JP2000332571A - Piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric device which prevents frequency stability from decreasing due to an external force such as vibration, a shock, and changes of use environment conditions by minimizing the influence of thermal stress generated by a difference in coefficient of thermal expansion among a surface mount container, a conductive adhesive, and a crystal raw plate as a piezoelectric device in structure supporting a piezoelectric vibrator such as a crystal vibrator in the surface mount container at two points by using a conductive adhesive. SOLUTION: This piezoelectric device consists of raw quartz plate 2 which has a recessed part 3 at an arbitrary position on a main surface and also has a thin-plate area 4 on the bottom surface of the recessed part 3 and a thick reinforcement part 5 at the periphery of the recessed part 3, a crystal vibrating element 1 which is formed of electrode films 6 and 7 for excitation formed on both the surfaces of the thin plate area 4 of the quartz raw plate 2 and can excite thickness slip vibration, and the surface mount container 10 which supports the end edge of the reinforcement part 5 at two places by using adhesives, and the straight line connecting the two support places extends obliquely at ±(30±10) to the crystal axis zz' of the quartz raw plate 2.

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 stress applied to a piezoelectric vibrating element using a piezoelectric element having a thin plate region in a part of a main surface. The present invention relates to a technique for improving frequency stability due to a change.

[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. 4A and 4B are a plan view and a cross-sectional view taken along the line AA, respectively, showing the structure of a conventional quartz resonator. This quartz resonator uses an AT-cut quartz material and a xx ′ axis that is a crystal axis. The two corners of one end along the zz 'axis of the quartz vibrating element 1 formed in a rectangular shape or a strip shape along the zz' axis are formed on the surface mounting container 10 made of ceramic or the like.
And a structure in which the conductive adhesive 11 is used to fix and connect to the electrode 10a provided on the inner bottom surface. Further, the opening of the surface mount container 10 is hermetically sealed by the metal lid 12. Further, in order to realize a high frequency by the fundamental wave vibration, it is necessary to thin the quartz crystal plate 2, but there is a limit in machining technology to thin the whole plate into a film shape, Even if a film-shaped base plate is manufactured, workability such as handling becomes extremely poor. For this reason, as shown in the drawing, a part of one surface of the quartz crystal plate 2 constituting the crystal resonator element 1 is recessed into an arbitrary shape by a method such as chemical etching or ion etching, and is formed on the inner bottom surface of the recess 3. A thin plate region (vibrating portion) 4 is formed, and an outer peripheral portion surrounding the concave portion 3 is a thick reinforcing portion (annular surrounding portion) 5.
And On the upper and lower surfaces of the thin plate region 4 of the quartz crystal plate 2, electrode films 6 and 7 for exciting piezoelectric vibration are formed in arbitrary shapes, respectively, and lead electrodes 6a and 7a drawn out from the respective electrode films 6 and 7 are respectively provided. Extend to both corners of the piezoelectric element,
Each lead electrode 6a and the container-side electrode 10a are connected by the conductive adhesive 11.

However, when the crystal vibrating element 1 is directly mounted on the inner bottom surface of the container 10, differences in physical constants (particularly, thermal expansion coefficients) of the container 10, the conductive adhesive 11, and the quartz crystal plate 2 are different. Accordingly, stress is generated when, for example, the conductive adhesive is cured (heat-cured) and returned to room temperature. These stresses tend to propagate to the thin plate region 4 of the quartz crystal plate 2, resulting in frequency fluctuations. And these accumulated stresses
It was easily released due to the effects of vibration, shock, and use environment, and as a result, appeared as a factor of frequency instability, causing short-term and long-term frequency stability to deteriorate. In particular, when the quartz vibrating element is cantilevered as shown in the figure, a maximum stress occurs between two points connected by an adhesive, and then these stresses propagate while attenuating all over the quartz crystal plate. The stress sensitivity when the thin plate region 4 is formed in a part of the quartz plate increases in inverse proportion to the thickness of the thin plate region. For example, when a high frequency output is to be obtained by the fundamental vibration of the quartz plate, for example, 156 MHz In order to obtain the above, the thickness of the thin plate region 4 of the quartz crystal plate 2 becomes about 10 μm, and when further increasing the frequency, the thin plate region 4 becomes even thinner. Note that these relationships are defined as “thin plate region thickness”
= Expressed as "frequency constant" / "frequency". 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]

The problem to be solved by the present invention is that a piezoelectric vibrating element such as a quartz vibrating element is supported at two points in a cantilevered state using a conductive adhesive in a surface mount container. In a piezoelectric device, the effect of thermal stress caused by the difference in the coefficient of thermal expansion between the surface mount container or the conductive adhesive and the quartz crystal plate was minimized, resulting from external forces such as vibration and impact, and fluctuations in the use environment. An object of the present invention is to provide a piezoelectric device in which a decrease in frequency stability is prevented.

[0005]

According to a first aspect of the present invention, a concave portion is formed at an arbitrary position on a main surface to make a bottom surface of the concave portion a thin plate region. A quartz crystal plate having a thick reinforcing portion provided on the outer periphery thereof, and excitation electrode films respectively formed on both surfaces of a thin plate region of the quartz crystal plate, and a quartz vibrating element capable of exciting thickness shear vibration, In a piezoelectric device comprising: a surface mount container that supports the edge of the reinforcing portion of the crystal resonator element at two locations using an adhesive; a straight line connecting the two locations supported using the adhesive is:
The crystal plate extends in a tilt direction of ± (30 ± 10) degrees with respect to a crystal axis zz ′ of the quartz crystal plate. The invention according to claim 2 uses a quartz vibrating element capable of exciting thickness-shear vibration by forming excitation electrodes on both sides of a strip-shaped quartz crystal plate, and using an adhesive at two edges of the quartz vibrating element. In a piezoelectric device comprising a surface mounting container supported by the adhesive, the straight line connecting the two places supported by the adhesive is inclined at ± (30 ± 10) degrees with respect to the crystal axis zz ′ of the quartz plate. It extends in the direction. The invention according to claim 3 is characterized in that the quartz crystal plate used for the quartz vibrating element is an AT cut.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. Figures 1 (a), (b) and (c)
FIG. 1 is a plan view, a cross-sectional view taken along line BB, and a cross-sectional view taken along line CC of a piezoelectric device according to an embodiment of the present invention. The piezoelectric device is a crystal unit packaged for surface mounting. . This crystal resonator includes a crystal resonator element 1, a surface mount container 10 containing the crystal resonator element 1, and a metal lid 12 for hermetically sealing an opening of the surface mount container 10. It is. Crystal vibrating element 1
Is made of an AT-cut quartz material in a rectangular shape or a strip shape along the xx ′ axis and zz ′ axis which are crystal axes, and a part of one surface thereof is chemically etched or ionized. It is recessed into an arbitrary shape by a method such as etching, and a rectangular thin plate region (vibrating portion) 4 is formed on the inner bottom surface of the recess 3, and the outer peripheral portion surrounding the recess 3 is formed with a thick reinforcing portion ( (Circular surrounding portion) 5. Further, on the upper and lower surfaces of the thin plate region 4 of the quartz crystal plate 2, electrode films 6 and 7 for exciting the piezoelectric vibration are formed in an arbitrary shape, respectively, and an end of a lead electrode 6a drawn out from one of the electrode films 6 is formed. The portion is terminated at one corner 2A of the quartz crystal plate 2. On the other hand, the lead electrode 7a drawn from the other electrode film 7
Is disposed on the zz ″ axis extending from the corner 2A and inclined at an angle θ ｛± (30 ± 10) degrees｝ with respect to the zz ′ axis. That is, the lead electrode 7a is arranged on the zz ″ axis. And the raw plate edge 2B. And
The end of the lead electrode 6a located at one corner 2A where the xx 'axis and the zz' axis of the crystal vibrating element 1 intersect,
An electrode 10a on a pedestal provided on the inner bottom surface of a surface mount container 10 made of ceramic or the like is fixedly connected to the electrode 10a using a conductive adhesive 11, and furthermore, a lead at an intersection of the zz "axis and the edge 2B of the base plate The end of the electrode 7a is fixedly connected to the electrode 10b on the pedestal provided on the inner bottom surface of the surface mount container 10 using the conductive adhesive 11, and the container opening is hermetically sealed with a metal lid 12. In addition, in the illustrated example, the lead electrode 6a derived from the excitation electrode 6 formed on the surface of the base plate having the recess is connected to the corner 2A.
And the lead electrode 7a derived from the excitation electrode 7 formed on the flat base plate surface is extended to another connection portion on the zz "axis. This is an example, and this is an example. The positions where the portions extend may be reversed.

In this embodiment, when the AT-cut quartz crystal plate is adhered and supported at two points in the surface mount container 10, a straight line connecting the two connection portions by the conductive adhesive 11 has a crystal axis zz 'in advance. Since the direction is set to be inclined by ± (30 ± 10) degrees with respect to the axis, it is possible to minimize the influence of the stress generated at each of the connection portions. FIG. 2 is a schematic diagram showing a correlation between a horizontal axis of a general circular quartz crystal plate, that is, a pressure application angle θ based on a zz ′ axis of the quartz crystal plate, and a vertical axis, that is, a stress sensitivity ratio. It shows that when the pressure application angle θ from ′ is in the range of about ± 30 degrees, the sensitivity K approaches zero and is less affected by stress.
The present invention is based on the knowledge as shown in FIG. 2, and when the piezoelectric vibration element is bonded and supported at two points, the piezoelectric vibration element is fixed using a conductive adhesive at a position where the stress sensitivity is minimized. As a result, the frequency change caused by the fluctuation of the stress under the vibration, shock or heating conditions can be reduced to about ２. FIG. 3 is an explanatory view of a configuration of a crystal resonator element constituting a crystal resonator according to another embodiment of the present invention. The configuration using a strip (rectangular flat plate) as a quartz crystal plate is described in the above embodiment. Is different from the form. In other words, even in the case of a quartz resonator using a strip-shaped thickness-slip quartz crystal plate, when two points are cantilevered in the same manner as in the case of the quartz resonator using the ultra-thin quartz crystal plate, Thermal stress caused by the difference in the coefficient of thermal expansion between the surface mount container or the conductive adhesive and the quartz crystal plate causes external forces such as vibration and shock, and reduced frequency stability due to fluctuations in operating environment conditions. I do. In order to solve such a problem, in the quartz-crystal vibrating element according to the present embodiment, two connecting portions fixed in the surface mounting container 10 by the conductive adhesive 11 are arranged along the zz ″ axis. Have been placed.

That is, the excitation electrodes 6 and 7 are formed on both the front and back surfaces of the strip-shaped quartz crystal plate 2, and the lead electrode 6 a pulled out from one of the excitation electrodes 6 is terminated at one corner 2 A. Further, the lead electrode 7a drawn out from the other excitation electrode 7 is terminated at a position where the edge 2B of the base plate intersects the zz ″ axis. As described above, the zz ″ axis is the crystal axis zz. 'A straight line inclined ± (30 ± 10) degrees with respect to the axis. That is, the electrode 10 provided in the surface mount container
a and 10b are positions where the sensitivity to stress is most reduced. Therefore, by connecting the ends of the lead electrodes 6a, 7a to the electrodes 10a, 10b provided on the surface mount container with the conductive adhesive 11, respectively, the thermal expansion of the surface mount container or the conductive adhesive and the quartz crystal plate is achieved. A support structure that is least susceptible to the effects of thermal stress resulting from the difference in rate can be realized. As described above, in the crystal resonator of the present invention,
Surface mount container 10, conductive adhesive 11, and quartz plate 2
Due to the difference in thermal expansion coefficient between the two parts, even if the stress concentrated on the bonding part of the conductive adhesive propagates to the entire surface of the quartz crystal plate, the two connecting parts are located between the crystal axis zz 'axis ±
Since it is located on the zz ″ axis having an inclination angle of (30 ± 10) degrees, the stress that propagates to the vibrating part is greatly attenuated,
Fluctuations in frequency are effectively prevented. As a result, when the stress is released and changed due to external environmental factors such as impact, vibration, and change in the use environment, the width of the frequency that fluctuates due to the change is reduced, and the frequency stability can be improved. Further, even if the crystal resonator provided with the crystal resonator is exposed to a high-temperature environment such as reflow, the generation and propagation of stress can be suppressed, so that short-term frequency fluctuation is reduced. Furthermore, the stress generated and propagated on the quartz crystal plate side when the quartz vibrating element is cantilevered in the mounting container as in the prior art is greatly attenuated by employing the support structure of the present invention.
Frequency fluctuation due to long-term stress release can be reduced, and a stable and high-precision vibrator can be obtained. In each of the above-described embodiments, an example is shown in which the concave portion is formed only on one surface of the quartz crystal plate. Each of the above embodiments may be applied to a piezoelectric element plate, and similar effects can be obtained.

[0009]

As described above, according to the present invention, a depression is formed on at least one surface of a piezoelectric plate such as a quartz plate, and an electrode film for excitation is formed in a thin plate region on the bottom surface of the depression. When the piezoelectric vibrating element is adhered and supported in a surface mount container at two connection portions, vibration, external force such as impact, short-term stability when heat or the like during reflow is applied,
It is possible to provide a highly accurate and highly stable piezoelectric device at low cost while maintaining long-term aging stability. That is, according to the first aspect of the present invention, a quartz vibrating element using a quartz crystal plate having a structure in which the outer periphery of a thin plate region is surrounded and integrated by a thick reinforcing portion, and two lead electrodes on the quartz vibrating element are respectively bonded. In a piezoelectric device composed of a surface mount container supported by an agent, a straight line connecting two places supported by an adhesive is defined as ± (30 ± 10) with respect to the crystal axis zz ′ of the quartz plate.
It was configured to extend in the inclination direction. For this reason, the effect of thermal stress caused by the difference in the coefficient of thermal expansion between the surface mount container or the conductive adhesive and the quartz plate is minimized, and the frequency caused by external forces such as vibration and impact, and fluctuations in the operating environment conditions are minimized. A decrease in stability can be prevented. In particular, the edge of the quartz crystal plate supported at two points has a predetermined angle θ ｛± (3
0 ± 10) degree, the stress buffering effect can be exhibited. That is, since the two connecting portions are disposed along a straight line having an inclination of ± (30 ± 10) degrees with respect to the crystal axis zz ′ of the raw plate, the two connecting portions are not affected by the stress generated at each connecting portion. The sensitivity can be made as close to zero as possible, and the stability of the frequency of the crystal resonator element can be improved. According to the second aspect of the present invention, since the structure of the connecting portion is applied to the crystal resonator element using the strip-shaped quartz plate, the same effect as the first aspect can be obtained. According to the third aspect of the present invention, since the quartz crystal plate is AT-cut, when applied to a quartz oscillator or the like, the reliability can be enhanced and the value as a product can be enhanced.

[Brief description of the drawings]

FIGS. 1 (a), 1 (b) and 1 (c) are plan views of a principal part of a piezoelectric device according to an embodiment of the present invention, a sectional view taken along line BB, and a sectional view taken along line CC-
C sectional drawing.

FIG. 2 is a correlation diagram between a pressure applied angle θ and a stress sensitivity ratio.

FIG. 3 is a plan view of a crystal resonator element according to a second embodiment of the present invention.

FIGS. 4A and 4B are a plan view and a cross-sectional view taken along line AA, respectively, showing a package structure of a conventional crystal unit.

[Explanation of symbols]

1. Quartz vibrating element, 2 quartz crystal plate, 2A corner, 2B
Edge of raw plate, 3 concave portion, 4 thin plate region (vibrating portion), 5
Reinforcing part (annular surrounding part), 6, 7 Electrode film, 6a, 7a
Lead electrode, 10 surface mount container, 11 conductive adhesive, 12 metal lid.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03H 9/10 H01L 41/08 CF term (Reference) 5J079 AA04 BA43 BA49 HA04 HA05 HA16 HA22 JA01 5J108 AA04 BB03 CC04 CC11 DD02 EE03 EE07 EE18 FF07 FF11 FF13 GG03 GG15 GG16

Claims (3)

[Claims] A quartz plate having a concave portion formed at an arbitrary position on a main surface so that a bottom surface of the concave portion is a thin plate region, and a thick reinforcing portion provided on an outer periphery of the concave portion; A quartz vibrating element capable of exciting thickness-shear vibration, comprising excitation electrode films formed on both sides of the thin plate region of the base plate, and an edge of a reinforcing portion of the quartz vibrating element at two locations using an adhesive. In a piezoelectric device comprising: a surface mount container to be supported; and a straight line connecting two places to be supported by using the adhesive, a tilt direction of ± (30 ± 10) degrees with respect to a crystal axis zz ′ of the quartz plate. A piezoelectric device, wherein the piezoelectric device extends in a direction. 2. A quartz vibrating element capable of exciting thickness-shear vibration by forming excitation electrodes on both sides of a strip-shaped quartz crystal plate, and supporting two edges of the quartz vibrating element using an adhesive. A straight line connecting two places supported by the adhesive is inclined at ± (30 ± 10) degrees with respect to the crystal axis zz ′ of the quartz crystal plate. A piezoelectric device extending. 3. The crystal blank used in the crystal resonator element is an AT cut.
The piezoelectric device as described.