     The capsule type endoscope  10100  includes a housing  10101  of the capsule type, in which a light source unit  10111 , an image pickup unit  10112 , an image processing unit  10113 , a wireless communication unit  10114 , a power feeding unit  10115 , a power supply unit  10116  and a control unit  10117  are accommodated. 
     The light source unit  10111  includes a light source such as, for example, a light emitting diode (LED) and irradiates light on an image pickup field-of-view of the image pickup unit  10112 . 
     The image pickup unit  10112  includes an image pickup element and an optical system including a plurality of lenses provided at a preceding stage to the image pickup element. Reflected light (hereinafter referred to as observation light) of light irradiated on a body tissue which is an observation target is condensed by the optical system and introduced into the image pickup element. In the image pickup unit  10112 , the incident observation light is photoelectrically converted by the image pickup element, by which an image signal corresponding to the observation light is generated. The image signal generated by the image pickup unit  10112  is provided to the image processing unit  10113 . 
     The image processing unit  10113  includes a processor such as a central processing unit (CPU) or a graphics processing unit (GPU) and performs various signal processes for an image signal generated by the image pickup unit  10112 . The image processing unit  10113  provides the image signal for which the signal processes have been performed thereby as RAW data to the wireless communication unit  10114 . 
     The wireless communication unit  10114  performs a predetermined process such as a modulation process for the image signal for which the signal processes have been performed by the image processing unit  10113  and transmits the resulting image signal to the external controlling apparatus  10200  through an antenna  10114 A. Further, the wireless communication unit  10114  receives a control signal relating to driving control of the capsule type endoscope  10100  from the external controlling apparatus  10200  through the antenna  10114 A. The wireless communication unit  10114  provides the control signal received from the external controlling apparatus  10200  to the control unit  10117 . 
     The power feeding unit  10115  includes an antenna coil for power reception, a power regeneration circuit for regenerating electric power from current generated in the antenna coil, a voltage booster circuit and so forth. The power feeding unit  10115  generates electric power using the principle of non-contact charging. 
     The power supply unit  10116  includes a secondary battery and stores electric power generated by the power feeding unit  10115 . In  FIG. 17 , in order to avoid complicated illustration, an arrow mark indicative of a supply destination of electric power from the power supply unit  10116  and so forth are omitted. However, electric power stored in the power supply unit  10116  is supplied to and can be used to drive the light source unit  10111 , the image pickup unit  10112 , the image processing unit  10113 , the wireless communication unit  10114  and the control unit  10117 . 
     The control unit  10117  includes a processor such as a CPU and suitably controls driving of the light source unit  10111 , the image pickup unit  10112 , the image processing unit  10113 , the wireless communication unit  10114  and the power feeding unit  10115  in accordance with a control signal transmitted thereto from the external controlling apparatus  10200 . 
     The external controlling apparatus  10200  includes a processor such as a CPU or a GPU, a microcomputer, a control board or the like in which a processor and a storage element such as a memory are mixedly incorporated. The external controlling apparatus  10200  transmits a control signal to the control unit  10117  of the capsule type endoscope  10100  through an antenna  10200 A to control operation of the capsule type endoscope  10100 . In the capsule type endoscope  10100 , an irradiation condition of light upon an observation target of the light source unit  10111  can be changed, for example, in accordance with a control signal from the external controlling apparatus  10200 . Further, an image pickup condition (for example, a frame rate, an exposure value or the like of the image pickup unit  10112 ) can be changed in accordance with a control signal from the external controlling apparatus  10200 . Further, the substance of processing by the image processing unit  10113  or a condition for transmitting an image signal from the wireless communication unit  10114  (for example, a transmission interval, a transmission image number or the like) may be changed in accordance with a control signal from the external controlling apparatus  10200 . 
     Further, the external controlling apparatus  10200  performs various image processes for an image signal transmitted thereto from the capsule type endoscope  10100  to generate image data for displaying a picked up in-vivo image on the display apparatus. As the image processes, various signal processes can be performed such as, for example, a development process (demosaic process), an image quality improving process (bandwidth enhancement process, a super-resolution process, a noise reduction (NR) process and/or image stabilization process) and/or an enlargement process (electronic zooming process). The external controlling apparatus  10200  controls driving of the display apparatus to cause the display apparatus to display a picked up in-vivo image on the basis of generated image data. Alternatively, the external controlling apparatus  10200  may also control a recording apparatus (not depicted) to record generated image data or control a printing apparatus (not depicted) to output generated image data by printing. 
     One example of the in-vivo information acquisition system to which the technology according to the present disclosure is applicable has been described above. The technology according to the present disclosure is applicable to, for example, the image pickup unit  10112  of the configurations described above. This makes it possible to improve accuracy of an inspection. 
     Practical Application Example to Endoscopic Surgery System 
     The technology (present technology) according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 18  is a view depicting an example of a schematic configuration of an endoscopic surgery system to which the technology according to an embodiment of the present disclosure (present technology) can be applied. 
     In  FIG. 18 , a state is illustrated in which a surgeon (medical doctor)  11131  is using an endoscopic surgery system  11000  to perform surgery for a patient  11132  on a patient bed  11133 . As depicted, the endoscopic surgery system  11000  includes an endoscope  11100 , other surgical tools  11110  such as a pneumoperitoneum tube  11111  and an energy device  11112 , a supporting arm apparatus  11120  which supports the endoscope  11100  thereon, and a cart  11200  on which various apparatus for endoscopic surgery are mounted. 
     The endoscope  11100  includes a lens barrel  11101  having a region of a predetermined length from a distal end thereof to be inserted into a body cavity of the patient  11132 , and a camera head  11102  connected to a proximal end of the lens barrel  11101 . In the example depicted, the endoscope  11100  is depicted which includes as a rigid endoscope having the lens barrel  11101  of the hard type. However, the endoscope  11100  may otherwise be included as a flexible endoscope having the lens barrel  11101  of the flexible type. 
     The lens barrel  11101  has, at a distal end thereof, an opening in which an objective lens is fitted. A light source apparatus  11203  is connected to the endoscope  11100  such that light generated by the light source apparatus  11203  is introduced to a distal end of the lens barrel  11101  by a light guide extending in the inside of the lens barrel  11101  and is irradiated toward an observation target in a body cavity of the patient  11132  through the objective lens. It is to be noted that the endoscope  11100  may be a forward-viewing endoscope or may be an oblique-viewing endoscope or a side-viewing endoscope. 
     An optical system and an image pickup element are provided in the inside of the camera head  11102  such that reflected light (observation light) from the observation target is condensed on the image pickup element by the optical system. The observation light is photo-electrically converted by the image pickup element to generate an electric signal corresponding to the observation light, namely, an image signal corresponding to an observation image. The image signal is transmitted as RAW data to a CCU  11201 . 
     The CCU  11201  includes a central processing unit (CPU), a graphics processing unit (GPU) or the like and integrally controls operation of the endoscope  11100  and a display apparatus  11202 . Further, the CCU  11201  receives an image signal from the camera head  11102  and performs, for the image signal, various image processes for displaying an image based on the image signal such as, for example, a development process (demosaic process). 
     The display apparatus  11202  displays thereon an image based on an image signal, for which the image processes have been performed by the CCU  11201 , under the control of the CCU  11201 . 
     The light source apparatus  11203  includes a light source such as, for example, a light emitting diode (LED) and supplies irradiation light upon imaging of a surgical region to the endoscope  11100 . 
     An inputting apparatus  11204  is an input interface for the endoscopic surgery system  11000 . A user can perform inputting of various kinds of information or instruction inputting to the endoscopic surgery system  11000  through the inputting apparatus  11204 . For example, the user would input an instruction or a like to change an image pickup condition (type of irradiation light, magnification, focal distance or the like) by the endoscope  11100 . 
     A treatment tool controlling apparatus  11205  controls driving of the energy device  11112  for cautery or incision of a tissue, sealing of a blood vessel or the like. A pneumoperitoneum apparatus  11206  feeds gas into a body cavity of the patient  11132  through the pneumoperitoneum tube  11111  to inflate the body cavity in order to secure the field of view of the endoscope  11100  and secure the working space for the surgeon. A recorder  11207  is an apparatus capable of recording various kinds of information relating to surgery. A printer  11208  is an apparatus capable of printing various kinds of information relating to surgery in various forms such as a text, an image or a graph. 
     It is to be noted that the light source apparatus  11203  which supplies irradiation light when a surgical region is to be imaged to the endoscope  11100  may include a white light source which includes, for example, an LED, a laser light source or a combination of them. Where a white light source includes a combination of red, green, and blue (RGB) laser light sources, since the output intensity and the output timing can be controlled with a high degree of accuracy for each color (each wavelength), adjustment of the white balance of a picked up image can be performed by the light source apparatus  11203 . Further, in this case, if laser beams from the respective RGB laser light sources are irradiated time-divisionally on an observation target and driving of the image pickup elements of the camera head  11102  are controlled in synchronism with the irradiation timings. Then images individually corresponding to the R, G and B colors can be also picked up time-divisionally. According to this method, a color image can be obtained even if color filters are not provided for the image pickup element. 
     Further, the light source apparatus  11203  may be controlled such that the intensity of light to be outputted is changed for each predetermined time. By controlling driving of the image pickup element of the camera head  11102  in synchronism with the timing of the change of the intensity of light to acquire images time-divisionally and synthesizing the images, an image of a high dynamic range free from underexposed blocked up shadows and overexposed highlights can be created. 
     Further, the light source apparatus  11203  may be configured to supply light of a predetermined wavelength band ready for special light observation. In special light observation, for example, by utilizing the wavelength dependency of absorption of light in a body tissue to irradiate light of a narrow band in comparison with irradiation light upon ordinary observation (namely, white light), narrow band observation (narrow band imaging) of imaging a predetermined tissue such as a blood vessel of a superficial portion of the mucous membrane or the like in a high contrast is performed. Alternatively, in special light observation, fluorescent observation for obtaining an image from fluorescent light generated by irradiation of excitation light may be performed. In fluorescent observation, it is possible to perform observation of fluorescent light from a body tissue by irradiating excitation light on the body tissue (autofluorescence observation) or to obtain a fluorescent light image by locally injecting a reagent such as indocyanine green (ICG) into a body tissue and irradiating excitation light corresponding to a fluorescent light wavelength of the reagent upon the body tissue. The light source apparatus  11203  can be configured to supply such narrow-band light and/or excitation light suitable for special light observation as described above. 
       FIG. 19  is a block diagram depicting an example of a functional configuration of the camera head  11102  and the CCU  11201  depicted in  FIG. 18 . 
     The camera head  11102  includes a lens unit  11401 , an image pickup unit  11402 , a driving unit  11403 , a communication unit  11404  and a camera head controlling unit  11405 . The CCU  11201  includes a communication unit  11411 , an image processing unit  11412  and a control unit  11413 . The camera head  11102  and the CCU  11201  are connected for communication to each other by a transmission cable  11400 . 
     The lens unit  11401  is an optical system, provided at a connecting location to the lens barrel  11101 . Observation light taken in from a distal end of the lens barrel  11101  is guided to the camera head  11102  and introduced into the lens unit  11401 . The lens unit  11401  includes a combination of a plurality of lenses including a zoom lens and a focusing lens. 
     The number of image pickup elements which is included by the image pickup unit  11402  may be one (single-plate type) or a plural number (multi-plate type). Where the image pickup unit  11402  is configured as that of the multi-plate type, for example, image signals corresponding to respective R, G and B are generated by the image pickup elements, and the image signals may be synthesized to obtain a color image. The image pickup unit  11402  may also be configured so as to have a pair of image pickup elements for acquiring respective image signals for the right eye and the left eye ready for three dimensional (3D) display. If 3D display is performed, then the depth of a living body tissue in a surgical region can be comprehended more accurately by the surgeon  11131 . It is to be noted that, where the image pickup unit  11402  is configured as that of stereoscopic type, a plurality of systems of lens units  11401  are provided corresponding to the individual image pickup elements. 
     Further, the image pickup unit  11402  may not necessarily be provided on the camera head  11102 . For example, the image pickup unit  11402  may be provided immediately behind the objective lens in the inside of the lens barrel  11101 . 
     The driving unit  11403  includes an actuator and moves the zoom lens and the focusing lens of the lens unit  11401  by a predetermined distance along an optical axis under the control of the camera head controlling unit  11405 . Consequently, the magnification and the focal point of a picked up image by the image pickup unit  11402  can be adjusted suitably. 
     The communication unit  11404  includes a communication apparatus for transmitting and receiving various kinds of information to and from the CCU  11201 . The communication unit  11404  transmits an image signal acquired from the image pickup unit  11402  as RAW data to the CCU  11201  through the transmission cable  11400 . 
     In addition, the communication unit  11404  receives a control signal for controlling driving of the camera head  11102  from the CCU  11201  and supplies the control signal to the camera head controlling unit  11405 . The control signal includes information relating to image pickup conditions such as, for example, information that a frame rate of a picked up image is designated, information that an exposure value upon image picking up is designated and/or information that a magnification and a focal point of a picked up image are designated. 
     It is to be noted that the image pickup conditions such as the frame rate, exposure value, magnification or focal point may be designated by the user or may be set automatically by the control unit  11413  of the CCU  11201  on the basis of an acquired image signal. In the latter case, an auto exposure (AE) function, an auto focus (AF) function and an auto white balance (AWB) function are incorporated in the endoscope  11100 . 
     The camera head controlling unit  11405  controls driving of the camera head  11102  on the basis of a control signal from the CCU  11201  received through the communication unit  11404 . 
     The communication unit  11411  includes a communication apparatus for transmitting and receiving various kinds of information to and from the camera head  11102 . The communication unit  11411  receives an image signal transmitted thereto from the camera head  11102  through the transmission cable  11400 . 
     Further, the communication unit  11411  transmits a control signal for controlling driving of the camera head  11102  to the camera head  11102 . The image signal and the control signal can be transmitted by electrical communication, optical communication or the like. 
     The image processing unit  11412  performs various image processes for an image signal in the form of RAW data transmitted thereto from the camera head  11102 . 
     The control unit  11413  performs various kinds of control relating to image picking up of a surgical region or the like by the endoscope  11100  and display of a picked up image obtained by image picking up of the surgical region or the like. For example, the control unit  11413  creates a control signal for controlling driving of the camera head  11102 . 
     Further, the control unit  11413  controls, on the basis of an image signal for which image processes have been performed by the image processing unit  11412 , the display apparatus  11202  to display a picked up image in which the surgical region or the like is imaged. Thereupon, the control unit  11413  may recognize various objects in the picked up image using various image recognition technologies. For example, the control unit  11413  can recognize a surgical tool such as forceps, a particular living body region, bleeding, mist when the energy device  11112  is used and so forth by detecting the shape, color and so forth of edges of objects included in a picked up image. The control unit  11413  may cause, when it controls the display apparatus  11202  to display a picked up image, various kinds of surgery supporting information to be displayed in an overlapping manner with an image of the surgical region using a result of the recognition. Where surgery supporting information is displayed in an overlapping manner and presented to the surgeon  11131 , the burden on the surgeon  11131  can be reduced and the surgeon  11131  can proceed with the surgery with certainty. 
     The transmission cable  11400  which connects the camera head  11102  and the CCU  11201  to each other is an electric signal cable ready for communication of an electric signal, an optical fiber ready for optical communication or a composite cable ready for both of electrical and optical communications. 
     Here, while, in the example depicted, communication is performed by wired communication using the transmission cable  11400 , the communication between the camera head  11102  and the CCU  11201  may be performed by wireless communication. 
     One example of the endoscopic surgery system to which the technology according to the present disclosure is applicable has been described above. The technology according to the present disclosure is applicable to, for example, the image pickup unit  11402  of the configurations described above. Applying the technology according to the present disclosure to the image pickup unit  11402  makes it possible to improve accuracy of an inspection. 
     It is to be noted that the endoscopic surgery system has been described here as an example, but the technology according to the present disclosure may be additionally applied to, for example, a microscopic surgery system and the like. 
     (Practical Application Example to Mobile Body) 
     The technology according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be achieved in the form of an apparatus to be mounted to a mobile body of any kind such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a vessel, a robot, a construction machine, and an agricultural machine (tractor). 
       FIG. 20  is a block diagram depicting an example of schematic configuration of a vehicle control system as an example of a mobile body control system to which the technology according to an embodiment of the present disclosure can be applied. 
     The vehicle control system  12000  includes a plurality of electronic control units connected to each other via a communication network  12001 . In the example depicted in  FIG. 20 , the vehicle control system  12000  includes a driving system control unit  12010 , a body system control unit  12020 , an outside-vehicle information detecting unit  12030 , an in-vehicle information detecting unit  12040 , and an integrated control unit  12050 . In addition, a microcomputer  12051 , a sound/image output section  12052 , and a vehicle-mounted network interface (I/F)  12053  are illustrated as a functional configuration of the integrated control unit  12050 . 
     The driving system control unit  12010  controls the operation of devices related to the driving system of the vehicle in accordance with various kinds of programs. For example, the driving system control unit  12010  functions as a control device for a driving force generating device for generating the driving force of the vehicle, such as an internal combustion engine, a driving motor, or the like, a driving force transmitting mechanism for transmitting the driving force to wheels, a steering mechanism for adjusting the steering angle of the vehicle, a braking device for generating the braking force of the vehicle, and the like. 
     The body system control unit  12020  controls the operation of various kinds of devices provided to a vehicle body in accordance with various kinds of programs. For example, the body system control unit  12020  functions as a control device for a keyless entry system, a smart key system, a power window device, or various kinds of lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or the like. In this case, radio waves transmitted from a mobile device as an alternative to a key or signals of various kinds of switches can be input to the body system control unit  12020 . The body system control unit  12020  receives these input radio waves or signals, and controls a door lock device, the power window device, the lamps, or the like of the vehicle. 
     The outside-vehicle information detecting unit  12030  detects information about the outside of the vehicle including the vehicle control system  12000 . For example, the outside-vehicle information detecting unit  12030  is connected with an imaging section  12031 . The outside-vehicle information detecting unit  12030  makes the imaging section  12031  image an image of the outside of the vehicle, and receives the imaged image. On the basis of the received image, the outside-vehicle information detecting unit  12030  may perform processing of detecting an object such as a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance thereto. 
     The imaging section  12031  is an optical sensor that receives light, and which outputs an electric signal corresponding to a received light amount of the light. The imaging section  12031  can output the electric signal as an image, or can output the electric signal as information about a measured distance. In addition, the light received by the imaging section  12031  may be visible light, or may be invisible light such as infrared rays or the like. 
     The in-vehicle information detecting unit  12040  detects information about the inside of the vehicle. The in-vehicle information detecting unit  12040  is, for example, connected with a driver state detecting section  12041  that detects the state of a driver. The driver state detecting section  12041 , for example, includes a camera that images the driver. On the basis of detection information input from the driver state detecting section  12041 , the in-vehicle information detecting unit  12040  may calculate a degree of fatigue of the driver or a degree of concentration of the driver, or may determine whether the driver is dozing. 
     The microcomputer  12051  can calculate a control target value for the driving force generating device, the steering mechanism, or the braking device on the basis of the information about the inside or outside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030  or the in-vehicle information detecting unit  12040 , and output a control command to the driving system control unit  12010 . For example, the microcomputer  12051  can perform cooperative control intended to implement functions of an advanced driver assistance system (ADAS) which functions include collision avoidance or shock mitigation for the vehicle, following driving based on a following distance, vehicle speed maintaining driving, a warning of collision of the vehicle, a warning of deviation of the vehicle from a lane, or the like. 
     In addition, the microcomputer  12051  can perform cooperative control intended for automatic driving, which makes the vehicle to travel autonomously without depending on the operation of the driver, or the like, by controlling the driving force generating device, the steering mechanism, the braking device, or the like on the basis of the information about the outside or inside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030  or the in-vehicle information detecting unit  12040 . 
     In addition, the microcomputer  12051  can output a control command to the body system control unit  12020  on the basis of the information about the outside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030 . For example, the microcomputer  12051  can perform cooperative control intended to prevent a glare by controlling the headlamp so as to change from a high beam to a low beam, for example, in accordance with the position of a preceding vehicle or an oncoming vehicle detected by the outside-vehicle information detecting unit  12030 . 
     The sound/image output section  12052  transmits an output signal of at least one of a sound and an image to an output device capable of visually or auditorily notifying information to an occupant of the vehicle or the outside of the vehicle. In the example of  FIG. 20 , an audio speaker  12061 , a display section  12062 , and an instrument panel  12063  are illustrated as the output device. The display section  12062  may, for example, include at least one of an on-board display and a head-up display. 
       FIG. 21  is a diagram depicting an example of the installation position of the imaging section  12031 . 
     In  FIG. 21 , the imaging section  12031  includes imaging sections  12101 ,  12102 ,  12103 ,  12104 , and  12105 . 
     The imaging sections  12101 ,  12102 ,  12103 ,  12104 , and  12105  are, for example, disposed at positions on a front nose, sideview mirrors, a rear bumper, and a back door of the vehicle  12100  as well as a position on an upper portion of a windshield within the interior of the vehicle. The imaging section  12101  provided to the front nose and the imaging section  12105  provided to the upper portion of the windshield within the interior of the vehicle obtain mainly an image of the front of the vehicle  12100 . The imaging sections  12102  and  12103  provided to the sideview mirrors obtain mainly an image of the sides of the vehicle  12100 . The imaging section  12104  provided to the rear bumper or the back door obtains mainly an image of the rear of the vehicle  12100 . The imaging section  12105  provided to the upper portion of the windshield within the interior of the vehicle is used mainly to detect a preceding vehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, or the like. 
     Incidentally,  FIG. 21  depicts an example of photographing ranges of the imaging sections  12101  to  12104 . An imaging range  12111  represents the imaging range of the imaging section  12101  provided to the front nose. Imaging ranges  12112  and  12113  respectively represent the imaging ranges of the imaging sections  12102  and  12103  provided to the sideview mirrors. An imaging range  12114  represents the imaging range of the imaging section  12104  provided to the rear bumper or the back door. A bird&#39;s-eye image of the vehicle  12100  as viewed from above is obtained by superimposing image data imaged by the imaging sections  12101  to  12104 , for example. 
     At least one of the imaging sections  12101  to  12104  may have a function of obtaining distance information. For example, at least one of the imaging sections  12101  to  12104  may be a stereo camera constituted of a plurality of imaging elements, or may be an imaging element having pixels for phase difference detection. 
     For example, the microcomputer  12051  can determine a distance to each three-dimensional object within the imaging ranges  12111  to  12114  and a temporal change in the distance (relative speed with respect to the vehicle  12100 ) on the basis of the distance information obtained from the imaging sections  12101  to  12104 , and thereby extract, as a preceding vehicle, a nearest three-dimensional object in particular that is present on a traveling path of the vehicle  12100  and which travels in substantially the same direction as the vehicle  12100  at a predetermined speed (for example, equal to or more than 0 km/hour). Further, the microcomputer  12051  can set a following distance to be maintained in front of a preceding vehicle in advance, and perform automatic brake control (including following stop control), automatic acceleration control (including following start control), or the like. It is thus possible to perform cooperative control intended for automatic driving that makes the vehicle travel autonomously without depending on the operation of the driver or the like. 
     For example, the microcomputer  12051  can classify three-dimensional object data on three-dimensional objects into three-dimensional object data of a two-wheeled vehicle, a standard-sized vehicle, a large-sized vehicle, a pedestrian, a utility pole, and other three-dimensional objects on the basis of the distance information obtained from the imaging sections  12101  to  12104 , extract the classified three-dimensional object data, and use the extracted three-dimensional object data for automatic avoidance of an obstacle. For example, the microcomputer  12051  identifies obstacles around the vehicle  12100  as obstacles that the driver of the vehicle  12100  can recognize visually and obstacles that are difficult for the driver of the vehicle  12100  to recognize visually. Then, the microcomputer  12051  determines a collision risk indicating a risk of collision with each obstacle. In a situation in which the collision risk is equal to or higher than a set value and there is thus a possibility of collision, the microcomputer  12051  outputs a warning to the driver via the audio speaker  12061  or the display section  12062 , and performs forced deceleration or avoidance steering via the driving system control unit  12010 . The microcomputer  12051  can thereby assist in driving to avoid collision. 
     At least one of the imaging sections  12101  to  12104  may be an infrared camera that detects infrared rays. The microcomputer  12051  can, for example, recognize a pedestrian by determining whether or not there is a pedestrian in imaged images of the imaging sections  12101  to  12104 . Such recognition of a pedestrian is, for example, performed by a procedure of extracting characteristic points in the imaged images of the imaging sections  12101  to  12104  as infrared cameras and a procedure of determining whether or not it is the pedestrian by performing pattern matching processing on a series of characteristic points representing the contour of the object. When the microcomputer  12051  determines that there is a pedestrian in the imaged images of the imaging sections  12101  to  12104 , and thus recognizes the pedestrian, the sound/image output section  12052  controls the display section  12062  so that a square contour line for emphasis is displayed so as to be superimposed on the recognized pedestrian. The sound/image output section  12052  may also control the display section  12062  so that an icon or the like representing the pedestrian is displayed at a desired position. 
     7. EXAMPLES 
     Next, examples of the present disclosure are described in detail. 
     Experimental Example 1 
     An ITO film having a thickness of 100 nm was formed on a quartz substrate  111  with use of a sputtering apparatus. The ITO film was patterned by photolithography and etching to form an ITO electrode (a lower electrode). Subsequently, the quartz substrate provided with the ITO electrode was cleaned by an UV/ozone treatment, and thereafter, the quartz substrate was moved into a vacuum evaporation apparatus, and an organic material was deposited on the quartz substrate under a reduced pressure of 1×10 −5  Pa or less with use of a resistive heating method while rotating a substrate holder. First, an electron blocking material represented by the following formula (3) was deposited with a thickness of 10 nm at a substrate temperature of 0° to form an electron blocking layer. Next, a benzothienobenzothiophene derivative represented by the following formula (1-1), and C 60  fullerene (the following formula (2)) were respectively deposited at a substrate temperature of 40° C. at deposition rates of 0.50 Å/sec and 0.25 Å/sec to form a mixture layer having a thickness of 230 nm, thereby forming a photoelectric conversion layer. Subsequently, a hole blocking material represented by the following formula (4) was deposited with a thickness of 10 nm at a substrate temperature of 0° C. to form a hole blocking layer. Finally, the quartz substrate was moved into a sputtering apparatus, and ITO was deposited with a thickness of 50 nm on the hole blocking layer to form an upper electrode. A photoelectric conversion element (an experimental example 1) having a 1 mm×1 mm photoelectric conversion region was fabricated by a fabrication method described above. The fabricated photoelectric conversion element was annealed at 150° C. for 120 minutes in a nitrogen (N 2 ) atmosphere. 
     
       
         
         
             
             
         
       
     
     Experimental Example 2 
     A photoelectric conversion element (an experimental example 2) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-2) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 3 
     A photoelectric conversion element (an experimental example 3) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-3) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 4 
     A photoelectric conversion element (an experimental example 4) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-4) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 5 
     A photoelectric conversion element (an experimental example 5) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-5) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 6 
     A photoelectric conversion element (an experimental example 6) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-6) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 7 
     A photoelectric conversion element (an experimental example 7) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-7) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 8 
     A photoelectric conversion element (an experimental example 8) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-8) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 9 
     A photoelectric conversion element (an experimental example 9) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-9) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 10 
     A photoelectric conversion element (an experimental example 10) was fabricated by a method similar to that in the experimental example 1, except that a benzothienobenzothiophene derivative represented by the following formula (1-10) was used in place of the benzothienobenzothiophene derivative represented by the formula (1-1) used in the experimental example 1. 
     
       
         
         
             
             
         
       
     
     Experimental Example 11 
     A photoelectric conversion element (an experimental example 11) was fabricated by a method similar to that in the experimental example 1, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-1) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 12 
     A photoelectric conversion element (an experimental example 12) was fabricated by a method similar to that in the experimental example 2, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-2) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 13 
     A photoelectric conversion element (an experimental example 13) was fabricated by a method similar to that in the experimental example 3, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-3) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 14 
     A photoelectric conversion element (an experimental example 14) was fabricated by a method similar to that in the experimental example 4, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-4) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 15 
     A photoelectric conversion element (an experimental example 15) was fabricated by a method similar to that in the experimental example 5, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-5) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 16 
     A photoelectric conversion element (an experimental example 16) was fabricated by a method similar to that in the experimental example 6, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-6) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 17 
     A photoelectric conversion element (an experimental example 17) was fabricated by a method similar to that in the experimental example 8, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-8) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 18 
     A photoelectric conversion element (an experimental example 18) was fabricated by a method similar to that in the experimental example 9, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-9) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 19 
     A photoelectric conversion element (an experimental example 19) was fabricated by a method similar to that in the experimental example 10, except that a photoelectric conversion layer was formed by using two kinds of benzothienobenzothiophene derivatives represented by the formula (1-10) and the formula (1-7) and C 60  fullerene (the formula (2) described above). 
     Experimental Example 20 
     A photoelectric conversion element (an experimental example 20) was fabricated by a method similar to that in the experimental example 1, except that a photoelectric conversion layer was formed by using DNTT represented by the following formula (5) and C 60  fullerene (the formula (2) described above). 
     
       
         
         
             
             
         
       
     
     Experimental Example 21 
     A photoelectric conversion element (an experimental example 20) was fabricated by a method similar to that in the experimental example 1, except that a photoelectric conversion layer was formed by using DPh-BTBT represented by the following formula (6) and C 60  fullerene (the formula (2) described above). 
     
       
         
         
             
             
         
       
     
     Evaluation of external quantum efficiency (EQE) and response time of each of the photoelectric conversion elements fabricated in the experimental examples 1 to 21 was performed by the following method. Table 1 is a summary of results of the evaluation with the benzothienobenzothiophene derivatives used in the respective experimental examples. 
     A wavelength of light to be applied from a blue LED light source to each of the photoelectric conversion elements via a band-pass filter was set to 450 nm and a light amount was set to 1.62 μW/cm 2 , and a bias voltage to be applied between electrodes of each of the photoelectric conversion elements was controlled with use of a semiconductor parameter analyzer to sweep a voltage to be applied to a lower electrode with respect to an upper electrode, thereby obtaining a current-voltage curve. A light current value and a dark current value in a short circuit state were measured to calculate EQE. Further, in a state in which a bias voltage to be applied between electrodes of each of the photoelectric conversion elements was controlled and a voltage of −2.6V was applied to the lower electrode with respect to the upper electrode, the photoelectric conversion elements were irradiated with a rectangular optical pulse having a wavelength of 450 nm and a light amount of 1.62 μW/cm 2 , and an attenuation waveform of a current was observed with use of an oscilloscope. A period of time until a current attenuated to 3% from a current at the time of optical pulse irradiation immediately after optical pulse irradiation was used as an index of response speed. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 EQE 
                 Response Time 
               
               
                   
                 Configuration of Photoelectric Conversion Layer 
                 (Normalization) 
                 (Normalization) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Experimental Example 1 
                 Formula (1-1), Formula (2) 
                 1.00 
                 1.00 
               
               
                 Experimental Example 2 
                 Formula (1-2), Formula (2) 
                 1.05 
                 0.85 
               
               
                 Experimental Example 3 
                 Formula (1-3), Formula (2) 
                 0.65 
                 2.50 
               
               
                 Experimental Example 4 
                 Formula (1-4), Formula (2) 
                 0.80 
                 1.15 
               
               
                 Experimental Example 5 
                 Formula (1-5), Formula (2) 
                 0.90 
                 0.50 
               
               
                 Experimental Example 6 
                 Formula (1-6), Formula (2) 
                 1.10 
                 0.60 
               
               
                 Experimental Example 7 
                 Formula (1-7), Formula (2) 
                 0.60 
                 0.90 
               
               
                 Experimental Example 8 
                 Formula (1-8), Formula (2) 
                 1.00 
                 0.70 
               
               
                 Experimental Example 9 
                 Formula (1-9), Formula (2) 
                 0.50 
                 5.00 
               
               
                 Experimental Example 10 
                 Formula (1-10), Formula (2) 
                 0.90 
                 1.00 
               
               
                 Experimental Example 11 
                 Formula (1-1), Formula (1-7), Formula (2) 
                 0.95 
                 0.95 
               
               
                 Experimental Example 12 
                 Formula (1-2), Formula (1-7), Formula (2) 
                 1.00 
                 0.80 
               
               
                 Experimental Example 13 
                 Formula (1-3), Formula (1-7), Formula (2) 
                 0.60 
                 2.50 
               
               
                 Experimental Example 14 
                 Formula (1-4), Formula (1-7), Formula (2) 
                 0.70 
                 1.10 
               
               
                 Experimental Example 15 
                 Formula (1-5), Formula (1-7), Formula (2) 
                 0.80 
                 0.40 
               
               
                 Experimental Example 16 
                 Formula (1-6), Formula (1-7), Formula (2) 
                 1.00 
                 0.50 
               
               
                 Experimental Example 17 
                 Formula (1-8), Formula (1-7), Formula (2) 
                 0.95 
                 0.60 
               
               
                 Experimental Example 18 
                 Formula (1-9), Formula (1-7), Formula (2) 
                 0.10 
                 &gt;10 
               
               
                 Experimental Example 19 
                 Formula (1-10), Formula (1-7), Formula (2) 
                 0.80 
                 1.00 
               
               
                 Experimental Example 20 
                 Formula (5), Formula (2) 
                 1.00 
                 &gt;1000 
               
               
                 Experimental Example 21 
                 Formula (6), Formula (2) 
                 0.60 
                 &gt;1000 
               
               
                   
               
            
           
         
       
     
     As can be seen from Table 1, in the experimental examples 1 to 19 in which the photoelectric conversion layer was formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above, obtained EQE was substantially equal to EQE in the experimental examples 20 and 21 in which the photoelectric conversion layer was formed by using typical materials. In addition, it was found out that in the experimental examples 1 to 19 in which the photoelectric conversion layer was formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above, the response time was remarkably improved, as compared with the experimental examples 20 and 21 in which the photoelectric conversion layer was formed by using the typical materials. Accordingly, it was found out that forming the photoelectric conversion layer by using the benzothienobenzothiophene-based compound represented by the general formula (1) makes it possible to improve optical responsivity while maintaining high EQE. 
     Although the description has been given by referring to the first to fourth embodiments, the examples, and the application examples, the contents of the present disclosure are not limited to the embodiments and the like described above, and may be modified in a variety of ways. In addition, the number of organic photoelectric converters, the number of inorganic photoelectric converters, a ratio between the organic photoelectric converters and the inorganic photoelectric converters are not limited, and color signals of a plurality of colors may be acquired only by the organic photoelectric converter. 
     Further, in the embodiments and the like described above, an example in which two electrodes, that is, the readout electrode  21 A and the accumulation electrode  21 B are provided as a plurality of electrodes included in the lower electrode  21  has been described; however, three, or four or more electrodes such as a transfer electrode or an discharge electrode may be provided. 
     It is to be noted that the effects described herein are merely illustrative and non-limiting, and other effects may be included. 
     It is to be noted that the present disclosure may have the following configurations. According to the present technology having the following configuration, the organic photoelectric conversion layer is formed by using the benzothienobenzothiophene-based compound represented by the general formula (1) described above, thereby improving carrier mobility to the first electrode and the second electrode that are opposed to each other with the organic photoelectric conversion layer interposed therebetween. This makes it possible to improve external quantum efficiency and optical responsivity. 
     [1] 
     A photoelectric conversion element including: 
     a first electrode; 
     a second electrode that is opposed to the first electrode; and 
     an organic photoelectric conversion layer that is provided between the first electrode and the second electrode, and includes, as a first organic semiconductor material, a benzothienobenzothiophene-based compound represented by the following general formula (1). 
     
       
         
         
             
             
         
       
         
         (R1 to R4 are each independently a phenyl group, a biphenyl group, a terphenyl group, a naphthalene group, a phenylnaphthalene group, a biphenylnaphthalene group, a binaphthalene group, a thiophene group, a bithiophene group, a terthiophene group, a benzothiophene group, a phenyl benzothiophene group, a biphenyl benzothiophene benzofuran group, a phenyl benzofuran group, a biphenyl benzothiophene group, an alkane group, a cycloalkane group, a fluorene group, a phenylfluorene group, or any of derivatives thereof.)
 
[2]
 
       
    
     The photoelectric conversion element according to [1], in which the organic photoelectric conversion layer further includes fullerene or a fullerene derivative as a second organic semiconductor material. 
     [3] 
     The photoelectric conversion element according to [1] or [2], in which the organic photoelectric conversion layer further includes a third organic semiconductor material. 
     [4] 
     The photoelectric conversion element according to [3], in which the third organic semiconductor material absorbs light of any of wavelengths from 400 nm to 700 nm both inclusive. 
     [5] 
     The photoelectric conversion element according to any one of [1 ] to [4], in which the organic photoelectric conversion layer absorbs light of all wavelengths within a range from 400 nm to 700 nm both inclusive. 
     [6] 
     The photoelectric conversion element according to any one of [1] to [5], in which the first electrode includes a plurality of electrodes. 
     [7] 
     The photoelectric conversion element according to any one of [1] to [6], in which a first electric charge blocking layer is further provided between the first electrode and the organic photoelectric conversion layer. 
     [8] 
     The photoelectric conversion element according to any one of [1] to [7], in which a second electric charge blocking layer is further provided between the organic photoelectric conversion layer and the second electrode. 
     [9] 
     An imaging device provided with a plurality of pixels each including one or a plurality of organic photoelectric converters, the organic photoelectric converters each including: 
     a first electrode; 
     a second electrode that is opposed to the first electrode; and 
     an organic photoelectric conversion layer that is provided between the first electrode and the second electrode, and includes, as a first organic semiconductor material, a benzothienobenzothiophene-based compound represented by the following general formula (1). 
     
       
         
         
             
             
         
       
         
         (R1 to R4 are each independently a phenyl group, a biphenyl group, a terphenyl group, a naphthalene group, a phenylnaphthalene group, a biphenylnaphthalene group, a binaphthalene group, a thiophene group, a bithiophene group, a terthiophene group, a benzothiophene group, a phenyl benzothiophene group, a biphenyl benzothiophene benzofuran group, a phenyl benzofuran group, a biphenyl benzothiophene group, an alkane group, a cycloalkane group, a fluorene group, a phenylfluorene group, or any of derivatives thereof.)
 
[10]
 
       
    
     The imaging device according to [9], in which one or a plurality of the organic photoelectric converters and one or a plurality of inorganic photoelectric converters that performs photoelectric conversion in a wavelength band different from the organic photoelectric converters are stacked in each of the pixels. 
     [11] 
     The imaging device according to [10], in which 
     the inorganic photoelectric converter is formed to be embedded in a semiconductor substrate, and 
     the organic photoelectric converter is formed on a first surface side of the semiconductor substrate. 
     [12] 
     The imaging device according to [11], in which the semiconductor substrate has a second surface that is opposed to the first surface, and a multilayer wiring layer is formed on the second surface side. 
     [13] 
     The imaging device according to [11] or [12], in which 
     the organic photoelectric converter performs photoelectric conversion of blue light, and 
     an inorganic photoelectric converter that performs photoelectric conversion of green light and an inorganic photoelectric converter that performs photoelectric conversion of red light are stacked in the semiconductor substrate. 
     [14] 
     The imaging device according to any one of [9] to [13], in which a plurality of the organic photoelectric converters that performs photoelectric conversion in wavelength bands different from each other is stacked in each of the pixels. 
     This application claims the benefit of Japanese Priority Patent Application JP2019-062367 filed with the Japan Patent Office on Mar. 28, 2019, the entire contents of which are incorporated herein by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.