JP2551658C - - Google Patents

Description

The present invention relates to a photoelectric conversion device for reducing sensor noise. [Problems to be Solved by the Related Art and the Invention] As a sensor used in a solid-state imaging device or the like, an amplification type sensor is preferably used in order to increase an output signal level or the like. Amplification type sensors are composed of MOS, SIT, FET, and bipolar transistors, etc., and charge-amplify or current-amplify the charge accumulated in their control electrodes and output from the main electrode. . For example, Japanese Patent Publication No. 55-28456 discloses an example of an amplification type sensor. One of the problems of such an amplification type sensor
First, the sensor noise is large. Sensor noise is generally a fixed pattern noise (hereinafter referred to as FPN) which appears fixedly.
), There is random noise that is introduced into the control electrode when the control electrode is reset. Since FPN appears fixedly in the sensor noise, it can be completely eliminated by subtracting the dark output of the sensor from the optical signal output of the sensor. The dark output can be obtained by reading the storage time almost zero, that is, immediately after resetting the sensor. On the other hand, in order to also remove the random noise incorporated in the control electrode, the sensor output (optical signal) after accumulation may be subtracted from the sensor output (sensor noise) immediately after the start of accumulation. A photoelectric conversion device capable of performing such a subtraction process is disclosed in Japanese Patent Application No. 63-47492 filed by the present applicant. This photoelectric conversion device includes means for storing an optical signal and storage means for storing sensor noise, and calculates the difference between the optical signal and sensor noise stored in both storage means. Such a photoelectric conversion device is very practical when used for a line sensor, but when used for an area sensor, the chip area of the storage means for storing sensor noise increases. Even when the storage means is provided outside the image sensor, a field memory or a frame memory is required, which is a problem in terms of cost, and is difficult to put to practical use. Further, in order to increase the sensitivity of the sensor and relatively reduce the influence of sensor noise, there is a type in which a photoelectric conversion region is stacked above an amplification transistor. An example of such a solid-state imaging device is disclosed in Japanese Patent Application No. 1-9089 filed earlier by the present applicant. In this solid-state imaging device, when the photoconductive film is laminated, the aperture ratio of the receiving port of the photoelectric conversion region becomes very large, so that the sensor output (S) also becomes large. However, to achieve a higher S / N ratio, it is necessary to reduce the sensor noise (N). An object of the present invention is to provide a photoelectric conversion device suitable for removing sensor noise in view of the above problems. [Means for Solving the Problems] A photoelectric conversion device according to the present invention includes a storage unit for storing a photo-excited charge, an amplification unit for amplifying a charge of a control electrode and outputting the charge via a main electrode; Switch means for connecting the control means and the control electrode; and reading out the output of the amplifying means when the switch means is non-conductive as a first signal, and immediately before the reading, the main means in a state where the amplifying means is not turned on. First readout means for setting an electrode to a predetermined potential; transfer means for turning on the switch means thereafter to transfer the charge of the storage means to the control electrode; and amplifying means after transfer of the charge by the transfer means. Is read out as a second signal, and the main electrode is again set to the predetermined potential immediately before this reading, without turning on the amplifying means. And second reading means, characterized by comprising a subtraction processing means for performing subtraction processing between the first signal and the second signal. [Operation] The photoelectric conversion device of the present invention provides a switch between the accumulation unit for accumulating the photo-excited charge and the amplification unit for amplifying the charge of the control electrode, so that the sensor can be operated regardless of the operation of the accumulation unit. It is possible to read out noise independently.
This makes it possible to remove not only PN but also a dark current component and random noise of the amplifying element. In addition, a storage area serving as a storage means and an amplification area serving as an amplification means are formed on a substrate, and a photoelectric conversion area is laminated thereon, and the photoelectric conversion area and the amplification area are connected to each other. Can be increased, and the S / N ratio can be increased. Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial circuit diagram of a first embodiment of the photoelectric conversion device of the present invention. FIG. 2 is a schematic plan view of a pixel of the photoelectric conversion device. FIG. 3 is a cross-sectional view taken along line XX 'of the photoelectric conversion device of FIG. FIG. 4 is a sectional view taken along line YY 'of the photoelectric conversion device of FIG. As shown in FIG. 1, one pixel includes a PMOS transistor Tr _A for resetting the pixel and a capacitor C for controlling transient reset of the pixel and accumulation / readout of signals.
o _X , a photodiode D which is storage means for storing the photoexcited charge, an amplifying transistor Tr _C for amplifying a signal from the photodiode D, and amplifying the charge generated in the photoelectric conversion unit of the photodiode D composed of PMOS transistor Tr _B serving switching element for transferring control to the base is a use transistor Tr _C control electrode. φ _VR and φ _TB are pulses for controlling the PMOS transistors Tr _A and Tr _B , respectively. The emitter of the amplifying transistor Tr _C is connected to the storage capacitors C ₁ and C ₂ via the MOS transistors T ₁ and T ₂ . φ _T1 and φ _T2 are pulses for controlling the MOS transistors T ₁ and T ₂ , respectively. T _VC is a MOS transistor for resetting the vertical signal line, and is set to the potential V _VC by controlling the pulse φ _VC . As shown in FIGS. 2 and 3, each pixel is separated by a PMOS transistor Tr _A (
In FIG. 3, a portion of the base B of the amplifying transistor Tr _C is formed of SiO 2.
_The capacitance Co _X is formed by the poly layer L ₁ provided on the _second layer ₂ . The emitter E by A1 layer L _2, are hardwired on the pixel separation as a vertical output line. As shown in FIGS. 2 and 4, the photo diode D, which is a photoelectric conversion unit, and the base B of the amplifying transistor Tr _C are connected by a switch element composed of a PMOS transistor Tr _B (shown by a broken line in FIG. 4). Are separated. Note that, except for the photodiode D, the light is normally shielded from light, but is omitted in FIGS. 2 to 4. Hereinafter, the operation of the photoelectric conversion device will be described with reference to FIGS. FIG. 5 is a timing chart for explaining the operation of the photoelectric conversion device. In Figure 5, firstly, the period T ₁ is a reset period in the horizontal direction pixel rows (f0), and a pulse phi _VR and pulse phi _TB to a negative potential (-V), PMOS transistor Tr
_A and switching elements Tr _B as ON state, the reset of the horizontal pixel row read is completed is performed. Period T ₂ are a excessive reset period of the horizontal pixel rows, a pulse phi _VR positive potential (
When the + V), PMOS transistor Tr _A is turned OFF, the base potential and the potential of the photodiode D of the amplifying transistor Tr _C via the capacitor Co _X decreases. At the same time, the pulse φ _{VC is set} to the high level, the MOS transistor T _VC is turned on, and the emitter of the amplifying transistor Tr _C is set to the predetermined potential V _VC . At this time, the base residual charges of the amplifying transistor Tr _C and photodiode D is (referred to as transient reset) to be removed by recombination of the emitter current. Thereafter, the pulse phi _VC the MOS transistor T _VC is turned OFF as low level, the pulse phi when _VR from a positive potential to the ground potential (GND), the amplifying transistor T via the capacitor Co _X
The potential at the base of r _C and the potential at the photodiode D also decrease. Further, when the pulse φ _{TB rises} to the ground potential (GND), the PMOS transistor Tr _B turns off.
The state becomes the F state, and the photodiode D starts accumulation. Period T ₃ is a vertical scanning switching period (f ₀ → f _1), a vertical scanning is performed by the vertical shift register (not shown), the next horizontal pixel row is selected by the control pulse phi _V1, phi _V2 . Period T ₄ is a residual charge clearing period of the storage capacitor C _1, when the pulse phi _VC and pulse phi _T1 to the high level, MOS transistors T _VC and MOS transistors T _T1 is O
Becomes N state, the residual charge on the storage capacitor C ₁ is cleared. Thereafter, the pulse φ _{VC is changed} to low level, and the MOS transistor T _VC is turned off. Period T ₅ is the readout period of the sensor noise, the pulse phi _VR positive potential (+
As V), raising the base of the amplifying transistor Tr _C, readout driving is performed from the amplifying transistor Tr _c. The base potential at this time is the dark output potential, and the emitter is an amplifying transistor.
An output voltage depending on the characteristics of Tr _C appears. This is generally called an offset voltage, and since the parameters of the plurality of amplifying transistors are slightly different, the emitter output voltage, that is, the offset voltage is also different. Here, the difference between these offset potentials is called sensor noise. The sensor noise is accumulated in the storage capacitor C _1. Period T ₆ is the residual charge clearing period of the storage capacitor C _2, when the pulse phi _VC and pulse phi _T2 to the high level, MOS transistors T _VC and MOS transistor T _T2 is turned ON, on the storage capacitor C ₂ Residual charges are cleared. Then pulse φ _VC
As a low level, the MOS transistor T _VC and the OFF state. Period T ₇ is a period for transferring the photoelectric charges of the photodiode D to the base of the amplifying transistor Tr _C, if it falls pulses phi _TB and a negative potential (-V), PMOS transistor Tr _B There turned oN, the photocharge accumulated in the photodiode D is transferred to the base of the amplifying transistor Tr _C. Period T ₈ is the readout period of the optical signal, the pulse phi _VR If a positive potential (+ V), increases the base potential of the amplifying transistor Tr _C via the capacitor Co _X, from the amplifying transistor Tr _C The optical signal output is read. Includes the above-described sensor noise to the optical signal, are accumulated in the storage capacitor C _2. Column of storage have accumulated sensor noise capacitance C ₁ of the column and the storage capacitor C ₂ are the optical signal accumulation horizontal output lines from the horizontal transfer switch of the drive selected not shown by the horizontal shift register (not shown) Is forwarded to Since the output terminal of the horizontal output line is connected to the differential amplifier, as a result, sensor noise is subtracted from the optical signal,
Only an optical signal can be obtained. Hereinafter, the sensor noise subtraction processing will be described in detail. According to our experimental results, the FPN after the transient reset is the amplifying transistor Tr
Unlike by differences in parameters such as _C in h _FE, post-transient reset completion base potential V _B is the variation of ΔV occurs. This variation ΔV is determined by the read operation. The amount C _bc is the combined capacitance of the base-emitter capacitance C _be and the capacitance C _ox . Further, the random noise component is reset when the kTC noise which depends on the combined capacitance C _B in the period T _1, the time of light charge transfer of the photo-diode D in the random noise and the period T _7, T ₈ when the sensor transistor read operation It is random noise. KTC noise at reset is slightly reduced by transient reset, In addition, random noise during photocharge transfer is band-limited by the base input time constant,
Small enough to ignore. Further, the random noise at the time of the read operation depends on the base capacitance C _B , the load capacitance C _V and the storage capacitance C _T viewed from the emitter, the current amplification factor h _FE, etc.
_It was found that if the _FE is increased to increase the degree of non-destruction, the random noise at the time of resetting can be significantly reduced. This is due to the sensor FPN and kTC
The noise means that the S / N ratio can be greatly improved by the subtraction processing of the optical signal and the sensor noise. In the CCD, kTC noise due to the reset transistor is removed by the correlated double sampling method after the charge / voltage conversion output amplifier, but the amplifier noise is dominant because of high-speed driving. In the case where each pixel is formed of an amplifying element as in the present invention, since the scanning is performed at a low speed every 1H, amplifier noise, that is, readout noise is extremely small. Further, the dark current component of the amplifying transistor is also removed when the sensor noise and the optical signal are subtracted. FIG. 6 is a partial circuit diagram of a second embodiment of the photoelectric conversion device of the present invention. The feature of this embodiment is that PMOS transistors Tr _A and Tr _B are connected in series, and a photodiode D is arranged at the connection point. Such an arrangement is suitably used when the horizontal pixel size is larger than the vertical pixel size. The pixel is reset by setting the pulses φ _VR1 and φ _VR2 to a negative potential and setting the PMOS transistor Tr _A
, Tr _B are turned on. In the transient reset, the pulse φ _{VR2 is set} to a positive potential to turn off the PMOS transistor Tr _B , and the potential of the base of the amplification transistor Tr _C is increased through the capacitor Co _X to change the emitter of the amplification transistor Tr _C. This is performed by setting a predetermined potential. The charge is accumulated by setting the pulses φ _VR1 and φ _VR2 to the ground potential (GND), turning off the PMOS transistors Tr _A and Tr _B , and accumulating the charges in the photodiode D. After reading out the sensor noise, set the pulse φ _VR2 to the positive potential and set the PMOS
With the transistor Tr _B and OFF state, to raise the base potential of the amplifying transistor Tr _C via the capacitor Co _X, is performed by reading the sensor noise from the emitter of the amplifying transistor Tr _C. To read the optical signal, the pulse φ _{VR2 is set} to the ground potential (GND), the PMOS transistor Tr _B is turned off, the pulse φ _{VR1 is set} to the negative potential, the PMOS transistor Tr _A is turned on, and the photo charge of the photodiode D is changed. _Is transferred to the base of the amplification transistor Tr _C , the pulse φ _{VR1 is set} to the ground potential (GND), the PMOS transistor Tr _A is turned off, the pulse φ _{VR2 is set} to the positive potential, and the PMOS transistor Tr _B is turned off. to raise the base potential of the MOS transistor Tr _C for amplification via the capacitor Co _X, it reads the optical signal from the emitter of the MOS transistor Tr _C for amplification. This embodiment is slightly different in operation method from the first embodiment, but can remove sensor noise similarly to the first embodiment. FIG. 7 is a partial circuit diagram of a third embodiment of the photoelectric conversion device of the present invention. The feature of this embodiment is that the amplifying element is a MOS transistor. In the figure, a MOS transistor Tr _A ′ is a reset MOS transistor for clearing residual charges in a gate region that is a control electrode of the MOS transistor Tr _C ′. In the first embodiment, the transient reset is performed because the amplifying element is constituted by the bipolar transistor. However, in the present embodiment, the transient reset operation is unnecessary because the amplifying element is the MOS transistor. When the photocharge accumulated in the photo diode D is transferred to the gate and the optical signal is read out from the MOS transistor of the amplifying element, random noise is a control electrode at the time of reading if a MOS or FET is used for the amplifying element of the sensor MOS. Since the gate charge is not destroyed, the correlation between the sensor noise and the sensor noise included in the optical signal output becomes very high, and as a result, a high S / N sensor can be obtained. FIG. 8 is a sectional view of a sensor according to a fourth embodiment of the present invention. In the present embodiment, the photoelectric conversion region is a photoconductive film formed by lamination. As shown in the figure, a pixel electrode from a photoconductive film is connected to the photodiode section of FIG. 4 which is the first embodiment of the photoelectric conversion device. In the drawing, 1 is a photoconductive film, 2 is a transparent electrode, 3 is a pixel electrode, 4 is an insulating layer, and the photoconductive film 1 is connected to a p-type semiconductor region forming a photodiode section through the pixel electrode 3. You. According to the present embodiment, since the photoconductive film can be provided also on the amplification element portion, the aperture ratio of the receiving port can be increased and the S / N ratio can be increased. FIG. 9 is a schematic configuration diagram of a solid-state imaging device to which the present invention is applied. In the drawing, a vertical scanning unit 202 and a horizontal scanning unit 203 perform television scanning on an image sensor 201 in which optical sensors are arranged in an area. The signal output from the horizontal scanning unit 203 is output as a standard television signal through the processing circuit 204. Drive pulses φ _HS , φ _H1 , φ _H2 , φ _{VS for the} vertical and horizontal scanning units 202 and 203
, Φ _V1 , φ _V2, etc. are supplied by the driver 205. The driver 205 is restricted by the controller 206. [Effects of the Invention] As described in detail above, according to the photoelectric conversion device of the present invention, the switch means is provided between the accumulation means for accumulating the photoexcited charge and the amplification means for amplifying the charge of the control electrode. As a result, the sensor noise of the amplifying element can be read out independently of the operation of the storage means, not only the FPN but also the dark current component and random noise of the amplifying element can be removed, and the amplifying element can be driven at low speed. In addition, it is possible to realize an imaging device with very low noise at the time of reading and a high S / N ratio. In addition, a storage area serving as a storage means and an amplification area serving as an amplification means are formed on a substrate, and a photoelectric conversion area is laminated thereon, and the photoelectric conversion area and the amplification area are connected to each other. Can be increased, and the S / N ratio can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial circuit diagram of a first embodiment of the photoelectric conversion device of the present invention. FIG. 2 is a schematic plan view of a pixel of the photoelectric conversion device. FIG. 3 is a cross-sectional view taken along line XX 'of the photoelectric conversion device of FIG. FIG. 4 is a sectional view taken along line YY 'of the photoelectric conversion device of FIG. FIG. 5 is a timing chart of the photoelectric conversion device. FIG. 6 is a partial circuit diagram of a second embodiment of the photoelectric conversion device of the present invention. FIG. 7 is a partial circuit diagram of a third embodiment of the photoelectric conversion device of the present invention. FIG. 8 is a sectional view of a sensor according to a fourth embodiment of the present invention. FIG. 9 is a schematic configuration diagram of a solid-state imaging device to which the present invention is applied. Tr _A, Tr _B: PMOS transistors, Co _X: Capacity, D: photodiode D, tr _C:
Amplifying transistor, φ _VR , φ _TB , φ _T1 , φ _T2 , φ _VC : pulse, T _VC , T ₁ , T ₂ :
MOS transistors, C ₁ and C ₂ : capacitors.

Claims (1)

Claims: (1) accumulating means for accumulating photo-excited electric charge, amplifying means for amplifying electric charge of a control electrode and outputting it via a main electrode, connecting said accumulating means and said control electrode Switching means for reading out the output of the amplifying means when the switching means is non-conductive as a first signal, and setting the main electrode to a predetermined potential immediately before the reading without turning on the amplifying means. 1, a transfer means for turning on the switch means and transferring the charge of the storage means to the control electrode, and an output of the amplification means as a second signal after the transfer of the charge by the transfer means. A second reading means for reading and simultaneously setting the main electrode to the predetermined potential again without turning on the amplifying means immediately before the reading; 1. A photoelectric conversion device, comprising: subtraction processing means for performing a subtraction process between the first signal and the second signal. (2) Forming a storage area as the storage means and an amplification area as the amplification means on a substrate, stacking a photoelectric conversion area thereon, and electrically connecting the photoelectric conversion area and the amplification area. The photoelectric conversion device according to claim 1, wherein: