JPH11230826A - Pyroelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pyroelectric element from which the occurrence of such a trouble as the shifting of electrodes on the front and rear surfaces of the element, the turning over of the electrodes during a vapor depositing process, etc., can be eliminated and, at the same time, which can easily be inspected individually for appearance and electrical characteristics after a dicing process, etc., is completed by only arranging the electrodes on one surface of the element. SOLUTION: A pyroelectric element is constituted by arranging a pair of parallel counter electrodes 5 on one surface of a single-crystal lithium tantalate plate 4, the front and rear surfaces of which are normal to the x-axis of the crystal axis of the plate 4 in such a way that the electrodes 5 respectively intersect the z-axis of the crystal axis at about right angles. It is preferable to dig down the arranging areas of the electrodes 5 in advance. It is also preferable to constitute the pyroelectric element in such a way that the surface of the plate 4 is held between or surrounded by the dug or through grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Various pyroelectric materials having pyroelectricity are used for thermoelectric conversion elements of pyroelectric infrared sensors used as heat and temperature detectors. Among them, lithium tantalate has a large pyroelectric effect, and in recent years, a high-quality single crystal wafer has become available.
In addition, there is also an improvement in the polishing technique for processing the thin film, and it is the most widely used material for a pyroelectric element manufactured in bulk.

[0003] In a manufacturing process of a lithium tantalate wafer, a single domaining process called poling is performed. This is a process for uniformly aligning the direction of spontaneous polarization inherent in the material. The directions of spontaneous polarization of the material subjected to this treatment are all parallel to the z-axis of the crystal axis and point in the same direction. If the temperature is constant, the magnitude of this spontaneous polarization is also constant, but if the temperature changes, the magnitude of the spontaneous polarization also changes, and the change temporarily breaks the electrical neutral condition, In order to neutralize this, transfer of electric charge (from the outside) occurs. A temperature change is detected by detecting the movement of the electric charge.

The charge is generated on the surface at which the spontaneous polarization terminates, that is, on the z-plane (the surface having a higher spontaneous polarization potential is referred to as a + z surface, and the smaller surface is referred to as a -z surface). Therefore, when a single-crystal lithium tantalate is made into a wafer, the front and back surfaces are made to be both z-planes (hereinafter, such a wafer is called a z-cut wafer), and the counter electrode is formed on each of the surfaces. The charges generated by the change can be taken out.

[0005] The structure of a pyroelectric element using a conventional single-crystal lithium tantalate wafer is all the above-mentioned structure, that is, z
The structure is such that opposed electrodes are provided on both sides of the cut wafer. FIG. 23 shows a basic structure of a conventional example. In the figure, 1 is a plate obtained by cutting a z-cut single crystal lithium tantalate wafer into an appropriate size, 1a is a + z plane, 1b is a -z plane, 2 is an electrode, and 3 is a lead line. Of course, various structures have been devised, such as the planar shape, arrangement, wiring, etc. of the electrodes, and a coating film on the electrodes, but the common point is that electrodes are provided on both sides of the z-cut plate. .

[0006]

In the pyroelectric element constructed as described above, it is necessary to form electrodes on both sides of the wafer without fail, and there is a problem of electrode misalignment on the front and back, and the front and back of the wafer during the process. Very complicated and inefficient, such as inversion. Also, when the wafer is cut into individual pieces, the wafer is generally separated by dicing, but if the wafer is diced as it is, the wafer is thin and easily broken. I do. Even after the steps such as dicing, the separated pieces are stuck on the support plate.In this state, we would like to inspect once and select only good products, but because the back surface is in contact with the support plate In addition, it is not possible to perform an appearance inspection such as a failure in vapor deposition wiring on the back surface, and an electrical inspection cannot be performed because the back electrode cannot be used. Even after the element piece is removed from the support plate, it is almost impossible to handle the electrical inspection by touching the probe to the front and back, since it is a very small piece. ,
It takes a lot of time because you have to observe both sides. Therefore, the quality of the element piece is determined only at the stage of the electrical inspection of the mounted product after the element piece is completely mounted, which is very inefficient.

[0007] The difficulty in handling element pieces is
This is because the thickness of the element is as thin as about 50 μm.However, the element thickness affects the speed at which the element receives infrared rays and changes its temperature, that is, the response speed as a sensor. Can not.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an opposing electrode is formed on the same surface and only on one surface. Since the counter electrode must be formed on the z-axis, in order to form it on the same plane, a so-called x-cut wafer cut on a plane whose normal is the x-axis of the crystal axis is used. That is, two electrodes perpendicular to the z-axis and parallel to each other are formed on one surface (eg, + x surface) of the x-cut wafer by vapor deposition or the like.

The two electrodes form one capacitor. To increase the spontaneous polarization density between the electrodes, the electrode formation region is dug in advance in the -x direction, and the inner surface is vapor-deposited. Alternatively, a metal layer serving as an electrode material is formed by a method such as screen printing. The opposing surface of the two electrodes forming the capacitor is widened by digging (this opposing surface naturally corresponds to the z-plane), and an increase in spontaneous polarization density in proportion to the digging depth is expected. However, this digging is not impossible even by a dry etching method using ions such as ion milling and reactive ion etching, but the digging depth is several tens of μm, so that the digging is not performed by the above-mentioned method. Takes time (approx. 1 μm
/ 1 hour).
A technique such as sandblasting for precision machining, in which fine powder of not more than μm is sprayed to perform machining, is very preferable. With this method, it is possible to excavate at a speed of about 50 to 100 μm / hour or more, and it is also possible to excavate only a region of several tens μm level.

Furthermore, in order to improve the response speed of the element, it is necessary to prevent the heat generated by the incident infrared rays from diffusing out of the infrared detecting section, that is, outside the area sandwiched by the pair of opposed parallel electrodes. A groove for preventing this is formed at the same time when the electrode portion is dug. This groove may be simply dug down or penetrated, but from the viewpoint of heat separation performance, a through groove is preferable.

Further, when the thickness of the wafer is to be 100 μm or more (eg, 500 μm) in order to facilitate the handling of the wafer and the element pieces, the wafer is sandwiched by an infrared detector, ie, a pair of opposed parallel electrodes. Only the area,
By digging in advance from the opposite surface side (−x surface side), it is possible to avoid a decrease in thermal responsiveness. The digging on the opposite surface also has a depth of about several hundred μm, so that it is manufactured using the above-described technique such as sandblasting.

Further, by arranging and connecting a plurality of detecting portions each comprising a pair of counter electrodes described above (in the vapor deposition step), it is possible to manufacture an element further improved in detecting ability and noise resistance. Can be done. Since the method of combining the elements is determined in principle by the vapor deposition process, the wiring can be freely combined.

[0013]

1 and 2 show an example of an embodiment of the present invention. FIG. 1 is a plan view of the device, and FIG.
FIG. 2 is a sectional view taken along a line AA ′ shown in FIG. 1. In the present embodiment, an x-cut wafer having the same thickness (about 50 μm) as a conventionally used wafer is used, and the electrodes are manufactured only by a simple vapor deposition process. In the figure, 4 is a plate obtained by cutting an x-cut single crystal lithium tantalate wafer into an appropriate size, 4a is a + x plane, 4
b is the −x plane, and 5 is formed so as to intersect the z-axis at right angles.
A set of opposed parallel electrodes. Of course, 4a is the -x plane and 4a
b may be the + x plane.

FIGS. 3 and 4 also show an example of the embodiment of the present invention. FIG. 3 is a plan view of the device, and FIG. 4 is a cross-sectional view taken along a line AA ′ shown in FIG. This form also
The same thickness as that of a conventionally used wafer (about 50 μm)
In the case of using the x-cut wafer of m), one set of the opposing parallel electrodes 6 arranged so as to intersect at right angles to the z-axis is a case where it is manufactured by a digging process and a technique such as evaporation or screen printing. In the figure, reference numeral 6 denotes a pair of dug opposed parallel electrodes formed so as to intersect the z-axis at right angles.

FIGS. 5 to 7 also show an example of the embodiment of the present invention. FIG. 5 is a plan view of the device, and FIGS. 6 and 7 are broken lines AA ′ and B-
It is sectional drawing in B '. This embodiment also uses an x-cut wafer having the same thickness (about 50 μm) as a conventionally used wafer, and a pair of opposed parallel electrodes 6 arranged so as to intersect at right angles to the z-axis is formed by a digging process. In addition, the structure is formed by a method such as vapor deposition or screen printing, and a region sandwiched by the opposed parallel electrodes 6 is sandwiched by the heat separation grooves 7. In the figure, the heat separation groove 7 does not penetrate, but of course there may be a through groove.

FIGS. 8 and 9 also show an example of the embodiment of the present invention. FIG. 8 is a plan view of the element, and FIG. 9 is a cross-sectional view taken along a line AA ′ shown in FIG. This embodiment is thicker (100 to 5) than a conventionally used wafer.
In this case, an x-cut wafer (of about 00 μm) is used, and one set of opposed parallel electrodes 5 arranged so as to intersect at right angles to the z-axis is made only by a simple vapor deposition process. In the drawing, reference numeral 8 denotes a plate obtained by cutting an x-cut single-crystal lithium tantalate wafer having a thickness of 100 to 500 μm into an appropriate size, 8a denotes a + x plane, and 8b denotes a −x plane. Of course, 8a may be the -x plane and 8b may be the + x plane. In the figure,
Reference numeral 9 denotes a detection portion, that is, a region dug in the back surface of the region sandwiched by the opposing parallel electrodes 5. Due to this back surface digging 9, only the region sandwiched between the opposing parallel electrodes 5 has a thickness of about 50 μm.

FIGS. 10 and 11 also show an example of the embodiment of the present invention. FIG. 10 is a plan view of the element, and FIG. 11 is a cross-sectional view taken along a line AA ′ shown in FIG. This embodiment also uses an x-cut wafer (thickness of about 100 to 500 μm) which is thicker than a conventionally used wafer. It is produced by a technique such as vapor deposition or screen printing. In the drawing, reference numeral 9 denotes a region in which the back surface of a region sandwiched by the detection portions, that is, the dug opposed parallel electrodes 6 is dug, as in FIG. Due to the back surface digging 9, only the region sandwiched between the digging opposed parallel electrodes 6 has a thickness of about 50 μm.

FIGS. 12 to 14 also show an example of the embodiment of the present invention. FIG. 12 is a plan view of the device, and FIG.
3 and FIG. 14 correspond to the broken line AA ′ shown in FIG.
It is sectional drawing in BB '. This embodiment is also thicker (100-500 μm) than a conventionally used wafer.
When an x-cut wafer is used, a pair of opposing parallel electrodes 6 arranged so as to intersect the z-axis at right angles are formed by a digging process and a technique such as vapor deposition or screen printing, and furthermore, the opposing parallel electrodes 6 are formed. The region sandwiched by 6 is sandwiched by the thermal isolation grooves 7 and has a back surface dug 9. In the figure, the heat separation groove 7 is in contact with and penetrates the back surface digging 9, but may be a non-through groove.

FIGS. 15 to 17 also show an example of the embodiment of the present invention. FIG. 15 is a plan view of the present embodiment, FIG. 16 is a cross section taken along the line AA ′ shown in FIG. 15, and FIG. 17 is an electric circuit. In this embodiment, two elements of the form shown in FIGS. 12 to 14 are connected by wiring 10 in the arrangement shown in FIG. 15, and is a composite element type form generally called dual. Here, the composite element of this embodiment is constituted by the unit elements shown in FIGS. 12 to 14, but is shown in FIGS. 1 and 2, FIGS. 3 and 4, and FIGS. 5 to 7. It is a matter of course that the composite element may be constituted by the unit elements of the form, the form shown in FIGS. 8 and 9, and the form shown in FIGS. 10 and 11. As can be seen in FIG. 17, the dual element is obtained by connecting unit elements 11 and 12 in different polarization directions (that is, the z-axis direction) in parallel. In the present embodiment, one electrode of the unit element is shared with each other, and One electrode 13 as a dual element,
In addition, wiring 1
0 constitutes the other electrode 14 as a dual element.

FIGS. 18 and 19 also show an example of the embodiment of the present invention. FIG. 18 is a plan view of the present embodiment,
FIG. 19 shows this in an electric circuit. The cross section is omitted because it can be easily imagined from FIG. This embodiment is shown in FIG.
This is a composite device type configuration in which four devices having the configurations shown in FIGS. 2 to 14 are connected by wiring 10 in the arrangement shown in FIG. Here, the composite element of this embodiment is constituted by the unit elements shown in FIGS. 12 to 14, but is shown in FIGS. 1 and 2, FIGS. 3 and 4, and FIGS. 5 to 7. It is a matter of course that the composite element may be constituted by the unit elements of the form, the form shown in FIGS. 8 and 9, and the form shown in FIGS. 10 and 11. In the four-unit-element composite embodiment of this embodiment, unit elements 11, 12, 15, and 16 are connected in parallel as shown in FIG.

FIG. 20 is also a plan view showing an example of the embodiment of the present invention.
This is a different arrangement form of a unit element composite type. FIG. 21 and FIG.
Also shows an example of the embodiment of the present invention. FIG.
1 is a plan view of the present embodiment, and FIG. 22 is an electric circuit showing this. In this embodiment, the device shown in FIGS.
FIG. 21 shows a composite element type configuration connected in an arrangement as shown in FIG. Here, the composite element of this embodiment is constituted by the unit elements shown in FIGS.
, The forms shown in FIGS. 3 and 4, the forms shown in FIGS. 5 to 7, the forms shown in FIGS. 8 and 9, and the unit elements shown in FIGS. Of course it doesn't matter. In this embodiment, each of the unit elements 11, 12, and 15 to
Output signals from 20 are individually output from terminals 21 to 28, respectively. The terminal 29 is connected to each of the unit elements 11, 12
And 15 to 20 common terminals.

[0022]

According to the present invention, a pair of opposed parallel electrodes are provided on one side of a single-crystal lithium tantalate plate constituting the front and back sides with respect to the normal to the x-axis of the crystal axis, respectively. Since it has a structure arranged so as to intersect at a substantially right angle, the problem of electrode misalignment between the front and back as well as the problem of complicated inversion of the wafer during the vapor deposition process do not occur. Similarly, the appearance inspection and the electrical inspection process of the wafer after the processes such as dicing, that is, the element pieces, can be performed while the wafer is still attached to the support plate, so that the final inspection of the mounted product is performed. The efficiency with which defective element pieces can be dropped by this time is greatly improved, wasteful mounting and post-mounting inspection are eliminated, and the yield is improved. In particular, in the case of a compound type device in which a plurality of unit elements are arranged and connected as in claim 5, an electrode, that is, a signal extraction terminal, is provided only on one surface of the wafer in consideration of an increase in the number of inspection items. Is very convenient and realistic.

Further, since the dimensions of each part such as the distance between electrodes and the area which determine the performance of the element and the arrangement of the elements are determined by various masks used in each step, there is an advantage that each dimension can be manufactured very accurately. There is. In other words, the dimensions of the electrodes and wirings are determined by the vapor deposition mask, and the dimensions of the dug-out portions in claims 2 and 3 are determined by the photoresist mask. Because it is possible, the degree of freedom of design increases.

Further, according to the invention of claim 4 or 6, not only a wafer as thin as about 50 μm as in the prior art but also
Since elements can be manufactured even on a wafer as thick as 500 μm, handling of element pieces is greatly facilitated, element damage during the process is avoided, and mechanical strength is high.
Handling of the mounted product in actual use is also facilitated.

[Brief description of the drawings]

FIG. 1 is a plan view of an element showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line A-A 'of FIG.

FIG. 3 is a plan view of an element showing a second embodiment of the present invention.

FIG. 4 is a sectional view taken along line A-A ′ of FIG. 3;

FIG. 5 is a plan view of an element showing a third embodiment of the present invention.

FIG. 6 is a sectional view taken along line A-A ′ of FIG. 5;

FIG. 7 is a sectional view taken along line B-B 'of FIG.

FIG. 8 is a plan view of an element showing a fourth embodiment of the present invention.

9 is a cross-sectional view taken along line A-A 'of FIG.

FIG. 10 is a plan view of an element showing a fifth embodiment of the present invention.

11 is a cross-sectional view taken along line AA ′ of FIG.

FIG. 12 is a plan view of a device according to a sixth embodiment of the present invention.

FIG. 13 is a sectional view taken along line AA ′ of FIG. 12;

FIG. 14 is a sectional view taken along line BB ′ of FIG. 12;

FIG. 15 is a plan view of an element showing a seventh embodiment of the present invention.

FIG. 16 is a cross-sectional view taken along line AA ′ of FIG.

17 is an electric circuit diagram of the device of FIG.

FIG. 18 is a plan view of a device according to a seventh embodiment of the present invention.

FIG. 19 is an electric circuit diagram of the device of FIG. 18.

FIG. 20 is a plan view of an element according to an eighth embodiment of the present invention.

FIG. 21 is a plan view of a device according to a ninth embodiment of the present invention.

FIG. 22 is an electrical circuit diagram of the device of FIG. 21.

FIG. 23 is a sectional view showing a sectional structure of a conventional device.

[Description of sign]

 4 x-cut single-crystal lithium tantalate plate 4a + x-plane 4b -x-plane 5 parallel counter electrode 6 dug parallel counter electrode 7 thermal separation groove

Claims (6)

[Claims] 1. A pair of opposed parallel electrodes, each of which is substantially perpendicular to the z-axis of the crystal axis, on one side of a single-crystal lithium tantalate plate constituting the front and back sides with the normal to the x-axis of the crystal axis. A pyroelectric element having a structure arranged in a pyroelectric element. 2. The pyroelectric element according to claim 1, wherein the pair of opposed parallel electrodes according to claim 1 is provided in a region dug down in advance. 3. A structure in which a surface sandwiched by a pair of opposed parallel electrodes according to claim 1 or 2 is sandwiched or surrounded by a groove dug down or penetrated outside. A pyroelectric element comprising: 4. A structure in which a surface sandwiched between a pair of opposed parallel electrodes according to claim 1, 2 or 3 is dug from the opposite surface side to make only the region thinner. A pyroelectric element comprising: 5. A pyroelectric element comprising a plurality of pyroelectric elements according to claim 1, 2, 3 or 4, arranged as a single element. 6. The pyroelectric element according to claim 4, wherein the digging from the opposite surface side is formed by a sandblast technique using fine powder having an average particle diameter of 12 μm or less.