JP2008177593A - Solid-state image sensor and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a sufficient exposure time by creating a quick action through reducing restrictions exerted on the exposure time before realizing an entire-screen simultaneous shutter function using a solid-state image sensor which has a device structure as a CMOS solid-state image sensor. <P>SOLUTION: In this solid-state image sensor, a discharge Tr 215 for discharging the signal charge of an embedded PD 219 is provided separately from a transfer Tr 211 which transfers the signal charge of the PD 219 to an FD 216. Then both the channel potential which is provided when the discharge Tr 215 is turned on and the channel potential which is provided when the transfer Tr 211 is turned on are set as to be higher than the completely depleted potential of the PD 219. This makes it possible to completely transfer the signal charge of the PD 219 from both the transfer Tr 211 and the drain Tr 215, and in the operation to sequentially read out a signal charge from the FD 216 on a pixel-row basis, PD 219 exposure operation is started in a course of reading out the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device such as a CMOS image sensor having an electronic shutter function and a control method thereof.

Conventionally, many CMOS image sensors have an electronic shutter function, but unlike a CCD image sensor, a focal plane that resets a signal by sequentially scanning a large number of two-dimensionally arranged pixels for each pixel row. Since it is a shutter (rolling shutter), there is a problem that the exposure period is shifted for each screen row.
In this case, for example, when an image of a vertical object moving in the horizontal direction is taken, the image appears as if it is tilted.
FIG. 7A is an explanatory diagram showing the state. After resetting each row, an operation of transferring and outputting (signal reading) after a predetermined exposure time is sequentially performed in each row. As a result, an image obtained as a result is shown. For example, as shown in FIG. 7C, the vertical object a moving in the horizontal direction is reflected in an inclined state.

On the other hand, there are those that release the shutter at the same time for all rows. In that case, the photodiodes (PD) are simultaneously reset at a certain point in time, and after a predetermined exposure time, the charges of the PD are transferred to the floating diffusion (FD) at the same time for all the rows. This FD signal is output in order line by line.
FIG. 7B is an explanatory diagram showing the situation. After all the rows are collectively reset, all the rows are transferred simultaneously, and then output is performed for each row. By doing so, as shown in FIG. 7D, for example, even when a vertically straight object a moving in the horizontal direction is photographed, it is reflected straight.

  In addition, as a pixel circuit configuration for simultaneously resetting the signal charges of the photodiodes (PD) of all the pixels with a CMOS type image sensor, a transistor that can discharge the surplus charges of the PD directly to the drain without passing through the FD ( A device having a discharge Tr) has also been proposed (see Patent Document 1).

JP 2001-238132 A

However, the all-pixel shutter CMOS image sensor shown in FIG. 7B has the following problems.
(1) Light is leaked into the FD between the transfer of all rows at the same time and the output sequentially for each pixel row, the amount of which differs between the first output row and the later output row. make worse.
(2) Since the PD is reset after the information of all rows is output, the exposure cannot be performed until the information of all rows is output one by one after the transfer of all rows at the same time, and time is wasted. Further, since it is difficult to increase the exposure time, the sensitivity is lowered when the subject is dark.

Hereinafter, these problems will be described in detail.
First, with regard to (1), since the time length from transfer to output differs between the first output line and the last output line by one frame read time, the amount of light leaking into the FD is also the first. Although it is almost 0 in the row, in the last row, there is a leakage amount for one frame reading time.
Since the FD also performs photoelectric conversion, a charge corresponding to the amount of light accumulates in the FD, and this is added to the signal charge transferred from the PD.
This not only causes noise and shading, but also exceeds the saturation signal amount when the light is strong, and causes overexposure. As described above, leakage of light into the FD significantly deteriorates the captured image.

This will be described with reference to FIGS.
First, FIG. 8 is a cross-sectional view showing the structure of the peripheral portion of a photodiode of a conventional CCD type solid-state imaging device.
In this CCD type solid-state imaging device, a photodiode (PD) 12, a read channel portion 14, a channel stop portion 16, a vertical transfer register 18, and the like are formed on the upper layer portion of the semiconductor substrate 10, and a gate insulating film is formed on the upper surface of the semiconductor substrate 10. A polysilicon transfer electrode 22 is disposed via 20, and a light shielding film 26 is disposed above the polysilicon transfer electrode 22 via an insulating film 24.
In the light shielding film 26, an opening 26A corresponding to the light receiving surface of the PD 12 is formed. Further, a planarizing film (upper insulating film) 28 is formed on the light shielding film 26, and a color filter 30 and a microlens 32 are mounted thereon.

In such a CCD type solid-state imaging device, the photocharge of the PD 12 is simultaneously transferred to the vertical transfer register 18 through the read channel section 14.
Thereafter, the photoelectric charges are carried line by line to the output amplifier section (not shown) by the CCD of the vertical transfer register 18 and output.
As shown in the figure, in the CCD type solid-state imaging device, a metal layer such as aluminum serving as the light shielding film 26 is dropped to the immediate vicinity of the PD 12 so that light does not leak into the vertical transfer register 18. Nevertheless, a slight amount of light leaks into the vertical transfer register 18, which causes vertical streak-like image deterioration called smear.

Next, FIG. 9 is a cross-sectional view showing the structure of the peripheral portion of a photodiode of a conventional CMOS solid-state imaging device.
In this CMOS type solid-state imaging device, P well regions 42 and 44 as element forming regions are formed in an upper layer portion of a semiconductor substrate (N type silicon substrate) 40, and PD 46 and various gate elements are provided in the P well regions 42 and 44. Is formed. In the illustrated example, a PD 46, a transfer gate (MOS transistor) 48, and an FD 50 are formed in the P well region 42, and a MOS transistor 52 in the peripheral circuit portion is formed in the P well region 44.
A polysilicon transfer electrode 56 for each gate is formed on the semiconductor substrate 40 via a gate insulating film 54, and multilayer wiring layers 60, 62, 64 are formed on the upper layer via an interlayer insulating film 58. Has been. The wiring film of the upper layer film 64 of this multilayer wiring layer is formed as a light shielding film.
On the multilayer wiring layer, a color filter 72 and a microlens 74 are arranged via a protective film (SiN) 70.

As described above, in the CMOS type solid-state imaging device, the pixels are formed using the same CMOS process as that of the peripheral circuit. Therefore, the light shielding film (wiring layer 64) cannot be dropped to the immediate vicinity of the PD 46, and light is incident only on the PD 46. I can't make a structure.
Moreover, since there are many metal wiring layers, light is irregularly reflected in each layer. For this reason, as can be seen from FIG. 9, a larger amount of light leaks into the FD 50 than in the case of the CCD solid-state imaging device.
As described above, the CMOS type solid-state imaging device has a problem that image deterioration is severe when all rows are transferred simultaneously.

Next, regarding (2) above, the PD is reset by discharging the charge of the PD to the FD. At this time, if the signal is held in the FD, the signal is broken. Therefore, the PD cannot be reset unless the FD signals of all rows are read out.
Therefore, as disclosed in Patent Document 1 described above, there is a CMOS sensor including a transistor (discharge Tr) that can discharge the surplus charge of PD directly to the drain without passing through the FD. It is necessary to reset the PD via the FD. Therefore, if the PD is not reset after reading the FD signals of all rows, the image deteriorates.
This is because the transfer Tr for transferring the charge of the PD to the FD and the characteristics of the discharge Tr, such as the threshold value, cannot be perfectly aligned. Therefore, if the PD is reset by the discharge Tr at the beginning of the accumulation period, the end of the accumulation period is reached. This is because, when the charge is transferred to the FD by the transfer Tr, the PD is not returned to the reset state, and the difference causes problems such as fixed pattern noise and afterimage that cannot be removed by a later circuit.
Therefore, in order to obtain a good image, the PD cannot be reset until the FD signals of all rows are read out, and the exposure period cannot be performed, so that sensitivity is lowered.

Furthermore, if the PD is reset by the discharge Tr during reading of the FD signal, the pixel state is slightly different before and after the PD reset, in addition to the above problem, and the portion of the captured image is the same. It turned out that there was also a problem that the horizontal stripes could be seen.
Further, it has been found that if there is a drain Tr, a dark current is generated from the oxide film interface under the gate and flows into the PD.

  Accordingly, an object of the present invention is to reduce the restriction of exposure time and realize quick operation when a full-screen simultaneous shutter function is realized using a solid-state image sensor having an element structure such as the above-described CMOS type solid-state image sensor. It is an object of the present invention to provide a solid-state imaging device capable of ensuring a sufficient exposure time, relatively reducing the amount of noise due to light leakage, and performing a good image output, and a control method thereof.

  In order to achieve the above-described object, the present invention provides a solid-state imaging device including an imaging region unit provided with a plurality of pixels and a processing circuit unit that processes an image signal output from the imaging region unit. A photoelectric conversion element that generates a signal charge according to the amount of received light, a floating diffusion unit that detects the amount of signal charge generated by the photoelectric conversion element, and a signal charge generated by the photoelectric conversion element to the floating diffusion unit A transfer transistor for transferring, and a discharge transistor for discharging the signal charge generated by the photoelectric conversion element, the photoelectric conversion element from a first conductivity type high-concentration impurity layer formed on the outermost surface of the semiconductor substrate And a charge storage region comprising a second conductivity type impurity layer formed under the charge separation region. The channel potential when the discharge transistor is turned on and the channel potential when the transfer transistor is turned on are both set to be higher than the fully depleted potential of the photodiode. It is characterized by.

  The present invention further includes an imaging region unit provided with a plurality of pixels, and a processing circuit unit that processes an image signal output from the imaging region unit, and the pixels have signal charges corresponding to the amount of received light. A photoelectric conversion element to be generated; a floating diffusion portion that detects a signal charge amount generated by the photoelectric conversion element; a transfer transistor that transfers the signal charge generated by the photoelectric conversion element to the floating diffusion portion; A discharge transistor for discharging the signal charge generated by the conversion element, wherein the photoelectric conversion element includes a charge separation region formed of a first conductivity type high-concentration impurity layer formed on an outermost surface of a semiconductor substrate, and the charge Formed from a buried photodiode having a charge storage region made of a second conductivity type impurity layer formed under the isolation region. The solid-state imaging device control method is such that both the channel potential when the discharge transistor is turned on and the channel potential when the transfer transistor is turned on are higher than the fully depleted potential of the photodiode. Setting, enabling the signal charge of the photodiode to be completely transferred from both the transfer transistor and the discharge transistor, and starting the exposure operation of the photodiode in the middle of reading the signal charge from the floating diffusion portion. .

  According to the present invention, in the camera device that outputs an image picked up by a solid-state image pickup device, the solid-state image pickup device performs processing of an image pickup area section provided with a plurality of pixels and an image signal output from the image pickup area section. A processing circuit unit, and the pixel includes a photoelectric conversion element that generates a signal charge according to a received light amount, a floating diffusion unit that detects a signal charge amount generated by the photoelectric conversion element, and the photoelectric conversion element A transfer transistor that transfers the signal charge generated by the photoelectric conversion element to the floating diffusion portion, and a discharge transistor that discharges the signal charge generated by the photoelectric conversion element. The photoelectric conversion element is disposed on the outermost surface of the semiconductor substrate. A charge separation region formed of a first conductivity type high-concentration impurity layer and a lower layer of the charge separation region are formed. It is formed of a buried photodiode having a charge accumulation region composed of a two-conductivity type impurity layer, and both the channel potential when the discharge transistor is turned on and the channel potential when the transfer transistor is turned on are completely connected to the photodiode. It is characterized by being set to be higher than the depletion potential.

  In the solid-state imaging device and the control method thereof according to the present invention, the signal charge of the embedded photodiode is discharged separately from the transfer transistor that transfers the signal charge of the embedded photodiode serving as the photoelectric conversion element of each pixel to the floating diffusion portion. By providing a drain transistor and setting both the channel potential when the drain transistor is turned on and the channel potential when the transfer transistor is turned on to be higher than the fully depleted potential of the photodiode, The charge can be completely transferred from both the transfer transistor and the discharge transistor.

Therefore, in order to perform photographing without tilting the moving subject, after performing all-pixel simultaneous shutter operation and transfer operation, in the operation of sequentially reading out the signal charges in units of pixel rows from the floating diffusion portion, the photodiode is started from the middle of the readout The exposure operation can be started, and a sufficient exposure time can be secured with a quick operation, and a high-sensitivity and good image output can be realized. In addition, by securing a sufficient exposure time, the amount of noise due to light leakage can be relatively reduced, and a favorable image output can be realized also in this respect.
Similarly, in a camera device equipped with such a solid-state imaging device, a sufficient exposure time can be ensured and high-sensitivity and good image output can be realized.

Embodiments of a solid-state imaging device, a camera device, and a control method thereof according to the present invention will be described below.
This embodiment has an element structure in which a discharge gate and a transfer gate are provided on both sides of a PD of a CMOS solid-state imaging device, and the charge accumulated in the PD can be completely reset and transferred by both the discharge gate and the transfer gate. By doing so, the accumulation can be started from the middle of reading the FD signal.
Further, by applying a negative voltage to the discharge gate and the transfer gate, dark current is prevented.

FIG. 1 is a block diagram showing a configuration example of a camera system according to an embodiment of the present invention.
This camera system includes an imaging lens system 101, a solid-state imaging device 102, an analog circuit 103, an A / D converter 104, a camera signal processing circuit 105, a compression / decompression circuit 106, and a storage medium 107.
First, the light ray incident from the imaging lens system 101 forms an image on the two-dimensional pixel array of the solid-state imaging device 102. The solid-state image sensor 102 is an element such as a CMOS image sensor, and has an all-pixel simultaneous shutter function (reset / FD transfer) and a function of sequentially reading out rows from the FD, which are features of the present embodiment.

The analog circuit 103 performs processing such as CDS (correlated double sampling) and AGC (auto gain control). The image signal processed by the analog circuit 103 is converted from analog data to digital data by the A / D converter 104 and output to the camera signal processing circuit 105.
The camera signal processing circuit 105 is a circuit that performs signal processing such as color signal processing, gain control processing, and white balance processing for converting the output data of the solid-state imaging device 102 into a video signal.
The compression / decompression circuit 106 is a circuit that compresses or decompresses the image data processed by the camera signal processing circuit 105 and converts the image into a format that can be stored in the storage medium 107. The storage medium 107 is, for example, a memory stick and is an example of a unit that outputs image data, but may be, for example, a display panel or various networks.

FIG. 2 is a block diagram illustrating a configuration example of the solid-state imaging device 102 and the analog circuit 103 illustrated in FIG.
As shown in the figure, the solid-state imaging device of this example includes a pixel unit (imaging region unit) 210, a constant current unit 220, a column signal processing unit (column unit) 230, and a vertical (V) selection driving unit on a semiconductor element substrate 200. 240, a horizontal (H) selection unit 250, a horizontal signal line 260, an output processing unit 270, a timing generator (TG) 280, and the like.
The pixel unit 210 has a large number of pixels arranged in a two-dimensional matrix, and a pixel circuit as shown in FIG. 3 is provided for each pixel. The signal of each pixel from the pixel unit 210 is output to the column signal processing unit 230 through a vertical signal line (not shown in FIG. 2) for each pixel column.
In the constant current section 220, a constant current source (not shown in FIG. 2) for supplying a bias current to each pixel is arranged for each pixel column.
The V selection driving unit 240 selects each pixel of the pixel unit 210 one row at a time, and drives and controls the shutter operation and readout operation of each pixel.

The column signal processing unit 230 receives the signal of each pixel obtained through the vertical signal line one row at a time, performs predetermined signal processing for each column, and temporarily holds the signal. For example, CDS (removing fixed pattern noise caused by variations in threshold values of pixel transistors) processing, AGC (auto gain control) processing, A / D conversion processing, and the like are appropriately performed.
The H selection unit 250 selects the signals of the column signal processing unit 230 one by one and guides them to the horizontal signal line 260.
The output processing unit 270 performs predetermined processing on the signal from the horizontal signal line 160 and outputs the signal to the outside, and has, for example, a gain control circuit and a color processing circuit. Instead of performing A / D conversion by the column signal processing unit 230, it may be performed by the output processing unit 270.
The timing generator 280 supplies various pulse signals necessary for the operation of each unit based on the reference clock.

FIG. 3 is a circuit diagram showing a configuration example of a pixel circuit provided in each pixel of the solid-state imaging device shown in FIG.
In the configuration shown in the figure, a photodiode (PD) 219 and five pixel transistors (Tr) 211, 212, 213, 214, and 215 for transfer, amplification, selection, reset, and discharge are provided in each pixel.
The PD 219 accumulates electrons generated by photoelectric conversion, and transfers the electrons of the PD 219 to the floating diffusion (FD) 216 by turning on the transfer Tr 211. Since the FD 216 has a parasitic capacitance, photoelectrons are stored here.

The amplifying Tr 212 has a gate connected to the FD 216 and converts a potential fluctuation of the FD 216 into an electric signal. The selection Tr 213 selects a pixel from which a signal is read out in units of rows. When the selection Tr 213 is turned on, the amplification Tr 212 and the constant current source 218 connected to the vertical signal line 217 outside the pixel form a source follower. Therefore, a voltage interlocked with the voltage of the FD 216 is output to the vertical signal line.
The reset Tr 214 resets the potential of the FD 216 to the wiring of Vdd.
The discharge Tr 215 directly resets the photoelectrons of the PD 219 to the wiring of the power supply Vdd. The wiring of the power supply Vdd is common to all pixels.

Further, the wirings 211A, 213A, and 214A of the transfer Tr 211, the selection Tr 213, and the reset Tr 214 extend in the horizontal direction (horizontal = row direction), and simultaneously drive pixels included in the same row. Thereby, it is possible to cope with driving of the focal plane shutter.
Further, the wiring 215A of the discharge Tr 215 extends vertically, but is short-circuited at the upper and lower ends of the pixel portion, and is common to all the pixels.

Next, as the PD 219, an embedded PD is used. For example, in the case of a photodiode in a P-well, the buried PD is a p-type region in the vicinity of the interface of the gate oxide film, and an n-type region is formed thereunder. Since the interface is covered with the p + region, dark current generated at the interface can be prevented.
In addition, if the design of the transfer Tr 211 and the PD 219 is appropriate, all the photoelectrons of the PD 219 can be transferred to the FD 216, which is a structure widely used in CCD sensors. For example, it is commercialized under the name HAD (Hole Accumulation Diode).

In the CMOS solid-state imaging device having such a configuration, the feature of this example is that both the channel potential when the discharge Tr 215 is turned on and the channel potential when the transfer Tr 211 is turned on are embedded. That is, the gate voltage and threshold value of each Tr 211 and 215 and the dose amount of PD 219 are adjusted so as to be higher than the fully depleted potential of PD 219.
Thereby, the transfer Tr 211 can transfer almost all the photoelectrons of the PD 219 to the FD 216, and the discharge Tr 215 can discharge almost all of the photoelectrons of the PD 219 to the drain.
Here, “substantially all” means that in the case of an image that can be appreciated by a human being such as a digital camera, it is sufficient that the number of remaining electrons is about 20 or less.

In general, it is difficult to provide two Trs with a characteristic that allows complete transfer of both Trs for one embedded PD. There is already a transfer Tr that can be completely transferred. Therefore, in this example, the gate voltage when the discharge Tr 215 is ON is set higher than the transfer Tr 211 so that complete transfer can be performed here.
In particular, it is preferable to make this higher than the power supply voltage of the digital circuit on-chip on the solid-state image sensor. For this purpose, another power supply is supplied from the outside of the solid-state image sensor or a booster circuit is provided inside. it can.

In addition, in the solid-state imaging device having the above-described structure, the inventors have applied a negative voltage of, for example, -1 V (here, referred to as a transfer bias voltage) when the transfer gate electrode is turned off, so that It has been proposed to suppress a dark current from the interface (a current whose component is electrons flowing into the PD even when no light is incident).
This is because, by biasing the transfer gate electrode to a negative voltage, a P-type channel is formed at the interface of the gate oxide film in the transfer gate portion, and dark current from the interface state can be prevented like the buried PD. is there.
Therefore, in the present embodiment, a negative voltage is applied to the gate electrode of the transfer Tr and a negative voltage (herein referred to as “discharge bias voltage”) is applied to the gate electrode of the discharge Tr as well, so that both Tr The dark current in is properly removed. The reference 0V is GND, and the P well region is also 0V.
It was confirmed by actual measurement that applying the negative voltage to the gate electrode of the discharge Tr as described above can obtain the same effect as when applying the negative voltage to the gate electrode of the transfer Tr.

Next, the operation of the solid-state imaging device according to this embodiment will be described.
FIG. 4 is a timing chart showing the operation of the solid-state imaging device of this example.
First, the FD 216 is reset and the photoelectrons of the PD 219 are transferred to the FD 216 at the same time for all rows. Specifically, for example, a pulse is input to the reset wiring 214A of all rows to reset the FD 216 of all pixels, and a pulse is further applied to the transfer wiring 211A of all rows to transfer the photoelectrons of the PD 219 of all pixels to the FD 216.
Then, the signal of the FD 216 is read line by line. Here, since the period of one frame is determined to be a certain fixed period such as 1/30 seconds, the time is adjusted by dummy output or the like after all the rows are read out.

As described above, in the prior art, the exposure period can be taken only in this dummy period after reading out all rows. In this example, the exposure period can be set from the time when one row is still being read out. The details will be described below.
Here, the nth row of one frame is the non-exposure period, and the subsequent frames are the exposure period. The operation up to the (n-1) th row, the operation of the nth row, and the operation after the (n + 1) th row will be sequentially described.

(1) To the n-1th line:
When the selection Tr 213 is turned on, a voltage corresponding to the potential of the FD 216 in that row is output to the vertical signal line 217. This signal is taken into the column signal processing circuit 230 by the sample hold pulse SHD supplied to the column signal processing circuit 230. Then, a reset pulse is input to reset the FD 216 in that row.
As a result, a voltage corresponding to the reset potential of the FD 216 is output to the vertical signal line 217, and this is again taken into the column signal processing circuit 230 by the sample hold pulse SHR supplied to the column signal processing circuit 230.
Since these differences are signals, the column signal processing circuit 230 takes the difference or performs the signal processing as described above.
The discharge Tr 215 is OFF during the reading period to the column signal processing circuit 230 and is turned ON at other times, and discharges the electrons of the PD 219 to the drain. Since all the pixels are connected to the gate of the discharge Tr 215 as described above, all the PDs 219 are reset.

(2) Line n:
The signal read operation is the same. The discharge Tr 215 is always OFF with this line as a boundary. From here, the photoelectrons of the PD 219 remain in the PD 219, and the exposure period begins.
(3) From the (n + 1) th line:
The signal read operation is the same. Further, the discharge Tr 215 is always OFF.

FIG. 5 is a cross-sectional view showing the structure of the PD of the solid-state imaging device and its peripheral portion in this example.
This solid-state imaging device is obtained by forming each element in a P well region 310 provided on a silicon substrate 300. FIG. 5 shows a region where PD 219, FD 216, transfer Tr 211, reset Tr 214, and discharge Tr 215 are formed. .
The PD 219 is a buried type (HAD structure) PD having a p + region 219A formed on the outermost surface of the silicon substrate 300 and an n region 219B formed in the lower layer.
The FD 216 includes an n + region formed on the side of the PD 219 via a transfer gate portion (transfer Tr 211).

The transfer Tr 211 has a transfer gate portion that is an intermediate region between the PD 219 and the FD 216, and a transfer electrode 211 B made of a polysilicon film is formed on the upper surface of the silicon substrate 300 via a gate insulating film 320.
The reset Tr 214 has a region opposite to the transfer Tr 211 of the FD 216 as a reset gate portion, and a reset electrode 214B made of a polysilicon film is formed on the upper surface of the silicon substrate 300 via a gate insulating film 320. The signal charge is discharged to the drain 214C. The drain 214C is connected to the wiring of the power source Vdd via a contact or the like (not shown).

The discharge Tr 215 is obtained by forming a discharge electrode 215 B made of a polysilicon film on the upper surface of the silicon substrate 300 via a gate insulating film 320, using the region opposite to the transfer Tr 211 of the PD 219 as a discharge gate portion. The signal charge is output to the drain 215C. The drain 215C is connected to the wiring of the power source Vdd via a contact or the like (not shown).
Note that an upper layer stack is provided above the electrodes 211B, 214B, and 215B with an insulating film 330 interposed therebetween, but the description is omitted because it is not directly related to the present invention.

FIG. 6 is an explanatory diagram showing potential transition at the time of charge reading in such a solid-state imaging device, and shows a positive potential in the downward direction.
FIG. 6A shows the potential immediately after all pixels are reset, and photocharges are gradually accumulated in each PD 219. In FIG. 6B, the transfer Tr 211 is turned on, the channel voltage of the transfer gate is set to Va, and the photocharge of the PD 219 is moved to the FD 216.
FIG. 6 (3) shows the state of the non-exposure time after the transfer. The discharge Tr 215 remains OFF, and photocharges are gradually accumulated in each PD 219.
Next, FIG. 6 (4) shows a state in which the discharge Tr 215 is turned on. The channel voltage of the discharge gate is set to Vb, and the photocharge of the PD 219 is output to the drain 215 C of the discharge Tr 215. Note that the characteristics of the transfer Tr 211 and the discharge Tr 215 cannot be completely matched, and Vb and Va have different values (Vb> Va (downward in FIG. 6) in the illustrated example).

The first feature of the present embodiment as described above is that the PD 219 has an HAD structure, the channel voltage when the discharge Tr 215 is ON is higher than the depletion potential of the PD 219, and almost all electrons of the PD 219 are discharged. It can be done. As a result, the residual electrons of the PD 219 become almost zero, so that even if the characteristics of the discharge Tr 215 vary, the initial state of the PD 219 does not vary greatly.
The second feature is that the channel voltage when the transfer Tr 211 is ON is also higher than the depletion potential of the PD 219, and almost all electrons of the PD 219 can be transferred. As a result, the residual electrons of the PD 219 become almost zero, so that even if the characteristics of the transfer Tr 211 vary, there is no great variation in the state after the transfer of the PD 219.

Due to these two feature points, the state of PD 219 at the start of storage and the state after transfer are substantially equal, so that a good image signal can be obtained even though both are defined by different transistors.
Therefore, it is possible to define the start of exposure by the discharge Tr 215 while avoiding deterioration of the image quality. Therefore, the exposure can be started when the signal of the FD 216 is still read line by line.
The value of the exposure start line n can be variably controlled according to the brightness of the subject, and the exposure start can be set in any period of one frame.
Note that during reading to the column signal processing circuit 230, the discharge Tr 215 is turned OFF even during the non-exposure period. If it is ON at this time, the output of the pixel is subtly affected. As a result, in the output image, the signals from the n-th row are slightly different from those up to the n-th row, and a horizontal stripe is seen there. In order to prevent this, the discharge Tr 215 is turned off at least during the output of the pixels in the non-exposure period as in the exposure period.

The following effects can be obtained when realizing the so-called simultaneous shutter in which the start and end of the exposure period of the entire screen are the same in the CMOS sensor by the above configuration and operation.
(1) Image deterioration can be prevented even if PD is reset in the middle of outputting all lines of information. Therefore, even after all lines of information are transferred simultaneously, all lines of information are output one line at a time. It can be used during the exposure period while avoiding deterioration in image quality, and the sensitivity can be increased with sufficient exposure time.
(2) It is possible to prevent horizontal lines from entering the captured image during the operation according to (1) above.
(3) By setting the gate voltage when the discharge Tr is OFF in addition to the transfer Tr to a negative voltage, the dark current can be greatly reduced.

Although the above description has been given of the configuration and operation of a CMOS solid-state image sensor provided in the camera apparatus, the present invention can be similarly implemented as a single solid-state image sensor and its control method.
Further, it is possible to select and use the all-pixel simultaneous shutter operation and the conventional focal plane shutter operation described above, and it is also possible to provide an operation key or the like that can be selected by the user as a selection means. .
Further, the above-described exposure time can also be used as a selection means by providing an operation key or the like that can be appropriately selected by the user, and the above-described exposure start line is selected according to the exposure time selected by the user. It is possible to perform such control.

  As described above, in the solid-state imaging device and the control method thereof according to the present invention, the embedded photodiode is separated from the transfer transistor that transfers the signal charge of the embedded photodiode serving as the photoelectric conversion element of each pixel to the floating diffusion portion. A discharge transistor for discharging signal charges is provided, and both the channel potential when the discharge transistor is turned on and the channel potential when the transfer transistor is turned on are set to be higher than the fully depleted potential of the photodiode. As a result, the signal charge of the photodiode can be completely transferred from both the transfer transistor and the discharge transistor.

Therefore, in order to perform photographing without tilting the moving subject, after performing all-pixel simultaneous shutter operation and transfer operation, in the operation of sequentially reading out the signal charges in units of pixel rows from the floating diffusion portion, the photodiode is started from the middle of the readout The exposure operation can be started, and a sufficient exposure time can be secured with a quick operation, and a high-sensitivity and good image output can be realized. In addition, by securing a sufficient exposure time, the amount of noise due to light leakage can be relatively reduced, and a favorable image output can be realized also in this respect.
Similarly, in a camera device equipped with such a solid-state imaging device, a sufficient exposure time can be ensured and high-sensitivity and good image output can be realized.

It is a block diagram which shows the structural example of the camera system of the embodiment of this invention. It is a block diagram which shows the structural example of the solid-state image sensor and analog circuit of the camera system shown in FIG. FIG. 3 is a circuit diagram illustrating a configuration example of a pixel circuit provided in each pixel of the solid-state imaging device illustrated in FIG. 2. 3 is a timing chart showing the operation of the solid-state imaging device shown in FIG. It is sectional drawing which shows PD of the solid-state image sensor shown in FIG. 2, and the structure of its peripheral part. FIG. 3 is an explanatory diagram showing a potential transition at the time of charge reading in the solid-state imaging device shown in FIG. 2. It is explanatory drawing which shows two types of examples, the conventional shutter operation | movement and signal read-out operation | movement, and an output image. It is sectional drawing which shows the laminated structure of the conventional CCD type solid-state image sensor. It is sectional drawing which shows the laminated structure of the conventional CMOS type solid-state image sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Imaging lens system, 102 ... Solid-state image sensor, 103 ... Analog circuit, 104 ... A / D converter, 105 ... Camera signal processing circuit, 106 ... Compression / decompression circuit, 107 ... Storage medium, 211 Transfer Tr, 212 ... Amplification Tr, 213 ... Selection Tr, 214 ... Reset Tr, 215 ... Discharge Tr, 216 ... FD, 219 ... Embedded PD.

Claims (26)

In a solid-state imaging device having an imaging region unit provided with a plurality of pixels, and a processing circuit unit that processes an image signal output from the imaging region unit,
The pixel includes a photoelectric conversion element that generates a signal charge according to a received light amount, a floating diffusion unit that detects a signal charge amount generated by the photoelectric conversion element, and a signal charge generated by the photoelectric conversion element. A transfer transistor for transferring to the floating diffusion portion, and a discharge transistor for discharging the signal charge generated by the photoelectric conversion element,
The photoelectric conversion element includes a charge separation region formed of a first conductivity type high concentration impurity layer formed on an outermost surface of a semiconductor substrate, and a charge accumulation formed of a second conductivity type impurity layer formed below the charge separation region. An embedded photodiode having a region,
Both the channel potential when the discharge transistor was turned on and the channel potential when the transfer transistor was turned on were set to be higher than the fully depleted potential of the photodiode.
A solid-state imaging device.   A reset transistor that resets a signal charge of the floating diffusion portion; an amplification transistor that outputs an electric signal corresponding to a potential of the floating diffusion portion; and a selection transistor that selectively activates the amplification transistor. The solid-state imaging device according to claim 1.   A transfer bias voltage for forming a first conductivity type channel layer at the interface of the gate insulating film of the transfer transistor is applied to the gate electrode of the transfer transistor during a charge accumulation period in the photoelectric conversion element, The discharge bias voltage for forming the first conductivity type channel layer at the interface of the gate insulating film of the discharge transistor is applied to the gate electrode during a charge accumulation period in the photoelectric conversion element. The solid-state imaging device according to 1.   After simultaneously resetting the floating diffusion portions of all the pixels in the imaging region portion, the signal charges of the photodiodes of all the pixels are simultaneously transferred to the floating diffusion portion, and then the signal charges transferred to the floating diffusion portion are transferred to each pixel row. The discharge transistor is turned on until the read operation proceeds to a predetermined exposure start row, the signal charges of the photodiodes of all the pixels are discharged, and the discharge transistor is reached when the predetermined exposure start row is reached. The solid-state image pickup device according to claim 1, wherein exposure to all pixels is started.   The remaining charge of the photodiode immediately after transferring the signal charge of the photodiode to the floating diffusion portion by the transfer transistor is 20 charges or less, and the photodiode after discharging the signal charge of the photodiode by the discharge transistor The solid-state imaging device according to claim 4, wherein the residual charge is 20 charges or less.   5. The solid-state imaging device according to claim 4, wherein a gate voltage level when the discharge transistor is ON is higher than a gate voltage level when the transfer transistor is ON.   5. The solid-state image pickup device according to claim 4, wherein a gate voltage level when the discharge transistor is ON is higher than a power supply voltage of a digital circuit mounted on the solid-state image pickup device.   5. The solid-state imaging device according to claim 4, wherein the discharge transistor is turned off during an operation of reading the signal charge of the floating diffusion portion in a pixel row before the exposure start row.   Each transfer transistor, reset transistor, and amplification transistor gate wiring is provided in a direction along a pixel row, and is driven for each pixel row, and the discharge transistor gate wiring is provided in a direction along a pixel column, The solid-state imaging device according to claim 2, further short-circuited in common to all pixels outside the imaging region portion. An imaging region unit provided with a plurality of pixels, and a processing circuit unit for processing an image signal output from the imaging region unit,
The pixel includes a photoelectric conversion element that generates a signal charge according to a received light amount, a floating diffusion unit that detects a signal charge amount generated by the photoelectric conversion element, and a signal charge generated by the photoelectric conversion element. A transfer transistor for transferring to the floating diffusion portion, and a discharge transistor for discharging the signal charge generated by the photoelectric conversion element,
The photoelectric conversion element includes a charge separation region formed of a first conductivity type high concentration impurity layer formed on an outermost surface of a semiconductor substrate, and a charge accumulation formed of a second conductivity type impurity layer formed below the charge separation region. A method for controlling a solid-state imaging device formed from an embedded photodiode having a region,
Both the channel potential when the drain transistor is turned on and the channel potential when the transfer transistor is turned on are set to be higher than the fully depleted potential of the photodiode,
The signal charge of the photodiode can be completely transferred from both the transfer transistor and the discharge transistor, and the exposure operation of the photodiode is started in the middle of reading the signal charge from the floating diffusion portion.
A method for controlling a solid-state imaging device.   After simultaneously resetting the floating diffusion portions of all the pixels in the imaging region portion, the signal charges of the photodiodes of all the pixels are simultaneously transferred to the floating diffusion portion, and then the signal charges transferred to the floating diffusion portion are transferred to each pixel row. The discharge transistor is turned on until the read operation proceeds to a predetermined exposure start row, the signal charges of the photodiodes of all the pixels are discharged, and the discharge transistor is reached when the predetermined exposure start row is reached. The solid-state imaging device control method according to claim 10, wherein exposure to all pixels is started.   The remaining charge of the photodiode immediately after transferring the signal charge of the photodiode to the floating diffusion portion by the transfer transistor is 20 charges or less, and the photodiode after discharging the signal charge of the photodiode by the discharge transistor The method for controlling a solid-state imaging device according to claim 11, wherein the residual charge is 20 charges or less.   12. The method of controlling a solid-state imaging device according to claim 11, wherein a gate voltage level when the discharge transistor is ON is higher than a gate voltage level when the transfer transistor is ON.   12. The method of controlling a solid-state image pickup device according to claim 11, wherein the gate voltage level when the discharge transistor is ON is higher than a power supply voltage of a digital circuit mounted on the solid-state image pickup device.   12. The method of controlling a solid-state imaging device according to claim 11, wherein the discharge transistor is turned off during the operation of reading the signal charge of the floating diffusion portion in the pixel before the exposure start row. In a camera device that outputs an image captured by a solid-state image sensor,
The solid-state imaging device includes an imaging region unit provided with a plurality of pixels, and a processing circuit unit that processes an image signal output from the imaging region unit,
The pixel includes a photoelectric conversion element that generates a signal charge according to a received light amount, a floating diffusion unit that detects a signal charge amount generated by the photoelectric conversion element, and a signal charge generated by the photoelectric conversion element. A transfer transistor for transferring to the floating diffusion portion, and a discharge transistor for discharging the signal charge generated by the photoelectric conversion element,
The photoelectric conversion element includes a charge separation region formed of a first conductivity type high concentration impurity layer formed on an outermost surface of a semiconductor substrate, and a charge accumulation formed of a second conductivity type impurity layer formed below the charge separation region. An embedded photodiode having a region,
Both the channel potential when the discharge transistor was turned on and the channel potential when the transfer transistor was turned on were set to be higher than the fully depleted potential of the photodiode.
A camera device characterized by that.   The solid-state imaging device includes a reset transistor that resets a signal charge of the floating diffusion portion, an amplification transistor that outputs an electric signal corresponding to the potential of the floating diffusion portion, and a selection transistor that selectively activates the amplification transistor The camera apparatus according to claim 16, further comprising:   In the solid-state imaging device, a transfer bias voltage for forming a first conductivity type channel layer at the interface of the gate insulating film of the transfer transistor is applied to the gate electrode of the transfer transistor during a charge accumulation period in the photoelectric conversion device. The discharge bias voltage for forming the first conductivity type channel layer at the interface of the gate insulating film of the discharge transistor is applied to the gate electrode of the discharge transistor during the charge accumulation period of the photoelectric conversion element. The camera device according to claim 16.   The solid-state imaging device simultaneously resets the floating diffusion portions of all the pixels in the imaging region portion, and then simultaneously transfers the signal charges of the photodiodes of all the pixels to the floating diffusion portion, and then transferred to the floating diffusion portion. The signal charge is read out for each pixel row, and the discharge transistor is turned on until the reading operation proceeds to a predetermined exposure start row, the signal charges of the photodiodes of all the pixels are discharged, and the operation proceeds to the predetermined exposure start row. 17. The camera device according to claim 16, wherein at the time point, the discharge transistor is turned off and exposure of all pixels is started.   In the solid-state imaging device, the remaining charge of the photodiode immediately after transferring the signal charge of the photodiode to the floating diffusion portion by the transfer transistor is 20 charges or less, and the signal charge of the photodiode is discharged by the discharge transistor. 20. The camera device according to claim 19, wherein the remaining charge of the photodiode after being performed is 20 charges or less.   The camera device according to claim 19, wherein the solid-state imaging device has a gate voltage level when the discharge transistor is ON higher than a gate voltage level when the transfer transistor is ON.   The camera device according to claim 19, wherein the solid-state imaging device has a gate voltage level when the discharge transistor is ON higher than a power supply voltage of a digital circuit mounted on the solid-state imaging device.   The camera device according to claim 19, wherein the solid-state imaging device turns off the discharge transistor during an operation of reading a signal charge of the floating diffusion portion in a pixel row before the exposure start row.   In the solid-state imaging device, the gate wirings of the transfer transistor, the reset transistor, and the amplification transistor are provided in a direction along the pixel row, and are driven for each pixel row, and the gate wiring of the discharge transistor is along the pixel column. 18. The camera device according to claim 17, wherein the camera device is provided in the same direction and is short-circuited in common for all pixels outside the imaging region.   17. The camera apparatus according to claim 16, further comprising switching means for switching a shutter operation of the solid-state imaging device between a focal plane shutter operation and an all-pixel simultaneous shutter operation.   Exposure time selection means for selecting an exposure time in the solid-state imaging device; and exposure start line selection means for selecting the predetermined exposure start line based on the exposure time selected by the exposure time selection means. The camera device according to claim 19.

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