JP2000278079A - Piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric device wherein any outer force such as vibration or an impact or the deterioration of frequency stability due to the fluctuation of a use environment condition is prevented by reducing the influence of a thermal stress generated due to the difference of the thermal expansion ratios of the surface mounted container or the conductive adhesive and a crystal base plate to the minimum, with respect to a piezoelectric device having such a structure that a crystal vibrating element is supported in a cantilever state by using conductive adhesive in a surface mounted container. SOLUTION: This piezoelectric device is provided with a piezoelectric vibrating element equipped with a piezoelectric base plate having a superthin vibrating part on the inner bottom face of a recessed part 3 formed on one face, and a thick circular surrounding part 5 at the periphery of the recessed part and electrode films 6 formed on the both faces of the piezoelectric base plate, and a surface mounted container 10 for housing the piezoelectric vibrating element. In this case, one end of the piezoelectric vibrating element is connected and fixed through conductive adhesive 22 on a piezoelectric element piece fixed to the inner bottom face of the surface mounted container 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for increasing the frequency of a surface mount type piezoelectric device, and more particularly, to a thermal or mechanical method for a piezoelectric vibrating element formed by thinning a part of the plane of a rectangular or strip-shaped piezoelectric element plate. The present invention relates to a piezoelectric device that has solved the problem that the frequency stability is reduced due to a change in mechanical stress.

[0002]

2. Description of the Related Art Piezoelectric devices such as a piezoelectric vibrator using a piezoelectric vibrating element typified by a quartz crystal include a piezoelectric oscillator,
It is used as an indispensable main part in various electronic devices, especially in communication devices, as a resonator or a filter. In recent years, various types of piezoelectric vibrating elements have been proposed in order to satisfy the demand for higher frequency, while making the piezoelectric element plate ultra-thin, while taking into account the mechanical strength that is reduced by making it ultra-thin. Have been. 5 (a) and 5 (b) are a plan view and a longitudinal sectional view showing a package structure of a conventional crystal unit. This crystal unit is formed by forming an AT-cut crystal material into a rectangular or strip shape. A structure is provided in which one end of the crystal resonator element 1 is fixedly connected to the inner bottom surface of a surface mounting container 10 made of ceramic or the like in a cantilever state using a conductive adhesive 11. There is also known a type in which a protruding step is provided on the inner bottom surface of the surface mount container, and the quartz vibrating element is supported in a cantilever state using a conductive adhesive on the step. Further, in order to realize a high frequency by the fundamental wave vibration, it is necessary to make the quartz crystal plate 2 thin. However, there is a limit from machining technology to make the whole plate thin in a film shape. Even if a plate-shaped base plate is manufactured, the mechanical strength is remarkably reduced and the plate is easily broken, so that workability such as handling is extremely deteriorated. For this reason, as shown in the drawing, a part of one surface of the crystal element plate 2 constituting the crystal resonator element 1 is recessed into an arbitrary shape by chemical etching or the like.
A thin plate region (vibrating portion) 4 is formed on the inner bottom surface of the concave portion 3,
An outer peripheral portion surrounding the concave portion 3 is a thick reinforcing portion (annular surrounding portion) 5.

On the upper and lower surfaces of the thin plate region 4 of the quartz crystal plate 2, an electrode film 6 for exciting piezoelectric vibration is formed in an arbitrary shape. However, when the crystal resonator element 1 is directly mounted on the inner bottom surface of the container 10, the container 10 and the conductive adhesive 1
Due to the difference between the respective physical constants (particularly the coefficient of thermal expansion) of the crystal element 1 and the quartz crystal plate 2, stress is generated when, for example, the conductive adhesive is cured (heat-cured) and returned to room temperature. These stresses propagate directly to the quartz crystal plate 2 to cause frequency fluctuation. In addition, these accumulated stresses are easily released due to the effects of vibration, shock, operating environment, etc., and consequently appear as frequency fluctuations of the quartz plate, degrading short- and long-term frequency stability. Was causing a malfunction. In particular, when a high-frequency output is to be obtained by the fundamental wave vibration of the crystal element plate, for example, when 156 MHz is to be obtained, the thickness of the thin plate region 4 of the crystal element plate 2 is about 10 μm, and the frequency is further increased. In that case, the thin plate area 4 becomes even thinner. As described above, as the thin plate region 4 of the quartz crystal plate becomes thinner, the stress concentrates on the thin plate region 4 and becomes large, and the width of the frequency fluctuation becomes extremely large in proportion thereto.

[0004]

An object of the present invention is to provide a piezoelectric device having a structure in which a quartz-crystal vibrating element is supported in a cantilevered state by using a conductive adhesive in a surface-mounted container. Of the thermal stress caused by the difference in the thermal expansion coefficient between the crystal expansion plate and the conductive adhesive and the quartz plate to minimize the frequency stability caused by external forces such as vibration and shock, and fluctuations in the operating environment It is an object of the present invention to provide an improved piezoelectric device.

[0005]

In order to solve the above-mentioned problems,
According to the first aspect of the present invention, there is provided a piezoelectric element plate having an ultra-thin vibrating portion on the inner bottom surface of a concave portion formed on one surface and a thick annular surrounding portion on the outer periphery of the concave portion, and both surfaces of the piezoelectric element plate. A piezoelectric vibrating element having an electrode film formed thereon, and a surface mount container accommodating the piezoelectric vibrating element, wherein the piezoelectric element is fixed on a piezoelectric element fixed to the inner bottom surface of the surface mount container. One end of the vibration element is connected and fixed by a conductive adhesive. The invention according to claim 2 is characterized in that the piezoelectric element is a crystal element, and the piezoelectric element is a crystal element having a crystal cutting orientation equivalent to that of the crystal element. According to a third aspect of the present invention, a metallized portion is formed on the upper and lower surfaces and side surfaces of the corners of the piezoelectric element, and a lead electrode extending from both electrode films of the piezoelectric element is electrically conductive in a state of being superposed on each metallized portion. It is characterized by being fixed with a conductive adhesive. The invention according to claim 4 is such that the piezoelectric element is fitted and housed in a cavity provided on an inner bottom surface of the surface mount container,
One end of the piezoelectric vibrating element is connected to the upper surface of the piezoelectric element projecting from the inner bottom surface of the surface mount container by a conductive adhesive. The invention according to claim 5 is characterized in that the piezoelectric element pieces are superimposed and fixed with a conductive adhesive so that the crystal cutting directions of the piezoelectric element plate and the piezoelectric element plate coincide with each other. The invention according to claim 6 is that, as the piezoelectric element plate,
It is characterized by using a flat base plate.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIGS. 1A and 1B are a plan view of a main part of a piezoelectric device according to a first embodiment of the present invention and a cross-sectional view taken along line AA. The same parts as those of the piezoelectric device shown in FIG. Further, in the present embodiment, a description will be given using a quartz vibrating element as an example of the piezoelectric vibrating element. This piezoelectric device (quartz oscillator) supports the crystal vibrating element 1 in a cantilever state on the inner bottom surface of a surface mounting container 10 such as a ceramic package, and hermetically seals an opening of the surface mounting container 10 with a metal cover (not shown). It has the following configuration. The point that the crystal unit of this embodiment is different from the conventional one is that the crystal unit 1 is not directly adhered to the inner bottom surface of the surface mount container 10 but the crystal unit 20 is fixed on the crystal element piece 20 fixed to the inner bottom surface in advance. The point is that the vibration element 1 is connected and fixed in a cantilever state. Hereinafter, the present embodiment will be described in detail. A concave portion 3 having an arbitrary shape is formed at an arbitrary position on the surface of a quartz crystal plate 2 made of an AT-cut quartz plate, and an inner bottom surface of the concave portion 3 is a thin plate region (vibrating portion) 4. I have. The thick portion on the outer periphery of the thin plate region 4 is a reinforcing portion (annular surrounding portion) 5. On the upper and lower surfaces of the thin plate region 4, electrode films 6 for exciting thickness-shear vibration are formed. Lead electrodes 6 a are drawn out from the respective electrode films 6, and each lead electrode 6 a terminates at two corners of the quartz crystal plate 2. In this example, an example is shown in which the crystal vibrating element 1 is supported such that the concave portion 3 of the quartz crystal plate 2 faces upward. However, this is merely an example, and the concave portion may be directed downward, or the concave portion may be directed downward. It is also possible to use a conventional quartz-crystal vibrating element using a plate-shaped elementary plate that does not have the same.

The surface mounting container 10 is made of, for example, a ceramic material having a seam ring 12 on the upper surface of an outer frame. The crystal element 20 has an arbitrary shape having a crystal cutting direction equivalent to that of the crystal element plate 2, and is formed by vapor deposition or sputtering from the upper and lower surfaces to the side surfaces at both corners of one side of the crystal element 20. A metallized portion 21 is formed. In this example, the crystal element piece 20 has the same area as the crystal element plate 2,
Although the area is larger than the quartz crystal plate, this is only an example as described later. The material of the surface mount container 10 may be a material other than ceramic, for example, resin or glass. The crystal element 20 is formed by positioning and mounting the metallized portion 21 of the crystal element 20 on a conductive adhesive 22 applied on a metallization pattern (not shown) formed on the inner bottom surface of the surface mount container 10. It is fixed to the bottom inside the container. As shown in FIG.
It is preferable to fix the cantilever to the inner bottom surface of the container. If necessary, the conductive adhesive 22 may be applied to the side and upper surfaces of the metallized portion 21 of the crystal element. Next, a conductive adhesive 11 is applied on each metallized portion 21 exposed on the upper surface of both corners of the crystal element piece 20, and then the terminal ends of the lead electrodes 6 a pulled out from the respective electrode films 6 of the crystal vibrating element 1. The parts are overlapped and glued. The crystal vibrating element 1 is supported on the crystal element piece 20 in a cantilever state. Further, as shown in the figure, the conductive adhesive 11 is applied also from the side surface to the upper surface of each corner of the crystal resonator element 1. When the crystal resonator element 1 is connected to the crystal element 20, the crystal cutting direction of the crystal element 20 is set in advance so that the crystal cutting directions of the two are the same. After the mounting of the crystal resonator element 1 in this manner, the inside of the container is hermetically sealed by fixing a metal cover (not shown) to the opening of the container. In this embodiment, the quartz vibrating element 1 is not fixed to the inner bottom surface of the surface mount container 10 having a different coefficient of thermal expansion, but is fixed via the crystal element 20. Stress from the surface mount container 10 generated due to external force such as vibration and shock is absorbed and reduced by the crystal element 20, and the crystal element 20 has the same thermal expansion coefficient as the crystal vibrating element 1. As a result, thermal distortion does not occur between the crystal element 20 and the crystal vibrating element 1, and as a result, frequency fluctuation is prevented.

FIGS. 2A and 2B are a plan view and a sectional view taken along line B--B of another embodiment of the present invention. The crystal element 20 and the crystal vibrating element 1 are collectively formed on the inner bottom surface of the container by using a conductive adhesive 25 without forming a metallized portion on the crystal element. The configuration fixed in this way is different from the configuration of the above embodiment. That is, in this embodiment, the width of the quartz crystal plate 2 is wider than that of the quartz
Is placed on the inner bottom surface of the surface mounting container 10 so as not to cover the upper surface of a metallized pattern (not shown), and then the conductive adhesive 11 is applied on both corners of the quartz element 20. Then, the crystal vibrating element 1 is adhered onto the crystal element piece 20 so as to be in a cantilever state. Thereafter, the crystal element 20 and the crystal vibrating element 1 adhere to the inner bottom surface of the container,
Further, a conductive adhesive 11 is further applied so that the lead electrode 6a of the crystal resonator element is electrically connected to the metallized pattern.
Thereafter, the container is hermetically sealed by fixing a metal lid (not shown) to the container opening. As described above, in each of the above embodiments, the quartz vibrating element is not directly fixed to the inner bottom surface of the surface mount container, but the quartz vibrating element is bonded and mounted on the inner bottom surface of the container via a crystal element. Even if there is a difference in thermal expansion coefficient between the container and the quartz crystal plate, the generated stress is absorbed by the synergistic effect of the interposed quartz crystal piece and the conductive adhesive, and the Ripple is suppressed. For this reason, the frequency fluctuation of the crystal vibrating element is suppressed, and the reliability can be improved. In particular, the stress generated and propagated due to expansion and contraction due to the thermal expansion of the container is absorbed by the conductive adhesive interposed between the crystal element and the container, and the crystal element and the crystal plate are cut. Since the orientations are matched, the expansion and contraction due to thermal expansion become equal, and the stress generated due to the difference in physical properties of the materials is suppressed. Further, the stress is further absorbed by the conductive adhesive interposed between the crystal element and the crystal element plate, and is greatly reduced. As a result of the successive reduction of the stress in this manner, it is possible to obtain the effect of reducing the frequency fluctuation due to the release of the stress due to vibration, impact, environmental fluctuation, and the like. Also, since the crystal cutting direction of the piezoelectric element and the crystal cutting direction of the piezoelectric element plate are overlapped and fixed with a conductive adhesive, the piezoelectric element suppresses vibration of the piezoelectric vibration element. No longer a factor. In the present invention,
Although the ceramic is exemplified as the material of the surface mount container, another material (for example, resin or glass) may be used.

Next, FIG. 3 is a plan view of a main part of a piezoelectric device according to another embodiment of the present invention and a cross-sectional view taken along the line CC. The configuration of the piezoelectric vibrating element 1 is the same as that of each of the above embodiments. However, the configuration of the surface mount container 10 is different. That is, the surface mount container 10 is made of, for example, a ceramic material, and has a flat bottom plate 30, a middle plate 31 laminated on the bottom plate 30, and a seam ring 32 erected along the outer periphery of the upper surface of the middle plate 31. From one. A cavity 31a is formed at an appropriate position on the middle plate 31. A current-carrying electrode is formed on the inner bottom surface of the cavity 31a, and the current-carrying electrode is connected to an external electrode (not shown) provided on the container bottom surface. Next, the quartz crystal plate 2 is placed in the cavity 31a.
A rectangular rod-shaped crystal element 35 having the same crystal cutting direction as that described above is fitted and accommodated, and the conductive adhesive 36 is filled in the cavity 31a to fix the crystal element 35. The height of the crystal element 35 is set in advance so that the upper surface thereof slightly protrudes from the upper surface of the middle plate 31. At this time, care is taken so that the electrode provided on the inner bottom surface of the cavity and the conductive adhesive 36 are sufficiently conducted. Thereafter, the crystal plate 2 is superposed on the upper surface of the crystal element piece 35 so as to be aligned with the crystal cutting direction of the crystal plate 2 and cured with the conductive adhesive 37.
If necessary, the conductive adhesive 37 may be overcoated so as to be electrically connected to the lead electrode 6a on the upper surface of the crystal resonator element 1. Each lead electrode 6a is connected to an electrode on the bottom surface in the cavity via a conductive adhesive 37 and a conductive adhesive. In the present invention, ceramics is exemplified as the material of the surface mount container, but other materials (for example, resin and glass) may be used. In addition, by arbitrarily selecting the thickness of the crystal element piece with respect to the thickness of the middle plate (depth of the cavity) of the container, the quartz crystal plate 2 and the top surface of the middle plate (bottom surface in the container) are selected.
Can be freely controlled, and an effect of greatly improving the drop resistance characteristics can be obtained.

FIG. 4 is a modification of FIG. 3, which is different from the first embodiment in that a flat plate is used as the quartz plate 2 constituting the quartz vibrating element 1. Except that the quartz crystal plate is a rectangular flat plate, there is no difference from the embodiment of FIG. In addition, the quartz crystal plate used for the quartz-crystal vibrating element of the present invention may have a bevel shape or a convex shape. As described above, in the embodiment of FIGS. 3 and 4, a cavity is provided on the inner bottom surface of the surface mount container, and a crystal element is fixed in the cavity with a conductive adhesive, and protruded from the inner bottom surface of the container. Since the crystal resonator element is fixed on the upper surface of the crystal element, even if there is a difference in the coefficient of thermal expansion between the container and the crystal element, it is generated by the synergistic effect of the interposed crystal element and the conductive adhesive. The resulting stress is absorbed, and the ripple to the quartz vibrating element is suppressed. For this reason, the frequency fluctuation of the crystal vibrating element is suppressed,
Reliability can be improved. In particular, the stress generated and propagated due to expansion and contraction due to thermal expansion of the container is absorbed by the conductive adhesive interposed between the crystal element and the container,
Further, since the crystal element and the crystal plate have the same crystal cutting direction, the expansion and contraction due to thermal expansion become equal, and the stress generated due to the difference in physical properties of the materials is suppressed. Further, the stress is further absorbed by the conductive adhesive interposed between the crystal element and the crystal element plate, and is greatly reduced. Also, since the crystal cutting direction of the piezoelectric element and the crystal cutting direction of the piezoelectric element plate are overlapped and fixed with a conductive adhesive, the piezoelectric element suppresses vibration of the piezoelectric vibration element. No longer a factor. The present invention can be applied not only to a piezoelectric vibrator such as a quartz oscillator but also to a piezoelectric oscillator such as a crystal oscillator and other piezoelectric devices in general.

[0011]

As described above, according to the present invention, in a piezoelectric device having a structure in which a quartz-crystal vibrating element is supported in a cantilever state by using a conductive adhesive in a surface mount container, the surface mount container and the conductive adhesive The effect of thermal stress caused by the difference between the thermal expansion coefficient of the agent and the quartz plate is minimized, and external forces such as vibration and impact,
It is possible to prevent a decrease in frequency stability due to a change in use environment conditions. That is, according to the first aspect of the present invention, one end of the piezoelectric vibrating element is connected and fixed to the piezoelectric element fixed to the inner bottom surface of the surface mount container by a conductive adhesive. It comes into contact with a container made of a different material via the agent, so that the stress transmitted from the container due to an external force, a change in the temperature environment, or the like can be eliminated beforehand, and the frequency fluctuation of the piezoelectric vibration element can be suppressed. The present invention
In particular, when applied to a piezoelectric vibrating element using a piezoelectric element of a type having a concave portion and an ultra-thin vibrating portion provided on the inner bottom surface of the concave portion, frequency fluctuation due to external stress and thermal stress Can be effectively prevented. The present invention can be generally applied to piezoelectric devices such as a piezoelectric vibrator and a piezoelectric oscillator. According to a second aspect of the present invention, a crystal element is used as the piezoelectric element, and a crystal element having a crystal cutting direction equivalent to that of the crystal element is used as the piezoelectric element. The effect can be exhibited in the crystal resonator. According to a third aspect of the present invention, a metallized portion is formed on the upper and lower surfaces and side surfaces of the corners of the piezoelectric element, and a lead electrode extending from both electrode films of the piezoelectric element is electrically conductive in a state of being superposed on each metallized portion. Since it was fixed with a conductive adhesive,
The continuity between the electrode formed on the inner bottom surface of the surface mount container and the electrode film can be easily secured. According to a fourth aspect of the present invention, the piezoelectric element is fitted and housed in a cavity provided on an inner bottom surface of the surface mount container, and one end of the piezoelectric vibrating element is provided on an upper surface of the piezoelectric element protruding from the inner bottom surface of the surface mount container. Are connected by a conductive adhesive, so that not only the same frequency fluctuation preventing effect as in claims 1 and 2 can be exerted, but also the thickness of the crystal element piece with respect to the thickness of the middle plate of the container (depth of the cavity) is arbitrary. In this case, it is possible to freely control the gap generated between the quartz crystal plate and the upper surface of the middle plate (the inner bottom surface of the container), and it is possible to obtain an effect of greatly improving the drop resistance. According to a fifth aspect of the present invention, the piezoelectric element is overlaid and fixed with a conductive adhesive so that the crystal cutting direction of the piezoelectric element coincides with the crystal cutting direction of the piezoelectric element. It does not become a factor that suppresses the vibration of the motor. In the invention according to claim 6, a flat plate is used as the piezoelectric plate. That is, the shape and type of the piezoelectric element constituting the piezoelectric vibration element used in the present invention may be of any type.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a cross-sectional view taken along line AA of a main part of a piezoelectric device according to a first embodiment of the present invention.

FIGS. 2A and 2B are a plan view and a BB cross-sectional view of a main part of another embodiment of the present invention.

FIGS. 3A and 3B are a plan view and a CC sectional view of a main part of a piezoelectric device according to another embodiment of the present invention.

4A and 4B are views showing a modification of FIG. 3;

FIGS. 5A and 5B are a plan view and a longitudinal sectional view showing a package structure of a conventional crystal unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Quartz vibrating element, 2 quartz crystal plate, 3 concave part, 4 thin plate area (vibrating part), 5 reinforcing part (annular surrounding part), 6 electrode film, 6a lead electrode, 10 surface mount container, 11 conductive adhesive, 12 seam rings, 20 crystal pieces, 2
Reference Signs List 1 metallized portion, 22 conductive adhesive, 25 conductive adhesive, 30 bottom plate, 31 middle plate, 31a cavity, 35 crystal element, 36 conductive adhesive, 37 conductive adhesive.

Claims (6)

[Claims] 1. A piezoelectric plate having an ultra-thin vibrating portion on the inner bottom surface of a concave portion formed on one side and a thick annular surrounding portion on the outer periphery of the concave portion, and a piezoelectric plate on both surfaces of the piezoelectric plate, respectively. A piezoelectric vibrating element comprising: a formed electrode film; and a surface mount container accommodating the piezoelectric vibratory element. The piezoelectric device comprising: a piezoelectric element fixed on an inner bottom surface of the surface mount container; A piezoelectric device having one end connected and fixed by a conductive adhesive. 2. The piezoelectric element according to claim 1, wherein said piezoelectric element is a crystal element, and said piezoelectric element is a crystal element having a crystal cutting direction equivalent to that of said crystal element. device. 3. A metallized portion is formed on the upper and lower surfaces and the side surfaces of the corners of the piezoelectric element, and a lead electrode extending from both electrode films of the piezoelectric element is conductively bonded in a state of being superposed on each metallized portion. 3. The piezoelectric device according to claim 1, wherein the piezoelectric device is fixed by an agent. 4. The piezoelectric element is fitted and accommodated in a cavity provided on the inner bottom surface of the surface mount container, and one end of the piezoelectric vibrating element is electrically connected to the upper surface of the piezoelectric element protruding from the inner bottom surface of the surface mount container. The piezoelectric device according to claim 1, wherein the piezoelectric device is connected by a conductive adhesive. 5. The piezoelectric element according to claim 1, wherein the crystal cutting direction of the piezoelectric element and the crystal cutting direction of the piezoelectric element plate coincide with each other and are fixed by a conductive adhesive. 5. The piezoelectric device according to 3 or 4. 6. The piezoelectric device according to claim 1, wherein a flat plate is used as the piezoelectric plate.