JPH1051262A - Piezoelectric vibrator and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the spurious by preparing two piezoelectric single crystal plates which are unified together in the direction, almost opposite to the axial direction of spontaneous polarization and the drive electrodes which are formed opposite to each other on both main surfaces of those two single crystal plates that are bonded directly to each other. SOLUTION: Two sheets of piezoelectric single crystal wafers 11 and 12 are made of lithium niobate and have the same thickness with directions of polarization Ps shown by arrows respectively. These wafers 11 and 12 are bonded directly to each other in a single body. Then the drive electrodes 13 are formed on the upper and lower surfaces inverted polarization wafers 11 and 12 bonded to each other. Thus, an energy containment-type piezoelectric vibrator is obtained. When the wafers 11 and 12 are bonded to each other, the bonding surfaces of both wafers 11 and 12 are polished into mirror-finish surfaces and cleaned and undergo hydrophilic treatment. Such two wafers are touched with each other and then heated. From this, both wafers 11 and 12 can be directly bonded to each other at an atomic level without the use of any adhesive whatsoever. Therefore, the elastic loss is very small, when a bulk wave is transmitted. Thus, the mechanical quality counting Q and quality are improved for the vibrator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an element (piezoelectric vibrator, piezoelectric filter, etc.) made of a piezoelectric single crystal having spontaneous polarization and a method of manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, a piezoelectric vibrator has been used as an oscillator as a clock source for a computer, various microcomputer built-in devices, various digital devices, and the like. These piezoelectric vibrators are made of a piezoelectric single crystal such as quartz or a piezoelectric ceramic, and an appropriate drive electrode is formed on a body cut out of these piezoelectric materials. When a drive voltage having a frequency near the resonance frequency determined by the sound speed and the size of the piezoelectric element is applied to the drive electrode, strong resonance is obtained, and an electric signal is generated using this phenomenon. These piezoelectric vibrators have been widely used because of their high performance while having a simple shape. In these piezoelectric vibrators, the energy of vibration is confined immediately below the drive electrode. By holding the vibrator at a portion other than the drive electrode, the vibrator can be mounted on a package or a printed board without affecting the vibration. These vibrators are called energy trap type vibrators.

In recent years, with the increase in speed of various information devices represented by personal computers, hard disk drives and C
There is a strong demand for higher clock frequencies, including peripheral devices such as D-ROM drives. Conventionally, in the frequency band of tens of MHz to tens of MHz required for these devices, a vibrator using thickness vibration such as thickness slip, thickness torsion, and thickness vertical indicating an oscillation frequency inversely proportional to the thickness of the piezoelectric body is used. I have been. However, as the frequency increases, the thickness of the piezoelectric body becomes thinner. For example, when the frequency exceeds 40 MHz, the thickness of the piezoelectric body becomes approximately 100 μm, which causes various problems such as a decrease in relative accuracy of processing, a decrease in mechanical strength, and an increase in cost. Had occurred.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 63-311808, lithium niobate (LiNb
Attempts have been made to make the thickness of the piezoelectric body twice as large as that of a conventional vibrator corresponding to the frequency by using the polarization inversion layer formation phenomenon of O ₃ ). FIG. 1 shows a process for forming the domain-inverted layer. The piezoelectric vibrator 101 is formed by forming drive electrodes 103 and 104 on opposing main surfaces (upper and lower surfaces, for example, Z-plane) 102a and 102b of a piezoelectric plate 102 cut from a lithium niobate single crystal. In FIG. 1 (a), a polarization Ps is applied to a wafer 105 sliced from a poling-processed lithium niobate single crystal, that is, a wafer 105 sliced in a direction inclined by an appropriate angle from the polarization orientation generated by the poling process. When the azimuth is in the direction of the arrow in the drawing (for example, in the upward direction), a thin film of titanium (Ti) is deposited on the surface on the + c-axis side (the upper surface in the drawing, the + Z ′ surface). Then, the lithium thin film 106 is heated at a temperature between the Curie temperature of lithium niobate (about 1250 ° C.) and 1100 ° C. to diffuse the titanium thin film 106 into the wafer 105. As shown in FIG. Is generated. Assuming that the depth of the domain-inverted region 109 is t, the surface charge generated on the wafer 105 during the diffusion process is balanced when the depth t is の of the thickness T _3. depth t of the inverted regions 109, the extension of about half the wafer 107 thickness T ₃ stops, polarization Ps of the domain-inverted region 109 '
Has a direction opposite to that of the polarization Ps. Next, as shown in (c), after a plurality of drive electrodes 103 and 104 are formed on the upper and lower surfaces of the wafer 107 by patterning, the operation electrodes 103 and 104 opposing vertically are included in the drawing. The wafer 107 is cut along the dashed line. Thus, as shown in FIG. 1D, the piezoelectric vibrator 101 is completed. The thickness of the piezoelectric plate 102 having the polarization Ps' in the opposite direction to the polarization Ps is about twice the thickness of the conventional piezoelectric when the oscillation frequency is the same. For example, when the oscillation frequency is 26 MHz
z, the thickness of the piezoelectric body is about 1
When the thickness is 50 μm, the thickness of the piezoelectric body of the substrate having the domain-inverted layer is about 300 μm. This is due to the same electric field
In the former, half-wave resonance is excited, whereas in the latter, 1
This is because resonance at a wavelength can be electrically excited.

Further, lithium tantalate is used as a piezoelectric material.
When (LiTaO ₃ ) is used, for example, JP-A-01-158
As shown in JP-A-811, a method is used in which a proton exchange layer is formed in order to perform polarization inversion, and the polarization in that portion is selectively inverted. In FIG. 2A, a piezoelectric body 112 cut out from a 0 ± 10 ° rotation X plate of a lithium tantalate single crystal has one main surface (+ X ′ surface) 112a and the other upper surface (−X ′ surface) 112b. To the polarization Ps. Next, as shown in (b), a polyimide layer (polyimide mask) 113 having a thickness of about 5 μm is formed on the + X ′ surface 112a by, for example, spin coating, and then the proton heated to, for example, 250 ° C. as shown in (c). When immersed in the exchange treatment liquid 114 for about one hour, the proton exchange layer 1
15 are formed. Next, the piezoelectric body 112 taken out from the processing liquid 114 and washed is heated to a high temperature equal to or lower than the Curie point (600 ° C.) of lithium tantalate, for example, 560 to 610 ° C.
Is heated for an appropriate period of time at the temperature of (c), as shown in (d), a polarization Ps 'having a direction opposite to the polarization Ps is formed at a half depth of the piezoelectric body 112 from the -X' plane 112b. An inversion layer 112c is formed. Next, when the drive electrodes 116 and 117 are formed on the opposing main surfaces (+ X ′ plane and −X ′ plane) 112a and 112b of the piezoelectric body 112, the piezoelectric vibrator 1 shown in FIG.
11 is completed. The behavior of these vibrators is the same as that of lithium niobate described above, and is intended to double the upper limit of the frequency.

[0006] Since the vibrator made of lithium niobate and lithium tantalate has a high Q and a large electromechanical coupling coefficient, spurious due to an unnecessary vibration mode is easily generated. Therefore, in order to excite the pure vibration mode, either the thickness longitudinal vibration with the main displacement in the thickness direction or the thickness shear vibration with the main displacement in the direction parallel to the plate surface is forcibly excited. The vibrator is formed by selecting such a cut angle. The thickness vibrator has little coupling with other vibration modes, and if this is used, a vibrator having originally little spurious can be obtained. In lithium niobate and lithium tantalate, by optimally selecting the cut angle, it is possible to obtain a piezoelectric body having a coupling coefficient of the thickness shear vibration mode of 0 and exciting only the thickness longitudinal vibration mode. However, at these cut angles, the energy of the first-order (fundamental wave) resonance is not confined in the electrode, and the vibrator utilizes the third-order resonance. This is because the Poisson's ratio between lithium niobate and lithium tantalate becomes 1/3 or less, and the primary resonance energy in the thickness longitudinal vibration mode is not confined. In the vibrator using the third resonance, the vibration near the fundamental wave, which is the first resonance, is an unnecessary vibration.
If the level is not suppressed to a sufficiently low level, it will be oscillated by the fundamental wave, and the tertiary resonance will be inferior in characteristics to the primary resonance unless it is suppressed to a sufficiently low level. On the other hand, there is also a cut angle in which the thickness longitudinal vibration mode is not excited and only the thickness shear vibration mode is provided. The difference between the thickness-shear vibration mode and the thickness-longitudinal vibration mode is that two thickness-shear vibrations perpendicular to each other are simultaneously present in a plate excited in the slip mode. Therefore, a device is required to suppress spurious as compared with the thickness longitudinal vibrator. Since one of the vibrators utilizing the thickness shear vibration uses one of them as a main mode, the other shear vibration is regarded as an unnecessary wave (spurious). Normally, in X-cut lithium tantalate, a mode having a high sound velocity and a large coupling coefficient is used as a main mode.

[0007] In addition, in order to suppress unnecessary waves caused by contour vibration, the element is formed into a substantially square shape having a sufficient margin compared with the vibration space, and spurious components are reduced by a sound absorbing material or the like. A method of damping has been proposed. However, if the protruding portion of the sound absorbing material is applied to the vibration space, the vibration characteristics are remarkably deteriorated, which is not suitable for a small element. For this reason, as disclosed in Japanese Patent Application Laid-Open No. H5-160659, attempts have been made to form an amorphous layer on the side of an electrode or to provide an insulating film. However, in these square-shaped elements, the above-described unnecessary wave having a low sound velocity is excited to a level substantially equal to the main wave. This is the same for a circular element. For this reason, attempts have been made to form the element into a rectangular shape that is long in the displacement direction of the main vibration, and to suppress the level of the unnecessary wave with the slower sound velocity. In the X-cut lithium tantalate plate having good temperature characteristics, the displacement direction of the thickness shear vibration (main vibration) having a high sound velocity (the angle θ with the Y axis in FIG.
) Is -53 ° (Nihon Dempa Kogyo NDK Technical Report No.
6, '79, 11, "Voltage-controlled oscillator using lithium tantalate".

In Japanese Patent Application Laid-Open No. 58-143609, a lithium niobate oscillator is disclosed in
As disclosed in Japanese Patent No. 25312, a lithium niobate vibrator is stripped to reduce the size and the performance of the lithium niobate or lithium tantalate vibrator. As shown in FIG. 3 (b), the strip-type vibrator referred to here is a vibrating element 200 which is cut out into a rectangle having a rectangular cross section and provided with opposing electrodes 201 and 201 ′ over its entire width. That is. With this configuration, the thickness torsional vibration mode that propagates perpendicular to the displacement direction of the main vibration (the longitudinal direction of the vibrator) and the excitation of the thickness-shear vibration with a low sound velocity are suppressed, and a high-Q vibrator can be obtained. it can. It is desirable that the longitudinal direction of such a strip-type piezoelectric vibrator using an X-plate of lithium tantalate be nearly parallel to the displacement direction of the thickness shear vibration in order to suppress spurious vibrations.
(The angle θ formed with the Y axis in FIG. 3) is −50 ° ± 2 °.
(In JP-A-1-36724), -57 ° ±
Examples such as 0.5 ° (in JP-A-2-13007) are disclosed. Further, the error ranges of these angles are respectively ± several degrees, but these are derived from the symmetry of the crystal, and if they are within these ranges, there is little change in characteristics and it is acceptable. In each of these elements, the optimum ratio W / H of the width W to the thickness H, and the lengths L and H
Is determined, and the spurs related to the width and the length are used so as not to overlap the thickness shear vibration mode which is the main vibration.

[0009]

The piezoelectric vibrators 101 and 111 which have been subjected to the polarization reversal processing shown in FIGS. 1 and 2 satisfy various characteristics such as resonance frequency, resonance resistance and dynamic range required for the vibrator. In order to do this, the thickness of the domain-inverted layers must be equal (that is, the layer of the polarization Ps' in the opposite direction to the layer of the polarization Ps shown in FIGS. 1 and 2 must be equal).
is necessary. In addition, if a uniform domain-inverted layer without waviness is not formed in a wide range of the wafers 107 and 112, the characteristics as a piezoelectric vibrator deteriorate. However, as described above, in the case of lithium niobate, the formation of a diffusion titanium thin film,
In the case of lithium tantalate, masking or the like for selective proton exchange is required, and its film thickness control,
Various parameters such as stress control intervene. as a result,
It is difficult to control the depth of the domain-inverted layer accurately to half the thickness of the piezoelectric plate, and the characteristics such as resonance frequency, resonance resistance, and dynamic range required for the vibrator are reduced. Had.

The processing temperature for forming the domain-inverted layer is close to the Curie point of lithium niobate and lithium tantalate.
The temperature is as high as around 0 ° C. For this reason, it is difficult to control the soaking temperature, it is necessary to control the atmosphere to prevent lithium desorption, and contamination of the substrate from the heating furnace tube wall occurs.
For this reason, there is also a problem that characteristics as a vibrator are reduced. Further, the domain-inverted layer has a disadvantage that the symmetry between the domain-inverted layers is lost due to the change in composition, such as the diffusion layer of titanium and the movement of lithium, which occur in the manufacturing process, and the transducer characteristics are deteriorated. . It should be noted that a piezoelectric filter using a piezoelectric material has the same problem as the vibrator described above.

In order to solve this problem, we have disclosed in Japanese Patent Application Laid-Open No. Hei 7-206600 a new method of direct bonding of laminated ferroelectrics to obtain a laminated piezoelectric body in which the polarization is inverted without any characteristic deterioration. Suggest a way.
However, this publication only mentions a joining method, and does not give any suggestion about guidelines for using the structure as a piezoelectric vibrator. Also, in lithium niobate and lithium tantalate, even if the cut angles at which only the thickness longitudinal vibration mode is excited are selected, at these cut angles, the energy of the primary (basic) resonance is confined in the electrode. Instead, the vibrator uses the third-order resonance, and the coefficient becomes 1/9 in the case. Since the characteristics of the vibrator are proportional to the magnitude of the coupling coefficient, the vibrator of the third harmonic has a problem that the characteristics are deteriorated as compared with the vibrator of the fundamental wave. Further, an unconfined vibration near the fundamental wave is combined with another vibration mode to become a forced vibration, causing a fundamental wave oscillation, and an element design for properly operating as a third harmonic vibration element is required. there were.

[0012] In the thickness-shear mode oscillator,
When a square or circular element is used, there is a problem that a thickness slip wave having a high sound speed (main wave) and a thickness slip wave having a low sound speed (unnecessary wave) are excited to substantially the same level.
In order to improve the characteristics, even if the thickness-sliding element has a rectangular shape whose longitudinal direction is in the displacement direction of the main wave, there is a limit in suppressing a slow unnecessary wave. Furthermore, in order to suppress the generation of spurious components by stripping, the element must be formed into a thin rod shape, and the finish of the end face greatly affects the element characteristics. Further, even if the dimensions are designed as designed, if the cut shape of the end face is poor, Q is deteriorated or new spurs are generated, and desired characteristics cannot be obtained in many cases. In particular, as the element becomes thinner in a high-frequency element, the width of the element also becomes narrower, which makes processing difficult, and the element itself becomes fragile. An object of the present invention is to solve these various problems and to provide an inexpensive domain-inverted piezoelectric vibrator having a stable and highly symmetric domain-inverted structure and an excellent spurious suppression effect, and a method of manufacturing the same. That is.

[0013]

The piezoelectric vibrator according to the present invention has spontaneous polarization, and the axes of the spontaneous polarization are substantially opposite to each other, and the other crystal axes are at an angle formed by each other. Are formed by direct bonding so as to be shifted by a certain angle not including 0 degree, and two piezoelectric single crystal plates which are directly bonded to each other are formed facing each other on two main surfaces of the piezoelectric single crystal plate directly bonded to each other. Drive electrode. By making the thicknesses of the two piezoelectric single crystal plates substantially the same, the piezoelectric vibrator has a stable and highly symmetric polarization inversion structure. Also,
The spurious is suppressed by intentionally shifting the crystal axis. Preferably, the piezoelectric single crystal plate is made of lithium niobate, lithium tantalate or lithium borate.

The piezoelectric vibrator according to the present invention preferably has a shape in which the integrated piezoelectric single crystal plate excites even harmonics of thickness longitudinal vibration by a drive electrode.
Preferably, the two piezoelectric single crystal plates are integrated so that the deviation of the azimuth of the crystal axis orthogonal to the axis of spontaneous polarization is limited to an angle within ± 5 °. Preferably, the two piezoelectric single crystal plates have a Poisson's ratio of 1/3 or less, and the value of the electromechanical coupling coefficient in the thickness longitudinal vibration mode is larger than the value of the electromechanical coupling coefficient in the thickness shear vibration mode. The drive electrode is made of a sufficiently large piezoelectric material and is arranged so as to confine even-order harmonic energy. Poisson's ratio is 1/3
The following piezoelectric single crystal plate can also confine energy in the thickness longitudinal mode. Preferably, the piezoelectric single crystal plate,
It is made of Z-cut lithium niobate or Z-cut lithium tantalate. Each of the drive electrodes has at least 2 when the thickness of the integrated piezoelectric single crystal plate is H.
It has a length and width of H or more and 7H or less. Preferably, the apparatus further includes a substrate for supporting the piezoelectric vibrator, and an external connection electrode is formed on the substrate. The piezoelectric vibrator is supported by the external connection electrode with a conductive adhesive, and a drive electrode is drawn out. The direction and the direction in which the piezoelectric vibrator is supported substantially coincide with the X-axis direction of the single crystal plate. This optimizes the direction in which the electrodes are taken out when mounting the piezoelectric vibrator on the mounting substrate. Preferably, the two piezoelectric single crystal plates have the same thickness, and the second harmonic of the thickness longitudinal vibration among the even harmonics is excited as the main wave.

In the piezoelectric vibrator according to the present invention, preferably, the integrated piezoelectric single crystal plate has a shape in which even-order harmonics of thickness shear vibration are excited by the driving electrode. Preferably, the two piezoelectric single crystal plates have an orientation of a crystal axis orthogonal to the axis of spontaneous polarization of ± 1 except for 0 °.
The joints are intentionally shifted at an angle within 5 °. Preferably, the two piezoelectric single crystal plates are X ± 10 ° rotating plates of lithium tantalate, and among the two types of thickness shear vibration modes excited by the piezoelectric plate, the value of the electromechanical coupling coefficient is large. In the thickness-shear oscillator using the main wave and suppressing the unnecessary wave having a small value of the other electromechanical coupling coefficient, the two piezoelectric single crystal plates are arranged so that the directions of the spontaneous polarization are substantially opposite to each other. The crystal orientations perpendicular to each other are intentionally shifted within ± 15 ° excluding 0 °. Preferably, the two piezoelectric single crystal plates are rod-shaped lithium tantalate X ± 10 ° rotating plates, and the driving electrodes are formed on two surfaces parallel to the X ± 10 ° rotating surface of the vibrator, respectively. Formed over Here, the longitudinal direction in which the thickness shear vibration of the piezoelectric crystal plate is excited is taken to be a direction rotated clockwise by 38 ° to 58 ° from the Y ′ axis in the Y ′, Z ′ plane, and the longitudinal end is held. . Preferably, the two piezoelectric single crystal plates have the same thickness, and the second harmonic of the thickness shear vibration among the even harmonics is excited as the main wave.

In the method of manufacturing a piezoelectric vibrator according to the present invention, the bonding surfaces of two piezoelectric single crystal plates having spontaneous polarization are mirror-polished, and the bonding surfaces of the piezoelectric single crystal plates are cleaned and hydrophilic. And the piezoelectric single crystal plates are superposed so that the crystal orientations thereof are shifted at a certain angle not including 0 °, and the bonding surfaces are adhered so that the axial direction of spontaneous polarization is in the opposite direction, and the adhered Two piezoelectric single crystal plates are heated to integrate the two piezoelectric single crystals, and drive electrodes facing each other are formed on two main surfaces of the two integrated piezoelectric single crystals. It is characterized by the following. Preferably, after the two piezoelectric single crystal plates are integrated, one surface of the integrated piezoelectric single crystal plate is polished to uniform thickness, and then the two main surfaces are opposed to each other by the drive electrode. To form Preferably, after the two piezoelectric single crystal plates are integrated, both surfaces of the integrated piezoelectric single crystal plate are polished to make the thickness uniform, and then the two main surfaces are opposed to each other by the drive electrode. To form Preferably, the piezoelectric single crystal plate is made of lithium niobate, lithium tantalate or lithium borate.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Embodiment 1 FIG. 4 shows a process of manufacturing a piezoelectric vibrator according to Embodiment 1 of the present invention. 4A is a side view of two piezoelectric single crystal wafers 11 and 12 having the same thickness, and the direction of polarization Ps is indicated by an arrow in the figure. As the piezoelectric single crystal wafers 11 and 12, Z-cut lithium niobate having a diameter of 2 inches and a thickness t = 50 μm is used. These two piezoelectric single crystal wafers 11 and 12 are
As shown in (b), they are directly joined and integrated. Finally, drive electrodes 13 are formed on the upper and lower surfaces of the bonded domain-inverted wafers 11 and 12, and as shown in (c), an energy trap type piezoelectric vibrator is completed. FIG. 5 shows the frequency characteristics of the piezoelectric vibrator thus obtained. Next, the direct joining will be described in detail. Direct bonding is achieved at the atomic level by direct bonding without using any adhesive,
The elastic loss during bulk wave propagation is very small. Therefore, by using the present bonded body as a vibrator, a high-quality vibrator having a high mechanical quality factor Q can be provided. Also, since the direct bonding surface is bonded at the atomic level,
The joint surface has the same flatness as mirror finish. Therefore, the thickness of the domain-inverted region can be determined with the accuracy of the thickness of the upper wafer 11 and the thickness of the lower wafer 12. Therefore, since the ratio of the thickness of the domain-inverted region is constant over the entire wafer, a substrate can be obtained on which a resonator having excellent characteristics such as resonance frequency, resonance resistance, and dynamic range is obtained. Further, since the mechanical strength is extremely high, it is possible to reduce the thickness of the sheet by polishing or grinding after joining.

The direct bonding is performed by mirror-polishing the two surfaces of the wafers 11 and 12 to be bonded, cleaning the surfaces, bringing the surfaces of which have been subjected to a hydrophilic treatment into contact, and then performing a heat treatment. The heating temperature is sufficiently lower than the conventional temperature of the domain-inverted layer forming treatment, and is 200 to 5 times.
It is about 00 ° C. Therefore, complicated temperature control is not required, and the production equipment can be simplified. Further, the quality of the single crystal substrate does not deteriorate at high temperatures. Also for the lithium niobate used in the present embodiment, no warping, breakage, or alteration of the material due to direct bonding was observed.

In this vibrator, the polarization axis is perpendicular to the plate surface, and this is the axis of symmetry of the crystal. When joining by reversing the polarization, it is preferable to match the coefficient of thermal expansion in a plane, so that the crystal axes in the plane are almost matched. However, even if they are misaligned, there is no significant change in the bonding state, and the deterioration in the characteristics of the vibrator is small. However, if this deviation exceeds ± 15 °, as shown in FIG. 6, the characteristics are greatly degraded. Therefore, it is necessary to suppress the deviation of the angle to within ± 15 °. More preferably, if the angle is kept within ± 3 °, characteristics comparable to those in the optimal case can be obtained.

In the energy trap type piezoelectric vibrator shown in FIG. 4C, the curve between the electrodes 13 shows an example of displacement of one wavelength. The vibrator is a wafer 1 having the same thickness.
Since Nos. 1 and 12 were bonded, the bonding interface = Polarized Inverted Interface at a position of 1/2 of the thickness T3 with _high accuracy, and the flatness of the Polarized Inverted Interface is good. Therefore, it is possible to excite resonance of one wavelength in an ideal state as shown in FIG. FIG.
The frequency characteristics of this vibrator are shown. As shown in the figure, it is possible to obtain characteristics in which the resonance resistance is small, the dynamic range (the difference between the maximum value and the minimum value of the amplitude level) is large, and the spurious is extremely small near the resonance frequency. In a conventional vibrator using one wafer, a half wavelength is excited in a thickness direction in a vibration mode of a fundamental wave, and a resonance frequency is about 36 MHz.
(Theoretical value). In this embodiment, a vibrator having a thickness of 100 μm is obtained by directly bonding two wafers having a thickness of 50 μm, and the fundamental mode is a secondary vibration mode in which one wavelength is excited in the thickness direction. Therefore, the resonance frequency is about 72 MHz, which is twice that of the conventional vibrator.

Such an energy confined thickness longitudinal mode vibrator that excites resonance of one wavelength cannot be achieved by a conventional vibrator of a solid piezoelectric plate (hereinafter also referred to as a single plate) that is not bonded. . This principle will be described below. The vibrator according to the present embodiment utilizes energy confinement of thickness longitudinal vibration. Usually, energy confinement of the piezoelectric vibrator is achieved by using frequency-increased energy confinement and frequency-decreased energy confinement. 7 and 8 show the structure and dispersion curve in each case. These are described in detail in “Elastic Wave Device Technology Handbook”, edited by the 150th Committee of the JSPS Acoustic Wave Technology, Ohmsha, pages 82 to 89. 7 and 8
In, ωo is the angular frequency of the thickness vibration wave at the electrode (thickness slip, thickness vertical, thickness torsion, etc.), ωo 'is the angular frequency of the thickness vibration wave at the non-electrode portion, k is the wave number of the electrode portion along the plate, k ′ is the wave number in the direction along the plate in the electrodeless part. In FIG. 7, (a) shows the structure of a frequency-increased confinement vibrator such as a Z-cut lithium niobate plate having a Poisson's ratio of 1/3 or less. The main vibration of the thickness vibration wave of the vibrator has a wave number k, k ′ in the direction along the plate as shown by the dispersion curve in FIG.
It becomes an imaginary number on the higher frequency side than o and ωo '. In contrast, FIG.
In (a), the structure of the frequency-reduced confinement oscillator when the Poisson's ratio is 1/3 or more is shown. For harmonics,
As shown in the dispersion curve of (b), the wave numbers k and k ′ are imaginary numbers on the lower frequency side than the cutoff frequencies ωo and ωo ′. That is, in the case of a frequency lowering type structure, ωo
In the range from to ωo ′, the boundary condition that k is a real number and k ′ is an imaginary number is satisfied, and the energy can be confined to the electrode portion. However, in the main vibration, as shown in (c), a boundary condition where k is a real number and k ′ is an imaginary number is not satisfied, and it becomes difficult to extract vibration energy from the electrode unit. As described above, from FIG. 7 and FIG. 8, the main resonance and the harmonics are different in the confinement type of the vibration energy. Therefore, when one of the energies is confined, the confinement type of the vibration energy different from that is required. Such a vibration wave leaks out of the electrode, and its vibration is suppressed.

In order to confine the energy of the main vibration in the frequency lowering type, it is necessary to lower ωo ′ and create a boundary condition where k is a real number and k ′ is an imaginary number. Therefore, as a method of confining the energy of the main vibration, a frequency rising type structure as shown in FIG. Such a structure cannot be achieved without thinning a part of the piezoelectric body in addition to forming the electrodes, so that it is inferior in mass productivity, and in chemically stable crystals such as lithium niobate and lithium tantalate. Is
Even the processing becomes difficult. In an ordinary frequency-reduced vibrator as shown in FIG. 8A, the energy of the fundamental wave (half-wave resonance) is not confined, and a third or higher harmonic having a lower coupling coefficient than the fundamental wave is used. The method used as the harmonic oscillator is selected. Higher order resonances are usually 3, 5,
7,..., 2n + 1 order (n is a natural number) resonance is simultaneously confined under the electrode, but the frequency characteristic of the oscillation circuit is reduced in a high frequency range, so in this case (the Poisson ratio is 1/3 or less) ), And oscillate at the lowest third harmonic.

However, in an actual frequency-reduced vibrator, there is a problem that the fundamental wave is insufficiently suppressed, and if there is forced vibration in the fundamental wave region, a fundamental wave oscillation is caused. However, according to the directly joined piezoelectric vibrator of the present embodiment, the piezoelectric vibrator having a coupling coefficient larger than the third harmonic
The energy can be confined at the harmonic resonance (the coupling coefficient is almost the same as the fundamental wave because the two plates are involved in the vibration), and the fundamental wave is also sufficiently suppressed. FIG.
6 is a graph showing resonance characteristics of the piezoelectric vibrator made of the Z-cut lithium niobate plate directly joined shown in FIG. 5 in the vicinity of main resonance. On the other hand, FIG. 10 shows a Z-cut single plate (comparative example).
6 is a graph showing resonance characteristics near the main resonance of FIG. In each figure, the vertical axis represents the amplitude level, the horizontal axis represents the frequency, and the amount of attenuation increases in the downward direction of the vertical axis. In the characteristic curve, a curve having an upward peak indicates frequency characteristics, and a curve indicating a downward peak indicates phase characteristics.

In the vibrator of this embodiment (FIG. 9),
As for the frequency of the main resonance, the peak P1 corresponding to the second harmonic (one wavelength resonance) of the thickness longitudinal vibration of the Z-cut lithium niobate having a total thickness of 100 μm is sufficiently larger than the peak P0 corresponding to the resonance of the fundamental wave. On the other hand, in a resonator using a Z-cut single plate (comparative example), energy trapping of the fundamental wave (half-wave resonance) having the largest coupling coefficient was not achieved, and as shown in FIG. Produces the most significant resonance in the high frequency range of For higher-order resonances, the coupling coefficient is 1
/ N ² (where n is the order of resonance). The lower the resonance, the larger the coupling coefficient and the smaller the characteristic degradation. FIG.
10 and FIG. 10, comparing the characteristics in the lowest order mode excited by these piezoelectric plates shows that the piezoelectric vibrator directly bonded with Z-cut lithium niobate according to the present embodiment cannot be realized with the conventional single plate. The lower vibration mode (1
Wavelength resonance) can be confined. For this reason, a high-performance vibrator can be obtained. In this embodiment, the case where piezoelectric single crystal wafers having the same thickness are bonded is described. However, similar effects can be obtained by bonding piezoelectric single crystal wafers having slightly different thicknesses to form a vibrator. Can be

In the present embodiment, the coupling coefficient of the thickness shear vibration excited by the drive electrodes disposed opposite to the plate surface is small, and the cut angle is such that only the thickness longitudinal vibration can be excited. As an example in which the energy of the fundamental wave cannot be confined because the Poisson's ratio is 1/3 or less, a Z-cut plate is used for lithium niobate, but a 36 ° Y-cut plate having similar characteristics has the same effect. Also, lithium tantalate of the same crystal system,
The same can be said for lithium borate (Li ₂ B ₄ O ₇ ). FIG. 4 shows a process of forming one piezoelectric vibrator. After directly bonding a large-area wafer, a plurality of drive electrodes are collectively formed and cut. It goes without saying that it is equally possible to manufacture as many piezoelectric vibrators as possible.

(Embodiment 2) FIG. 11 is a side view of a piezoelectric vibrator according to Embodiment 2 of the present invention. In FIG.
(a) is a side view of two piezoelectric single crystal wafers having different thicknesses. In the second embodiment, the piezoelectric single crystal wafer 1
Z-cut lithium niobate having a diameter of 2 inches and a thickness of t = 50 μm as 1 and 12;
μm was used. Next, as shown in (b), these are directly bonded and integrated. Thereafter, as shown in (c), the thick lower wafer is thinned by single-side polishing. Finally, drive electrodes 13 are formed on the upper and lower surfaces of the integrated domain-inverted wafer, and the same piezoelectric vibrator as shown in FIG. 5 is completed. In the present piezoelectric vibrator, since a thin wafer is joined to a thick wafer, the overall thickness before polishing is increased and the mechanical strength is increased, so that the handling becomes easy. FIG.
In the embodiment shown in FIG. 1, a process of forming one piezoelectric vibrator is shown. However, after directly bonding a large-area wafer, a plurality of drive electrodes are collectively formed and cut. It is likewise possible to produce many piezoelectric vibrators at once. Although lithium niobate is used as the piezoelectric single crystal in the present embodiment, it goes without saying that the same effect can be obtained by using a single crystal piezoelectric material such as lithium tantalate and lithium borate. .

(Third Embodiment) FIG. 12 is a side view of a piezoelectric vibrator according to a third embodiment of the present invention. In FIG.
(a) shows piezoelectric single crystal wafers 11 and 1 having substantially the same thickness.
FIG. 2 is a side view of FIG. In the third embodiment, the piezoelectric single crystal wafers 11 and 12 have a diameter of 3 inches and a thickness t = 100 μm.
Z-cut lithium tantalate was used. These are then directly bonded and integrated as shown in (b) to obtain a domain-inverted wafer. Thereafter, as shown in (c), the sheet is thinned by double-side polishing. Finally, the drive electrodes 13 are formed on the upper and lower surfaces of the domain-inverted wafer, and a piezoelectric vibrator similar to that shown in FIG. 5 is completed. Since the vibrator has a thicker wafer bonded thereto, the overall thickness before polishing increases, and the mechanical strength increases, thereby facilitating handling. Since a thicker wafer can be polished with high accuracy, an improvement in accuracy can be expected by processing the thick wafers after bonding them together. In addition, since the surfaces to be polished have the same polarity and the same crystallinity (because there is no change in crystal composition due to Ti diffusion or the like), there is an advantage that the polishing rates on both surfaces are almost equal.

There is no particular limitation on the cut angle of the substrate, and if the bonding is performed with the directions of the polarization axes substantially reversed, one-wavelength resonance can be obtained in a desired mode. Temperature characteristics, coupling coefficient, and the like required for a product can be easily selected as appropriate. Further, in the embodiment shown in FIG. 12, a process of forming one piezoelectric vibrator is shown, but after directly bonding a large area wafer, a plurality of drive electrodes are collectively formed, It is also possible to manufacture many piezoelectric vibrators at once by cutting. Although lithium niobate is used as the piezoelectric single crystal in the present embodiment, it goes without saying that the same effect can be obtained by using a single crystal piezoelectric material such as lithium tantalate and lithium borate. .

(Embodiment 4) As described above, the vibrator of the present invention can increase the upper limit of the resonance frequency by direct bonding of two wafers, and cannot confine it conventionally. It is also excellent in that a high-performance vibrator can be obtained in the thickness longitudinal vibration mode. In the energy trap type piezoelectric vibrator, when the cross width of the drive electrodes becomes excessive, a vibration called an anharmonic vibration mode is excited in the electrodes and appears as spurious. However, if the intersection width is too small, sufficient energy will not be confined under the electrode,
It has contradictory characteristics that the characteristics of the vibrator are deteriorated. Therefore, it is necessary to optimize and use the intersection width of the drive electrodes. Accordingly, the optimum value was experimentally obtained by actually changing the intersection width of the drive electrodes. Note that the intersection width is defined by the diameter of the circular electrode.

FIG. 13 is a diagram showing the relationship between the cross width of the driving electrodes of the piezoelectric vibrator manufactured by the process shown in the first embodiment of the present invention and the spurious. FIG. 3 is a diagram illustrating a relationship between a cross width of a drive electrode of an energy trap type piezoelectric vibrator and a spurious frequency. The horizontal axis represents the intersection width l of the drive electrodes normalized by the substrate thickness H, and the vertical axis represents the spurious frequency normalized based on the resonance frequency. FIG. 14 shows the frequency characteristics of an actually manufactured piezoelectric vibrator. As can be seen from the data in FIGS. 13 and 14, as the intersection width of the electrodes is increased, the spurious S1 and S2 due to the nonharmonic higher-order mode appear closer to the main resonance. This is a phenomenon peculiar to the energy trap type vibrator, and also proves that the vibrator according to the present invention satisfactorily confines the second harmonic. By optimizing the electrode crossing width, it is possible to obtain a piezoelectric vibrator that is less affected by spurious.

FIG. 14 shows that the 1 / H of the piezoelectric vibrator is 3, 4,
These are the results measured for cases 5 and 6, where 1 / H is 3
In the following, it can be seen that the mode is almost the single mode. The l / H was further changed, and the optimum intersection width was experimentally obtained. As a result, the level difference between the main resonance and the nearest spurious S1 mode in the range of 2 <l / H <7 was 10d.
B or more, and good spurious characteristics were obtained. Since the vibrator of the present invention has good reproducibility at the time of production, this condition became clear, and it was confirmed that a vibrator having the same characteristics was always stably obtained.

(Embodiment 5) Furthermore, the performance of the resonator of the present invention can be further improved by optimizing the mounting method on the mounting board. FIG. 15 is a perspective view of a device using the piezoelectric vibrator manufactured by the process of the first embodiment of the present invention. The vibrator 51 is supported by an external connection electrode 53 on a mounting substrate 52 with a conductive adhesive 54, and the direction in which the electrode is pulled out and the direction in which the electrode is supported substantially match the X-axis direction of the single crystal. When the electrode is pulled out in the Y direction, as shown in FIG. 16B, many spurious components appear on the higher frequency side than the anti-resonance frequency.
It is preferable to take out and hold in the X-axis direction. Such characteristics have also been made clear by using the vibrator of the present invention having high manufacturing reproducibility. With such mounting, a single resonance as shown in FIG. 16A is obtained. As described above, in the thickness longitudinal mode vibrator directly joined by inverting the polarization axis according to the present invention, the thickness is doubled by the direct joining as compared with the conventional one, and further, the intersection width of the drive electrode is optimized, and the electrode is taken out. By optimizing the direction, a high-performance, high-frequency piezoelectric vibrator that cannot be obtained by the conventional method can be obtained.

(Embodiment 6) Further, the vibrator of the present invention has a special effect even in a vibrator utilizing a thickness-shear vibration mode. FIG. 17 is a side view of the piezoelectric vibrator according to the sixth embodiment of the present invention using the thickness-shear vibration mode. In FIG. 17, (a) is a side view of two piezoelectric single crystal wafers having the same thickness, and the direction of polarization Ps is indicated by an arrow in the figure. In this embodiment, the piezoelectric single crystal wafers 11 and 12 have a diameter of 2 inches and a thickness t = 100 μm.
X-cut lithium tantalate is used. Next, as shown in (b), the polarization axes of these plates are reversed, and they are directly joined and integrated. Thereafter, as shown in FIG. 3C, drive electrodes are formed on the upper and lower surfaces of the bonded domain-inverted wafer, and an energy trap type piezoelectric vibrator is completed as shown in FIG. In these plates, the thickness shear vibration wave is excited by the drive electrodes arranged opposite to each other.

In the present oscillator, since a wafer (single crystal plate) having the same plate thickness is bonded, a bonding interface = a polarization reversal interface at a position of 1/2 of the thickness with high accuracy, and the flatness of the polarization reversal interface is good. For this reason, it is possible to excite resonance of one wavelength in an ideal state like the displacement curve shown in (c) of FIG. 17, and the resonance resistance as in the vibrator of FIG. , And a characteristic in which spurious is extremely small near the resonance frequency can be obtained. In the X-plate, since the polarization axis is parallel to the plate surface, the conventional domain-inverted layer forming technique does not generate an electric field in the direction contributing to domain-inversion even after heat treatment and proton exchange, as in the present invention. The structure is difficult to realize. Further, when an X-cut ± 10 ° lithium tantalate plate is used, usually, as described above, a thickness having a high sound velocity and a low thickness having a low sound velocity displaced in a direction perpendicular to the displacement direction of the shear vibration (main vibration). Slip wave (unnecessary wave)
However, this unwanted wave can be effectively suppressed by directly joining the crystal axes while shifting them intentionally.

FIG. 18 (b) shows the admittance characteristics of a comparative example in which the crystal axes are aligned and directly joined. Despite having a total thickness of 200 μm, this corresponds to a thickness shear wave of a 100 μm thick single plate.
It can be seen that resonance occurs near 0 MHz. But,
As shown in (b), similar to the single plate, resonance occurs at about the same level around 16 MHz. These two resonances are resonances of a thickness shear wave having a high sound velocity and a thickness shear wave having a low sound velocity, and their displacement directions are orthogonal to each other. These resonances occur in square or circular elements,
When a square or circular electrode is formed, it is difficult to suppress the wave because it is essentially a generated wave. for that reason,
Usually, a method has been employed in which the aspect ratio of the electrodes is changed to reduce the confinement of unnecessary waves or to strip the unnecessary waves to suppress the excitation of unnecessary waves. However, in order to form a thin high-frequency element into a strip, an advanced processing technique is required.
Several MHz. For example, in a device in the 12 MHz band, the optimum dimension is approximately W300 μm × L2.0 mm × H1.
It is on the order of 50 μm, making handling very difficult.

This problem can be solved as follows in the piezoelectric vibrator of the present embodiment. In FIG. 18, (a) shows that the crystal axis of the piezoelectric single crystal plate is intentionally shifted by 1 °,
It is the admittance characteristic of the plate joined directly. As can be seen from the figure, while the levels of the main waves are substantially the same, the slip wave having a low sound speed, which is an unnecessary wave, is remarkably suppressed. This can be explained by the difference in the magnitude of the electromechanical coupling coefficient between the two vibration modes. The thickness shear vibration having a high sound velocity has a large coupling coefficient of about 47%. On the other hand, the coupling coefficient of the thickness shear vibration having a low sound velocity is about 6%. Therefore, if the crystal axes of the bonded piezoelectric bodies are intentionally shifted, as a result, the displacement directions of the vibrations excited in the respective piezoelectric bodies shift, resulting in a propagation loss.
Vibration waves having a small coupling coefficient are suppressed. On the other hand, since the thickness shear vibration wave having a high sound velocity has a large coupling coefficient, the displacement in the displacement direction is allowed, and the characteristic deterioration is reduced. By utilizing this characteristic, in the vibrator of the present embodiment, it is possible to effectively suppress unnecessary waves which have been difficult to suppress.

In this embodiment, two X plates are used, and the Z and Y axes are shifted from each other to suppress spurious.
It goes without saying that the same effect can be obtained even if the axis is shifted. In this case, an X ± 10 ° rotating plate may be attached. For example, by laminating the X + 1 ° rotary plate and the X-1 ° rotary plate, the directions of displacement are slightly shifted from each other, and unnecessary waves are suppressed. In this case, the X and Y axis directions of each other are
They may be joined together or slightly shifted. If the angle deviation at this time exceeds ± 15 °, the characteristics are remarkably deteriorated as in the case of the thickness longitudinal vibrator, and therefore, it is preferable to suppress the deviation within ± 15 °. More preferably, the vibration is suppressed to within 3 °, and if it is within ± 3 °, deterioration of main vibration is smaller than the effect of suppressing unnecessary waves, and an excellent thickness shear resonator can be obtained. This configuration is an effect peculiar to the direct bonding technology that enables the bonding even when the crystal axes are slightly shifted from each other, and cannot be obtained by the above-described conventional domain-inverted layer forming technology. . In the above-mentioned thickness longitudinal mode resonator, the spuriousness was originally small, so the effect of suppressing the spuriousness by shifting the joining angle was not conspicuously obtained, but depending on the design, new spuriousness may occur. . However, in the direct joining used in the present invention,
Since the joining can be performed with the angle shifted by a desired angle, an effect of suppressing unnecessary vibration having a small coupling coefficient can be expected. It should be noted that a deviation of 0.1 ° or more is sufficient for suppressing spurious vibrations in the thickness direction.

(Embodiment 7) In addition, since the thickness-slip domain-inverted junction can be doubled in the same frequency band, an element having high mechanical strength can be obtained even if the element is stripped. Excellent in point. A strip type vibrator is a rectangular piezoelectric body having a rectangular cross section,
This is an element in which a counter electrode is provided in the entire width direction. FIG.
9A is a top view of the strip-type piezoelectric vibrator. FIG. In this vibrator, the Z axis (polarization axis) of the other X-cut lithium tantalate is rotated by 0.4 ° with respect to the crystal axis of the other X-cut lithium tantalate, and the Z-axis of each other is The strip is substantially inverted, and the longitudinal direction of the strip is an axis inclined by 0.2 ° with respect to each of the axes that are bonded. Since the direction of the X axis is determined by the cut surface of the substrate, they substantially match. Further, as shown in (b), the electrodes 72 are formed over the entire width of the main surface of the piezoelectric vibrator 71, and the ends in the longitudinal direction are held by the conductive adhesive 73. When this element is used, for example, in an element in the 12 MHz band, the optimum dimension is about W300 μm ×
What was on the order of L2.0 mm × H150 μm was changed to W
The thickness is 300 μm × L2.0 mm × H300 μm, and the thickness can be doubled, so that the handling becomes easy. Furthermore, by intentionally displacing the crystal axes of each other, a device having good spurious characteristics can be obtained, and the processing accuracy can be reduced.

FIG. 20 shows admittance characteristics of the piezoelectric vibrator according to the seventh embodiment of the present invention. As mentioned earlier,
This vibrator is obtained by intentionally shifting the crystal axes of each other by 0.4 °, and cutting out a directly joined piezoelectric plate in a direction intermediate to each X axis (48 ° direction in the present embodiment) to form a strip. It is. As can be seen from the figure, a good spurious characteristic in which unnecessary waves are suppressed is shown. Note that the cutout angle is not limited to this, and in consideration of the symmetry of the crystal with respect to the displacement direction of the main wave, a clockwise direction of 48 ° ± 10 ° with respect to each Y axis. It can be set arbitrarily. In addition, other misalignment angles of the crystal axes are allowed if they are within ± 15 °. In the above-described embodiment, the oscillator formed by direct bonding has been described. However, it is needless to say that a configuration using a domain-inverted wafer by direct bonding can be applied to a piezoelectric filter.

[0040]

As described above, according to the present invention, a domain-inverted wafer having a domain-inverted structure can be easily manufactured by a simple process of direct bonding without using any adhesive.
Compared with a conventional piezoelectric vibrator that excites an odd-order vibration mode of primary and tertiary by exciting even-order vibration modes of second and fourth order, if it is attempted to obtain the same resonance frequency, The thickness of the body plate can be doubled compared to the conventional case. Therefore, it is possible to obtain a piezoelectric vibrator having a higher frequency accuracy and a higher frequency accuracy by using the conventional thin plate processing technique. By intentionally shifting the crystal axis of the piezoelectric single crystal plate to be joined, spurious can be suppressed, and the characteristics of the element are improved. Further, since the handling is easy, the productivity of the piezoelectric vibrator is improved, and the yield of the element is also increased. In addition, the adoption of direct bonding suppresses variations in the thickness of the domain-inverted regions,
The flatness of the domain-inverted boundary also increases, and performance such as resonance resistance and dynamic range can be improved. Furthermore, even in a piezoelectric body in which the Poisson's ratio is 1/3 or less, in which the energy cannot be confined in the thickness longitudinal mode in the past, the confinement is possible in the piezoelectric body directly joined by reversing the polarization. The generation of spurious components is small. Needless to say, this can be applied to a vibrator having no strip shape. Furthermore, in the thickness mode slip resonator with good temperature characteristics, the crystal axis of the piezoelectric body directly joined is intentionally shifted,
The spurious can be suppressed effectively. In order to further increase the thickness, it is possible to obtain a strip element which is strong and has excellent spurious characteristics at a higher frequency than in the past.

[Brief description of the drawings]

FIG. 1 is a side view showing a manufacturing process of a first piezoelectric vibrator by a conventional method.

FIG. 2 is a side view showing a manufacturing process of a second piezoelectric vibrator by a conventional method.

FIG. 3 is a top view and a perspective view of a conventional strip resonator.

FIG. 4 is a side view showing steps of the piezoelectric vibrator according to the first embodiment of the present invention.

FIG. 5 is a graph of a frequency characteristic of the piezoelectric vibrator according to the first embodiment of the present invention.

FIG. 6 is a diagram showing characteristics when an unfavorable configuration is employed in the first embodiment of the present invention;

FIG. 7 is a diagram showing a frequency-rising confinement oscillator and its dispersion curve.

FIG. 8 is a diagram showing a reduced-frequency confinement oscillator and its dispersion curve.

FIG. 9 is a frequency characteristic diagram of the piezoelectric vibrator manufactured according to the first embodiment of the present invention.

FIG. 10 is a frequency characteristic diagram of a conventional harmonic piezoelectric vibrator.

FIG. 11 is a side view showing a step of manufacturing a piezoelectric vibrator according to Embodiment 2 of the present invention.

FIG. 12 is a side view showing a step of manufacturing a piezoelectric vibrator according to Embodiment 3 of the present invention.

FIG. 13 is a diagram showing the relationship between the intersection width of the drive electrode of the piezoelectric vibrator of the present invention and the higher harmonic mode.

FIG. 14 is a diagram showing frequency characteristics when the width of intersection of drive electrodes of the piezoelectric vibrator is changed.

FIG. 15 is a diagram of a mounting form of a piezoelectric vibrator according to a fifth embodiment of the present invention.

FIG. 16 is a frequency characteristic diagram of the piezoelectric vibrator according to the fifth embodiment of the present invention.

FIG. 17 is a side view showing a step of manufacturing a piezoelectric vibrator according to Embodiment 6 of the present invention.

FIG. 18 is a frequency characteristic diagram of the piezoelectric vibrator manufactured according to the sixth embodiment of the present invention.

FIG. 19 is a top view and a perspective view of a piezoelectric vibrator according to a seventh embodiment of the present invention.

FIG. 20 is a frequency characteristic diagram of the piezoelectric vibrator according to the seventh embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 piezoelectric single crystal (upper wafer) 12 piezoelectric single crystal (lower wafer) 13 drive electrode 51 piezoelectric vibrator 52 mounting board 53 external connection electrode 54 conductive adhesive 71 piezoelectric vibrator 72 drive electrode 73 conductive adhesive

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Osamu Kawasaki, Inventor 1006 Ojidoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (17)

[Claims] 1. Spontaneous polarization, wherein the axis directions of the spontaneous polarization are substantially opposite to each other, and the other crystal axes are directly shifted so that the angle between them is shifted by an angle not including 0 degree. A piezoelectric device comprising: two piezoelectric single crystal plates integrated by bonding; and drive electrodes formed on two main surfaces of the directly bonded piezoelectric single crystal plates so as to face each other. Vibrator. 2. The piezoelectric vibrator according to claim 1, wherein said piezoelectric single crystal plate is made of lithium niobate, lithium tantalate or lithium borate. 3. The piezoelectric vibrator according to claim 1, wherein the integrated piezoelectric single crystal plate has a shape for exciting even-order harmonics of thickness longitudinal vibration by a drive electrode. 4. The two piezoelectric single crystal plates are integrated so that the deviation of the orientation of a crystal axis orthogonal to the axis of spontaneous polarization is limited to an angle of ± 5 ° or less. 3. The piezoelectric vibrator according to 3. 5. The two piezoelectric single crystal plates have a Poisson's ratio of 1/3 or less, and a value of an electromechanical coupling coefficient in a thickness longitudinal vibration mode is a value of an electromechanical coupling coefficient in a thickness shear vibration mode. The piezoelectric vibrator according to claim 3, wherein the piezoelectric vibrator is made of a piezoelectric material that is sufficiently larger than the piezoelectric material, and the driving electrodes are arranged so as to confine even-order harmonic energy. 6. The piezoelectric single crystal plate is made of Z-cut lithium niobate or Z-cut lithium tantalate, and each of the drive electrodes is at least assuming that the thickness of the integrated piezoelectric single crystal plate is H. The piezoelectric vibrator according to claim 3, having a length and a width of 2H or more and 7H or less. 7. A substrate for supporting the piezoelectric vibrator, wherein an electrode for external connection is formed on the substrate, and the piezoelectric vibrator is supported by the external connection electrode with a conductive adhesive, and a driving electrode 4. The piezoelectric vibrator according to claim 3, wherein a pulling-out direction and a direction in which the piezoelectric vibrator is supported substantially coincide with the X-axis direction of the single crystal plate. 8. The two piezoelectric single crystal plates having the same thickness, and the second harmonic of thickness longitudinal vibration among the even harmonics is excited as a main wave. Piezoelectric vibrator. 9. The piezoelectric vibrator according to claim 1, wherein the integrated piezoelectric single crystal plate has a shape in which an even harmonic of thickness shear vibration is excited by the drive electrode. 10. The two piezoelectric single crystal plates are bonded by shifting the orientation of a crystal axis orthogonal to the axis of spontaneous polarization by an angle within ± 15 ° excluding 0 °. The piezoelectric vibrator according to claim 9. 11. The two piezoelectric single crystal plates are lithium tantalate X ± 10 ° rotating plates, and the value of the electrode mechanical coupling coefficient among the two types of thickness shear vibration modes excited by the piezoelectric plates. In the thickness-shear vibrator using the main wave having a large value and suppressing the unnecessary wave having the small value of the other electromechanical coupling coefficient, the two piezoelectric single crystal plates have the spontaneous polarization directions substantially opposite to each other. 10. The piezoelectric vibrator according to claim 9, wherein the crystal orientations orthogonal to each other are shifted within ± 15 ° excluding 0 °. 12. The two piezoelectric single crystal plates are rod-shaped lithium tantalate X ± 10 ° rotating plates, and the driving electrodes are formed on two surfaces parallel to the X ± 10 ° rotating surface of the vibrator. Each is formed over the entire width, and the longitudinal direction of exciting the thickness shear vibration of the piezoelectric crystal plate is taken in a direction rotated clockwise by 38 ° to 58 ° from the Y ′ axis in the Y ′, Z ′ plane,
The piezoelectric vibrator according to claim 9, wherein an end in a longitudinal direction is held. 13. The method according to claim 9, wherein the two piezoelectric single crystal plates have the same thickness, and of the even harmonics, the second harmonic of the thickness shear vibration is excited as the main wave. Piezoelectric vibrator. 14. A piezoelectric single crystal plate having two spontaneous polarizations, each of which has a mirror surface polished to a mirror surface, and the bonded surface of the piezoelectric single crystal plate is cleaned and hydrophilized to form a crystal of the piezoelectric single crystal plate. The azimuths are superposed so as to be shifted at a certain angle not including 0 degree, and the bonding surfaces are adhered so that the axial direction of the spontaneous polarization is in the opposite direction, and the two adhered piezoelectric single crystal plates are heated. And said 2
A method for manufacturing a piezoelectric vibrator, comprising: integrating two piezoelectric single crystals; and forming drive electrodes facing each other on two main surfaces of the two integrated piezoelectric single crystal plates. 15. After the two piezoelectric single crystal plates are integrated, one surface of the integrated piezoelectric single crystal plate is polished to uniform thickness, and then the two main surfaces are opposed to each other. The method for manufacturing a piezoelectric vibrator according to claim 14, wherein a driving electrode is formed. 16. After the two piezoelectric single crystal plates are integrated, both surfaces of the integrated piezoelectric single crystal plate are polished to make the thickness uniform, and then the two main surfaces are opposed to each other. The method for manufacturing a piezoelectric vibrator according to claim 14, wherein a driving electrode is formed. 17. The method according to claim 14, wherein the piezoelectric single crystal plate is made of lithium niobate, lithium tantalate or lithium borate.