JPH04355331A - Pyroelectric two-dimensional array infrared sensor - Google Patents

Abstract

PURPOSE:To enable piezoelectric noise which is peculiar to a pyroelectric element to be eliminated and achieve a heat infrared camera, etc., by a simple and highly sensitive two-dimensional array element which does not require any cooling for a pyroelectric-type two-dimensional array infrared sensor which is used for a heat infrared measurement. CONSTITUTION:A two-dimensional array pyroelectric element 11 is set to an infrared-rays incidence side and a similar element 12 is set to a position which is not irradiated by infrared-rays as a dummy. A CCD chip 15 for reading signal is combined to each by an indium bump 14 and is placed on both surfaces of a substrate 13, thus enabling vibrations from an outside which are propagated through the substrate to have equal frequency, amplitude, and phase. Also, both CCDs 15 are driven by the same clock 16, both outputs 17 are amplified by a buffer amplifier 18 and are input to a differential amplifier 19, and a difference between both is output, thus obtaining a high-sensitive pyroelectric two-dimensional array infrared sensor where a piezoelectric noise due to vibration from the outside is greatly reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a pyroelectric two-dimensional array infrared camera used in an infrared camera that can convert the temperature distribution and infrared radiation distribution of an object into two-dimensional electrical signals and convert them into visible images. It is related to sensors.

0002

[Prior Art] Recently, infrared sensors have been used in the thermal management process of products.
It has come to be used for night surveillance, disaster prevention, crime prevention, etc. These sensors have evolved from a point type that measures only one point, to a one-dimensional array type that can measure a one-dimensional distribution at once, and then to a two-dimensional array type. In these two-dimensional infrared sensors, a pyroelectric element is most often used as an infrared detection element, but since this element generates piezoelectric noise, a method is used to eliminate that noise by combining it with a dummy element. ing.

A conventional pyroelectric two-dimensional array infrared sensor will be described below with reference to FIG.

In FIG. 4(a), 1 is a pyroelectric infrared detection element, and 2 is the same infrared detection element, which is installed so that infrared rays do not enter, and functions as a dummy element. Reference numeral 3 denotes an insulating plate with a conductive path, which serves to connect both elements to form an equivalent circuit as shown in FIG. 4(b). As shown in the figure, the polarization directions of both elements are reversed, so that the same piezoelectric noise is eliminated. 5 is a semiconductor for reading out the output signal 7 of the infrared detection element in time sequence. With such a configuration, piezoelectric noise is eliminated.

[0005]

However, in the above configuration, since the capacitive elements are connected in series, the combined capacitance of the elements is halved. In a two-dimensional array sensor, the area of each element 1 is small, so the element capacitance is small.
Since the capacitance is about the same as the stray capacitance, signal readout efficiency is reduced. Therefore, there is a problem in that a decrease in capacitance directly leads to a decrease in sensor performance.

The present invention solves the problems of the prior art described above, and aims to provide a highly sensitive pyroelectric two-dimensional array infrared sensor with low piezoelectric noise.

[0007]

[Means for Solving the Problems] In order to achieve this object, the present invention combines a two-dimensional array pyroelectric infrared detection element and a dummy element with a signal readout semiconductor, and clocks both of them using the same clock. The configuration is such that the output signal is amplified by a buffer amplifier, and then the difference signal between the two is extracted by a differential amplifier.

[0008]

[Operation] With the above configuration, the present invention is a method in which a difference signal is extracted by a differential amplifier through a buffer amplifier without connecting capacitive elements in series, so there is no reduction in the capacitance of the elements, and a reduction in signal readout efficiency is suppressed. Furthermore, since the signals are read out using the same clock, the signals can be read out at the same time even if the signal readout semiconductors are used separately, and piezoelectric noise becomes the same signal, which can be eliminated by extracting the difference.

[0009]

[Embodiment] (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a pyroelectric two-dimensional array infrared sensor according to a first embodiment of the present invention. In FIG. 1, reference numeral 11 indicates a two-dimensional array pyroelectric infrared detection section, and reference numeral 12 indicates a dummy element section having the same dimensions, the same material, and the same characteristics. Each is made of lead titanate ceramic with a pitch of 0.1 mm2 in both length and width, effective element surface dimension of 0.08 mm2, and a thickness of 10 μm, and a nichrome common electrode (not shown) on one side of the ceramic has a sheet resistance of 350 Ω. /cm2. On the other side, aluminum electrodes of 0.08 mm2 with a pitch of 0.1 mm2 are 1 μm thick.
128 x 128 pieces were deposited, and gold (A
u, Gold) An electrode film is deposited. An indium bump 14 shown in FIG. 1 is connected to the separation electrode and to a CCD chip 15 for signal readout to electrically and mechanically connect the two. This connection is made by thermocompression bonding at a high temperature of approximately 160°C.

Although the signal reading electrodes of the CCD 15 are not shown, they are of course 128×128 with a pitch of 0.1 mm2.
They are arranged in an array.

As shown in FIG. 1, the two assembled chips are glued with the CCD 15 sides on both sides of the substrate 13, and placed in a package (not shown) in which only the infrared detection section 11 receives infrared rays as an input signal. Install it so that it receives light. two CCDs
15 are driven by the same clock signal 16, both outputs 17 are amplified with the same amplification degree by two buffer amplifiers 18, and their outputs are input to a differential amplifier 19 to extract the difference signal between the two.

The operation of the pyroelectric two-dimensional array infrared sensor constructed as described above will be explained using the equivalent circuit shown in FIG. Two two-dimensional array pyroelectric infrared detectors (two-dimensional array pyroelectric element) 1 are generated by external vibration.
The vibrations applied to the parts 1 and 1 are almost the same because they are installed at positions with almost equivalent vibration characteristics. Therefore, the piezoelectric noise has substantially the same frequency, amplitude, and phase, and if the difference is calculated by the differential amplifier 19, the vibration noise is eliminated except for the output due to infrared rays, which is the input signal. Furthermore, signal readout efficiency is higher than in the case where the dummy elements 12 are connected in series. Specifically, the capacitance of the pyroelectric element 11 is 1 pF, but since the stray capacitance is 0.5 pF, the readout efficiency can be calculated using equation (1) and is about 66%.

[0014]

[Math 1]

On the other hand, when the dummy elements 12 are directly combined in series, the capacitance of the pyroelectric element 11 is 0.5 pF, and the readout efficiency is reduced to 50%. Furthermore, if the piezoelectric characteristics of the dummy elements 12 are different, the piezoelectric noise cancellation effect will be reduced; however, in the configuration of this embodiment, two buffer amplifiers 18 are used, so if the piezoelectric characteristics are different, If they differ, the difference can be suppressed by adjusting the amplification degree of each buffer amplifier 18.

As described above, according to this embodiment, two pyroelectric type two-dimensional array infrared sensors with the same characteristics are installed on the same substrate at a position with the same vibration characteristics, and one sensor, that is, the pyroelectric By making the signal infrared rays incident only on the infrared detector 11, driving the two semiconductors with the same clock, and extracting the difference signal between them with the differential amplifier 19 through the buffer amplifier 18, the readout efficiency is reduced. It is possible to realize a highly sensitive pyroelectric two-dimensional array infrared sensor that suppresses piezoelectric noise and significantly reduces piezoelectric noise.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a sectional view of a pyroelectric two-dimensional array infrared sensor according to a second embodiment of the present invention.

In FIG. 3, 21 is a two-dimensional array pyroelectric infrared detection section, and 22 is a dummy element section having the same dimensions, the same material, and the same characteristics, which is the same as the structure shown in FIG. 1. The difference from the configuration in FIG. 1 is that instead of attaching the two two-dimensional array infrared sensors to the substrate separately, they are attached on the surface of the CCD 15 and integrated, and then the dummy element 22
This is the point where the surface is attached to the substrate 23.

The operation of the pyroelectric two-dimensional array infrared sensor constructed as described above will be explained below. First of all, strictly speaking, the vibration conditions due to external excitation are different because they are not placed at equivalent positions in terms of vibration characteristics.
While the thickness of the substrate 23 is 10 mm, the CCD 1
5 is 0.3 mm, and the pyroelectric element 21 is 0.01 mm.
, the latter together with the indium junction are of negligible size. Therefore, considering only the former thickness,
In the vibration of the substrate 23 having a thickness of 10 mm, it is only necessary to consider how the difference in the position of the thickness of the CCD 15 manifests as a difference in vibration mode. Vibration is usually from several Hz to 2
Since the target range is about kHz, if the speed of sound on the board is 8000 m/s, the wavelength can be found by (Equation 2),
The shortest length is 4m.

[0021]

[Math 2]

[0022] Therefore, at a wavelength of 4 m, the position is 0.3 mm.
It can be seen that in the case of a difference of , the phase shift is about 0.025° and can be almost ignored. As described above, piezoelectric noise can be reduced by installing the two two-dimensional array infrared sensors on one side of the board 23, and since no sensors are installed on the other side of the board, the package base It is possible to realize a pyroelectric two-dimensional array infrared sensor that can be directly adhered to, is durable, and relatively easy to assemble.

In the first embodiment, the common electrode of the dummy element is made of a nichrome vapor deposited film, but since it is not always necessary to increase the absorption efficiency of infrared rays, an aluminum vapor deposited film may be used. Further, in the second embodiment, since the dummy element surface is bonded to the substrate, it goes without saying that an aluminum vapor-deposited film may be used.

[0024]

[Effects of the Invention] As described above, the present invention uses two sets of two-dimensional array infrared sensors that are a combination of a pyroelectric element and a signal readout semiconductor, are driven by the same clock, and only one of them receives an input signal. By injecting infrared rays and obtaining a difference signal via a buffer amplifier, piezoelectric noise can be significantly reduced, and the highly sensitive pyroelectric type 2 suppresses reduction in signal readout efficiency.
A dimensional array infrared sensor can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a pyroelectric two-dimensional array infrared sensor in a first embodiment of the present invention.

[Fig. 2] Equivalent circuit diagram of the pyroelectric two-dimensional array infrared sensor in the first embodiment.

FIG. 3 is a cross-sectional view of a pyroelectric two-dimensional array infrared sensor according to a second embodiment of the present invention.

[Figure 4] (a) Cross-sectional view of a conventional pyroelectric two-dimensional array infrared sensor (b) Equivalent circuit diagram of a conventional pyroelectric two-dimensional array infrared sensor

[Explanation of symbols]

11 Two-dimensional array pyroelectric infrared detection section 12 Two-dimensional array pyroelectric dummy element section 13 Substrate 14 Indium bump junction section 15 Two-dimensional array semiconductor (CCD) for signal readout
16 Clock signal 17 Output signal end 18 Buffer amplifier 19 Differential amplifier

Claims (3)

[Claims] 1. A first infrared detection section having the same characteristics, consisting of an infrared detection section in which a plurality of pyroelectric infrared detection elements are two-dimensionally arranged, and a semiconductor that reads out the output signals of the infrared detection section in time sequence. A second two-dimensional array infrared sensor is provided, the two-dimensional array infrared sensor is installed on the same substrate at a position where the vibration characteristics are approximately the same, and a signal is sent only to the first two-dimensional array infrared sensor. Infrared rays are made incident, the first and second two-dimensional array infrared sensors are driven by the same clock, each is provided with a buffer amplifier, both outputs are input to a differential amplifier, and the difference between the two is output. A pyroelectric two-dimensional array infrared sensor characterized in that it is obtained as follows. Claim 2: Claim 1, wherein the first and second two-dimensional array infrared sensors are installed at symmetrical positions on both sides of the substrate.
The pyroelectric two-dimensional array infrared sensor described above. 3. The first and second two-dimensional array infrared sensors are bonded together on the CCD side in a plane-symmetrical positional relationship, and one surface of the pyroelectric two-dimensional array element disposed on the outside is attached to the substrate. The pyroelectric two-dimensional array infrared sensor according to claim 1, which is attached to a pyroelectric two-dimensional array infrared sensor.