Abstract:
For simplification of a structure and a manufacturing process of an element, and reduction of manufacturing cost, the present disclosure provides a light-receiving device including: a photoelectric conversion element; and an active element, wherein the active element includes at least one of a reset element configured to reset the photoelectric conversion element, an amplifier element configured to amplify a detection signal based on the photoelectric conversion element, or a selection element configured to selectively output the detection signal based on the photoelectric conversion element, and the photoelectric conversion element and at least part of the active element are formed by using an identical organic semiconductor material or an identical high molecular functional material.

Description:
TECHNICAL FIELD 
     The present disclosure relates to light-receiving devices having photoelectric conversion elements, such as image sensors, etc., particularly to light-receiving devices using an organic semiconductor material. 
     BACKGROUND ART 
     Technologies using an organic material as a material of a photoconductive film for forming photoelectric conversion elements have been known. The organic material has a wide variety of types and characteristics, and can flexibly be processed into various shapes (see, e.g., Patent Document 1, and Non-Patent Document 1). 
     A light-receiving device using the photoelectric conversion elements described above, such as an image sensor, etc., is provided with transistors for selectively extracting an electrical signal obtained by photoelectric conversion, such as switching elements, etc. There are known technologies for forming the photoelectric conversion elements using the organic material on a monocrystalline silicon substrate on which the transistors are formed by a so-called CMOS process, or on a glass substrate on which thin transparent organic film transistors are formed (see, e.g., Patent Documents 2 and 3). 
     CITATION LIST 
     Patent Documents 
     
         
         [Patent Document 1] Japanese Unexamined Patent Publication No. 2003-158254 
         [Patent Document 2] Japanese Unexamined Patent Publication No. 2007-123707 
         [Patent Document 3] Japanese Unexamined Patent Publication No. 2009-212389 
       
    
     Non-Patent Document 
     
         
         [Non-Patent Document 1] Jun Sakai, et. al., “Stacked Organic Thin-Film Solar Cell Manufactured with Coating Process,” Panasonic Electronic Works Technical Report, September 2009, Volume 57, No. 1, pp. 46-50 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     When the transistors formed on the monocrystalline silicon substrate or the thin transparent organic film transistors formed on the glass substrate and the photoelectric conversion elements using the organic material are layered as described above, a structure and a manufacturing process of the elements tend to be complicated, and a manufacturing cost increases due to use of many different types of materials. 
     In view of the foregoing, the present disclosure has been achieved to simplify the structure and the manufacturing process of the elements, thereby facilitating reduction of the manufacturing cost. 
     Solution to the Problem 
     A first aspect of the present disclosure is related to a light-receiving device, including: a photoelectric conversion element; and an active element, wherein the active element includes at least one of a reset element configured to reset the photoelectric conversion element, an amplifier element configured to amplify a detection signal based on the photoelectric conversion element, or a selection element configured to selectively output the detection signal based on the photoelectric conversion element, and the photoelectric conversion element and at least part of the active element are formed by using an identical organic semiconductor material or an identical high molecular functional material. 
     According to the first aspect, a layered structure is avoided, a manufacturing process can easily be simplified, the number of manufacturing steps can easily be reduced, and commonality of materials can easily be promoted. Therefore, the manufacturing cost can easily be reduced. 
     A second aspect of the present disclosure is related to the light-receiving device of the first aspect of the present disclosure, wherein the photoelectric conversion element and the active element are formed by using at least one of an identical electrode material or an identical insulating material. 
     According to the second aspect, the simplification of the manufacturing process, etc. can easily be achieved, and the manufacturing cost can be reduced more easily. 
     A third aspect of the present disclosure is related to the light-receiving device of any one of the first or second aspect of the present disclosure, wherein the photoelectric conversion element is a phototransistor constituted of a pnp-type or npn-type layered organic semiconductor bipolar transistor. 
     A fourth aspect of the present disclosure is related to the light-receiving device of any one of the first to third aspects of the present disclosure, wherein a base layer of the phototransistor has a thickness of 10 nm or larger and 40 nm or smaller. 
     According to the third and fourth aspects, sensitivity to incident light can relatively easily be enhanced. 
     A fifth aspect of the present disclosure is related to the light-receiving device of any one of the first to fourth aspects of the present disclosure, wherein the photoelectric conversion element and the active element are formed on a glass substrate. 
     According to the fifth aspect, the elements can easily be formed. 
     A sixth aspect of the present disclosure is related to the light-receiving device of any one of the first to fourth aspects of the present disclosure, wherein the photoelectric conversion element and the active element are formed on a film substrate. 
     According to the sixth aspect, a lightweight, flexible, and unbreakable image sensor can easily be obtained. 
     Advantages of the Invention 
     According to the present disclosure, the structure and the manufacturing process of the elements can easily be simplified, and the manufacturing cost can easily be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing a structure of a major part of an image sensor of a first embodiment. 
         FIG. 2  is a plan view showing a wiring pattern in the major part of the image sensor of the first embodiment. 
         FIG. 3  is a cross-sectional view taken along the line III-III in  FIG. 2 . 
         FIG. 4  is a timing chart of an image capturing operation. 
         FIG. 5  is a plan view showing an example shape of a metal interconnection of an image sensor of a third embodiment. 
         FIG. 6  is a circuit diagram showing a structure of a major part of an image sensor of a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As an example embodiment of the present disclosure, an example image sensor including phototransistors as photoelectric conversion elements formed by using an organic semiconductor material or a high molecular functional material and arranged in a matrix array will be described in detail with reference to the drawings. In the following embodiments, components having the similar function are referenced by the same reference numerals to omit explanation thereof. 
     First Embodiment 
     Circuit Structure 
     Each of pixels of an image sensor includes, as shown in  FIG. 1 , for example, a pnp-type phototransistor  110 , as well as a reset transistor  120  (a reset element), an amplifier transistor  130  (an amplifier element), and a row selection transistor  140  (a row selection element) which are p-type thin film transistors (TFTs) as active elements. 
     The reset transistor  120  and the phototransistor  110  are connected in series between a power supply line  151  and a ground line  152  so that a power supply voltage is applied to an emitter of the phototransistor  110  when a reset line  153  is at a low (L) level. The amplifier transistor  130  is configured to amplify a potential of the emitter of the phototransistor  110 . The row selection transistor  140  is configured to output a signal amplified by the amplifier transistor  130  to a column output line  155  when a selection line  154  is at a L level. 
     (Substantive Structure) 
     Each of the elements described above is formed on a glass substrate  101  as shown in  FIGS. 2 and 3 , for example. Specifically, the power supply lines  151 , the ground lines  152 , and the reset lines  153  parallel to each other, and the column output lines  155  extending in a direction perpendicular to these lines are formed on the glass substrate  101 . Every region surrounded by the adjacent power supply lines  151  and the adjacent column output lines  155  constitutes a single pixel, and the phototransistor  110  is configured to detect light L incident from an open region  161  and reflected on a source document D. 
     The phototransistor  110  includes a transparent conductive film  201 , a p-type organic semiconductor film  112 , an n-type organic semiconductor film  113 , a p-type organic semiconductor film  114 , and a metal interconnection  203  which are sequentially stacked on the glass substrate  101  to cover a metal interconnection  111  connected to the ground line  152 . The metal interconnection  111  serves as a current extracting electrode of a collector of the phototransistor  110 , and is comb-shaped, for example, so that light through the glass substrate  101  can enter the phototransistor  110 . The transparent conductive film  201  and the metal interconnection  203  serve as a collector electrode and an emitter electrode of the phototransistor  110 , respectively. The metal interconnection  203  also serves as a light blocking film preventing exposure of the organic semiconductor films  112 - 114  to light incident from above in  FIG. 3 . An insulating film  202  is formed on the ground line  152  present at an edge of the phototransistor  110  to insulate the organic semiconductor films  112 - 114  and the metal interconnection  203  from the ground line  152 . 
     The reset transistor  120  is formed by sequentially stacking the insulating film  202  and a p-type organic semiconductor film  122  on part of the reset line  153  which is formed on the glass substrate  101  and also serves as a gate electrode. An end of the p-type organic semiconductor film  122  is connected to the power supply line  151  through a source electrode  123 , and the other end is connected to a drain electrode  124  formed to be continuous with the metal interconnection  203  of the phototransistor  110 . 
     The amplifier transistor  130  is formed by sequentially stacking the insulating film  202  and a p-type organic semiconductor film  132  on part of a gate electrode  131  formed on the glass substrate  101 , and the row selection transistor  140  is formed by sequentially stacking the insulating film  202  and a p-type organic semiconductor film  142  on part of the selection line  154  which is formed on the glass substrate  101  and also serves as a gate electrode. The gate electrode  131  of the amplifier transistor  130  is connected to the metal interconnection  203  of the phototransistor  110  and the drain electrode  124  of the reset transistor  120 . An end of the p-type organic semiconductor film  132  is connected to the power supply line  151  through a source electrode  133 , and the other end is connected to a drain electrode  134 . The drain electrode  134  is connected to a source electrode  143  connected to an end of the p-type organic semiconductor film  142  of the row selection transistor  140 . The other end of the p-type organic semiconductor film  142  of the row selection transistor  140  is connected to the column output line  155  also serving as a drain electrode. 
     The p-type organic semiconductor films  112 ,  122 ,  132 ,  142 , etc. constituting the phototransistor  110 , the reset transistor  120 , the amplifier transistor  130 , and the row selection transistor  140  are formed in the same step using the same organic semiconductor material as described in detail below. 
     (Manufacturing Step) 
     The image sensor described above, in the shape of a film, can easily be formed in a manufacturing process which is based on a so-called coating step, and does not require high vacuum environment by using an organic semiconductor material, a high molecular functional material, etc. at a lower temperature and lower cost as compared with a manufacturing process using an inorganic material, such as silicon, etc. More specifically, the image sensor can be manufactured as described below, for example. 
     (1) A metal electrode pattern is formed on the glass substrate  101  to provide the power supply line  151 , the ground line  152 , the metal interconnection  111  of the phototransistor  110 , the reset line  153  also serving as the gate electrode of the reset transistor  120 , the gate electrode  131  of the amplifier transistor  130 , and the selection line  154  also serving as the gate electrode of the row selection transistor  140 . 
     More specifically, for example, the metal electrode pattern can be formed by gravure printing, offset printing, reverse offset printing, etc. using a conductive polymer solution or dispersion, or a dispersion of fine metal particles. Examples of materials for forming the metal electrode may include silver, gold, copper, etc. having a particle diameter in a nanometer order and being dispersed in a solution, for example. The metal electrode may be about 100-500 nm in thickness. The obtained pattern is preferably baked for several minutes to several ten minutes at about 100-150° C., for example, to evaporate a solvent, and to reduce resistance of a metal interconnection. 
     (2) A pattern of the insulating film  202  is formed on the metal interconnection. The insulating film  202  will be an insulating film insulating the organic semiconductor films  112 - 114  and the metal interconnection  203  of the phototransistor  110 , or gate insulating films of the reset transistor  120 , the amplifier transistor  130 , and the row selection transistor  140 . 
     The pattern of the insulating film  202  can also be formed by a printing method in the same manner as the formation of the metal electrode pattern. Examples of materials for forming the insulating film may include polyimide, polystyrene, poly(4-vinylphenol) (PVP), poly(vinyl alcohol) (PVA), poly(methyl methacrylate) (PMMA), divinyl-tetramethyl-disiloxane-bis(benzocy-clobutene) (BCB), etc., and the insulating film may be about 100-1000 nm in thickness. The obtained pattern is preferably baked for several minutes to several ten minutes at about 100-150° C., for example, to evaporate a solvent to form the insulating film. 
     (3) A pattern of the transparent conductive film  201  of a coating type, for example, is printed on a region for forming the phototransistor  110 . 
     Examples of materials for forming the transparent conductive film  201  may include an indium tin oxide (ITO) coating, metal nanowire, carbon nanotube, etc. The transparent conductive film  201  may be about 100-300 nm in thickness. The obtained pattern is preferably baked at about 100-150° C. for several minutes to several ten minutes, for example, to evaporate a solute, and to reduce resistance of the transparent conductive film. 
     (4) A pattern of the p-type organic semiconductor film  112  serving as a collector layer of the phototransistor, and the p-type organic semiconductor films  122 ,  132 ,  142  serving as active layers of the reset transistor  120 , the amplifier transistor  130 , and the row selection transistor  140  is formed by printing. 
     Examples of materials for forming the p-type organic semiconductor layer may include low molecular p-type organic semiconductors including soluble semiconductors such as TIPS pentacene (6,13-Bis(triisopropylsilylethynyl)pentacene), TIPS anthracene (9,10-Bis[(triisopropylsilyl)ethynyl]anthracene), TES pentacene (6,13-Bis((triethylsilyl)ethynyl)pentacene), etc., precursors of soluble organic semiconductors such as NSFAAP (13,6-N-Sulfinylacetamidopentacene), pentacene-N-sulfinyl-tert-butylcarbamate, etc. 
     Examples of materials for forming the p-type organic semiconductor layer may also include high molecular p-type semiconductors such as poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3-octylthiophene-2,5-diyl) (P3OT), poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV), poly(3-dodecylthiophene-2,5-diyl) (P3DDT), poly((9,9-diocthlfluorennyl-2,7-diyl)-co-bithiophene) (F8T2), poly((9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo(2,1,3)thiadiazol-4,8-diyl)) (F8BT), poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), etc. The low molecular and high molecular p-type organic semiconductors may be blended. 
     The obtained pattern is preferably baked for several minutes to several ten minutes at about 100-150° C., for example, to evaporate the solvent to form the p-type organic semiconductor layer. 
     (5) A pattern of the n-type organic semiconductor film  113  serving as a base layer of the phototransistor  110  is formed by printing. When n-type transistors are used as the reset transistor  120 , etc., an n-type organic semiconductor film serving as an active layer of the transistor may simultaneously be formed. 
     Examples of materials for forming the n-type organic semiconductor layer may include low molecular n-type organic semiconductors such as (6,6)-phenyl C61 butyric acid methyl ester ([60]PCBM), (6,6)-phenyl C71 butyric acid methyl ester ([70]PCBM), (6,6)-phenyl C61 butyric acid octyl ester (PCBO), (6,6)-phenyl-C61 butyric acid butyl ester (PCBB), (6,6)-thienyl C61 butyric acid methyl ester ([60]ThPCBM), (6,6)diphenyl C62 bis(butyric acid methyl ester), fullerene-C60, fullerene-C70, etc. 
     Examples of the materials for forming the n-type organic semiconductor layer may also include high molecular p-type organic semiconductors such as poly(benzimidazobenzophenanthroline) (BBL), etc. The low molecular and high molecular n-type organic semiconductors may be blended. 
     The obtained pattern is preferably baked for several minutes to several ten minutes at about 100-150° C., for example, to evaporate a solvent to form the p-type organic semiconductor layer. 
     Taking into account that a region contributable to a photoelectromotive force is at a distance of about ±20 nm from a pn junction, the base layer preferably has a thickness of about 10 nm or larger and 40 nm or smaller, for example. 
     (6) The p-type organic semiconductor film  114  serving as an emitter layer of the phototransistor  110  is formed in the same manner using the same material as the step (4). All or some of the p-type organic semiconductor film  122 , etc. of the reset transistor  120 , etc. may be formed in this step in place of the step (4). 
     (7) The column output line  155  also serving as the metal interconnection  203  of the phototransistor  110 , the source electrode  123  and the drain electrode  124  of the reset transistor  120 , the source electrode  133  and the drain electrode  134  of the amplifier transistor  130 , the source electrode  143  of the row selection transistor  140 , and the drain electrode of the row selection transistor  140  is formed in the same manner using the same material as the step (1). 
     (8) An insulating layer such as a protective film may be formed on the phototransistor  110  (i.e., the metal interconnection  203 ), the reset transistor  120 , etc. Prior to the formation of the layers such as the metal interconnection  111 , the insulating film  202 , the organic semiconductor films  112 - 114 , etc., ultraviolet irradiation, plasma treatment, surface cleaning such as wet cleaning, etc. may be performed as required. 
     (Operation of Image Sensor) 
     In the image sensor configured as described above, when the reset transistor  120  is turned on to reset the phototransistor  110 , and then the reset transistor  120  is turned off, a potential of the emitter of the phototransistor  110  decreases depending on the intensity of incident light. The decrease, as a signal component, is amplified by the amplifier transistor  130 , and is output through the column output line  155  when the row selection transistor  140  is turned on. Thus, photoelectric conversion is performed in each pixel, thereby performing image capturing. 
     The phototransistor  110 , the reset transistor  120 , etc. are formed in the same step using the same organic semiconductor material, the same metal interconnection, and the same insulating film, etc. as described above. Thus, a layered structure can be avoided, the manufacturing process can be simplified, the number of steps can be reduced, and commonality of materials can be promoted. Therefore, the manufacturing cost can easily be reduced. 
     Second Embodiment 
     The above-described elements may be formed on a film substrate in place of the glass substrate  101  described above. Preferable examples of materials for forming the film substrate may include highly transparent materials, such as polyethylene terephthalate, polyether sulfone, polypropylene, polycarbonate, polyester, etc. Forming the elements on the film substrate can provide a flexible and unbreakable image sensor which is lighter than the image sensor using the glass substrate  101 . 
     Third Embodiment 
     The metal interconnection  111  of the first embodiment is in the shape of a comb. However, the shape of the metal interconnection is not limited thereto, and the metal interconnection may be in the shape of a grid as shown in  FIG. 5 . As another example, the metal interconnection  111  may be formed as a continuous film, and the metal interconnection  203  provided in an upper part of the phototransistor  110  in  FIG. 3  may be comb-shaped or grid-shaped so that light incident from above can be received. As yet another example, both of the metal interconnection  111  and the metal interconnection  203  may be comb-shaped or grid-shaped so that light incident from above and below can be received. When a two-layer structure of the comb-shaped or grid-shaped metal interconnection  111  and the transparent conductive film  201  is provided, a current generated by an exciter generated through light absorption can efficiently be collected. 
     Fourth Embodiment 
     In addition to the phototransistor  110 , the reset transistor  120 , etc. described above, a vertical shift register  301  constituted of a CMOS circuit, etc. and configured to drive a circuit of each pixel, a noise canceller circuit  302 , a horizontal shift register  303 , a row selection transistor  304 , an output line  305 , etc. may be formed on the same substrate as shown in  FIG. 6 . In  FIG. 6 , for simplicity&#39;s sake, the power supply line  151 , the ground line  152 , and the reset line  153  are not shown, and the reset transistor  120 , the amplifier transistor  130 , and the row selection transistor  140  are depicted as an amplifier/operation control circuit  170 . 
     In the case where the circuits described above are formed, the p-type and/or n-type transistors constituting the circuits may also be formed in the same step using the same organic semiconductor material for forming the organic semiconductor films  112 - 114 , etc. of the phototransistor  110 . This can further facilitate the reduction in manufacturing cost. 
     Other Embodiments 
     In the above-described embodiments, the pnp-type phototransistor  110  has been described as an example of the phototransistor  110 . However, the phototransistor is not limited thereto, and an npn-type phototransistor may be used. The p-type reset transistor  120 , etc. used in the above-described embodiments may be replaced with an n-type transistor, or a combination of p-type and n-type transistors. 
     When the phototransistor is used as the photoelectric conversion element as described above, current amplification can be achieved by a bipolar transistor structure using generated carriers as a base current. Thus, sensitivity to the incident light can relatively easily be enhanced. However, in the case of a heterojunction photoelectric conversion element including p-type and n-type organic semiconductors joined together, or a bulk heterojunction photoelectric conversion element including a photoelectric conversion layer in which the n-type and p-type organic semiconductors are mixed in a nanometer order so that probability of generated exciters reaching a pn interface can be improved, the manufacturing cost can be reduced by forming the row selection transistor  140 , etc. using the same organic semiconductor material. 
     It will be appreciated that not all the reset transistor  120 , the amplifier transistor  130 , and the row selection transistor  140  are necessarily provided, and they may be provided as needed. The manufacturing cost can be reduced by forming at least some of the p-type organic semiconductor films  122 ,  132 ,  142 , etc. of these transistors in the same step using the same material as the p-type organic semiconductor film  112 , etc. of the phototransistor  110 . 
     An example of the image sensor including the photoelectric conversion elements arranged in a matrix array has been described in the above-described embodiments. However, the image sensor is not limited thereto, and a line sensor including the photoelectric conversion elements arranged in a straight line may be provided. 
     The above-described embodiments have described an example in which the light L incident through the open region  161  and reflected on the source document D brought into close contact with the glass substrate  101  enters the phototransistor  110 . However, the present disclosure is not limited thereto. An example in which light from an object at a distance enters the phototransistor  110  in the absence of the open region  161  may also be provided. 
     INDUSTRIAL APPLICABILITY 
     As described above, the present disclosure is useful for an image sensor using an organic semiconductor material, etc. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           101  Glass substrate 
           110  Phototransistor 
           111  Metal interconnection 
           112 ,  114 ,  122 ,  132 ,  142  P-type organic semiconductor film 
           113  N-type organic semiconductor film 
           120  Reset transistor 
           123  Source electrode 
           124  Drain electrode 
           130  Amplifier transistor 
           131  Gate electrode 
           133  Source electrode 
           134  Drain electrode 
           140  Row selection transistor 
           143  Source electrode 
           151  Power supply line 
           152  Ground line 
           153  Reset line 
           154  Selection line 
           155  Column output line 
           161  Open region 
           170  Amplifier/operation control circuit 
           201  Transparent conductive film 
           202  Insulating film 
           203  Metal interconnection 
           301  Vertical shift register 
           302  Noise canceller circuit 
           303  Horizontal shift register 
           304  Row selection transistor 
           305  Output line