JPH10300570A - Pyroelectric infrared ray detection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared ray detection element wherein a popcorn noise is reduced. SOLUTION: Relating to the element, an electrode 2 which is an infrared ray detection region is so formed as to face both sides of substrate 1 of single crystal LiTaO3 . Relating to the substrate 1 of single crystal LiTaO3 between facing electrodes 2, the orientation of a spontaneous polarization is a single single-division structure region 1a, while the orientation of the spontaneous polarization is a random multi-division structure region 1b, relating to such region as other than the single-division structure region 1a of the substrate 1 of single crystal LiTaO3 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared detecting element.

[0002]

In conventional infrared detecting element, lead titanate (Pb (Zr was added zirconium (Zr) as the pyroelectric material, Ti) O _3: PZT (registered trademark of the Kurebaito Inc.) and, lanthanum (La) -added lead titanate (Pb
Piezoelectric ceramic materials such as (La, Ti) O ₃ ) and composite oxide films of the same family as those are widely used.

The pyroelectric infrared detecting element has a structure in which an electrode serving as an infrared detecting unit is formed so as to face the front and back surfaces of a pyroelectric body obtained by subjecting a pyroelectric substrate to polarization processing.

Here, the detection principle of the pyroelectric infrared detecting element will be described. 7A and 7B are schematic diagrams showing the detection principle of the pyroelectric infrared detecting element, wherein FIG. 7A shows an equilibrium state in the electrode 2 forming region before infrared rays are incident, and FIG. And (c) shows an equilibrium state in the electrode 2 formation region after infrared rays are incident. The charge generated by the spontaneous polarization in the pyroelectric body 7 is electrically neutralized by floating charges such as ions and electrons in the air as shown in FIG. As shown in (2), when infrared rays are incident on the pyroelectric body 7, the temperature inside the crystal rises, the lattice spacing increases, and the magnitude of the electric polarization changes.

In response to the change in the polarization, the parallel state of the charges is broken on the surface of the area where the electrode 2 of the pyroelectric body 7 is formed, and an output is generated. The voltage at this time is measured, and infrared rays are detected. Thereafter, as shown in FIG. 7 (c), the electric charge on the surface of the area where the electrode 2 of the pyroelectric body 7 is formed is usually neutralized by the floating electric charge in the air, and the equilibrium state is established.

For this reason, it is, of course, necessary to keep the polarization direction constant even in the above-mentioned piezoelectric ceramic material and the like.

[0007]

These pyroelectric infrared detectors have excellent sensitivity characteristics and are actually widely commercialized. However, sudden noise (popcon noise) due to temperature changes in the use environment. There is a problem that occurs. Various causes of this popcon noise have been studied, but the cause has not been elucidated yet.

Since the cause has not been clarified, industrially completed devices are subjected to a noise test to select devices that do not generate popcon noise, which inevitably increases the cost of the devices. ing.

[0009] For those involved in the research, development and manufacture of pyroelectric infrared detectors, it is necessary to elucidate the cause of this popcon noise and take countermeasures to mass-produce pyroelectric infrared detectors that do not generate popcon noise with good reproducibility. It is a dream for many years.

[0010] The present invention has been made in view of the above points, and an object of the present invention is to provide a pyroelectric infrared detection element capable of reducing popcon noise.

[0011]

According to the first aspect of the present invention,
Polarized single-crystal LiTaO ₃ substrate, and the single-crystal LiTa
An electrode formed so as to face both sides of an O ₃ substrate, wherein the single-crystal LiTa
The region where the electrode is formed on the O ₃ substrate has a unipolar structure in which the direction of spontaneous polarization is constant, and the region other than the region where the electrode is formed on the single crystal LiTaO ₃ substrate has a multi-domain structure in which the direction of the spontaneous polarization is random. It is characterized by having done.

According to a second aspect of the present invention, in the pyroelectric infrared detecting element according to the first aspect, the temperature of the single-crystal LiTaO ₃ substrate, in which the direction of spontaneous polarization is constant, is once increased to the Curie point of LiTaO ₃ or more. Then, after the single-crystal LiTaO ₃ substrate is changed from a ferroelectric to a paraelectric, the temperature is lowered while applying an electric field to the electrode, thereby obtaining the single-crystal LiTaO _3.
A region other than the electrode formation region on the substrate has a multi-domain structure in which the direction of spontaneous polarization is random.

According to a third aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the first aspect, wherein an Al mask is provided on the single-crystal LiTaO ₃ substrate where the direction of the spontaneous polarization is constant, where the multi-domain structure region is formed. After forming the single crystal LiTa
O ₃ substrate is put in benzoic acid to perform proton substitution treatment,
By subjecting the single crystal LiTaO3 substrate to a region other than the electrode formation region, a spontaneous polarization direction is random in a multi-domain structure by performing a heat treatment for a certain time to invert the polarization.

According to a fourth aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the first aspect, wherein an Al mask is provided on the single-crystal LiTaO ₃ substrate where the direction of the spontaneous polarization is constant, where the multi-domain structure region is formed. After the formation, proton ions are implanted by an ion implantation method, and annealing is performed to obtain a multi-domain structure in which the direction of spontaneous polarization is random except for the region where the electrode is formed on the single-crystal LiTaO ₃ substrate. It is characterized by the following.

According to a fifth aspect of the present invention, there is provided the pyroelectric infrared detecting element according to the first aspect, wherein a laser is provided in the single-crystal LiTaO ₃ substrate where the direction of the spontaneous polarization is constant, where the multi-domain structure region is formed. By irradiating the beam, by raising the temperature of the single-crystal LiTaO ₃ substrate in the region to be the multi-domain structure region once to the Curie point of LiTaO ₃ or more, and lowering the temperature of the single-crystal LiTaO ₃ substrate, Except for the electrode formation region on the single crystal LiTaO ₃ substrate,
It has a multi-domain structure in which the direction of spontaneous polarization is random.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing a pyroelectric infrared detecting element according to an embodiment of the present invention. In the pyroelectric infrared detecting element according to the present embodiment, an electrode 2 serving as an infrared detecting region is formed so as to face both surfaces of a single crystal lithium tantalate (LiTaO ₃ ) substrate 1. Single crystal LiTaO ₃
The substrate 1 has a single domain structure region 1a having a single direction of spontaneous polarization.
And the single-domain structure region 1 in the single-crystal LiTaO ₃ substrate 1
Parts other than a have a configuration in which the direction of spontaneous polarization is a random domain structure region 1b. In this embodiment, the single-domain structure region 1a in the single-crystal LiTaO ₃ substrate 1 is used.
Other parts are arranged in a plurality so that the direction of spontaneous polarization is opposite.

Hereinafter, the manufacturing process of the infrared detecting element according to the present embodiment will be described. FIG. 2 is a schematic diagram showing a heat treatment apparatus for multi-domaining the pyroelectric infrared detection element according to the present embodiment. First, pyroelectric single crystal LiTaO ₃
A voltage is supplied between the front surface and the back surface of the substrate 1 so that the single crystal Li
Applying a high electric field between the front and back surfaces of the TaO ₃ substrate 1
The electric polarization directions in the LiTaO ₃ substrate 1 are aligned (polling processing).

Subsequently, the single crystal LiTaO ₃ substrate 1 is formed into a desired thickness, processed into a desired size and shape by dicing or the like, and is made of aluminum (Al) or the like so as to face the front and back surfaces of the single crystal LiTaO ₃ substrate 1. The electrode 2 is formed as an infrared detecting section.

Next, the processed single-crystal LiTaO ₃ substrate 1 is placed in an electric furnace 3, and the ambient temperature is raised to 650 ° C., which is the Curie point at which ferroelectricity disappears, and held for 30 minutes. Thereafter, by cooling to room temperature while applying an electric field of 5 kV / cm between the opposing electrodes 2, the single crystal LiTaO ₃ substrate 1 between the opposing electrodes 2 is converted into a single domain structure having a single spontaneous polarization direction. A region other than the single-domain structure region 1a in the single-crystal LiTaO ₃ substrate 1 is defined as a multi-domain structure region 1b in which the direction of spontaneous polarization is random.

Although the atmosphere in the electric furnace 3 used in the present embodiment was air, if the thickness of the single-crystal LiTaO ₃ substrate 1 is very small and the specific surface area is relatively small, the single-crystal LiTaO ₃
In order to prevent Li from evaporating from the surface of the TaO ₃ substrate 1, LiTaO ₃
The processing may be performed by placing the single crystal LiTaO ₃ substrate 1 in the powder.

After multi-domaining, the device was etched with a mixed solution of hydrofluoric acid and nitric acid, and the polarization state of the single crystal LiTaO ₃ substrate 1 was observed. Is approximately 2 in the + and-directions as viewed from the element surface.
It was observed that they were randomly arranged in a size of ５5 μm. Further, observation after removing the electrode 2 confirmed that the polarization directions were uniform in that region.

After mounting an electric circuit or the like on the element subjected to the multi-domain processing as described above, the noise characteristics were examined. As a result, it was found that no popcon noise was generated. The temperature conditions in the noise test were as shown in FIG. 3, and the temperature gradient at this time was 1.0 ° C./min.

The present inventors have been conducting research for many years,
We concluded that the generation of popcon noise can be explained as follows. As described in the related art, when infrared light is incident on the pyroelectric infrared detection element, the magnitude of spontaneous polarization changes with the change in the crystal in the pyroelectric material, and the size of the spontaneous polarization changes. In order to maintain the sum), an attempt is made to neutralize the surplus charge with ions and the like in the air. However, if the temperature change is too large, the change in the magnitude of the polarization is larger, and on the element surface, the change due to the ions and the like in the air is caused. The sum cannot cope with it, and as a result, an excess charge that cannot be neutralized is formed on the surface of the portion where the electrode of the element is not formed. Due to some cause (for example, triggered by the generation of a piezoelectric effect due to expansion or contraction of the pyroelectric material due to a temperature change), the surplus charge propagates to the portion where the electrode of the element is formed, and is observed as popcon noise.

Therefore, in this embodiment, the single crystal Li
By making the TaO ₃ substrate 1 a region other than the region where the electrode 2 is formed, the surplus electric charges generated on the substrate surface can be quickly neutralized, and the occurrence of popcon noise can be prevented.

In this embodiment, the single-crystal LiTa
As a method of dividing the O ₃ substrate 1 into single domains, a single-crystal LiTaO ₃ substrate 1
Single crystal by applying a high electric field between the front and back
The direction of electric polarization in the LiTaO ₃ substrate 1 was aligned.
The invention is not limited to this. For example, a single domain may be formed by cooling from a temperature of 400 ° C. while applying an electron beam to the electrode 2 formation region of the element.

Embodiment 2 = FIG. 4 is a schematic diagram showing a method for multi-domaining a pyroelectric infrared detecting element according to another embodiment of the present invention. In the present embodiment, the steps up to the single domainization of the single-crystal LiTaO ₃ substrate 1 are the same as those in the first embodiment, and thus the description is omitted here. Laser irradiation is performed so that heat of 1 W / cm ² is applied to the surface of the desired region of the single-crystal LiTaO ₃ substrate 1 on which the electrode 2 and the electric wiring portion 4 electrically connected to the electrode 2 are formed. In the region irradiated with the laser beam 4, the temperature of the single crystal LiTaO ₃ substrate 1 has risen to about 600 ° C.

As a result, the temperature of the single crystal LiTaO ₃ substrate 1 becomes equal to or higher than the Curie point, crystal transformation occurs locally, and the ferroelectricity disappears. Thereafter, the ferroelectricity reappears at the same time as the temperature is lowered, but in order to minimize the electric energy in the single-crystal LiTaO ₃ substrate 1, a multi-domain structure having a random polarization direction is formed.

In this way, a desired region is formed into a multi-domain structure while scanning the laser beam 5. The irradiation time of the laser beam 5 per point in this embodiment was 0.45 seconds.

Therefore, also in the present embodiment, as in the first embodiment, the region other than the region where the electrode 2 is formed on the single-crystal LiTaO ₃ substrate 1 is divided into multiple domains, so that the excess charge generated on the substrate surface can be quickly eliminated. And the occurrence of popcon noise can be prevented.

Embodiment 3 = FIG. 5 is a schematic sectional view showing a part of a manufacturing process of a pyroelectric infrared detecting element according to another embodiment of the present invention. In the present embodiment, the steps up to the single domainization of the single-crystal LiTaO ₃ substrate 1 are the same as those in the first embodiment, and thus the description is omitted here. In this embodiment, aluminum (Al) is formed on both surfaces of a single crystal LiTaO ₃ substrate 1 on which electrodes 2 are formed.
A film is formed by vapor deposition, and a desired Al mask 6 is formed by photolithography and etching in a desired region where a multi-domain structure is to be formed (FIG. 5A).

Subsequently, the substrate is placed in benzoic acid at about 220 ° C., and after performing proton substitution, heat treatment is performed.
Polarization inversion occurs, and the Al mask 6 is removed (FIG. 5).
(B)).

Although this polarization inversion mechanism has not been elucidated yet, it is speculated as follows. When a part of the Li ions in the single crystal LiTaO ₃ substrate 1 is replaced with H ⁺ ions, Li decreases, and the Curie point of that part decreases. Thereafter, if heat treatment is performed, polarization reversal occurs due to the pyroelectric voltage during cooling.

Therefore, also in this embodiment, as in the first embodiment, the region other than the region where the electrode 2 is formed on the single crystal LiTaO ₃ substrate 1 is divided into multiple domains, so that the excess charge generated on the substrate surface can be quickly eliminated. And the occurrence of popcon noise can be prevented.

Embodiment 4 = FIG. 6 is a schematic sectional view showing a part of a manufacturing process of a pyroelectric infrared detecting element according to another embodiment of the present invention. In the present embodiment, the steps up to the single domainization of the single-crystal LiTaO ₃ substrate 1 are the same as those in the first embodiment, and thus the description is omitted here. In the present embodiment, a single crystal LiTaO ₃ substrate 1 on which an electrode 2 is formed is provided with aluminum (A) on one surface.
1) A film is formed by vapor deposition, and a desired Al mask 6 is formed by photolithography and etching in a desired region where a multi-domain structure is to be formed.

Subsequently, proton ions (H ⁺ ) are implanted from the surface of the single-crystal LiTaO ₃ substrate 1 on which the Al mask 6 is formed by an ion implanter (FIG. 6A). In this embodiment, the dose is set to 1 × 10 ¹⁵ / cm ² , the implantation energy of the ion implantation apparatus used is 3 MeV, the ion implantation depth is 100 μm or more,
The injection in the thickness direction was performed without any problem.

After the ion implantation, the Al mask 6 is removed and an annealing process is performed thereafter, whereby the single-domain structure region 1 is formed.
a is changed to the multi-domain structure region 1b (FIG. 6B).

Therefore, also in the present embodiment, as in the first embodiment, the region other than the region where the electrode 2 is formed on the single-crystal LiTaO ₃ substrate 1 is divided into multiple domains, so that the excess charge generated on the substrate surface can be quickly eliminated. And the occurrence of popcon noise can be prevented.

The ion implantation energy is 400 keV.
Although the ion implantation depth of only about several μm is used when using the ion implantation apparatus of
The same effect as in the above-described embodiment can be obtained by forming the l mask 6 and implanting ions from the front and back surfaces of the substrate to form a multi-domain structure only in a portion of several μm in the depth direction from the substrate surface. This means that the multi-domain structure does not need to continue from the front surface to the back surface of the substrate in order to neutralize the surplus electric charges on the substrate surface, and is opposed to the vicinity of the substrate surface so that the surplus electric charges are easily neutralized. It is shown that the charge having the polarity of?

[0040]

According to the first to fifth aspects of the present invention, there is provided a single-crystal LiTaO ₃ substrate which has been subjected to a polarization treatment, and electrodes formed so as to face both surfaces of the single-crystal LiTaO ₃ substrate. in the pyroelectric infrared detector comprising, a formation region of the electrode in the single crystal LiTaO ₃ substrate direction of the spontaneous polarization and single polarization structure is constant, the non-forming region of the electrode in the single crystal LiTaO ₃ substrate, the direction of the spontaneous polarization Has a random multi-domain structure, so that a surplus charge generated on the substrate surface can be quickly neutralized, and a pyroelectric infrared detecting element capable of reducing popcon noise can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a pyroelectric infrared detecting element according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a heat treatment apparatus for multi-domaining the pyroelectric infrared detection element according to the embodiment.

FIG. 3 is a diagram showing heat cycle conditions in a popcon noise test of the infrared detection element according to the embodiment.

FIG. 4 is a schematic diagram showing a method for multi-domaining a pyroelectric infrared detecting element according to another embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view showing a part of a manufacturing process of a pyroelectric infrared detection element according to another embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a part of a manufacturing process of a pyroelectric infrared detecting element according to another embodiment of the present invention.

FIGS. 7A and 7B are schematic diagrams illustrating the detection principle of a pyroelectric infrared detection element, wherein FIG. 7A shows an equilibrium state in an electrode formation area before infrared rays are incident, and FIG. (C) shows an equilibrium state in the electrode formation region after the infrared rays are incident.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Single crystal LiTaO ₃ substrate 2 Electrode 3 Electric furnace 4 Electric wiring part 5 Laser beam 6 Al mask 7 Pyroelectric

Continued on the front page (72) Inventor Motoo Ikari 1048 Odakadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd.

Claims (5)

[Claims] And 1. A single crystal LiTaO ₃ substrate formed by polarization processing, the pyroelectric infrared detection element comprising an electrode formed so as to face both surfaces of the single crystal LiTaO ₃ substrate, the single In the crystalline LiTaO ₃ substrate, a region where the electrode is formed has a monopolar structure in which the direction of spontaneous polarization is constant, and other than the region in which the electrode is formed in the single crystal LiTaO ₃ substrate, a multi-domain structure in which the direction of spontaneous polarization is random. A pyroelectric infrared detection element, characterized in that: 2. The single crystal in which the direction of spontaneous polarization is constant.
Once the temperature of the LiTaO ₃ substrate is once raised to the Curie point of LiTaO ₃ or more and the single crystal LiTaO ₃ substrate is changed from a ferroelectric to a paraelectric, the temperature is lowered while applying an electric field to the electrode. 2. The pyroelectric infrared detecting element according to claim 1, wherein the single crystal LiTaO ₃ substrate has a multi-domain structure in which the direction of spontaneous polarization is random except the region where the electrode is formed. 3. The single crystal wherein the direction of spontaneous polarization is constant.
In the LiTaO ₃ substrate, A
After forming the l mask, the single crystal LiTaO ₃ substrate subjected to proton substitution process put into benzoic acid by polarization inversion into certain time heat treatment, the single crystal LiTaO ₃
2. The pyroelectric infrared detecting element according to claim 1, wherein a region other than the electrode forming region on the substrate has a multi-domain structure in which directions of spontaneous polarization are random. 4. The single crystal wherein the direction of spontaneous polarization is constant.
In the LiTaO ₃ substrate, A
After forming a mask, proton ions are implanted by an ion implantation method, and annealing is performed to obtain a multi-domain structure in which the direction of spontaneous polarization is random except for the region where the electrode is formed on the single crystal LiTaO ₃ substrate. The pyroelectric infrared detecting element according to claim 1, wherein: 5. The single crystal wherein the direction of spontaneous polarization is constant
In the LiTaO ₃ substrate where the multi-domain structure region is,
By irradiating a laser beam, the single crystal LiTaO ₃
The temperature of the portion to be the multi-domain structure region on the substrate is once increased to a temperature equal to or higher than the Curie point of LiTaO ₃ so that the single crystal LiTaO ₃
By lowering the temperature of the substrate, said non-formation region of the electrode in the single crystal LiTaO ₃ substrate, pyroelectric infrared according to claim 1, wherein the direction of spontaneous polarization is characterized in that a possibly zone structure is random Detection element.