JP2004297727A - Piezoelectric vibrator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator which confines a thickness longitudinal fundamental wave by simple machining. <P>SOLUTION: One or more grooves 2 are formed on the front face of a substrate 1 composed of a piezoelectric material. On the rear face of the substrate 1, grooves 3 are formed across the grooves 2. In each of the grooves 2 and of the grooves 3 on the front and rear faces of the substrate 1, vibrating electrodes 4, 5 are provided to face each other in a portion where the grooves 2, 3 intersect. The thickness of the portion where the grooves 2, 3 intersect is preferably made equal to or thicker than 1/2 of the thickness (t) of the substrate 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric vibrator that realizes energy confinement of a fundamental wave having a longitudinal thickness.
[0002]
[Prior art]
For example, in the case of a piezoelectric material having an effective Poisson's ratio of less than 1/3, such as PT (lead titanate) or a bismuth layered compound, even if partial electrodes facing both surfaces of a substrate made of a piezoelectric material are formed, the thickness is basically the same as the thickness. I can't trap the waves. As a means for solving this, there is a method in which only the vibrating portion of the substrate is processed into a concave shape by an ultrasonic processing machine, but there is a problem that the processing is difficult.
[0003]
In order to solve such a problem, Patent Documents 1 and 2 disclose a structure in which a piezoelectric vibrator is realized by a laminated body structure and a vibrating electrode is formed by internal electrodes thereof. Further, Patent Document 3 discloses that the above problem is caused by providing a difference between at least one of density and compliance between an electrode portion and a non-electrode portion using a paste containing an element which can be changed by thermal diffusion and a conductive metal. Has been resolved. Patent Document 4 discloses a structure in which grooves are formed on the front and back surfaces of a substrate in the same direction, and vibration electrodes are formed so as to face each groove.
[0004]
[Patent Document 1]
JP-A-2-171010 [Patent Document 2]
JP 2003-32073 A [Patent Document 3]
JP-A-5-48378 [Patent Document 4]
JP-A-2000-323954.
[0005]
[Problems to be solved by the invention]
As described in Patent Literatures 1 and 2, in the case where the piezoelectric vibrator is configured by the laminated body, the laminating step is required, and the number of manufacturing steps is increased, which causes a problem that the cost is increased.
[0006]
Further, in the case of Patent Document 3, it is necessary to prepare a special paste for performing thermal diffusion according to the composition of the piezoelectric material, which also complicates the manufacturing process and raises the cost. is there.
[0007]
In addition, it has been found that the one described in Patent Document 4 is difficult to obtain one having sufficient characteristics.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method capable of confining a fundamental wave in a thickness direction by simple machining.
[0009]
[Means for Solving the Problems]
(1) The piezoelectric vibrator of the present invention has at least one groove formed on the surface of a substrate made of a piezoelectric material,
On the back surface of the substrate, a groove is formed so as to intersect the groove,
Vibrating electrodes facing each other are provided in the grooves on the front and back surfaces of the substrate at the intersections of the grooves on the front and back surfaces.
[0010]
(2) The piezoelectric vibrator of the present invention is characterized in that the thickness of the intersection of the grooves is at least half the thickness of the substrate.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a perspective view showing an embodiment of a piezoelectric vibrator according to the present invention, and FIGS. 2 and 3 are sectional views taken along lines XX and YY of FIG. 1, respectively. 1 to 3, reference numeral 1 denotes a substrate made of a piezoelectric material. The piezoelectric material used for the substrate 1 has an effective Poisson's ratio of less than 1/3. Specifically, it is preferable to use a lead titanate (PT) system, a bismuth layered compound, or the like. Also, a part of lead zirconate titanate (PZT) can be used. In addition to these piezoelectric materials, quartz, a compound having a langasite structure, a tantalum compound, a tungsten-bronze compound, and a compound having a (Bi _0.5 Na _0.5 ) TiO ₃ structure can be used.
[0012]
Reference numerals 2 and 3 denote grooves provided on the front and back surfaces of the substrate 1. These grooves 2 and 3 are formed so as to intersect at substantially the center of the substrate 1 (meaning a three-dimensional intersection). Note that the intersection angle between the grooves 2 and 3 need not be 90 degrees. These grooves 2 and 3 can be processed using a dicing saw or a rotary grindstone. Although the side surfaces of the grooves 2 and 3 may be 90 degrees with respect to the bottom surface, the extraction electrodes 4 and 3 may be formed on an inclined surface (that is, the angle between the bottom surface and the side surfaces of the grooves 2 and 3 exceeds 90 degrees). This is preferable in that the formation of No. 5 becomes easy.
[0013]
Vibration electrodes 4 and 5 are formed at the intersections of the grooves 2 and 3, respectively. Reference numerals 6 and 7 denote extraction electrodes of these vibrating electrodes 4 and 5, respectively.
[0014]
FIG. 4 is a diagram for explaining vibration confinement in a piezoelectric substrate having an effective Poisson's ratio of less than 1/3. FIG. 4A shows a configuration of the present embodiment in an approximate manner, and the interval between the vibrating electrodes 4 and 5 is narrower than other portions. In this case, ω ₀ is the resonance frequency of the thickness vibration, κ is the wave number of the thickness vibration, a real number means that the vibration is transmitted, and an imaginary number means that it is not transmitted. ω ₀ ′ is the resonance frequency of the electrodeless portion, and κ ′ is the wave number in the direction of the plate surface of the substrate.
[0015]
As shown in FIG. 4B, when a material having an effective Poisson's ratio of less than 1/3 is used for the substrate, the wave number becomes a real number on the higher frequency side than the cutoff frequency (resonant frequency) ω ₀ , ω ₀ ′, and the lower frequency side Is an imaginary number. As can be seen from FIG. 4 _(B), ω _0, the frequency between ~ω _{0 ',} a real number in the thin portion where the wave number is present in the electrode, since the imaginary number in the non-electrode portion, the vibrating electrodes 4 and 5 Vibration is confined in the opposite portion of the substrate, that is, in the thinned portion of the substrate.
[0016]
Such a piezoelectric vibrator can be manufactured by the following steps. First, raw material powders are weighed and mixed so that the composition ratio after firing becomes a target value. Next, it is calcined and finely pulverized. Next, the mixture is granulated, molded, debindered, and fired at 1100 to 1250 ° C. Next, this is primarily polished to obtain a mother substrate. A temporary electrode for polarization is attached to this mother substrate, and polarization is performed. This polarization is performed by applying a voltage of 3 kV / mm to 20 kV / mm in a silicon oil bath at 150 to 300 ° C.
[0017]
Next, secondary polishing is performed to remove the temporary electrode and obtain a target thickness. Next, the grooves 2 and 3 are processed for a plurality of piezoelectric vibrators. The electrodes 6 and 7 are formed by, for example, sputtering and vapor deposition of a silver electrode. In addition, as an electrode material, besides silver, an alloy of one or more of copper, aluminum, gold, chromium, nickel, tin, palladium, platinum, tungsten, molybdenum, and carbon can be used. .
[0018]
Thereafter, the mother substrate is cut vertically and horizontally to obtain individual substrates. After that, it is mounted on a package, and the characteristics are evaluated using an impedance analyzer.
[0019]
To explain a specific example, as a bismuth layered compound,
A material obtained by adding 0.5 wt% of MnCO ₃ to (Ba _0.6 Sr _0.3 La _0.1 ) Bi ₄ Ti ₄ O ₁₅ and calcining it was used. The polarization was performed by applying a voltage of 6 kV / mm in silicon oil for 5 minutes. The secondary polishing was performed to a thickness of 0.44 mm (t = 0.44 mm in FIG. 1). Moreover, it cut | disconnected by dicing saw so that the whole size might be (a = of FIG. 1) 7 mm x (b = of FIG. 1) 4.5 mm. The grooves 2 and 3 were formed with a dicing saw at a depth of 24 μm (c in FIG. 2) and a width of 1.6 mm (w in FIG. 1). The inclination angles of the side surfaces of the grooves 2 and 3 were set to about 100 degrees.
[0020]
In order to confirm the effect of confining the thickness longitudinal fundamental wave by the configuration of the present invention, the following samples (1) to (4) were prepared and their characteristics were compared. The material, size, groove depth, material, thickness, and size of the vibrating electrodes 4 and 5 of each sample were the same as described above.
[0021]
{Circle around (1)} (Conventional example) The vibrating electrodes 4 and 5 and the lead electrodes 6 and 7 were formed on a substrate on which the grooves 2 and 3 were not provided.
[0022]
{Circle around (2)} (Comparative Example 1) The groove 2 is provided only on the surface of the substrate 1, the groove 3 on the back surface of the substrate 1 is not provided, the vibration electrode 4 is provided at the center of the groove 2, and the vibration electrode 5 is provided on the opposite back surface. Was.
[0023]
{Circle around (3)} (Comparative Example 2) A groove 2 is provided on the front surface of the substrate 1, a groove is provided on the back surface of the substrate in parallel with the groove 2 on the front surface, and a vibration electrode 4 is provided at the center of the groove 2 to face the groove on the back surface. The vibrating electrode 5 is provided.
[0024]
(4) (Embodiment of the present invention) As shown in FIGS. 1 to 3, grooves 2 and 3 are provided on the front and back surfaces of the substrate 1 and vibration electrodes 4 and 5 are provided at the intersections of the grooves 2 and 3. Was.
[0025]
5 to 8 show changes in impedance and phase angle θz with respect to the frequency of each of the samples (1) to (4). As for the phase angle θz, −90 degrees indicates capacitive, and +90 degrees indicates inductive.
[0026]
In the conventional example of the sample (1) shown in FIG. 5, a plurality of modes (resonance and anti-resonance) are observed in the fundamental wave, and confinement of the frequency reduction type is not achieved. It can be seen that in the third harmonic, a single mode (resonance, antiresonance) is observed, and the phase (phase angle) is 0 degree or more, so that a frequency-reduced confinement is achieved.
[0027]
In Comparative Example 1 of Sample (2) shown in FIG. 6, a plurality of modes (resonance and anti-resonance) are observed for both the fundamental wave and the third harmonic, and a frequency-reduction type confinement is not achieved.
[0028]
In the comparative example 2 of the sample (3) shown in FIG. 7, a plurality of modes (resonance and anti-resonance) are observed in the fundamental wave, and confinement of the frequency reduction type is not achieved. Although the mode (resonance and antiresonance) of the third harmonic has become a single layer, the phase is 0 degrees or less, and confinement of a frequency lowering type has not been achieved.
[0029]
In the embodiment of the present invention of sample {circle around (4)} shown in FIG. 8, the fundamental wave has a single mode (resonance and anti-resonance), and the face is at 0 degrees or more, so that the frequency rise type confinement is obtained. You can see that is done. Although the mode (resonance and antiresonance) of the third harmonic is becoming a single layer, the face is at 0 degrees or less, and confinement of a frequency rising type is not performed.
[0030]
As described above, the grooves 2 and 3 are provided on the front and back surfaces of the substrate 1 so as to intersect with each other, and the vibration electrodes 4 and 5 are provided so as to face each other at the intersections of the grooves 2 and 3. The fundamental wave can be confined.
[0031]
According to the present invention, in a piezoelectric material having an effective Poisson's ratio of less than 1/3, the structure in which the grooves 2 and 3 are not provided can confine a third harmonic in a frequency-reduced manner. Has the advantage that it is possible to confine waves of different frequencies with one type of material. In addition, since the vibrating portion can be formed thin by simple machining and can be manufactured from a single plate, cost can be reduced.
[0032]
In practicing the present invention, the thickness of the portion where the grooves 2 and 3 intersect, that is, the thinnest portion (s in FIG. 2) is at least half (s / t ≧ 1/2) of the thickness of the substrate (t in FIG. 1). It is preferable to maintain the strength of the substrate 1. Further, it is necessary for the depth of the grooves 2 and 3 (c in FIG. 2) to be greater than the surface roughness (1 μm) of the substrate 1 in order to obtain the confinement effect.
[0033]
The shape of the vibration electrodes 4 and 5 is not limited to the circular shape in the illustrated example, but may be other shapes such as a polygon. Further, the vibration electrodes 4 and 5 are set to be equal to or less than the width of the grooves 2 and 3. The vibrating electrodes 4 and 5 may have a shape that is long in the longitudinal direction of the grooves 2 and 3 as long as the portions facing each other intersect with the grooves 2 and 3. It is also possible to provide a configuration in which a plurality of grooves are provided on at least one of the front and back surfaces of the substrate 1.
[0034]
【The invention's effect】
According to the present invention, grooves are formed so as to intersect on the front and back surfaces of a substrate made of a piezoelectric material, and the vibrating electrodes are configured to face each other at the intersections. Since it can be used and the grooves can be formed by machining, it is possible to provide a piezoelectric vibrator simply and inexpensively.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a piezoelectric vibrator according to the present invention.
FIG. 2 is a sectional view taken along line XX of FIG.
FIG. 3 is a sectional view taken along line YY of FIG. 1;
FIG. 4A is a schematic configuration diagram of the present invention, and FIG. 4B is a diagram for explaining that vibration of a thickness longitudinal fundamental wave can be confined.
FIG. 5 is a characteristic diagram showing changes in impedance and phase angle with respect to frequency in the case of a conventional example in which a groove is not provided in a substrate, for a thickness longitudinal fundamental wave and a third harmonic.
FIG. 6 is a characteristic diagram showing changes in impedance and phase angle with respect to frequency in a thickness longitudinal fundamental wave and a third harmonic in Comparative Example 1 in which a groove is provided only on one surface of a substrate.
FIG. 7 is a characteristic diagram showing changes in impedance and phase angle with respect to frequency for a thickness longitudinal fundamental wave and a third harmonic in Comparative Example 2 in which grooves are provided in the same direction on both surfaces of a substrate.
FIG. 8 is a characteristic diagram showing changes in impedance and phase angle with respect to frequency for a thickness longitudinal fundamental wave and a third harmonic in an embodiment of the present invention in which grooves are provided so as to cross each other on both surfaces of a substrate.
[Explanation of symbols]
1: Substrate, 2, 3: groove, 4, 5: vibration electrode, 5, 7, extraction electrode

Claims (2)

Forming at least one groove on the surface of the substrate made of piezoelectric material,
On the back surface of the substrate, a groove is formed so as to intersect the groove,
A piezoelectric vibrator, wherein vibration electrodes facing each other are provided in the grooves on the front and back surfaces of the substrate at locations where the grooves on the front and back surfaces intersect. The piezoelectric vibrator according to claim 1,
The thickness of the intersection of the grooves is at least half the thickness of the substrate.

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