JPH0862038A - Infrared detection element and production thereof - Google Patents

Abstract

PURPOSE: To enhance the practical performance index by employing a porous ferroelectric ceramics having a structure sandwiched by compact ferroelectric ceramics thereby lowering the permittivity and thermal capacity. CONSTITUTION: The pyroelectric infrared detection element is composed of a porous ferroelectric ceramics 1 and a sintered ferroelectric ceramics 2 wherein a plumbum titanate(PT) based or a plumbum zirconate titanate(PZT) based ceramic having a relatively high pyroelectric coefficient is preferably employed. An organic bubble forming material having particle size of 100μm or less is mixed with a ferroelectric ceramic powder and a thick film of a slurry having volume fraction of 20-70% is formed to obtain a green sheet for porous thick film. It is superposed on a green sheet for compact thick film obtained by forming a thick film of slurry from which the bubble forming material is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting element for detecting a human body and a living body and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, two types of infrared detection elements are known: a quantum type and a thermal type. Among them, the quantum infrared detection element has features such as high sensitivity and fast response speed because infrared rays are captured as a band gap of a semiconductor.
However, on the other hand, it is necessary to cool to the liquid nitrogen temperature at the time of use, and it is necessary to provide a cooling unit, which is large and expensive. Further, it has a wavelength selectivity and does not respond to far infrared rays.

A thermal infrared detecting element is a type that converts infrared rays into thermal energy and detects it as temperature, which is a thermocouple type utilizing thermoelectromotive force, a bolometer type utilizing resistance change with temperature, and a pyroelectric effect of a ferroelectric substance. It is roughly divided into pyroelectric type using. The inner pyroelectric type has a sensitivity higher than that of other types by one digit or more, has a simple structure, has no wavelength dependence, and operates at room temperature. It is an electric infrared detector.

The pyroelectric infrared detecting element utilizes the pyroelectric phenomenon of a ferroelectric substance to detect a change in polarizability with a change in temperature as a change in surface charge. For this reason, the structure of the pyroelectric detection element should be as thin as possible compared to the light receiving area so that the temperature rise is larger for the same incident infrared energy, and the contact with the substrate or body with high heat capacity Consideration is given to making the structure as small as possible.

Further, the material of the pyroelectric infrared detecting element is generally selected from ferroelectric ceramics so that the pyroelectric figure of merit (p1) of the formula (1) becomes large.

## EQU1 ## p1 = (dI / dT) / (A.ε) (1) (where, I: pyroelectric current, T: temperature, A: area, ε: permittivity) From the aspect, it is also known that p2 in the equation (2) is an actual electromotive voltage and that having a small heat capacity is actually suitable.

## EQU00002 ## p2 = p1 / Cp (2) (where Cp: heat capacity) Since the heat capacity is generally considered to be proportional to the density of the substance, the expression (3) is used instead of the expression (2). It can be treated as a performance index.

## EQU00003 ## p3 = p1 / D (3) (where D: density)

[0006]

However, in order to maintain the self-sustaining strength, the so-called pyroelectric infrared detecting element made of a so-called dense ferroelectric ceramic or ferroelectric single crystal is put into practical use at present. The thickness is limited to about 0.3 mm, and it is very difficult to make it thinner, and the heat capacity of the element itself is limited, and the above-mentioned values of p1 to p3 are also limited. However, in order to realize a higher performance infrared detection element, it is required to improve these performance indexes.

[0007]

The present invention has been made in order to solve the above problems, and has a structure in which porous ferroelectric ceramics are sandwiched between dense ferroelectric ceramics. This is achieved by a pyroelectric infrared detection element.

The infrared detecting element of the present invention is 100 μm
Porous thick film green sheet obtained by mixing an organic pore-forming material having the following particle size with a ferroelectric ceramic powder and forming a thick film of a slurry having a volume fraction of 20 to 70%, and pores from the slurry. This is achieved by a method for manufacturing a pyroelectric infrared detection element, which comprises stacking dense green films for thick films, which are formed by thickening the slurry excluding the forming material.

Since the infrared detecting element of this structure includes the porous portion in the central portion, when compared with the same volume, the dielectric constant of the element becomes lower than that of the dense one, and as a result, the figure of merit p1 is improved. Also, the heat capacity becomes smaller, and the practical performance index p3
Is inversely proportional to it. Furthermore, since the dense layer is provided on the surface of the device, the self-supporting strength is improved to the same level as that of the dense body, and the electrodes can be installed with the same ease as that of the device composed of only the dense body.

Details of the pyroelectric infrared detection element of the present invention will be described with reference to the attached FIG. In the figure, reference numeral 1 is a porous ferroelectric ceramic, and any material may be used as long as it is a ferroelectric ceramic showing pyroelectricity, but it is sintered by an ordinary sintering method and has a relatively large pyroelectric coefficient. Lead titanate (PT) based or lead zirconate titanate (PZT) based materials are preferred. The structure of No. 1 needs to be porous, and its porosity is preferably 20% or more in order to obtain the effect of the present invention. The higher the porosity, the greater the effect, but it is inappropriate to use a material having a porosity of 80% or more in terms of workability during production and yield.
The shape of the pores may be either continuous pores or single pores, but spherical continuous pores are desirable because they can achieve high porosity and high strength.

Reference numeral 2 in the figure may be a dense ferroelectric ceramic. The denseness referred to here means a material having a porosity of 10% or less. In order to make the shrinkage rate the same as that of the porous portion, the material is preferably the same as that of the part. Furthermore, in order to install the electrode shown by 3, the dense ferroelectric ceramics of 2 must be provided on the upper and lower surfaces of 1. The electrode 3 may be any known electrode, and examples thereof include silver paste, gold and platinum sputtering, and electroless plating of noble metal.

The thickness of the infrared detecting element of the present invention is preferably as thin as possible, but it is necessary to have a certain thickness because it exists in a self-supporting manner. Specifically, it is preferable that the final thickness of the detection element is 2 to 0.2 mm. If it exceeds 2 mm, the merit of making it porous is lost, and if it is less than 0.2 mm, the workability is extremely poor. If it is necessary to perform polarization treatment (poling) before using it as an infrared detector, it is put to practical use.

The present invention will be specifically described below with reference to specific examples. Example A water-based PZT-based raw material obtained by adding 10% by weight of polyvinyl alcohol (PVA) as a binder to ceramics, 9% by weight of glycerin as a plasticizer, and 0.4 parts by weight of ammonium polyacrylate as a dispersant ( A Fuji Titanium PE-650) slurry (slurry-A) was prepared. A thick film was formed from this slurry by a doctor blade method to obtain a green sheet (A) having a dry thickness of 0.10 mm.
On the other hand, potato slurry (particle size: 10
μm) was added to PZT in a volume ratio of 1: 1 and further ball-milled to prepare a slurry B, and a doctor blade method was similarly used to obtain a green sheet (B) having a dry thickness of 0.15 mm.

The obtained green sheet was cut into a piece of 1 cm × 2 cm, and the sheets shown in Table 1 were stacked so that the sheet A was on the surface. In this case, water was applied to the adhesive surface, pressure-bonded, and then dried to obtain a layered green body. An electric furnace was used for firing, and after degreasing at 400 ° C for 2 hours, 1330
It carried out at 1 degreeC for 1 hour. Silver paste (Dotite made by Fujikura Kasei Co., Ltd.) was applied to both sides of the fired body, dried and baked at 600 ° C., and further, poling treatment was performed by applying a voltage of 2 kV / mm at 140 ° C. in silicone oil.

Environmental tester (SU-2 made by Tabai Espec
In 20), the pyroelectric coefficient was determined by measuring the generated current with a minute current measuring device (R8240 manufactured by Advantest) while heating the sample at a constant rate (1 ° C./min). or,
The relative permittivity was determined by dividing the permittivity calculated from the capacitance measured by an LCR meter (4192A manufactured by Hewlett Packard) in the same environment as the pyroelectric measurement by the permittivity of vacuum. The results are shown in Table 1. The porosity of the B layer portion in the table was calculated from the relative density of the whole, the porosity of the A layer portion obtained in Comparative Example 1 and the thickness of each layer by cross-sectional observation. The relative density is a value calculated from the outer size and the weight and divided by the theoretical density (7.9).

[0016]

[Table 1]

[Table 1 (continued)]

In Table 1, by comparing with the detector of Comparative Example 1 which is a detector made of the same material, a remarkable improvement in the performance index (p1 and p3) by the structure of the present invention is revealed, and its effect is obtained. I was confirmed.

Next, using a PT-based raw material in which 20 mol% of calcium oxide was added to lead titanate (PT), an aqueous slurry was prepared in the same manner as in the above-mentioned example, and then a green sheet for compact was molded ( Sheet C). The resulting green sheet had a thickness of 0.040 mm. Polystyrene beads having a median particle diameter of 30 μm were charged into the slurry and mixed so as to have a volume ratio of 70%, and a sheet was formed by changing blade intervals to obtain various thicknesses (sheet D).

The obtained green sheet was cut into a piece of 1 cm × 2 cm, and the sheets were stacked one by one in the order of C-D-C to give an example. On the other hand, the sheet C was used as a comparative example of stacking five layers. The firing was performed using an electric furnace at 1380 ° C. for 1 hour after degreasing at 400 ° C. for 2 hours. Silver paste (Dotite made by Fujikura Kasei) is applied to both sides of the fired body and dried at 600 ° C.
Baked at 140 ° C for 2k in silicone oil
A poling treatment was performed by applying a voltage of V / mm.

[0020]

[Table 2]

[Table 2 (continued)]

The results obtained are shown in Table 2. The porosity of the porous layer portion (D layer portion) was calculated from the relative density of the whole, the porosity of the C layer portion obtained in Comparative Example 2 and the thickness of each layer by cross-sectional observation. Further, the relative density was calculated assuming a theoretical density of 7.7. The relative permittivity and the pyroelectric coefficient were measured in the same manner as in Examples 1 to 3 and Comparative Example 1.

As is clear from Table 2, in this case as well, both the p1 value and the p2 value are larger than in Comparative Example 2, and the effect of the structure of the present invention is clear.

[0023]

The infrared detecting element according to the present invention has an improved detector structure while using the conventional ferroelectric ceramics. Since the infrared detector of the present invention can significantly reduce its dielectric constant and heat capacity, it has an advantage of dramatically improving the practical performance index.

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[Procedure amendment]

[Submission date] November 30, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Added

[Correction content]

[Brief description of drawings]

FIG. 1 is an explanatory view of a pyroelectric infrared detection element of the present invention.

[Explanation of symbols] 1 porous ferroelectric ceramics 2 dense ferroelectric ceramics 3 electrode

Claims (2)

[Claims] 1. A pyroelectric infrared detector having a structure in which porous ferroelectric ceramics are sandwiched between dense ferroelectric ceramics. 2. A porous thick film obtained by mixing an organic pore forming material having a particle size of 100 μm or less with a ferroelectric ceramic powder, and forming a slurry having a volume fraction of 20 to 70% into a thick film. The method for producing a pyroelectric infrared detection element according to claim 1, wherein a green sheet and a dense green sheet for thick thick film obtained by forming a thick slurry of the slurry from which the pore-forming material has been removed are laminated.