WO2016204225A1 - Solid-state imaging device, method of driving solid-state image capturing device, and electronic instrument - Google Patents

Abstract

A solid-state image capturing device 10 comprises: a photodiode PD, which is an opto-electrical conversion element that accumulates electric charge generated by opto-electrical conversion during an accumulation period (exposure period); a transfer transistor TG-Tr which serves as an electric charge transfer gate portion with which charge accumulated by the photodiode can be transferred during a transfer period; and a state control unit 70 which, during the accumulation period (exposure period), controls the state below the gate of the transfer transistor TG-Tr to be a mixture of a state in which accumulation is occurring and a state in which accumulation is not occurring. By this means, it is possible to suppress a dark current without losing the function of discharging surplus electric current during accumulation.

Description

Solid-state imaging device, driving method of solid-state imaging device, and electronic apparatus

The present invention relates to a solid-state imaging device, a driving method for the solid-state imaging device, and an electronic apparatus.

A CMOS (Complementary Metal Oxide Semiconductor) image sensor has been put to practical use as a solid-state imaging device (image sensor) using a photoelectric conversion element that detects light and generates charges.
CMOS image sensors are widely applied as a part of various electronic devices such as digital cameras, video cameras, surveillance cameras, medical endoscopes, personal computers (PCs), and mobile terminal devices (mobile devices) such as mobile phones. Yes.

The CMOS image sensor has an FD amplifier having a photodiode (photoelectric conversion element) and a floating diffusion layer (FD: Floating Diffusion) for each pixel, and the readout selects one row in the pixel array. However, a column parallel output type in which these are simultaneously read in the column output direction is the mainstream.

Each pixel of the CMOS image sensor has, for example, a transfer transistor as a transfer gate, a reset transistor as a reset gate, a source follower transistor as a source follower gate (amplification gate), and a selection gate for one photodiode. The configuration includes four elements of the selection transistor as active elements (see, for example, Patent Document 1).
Each pixel may be provided with an overflow gate (overflow transistor) for discharging overflow charges overflowing from the photodiode during the photodiode accumulation period.

The transfer transistor is connected between the photodiode and the floating diffusion FD as an output node.
The transfer transistor is held in a non-conducting state during the charge accumulation period of the photodiode, and a drive signal is applied to the gate and held in the conducting state during a transfer period in which the accumulated charge of the photodiode is transferred to the floating diffusion. The charge photoelectrically converted by the diode is transferred to the floating diffusion FD.

The reset transistor is connected between the power supply line and the floating diffusion FD.
The reset transistor resets the potential of the floating diffusion FD to the potential of the power supply line when a reset signal is given to its gate.

A gate of a source follower transistor is connected to the floating diffusion FD. The source follower transistor is connected to the vertical signal line via the selection transistor, and constitutes a constant current source and a source follower of the load circuit outside the pixel portion.
Then, a control signal (address signal or select signal) is supplied to the gate of the selection transistor, and the selection transistor is turned on.
When the selection transistor is turned on, the source follower transistor amplifies the potential of the floating diffusion FD and outputs a voltage corresponding to the potential to the vertical signal line. The voltage output from each pixel through the vertical signal line is output to a column parallel processing unit as a pixel signal readout circuit.

In each pixel, a buried photo diode (BPD) is widely used as a photodiode (PD).
Since surface levels due to dangling bonds and other defects exist on the surface of the substrate on which the photodiode (PD) is formed, a large amount of charge (dark current) is generated due to thermal energy, and a correct signal may not be read out. .
In the embedded photodiode (BPD), it is possible to reduce mixing of dark current into the signal by embedding the charge storage portion of the photodiode (PD) in the substrate.
The sensitivity of the photodiode (PD) can be changed by changing the exposure time, for example.

Japanese Patent Laid-Open No. 2005-223681

However, in the above-described solid-state imaging device (image sensor), during the accumulation period of the photodiode, the transfer transistor or the overflow transistor having a function of transferring charge is held in a non-conductive state, but the excess charge at the time of accumulation. Is always depleted in order to discharge the light, and there is a disadvantage that dark current increases.

It is an object of the present invention to provide a solid-state imaging device, a driving method for the solid-state imaging device, and an electronic apparatus that can suppress dark current without impairing the function of discharging surplus charges during accumulation.

A solid-state imaging device according to a first aspect of the present invention includes a photoelectric conversion element that accumulates charges generated by photoelectric conversion during an accumulation period, and at least one charge transfer gate unit that can transfer charges accumulated in the photoelectric conversion element And a state control unit that controls so that at least the state under the gate of the charge transfer gate unit is accumulating and the state of not accumulating at least during the accumulation period.

A second aspect of the present invention includes a photoelectric conversion element that accumulates charges generated by photoelectric conversion during an accumulation period, and at least one charge transfer gate unit that can transfer the charges accumulated in the photoelectric conversion element. In the solid-state imaging device driving method, control is performed so that at least the state below the gate of the charge transfer gate unit is accumulated and the state is not accumulated at least in the accumulation period.

An electronic apparatus according to a third aspect of the present invention includes a solid-state imaging device and an optical system that forms a subject image on the solid-state imaging device, and the solid-state imaging device is generated by photoelectric conversion during an accumulation period. A photoelectric conversion element for accumulating charge; at least one charge transfer gate part capable of transferring charge accumulated in the photoelectric conversion element; and accumulating at least a state under the gate of the charge transfer gate part during at least the accumulation period And a state control unit that performs control so that a state that is being performed and a state that is not being accumulated are mixed.

According to the present invention, dark current can be suppressed without impairing the function of discharging surplus charge during storage.

FIG. 1 is a block diagram illustrating a configuration example of a solid-state imaging apparatus according to the first embodiment of the present invention. FIG. 2A and FIG. 2B are diagrams illustrating operation timings of the shutter scan and the readout scan during the normal pixel readout operation in the present embodiment. FIG. 3 is a circuit diagram illustrating an example of a pixel according to the first embodiment. FIG. 4 is a diagram schematically showing a cross section of the embedded photodiode, the transfer transistor, and the floating diffusion in the pixel according to the first embodiment. FIG. 5 is a diagram for explaining the behavior of electrons and holes in the GR center at the Si / insulating layer interface. 6A to 6C are diagrams showing a configuration example of the column signal processing circuit in the readout circuit according to the present embodiment. FIG. 7A and FIG. 7B are diagrams for explaining the read operation according to the first embodiment. FIGS. 8A to 8C are diagrams showing the relationship between the state of the depletion region in the gate bias to the gate electrode of the transfer transistor and the suppression state of dark current, blooming, and saturation. 9A to 9C show the case where a transfer gate pulse is applied to the gate electrode of the transfer transistor, the case where an intermediate voltage is applied, and the case where a pulse is applied to a substrate or the like, dark current, It is a figure which shows the relationship with the suppression state of blooming and saturation by potential transition. FIG. 10 is a diagram illustrating that blooming is suppressed by pulsing in the photoelectric conversion characteristics. FIG. 11 is a diagram for explaining that an overflow function via a buried channel under a gate electrode can be easily realized in accordance with pulsing in the first embodiment. FIG. 12A and FIG. 12B illustrate a read operation including control for mixing the accumulating state and the non-accumulating state by the state control unit according to the second embodiment of the present invention. FIG. FIGS. 13A and 13B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the third embodiment of the present invention. FIG. FIG. 14 is a circuit diagram illustrating an example of a pixel according to the fourth embodiment. FIGS. 15A and 15B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the fourth embodiment of the present invention. It is a figure for doing. FIGS. 16A and 16B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the fifth embodiment of the present invention. FIG. FIGS. 17A and 17B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the sixth embodiment of the present invention. FIG. FIG. 18 is a circuit diagram illustrating an example of a pixel according to the seventh embodiment. FIG. 19A and FIG. 19B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the seventh embodiment of the present invention. FIG. FIG. 20 is a circuit diagram illustrating an example of a pixel according to the eighth embodiment. FIGS. 21A and 21B illustrate a read operation including a control for mixing an accumulating state and an unaccumulated state by the state control unit according to the eighth embodiment of the present invention. FIG. FIG. 22 is a circuit diagram illustrating an example of a pixel according to the ninth embodiment. FIG. 23 (A) and FIG. 23 (B) explain a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the ninth embodiment of the present invention. FIG. FIG. 24 is a circuit diagram illustrating an example of a pixel according to the tenth embodiment. FIGS. 25A and 25B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit according to the tenth embodiment of the present invention. FIG. FIG. 26 is a diagram illustrating an example of a configuration of an electronic apparatus to which the solid-state imaging device according to the embodiment of the present invention is applied.

DESCRIPTION OF SYMBOLS 10 ... Solid-state imaging device, 20 ... Pixel part, 30 ... Vertical scanning circuit, 40 ... Horizontal scanning circuit, 50 ... Read-out circuit, 60 ... Timing control circuit, 70 ... State controller 80 ... Reading unit 100 ... Electronic device 110 ... CMOS image sensor 120 ... Optical system 130 ... Signal processing circuit (PRC)

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration example of a solid-state imaging apparatus according to the first embodiment of the present invention.
In the present embodiment, the solid-state imaging device 10 is configured by, for example, a CMOS image sensor.

As shown in FIG. 1, the solid-state imaging device 10 includes a pixel unit 20 as an imaging unit, a vertical scanning circuit (row scanning circuit) 30, a readout circuit (column readout circuit) 40, and a horizontal scanning circuit (column scanning circuit) 50. , And a timing control circuit 60 as main components.
Among these components, for example, the state control unit 70 includes the vertical scanning circuit 30 and the timing control circuit 60.
Among these components, for example, the vertical scanning circuit 30, the readout circuit 40, and the timing control circuit 60 constitute a pixel signal readout unit 80.

In the present embodiment, as will be described in detail later, the solid-state imaging device 10 includes the pixel unit 20 so that dark current can be suppressed without impairing the function of discharging surplus charges during accumulation. The state under the gate of the transfer transistor (or overflow gate) as a charge transfer gate part capable of transferring the charge accumulated in the photoelectric conversion element (photodiode) of the arranged pixel is the state during the accumulation period (exposure period). The control unit 70 performs control so that an accumulating state and an unaccumulated state are mixed.
For example, the state control unit 70 applies a pulse, which is an intermittent (or periodic) voltage signal, to the gate electrode of the transfer transistor, for example, so that the accumulated state and the unaccumulated state are mixed. To do. In other words, the state control unit 70 suppresses depletion under the gate electrode by applying a pulse.

FIG. 2A and FIG. 2B are diagrams illustrating operation timings of the shutter scan and the readout scan during the normal pixel readout operation in the present embodiment.
2A shows the relationship between the shutter scan, the exposure period, and the readout scan, and FIG. 2B shows specific operation timings of the shutter scan and readout scan.

In a normal pixel readout operation, a shutter scan is performed by driving by the readout unit 80, and then a readout scan is performed, but an accumulation state and an unaccumulation state by the state control unit 70 are mixed. The control is performed during the accumulation period (exposure period) EXP of the shutter scan period PSHT.

Further, in the present embodiment, the reading unit 80 performs the first reading in which the reset voltage Vrst is read in the first reading period PRD1 following the reset period PR, and the first reading period following the reset period PR in one reading scan period PRDO. In the second read period PRD2 after the transfer period PT performed after PRD1, the second read that reads the signal voltage Vsig corresponding to the accumulated charge of the photoelectric conversion element can be performed.

Hereinafter, after describing the outline of the configuration and functions of each unit of the solid-state imaging device 10, the control of mixing the accumulated state and the unaccumulated state by the state control unit 70 will be described in detail.

(Configuration of the pixel unit 20 and the pixel PXL)
In the pixel unit 20, a plurality of pixels including photodiodes (photoelectric conversion elements) and in-pixel amplifiers are arranged in a two-dimensional matrix (matrix) of N rows × M columns.

FIG. 3 is a circuit diagram illustrating an example of a pixel according to the first embodiment.

The pixel PXL includes, for example, a photodiode (PD) that is a photoelectric conversion element.
For this photodiode PD, a transfer transistor TG-Tr as a charge transfer gate portion, a reset transistor RST-Tr as a reset element, a source follower transistor SF-Tr as a source follower element, and a selection transistor SEL as a selection element Each has one -Tr.

For example, a buried photo diode (BPD) is used as the photodiode PD.
Since surface levels due to dangling bonds and other defects exist on the surface of the substrate on which the photodiode PD is formed, a large amount of charge (dark current) is generated due to thermal energy, and a correct signal may not be read out.
In the embedded photodiode (BPD), it is possible to reduce the incorporation of dark current into the signal by embedding the charge storage portion of the photodiode PD in the substrate.

The photodiode PD generates and accumulates signal charges (electrons here) in an amount corresponding to the amount of incident light.
Hereinafter, a case where the signal charge is an electron and each transistor is an n-type transistor will be described. However, the signal charge may be a hole or each transistor may be a p-type transistor.
This embodiment is also effective when a plurality of photodiodes share each transistor or when a three-transistor (3Tr) pixel that does not have a selection transistor is employed.

The transfer transistor TG-Tr is connected between the photodiode PD and a floating diffusion FD (floating diffusion layer), and is controlled through a control line TG.
Under the control of the state control unit 70, the transfer transistor TG-Tr becomes conductive when the control line TG is selected during a high level H of a predetermined level LV (eg, power supply voltage level), for example, during a read scan. Charges (electrons) photoelectrically converted and stored by the PD are transferred to the floating diffusion FD.

In the first embodiment, as shown in FIG. 2B, the transfer transistor TG-Tr is, for example, an accumulation period (exposure period) EXP during the shutter scan period PSHT under the control of the state control unit 70. In addition, a transfer gate pulse PLST which is an intermittent (or periodic) voltage signal set to an intermediate level LM lower than a predetermined level is applied to the control line TG.
As described above, the transfer transistor TG-Tr is controlled so that the accumulation state and the non-accumulation state are mixed under the gate electrode by applying the pulse PLST to the gate electrode.
In other words, in the transfer transistor TG-Tr, depletion under the gate electrode is suppressed by applying the pulse PLST to the gate electrode.

Note that the level of the transfer gate pulse PLST can be adjusted by the state control unit 70.
In the present embodiment, as shown in FIG. 2B, the level (potential) LP of the transfer gate pulse PLST to be applied is between a predetermined level LV, for example, a power supply voltage level, and a reference level LR, for example, a ground level. Is set to an intermediate level LM. That is, the pulse level LP is set with the relationship {LR <LP (= LM) <LV}.

FIG. 4 is a diagram schematically showing a cross section of the embedded photodiode, the transfer transistor, and the floating diffusion in the pixel according to the first embodiment.

The embedded photodiode BPD is formed with a first conductivity type p + layer 201 as a seal layer and a second conductivity type n− layer 202 as a charge storage portion from the surface side. Reference numeral 203 denotes a p− region, and 204 denotes an n + layer that forms the floating diffusion FD.
An n + layer 204 is formed on the side of the photodiode PD with a p-region 203 having a predetermined width, and a gate electrode (GT) of the transfer transistor TG-Tr is formed on the p-region 203 having a predetermined width via a gate oxide film. 205 is formed.

As described above, the transfer transistor TG-Tr has a potential profile (potential profile) under the gate electrode 205 when a pulse PLST, which is an arbitrary voltage, is applied to the gate electrode during the accumulation period (exposure period) EXP. It may be an embedded type. The potential profile under the gate electrode can be controlled by a pulse that is a voltage signal applied to the minimum point.
Thus, in the present embodiment, a so-called transfer electrode portion under the gate electrode of the transfer transistor TG-Tr may be formed by a buried channel.
The transfer transistor TG-Tr applies a pulse PLST having an arbitrary voltage level to the gate electrode during the accumulation period (exposure period) EXP, so that majority carriers are transferred to the Si / insulating layer interface under the gate electrode 205. It can be collected and buried in a generation recombination center (GR center) at the Si / insulating layer interface.

FIG. 5 is a diagram for explaining the behavior of electrons and holes in the GR center at the Si / insulating layer interface.
In the GR center, recombination of electrons and holes occurs.
In the GR sensor, as shown in FIG. 5, the holes are recombined or occupied by generated holes or electrons.
Then, by applying a pulse PLST having an arbitrary voltage level to the gate electrode during the accumulation period (exposure period) EXP, generation of electrons from the GR center is suppressed, and a GR center occupied by holes is obtained. be able to.
As a result, dark current can be suppressed without impairing the function of discharging excess charge during storage.

As shown in FIG. 3, the reset transistor RST-Tr is connected between the power supply line VRst and the floating diffusion FD, and is controlled through the control line RST.
The reset transistor RST-Tr may be connected between the power supply line VDD and the floating diffusion FD, and may be configured to be controlled through the control line RST.
Under the control of the state control unit 70, the reset transistor RST-Tr becomes conductive when the control line RST is selected during the period of the read scan, for example, during the read scan, and the floating diffusion FD is set to the potential of the power supply line VRst (or VDD). Reset to.

In the first embodiment, the reset transistor RST-Tr is set to a predetermined level LV on the control line RST, for example, during the accumulation period (exposure period) EXP during the shutter scan period PSHT under the control of the state control unit 70. The reset gate pulse PLSR, which is an intermittent (or periodic) voltage signal, is applied.
In the reset transistor RST-Tr, depletion under the gate electrode is suppressed by applying a pulse PLSR to the gate electrode.
The reset gate pulse PLSR is a pulse signal in phase with the transfer gate pulse PLST, and its level is a predetermined level (power supply voltage level) LV, which is higher than the level of the transfer gate pulse PLST (intermediate level LM).

The source follower transistor SF-Tr and the selection transistor SEL-Tr are connected in series between the power supply line VDD and the vertical signal line LSGN.
A floating diffusion FD is connected to the gate of the source follower transistor SF-Tr, and the selection transistor SEL-Tr is controlled through a control line SEL.
The source follower transistor SF-Tr is connected to the column output signal line LSGN via the selection transistor SEL-Tr, and constitutes a source follower with a load circuit connected to the output signal line LSGN outside the pixel unit 20.
The selection transistor SEL-Tr is selected during the period when the control line SEL is at the H level and becomes conductive. As a result, the source follower transistor SF-Tr outputs the column output read voltage (signal) VSL (PIXOUT), which is obtained by converting the charge of the floating diffusion FD into a voltage signal with a gain corresponding to the amount of charge (potential), to the vertical signal line LSGN. To do.
For example, the gates of the transfer transistor TG-Tr, the reset transistor RST-Tr, and the selection transistor SEL-Tr are connected in units of rows. Is called.

Since the pixel unit 20 has N rows × M columns of pixels PXL, there are N control lines SEL, RST, and TG, respectively, and M vertical signal lines LSGN.
In FIG. 1, each control line SEL, RST, TG is represented as one row scanning control line.

The vertical scanning circuit 30 drives the pixels through the row scanning control lines in the shutter row and the readout row in accordance with the control of the timing control circuit 60.
In addition, the vertical scanning circuit 30 outputs a row selection signal of a row address of a read row that reads out the signal and a shutter row that resets the charge accumulated in the photodiode PD in accordance with the address signal.

As described above, in a normal pixel readout operation, a shutter scan is performed by driving by the vertical scanning circuit 30 of the readout unit 80, and then a readout scan is performed.

As described above, FIG. 2A and FIG. 2B show the operation timing of the shutter scan and the readout scan during the normal pixel readout operation in the present embodiment.

The control line SEL for controlling the on (conducting) and off (non-conducting) of the selection transistor SEL-Tr is set to L level during the shutter scan period PSHT, and the selection transistor SEL-Tr is held in the non-conducting state and read. In the scan period PRDO, the selection transistor SEL-Tr is set in the conductive state by being set to the H level.
In the shutter scan period PSHT, first, the control line TG is set to the H level for a predetermined period while the control line RST is at the H level, and the photodiode PD and the floating diffusion FD are passed through the reset transistor RST-Tr and the transfer transistor TG-Tr. Is reset.
Then, as described above, in the accumulation period (exposure period) EXP of the shutter scan period PSHT, the transfer is an intermittent (or periodic) voltage signal that is set to the intermediate level LM lower than the predetermined level LV on the control line TG. A gate pulse PLST is applied. As described above, the transfer transistor TG-Tr is controlled so that the accumulation state and the non-accumulation state are mixed under the gate electrode by applying the pulse PLST to the gate electrode.
At this time, the reset transistor RST-Tr is intermittently set to a predetermined level LV on the control line RST under the control of the state control unit 70, for example, in the accumulation period (exposure period) EXP in the shutter scan period PSHT. A reset gate pulse PLSR, which is a (or periodic) voltage signal, is applied.

In the read scan period PRDO, the control line RST is set to H level, the floating diffusion FD is reset through the reset transistor RST-Tr, and the pixel read voltage is in the reset state in the first read period PRD1 after the reset period PR. The reset voltage Vrst is read out.
After the read period PRD1, the control line TG is set to H level for a predetermined period, and the charge stored in the photodiode PD is transferred to the floating diffusion FD through the transfer transistor TG-Tr. In the second read period PRD2 after the transfer period PT, A signal voltage Vsig, which is a pixel readout voltage corresponding to the accumulated electrons (charges), is read out.

The readout circuit 40 includes a plurality of column signal processing circuits (not shown) arranged corresponding to the respective column outputs of the pixel unit 20, and may be configured to allow column parallel processing by the plurality of column signal processing circuits. Good.

The readout circuit 40 can be configured to include a correlated double sampling (CDS) circuit, an ADC (analog / digital converter; AD converter), an amplifier (AMP), a sample hold (S / H) circuit, and the like. It is.

As described above, the readout circuit 40 may include an ADC 41 that converts the readout signal VSL output from each column of the pixel unit 20 into a digital signal, for example, as illustrated in FIG.
Alternatively, in the readout circuit 40, for example, as shown in FIG. 6B, an amplifier (AMP) 42 that amplifies the readout signal VSL output from each column of the pixel unit 20 may be arranged.
For example, as shown in FIG. 6C, the read circuit 40 may include a sample hold (S / H) circuit 43 that samples and holds the read signal VSL output from each column of the pixel unit 20.

The horizontal scanning circuit 50 scans a signal processed by a plurality of column signal processing circuits such as ADC of the reading circuit 40, transfers it in the horizontal direction, and outputs it to a signal processing circuit (not shown).

The timing control circuit 60 generates timing signals necessary for signal processing of the pixel unit 20, the vertical scanning circuit 30, the readout circuit 40, the horizontal scanning circuit 50, and the like.

As described above, the state control unit 70 sets the state under the gate electrode 205 of the transfer transistor TG-Tr during the accumulation period (exposure period) EXP in the shutter scan period PSHT and the transfer gate of the intermediate level LM to the gate electrode 205. By applying the application pulse PLST, control is performed so that the accumulation state and the non-accumulation state are mixed.
In other words, the state control unit 70 applies the pulse PLST to the gate electrode of the transfer transistor TG-Tr, thereby suppressing the depletion under the gate electrode and impairing the function of discharging excess charge during accumulation. No dark current is suppressed.
In parallel with this, the state control unit 70 intermittently sets the gate electrode of the reset transistor RST-Tr and the control line RST at a predetermined level LV during the accumulation period (exposure period) EXP during the shutter scan period PSHT. A reset gate pulse PLSR, which is a target (or periodic) voltage signal, is applied.
This suppresses depletion in the vicinity of the transfer transistor TG-Tr and further suppresses dark current.

The outline of the configuration and function of each unit of the solid-state imaging device 10 has been described above.
Next, a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the first embodiment will be described.

FIG. 7A and FIG. 7B are diagrams for explaining the read operation according to the first embodiment.
FIG. 7A shows an equivalent circuit of a pixel, and FIG. 7B shows an operation waveform.

In the shutter scan period PSHT, the control line SEL for controlling on (conductive) and off (non-conductive) of the selection transistor SEL-Tr is set to L level, and the selection transistor SEL-Tr is held in a non-conductive state.
In the shutter scan PSHT, first, for example, the control line TG is set to H level for a predetermined period while the control line RST is at H level, and the photodiode PD and the floating diffusion FD are passed through the reset transistor RST-Tr and the transfer transistor TG-Tr. Is reset.

In the accumulation period (exposure period) EXP after the reset of the photodiode PD and the floating diffusion FD, the transfer gate pulse PLST set to the intermediate level LM lower than the predetermined level LV is applied to the control line TG.
The transfer transistor TG-Tr is controlled so that the accumulation state and the non-accumulation state are mixed under the gate electrode by applying the pulse PLST to the gate electrode.
As a result, depletion under the gate electrode of the transfer transistor TG-Tr is suppressed, and dark current is suppressed without impairing the function of discharging surplus charge during accumulation.
In parallel with this, in the accumulation period (exposure period) EXP during the shutter scan period, a reset gate pulse PLSR set to a predetermined level LV is applied to the gate electrode of the reset transistor RST-Tr through the control line RST. Is done.
As a result, depletion in the vicinity of the transfer transistor TG-Tr is suppressed, and dark current is reliably suppressed.

Subsequently, the read operation shifts from the shutter scan to the read scan.
In the read scan period PRDO, as shown in FIG. 7B, in order to select a certain row in the pixel array, the control line SEL connected to each pixel PXL in the selected row is set to the H level. Thus, the selection transistor SEL-Tr of the pixel PXL is turned on.
In this selected state, as shown in FIG. 7B, the reset transistor RST-Tr is selected during the reset period PR1 while the control line RST is at the H level and becomes conductive, and the floating diffusion FD is connected to the power supply line VDD. Reset to potential.
After the reset period PR1 has elapsed (the reset transistor RST-Tr is in a non-conductive state), the period until the transfer period PT1 is started is a first read period PRD1 for reading the reset voltage Vrst in the reset state.

In the first readout period PRD1 after the reset period PR1, the reset voltage Vrst, which is the pixel readout voltage in the reset state, is read out through the vertical signal line LSGN. At this time, the reset voltage Vrst is supplied to the read circuit 40 and is held, for example.

Here, the first read period PRD1 ends and the transfer period PT1 starts.
As shown in FIG. 7B, in the transfer period PT1, the transfer transistor TG-Tr is selected during the period when the control line TG is at the high level (H) and becomes conductive, and is photoelectrically converted and stored by the photodiode PD. Charges (electrons) are transferred to the floating diffusion FD.
After the transfer period PT1 has elapsed (the transfer transistor TG-Tr is in a non-conducting state), the second read period PRD2 in which the signal voltage Vsig corresponding to the charge accumulated by photoelectric conversion of the photodiode PD is read.

As described above, after the first read period PRD1, the control line TG is set to H level for a predetermined period, and the accumulated charge of the photodiode PD is transferred to the floating diffusion FD through the transfer transistor TG-Tr. A signal voltage Vsig that is a pixel readout voltage corresponding to the electrons (charges) accumulated in the second readout period PRD2 is read out.
At this time, the signal voltage Vsig is supplied to the read circuit 40 and is held, for example.

For example, in the read circuit 40 constituting a part of the read unit 80, the difference (Vsig−) between the signal voltage Vsig read in the second read period PRD2 and the reset voltage Vrst read in the first read period PRD1. Vrst) is taken and the CDS process is performed.

As described above, according to the first embodiment, the state controller 70 changes the state under the gate electrode 205 of the transfer transistor TG-Tr during the accumulation period (exposure period) EXP in the shutter scan period. By applying a transfer gate pulse PLST of an intermediate level LM to the gate electrode 205, control is performed so that an accumulating state and an unaccumulated state are mixed.
As described above, according to the first embodiment, the state control unit 70 applies the pulse PLST to the gate electrode of the transfer transistor TG-Tr, thereby suppressing depletion under the gate electrode and It is possible to suppress the dark current without impairing the function of discharging the surplus charge, and it is possible to reduce image defects caused by the dark current from the GR center under the gate electrode, thereby improving the image quality. There is an advantage that can be realized.

FIGS. 8A to 8C are diagrams showing the relationship between the state of the depletion region in the gate bias to the gate electrode of the transfer transistor and the suppression state of dark current, blooming, and saturation.
In FIGS. 8A to 8C, a region indicated by reference sign DPL is a depletion region.

FIG. 8A shows a case where depletion under the gate electrode is suppressed by applying a negative gate bias Vg to the gate electrode of the transfer transistor TG-Tr in the first embodiment. .
In this case, since depletion in substantially the entire area under the gate electrode can be suppressed, dark current can be suppressed without impairing the function of discharging surplus charges during accumulation. However, in this case, a sufficient effect cannot be obtained for blooming.

FIG. 8B shows a case where a depletion region and a region where depletion is suppressed are mixed under the gate electrode without applying the pulse PLST or the like of the present embodiment to the gate electrode of the transfer transistor TG-Tr. ing.
FIG. 8C shows a case where a positive gate case is applied to the gate electrode of the transfer transistor TG-Tr without applying the pulse PLST of the present embodiment, and a depletion region is present in substantially the entire area under the gate electrode. Shows when to do.
In this case, since depletion in substantially the entire area under the gate electrode cannot be suppressed, saturation output is impaired and it is difficult to suppress dark current. However, a sufficient effect can be obtained for blooming.

9A to 9C show the case where a transfer gate pulse is applied to the gate electrode of the transfer transistor, the case where an intermediate voltage is applied, and the case where a pulse is applied to a substrate or the like, dark current, It is a figure which shows the relationship with the suppression state of blooming and saturation by potential transition.
FIG. 10 is a diagram illustrating that blooming is suppressed by pulsing in the photoelectric conversion characteristics.

FIG. 9A shows the depletion under the gate electrode by applying the transfer gate pulse PLST instead of the negative gate bias Vg to the gate electrode of the transfer transistor TG-Tr in the first embodiment. The case where it suppressed is shown.
In this case, since depletion in substantially the entire area under the gate electrode can be suppressed, dark current can be suppressed without impairing the function of discharging surplus charges during accumulation. In this case, unlike the case of the negative gate bias in FIG. 8A, as shown in FIG. 10, a sufficient effect for blooming can be obtained by pulsing.

FIG. 9B shows a case where a constant intermediate voltage is applied to the gate electrode of the transfer transistor TG-Tr without applying the pulse PLST of the present embodiment.
In this case, since depletion in substantially the entire area under the gate electrode cannot be suppressed, saturation output is impaired and it is difficult to suppress dark current. However, a sufficient effect can be obtained for blooming.

FIG. 9C shows a case where a pulse is applied to the other part of the gate electrode of the transfer transistor TG-Tr in the first embodiment.
In this case, it is possible to suppress dark current without impairing the function of discharging surplus charges during accumulation. However, in this case, a sufficient effect cannot be obtained for blooming.

In the first embodiment, the overflow function via the buried channel under the gate electrode can be easily realized.
FIG. 11 is a diagram for explaining that an overflow function via a buried channel under a gate electrode can be easily realized in accordance with pulsing in the first embodiment.
In FIG. 11, the horizontal axis indicates the depth of Si, and the vertical axis indicates the potential.

Conventionally, it is not easy to design the potential of the overflow path with the accumulation under the gate electrode. In particular, when charge is accumulated in the photodiode, the modulation makes the overflow bus ineffective.
In addition, a method is considered in which the potential of the floating diffusion FD is set high during the accumulation period and modulated to enable the overflow, but there are restrictions on the power supply voltage and the readout system circuit.

On the other hand, according to the first embodiment, as shown in FIG. 11, the overflow function via the buried channel under the gate electrode can be easily realized with the pulse formation.
Further, according to the first embodiment, the saturation charge amount can be adjusted to the optimum value from the outside or automatically.

Further, according to the first embodiment, the state controller 70 sets the reset transistor RST-Tr in parallel with the application of the transfer gate pulse PLST in the accumulation period (exposure period) EXP in the shutter scan period. A reset gate pulse PLSR, which is an intermittent (or periodic) voltage signal, set to a predetermined level LV through the control line RST is applied to the gate electrode.
As a result, it is possible to suppress the depletion of the region near the transfer transistor TG-Tr, further suppress the dark current, and thus further improve the image quality.

(Second Embodiment)
FIGS. 12A and 12B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the second embodiment of the present invention. It is a figure for doing.
FIG. 12A shows an equivalent circuit of a pixel, and FIG. 12B shows an operation waveform.

The second embodiment is different from the first embodiment as follows.
In the first embodiment, the state control unit applies a control line to the gate electrode of the reset transistor RST-Tr in parallel with the application of the transfer gate pulse PLST in the accumulation period (exposure period) EXP during the shutter scan period. A reset gate pulse PLSR which is an intermittent (or periodic) voltage signal set to a predetermined level LV through RST is applied.
In contrast, in the second embodiment, a constant voltage signal VR set to a predetermined level LV is applied to the gate electrode of the reset transistor RST-Tr through the control line RST.

According to the second embodiment, the same effect as that of the first embodiment described above can be obtained.

(Third embodiment)
FIGS. 13A and 13B illustrate a read operation including a control for mixing an accumulating state and an unaccumulated state by the state control unit 70 according to the third embodiment of the present invention. It is a figure for doing.
FIG. 13A shows an equivalent circuit of a pixel, and FIG. 13B shows an operation waveform.

The third embodiment is different from the first embodiment as follows.
In the third embodiment, the state control unit applies a pulse to the gate electrode of the reset transistor RST-Tr in the accumulation period (exposure period) EXP during the shutter scan period in parallel with the application of the transfer gate pulse PLST. Instead of applying, a pulse IPLSG having a phase opposite to that of the transfer gate pulse PLST is applied to the ground line (GND) in order to stabilize the potential of the substrate well.

According to the third embodiment, the potential of the substrate well can be stabilized as well as the same effect as that of the first embodiment described above.

(Fourth embodiment)
FIG. 14 is a circuit diagram illustrating an example of a pixel according to the fourth embodiment.
FIGS. 15A and 15B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the fourth embodiment of the present invention. It is a figure for doing.
FIG. 15A shows an equivalent circuit of a pixel, and FIG. 15B shows an operation waveform.

The fourth embodiment is different from the first embodiment as follows.
In the fourth embodiment, the pixel PXLA discharges the charge overflowing from the photodiode PD between the cathode side (charge storage unit side) of the photodiode PD and the power supply line VDD in addition to the configuration of FIG. For this purpose, an overflow gate transistor OFG-Tr is connected.
The gate electrode of the overflow gate transistor OFG-Tr is connected to the control line OFG, and instead of the transfer gate pulse PLST, the overflow gate pulse PLSOF of the intermediate level LM is connected to the gate electrode of the overflow gate transistor OFG-Tr through the control line OFG. Is applied.
Then, in order to stabilize the potential of the substrate well, a pulse IPLSOF having an opposite phase to the overflow gate pulse PLSOF is applied to the gate electrode of the transfer transistor TG-Tr.

According to the fourth embodiment, the potential of the substrate well can be stabilized as well as the same effect as that of the first embodiment described above.

(Fifth embodiment)
FIGS. 16A and 16B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the fifth embodiment of the present invention. It is a figure for doing.
FIG. 16A shows an equivalent circuit of a pixel, and FIG. 16B shows an operation waveform.

The fifth embodiment is different from the fourth embodiment as follows.
In the fifth embodiment, in order to stabilize the potential of the substrate well at the gate electrode of the transfer transistor TG-Tr, a constant voltage signal IVOF having a reverse phase is used instead of the pulse having a phase opposite to that of the overflow gate pulse PLSOF. Apply.

According to the fifth embodiment, the same effect as that of the fourth embodiment described above can be obtained.

(Sixth embodiment)
FIGS. 17A and 17B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the sixth embodiment of the present invention. It is a figure for doing.
FIG. 17A shows an equivalent circuit of a pixel, and FIG. 17B shows an operation waveform.

The sixth embodiment is different from the fourth embodiment as follows.
In the sixth embodiment, in order to stabilize the potential of the substrate well, instead of applying a pulse having a phase opposite to that of the overflow gate pulse PLSOF to the gate electrode of the transfer transistor TG-Tr, the overflow gate is applied to the ground line. A pulse IPLSGOF having a phase opposite to that of the pulse PLSOF is applied.

According to the sixth embodiment, the same effect as that of the fourth embodiment described above can be obtained.

(Seventh embodiment)
FIG. 18 is a circuit diagram illustrating an example of a pixel according to the seventh embodiment.
FIG. 19A and FIG. 19B illustrate a read operation including control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the seventh embodiment of the present invention. It is a figure for doing.
FIG. 19A shows an equivalent circuit of a pixel, and FIG. 19B shows an operation waveform.

The seventh embodiment is different from the first embodiment as follows.
In the seventh embodiment, the pixel PXLB has a pixel sharing structure in which one floating diffusion FD is shared by two photodiodes PD1 and PD2 and transfer transistors TG1-Tr and TG2-Tr.
The state control unit of the seventh embodiment shifts the timing of the transfer gate pulses to the gate electrodes of the shared transfer transistors TG1-Tr and TG2-Tr in order to stabilize the potential of the substrate well. PLST1 and PLST2 are applied.

According to the seventh embodiment, even in the case of the pixel sharing structure, the same effect as the effect of the first embodiment described above can be obtained.

(Eighth embodiment)
FIG. 20 is a circuit diagram illustrating an example of a pixel according to the eighth embodiment.
FIGS. 21A and 21B illustrate a read operation including a control for mixing an accumulating state and an unaccumulated state by the state control unit 70 according to the eighth embodiment of the present invention. It is a figure for doing.
FIG. 21A shows an equivalent circuit of a pixel, and FIG. 21B shows an operation waveform.

The eighth embodiment is different from the first embodiment as follows.
In the eighth embodiment, the pixel PXLC shares one floating diffusion FD with the four photodiodes PD1, PD2, PD3, PD4 and the transfer transistors TG1-Tr, TG2-Tr, TG3-T, TG4-Tr. It has a pixel sharing structure.
The state control unit of the eighth embodiment uses the gate electrodes of the shared transfer transistors TG1-Tr, TG2-Tr, TG3-Tr, and TG4-Tr to stabilize the potential of the substrate well. Transfer gate pulses PLST1, PLST2, PLST3, and PLST4 are applied at different timings.

According to the eighth embodiment, even in the case of the pixel sharing structure, the same effect as the effect of the first embodiment described above can be obtained.

(Ninth embodiment)
FIG. 22 is a circuit diagram illustrating an example of a pixel according to the ninth embodiment.
FIGS. 23A and 23B illustrate a read operation including a control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the ninth embodiment of the present invention. It is a figure for doing.
FIG. 23A shows an equivalent circuit of a pixel, and FIG. 23B shows an operation waveform.

The ninth embodiment is different from the fourth embodiment as follows.
In the ninth embodiment, the pixel PXLD shares one floating diffusion FD with two photodiodes PD1, PD2, transfer transistors TG1-Tr, TG2-Tr, and overflow gate transistors OFG1-Tr, OFG2-Tr. It has a pixel sharing structure.
The state control unit of the ninth embodiment shifts the timing of the gate electrodes of the shared overflow gate transistors OFG1-Tr and OFG2-Tr for the overflow gate in order to stabilize the potential of the substrate well. Pulses PLSOF1 and PLSOF2 are applied.

According to the ninth embodiment, even in the case of the pixel sharing structure, the same effect as that of the fourth embodiment described above can be obtained.

(Tenth embodiment)
FIG. 24 is a circuit diagram illustrating an example of a pixel according to the tenth embodiment.
FIG. 25A and FIG. 25B illustrate a read operation including control for mixing the accumulating state and the non-accumulating state by the state control unit 70 according to the tenth embodiment of the present invention. It is a figure for doing.
FIG. 25A shows an equivalent circuit of a pixel, and FIG. 25B shows an operation waveform.

The tenth embodiment is different from the fourth embodiment as follows.
In the tenth embodiment, the pixel PXLE includes one floating diffusion FD, four photodiodes PD1, PD2, PD3, PD4, transfer transistors TG1-Tr, TG2-Tr, TG3-Tr, TG4-Tr, and overflow. It has a pixel sharing structure shared by the gate transistors OFG1-Tr, OFG2-Tr, OFG3-Tr, OFG4-Tr.
The state control unit of the ninth embodiment uses the gate electrodes of the shared overflow gate transistors OFG1-Tr, OFG2-Tr, OFG3-Tr, OFG4-Tr to stabilize the potential of the substrate well. Applies the overflow gate pulses PLSOF1, PLSOF2, PLSOF3, PLSOF4 at different timings.

According to the tenth embodiment, even in the case of the pixel sharing structure, the same effect as the effect of the fourth embodiment described above can be obtained.

The solid-state imaging device 10 described above can be applied as an imaging device to an electronic apparatus such as a digital camera, a video camera, a portable terminal, a monitoring camera, or a medical endoscope camera.

FIG. 26 is a diagram illustrating an example of the configuration of an electronic apparatus equipped with a camera system to which the solid-state imaging device according to the embodiment of the present invention is applied.

As shown in FIG. 26, the electronic apparatus 100 includes a CMOS image sensor 110 to which the solid-state imaging device 10 according to the present embodiment can be applied.
The electronic device 100 further includes an optical system (lens or the like) 120 that guides incident light (forms a subject image) to the pixel region of the CMOS image sensor 110.
The electronic device 100 includes a signal processing circuit (PRC) 130 that processes an output signal of the CMOS image sensor 110.

The signal processing circuit 130 performs predetermined signal processing on the output signal of the CMOS image sensor 110.
The image signal processed by the signal processing circuit 130 can be displayed as a moving image on a monitor composed of a liquid crystal display or the like, or output to a printer, or directly recorded on a recording medium such as a memory card. Is possible.

As described above, by mounting the above-described solid-state imaging device 10 as the CMOS image sensor 110, it is possible to provide a high-performance, small, and low-cost camera system.
Electronic devices such as surveillance cameras and medical endoscope cameras are used for applications where the camera installation requirements include restrictions such as mounting size, number of connectable cables, cable length, and installation height. Can be realized.

Claims (21)

1. A photoelectric conversion element for accumulating charges generated by photoelectric conversion during the accumulation period;
   At least one charge transfer gate portion capable of transferring charges accumulated in the photoelectric conversion element;
   A solid-state imaging device comprising: a state control unit that controls at least the state under accumulation of the charge transfer gate unit and a state of non-accumulation at least during the accumulation period.
2. The state control unit
   The solid-state imaging device according to claim 1, wherein control is performed so that an accumulation state and a non-accumulation state are mixed by applying a pulse.
3. The charge transfer gate portion is
   Including a transfer transistor for transferring the charge accumulated in the photoelectric conversion element to the floating diffusion,
   The state control unit
   The solid-state imaging device according to claim 2, wherein the pulse is applied to a gate electrode of the transfer transistor at least during the accumulation period.
4. The solid-state imaging device according to claim 3, wherein a transfer electrode portion of the transfer transistor is formed by a buried channel.
5. The state control unit
   The solid-state imaging device according to claim 3, wherein a level of the pulse applied to the gate electrode of the transfer transistor is set to an intermediate level between a predetermined level and a reference level.
6. Including a reset transistor that resets the floating diffusion to a predetermined potential during a reset period;
   The state control unit
   The solid-state imaging device according to claim 3, wherein a voltage signal of a predetermined level is applied to the gate electrode of the reset transistor while applying the pulse to the gate electrode of the transfer transistor.
7. The state control unit
   The solid-state imaging device according to claim 6, wherein a reset gate pulse having the same phase as the transfer gate pulse applied to the gate electrode of the transfer transistor is applied to the gate electrode of the reset transistor.
8. The solid-state imaging device according to claim 7, wherein a level of the transfer gate pulse is smaller than a predetermined level of the reset gate pulse.
9. The state control unit
   The solid-state imaging device according to claim 3, wherein a pulse having a phase opposite to that of the pulse applied to the gate electrode of the transfer transistor is applied to the ground line.
10. The pixel portion is
    Having a pixel sharing structure in which one floating diffusion is shared by a plurality of the photoelectric conversion elements and the transfer transistors;
    The state control unit
    The solid-state imaging device according to claim 3, wherein the pulse is applied to the shared gate electrode of each transfer transistor at different timings.
11. The charge transfer gate portion is
    A transfer transistor for transferring the charge accumulated in the photoelectric conversion element to a floating diffusion;
    An overflow gate for discharging the overflowing charge from the photoelectric conversion element,
    The state control unit
    The solid-state imaging device according to claim 2, wherein the pulse is applied to at least the overflow gate among the gate electrode of the transfer transistor and the overflow gate at least during the accumulation period.
12. The state control unit
    The solid-state imaging device according to claim 11, wherein a level of the pulse applied to the gate electrode of the overflow gate is set to an intermediate level between a predetermined level and a reference level.
13. The state control unit
    The solid-state imaging device according to claim 11, wherein a pulse having a phase opposite to that of the pulse applied to the overflow gate is applied to a gate electrode of the transfer transistor.
14. The state control unit
    The solid-state imaging device according to claim 11, wherein a voltage signal having a phase opposite to that of the pulse applied to the overflow gate is applied to a gate electrode of the transfer transistor.
15. The state control unit
    The solid-state imaging device according to claim 11, wherein a pulse having a phase opposite to that of the pulse applied to the overflow gate is applied to a ground line.
16. The pixel portion is
    Having a pixel sharing structure in which one floating diffusion is shared by the plurality of photoelectric conversion elements, the transfer transistor, and the overflow gate;
    The state control unit
    The solid-state imaging device according to claim 11, wherein the pulses are applied to the shared overflow gates at different timings.
17. The solid-state imaging device according to claim 2, wherein a potential level of the pulse is adjustable.
18. A photoelectric conversion element for accumulating charges generated by photoelectric conversion during the accumulation period;
    A solid-state imaging device driving method comprising: at least one charge transfer gate portion capable of transferring charges accumulated in the photoelectric conversion element;
    A method for driving a solid-state imaging device, wherein at least the state under the gate of the charge transfer gate unit is controlled so that a state where accumulation is performed and a state where accumulation is not performed exist at least in the accumulation period.
19. The solid-state imaging device driving method according to claim 18, wherein the control is performed so that an accumulation state and a non-accumulation state are mixed by applying a pulse.
20. A solid-state imaging device;
    An optical system that forms a subject image on the solid-state imaging device,
    The solid-state imaging device
    A photoelectric conversion element for accumulating charges generated by photoelectric conversion during the accumulation period;
    At least one charge transfer gate portion capable of transferring charges accumulated in the photoelectric conversion element;
    An electronic device comprising: a state control unit that controls at least the state under accumulation of the charge transfer gate unit and a state of non-accumulation in at least the accumulation period.
21. The state control unit
    21. The electronic apparatus according to claim 20, wherein a pulse is applied so that an accumulation state and a non-accumulation state are mixed.

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