JP2777162B2 - Driving method of solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial Application Field) The present invention relates to a driving method of a stacked solid-state imaging device,
In particular, the present invention relates to a driving method of a solid-state imaging device having a means for injecting and discharging bias charges.

(Prior Art) A solid-state imaging device having a two-story structure in which a photoconductive film is stacked on a solid-state imaging device chip (stacked solid-state imaging device) can increase the opening area of a photosensitive portion, and therefore has high sensitivity and high sensitivity. It has an excellent feature of low smear. For this reason, this solid-state imaging device is promising as a camera for various monitoring televisions and high-definition televisions. At present, an amorphous material film is used as a photoconductive film for a stacked solid-state imaging device. For example, Se-As-Te film, Z
nSe-ZnCdTe, a-Si: H film (hydrogenated amorphous silicon film) and the like. Among these materials, the a-Si: H film is becoming a favorite especially because of its excellent properties and workability and the possibility of forming at low temperatures.

FIG. 7 is a sectional view showing a schematic structure of a conventional stacked solid-state imaging device. In the figure, 110 is a p-type Si substrate, 111 is a p ⁺ -type element isolation layer, 112 is an n ⁺ -type channel (vertical CCD channel), and 113 is n
⁺⁺ type storage diode, 114 is signal charge readout gate, 115
a and 115b are transfer gates, 116 is a first insulating layer, 117 is a pixel electrode wiring, 118 is a second insulating layer, 120 is a pixel electrode, and 121 is a-Si:
The H photoconductive film 122 indicates a transparent electrode such as ITO. Here, a part of the transfer electrode 115a is
It also serves as.

In the configuration of FIG. 7, light incident from the transparent electrode 122 is photoelectrically exchanged by the photoconductive film 121, thereby forming an electron-hole pair. Since the potential of the pixel electrode 120 electrically connected to the storage diode 113 is higher than that of the transparent electrode 122, electrons move toward the pixel electrode 120 and holes move toward the transparent electrode 122. The holes flow out to an external circuit via the transparent electrode 122, and the electrons are stored in the storage diode 113 connected to the pixel electrode 120, and the diode 113
To lower the potential. The signal charge (electrons) accumulated for a certain period is read from the storage diode 113 to the vertical CCD channel 112 when a signal charge readout pulse is applied to the signal charge output gate 114. The electric charges read and transferred to the vertical CCD channel 112 are output via a horizontal CCD channel (not shown).

However, this type of solid-state imaging device has the following problems. That is, the storage diode 113 and free electrons are full. Since the pixel electrode wiring 117 is electrically connected to the pixel electrode 117, the storage diode 113 is not completely depleted, and the reading of the signal charge is incompletely transferred, thereby causing a problem that a capacitive afterimage occurs. In addition, the charge that has been photoelectrically exchanged in the photoconductive film 121 is trapped by a trap level existing in the film and is emitted after a certain period of time, so that there is a problem that the afterimage characteristic of the solid-state imaging device is deteriorated.

The photoconductive afterimage can be reduced by injecting a bias charge and steadily filling the trap level. However, in order to sufficiently reduce the level, it is necessary to inject a bias charge of a standard signal amount or more. In a stacked solid-state imaging device having a conventional structure, a light source is required to inject a bias charge,
In addition, the excess of the bias charge after filling the trap level is read out together with the signal charge, and there is a problem that the dynamic range is narrowed.

(Problems to be Solved by the Invention) As described above, in the conventional stacked solid-state imaging device,
There has been a problem that the operation of reading out the signal charges from the storage diode is incomplete, and a capacitive afterimage occurs. Further, in the conventional method of reducing the afterimage by injecting the bias charge using the photoelectric, the bias charge cannot be injected uniformly, and the configuration is further complicated.

In addition, since the photoconductive film is used as a photoelectric conversion unit, there is a problem in that a part of the charge photoelectrically exchanged is trapped in a trap level existing in the film, and a photoconductive afterimage is generated. Further, there is a problem that a light source is required to inject a bias charge in order to reduce a photoconductive afterimage, and a dynamic range is reduced due to a surplus of the bias charge.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to make it possible to uniformly inject a bias charge into a signal charge storage diode without using a light source or the like, and to reduce a dynamic range. It is an object of the present invention to provide a driving method of a solid-state imaging device which can perform injection of a bias charge sufficient to reduce a photoconductive afterimage without accompanying it and can improve an afterimage characteristic.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to provide a gate and a diode for injecting and discharging a bias charge to electrically inject and discharge a bias charge to and from a storage diode. In other words, after the bias charge is injected into the photoconductive film via the signal charge storage diode, the surplus of the injected bias charge is discharged.

That is, according to the present invention, a signal charge storage diode, a signal charge readout unit and a signal charge transfer unit are formed on a semiconductor substrate,
A solid-state image sensor chip on which a pixel electrode electrically connected to a signal charge storage diode is formed, a photoconductive film laminated on the chip, and a transparent electrode formed on the photoconductive film A gate and a diode for injecting and discharging a bias charge to and from the signal charge storage diode via the signal charge readout unit are provided adjacent to the signal charge transfer unit; As a method of driving the imaging device, by applying a voltage applied to the transparent electrode to be larger or smaller than the voltage of the signal charge storage period, a bias charge is injected into the photoconductive film through the signal charge storage diode, Next, the voltage applied to the transparent electrode is returned to the voltage in the signal charge storage period again, and the excess charge injected into the photoconductive film is transferred to the storage diode. It is a method to discharge through the de.

(Operation) According to the present invention, a bias charge is injected into a signal charge storage diode without using a light source by providing a gate and a diode for electrically injecting a bias charge into the signal charge storage diode. It is possible. Therefore, it is possible to uniformly inject the bias charge enough to sufficiently reduce the capacitive afterimage. Further, since the once injected bias charge is discharged through the signal charge readout gate, the dark-time output current does not depend on the bias charge of a certain amount or more, so that the variation of the bias charge can be ignored.

According to the present invention, a gate and a diode for electrically injecting a bias charge are provided, and a bias charge is electrically injected into a photoconductive film through a signal charge storage diode. Injection of a bias charge sufficient to satisfy an existing trap level can be performed, and a surplus of the bias charge can be swept out separately from the signal charge. Therefore, the photoconductive afterimage can be sufficiently reduced without reducing the dynamic range due to the injection of the bias charge.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a schematic plan view illustrating a basic configuration of a solid-state imaging device according to an embodiment of the present invention. The basic configuration is the same as that of the conventional stacked solid-state imaging device. That is, signal charge storage diodes 10 are arranged in a matrix on an unillustrated Si substrate, and a vertical CCD transfer electrode 20 is provided adjacent to the storage diodes 10 in the column direction. These transfer electrodes 20 have driving pulses φ _V1 , φ _V2 ,
φ _V3 and φ _V4 are applied, and the vertical CCD is driven in four phases. Here, a part of the electrode 20 to which the drive pulses φ _V1 and φ _V3 are applied also serves as the signal charge read gate 30.

This device differs from the conventional device in that a gate and a diode for charge injection are provided. That is, the gate 40 for bias charge injection and the diode 50 for bias charge injection are provided on the side opposite to the storage diode 10 of the vertical CCD. Drive pulses φ _B1 and φ _B2 are applied to the gate 40,
Drive pulses φ _D1 and φ _D2 are applied to the diode 50.
A bias charge is injected from the diode 50 into the storage diode 10 via the gate 40 and further via the read gate 30.

FIG. 2 is a plan view more specifically showing FIG.
Of the transfer electrodes 20, the electrodes 21 and 23 to which the driving pulses φ _V1 and φ _V3 are applied are the first layer poly-Si, and the electrodes 22 and 24 to which the driving pulses φ _V2 and φ _V4 are applied are the second layer poly-Si. It is. The bias charge injection gate 40 is a third layer poly-Si. In the drawing, reference numeral 60 denotes a vertical CCD channel, and reference numeral 70 denotes an electrode connected to the bias charge injection diode 50. Also,
In the storage diode 10 (11, 12), 11 is adjacent to the transfer electrode 21 and 12 is adjacent to the transfer electrode 23. Similarly, in the signal charge readout gate 30 (31, 32), the bias charge injection gate 40 (41, 42), the bias charge injection diode 50 (51, 52), and the electrode 70 (71, 72), the storage diode 11 Are corresponding to 31, 41, 51, 71, and those corresponding to the storage diode 12 are 32, 42, 52, 72. In the figure, the pixel electrode wiring 117, the pixel electrode 120, the photoconductive film 121, the transparent electrode 122, and the like are omitted.

 Next, a driving method of the present apparatus will be described.

FIG. 3 shows drive pulses φ _V1 to φ _V4 to the transfer electrode 20, and FIG. 4 shows a schematic cross section taken along the line AA in FIG. 2 and a change in the potential state. It should be noted that the numbers 1 to 1 given in FIG.
Reference numeral 16 denotes timings respectively corresponding to the numbers 1 to 16 given in FIG.

As shown in FIG. 3, when the voltage φ _V1 of the signal charge read gate 31 becomes the read voltage V _{FS from} time t _{0 to} t ₁ ,
Signal charges are read out from the storage diode 11 to the channel below the transfer electrode 21 as shown in FIGS. Subsequently, the time t ₁ ~t ₄ by the drive pulse phi _V1 to [phi] _V4 of the respective transfer electrodes 20
Are changed as shown in FIG. 3 to obtain FIG.
The signal charge is transferred to the channel below the transfer electrode 23 as shown in FIG. Then, between times t ₄ and t ₅ , the bias charge is injected into the photoconductive film 121 via the storage diode 11 according to the present invention. The operation of injecting the bias charge will be described later.

Voltage of the signal charge read gate 32 between times t ₅ ~t ₇ φ _V3
Becomes a read voltage _VFS , a signal charge is read from the storage diode 12 as shown in FIGS. 4 (e) to 4 (g).
It is added to 11 signal charges. Subsequently, when the drive pulse phi _V1 to [phi] _V4 of the transfer electrodes 20 at time t ₇ ~t ₁₀ is varied as shown in FIG. 3, the signal as shown in FIG. 4 (g) ~ (j) charge the following Is transferred to the channel below the transfer electrode 21. Then, at time t ₁₀ ~t _11, bias charges are injected into the photoconductive layer 121 through the storage diode 12. The transfer of the signal charge described above is the same as in the conventional interleave method.

Next, a method of injecting bias charges will be described. Here, the injection of the bias charge into the photoconductive film 121 through the storage diode 11 will be described, but the injection of the bias charge into the photoconductive film 121 through the storage diode 12 is also performed in the same manner as described below. FIG. 5 shows drive pulses φ _V1 , φ _B1 , φ _D1 , φ for the transfer electrode 21, the gate 41 for bias charge injection, the diode 51 for bias charge injection, and the transparent electrode 122.
FIG. 6 schematically shows the _TE and FIG. 6 shows a cross section taken along the line BB in FIG. The numbers 1 to 6 in FIG. 5 are timings corresponding to the numbers 1 to 6 in FIG. 6, respectively. In addition, ta in FIG.
corresponds to t _4, te corresponds to t _5.

As shown in FIG. 5, when the time ta~tb at the same voltage V _FS as when the signal charges read transfer electrode 21 is applied to the signal charge readout gate 31 as shown in FIG. 6 (b) is ON Become. From time tb to tc, the gate 41 for bias charge injection
When _VON is applied to this gate, this gate 41 opens as shown in FIG. 6 (c). Subsequently, when the voltage applied to the bias charge injection diode 51 changes from V _DR → V _INJ during the time tc to td, the bias charge is changed to the bias charge injection gate 41 and the bias charge injection gate 41 as shown in FIG. The charge is injected into the storage diode 11 via the signal charge read gate 31.

Next, when the voltage applied to the transparent electrode 122 changes from Vo to Vf at times td to te, a bias charge is injected into the photoconductive film 121 via the storage diode 11 as shown in FIG. Here, a part of the bias charge injected into the photoconductive film 121 fills a trap level which is a cause of the photoconductive afterimage. Thereafter, from time te to tf, the transparent electrode 12
When the voltage applied to 2 changes from vf to Vo, FIG. 6 (f)
As shown in (2), the excess of the bias charge that does not fill the trap level is swept to the storage diode 11 side.

Next, from time tf to tg, when the voltage applied to the bias charge injection diode 51 changes from V _{INJ to} V _DR ,
As shown in FIG. 6 (g), the bias charge in the storage diode 11 is also discharged to the bias charge injection diode 51. Then, when the voltage applied to the transfer electrode 21 changes from V _FS → 0, the signal charge read gate is turned off as shown in FIG. 6 (h). Finally, the voltage of the gate 41 for bias charge injection changes to 0 V, the gate 41 closes as shown in FIG. 6 (i), and a series of bias charge injection operations ends.

Thus, according to the present embodiment, the signal charge storage diode
Since the gate 40 and the diode 50 for electrically injecting and discharging the bias charge are provided for the device 10, the bias charge can be injected into the storage diode 50 without using a light source. Therefore, the bias charge enough to sufficiently reduce the capacitive afterimage can be uniformly injected into the storage diode 50, which is extremely effective in reducing the afterimage.

Further, in this embodiment, the voltage applied to the transparent electrode 122 is changed to electrically inject a bias charge into the photoconductive film 121 via the storage diode 50, so that the photoconductive afterimage is reduced. In this case, a sufficient amount of bias charge can be injected. Furthermore, since the surplus of the injected bias charge is discharged to the bias charge injection diode 50 via the storage diode 50 separately from the signal charge, there is no inconvenience that the dynamic range is reduced.

Note that the present invention is not limited to the embodiments described above. For example, the gate and the diode for signal charge injection are not limited to the opposite side of the CCD channel from the signal charge storage diode, and any signal charge storage diode can be used as long as the bias charge can be injected through the signal charge readout gate. It may be provided on the side. Also,
A gate and a diode for bias charge injection may be provided adjacent to the signal charge storage diode, and a gate and diode for bias charge discharge may be provided adjacent to the charge transfer unit. Further, the present invention can be applied to a structure in which a gate and a diode for injecting and discharging bias charges and a diode are separately provided. Furthermore, in general, CC
It can be applied to a D imaging device.

As for the drive timing, the voltage applied to the transparent electrode may be changed so that the bias charge can be injected into and discharged from the photoconductive film while the potential of the storage diode is determined by the potential of the bias charge injection diode.
Further, if the voltage applied to the transparent electrode is returned to the voltage at the time of accumulating the signal charge while the potential of the storage diode is determined by the potential of the bias charge injection diode, the efficiency of discharging the excess bias charge is increased. The voltage applied to the transparent electrode may be changed so as to increase the electric field from the transparent electrode to the storage diode. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above, according to the present invention, by providing a gate and a diode for injecting and discharging a bias charge, it is possible to electrically inject and discharge a bias charge to and from a storage diode. . Therefore, the bias charge can be uniformly injected into the signal charge storage diode without providing a light source or the like, and the afterimage characteristic can be improved. In addition, it is possible to electrically inject and discharge bias charges to and from the photoconductive film. Therefore, it is possible to inject a bias charge sufficient to reduce the photoconductive afterimage without using a light source, and to discharge a surplus of the bias charge, thereby suppressing a decrease in the dynamic range.

[Brief description of the drawings]

1 to 6 are views for explaining a solid-state imaging device according to an embodiment of the present invention. FIG. 1 is a schematic plan view showing a basic configuration of the solid-state imaging device, and FIG. FIG. 1 is a plan view showing the embodiment more specifically, FIG. 3 is a signal waveform diagram showing a drive pulse to the transfer electrode, and FIG. 4 is a schematic cross-sectional view taken along the line AA of FIG. FIG. 5 is a signal waveform diagram showing drive pulses to a transfer electrode, a gate for bias charge injection, a diode, and a transparent electrode.
FIG. 1 is a schematic diagram showing a schematic cross section taken along the line BB of FIG. 2 and a change in its potential state, and FIG. 7 is a cross-sectional view showing a schematic structure of a conventional stacked solid-state imaging device. 10 (11,12) ...... Signal charge storage diode, 20 (21, ~, 2
4) Transfer electrode, 30 (31, 32) Signal readout gate, 40 (41, 42) Bias charge injection gate, 50 (5
1,52) …… Bias charge injection diode, 60 …… Vertical
CCD channel, 70 (71, 72) ... electrode, 121 ... photoconductive film, 122 ... transparent electrode.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-7985 (JP, A) JP-A-59-198084 (JP, A) JP-A-62-162356 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04N ^5/ 30-5/335

Claims (3)

(57) [Claims] A signal charge storage diode on a semiconductor substrate;
A solid-state imaging device chip on which a signal charge readout portion and a signal charge transfer portion are formed, and a pixel electrode formed on the uppermost portion and electrically connected to the signal charge storage diode; and a photoconductive film laminated on the chip And a transparent electrode formed on the photoconductive film, and a transparent electrode provided adjacent to the signal charge transfer unit for injecting and discharging bias charges to and from the signal charge storage diode via the signal charge readout unit. A solid-state imaging device comprising a gate and a diode, wherein when injecting a bias charge into the signal charge storage diode, a voltage applied to the transparent electrode is made larger or smaller than a voltage in a signal charge storage period, and the signal A bias charge is injected into the photoconductive film through the charge storage diode, and then the voltage applied to the transparent electrode is returned to the voltage during the signal charge storage period. The driving method of the solid-state imaging apparatus characterized by discharging the excess charge injected into the photoconductive film through the accumulation diode. 2. A signal charge storage diode on a semiconductor substrate,
A solid-state imaging device chip in which a signal charge readout portion and a signal charge transfer portion are formed, and a pixel electrode electrically connected to the signal charge storage diode is formed on the uppermost portion; and a photoconductive film laminated on the chip A transparent electrode formed on the photoconductive film, a bias charge injection gate and a diode provided adjacent to the signal charge storage diode for injecting a bias charge into the signal charge storage diode, A solid-state imaging device provided adjacent to a signal charge transfer unit and including a bias charge discharge gate and a diode for discharging bias charge injected into the signal charge storage diode through the signal charge readout unit. When a bias charge is injected into the signal charge storage diode, the voltage applied to the transparent electrode is changed to a voltage during the signal charge storage period. Pressure, and a bias voltage is injected into the photoconductive film through the signal charge storage diode, and then the voltage applied to the transparent electrode is returned to the voltage in the signal charge storage period again. A method for driving a solid-state imaging device, comprising: discharging excess charge injected therein through the storage diode. 3. The pixel electrode and the signal charge storage diodes are arranged in a matrix, and a plurality of the signal charge transfer units are arranged in a row along the arrangement of the signal charge storage diodes. The gate and the diode are provided corresponding to each signal charge storage diode, and the injection of the bias charge is performed after reading the signal charge from the signal charge storage diode, and all the signal charge storage diodes 3. The method of driving a solid-state imaging device according to claim 1, wherein the step (c) is performed every other row, not simultaneously.