JPH0828845B2 - Pyroelectric infrared imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pyroelectric infrared imaging device using a solid-state scanning circuit.

2. Description of the Related Art FIGS. 5 (a) and 5 (b) show the configuration of a conventional pyroelectric CCD (pyro CCD) in which a pyroelectric sensor is connected on a CCD scanning circuit and a conventional signal reading method (signal injection method). 3] is a conceptual diagram of an equivalent circuit of a unit pixel and a drive potential for explaining (1).

Positive and negative charges 52 and 53 are generated in the pyroelectric sensor 51 according to opening and closing of the optical chopper. However, the Si-CCD operates to read out only one of the charges. Therefore, in order to accept the input signals of both codes, in the conventional example,
Half of the maximum charge that can be transferred from the CCD was used as the bias charge 54 and was electrically injected in synchronization with the opening and closing of the optical chopper.

In FIGS. 5A and 5B, positive and negative signal charges 52 and 53 generated in the pyroelectric sensor 51 in response to opening and closing of the optical chopper.
Is transferred to the CCD scanning unit 56 via the read gate 55. At this time, in synchronization with the opening and closing of the optical chopper, the input diode unit 57 is once reset to the reset level, and then the charge injection mechanism 58 injects the bias charge 54 into the input diode unit 57 and the positive and negative of the pyroelectric sensor. The signal charges 52 and 53 of both polarities are accumulated, and after a certain accumulation time, an operation of reading out to the CCD scanning unit 56 via the gate 55 (for example, R. Watton, et al. Infrared physics (I
nfrared Phays). Vol.22 pp.259-275, 1982).

However, when an input mechanism (for example, a diode cutoff method) for bias charge injection is added to each pixel as in the conventional example, the following problems occur.

(1) The bias charge for each pixel becomes non-uniform.

(2) The number of wiring lines of the unit pixel increases, and the yield decreases.

(3) The cell size of the unit pixel becomes large.

Since the bias charge is non-uniform, there is a lot of fixed pattern noise on the image, and in order to obtain a practical image, an external signal processing circuit is required for each pixel, which makes the entire system large and complicated. Accompanied.

Also, due to the increase in the wiring of the unit pixel and the increase in the cell size, it was very difficult to obtain the number of pixels (400 ^H × 500 ^U ) having a practical resolution.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a novel pyroelectric infrared imaging device for improving the signal reading method of the pyroelectric infrared imaging device.

Means for Solving the Problem In order to solve the above problems, the present invention provides a bias charge input mechanism outside the pixel portion, and transfers the charges injected from the charge input mechanism to a diode region by a scanning line,
By mixing the injected charges and the charges accumulated in the diode region, the signal charges of both polarities of the pyroelectric infrared sensor generated by the irradiation of infrared light are read out to the scanning line.

Effect According to the present invention, by injecting bias charges from a single charge input mechanism into a plurality of pixels with the above configuration, the bias charges of each pixel are made uniform, and a large and cumbersome external signal processing is unnecessary. it can.

Further, since the charge injection mechanism is provided outside the pixel portion, the cell size of the unit pixel does not change and the wiring of the pixel portion does not increase, so that a practical resolution can be obtained.

Embodiment FIG. 1 shows a sectional structure of a pixel portion of a pyroelectric CCD according to an embodiment of the present invention. Here, the infrared image 1 interrupted by the optical chopper enters the upper surface electrode 2, is absorbed by the pyroelectric sensor 3, and the temperature of the pyroelectric sensor 3 rises and falls with the opening and closing of the chopper. Since the pyroelectric sensor 3 generates electric charges on the electrodes at both ends due to the temperature change, positive and negative electric charges are generated on the pixel electrode 4 as the chopper is opened and closed. This signal charge is injected into the storage diode 7 of the CCD through the Au bump 5 and the Al injection electrode 6 to modulate the bias charge in the storage diode 7. After the charges accumulated in the accumulation diode 7 and the bias charges are mixed for a certain period of time, they are read out to the CCD transfer stage 9 through the read gate 8 and taken out as an image signal to the outside. The bias charge is injected by transferring the bias charge to the CCD transfer stage 9 in advance and reading the gate 8
Through the storage diode 7. As other components, 10 is a Si substrate, 11 is a gate oxide film, 12 is a field oxide film, 13 is a channel stop, 8 and 14 are read gate electrodes and transfer electrodes made of polysilicon,
Reference numeral 15 is an interlayer insulating film formed of a SiO ₂ film or the like.

Here, the operation of the present invention will be briefly described with reference to FIG. FIG. 2 (a) shows an equivalent circuit of the unit pixel.
FIG. 6B shows the potential under the gate during the operation. When the signal charge of the pyroelectric sensor 22 is being accumulated in the input diode 21, the reading gate 23 below is at the OFF level,
It is separate from the transfer stage 24. During this accumulation time, the transfer stage 24 is used to bias the bias charge 26 below the transfer electrode 25 of each pixel.
Have been transferred. When calling a signal, set the read gate 23 below to the Read level and below the transfer electrode 25 to Mix.
The level is set to the level, and the bias charge 26 and the accumulated charge in the input diode 21 are added. Read under the read gate 23
By setting the level to the Read level below the transfer electrode 25, the added charges are read out to the transfer stage 24.
At this time, the potential of the input diode 21 becomes the same as the Read level. This is called the Reset level. Immediately after the end of reading, the lower part of the reading gate 23 is set to the OFF level, the input diode 21 and the transfer stage 24 are separated, and the charges read by each pixel are transferred in the transfer stage 24 in the direction perpendicular to the paper surface and taken out as an image signal. On the other hand, in the input diode 21, the next charge accumulation starts from the time when the read gate 23 is set to the OFF level, and the above operation is repeated.

Next, the driving of this embodiment will be described based on the time charts of FIGS. 3 (a) to 3 (e).

Here, the transfer pulse is the voltage applied to the transfer gate 25,
The read pulse is a voltage applied to the read gate 23. Positive and negative charges are generated in the pyroelectric sensor as the optical chopper is opened and closed. When the pyroelectric sensor is not connected to any other, the signals become positive and negative alternating signals centered on the average level as shown in FIG. 3 (d). Here, the timing of signal reading is
By synchronizing just before the chopper opens and immediately before the chopper closes, a positive charge is accumulated from the Reset level when the chopper is open, a negative charge is accumulated from the Reset level when the chopper is closed, and the maximum positive and negative charges are accumulated. Can accumulate quantity. The number of electrons of bias charge is N, the number of electrons of signal charge is ±
As n, when the bias charge qN and the signal charge ± qn are added during signal reading, the bias charge and the positive signal are subtracted q (N−n) when the chopper is open, and the charge amount is small, and when the chopper is closed, the bias charge and the negative charge are negative. Signal addition q
It becomes (N + n), and the amount of charge increases. Both positive and negative signals can be read by setting the amount of bias charge to a value larger than the positive signal. In this embodiment, the transfer of the bias charge and the transfer of the image signal charge to the transfer stage are simultaneously realized by the same clock pulse, and the transfer time is effectively used.

There are several possible means for injecting and transferring bias charges, and three types of plane equivalent circuits are shown in FIGS. 4 (a) to 4 (c). The basic configuration is that the storage diode 41 of each pixel is connected to the vertical CCD 42,
42 is connected to the horizontal CCD 43, and the output amplifier 44 is connected to the end of the horizontal CCD 43.
Is provided. An image signal is output by sequentially transferring the vertical CCD 42 and the horizontal CCD 43.

In FIG. 4A, each vertical CCD 42 is provided with a charge injection mechanism 45, and bias charges are injected in synchronization with the vertical CCD 42 during image signal transfer. At the same time as the transfer of the image signal is completed, the injection of the bias charge is also completed. This configuration
The design and drive could be easily realized simply by providing a charge injection mechanism in the vertical CCD of the conventional CCD.

In FIG. 4B, a lateral injection CCD 46 having a charge injection mechanism 45 is provided at one end, bias charges are injected into the horizontal CCD 46, and then the bias charges are sequentially transferred to each vertical CCD 42. In this case as well, the bias charge is transferred during the image signal transfer. With this configuration, since the bias charge of all pixels is generated by one charge injection mechanism, an image with very little pattern noise was obtained.

FIG. 4 (c) shows the lateral CCD 46 for injection and the lateral C of FIG. 4 (b).
In the example that doubles as CD43, charge injection mechanism 45 provided on the lateral CCD43
Bias charges are injected into the horizontal CCDs 43 from the above, and the bias charges are sequentially transferred downward in each vertical CCD 42. The image signal is output by transferring the vertical CCD 42 upward. In this configuration, the conventional vertical CCD has the same configuration as the four-phase driving CCD, and the design is very easy, and the pattern noise is extremely small as in FIG. 4 (b). However, there is a drawback that the driving is complicated.

The embodiment of FIG. 1 has a hybrid structure in which the pyroelectric sensor and the Si substrate are bonded together by bumps, but the same effect can be obtained as a monolithic structure in which the pyroelectric thin film is directly formed on the Si substrate.

Although the CCD is used as the scanning circuit in the description,
Similar effects can be obtained by using other solid-state scanning circuits such as MOS and CPD.

Effect of the Invention In the present invention, the bias charge is injected from a single charge input mechanism into a plurality of pixels, and the charge injection mechanism is provided outside the pixel portion, whereby the following effects are obtained.

(1) The bias charge of each pixel becomes uniform.

(2) The number of wiring lines in the unit pixel is small.

(3) Driving the pixel part is easy.

(4) The cell size of the unit pixel is the same as before.

Therefore, it was possible to realize a pyroelectric infrared imaging device which has a practical resolution, has a small fixed pattern noise, and does not require an external signal processing circuit.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is a sectional view of a unit pixel of a pyroelectric image pickup device, FIG. 2 is a schematic view showing an operation of a pixel portion, and FIG. 3 is a pixel. FIG. 4 is a schematic view showing the drive of the unit, FIG. 4 is a plan view showing the entire equivalent circuit, and FIG. 5 shows a conventional example, which is a conceptual diagram of the equivalent circuit of the unit pixel and the drive potential. 1 ... Infrared image, 3 ... Pyroelectric infrared sensor, 7 ... Diode region, 10 ... Semiconductor substrate, 9 ... Scan line,
26 …… Bias charge, 45 …… Charge input mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nomura 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Atsushi Abe 1006, Kadoma, Kadoma City, Osaka Prefecture 72) Inventor Mitsuo Andaira 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A diode region having a conductivity type opposite to that of the semiconductor substrate, a scan line for scanning a signal charge accumulated in the diode region, and a charge for injecting an electric charge into the scan line. A pyroelectric infrared sensor having an input mechanism and formed on an electrode connected to the diode region, wherein the infrared sensor generates positive and negative signal charges according to opening and closing of an optical chopper. In the device, the charge injected from the charge input mechanism is transferred to the diode region by the scan line, and the injected charge and the charge accumulated in the diode region are mixed to generate the infrared light. A pyroelectric infrared imaging device, wherein signal charges of both polarities of a pyroelectric infrared sensor are read out to the scanning line. 2. A plurality of scan lines are arranged, a charge input mechanism is provided at one end of each scan line, and charges are injected from the charge input mechanism to the scan lines. The pyroelectric infrared imaging device according to claim 1. 3. A plurality of vertical scanning lines, a horizontal scanning line connected to each of the vertical scanning lines, and a charge input mechanism provided at one end of the horizontal scanning line. 2. The pyroelectric infrared imaging device according to claim 1, wherein the electric charges injected by the input mechanism are injected into each of the vertical scanning lines by the horizontal scanning lines. 4. A horizontal scanning line for signal reading and a horizontal scanning line for charge injection are common, and a signal is read by sequentially scanning each vertical scanning line and the horizontal scanning line. The described pyroelectric infrared imaging device.