JP2008228265A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of preventing the deterioration of image quality and the degradation of sensitivity caused by a charge stored in a charge storage section in any other period of time than an exposure period of time and extending the exposure period of time. <P>SOLUTION: A lower electrode 56, a photoelectric conversion layer 57, and an upper electrode 58 are stacked in this order above a semiconductor substrate, and an n+ layer 53 that stores a charge generated in the photoelectric conversion layer 57 is connected to the lower electrode 56. The charge stored in the n+ layer 53 is swept away by a reset drain power source 64 by turning on a reset transistor 63. An image pickup element driving section 10 turns on the reset transistor for a given time from the endpoint of exposure. The given time is a time taken until the residual image charge existing in the photoelectric conversion layer 57 at the exposure end point time is sufficiently discharged to the outside of the photoelectric conversion layer 57 in a state that the same bias as that at the exposure start time point is applied to the photoelectric conversion layer 57. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a photoelectric conversion element stacked above a semiconductor substrate, and a charge storage unit formed in the semiconductor substrate that stores charges generated in the photoelectric conversion element, and is stored in the charge storage unit The present invention relates to an imaging apparatus having an imaging element that outputs a signal corresponding to an electric charge to the outside.

  In a single-plate color solid-state imaging device typified by a CCD type or CMOS type image sensor, three or four types of color filters are arranged in a mosaic pattern on an array of light receiving units that perform photoelectric conversion. Accordingly, color signals corresponding to the color filters are output from the respective light receiving units, and a color image is generated by performing signal processing on these color signals.

  However, in a color solid-state imaging device in which color filters are arranged in a mosaic shape, about 2/3 of incident light is absorbed by the color filter in the case of a primary color filter, light use efficiency is poor and sensitivity is low. There's a problem. Further, since only one color signal can be obtained at each light receiving unit, the resolution is poor, and in particular, there is a problem that false colors are conspicuous.

  Therefore, in order to overcome such a problem, a stacked solid-state imaging device having a structure in which three photoelectric conversion layers are stacked on a semiconductor substrate has been researched and developed (for example, Patent Documents 1 and 2 below). . This stacked solid-state imaging device includes, for example, a light receiving unit structure in which photoelectric conversion layers that generate charges (electrons, holes) for B, G, and R light are sequentially stacked from a light incident surface. A charge storage unit that stores signal charges generated in each photoelectric conversion layer is provided for each light receiving unit, and a signal readout circuit that can read a signal corresponding to the charges stored in the charge storage unit is provided. Each photoelectric conversion layer is sandwiched between a pair of electrodes, and one of the pair of electrodes is electrically connected to the charge storage unit, so that the charge generated in the photoelectric conversion layer and moved to the one electrode is stored in the charge storage unit. Has been accumulating.

  In the case of an image pickup device having such a structure, incident light is almost photoelectrically converted and read out, the utilization efficiency of visible light is close to 100%, and color signals of three colors of R, G, and B are obtained in each light receiving unit. Therefore, it is possible to generate a good image with high sensitivity and high resolution (false color is not noticeable).

Special Table 2002-502120 JP 2002-83946 A

  As a signal readout circuit of the multilayer image sensor, a CCD circuit that reads out and transfers the charge accumulated in the charge accumulation unit to a charge transfer path, converts the transferred charge into a signal voltage with an FD amplifier or the like, A MOS circuit or the like that converts the charge accumulated in the charge accumulation unit into a signal voltage by a MOS transistor and outputs the signal voltage can be considered. Regardless of whether the CCD circuit or the MOS circuit is used, after the signal is read out, the charge remaining in the charge storage unit (transfer charge in the case of the CCD circuit) needs to be swept away to the substrate or the like. As the technique, a technique used in a single-plate image sensor can be employed.

  For example, in the case of a MOS circuit, after the exposure period ends, a signal corresponding to the charge accumulated in the charge accumulation unit during the exposure period is output from the MOS circuit, and then a reset pulse is supplied to the gate of the reset transistor. A structure in which the electric charge is discharged to the reset drain can be employed.

FIG. 8 is a timing chart for explaining the reset operation of the multilayer image sensor. FIG. 8 shows an example in which the exposure period and the non-exposure period of the image sensor are controlled by a mechanical shutter.
When incident light enters the image sensor and charges generated in the photoelectric conversion layer are accumulated in the charge accumulation unit, the potential of the charge accumulation unit rises as illustrated. Then, after the exposure is completed, a signal corresponding to the charge accumulated in the charge accumulation unit in the MOS circuit is output, and the charge in the charge accumulation unit is reset. In the case where light does not enter after the reset operation, if the carriers generated in the photoelectric conversion layer are instantaneously stored in the charge storage portion, the potential of the charge storage portion should not increase after the reset operation. However, since it may take a certain amount of time for the carriers generated in the photoelectric conversion layer to reach the electrode connected to the charge storage portion, the charge generated even though it was generated in the photoelectric conversion layer during the exposure period. Carriers that could not move to the accumulation unit are accumulated in the charge accumulation unit after reset as an afterimage component. This afterimage component is mixed with carriers accumulated in the charge accumulation section in the next exposure period, so that the image quality is deteriorated. In addition, if there is an afterimage component in the charge storage portion, the potential of the electrode connected to the charge storage portion increases, so the bias voltage applied to the photoelectric conversion layer becomes relatively low, the carrier transport performance decreases, and the sensitivity increases. The problem of getting worse is also possible. It has been confirmed that the afterimage component in the photoelectric conversion layer decreases exponentially with time.

  Therefore, it is considered effective to prevent image quality deterioration and sensitivity reduction by supplying another reset pulse when the afterimage component in the photoelectric conversion layer is sufficiently reduced. For example, as shown in FIG. 9, after the signal is read out, the reset operation is performed once again when the afterimage component in the photoelectric conversion layer is sufficiently reduced, and the next exposure is started with almost no afterimage component. You can do that.

  However, in this case, since the potential of the charge storage portion varies between the reset timing and the reset timing shown in FIG. 9, the force for pulling the afterimage component in the photoelectric conversion layer to the electrode is weak during this period. As a result, the time until the afterimage component in the photoelectric conversion layer is sufficiently reduced becomes long, and the exposure time becomes short.

  The present invention has been made in view of the above circumstances, and is an imaging apparatus capable of preventing image quality deterioration and sensitivity reduction due to charges accumulated in the charge accumulation unit during periods other than the exposure period and extending the exposure period. The purpose is to provide.

  An image pickup apparatus according to the present invention includes a photoelectric conversion element stacked above a semiconductor substrate, and a charge storage unit formed in the semiconductor substrate that stores charges generated in the photoelectric conversion element. An image pickup apparatus having an image pickup device for outputting a signal corresponding to the accumulated electric charge to the outside, wherein the photoelectric conversion device includes a lower electrode formed above the semiconductor substrate and a photoelectric device formed above the lower electrode. A charge generation unit including a conversion layer and an upper electrode formed above the photoelectric conversion layer, wherein the charge storage unit is electrically connected to the lower electrode or the upper electrode, and the charge stored in the charge storage unit The charge sweeping means for sweeping away the charge storage unit and the charge storage unit connected to the charge storage unit for at least a continuous period from the end of the exposure period of the image sensor to the start of the next exposure period. Electrode potential fixing means that keeps the potential of the partial electrode or the upper electrode constant, and the charge is stored in the charge storage unit while the maximum amount of charge that can be stored in the charge storage unit is stored for a certain period of time. The time is longer than the minimum time required for sweeping away the maximum amount of charge by the sweeping means.

  The imaging apparatus of the present invention includes a light shielding unit that shields the image sensor between an exposure period and an exposure period, wherein the certain period starts from the end of the exposure period, and the exposure period ends When the afterimage charge existing in the photoelectric conversion layer at the time is discharged to the outside of the photoelectric conversion layer with the same bias voltage applied to the photoelectric conversion layer as the start time of the exposure period, The time is equal to the decay time constant of the afterimage charge.

  In the imaging apparatus of the present invention, the charge sweeping means is a reset transistor, and the electrode potential fixing means keeps the potential constant by applying a reset voltage to the gate electrode of the reset transistor for the certain period.

  In the image pickup apparatus of the present invention, when the electrode potential fixing unit represents the image pickup device with an equivalent circuit, an inversion input terminal is connected to the lower electrode or the upper electrode connected to the charge storage unit and fixed. A non-inverting input terminal is connected to the potential, and a differential amplifier in which a capacitor corresponding to the charge storage unit is connected between the inverting input terminal and the output terminal, wherein the potential is applied during an operation period of the imaging device. The fixed potential is always maintained.

  The imaging device of the present invention includes a series circuit connected in parallel to the capacitor between the inverting input terminal and the output terminal, and the series circuit includes a switch connected to the inverting input terminal; , And another capacitor connected to the switch.

  The image pickup apparatus of the present invention turns on the switch and turns on the inverting input terminal only when the charge accumulated in the capacitor by pre-shooting performed before the main shooting exceeds the capacity of the capacitor. Switch control means is provided for performing control for connecting the capacitor.

  According to the present invention, it is possible to provide an imaging apparatus capable of preventing image quality deterioration and sensitivity reduction due to charges accumulated in the charge accumulation unit during a period other than the exposure period and extending the exposure period.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a digital camera which is an example of an imaging apparatus for explaining a first embodiment of the present invention.
The imaging system of the illustrated digital camera includes a mechanical shutter MS, a photographing lens 1, an imaging element 5, an aperture 2 provided between the two, an infrared cut filter 3, and an optical low-pass filter 4.

  A system control unit 11 that performs overall control of the electrical control system of the digital camera controls the flash light emitting unit 12 and the light receiving unit 13 and controls the lens driving unit 8 to adjust the position of the photographing lens 1 to the focus position and zoom. Adjustment is performed, exposure amount adjustment is performed by controlling the aperture amount of the aperture 2 via the aperture drive unit 9, and opening / closing control of the mechanical shutter MS is performed via the shutter drive unit MSD. The exposure period and non-exposure period of the image sensor 5 are controlled by the shutter opening / closing control of the shutter drive unit MSD.

  In addition, the system control unit 11 drives the imaging device 5 via the imaging device driving unit 10 and outputs the subject image captured through the photographing lens 1 as a color signal. An instruction signal from the user is input to the system control unit 11 through the operation unit 14.

  The electric control system of the digital camera further includes an analog signal processing unit 6 for performing analog signal processing such as correlated double sampling processing connected to the output of the image sensor 5, and RGB output from the analog signal processing unit 6. And an A / D conversion circuit 7 for converting the color signal into a digital signal, which are controlled by the system control unit 11.

  Furthermore, the electric control system of this digital camera generates image data by performing main memory 16, memory control unit 15 connected to main memory 16, interpolation calculation, gamma correction calculation, RGB / YC conversion processing, and the like. A digital signal processing unit 17, a compression / decompression processing unit 18 that compresses image data generated by the digital signal processing unit 17 into a JPEG format or decompresses compressed image data, and a digital signal processing unit 17 that integrates photometric data. The integration unit 19 for obtaining the gain of white balance correction performed by the camera, the external memory control unit 20 to which the removable recording medium 21 is connected, and the display control unit 22 to which the liquid crystal display unit 23 mounted on the back of the camera is connected. These are connected to each other by a control bus 24 and a data bus 25, and are controlled by commands from the system control unit 11. That.

FIG. 2 is a schematic cross-sectional view of one pixel of the image sensor 5 of FIG. The imaging element 5 has a configuration in which a large number of one pixel shown in FIG. 2 is arranged in a one-dimensional or two-dimensional manner.
The imaging device 5 includes a lower electrode 56, a photoelectric conversion layer 57 formed above the lower electrode 56, and a photoelectric conversion layer above a semiconductor substrate including an n-type substrate 51 and a p-well layer 52 formed thereon. 57. The photoelectric conversion element including the upper electrode 58 formed above 57 has a structure in which the lower electrode 56 is laminated toward the semiconductor substrate side.

  The lower electrode 56 is a highly transparent electrode divided for each pixel, and for example, ITO is used.

  The photoelectric conversion layer 57 is a layer shared by all the pixels, absorbs light in a specific wavelength region, and generates signal charges (electrons and holes) corresponding to the light. The photoelectric conversion layer 57 includes either an organic photoelectric conversion material or an inorganic photoelectric conversion material. In the present embodiment, the photoelectric conversion layer 57 will be described as absorbing light in a green wavelength region, for example. An example of such an organic photoelectric conversion material is quinacridone. The photoelectric conversion layer 57 may be divided for each pixel.

  The upper electrode 58 is a highly transparent electrode shared by all pixels, and for example, ITO is used. A wiring (not shown) is connected to the upper electrode 58 so that a predetermined bias voltage is applied. A transparent protective film 59 is formed on the upper electrode 58. The upper electrode 58 may be divided for each pixel.

  The polarity of the bias voltage applied to the upper electrode 58 is determined so that electrons out of charges generated in the photoelectric conversion layer 57 move to the lower electrode 56 and holes move to the upper electrode 58. .

  A high concentration n-type impurity layer (n + layer) 53 for accumulating electrons generated in the photoelectric conversion layer 57 and moved to the lower electrode 56 is formed in the p-well layer 52. A via plug 55 made of a conductive material such as aluminum is formed on the n + layer 53, and a lower electrode 56 is formed on the via plug 55. The lower electrode 56 and the n + layer 53 are electrically connected by the via plug 55.

  In the p-well layer 52 and on the surface of the p-well layer 52, a signal readout unit 54 is formed for converting electrons accumulated in the n + layer 53 into a signal voltage and outputting the signal voltage to the outside of the imaging device 5. The signal reading unit 54 includes a source follower circuit that converts electrons accumulated in the n + layer 53 into a signal voltage, and a reset transistor that resets the electrons accumulated in the n + layer 53.

FIG. 3 is an equivalent circuit diagram of the image sensor 5 shown in FIG. In FIG. 3, the same components as those in FIG.
As shown in FIG. 3, a bias power supply 65 that supplies a bias voltage is connected to the upper electrode 58, and a capacitor 53 corresponding to the n + layer 53 is connected to the lower electrode 56. A first-stage transistor 62 of a source follower circuit is connected to the capacitor 53, and a reset drain power supply 64 is connected via a reset transistor 63. The electrons accumulated in the capacitor 53 are converted to a signal voltage corresponding to the amount by the first stage transistor 62 of the source follower circuit, amplified, and then output to the outside of the image sensor 5.

  The reset transistor 63 functions as charge sweeping means for sweeping electrons accumulated in the capacitor 53 to the semiconductor substrate, and is turned on when a reset voltage is supplied to the gate electrode from the image sensor driving unit 10 in FIG. The electrons accumulated in the capacitor 53 are swept away to the reset drain power supply 64 side.

  The imaging element driving unit 10 functions as an electrode potential fixing unit in the claims, and is a capacitor for a fixed period of time from the end of the exposure period to the start of the next exposure period. Control is performed to keep the potential of the lower electrode 56 connected to 53 constant. Specifically, the potential of the lower electrode 56 is kept constant by applying a reset voltage to the gate electrode of the reset transistor 63 for the above-mentioned fixed period.

  Here, the fixed period is a state in which the maximum amount of electrons that can be stored in the capacitor 53 is stored in the capacitor 53 and the minimum amount of time (hereinafter, referred to as “reset transistor 63”) required to sweep away the maximum amount of electrons by the reset transistor 63. The afterimage component (afterimage charge) present in the photoelectric conversion layer 57 at the end of the exposure period is applied with the same bias voltage as that at the start of the exposure period. It means the time taken for the liquid to be sufficiently discharged outside the photoelectric conversion layer 57 in the applied state.

  As described above, it is known that the afterimage charge in the photoelectric conversion layer 57 decreases exponentially with time. For this reason, in the present embodiment, the afterimage charge existing in the photoelectric conversion layer 57 at the end of the exposure period is applied to the outside of the photoelectric conversion layer 57 in a state where the same bias voltage as that at the start of the exposure period is applied to the photoelectric conversion layer 57. The amount of discharged image is measured, and the amount of discharged afterimage charge decreases exponentially to about 37% of the peak (this is the decay time constant of the afterimage charge in the photoelectric conversion layer 57). The time required until the afterimage charge is sufficiently discharged to the outside of the photoelectric conversion layer 57 may be set to be equal to or greater than the decay time constant. Ideally, the time required from the end of the exposure period until the amount of afterimage charge discharged from the photoelectric conversion layer 57 becomes zero with the same bias voltage applied to the photoelectric conversion layer 57 as at the start of the exposure period. It is.

  In the present embodiment, the imaging element driving unit 10 supplies the reset voltage to the gate electrode of the reset transistor 63 for a certain period from the end of the exposure period, so that the charge storage unit 53 stores the reset voltage in a period other than the exposure period. It is possible to suppress image quality deterioration and sensitivity reduction due to afterimage charges without reducing the exposure period.

Next, the imaging operation of the digital camera of this embodiment will be described.
FIG. 4 is a timing chart for explaining the reset operation of the image sensor 5.
When electrons generated in the photoelectric conversion layer 57 are accumulated in the capacitor 53 in accordance with light incident during the exposure period in which the mechanical shutter MS is open, the potential of the capacitor 53 rises as illustrated. When the mechanical shutter MS is closed and the exposure period is ended, a signal corresponding to the electrons accumulated in the capacitor 53 is output by the source follower circuit, and supply of the reset voltage to the reset transistor 63 is started. Is continuously supplied for the predetermined period. The electrons in the capacitor 53 are swept away to the reset drain power supply 64 when the reset voltage starts to be supplied, and the afterimage charge moved to the lower electrode 56 after the exposure period is also swept away to the reset drain power supply 64. Further, while the reset voltage is supplied, the potential of the capacitor 53 maintains the state immediately after the reset. After the fixed period has elapsed, the supply of the reset voltage is stopped. At this time, the afterimage charge hardly moves to the capacitor 53, and therefore the potential of the capacitor 53 hardly fluctuates. Then, the next exposure period starts from that state.

  According to the digital camera of this embodiment, since the reset operation is continuously performed for a certain period immediately after the exposure period ends, the potential of the capacitor 53 (corresponding to the potential of the lower electrode 56) during this period is set to the potential of the reset drain power supply 64. Can be fixed to. During this period, since the potential of the capacitor 53 is fixed, the bias voltage applied to the photoelectric conversion layer 57 is higher than that in the driving example shown in FIG. 7, and the transport performance of the afterimage charge generated in the photoelectric conversion layer 57 is improved. improves. For this reason, the time until the afterimage charge is discharged out of the photoelectric conversion layer 57 can be made shorter than in the driving example shown in FIG. In the case of the present embodiment, the reset operation may be performed for the predetermined period equal to the decay time constant of the afterimage charge in the photoelectric conversion layer 57 in a state where an optimum bias voltage is applied to the photoelectric conversion layer 57. As a result, the time for performing the reset operation can be made shorter than in the case of FIG. Since the time required for the reset operation can be shortened, the start timing of the next exposure time can be accelerated and the exposure time can be increased.

  As described above, according to the digital camera of the present embodiment, it is possible to prevent image quality deterioration due to the afterimage charge, and the photoelectric conversion layer 57 by starting exposure while the afterimage charge is accumulated in the capacitor 53. It is possible to improve the sensitivity by preventing a decrease in carrier transport efficiency.

  In the above description, the imaging element driving unit 10 applies the reset voltage to the gate electrode of the reset transistor 63 for the certain period from the end of the exposure period, thereby keeping the potential of the lower electrode 56 constant. However, the timing for applying the reset voltage is not limited to this. For example, the reset voltage may be continuously applied from the end of the exposure period to the next exposure start time.

  In the above description, the exposure period is controlled by the mechanical shutter MS. However, the present invention can also be applied to a digital camera not equipped with the mechanical shutter MS. When the mechanical shutter MS is not mounted in the digital camera of FIG. 1, light is incident on the image sensor 5 even during the light shielding period shown in FIG. 4. For this reason, in this case, it is necessary to reset the electrons accumulated in the capacitor 53 at least immediately before the start of the exposure period.

  If the reset voltage is applied only for the minimum reset period immediately before the start of the exposure period (assumed to be the first case), the carrier transport efficiency is lowered by the electrons accumulated in the capacitor 53 before the application of the reset voltage. Therefore, a large amount of afterimage charge exists in the photoelectric conversion layer 57 at the start of the exposure period.

  On the other hand, immediately before the start of the exposure period, when the reset voltage is applied for a period longer than the minimum reset period (for example, the entire period between the exposure period and the exposure period), Since the amount of afterimage charge is reduced as compared with the first case, the image quality can be improved as compared with the first case. Thus, even when the exposure period is controlled using the reset voltage as an electronic shutter pulse without using the mechanical shutter, the image quality can be improved by applying the reset voltage for a period longer than the minimum reset period. .

(Second embodiment)
In the first embodiment, it has been realized that the potential of the lower electrode 56 is kept constant by controlling the application time of the reset voltage. However, in the present embodiment, this is achieved by devising the circuit configuration of the signal readout unit 54. Is realized. The overall configuration of the digital camera described in the second embodiment and the configuration of the image sensor mounted thereon are the same as those shown in FIGS. 1 and 2, and only the configuration of the signal readout unit 54 and the function of the image sensor drive unit 10 shown in FIG. It is different. Hereinafter, the configuration of the signal reading unit 54 in the second embodiment will be described.

FIG. 5 is an equivalent circuit diagram of an image sensor mounted on the digital camera according to the second embodiment of the present invention. In FIG. 5, the same components as those in FIG.
5 includes a reset transistor 63, a reset drain power supply 64, and an inverting amplifier 66 functioning as an electrode potential fixing unit. A bias power supply 65 for supplying a bias voltage is connected to the upper electrode 58, and the lower electrode 56 is connected to the inverting input terminal of the inverting amplifier 66. A non-inverting input terminal of the inverting amplifier 66 is connected to the reset drain power supply 64. A capacitor 53 corresponding to the n + layer 53 is connected between the inverting input terminal and the output terminal of the inverting amplifier 66, and a reset transistor 63 is connected to both ends of the capacitor 53.

  The reset transistor 63 functions as charge sweeping means for sweeping electrons accumulated in the capacitor 53 to the semiconductor substrate, and is turned on when a reset voltage is supplied to the gate electrode from the image sensor driving unit 10 in FIG. The electrons accumulated in the capacitor 53 are swept away. In the present embodiment, it is assumed that the image sensor driving unit 10 resets the accumulated charge and the afterimage charge by applying a reset voltage for the minimum reset period immediately before the start of the exposure period.

The operation of the signal reading unit 54 configured as described above will be described.
When electrons generated in the photoelectric conversion layer 57 are accumulated in the capacitor 53, a potential difference is generated by the accumulated electrons at both ends of the capacitor 53 depending on the amount of electrons and the capacitance of the capacitor. Since the capacitor 53 is between the inverting input terminal and the output terminal of the inverting amplifier 66, a signal voltage corresponding to this potential difference is inverted and amplified by the inverting amplifier 66 and output to the outside of the image sensor 5. After the signal output, the reset transistor 63 is turned on immediately before the start of the exposure period, the electrons accumulated in the capacitor 53 are reset, and the output terminal of the inverting amplifier 66 settles at the potential of the reset drain power supply 64. Since the lower electrode 56 is connected to the inverting input terminal of the inverting amplifier 66, the potential of the lower electrode 56 is always fixed to the potential of the reset drain power supply 64 during the operation period of the imaging device 5.

  By making the signal reading unit 54 have a circuit configuration as shown in FIG. 5, the potential of the lower electrode 56 can always be kept at a fixed potential supplied from the reset drain power supply 64. For this reason, it is possible to prevent deterioration in image quality and sensitivity due to afterimage charges without devising control of the reset voltage. Further, since the period for performing the reset operation is only the minimum reset period, the exposure time can be extended. Further, since an optimal bias voltage is always applied to the photoelectric conversion layer 57, the carrier transport efficiency can always be maximized, and further sensitivity improvement can be realized.

(Third embodiment)
FIG. 6 is an equivalent circuit diagram of an image sensor mounted on the digital camera according to the third embodiment of the present invention. In FIG. 6, the same components as those in FIG.
6 is provided with a series circuit including a capacitor 70 and a switch 71 in parallel with the capacitor 53 between the inverting input terminal and the output terminal of the inverting amplifier 66 of the imaging element shown in FIG. It becomes the composition. The switch 71 has one end connected to the inverting input terminal of the inverting amplifier 66 and the other end connected to one end of the capacitor 70. The other end of the capacitor 70 is connected to the output terminal of the inverting amplifier 66.

  The system control unit 11 of the digital camera performs pre-shooting (autofocus function is performed or exposure conditions are set) before the main shooting (shooting for shooting the subject and recording the shot image data on the recording medium 21). Whether or not the electric charge accumulated in the capacitor 53 exceeds the capacity of the capacitor 53, and only when it exceeds, the switch 71 is turned on via the image sensor driving unit 10. Thus, control for connecting the inverting input terminal of the inverting amplifier 66 and the capacitor 70 is performed.

The operation of the digital camera equipped with the image sensor shown in FIG. 6 will be described below. FIG. 7 is a diagram for explaining an operation flow of the digital camera of the third embodiment.
When the photographing mode is set and the user instructs to pre-shoot (step S1), the system control unit 11 turns off the switch 71 via the image sensor driving unit 10 (step S2), and responds to this instruction. Control for executing pre-shooting is performed (step S3). When pre-shooting is performed, electrons generated in the photoelectric conversion layer 57 are accumulated in the capacitor 53. Then, the system control unit 11 determines whether or not there is a pixel in which the charge accumulated in the capacitor 53 by pre-shooting exceeds the capacity of the capacitor 53 among all the pixels of the image sensor 5 (step S4). Only when there is a pixel whose charge amount exceeds the capacity of the condenser 53 (step S4: YES), a control to turn on the switch 71 is performed (step S5).

  For example, when the signal level output from the inverting amplifier 66 reaches the signal level output when the same amount of charge as the capacitance of the capacitor 53 is accumulated in the capacitor 53, the system control unit 11 It is determined that there is a pixel in which the charge accumulated in 53 exceeds the capacity of the capacitor 53.

  Thereafter, when the user instructs the main photographing, the main photographing is performed according to the instruction (step S6), and the electrons generated in the photoelectric conversion layer 57 are accumulated in the capacitor 53 and the capacitor 70 and accumulated. A signal corresponding to the received electron is output from the output terminal of the inverting amplifier 66, and photographed image data obtained from the output signal is recorded on the recording medium 21. After the main photographing is completed, the charges accumulated in the capacitor 53 and the capacitor 70 are simultaneously reset by turning on the reset transistor 63 with the switch 71 turned on. The digital camera performs such an operation every time a pre-shooting instruction is given.

  In the state in which the switch 71 is on, there are two storage destinations for the charge generated in the photoelectric conversion layer 57, the capacitor 53 and the capacitor 70, and the charge capacity that can be stored is the capacity of the capacitor 53 and the capacity of the capacitor 70. Increase to total. For this reason, it is possible to perform shooting with an expanded dynamic range.

  As described above, according to the digital camera of the present embodiment, whether to perform wide dynamic range shooting with the switch 71 turned on or normal dynamic range shooting with the switch 71 turned off is determined by pre-shooting. Since either one can be selected and executed, it is possible to perform shooting in an optimal shooting mode according to the subject.

  In the first embodiment and the second embodiment, the lower electrode 56 is electrically connected to the charge storage unit 53. However, the upper electrode 58 may be electrically connected to the charge storage unit 53. . In this case, a bias voltage may be applied to the lower electrode 56 so that holes move to the lower electrode 56 and electrons move to the upper electrode 58.

  In the first embodiment and the second embodiment, electrons are used as carriers for generating a signal to be output to the outside of the image sensor 5, but holes may be used. In this case, in FIG. 2, a bias voltage may be applied to the upper electrode 58 so that holes move to the lower electrode 56 and electrons move to the upper electrode 58.

  Further, in the first embodiment and the second embodiment, the structure in which one photoelectric conversion layer 57 is stacked above the semiconductor substrate as one pixel of the image sensor 5 is described as an example. This is effective in a structure in which at least one photoelectric conversion layer is laminated and this photoelectric conversion layer and the charge storage portion are electrically connected, and is not limited to the configuration shown in FIG.

The figure which shows schematic structure of the digital camera which is an example of the imaging device for demonstrating 1st embodiment of this invention. Cross-sectional schematic diagram of one pixel of the image sensor of the first embodiment Equivalent circuit diagram of the image sensor of the first embodiment Timing chart explaining reset operation of image pickup device of first embodiment Equivalent circuit diagram of image sensor of second embodiment The equivalent circuit diagram of the image sensor mounted in the digital camera which is 3rd embodiment of this invention The figure for demonstrating the operation | movement flow of the digital camera of 3rd embodiment. Timing chart explaining the reset operation of the multilayer image sensor Timing chart explaining the operation when the stacked image sensor is reset multiple times

Explanation of symbols

5 Image sensor 10 Image sensor drive unit 53 Charge storage unit (capacitor)
54 signal readout section 55 via plug 56 lower electrode 57 photoelectric conversion layer 58 upper electrode 62 source follower first stage transistor 63 reset transistor 64 reset drain power supply 65 bias power supply 66 inverting amplifier

Claims (6)

A photoelectric conversion element stacked above the semiconductor substrate; and a charge storage unit formed in the semiconductor substrate for storing the charge generated in the photoelectric conversion element, according to the charge stored in the charge storage unit An image pickup apparatus having an image pickup device for outputting a signal to the outside,
The photoelectric conversion element includes a lower electrode formed above the semiconductor substrate, a photoelectric conversion layer formed above the lower electrode, and an upper electrode formed above the photoelectric conversion layer,
The charge storage portion is electrically connected to the lower electrode or the upper electrode;
A charge sweeping means for sweeping away the charge accumulated in the charge accumulation unit;
The potential of the lower electrode or the upper electrode connected to the charge storage unit is kept constant for at least a certain continuous period of time from the end of the exposure period of the image sensor to the start of the next exposure period. Electrode potential fixing means to maintain,
The predetermined period is less than the minimum time required for sweeping away the maximum amount of charge by the charge sweeping means in a state where the maximum amount of charge that can be accumulated in the charge accumulation unit is accumulated in the charge accumulation unit. An imaging device that is a long time. The imaging apparatus according to claim 1,
A light shielding means for shielding the image sensor between an exposure period and an exposure period;
The fixed period is started from the end of the exposure period, and the afterimage charge existing in the photoelectric conversion layer at the end of the exposure period is the same as the start time of the exposure period in the photoelectric conversion layer. An imaging apparatus having a time equal to a decay time constant of the afterimage charge in the photoelectric conversion layer when the bias voltage is applied and discharged to the outside of the photoelectric conversion layer. The imaging apparatus according to claim 1 or 2,
The charge sweeping means is a reset transistor;
The image pickup apparatus, wherein the electrode potential fixing means keeps the potential constant by applying a reset voltage to the gate electrode of the reset transistor for the certain period. The imaging apparatus according to claim 1,
When the electrode potential fixing means represents the imaging device in an equivalent circuit, an inverting input terminal is connected to the lower electrode or the upper electrode connected to the charge storage unit, and a non-inverting input terminal is connected to the fixed potential. A differential amplifier connected and connected between the inverting input terminal and the output terminal, the capacitor corresponding to the charge storage unit, wherein the potential is always kept at the fixed potential during the operation period of the imaging device An imaging device. The imaging apparatus according to claim 4,
A series circuit connected in parallel to the capacitor is provided between the inverting input terminal and the output terminal,
The series circuit is an imaging apparatus including a switch connected to the inverting input terminal and another capacitor connected to the switch. The imaging apparatus according to claim 5, wherein
Control to turn on the switch and connect the inverting input terminal and the other capacitor only when the electric charge accumulated in the capacitor by the pre-photographing performed before the main photographing exceeds the capacity of the capacitor. An imaging apparatus comprising switch control means for performing.

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