JPS6038070B2 - solid-state imaging device - Google Patents

Description

Detailed Description of the Invention The present invention provides a solid-state imaging device that combines a photoconductor and an element having a self-scanning function, in which a plurality of electrodes are arranged to apply a voltage to the light guide, and a predetermined voltage is applied. This invention relates to a solid-state imaging device that improves the photoelectric characteristics of a light guide by providing a waveform.

Many conventional solid-state image devices have a photosensitive section on a silicon (Si) semiconductor substrate and a readout section adjacent to the photosensitive section for reading out signal charges accumulated in the photosensitive section.

One of the points of interest in expanding the dynamic range of photoelectric conversion of such a solid-state imaging device is to increase the maximum amount of signal charge that the photosensitive section and the reading section can handle. This amount is determined by physical quantities such as the shape of the photosensitive area and the extension area, impurity concentration there, and oxide film thickness. However, if a very strong light spot, such as one that causes signal charges of the maximum handleable amount to be generated in the semiconductor substrate, is incident directly on such an interbody imaging device, blooming is likely to occur.
FIG. 1 shows a conventional example for solving such problems. That is, for example, an N+ layer 2 corresponding to the drain and source of a MOS field effect transistor is formed on a P-type semiconductor substrate 1.
, 3 are provided. Here, the first N0 layer 2 is a signal charge output line, and a gate electrode 5 is provided between the first N0 layer 2 and the second N+ layer 3 with a gate oxide film 4 interposed therebetween. When reading signal charges, a voltage is applied to the gate electrode 5 to bring the surface of the semiconductor substrate 1 under the gate electrode 5 into a conductive state. An electrode 6 made of aluminum M, for example, is provided connected to the second N+ layer 3. This AI electrode 6 is formed so as to cover the first N+ layer 2 and the gate electrode 5 as well. Thick oxide films 9-1 and 9-2 are formed around the MOS field effect transistor formed by the first N+ layer 2, the second N+ layer 3, and the gate electrode 5. This oxide film 9-], 9-2, and the above A! A photoconductor layer 7 is formed on the electrode 6 . A transparent electrode 8 is then formed on this photoconductor layer 7. In the solid green camouflage layer as described above, since photoelectric conversion is performed within the photoconductor layer 7, the signal charge generated within the semiconductor substrate 1 can be extremely reduced, and therefore, the above-mentioned blooming can be reduced. can do. Furthermore, this solid-state imaging device has the advantage of high sensitivity because the photosensitive region covers the entire surface of the solid-state imaging device. In this way, a solid-state image sensor made of a combination of a photoconductor and an element having a self-scanning function can improve the drawbacks of conventional solid-state image sensors.

However, on the other hand, a new drawback arises in that the drawbacks of the photoconductor are carried over as they are. The biggest of these shortcomings is a phenomenon called "burn-in," in which an image captured once remains intact even after the subject is removed. In some cases, this phenomenon can be considered as a long-term afterimage in the image pickup tube, and it may disappear in just a few seconds, but it can also last for a long time, from tens of seconds to several minutes or more. Not only does this degrade image quality, but in severe cases it can even make continuous imaging impossible. This will be explained in more detail using figures.

FIG. 2 is a diagram of the conventional pixel of FIG. 1 viewed from above, showing the positions of the electrodes that sandwich the pixel and the photoconductor layer. In other words, the dotted rectangle in the figure is the AI electrode 6 in Figure 1.
represents and constitutes a pixel. The photoconductor layer 7 and transparent electrode 8 shown in FIG. 1 are formed over countless pixels over the entire area within the solid curve shown in FIG. For example, a positive voltage VT is applied to the transparent electrode 8 from the outside through a load resistor R. To explain the operation in relation to Fig. 1, the transparent electrode and the
The signal component due to the charge carriers photogenerated between the I electrodes is transmitted to the A field of the television image scan and is transmitted to A, . The voltages applied for a predetermined period to the gate electrodes 5 of the pixels corresponding to ~A, 4 and A2, ~A24 are transferred horizontally to the second N+ layer 3 and read out.

In the next B field, B, . The pixels corresponding to ~B4 and &, ~Chin4 are similarly read out. During this time, the voltage applied to the transparent electrode is always kept constant. If the photoconductor has extremely good photoelectric properties, a green image recorder with high sensitivity without blooming can be realized. However, since the self-scanning function element has the role of faithfully transmitting the signal converted by the photoconductor layer to the outside, if burn-in or photoconductive afterimage occurs in the photoconductor layer, it will not be reflected in the output image. Appears. The present invention has been made in view of the above points.

That is, the present invention has a structure in which the transparent electrode, which was conventionally formed uniformly on the photoconductor layer, is divided into a plurality of parts, and the voltage is changed over a predetermined period instead of applying a constant voltage. This eliminates the above-mentioned drawbacks and also makes it possible to add a function to control photosensitivity and photoelectric conversion characteristics. The present invention will be explained in detail below with reference to the drawings.

FIG. 3 shows the electrode arrangement of the photoconductor layer portion of the solid state imaging device according to the present invention.

The difference from the conventional device configuration is that the upper transparent electrodes are not uniform over the entire surface, but are arranged in A-1, A-2, B-1,
This point is that it is separated into multiple parts from B-2. The self-scanning functional element section is the same as in FIG. FIG. 4 shows the voltage waveforms connected to the device of FIG. 3.

The operation of the solid-state imaging device of the present invention will be described below with reference to FIGS. 3 and 4. The self-scanning functional element has an X-Y address type MOS structure as shown in FIG. The pulse VY for selecting the scanning line in the vertical direction gives the Y address corresponding to A-1, and the pulse Vx gives the Y address corresponding to A, . ~
Assume that addresses A and 4 are given. The number of pulses that address pixels in the horizontal direction is omitted. The pulse VY remains on during the IH period of the horizontal scanning period, and the pulse Vx causes each pixel A, . -A, 4 signals are read out sequentially. During this time, the transparent electrode of A-1 has V
As shown in ^-, for example, a positive voltage VT is applied, but after each horizontal pixel is read out, it is set to OV for an appropriate time (hereinafter referred to as the erase period) shown as T8 in the figure. After that, you will be returned to VT again. During this time, signals are read out using the X-Y address in the portion A-2 corresponding to the next scanning line, and a voltage of V^-2 that goes back and forth between VT and 0 is applied to the transparent electrode of A-2. This scanning is repeated in the vertical direction, and in the next B field, B-1, B-
After repeating the same operation in the order of 2, the process returns to A-1 and A-2 of the A field after one frame. By setting the voltage of the transparent electrode to OV during the erasing period TE, the noise is eliminated. In conventional image pickup tubes that use photoconductors, when image sticking occurs, the imaging operation is abandoned, the application of the target voltage is stopped, and the entire surface of the target is irradiated with uniform light to remove the image sticking, and the target voltage is applied again and the image is taken again. It was often done. However, the present invention can eliminate burn-in while continuously outputting images without interrupting the pseudo bale operation.

This J advantage is due to the fact that the transparent electrode, which was conventionally formed on the entire surface, is divided, and after reading out the signal at that location, the voltage applied to that part is removed and the burn-in is erased, while the signal is read out at the next location. This is because they are doing it.
It would seem that the present invention could be applied to an image pickup tube by dividing the transparent electrode of the target, but this is almost impossible. In other words, the part corresponding to the AI electrode 6 in FIG. 1 is the electron beam scanning surface of the target photoconductor and is not a fixed potential surface, so when the potential of the divided transparent electrode is lowered from VT to OV, the scanning surface becomes It falls relatively to -VT. When the divided transparent electrode was returned to VT again, the surface potential returned to its original value, and as a result, no change in the electric field occurred in the photoconductor. Burn-in and the like can be erased when the internal electric field of the photoconductor layer weakens, disappears, or becomes a reverse electric field. Therefore, in the image pickup tube, it is not possible to erase burn-in during the imaging operation. In the solid-state imaging device, the potential of the second N+ layer 3 in FIG. 1 is floating, but when the voltage of the transparent electrode is changed from VT to OV, it does not fall as much as the target surface potential of the image pickup tube.

Although there is some variation, the potential remains near the set potential after the signal is read or the substrate potential, so it is easy to weaken the electric field in the photoconductor or make it almost zero. In addition, in order to erase burn-in, it is not necessary to set the voltage of the transparent electrode to OV, and in the sense of limiting the electric field, it may be a value slightly lower than the VT that is constantly applied, and furthermore, it is possible to create a reverse electric field. The potential may be set as follows. It is thought that the burn-in is erased because the change in the electric field promotes the recombination of the carriers that were polarized and trapped inside the photoconductor.

Furthermore, it is thought that when a reverse electric field is applied, carriers injected from the electrodes are effective for recombination, so that burn-in can be eliminated in a short time. Furthermore, the present invention provides the following advantages.

Although the erasing period indicated by TE in FIG. 4 is set to be shorter than the IH period, it is not limited to this and may be extended to an appropriate period. By making this period longer, not only the burn-in can be completely erased, but also the photoelectric change characteristics can be controlled. That is, if there is no electric field during the erasing period, even if light is incident, the separation of generated carriers will be insufficient and photoelectric conversion will not occur. Therefore, while the conventional signal accumulation period is one frame, the accumulation period is reduced by the erasing period, and the photoelectric sensitivity is reduced. That is, sensitivity adjustment becomes possible by changing the erasing period. In addition, if the voltage is not set to OV during the TE period of the erase period and is set to a voltage lower than VT, the electric field is weak, so photoelectric conversion with poor sensitivity is performed, and when the voltage is returned to VT after the TE period, the sensitivity returns to normal, so photoelectric conversion is performed. The y axis of the conversion characteristic can be controlled.

In order to obtain the same effect, the voltage change and the erase period TE are almost inversely proportional. Further, the voltage may be changed not by one voltage change but by a plurality of pulses. By dividing the transparent electrode in this way and controlling the applied voltage, the photoelectric properties of the photoconductor can be improved. Note that when the self-scanning functional element is of the X-Y address type with a MOS configuration as shown in FIGS. 3 and 4, it is necessary to apply an erasing voltage to each of the divided electrodes at different times.

For this reason, a scanning circuit similar to the Y address for selecting the scanning line is required, but if the self-scanning functional element is, for example, an interline transfer type CCD, it is necessary to divide the electrodes and change the potential to obtain the same effect. It will be extremely easy to give.
In such a device, A field'
、． Signals from pixels ~A, 4, A2, ~4 are transferred to the transfer CCD all at once by turning on the transfer gate. Therefore, as shown in FIG. 5, in the case of A field, V^r. After turning on the voltage of the transfer gate indicated by , it is sufficient to set an erase period in common for V^-, V^-2, etc., and drop the potential from VT to OV. In the next B field, the signals from B, ~B, 4, &, ~B24 are sent to VB at once.
After the transfer as shown in Tc, an erase operation may be performed using VB-, VB-2, etc. in common. Therefore, the fin pole arrangement may be arranged in a comb-like manner in the horizontal direction, as shown in FIG. In the figure, transparent electrodes are shown by solid lines, and pixel electrodes are shown by dotted lines. Alternatively, they may have a shape that intersects in the vertical direction as shown in FIG. Although an example is shown in which each electrode is drawn out at two locations on the left and right or top and bottom, it is of course possible to collect the electrodes on one side using two-layer wiring. Next, another embodiment according to the present invention will be described using FIGS. 8 and 9. First, the 8th
In the figure, a P-type semiconductor substrate 1, a first N+ layer 2, a second
N layer 3, gate oxide film 4, gate electrode 5, AI electrode 6, and thick oxide films 9-1, 9-2 surrounding this MOS field effect transistor are provided, and an even thicker oxide film 9 is provided. For example, the AI electrode 10-1,
10-2 is provided. And on top of this, a photoconductor layer 11
The photoconductor layer 11 is connected to the AI electrode 6. In the above-mentioned solid-state imaging device, the photoconductor layer 11 is where photoelectric conversion is performed, but since there is no transparent electrode on the photoconductor layer 11, the signal charges generated in this layer 11 are transferred to the AI electrode 10- It moves due to the potential difference between 1 and 10-2 and the AI electrode 6. Even if there is a pinhole in the photoconductor layer 11 having such a structure, there is an advantage that an electrical short circuit between the AI electrodes 10-1, 10-2 and the N electrode 6 does not occur directly. The method of dividing the electrodes and operating them as described above is also effective for a device having such a configuration. That is, if we consider that a 10-1 or 10-2 mountain electrode is formed instead of a transparent electrode, it is sufficient to divide this N electrode and apply a predetermined voltage.

FIG. 9 shows the electrode arrangement when viewed from above. For ease of viewing, electrodes corresponding to 10-1 and 10-2 in FIG. 8 are shown with diagonal lines. Further, the electrode corresponding to 6 in FIG. 8 is indicated by a dotted rectangle. The device shown in FIG. 1 is different in that the electric field is mainly applied in the longitudinal or vertical direction of the photoconductor, whereas the device shown in FIG. 8 is applied in the lateral or horizontal direction. For this reason, in FIG. 9, the structure is such that a horizontal electric field is formed, and the electrodes are divided for each horizontal scanning line. As already explained, the voltage waveforms applied to these electrodes are as shown in Figure 4 when the self-scanning function element is a MOS x-Y address type, and as shown in Figures 6 and 7 in the case of a CCD transfer element. It is also possible to divide the electrodes in the figure, and the voltage waveform is the fifth
It will be as shown in the figure. FIG. 10 shows a modification of FIG. 8, in which the electrodes 10-1 and 10-2 to be divided are formed on the top of the photoconductor.

It is clear that the electrode division shown in FIG. 9 can be applied to this configuration as well, and it corresponds to the configuration and operation method of the present invention. Note that since the configurations shown in FIGS. 8 and 10 utilize lateral light guide, various electrode shapes are possible.

An example of this is shown in FIG. 11, where the parts corresponding to electrodes 10-1 and 10-2 are shown by diagonal lines, and the parts corresponding to electrode 6 are shown by black dots. As described in detail above, in a field imaging device that combines a photoconductor and a self-scanning functional element, the electrode that contacts the photoconductor, which is formed in a pair with the electrode that contacts the scanning functional element, is provided separately. By applying a voltage to the electrodes that weakens the electric field in the photoconductor for an appropriate period of time after signal readout, we can prevent burn-in and provide a new solid-state imaging device that can control photoelectric conversion ≠ depth characteristics and photosensitivity. can do.

Incidentally, as the electrode material, S-N2,1 to 03 may be used as a transparent electrode, and electrodes such as Mo and Ta may be used in addition to the N electrode, and the material may be selected depending on the purpose and manufacturing process.

The light guide body includes photoconductors conventionally used in image pickup tubes such as Sb-8 series, rudder-Se series, As-Se-Te series, and C.
Materials that exhibit a photoconductive phenomenon, such as dSe, ZnxCd, -xTe, or amorphous Si, can be used. Of course, the photoconductor may have a single layer or a plurality of composite layers. In addition, materials that have not conventionally been used for imaging due to their severe burn-in can also be used in the apparatus of the present invention. The electrodes may be formed by dividing them by using a suitable mask during vapor deposition or sputtering, or by etching after forming the electrodes over the entire surface.

Alternatively, a method may be used in which a thick oxide film or photoconductor is formed between the electrodes to be divided to provide a step, and the electrodes are diagonally deposited and formed separately. In addition, in the embodiment, examples of MOS X-Y address type and CCD were described as self-scanning functional elements.
The present invention is not limited to this, but can also be applied to BBD and CID.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional solid-state imaging device, FIG. 2 is a diagram showing the relationship between electrodes and pixels in the conventional example, FIG. 3 is a diagram showing the relationship between electrodes and pixels in the present invention, and FIG. FIG. 5 is a diagram showing the time relationship of electrode voltage waveforms according to the present invention, FIGS. 6 and 7 are diagrams showing other embodiments of the electrode arrangement of the present invention, and FIG. 8 is a diagram showing an example in which the electrode positions are changed. FIG. 9 is a diagram showing an example of electrode division, FIG. 10 is a diagram showing another embodiment in which the position of the electrode is changed, and FIG. 11 is a diagram showing an example of the configuration of electrodes for a unit pixel. It is a diagram. 1: semiconductor substrate, 2, 3: N ten layer, 4: gate oxide film,
5: Gate electrode, 6, 10-1, 10-2, 12: AI
Electrode, 7, 11: Photoconductor, 8: Transparent electrode, 9-1, 9
-2: Thick oxide film, A-1, A-2, B-1, B-2:
Split area. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Scope of Claims] 1. In a solid-state imaging device combining a photoconductor and a semiconductor element having a self-scanning function, an electrode electrically coupled to the photoconductor is formed by being divided into a plurality of parts, and the electrode is divided into a plurality of parts. After the signal of the pixel of the divided electrode section is read out, a voltage is applied to the divided electrode to at least weaken the electric field formed in the photoconductor for a predetermined period of time. Solid-state imaging device. 2. Applying a voltage to the divided electrodes such that the electric field formed in the photoconductor becomes almost zero for a predetermined period after the signals of the pixels of the divided electrode portions are read out. Claim 1 characterized in that
The solid-state imaging device described in . 3. Applying a voltage to the divided electrodes such that the electric field formed in the photoconductor is reversed for a predetermined period after the signal of the pixel of the divided electrode portion is read out. Claim 1 characterized in that
The solid-state imaging device described in .