JP4715652B2 - Piezoelectric vibrating piece - Google Patents

Description

  The present invention relates to an improvement of a piezoelectric vibrating piece using a piezoelectric material.

Piezoelectric vibrators are widely used in small information devices such as HDDs (hard disk drives), mobile computers, and IC cards, and mobile communication devices such as mobile phones, car phones, and paging systems.
As a piezoelectric vibrating piece used in such a piezoelectric vibrator, a so-called tuning fork including a base portion formed of a piezoelectric material, a pair of vibrating arms extending in parallel from the base portion, and a driving electrode formed on the vibrating arm. There is a so-called piezoelectric vibrating piece.

FIG. 7 is a schematic cross-sectional view of the tuning fork-type piezoelectric vibrating piece 1 having the pair of vibrating arms cut in the longitudinal direction.
In the figure, a pair of vibrating arms 2 and 3 are integrally fixed to a base part, extend in parallel with each other in a cantilevered manner from the base part, and when a driving voltage is applied, the tip parts of the vibration arms 2 and 3 come close to each other It bends and vibrates so as to be separated.
As shown in the figure, grooves 4, 4 and grooves 5, 5 are formed on the respective main surfaces of the vibrating arms 2, 3 from the front and back, and paired drive electrodes 6, 6, 7 are formed in these grooves. , 7 are formed. In addition, drive electrodes 7, 7, 6, and 6 are formed on both side surfaces of each vibrating arm so as to be paired with the inner electrodes. As a result, when a driving voltage is applied, each of the vibrating arms 2 and 3 is subjected to the bending vibration by forming an electric field as indicated by an arrow.

The tuning fork-type piezoelectric vibrating piece 1 having such a structure has grooves 4, 4, 5, 5 formed in the vibrating arms 2 and 3 in order to further increase the electric field efficiency and reduce the size. Therefore, the rigidity is lowered and stable bending vibration cannot be obtained.
When a tuning fork type outer shape is formed by wet etching, depending on the material, there is so-called etching anisotropy in which the etching rate varies depending on the direction due to the crystal structure. I can't.
That is, the formation of a deformed portion such as a fin due to etching anisotropy also inhibits bending vibration, leading to an increase in crystal impedance.

Therefore, as in Patent Document 1, a method is proposed in which a piezoelectric thin film sandwiched between drive electrodes is formed in each vibrating arm, and bending vibration is caused to each vibrating arm by deformation of the piezoelectric thin film.
According to such a configuration, it is not necessary to form a groove in each vibrating arm, and a bending vibration defect caused by a decrease in rigidity does not occur.
JP 2003-227719 A

However, the resonator disclosed in Patent Document 1 forms a tuning fork from silicon, which is a non-piezoelectric material.
However, the frequency generated by the bending vibration of silicon is high, and it is difficult to obtain a frequency in the frequency range (32.768 kHz (“kilohertz”)) of a so-called normal tuning fork type piezoelectric vibrating piece.
In addition, silicon has a very poor frequency-temperature characteristic and has a drawback that a stable frequency cannot be obtained.

  An object of the present invention is to provide a piezoelectric vibrating piece that can be configured in a small size and can stably generate a relatively low frequency.

In the first invention, the object is integrally formed of a base made of quartz, GaPO ₄ , or Li ₂ B ₄ O ₇ , the same material as the base, and the base At least one pair of vibrating arms extending from the first electrode, wherein one first electrode is formed in one region divided by the center line of the vibrating arm on the main surface of the vibrating arm, and the other region A first electrode is formed, the one and the other first electrodes are different from each other, a piezoelectric thin film is formed on a surface of the one and the other first electrode, and the one electrode is sandwiched between the one and the other One second electrode is formed on the surface of the piezoelectric thin film so as to be paired with the first electrode, and the other electrode is paired with the other first electrode across the piezoelectric thin film. A second electrode is formed on the surface of the piezoelectric thin film; In the vibrating arm, a groove is formed between the one first electrode and the other first electrode on the main surface of the vibrating arm, and the groove forms a groove between the first electrode and the first electrode. This is achieved by a piezoelectric vibrating piece configured to suppress the formation of an electric field between the other first electrode .

According to the configuration of the first invention, the first and second electrodes are formed on the surface of the vibrating arm extending in parallel from the base so as to be paired with the piezoelectric thin film interposed therebetween. When a driving voltage is applied to the two electrodes, an electric field is formed in the piezoelectric thin film. Due to this electric field formation, the piezoelectric thin film is deformed, and accordingly, each vibrating arm performs flexural vibration according to the deformation of the piezoelectric thin film.
For this reason, when the piezoelectric vibrating piece is formed in a small size, even if the outer shape is not necessarily an ideal shape, the bending vibration is not greatly affected. Further, it is not necessary to provide a groove for forming an electrode in each vibrating arm. Therefore, since there is no fear of a decrease in rigidity due to the groove, it is possible to eliminate an adverse effect on the bending vibration due to the decrease in rigidity. For these reasons, since there are no restrictions on downsizing, a small piezoelectric vibrating piece can be easily produced.
Furthermore, in the present invention, when viewed from the relationship between the piezoelectric thin film and the base material, the piezoelectric thin film is much thinner than the base material, and therefore, bending vibration can be performed by utilizing the characteristics of the base material. And since the base material of the present invention is formed of a base material having a small Young's modulus and good frequency-temperature characteristics, a relatively low frequency is realized even if it is formed in a small size due to a low Young's modulus. can do. In other words, it is possible to reduce the size without increasing the frequency.
In addition, it is possible to suppress electric field formation between adjacent electrodes, that is, crosstalk.
Also, if the base material is quartz, compared to silicon that has been used in the past, in terms of Young's modulus, silicon of 100 orientation is a hard material of 131 (Gpa) (gigapascal), whereas quartz is Since the material is soft as 78 (Gpa), the frequency can be made sufficiently low, or at the same frequency, the piezoelectric vibrating piece (piezoelectric vibrator) of the present invention can be about ½ in size.

The second invention is the configuration of the first aspect of the invention, the one and the other of the first electrode, the piezoelectric thin film, the hand and the other second electrode, and the groove, the surface side of the vibrating arm And it is formed in the back surface side, It is characterized by the above-mentioned.

FIG. 1 is a schematic perspective view showing a first embodiment of a piezoelectric vibrating piece according to the present invention.
In the figure, the piezoelectric vibrating piece 20 has a base portion 21 and a pair of vibrating arms 22 and 23 extending in the same direction from the base portion in parallel to one direction.

Here, the piezoelectric vibrating piece 20 can form a piezoelectric vibrator by applying a driving voltage and exciting it in a predetermined mode.
The piezoelectric vibrating piece 20 is made of, for example, a piezoelectric material. Preferably, among the piezoelectric materials, in particular, as a piezoelectric substrate, for example, a quartz crystal wafer having a size capable of separating a plurality or a large number of piezoelectric vibrating pieces 20 is used. By using quartz, a soft material having a Young's modulus of about 78 (Gpa) can be selected as a base material for forming the piezoelectric vibrating piece 20 so that a stable property can be used in terms of frequency-temperature characteristics. Become.
That is, by using quartz, a relatively low frequency can be realized even if the piezoelectric vibrating piece is formed in a small size due to its low Young's modulus. In other words, it is possible to reduce the size without increasing the frequency.
In addition to quartz, GaPO ₄ (59 GPa), Li ₂ B ₄ O ₇ (96 GPa), or the like can be used as a material having a small Young's modulus.

In the case of this embodiment, in particular, for example, when the substrate is cut out from a single crystal of quartz, the X axis, the Y axis, and the X axis are the electrical axis, the Y axis is the mechanical axis, and the Z axis is the optical axis. In the orthogonal coordinate system composed of the Z axis, a crystal Z plate obtained by cutting and polishing to a predetermined thickness is used for a quartz Z plate that is cut by rotating clockwise around the Z axis in the range of 0 to 5 degrees.
As illustrated, in the piezoelectric vibrating piece 20, the direction in which the vibrating arms 22 and 23 extend may be the Y-axis direction or the X-axis direction.
However, as shown in FIG. 1, if each of the vibrating arms 22 and 23 is formed to extend along the X-axis direction, as illustrated in FIG. Even if an electric field causing crosstalk occurs between the electrodes adjacent to each other in the Y-axis direction, the piezoelectric phenomenon does not occur in the Y-axis direction in the crystal. For this reason, it is advantageous to form the vibrating arms 22 and 23 so as to extend along the X-axis direction in order to prevent the adverse effect of crosstalk between adjacent electrodes.

  By etching such a quartz wafer, the outer shape of the piezoelectric vibrating piece 20 of FIG. 1 is formed. For etching, wet etching is more suitable than dry etching in terms of efficiency. For example, the quartz wafer is subjected to predetermined masking, and wet etching is performed by immersing in an etching solution containing a hydrofluoric acid solution. Or the external shape of many piezoelectric vibrating pieces 20 can be formed at once.

Next, the electrode arrangement of the piezoelectric vibrating piece 20 and the arrangement of the piezoelectric thin film will be described.
A thin electrode 26a is formed on the outer side edge of the surface of the vibrating arm 22 along the direction in which the vibrating arm 22 extends. A thin electrode 26b is formed inside the surface of the vibrating arm 22 along the direction in which the vibrating arm 22 extends. The electrodes 26 a and 26 b constitute a first electrode of the vibrating arm 22.
A thin electrode 27a is formed on the outer side edge of the surface of the vibrating arm 23 along the direction in which the vibrating arm 23 extends. Further, a thin electrode 27b is formed inside the surface of the vibrating arm 23 along the direction in which the vibrating arm 23 extends. The electrodes 27a and 27b constitute a first electrode of the vibrating arm 23.

The electrode 26a and the electrode 27a are connected by a conductive portion (not shown). The electrode 26b and the electrode 27b are also connected by a conductive portion (not shown).
The above electrodes are formed by, for example, forming an electrode film formed by forming a base of chromium on a crystal by sputtering and forming a gold film thereon into the shape shown in FIGS. It is obtained by processing by a lithography technique or the like.

Next, as shown in FIG. 2, the piezoelectric thin films 24 and 25 are formed on the first electrodes 26 and 27 of the vibrating arms 22 and 24.
Preferably, the piezoelectric thin film is individually formed on the electrode 26a, on the electrode 26b, and on each of the electrode 27a and the electrode 27b. As this piezoelectric thin film, zinc oxide (ZnO) can be preferably used, but in addition, AIN, PZT, or the like can be used, and a quartz thin film may be used. The piezoelectric thin films 24 and 25 can be formed by sputtering or the like.
Next, as will be understood with reference to FIG. 4 which is an end view taken along line AA of FIG. 1 and FIG.
Second electrodes 28 and 29 are formed on the first electrodes 26 and 27 with the piezoelectric thin films 24 and 25 interposed therebetween.
Specifically, the electrode 28a is formed on the electrode 26a, the electrode 28b is formed on the electrode 26b, the electrode 29a is formed on the electrode 27a, and the electrode 29b is formed on the electrode 27b. The electrode 28a and the electrode 29a are connected to the electrodes 26b and 27b. The electrode 28b and the electrode 29b are connected to the electrode 26a and the electrode 27a.

  The piezoelectric vibrating piece 20 is configured as described above, and an electric field is formed as shown by the arrows in FIG. 4 by applying a driving voltage to the electrodes sandwiching the piezoelectric thin films 24 and 25, respectively. Thus, in the vibrating arm 22 and the vibrating arm 23, when the crystal material on one side edge extends slightly along the Y direction across the virtual center line C1, the material on the other side edge extends in the Y direction. Shrink along. By repeating this alternately, as shown by the arrows in FIG. 1, the vibrating arm 22 and the vibrating arm 23 on which the respective piezoelectric thin films are formed bend and vibrate so that the tips of the piezoelectric thin films approach and separate from each other. A predetermined frequency can be generated in the same manner as the tuning fork piezoelectric vibrating piece.

FIG. 3 is an equivalent circuit showing a state in which the piezoelectric vibrating piece 20 is connected to an oscillation circuit that excites in a specific vibration mode.
The oscillation circuit 30 includes an amplifier circuit 31 and a feedback circuit 32.
The amplifier circuit 31 includes an amplifier 33 and a feedback resistor 34. The feedback circuit 32 includes a drain resistor 35, capacitors 36 and 37, and the piezoelectric vibrating piece 20.
Here, the amplifier 33 can use a CMOS inverter.
With such a configuration, an oscillator can be formed using the piezoelectric vibrating piece 20.

  The present embodiment is configured as described above, and the first and second electrodes 26, 27 and 28, 29 are formed so as to be paired with the piezoelectric thin films 24, 25 interposed therebetween. When a drive voltage is applied to the second electrodes 26, 27, and 28, 29, an electric field is formed in the piezoelectric thin films 24, 25 as shown in FIG. Due to the formation of the electric field, the piezoelectric thin films 24 and 25 are deformed, and the vibrating arms 22 and 23 bend and vibrate accordingly.

  For this reason, in forming the piezoelectric vibrating piece 20 in a small size, even if the outer shape is not necessarily an ideal shape, the bending vibration is not greatly affected. Further, it is not necessary to provide a groove for electrode formation in each of the vibrating arms 22 and 23, and there is no fear of a decrease in rigidity due to the groove, so that it is possible to eliminate an adverse effect on bending vibration due to a decrease in rigidity. For these reasons, there is no restriction on downsizing, and the small piezoelectric vibrating piece 20 can be easily obtained.

  Further, when looking at the relationship between the piezoelectric thin film and the quartz crystal that is the base material, the piezoelectric thin films 24 and 25 are much thinner than the quartz crystal portion, so that the bending vibration can be performed by utilizing the characteristics of the base material. it can. And since the base material is quartz, compared to silicon that has been used in the past, in terms of Young's modulus, silicon of 100 orientation is a hard material of 131 (Gpa) (gigapascal), whereas quartz Is a soft material of 78 (Gpa), the frequency can be made sufficiently low, or at the same frequency, the piezoelectric vibrator (piezoelectric vibrator 20) can be about ½ the size.

FIG. 5 is a diagram of a main part showing a modification of the first embodiment.
That is, FIG. 5 shows the same part as FIG. 4 regarding the piezoelectric vibrating piece of the modification.
In the figure, grooves 33 and 34 are formed on the surface of the crystal serving as the base material between the first electrodes 26a and 26b and 27a and 27b formed on both side edges of the vibrating arms 22 and 23, respectively.
Thereby, since the grooves 33 and 34 can be formed between the adjacent electrodes 26a and 26b or between the electrodes 27a and 27b, respectively, an electric field is formed between the adjacent electrodes via the base material (crystal), that is, a cross Talk can be suppressed.
In addition, if the length direction of the vibrating arms 22 and 23 is set along the X axis of the crystal, there is no such harmful effect of crosstalk, and no groove is required.

FIG. 6 is a diagram of a main part showing a modification of the second embodiment.
That is, FIG. 6 shows the same part as FIG. 4 regarding the piezoelectric vibrating piece of the second embodiment. Since the piezoelectric vibrating piece according to the second embodiment has the same configuration as that of the first embodiment described with reference to FIGS. 1 to 5 except for the portions shown in the drawings, overlapping description will be omitted, and only differences will be described. .

FIG. 6 shows only the structure of the vibrating arm 22 because the vibrating arms 22 and 23 have the same structure.
In this embodiment, the first and second electrodes 26, 28 and the piezoelectric thin film 24 disposed therebetween are formed on both front and back surfaces of the vibrating arm 22.
In the second embodiment, with such a configuration, the vibration arm 22 is driven to bend and vibrate in a balanced manner on the front surface side and the back surface side, so that the efficiency is improved and the CI (crystal impedance) value is improved. Is reduced.

The present invention is not limited to the above-described embodiment. Each configuration of each embodiment or modification may be combined or omitted as appropriate, and may be combined with other configurations not shown.
In the present invention, as long as the piezoelectric vibrating piece is used, the piezoelectric vibrating piece may be used in a container such as a package. In this case, the package is not limited to a box shape using ceramic. Alternatively, the piezoelectric vibrating piece may be housed in a housing container equivalent to a package such as a metal cylindrical case.
In addition, since the present invention is applied to a piezoelectric vibrating piece including at least a pair of vibrating arms extending in parallel from a base portion, the present invention is not limited to the tuning fork type piezoelectric vibrating piece described in the embodiment, and is a double tuning fork piezoelectric vibrating piece or a gyro vibrator. The present invention can also be applied to a piezoelectric vibrating piece for forming the film.

1 is a schematic perspective view of a piezoelectric vibrating piece according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view showing the middle of formation of the piezoelectric vibrating piece in FIG. 1. The block diagram at the time of forming an oscillator with the piezoelectric vibrating piece of FIG. FIG. 2 is an end view taken along line AA in FIG. 1. The figure of the principal part of a modification. The figure of the principal part of 2nd Embodiment. FIG. 6 is a schematic cross-sectional view of a vibrating arm of a conventional piezoelectric vibrating piece.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Piezoelectric vibrating piece, 21 ... Base, 22, 23 ... Vibrating arm, 24, 25 ... Piezoelectric thin film, 26, 27 ... First electrode, 28, 29 ... First 2 electrodes

Claims (2)

A base formed by a substrate that is quartz, GaPO ₄ , or Li ₂ B ₄ O ₇ ;
At least a pair of vibrating arms integrally formed of the same material as the base and extending from the base;
With
In the main surface of the vibrating arm, one first electrode is formed in one region divided by the center line of the vibrating arm, and the other first electrode is formed in the other region,
The one and the other first electrodes are different from each other,
A piezoelectric thin film is formed on the surfaces of the one and the other first electrodes;
One second electrode is formed on the surface of the piezoelectric thin film so as to be paired with the one first electrode across the piezoelectric thin film,
The other second electrode is formed on the surface of the piezoelectric thin film so as to be paired with the other first electrode across the piezoelectric thin film,
In the vibrating arm, a groove is formed between the one first electrode and the other first electrode on the main surface of the vibrating arm, and the groove forms the one first electrode. A piezoelectric vibrating piece configured to suppress formation of an electric field between the first electrode and the other first electrode . The one and the other of the first electrode, the piezoelectric thin film, the hand and the other second electrode, and the groove, wherein, characterized in that formed on the surface side and the back side of the vibrating arm Item 2. The piezoelectric vibrating piece according to Item 1 .

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