Method of manufacturing piezoelectric resonator unit

A method of manufacturing a piezoelectric resonator unit that includes mounting a piezoelectric resonator on a base member using a conductive adhesive, keeping the piezoelectric resonator in an environment having a temperature and a humidity higher than those of a surrounding region for a predetermined time, performing frequency adjustment of the piezoelectric resonator by etching using an ion beam, and joining a lid member to the base member using a joining material such that the piezoelectric resonator is hermetically sealed between the lid member and the base member.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a piezoelectric resonator unit.

BACKGROUND OF THE INVENTION

As a method of manufacturing a piezoelectric resonator unit used in, for example, an oscillation device or a bandpass filter, the following method is known. For example, as described in Patent Document 1, a piezoelectric resonator unit is manufactured by mounting a piezoelectric resonator (such as a quartz crystal blank) on a substrate by using a conductive adhesive, performing frequency adjustment of the piezoelectric resonator so as to have desired frequency characteristics, and then hermetically sealing the piezoelectric resonator in an internal space by a recessed metal cover.

However, hitherto, for example, in a manufacturing process of sealing a piezoelectric resonator or in using a completed product, changes in physical properties of a conductive adhesive have occurred due to the humidity of the hermetically sealed internal space, as a result of which variations in frequency characteristics of the piezoelectric resonator unit sometimes occurred. Such variations in frequency characteristics occur after performing a frequency adjustment step for acquiring desired frequency characteristics, and the amounts of variations in frequency characteristics differ according to products and are difficult to predict. Therefore, it may be difficult to manufacture a piezoelectric resonator unit having desired frequency characteristics.

SUMMARY OF THE INVENTION

The present invention is made in view of such circumstances, and an object thereof is to easily manufacture a piezoelectric resonator unit having desired frequency characteristics.

A method of manufacturing a piezoelectric resonator unit according to an aspect of the present invention includes (a) mounting a piezoelectric resonator on a base member by using a conductive adhesive; (b) keeping the piezoelectric resonator mounted on the base member in an environment having temperature and humidity higher than those of a surrounding region for a predetermined time; (c) performing frequency adjustment of the piezoelectric resonator by etching using an ion beam; and (d) joining a lid member to the base member with a joining material such that the piezoelectric resonator is hermetically sealed.

According to the above-described structure, the piezoelectric resonator mounted on the substrate is kept in a high-temperature and high-humidity environment, and then frequency adjustment of the piezoelectric resonator is performed. This makes it possible to, while revealing the variations in frequency characteristics and considering the revealed variations in frequency characteristics according to products, perform frequency adjustment of the piezoelectric resonator for acquiring desired frequency characteristics. Therefore, it is possible to easily manufacture a piezoelectric resonator unit having desired frequency characteristics.

In the method of manufacturing a piezoelectric resonator unit, the step (b) may include keeping the piezoelectric resonator in an environment having a temperature in a range of 40° C. to 121° C. and a humidity in a range of 70% RH to 95% RH for a time in a range of 30 minutes to 168 hours.

In the method of manufacturing a piezoelectric resonator unit, the base member may include a connection electrode formed on an upper surface on which the piezoelectric resonator is mounted, and an extended electrode that is extended from the connection electrode towards an outer edge of the upper surface of the base member; and the step (a) may include electrically connecting the piezoelectric resonator to the connection electrode by using the conductive adhesive.

In the method of manufacturing a piezoelectric resonator unit, the piezoelectric resonator may include a piezoelectric substrate and an excitation electrode formed on the piezoelectric substrate; and the step (c) may include trimming the excitation electrode by etching the excitation electrode by using the ion beam.

In the method of manufacturing a piezoelectric resonator unit, the piezoelectric substrate may be a quartz crystal substrate.

In the method of manufacturing a piezoelectric resonator unit, the lid member may be a cap including a recessed portion that faces the base member.

In the method of manufacturing a piezoelectric resonator unit, the joining material may be a resin adhesive.

This makes it possible to suppress the influence of humidity resulting from the resin adhesive.

According to the present invention, it is possible to easily manufacture a piezoelectric resonator unit having desired frequency characteristics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below. In the description of the drawings below, the same or similar structural elements are given the same or similar symbols. The drawings are examples, and the dimension and form of each portion are a typical dimension and form. Accordingly, the technical scope of the invention of the present application should not be understood as being limited to the embodiments.

A piezoelectric resonator unit according to an embodiment of the present invention is described with reference toFIGS. 1 and 2. The piezoelectric resonator unit is manufactured by applying a method of manufacturing a piezoelectric resonator unit according to an embodiment of present invention described below. Here,FIG. 1is an exploded perspective view of the piezoelectric resonator unit.FIG. 2is a sectional view along line II-II ofFIG. 1.FIG. 2does not illustrate various electrodes of a piezoelectric resonator.

As shown inFIG. 1, the piezoelectric resonator unit1according to the embodiment includes a piezoelectric resonator100; a cap200, which is an example of a lid member; and a substrate300, which is an example of a base member. The cap200and the substrate300are a case or a package for accommodating the piezoelectric resonator100.

The piezoelectric resonator100includes a piezoelectric substrate110, and a first excitation electrode120and a second excitation electrode130that are formed on the piezoelectric substrate110. The first excitation electrode120is formed on a first surface112of the piezoelectric substrate110. The second excitation electrode130is formed on a second surface114that is opposite to the first surface112of the piezoelectric substrate110.

The piezoelectric substrate110is made of a predetermined piezoelectric material. The material thereof is not limited to a particular material. In the example shown inFIG. 1, the piezoelectric resonator100is a quartz crystal resonator including the piezoelectric substrate110, which is an AT-cut quartz crystal substrate. The AT-cut quartz crystal substrate is one in which when, of an X axis, a Y axis, and a Z axis, which are crystallographic axes of synthetic quartz crystals, the Y axis and the Z axis are rotated by 35 degrees and 15 minutes ±1 degree and 30 minutes around the X axis in a direction from the Y axis to the Z axis, and when resulting axes are defined as a Y′ axis and a Z′ axis, surfaces that are parallel to surfaces specified by the X axis and the Z′ axis (hereunder referred to as “XZ′ surfaces”; other surfaces specified by other axes are similarly specified) are cut out as principal surfaces. In the example shown inFIG. 1, the piezoelectric substrate110, which is an AT-cut quartz crystal substrate, has a longitudinal direction parallel to a Z′-axis direction, a lateral direction parallel to an X-axis direction, and a thickness direction parallel to a Y′-axis direction; and the XZ′ surfaces thereof have a substantially rectangular shape. The quartz crystal resonator that uses the AT-cut quartz crystal substrate has a very high frequency stability in a wide temperature range, and may be manufactured with good temporal change characteristics and at a low cost. The AT-cut quartz crystal resonator often uses a thickness shear mode as a principal vibration mode.

The piezoelectric substrate according to the embodiment is not limited to the structure described above; and may be, for example, an AT-cut quartz crystal substrate having a longitudinal direction parallel to the X-axis direction and a lateral direction parallel to the Z′-axis direction, a quartz crystal substrate of a cut type other than an AT-cut type, or a piezoelectric substrate made of a piezoelectric material other than a quartz crystal, such as ceramic.

The first excitation electrode120is formed on the first surface112(XZ′ surface on a positive-direction side of the Y′ axis) of the piezoelectric substrate110, and the second excitation electrode130is formed on the second surface114(that is, the XZ′ surface on a negative-direction side of the Y′ axis) opposite to the first surface112of the piezoelectric substrate110. The first excitation electrode120and the second excitation electrode130are a pair of electrodes, and are disposed so that substantially the entire first excitation electrode120and the substantially entire second excitation electrode130overlap each other at their XZ′ surfaces.

A connection electrode124is electrically connected to the first excitation electrode120via the extended electrode122, and a connection electrode134is electrically connected to the second excitation electrode130via the extended electrode132are formed on the piezoelectric substrate110. More specifically, the extended electrode122is extended from the first excitation electrode120towards a short side on a negative-direction side of the Z′ axis on the first surface112, is further extended past a side surface of the piezoelectric substrate110on the negative-direction side of the Z′ axis, and is connected to the connection electrode124formed on the second surface114. The extended electrode132is extended from the second excitation electrode130towards the short side on the negative-direction side of the Z′ axis on the second surface114, and is connected to the connection electrode134formed on the second surface114. The connection electrodes124and134are disposed along the short side on the negative-direction side of the Z′ axis, and are electrically connected to the substrate300and are mechanically held by using conductive adhesives340and342(described later). In the embodiment, the pattern forms and arrangements of the connection electrodes124and134and the extended electrodes122and132are not limited to particular pattern forms and arrangements, so that various changes can be made as appropriate by considering electrical connection with other members.

In the above-described electrodes including the first excitation electrode120and the second excitation electrode130, for example, a foundation may be formed by forming a chromium (Cr) layer and a gold (Au) layer may be formed on a surface of the chromium layer. The materials thereof are not limited to certain materials.

The cap200includes a recessed portion204that opens so as to face a first surface302of the substrate300. The recessed portion204has edge portions202formed over the entire opening and from a bottom surface of the recessed portion204in a standing manner, and end surfaces205that face the first surface302of the substrate300. As shown inFIG. 2, each end surface205may be an end surface of its corresponding edge portion202that protrudes from the bottom surface of the recessed portion204substantially vertically in a standing manner. The cap200may be made of, for example, a metal. According to this structure, by electrically connecting the cap200to ground potential, the cap200can be provided with a shielding function. Alternatively, the material of the cap200may be an insulating material, or a composite material of a metal material and an insulating material.

In a modification, the cap200may include a flange portion that protrudes from the opening edge in a direction from an opening center of the recessed portion to the opening edge. In this case, the flange portion may include end surfaces that face the first surface of the substrate. According to the cap including the flange portion, since the size of the end surfaces, that is, the area of a joining region between the cap and the substrate can be made large, it is possible to increase the joining strength between the cap and the substrate.

The piezoelectric resonator100is mounted on the first surface302of the substrate300. In the example shown inFIG. 1, the substrate300has a longitudinal direction parallel to a Z′-axis direction, a lateral direction parallel to an X-axis direction, and a thickness direction parallel to a Y′-axis direction; and the XZ′ surfaces thereof have a substantially rectangular shape. The substrate300may be made of, for example, insulating ceramic. More specifically, the substrate300is formed by laminating a plurality of insulating ceramic sheets and by firing. Alternatively, the substrate300may be made of, for example, a glass material (such as silicate glass or a material containing a substance other than silicate as a main component and exhibiting glass transition phenomenon due to a temperature rise), a quartz crystal material (such as an AT-cut quartz crystal), or a glass epoxy material. It is desirable that the substrate300be made of a heat-resistant material. The substrate300may include a single layer or a plurality of layers. When the substrate300includes a plurality of layers, the substrate300may include an insulating layer at an outermost layer of the first surface302. The substrate300may have the shape of a flat plate, or may have a recessed shape that opens so as to face the cap200. As shown inFIG. 2, when the cap200and the substrate300are both joined to each other by using a joining material350, the piezoelectric resonator100is hermetically sealed in an internal space (cavity)206surrounded by the recessed portion204of the cap200and the substrate300.

The joining material350is provided in the form of a ring over the entire periphery of the cap200or the substrate300. The joining material350is interposed between each end surface205of its corresponding edge portion202of the cap200and the first surface302of the substrate300. The joining material350is a resin adhesive (such as an epoxy adhesive). The joining material350may be low-melting glass (such as lead borate based materials and tin phosphate based materials).

In the example shown inFIG. 2, one end of the piezoelectric resonator100(end portion on the side of the conductive adhesives340and342) is a fixed end, and the other end thereof is a free end. In a modification, both ends of the piezoelectric resonator100in the longitudinal direction may be fixed to the substrate300.

As shown inFIG. 1, the substrate300includes connection electrodes320and322that are formed on the first surface302(upper surface), and extended electrodes320aand322athat extend from the corresponding connection electrodes320and322towards outer edges of the first surface302. The connection electrodes320and322are disposed inwardly of the outer edges of the substrate300so as to allow the piezoelectric resonator100to be disposed on a substantially central portion of the first surface302of the substrate300.

The connection electrode124of the piezoelectric resonator100is connected to the connection electrode320by using the conductive adhesive340, and the connection electrode134of the piezoelectric resonator100is connected to the connection electrode322by using the conductive adhesive342.

The extended electrode320aextends from the connection electrode320towards one of the corner portions of the substrate300, and the extended electrode322aextends from the connection electrode322towards another corner portion of the substrate300. A plurality of outer electrodes330,332,334, and336are each formed on a corresponding one of the corner portions of the substrate300. In the example shown inFIG. 1, the extended electrode320ais connected to the outer electrode330formed on the corner portion in the negative direction of the X axis and on the negative-direction side of the Z′ axis, and the extended electrode322ais connected to the outer electrode332formed on the corner portion in the positive direction of the X axis and on a positive-direction side of the Z′ axis. As shown inFIG. 1, the outer electrodes334and336may be formed on the remaining corner portions. These outer electrodes may be dummy patterns that are not electrically connected to the piezoelectric resonator100. The dummy patterns may be electrically connected to terminals (terminals that are not connected to any other electronic elements) provided on a mounting substrate (not shown) on which the piezoelectric resonator unit is mounted. When such dummy patterns are formed, application of a conductive material for forming outer electrodes is facilitated. When outer electrodes are formed on all of the corner portions, a processing step of electrically connecting the piezoelectric resonator unit to other members is also facilitated.

In the example shown inFIG. 1, the corner portions of the substrate300each have a cutout side surface formed by cutting a portion thereof into a cylindrically curved shape (also called a castellation shape). The outer electrodes330,332,334, and336are each continuously formed from such a cutout side surface to the second surface304(lower surface). The shape of the corner portions of the substrate300is not limited to such a shape. The shape of each cutout may be a planar shape, or the corner portions may be angular without cutouts.

The structures of the connection electrodes, the extended electrodes, and the outer electrodes of the substrate300are not limited to the above-described examples, and may be variously modified and used. For example, the connection electrodes320and322may be disposed on different sides on the first surface302of the substrate300such that, for example, one of the connection electrodes320and322is formed on the positive-direction side of the Z′ axis, and the other of the connection electrodes320and322is formed on the negative-direction side of the Z′ axis. In such a structure, the piezoelectric resonator100is supported by the substrate300at two ends in the longitudinal direction. The number of outer electrodes is not limited to four, and may be, for example, two, each being disposed on a diagonal. The outer electrodes are not limited to those disposed on the corner portions, and may each be formed on any one of the side surfaces of the substrate300excluding the corner portions. In this case, as already described, each side surface may be formed into a cutout side surface formed by cutting a portion of the side surface into a cylindrically curved shape, and each outer electrode may be formed on a corresponding one of the side surfaces excluding the corner portions. Further, the outer electrodes334and336, which are dummy patterns, need not be formed. It is possible to achieve electrical conduction to the second surface304from the connection electrodes formed on the first surface302by using a through hole that is formed in the substrate300and that extends from the first surface302to the second surface304.

In the piezoelectric resonator unit1shown inFIG. 1, when alternating current is applied to a portion between the pair of first excitation electrode120and the second excitation electrode130of the piezoelectric resonator100via the outer electrodes330and332, the piezoelectric substrate110vibrates in a predetermined vibration mode, such as the thickness shear vibration mode, and resonance characteristics resulting from the vibration can be obtained.

Next, a method of manufacturing the piezoelectric resonator unit according to an embodiment of the present invention is described on the basis of the flowchart ofFIG. 3. In the embodiment, a method of manufacturing the piezoelectric resonator unit shown inFIGS. 1 and 2is described as an example.

As shown inFIG. 3, the piezoelectric resonator100is mounted on the substrate300by using the conductive adhesives340and342(S10).

First, the piezoelectric resonator100and the substrate300are prepared. When the piezoelectric resonator100is a quartz crystal resonator, first, a quartz crystal material is cut in the form of a wafer at a predetermined cut angle from synthetic quartz crystal or natural quartz crystal stones, and the material in the form of a wafer is cut with a dicing machine or etched into a predetermined rectangular external shape. Then, the resulting material is subjected to, for example, a sputtering method or a vacuum deposition method to form various electrodes including the first excitation electrode120and the second excitation electrode130. For example, a conductive material in the form of a paste is applied to a predetermined region on the first surface302of the substrate300, and the applied conductive material is fired, so that an electrode pattern including the connection electrodes, the extended electrodes, and the outer electrodes is formed. The electrode pattern may be formed even by combining as appropriate a sputtering method, a vacuum deposition method, or a plating method.

With, for example, the conductive adhesives340and342previously provided on the connection electrodes320and322of the substrate300or the connection electrodes124and134of the piezoelectric resonator100, after mounting the piezoelectric resonator100on the substrate300, the conductive adhesives340and342are subjected to thermosetting. The thermosetting of the conductive adhesives340and342are performed by, for example, keeping them at temperatures of approximately 180° C. to 190° C. for approximately 30 minutes.

Piezoelectric resonators100may be mounted on individual substrates300formed from a wafer-like substrate, or may be mounted on individual regions on the wafer-like substrate. When the piezoelectric resonators100are mounted on the wafer-like substrate, in a post-processing step, for example, the substrate300is cut with a dicing machine for each piezoelectric resonator100, and formed into individual pieces.

Next, the piezoelectric resonator100mounted on the substrate300is kept in a high-temperature-and-high humidity environment (S11).

More specifically, the piezoelectric resonator100on the substrate300is accommodated in a hermetically sealed space in a processing device, such as an oven. In air, the temperature and the humidity of the hermetically sealed space are controllable independently of a surrounding region, which is the manufacturing environment of the piezoelectric resonator unit.

Here, the temperature environment in Step S11may be, for example, in a range of 40° C. to 121° C. At less than 40° C., there is not much difference with the ambient temperature of the manufacturing environment (for example, 25° C.). At temperatures exceeding 121° C., the materials of the piezoelectric resonator100and the substrate300may deteriorate. Desirably, the temperature environment may be in a range of 92° C. to 98° C. (that is, near 95° C.)

The humidity environment in Step S11may be, for example, in a range of 70% RH to 95% RH. At less than 70% RH, there is not much difference with the ambient humidity of the manufacturing environment. At a humidity exceeding 95% RH, condensation may occur at the piezoelectric resonator100or the substrate300. Desirably, the humidity environment may be in a range of 82% RH to 88% RH (that is, near 85% RH).

The processing time in Step S11may be, for example, in a range of 30 minutes to 168 hours. At less than 30 minutes, the effect of high temperature and high humidity may not be easily provided. Processing times exceeding 168 hours may hinder the efficiency of the manufacturing process of the piezoelectric resonator unit. The longer the processing time, the greater the effect of high temperature and high humidity. Desirably, the processing time may be in a range of 30 minutes to 24 hours.

The temperature and humidity environment in Step11may be such that the temperature thereof is lower than and the humidity is higher than those in processing the conductive adhesives340and342(Step S10) or in processing the joining material350(Step S13). The processing time in Step11may be longer than that in processing the conductive adhesives340and342(Step S10) or that in processing the joining material350(Step S13).

Accordingly, by keeping the piezoelectric resonator100on the substrate300in an environment whose temperature and humidity are higher than those of the surrounding region for a predetermined time, changes in the physical properties of the conductive adhesives340and342caused by humidity are made to forcefully occur, and thermal stress remaining in the conductive adhesives340and342can be reduced. Since the conductive adhesives340and342are portions that mechanically and electrically connect the piezoelectric resonator100and the substrate300, they tend to be factors causing remaining thermal stress and physical changes resulting from humidity to vary the frequency characteristics of the piezoelectric resonator unit. Therefore, by the processing in Step S11, the variations in frequency characteristics of the piezoelectric resonator unit are revealed before frequency adjustment described below.

Since the above-described Step S11is performed before mounting the cap200and with the piezoelectric resonator100on the substrate300exposed to the outside, the temperature and the humidity of the conductive adhesives340and342can be easily controlled to a target temperature and a target humidity.

Next, frequency adjustment of the piezoelectric resonator100for acquiring desired frequency characteristics is performed (S12).

More specifically, plasma is formed in a vacuum. By applying a high voltage to Ar ions in the plasma, an ion beam of Ar ions is formed. The ion beam is applied to the first excitation electrode120of the piezoelectric resonator100(that is, the excitation electrode opposite to the side facing the substrate300). The first excitation electrode120of the piezoelectric resonator100is trimmed by etching it by using the ion beam, and its thickness is gradually reduced, so that the frequency of the piezoelectric resonator100is adjusted so as to gradually increase towards a desired target value. The amount of application of the ion beam can be controlled by opening and closing a shutter (not shown) provided between an ion beam applying source and the piezoelectric resonator100. Such a step of applying an ion beam may be performed once or a plurality of times in accordance with the difference between a measured value and the target value before the frequency adjustment. When performed a plurality of times, it is possible to measure frequency for each application to repeat the step of applying an ion beam based on such measured values and the target value.

In this way, when the frequency adjustment of the piezoelectric resonator100in Step S12is performed at any timing after the step of revealing the variations in the frequency characteristics in the aforementioned Step S11, it is possible to, by considering the variations in frequency characteristics that have been revealed by the aforementioned Step S11for different products, easily adjust the frequency characteristics to acquire the desired frequency characteristics.

Thereafter, the cap200is joined to the substrate300by using the joining material350(S13).

For example, when the joining material350is a resin adhesive, by, for example, a dipping method, the resin adhesive in the form of a paste is provided on the end surfaces205of the cap200, and the cap200can thereafter be joined to the substrate300. When the joining material350is a resin adhesive, after mounting the cap, the joining material is solidified by heating the joining material350in, for example, a range of 150° C. to 180° C., so that the cap200and the substrate300are joined to each other. Alternatively, the joining material350may be low-melting glass. In this case, after mounting the cap, the joining material350is fired by heating the joining material350in, for example, a range of 300° C. to 360° C., so that the cap200and the substrate300are joined to each other. Resin adhesive more easily causes the internal space206to be humid than glass material. However, according to the embodiment, the influence of humidity resulting from such resin adhesive can be suppressed. Therefore, this is also beneficial to the case in which a resin adhesive is used as the joining material350.

According to the method of manufacturing the piezoelectric resonator unit according to the embodiment, the piezoelectric resonator100mounted on the substrate300is kept in a high-temperature and high-humidity environment, and then frequency adjustment of the piezoelectric resonator100is performed. This makes it possible to, while revealing variations in frequency characteristics and considering the revealed variations in frequency characteristics according to products, perform frequency adjustment of the piezoelectric resonator100for acquiring desired frequency characteristics. Therefore, it is possible to easily manufacture a piezoelectric resonator unit having desired frequency characteristics.

Next, with reference toFIGS. 4 and 5, experimental examples of the step of keeping the piezoelectric resonator100in a high-temperature and high-humidity environment (Step S11inFIG. 3) are described.

The graph ofFIG. 4shows experimental data for high-temperature-and-high-humidity processing (Step S11). More specifically, the high-temperature-and-high-humidity processing (condition: temperature of 95° C. and humidity of 85% RH) was performed on four samples for corresponding processing times: (1) 0 minutes, (2) 30 minutes, (3) 2 hours, and (4) 24 hours. Then, in an environment test performed thereafter, these samples were allowed to stand at a temperature of 85° C. and a humidity of 85% RH for a predetermined time.FIG. 4shows frequency variations when the samples were allowed to stand at 85° C. and 85% RH for the predetermined time. The vertical axis of the graph ofFIG. 4indicates frequency variation rate [ppm] (ratio of the difference between resonance frequencies before and after the high-temperature-and-high-humidity processing with respect to the resonance frequency before the high-temperature-and-high-humidity processing, and the horizontal axis indicates the test time [hr] (time the samples were allowed to stand in the environment test).

The graph ofFIG. 5shows, of the graph ofFIG. 4, normal distributions of data after the samples were allowed to stand for 500 hours in the environment test (shows ±3 σ range and average values).

As shown inFIG. 4, the absolute value of the frequency variation rate can be made small when the high-temperature-and-high-humidity processing time is 30 minutes than when the high-temperature-and-high-humidity processing time is 0 minutes.FIG. 5shows that when the data after the samples were allowed to stand for 500 hours is seen in terms of average values, the longer the high-temperature-and-high-humidity processing time, the smaller the absolute value of the frequency variation rate, and the absolute value approaches 0 [ppm].

The above-described embodiments are each described to facilitate the understanding of the present invention, and are not to be construed as limiting the present invention. The present invention may be modified/improved without departing from the gist thereof, and includes equivalents thereof. That is, changes in design made by a person skilled in the art as appropriate to each embodiment are included within the scope of the present invention as long as they include the features of the present invention. For example, the elements, and the arrangements, materials, conditions, shapes, sizes, and the like of the elements in the embodiments are not limited to those exemplified, and may be changed as appropriate. The elements in the embodiments may be combined as long as it is technically possible, and such combinations are included within the scope of the present invention as long as they include the features of the present invention.

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