JP2501207B2 - Photoelectric conversion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion device of a type in which carriers generated by photoexcitation are accumulated in a control electrode region of a transistor, and particularly to prevent outflow of excess carriers. The present invention relates to an intended photoelectric conversion device.

[Prior Art] FIG. 7 (A) is a schematic sectional view of a photoelectric conversion device, FIG.
FIG. 1B is an equivalent circuit diagram of the one photoelectric conversion cell.

In FIG. 7 (A), an n ⁻ epitaxial layer 4 is formed on an n silicon substrate 1, and photoelectric conversion cells electrically isolated from each other by an element isolation region 6 are arranged therein.

First, a p base region 9 of a bipolar transistor is formed on the n ⁻ epitaxial layer 4, and an n ⁺ emitter region 15 is formed therein. 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 oxide film 12 in between.

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

In the basic operation of the photoelectric conversion cell, first, the p base region 9 biased to a negative potential is brought into a floating state, and holes of electron-hole pairs generated by photoexcitation are accumulated in the p base region 9 (accumulation operation).

Subsequently, a positive voltage is applied to the capacitor electrode 14 to bias the emitter and the base in the forward direction, and the accumulated voltage generated by the accumulated holes is read to the floating emitter side (reading 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 the initial state when the positive voltage pulse for refresh falls (refresh operation).

In such a photoelectric conversion device, the accumulated charge is amplified by the amplification function of each cell and then read.
High output, high sensitivity, and low noise can be achieved. In addition, since it is structurally simple, it can be said that it is also advantageous for increasing the resolution.

[Problems to be Solved by the Invention] However, when a plurality of photoelectric conversion cells are arrayed to form a photoelectric conversion device, smear occurs when a certain pixel is irradiated with light of a saturated light amount or more. Had. That is, when strong light enters, a large amount of holes are accumulated in the p base region 9 and the base potential rises. When this base potential rises above the collector potential, the depletion layer 22 between the base and collector disappears and the accumulated carriers in the base flow out to the adjacent cell (arrow 2
3). As a result, an inflowing hole is added to the p base region 9 of the adjacent cell, which causes a storage state, which causes smearing when the read signal is image-reproduced.

[Means for Solving Problems] The present invention is intended to solve the above conventional problems, and an object thereof is to provide a photoelectric conversion device capable of preventing smear and the like and obtaining an accurate output signal. To provide.

A photoelectric conversion device according to the present invention stores a carrier generated by photoexcitation in the control electrode region by controlling a potential of a control electrode region of the semiconductor transistor, and stores a storage voltage generated by the storage in one of the semiconductor transistors. In a photoelectric conversion device having a plurality of photoelectric conversion cells of a method of reading from a main electrode region, the main electrode regions of the plurality of photoelectric conversion cells are connected to one end of a semiconductor element that performs a switching operation depending on a potential difference between both ends. At the same time, by connecting to the other end of the semiconductor element a predetermined common potential at which the semiconductor element conducts when excess carriers of a predetermined level or more are accumulated in the control electrode area, excess carrier in the control electrode area is connected. Is provided from the main electrode region side so as to remove excess carrier.

[Operation] Since excess carriers accumulated in the control electrode region can be automatically removed by such excess carrier removing means, excess carriers do not flow out to an adjacent cell, and smearing of a reproduced image is prevented. can do.

EXAMPLES Examples of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic circuit diagram of a first embodiment of the photoelectric conversion device according to the present invention.

In the figure, a photoelectric conversion cell S ₁ to S _n shown in FIG. 7 are arranged in a line, a constant positive voltage Vcc is applied to the collector electrode 12 of each photoelectric conversion cell. Each capacitor electrode 17 is connected to a parallel output terminal of the scanning circuit, and each photoelectric conversion cell performs a read operation or a refresh operation according to signals φh _{1 to} φh _n from each output terminal.

Further, each emitter electrode 19 is commonly connected to the output line 103 via each of the transistors Q _{1 to} Q _n.
The gate electrodes _{1 to} Q _n are connected to the parallel output terminals of the scanning circuit, similarly to the capacitor electrodes 17. Further, each emitter electrode 19 is connected to a constant voltage line Lrh via PN diodes D _{1 to} D _n , and a voltage Vcc is applied to the line Lrh.
A lower constant voltage Ve is applied. Therefore, the p base region 9 of each cell is connected to the line Lrh via the PN junction with the emitter region 15 and the PN junction of the diodes D _{1 to} D _n .

The output line 103 is grounded via the transistor 104 and is also connected to the amplifier 105. A read signal is serially output from the output terminal 106 of the amplifier 105 to the outside. The signal φhrs is applied to the gate electrode of the transistor 104.
Is applied to refresh the output line 103.

Next, the operation of this embodiment having such a configuration will be described as a second operation.
This will be described with reference to the drawings.

FIG. 2 is a timing chart for explaining the operation of this embodiment.

(Refresh Operation) First, the transistor 104 is turned on by the signal φhrs, the output line 103 is grounded, and the signals φh _{1 to} φh _n are sequentially output from the parallel output terminals of the scanning circuit.

As a result, the transistors Q _{1 to} Q _n are sequentially turned on, the emitter electrodes 19 are sequentially grounded through the output line 103, and the pulses φh ₁ to
φh _n is sequentially applied to each capacitor electrode 17. With this, the refresh operation as described above is performed,
The carriers accumulated in p base region 9 are removed.

(Storage operation) No voltage is applied to the capacitor electrode 17 and the transistor Q ₁
The to Q _n as the OFF state, to accumulate the amount of carriers corresponding to the illuminance of the incident light in the p base region 9.

At that time, when strong light is incident and excess carriers (holes here) are accumulated and the base potential rises to about 1.4V higher than the constant voltage Ve, the PN junction between the constant voltage Ve and the line Lrh is formed. In the forward bias state, excess carriers flow out to the line Lrh through the PN junction between the base and the emitter and the PN junction of the diode D.

Thus, even if strong light is incident, excess carriers in the base region 9 are removed to the line Lrh, and the outflow to the adjacent cell as in the conventional case is prevented.

(Read operation) After the accumulation operation is performed for a fixed time, the signal φhrs is set to the low level to turn off the transistor 104, and the output line 10
Make 3 floating.

Subsequently, first, the signal φh ₁ is output from the scanning circuit, and the read pulse is applied to the capacitor electrode 17 of the photoelectric conversion cell S ₁ . As a result, the transistor Q ₁ is turned on, the signal of the cell S ₁ is read to the output line 103 through the transistor Q ₁ , and the output signal from the output terminal 106 is output through the amplifier 105.
It is output as V ₁ .

When the output signal V ₁ is output, the signal φhrs turns on the transistor 104, and the carriers remaining on the output line 103 are removed.

Similarly, the signal φh ₂ ~φh _n are sequentially outputted from the scanning circuit, the read pulse is applied to the photoelectric conversion cell S ₂ to S _n of the capacitor electrode 17. Then, each output signal V ₂ , V ₃ ...
Is output from the output terminal 106, the transistor 104
Is turned on and the output line 103 is refreshed.

In this way, the signals of the photoelectric conversion cells S _{1 to} S _n are directly read to the output line 103 through the transistors Q _{1 to} Q _n ,
It is output to the outside through the amplifier 105. Therefore, the high output signal of the photoelectric conversion cell appears on the output line 103.

Further, as shown in the figure, in order to supply the voltage applied to the capacitor electrode 17 and the gate voltages of the transistors Q _{1 to} Q _n together by the outputs φh _{1 to} φh _n from the scanning circuit,
The circuit configuration is simple.

Furthermore, since excess carriers are removed to the line Lrh, smearing of reproduced images can be prevented.

The pulse φrh in FIG. 2 is a pulse required in the second embodiment described below.

FIG. 3 is a schematic circuit diagram of the second embodiment of the present invention. However, the same circuit parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the emitter electrode 19 of each cell is connected to the constant voltage line Lrh via the transistors Q _{e1 to} Q _en . The pulse φrh is applied to the gate electrode of the transistor Q _e1 to Q _en, as in a state where the pulse φrh is applied source-drain voltage of the transistor Q _e1 to Q _en becomes conductive and exceeds a certain value It is set.

With this configuration, the operation is performed at the timing including the pulse φrh shown in FIG. This causes the transistors Q _{e1 to} Q
_A pulse φrh is applied to the gate electrode of _en only during the storage operation, and the transistors Q _{e1 to} Q _en at this time are turned on by the potential difference between the source-drain voltage, that is, the constant voltage Ve and the emitter voltage of each cell. Is determined. Therefore, excess carriers accumulated in the p base region 9 can be removed to the line Lrh through the transistors Q _{e1 to} Q _en .

Next, the photoelectric conversion cell used in the third embodiment of the present invention will be described.

FIG. 4 (A) is a schematic plan view of a photoelectric conversion cell described in Japanese Patent Application No. 60-252653, FIG. 4 (B) is a sectional view taken along line AA, and FIG. ) Is an equivalent circuit diagram thereof.

In the drawings, on an n silicon substrate 201 n ^- epitaxial layer 203 is formed, n ^- the epitaxial layer 203 p
A base region 204 is formed, and n ⁺ emitter regions 205 and 205 'are formed in the p base region 204. And n ⁺
Emitter electrodes 208 and 208 'are connected to the emitter regions 205 and 205', respectively.

In this example, the isolation region 202 is formed by the insulating region 214 and the n ⁺ region 215 provided immediately below the insulating region 214,
Adjacent photoelectric conversion cells are electrically separated from each other.

A capacitor electrode 207 is formed on the p base region 204 with the oxide film 6 interposed therebetween, and a light shielding film 217 is further sandwiched with an insulating film 216 interposed therebetween.
Are formed. The light-shielding film 217 shields the portion where the capacitor electrode and the emitter electrode are formed from light, and forms a light-receiving surface in the main portion of the p base region 204. In addition, a protective insulating film is formed on the light-shielding film 217 and the insulating film 216 serving as the light-receiving surface.
218 is formed.

The basic operation is the same as in the above embodiment. First, photoexcited carriers are accumulated and the potential of the p base region 4 changes in the positive direction (accumulation operation).

Then, a positive voltage pulse for reading is applied to the capacitor electrode 207, and the reading signal is applied to the emitter electrode 208 and / or
Or it is output from 208 '(reading operation).

In addition, the emitter electrode is grounded and a refresh pulse of a positive voltage is applied to the capacitor electrode 207 to perform the refresh operation.

In the photoelectric conversion cell having such a double-emitter structure, one emitter can be used for signal reading and the other emitter can be used for removing excess carriers, as shown below.

FIG. 5 is a schematic circuit diagram of a reference example using the photoelectric conversion cell shown in FIG. However, the same circuit parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this reference example, one emitter electrode 208 'of each cell is commonly connected to a constant voltage line Lrh and a constant voltage Ve is applied.

As a result, the voltage Ve is applied to the n ⁺ emitter region 205 ′, and when strong light is incident and the base potential rises, excess carriers are removed to the line Lrh through the PN junction of the emitter region 205 ′.

In each of the above-mentioned embodiments, the case of the line sensor is shown, but it is obvious that it can be applied to the area sensor as it is, and the same effect can be obtained.

FIG. 6 is a schematic configuration diagram of an example of an image pickup apparatus using the above embodiment.

In the figure, the image pickup device 301 has the configuration of each of the above-described embodiments, and the output signal Vout is subjected to processing such as gain adjustment by the signal processing circuit 302 and output as a standard television signal such as an NTSC signal.

Further, various pulses φ for driving the image sensor 301,
The voltage Vcc and the constant voltage Ve are supplied by the driver 303, and the driver 303 operates under the control of the control unit 304.
Further, the control unit 304 adjusts the gain of the signal processing circuit 302 based on the output of the image pickup device 301, and the exposure control unit 3
05 is controlled to adjust the amount of light incident on the image sensor 301.

As described above, the image pickup device 301 according to the present invention accurately converts the information of incident light into an electric signal, and a high-quality image without smear can be obtained.

[Advantages of the Invention] As described in detail above, the photoelectric conversion device according to the present invention can automatically remove excess carriers accumulated in the control electrode region of the transistor by the excess carrier removal means. Will not leak to the adjacent cells, and smearing of reproduced images can be prevented.

Moreover, since the excess carrier removing means is provided on the main electrode region side, the aperture ratio is not impaired.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of a first embodiment of a photoelectric conversion device according to the present invention, FIG. 2 is a timing chart for explaining the operation of the present embodiment, and FIG. 3 is a second diagram of the present invention. FIG. 4A is a schematic plan view of a photoelectric conversion cell described in Japanese Patent Application No. 60-252653, and FIG. 4B is a schematic circuit diagram of the embodiment.
FIG. 4C is a sectional view taken along the line A, FIG. 4C is an equivalent circuit diagram thereof, FIG. 5 is a schematic circuit diagram according to a reference example using the photoelectric conversion cell shown in FIG. 4, and FIG. FIG. 7 (A) is a schematic configuration diagram of an example of an image pickup apparatus using the example, which is disclosed in JP-A-60-12759 to JP-A-60-127.
FIG. 7 (B) is a schematic cross-sectional view of a photoelectric conversion cell described in Japanese Patent Publication No. 65-65, which is an equivalent circuit diagram. 1 ... n substrate 4 ... n ^- epitaxial layer 6 ... element isolation region 9 ... p base region 12 ... insulating layer 14, 17 ... capacitor electrode 15 ... n ⁺ emitter region 19 ... emitter electrode 21 ... … Collector electrode 103 …… Output line 105 …… Output amplifier D _{1 to} D _n …… Diode Qe _{1 to} Qe _n …… Transistor Lrh …… Constant voltage line

Claims (5)

(57) [Claims] 1. A carrier electrode generated by photoexcitation is accumulated in the control electrode region by controlling the potential of the control electrode region of the semiconductor transistor, and the accumulated voltage generated by the accumulation is stored in one of the main electrode regions of the semiconductor transistor. In a photoelectric conversion device having a plurality of photoelectric conversion cells of the method of reading from, while connecting the main electrode regions of the plurality of photoelectric conversion cells to one end of a semiconductor element that performs a switching operation depending on the potential difference between both ends, The other end of the semiconductor element is connected to a predetermined common potential that makes the semiconductor element conductive when excess carriers of a predetermined level or higher are accumulated in the control electrode region, thereby eliminating excess carriers in the control electrode region. A photoelectric conversion device having an excess carrier removing means that can be removed from the main electrode region side. 2. The semiconductor element comprises a potential barrier that depends on a potential difference between both ends.
The photoelectric conversion device according to the item. 3. The photoelectric conversion device according to claim 2, wherein the semiconductor element is a PN junction. 4. The photoelectric conversion device according to claim 3, wherein the PN junction is a PN junction diode. 5. The photoelectric conversion device according to claim 1, wherein the semiconductor element is a transistor which becomes conductive when the potential difference between both ends exceeds a predetermined level.