JPH07106541A - Ccd element prevented from darkening - Google Patents

Abstract

PURPOSE:To prevent the dark current of a CCD element from increasing in a radiation environment, by providing a light shielding film made of a nonconductive material in the optical-black region of the CCD element. CONSTITUTION:In a CCD element, a plurality of electrodes 15 and a plurality of photodiodes 17 are provided on an insulation layer 14 formed on the surface of a p-type semiconductor substrate 13, and a part of the electrodes 15 is so shielded with a light shielding film 24 that the part is made to be an optical- black region 23 for determining the black level of a video signal. In this CCD element, the light shielding film 24 is so made of a nonconductive material that a CCD element 18 prevented from darkening is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a CC for various inspection and monitoring.
The present invention relates to a D camera, and particularly to an anti-darkening CCD element that can be used in a radiation environment in a nuclear power plant in use.

[0002]

2. Description of the Related Art In recent years, maintenance and inspection in a high dose environment of radiation in a nuclear power plant has been difficult in many places due to exposure of workers, so maintenance and inspection of equipment installed especially in a high dose environment. In the field, fixed type or mobile type monitoring devices that run along a track laid on the ceiling have been put into practical use, and these monitoring devices include charge coupled devices (CCD devices) as visual systems. An abbreviated camera is installed.

The perspective view of FIG. 4 shows a schematic structure of a mobile monitoring device using a CCD camera. A visual inspection robot 2 is suspended on a track 1 laid along the inspection route. 2 is controlled by the operation of the operation panel 3 via the host computer 4. A signal transmission path 5 connected to the host computer 4 is installed on the track 1, and a signal transmitter 6 is connected to the operation panel 3 and the host computer 4.

A visual inspection robot 2 suspended on a track 1
Is a vehicle body 7 including an electric circuit, a rack pinion and a guide wheel 9 (not shown) rotated by a drive mechanism 8 integrally provided on the upper surface of the vehicle body 7, and the vehicle body 7
It is composed of a platform 10 provided on the lower surface of the platform and capable of horizontal and vertical rotation within a certain range, and a CCD camera 11 attached to the platform 10.

This CCD camera 11 has an optical lens for photographing an object to be monitored, a CCD element in which a large number of CCDs arranged at the rear of the lens to convert a projected image into an electric signal are arranged in a matrix on a plane, and It consists of a preamplifier and so on.

The electric circuit contained in the vehicle body 7 includes a control circuit for controlling the platform 10, a signal transmission circuit for frequency-modulating and transmitting the image pickup signal of the CCD camera 11, and a start / stop of the drive mechanism 8. Control circuit, and signal transmission line 5
It includes a contact current collector or the like that comes into contact with and exchanges signals. The control circuit includes a signal transmitter for exchanging signals with the signal transmission path 5, and a microcomputer.

The cross section of the track 1 is a rectangle with a part of the bottom cut off, the guide wheels 9 of the drive mechanism 8 are mounted on both inner sides of the bottom side, and the rack and pinion (not shown) is also a rack rail in the track 1 (not shown). , So that the visual inspection robot 2 can move.

Therefore, the visual inspection robot 2 is moved on the track 1 to photograph the inside of the nuclear power plant with the CCD camera 11 even in a radiation environment, and the image pickup signal is sent to the operation panel 3 to perform various operations. Operation panel 3
It is monitored by the monitor 3a such as a CRT above.

As described above, in general, the inside of a nuclear power plant is narrow, and one operation cycle is as long as about one year. Therefore, the visual inspection robot 2 has a CCD as its image pickup means.
Although the camera 11 is frequently used, the CCD camera 11 is characterized in that it uses a solid-state image sensor, is small and lightweight, has excellent vibration resistance and impact resistance, and has a long life.

[0010]

[Problem to be Solved by the Invention] Conventional CCD camera 11
The CCD device in (1) has the following problems of temperature-dependent deterioration and being affected by radiation. (1) Deterioration of temperature dependence is such that when the temperature of the CCD element rises, the dark current flowing in the CCD element increases. As shown in the temperature characteristic diagram of FIG. 5, as the temperature rises, the dark current increases, and the dark current increases to increase the S of the video signal.
The / N ratio deteriorates and appears as thermal noise in the image.

In the CCD element used in the CCD camera 11, a part of the CCD element is shielded by a light-shielding film formed by aluminum vapor deposition as an optical black area for determining the black level. The dark current also increases as the temperature rises, and the black level of the video signal fluctuates.

As a measure against the decrease of the S / N ratio of these video signals and the fluctuation of the black level, the temperature is corrected so that the temperature of the temperature guaranteed by the CCD camera 11 in the normal state is 0 to 0.
It is designed so that there is no problem in use in the range of 40 ° C.

(2) The influence of radiation is that when the CCD element is irradiated with radiation (mainly γ-rays with large energy), the insulating layer of the CCD element is damaged, and as the damage progresses, various characteristics of the insulating layer. Deteriorates. That is, an interface order (recombination center) is generated at the interface between the insulating layer and silicon that is the semiconductor substrate, causing a deterioration phenomenon.

As a result, the dark current of the CCD element (the signal current flowing when the light from the lens is blocked) increases, and the S / N ratio of the video signal (the output signal of the video signal and the output signal is included in the output signal). The ratio to the noise component present, that is, the ratio between the rated signal output and the output when light is blocked is expressed in decibels).

The radiation characteristic diagram of FIG. 6 shows the dark current characteristics of the optical black region and the image signal region when the integrated radiation dose is increased. As shown in FIG. 6, the dark current in the optical black region and the dark current in the video signal region both increase with an increase in the cumulative radiation dose.

Moreover, the dark current in the optical black area tends to increase more than the dark current in the video signal area. Normally, in a CCD element, the dark current in the optical black region determines the black level. However, the dark current in the optical black region relatively increases as compared with the dark current in the image signal region, so that the image reference becomes negative. The image shifts in the direction of and the whole image becomes black.

The above is the influence of the temperature and radiation on the CCD element, but the CCD element of the CCD camera 11 installed in the nuclear power plant inevitably combines the influence of temperature and the influence of radiation. To receive.

First, the CCD element is affected by temperature rather than radiation. However, when the dark current increases in the CCD element due to temperature, it is usually within the temperature correction range, so that an image can be displayed without any trouble. However, if the CCD camera 11 is placed in a radiation environment for a long time in this state, dark current increases in the CCD element due to the influence of radiation.

The dark current difference characteristic diagram of FIG. 7 shows the relationship between the dark current difference between the optical black area and the video signal area, and the temperature and the integrated radiation dose. If the dark current difference becomes larger than the temperature correction range as shown in FIG. 7, the image reference is shifted in the negative direction. When the image from the CCD camera 11 is being viewed on the monitor 3a of the operation panel 3, such a phenomenon is an image in which the entire black level and the image signal are shifted in the negative direction, and the entire image becomes black and is clear. The image cannot be obtained.

In such an image darkening phenomenon, when the CCD element is exposed to radiation, insulation deterioration occurs in the insulating layer, and further, the aluminum vapor deposition portion of the light shielding film forming the optical black region serves as an electric path to flow a current. It is expected that this will increase the dark current.

An object of the present invention is to provide an anti-darkening CCD device which prevents an increase in dark current under a radiation environment by using a non-conductive material for a light shielding film provided in an optical black region of the CCD device. To do.

[0022]

In order to achieve the above object, an anti-darkening CCD element according to the present invention comprises a plurality of electrodes and a photodiode arranged on an insulating layer formed on the surface of a p-type semiconductor substrate, In a CCD element in which a part of the electrode is shielded by a light-shielding film to form an optical black region that determines a black level of a video signal, the light-shielding film is made of a non-conductive material.

[0023]

According to the present invention, even if the insulation deterioration of the insulating layer of the CCD element occurs in a radiation environment, the light-shielding film forming the optical black region is a non-conductive material, so that there is no electric path. In addition, since the dark current does not increase, the darkening phenomenon does not occur in the image.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those in the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. The basic configuration diagram of FIG. 1 shows the basic configuration of a CCD element used in a CCD camera, FIG. 1 (a) is a plan view, and FIG. 1 (b) is FIG.
The bb arrow sectional drawing of (a) is shown. Further, the perspective view of FIG. 2 shows the configuration of the CCD alone.

As shown in FIG. 2, the CCD 12 has a structure in which an electrode 15 is arranged on an insulating layer 14 formed of an oxide film on the surface of a p-type semiconductor substrate 13 made of, for example, silicon. Is applied, a depletion layer 16 (potential well) is formed in the vicinity of the insulating layer 14 and the p-type semiconductor substrate 13, and if charges are injected into the depletion layer 16, the depletion layer 16 is temporarily stored as an analog amount.

The charge injected into the depletion layer 16 is generated by photoelectric conversion in the photodiode 17 arranged in the vicinity of the electrode 15, whereby a CCD can be formed by light input. Generally, as shown in FIG. 1, a CCD device using light input is configured by arranging a plurality of CCDs close to each other and integrally forming them, and projecting an image on the light receiving surface of each CCD.
It is possible to capture an image by accumulating charges due to light input to a single body and sequentially taking out the accumulated charges.

As shown in FIG. 1A, the CCD camera 11
The CCD element 18 used for is a matrix of a large number of CCDs arranged on the surface of the p-type semiconductor substrate 13 and has a large number of pixels (a lattice of an optical pattern of an object to be imaged divided into a two-dimensional lattice). Form one square).

An image receiving portion 19 is provided at the center of the CCD element 18,
Sweep drain 20 at the top, horizontal CCD 21 at the bottom,
Further, a photodiode 17 and a vertical CCD 22 are formed in the vertical direction. Further, in order to form the optical black region 23 on a part of the light-receiving surface side, for example, a light-shielding film made of a non-conductive material such as synthetic resin or paper which is an insulator and has a high light-shielding property.
It is covered with 24.

As a result, as shown in FIG.
The D element 18 is provided with a light shielding film 24 only in the optical black region 23 in order from the light receiving surface side upward, the photodiode 17 and the electrode 15 not shown, and then the insulating layer 1 of the oxide film.
4 and further comprises a p-type semiconductor 13.

Next, the operation of the above configuration will be described. On the light receiving surface of the CCD element 18, a photographed image is projected by an optical lens or the like (not shown), and when a voltage is applied to the electrode 15 of each CCD unit in the CCD element 18, the surface of the p-type semiconductor 13 under each electrode 15 is applied. A depletion layer 16 is formed, and by the photodiode 17 corresponding to each part of the projected image on the depletion layer 16,
The charges generated by photoelectric conversion are stored according to the amount of light.

Next, the voltage applied to each electrode 15 is pulsed, and the pulse voltage is shifted so that each depletion layer 16
The electric charges accumulated in are sequentially moved and finally obtained as a video signal. An example of the video signal output at this time is shown in the output characteristic diagram of FIG.

The transfer order of charges is horizontal in FIG. 1, and as shown in FIG. 3, the blanking signal 25, the video signal 26, and the optical black signal 27 are sequentially and repeatedly output from each CCD alone. By performing signal processing on this signal with the optical black signal (black level) 27 as a reference, a clear photographed image is displayed on the monitor 3a of the operation panel 3.

In the CCD element 18 of the present invention, since the light-shielding film 24 for forming the optical black region 23 is made of a non-conductive material, the accumulated radiation dose becomes large due to long-term use in a radiation environment, and Even if insulation of the insulating layer 14 deteriorates, the dark current does not increase.

Therefore, since the photographed image is not darkened by being exposed to the radiation, if the CCD camera 11 is used, the equipment to be monitored in the nuclear power plant can be inspected without any trouble.

Further, although the mobile type monitoring device has been described in the above-mentioned one embodiment, the same action and effect can be obtained even if it is used for the fixed type monitoring device. In the case of the mobile type monitoring device, CCD camera due to cross-sectional area and weight
Shielding 11 is difficult, but in the case of fixed monitoring equipment,
By providing the shielding, it becomes possible to easily prevent the image from being darkened.

[0036]

As described above, according to the present invention, even when the monitoring device using the CCD camera is used in a radiation environment, the captured image is not darkened, the reliability of the monitoring device used in the nuclear power plant is improved, and the monitoring is performed. This has the effect of easily inspecting the target equipment.

[Brief description of drawings]

FIG. 1 is a basic structure of a CCD device according to an embodiment of the present invention, in which (a) is a plan view and (b) is a sectional view taken along the line bb of (a).

FIG. 2 is a perspective view of a CCD alone.

FIG. 3 is an output characteristic diagram of a video signal.

FIG. 4 is a perspective view of a mobile monitoring device using a CCD camera.

FIG. 5 is a dark current characteristic diagram according to the temperature of a CCD element.

FIG. 6 is a dark current characteristic diagram of a CCD device according to a cumulative radiation dose.

FIG. 7 is a dark current difference characteristic diagram of a CCD element.

[Explanation of symbols]

1 ... Orbit, 2 ... Visual inspection robot, 3 ... Control panel, 3a ...
Monitor, 4 ... Host computer, 5 ... Signal transmission path, 6
... signal transmitter, 7 ... vehicle body, 8 ... drive mechanism, 9 ... guide wheel, 10 ... pan, 11 ... CCD camera, 12 ... CCD single unit, 13
... p-type semiconductor substrate, 14 ... Insulating layer, 15 ... Electrode, 16 ... Depletion layer, 17 ... Photodiode, 18 ... CCD element, 19 ... Image receiving part, 20 ... Sweep drain, 21 ... Horizontal CCD, 22 ... Vertical CCD, 23 ... Optical black area, 24 ... Light-shielding film,
25 ... Blanking signal, 26 ... Video signal, 27 ... Optical black signal.

Claims (1)

[Claims] 1. A plurality of electrodes and a photodiode arranged on an insulating layer formed on the surface of a p-type semiconductor substrate,
In order to form an optical black region that determines the black level of the video signal, a part of the electrode is shielded by a light shielding film C
In a CD element, an anti-darkening CCD element characterized in that the light shielding film is made of a non-conductive material.