JPS58148572A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the S/N of a picture output signal due to the increase in a dark current at an external temperature, by placing a solid- state image pickup element and a part of a cooling means in a cavity and evacuate the cavity. CONSTITUTION:A thermal conduction shaft 8 is operated to contact a heat sink 11 on a semiconductor fitting base 2, allowing to dissipate heat sufficiently from a semiconductor base 1 provided with a CCD. The heat sink 11 is detached from the base 2. Since the cavity 13 is in this state, the bases 1, 2 are interrupted from the surrounding thermally almost completely. The CCD is exposed and picture information is read out. Since the time required for the readout is one frame period, the power application is performed during this period only, then the self-heating of the CCD is minimized. In operating a CCD camera several times, the temperature of the base 1 is increased due to the self-heating and a dark current level is increased, then the heat sink 11 is contacted on the base 2 for the heat dissipation. Thus, the deterioration in the S/N of a picture output signal is reduced and the picture having high resolution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides COD, silicon diode array, MO&
) It relates to a solid-state imaging device using a transistor array, CHD, etc.

A solid-state image sensor as described above is generally formed on a silicon semiconductor substrate. However, as is well known, a semiconductor element using silicon as a semiconductor material has a relatively large dark current of about 10 nA even at room temperature, and the dark current increases approximately twice as much as the temperature rises by 10C. Therefore, in a solid-state image sensor using silicon, a problem arises in that the noise component caused by the dark 11L flow increases or decreases depending on the temperature. In other words, if the light incident on the imaging probe is constant, the S/N of the imaging output signal at a constant level depends on the temperature, and therefore the sensitivity has temperature dependence.

Furthermore, in solid-state imaging devices such as OOD, it is known that dark current accumulates over time and resolution deteriorates. For example, when electrically reading out weak optical information from the fluorescent surface of an X-ray device through a COD, the amount of input light from the fluorescent surface is extremely low, so it is difficult to extract sufficient image information. It is necessary to perform long-time exposure to OOD. However, the dark current of the element is accumulated in the potential well of the COD over time, and the S/N of the read image signal eventually deteriorates.

Therefore, considering that the light-to-charge conversion efficiency of solid-state imaging devices such as CODs does not depend much on temperature in the normal temperature range, imaging sensitivity can be improved by lowering the temperature of the semiconductor substrate on which CODs are formed. It is possible to significantly improve this. ! #Geki No. 56-37751,
One technical means for this purpose has been disclosed.

However, lowering the temperature of the COD requires large power consumption and also causes the problem of dew droplets.

In view of this problem, it is an object of the present invention to improve cooling efficiency, reduce power consumption, and avoid the dew drop problem.

Embodiments of the present invention will be explained below based on the drawings.

Figure 1 is a longitudinal sectional view along the optical axis of a solid-state imaging device to which the present invention is applied. This imaging device was designed to be used in a system that electrically reads out weak optical information, such as from the fluorescent surface of an X-ray photographic device, through a COD camera and records it on a magnetic sheet recorder or the like. Of course, it can also be used for general purposes. In this case, since the amount of input light is extremely low, it is necessary to minimize the dark current of the COD and maximize the sensitivity.

In FIG. 1, a solid-state imaging device such as an OOD is formed on a semiconductor substrate (1). The semiconductor substrate (1) is fixed to a thermally conductive (e.g. metal) semiconductor mounting substrate (2),
This semiconductor mounting board (2) is held in a thermally insulated state on the inner wall surface of a cylindrical or square tube-shaped holding member (3) made of a heat insulating material. A transparent plate (47) made of glass or the like is fixed to the upper part of the imaging surface of the semiconductor substrate (11) so as to seal and cover the front opening of the holding member (3) via the frame (5). There is.

A diaphragm holding member (6) is attached to the back side of the holding member (3) so as to surround the opening on the back side, and a diaphragm (7) is attached so as to seal the opening in the center. The diaphragm (7) inserts and holds the heat conduction shaft (8) through an opening in the center thereof. The diaphragm (7) and the shaft (8) are tightly fixed by an airtight ring (9). Note that the heat conduction shaft (8) may be a rod-shaped metal pipe or a heat pipe filled with a heat conduction material.

The heat conduction shaft (8) is slidably held by the bearing member 01, and a heat receiving plate aυ with good heat conduction is fixed to m- on the side of the semiconductor mounting board (2), and a heat receiving plate aυ with good heat conduction is fixed to the other end. A radiation fin a2 is fixed.

Note that the output of the image sensor on the semiconductor substrate (1) is the signal αQ.
It is led out to the terminal u7t via. In this case, the output of the image sensor may be directly emitted, but
An amplification circuit may be formed on the amplification circuit 1, and the output signal may be amplified by the amplification circuit and then outputted to the terminal a7).

According to the configuration shown in FIG. 1 described above, the inner wall of the cylindrical holding member (3), the transparent plate (4) that covers the front opening, the diaphragm (7) that covers the back opening, and the diaphragm holding member (6).
Thus, a sealed cavity OJ is formed.

The inside of this cavity 03 is depressurized by discharging air from a hole into which an air vent plug α is fitted. For this reason, a plurality of holes a are formed in the semiconductor mounting board +21 to communicate the front side and the back side thereof. 9 caves (
The inside of the chamber 13 does not need to be completely filled with nitrogen, and may be reduced to, for example, about 0.1 atmosphere.

Thermal conduction @ f81 that connects the heat receiving plate aD in the depressurized cavity OJ and the external heat radiation fin a3 is attached via the diaphragm (7), so the airtight and depressurized state is maintained. In addition, the back side of the semiconductor mounting board Uυ and the surface of the heat receiving plate Uυ can be moved into and out of contact with each other and can be operated from the outside.

Next, the operation of the solid-state imaging device shown in FIG. 81 will be explained in detail.

Connect the conductor by operating the heat conduction shaft (8) without talking; the attached board (2)
The heat receiving plate aυ is brought into contact with the semiconductor substrate (11) provided with the COD to sufficiently release heat. Next, the heat receiving plate a1 is separated from the semiconductor substrate (2). In this state, the semiconductor substrate (1) and the semiconductor mounting substrate (2) are almost completely thermally isolated from the surroundings. That is, the heat conduction through the structural member is at an extremely low level that can be ignored through the retaining member (3) which is a thermal insulator, and the heat conduction through the structural member is at an extremely low level that can be ignored.
), the convective heat transfer is also at an extremely low level. Therefore, there is almost no temperature increase factor other than self-heating due to energization of the COD, and the temperature of the semiconductor substrate can be kept low for a long time.

Next, the COD is exposed to light, and in a state in which the original information is sufficiently converted into electric charge, the COD is energized for printing, and image information is printed. The time required for threading is 17 nm period (1
730 seconds), so if the current is turned on only during this period, C
Self-heating of the OD is kept to a minimum.

When the COD camera is operated several times and the temperature of the substrate (11) rises due to self-heating and the dark current level increases, the heat receiving plate 01 is brought into contact with the semiconductor mounting substrate (2) again to dissipate heat. In this case, measure the dark current level and display that it has exceeded that value or a certain value, and based on this display, heat receiving plate 0υ, heat conduction shaft (8) and heat dissipation fin a.
It may be configured to operate a cooling device consisting of two.

FIG. 2 is a similar longitudinal cross-sectional view showing another embodiment of the invention. In Fig. 2, a thermoelectric element (11) utilizing the Beltier effect or Thomson effect is interposed between the heat conduction axis (8) and the radiation fin a2, and a current source (to) is connected to this thermoelectric element σ.
The semiconductor substrate (1) and the semiconductor mounting substrate (2) are cooled by passing a current through the semiconductor substrate (1) and the semiconductor mounting substrate (2).

Other structures are the same as the gi diagram.

llX2Enomt, 4cyoht! , + conductor Ti, lIi
mf--5.

It is possible to maintain the C degree, and to make the COD dark current sufficiently small, it is possible to make the resolution of successive #jJ images sufficiently high. The semiconductor mounting board (2) and the heat receiving plate aυ are brought into contact, and the thermoelectric cable a1 is energized to attach the semiconductor board (1).
Once the semiconductor substrate ) is cooled and the cooling device and the substrate f2+ are separated, the heat flowing into the semiconductor substrate (11) can be sufficiently blocked as described above, so that the cooled state can be maintained for a long time. Since the energization during reading of the CCD is 1/30 seconds per frame as described above, the self-heating caused by kneading is extremely small.

Since the thermoelectric element α9 only needs to be energized during cooling,
It is possible to keep the power consumption to a sufficiently low level ◇ Furthermore, since the air around the semiconductor substrate (1) is exhausted and remains at f+, even if the substrate temperature is about 150℃, dew droplets will not form on the substrate surface. It will not stick. Also, since the transparent plate (4) on the front side of the COD is at the same temperature as the room temperature, it is possible to prevent dew droplets from adhering to the front and back surfaces of the transparent plate (4). , the cooling device can be operated or operated according to the inspection result, but it is also possible to make this automatic. In other words, the CO
When the dark current level exceeds a certain reference value due to self-heating of D, this is detected and the MIH device is activated, and the cooling device is moved forward so that the heat receiving plate aυ contacts the semiconductor mounting board (2). let At the same time, the switch element is operated to energize the thermoelectric element α. When the dark current level falls below a reference value, the electromagnetic device and switch element described above are turned off.

As a modification of Fig. 2, a semiconductor substrate (1) provided with a COD is attached to the cooling surface of the thermoelectric element (1), and these semiconductor substrates (11) and the thermoelectric element a9b are held as shown in Fig. 1 or 2. The member (31 is held in a vacuumed cavity 0
It may be placed within 3. In this case, it is preferable that a cooling device having a structure similar to that shown in FIG. 1 be provided so as to be able to come into contact with and separate from the discharge surface of the thermoelectric element section. In addition, without providing the removable cooling device and diaphragm (7) 8 as shown in Fig. 1, the inside of the cavity 03 is completely sealed, and the heat dissipation member fixed to the heat dissipation surface of the thermoelectric element (■) is led out to the outside of the cavity. Heat dissipation may also be achieved by In this case, there is some heat conduction from the outside to the inside through the heat dissipation member, but this problem can be avoided by keeping the thermal 11X element running all the time, or by detecting the dark electricity R8 and turning it on and off. Can be done. Further, by reducing the pressure inside the cave as described above, convective heat transfer can be reduced and dew condensation can be prevented.

Furthermore, as a modification of FIG. 2, a structure in which the heat receiving plate Oυ is fixed to the semiconductor mounting board (2) and the cooling means is fixed without being freely detachable is also considered. In this case, the thermoelectric element α
It is desirable that the temperature of the semiconductor substrate (1) is controlled to be below a certain value by turning on and off the current of 9.

Next, FIG. 6 is a longitudinal sectional view of a solid-state imaging device showing still another embodiment. In this example, the thermoelectric element a9 is configured to be brought into direct contact with the semiconductor mounting board (2) and separated from it by an external operation.

The thermoelectric element (1) has a double 1g structure, and vertically long semi-cylindrical dissimilar metals (19a) (19b) are joined to form one thermoelectric element, and these gold jpA (19a)
flat semi-cylindrical dissimilar gold 1I4 (1
9c) (19d) are joined, metal (19a) and (1
9c) and one thermoelectric cord, metal (19b) and (19d
) and one more thermoelectric cord is formed. Metal (1
9a) (19b) are the endothermic side, metal (19c) (1
9d) is the heat radiation side.

As described above, the present invention is such that the solid-state image sensing device and at least a portion of its cooling means are placed in nine cavities, and the pressure inside these cavities is reduced. Therefore, according to the present invention, the convection heat transfer due to the air surrounding the solid-state image sensor is reduced, and the solid-state image sensor gII
It is now possible to thermally insulate the element, reduce the deterioration of the S/N of the Ili image output signal due to an increase in dark current due to external temperature, and obtain a single image with high resolution. . Furthermore, by reducing the pressure inside the cavity, it is possible to prevent mist droplets from adhering to the solid-state image sensor and the inner wall of the cavity.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view along the original axis showing one embodiment of the solid-state imaging device of the present invention, and FIG. H2 and FIG. 3 are longitudinal sectional views similar to FIG. 1 showing different embodiments, respectively. be. Note that in the code used for 111njC, 1(1j・-
・−・・・−Semiconductor substrate (8)−・−・−・−・・
・Heat conduction axis aυ−・・・・・・・−・Heat receiving plate σ2・・・・・・・・・・・・・・・Radiation fin α3・
・・・・・・－・・・・・・・・・
・・・・・・It is a thermoelectric element. Agent Ueya I Yoshio Tsuneko I Toshiki Sugiura III Figure 2 Figure 3

Claims (1)

[Claims] It has a solid-state image sensor and a means for cooling the solid-state image sensor, and is characterized in that the solid-state image sensor and at least a part of the cooling means are respectively installed in a cavity, and the pressure inside the cavity is reduced. Solid-state imaging device