JPS5880975A - Image pickup 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 The present invention mainly relates to a solid-state imaging device in which an image pickup tube target or a photoconductive film is stacked (hereinafter referred to as a stacked solid-state imaging device).
The purpose of this invention is to eliminate afterimages, burning, and pluming phenomena that occur when the amount of charge generated by a photoconductive film exceeds the amount of charge that can be charged by a scanning circuit.

With the spread of home video tape recorders (vrR), video tape recorder cameras have also become increasingly popular over the past few years. There is an urgent need to develop image pickup tubes and solid-state imaging devices that can be applied with optical systems ranging from % inch to inch inch. In particular, in the case of solid-state imaging devices, as they become smaller, there is a concern that they may lack sensitivity when used alone. Therefore, in order to increase the light-receiving area, a photoconductive film is used as the light-receiving part, and this is combined with a scanning circuit board. Attention has been paid.

In image pickup tubes, if you try to maintain the resolution before miniaturization while the image pickup tube is downsized, it is necessary to narrow down the electron beam more, but if you narrow down the electron beam more, the current consumption will increase, and the beam current will increase accordingly. The only way to reduce power consumption is to reduce the power consumption. At this time, it is difficult to secure the necessary charging charge determined by the product of the photoconductive film capacitance and the knee voltage, and the uncharged charge causes an afterimage phenomenon.

In the case of a photoconductive film stacked solid-state imaging device, the scanning circuit board is an X-Y one in which MO8 switches are arranged in a matrix.
Address type and charge transfer type using C0D ('BBD etc.) are currently mainstream, but in the case of X-Y address type, reduction of random noise is an issue, and with BBD, transfer efficiency is essential. Since there is no improvement in CCD, the one using CCD is the most promising.In the case of CAN, the embedded channel C0D (BCO
However, the maximum amount of charge handled per cell of BOOD is small, and is about a fraction of the maximum amount of charge generated in a photoconductor. Therefore, in the case of a photoconductive film stacked solid-state imaging device, not only does it cause an afterimage phenomenon, but depending on the operating conditions, excessive charges may overflow to the transfer stage, causing a blooming phenomenon. The same is true for image pickup tubes, but in a photoconductive film stacked solid-state imaging device, the charge generated in the photoconductive film can be reduced by lowering the reset voltage (target voltage in the case of an image pickup tube); It goes without saying that a sufficient permeable voltage is not applied to the film, resulting in burnout.

In the case of the X-Y address type, in order to reduce the random noise mentioned above, it is necessary to reduce the vertical transfer line capacitance! However, in this case, the same phenomenon as in charge transfer type and image pickup tubes occurs. Further, when there is strong incident light, a charge exceeding the vertical transfer line capacity is generated, and at this time, the charge that cannot be read in the negative times causes afterimages and blooming.

In the present invention, an electrode is formed on a part of the photoconductive film of an image pickup tube target or a solid-state imaging device in which photoconductive films are laminated, and by applying an appropriate voltage to the electrode, excessive charges are generated in the photoconductive film. This is to prevent this from happening. The imaging device of the present invention can prevent image retention, burn-in and blooming that occur when the signal charge generated in the film on the light guide 1 exceeds the photoelectric charge of the scanning circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image pickup apparatus according to an embodiment of the present invention, particularly an excess charge limiting mechanism thereof, will be described below with reference to the drawings. Although the present invention is applicable to a one-type solid-state imaging device with a combination of an image pickup tube and a photoconductive film, a photoconductive film-stacked solid-state imaging device in which the scanning circuit is a COD will be used for explanation here. FIG. 1 shows a cross-sectional view of one pixel of a photoconductive film stacked solid-state imaging device.

In the figure, an n-well 11 and a diode 12 for forming a COD are formed on a p-type semiconductor substrate 10. 1
3 is a channel stop layer 91, and 14 is a selective oxidation region (LOGO8). From the transfer gate 16 and diode 12 of the COD to the CCD n well 11'
The gate 16 (hereinafter referred to as the reading gate), which is used to carry the technology to the
A gate oxide film 17 is formed below 6° 16 with a thickness of about 10 μm. The 5I8J1'-pole 18 which makes contact with a part of the diode 12 and the gate 16°16 are made of low melting point glass 19, for example P with a phosphorus concentration of 7 to 16%.
Insulated with EG. The first electrode 18 is a hole blocking layer Zn8e.
20 electrodes, and on the hole blocking layer 20 (Znz
cal-)CTe)7 (In, Te3)+-y
A photoconductive film 21 and a signal charge control electrode 22 according to the present invention are formed, and a transparent electrode 23 is formed thereon. In addition, in this embodiment, the signal charge control electrode 22 is
It is formed by etching after Mo is vapor-deposited. Reference numeral 24 denotes incident light irradiated onto the light receiving surface of the device.

FIG. 2 is an equivalent circuit diagram of one pixel of the solid-state imaging device having the above configuration, and the MO8FMT 31 is composed of the diode 12, n-well 11, and read gate 16 shown in FIG.
Its drain is not used as a transfer stage for COD. 32 is
This is a parasitic capacitance formed between the read gate 16 and the first electrode 18.

The numbers of other parts of the equivalent circuit are given in correspondence with those in FIG.

FIG. 3 is a plan view of the light-receiving surface of the same solid-state imaging device in which a plurality of picture elements having the configuration shown in FIG. 1 are formed, mainly showing the positional relationship between the first electrode 18 and the signal charge control electrode 22. There is. 12&
, 12b, 12c, 12d are diodes, 11a, 11
b is a C0Dn well.

As shown in the figure, in the case of the photographing device of this embodiment,
The signal charge control electrodes 22 are formed in a lattice shape with a pattern opposite to that of the first electrodes 18 .

FIG. 4 shows drive pulse waveforms of the above-described configuration and solid-state imaging device, and the operation of the device will be explained below. Read gate 16. at time to. When “on”, diode 12. The photoconductive film 21 and the blue trough 32 are charged to a predetermined potential C.
Ru. At the same time, diode 12 (121L in the case of i3 diagram)
The signal charge Qs is carried from ~12d) to C0D11b), and then transferred in the vertical direction by 8rQ at 15.76.

If the dark current is negligible, each charged capacitor discharges a charge proportional to the open signal for one frame period (33, 31115 ec), and is then charged again.

By the way, if the charging voltage of the photoconductive film 21 is To, the capacitance is Co, and the capacitances of the diode 12 and the parasitic capacitance 32 are CJ and c, respectively, the discharge of the charged charge is due to carriers generated in the photoconductive film. Maximum value of signal charge Q: *ax is Q', ILx: VO@ (00+01' +Cp)
+++・+++ (11. (In the case of an image pickup tube, if the target voltage is vT, then Q-8=-・00.) As mentioned above, in the case of a conventional image pickup device, the maximum value of this charge Q'm &:lC is several times larger than the maximum charge handling capacity "ll&!" of the CCD transfer stage, and cannot be fully charged with - times of charging, which may cause afterimage phenomenon, charge overflow at the transfer stage, and pluming phenomenon. If an attempt was made to make Q'max equal to QmlLX, sufficient voltage would not be applied to the light guide Ik film, resulting in a burn-in phenomenon.

In contrast, the signal charge limiting mechanism in the imaging device of the present invention eliminates the above-mentioned conventional drawbacks, and will be described below. FIG. 6(a) shows an energy band diagram of the photoconductive film 21 in the image pickup device of the present invention, where the solid line 9 points and scarlet indicate the part 1) where there is no signal charge control electrode 22). shows the energy band state when an appropriate applied voltage is applied. In the case of low illuminance, the lateral resistance of the photoconductive film 21 is sufficiently high ((10"Ω-
m or more) The charge generated in the area where the signal charge control electrode 22 is not present almost always reaches the first electrode 18, but under high illumination, the lateral resistance decreases and the charge is mostly transferred to the control electrode 22. moves. On the other hand, the charge that is not caught and reaches the 1st 4th electrode 18 lowers the potential of the 1st 4th electrode 18, as shown in Fig. 6 (b).
), the first electrode 18
The charge outside the control electrode moves from the direction of the first electrode 1.
The potential of 8 is 10,.

It is equal to the signal charge control electrode 22 and cannot be less than that. Therefore, the signal charge control electrode 22 can limit the amount of signal charge.

In this example, Zn5e was used as the hole blocking layer 20 with a film thickness of 30 Ω, and the photoconductive film 21 was made with ZnOtl,
'I'e) (InzTes), -, film thickness
-17 When formed at 7ec0, the knee voltage of the photoconductive film (Kn
6.voltage) is approximately 6v. At this time, when a voltage of 4V is applied to the signal charge control electrode 22, the voltage at the first electrode cannot be less than 4V. Therefore, from equation (1), the maximum signal charge is The quantity Q-8 becomes Akira. The charge limiting function described above tends to be effective even when applied to solid-state imaging devices with large vertical transfer line capacitance, as in the case of the X-Y address type. Reading the signal during the blanking blanking period is as follows:
Corresponding to reverse biasing the photoconductor, if there is strong incident light, the charge generated during the signal reading period will exceed the vertical transfer line capacitance, causing image retention or pluming11. When a predetermined potential is applied to the signal charge control electrode during the storage period as in the invention, the afterimage or blooming phenomenon is greatly reduced. Also, during the signal reading period, if a pulse is applied to the signal charge control electrode so that the potentials of the first electrode and the signal charge control electrode are the same, the charge generated during the signal reading period when there is strong incident light is can be completely prevented from being loaded.

This also applies to charge transfer type imaging devices.

In the case of an image pickup tube, the back surface potential may be considered instead of the above-mentioned first electrode, and it is a limiting force button for the amount of signal charge as in the case of the solid-state image pickup device embodiment.

If there is a risk of hole injection or breakdown of the photoconductive film due to the control electrode on the hole blocking layer, it is preferable to form the control electrode in the hole blocking layer. Further, even when using only one layer such as amorphous 19i and no hole blocking layer, the same effect can be obtained by forming the control electrode in iL-. Furthermore, the signal control electrode.

- It only needs to exist in a part of the picture element, but if it is structured like the third factor and made non-transparent, even strong incident light can pass through the gap between the first electrodes and penetrate into the Si substrate. The carriers generated in the charge transfer stage enter the charge transfer stage, and
It is also possible to suppress the phenomenon of white trailing in areas where there is no Gogo (smearing).

As explained above, even when the charge generated in the photoconductive film is larger than the chargeable charge of the scanning circuit, the imaging device of the present invention enables imaging without causing image retention, burn-in, or blooming phenomena, and is industrially applicable. has high utility value.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of an imaging device according to an embodiment of the present invention, FIG. 2 is an isometric schematic diagram of the same imaging device, FIG. Figure (IL), (b
) is a diagram showing the driving pulse of the imaging device, and FIG. 6 (IL
) and (b) are diagrams of energy bands for explaining the operation of the imaging device. 1o...p-type semiconductor substrate, 11...-n
well, conversion region, 16...transfer gate, 16.
...reading gate, 17...gate oxide film, 18...first electrode, 19...insulator layer, 20...hole Blocking layer, 21...
・Photoconductor, 22...Signal charge control electrode, 23
...Transparent electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 4 Figure 5 Figure 1

Claims (1)

[Scope of Claims] (1) A photoconductive film, a transparent electrode formed on at least one surface of the photoconductive film, and a scanning circuit, the photoconductive film having an electrode in a partial area. Characteristic imaging device. (2) The imaging device according to claim 1, wherein the scanning circuit comprises a charge transfer element. (3) The imaging device according to claim 1, wherein the scanning circuit is a semiconductor circuit element having an X-Y AV 11 function. (4) The imaging device according to claim 1, wherein the scanning circuit is composed of an electron beam. (6) The imaging device according to claim 1, wherein the electrode is made of a non-transparent material. (6) The imaging device according to claim 1, wherein the knee voltage of the photoconductive film is applied to the electrode provided on the photoconductive film at least during the signal charge accumulation period. (71) The imaging device according to claim 1, wherein the same potential as the signal reading potential is applied to the electrode provided on the photoconductive film at least during the signal reading period.