JPS60213057A - Pyroelectric type infrared image pickup device and driving method thereof - Google Patents

Abstract

PURPOSE:To simplify constitution, and to increase density by constituting a photoelectric conversion section for a unit cell by a pyroelectric body leaf formed on the upper surface of an insulating thin-film on a semiconductor substrate and a means applying voltage to the leaf and reading charges stored under the insulating thin-film by beam irradiation. CONSTITUTION:A pyroelectric body 108 is formed on an MOS capacitance shaping a light-receiving section for an interline transfer system CCD sensor, and voltage is applied onto the surface of the pyroelectric body. A period when an infrared image is projected and a period when the irradiation of the infrared image is interrupted are equalized approximately. A transfer gate 303 is brought to an ON state during a vertical blanking period, and voltage applied to an electrode 203 on the surface of the pyroelectric body 108 is brought to approximately zero. Charges stored under a gate oxide film 301 are transferred to a vertical register. The transfer gate is turned OFF, voltage is applied to the electrode 203 on the surface of the pyroelectric body 108, and signal charges are stored under the gate oxide film 301. Signal charges are stored under a gate oxide film 201 during the next storage period while charges transferred to the vertical register 105 are read from an output terminal in succession.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an imaging device, and particularly to a pyroelectric infrared image sensor.

(Prior art and its problems) There are two types of infrared image sensors: pyroelectric type, which utilizes the thermal properties of infrared rays, and quantum type, which utilizes the properties of infrared rays as light quanta. The former can be used at room temperature, so it is expected to be useful for household or general public use, despite its low temperature resolution. The latter is also expected to be used in space and defense applications due to its patented high temperature resolution, which is characterized by cooling to liquid nitrogen temperature. Figure 1 is a block diagram of what is traditionally considered the most high-performance pyroelectric image sensor.
This sensor is LiTa0. , Pbi'i0. ,
This device attempts to read out changes in polarization '1 charge caused by temperature changes on the surface of a pyroelectric material such as PZT using a charge transfer device, and is constructed from an N-channel silicon IC. In the figure, 101 is the joint source, 103 is the N+ region 1
02 is a region for transferring electrons from the N+ area 101 to the N+ region 03, 105 is a CCD vertical register, 104 is a region for transferring electrons from the N+ region 103 to the CCD vertical register 105, and 106 is a horizontal CCD.
CD register 107 is an output amplifier. A focusing body 108 is arranged above the N+ region 103. Second
The figure is a cross-sectional view showing this state, where 201 is a P-type substrate, 202 is an insulating film, and 203 is an electrode formed on the upper surface of the pyroelectric body.

Further, the pyroelectric body is energized to a constant potential via the electrode 203. Further, in FIG. 1, the N+ source 101, the transfer regions 102 and 104, the N+ region 103, and the pyroelectric body 108 constitute one photoelectric conversion element, and this element is two-dimensionally arranged in the horizontal and vertical directions.

The operation of this device is as follows. First, from the N+ source 101 to the N+ region 103 via the charge transfer region 102.
A certain amount of charge is sent to the terminal and its potential is reset. At this time, an infrared image chopped at 30 to 59 Hz begins to hit the pyroelectric body. Assuming that the period during which the infrared rays are incident and the period during which the infrared rays are off are approximately equal, the temperature of the pyroelectric body rises, and a change in charge caused by polarization is sent to the N+ region. The charge violet sent in reaches its maximum at the moment when the temperature of the pyroelectric body reaches its maximum, that is, just before the chopper turns off.

At this time, the sum of the polarization charge change QP and the charge QB previously sent to the N+ region is sent to the vertical register via the charge transfer region 104.

These charges are transferred using the normal interline transfer method (as in the case of a CD sensor), where each horizontal line is transferred horizontally to CC1.
) are transferred in parallel to the register and read out from the output amplifier 107.

Further, at the beginning of this read period, that is, immediately after QP+QB is transferred to the vertical register, charge QB is again sent to N+ region 103 from the source side and reset to a constant potential. At this time, the infrared image is cut by a chopper. Then, the temperature of the pyroelectric body begins to decrease, and the pyroelectric body absorbs the polarization charge Qp from the N+ region. The maximum amount of charge is absorbed at the moment when the temperature of the pyroelectric material is the lowest.
That is, just before the chopper is turned on. At this time, QB
The charge of QP is fed into the vertical register and read out from the output terminal in the same manner as before. Of course Qa
At the time when the charge of Qp is sent to the vertical register, all the charges of the previous field must be read out from the output terminal. By alternating fields in which the temperature of the pyroelectric body increases and decreases, it is possible to constantly convert infrared waves into signal charges in the first quadrant and read out video signals from the output section. I can do it. In this case, a video signal in which brightness and darkness are inverted for each -field is obtained, but it is easy to convert this into a normal video signal.

The disadvantages of such an infrared sensor are 1) the complicated configuration of the photoelectric conversion element, making it difficult to increase the density; 2) the drive is complicated, as it is necessary to send bias charges to the N+ area; 3) the total The problem is that infrared rays cannot be used effectively because the ratio of the area of the pyroelectric material to the device area is small.

(Objective of the Invention) An object of the present invention is to provide a pyroelectric infrared virtual image device and a method for driving the same, which improve the above-mentioned conventional drawbacks.

(Structure of the Invention) According to the present invention, the light 11L conversion portion of a unit cell is connected to an insulating thin film provided on a semiconductor substrate side, a pyroelectric thin piece formed on the upper surface of the insulating thin film, and the thin piece on the opposite side from the semiconductor substrate. The method is characterized by comprising a means for applying a voltage to the photoelectric conversion section, and a means for irradiating the photoelectric conversion section with light from the semiconductor substrate side, and a means for sequentially reading out charges stored under the insulating thin film by the light irradiation from an output terminal. A pyroelectric infrared imaging device is obtained.

Furthermore, according to the present invention, the combined effect of the polarization magnetic pressure generated in the pyroelectric body by the voltage applied to the pyroelectric thin piece of the pyroelectric infrared imaging device and the infrared image incident on the pyroelectric thin piece is The pyroelectric infrared ? ! A method for driving an Mm image device is obtained.

(Example) Hereinafter, the present invention will be explained using some examples.

FIG. 3 shows an embodiment of the present invention. An infrared sensor according to a non-embodiment will also be described as an N-channel silicon device. In FIG. 3, 301 is a gate oxide film formed on the P-type substrate 201, and 302 is a pyroelectric thin film formed on the gate oxide film.

304 applies a voltage of 1 to the electrode formed on the pyroelectric thin film.
The wiring means for adding '4J is shown. Further, 305 is a unit cell, and 303 is a transfer gate. FIG. 4 shows a horizontal cross-sectional view of a unit cell, in which 401 is a transfer electrode of a vertical COD register, 402 is a field oxide film, 403 is a transfer gate 303 and a vertical COD register.
Gate oxide film in the region corresponding to the CD register, 404
is an oxide film that separates the electrodes. As can be seen from FIGS. 3 and 4, the unit cell is a P-type substrate 201. It consists of a gate oxide film 301, a focus 14, a body thin film 108, an electrode 203, a photoelectric conversion section consisting of a wiring means 304, a transfer gate, and a part of a vertical register.Although not shown in FIG. Visible light or near-infrared light can be irradiated in pulses from the back side.

As mentioned above, this device has a structure in which a pyroelectric material is formed on the MO8 capacitor that forms the light receiving part of a normal interline transfer type COD sensor, and a means for applying a voltage to the surface of the pyroelectric material is provided. There is.

In addition, the infrared image that enters the device has a frequency of approximately 30 to 60 Hz.
It is assumed that the period during which the infrared image is incident and the period during which the infrared image is cut are approximately equal.

This device uses the normal interline method (, “CD
Since it operates similarly to a sensor, we will explain its operation accordingly. First, during the vertical blanking period, the transfer gate 303 is turned on, and the electrode 203 on the surface of the pyroelectric body is turned on.
The voltage applied to the gate oxide film 301 is brought close to zero, and the charges stored under the gate oxide film 301 are transferred to the vertical register.

Next, the transfer gate is turned off and a voltage is applied to the electrode 203 on the surface of the pyroelectric body so that signal charges can be accumulated under the gate oxide film 301. In the next accumulation period, signal charges are accumulated under the gate oxide film 201, while the charges transferred to the vertical register 105 are sequentially read out from the output terminal.

The accumulation of the signal charges described above is performed as follows. First, at the beginning of the storage period, infrared rays begin to hit the pyroelectric body, causing its temperature to rise, and at the end of the storage period, a potential difference vP is generated between the front and back sides of the pyroelectric body due to polarization of the pyroelectric body. Now vP is pyroelectric 1
It is assumed that - on the surface of the gate oxide film 301 and - on the surface of the gate oxide film 301. At this time, the maximum amount of charge Q that can be stored under the gate oxide film 301 is the sum of the charge QB stored when there is no polarization and the charge QP due to polarization. Now, the capacitance per cell of the pyroelectric body is CP, the capacitance per cell of the gate oxide film is COX, and the voltage applied to the surface of the pyroelectric body during storage is V.
Then, since Qa=V/(Cp+Cox) and Qp=''/Cox, the following equation holds.That is, the amount of charge that can be accumulated under the gate oxide film 301 can be changed by the voltage vP generated in the pyroelectric body. When this device is irradiated with light from the back side at the end of the storage period, if the irradiation amount is large enough, an amount of charge expressed by equation (1) will accumulate under the gate oxide film, that is, a charge proportional to the intensity of the infrared image. I will do what is done to me.

During the next accumulation period, the temperature of the pyroelectric body decreases, so that the charges under the gate oxide film are accumulated. These charges can also be read out in exactly the same way as the previous field.

As described above, in this embodiment, the phase of the signal read from the output terminal is inverted for each field. Therefore, processing to invert the phase of the output signal every other field or signal processing to take the difference between fields is required.

The present invention can also be implemented in the following forms.

ta) P-channel device Although the above embodiments have been described in the case of an n-channel device, the present invention can also be applied to the case of a p-channel device. However, if the direction of the spontaneous polarization of the pyroelectric body is kept as in the previous example, Qa Qp
, signals of Qa+Qp are read out in the falling fields, respectively.

tb) In the above embodiment, the pyroelectric material was provided in the form of an island on the gate oxide film, but it is possible to provide an organic pyroelectric material made of PVF' or the like over the entire surface of the device and apply a voltage from above. is also possible.

tel In the above embodiment, after the device is irradiated with light, the charge accumulated under the gate oxide film is transferred to the vertical register and read out. This is the sum of the accumulated charge and the charge accumulated in the vertical register due to light irradiation, and a large transfer capacity is required. Therefore, by using a driving method that reads out the charge accumulated in the vertical register from the output terminal after irradiating the device with light, and then transfers the charge accumulated under the gate oxide film to the vertical register, the width of the vertical register can be narrowed. As a result, the area of the photoelectric conversion section can be increased, which is advantageous.

(dj In the embodiment, the case where C uses a normal silicon substrate has been described, but the silicon substrate can also be made to have a thickness of several tens of microns or less in order to make the crystal body sensitive to temperature changes.

In the example, the pyroelectric material was arranged with a polarity such that the amount of charge that can be accumulated under the gate oxide film increases as the pyroelectric material increases by 1M degrees, but almost the same device operation is expected even if the polarity is the opposite. can. However, in this case, in the field where the temperature rises, the charges of QB+QP are read out in the field where Qa and Qp drop.

ff) In the embodiment, an interline system device configuration has been described, but the present invention can also be applied to a frame transfer system. That is, by using the structure of the photoelectric conversion unit explained in this example for the frame transfer type photoelectric conversion unit, vertical COD
It is sufficient to construct a register and provide a normal CCD memory below it. In this configuration, charges corresponding to an infrared image are accumulated in the photoelectric conversion section, transferred at high speed to the memory section during the vertical blanking period, and signals are read out one horizontal line at a time via the horizontal register during the first field period. become.

In the tgl embodiment, the field from which QB+QP is read and the field from which QB QP is read are performed alternately, but only one of the fields may be read intermittently.

(Effects of the Invention) As described above, the present invention has a very simple structure in which the photoelectric conversion section is just a pyroelectric material formed on the MO8 type photodiode of a normal interline type device, and the density can be easily improved. can be done. In addition, the driving method is almost as simple as the normal interline method (,'CI), and the light receiving area is about 5/2 times more sensitive than the case shown in Figure 1, which was given as an official example. ,

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional pyroelectric infrared imaging device.
01 is the source, 102 and 104 are charge transfer regions, 103
is an N+ diffusion layer, 105 is a vertical register, 106 is a horizontal register, 107 is an output amplifier, and 108 is a pyroelectric body. Figure 2 is a cross-sectional view of the pyroelectric part in Figure 1, and 201 is P
A substrate, 202 is an insulating film, and 203 is an electrode. FIG. 3 shows an embodiment of the present invention, in which 301 is a gate oxide film, 302
is a pyroelectric thin film, 303 is a transfer gate, 304
is a wiring means for connecting the electrodes. The fourth section is a cross-sectional view of the unit cell of the present invention, 401 is a transfer electrode of the COD vertical register, 402 is a field oxide film, 403 is a gate electrode of the transfer gate part and a part of the vertical register, 404 is an interelectrode insulating film It is.

Claims (1)

[Claims] +11 A photoelectric conversion section of a unit cell applies a voltage to an insulating thin film provided on a semiconductor substrate, an inert thin piece formed on the upper surface of the insulating thin film, and the thin piece from the side opposite to the semiconductor substrate. pyroelectric infrared rays comprising: means for irradiating the photoelectric conversion section with light from the semiconductor substrate side; and means for sequentially reading out charges accumulated under the insulating thin film by the light irradiation from an output terminal. Imaging device. (2) The unit cell's light [conversion unit consists of an insulating thin film provided on a semiconductor substrate, a pyroelectric thin film formed on the upper surface of the insulating thin film, and means for applying a voltage to the thin film from the side opposite to the semiconductor substrate, Further, in driving a pyroelectric infrared imaging device having means for irradiating the photoelectric conversion section with light from the semiconductor substrate side and means for sequentially reading out charges accumulated under the insulating thin film by the light irradiation from an output terminal, A voltage is applied to the insulating thin film as a composite effect of a voltage applied to the electric thin film and a polarization voltage generated in the pyroelectric body by an infrared image incident on the pyroelectric thin film, and the insulating thin film is irradiated with light. A method for driving a pyroelectric infrared imaging device according to the preceding item, characterized in that the maximum amount of charge that can be accumulated in a pyroelectric infrared imaging device is read out as a video signal.