JPS6210370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared detector equipped with a pyroelectric pellet whose charge amount changes depending on the amount of change in incident infrared radiation.

Embodiments of the present invention will now be described in detail with reference to the drawings, regarding an infrared detector used in the detection section of an intruder alarm that issues an alarm when it detects human intrusion.

In the figure, 1 is a pyroelectric pellet with a thickness of 50 μm formed of lithium tantalate (LiTaO ₃ ) crystal, etc., whose charge amount changes depending on the amount of change in incident infrared radiation;
2 is coated with nichrome (Ni-) on the entire back surface of the pellet.
Back electrode applied by vacuum evaporation of Cr), 3a
and 3b are first and second surface electrodes which are similarly applied on the surface of the pellet 1 by vacuum evaporation of nichrome, and the first and second surface electrodes have the same rectangular shape and are separated in parallel to each other. has been done. Furthermore, as a feature of the present invention, in the first and second surface electrodes 3a and 3b, the three sides other than the opposing sides are located on the inside with a distance a (see FIG. 2) from the outer peripheral edge of the surface of the pellet 1. It is located in
4a and 4b are the first and second surface electrodes 3, respectively.
The first and second pads 5a and 5b are formed of a vacuum-deposited film of aluminum or the like on the pads a and 3b, and the first and second lead wires are ultrasonically bonded to the first and second pads, respectively. .

The pyroelectric pellet 1 is polarized so that the front side is positively charged and the back side is negatively charged, as shown in FIG. 3a, for example. Therefore, the first and second electrodes 3a, 3b and the exposed surface of the pellet 1 attract the same amount of negative floating charge in the air as the positive charge on the pellet, and the surface of the back electrode 2 attracts the same amount of negative floating charge as the positive charge on the pellet. The same amount of positive floating charge in the air will be attracted to the amount of negative charge.

Now, when a person passes in front of the pyroelectric pellet 1 as indicated by arrow A (see FIG. 1), infrared rays emitted from the human body first enter the pellet 1 on the first surface electrode 3a side. In such a case, the amount of charge in the pellet 1 directly under the first surface electrode 3a changes.
There are two cases of change: increase and decrease, but for convenience of explanation, if we assume that the charge amount decreases as shown in FIG. 3b, the negative charge on the first surface electrode 3a A portion of the pellet is not bound by the positive charges in the pellet 1 and becomes movable through the electrode 3a. In addition, in such a case, the positive charges in the pellet 1 directly under the second surface electrode 3b do not change, so that all the negative charges on the second surface electrode 3b cannot be moved. Therefore, a signal corresponding to the difference in movable charges on the first and second surface electrodes 3a and 3b is led out from the first and second lead lines 5a and 5b.

Next, infrared rays emitted from the human body enter the pellet 1 on the second surface electrode 3b side. In such a case,
The amount of charge in the pellet 1 directly under the second surface electrode 3b changes due to the incidence of infrared rays, and the amount of charge in the pellet 1 directly under the first surface electrode 3a also changes due to the absence of the incidence of infrared rays. Therefore, at this time as well, signals corresponding to the difference in the movable charges on the first and second surface electrodes 3a and 3b are led out from the first and second lead lines 5a and 5b.

Based on these signals, the intruder alarm issues an alarm.

Furthermore, even if the infrared rays are applied uniformly over the entire surface of the pellet 1, or if the ambient temperature changes, the amount of charge in the pellet 1 will change. Second surface electrode 3
The amounts of changed charges in the pellet 1 directly under a and 3b are the same, and therefore the movable charges on the first and second surface electrodes 3a and 3b are also the same, so there is no difference between the first and second surface electrodes 3a and 3b. No signal is output to the two lead lines 5a and 5b.

Reference numeral 6 denotes a support base on the upper surface of which the pellet 1 is adhered and supported using an epoxy adhesive 7 or the like, and the support base is made of a metal such as copper, aluminum, or a resin material such as epoxy.

However, in the conventional infrared detector, the three sides of the first and second surface electrodes 3a and 3b other than the opposing sides coincide with the outer peripheral edge of the surface of the pellet 1, and the above-mentioned interval a is It had not been formed. Therefore, if the infrared rays are uniformly incident over the entire surface of the pellet 1, or if the movable charges on the first and second surface electrodes 3a and 3b increase in response to changes in ambient temperature, the first and second surface electrodes 3a and 3b may - The respective ends of the second front electrodes 3a, 3b and the back electrode 2 have a thickness of approximately
Since they are very close to each other with a 50 μm pellet 1 in between, a discharge phenomenon occurs between the first and second electrodes 3a, 3b and the back electrode 2 due to the movable charges. In addition, due to such a discharge phenomenon, a signal called so-called popcorn noise is generated in the first and second
Since this occurred on the lead lines 5a and 5b, the S/N ratio of the infrared detector was degraded.

However, in the structure of the present invention, as described above, the first and second surface electrodes 3a and 3b are formed such that the ends of their three sides are located inside the outer peripheral edge of the pellet 1 with a distance a. Therefore, even if the amount of charge in the pellet 1 changes, since there are no electrodes at the outer peripheral edge of the pellet 1, the above-mentioned movable charge does not exist, and therefore popcorn noise due to electric discharge as in the conventional case does not occur. The occurrence can be reduced.

FIG. 4 shows the results of an experiment investigating the relationship between the above-mentioned interval a and the occurrence of popcorn noise. In this experiment, the distance a was set to 0 μm, 20 μm, 50 μm, 80 μm,
Prepare 50 samples each with diameters of 100 μm, 150 μm, and 200 μm, place the samples in a dark box for one week, and measure the number of popcorn noises caused by changes in ambient temperature.Based on the measurement results. The average number of popcorn noise occurrences for each interval a was investigated.

As is clear from FIG. 4, popcorn noise is no longer generated when the distance a is 100 μm or more.

Note that the above-mentioned noise occurs between 0 μm < a < 100 μm, but this is due to the movable charge on the electrode flowing through the slight dirt etc. attached to the surface of the pellet 1 and flowing to the outer peripheral edge, causing a discharge. This is to contribute. However, if the distance a is 100 μm, the outflow charge reaching the outer peripheral edge will be approximately 0, and no discharge phenomenon will occur.

Therefore, when considering the above charge flow,
It is preferable that the distance a is 100 μm or more. Further, from a practical point of view, it is desirable that the electrodes 3a and 3b be as wide as possible, and therefore, it is practical for the above-mentioned distance a to be at most 200 μm or less.

As is clear from the above description, according to the present invention, there is provided a pyroelectric pellet that generates a charge depending on the amount of change in incident infrared rays, a back electrode provided on the entire back surface of the pellet, and a pyroelectric pellet that is formed on the surface of the pellet from its outer peripheral edge. Since the surface electrode is provided on the inside, it is possible to provide an infrared detector with an improved S/N ratio compared to the conventional one.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an infrared detector according to an embodiment of the present invention;
Fig. 2 is a plan view of the same, Fig. 3 a and b are schematic diagrams for explaining changes in charge, and Fig. 4 shows experimental results investigating the relationship between interval a and the number of popcorn noise occurrences. It is a characteristic diagram. 1... Pyroelectric pellet, 2... Back electrode, 3
a, 3b...first and second surface electrodes.

Claims (1)

[Scope of Claims] 1. A pyroelectric pellet whose charge amount changes depending on the amount of change in incident infrared rays, a front surface electrode and a back surface electrode formed on the front and back surfaces of the pellet, respectively, and at least one of the above electrodes. An infrared detector characterized in that the entire periphery is separated from the outer periphery of the pellet by 100 μm or more.