JP2005094254A - Piezoelectric resonance element, piezo-resonator, filter, and composite substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric resonance element which can reduce in thickness a piezoelectric substrate and which can prevent the piezoelectric substrate from cracking, and to provide a piezo-resonator, a filter using the same, and a composite substrate. <P>SOLUTION: The piezoelectric resonance element is obtained by forming an interdigital transducer (IDT) made of a pair of combtooth-like electrodes 5 on a part of a main surface of one side of the piezoelectric substrate 1a, and providing a groove 6 for reflecting a surface wave of an SH type in parallel adjacent to the electrode finger 55a at the outside of the electrode finger 55a of the IDT on a main surface of one side of the piezoelectric substrate 1a. A reinforcing substrate 1b is adhered with a synthetic resin to the main surface of the other side of the piezoelectric substrate 1a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric resonator, a piezoelectric resonator and a filter, and a composite substrate, and more particularly to an end-face reflection type piezoelectric resonator using a surface wave of an SH wave applied to a resonator, a filter, and the like, a piezoelectric resonator, and the same And a composite substrate.

  Conventionally, microcomputers and the like have been frequently used for communication devices and electronic devices, and a clock oscillation circuit or the like has been connected to such microcomputers.

  Here, in the oscillation circuit, two load capacitance components 15 (C1, C2) are connected between the both ends of the piezoelectric resonant element 1 and the ground potential, as in the equivalent circuit shown in FIG. A feedback resistor 13 and an inverter 14 are connected between both ends of 1.

  Generally, in order to obtain stable oscillation, it is necessary to increase the P / V value of the main vibration of the piezoelectric resonant element. The P / V value is expressed by 20 × log (Ra / Rb), where Ra is defined as an anti-resonance impedance and Rb is defined as a resonance impedance.

  Conventionally, in order to reduce the size of a piezoelectric resonator element as an oscillator, an end surface reflection type surface wave resonator element using a surface wave or a surface wave device with a lead in which the surface wave resonator element is covered with an exterior resin, etc. The structure is proposed.

Moreover, as such an end face reflection type, in order to suppress spurious, an end face reflection type piezoelectric resonance in which a groove or a recess is provided in the piezoelectric substrate and the upper end face of the substrate end face or the inner face of the groove is a reflection end face. An element is disclosed (for example, see Patent Document 1).
JP 2001-119266 A

  In recent years, there has been a demand for miniaturization and thinning of the piezoelectric resonant element, but since the strength of the piezoelectric substrate itself is low, it is necessary to ensure a certain thickness, and there is a limit to thinning. That is, when the piezoelectric substrate is made thin in order to reduce the thickness, there is a problem that the piezoelectric substrate is likely to be leaked due to the low strength of the piezoelectric ceramic.

  In particular, as shown in Patent Document 1, when a groove or a recess is provided in a piezoelectric substrate and the upper end surface of the substrate end surface or the inner surface of the groove is used as a reflection end surface, good reflection characteristics can be obtained. Or since the thickness in the part which formed the recessed part was thin, there existed a problem that a crack would generate | occur | produce easily from this part.

  In order to prevent the occurrence of such cracking of the piezoelectric substrate, it is necessary to increase the thickness of the piezoelectric substrate. However, this makes it impossible to reduce the thickness of the piezoelectric resonant element.

  An object of the present invention is to provide a piezoelectric resonator element, a piezoelectric resonator, a filter using the piezoelectric resonator, and a composite substrate that can reduce the thickness of the piezoelectric substrate and prevent cracking.

  The inventors of the present invention can reinforce the piezoelectric substrate by bonding a high-strength reinforcing substrate to a piezoelectric substrate generally composed of a low-strength piezoelectric ceramic, and prevent the piezoelectric resonant element from being damaged. Even if it is bonded to the substrate, surface waves are used, so there is almost no effect on the resonance characteristics, and the piezoelectric substrate can be thinned to separate bulk wave vibrations to prevent spurious generation. The inventors have found that it is possible to reduce the thickness and prevent cracking of the piezoelectric resonant element and obtain good resonance characteristics, and the present invention has been achieved.

  That is, the piezoelectric resonant element of the present invention forms an interdigital transducer (IDT) composed of a pair of comb electrodes on a part of one side main surface of a piezoelectric substrate having a thickness of 320 μm or less and the other side main piezoelectric substrate. A reinforcing substrate is bonded to the surface with a synthetic resin.

  In addition, the piezoelectric resonant element of the present invention forms an interdigital transducer (IDT) comprising a pair of comb electrodes on a part of one side main surface of the piezoelectric substrate, and the IDT electrode on one side main surface of the piezoelectric substrate. A piezoelectric resonant element having a groove on the outside of a finger adjacent to the electrode finger for reflecting SH type surface waves in parallel, and a reinforcing substrate is synthesized on the other principal surface of the piezoelectric substrate It is characterized by being bonded with a resin. The thickness of the piezoelectric substrate is desirably 320 μm or less.

  As described later, by reducing the thickness of the piezoelectric substrate to 320 μm or less, it is possible to separate the surface wave and bulk wave vibration of the SH wave, and when applied as a resonator, stable oscillation can be obtained. Become.

  Therefore, the resonance characteristic is better as the piezoelectric substrate is thinner, and it meets the requirement for thinning. However, as the thickness of the piezoelectric substrate is reduced, the strength of the piezoelectric substrate is lowered. There is a tendency for the strength to decrease in the groove formed in parallel with the electrode finger provided in order to make it possible.

  Therefore, in the piezoelectric resonant element of the present invention, the reinforcing substrate is bonded to the other main surface of the piezoelectric substrate with a synthetic resin to reinforce the piezoelectric substrate and prevent damage even if the piezoelectric substrate is thinly formed. In particular, in a piezoelectric resonant element provided with a groove for reflecting SH type surface waves, the strength is low in the groove portion of the piezoelectric substrate and cracking easily occurs. In the present invention, the piezoelectric substrate is reinforced by the reinforcing substrate. For this reason, even if the groove is formed, the crack from the groove portion can be prevented.

  Further, since the piezoelectric substrate can be made thin, it is possible to separate the surface wave and bulk wave vibration of the SH wave, to prevent spurious generation, and to obtain stable oscillation.

  Furthermore, since an SH type surface wave having an IDT composed of a comb-teeth electrode is partially used on one main surface of the piezoelectric substrate, the vibration part can be concentrated only on one side of the piezoelectric substrate, Even if it adheres to the piezoelectric substrate, it does not affect the resonance characteristics.

  Moreover, the piezoelectric resonant element of the present invention is characterized in that the groove penetrates the piezoelectric substrate. In such a piezoelectric resonant element, the SH type surface wave can be completely reflected, and the resonance characteristics can be improved.

  Furthermore, the piezoelectric resonant element of the present invention is characterized in that the groove is continuously formed from one end face to the other end face of the piezoelectric substrate. If the length of the groove constituting the reflection end surface for reflecting the SH type surface wave is longer than the crossing length of the electrode fingers of the comb-teeth electrode, the reflection of the SH type surface wave can be further improved and spurious generation can be further improved. It can be effectively suppressed. That is, spurious generation near the resonance and anti-resonance can be suppressed, and a large P / V value can be obtained. Further, in such a piezoelectric resonant element, it is possible to easily form a groove during manufacturing.

The piezoelectric resonant element of the present invention is characterized in that the Young's modulus of the synthetic resin for bonding the piezoelectric substrate and the reinforcing substrate is 1 × 10 ¹⁰ Pa or less. In such a piezoelectric resonant element, it is possible to damp the bulk wave and reduce the P / V value of the bulk wave.

Furthermore, the piezoelectric resonant element of the present invention is characterized in that the load per unit area of the IDT is 2 × 10 ⁻⁵ g / cm ² or more. In such a piezoelectric resonance element, the mass load effect of the electrode load applied to the electrode substrate is increased, the so-called energy confinement effect in which the SH wave type surface wave vibration is concentrated in the vicinity of the electrode is increased, and the P / V value is increased. can do.

In the piezoelectric resonant element of the present invention, the reinforcing substrate is mainly composed of one or more of Al ₂ O ₃ , MgO, ZrO ₂ , AlN, Si ₃ N ₄ , and SiC. In such a piezoelectric resonant element, since the strength of the reinforcing substrate is high, the thickness of the reinforcing substrate can be reduced, and the thickness of the piezoelectric resonant element can be reduced. The reinforcing substrate is desirably a material that can provide sufficiently high strength and high toughness than a piezoelectric ceramic even if the thickness of the reinforcing substrate is reduced, since a high strength can be obtained even if the product thickness is reduced. For this, a material mainly composed of alumina Al ₂ O ₃ , partially stabilized zirconia ZrO ₂ , stabilized zirconia ZrO ₂ , magnesia MgO, silicon nitride Si ₃ N ₄ , silicon carbide SiC, or the like is desirable.

  The piezoelectric resonator according to the present invention has a space for accommodating the IDT so as to face one side main surface of the piezoelectric substrate in which the IDT of the piezoelectric substrate is formed and does not disturb the vibration of the SH type surface wave. A base substrate is bonded to the piezoelectric substrate so as to be formed.

  In such a piezoelectric resonator, since an SH type surface wave provided with an IDT made of a comb-like electrode is partially used on one side main surface of the piezoelectric substrate, the vibration part is concentrated only on one side of the piezoelectric substrate. Therefore, the base substrate disposed for the purpose of forming and sealing a vibration space that does not hinder vibration may be disposed only on one side main surface of the piezoelectric substrate on which the comb electrodes are formed. A laminated structure of the resonant element and the base substrate can be used as a basic structure, and since the piezoelectric resonant element does not need to be covered with a casing, the thickness of the piezoelectric resonator can be significantly reduced.

  In addition, the piezoelectric resonator of the present invention is provided with a groove for reflecting SH type surface waves in parallel with the electrode finger on the outer side of the electrode finger of the IDT on one side main surface of the piezoelectric substrate. And a base substrate is bonded to the piezoelectric substrate so as to form a space for accommodating a groove in a portion adjacent to the intersection of the electrode fingers, and the groove present in the bonded portion between the piezoelectric substrate and the base substrate. It is characterized by being filled with a synthetic resin.

  In the present invention, the space that accommodates the groove in the portion adjacent to the intersecting portion (overlapping portion) of the electrode finger so as to face the surface on which the IDT of the piezoelectric substrate is formed and does not hinder the vibration of the SH type surface wave. Since the base substrate is bonded to the piezoelectric substrate so as to form an air, the synthetic resin is not filled in the groove in the portion adjacent to the intersecting portion of the electrode fingers, and the SH type surface wave is present. Can be effectively reflected, and can be uniformly reflected by the grooves, and spurious can be prevented without reducing the P / V value of the surface wave.

  In addition, since the synthetic resin is filled in the groove existing in the bonding portion between the piezoelectric substrate and the base substrate, except for the portion adjacent to the intersection of the electrode fingers, the fixing portion between the piezoelectric substrate and the base substrate Further, the space in the base substrate is completely sealed by the synthetic resin in the groove, and the sealing reliability with the outside air can be improved.

  Further, the groove extends to the end surface of the piezoelectric substrate, that is, continuously formed from one end surface to the other end surface of the piezoelectric substrate, and a synthetic resin is filled in the groove in the vicinity of the end surface of the piezoelectric substrate. Can be prevented, and the sealing property and airtightness of the vibration part region can be improved.

  The piezoelectric resonator of the present invention is characterized in that an electrode for forming a capacitor is formed on a base substrate. In such a piezoelectric resonator, it is possible to obtain a piezoelectric resonator suitable for a resonator having a built-in load capacitor by using a dielectric ceramic on a base substrate and forming an electrode for forming a capacitor.

  The filter of the present invention is characterized in that a plurality of IDTs are formed on one main surface of the piezoelectric substrate of the piezoelectric resonant element, and each IDT is electrically connected. In such a filter, a function of a band-pass filter having an attenuation characteristic as a filter is provided by providing a plurality of independent comb-tooth electrodes on one surface of the piezoelectric substrate, and adjusting the capacitance ratio by changing the number of each comb-tooth electrode. Can be obtained.

  The composite substrate of the present invention is characterized in that a microcomputer IC chip and the piezoelectric resonance element are mounted on a mother substrate. With such a composite substrate, the degree of integration of components can be increased, and a low-profile composite substrate can be obtained.

  According to the piezoelectric resonant element of the present invention, the reinforcing substrate is bonded to the other principal surface of the piezoelectric substrate with a synthetic resin, so that the piezoelectric substrate is reinforced and can be prevented from being damaged even if the piezoelectric substrate is formed thin. Since the piezoelectric substrate can be thinned, the surface wave of the SH wave and the bulk wave vibration can be separated, spurious generation can be prevented, and stable oscillation can be obtained.

  Therefore, it is possible to reduce the thickness of the piezoelectric substrate, obtain the characteristics of SH type surface waves that do not superimpose spurious vibrations caused by bulk waves, are thin, have excellent mechanical strength, and have a large P / V A thin surface wave type piezoelectric resonance element having a value can be obtained.

  FIG. 1 is a perspective view of a piezoelectric resonator element in which a piezoelectric substrate and a reinforcing substrate of the present invention are bonded together, FIG. 2 is a perspective view of the piezoelectric resonator of the present invention, and FIG. 3 is a line AA in FIG. FIG. 4 is a plan view of a surface on which an IDT made of comb-teeth electrodes is formed in FIG. 3, and is grooved to the porcelain end surface in parallel adjacent to the outside of the electrode finger of the IDT. .

  1 to 4, reference numeral 1 is a piezoelectric resonance element, 1a is a piezoelectric substrate, 1b is a reinforcing substrate, 2 is a base substrate, 3 is an insulating adhesive, 4 is an external terminal, 5 is a comb-teeth electrode, 5a and 5b Is a lead electrode electrically connected to the IDT, 6 is a groove formed in parallel with the IDT composed of comb-tooth electrodes, and 8 is a conductive bump.

  The piezoelectric resonance element of the present invention is configured by bonding and fixing a piezoelectric substrate 1a and a reinforcing substrate 1b and forming an IDT on one side main surface of the piezoelectric substrate 1a. The IDT is composed of a pair of comb electrodes 5. Has been. That is, the comb electrode 5 is configured by forming a plurality of electrode fingers 55a parallel to the electrode base 55b, the electrode fingers 55a of the pair of comb electrodes 5 are alternately arranged, and the electrode fingers of the pair of comb electrodes 5 55a intersects at the center of the piezoelectric substrate 1a.

  In the piezoelectric resonant element according to the present invention, when the piezoelectric substrate 1a and the reinforcing substrate 1b are bonded, a groove is formed in parallel to the outermost electrode finger 55a of the interdigital transducer (IDT) to the porcelain end face in parallel. In this case, the strength of the piezoelectric resonance element 1 can be improved by the reinforcing substrate 1b. Further, by bonding and fixing the piezoelectric substrate 1a and the reinforcing substrate 1b, the strength can be ensured by the reinforcing substrate 1b. Therefore, the thickness of the piezoelectric substrate 1a can be reduced, which is caused by SH type surface waves and bulk waves. Can be separated from the spurious, and a large P / V value can be obtained.

  That is, FIG. 5 shows the relationship between the resonance frequency fr and anti-resonance frequency fa of the SH type surface wave and the spurious of the bulk wave. As the porcelain thickness becomes thinner from FIG. 5, the spurious due to the bulk wave vibration is shown. It can be seen that the SH type surface wave fr and fa can be separated from the bulk wave vibration spurious. For this reason, since spurious is not superimposed between and near the fr and fa of the SH type surface wave, a large P / V value is obtained, and when applied as a resonator, stable oscillation can be obtained. Accordingly, the thickness of the piezoelectric substrate is preferably thin, and is desirably 320 μm or less, particularly 300 μm or less, and more preferably 200 μm or less. On the other hand, it is desirable that it is 150 micrometers or more from a viewpoint on handling.

The reinforcing substrate 1b is made of alumina (a porcelain containing Al ₂ O ₃ as a main component), zirconia (a porcelain containing ZrO ₂ as a main component), magnesia (mainly MgO), which is stronger and tougher than the piezoelectric ceramic constituting the piezoelectric substrate 1a. Component ceramics), aluminum nitride (aluminum based on AlN), silicon nitride (a ceramic based on Si ₃ N ₄ ), and silicon carbide (a ceramic based on SiC) can be used. Among these, alumina is desirable because it can be set at a low cost and is excellent in productivity.

The Young's modulus of the synthetic resin that bonds the piezoelectric substrate 1a and the reinforcing substrate 1b is desirably 1 × 10 ¹⁰ Pa or less. By adhering with such a synthetic resin having a low Young's modulus, spurious due to bulk waves can be effectively suppressed. Examples of such a synthetic resin include, but are not limited to, epoxy resins, silicon resins, acrylic resins, and urethane resins.

The piezoelectric substrate 1a is, PT (lead titanate), PZT (lead zirconate titanate) or a piezoelectric ceramic material such as sodium niobate NaNbO _3, lithium tantalate, lithium niobate, a single crystal material such as Yontanasan lithium Is formed. Preferably, the electromechanical coupling factor large, easy to obtain a large P / V value If it is piezoelectric ceramics mainly composed of lead titanate PbTiO ₃ and lead zirconate titanate PbZrTiO ₃ and sodium niobate NaNbO _3. Furthermore, if the resonator applications, the dielectric constant is desirable piezoelectric ceramic mainly composed of lead titanate PbTiO ₃ and sodium niobate NaNbO ₃ to be 300 or less.

Moreover, the material of the comb electrode can be suitably used Al, Cr, Ag, Au, Pt, Ni or the like. The load per unit area (determined by electrode thickness × electrode density) of the comb electrode 5 constituting the IDT is desirably 2 × 10 ⁻⁵ g / cm ² or more. In order to form such an IDT, for example, in the case of an Al electrode, the thickness is 0.08 μm or more, and in the case of an Au electrode, the thickness is 0.01 μm or more. Thereby, even when the piezoelectric substrate and the reinforcing substrate are bonded with a synthetic resin, it is possible to obtain a large P / V because there is little suppression of SH type surface wave vibration due to damping.

  Moreover, the groove | channel provided in parallel and adjacent to the electrode finger on the outer side of the electrode finger of a comb-tooth electrode can be processed from a piezoelectric resonance element end surface to an end surface with a slicer processing machine, a laser processing machine, etc.

  Here, when the electrode width of the outermost electrode finger of the comb-teeth electrode is set to a width of about λ / 8, the outermost electrode finger is formed adjacent to the groove to reflect the end face reflection of the SH type surface wave. It becomes possible to be more effective. Further, from the viewpoint of the end face reflection of the surface wave, it is desirable that the length of the groove adjacent to the outside of the electrode finger is processed so as to be longer than the intersection length of the electrode finger. Furthermore, it is desirable that the depth of the groove penetrates the piezoelectric substrate from the point of the end face reflection of the surface wave.

  Further, lead electrodes 5a and 5b are connected to the pair of electrode bases 55b, respectively, and conductive bumps 8 are provided on the lead electrodes 5a and 5b, respectively, and are electrically connected to the external terminals 4, respectively. .

  A groove 6 for reflecting SH type surface waves is formed along the outermost electrode finger 55a, in other words, along the electrode finger 55a group, in parallel with the electrode finger 55a. . The groove 6 near the end face of the piezoelectric substrate 1a is filled with synthetic resin, and the remaining grooves 6 are not filled at all.

  The synthetic resin 3 in the groove 6 is filled when the piezoelectric resonant element 1 and the base substrate 2 are bonded. In addition, after filling the groove 6 with the synthetic resin in advance, the piezoelectric resonant element 1 and the base substrate 2 may be bonded. The adhesion region is a region from the end face of the piezoelectric ceramic to a position indicated by a broken line A in FIG.

  As can be understood from FIG. 4, the base substrate 2 is disposed in the piezoelectric substrate 1a so as to form a space L that does not hinder the vibration of the SH type surface wave, and the piezoelectric substrate 1a and the base substrate 2 are connected to the electrodes. It is fixed so as to surround the groove 6 in the portion adjacent to the intersection of the fingers 55a. That is, the base substrate 2 is a groove 6 formed at both ends of the intersecting portion of the electrode finger 55a, and only the both end portions are filled with the synthetic resin 3, and the portion filled with the synthetic resin is the base 6 It is joined to the outer peripheral part of the substrate 2 and the central part is not filled at all.

  In FIG. 4, the vicinity of the end face of the groove 6 processed to the end face of the piezoelectric resonator element 1 can be closed by filling with synthetic resin or applying the insulating adhesive 3, and can also be closed by forming an external terminal. Therefore, the drive unit of the interdigital transducer (IDT) made up of comb electrodes can be completely hermetically sealed.

  The base substrate 2 is not particularly limited as long as it has an insulating property. For example, the base substrate 2 has a heat resistance such as a dielectric material containing barium titanate, ceramics such as an alumina substrate, polyimide, liquid crystal polymer, or the like. It is desirable to be composed of an excellent resin material.

The synthetic resin 3 used for filling the grooves has a Young's modulus of 1 × 10 ¹⁰ Pa or less and can effectively suppress spurious due to bulk waves. Examples of such a synthetic resin include, but are not limited to, epoxy resins, silicon resins, acrylic resins, and urethane resins.

  In addition, by applying a dielectric material to the base substrate 2 to form a laminated structure, two load capacitors are formed, and a piezoelectric resonator having a built-in load capacitor can be obtained. Moreover, a filter can be obtained by forming an independent comb-tooth electrode and achieving electrical connection. For example, in the case of a ladder type filter, the center frequency of the filter is determined by combining the resonance frequency of the piezoelectric resonance element arranged in series and the anti-resonance frequency arranged in parallel, and the capacitance in which the guaranteed attenuation amount is arranged in series. A desired attenuation can be obtained by increasing the capacity of the parallel arrangement. That is, the amount of attenuation can be increased by increasing the number of IDTs of the resonators arranged in parallel to the IDTs of the resonators arranged in series. FIG. 6 shows a ladder type filter.

Furthermore, as shown in FIG. 7, a composite substrate can also be produced. That is, a cavity is formed in the circuit mother board 21, and the piezoelectric resonator element 1 shown in FIGS. 1 to 4 is accommodated in this cavity so that the 1DT formation surface faces the cavity bottom surface, and the bonding region shown in FIG. Adhering with a synthetic resin having a Young's modulus of 1 × 10 ¹⁰ Pa or less. On the other hand, two capacitors 23 are built in the circuit motherboard 21, and these capacitors 23 are electrically connected to the piezoelectric resonant element 1. An IC chip 25 for microcomputer is disposed on the cavity, and the outer peripheral surface thereof is bonded to the upper surface of the circuit mother board 21 to seal the inside of the cavity.

  In such a composite substrate, a low-profile composite substrate can be obtained by mounting the microcomputer IC chip 25 so as to seal the piezoelectric resonator in the cavity.

A 150 μm thick PT-type piezoelectric ceramic wafer and a 100 μm thick reinforcing substrate made of alumina are bonded via an epoxy resin with a Young's modulus of 2 × 10 ⁹ Pa and then polarized in the length (L) direction. On the main surface of the mirror-finished porcelain, an Au electrode was deposited by 1 μm.

A plurality of IDTs composed of comb-tooth electrodes and lead electrodes that are electrically connected to the IDTs were formed using a photolithography process. The load per unit area of the comb electrode was 2 × 10 ⁻³ g / cm ² . The IDT is disposed in a region corresponding to the central portion of each piezoelectric resonant element. At this time, the direction of the electrode finger of the IDT composed of comb-teeth electrodes was matched with the polarization direction.

  Thereafter, a groove for reflecting the SH type surface wave was formed by processing with a slicer so as to penetrate the piezoelectric substrate. The reinforcing substrate was exposed in the groove. At this time, the number of crossing electrodes of the IDT was 16 pairs, and the electrode crossing length was 400 μm. Furthermore, the width of the electrode finger of the IDT was 15 μm, the distance between the electrode finger was 15 μm, and the metallization ratio (IDT electrode width / no electrode width between electrodes) was set to 1. The electrode width of the outermost electrode finger of the IDT electrode is λ / 8 (about 7.5 μm), and the groove processing for reflecting the SH type surface wave penetrates the piezoelectric substrate, and the groove extends to the end surface of the piezoelectric substrate. Processed to extend.

  As shown in FIG. 8, the impedance characteristic at this time did not generate spurious in the main frequency band, and the P / V value was as large as 63 dB. In addition, when this piezoelectric resonance element was subjected to a so-called drop test in which it was dropped from a height of 1.5 m on the concrete to give an impact, it was not damaged.

  On the other hand, in Example 1, a piezoelectric substrate having a thickness of 300 μm was used (no reinforcing substrate), and a piezoelectric resonant element of a comparative example having a groove depth of 150 μm was produced. When this piezoelectric resonant element was tested in the same manner as described above, it was damaged at the groove portion.

Next, in Example 1, when the Au electrode for forming the IDT is deposited by a thickness of 2 μm (the load per unit area of the comb electrode is 4 × 10 ⁻³ g / cm ² ), the impedance characteristic is shown in FIG. Shown in From FIG. 9, no spurious was generated in the frequency band of the SH type surface wave, and a large P / V value of 68 dB was obtained. It is understood that this phenomenon is caused by increasing the so-called energy confinement effect in which the vibration of the SH type surface wave is confined in the vicinity of the electrode by increasing the electrode load per unit area.

  Next, in Example 1, the relationship between the resonance frequency fr and antiresonance frequency fa of the surface wave and the spurious of the bulk vibration when the thickness of the piezoelectric ceramic is changed is shown in FIG. It can be seen that when the thickness of the piezoelectric ceramic is 320 μm or less, spurious vibration due to the bulk wave is not superimposed between fr and fa of the surface wave vibration. Accordingly, the thickness of the piezoelectric ceramic is desirably 320 μm or less. In particular, in the case of 200 μm or less, it can be seen that SH type surface wave vibration and bulk wave vibration can be completely separated and can be further thinned.

Next, the piezoelectric resonance element of Example 1 and a base substrate made of a dielectric material incorporating two load capacitors (10 to 50 pF / piece) are placed on the base substrate so that the epoxy resin does not face the IDT. It was printed in a ring shape (shown in FIG. 4), and bonded and fixed through an epoxy resin having a Young's modulus of 3 × 10 ⁹ Pa so as to face the surface on which the IDT of the piezoelectric ceramic wafer was formed. Then, it cut | disconnected with the dicing machine into the shape of each piezoelectric resonator. Thereafter, an external terminal was formed by Ag sputtering, and electrical conduction between the IDT and the external terminal was performed. After that, as a result of evaluating the oscillation by the inverter oscillation circuit shown in FIG. 10, the oscillation start voltage when using the third harmonic oscillation generally used at a high frequency is about 3.5 V despite the high frequency of about 50 MHz. Thus, the SH type surface wave can oscillate at a low voltage of about 2 V, and stable desired oscillation characteristics can be obtained.

It is an external appearance perspective view which shows the piezoelectric resonance element which bonded the piezoelectric substrate and reinforcement board | substrate of this invention together. It is an external appearance perspective view which shows the piezoelectric resonator of this invention. It is a longitudinal cross-sectional view along the AA line of FIG. It is a top view of the IDT formation surface of the piezoelectric resonance element in FIG. It is a graph which shows the piezoelectric ceramic thickness dependence of the vibration of the spurious resulting from the resonance of the SH type of Example 3, an antiresonance frequency, and a bulk wave. It is a top view which shows the piezoelectric filter of this invention. It is a schematic cross section of the composite substrate which mounted the piezoelectric resonance element on the circuit board of this invention. 6 is an impedance characteristic diagram of Example 1. FIG. 6 is an impedance characteristic diagram of Example 2. FIG. It is an oscillation circuit diagram of a piezoelectric resonator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric resonance element 1a Piezoelectric substrate 1b Reinforcement substrate 2 Base substrate 3 Synthetic resin 5 Comb electrode 6 Groove 12 Microcomputer IC
21 Mother board L space

Claims (13)

An interdigital transducer (IDT) composed of a pair of comb electrodes is formed on a part of one side main surface of a piezoelectric substrate having a thickness of 320 μm or less, and a reinforcing substrate is bonded to the other side main surface of the piezoelectric substrate with a synthetic resin. A piezoelectric resonant element characterized by comprising: An interdigital transducer (IDT) comprising a pair of comb electrodes is formed on a part of one side main surface of the piezoelectric substrate, and on the outside of the IDT electrode finger on one side main surface of the piezoelectric substrate, adjacent to the electrode finger. A piezoelectric resonance element provided with a groove for reflecting SH type surface waves in parallel, wherein a reinforcing substrate is bonded to the other main surface of the piezoelectric substrate with a synthetic resin. Piezoelectric resonant element. The piezoelectric resonant element according to claim 2, wherein the thickness of the piezoelectric substrate is 320 µm or less. 4. The piezoelectric resonance element according to claim 2, wherein the groove penetrates the piezoelectric substrate. 5. The piezoelectric resonance element according to claim 2, wherein the groove is formed continuously from one end face to the other end face of the piezoelectric substrate. 6. The piezoelectric resonant element according to claim 1, wherein the Young's modulus of the synthetic resin for bonding the piezoelectric substrate and the reinforcing substrate is 1 × 10 ¹⁰ Pa or less. 7. The piezoelectric resonant element according to claim 1, wherein a load per unit area of the IDT is 2 × 10 ⁻⁵ g / cm ² or more. The reinforcing substrate is mainly composed of at least one of Al ₂ O ₃ , MgO, ZrO ₂ , AlN, Si ₃ N ₄ , and SiC, according to claim 1. Piezoelectric resonance element. The piezoelectric substrate according to any one of claims 1 to 8, wherein the piezoelectric substrate is disposed on the base substrate so as to face a main surface of the piezoelectric substrate on which the IDT is formed and to form a space for accommodating the IDT. A piezoelectric resonator characterized by being bonded to a substrate. A groove for reflecting SH type surface waves is provided on the outer side of the electrode finger of the IDT on one side main surface of the piezoelectric substrate, adjacent to the electrode finger, and in parallel with the electrode finger. A base substrate is bonded to the piezoelectric substrate so as to form a space for accommodating a groove in an adjacent portion, and a synthetic resin is filled in the groove existing in the bonded portion between the piezoelectric substrate and the base substrate. The piezoelectric resonator according to claim 9. 11. The piezoelectric resonator according to claim 9, wherein an electrode for forming a capacitor is formed on the base substrate. 9. A filter comprising a plurality of IDTs formed on one principal surface of a piezoelectric substrate of the piezoelectric resonance element according to claim 1 and electrically connected to each IDT. 9. A composite substrate comprising a microcomputer IC chip and the piezoelectric resonant element according to claim 1 mounted on a mother substrate.

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