JP2001235364A - Pyroelectric infrared detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable pyroelectric element for detecting infra-red rays reduced in popcorn noise. SOLUTION: In this pyroelectric element for detecting infra-red rays, an infra-red rays receiving part 3 is formed while making conductive patterns 2 opposed to each other on the front and back faces of a pyroelectric body base material 1', and a through slits 10 are provided around the infra-red rays receiving part 3. The infra-red rays receiving part 3 surrounded by the through slits 10 is made to be single domain, and the residual part is made to be either multi domain or a multi domain region where single domain regions are mixed such that electric output is made not to appear to the outside of the element. To make the multi domain region near a tip of the through slit 10 where stress is easily concentrated is especially desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-noise, highly-reliable pyroelectric infrared detecting element.

[0002]

2. Description of the Related Art A pyroelectric infrared detecting element used as a heat or temperature detector usually comprises a ferroelectric substrate (hereinafter referred to as a pyroelectric substrate) having a pyroelectric property and a counter electrode serving as an infrared sensing part. It is made by forming. FIG. 23 shows the basic cross-sectional structure. In the figure, 1 is a pyroelectric substrate, 1a and 1
b is a vertical plane in the direction in which the pyroelectric substrate 1 has the largest pyroelectric coefficient (indicated as P in the figure), and the surfaces 1a and 1b
The front and back facing electrodes 2 are formed by a method such as vapor deposition, sputtering, or screen printing, and such a region functions as the infrared sensing section 3. The surface 1a is a surface on which the electrode 2 is formed and also a surface on which infrared light (indicated as IR in the figure) is incident. A change in the spontaneous polarization of the pyroelectric substrate 1 corresponding to the temperature rise of the sensing unit 3 due to the incidence of the infrared IR appears as a pyroelectric charge on the electrode 2 and is led to an external circuit by the lead wire 4. FIG. 24 is a circuit symbol representation of the infrared sensing section 3 of FIG. 23, and the arrow corresponds to the direction P in which the pyroelectric substrate 1 of FIG. 23 has the largest pyroelectric coefficient.

In a pyroelectric infrared detecting element that is widely used, two to four infrared sensing parts 3 are formed on a single pyroelectric substrate 1 in view of the purpose of use and improvement of performance. That is common. FIG. 25 shows an example in which two infrared sensing units 3 are arranged (hereinafter referred to as a dual type), and FIG.
Is an example (hereinafter referred to as a quad type) in which four infrared sensing units 3 are arranged. In each figure, (a) is a plan view seen from the front side, and (b) is a back view seen through the back side from the front side. Usually, an electrode constituting the infrared sensing section 3, a signal extraction electrode (connection electrode to an external circuit board) 5 to an external circuit, and a wiring connecting between the infrared sensing section 3 and the connection electrode 5 to the external circuit board ( The conductive pattern 2 is collectively and simultaneously formed on the same pyroelectric substrate 1 as the infrared sensing section 3 by a method such as vapor deposition, sputtering, or screen printing using a metal mask or the like. Due to the formation of the conductive pattern 2, the element structure shown in FIGS. 25 and 27 is equivalent to the connection of the infrared sensing unit 3 shown in the circuit diagrams of FIGS. 26 and 28, respectively (however, in FIG. This equivalent circuit is obtained when the connection electrodes 5 with the external circuit board formed on the front and back surfaces of one pyroelectric substrate 1 are electrically short-circuited on the front and back surfaces). Of course, the electrical connection (serial connection, parallel connection, etc.) between the infrared sensing portions 3 can be formed by changing the conductive pattern 2 other than those shown in FIGS. 26 and 28.

[0004] Electrical connection to an external circuit is made by a lead wire (wire) 4 as shown in FIG.
For example, there is a method using a conductive adhesive 7 as shown in FIG. 9, or a combination of the two, for example, by forming a conductive pattern 2 on the front and back surfaces of a single pyroelectric substrate 1 as shown in FIG. In the pyroelectric infrared detecting element, the connection electrode portion 5 with the external circuit board is normally electrically short-circuited on both sides by a conductive adhesive 7 and at the same time is also conductively bonded to the circuit input terminal portion 6 of the external circuit board. You. Here, the external circuit is a circuit for processing an output signal from the pyroelectric infrared detecting element, and a processing circuit for lowering the impedance because the impedance of the element is very high, for example, an electric field shown in FIG. A current amplifying circuit section and a band pass circuit mounted on an impedance conversion circuit using the effect type transistor 16 or a three-dimensional circuit block (hereinafter, referred to as an MID board) made of a resin molded product described in Japanese Patent Application No. Hei 8-100769. Refers to a circuit in which an amplifier, a window comparator, and the like are integrated. Generally, a pyroelectric infrared detecting element and the external circuit board to which the infrared detecting element is connected include a filter window for transmitting infrared light of a desired wavelength, a terminal for outputting an infrared detecting signal, a terminal for supplying power to the external circuit, and the like. It is housed in a metal case equipped with and is commercially available.

In general, in such a pyroelectric infrared detecting element, the heat / electric conversion efficiency and the response speed are changed due to the principle of converting the temperature rise of the infrared sensing section due to the incidence of infrared light into an electric signal. In order to increase the temperature, a structure is adopted in which the heat capacity of the infrared sensing unit is reduced and the heat is prevented from dissipating to places other than the sensing unit. Also in connection with the external circuit board described in the previous paragraph, the pyroelectric substrate 1 in which the pyroelectric infrared detecting element is formed is supported on the external circuit board only by the connection electrode portion 5 with the external circuit, The thermal isolation from the external circuit board is achieved. Also, the pyroelectric substrate 1
The thickness itself is set to several tens μm to about 100 μm to reduce the heat capacity.

[0006]

As described above, in general, a pyroelectric infrared detecting element can reduce the connection area between a pyroelectric substrate 1 having a thickness of about several tens μm to about 100 μm and a mounting substrate as much as possible. For example, Japanese Patent Application Laid-Open Nos. 58-182522 and 10-2793 (prior application by the present inventors) for mounting in a form such as cantilever or two-point support.
As described in the above, when a difference in thermal expansion occurs between the pyroelectric substrate 1, the external circuit board, and the adhesive for fixing the two due to the change in the external environment temperature, the pyroelectric substrate 1 is compressed or pulled. Or stress, such as torsion, is applied, and another characteristic of ferroelectrics is the piezoelectricity,
An electric charge corresponding to the size is generated. When this piezoelectric charge is locally accumulated and discharged, it is observed as a sudden erroneous signal output. Such a sudden erroneous output signal is called so-called spike noise, popcorn noise, or the like (hereinafter, popcorn noise), and includes a pyroelectric infrared detecting element or a piezoelectric device using a ferroelectric material having pyroelectricity and piezoelectricity. This is a common problem for surface acoustic wave devices and the like. A substantially U-shaped hollow hole is provided around the infrared sensing portion 3 disclosed in Japanese Patent Application Laid-Open No. 10-2793, and the sensing portion 3 is cantilevered by a part of the pyroelectric substrate 1. The structure in which the stress is not applied to the sensing part 3 has been devised based on the above findings.

Further, as another cause system of the popcorn noise, Japanese Patent Application Laid-Open Nos. 60-3528 and 61-48 are disclosed.
No. 215 and the like due to pyroelectricity. This is because the pyroelectric charge (which is a charge that does not contribute to the infrared detection circuit at all) due to a change in the external environment temperature also occurs in a portion other than the infrared sensing section 3 on the pyroelectric substrate 1. Occurs), but the conductive pattern 2
The defective charge generated on the surface where no is present is a bound charge, and is mainly eliminated by recombination due to attachment (accurately, desorption) of ions floating around the pyroelectric substrate 1. Therefore, depending on the conditions of the external environmental temperature change, the compensation of the high voltage due to the generated defective charge cannot be made in time, and the electric discharge to the nearby conductive pattern 2, the external circuit board, or the metal case accommodating these, and output as popcorn noise. Is done. As a method for avoiding this, Japanese Patent Application Laid-Open No.
No. 528 and JP-A-61-48215 disclose a method of providing a discharge prevention film on an element.

Another method is disclosed in, for example,
In Japanese Patent Application Laid-Open No. 61618/1994 and Japanese Patent Application Laid-Open No. Hei 10-300570 (prior application by the present inventors), only the infrared sensing portion is subjected to polarization treatment (detailed meaning will be described later), and the other portions are made of material (ferroelectric). In this structure, a defective charge cannot be generated except at the infrared sensing unit, so that the frequency of popcorn noise can be reduced.

However, in any of the prior arts described above, it is possible to simultaneously solve the main causes of popcorn noise, those caused by piezoelectricity and those caused by pyroelectricity, and those caused by the interaction between the two. Dramatic effects were not achieved. Here, the interaction factor between the above-described one caused by the piezoelectricity and the one caused by the pyroelectricity is a result of experiments and studies by the present inventors, which led to the conclusion that the main factor was popcorn noise. Even if the high voltage due to the pyroelectric accumulated defective charge generated by the external environment temperature change was not excessive,
Simultaneously generated stress due to a difference in thermal expansion between the pyroelectric substrate 1, the external circuit board, and the adhesive for fixing the two, mechanical vibration from the outside, and the like are applied when such a defective charge accumulation location is applied. The piezoelectric action instantaneously promotes the accumulation or discharge of the defective charge, that is, plays a triggering role (hereinafter referred to as a piezoelectric triggering action, etc.). This leads to discharge to a metal case or the like that stores the, and is output as popcorn noise.

The present invention has been devised on the basis of the conventional knowledge and the knowledge obtained as a result of intensive studies by the present inventors. It is an object to provide an element.

[0011]

In order to solve the above-mentioned problems, according to the present invention, as shown in FIGS. 1 and 2, for example, conductive patterns 2 are formed on both front and back surfaces of a pyroelectric substrate 1 '. In a pyroelectric infrared detecting element having a structure in which an infrared sensing section 3 is formed facing the infrared sensing section 3 and a through slit 10 is provided around the infrared sensing section 3, the infrared sensing section 3 surrounded by the through slit 10 is a single element. The domaining (the meaning is described later), and at least the vicinity of the tip of the through slit 10 (the area where the stress is concentrated in FIGS. 17 to 19 described later) is multi-domained (the meaning is described later). It is a feature. Therefore, even if stress due to a difference in thermal expansion between the pyroelectric substrate 1, the external circuit board, and the adhesive for fixing the two, and mechanical vibration from the outside occur simultaneously, the piezoelectric triggering action is generated. Therefore, popcorn noise due to such factors does not occur. Further, the effect of reducing popcorn noise due to the substantially U-shaped hollowed hole and the stress relief hole around the infrared sensing portion 3 described in JP-A-10-2793 (prior application by the present inventors) continues. Needless to say. As described above, the popcorn noise can be significantly reduced more than before.

Here, the meaning of the single domain and the multiple domain will be described. In general, when referring to a pyroelectric substrate, unless otherwise specified, it refers to a substrate having pyroelectricity as a whole, and is roughly divided into a single crystal substrate and a ceramic (sintered) substrate.
For a single crystal substrate, at the stage of a crystal growth body (generally referred to as an ingot) before being cut into a substrate, and for a ceramic substrate, at the stage of a sintered formed sheet, a polarization process (poling) inside the substrate is performed. Spontaneous polarization 8
Are made uniform to show pyroelectricity (FIG. 31).
The processing for (a)) is performed. If the polarization process is not performed, the spontaneous polarization 8 in the substrate is oriented in a random direction, and is in a state showing no pyroelectricity as a whole (FIG. 31B). Spontaneous polarization in random directions 8
In general, each minute region having the above is called a domain 9 (or domain), and since there are many domains in the substrate, this structure (state) is called a multi-domain structure (state). A structure (state) in which the entire spontaneous polarization 8 is uniform is referred to as a single domain structure (state). For this reason, the polarization process is also referred to as a single-domain process (the direction P in which the pyroelectric substrate 1 has the largest pyroelectric coefficient shown in FIG. 23 corresponds to the spontaneous polarization 8 in which the single domain is uniform). Direction). In addition, even in the single domain state, by adopting a structure in which the electrical output does not appear outside the element by the method described later, it is possible to obtain the same effect as the multi-domain state in appearance. it can.

According to a second aspect of the present invention, as shown in FIGS. 1 and 2, or FIGS.
In a pyroelectric infrared detecting element having a structure in which an infrared sensing portion 3 is formed by opposing conductive patterns 2 on both front and back surfaces and a through slit 10 is provided around the infrared sensing portion 3, the infrared sensing portion is surrounded by the through slit 10. The infrared sensing unit 3 is divided into single domains (region 11 in FIG. 2 and region 1 in FIG. 8).
1 (a) corresponds to the infrared sensing part 3 in FIGS. 7 (a) and 7 (b)), and the other parts are multi-domains (region 12 in FIG. 2) or electrical output. Is a single-domain region that does not appear outside the element (a region corresponding to the connection portion 5 ′ of the back-side conductive pattern in the region 11 ′ of FIG. 5 '
And the connection portion of the front-side conductive pattern 5 is electrically short-circuited in a later step, so that an electric output is not generated from the single-domain region. Things. Therefore, in regions other than the infrared sensing section 3, there is no generation of defective charge due to a change in external environment temperature, and stress due to a difference in thermal expansion between the pyroelectric substrate 1, the external circuit substrate, and the adhesive for fixing the both. Also, even if external mechanical vibrations occur simultaneously, the piezoelectric triggering does not occur, and popcorn noise due to such factors does not occur. Needless to say, the popcorn noise reduction effect of the substantially U-shaped hollow around the infrared sensing portion 3 described in Japanese Patent Application Laid-Open No. Hei 10-2793 (prior application by the present inventors) persists. No. As described above, the popcorn noise can be significantly reduced more than before.

According to a third aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the second aspect, wherein only the front and back opposing portions of the conductive pattern are single-domain. Since it is a sensing element, a conductive pattern formed on both front and back surfaces of the pyroelectric substrate in advance can be used as it is as a conductive pattern for applying an electric field (described later) required for polarization processing.

According to a fourth aspect of the present invention, in the pyroelectric infrared detecting element according to the second aspect, a region corresponding to the conductive pattern on the front surface side is formed into a single domain. Since it is a type infrared detecting element, it is possible to apply an electric field (described later) required for polarization processing by using a conductive pattern formed in advance on at least the front side of the pyroelectric substrate and an electrode plate for polarization processing contacting the entire back surface. The configuration of the polarization processing apparatus can be relatively simplified. In this specification, the front surface means the front surface which is compared with the back surface.

According to a fifth aspect of the present invention, in the pyroelectric infrared detecting element according to the second aspect, a region corresponding to the conductive pattern on the back side is formed into a single domain. Since it is a type infrared detection element, an electric field (described later) required for polarization processing is performed by a conductive pattern formed in advance on at least the back side of the pyroelectric substrate and a polarization processing electrode plate in contact with the entire front surface. Therefore, the configuration of the polarization processing apparatus can be relatively simplified.

According to a sixth aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the second aspect, wherein a single-domain area other than the infrared sensing section is configured so that an electrical output does not appear outside the element. Is a pyroelectric infrared sensing element characterized by being formed by electrical connection of the conductive pattern formed on the front and back surfaces of the region including at least such a single domaining region, or the same potential, No electric output is generated from the single-domain region other than the infrared sensing portion, and the popcorn noise reduction effect of the present invention described above is not impaired at all.

[0018]

1 to 3 show a first embodiment of the present invention. The pyroelectric infrared detecting element shown in FIG. 1 has a pyroelectric substrate 1 ′ which is entirely processed for multi-domain processing before polarization processing, and front and back conductive layers including a connection electrode section 5 for an external circuit. It comprises a pattern 2, two infrared sensing parts 3 and a substantially U-shaped hollow hole 10 provided therearound. FIG. 2 shows a region 11 which is made into a single domain by the polarization processing shown in FIG. 3 and a region 12 which remains in a multi-domain structure. The equivalent circuit of this embodiment is the same as FIG.

Next, the polarization process will be described with reference to FIG. The pyroelectric infrared detecting element is shown in a cross-sectional view taken along line AA ′ shown in FIG. A DC voltage 13 is applied at an appropriate value to the front and back conductive patterns 2 of the element, and the entire element is heated by a heater 14 as necessary. Then, a voltage is applied only to the opposing portions of the front and back conductive patterns 2, and the partial single domain region 11 is formed. The treatment for multi-domaining of the pyroelectric substrate performed before the above-mentioned polarization treatment is performed when the temperature of the material of the pyroelectric substrate becomes higher than the temperature at which the ferroelectric phase transitions to the paraelectric phase (Curie temperature). There are a method of heating the substrate, and a method of using a pyroelectric substrate that is originally in a multi-domain state immediately after crystal growth or firing. The condition of the polarization treatment largely depends on the type of the pyroelectric substrate material, but as a result of the study of the present inventors, for example, when a lithium tantalate single crystal is used for the pyroelectric substrate, the electric field intensity is reduced. 10 ⁷ V / m or more (when temperature is 150 to 250 ° C)
That is, it was necessary to apply a voltage having a very large electric field strength. In the present embodiment, only the infrared sensing portion 3 is a portion facing the conductive pattern 2 on the front and back, and therefore, the substantially U-shaped hollow 1
Since only the infrared sensing section 3 surrounded by 0 is divided into single domains, as described above, popcorn noise can be further reduced as compared with the related art.

FIGS. 4 to 6 show a second embodiment of the present invention. The first embodiment is a dual type device, while the second embodiment is an example of a quad type device. That is, the pyroelectric infrared detecting element shown in FIG. 4 has a pyroelectric substrate 1 ′ which is entirely subjected to a process for multi-domain processing before polarization processing, and front and back surfaces including a connection electrode portion 5 for connecting to an external circuit. It comprises a conductive pattern 2, four infrared sensing parts 3, and a substantially U-shaped hollow hole 10 provided therearound. FIG.
Shows a region 11 ″ ′ which has been made into a single domain by the polarization processing shown in FIG. 6, and a region 12 which has a multi-domain structure. The equivalent circuit of this embodiment is the same as FIG. (Similar to the above description of the conventional example (FIG. 27), the front and back connection electrode portions 5 are electrically short-circuited in a later step).

FIGS. 7 to 9 show a third embodiment of the present invention. The pyroelectric infrared detection element shown in FIGS. 7A and 7B has a connection electrode between the pyroelectric substrate 1 ′, which is entirely subjected to multi-domain processing before polarization processing, and an external circuit. It is the same as that of the first embodiment in that it is composed of the front and back conductive patterns 2 including the portion 5, two infrared sensing portions 3, and a substantially U-shaped hollow hole 10 provided therearound. The equivalent circuit of the present embodiment is shown in FIG. 26 similarly to the first embodiment. In the polarization process shown in FIG. 9, the entire surface electrode 15 for applying a voltage necessary for the polarization process is adhered to the back surface of the pyroelectric substrate to be polarized, and the electrode 15 is heated by the polarization process. An optional heater 14 'is provided. For this reason, the single-domain region becomes a portion where the front-side conductive pattern 2 and the entire surface electrode 15 face each other, and thus a single-domain region 11 'as shown in FIG. 8 is formed. Although the single domaining region 11 ′ also extends to a region other than the infrared sensing portion 3 (a portion of the front conductive pattern 2 except the infrared sensing portion 3), an electrode 5 ′ is provided on the back surface side of the region,
Since the front and back electrodes 5 and 5 ′ are short-circuited (not shown) in a later process such as device mounting, a charge pair serving as a source of popcorn noise is generated on the front and back surfaces of the region 11 ′ other than the infrared sensing unit 3 due to an external environment change. Even so, it rejoins instantly,
It does not appear to the outside as an electrical signal. Of course, the shape of the back electrode 5 ′ is not limited to the shape shown in FIG. 7B, and includes at least a single-domain region other than the infrared sensing unit 3 and does not short-circuit the front and back facing electrodes of the infrared sensing unit 3. Anything is fine.

FIGS. 10 to 13 show a fourth embodiment of the present invention. The pyroelectric infrared detecting element shown in FIG. 10 has a pyroelectric substrate 1 ′ which is entirely subjected to a multi-domain processing before polarization processing, and a front and back conductive layer including a connection electrode portion 5 for connecting to an external circuit. The second embodiment is the same as the first and third embodiments in that the second embodiment includes a pattern 2, two infrared sensing units 3, and a substantially U-shaped hollow hole 10 provided around the infrared sensing unit 3. FIG. 13 shows an equivalent circuit of this embodiment. In the polarization processing shown in FIG. 12, the surface of the pyroelectric substrate to be polarized is
A full-surface electrode 15 for applying a voltage required for polarization processing is adhered to the electrode 15, and the electrode 15 is provided with a heater 14 ′ when heating is required for polarization processing. For this reason, the single-domain region becomes the portion where the back side conductive pattern 2 and the entire surface electrode 15 face each other, and thus a single-domain region 11 ″ is formed as shown in FIG. "Also extends to a region other than the infrared sensing portion 3 (a portion of the back side conductive pattern 2 excluding the infrared sensing portion 3), but the front side conductive pattern 2 is also sandwiched between the front and the back on the front side of such region. In order to short-circuit the connection electrode portions 5 on the front and back surfaces (not shown) in a later process such as device mounting, a charge pair serving as a source of popcorn noise is formed on the front and back surfaces of the region 11 ″ other than the infrared sensing portion 3 due to a change in external environment. Even if it occurs, it is recombined instantaneously, so that it does not appear as an electric signal outside.Of course, the shape of the surface conductive pattern 2 for inactivating the single domain region other than the infrared sensing portion 3 is shown in FIG. (A)
However, the present invention is not limited to the above, and may be any as long as it includes at least a single-domain region other than the infrared sensing unit 3 and does not short-circuit the front and back opposed electrodes of the infrared sensing unit 3.

FIGS. 14 to 16 show a fifth embodiment of the present invention. The pyroelectric infrared detecting element shown in FIG. 14 has a pyroelectric substrate 1 ′ entirely subjected to a multi-domain processing before polarization processing, and front and back conductive patterns including a connection portion 5 with an external circuit. It is a so-called quad type, which is composed of two or four infrared sensing parts 3 and a substantially U-shaped hollow hole 10 provided therearound. Fig. 15 shows the regions 11 "'and 11""which have been made into single domains by the polarization processing shown in Fig. 16 and the region 12 which remains in a multi-domain structure. In Fig. 16 showing the polarization process, the pyroelectric infrared detecting element is shown in a cross-sectional view taken along line AA 'shown in Fig. 14. The single domain region is a front-back conductive film. The regions 11 "'and 11""are the regions opposed to the pattern 2, and the region 11"' is the infrared sensing unit 3 and the region 1 "'is the region 1".
Since 1 "" is a region other than the infrared sensing portion including the connection electrode portion 5 with the external circuit, the region 11 "" is a region where it is not originally desired to form a single domain. However, as described above, in this element, the connection electrode portion 5 with the front and back external circuits is electrically short-circuited by a conductive adhesive or the like.
The conductive pattern portion sandwiching 1 "" is also in a front-back short-circuit state. Therefore, even if a charge pair serving as a source of popcorn noise is generated on the front and back surfaces of the region 11 "" due to a change in the external environment, the charge pair is instantaneously recombined and does not appear as an electric signal to the outside.

FIGS. 17 to 19 show simulation results obtained by analyzing the stress distribution due to errors and deviations when mounting the pyroelectric substrate. The stress distribution was analyzed by the finite element method by adding elements such as errors and deviations at the time of circuit mounting to the pyroelectric substrate in which the substantially U-shaped hollow hole 10 formed in the above-described embodiment was formed. It has been discovered that under a certain condition such as a deviation, a large stress concentration occurs near both ends of the substantially U-shaped hollow hole 10 (near the tip of the through slit according to claim 1). In addition, it was also found that such a stress concentration can be effectively absorbed by forming a relief hole for releasing the stress in that portion.

FIG. 17 shows a simulation result of the stress distribution of the pyroelectric substrate having the substantially U-shaped hollow 10 formed therein. FIG. 18 shows a case where a relief hole is formed in the vicinity of the tip of the substantially U-shaped hollow hole 10, and FIG. 19 shows a case where the size of the relief hole is larger than the width of the substantially U-shaped hollow hole 10. The simulation result is shown.

Here, it is assumed that the pyroelectric substrate receives an external force in the torsion direction when both ends are supported on the circuit board, and that one end is lifted and forcedly displaced. Then, the stress applied to the pyroelectric substrate was analyzed by simulation using the finite element method and compared. In each case, the stress distribution is shown as a contour map.

The stress generated in the pyroelectric substrate is indicated by the maximum principal stress (unit: Pascal) which is a measure of fracture as the most appropriate value indicating the stress state of the material. Indicates the magnitude of the value. Note that the absolute value of the stress unit (Pascal) used here has little meaning, and only the relative value has meaning.

In any of the results shown in FIGS. 17 to 19, the portion having a larger stress than the periphery is generated near both ends of the substantially U-shaped hollow hole (near the tip of the through slit according to claim 1). I understand. From this, claim 1
It can be seen that popcorn noise due to the piezoelectric triggering action can be prevented by defining at least the domain of the vicinity of the tip end of the through slit as specified by.

Referring to FIG. 17, the portion where the stress is larger than the surroundings is distributed outward from the base of the infrared sensing portion 3 surrounded by the through slit, but a stress relief hole is provided. In the structure of FIG. 18, the portion having a large stress is reduced and retreated to a position farther from the infrared sensing portion 3 as compared with the case of FIG. It can be seen that the influence of is small. Further, in the structure of FIG. 19 in which the size of the escape hole is larger than the width of the through slit, the portion where the stress is large recedes further outward than the infrared sensing portion 3 and becomes smaller as compared with the case of FIG. You can see that there is.

Therefore, as shown in FIG. 18 or FIG. 19, a stress relief hole is provided in the vicinity of the tip of the through slit to reduce the effect of the stress itself and to reduce the stress near the tip of the through slit. It is understood that it is preferable to make at least a multi-domain.

FIG. 20 shows the results of an experiment conducted to confirm the effectiveness of the present invention. The figure shows that all the samples are sealed in a test room and the temperature change shown in FIG. 21 is given to the sample, so that popcorn noise as shown in FIG. 22 occurs one or more times during a series of temperature changes shown in FIG. This shows the percentage of non-defective products when the occurrence is regarded as defective.
The conventional structure 1 has a substantially U-shaped hollow detection hole 10 and a pyroelectric infrared detecting element (appearance: FIG. 27) in which the entire area of the pyroelectric substrate is a single domain. Hollow 10
(Appearance is FIG. 14), and the pyroelectric infrared detecting element in which the whole area of the pyroelectric substrate is a single domain, and the conventional structure 3 does not have the substantially U-shaped hollow 10 (Appearance is FIG. 27). ) And a pyroelectric infrared detecting element having a structure in which only the infrared sensing section 3 functions as a single domain. In FIG. 21, the temperature change conditions are as follows: the temperature gradient is 1 ° C./min, and T1, T3 and T4 are 30.
Minutes and T2 were set to 0 minutes. Of course, the other conditions (the number of infrared sensing parts (4 pieces; quad type), the conductive pattern, the mounting structure, the dimensions of each element, etc.) are the same. As is clear from this figure, it was confirmed how dramatically the present invention is more effective in reducing popcorn noise than the conventional structure.
It has also been confirmed that the present invention is more effective when a substrate having a particularly low conductivity, such as a single crystal LiTaO ₃ wafer, is used as the pyroelectric substrate. This is presumably because the lower the conductivity of the substrate, the more easily the defective charge is accumulated.

In the above embodiment, FIGS. 3, 6, 9, 12, and 16 describe the situation in which a polarization process is performed on one pyroelectric infrared detecting element. If the body substrate is a single crystal substrate, a large number of pyroelectric infrared detectors (precisely, front and back conductive patterns) are collectively formed on the wafer if it is a ceramic substrate, or on one sheet after sintering if it is a ceramic substrate. Alternatively, the polarization process may be performed for each wafer or sheet. After such a process, it is separated into individual pyroelectric infrared detecting elements by a method such as dicing.

It should be noted that a method of applying a voltage to the front and back conductive patterns as a polarization treatment after forming the front and back conductive patterns on the pyroelectric substrate is known (for example, Japanese Patent No. 1995419 and Japanese Patent No. 2661654). No. 4,691,104)), but regarding the polarization treatment in the present invention, the pyroelectricity is limited only to the optimum region in order to maximize the effects of the present invention described later. Since it is performed by designing a conductive pattern to be applied, its significance is greatly different. For example, in the second embodiment (FIGS. 6 to 8) of the above-mentioned Japanese Patent No. 26616654, there is a description about the polarization process after the conductive pattern is provided. (A region sandwiched between the lead electrode portions on the front and back) or a conductive pattern that makes the region electrically inactive (short circuit, etc.) in a later process (such as mounting). In addition, the structure does not strictly limit the polarization region.

As described above, in the polarization treatment, several tens of μm are used.
Since a high voltage is applied between the front and back surfaces of a very thin pyroelectric substrate having a thickness of about m to about 100 μm, air breakdown easily occurs in an air atmosphere. For this reason, the atmosphere is evacuated or replaced with an electrically insulating gas (eg, an inert gas such as nitrogen, carbon dioxide, or argon, or a sulfur hexafluoride gas).
The polarization process can be performed more stably.

In the embodiments, the mounting mode of the pyroelectric infrared detecting element (connection (adhesion to an external circuit board)) is not particularly described. For example, a printed board on which an impedance conversion circuit is mounted, Japanese Patent Application No. 8-10076
Even if mounted on an MID board on which a circuit in which the current amplification circuit section, the band-pass amplifier, the window comparator section, and the like described in No. 9 are integrated is mounted, or any other board,
It goes without saying that the generation of popcorn noise is significantly reduced.

[0036]

According to the first aspect of the present invention, an infrared sensing portion is formed by opposing conductive patterns on both front and back surfaces of a pyroelectric substrate.
And, in the pyroelectric infrared detecting element having a structure in which a through slit is provided around the infrared sensing section, the infrared sensing section surrounded by the through slit is divided into a single domain, and at least the vicinity of the tip end of the through slit, Because it is a pyroelectric infrared detecting element characterized by being divided into multiple domains, stress due to the difference in thermal expansion between the pyroelectric substrate, the external circuit board and the adhesive fixing both, and external Even if mechanical vibrations or the like occur simultaneously, the piezoelectric trigger does not occur, and popcorn noise due to such factors does not occur. Needless to say, the effect of reducing the popcorn noise due to the substantially U-shaped hollow hole or the stress relief hole around the infrared sensing portion described in JP-A-10-2793 is described. As described above, popcorn noise can be more significantly reduced than before.

According to a second aspect of the present invention, there is provided a pyroelectric element having a structure in which an infrared sensing portion is formed by opposing conductive patterns on both front and back surfaces of a pyroelectric substrate, and a through slit is provided around the infrared sensing portion. In the infrared detecting element, the infrared sensing portion surrounded by the through slit is formed into a single domain, and the other portions are divided into multiple domains, or the electrical output is prevented from appearing outside the element. Since it is a pyroelectric infrared detecting element characterized by being a multi-domain area in which the domain areas are mixed, in an area other than the infrared sensing section,
There is no generation of defective charge due to changes in the external environment temperature.
Even if stress due to a difference in thermal expansion between the pyroelectric substrate, the external circuit board, and the adhesive fixing the two, and mechanical vibrations from the outside, etc. are simultaneously generated, the piezoelectric triggering does not occur, and such a phenomenon occurs. No popcorn noise due to the factor is generated. Needless to say, the effect of reducing the popcorn noise by the substantially U-shaped hollow around the infrared sensing portion described in JP-A-10-2793 still remains. As described above, popcorn noise can be more significantly reduced than before.

According to a third aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the second aspect, wherein only the front and back opposing portions of the conductive pattern are divided into single domains. Since it is a sensing element, a conductive pattern formed in advance on the front and back of the pyroelectric substrate can be used as it is as a conductive pattern for applying an electric field required for polarization processing.

According to a fourth aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the second aspect, wherein a region corresponding to the conductive pattern on the front surface is formed into a single domain. Since it is a type infrared detecting element, a conductive pattern previously formed on at least the front surface side of the pyroelectric substrate and a polarization processing electrode plate contacting the entire back surface can apply an electric field required for polarization processing, The configuration of the polarization processing apparatus can be relatively simplified.

According to a fifth aspect of the present invention, in the pyroelectric infrared detecting element according to the second aspect, a region corresponding to the conductive pattern on the back surface is formed into a single domain. Since it is a type infrared detecting element, a conductive pattern previously formed on at least the back side of the pyroelectric substrate and the electrode plate for polarization processing contacting the entire surface can apply an electric field required for polarization processing, The configuration of the polarization processing apparatus can be relatively simplified.

According to a sixth aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the second aspect, wherein a single-domain area other than the infrared sensing section is configured so that an electrical output does not appear outside the element. Is a pyroelectric infrared sensing element characterized by being formed by electrical connection of the conductive pattern formed on the front and back surfaces of the region including at least such a single domaining region, or the same potential, Since no electrical output is generated from a single-domain area other than the infrared sensing section, the popcorn noise reduction effect of the present invention can be maximized without any loss.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing an appearance structure of a first embodiment of the present invention, wherein FIG. 1A is a plan view, and FIG. 1B is a rear view of the back side seen from the front side.

FIG. 2 is a plan view showing a polarization state according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a polarization process according to the first embodiment of the present invention.

4A and 4B are diagrams showing an external structure of a second embodiment of the present invention, wherein FIG. 4A is a plan view, and FIG. 4B is a back view of the back side seen through from the front side.

FIG. 5 is a plan view showing a polarization state according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a polarization process according to the second embodiment of the present invention.

FIGS. 7A and 7B are diagrams showing an external structure of a third embodiment of the present invention, wherein FIG. 7A is a plan view, and FIG. 7B is a rear view of the back side seen through from the front side.

FIG. 8 is a plan view showing a polarization state according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram of a polarization process according to a third embodiment of the present invention.

FIGS. 10A and 10B are diagrams showing an appearance structure of a fourth embodiment of the present invention, wherein FIG. 10A is a plan view, and FIG. 10B is a rear view of the back side seen through from the front side.

FIG. 11 is a plan view showing a polarization state according to a fourth embodiment of the present invention.

FIG. 12 is an explanatory diagram of a polarization process according to a fourth embodiment of the present invention.

FIG. 13 is an equivalent circuit diagram of the pyroelectric infrared detection element of FIG.

14A and 14B are diagrams showing an appearance structure of a fifth embodiment of the present invention, wherein FIG. 14A is a plan view, and FIG. 14B is a rear view of the back side seen through from the front side.

FIG. 15 is a plan view showing a polarization state according to the fifth embodiment of the present invention.

FIG. 16 is an explanatory diagram of a polarization process according to the fifth embodiment of the present invention.

FIG. 17 is a diagram showing a simulation result of stress distribution of a pyroelectric substrate having a through slit around an infrared sensing portion.

FIG. 18 is a diagram showing a simulation result of a stress distribution of a pyroelectric substrate having a through slit of another shape around an infrared sensing portion.

FIG. 19 is a diagram showing a simulation result of a stress distribution of a pyroelectric substrate having a through slit of another shape around an infrared sensing portion.

FIG. 20 is a diagram showing experimental data showing the effectiveness of the present invention.

FIG. 21 is an explanatory diagram showing a heat cycle for performing a popcorn noise test.

FIG. 22 is a diagram illustrating an example of a popcorn noise waveform.

FIG. 23 is a cross-sectional view showing the basic structure of a conventional pyroelectric infrared detection element.

FIG. 24 is an equivalent circuit diagram of a pyroelectric infrared detection element.

25A and 25B are diagrams showing an external structure of a dual-type pyroelectric infrared detecting element having two infrared sensing units, wherein FIG. 25A is a plan view and FIG. 25B is a rear view of the back side seen through from the front side. It is.

FIG. 26 is an equivalent circuit diagram of a dual-type pyroelectric infrared detection element.

FIGS. 27A and 27B are diagrams showing the external structure of a quad-type pyroelectric infrared detecting element having four infrared sensing units, wherein FIG. 27A is a plan view and FIG. 27B is a rear view of the back side seen through from the front side. It is.

FIG. 28 is an equivalent circuit diagram of a quad-type pyroelectric infrared detecting element.

FIG. 29 is a cross-sectional view showing an example of a structure for connecting a pyroelectric infrared detecting element to an external circuit board.

FIG. 30 is a circuit diagram illustrating an example of an impedance conversion circuit using a field-effect transistor.

FIG. 31 is an explanatory diagram for explaining meanings of a domain, a single domain, and a multiple domain in a pyroelectric substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 '(Multiple domain) Pyroelectric substrate 2 Conductive pattern 3 Infrared sensing part 5 Connection electrode part 10 Substantially U-shaped hollow (through slit) 11 Single domain domain 12 Domain domain state 13 Polarization DC voltage source for processing 14 Heater for polarization processing

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Motoo Ikari 1048 Odakadoma, Kadoma-shi, Osaka Matsushita Electric Works, Ltd. (72) Inventor Yuji Takada 1048 Odakadoma, Kadoma-shi, Osaka Matsushita Electric Works, Ltd. (72 Inventor Ryo Taniguchi 1048 Kadoma Kadoma, Kadoma City, Osaka Prefecture (72) Inventor Makoto Nishimura 1048 Odaka Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Works Co., Ltd. Matsumoto Electric Works Co., Ltd. (72) Inventor Masato Kawashima 1048 Oji Kadoma, Kazuma City, Osaka Matsushita Electric Works, Ltd.

Claims (6)

[Claims] 1. A pyroelectric infrared sensing element having a structure in which an infrared sensing portion is formed by opposing conductive patterns on both front and back surfaces of a pyroelectric substrate, and a through slit is provided around the infrared sensing portion. A pyroelectric infrared detecting element, wherein an infrared sensing portion surrounded by a through slit is divided into a single domain, and at least the vicinity of the tip of the through slit is divided into multiple domains. 2. A pyroelectric infrared sensing element having a structure in which a conductive pattern is opposed to both front and back surfaces of a pyroelectric substrate to form an infrared sensing portion, and a through slit is provided around the infrared sensing portion. The infrared sensing part surrounded by the through slit is divided into single domains and the other parts are divided into multiple domains, or mixed with single domain domains that prevent electrical output from appearing outside the element. A pyroelectric infrared detecting element characterized by a multi-domain region. 3. The pyroelectric infrared detecting element according to claim 2, wherein only the front and back opposing portions of the conductive pattern are divided into single domains. 4. The pyroelectric infrared detecting element according to claim 2, wherein a region corresponding to the conductive pattern on the front side is divided into a single domain. 5. The pyroelectric infrared detecting element according to claim 2, wherein a region corresponding to the conductive pattern on the back side is formed into a single domain. 6. The pyroelectric infrared detecting element according to claim 2, wherein a single-domain area other than the infrared sensing section, in which electrical output does not appear outside the element, is at least such a single-domain. A pyroelectric infrared detecting element formed by electrical connection of conductive patterns formed on the front and back surfaces of a region including a localization region or by potential equalization.