JPH1038679A - Pyroelectric infrared detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared detector with a structure in which a pyroelectric element is mounted on a substrate and malfunctions due to vibrations hardly occur even when sudden vibrations such as impacts are added to the substrate. SOLUTION: An adhesive as soft as the 5B or 6B hardness of pencil lead is used as a conductive adhesive A1 which is used at the time of gluing the electrodes 2a and 3a of a pyroelectric element D to the conductive pattern 4a of a substrate 4. The area of a part glued by the conductive adhesive A1 is minimized as small as possible. By these methods, the vibrations propagating from the substrate 4 to the pyroelectric element D are managed to be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared detector used in fields such as human body detection and infrared analysis.

[0002]

2. Description of the Related Art A pyroelectric infrared detector is an infrared detector utilizing a pyroelectric body whose temperature has increased due to irradiation of infrared rays, converting the temperature change into an electric signal.

A pyroelectric element used in such a pyroelectric infrared detector has electrodes 12a and 12b formed on both surfaces of a thin plate-like pyroelectric body 11 as shown in FIG. In general, a structure having an infrared absorbing film 14 formed thereon is used.

Here, the pyroelectric body is polarized in one direction (see FIG. 1), and when a temperature change occurs in the pyroelectric body, the ratio of the polarization changes and charges are generated. Since the pyroelectric body is also a piezoelectric body, the pyroelectric body generates an electric charge even when an external force such as vibration is applied.

As an element taking this point into consideration, as shown in FIG. 2A, two pairs of opposing electrodes 22a and 22
There is a so-called dual type in which b and 23a, 23b are formed. In this dual type device, FIG.
As shown in the equivalent circuit of (b), the pyroelectric elements having different polarization directions are connected in series, so that disturbances such as ambient temperature change and vibration can be canceled. Usually, such a dual-type element is adhered to a substrate using a conductive adhesive while maintaining conduction (see FIG. 3). In such a dual-type pyroelectric element, an infrared-absorbing film is formed on one of the front and rear surfaces of the element in order to efficiently absorb infrared rays.

[0006]

However, even with the dual-type pyroelectric element as described above, sudden vibration due to impact or the like cannot be completely canceled. Therefore, when assembling a circuit such as a human body detector using a pyroelectric element, it reacts to sudden vibrations without detecting the human body, as if the human body entered the detection area Erroneous operation such as the output of the detection signal may occur.

[0007] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a pyroelectric infrared detector having a structure in which even if sudden vibration such as impact is applied, a malfunction due to the vibration is unlikely to occur. And

[0008]

According to a first aspect of the present invention, there is provided an infrared detector having a structure in which a pyroelectric element in which a counter electrode is formed on a thin plate-like pyroelectric body is mounted on a substrate. Is characterized in that the electrodes of the pyroelectric element are bonded to the conductor pattern of the substrate with a soft conductive adhesive having a hardness of about 5B to 6B in a solidified state, and suddenly by adopting such a structure. The effect of dynamic vibration can be reduced.

That is, in the pyroelectric infrared detector having this kind of structure, the vibration is transmitted to the pyroelectric element through the substrate, so that the hardness of the connecting portion between the substrate and the pyroelectric element is about pencil hardness 5B to 6B. By using the soft conductive adhesive, the vibration transmitted from the substrate to the pyroelectric element can be reduced, and the vibration received by the pyroelectric element can be reduced.

Here, the conductive adhesive used in the present invention is:
This is a composite material in which metal (silver) or carbon is added to epoxy or urethane resin, etc., and has a pencil hardness of 5B in a solidified state.
For example, an adhesive having a softness of about 6B may be an adhesive manufactured by Three Bond Co .;
B, 3302F, 3303, 3303B or 33A-
301 and the like.

In order to achieve the same object, a second invention is directed to an infrared detector in which a pyroelectric element is mounted on a substrate by a conductive adhesive in the same manner as described above, as shown in FIG. The area of the adhesive portion by the agent A2 is characterized by being a minimum area for obtaining an electrical connection enough to take out the signal from the pyroelectric element D to the outside. By reducing the area of the agent A2, even if sudden vibration due to impact or the like is applied to the substrate 4, the vibration is less likely to be transmitted to the pyroelectric element D.

Here, if the area of the conductive portion between the conductor pattern of the substrate and the element electrode is greatly reduced as in the second invention, there is a concern that the conductivity may be reduced. However, this type of pyroelectric infrared detector In (2), the load (resistance) connected between the opposing electrodes is very large (giga ohm level), and the magnitude of the resistance at the bonding portion does not matter at all. Even if the area is considerably reduced, the element operates normally as long as the area is large enough to provide an electrical connection capable of extracting a signal from the pyroelectric element D to the outside.

The hardness of the conductive adhesive used in the pyroelectric infrared detector according to the second aspect of the present invention is not particularly limited, and the hardness is generally used for mounting this type of pyroelectric element. However, as in the first invention, the pencil hardness is 5B or more.
If you use a conductive adhesive with a softness of about 6B,
Due to the synergistic effect, the influence of sudden vibration can be further reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing a schematic structure of the first embodiment of the present invention, wherein (a) and (b) are a front view and a side view, respectively.

First, in the pyroelectric element D of this embodiment, two pairs of opposing electrodes 2a, 2b and 3a, 3b are formed on a pyroelectric body 1 formed by processing a TGS crystal, PZT, LiTaO ₃ or the like into a thin plate. Dual-type element, electrode 2b on one side
3b are electrically connected to each other, and two pairs of opposing electrodes 2a, 2b and 3a, 3b connect two pyroelectric elements having different polarization directions in series, as shown in the equivalent circuit of FIG. It has a shape connected to.

The above-mentioned dual type pyroelectric element D is adhered to the conductive pattern 4a of the substrate 4 by using a conductive adhesive A1 while maintaining conduction. In this example,
Hardness in solidified state as conductive adhesive A1 is pencil hardness 5
Those having a softness of about B to 6B, for example, an adhesive manufactured by Three Bond; product numbers 3302, 3302B, 3
302F, 3303, 3303B or 33A-301
There is a feature in using.

By using the soft conductive adhesive A1 having a pencil hardness of about 5B to 6B for mounting the pyroelectric element D on the substrate 4 as described above, even if sudden vibration due to impact or the like is applied to the substrate 4, Since the vibration is reduced by the conductive adhesive A1, the vibration received by the pyroelectric element D is reduced. Therefore, when the pyroelectric infrared detector of this example is applied to, for example, a human body detector, when a sudden vibration such as an impact is applied to the detector, a signal indicating that a human body is detected is output. Malfunctions are less likely to occur.

FIG. 4 is a diagram showing a schematic structure of the second embodiment of the present invention, wherein (a) and (b) are a front view and a side view, respectively. What is noteworthy in this example is that when the pyroelectric element D having the same structure as above is mounted on the substrate 4 with the conductive adhesive A2, the application shape of the conductive adhesive A2 is determined by the width of the conductive pattern 4a. The area of the bonding portion between the electrodes 2a and 3a of the pyroelectric element D and the conductor pattern 4a is set to a minimum value such that an electrical connection can be obtained such that a signal from the pyroelectric element D can be extracted to the outside. The point is that the transmission of the vibration at the connection portion is made as small as possible.

Also in this example, when sudden vibration due to impact or the like is applied to the substrate 4, the vibration is reduced by the conductive adhesive A2, and the vibration received by the pyroelectric element D is reduced. Therefore, the possibility that an erroneous signal due to vibration is output is reduced.

In the example of FIG. 4, the pyroelectric element D
The conductive adhesive A2 for bonding the electrodes 2a, 3a to the conductor pattern 4a is not particularly limited, and a sufficient effect can be obtained even if the conductive adhesive A2 is of such a hardness as is generally used for this type of device mounting. be able to. Also, the conductive adhesive A2
If a material having a softness with a pencil hardness of about 5B to 6B is used, a further effect can be expected.

Here, in the above embodiment, an example of an infrared detector using a dual type pyroelectric element has been described. However, the present invention is not limited to this, and may be configured as shown in FIG. Of course, the present invention can be applied to a case where an infrared detector is configured using a pyroelectric element having a pair of counter electrodes.

[0022]

As described above, according to the pyroelectric infrared detector of the present invention, the hardness of the conductive adhesive used for bonding the electrodes of the pyroelectric element to the conductor pattern of the substrate is pencil hardness. The vibration transmitted from the substrate to the pyroelectric element is reduced by using a soft material of about 5B to 6B and minimizing the area of the bonded part as much as possible. Even if vibration is applied, malfunction due to the vibration can be prevented. In addition, since the background level vibration and the like are reduced, the influence of the noise component is reduced, and the sensitivity is improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 shows a structural example of a pyroelectric element and an equivalent circuit thereof.

FIG. 2 shows a structural example of a dual type pyroelectric element and an equivalent circuit thereof.

FIG. 3 is a diagram showing a schematic structure of the embodiment of the first invention.

FIG. 4 is a diagram showing a schematic structure of an embodiment of the second invention.

[Explanation of symbols]

 D Pyroelectric element 1 Pyroelectric body 2a, 2b, 3a, 3b Electrode 4 Substrate 4a Conductive pattern A1, A2 Conductive adhesive

Claims (2)

[Claims] 1. An infrared detector having a structure in which electrodes are formed on both sides of a thin plate-like pyroelectric body, wherein the electrodes of the pyroelectric elements are solidified in a conductor pattern on the substrate. A pyroelectric infrared detector characterized by being bonded with a soft conductive adhesive having a pencil hardness of about 5B to 6B. 2. An infrared detector having a structure in which electrodes are formed on both sides of a thin plate-like pyroelectric body, and the electrodes of the pyroelectric elements are attached to a conductive pattern of the substrate by a conductive adhesive. Characterized in that the area of the bonded portion is defined as a minimum area that can provide an electrical connection that can take out a signal from the pyroelectric element to the outside. Infrared detector.