JP2007189492A - Method of manufacturing piezoelectric substrate, piezoelectric substrate, piezoelectric transducer, and piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for mass-producing a mesa type piezoelectric substrate having a trapezoidal projection. <P>SOLUTION: In the piezoelectric substrate where masks with openings are arranged on both principal planes of the piezoelectric substrate at a prescribed interval between the principal planes and the masks and piezoelectric films are epitaxially grown under atmospheric pressure, the piezoelectric films formed at the openings of the masks and their vicinities are formed in trapezoidal shapes nearly in almost middles of both the principal planes of the piezoelectric substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a trapezoidal mesa type piezoelectric substrate in which a piezoelectric film is formed on a surface of a piezoelectric substrate using an epitaxial growth method, a manufacturing method thereof, and a piezoelectric vibrator and a piezoelectric oscillator using the piezoelectric substrate.

A crystal resonator is widely used as a reference frequency source for industrial equipment and consumer equipment because it has advantages such as small size, small secular change, high accuracy, and high frequency stability. In recent years, the size and weight of devices have been reduced, and the demand for miniaturization of crystal resonators has increased, and there is a great demand for surface mount crystal resonators suitable for automating the assembly of electronic components.
Quartz is a physically and chemically stable substance, but natural quartz is problematic in terms of quality and quantity, so today we use artificial quartz that is superior in terms of quality stability and supply stability. To manufacture crystal units. Among them, AT-cut crystal resonators having a frequency-temperature characteristic exhibiting a cubic curve are used in large quantities in communication devices such as mobile phones. As is well known, an AT-cut crystal unit is a crystal plate (AT-cut crystal plate) obtained by rotating a crystal plate (Y plate) perpendicular to the crystal axis Y of the crystal around the crystal axis X for about 35 degrees 15 minutes. ) And a metal film are attached to both main surfaces using a vacuum deposition or sputtering apparatus, and the package is hermetically sealed. The vibration mode of the AT-cut quartz resonator is thickness shear vibration, the resonance frequency f is proportional to the reciprocal of the thickness t, and the proportional constant k is determined from the crystal density ρ and the elastic constant c ′ that depends on the cutting angle. Approx. 1.65MH
z · mm.

FIG. 6 is a diagram showing a configuration of a conventional AT-cut crystal resonator element, in which FIG.
(B) is a cross-sectional view taken along the line PP, (c) is a cross-sectional view taken along the line Q-Q, (d),
(E) is a figure which shows the displacement distribution of the thickness shear vibration seen from the X-axis direction (longitudinal direction) and the Z'-axis direction (short side direction), respectively. As shown on the left side of FIG. 6, the rectangular AT-cut quartz plate 11 generally has the longitudinal direction (length L) as the X-axis direction and the short direction (width W) as the Z′-axis direction. is there. Electrodes 12a and 12b are formed on the front and back surfaces of the AT-cut quartz plate 11 through a mask in a vacuum deposition or sputtering apparatus to form a quartz crystal resonator element. The terminal electrode (not shown) on the package side and the lead electrode extending from each of the electrodes 12a and 12b to the edge of the AT-cut quartz plate 11 are conductively fixed using the conductive adhesives 13a and 13b, and the crystal is crystallized. Configure the vibrator.

An electrical equivalent circuit of a crystal resonator element configured as described above generally has an inductance L
1, a circuit in which a capacitance C0 is connected in parallel to a series circuit of a capacitor C1 and a resistor R1. Here, the inductance L1, the capacitance C1, and the capacitance C0 depend on the thickness of the crystal plate and the area of the electrode, and the resistance R1 represents the loss of vibration energy.

As shown in FIGS. 6D and 6E, the vibration displacement distribution in the thickness-slip mode, the side ratio of the crystal plate 11 (the ratio of the length L or width W of the crystal plate to the thickness t, L / t or When (W / t) is reduced, the distance between the electrodes 12a and 12b and the end of the AT-cut quartz plate 11 is narrowed, and even if designed using the energy confinement theory, the vibration energy cannot be confined under the electrodes and the support portion. Leaks to increase the series resonance resistance R1. Even if the side ratio is selected as the optimum value, a part of the vibration energy of the main vibration is converted into the contour mode at the end of the AT-cut quartz plate 11 to degrade the series resonance resistance R1 of the quartz vibration element and the resonance frequency. An unnecessary mode is excited in the vicinity.

As means for improving the series resonance resistance, a method of beveling the end of the AT-cut quartz plate 11, or a quartz plate having a mesa structure at the center of the main surface of the quartz plate 14 as shown in the sectional view of FIG. By confining the vibration energy of thickness-shear vibration in the center of the quartz plate, the influence of the support and conversion to other modes at the edges are reduced as much as possible, and the resistance R1 of the quartz resonator is improved. A crystal that suppresses unnecessary modes is used.

In recent years, with the miniaturization and high functionality of mobile phones and the like, there is a strong demand for miniaturization and thinning of crystal resonators. For example, there is a demand for 2.5 mm × 2.0 mm × 0.7 mm in which the external dimensions of the crystal resonator are further reduced from 3.2 mm × 2.5 mm × 1.0 mm. In response to such demands, unlike conventional methods in which a quartz plate is obtained by cutting an artificial quartz grown by a hydrothermal synthesis method in a predetermined direction and polishing it to a predetermined thickness, a substrate such as sapphire, silicon, GaAs, etc. Patent Document 1 discloses a vapor phase growth method for epitaxially growing a quartz film thereon. FIG. 8 is a schematic diagram of an apparatus for performing epitaxial growth disclosed in Patent Document 1. A quartz film grown using this apparatus is evaluated using an X-ray diffraction, a scanning electron microscope, and an infrared spectrometer. As a result, it is disclosed that the crystal thin film has excellent crystallinity.

In Patent Document 2, after a crystal film is epitaxially grown on a silicon (Si) substrate using the apparatus shown in FIG. 8, the substrate is etched into a concave shape while leaving the crystal film, and the crystal film is cut out. A method is disclosed in which a crystal part is formed by processing to form a vibration part and attaching electrodes to both sides of the vibration part. Further, in Patent Document 3, as shown in FIG. 9, a substrate 21 is arranged on a substrate table 20 in an apparatus for epitaxial growth of a crystal film, and a mask 22 is placed on the substrate 21. A method of epitaxially growing a quartz film through the mask 22 to obtain a quartz thin film having a shape corresponding to the size of the opening of the mask is disclosed.

Patent Document 4 discloses a method for producing a plano-convex crystal epitaxial thin film. As shown in FIG. 10A, a base 31 having a large number of depressions having a desired curvature is formed in a material such as sapphire, silicon, or gallium arsenide. The base 31 is placed in the apparatus shown in FIG. 8, and alcohol is vaporized as a silicon source to flow in. A buffer layer is formed in the depression, and a crystal epitaxial thin film is formed thereon. Then, as shown in FIG. 10B, the crystal epitaxial thin film 32 is peeled off from the base 31 and placed so as to be fitted into a dummy base having the same shape as in FIG. It is disclosed that a plano-convex crystal thin film can be obtained by polishing while pressing against an epitaxial thin film.
In Patent Document 5, as shown in FIG. 11, a mask 41 is placed on a sapphire base 40 on which a SiO ₂ film is processed. A method of forming a quartz film by ejecting a piezoelectric material in a gas phase state from a nozzle 42 provided on an upper portion of a mask 41 is disclosed. At this time, it is disclosed that by making the inner diameter of the nozzle 42 smaller than the inner diameter of the mask 41, the formed thin film crystal 43 becomes similar to the shape (semi-ellipsoid) subjected to the beveling process.
JP 2002-80296 A Japanese Patent No. 3703773 Japanese Patent Laid-Open No. 2005-213080 JP 2005-239495 A JP 2005-295229 A

However, the crystal thin film resonator of Patent Document 2 is a crystal resonator having a flat vibrating portion, and the crystal thin film of Patent Document 3 is also a flat crystal substrate, where the center portion of the desired crystal substrate is thick and the peripheral portion is A quartz substrate that is gently thinned cannot be obtained.
Further, in the method for producing a plano-convex crystal thin film disclosed in Patent Document 4, a base having a large number of depressions is made of a material such as sapphire, silicon, or gallium arsenide, and a buffer layer is previously formed in the depressions of the base. After forming the crystal, it is necessary to form a quartz epitaxial thin film, peel it off, and then polish and finish it, resulting in a significant increase in man-hours and increased costs.
Further, in the configuration of Patent Document 5, although a quartz thin film having a beveled shape (semi-ellipsoid) can be obtained, there is a problem that it is difficult to handle the quartz thin film.
An object of the present invention is to provide a manufacturing method for manufacturing a mesa crystal substrate having a trapezoidal protrusion at the center of both surfaces of a crystal substrate at a low cost, and a crystal resonator and a crystal oscillator using the crystal substrate. The purpose is to do.

In the piezoelectric substrate according to the present invention, in order to reduce the size of the piezoelectric substrate, a mask having a plurality of openings is arranged at a predetermined interval from both main surfaces of the piezoelectric substrate, and the piezoelectric substrate exposed in the openings is provided. A method of manufacturing a piezoelectric substrate in which a piezoelectric film is epitaxially grown on a surface under atmospheric pressure, wherein the quartz film formed in and near the opening of the mask forms a plurality of trapezoidal protrusions on both sides of the piezoelectric substrate In this manufacturing method, the piezoelectric substrate is cut along the periphery of the trapezoidal protrusion to obtain a piezoelectric substrate piece having the trapezoidal protrusion.
By using a large piezoelectric substrate and a mask having a matrix-like opening as the piezoelectric substrate, it becomes possible to manufacture a large number of piezoelectric substrates having trapezoidal protrusions with high accuracy, and the manufacturing cost can be greatly reduced. There is an advantage. Further, since the trapezoidal protrusion of the piezoelectric film depends on the shape of the opening of the mask, the distance between the quartz substrate and the mask, and the time for forming the piezoelectric epitaxial thin film, there is an advantage that it can be configured with extremely high accuracy.

The piezoelectric substrate according to the present invention is a piezoelectric substrate provided with trapezoidal protrusions facing substantially central portions of both main surfaces of the piezoelectric substrate, and the trapezoidal protrusions are formed by an epitaxial growth method.
The piezoelectric substrate having the trapezoidal protrusion portion of the piezoelectric film has an effect of confining vibration energy in the central portion, which is advantageous for downsizing the piezoelectric substrate.

A piezoelectric vibrator according to the present invention includes a piezoelectric vibration element in which electrodes are formed on both surfaces of a piezoelectric substrate formed as described above, a surface mounting package, and a lid for sealing the opening of the package, A piezoelectric vibrator in which the piezoelectric vibration element is accommodated in the package and the package is hermetically sealed by the lid.
The piezoelectric vibrator configured in this way can be reduced in size and has a small series resonance resistance,
In addition, a piezoelectric vibrator in which unnecessary modes near the resonance frequency are suppressed can be realized at low cost.

A piezoelectric oscillator including the piezoelectric vibrator configured as described above and an oscillation circuit is configured. The piezoelectric oscillator configured as described above has an effect that a piezoelectric oscillator having a small size, a high frequency, and a wide frequency variable range can be obtained and a piezoelectric oscillator with less frequency jump phenomenon can be obtained.

The piezoelectric substrate is an AT-cut quartz substrate, its manufacturing method, and the piezoelectric substrate as A
A crystal resonator is configured as a T-cut crystal substrate. The crystal resonator configured as described above has excellent temperature characteristics and frequency aging characteristics.

A crystal oscillator including the crystal resonator and an oscillation circuit is configured. The crystal oscillator configured as described above is a crystal oscillator having excellent temperature characteristics and frequency aging.

The piezoelectric substrate is a PZT (lead zirconate titanate) substrate;
And a piezoelectric vibrator is constituted by using the piezoelectric substrate as PZT. Since the PZT vibrator configured in this way has a large electromechanical coupling coefficient, a PZT vibrator having a wide resonator-antiresonator frequency interval can be obtained.

A piezoelectric oscillator including the PZT vibrator and an oscillation circuit is configured. Since the PZT oscillator configured as described above has a wide interval between the resonator and antiresonator frequencies of the PZT vibrator, a PZT oscillator having a wide frequency variable range can be obtained.

An embodiment of a quartz crystal substrate and a method for manufacturing the same according to the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged schematic view showing a quartz substrate and a mask arranged in the apparatus for performing epitaxial growth shown in FIG.
As shown in FIG. 1, in this embodiment, masks 2a and 2b are arranged with a distance 5 from both main surfaces of an AT-cut quartz substrate (hereinafter referred to as a quartz substrate) 1, and the masks 2a and 2b. Is mounted in an apparatus for performing epitaxial growth, and nozzles 3 are disposed above and below the masks 2a and 2b. Then, the raw material gas for the crystal thin film is discharged from the nozzle 3. The quartz substrate 1 is held at a high temperature (550 ° C. or higher), and the source gases ((tetraethoxysilane + N ₂ ), (O ₂ + N ₂ ), (HCl + N ₂ ), N ₂ )) are also heated to a predetermined flow rate. To do.

FIG. 2 is a perspective view in which masks 2a and 2b are mounted on both sides of the quartz substrate 1 at a predetermined interval. The quartz substrate 1 is polished to a predetermined thickness and polished or etched. And masks 2a and 2b having a plurality of openings 4 in a matrix.
In order to provide the gap 5 between the quartz substrate 1 and the masks 2a and 2b, a plurality of protrusions having a predetermined thickness may be formed on the masks 2a and 2b facing the quartz substrate 1. The mask 2a
The material 2b is one that can withstand high temperatures. The source gas discharged from the nozzle 3 is epitaxially grown on the quartz substrate 1 exposed in the opening 4 to form a quartz film 6. Further, the raw material gas entering from the gap 5 between the quartz substrate 1 and the masks 2a and 2b forms the inclined quartz film 6 from the edge of the opening 4 to the bottom of the shielding portion of the masks 2a and 2b. FIG.
(A) is a quartz crystal substrate 1 and a quartz crystal film 6 deposited on the quartz substrate 1 and crystallized in a trapezoidal shape. By cutting the quartz substrate 1 along the periphery of the trapezoidal projection, that is, along the broken line 7, a mesa crystal substrate having a trapezoidal projection shown in the cross-sectional view of FIG. It is done.

The thickness of the quartz substrate 1 and the size and thickness of the quartz film 6 formed thereon may be determined by design based on the required specifications.
FIG. 4 is a cross-sectional view of the crystal resonator of the present invention.
In the crystal resonator shown in FIG. 4, an electrode is attached to a mesa-type crystal substrate having a trapezoidal protrusion formed as described above to form a crystal resonator element X1, and this crystal resonator element X1 is attached to the ceramic package 8. And conductively fixed to the internal electrode 8a of the ceramic package 8 using the conductive adhesive 9. Further, the metallized portion 8b formed on the upper peripheral edge of the ceramic package 8 and the metal lid 10 are hermetically sealed by a sealing machine such as a resistance welding machine, an Au-Sn sealing machine, a solder sealing machine, a glass sealing machine or the like. The small crystal resonator Y1 is configured by stopping. With this configuration, it is possible to obtain a crystal resonator that is small in size, has a small series resonance resistance R1, and suppresses unnecessary modes.

FIG. 5 is a diagram showing a circuit configuration of a Colpitts-type crystal oscillator using the crystal resonator Y1 of the present invention. As is well known, the Colpitts oscillation circuit is an oscillation circuit configured by connecting an inductive element between the collector and base of a transistor Tr, and a capacitive element between the base and emitter and between the collector and emitter. As an inductive element between the collector and the base of the transistor Tr, a crystal resonator Y1 is used between the base and the ground. A resistor R1 is connected between the emitter and ground, a series connection circuit of capacitors C1 and C2 is connected between the base and ground, and capacitors C1 and C2 are connected.
A Colpitts type oscillation circuit is configured by connecting the connection midpoint of each of these and the emitter. Since the power source Vc and the ground are short-circuited at high frequency by the bypass capacitor, the crystal resonator Y1 used as an inductive element is inserted between the collector and the base in an equivalent circuit. Further, since the midpoint between the capacitors C1 and C2 is connected to the emitter, the capacitor C1 is inserted between the base and emitter of the transistor Tr, and the capacitor C2 is inserted between the collector and emitter. It will act as capacitive. The resistors R2 and R3 are bleeder resistors and set a base bias voltage.

Although the present invention has been described by taking an AT-cut quartz substrate as an example, the present invention is not limited to this,
LiTaO ₃ , LiNbO ₃ , LBO (Li ₂ B ₄ O ₇ ), Langasite (La ₃ Ga ₅ SiO _1)
4 ) Needless to say, the present invention can be widely applied to piezoelectric substrates such as PZT (lead zirconate titanate) substrates.

The enlarged schematic diagram of the quartz substrate and mask which are arrange | positioned in an apparatus. The perspective view of a quartz substrate and a mask. (A) is a figure showing an example of a quartz film formed on a quartz substrate, and (b) is a figure showing an example of a piece trapezoidal mesa type quartz substrate. Sectional drawing of the quartz oscillator formed using the quartz substrate of this invention. The figure which showed an example of the crystal oscillator comprised using the crystal oscillator of this invention. (A)-(e) is the schematic of the conventional crystal oscillator. (A)-(d) is sectional drawing of the conventional mesa type | mold crystal substrate. The figure which showed an example of the apparatus for performing epitaxial growth. The figure which showed an example of the manufacturing method of a crystal thin film. (A) and (b) are diagrams showing a method for producing a plano-convex crystal thin film. The figure which showed the formation method of a semi-elliptical crystal thin film.

Explanation of symbols

1 AT-cut quartz substrate, 2a, 2b mask, 3 nozzles, 4 openings, 5 gaps,
6 Crystal film, 7 Cutting line, 8 Ceramic package, 8a Terminal electrode, 8b Metallized part, 9 Conductive adhesive, 10 Metal lid, X1 Crystal resonator element, Y1 Crystal resonator, R1
, R2, R3, R4 resistance, C ₀ , C1, C2, C4, CL capacitance, Tr transistor, Vc power supply, V _O output

Claims (12)

A method for manufacturing a piezoelectric substrate, comprising: a mask having a plurality of openings arranged at a predetermined distance from both main surfaces of a piezoelectric substrate; and a piezoelectric film epitaxially grown at atmospheric pressure on the surface of the piezoelectric substrate exposed in the openings. Because
The quartz film formed in and near the opening of the mask forms a plurality of trapezoidal protrusions on both sides of the piezoelectric substrate, and cuts the piezoelectric substrate along the periphery of the trapezoidal protrusion, A method of manufacturing a piezoelectric substrate, comprising obtaining a piezoelectric substrate piece having a shape protrusion. A piezoelectric substrate comprising a trapezoidal protrusion facing substantially the center of both main surfaces of the piezoelectric substrate, the trapezoidal protrusion being formed by an epitaxial growth method. A piezoelectric vibration element having electrodes formed on both surfaces of the piezoelectric substrate according to claim 2, a surface mounting package, and a lid for sealing an opening of the package, wherein the piezoelectric vibration element is placed in the package. A piezoelectric vibrator characterized by being housed and hermetically sealing the package with the lid.   A piezoelectric oscillator comprising the piezoelectric vibrator according to claim 3 and an oscillation circuit. 2. The method for manufacturing a piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is an AT-cut quartz substrate.   The piezoelectric substrate according to claim 2, wherein the piezoelectric substrate is an AT-cut quartz substrate. The piezoelectric vibrator according to claim 3, wherein the piezoelectric substrate is an AT-cut quartz substrate.   A piezoelectric oscillator comprising the piezoelectric vibrator according to claim 7 and an oscillation circuit. 2. The method for manufacturing a piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is a PZT (lead zirconate titanate) substrate. The piezoelectric substrate according to claim 2, wherein the piezoelectric substrate is a PZT (lead zirconate titanate) substrate. 4. The piezoelectric vibrator according to claim 3, wherein the piezoelectric substrate is a PZT (lead zirconate titanate) substrate. A piezoelectric oscillator comprising the piezoelectric vibrator according to claim 11 and an oscillation circuit.

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