JPH05231933A - Pyroelectric element - Google Patents

Abstract

PURPOSE:To obtain a pyroelectric element being excellent in production and having excellent sensitivity by forming a heat capacity reducing part in a part of a substrate having a pyroelectric effect. CONSTITUTION:In a pyroelectric element, a light-sensing electrode and a compensating electrode are provided on a substrate having a pyroelectric effect and a heat capacity reducing part is formed in a part of the substrate. Due to the existence of the heat capacity reducing part, a heat capacity is reduced and sensitivity is increased. As for manufacture of the pyroelectric element, the part of the substrate 10 of ZnO, for instance, wherein a light-sensing part and a compensating part are to be formed is patterned by a method of photo-lithography. Successively, etching is made by a 10% hydrofluoric acid at a room temperature until the thickness of the light-sensing part and the compensating part becomes 5mum, so that a shape having a recessed part S be formed. Next, a gold black conductive film is formed by evaporation, patterning is conducted by the method of photolithography and a light sensing electrode 20, a compensating electrode 21 and an electrode connecting part 22 are formed by a method of selective wet etching using an iodine etchant. On the rear side of the substrate 10, too, an opposed electrode 30 for the light-sensing electrode and an opposed electrode 31 for the compensating electrode are provided at positions being opposite to the electrodes 20 and 21 respectively by the same technique, and a lead-out part for external connection is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric element for detecting infrared rays, especially heat rays, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a pyroelectric element for detecting infrared rays, particularly a heat ray, uses infrared ray receiving electrodes provided on both surfaces of a substrate having a pyroelectric effect, and the potential between the electrodes is changed by infrared ray irradiation. It is something to detect. As the base material, glycine sulfate-based, polyvinylidene fluoride-based, LiTaO ₃ ,
Materials such as PbTiO ₃ and ZnO are used, and morphology is glycine sulfate, LiTaO _{3 and the} like are crystalline, and PbTiO ₃ is formed by sintered ceramic or thin film technology because it is difficult to form crystals. It is general to use a thin film.

[0003]

Generally, a pyroelectric element using a thin film has a high sensitivity, but has problems in cost and reliability. In comparison, a pyroelectric element using a crystal body or a ceramic body is more productive. Also, it is excellent in reliability, but has a problem of low sensitivity.

The reason why the crystalline or ceramic pyroelectric sensor is inferior to the thin film pyroelectric sensor in terms of sensitivity is that the element heat capacity is large. By thinning the material, it is possible in principle to reduce the heat capacity of the element part and manufacture a highly sensitive sensor comparable to a thin film pyroelectric sensor.

By the way, conventionally, the thinning of the pyroelectric body has been performed mainly by cutting and polishing. However, in this case, since the pyroelectric material can withstand the polishing process in terms of physical strength up to several tens of μm, there has been a limit in reducing the heat capacity. This has been an obstacle to increasing the sensitivity of the crystalline or ceramic pyroelectric sensor.

The present invention has been made in consideration of the problems of the conventional pyroelectric element, and an object thereof is to provide a pyroelectric element which is excellent in reliability and productivity and which is also pleasant to move. is there.

[0007]

The present invention provides a pyroelectric element in which a substrate having a pyroelectric effect is provided with a light receiving electrode and a compensating electrode, in which a heat capacity reducing portion is formed in a part of the substrate. Is.

Further, the present invention is the pyroelectric element, wherein the heat capacity reducing portion is a concave portion formed by physically or chemically etching one surface of the substrate.

The present invention is also a pyroelectric element in which a light receiving electrode and a compensating electrode are formed in the concave portion of the heat capacity reducing portion.

The present invention is also a pyroelectric element whose substrate is made of a crystalline material or a ceramic material.

The present invention also uses PbT as a material for the substrate.
This is a method for manufacturing a pyroelectric element in which a heat capacity-reduced portion is formed by chemical dry etching using chlorine-based or fluorine-based etching gas using a crystal or sintered body of iO ₃ or LiTaO ₃ .

[0012]

According to the present invention, the existence of the heat capacity reducing section described above
The heat capacity can be reduced, and as a result, a highly sensitive pyroelectric element can be provided at a low price.

[0013]

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

(Embodiment 1) FIG. 1 is a schematic view for explaining a pyroelectric element and a manufacturing process according to a first embodiment of the present invention. In the figure, (x) is the initial state, (a)
Is a resist coating, exposure and development process, (b) is a pyroelectric substrate etching resist stripping process, (c) is a metal film formation, resist coating, exposure and development process, and (d) is a metal film etching ( Light receiving and compensating electrode formation), resist stripping step, and (e) shows the light receiving and compensating electrode counter electrode forming step. Further, each drawing of the right side portion (shown in (2)) is a plan view, and each drawing of the left side portion (shown in (1)) is a sectional view taken along the line AA ′ of the right side portion. Shows.

FIG. 1- (x) shows a pyroelectric substrate 10 made of ZnO thinned to several tens of μm by cutting and polishing, and as shown in FIG. The portion where the portion is formed is patterned by a photolithography method.

Subsequently, with 10% hydrofluoric acid at room temperature, FIG.
Etching was performed until the thickness of the light receiving portion and the compensation portion became 5 μm in the shape having the recess S shown in FIG. In this case, as an etchant, dilute hydrofluoric acid, an aqueous ammonia solution,
Boiling saline, boiling sodium tartrate aqueous solution, etc. can be used.

Next, as shown in FIG. 1- (c), a gold black conductive film is formed by vapor deposition, followed by patterning by photolithography, and then by selective wet etching using an iodine-based etchant.
The light-receiving electrode 20, the compensation electrode 21, and the electrode connecting portion 22 as shown in (d) were formed.

Subsequently, as shown in FIG. 1- (e), the counter electrode 3 for the light-receiving electrode is provided on the back surface of the pyroelectric substrate 10 at a position facing the light-receiving electrode 20 and the compensating electrode 21 by the same method.
0 and a compensating electrode counter electrode 31 are provided, and an electrode lead-out portion for connecting to an external circuit is formed.

The material of the conductive film is not limited to that in the above embodiment, and the conductive film forming method and the conductive film etching method should be appropriately selected according to the conductive film material. Is a sputtering method, a CVD method, etc.
As for the etching method, there are selective chemical wet etching, and dry etching methods such as sputter etching and reactive ion etching.

The advantages of the element shape described in this embodiment over the conventional shape are as follows. First, by adopting the above-mentioned manufacturing method, the heat capacity of the light receiving portion is remarkably reduced as compared with the conventional one, and thus the sensitivity can be greatly improved. further,
In the conventional shape element, since the light receiving portion has a relatively large amount of heat capacity relative to the entire element, there is a possibility that the temperature of the entire element is increased by the emitted infrared rays and the characteristics are deteriorated especially during long time measurement. However, in the shape described in the present embodiment, it is possible to keep the heat capacity of the entire element large compared to the heat capacity of the light receiving section, and thus to prevent the temperature rise of the entire element, that is, to perform the temperature compensating action of the compensating section. It will be possible.

Next, how to take out the pyroelectric output of the present pyroelectric element will be described. As shown in FIG. 2, an infrared selective transmission substrate 40 having an infrared selective transmission window 41 is arranged on the front surface (upper surface) of the light receiving surface of the pyroelectric element so that only the light receiving electrode 20 is irradiated with the infrared rays 50. The 21 side is shaded. An equivalent circuit of this pyroelectric element and the like is shown in FIG. When the infrared ray 50 is intermittently made incident by the chopper 60 in this state, the difference in charge between the light receiving section 25 and the compensating section 26 is detected as the pyroelectric output Vout. Here, the light receiving unit 25 is shown in FIG.
Is formed of the light receiving electrode 20 and the counter electrode 30 for the light receiving electrode via the pyroelectric substrate 10 in FIG. It is formed with the counter electrode 31.

In FIG. 4, a conventional pyroelectric element (substrate material ZnO, substrate and light receiving portion thickness 50 μm) and a pyroelectric element (substrate material ZnO, light receiving portion thickness 5 μm) according to the manufacturing method and shape of this embodiment are actually shown. ) Is a characteristic comparison diagram with. In addition, this experiment was conducted in a thermostatic chamber at a temperature of 20 ° C. with a black body having a temperature of 100 ° C. as a measured object and a chopping frequency set to 15 Hz. As is clear from FIG. 4, the pyroelectric element according to the present embodiment has a significantly higher pyroelectric output than the conventional one (symbol Vm in the figure).
It was also confirmed that the rise time (symbol t in the figure) when the chopper was closed / opened was significantly shortened as compared with the conventional one, that is, it had good characteristics of high sensitivity and excellent responsiveness. FIG. 5 is a diagram showing the shape and manufacturing method of a conventional pyroelectric element used for comparison with this example. The view (2) on the right side is a plan view, and the view (1) on the left side is its AA ′ sectional view. As shown in the figure, the conventional example is a flat pyroelectric plate 51.
A light receiving electrode 520, a light receiving electrode counter electrode 530, a compensation electrode 521, and a compensation electrode counter electrode 531 are formed on the surface 0.

(Embodiment 2) As another embodiment of the present invention,
Using a LiTaO ₃ sintered body as a material, a pyroelectric element was manufactured in the same manner as in Example 1. However, in this case, FIG.
As for the etching in the step (1), since there is no suitable chemical wet etchant, the reactive ion etching method was used. In this case, in a high output high frequency current of 250 to 500 W, the concentration of CF ₄ / A of several tens% or more.
When a fluorine-based or chlorine-based etching gas such as r, NF ₃ / Ar or CCl ₄ / Ar was used, the etching proceeded relatively effectively.

Actually, as in Example 1, the pyroelectric element according to this Example was compared and examined with the conventional shape, and the same good results as in Example 1 were obtained.

Even when PbTiO ₃ , LiNbO ₃ or the like, which is difficult to wet-etch like LiTaO ₃ , is used as the pyroelectric material, the element having the shape shown in FIG. 1 can be produced by the above-mentioned method. Moreover, as described above, these elements exhibited significantly excellent characteristics as compared with the conventional ones. As described above, the pyroelectric material is not limited to this embodiment as long as the condition that etching can be performed using an appropriate method is satisfied.

As described above, since the pyroelectric output extraction electrodes are all located on the back surface of the flat element in terms of shape, no special lead wiring is required and the mechanical strength generated when the thickness of the entire surface of the pyroelectric substrate is reduced. Easy to handle without worrying about shortage.

[0027]

As is apparent from the above description, the pyroelectric element according to the present invention has the heat capacity reducing portion formed in a part of the substrate, so that the pyroelectric element has much higher sensitivity and responsiveness than the conventional one. It is possible to provide a high-performance pyroelectric element without sacrificing productivity and reliability, which is excellent in characteristics stability during long-term use.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a plan view showing a manufacturing process of a pyroelectric element according to the present invention.

FIG. 2 is a perspective view for explaining a method for extracting a pyroelectric output of the pyroelectric element of the same example.

FIG. 3 is an equivalent circuit diagram of the same pyroelectric element.

FIG. 4 is a characteristic comparison diagram of conventional and invented pyroelectric elements.

FIG. 5 is a cross-sectional view and a plan view of a schematic shape of a conventional pyroelectric element.

[Explanation of symbols]

 10 Pyroelectric Substrate 11 Pyroelectric Substrate Front Surface 12 Pyroelectric Substrate Back Surface 20 Light-Receiving Electrode 21 Compensation Electrode 22 Electrode Connection 25 Light-Receiving Section 26 Compensation Section 30 Light-Receiving Electrode Counter Electrode 31 Compensation Electrode Counter-electrode 32 Electrode Lead-out 40 Infrared Selection Transparent substrate 41 Infrared selective transmission window 50 Infrared 60 Chopper S Recess

Claims (5)

[Claims] 1. A pyroelectric element in which a light receiving electrode and a compensation electrode are provided on a substrate having a pyroelectric effect, wherein a heat capacity reducing portion for reducing the heat capacity of the substrate is formed on a part of the substrate. And a pyroelectric element. 2. The pyroelectric element according to claim 1, wherein the heat capacity reducing portion is a concave portion formed by physically or chemically etching one surface of the substrate. 3. The pyroelectric element according to claim 2, wherein the light receiving electrode and the compensation electrode are formed in the recess of the heat capacity reducing portion. 4. The pyroelectric element according to claim 2, wherein the substrate is made of a crystalline material or a ceramic material. 5. A pyroelectric element characterized by using a PbTiO ₃ or LiTaO ₃ crystal or a sintered body as a substrate material and forming a heat capacity reducing portion by chemical dry etching with a chlorine-based or fluorine-based etching gas. Manufacturing method.