JPH07131722A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To suppress heat storage of a pyroelectric body so as to keep a stable operation and also to eliminate the need for a shutter function switching an optical incidence. CONSTITUTION:A cooling means individually cooling each pyroelectric body 3 is provided and each pyroelectric body 3 is cooled for a photodetection pause period for a photo detector 12. The cooling means is an electronic cooler 5 employing the Peltier effect and a conduction current through the electronic cooler 5 varies with a level of a photo detection signal before the current conduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device in which a photodetector element constituting a pixel has a pyroelectric body and each photodetector element periodically performs photodetection.

Recent solid-state image pickup devices for detecting infrared rays are
Along with the demand for higher performance such as higher pixel count and higher sensitivity, there is a strong demand for low prices. For this reason, a non-cooling type image pickup device is required, and a solid-state image pickup device using a pyroelectric body is being developed. However, infrared detection by the pyroelectric body changes depending on the temperature change of the pyroelectric body. In order to detect the spontaneous polarization, it is necessary to provide the pyroelectric body with a time period during which infrared rays are not irradiated to lower the temperature of the pyroelectric body.

[0003]

2. Description of the Related Art FIG. 5 is a perspective view (a) of a conventional example of a solid-state image pickup device using a pyroelectric body and a perspective view (b) of a photodetector thereof.
Is. In this conventional example, the photo-detecting elements 11 shown in (b) form a pixel and are arranged in a two-dimensional matrix arrangement, and a signal reading circuit 21 incorporated in a semiconductor chip such as silicon is arranged below that. A shutter mechanism (not shown) that opens and closes incident light is provided on the front surface of the light detection element 11.

The photo-detecting element 11 has a pixel size of, for example, about 50 to 100 μm, and absorbs infrared rays from the incident side of the infrared rays L, a common electrode 2 grounded, a pyroelectric body 3, The reading electrode 4 for detecting the electric charge of the pyroelectric body 3 is sequentially laminated, and the temperature of the pyroelectric body 3 rises with the incidence of the infrared rays L. Further, in order to prevent the temperature rise of the pyroelectric body 3 from being reduced by heat transfer, a cavity or a heat insulating spacer is provided between the signal reading electrode 4 and the signal reading circuit 22.

FIG. 6 is a diagram for explaining the operation of the conventional photodetector. The pyroelectric body 3 has a certain amount of polarization due to spontaneous polarization, but in the steady state, surface charges are neutralized by ions in the atmosphere. Then, the incidence of the infrared rays L is periodically performed by the shutter mechanism. When the infrared ray L enters, the spontaneous polarization of the pyroelectric body 3 changes due to a slight temperature rise (ΔT in the figure) of the pyroelectric body 3, and a voltage is generated between the electrodes 2 and 4. This voltage is detected by the signal reading circuit 21 and imaged. Next, when the incidence of the infrared rays L is stopped, the heat of the pyroelectric body 3 is dissipated to the signal reading circuit 21 side through the electrodes 2 and 4 and the temperature of the pyroelectric body 3 is lowered. By this cooling, the next infrared ray L can be imaged similarly to the previous time. The incident period and the incident stop period of the infrared ray L are, for example, 10 ms and 20 m.
It is about s.

[0006]

However, there is a case where the pyroelectric body 3 accumulates heat because the temperature of the pyroelectric body 3 is not sufficiently lowered during the infrared light L incident pause period. ΔT in FIG.
₀ is the temperature rise of the pyroelectric body 3 due to the heat storage. In such a case, when the strong infrared ray L is incident, the temperature of the pyroelectric body 3 rises and the dynamic range decreases, and in the worst case, the temperature of the pyroelectric body 3 rises to the Cucumber point and imaging becomes impossible. Was becoming.

The present invention relates to a solid-state image pickup device in which a photo-detecting element forming a pixel has a pyroelectric body, and each photo-detecting element periodically performs photo-detection. It is an object of the present invention to provide a solid-state imaging device capable of suppressing the heat storage of the above and further eliminating the shutter function for opening and closing the light incidence.

[0008]

FIG. 1 is a diagram for explaining the principle of the present invention, FIG. 1A is a perspective view of a photodetector, and FIG. 1B is a diagram for explaining the operation. In FIG. The same reference numeral indicates the same object, 5 indicates an electronic cooler, 6 indicates an insulator, and 12 indicates a photodetector.

In order to achieve the above object, referring to FIG. 1, the solid-state image pickup device according to the present invention has a pyroelectric body 3 as a photo-detecting element constituting a pixel, and each photo-detecting element 12 emits light. A solid-state imaging device that periodically performs detection, has a cooling unit that individually cools each pyroelectric body 3, and cools the pyroelectric body 3 during a light detection pause period of the photodetection element 12. It is characterized by that.

The cooling means is an electronic cooler 5 using the Peltier effect, and the energizing current of the electronic cooler 5 can be varied according to the magnitude of the photodetection signal before the energizing. .

[0011]

In the solid-state image pickup device of the present invention, as shown in FIG. 1 (b), the pyroelectric body 3 after the signal charge is read out from the pyroelectric body 3.
The pyroelectric body 3 can be forcibly cooled by the cooling means during the light detection pause period in which the heat is cooled by heat radiation. Therefore, it is possible to suppress the heat accumulation of the pyroelectric body 3, which is the cause of the unstable operation in which the dynamic range is reduced and the imaging becomes impossible in the conventional example. That is, the temperature rise ΔT ₀ due to the heat storage of the pyroelectric body 3 can be made almost zero. However, since the pyroelectric body 3 is forcibly cooled, the above heat storage can be suppressed in the same manner even if the light incidence is continued without interruption, so that the shutter mechanism for opening and closing the light incidence is unnecessary. Is possible. If the shutter mechanism is not needed, it is easy to downsize the imaging device.

If the cooling means is the electronic cooler 5, it is easy to position it behind the pyroelectric body 3, and the photodetector elements 12 can be arranged in the same manner as in the conventional example. It is convenient. Further, since the signal from the pyroelectric body 3 is proportional to the temperature rise of the pyroelectric body 3 (ΔT described above), if the above-mentioned change can be made by the energizing current of the electronic cooler 5,
It is easy to make the temperature of the pyroelectric body 3 constant after cooling between the photodetecting elements 12.

[0013]

Embodiments of the present invention will be described below with reference to FIGS. 2 is a perspective view (a) of the first embodiment and a perspective view (b) of the photodetector element thereof, FIG. 3 is a perspective view of the photodetector element of the second embodiment, and FIG. 4 is a control diagram of the electronic cooler of the third embodiment. circuit diagram,
Therefore, the same reference numerals denote the same objects throughout the drawings.

In FIG. 2, in Example 1, the photo-detecting elements 12A (corresponding to the photo-detecting elements 12 described above) shown in (b) constitute pixels and are arranged in a two-dimensional matrix arrangement.
A signal reading circuit 22 incorporated in a semiconductor chip made of silicon or the like is arranged below it. The shutter mechanism described in the conventional example is not provided.

The photodetector 12A has the same size as the pixel as the photodetector 11 of the conventional example, and the absorption layer 1, the common electrode 2, and the pyroelectric body 3 are arranged from above (from the incident side of the infrared ray L). , Under which the signal readout electrodes 4 are sequentially laminated,
That is, the electronic cooler 5A that cools by the Peltier effect in the portion provided with the cavity in the conventional example (corresponds to the electronic cooler 5 described above).
It has a structure with. The electronic cooler 5A has one Peltier element, and the signal readout electrode 4 is provided on the cooling side electrode.
Are shared. 5b is a heat dissipation side electrode. By sharing the electrodes, the efficiency of cooling the pyroelectric body 3 and the simplification of the photodetection element 12 are improved. This Peltier element can be formed by using a Peltier effect material as Bi ₂ Te ₃ or Sb ₂ Te ₃ and using a film forming technique or a photolithography technique used in a normal semiconductor process.

The signal readout circuit 22 has a circuit for reading out signal charges from the pyroelectric body 3 and a circuit for driving the electronic cooler 5A, similarly to the photodetection in the conventional example. And
A photodetection period (for example, about 10 ms) and a photodetection pause period (for example, about 20 ms) that configure a photodetection cycle are set, and signal charges are read out from the pyroelectric body 3 and imaged during the photodetection period, and the photodetection pause period is set. Then, the electronic cooler 5A is energized to cool the pyroelectric body 3 to a predetermined temperature. Since the shutter mechanism is not provided, the infrared energy L is continuously emitted, and thermal energy is supplied to the pyroelectric body 3 even during the light detection pause period.
Since the removal of heat energy by A is larger, the above cooling can be sufficiently performed.

Since the first embodiment does not have the shutter mechanism, it is smaller than the conventional example. In the first embodiment, the shutter mechanism may be provided as in the conventional example. In that case, the size is as large as that of the conventional example, but there is an advantage that the burden of removing the thermal energy by the electronic cooler 5A is reduced.

In FIG. 3, the second embodiment is the same as the first embodiment.
The photo-detecting element 12A is changed to the photo-detecting element 12B to have the same configuration as that of the first embodiment. Photodetector 12A
Uses the electronic cooler 5A with one Peltier element and shares the signal readout electrode 4 with its cooling side electrode. However, the photodetector element 12B has two Peltier elements connected in series. The cooler 5B is used, the cooling side electrode is 5a, and the insulator 6 is provided between the cooler 5B and the signal reading electrode 4.
Is intervened. Compared with Example 1, the efficiency of cooling the pyroelectric body 3 is slightly inferior due to the inclusion of the insulator 6,
There is an advantage that the energizing current of the electronic cooler 5B is small.

By the way, in such an image pickup device, the intensity of the infrared rays L which are incident between the two-dimensionally arranged photo-detecting elements is not uniform, and even if the individual photo-detecting elements are focused on, the intensity is not uniform. It changes over time. Therefore, in the solid-state imaging device using the pyroelectric body 3 as the photodetection element, it is necessary to adjust the cooling of the pyroelectric body 3 according to the intensity of the light incident on the photodetection element.

In order to control this cooling, in the first embodiment, the energizing current of the electronic cooler 5A is set to a large value, and when the pyroelectric body 3 reaches the predetermined temperature, the current is reduced to maintain the predetermined temperature. I am trying to do it. However, since the control needs to be performed for each photodetector 12A, a control circuit is possible and complicated. However, when the shutter mechanism described above is provided, the energization for maintaining the predetermined temperature can be omitted. The same applies to the second embodiment.

The third embodiment is such that the cooling can be controlled by a simple control circuit. Here, focusing on the fact that the photodetection signal obtained from the pyroelectric body 3 is proportional to the temperature rise of the pyroelectric body 3 (ΔT described above), for example, in the photodetection element 12A, an electronic cooler is used. The energizing current of 5 A is increased according to the magnitude of the photodetection signal before energizing. As a result, the pyroelectric body 3 can be brought to the predetermined temperature at the end of the light detection pause period, and the switching of the energization current is unnecessary. As a result, the control for each photodetecting element 12A is completed by a circuit using a shift register as shown in the circuit diagram of FIG.

[0022]

As described above, according to the present invention, there is provided a solid-state imaging device in which a photodetector element forming a pixel has a pyroelectric body and each photodetector element periodically performs photodetection. Provided is a solid-state imaging device capable of suppressing the heat storage of the electric body and further eliminating the shutter function for opening and closing the light incident, thereby preventing a decrease in the dynamic range and the inability to take an image caused by the heat storage of the pyroelectric body. Allows stable operation to be maintained,
Further, there is an effect that the size of the imaging device can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a perspective view of the first embodiment (a) and a perspective view of a photodetector element thereof (b).

FIG. 3 is a perspective view of the photodetector of Example 2.

FIG. 4 is a circuit diagram of a thermoelectric cooler control according to a third embodiment.

FIG. 5 is a perspective view of a conventional example (a) and a perspective view of a photodetector element thereof (b).

FIG. 6 is an operation explanatory diagram of a conventional photodetector.

[Explanation of symbols]

1 Absorption Layer 2 Common Electrode 3 Pyroelectric Material 4 Signal Readout Electrode 5, 5A, 5B Electronic Cooler 5a Cooling Side Electrode 5b Heat Dissipation Side Electrode 6 Insulators 11, 12, 12A, 12B Photodetector 21, 22 Signal Readout Circuit L Infrared ΔT Temperature rise due to incident light on pyroelectric body ΔT ₀ Temperature rise due to heat accumulation on pyroelectric body

Claims (2)

[Claims] 1. A solid-state image pickup device comprising a pyroelectric body (3) in a photodetecting element (12) constituting a pixel, wherein each photodetecting element (12) periodically performs photodetection. A solid-state imaging device having a cooling unit for individually cooling the pyroelectric body (3), wherein the pyroelectric body (3) is cooled during a photodetection pause period of the photodetection element (12). . 2. The cooling means is an electronic cooler (5) using the Peltier effect, and the energization current of the electronic cooler (5) is variable according to the magnitude of the photodetection signal before the energization. The solid-state imaging device according to claim 2, wherein the solid-state imaging device can.