Patent Publication Number: US-2020279884-A1

Title: Solid-state imaging element and imaging device

Description:
TECHNICAL FIELD 
     The present technology relates to a solid-state imaging element and an imaging device. Specifically, the present technology relates to a solid-state imaging element and an imaging device using a single-photon avalanche photodiode. 
     BACKGROUND ART 
     Thus far, an imaging device in which a single-photon avalanche diode (SPAD) is used as a photoelectric conversion element of a pixel has been used as an imaging device used for imaging or the measurement of the distance to a subject in a low-illuminance environment. The SPAD is a photodiode that performs photoelectric conversion in a state where a voltage exceeding the breakdown voltage is applied. Since a voltage exceeding the breakdown voltage has been applied, an electron avalanche derived from a carrier generated by photoelectric conversion occurs, and the SPAD enters a breakdown state. As a result, multiplication of carriers based on the photoelectric conversion is made, and an improvement in sensitivity in the imaging device is expected. However, since a relatively high voltage is applied to the SPAD, the SPAD requires a relatively large isolation region for being isolated from the surrounding circuits etc. Further, an electrode of the SPAD and wiring connected to the electrode are placed on a surface of the pixel. The region where the SPAD is formed corresponds to a light receiving surface in the surface of the pixel; therefore, by the isolation region etc. described above being placed, the ratio of the light receiving surface in the pixel surface, that is, the aperture ratio is reduced. Hence, photon detection efficiency is a relatively low value. Here, the detection efficiency is the ratio of the number of detected photons to the number of incident photons, and is a value showing characteristics of photon detection. 
     Thus, an imaging device in which light incident on an isolation region is guided to a SPAD and thereby detection efficiency is improved is used. For example, an imaging device in which a microlens is placed for each pixel and light is collected to a region of a SPAD that is formed in a central portion of the pixel is proposed (for example, see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2008-103614A 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     In the conventional technology described above, electrodes are placed in an end portion of a SPAD and incident light is collected to a central portion of the SPAD, and thereby detection efficiency is improved. However, since electrodes are placed in an end portion of the SPAD, the electric field between the electrodes is unequal, and electric fields concentrate in a partial region. Consequently, there arises a problem that a breakdown state not derived from incident light occurs and the noise of a signal output from the pixel is increased. 
     The present technology has been made in view of such circumstances, and an object of the present technology is to cause incident light to be collected to a region where a SPAD is formed while placing an electrode etc. in a central portion of the SPAD. 
     Solution to Problem 
     The present technology has been made to solve the above problem. According to a first aspect of the present technology, a solid-state imaging element includes: a photodiode that includes a light receiving surface and an electrode placed on the light receiving surface, and that outputs an electrical signal in accordance with light incident on the light receiving surface in a state where a voltage exceeding a breakdown voltage is applied to the electrode; and a light collecting section that causes light from a subject to be collected in the light receiving surface other than a region where the electrode is placed. Thereby, there is provided a solid-state imaging element including a SPAD that is a photodiode that includes a light receiving surface and an electrode placed on the light receiving surface and that outputs an electrical signal in accordance with light that is incident on the light receiving surface in a state where a voltage exceeding the breakdown voltage is applied to the electrode. This provides an action in which light derived from a subject is collected to the light receiving surface. 
     In addition, according to the first aspect, in the photodiode, the electrode may be placed substantially at a center of the light receiving surface. This provides an action in which the electric field in the light receiving surface of the SPAD is equalized. 
     In addition, according to the first aspect, the light collecting section may include a microlens having a concavity in a substantially central portion. This provides an action in which light is collected to the light receiving surface of the SPAD by a microlens having a concavity in a substantially central portion. 
     In addition, according to the first aspect, the microlens may have an opening in the concavity. This provides an action in which light is collected to the light receiving surface of the SPAD by a microlens having a concavity and an opening in a substantially central portion. 
     In addition, according to the first aspect, the solid-state imaging element may further include wiring that is electrically connected the electrode, and the microlens may have a concavity continuing along the wiring. This provides an action in which light is collected to the light receiving surface of the SPAD by a microlens having a concavity continuing along wiring. 
     In addition, according to the first aspect, the microlens may have a cut in a bottom portion of the continuing concavity. This provides an action in which Light is collected to the light receiving surface of the SPAD by a microlens having a concavity and a cut continuing along wiring. 
     In addition, according to the first aspect, the light collecting section may include a plurality of microlenses each of which is configured to cause light to be collected in the light receiving surface other than a region where the electrode is placed. This provides an action in which light is collected to the light receiving surface of the SPAD by a plurality of microlenses. 
     In addition, according to the first aspect, the solid-state imaging element may further include wiring that is placed between the plurality of microlenses adjacent to each other, and that is electrically connected to the electrode. This provides an action in which wiring is placed between microlenses. 
     In addition, according to the first aspect, each of the plurality of microlenses may have a quadrangular bottom surface. This provides an action in which light is collected to the light receiving surface of the SPAD by a plurality of microlenses each having a quadrangular bottom portion. 
     In addition, according to the first aspect, the light collecting section may include a first light collecting member and a second light collecting member that are sequentially arranged between the electrode and the subject, the second light collecting member having a larger refractive index than the first light collecting member. This provides an action in which light is collected to the light receiving surface of the SPAD by a first light collecting member and a second light collecting member with different refractive indices. 
     In addition, according to a second aspect of the present technology, an imaging device includes: a pixel circuit in which pixels each of which includes a photodiode and a light collecting section are arranged in a two-dimensional array form, the photodiode including a light receiving surface and an electrode placed on the light receiving surface, and outputting an electrical signal in accordance with light incident on the light receiving surface in a state where a voltage exceeding a breakdown voltage is applied to the electrode, the light collecting section causing light from a subject to be collected in the light receiving surface other than a region where the electrode is placed; and a processing circuit that processes the output electrical signal. This provides an action in which light derived from a subject is collected to a light receiving surface of a SPAD. 
     Advantageous Effects of Invention 
     According to the present technology, an excellent effect in which, while an electrode etc. are placed in a central portion of a SPAD, incident light is caused to be collected to a light receiving surface of the SPAD, and detection efficiency is improved can be exhibited. Note that the effect described herein is not necessarily a limitative one, and there may be any of the effects described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing an example of a configuration of an imaging system  1  in a first embodiment of the present technology. 
         FIG. 2  is a diagram showing an example of a configuration of a pixel  110  in the first embodiment of the present technology. 
         FIG. 3  is a cross-sectional view showing an example of a configuration of the pixel  110  in the first embodiment of the present technology. 
         FIG. 4  is a diagram showing an example of a configuration of a microlens  121  in the first embodiment of the present technology. 
         FIG. 5  is a diagram showing characteristics of a SPAD  112  in an embodiment of the present technology. 
         FIG. 6  is a diagram showing an example of a configuration of a microlens  123  in a second embodiment of the present technology. 
         FIG. 7  is a diagram showing an example of a configuration of the pixel  110  in a third embodiment of the present technology. 
         FIG. 8  is a cross-sectional view showing an example of a configuration of the pixel  110  in a fourth embodiment of the present technology. 
         FIG. 9  is a diagram showing an example of light collection in the fourth embodiment of the present technology. 
         FIG. 10  is a cross-sectional view showing an example of a configuration of the pixel  110  in a modification example of the fourth embodiment of the present technology. 
         FIG. 11  is a diagram showing an example of a configuration of an imaging device  10  in a fifth embodiment of the present technology. 
         FIG. 12  is a diagram showing an example of a configuration of a pixel  150  in the fifth embodiment of the present technology. 
         FIG. 13  is a diagram showing examples of arrangement of pixels in the fifth embodiment of the present technology. 
         FIG. 14  is a diagram showing examples of arrangement of pixels in a modification example of the fifth embodiment of the present technology. 
         FIG. 15  is a diagram showing an example of a configuration of the pixel  150  in a sixth embodiment of the present technology. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinbelow, embodiments for implementing the present technology (hereinafter, referred to as embodiments) are described. The description is given in the following order. 
     1. First embodiment (example of case of being used for distance measuring sensor)
 
2. Second embodiment (example of case where microlens having cut is used)
 
3. Third embodiment (example of case where plurality of microlenses are used)
 
4. Fourth embodiment (example of case where light is collected by light collecting members with different refractive indices)
 
5. Fifth embodiment (example of case of being used for imaging in low-illuminance environment)
 
6. Sixth embodiment (example of case where pupil correction is performed)
 
     1. First Embodiment 
     [Configuration of Imaging Device] 
       FIG. 1  is a diagram showing an example of the configuration of an imaging system  1  in a first embodiment of the present technology. The drawing shows an example of the configuration of the imaging system  1  that performs the measurement of the distance to a subject. The imaging system  1  includes an imaging device  10 , a distance measuring section  20 , and an infrared light emitting section  30 . 
     The imaging device  10  performs the detection of incident light. The imaging device  10  outputs an electrical signal in accordance with the incident light. 
     The infrared light emitting section  30  emits infrared light to a subject. The infrared light emitting section  30  emits infrared light under the control of the distance measuring section  20 . 
     The distance measuring section  20  measures the distance to the subject on the basis of an electrical signal output from the imaging device  10 . The distance measuring section  20  performs distance measurement of a time-of-flight (TOF) system. The measurement of the distance can be performed by the following procedure. First, the distance measuring section  20  controls the infrared light emitting section  30  to cause the infrared light emitting section  30  to start emitting infrared light. If the emitted infrared light is reflected by the subject and is incident on the imaging device  10 , the imaging device  10  detects the incident light, converts the incident light to an electrical signal, and outputs the electrical signal to the distance measuring section  20 . The distance measuring section  20  measures the time from the start of the radiation of infrared light by the infrared light emitting section  30  to the output of the electrical signal in the imaging device  10 , and performs the calculation of the distance to the subject on the basis of the measured time. 
     The imaging device  10  includes a pixel array section  100 , a power source section  200 , and a signal processing section  300 . 
     The pixel array section  100  includes pixels  110  arranged in a two-dimensional array form. The pixel  110  generates an electrical signal in accordance with incident light. The generation of an electrical signal in the pixel  110  is performed by a SPAD. The generated electrical signal is individually input to the signal processing section  300  by a signal line  301 . Further, electric power is supplied to these pixels  110  from the power source section  200  via a power supply line  201  and a grounding conductor  202 . Note that the pixel  110  is an example of a solid-state imaging element described in the claims. The pixel array section  100  is an example of a pixel circuit described in the claims. 
     The power source section  200  supplies electric power to the pixel  110  of the pixel array section  100 . 
     The signal processing section  300  processes electrical signals output from the plurality of pixels  110  arranged in the pixel array section  100 . As the processing, for example, the processing of shaping the waveform of an electrical signal and outputting the shaped waveform may be performed. Note that the signal processing section  300  is an example of a processing circuit described in the claims. 
     [Circuit Configuration of Pixel] 
       FIG. 2  is a diagram showing an example of the configuration of the pixel  110  in the first embodiment of the present technology. The drawing shows a circuit configuration of the pixel  110 . The pixel  110  includes a SPAD  112  and a resistance  111 . The cathode of the SPAD  112  is connected to the power supply line  201 , and the anode is connected to the signal line  301  and one end of the resistance  111 . The other end of the resistance  111  is connected to the grounding conductor  202 . 
     The SPAD  112  is an element that performs photoelectric conversion of converting light to an electrical signal. Further, the SPAD  112  further performs the multiplication of carriers generated by photoelectric conversion. Details of the configuration of the SAPD  112  are described later. 
     The resistance  111  is a resistance for performing quenching described later. A power supply voltage is applied to both ends of the SPAD  112  and the resistance  111  connected in series via the power supply line  201  and the grounding conductor  202 . The output of the pixel  110  can be extracted from an intermediate point between the SPAD  112  and the resistance  111  via the signal line  301 . It is also possible to use, in place of the resistance  111 , a constant current circuit including a MOS transistor or the like. Thus, unlike an ordinary photodiode, the SPAD  112  outputs an electrical signal in accordance with light that is incident in a state where a power supply voltage is applied. 
     [Configuration of Pixel] 
       FIG. 3  is a cross-sectional view showing an example of the configuration of the pixel  110  in the first embodiment of the present technology. The drawing is a schematic cross-sectional view showing an example of a configuration in which two pixels  110  are arranged. 
     The pixel  110  includes a microlens  121  and an insulating layer  101 , in addition to the SPAD  112 , the power supply line  201 , and the signal line  301 . Note that a description of the resistance  111  is omitted. 
     The SPAD  112  includes a first semiconductor region  105 , a second semiconductor region  106 , a third semiconductor region  107 , a guard ring  108 , an electrode  103 , and an electrode  104 . The SPAD  112  can be manufactured by the following procedure, for example. First, an n-type second semiconductor region  106  is formed as a well region of a p-type semiconductor substrate  109 . Next, a p-type first semiconductor region  105 , a p-type guard ring  108 , and an n-type third semiconductor region  107  are further formed in the interior of the second semiconductor region  106 . The well region and the semiconductor region can be formed by ion implantation or the like. Next, the electrodes  103  and  104  are formed on surfaces of the first semiconductor region  105  and the third semiconductor region  107 , respectively. Thereby, the SPAD  112  can be manufactured. 
     Each of the first semiconductor region  105  and the third semiconductor region  107  has a relatively high impurity concentration, and is formed in a relatively shallow region of the surface of the second semiconductor region  106 . As described later, the first semiconductor region  105  is formed in a disc-like shape. The guard ring  108  is formed in an annular shape, and is placed on the outside of the first semiconductor region  105 . Also the third semiconductor region  107  is formed in an annular shape similarly to the guard ring  108 , and is placed on the outside of the guard ring  108 . 
     The electrode  103  is an electrode formed on the first semiconductor region  105 , and operates as an anode electrode. The electrode  103  has a disc-like shape, and is placed on a substantially central portion of the first semiconductor region  105 . On the other hand, the electrode  104  is an electrode formed on the third semiconductor region  107 , and operates as a cathode electrode. The electrode  104  has an annular shape, and is formed along the third semiconductor region  107 . The signal line  301  and the power supply line  201  are connected to the electrode  103  and the electrode  104 , respectively. Note that the electrode  103  and the signal line  301  may be formed simultaneously as one body. Similarly, also the electrode  104  and the power supply line  201  may be formed simultaneously as one body. Further, the electrode  103  and  104  may contain a metal. Similarly, also the power supply line  201  and the signal line  301  may contain a metal. Note that the electrode  103  is an example of an electrode described in the claims. 
     If light from the subject is emitted to the first semiconductor region  105 , the emitted light is transmitted through the first semiconductor region  105 , and arrives at the second semiconductor region  106 . Here, photoelectric conversion is performed and carriers are generated. Thus, the first semiconductor region  105  corresponds to a light receiving surface in the SPAD  112 . As described in  FIG. 2 , a power supply voltage is always applied to the SPAD  112 . This voltage is applied in the reverse direction with respect to the SPAD  112 . That is, a voltage of a positive polarity is applied to the electrode  104  (the cathode electrode), and a voltage of a negative polarity is applied to the electrode  103  (the anode electrode). Hence, a depletion layer is formed in a p-n junction portion based on the first semiconductor region  105  and the second semiconductor region  106 . Most of the voltage applied to the SPAD  112  is divided in this depletion layer portion. 
     Thus, the photoelectric conversion in the SPAD  112  is performed in a state where a voltage is applied. As described later, the voltage applied to the SPAD  112  is a relatively high voltage exceeding the breakdown voltage. The guard ring  108  prevents the occurrence of a breakdown state that would occur because electric fields generated by the applied voltage concentrate in an end portion of the first semiconductor region  105 , what is called edge breakdown. The guard ring  108  may contain, in place of the semiconductor shown in the drawing, a dielectric such as a silicon oxide film, for example. 
     Note that the configuration of the SPAD  112  is not limited to the configuration shown in the drawing. For example, the first semiconductor region  105  may contain an n-type semiconductor, and each of the second semiconductor region  106  and the third semiconductor region  107  may contain a p-type semiconductor. Further, also a semiconductor other than silicon may be used. 
     The insulating layer  101  insulates the power supply line  201  and the signal line  301 , and transmits incident light. 
     The microlens  121  is a light collecting section that collects light incident on the pixel  110 . As described later, the microlens  121  has a doughnut-like shape having a hemispherical cross section, and collects light derived from the subject to the first semiconductor region  105  (a light receiving surface) other than the region where the electrode  103  and the signal line  301  are placed. This situation is shown in the right side of the drawing. Thereby, light emitted to a region not taking part in photoelectric conversion, such as the electrode  103 , can be guided to the p-n junction portion of the SPAD  112 , and detection efficiency can be improved. 
     [Configuration of Microlens] 
       FIG. 4  is a diagram showing an example of the configuration of the microlens  121  in the first embodiment of the present technology. “a” in the drawing shows a top view of the pixel  110 . “b” in the drawing shows a cross-sectional view of the microlens  121  taken along line A-A′ of “a” in the drawing. “c” in the drawing shows a top view of the pixel  110  excluding the microlens  121  and the signal line  301 . Note that  FIG. 3  described above corresponds to a cross-sectional view of the pixel  110  taken along line A-A′ of “a” in the drawing. 
     As shown in the drawing, the microlens  121  has a shape having a concavity in a substantially central portion. Furthermore, the microlens  121  of the drawing has a doughnut-like shape having an opening  122  in the concavity, and has a hemispherical cross section. Further, the microlens  121  is placed in a substantially central portion of the pixel  110 . As described above, the electrode  103  is placed on a substantially central portion of the first semiconductor region  105  formed in a disc-like shape, and the microlens  121  is placed in a position whereby the opening  122  and the electrode  103  overlap. Thereby, light incident on the pixel  110  avoids the electrode  103  and the wiring  301  placed on the electrode  103 , and is collected to the first semiconductor region  105 . Note that the configuration of the microlens  121  is not limited to the configuration shown in the drawing. For example, also a configuration in which the opening  122  is omitted and a concavity is provided in a central portion is possible. 
     [Method for Forming Microlens] 
     The microlens  121  can be formed by the following procedure. A resist is applied on the insulating layer  101 , and is patterned into an annular shape. Next, the whole workpiece is heated by a reflow furnace or the like to melt the resist. In this event, the cross section of the patterned resist becomes a hemispherical shape due to surface tension. After that, these are cooled; thereby, the microlens  121  of a doughnut shape can be formed. A photosensitive acrylic resin or the like may be used for the resist. 
     [Characteristics of SPAD] 
       FIG. 5  is a diagram showing characteristics of the SPAD  112  in an embodiment of the present technology. “a” in the drawing is a diagram showing a relationship between the applied voltage and the current of the SPAD  112 . It can be seen that, if a voltage is applied in the reverse direction with respect to the SPAD  112 , the flowing current rapidly increases at applied voltages more than or equal to a prescribed breakdown voltage Vbd. The breakdown voltage Vbd is a voltage at which an electron avalanche can occur in the depletion layer formed in the p-n junction portion based on the first semiconductor region  105  and the second semiconductor region  106 . In “a” in the drawing, the region where reverse voltages more than or equal to breakdown voltage Vbd are applied is referred to as an avalanche region, and is a region where the action of carrier multiplication by an electron avalanche occurs. The electron avalanche is a phenomenon in which impact ionization caused by an electron accelerated by a strong electric field in a depletion layer occurs and a new carrier is generated, and thereby carriers are multiplied. The action of carrier multiplication based on photoelectric conversion is made by the electron avalanche. However, in this region, there is a proportional relation between the amount of incident light and the current flowing through the SPAD  112 . 
     In the avalanche region, if a still higher reverse voltage is applied, the action of carrier multiplication based on an electron avalanche is increased, and the multiplication factor reaches a value of approximately 10 6 . This region is referred to as the Geiger region, which is a region where the output current is not proportional to the amount of incident light. In this region, the SPAD  112  can be used as an element that detects whether a photon is incident or not. For example, the SPAD  112  can be used in the Geiger region by applying a voltage higher than the breakdown voltage Vbd by several volts. 
     “b” in the drawing shows the waveform of a voltage based on the SPAD  112  that has entered a breakdown state. The solid line of “b” in the drawing shows the voltage between the cathode and the anode of the SPAD  112 . Further, the dotted line of “b” in the drawing shows the voltage of the signal line  301  described in  FIG. 2 . This corresponds to the output voltage of the SPAD  112 . The voltage between the cathode and the anode of the SPAD  112  before entering a breakdown state is a value substantially equal to the power supply voltage Vop. In this event, if light is incident on the SPAD  112 , a large current flows through the resistance  111  and the SPAD  112  due to the action of carrier multiplication. Accordingly, the voltage applied to the SPAD  112  rapidly decreases due to a voltage drop by the resistance  111 . Then, if the voltage applied to the SPAD  112  reaches the breakdown voltage Vbd, the action of carrier multiplication in the SPAD  112  stops, and the current decreases. After that, the SPAD  112  returns to the initial state. Such a return operation from a breakdown state by the resistance  111  is referred to as quenching. 
     Since carriers have been caught in traps or the like in the SPAD  112  immediately after returning from the breakdown state, there is a case where, when Vop is applied for the second time, the state returns to a breakdown state due to carriers released from traps or the like. The change in output voltage based on the breakdown state of the second time is referred to as an after-pulse. The power source section  200  described in  FIG. 1  can gradually increase the output voltage after quenching, as shown in “b” in the drawing. Thereby, the occurrence of an after-pulse can be prevented. The maximum voltage of the output of the signal line  301  is a pulsed voltage substantially equal to Vop−Vbd. This output is shaped by the signal processing section  300 , and is output to the distance measuring section  20  as an output signal of the imaging device  10 . Thus, the SPAD  112  outputs an electrical signal in accordance with light that is incident on the first semiconductor region  105 , which is a light receiving surface, in a state where a voltage exceeding the breakdown voltage is applied. 
     On the other hand, since a voltage exceeding the breakdown voltage Vbd is applied as described above, also a breakdown state not derived from the radiation of light may occur. In particular, in a case where the electric potential distribution of the first semiconductor region  105  is unequal, a local concentration of electric fields occurs, and a breakdown state not derived from the radiation of light occurs. This is a cause of noise. In order to prevent such a concentration of electric fields, the guard ring  108  is provided, and the electrode  103  is placed on a central portion of the first semiconductor region  105 . Thereby, the electric potential distribution of the first semiconductor region  105  can be equalized, and a concentration of electric fields can be prevented. 
     However, if the electrode  103  is placed at the center of the first semiconductor region  105 , light is blocked by the electrode  103 , and detection efficiency is reduced. Thus, the microlens  121  of the shape described in  FIGS. 3 and 4  is used, and incident light is caused to be collected to a region other than the central portion of the first semiconductor region  105 . That is, incident light is caused to be collected to a light receiving surface other than the region where the electrode  103  etc. are placed. Thereby, a reduction in detection efficiency can be prevented. 
     Thus, according to the first embodiment of the present technology, by placing the microlens  121  having a concavity in a substantially central portion, incident light can be collected to a light receiving surface so as to avoid the electrode  103  placed in a central portion of the SPAD  112 . Thereby, detection efficiency can be improved. 
     2. Second Embodiment 
     In the first embodiment described above, the microlens  121  having a concavity in a central portion is used. In contrast, in a second embodiment of the present technology, a microlens of a shape having a cut running along the signal line  301  is used. Thereby, detection efficiency can be further improved. 
     [Configuration of SPAD] 
       FIG. 6  is a diagram showing an example of the configuration of a microlens  123  in the second embodiment of the present technology. “a” in the drawing shows a top view of the pixel  110 . The pixel  110  of the drawing differs from the pixel  110  described in  FIG. 4  in that the microlens  123  is provided in place of the microlens  121 . Further, “b” in the drawing is a diagram showing a cross section of the microlens  123  taken along line B-B′ of “a” in the drawing. 
     As shown in “a” in the drawing, the microlens  123  has a shape having a concavity continuing along the signal line  301 . Furthermore, the microlens  123  has a cut  124  in a bottom portion of the continuing concavity. The cut  124  is placed along the signal line  301 , and therefore light emitted to a region of the signal line  301  excluding the region overlapping with the cut  124  can be caused to be collected onto the first semiconductor region  105 . That is, light emitted to a portion where the signal line  301  traverses the first semiconductor region  105  can be caused to be collected to the first semiconductor region  105 , which is a light receiving surface. Note that the configuration of the microlens  123  is not limited to the configuration shown in the drawing. For example, also a configuration in which the cut  124  is omitted and a concavity continuing along the signal line  301  is provided is possible. Note that the signal line  301  is an example of wiring described in the claims. 
     The configuration of the pixel  110  etc. other than the above is similar to the configuration of the pixel  110  etc. described in the first embodiment of the present technology, and therefore a description is omitted. 
     Thus, according to the second embodiment of the present technology, by using the microlens  123  having the cut  124 , light emitted to the signal line  301  excluding the region overlapping with the cut  124  can be collected to the first semiconductor region  105 . Thereby, detection efficiency can be further improved. 
     3. Third Embodiment 
     In the first embodiment described above, the microlens  121  having a concavity in a central portion is used. In contrast, in a third embodiment of the present technology, light collection is performed by a plurality of microlenses. Thereby, detection efficiency can be improved. 
     [Configuration of SPAD] 
       FIG. 7  is a diagram showing an example of the configuration of the pixel  110  in the third embodiment of the present technology. “a” in the drawing shows a top view of the pixel  110 . “b” in the drawing shows a cross-sectional view of microlenses  126  taken along line C-C′ of “a” in the drawing. “c” in the drawing shows a top view of the pixel  110  excluding the microlenses  126  and the wiring  301 . 
     The pixel  110  of the drawing includes four microlenses  126  in place of the microlens  121 . Each of these microlenses  126  has a quadrangular bottom portion, and collects light to the first semiconductor region  105 , which is a light receiving surface. Further, the pixel  110  of the drawing includes a quadrangular first semiconductor region  105 , and a guard ring  108  and a third semiconductor region  107  having a quadrangular outer peripheral portion. That is, in the pixel  110  of the drawing, a SPAD  112  having a quadrangular surface is placed. Further, the electrode  103  is placed on a central portion of the first semiconductor region  105 . Note that a cross section of the pixel  110  in the third embodiment of the present technology has a similar configuration to the pixel  110  described in  FIG. 4 , and therefore a description is omitted. 
     As shown in “a” in the drawing, a plurality of microlenses  126  are arranged in the pixel  110  of the third embodiment of the present technology. Each of these microlenses  126  causes incident light to be collected to the first semiconductor region  105 , which is a light receiving surface. Further, the electrode  103  and the signal line  301  are placed between ones of these microlenses  126 . Thereby, incident light can be collected to the first semiconductor region  105  other than the region where the electrode  103  etc. are placed. Since a bottom portion of the microlens  126  has a quadrangular shape, the occupation area of the microlenses in the pixel  110  can be larger than in the pixel  110  described in  FIG. 3 . Hence, light emitted to a large area of the pixel  110  can be collected to the first semiconductor region  105 , and detection efficiency can be further improved. Note that the configuration of the microlens  126  is not limited to the configuration shown in the drawing. For example, also a configuration having a circular bottom portion is possible. 
     The configuration of the pixel  110  etc. other than the above is similar to the configuration of the pixel  110  etc. described in the first embodiment of the present technology, and therefore a description is omitted. 
     Thus, according to the third embodiment of the present technology, by using a plurality of microlenses and placing the electrode  103  and the signal line  301  between ones of them, incident light can be collected to the first semiconductor region  105 . Thereby, detection efficiency can be improved. 
     4. Fourth Embodiment 
     In the first embodiment described above, light collection is performed by the microlens  121 . In contrast, in a fourth embodiment of the present technology, light collection is performed by two members with different refractive indices. 
     Thereby, the configuration of the pixel can be simplified. 
     [Configuration of SPAD] 
       FIG. 8  is a cross-sectional view showing an example of the configuration of the pixel  110  in the fourth embodiment of the present technology. The pixel  110  of the drawing includes, as compared to the pixel  110  described in  FIG. 4 , a first light collecting member  127  in place of the microlens  121 . Further, as compared to the SPAD  112  described in  FIG. 4 , the SPAD  112  of the drawing does not need to include the guard ring  108 . Furthermore, the SPAD  112  of the drawing includes, in place of the first semiconductor region  105  and the third semiconductor region  107 , a first semiconductor region  131  and a third semiconductor region  132 . 
     The first semiconductor region  131  is formed in a substantially central portion of the second semiconductor region  106 , and has a circular columnar shape. The third semiconductor region  132  has an annular shape similarly to the third semiconductor region  107  in  FIG. 3 . Further, a bottom portion of each of the first semiconductor region  131  and the third semiconductor region  132  is formed so as to reach a relatively deep region of the second semiconductor region  106 . Thus, the SPAD  112  of the drawing has a lateral structure in which a p-n junction portion is placed in a lateral direction with respect to the semiconductor substrate  109 . Hence, the SPAD  112  of the drawing does not need to consider the concentration of electric fields in an end portion of the first semiconductor region  131 , and can omit the guard ring  108 . In this case, a surface of the second semiconductor region  106  serves as a light receiving surface. 
     Further, the first light collecting member  127  is placed between the electrode  103  and the insulating layer  101 . The first light collecting member  127  transmits light similarly to the insulating layer  101 . Here, the refractive indices of the first light collecting member  127  and the insulating layer  101  are different, and the insulating layer  101  contains a material with a higher refractive index. Thus, in the light collecting section in the fourth embodiment of the present technology, the first light collecting member  127  and the insulating layer  101  are arranged in order between the electrode  103  and the subject. Further, the light collecting member  127  of the drawing has a bell-like shape. Note that the insulating layer  101  is an example of a second light collecting member described in the claims. 
     [Light Collection Method by Light Collecting Members] 
       FIG. 9  is a diagram showing an example of light collection in the fourth embodiment of the present technology. The drawing shows a situation of light collection by the first light collecting member  127  and the insulating layer  101 . In the drawing, the optical path of light incident from above the electrode  103  and the signal line  301  changes due to refraction at the interface between the insulating layer  101  and the first light collecting member  127 . As described above, the insulating layer  101  has a larger refractive index than the first light collecting member  127 ; thus, when light is incident on the first light collecting member  127  from the insulating layer  101 , the light is refracted in such a direction that the angle of refraction is larger. On the other hand, in a case where the angle of incidence is more than the critical angle, the light is totally reflected at the interface between the light collecting member  127  and the insulating layer  101 . Thus, as shown in the drawing, the optical path of incident light changes, and light can be collected to the second semiconductor region  106 , which is a light receiving surface. 
     The configuration of the pixel  110  etc. other than the above is similar to the configuration of the pixel  110  etc. described in the first embodiment of the present technology, and therefore a description is omitted. 
     Thus, according to the fourth embodiment of the present technology, by causing incident light to be totally reflected using the first light collecting member  127  and the insulating layer  101  with different refractive indices, the incident light can be collected to a light receiving surface, and a microlens can be omitted. Thereby, the configuration of the pixel  110  can be simplified. 
     Modification Example 
     Although the SPAD  112  of a lateral structure is used in the fourth embodiment described above, the SPAD  112  of the structure described in  FIG. 4  may be used. This is because light collection to a light receiving surface by the first light collecting member  127  and the insulating layer  101  is possible. 
     [Configuration of SPAD] 
       FIG. 10  is a cross-sectional view showing an example of the configuration of the pixel  110  in a modification example of the fourth embodiment of the present technology. The SPAD  112  of the drawing has a similar configuration to the SPAD  112  described in  FIG. 4 . Also in the pixel  110  of the drawing, light collection to the first semiconductor region  105 , which is a light receiving surface, by the light collecting member  127  and the insulating layer  101  can be performed. 
     The configuration of the pixel  110  etc. other than the above is similar to the configuration of the pixel  110  etc. described in the fourth embodiment of the present technology, and therefore a description is omitted. 
     5. Fifth Embodiment 
     In the first embodiment described above, a SPAD is used as a sensor for distance measurement. In contrast, in a fifth embodiment of the present technology, a SPAD is used for imaging. Thereby, the sensitivity of an imaging device in a low-illuminance environment can be improved. 
     [Configuration of Imaging Device] 
       FIG. 11  is a diagram showing an example of the configuration of the imaging device  10  in the fifth embodiment of the present technology. The imaging device  10  differs from the imaging device  10  described in  FIG. 1  in that a vertical driving section  400  is further provided and a signal processing section  500  is provided in place of the signal processing section  300 . 
     The pixel array section  100  of the drawing differs from the pixel array section  100  described in  FIG. 1  in that pixels  150  each including a SPAD and pixels  160 ,  170 , and  180  each including an ordinary photodiode are arranged in a two-dimensional array form. Each of the pixels  160 ,  170 , and  180  is a pixel that includes a color filter and generates an image signal in accordance with light of a specific wavelength. The drawing shows an example in which a red pixel that generates an image signal in accordance with red light, a green pixel that generates an image signal in accordance with green light, and a blue pixel that generates an image signal in accordance with blue light are arranged as the pixels mentioned above. In the drawing, the pixels marked with “R”, “G,” and “B” represent a red pixel (the pixel  160 ), a green pixel (the pixel  170 ), and a blue pixel (the pixel  180 ), respectively. Note that the pixel marked with “S” represents a pixel including a SPAD (the pixel  150 ). The pixel  150  in the fifth embodiment of the present technology performs the generation of an image signal in a low-illuminance environment. Hence, the pixel  150  does not need to include a color filter. These pixels are arranged in the pixel array section  100  on the basis of a prescribed rule. The drawing shows an example in which arrangement is made such that one of two green pixels in the Bayer array form is replaced with the pixel  150 . 
     Note that the configuration of the pixel array  100  is not limited to the example described above. For example, a color filter may be placed in a pixel including a SPAD. Specifically, like in the pixel  170 , a color filter having the property of transmitting green light may be placed for the pixel  150 . In this case, the arrangement of color filters may be set to the Bayer array form. The manufacturing of the imaging device  10  based on the manufacturing process of a common imaging device becomes possible. 
     Further, in the pixel array section  100 , row signal lines  401  and column signal lines  501  are arranged in an XY matrix form, and are each drawn to each pixel. The row signal line  401  is a signal line that transmits a control signal to each of the pixels  150  to  160 . Further, the column signal line  501  is a signal line that transmits an image signal generated by each of the pixels  150  to  160 . The row signal line  401  is drawn in common to, among the pixels  150  etc., the pixels  150  etc. arranged in the same row. Further, the column signal line  501  is drawn in common to the pixels  150  etc. arranged in the same column. 
     The vertical driving section  400  drives the pixels  150  etc. arranged in the pixel array section  100 . The vertical driving section  400  performs driving by outputting a control signal to each of the pixels  150  etc. via the row signal line  401 . In this event, the vertical driving section  400  sequentially outputs control signals for each row of the pixel array section  100 . 
     The signal processing section  500  processes an image signal generated by each of the pixels  150  etc. The signal processing section  500  may perform, for example, processing that performs analog/digital conversion on an analog image signal generated by each of the pixels  150  etc. and outputs a digital image signal. Further, image signals of one row are simultaneously input to the signal processing section  500  from the pixel array section  100 . The signal processing section  500  further performs horizontal transfer that sequentially outputs digital image signals of one row corresponding to the input image signals. The image signal output from the signal processing section  500  serves as an output image signal of the imaging device  10 . Note that the signal processing section  500  is an example of a processing circuit described in the claims. 
     The power source section  200  further performs the supply of electric power necessary for the operation of the pixels  150  etc., in addition to the supply of electric power to be applied to the SPAD. These flows of electric power are supplied to the pixels  150  etc. via the power supply line  201  and the grounding conductor  202 . 
     [Circuit Configuration of Pixel] 
       FIG. 12  is a diagram showing an example of the configuration of the pixel  150  in the fifth embodiment of the present technology. The drawing shows a circuit configuration of the pixel  150 . The pixel  150  includes the SPAD  112 , a resistance  153 , a waveform shaping section  154 , a retention section  155 , and MOS transistors  156  to  159 . Note that an N-channel MOS transistor may be used as each of the MOS transistors  156  to  159 . 
     The power supply line  201  includes a plurality of power supply lines (Vp and Vdd). The power supply line Vp is a power supply line that supplies electric power of the SPAD  112 . The power supply line Vdd is a power supply line that supplies electric power necessary for the operation of the pixel  150 . The row signal line  401  includes a plurality of signal lines (RST and SEL). The reset signal line RST (Reset) is a signal line that transmits a signal to the MOS transistor  157 . The selection signal line SEL (Select) is a signal line that transmits a signal to the MOS transistor  159 . If a voltage more than or equal to the threshold voltage between the gate and the source of each of the MOS transistors  157  and  159  (hereinafter, referred to as an ON signal) is input via each of these signal lines, the corresponding MOS transistor enters a conduction state. 
     The anode of the SPAD  112  is connected to the grounding conductor  202 , and the cathode is connected to an input of the waveform shaping section  154  and one end of the resistance  153 . The other end of the resistance  153  is connected to the power supply line Vp. An output of the waveform shaping section  154  is connected to the gate of the MOS transistor  156 . The source of the MOS transistor  156  is connected to the grounding conductor  202 , and the drain is connected to the source of the MOS transistor  157 , the gate of the MOS transistor  158 , and one end of the retention section  155 . The other end of the retention section  155  is connected to the grounding conductor  202 . The drain and the gate of the MOS transistor  157  are connected to the power supply line Vdd and the reset signal line RST, respectively. The drain and the source of the MOS transistor  158  are connected to the power supply line Vdd and the drain of the MOS transistor  159 , respectively. The gate and the source of the MOS transistor  159  are connected to the selection signal line SEL and the column signal line  501 , respectively. 
     Similarly to the resistance  111  described in  FIG. 2 , the resistance  153  is a resistance for performing quenching. Unlike the circuit of the pixel  110  in  FIG. 2 , in  FIG. 12  the SPAD  112  and the resistance  153  are connected so as to be exchanged. This is in order to make the same connection method as in the photodiodes in the pixels  160  to  180 . The output voltage from the SPAD  112  is equivalent to the voltage shown by the solid line of “b” in  FIG. 5 . 
     The waveform shaping section  154  shapes the waveform of a signal output from the SPAD  112 . If an output signal of the SPAD  112  is input, the waveform shaping section  154  generates a signal of a prescribed voltage and a prescribed pulse width, and outputs the generated signal. A comparator may be used for the waveform shaping section  154 , for example. 
     The MOS transistor  157  is a transistor that applies the power supply voltage Vdd to the retention section  155 . 
     The retention section  155  is a capacitor that retains a voltage in accordance with the output voltage of the SPAD  112 . 
     The MOS transistor  156  discharges the retention section  155 . Each time a pulse voltage output from the waveform shaping section  154  is input to the gate, the MOS transistor  156  short-circuits both terminals of the retention section  155  to perform discharging. In this event, the MOS transistor  156  discharges a part of the voltage retained in the retention section  155 . 
     The MOS transistor  158  is a transistor that generates a signal in accordance with the voltage retained in the retention section  155 . The MOS transistor  159  is a transistor that outputs the signal generated by the MOS transistor  158 , as an image signal. 
     Operations of the circuit shown in the drawing will now be described. First, an ON signal is input from the reset signal line RST, and the MOS transistor  157  enters a conduction state. Thereby, the retention section  155  is charged to the power supply voltage Vdd. That is, the retention section  155  is reset. If in this state light is emitted to the SPAD  112 , the voltage waveform shown by the solid line shown of “b” in  FIG. 5  is input to the waveform shaping section  154 . The waveform shaping section  154  outputs a pulse voltage in accordance with the input voltage waveform. The MOS transistor  156  is brought into conduction by this pulse voltage, and a part of the voltage retained in the retention section  155  is discharged. That is, each time a voltage waveform derived from the SPAD  112  is input to the waveform shaping section  154 , the voltage retained in the retention section  155  is gradually discharged. As described above, the SPAD  112  is caused to operate in the Geiger region; thus, each time one photon is incident, a voltage retained in the retention section  155  is discharged, and the voltage of the retention section  155  changes in accordance with the number of photons incident on the SPAD  112 . That is, the number of photons incident on the SPAD  112  can be measured by measuring the voltage of the retention section  155 . 
     If an ON signal is input from the selection signal line SEL after a prescribed exposure time has elapsed, the MOS transistor  159  is brought into conduction, and a signal generated by the MOS transistor  158  is output to the column signal line  501  as an image signal. 
     Note that a pixel of a publicly known configuration may be used for each of the pixels  160  to  180 . Thereby, a voltage in accordance with incident light is output from each of the pixels  160  to  180  as an image signal. Since as described above a voltage in accordance with the number of incident photons is output from the pixel  150 , the signal processing section  500  described in  FIG. 11  can perform common processing for the image signals output by the pixel  150  and the pixels  160  to  180 . 
     The configuration of the SPAD  112  etc. other than the above is similar to the configuration of the SPAD  112  etc. described in embodiment 1 of the present technology, and therefore a description is omitted. 
     [Arrangement of Pixels] 
       FIG. 13  is a diagram showing examples of the arrangement of pixels in the fifth embodiment of the present technology. The drawing shows examples of arrangements different from the arrangement described in  FIG. 11  in regard to the arrangement of the pixels  150  to  180  in the pixel array section  100 . “a” in the drawing shows an example in which pixels  150  are arranged in a checkered form, and other pixels are arranged in portions other than the above. Since a large number of pixels  150  each having the SPAD  112  are arranged, the resolution in a low-illuminance environment can be improved. “b” in the drawing shows an example in which pixels  170  are arranged in a checkered form. A large number of pixels  170 , which are green pixels, are arranged, and the resolution in an ordinary environment can be improved. Further, an arrangement further including a white pixel that generates an image signal in accordance with white light is possible. 
     Thus, according to the fifth embodiment of the present technology, by using the pixel array section  100  including the pixel  150  in which the SPAD  112  is placed, the sensitivity of the imaging device  10  can be improved. 
     Modification Example 
     Although in the fifth embodiment described above the pixel array section  100  including pixels of the same size is used, the size of the pixel  150  including a SPAD may be set larger than the size of the pixels  160  to  180  each including an ordinary photodiode. This is because the sensitivity of the pixel  150  including a SPAD can be improved. 
       FIG. 14  is a diagram showing examples of the arrangement of pixels in a modification example of the fifth embodiment of the present technology. The drawing shows examples of arrangements in a case where the sizes of the pixel  150  including the SPAD  112  and the pixels  160  to  180  each including an ordinary photodiode are different. “a” in the drawing shows an example in which arrangement is made such that some of the pixels  160  to  180  arranged in the Bayer array form are replaced with pixels  150 . The pixel  150  has four times the area of each of the pixels  160  to  180 , and therefore the sensitivity in a low-illuminance environment can be further improved. “b” in the drawing shows an example in which pixels  150  are arranged in a checkered form. Since a large number of pixels  150  are arranged, the sensitivity and resolution in a low-illuminance environment can be further improved. 
     The configuration of the pixel array section  100  other than the above is similar to the configuration of the pixel array section  100  described in the fifth embodiment of the present technology, and therefore a description is omitted. 
     6. Sixth Embodiment 
     In the fifth embodiment described above, a SPAD is used for imaging in a low-illuminance environment. In contrast, in a sixth embodiment of the present technology, pupil correction is performed on a pixel including a SPAD. Thereby, a reduction in the sensitivity of the imaging device  10  can be prevented. 
     [Configuration of Pixel] 
       FIG. 15  is a diagram showing an example of the configuration of the pixel  150  in the sixth embodiment of the present technology. The pixel  150  differs from the pixel  110  described in  FIG. 3  in that the microlens  121  is placed in a position shifted from the center of the pixel  150 . Pupil correction can be performed by thus placing the microlens  121  with a shift from the center of the pixel  150 . Here, the pupil correction is the correction of a reduction in the sensitivity of a peripheral portion by setting the position of the microlens  121  of a pixel placed in a peripheral portion among the pixels arranged in the pixel array section  100  to a position shifted in a direction toward a central portion of the pixel array section  100 . In a pixel placed in a peripheral portion, light is incident on the microlens  121  from an oblique direction, and consequently the incident light is collected to a position different from the position in a pixel placed in a central portion of the pixel array section  100 . In a case where the position of this light collection overlaps with an electrode or the like, a reduction in sensitivity in the pixel placed in a peripheral portion of the pixel array section  100  occurs. The reduction in sensitivity can be prevented by causing light to be collected to a desired position by performing pupil correction. 
     In the sixth embodiment of the present technology, in the SPAD  112  of the pixel  150  placed in a peripheral portion of the pixel array section  100 , light collection of incident light to a portion of the electrode  103  is prevented by performing pupil correction. Thereby, a reduction in detection efficiency can be prevented, and a reduction in sensitivity can be prevented. The pixel  150  of the drawing shows an example of the pixel  150  that is placed in a peripheral portion on the left side in the pixel array section  100  described in  FIG. 10 , and the microlens  121  is placed in a position shifted toward right with respect to the center of the pixel  150 . 
     The configuration of the pixel array section  100  other than the above is similar to the configuration of the pixel array section  100  described in the fifth embodiment of the present technology, and therefore a description is omitted. 
     Thus, according to the sixth embodiment of the present technology, by performing pupil correction, a reduction in detection efficiency in the pixel  150  placed in a peripheral portion of the pixel array section  100  can be prevented, and a reduction in the sensitivity of the imaging device  10  can be prevented. 
     As described above, according to the embodiments of the present technology, while the electrode  103  etc. are placed in a central portion of the SPAD  112 , incident light can be collected to the light receiving surface of the SPAD  112  by the light collecting section, and detection efficiency can be improved. 
     Note that the embodiments described above show examples for embodying the present technology, and matters in the embodiments and matters to define the invention in the claims have respective corresponding relationships. Similarly, matters to define the invention in the claims and matters in the embodiments of the present technology that are given names identical to those of the matters to define the invention in the claims have respective corresponding relationships. However, the present technology is not limited to the embodiments, and may be embodied by making various modifications to embodiments without departing from the spirit of the embodiments. 
     Further, each of the processing procedures described in the embodiments described above may be grasped as a method having each of these sequences of procedure, and furthermore may be grasped as a program for causing a computer to execute each of these sequences of procedure, or a recording medium that stores the program. As the recording medium, for example, a compact disc (CD), a MiniDisc (MD), a digital versatile disc (DVD), a memory card, a Blu-ray (registered trademark) Disc, and the like may be used. 
     Note that the effects described in the present specification are only examples and are not limitative ones, and furthermore there may be other effects. 
     Additionally, the present technology may also be configured as below. 
     (1) 
     A solid-state imaging element including: 
     a photodiode that includes a light receiving surface and an electrode placed on the light receiving surface, and that outputs an electrical signal in accordance with light incident on the light receiving surface in a state where a voltage exceeding a breakdown voltage is applied to the electrode; and 
     a light collecting section that causes light from a subject to be collected in the light receiving surface other than a region where the electrode is placed. 
     (2) 
     The solid-state imaging element according to (1), 
     in which, in the photodiode, the electrode is placed substantially at a center of the light receiving surface. 
     (3) 
     The solid-state imaging element according to (1) or (2), 
     in which the light collecting section includes a microlens having a concavity in a substantially central portion. 
     (4) 
     The solid-state imaging element according to (3), 
     in which the microlens has an opening in the concavity. 
     (5) 
     The solid-state imaging element according to (3) or (4), further including: 
     wiring that is electrically connected the electrode, 
     in which the microlens has a concavity continuing along the wiring. 
     (6) 
     The solid-state imaging element according to (5), 
     in which the microlens has a cut in a bottom portion of the continuing concavity. 
     (7) 
     The solid-state imaging element according to (1), 
     in which the light collecting section includes a plurality of microlenses each of which is configured to cause light to be collected in the light receiving surface other than a region where the electrode is placed. 
     (8) 
     The solid-state imaging element according to (7), further including: 
     wiring that is placed between the plurality of microlenses adjacent to each other, and that is electrically connected to the electrode. 
     (9) 
     The solid-state imaging element according to (7) or (8), 
     in which each of the plurality of microlenses has a quadrangular bottom surface. 
     (10) 
     The solid-state imaging element according to (1), 
     in which the light collecting section includes a first light collecting member and a second light collecting member that are sequentially arranged between the electrode and the subject, the second light collecting member having a larger refractive index than the first light collecting member. 
     (11) 
     An imaging device including: 
     a pixel circuit in which pixels each of which includes a photodiode and a light collecting section are arranged in a two-dimensional array form, the photodiode including a light receiving surface and an electrode placed on the light receiving surface, and outputting an electrical signal in accordance with light incident on the light receiving surface in a state where a voltage exceeding a breakdown voltage is applied to the electrode, the light collecting section causing light from a subject to be collected in the light receiving surface other than a region where the electrode is placed; and 
     a processing circuit that processes the output electrical signal. 
     REFERENCE SIGNS LIST 
     
         
           1  imaging system 
           10  imaging device 
           20  distance measuring section 
           30  infrared light emitting section 
           100  pixel array section 
           101  insulating layer 
           103 ,  104  electrode 
           105 ,  131  first semiconductor region 
           106  second semiconductor region 
           107 ,  132  third semiconductor region 
           108  guard ring 
           109  semiconductor substrate 
           110 ,  150 ,  160 ,  170 ,  180  pixel 
           111 ,  153  resistance 
           121 ,  123 ,  126  microlens 
           122  opening 
           124  cut 
           127  first light collecting member 
           154  waveform shaping section 
           155  retention section 
           156  to  159  MOS transistor 
           200  power source section 
           300 ,  500  signal processing section 
           301  signal line 
           400  vertical driving section