JPS63144667A - Photoelectric conversion device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photoelectric conversion device in which the potential of a control electrode region of a semiconductor transistor is controlled via a capacitor.

[Prior Art] FIG. 5(A) is a schematic plan view of a conventional photoelectric conversion device;
FIG. 5(B) is a sectional view taken along the line ^-A' of one of the photoelectric conversion cells.

In both figures, an n-epitaxial layer 4 is formed on an n-silicon substrate 1, and photoelectric conversion cells electrically insulated from each other by an element isolation region 6 are arranged therein.

First, n=p- base region 9 of a bipolar transistor on epitaxial layer 4, n+ emitter region 1 therein.
5 is formed. Further, a capacitor electrode 14 for controlling the potential of the p'' base region 9 and an emitter electrode 19 connected to the n+ emitter region 15 are formed with the oxidized IP 212 interposed therebetween.

An electrode 17 connected to the capacitor electrode 14, an n+ region 2 for ohmic contact on the back surface of the substrate 1, and a collector electrode 21 of a bipolar transistor are formed, respectively, to constitute a photoelectric conversion cell.

The basic operation of the photoelectric conversion cell is to first put the p-base region 9 biased to a negative potential into a floating state, and then transfer holes from the electron-hole pairs generated by photoexcitation to the p-base region 9.
(accumulation operation).

Subsequently, a positive voltage is applied to the capacitor electrode 14 to bias the emitter-base in the forward direction, and the accumulated voltage generated by the accumulated holes is read out to the floating emitter side (read operation).

Subsequently, the emitter side is grounded and a positive voltage pulse is applied to the capacitor electrode 14 to eliminate the holes accumulated in the p- base region 9. As a result, the p-base region 9 returns to its initial state at the point where the refresh positive voltage pulse falls (refresh operation).

Such a photoelectric conversion device uses the amplification function of each cell to amplify and read out the accumulated charges, and can achieve high output, high sensitivity, and low noise. Furthermore, since it is structurally simple, it can be said to be advantageous for future high resolution.

[Problems to be Solved by the Invention] However, since the capacitor in the conventional photoelectric conversion device is configured such that the capacitor electrode 14 faces the low concentration base region 9, it is unstable and the readout is difficult. This has the problem of causing signal variations.

That is, depending on the voltage applied to the capacitor electrode 14, the state of the interface between the oxide film 12 and the p- base region 9 changes between accumulation and depletion 1 inversion. This state change not only changes the capacitance value but also causes dark current to occur.

Furthermore, when a large number of photoelectric conversion cells are arranged, not all of them change their states uniformly, which causes fixed pattern noise due to variations in readout signals.

[Means for solving problems] A photoelectric conversion device according to the present invention is as follows.

In a photoelectric conversion device in which the potential of a control electrode region of a semiconductor transistor is controlled via a capacitor.

The capacitor has a structure in which an electrode faces the control electrode region with an insulating layer in between, and at least a portion of the control electrode region facing the electrode is a region with a high impurity concentration. do.

[Function] Since the control electrode region of the capacitor is formed with a high concentration in this way, the interface between the control electrode region and the insulating layer that constitute the capacitor is stabilized, and variations in the readout signal are reduced. .

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1(A) is a schematic cross-sectional view of one embodiment of a photoelectric conversion device according to the present invention, and FIG. 1(B) is an equivalent circuit diagram thereof.

In the figure, an n- region 102 is formed by epitaxial growth on an n-type silicon substrate 101, and surrounded by an element isolation region 103, a photoelectric conversion cell is formed.

The bipolar transistor of the photoelectric conversion cell has an n-region 1
02 is a collector region, and is composed of a p-base region 104 and an n-emitter region 105.

To improve the Senna sensitivity, lower the impurity concentration of the p- base region 104 to increase the base-emitter capacitance +1 pCbe.
However, if the impurity concentration is too small, the base region will be completely depleted in the operating state, resulting in a punch-through state. Here, the impurity concentration of the p- base region 104 is set to ”cm
"".

Furthermore, the p-base region 104 has a high impurity concentration ~10
A 18 cm -3 (7) P+ region 106 is formed, and the P+ region 106 faces a polysilicon capacitor electrode 108 with an oxide film 107 in between, forming a capacitor for controlling the base potential.

Note that although the oxide film 107 in the portion forming the capacitor is formed thinly, the base region 107 in other portions is thin.
It is formed sufficiently thick so as not to affect the 4th grade.

In addition, an emitter electrode 109 such as A1 is formed in contact with the n0 emitter region 105, and a collector electrode 110 is formed on the back surface of the substrate 101 via an ohmic contact layer.
is formed.

The basic operation of this embodiment is the same as that of the conventional example, and the voltage applied to the capacitor electrode 108 causes the p-base region 1 to
The potential of 04 is controlled and read, refresh, and storage operations are performed. At this time, since the p region 106 with a high impurity concentration faces the capacitor electrode 10g,
The state of the interface between the p-type region 106 and the oxide film 107 is stabilized.

Even if a large number of photoelectric conversion cells are arranged, uniform output can be obtained.

FIG. 2 is a circuit diagram of a line sensor using the photoelectric conversion cell described above.

In the figure, a constant positive voltage Vcc is applied to the collector electrodes 110 of the photoelectric conversion cells S1 to Sn. Each capacitor electrode 108 is commonly connected to a terminal 201, and a pulse φ1 for performing a read operation and a refresh operation is applied to the terminal 201. Further, each emitter electrode 109 is connected to the vertical lines L1 to Ln, respectively, and the vertical lines L1 to Ln are connected to the transistors Qa1 to Q a n, respectively.
#, ' are connected to the product capacitor CI''Cn through # and '. The gate electrodes of the transistors Q al ''Q a are commonly connected to a terminal 203, and a pulse φ3 is applied to the terminal 203.

Further, capacitors 01 to Cn are transistors Q1 to Q1, respectively.
It is connected to output line 204 via Qn. The gate electrodes of the transistors Q1 to Qn are respectively connected to parallel output terminals of the scanning circuit 205, and pulses φh1 to φhn are sequentially outputted from the parallel output terminals.

The output line 204 is grounded via a refresh transistor Qrh, and a pulse φr2 is applied to the gate electrode of the transistor Qrh.

Further, each of the vertical lines L1 to Ln is a transistor Qb1.
~Q b n to ground. Further, the gate electrodes of each transistor are commonly connected to a terminal 202, and a pulse φ2 is applied to the terminal 202.

FIG. 3 is a timing chart for explaining the operation of the line sensor.

First, it is assumed that carriers corresponding to the illuminance of incident light are accumulated in each of the photoelectric conversion cells S1 to Sn. In this state, the pulse φ3 causes the transistors Qa1 to Q a
n is turned on, and the transistor Q is turned on by the pulse φ2.
b1~Qbn is the emitter electrode 10 in the OFF state.
9 is placed in a floating state, and a positive voltage pulse φr for reading is applied to the terminal 201. This allows, as already mentioned,
The output signal of each cell is read out to the floating emitter side,
Each signal is stored in capacitors 01-Cn. When the reading is completed, the pulse φ3 causes the transistors Qa1 to Qa1 to
Qan is turned off.

Subsequently, the transistors Qbz to Qb are activated by the pulse φ2.
The emitter electrode 109 of each cell is grounded by setting n to ON state 77Q, and a refresh pulse φrC is applied to the terminal 201. As a result, the refresh operation described above is performed, and the holes accumulated in the base region 104 disappear.

When the refresh operation is completed, each cell starts an accumulation operation.

Further, in parallel with the refresh operation, the scanning circuit 205 outputs pulses φh1 to φhn, and transistors Q1 to Q
n are turned ON one after another. This makes the capacitor 0
Each signal accumulated in 1 to Cn is sequentially read out to the output line 204, and output signal Vout through the amplifier 206.
It is output to the outside as

At that time, each time each signal is output, pulses φh1 to φ
Pulse φr2 is applied at timings overlapping with hn. At this timing, transistor Qrh turns on,
Residual carriers in the output line 204 are removed, and
Residual carriers in capacitors 01-Cn are sequentially removed through transistors Q1-Qn, respectively.

After reading No. 4g of all cells 31 to Sn is output in this way, the next read operation is started, and the above operation is repeated in the same manner.

As already mentioned, in this embodiment, since the interface state of the capacitor is stable, a read signal without variation can be obtained, and an output signal Vout with suppressed fixed pattern noise can be obtained.

FIG. 4 is a schematic configuration diagram of an example of an imaging device using the above photoelectric conversion device.

In the figure, an image sensor 301 corresponds to the photoelectric conversion device shown in FIG. The output signal Vout of the image sensor 301 is subjected to processing such as gain adjustment by the signal processing circuit 302, and is output as a video signal.

Further, each of the above pulses for driving the image sensor 301 is supplied by a driver 303, and the driver 303 operates under the control of a control unit 304. In addition, the control unit 30
4 is a signal processing circuit 302 based on the output of the image sensor 301.
At the same time, the exposure control means 305 is controlled to adjust the amount of light incident on the image sensor 301.

Note that if an area sensor is configured instead of the line sensor shown in FIG. 2, a television signal can also be obtained from the signal processing circuit 302.

[Effects of the Invention] As described in detail above, in the photoelectric conversion device according to the present invention, since the control electrode region of the part constituting the capacitor is formed with a high concentration, the control electrode region and the insulating layer constituting the capacitor are This stabilizes the interface between the two and reduces the variation in readout signals. For this reason, for example, when an image sensor is constructed, a high-quality image signal with less fixed pattern noise can be obtained. .

[Brief explanation of the drawing]

FIG. 1(A) is a schematic sectional view of one embodiment of a photoelectric conversion device according to the present invention, and FIG. 1(B) is an equivalent circuit diagram thereof. Fig. 2 is a circuit diagram of a line sensor using the L light distribution electric conversion cell, Fig. 3 is a timing chart for explaining the operation of the above line sensor, and Fig. 4 is an image capturing using the above photoelectric conversion device. A schematic configuration diagram of an example of a device; FIG. 5(A) is a schematic plan view of a conventional photoelectric conversion device;
Figure 5 (B) shows A-A of one of the photoelectric conversion cells.
FIG. 101@...n-type silicon substrate 102...n'' region 103...element isolation region 104..."p- base region 105...n10 emifter region 106..."p+ region 07φΦ-oxide film 108φ-・Capacitor electrode 109・Nimitter electrode 110・Collector electrode Agent Patent attorney Seki Yamashita Figure 1 (A) (B) Figure 2, 2--Here Figure 4

Claims (1)

[Claims] (1) In a photoelectric conversion device in which the potential of a control electrode region of a semiconductor transistor is controlled via a capacitor, the capacitor has an electrode facing the control electrode region with an insulating layer in between, and A photoelectric conversion device characterized in that at least a portion of the electrode region facing the electrode is a region with a high impurity concentration.