JPS6125296B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a pyroelectric infrared detector.

In a pyroelectric infrared detector, how to reduce the distributed capacitance around the detection element is an important issue in order to increase the sensitivity of the detector, and ease of manufacture is also an important issue. An object of the present invention is to simplify the structure, reduce the distributed capacitance around the detection element, thereby increasing detection sensitivity, and facilitating manufacturing.

First, a conventional pyroelectric detector will be explained using FIG.

Figures 1a and 1b show the top and side cross-sections of a conventional infrared detector. Here, 10 is a pyroelectric element (with collecting electrodes deposited on both sides)
Two elements are installed in one detector with opposite polarity connected to each other. To explain in detail the pyroelectric element incorporating part, as shown in FIGS. 1c, d, and e, there is one in which a metal ring 121 is adhered to or in contact with the pyroelectric element 10. First, FIG. 1c shows a metal ring 121 bonded to a pyroelectric element 10 having vapor-deposited electrodes on both sides, and numeral 13 in the figure is a stepped portion to facilitate manufacturing. 1d shows an element unit formed by contacting another ring 122 from below to the one shown in FIG. 1b, and FIG. 1e shows two sets of the element units shown in FIG. They are assembled symmetrically with a reflecting plate 901 in between. Therefore, element 10 of unit 900 and element 10 of unit 902 are necessarily connected with opposite polarities.

In FIGS. 1a and 1b, 11 is a window material that transmits infrared rays. Reference numeral 21 is a ring-shaped metal body that receives the window material 11, and also serves to ground the front surface (electrode) of the pyroelectric element 10 to the housing 19 via the ring 121. 191 is a bent portion of the housing 19.

On the other hand, the lower side of the unit 902 is a printed circuit board 13.
The ring 121 is in contact with a metal receiving plate 14 which is in contact with the input gate of the amplifier 4 attached to the amplifier. A supporter 15 supports the substrate 13. These amplifying sections and two sets of element units are housed in a stacked manner in a cylinder 18 made of insulating plates, pressed by a cushion material 16, and enclosed by a back cover 17. 20 is its stopper. 5,
Reference numerals 6 and 7 are power supply and output leads for the amplifier 4.

With the above structure, a unit of 900
The pyroelectric output generated in the unit 902 is transmitted to the amplifier 4 through the unit 902 and amplified, but the output voltage caused by the change in room temperature cancels out because both units have opposite polarities and does not appear externally. By the way, in a detector with the above structure, a pair of metal rings with a relatively large surface area are placed symmetrically with each other sandwiching a pyroelectric element, so that the stray capacitance around the pyroelectric element increases. This resulted in a drawback that the sensitivity of infrared detection was low. Moreover, the structure was complicated and manufacturing was not easy.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional art, and embodiments thereof will be described below with reference to the drawings.

FIGS. 2 and 3 show an infrared detection element section in an embodiment of the present invention. FIG. 2a shows the top surface (front surface) of an element in which electrodes are deposited on a film having pyroelectric properties, FIG. 2b shows its side cross section, and FIG. 2c shows its bottom surface (back surface). In the figure,
31 is a pyroelectric film, 32 and 33
A pair of current collecting electrodes are simultaneously formed on the front surface of the film 31 by vapor deposition, and 34 is a counter electrode formed on the back surface by vapor deposition, which faces the current collecting electrodes 32 and 33. Each of the current collecting electrodes 32, 33 and the counter electrode 34 is formed symmetrically with respect to the center line A of the film 31, so that the current collecting electrodes 32, 3 of the counter electrode 34
The area of the portion overlapping with each of 3 is the same.

FIG. 3a shows a side cross section of a pyroelectric film on which the electrodes have been deposited as described above, which is bent and assembled into a mold 35, and each part 31 to 34 is the same as above. FIG. 1B is a diagram showing an equivalent diagram for explaining the built-in body.

Note that when forming the above electrode, unlike the conventional product (explained in Figure 1), a reflective plate is not inserted between the two sets of elements, so the electrode on the back side (i.e., the counter electrode) is exposed to infrared light. The film is formed by vapor deposition until it reaches a thickness that does not allow the film to pass through. On the other hand, the electrode on the surface side (that is, the current collecting electrode) is made to have a thickness that is most likely to absorb infrared light, as in the conventional case. When using Ni-Cr for electrode formation, the surface resistance of the front electrode is 400 to 600 Ω/cm ² , and the back electrode is 10 Ω/cm 2 .
Good results can be obtained if the thickness is set to Ω/cm ² or less.

As is already clear from the above, the collected voltage that appears due to changes in room temperature appears as +- to -+ on the left and right opposing surfaces, respectively, as shown in Figure 2b, and therefore does not appear on the electrodes at both ends of the surface because they cancel each other out. . However, if the bent structure shown in FIG. 3 is irradiated with infrared light from one side, the voltage appearing on that surface can be extracted from the electrodes at both ends through the capacitance of the other side, as shown by + and - in FIG. 3. FIG. 4 shows an embodiment of an infrared detector using the above-mentioned detection element section.

Here, 31 to 35 are the same as in Figures 2 and 3.
31 is a pyroelectric film, 32 and 33 are symmetrical vapor deposition electrodes, and 34 are both of the above electrodes 32 and 33.
The electrodes 32 and 33 have infrared absorption characteristics, and the electrode 34 has infrared opaque (reflection) characteristics.

Further, 41 is a window material for infrared incidence, 42 is a receiving frame ring thereof, and 43 is a ring 4 for attaching the electrode 32 on the upper surface.
It is a metal ring for connecting to the case through 2. 44 is a metal ring for connecting the electrode 33 on the lower surface to the amplifier 46 via the receiving plate 45.
47 is a printed circuit board of the amplification section, 48 is a supporter that supports it, 49 is an insulating cylinder surrounding these, 50 is a cushion material that applies a certain pressure to the element and ring, 51 is a metal case, 52 is a back cover, and 53 is its The stop spring 54 is the lead for the amplifier power supply and output.

For comparison with FIGS. 2 and 3, a cross section taken along line AA' in FIG. 4b is shown in FIG. 4c.

With this structure, the amount of stray capacitance that used to be generated around the ring has become extremely small, and it is easy to take out the lead from the ring part, and the detection element has a simple bending structure. It is also easy to manufacture.

FIGS. 5 and 6 show a multi-element type infrared detecting element section in which the electrodes described above are formed into rectangular strips and arranged in parallel.

FIG. 5a is a diagram showing a pyroelectric film in which a plurality of sets (four sets in this case) of electrodes are deposited on a pyroelectric film, as in the case of FIG. 2, in a bent state. Figure b shows an insulating frame that receives this film.

FIGS. 6a and 6b are a plan view and a side sectional view of the detection element section. Here, 61 is a pyroelectric film, 62 and 63 are electrodes deposited on the front surface of the film 61, and 64 (portion indicated by a solid line) is an electrode deposited on the back surface. In this case, as in the case of FIG. 2, the thickness of the vapor deposition on the front side is such that it transmits infrared rays best, and the thickness of the vapor deposited electrode on the back side is thick enough to reflect infrared rays. 65 is an insulating mold that holds the film 61. 62′, 62″, 6
2 are electrodes arranged in parallel similar to 62, and on the lower side are electrodes 63', 63'', 6
3 exists.

Further, 64', 64'', and 64 indicate electrodes on the back surface similar to the electrode 64 with dotted lines.

FIG. 6c shows the connection between this one electrode and the amplifier, and 61 to 64 are the same as those in FIG. 6a and b. When infrared IR is incident on one side of the film, a polarization voltage is generated on the electrodes 62 and 64 on both sides of the film 61, and the voltage on the electrode 64 is transmitted to the ground 68 through the capacitance formed with the lower electrode 63,
The voltage is transmitted to the gate of FET65. 66
is a diode that replaces the gate leakage resistance,
67 is a source resistance. As a result, the polarization voltage due to infrared input generated on the pyroelectric surface can be taken out from the terminal 69 with low impedance, and by arranging them in parallel, it can be easily used as a line sensor.

As is clear from the above embodiments, in the present invention, on the surface of a pyroelectric film, two external extraction electrodes are formed symmetrically from the center line of the film, and on the back surface of the pyroelectric film. is formed as a single electrode deposited to a thickness that does not transmit infrared light, and the two electrodes on the surface are bent so that they are positioned above and below to detect infrared light. This has the effect of reducing the stray capacitance of the electrodes and increasing the sensitivity of infrared detection while eliminating the influence of temperature inside the housing.

[Brief explanation of the drawing]

Figures 1a and b are a top view and side sectional view of a conventional pyroelectric infrared detector, respectively, and Figures 1c, d, and e
are partial cross-sectional side views of the main parts of the above detector, respectively.
Figures 2a, b, and c are a top view, a side sectional view, and a bottom view, respectively, of a pyroelectric film on which electrodes are formed and used in the detection element part of a pyroelectric infrared detector which is an embodiment of the present invention. , FIGS. 3a and 3b are diagrams showing a side sectional view and an equivalent circuit of the detection element section, respectively,
Figures 4a and b are a top view and a side sectional view of the infrared detector, respectively, and Figure 4c is the solid line in Figure 4b.
5 and 6 are cross-sectional views taken along the line AA', and are views showing modified examples of the above-mentioned detection element section, of which FIG. FIG. 5b is a diagram showing a frame used in the detection element, FIGS. 6a and b are a plan view and a side sectional view of the detection element, and FIG. 6c is a diagram showing a pyroelectric film. FIG. 3 is a diagram showing a connection between a detection element section and an amplifier. 31,61...Film, 32,33,34,
62, 62', 62'', 62, 63, 64, 6
4', 64'', 64... electrode, 35, 65... formwork.

Claims (1)

[Claims] 1. A pyroelectric film that charges in response to infrared rays, and first and second external extraction electrodes formed on the surface of the pyroelectric film in two parts symmetrically from the center line of the film. , and one electrode formed by vapor deposition on the back surface of the pyroelectric film to a thickness that does not transmit infrared light, and is bent so that the first and second external extraction electrodes are positioned above and below. is,
A pyroelectric infrared detector characterized by detecting infrared rays from these first and second external extraction electrodes.