JPH0724301B2 - Photoelectric conversion device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a photoelectric conversion device having at least an accumulation region for accumulating carriers generated by photoexcitation.

[Prior Art] FIG. 5A is a schematic sectional view of a conventional photoelectric conversion device,
FIG. 5B is an equivalent circuit diagram of the one photoelectric conversion cell.

In FIG. 5A, an n ⁻ region 2 is formed on an n silicon substrate 1 by epitaxial growth, and photoelectric conversion cells electrically isolated from each other by an element isolation region 4 are formed therein.

n ⁻ region 2 has a p base region 3 of a bipolar transistor
Is formed, and the n ⁺ emitter region 5 is formed therein.

Further, a capacitor electrode 7 is formed so as to face the p base region 3 with the oxide film 9 interposed therebetween, and constitutes a capacitor Cox for controlling the potential of the p base region 3.

An emitter electrode 6 is formed in the n ⁺ emitter region 5, and the whole is covered with a transparent protective film 8.

Then, an n ⁺ region 11 for ohmic contact and a collector electrode 12 of a bipolar transistor are formed on the back surface of the substrate 1 to form a photoelectric conversion cell.

In the basic operation of the photoelectric conversion cell, first, the p base region 3 biased to a negative potential is brought into a floating state, and holes among the electron-hole pairs excited and generated by the incident light 10 are accumulated in the p base region 3 (accumulation). motion).

Then, a positive voltage is applied to the capacitor electrode 7 to raise the base potential and forward bias between the emitter and the base, and the accumulated voltage generated by the accumulated holes is read out to the floating emitter side (readout operation). ).

Then, the emitter side is grounded and a positive voltage pulse is applied to the capacitor electrode 7 to erase the holes accumulated in the p base region 3. As a result, the p base region 3 returns to the initial state when the refresh positive voltage pulse falls (refresh operation).

In such a photoelectric conversion device, accumulated charges are amplified by the amplifying function of each cell before being read out, and thus high output, high sensitivity, and low noise can be achieved. Further, since it is structurally simple, it can be said that it is advantageous for future high resolution.

[Problems to be Solved by the Invention] However, the conventional photoelectric conversion device described above has the following problems.

First, part of the holes 13 generated in the substrate 1 due to incident light may move in the substrate 1 and flow into adjacent pixels.

Secondly, when strong light is incident, a large amount of holes are accumulated in the p base region 3, which raises the base potential. When the base potential rises above the collector potential, the depletion layer between the base and collector disappears and the accumulated holes in the base flow out to the adjacent cell.

When the holes moved from other pixels flow into the p base region 3 of the adjacent cell in this way, the read signal at that pixel does not correspond to the incident light, which causes smear at the time of image reproduction and causes image quality. Was significantly reduced.

[Means for Solving Problems] A photoelectric conversion device according to the present invention includes a first conductivity type semiconductor storage region (3) for storing carriers generated by photoexcitation, and a first conductivity type semiconductor opposite to the first conductivity type. A two-conductivity-type first main electrode region (5); a second-conductivity-type second main electrode region (2) provided in the depth direction of the accumulation region and joined to the accumulation region; The second main electrode region is provided in the depth direction,
A reverse bias voltage (+ Vcc, -Vc) is applied between the third semiconductor region (101) of the first conductivity type joined to the main electrode region and the second main electrode region and the third semiconductor region. Biasing means for applying, and a fourth region (4) provided around the accumulation region in the second main electrode region and having a concentration higher than that of the second main electrode region, Characterize.

[Operation] Since the present invention is configured as described above, carriers generated in a deep portion below the junction between the second main electrode region and the third semiconductor region or carriers overflowing from the accumulation region are treated as described above. 3 can be removed to the semiconductor region, and the effect of preventing charges from flowing out to the adjacent region and preventing smear can be obtained.

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

FIG. 1 is a schematic sectional view showing the structure of a first embodiment of the photoelectric conversion device according to the present invention.

In the figure, an n ⁺ buried layer 102 is formed on ap substrate 101, and an n ⁻ region 2, an n ⁺ element isolation region 4, ap base region 3,
Each n ⁺ emitter region 5 is formed, and a capacitor electrode 7 made of polysilicon or the like and an emitter electrode 6 made of Al or the like are further formed via an oxide film 9.

An electrode 104 is formed on the back surface of the p substrate 101 via a p ⁺ layer 103.

In the present embodiment, the electrode 104 is set to a negative voltage (for example, −5V), and the collector region n ⁻ region 2 applies a voltage to the n ⁺ buried layer 102 and the n ⁺ element isolation region 4 to generate a positive voltage Vcc.
Is set to.

As a result, the PN junction between n ⁺ buried layer 102 and p substrate 101 is reverse biased, and a depletion layer is formed mainly on the side of p substrate 101.
Therefore, the holes generated in the p substrate 101 are removed from the electrode 104 without flowing out to the adjacent pixel.

Further, even if strong light enters and holes overflow from the p base region 3, the outflow is suppressed by the n ⁺ element isolation region 4, and the light is attracted to the p substrate 101 side to prevent leakage into adjacent pixels. It

The configurations and operations of the capacitor Cox and the bipolar transistor are as already described.

FIG. 2 is a schematic sectional view showing the structure of the second embodiment of the present invention.

In this embodiment, since the n ⁺ buried layer 102 is formed excluding the lower portion of the n ⁺ element isolation region 4, a large depletion layer is formed below the element isolation region 4 also on the n ⁻ region 2 side. To be done.

Therefore, not only holes generated in the p substrate 101 but also holes overflowing from the p base region 3
It can be effectively removed to the side, and smear can be effectively prevented.

In each of the above embodiments, the base storage type photoelectric conversion cell is used, but the present invention can be applied to other methods such as an electrostatic induction type as long as it is a method of storing photoelectric charges.

FIG. 3 is a circuit diagram of a line sensor using the above embodiment.

In the figure, a constant positive voltage Vcc is applied to the n ⁻ region 2 which is the collector region of the photoelectric conversion cells S _{1 to} Sn through the n ⁺ buried layer 102. Further, a constant negative voltage Vc is applied to the electrode 104, and the PN junction 207 composed of the n ⁻ region 2 or the n ⁺ buried layer 102 and the p substrate 101 is in a reverse bias state.

Each capacitor electrode 7 is commonly connected to the terminal 201, and the terminal 2
A pulse φ ₁ for performing a read operation and a refresh operation is input to 01. The emitter electrodes 6 are connected to the vertical lines L _{1 to} Ln, respectively, and the vertical lines L _{1 to} Ln are connected to the storage capacitors C _{1 to} Cn via the transistors Qa _{1 to} Qan. The gate electrodes of the transistors Qa _{1 to} Qan are commonly connected to the terminal 203, and the pulse φ ₃ is input to the terminal 203.

The capacitors C _{1 to} Cn are connected to the output line 204 via the transistors Q _{1 to} Qn, respectively. Transistor Q ₁
Gate electrodes of Qn to Qn are respectively connected to parallel output terminals of the scanning circuit 205, and pulses φh _{1 to} φhn are sequentially output from the parallel output terminals.

The output line 204 is grounded via the transistor Qrh for refreshing, and the pulse φr ₂ is input to the gate electrode of the transistor Qrh.

The vertical lines L _{1 to} Ln are grounded via the transistors Qb _{1 to} Qbn, respectively, and the gate electrodes of the transistors are connected to the terminal 20.
2 is connected in common and pulse φ ₂ is input.

FIG. 4 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 stored in the photoelectric conversion cells S _{1 to} Sn. In this state,
The pulse φ ₃ turns on the transistors Qa _{1 to} Qan, the pulse φ ₂ turns off the transistors Qb _{1 to} Qbn to bring the emitter electrode 6 into a floating state, and the terminal 201 receives the positive voltage pulse φr for reading. As a result, as described above, the output signal of each cell is read to the floating emitter side, and each signal is stored in the capacitors C _{1 to} Cn. When the reading is completed, the transistors φa _{1 to} Qan are turned off by the pulse φ ₃ .

Then, turn on the transistors Qb _{1 to} Qbn by the pulse φ ₂ .
As a state, the emitter electrode 6 of each cell is grounded and the terminal 201
A refresh pulse φrc is applied to. As a result, the refresh operation already described is performed, and the holes accumulated in p base region 3 disappear. When the refresh operation is completed, each cell starts the accumulation operation.

Further, in parallel with the refresh operation, the scanning circuit 205 outputs pulses φh ₁ to φhn and sequentially turns on the transistors Q _{1 to} Qn.
Put in a state. As a result, the signals stored in the capacitors C _{1 to} Cn are sequentially taken out to the output line 204 and output to the outside as the output signal Vout through the amplifier 206.

At that time, each time each signal is output, pulses φh1 to φhn
A pulse φr ₂ is applied at the timing of overlapping with each other. At this timing, the transistor QRh turns ON and the output line 2
04 residual carrier is removed and capacitor C ₁ ~
The residual carriers of Cn are sequentially removed through the transistors Q _{1 to} Qn.

Thus the outputs of the read signals of all the cells S ₁ to Sn, the next read operation is started, the same way the operation is repeated.

By providing the PN junction 207, the image pickup apparatus using this embodiment can prevent unnecessary carriers from flowing out to the adjacent pixels. Therefore, smear can be suppressed and high image quality can be obtained.

The present invention can be applied to not only the above line sensor but also an area sensor.

[Effects of the Invention] As described in detail above, in the photoelectric conversion device according to the present invention, the second main electrode region and the third semiconductor region having different conductivity types are provided in the depth direction of the storage region, and the second main electrode region and the third semiconductor region are provided. A fourth bias electrode configured to apply a reverse bias voltage between the main electrode region and the third semiconductor region and having a higher concentration than the second main electrode region.
Region is provided around the storage region in the second main electrode region, carrier or storage region generated in a deep portion below the junction between the second main electrode region and the third semiconductor region is formed. Carriers overflowing from the can be removed to the third semiconductor region, and the outflow of charges to the adjacent region can be prevented.

As a result, smear, which has been a problem in the past, can be significantly reduced, and image quality can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the constitution of a first embodiment of the photoelectric conversion device according to the present invention, FIG. 2 is a schematic sectional view showing the constitution of the second embodiment of the present invention, and FIG. , A circuit diagram of a line sensor using the above embodiment, FIG. 4 is a timing chart for explaining the operation of the line sensor, FIG. 5 (A) is a schematic sectional view of a conventional photoelectric conversion device,
FIG. 5B is an equivalent circuit diagram of the one photoelectric conversion cell. 101 …… p substrate 102 …… n ⁺ buried layer 104 …… electrode 2 …… n ^- region 3 …… p base region 4 …… n ⁺ element isolation region 5 …… n ⁺ emitter region 6 …… emitter electrode 7 ...... Capacitor electrode 9 ...... Oxide film 10 ...... Incoming light

Claims (1)

[Claims] 1. An accumulation region (3) of a first conductivity type semiconductor for accumulating carriers generated by photoexcitation, and a second conductivity type first main electrode region (5) of a conductivity type opposite to the first conductivity type. A second main electrode region (2) of the second conductivity type provided in the depth direction of the storage region and joined to the storage region; and provided in the depth direction of the second main electrode region, The second
A reverse bias voltage (+ Vcc, -Vc) is applied between the third semiconductor region (101) of the first conductivity type joined to the main electrode region and the second main electrode region and the third semiconductor region. Biasing means for applying, and a fourth region (4) provided around the accumulation region in the second main electrode region and having a concentration higher than that of the second main electrode region, A characteristic photoelectric conversion device.