JPH0359370B2 - - Google Patents

Description

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

Normally, a pyroelectric pellet that generates electric charge according to the amount of change in incident infrared rays has a characteristic that the smaller the dissipated heat, the greater the output. Therefore, in conventional detectors, as shown in Figure 1, The pyroelectric pellet 1 was supported in a suspended state on a support stand 2 by gold wires 3, 3 so as to be thermally insulated. However, since the pyroelectric pellet 1 is extremely thin with a thickness of several tens of micrometers and has a small shape of several millimeters square, it is difficult to handle when suspended in the air as described above, and the mass productivity of the detector is low. It was.

Therefore, recent detectors, as shown in Figure 2,
The structure is such that the pellets 6 are supported by adhering the pyroelectric pellets 6 to the upper surface of a support base 5 having a recess 4 on the upper surface using an epoxy adhesive 7. Since the pellets 6 are sufficiently insulated due to the presence of the recesses 4, the heat dissipated from the pellets 6 is suppressed to an extremely low level.

In general, the pyroelectric pellets 1 and 6, together with the supports 2 and 5, respectively, are commonly used in this type of electrical industry.
It is stored in a storage can called Type-5.
That is, this storage can is a bottomed cylindrical container made of iron-nickel alloy with a diameter of 8 mm, a depth of 4 to 7 mm, and a wall thickness of 0.2 mm. Therefore, the area of the pyroelectric pellets stored therein is approximately It will be limited to ^25mm2 or less.
When joining signal lead wires made of thin metal wires (gold, aluminum, etc.) to the front and back electrodes of the pyroelectric pellets 1 and 6, the joining method is usually thermal welding, ultrasonic welding, or other methods. etc. are used in combination. However, no matter which method is used, pressurization during bonding is essential. Further, the thickness of the pyroelectric pellet made of a single crystal material (such as lithium tantalate) and a ceramic material (such as PZT) is generally about 30 to 100 μm. Some kind of contrivance is required to join the lead wire of the electrode onto such a thin film without damaging the thin film. Also,
Generally, a thin metal wire with a diameter of 30 μm is used for this lead wire.

However, in such a detector as shown in FIG. 2, so-called popcorn noise will occur unless the thickness of the adhesive layer is made uniform. In other words, if the thickness of the adhesive layer is uneven, each part of the adhesive layer will expand and contract unevenly when the external environment such as the ambient temperature of the detector changes, and this uneven stretching force will cause the focus to deteriorate. Distortion occurs in the electric pellet 6. When the strain exceeds a certain level, the pyroelectric pellet 6 instantaneously returns to its original state in order to eliminate the strain, that is, to release itself from the above-mentioned uniform expansion and contraction force. Here, since the pyroelectric pellet 6 always has a piezoelectric effect, when the applied external force changes instantaneously, that is, when the above-mentioned distortion is eliminated, a considerable amount of charge is suddenly generated, forming a so-called popcorn. This will generate noise.

Figure 3 shows the generation state of such popcorn noise. Popcorn noise is caused by changes in the white noise voltage level W (approximately ±300 mV) due to changes in the external environment as time passes, such as P ₁ , P ₂ , and P ₃ . ) It can be seen that this occurs suddenly at higher levels.

However, when such popcorn noise occurs, there is a drawback that the SN ratio of the detector decreases and the reliability of the detector deteriorates.

The present invention has been made in view of these points, and embodiments of the present invention will be described below in detail with reference to the drawings, regarding a pyroelectric infrared detector used in a detection section of an intruder alarm.

In FIGS. 4 and 5, reference numeral 8 indicates a pyroelectric pellet made of lithium tanchlorate (LiTaO ₃ ) crystal, etc., which generates an electric charge according to the amount of change in incident infrared rays;
Reference numerals 9 and 10 are front and back electrodes of the pellet 8 formed by vacuum evaporation of nichrome (Ni-Cr), respectively, and the front electrodes 9 are first and second front electrodes 9a and 9b that are separated from each other and have the same shape. The back electrode 10 is applied to the entire back surface of the pellet 8. 11a and 11b are first and second pads for ultrasonic bonding the first and second lead wires 12a and 12b to the first and second surface electrodes 9a and 9b, respectively;
The pads are each made of a vacuum-deposited film of aluminum or the like and are provided at the corners of the first and second surface electrodes 9a, 9b. Note that the first leader line 12 is grounded, and a signal is output from the second leader line 12b. 13 is made of phosphor bronze, etc., and the pellet 8 is
This is a support stand that is attached and supported on the upper surface with an epoxy adhesive 14 on the back electrode 10 side.

When a human body passes through the front surface of the pyroelectric pellet 8 as shown by arrow A, the amount of incident infrared rays changes based on the infrared rays emitted from the human body on the first surface electrode 9a side of the pellet 8. . Then, a charge is generated on the first surface electrode 9a side of the pellet 8, and a signal due to the charge is transmitted to the second lead line 12 via the back surface electrode 10 and the second surface electrode 9b.
b to the outside. Next, the amount of incident infrared rays changes on the second surface electrode 9b side of the pellet 8.
In such a case, the signal is similarly led out from the second leader line 12b. Then, based on these signals, an intruder alarm is issued.

Incidentally, the pellet 8 receives infrared rays from sunlight as well, but in this case it does not output any signal. That is, an equal amount of infrared rays from sunlight etc. is simultaneously incident on the entire surface of the pellet 8, and equal amounts of charges are simultaneously generated on the first and second surface electrodes 9a and 9b of the pellet 8. Since the charges cancel each other out, there is no signal output from the second leader line 12b.

Now, if popcorn noise is generated in such a detector, the intruder alarm will assume that a human body has invaded and will issue a false alarm. Therefore, various experiments and studies were conducted to suppress such popcorn noise. As a result, _the generation of popcorn noise is determined by the ratio _R (= It was found that this was largely caused by S ₂ /S ₁・100%).

That is, the voltage level of popcorn noise is 6th
As shown in the figure, when the ratio R is 8% or less, the white noise voltage level W is approximately as shown in FIG.
(approximately ±300 mV) or less, it becomes constant, and when it exceeds 8%, it gradually increases.

Therefore, it has been found that if the ratio R is suppressed to approximately 8% or less, the voltage level of popcorn noise falls within the voltage level of white noise, and the generation of popcorn noise can be substantially suppressed.

On the other hand, if the ratio R is too small, it becomes difficult to adhesively support the pellets 8. Further, in order to increase the output of the pellet 8 by insulating the pellet 8, it is necessary to provide a space between the back electrode 10 side of the pellet 8 and the support 13 except for the adhesive support portion of the support 13. In this case, the pressure at the time of ultrasonic bonding of the first and second extraction surfaces 12a and 12b is such that the first and second pads 11a and 11b are
By providing it opposite to the adhesive support section 3, it may be received by the support base 13 via the adhesive 14. Here, if the ratio R is too small (assuming the total area S ₁ of the surface electrode 9 is constant), the support base 1
Since the adhesive support part 3 becomes smaller, it becomes difficult to align the first and second pads 11a, 11b with the adhesive support part with high precision, and therefore the pressure during bonding is transmitted to the space part and the pellet is 8 may be broken.

As a result of various experiments and studies on the minimum value of the ratio R, we found that if the ratio R is maintained at approximately 0.8% or more, the adhesive support of the pellet 8 can be reliably achieved, and the first and second leader lines 12a, 12b
It has been found that the risk of the pellets 8 breaking during bonding can be significantly eliminated.

Therefore, the ratio R must be maintained within the range of approximately 0.8 to 8%.

Returning to FIGS. 4 and 5, 15, 15, ... are formed at the four corners by acid etching the upper surface of the support base 13, and have a height of approximately 0.1 to 0.2 mm. It is a quarter-shaped support. and,
The pillars adhesively support the pellets 8 with adhesive 14 applied only to their upper surfaces, and there is no space between the back electrode 10 side of the pellets 8 and the support base 13 except for the adhesive support portion. 16 are formed. In addition, the first and second pads 11
a, 11b are opposed to two pillars 15, 15.

That is, the lead wires 12a, 1 of the electrodes are attached to the first and second pads 11a, 11b on the thin film pyroelectric pellet 8 as described above without damaging the thin film.
In order to perform the bonding as shown in FIG. 2b, it is necessary to have a support on the back side of the pyroelectric pellet 8 facing the connection part of the lead wire, which is sufficient to support the pressure during bonding. I'm going. As mentioned above, thin metal wires with a diameter of 30 μm are used for the lead wires 12a and 12b. Therefore, the area of the top surface of the support column 15 is 1/4 of the area of a circle with a radius of 0.1 mm (i.e., 1/4
The minimum required degree is the shape of a sector of a circular arc.

The vertical dimension a and the horizontal dimension b of the first and second surface electrodes 9a and 9b are, for example, 2 mm and 1 mm, respectively.
The total area S ₁ is 4 mm ² , and the radius r of each of the pillars 15, 15, ... is, for example, 0.1 mm, and the total area S ₂ of the adhesive support part is S ₂ = 4 x (πr ₂ x 1 /4)=4×
(π×0.1mm×0.1mm×1/4)=0.0314mm ² , that is, approximately
It is ^0.0314mm2 . Therefore, the above ratio R (=S ₂ /S ₁・100%) is approximately 0.8% and falls within the above range (approximately 0.8% to 8%).
%).

As is clear from the above description, the present invention provides a pyroelectric pellet that has front and back electrodes and generates electric charge in accordance with the amount of change in incident infrared rays, and an adhesive support for attaching the pellet to the back electrode side. In the pyroelectric infrared detector equipped with the above, the ratio of the total adhesive support area of the support base to the total area of the surface electrode is approximately 0.8 to
8% range, and a space was formed between the back electrode side of the pellet and the support at a point other than the adhesive support part of the support, so the generation of popcorn noise could be substantially suppressed. Moreover, the output can be increased, the pellet can be reliably bonded and supported, and there is almost no risk of the pellet breaking when bonding a lead wire onto the surface electrode. A highly reliable pyroelectric infrared detector can be provided.

[Brief explanation of drawings]

Figures 1 and 2 are front views of a conventional pyroelectric infrared detector, Figure 3 is a characteristic diagram showing the popcorn noise generation state in the detector shown in Figure 2, and Figure 4 is a diagram showing the state of occurrence of popcorn noise in the detector of Figure 2. FIG. 5 is a perspective view of an example of a pyroelectric infrared detector, FIG. 5 is a perspective view of the main part thereof, and FIG. 6 is a characteristic diagram showing changes in the popcorn noise level. 8...Pyroelectric pellet, 9a, 9b...1st,
2nd surface electrode, 10... Back electrode, 13... Support stand.

Claims (1)

[Claims] 1 It has front and back electrodes 9 and 10 and is made of lithium tantalate, etc., which generates electric charge according to the amount of change in incident infrared rays, and has an area of 25 mm ² or less and a thickness of approximately 30 to 100 μm.
In a pyroelectric infrared detector equipped with a pyroelectric pellet 8 of Signal lead lines 11a and 11b are provided at opposing positions on the surface electrodes 10, and the total area _S1 of the surface electrodes 9 and the total adhesive support area _S2 on the plurality of pillars 15 provided on the support base are
(S ₂ is 0.03mm ² or more) and the ratio (S ₂ /S ₁ ) is approximately 0.8 ~
8% range, and a space 16 is formed between the back electrode side of the pellet and the support base in a region other than the adhesive support portion on the pillar.