JPH0127591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device having a photoconductor on its surface. The object of the present invention is to provide a solid-state imaging device that does not cause blooming and improves the yield of scratches on photoconductors by converting the changes in current flowing between the source and drain of the photoconductor and using this current change as an optical signal.

Conventionally, solid-state imaging devices have been proposed that combine photoconductors, charge transfer elements such as CCDs and BBDs, and MOSFETs (for example, see Japanese Patent Application Laid-Open No. 51-95720). Charge was once accumulated in a diode capacitor formed in a semiconductor substrate, and transferred to a charge transfer stage using a MOSFET during the read period. In other words, the photogenerated charge was directly used as optical information, and from another perspective, reading a signal is equivalent to applying a reverse bias to the diode and photoconductor. Therefore, even during the signal reading period, the photoconductor remains photosensitized and charges flow into the charge transfer stage. In normal cases, the charge generated during the above signal reading period can be ignored, but if there is strong incident light or if there is a large leakage current in a part of the photoconductor (such as a scratch), the charge generated during the above signal reading period may be ignored. Charges flowing into the transfer stage overflow into the charge transfer stage or flow into adjacent picture elements. As a result, when a part of the solid-state imaging device is irradiated with strong spot light, the spot light spreads in the vertical and horizontal directions, resulting in blooming. The same applies if there are scratches.

As is clear from the above, the above-mentioned blooming and spread of scratches are caused by using electric charges generated by a diode in a photoconductor or a semiconductor substrate as a direct signal. Therefore, it is possible not only to use a structure without a photoconductor, but also a structure that combines a photoconductor and an XY address type (for example,
91116), it is essentially irremovable. In order to overcome the drawbacks of solid-state imaging devices with the above configuration, one electrode of the photoconductor is
Solid-state imaging devices have been proposed in which the gate electrode of a MOSFET is connected to the source of another MOSFET, and a reverse bias is applied to the photoconductor in the latter MOSFET (for example, Publication No. 51-3223), per picture element, 2
Because two MOSFETs were required, there were many problems in creating a higher-resolution solid-state imaging device.

The present invention does not directly use charges photogenerated in a photoconductor as signal charges, but instead uses changes in the current flowing between the source and drain of a MOSFET due to changes in gate potential due to photogenerated charges as optical information. To provide a solid-state imaging device with a simpler configuration that does not cause blooming or spreading of scratches.

The present invention will be described below based on examples with reference to the drawings.

FIG. 1 shows a cross-sectional view of one pixel of an embodiment of the solid-state imaging device of the present invention, which includes a photoconductor formed to be electrically connected to the gate electrode of a MOSFET. N ⁺ type regions 11 and 12 are provided on a p-type semiconductor substrate 10 and used as sources and drains, respectively, and wirings 15 and 16 are formed using Al or the like. 13,
14 are a gate oxide film and a gate electrode, respectively. The above constitutes one MOSFET. 1
Reference numeral 7 denotes an insulator layer, which insulates the first electrode 18 and the MOSFET except for a part of the gate electrode 14.
19 is a photoconductor made of (Zn _x Cd _1-x Te) _1-y (In ₂ Te ₃ ) _y , on which a transparent electrode 20 is formed, and incident light 21 is irradiated from the transparent electrode side. .

FIG. 2 shows a circuit diagram when a plurality of units of the solid-state image sensor shown in FIG. 1 are formed.
-34 and 35-38 correspond to the MOSFET and photoconductor in FIG. 1, respectively. 39
42 corresponds to transparent electrodes. 43 and 44 are MOSFETs that are turned on by the output pulse of the vertical scanning circuit.
A constant voltage power supply 45 is connected to the source region.
46 and 47 are MOSFETs that are turned ON by a pulse from 48 every horizontal retrace period. The details will be described later.

The driving pulses shown in FIGS. 3a to 3d are applied to the solid-state imaging device of the above embodiment. Y ₁ and Y ₂ are vertical scanning pulses that drive MOS switches 43 and 44, and when turned on at times T ₁ and T ₅ , the power supply 45
Current is supplied to horizontal lines 49 and 50. Of the electron-hole pairs photogenerated in the photoconductor,
Electrons move to the transparent electrode side, holes move to the first electrode,
The potential of the first electrode increases in proportion to the photogenerated charge. Therefore, the current flowing through MOSFETs 31 to 34 is proportional to the number of photogenerated charges, that is, the light intensity, and at time _T2 , when MOSFETs 46 and 47 are turned on in response to the pulse shown in Figure 3b, the charges become horizontal. It is moved to a shift register and then output in chronological order. After transferring the charge to the horizontal shift register, at time T ₃ the pulses Z ₁ ,
The potential of the transparent electrode is lowered by _Z2 and the photoconductor is changed from the previous reverse bias state (accumulation state) to a forward bias state, so the potential of the first electrode is also lowered and the reset is completed. For interlacing, the transparent electrode is isolated for each horizontal pixel group, and for frame accumulation, a separate pulse is applied for each horizontal pixel group as shown in FIG. This pulse can be easily obtained using a shift resist. Also, when performing field accumulation, the pulse is 2
It is sufficient to reset the photoconductor for each field.

In the case of a solid-state image sensor with the above configuration, the photoconductor is not reset during the signal reading period, and even if there is strong incident light or scratches, the photoconductor will not be reset.
The gate electrode 18 of the MOSFET remains at the transparent electrode potential and no further charge is generated during this period. Therefore, unnecessary charges are not output, and spot lights and point scratches do not spread in the vertical direction. Furthermore, since the output can be amplified by changing the potential setting of the source section of the MOSFET or the pulse period of vertical scanning, there is no need for a preamplifier that is normally required for the output section.
Furthermore, the transparent electrode potential can be made sufficiently high, and even when using a photoconductor with knee characteristics,
Burn-in and the like do not occur, and the dynamic range can be made variable by changing the transparent electrode potential.

In the above, vertical transfer is performed using a bus line, and horizontal transfer is performed using a charge transfer element such as a CCD.
The drain portion 12 of the MOSFET may be used as a charge transfer stage such as a CCD or BBD to perform vertical transfer. Also as a photoconductor (Zn _x Cd _1-x
Although Te) _1-y (In ₂ Te ₃ ) _y was used, it is perfectly acceptable to use another photoconductor (for example, amorphous Si, etc.).

As is clear from what has been described above, if the present invention is used, the simple structure allows the signal to be transmitted in the vertical direction even when strong spot light is incident or when there is a large leakage current due to scratches on the photoconductor. It does not spread at all.

Further, since it is possible to amplify each pixel, there is no need for a preamplifier in the output section, and high sensitivity can be obtained even in low illuminance. Therefore, its industrial significance is extremely large.

[Brief explanation of drawings]

FIG. 1 is an elemental configuration diagram showing an embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of the present invention, and FIGS. 3 a to 3 d are explanatory diagrams of the operation of the above embodiment. DESCRIPTION OF SYMBOLS 10... Semiconductor substrate, 11, 12... N ⁺ type region, 13... Gate oxide film, 14... Gate electrode, 18... First electrode, 19... Photoconductor, 20
...Second electrode.

Claims (1)

[Claims] 1. A semiconductor substrate on which a circuit element having a charge scanning function is formed, a photoconductor provided via a first electrode formed for each picture element on the semiconductor substrate, and a photoconductor formed on the photoconductor. a control electrode of the MOS field effect transistor and a second electrode of the MOS field effect transistor that reads the charge generated by the photoconductor; are electrically connected to each other, a pulse voltage that reverse biases the photoconductor is applied to the second electrode during an optical information reading operation period, and after the optical information reading operation is completed, a pulse voltage is applied to the second electrode, A solid-state imaging device characterized in that a pulse voltage is applied to change the photoconductor from a reverse bias state to a forward bias state.