JP2006270465A - Method for adjusting frequency characteristics of piezoelectric vibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator having good characteristics by accurately and efficiently adjusting a frequency on a piezoelectric diaphragm without requiring a special package or a mounting substrate.
A piezoelectric diaphragm 1 is made of an AT-cut quartz diaphragm having a rectangular flat plate shape, and excitation electrode films 2 and 3 having a rectangular shape in plan view are formed in the center region of the front and back surfaces thereof, and an electrode thick portion 2a. , 3a are formed. The electrode thick portions 2a and 3a are always set to such a thickness that the electrode thick portion is a frequency characteristic adjustment target even when the maximum variation in the thickness of the piezoelectric diaphragm occurs, and this is an adjustment region. Yes. Frequency characteristics are adjusted for the region by ion milling.
[Selection] Figure 5

Description

  The present invention relates to a piezoelectric vibrator used in, for example, a voltage controlled piezoelectric oscillator (VCXO).

  A piezoelectric vibrator using a thickness vibration type piezoelectric vibration plate such as an AT-cut quartz plate generally has a configuration in which a pair of excitation electrodes are formed on the front and back surfaces of the piezoelectric vibration plate so as to face each other and an AC voltage is applied to the excitation electrode. It is. Various characteristics of such a piezoelectric vibrator depend on the configuration of the excitation electrode. For example, by using a large size electrode, the excitation region can be widened, the series resonance resistance can be improved, and the frequency variable amount can be widened.

  Various characteristics of the piezoelectric vibrator greatly depend on characteristics of the piezoelectric diaphragm. For example, a piezoelectric diaphragm may not have uniform plane parallelism due to processing conditions or processing variations. In such a case, spurious vibrations are strongly excited, and the characteristics as a piezoelectric vibrator may be deteriorated. Such a problem may be noticeable when the frequency is greatly varied in a voltage controlled piezoelectric oscillator that varies the main vibration frequency by changing the external voltage. That is, when the main vibration frequency is changed, there is a high possibility that the coupling with the above-described spurious vibration occurs, and there is a problem that the frequency jump phenomenon occurs or the oscillation becomes unstable.

  13 and 14 are diagrams showing a state in which spurious vibrations are excited by the plane parallelism of the plate thickness. FIG. 13A is a schematic cross-sectional view showing a state in which the excitation electrodes 71 and 72 are formed on the piezoelectric diaphragm 7, and shows a state where the plane parallelism of the plate surface is obtained when the plate thickness t1 = t2. Show. Such a piezoelectric diaphragm exhibits frequency characteristics in which spurious vibration does not appear in the vicinity of the main vibration as shown in FIG. In FIGS. 13B and 14B, the vertical axis represents attenuation (ATTENUATION), and the horizontal axis represents frequency (FREQUENCY).

  FIG. 14A is also a schematic cross-sectional view showing a state in which the excitation electrodes 71 and 72 are formed on the piezoelectric diaphragm 7, but in the case where the plate thickness t1 <t2, that is, the plate surface is not parallel to the plane. Is shown. Such a piezoelectric diaphragm has a resonance characteristic in which spurious vibrations Sp appear in the vicinity of the main vibration as shown in FIG. 14B. Such spurious vibrations Sp are considered to occur because the plane parallelism of the plate surface is not uniform. That is, in thickness shear vibration, it is known that a symmetric mode (fs mode) and an oblique symmetric mode (fa mode) are excited, and the oblique symmetric mode normally resonates because the vibration energy is canceled as a whole. Does not manifest as a peak. However, when the vibration balance is lost due to the imbalance of the piezoelectric diaphragm, the mode is considered to be manifested as spurious vibration.

  Such deterioration of characteristics due to variations in the plane parallelism of the piezoelectric diaphragm is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-196890 (Patent Document 1). In this patent document, one of the counter electrodes (excitation electrodes) is composed of two split electrodes, and the split electrodes improve the characteristics by making the resonance frequency between the counter electrodes substantially coincide with each other. And the structure which the division | segmentation electrode is mutually electrically connected by the conduction | electrical_connection means is disclosed. In order to make the resonance frequencies substantially the same for each divided electrode, for example, there is a method of adjusting the frequency by vapor deposition or the like for any one of the electrodes.

  However, in adjusting the resonance frequency, it is common to adjust either one of the divided electrodes. However, in order to adjust the vibration balance, a step of determining the divided electrode to be adjusted is required.

  In addition, the configuration for forming such divided electrodes requires the preparation of a package having electrode pads that are electrically and mechanically connected independently to each electrode of the piezoelectric diaphragm, and after frequency adjustment. There is a problem that handling is troublesome, for example, it is necessary to form a wiring pattern for commonly connecting the independent electrode pads on the mounting substrate side.

  Furthermore, this problem of plane parallelism becomes more apparent as the frequency increases. As is well known, the frequency of an AT-cut quartz diaphragm driven by thickness vibration, for example, thickness shear vibration, is determined by the thickness of the piezoelectric diaphragm, and the thickness and frequency are inversely proportional. As the frequency becomes higher, the amount of frequency change per unit thickness increases, and such frequency adjustment on the piezoelectric diaphragm surface has become important.

JP 2001-196890 A

  The present invention has been made in view of such points, and the object of the present invention is to accurately and efficiently adjust the frequency on the surface of the piezoelectric diaphragm without requiring a special package or mounting substrate, The object is to provide a good piezoelectric vibrator.

  In order to achieve the above object, the present invention provides a partial area where the frequency balance on the plate surface of the piezoelectric diaphragm is intentionally broken, and performs frequency characteristic adjustment on the partial area. It can be realized by the following configuration and adjustment method.

  That is, as shown in claim 1, an excitation electrode film is formed opposite to the front and back of a piezoelectric diaphragm that operates by thickness shear vibration, and the thickness of the piezoelectric vibrator is increased or decreased with respect to the excitation electrode film. A method of adjusting frequency characteristics, wherein a frequency of a partial region where at least one excitation electrode film is formed is different from that of another region, and the frequency characteristic is adjusted for the partial region. This is a method of adjusting the frequency characteristics of the vibrator.

  In addition, as a configuration in which the frequency of each region is made different, for example, as shown in claim 2, an excitation electrode film is formed opposite to the front and back of a piezoelectric diaphragm that operates by thickness shear vibration. A method for adjusting the frequency characteristics of a piezoelectric vibrator by adjusting a film thickness, wherein the thickness or / and shape of a partial region of at least one excitation electrode film is different from that of another region, and Thus, a method characterized by performing frequency characteristic adjustment can be given.

  As a configuration example in which the thickness of a part of the region is different, a configuration in which the thickness is extremely thicker than the other regions or extremely thinned can be given. As described above, the thickness may vary depending on the processing conditions of the piezoelectric diaphragm, but even if the variation is maximized, be sure to make it extremely thick or thin enough to adjust the partial area side. Good.

  Each of FIGS. 1 to 4 explains a frequency characteristic adjustment operation in which the thickness of a partial region of the excitation electrode film is varied and the adjustment is performed on the region when the thickness of the piezoelectric diaphragm varies. ing. In FIG. 1, the thicknesses t1 and t2 of one end and the other end of the piezoelectric diaphragm are in a relationship of t1 <t2, and the thicknesses E1 and E2 of the one end side and the other end side of the excitation electrode film are in a relationship of E1 <E2. In some cases, an adjustment example for reducing the thickness of the excitation electrode film is shown. In FIG. 1A, the relationship between E1 and E2 can always be adjusted by reducing the excitation electrode film on the E2 side (the other end side) even if the thickness of the piezoelectric diaphragm is t1> t2. It is formed to a thickness of about. In FIG. 1, since t1 <t2, as shown in FIG. 1B, the E2 side is adjusted to a state where the thickness is reduced from the E1 side.

In FIG. 2, the thicknesses t1 and t2 of one end and the other end of the piezoelectric diaphragm are in a relationship of t1 <t2, and the thicknesses E1 and E2 on one end side and the other end side of the excitation electrode film are in a relationship of E1> E2. In some cases, an adjustment example for increasing the thickness of the excitation electrode film is shown. In FIG. 2A, the relationship between E1 and E2 is a thickness that can be adjusted by increasing the excitation electrode film on the E2 side even if the thickness of the piezoelectric diaphragm is t1> t2. Is formed. In FIG. 2, since t1 <t2, the excitation electrode film thickness is increased on the E2 side as shown in FIG. 2 (b), but the adjustment is finally performed with the thickness being smaller than that on the E1 side. Complete.

In FIG. 3, the thicknesses t1 and t2 at one end and the other end of the piezoelectric diaphragm are in a relationship of t1> t2, and the thicknesses E1 and E2 at the one end side and the other end side of the excitation electrode film are in a relationship of E1 <E2. In some cases, an adjustment example for reducing the thickness of the excitation electrode film is shown. In FIG. 3A, the relationship between E1 and E2 is such that the thickness can be adjusted by reducing the excitation electrode film on the E2 side even if the thickness of the piezoelectric diaphragm is t1 <t2. Forming. In FIG. 3, since t1> t2, as shown in FIG. 3B, the adjustment is completed with the E2 side being thicker than the E1 side.

  In FIG. 4, the thicknesses t1 and t2 at one end and the other end of the piezoelectric diaphragm are in a relationship of t1> t2, and the thicknesses E1 and E2 at one end side and the other end side of the excitation electrode film are in a relationship of E1> E2. In some cases, an adjustment example for increasing the thickness of the excitation electrode film is shown. In FIG. 4A, the relationship between E1 and E2 is a thickness that can be adjusted by increasing the excitation electrode film on the E2 side even if the thickness of the piezoelectric diaphragm is t1 <t2. Is formed. In FIG. 4, since t1> t2, the adjustment is completed with the E2 side being thicker than the E1 side as shown in FIG. 4B.

  In each of the above adjustment methods, even when there is a variation in the piezoelectric diaphragm depending on the adjustment means (electrode thickness increase or electrode thickness decrease) in performing the spurious adjustment due to the plane parallelism of the piezoelectric diaphragm. The excitation electrode film thickness is set in advance in consideration of the maximum variation so as to adjust the predetermined adjustment region. As a result, since the adjustment area and the adjustment means can be determined in advance, the steps related to the determination of the adjustment area and the determination of the adjustment method, which have been conventionally required, can be eliminated. In addition, as a configuration in which the frequency of a partial region of at least one of the excitation electrode films is different from the other regions, the electrode shape may be different from the above-described method using the electrode film thickness, or the electrode film thickness and the electrode shape may be combined. The structure to match may be sufficient.

  The present invention is one of the feature points that the adjustment region is determined in advance, and can be applied even when there is no variation in the thickness of the piezoelectric diaphragm.

  Such frequency adjustment can be performed by a vacuum deposition method, a sputtering method, or an ion etching method as shown in claim 3. A vacuum deposition method or a sputtering method is used when the excitation electrode film is increased, and an ion etching method such as ion milling is used when the excitation electrode film is decreased.

  Further, according to a fourth aspect of the present invention, there may be provided a method of adjusting a frequency of a piezoelectric vibrator, wherein the surface of the excitation electrode film is wet-etched after the frequency adjustment.

  Depending on the adjustment means and the adjustment amount, a slight step may occur on the surface of the excitation electrode film. Such a step may have a sharp edge at its end, and may produce an unnecessary reflected wave. By performing the wet etching later, it is possible to reduce the influence of the sharp edge of the step and to suppress the suppression of new spurious due to unnecessary reflected waves.

  As described above, in the present invention, the adjustment region and the adjusting means are provided by providing a partial region where the frequency balance on the plate surface of the piezoelectric diaphragm is intentionally broken and performing frequency characteristic adjustment on the partial region. Since it can be determined in advance, it is possible to eliminate the steps related to the determination of the adjustment region and the determination of the adjustment method, which have been conventionally required. In addition, it is possible to accurately and efficiently adjust the frequency characteristics on the surface of the piezoelectric diaphragm without requiring a special package or mounting substrate, and to obtain a piezoelectric vibrator having good characteristics.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the frequency characteristic adjustment according to the present invention is applied to an AT-cut quartz diaphragm that operates by thickness shear vibration will be described.

  FIG. 5 is a side view showing a method for adjusting frequency characteristics by ion milling on a piezoelectric diaphragm having excitation electrode films formed on both sides, and FIG. 5 (a) is an excitation electrode in an unbalanced state. FIG. 5B is a side view of a piezoelectric diaphragm having a film formed thereon, and FIG. 5B is a side view showing a method for adjusting frequency characteristics by an ion milling method. FIG. 6 is a graph showing the frequency characteristics before and after the adjustment. FIG. 6A shows the frequency characteristics before adjustment, and FIG. 6B shows the frequency characteristics after adjustment.

  The piezoelectric vibration plate 1 is formed of a rectangular flat plate-shaped AT-cut quartz crystal vibration plate, and excitation electrode films 2 and 3 having a rectangular shape in plan view are formed in the center regions of the front and back surfaces thereof. Although not shown, extraction electrode films are drawn from the excitation electrode films 2 and 3 to the outer periphery of the piezoelectric diaphragm. These excitation electrode film and extraction electrode film have a laminated structure of chrome-gold, but are not limited to the metal material.

In this embodiment, as shown in FIG. 5A, in the excitation electrode films 2 and 3, the electrode thick portions 2a and 3a are formed so that the electrode film thickness on the right side of the drawing becomes large. The electrode thick portions 2a and 3a are always set to such a thickness that the electrode thick portion is a frequency characteristic adjustment target even when there is a maximum variation in the thickness of the piezoelectric diaphragm. Yes. That is, even when the thicknesses t1 and t2 of the one end and the other end of the piezoelectric diaphragm are t1 <t2 as shown in FIG. 1, the case where t1> t2 is shown as shown in FIG. However, it is set to an extremely thick thickness so that the electrode thick portion is always an adjustment target.

The electrode thick portions 2a and 3a are formed by selectively performing vacuum deposition only on the electrode thick portions 2a and 3a after the normal excitation electrode films 2 and 3 are formed. After the excitation electrode films 2 and 3 are formed, the electrode films are formed by selectively reducing the electrode film thickness by ion milling or the like other than the portions 2a and 3a. In order to selectively make the excitation electrode film thicker or thinner, a desired electrode can be formed, for example, by arranging an opening provided in a metal mask at a selected position.

In the present embodiment, the electrode thick portions 2a and 3a are provided, and it is planned to make adjustments to the regions. FIG. 5B shows a method for adjusting the frequency characteristics of the electrode thick portion 2a by ion milling, and a metal mask M having an opening M1 is placed close to the electrode thick portion 2a. The frequency characteristics are adjusted by ion milling. The adjustment status may be monitored in real time while exciting the piezoelectric diaphragm, or a predetermined adjustment amount of ion milling is performed on the piezoelectric diaphragm to be adjusted, and then the characteristics are checked. You may adopt the method of repeating this.

FIG. 6 is a graph showing the frequency characteristics before and after adjustment, FIG. 6 (a) shows the frequency characteristics before adjustment (with spurious), and FIG. 6 (b) shows the frequency characteristics after adjustment. Prior to adjustment, spurious Sp was present in the vicinity of the main vibration frequency due to the presence of the electrode thick portion. However, by performing adjustment, as shown in FIG. Can have a diaphragm.

Note that the frequency characteristic adjustment method is not limited to the ion milling disclosed in the above embodiment, and etching using a reactive gas may be used as another example of the adjustment method by mass reduction. Adjustment by laser beam and ion beam can be given. Moreover, the partial vapor deposition method and sputtering can be mention | raise | lifted as an example of the adjustment method by mass addition. Also in the case of adjustment by mass addition, as explained with reference to FIGS. 2 and 4 in the section of the solution means, the excitation electrode film thickness should be set in advance in consideration of the maximum variation of the piezoelectric diaphragm and the adjustment method. Set. As a result, since the adjustment area and the adjustment means can be determined in advance, the steps related to the determination of the adjustment area and the determination of the adjustment method, which are conventionally required, can be eliminated.

  The surface of the excitation electrode film may be wet etched after adjusting the frequency characteristics. When the frequency characteristic adjustment described above is performed, a slight step may occur on the surface of the excitation electrode film depending on the adjustment means and the adjustment amount. Such a step may have a sharp edge at its end, which may cause unnecessary reflected waves and spurious vibrations. By performing the wet etching later, it is possible to reduce the influence of the sharply stepped end portion and to suppress the suppression of new spurious due to unnecessary reflected waves.

Although not shown, after adjusting the above characteristics, the piezoelectric diaphragm is housed in a package such as a ceramic package, and the piezoelectric diaphragm is electrically and mechanically joined to the package, and then hermetically sealed with a lid. Thus, the piezoelectric vibrator is completed.

  Other embodiment by this invention is described based on drawing. FIG. 7 shows a configuration in which the excitation electrodes 2 and 3 (3 are not shown) formed on the piezoelectric diaphragm 1 have a large electrode region 2b and a small electrode region 2c. The large electrode region 2b can be set to have a lower frequency than the small electrode region 2c due to the load mass effect, whereby the frequency of a partial region of the excitation electrode film can be made different from other regions. In the frequency characteristic adjustment, the frequency can be adjusted in a higher direction by reducing the electrode shape relative to the large electrode region 2b, by reducing the electrode film thickness, or by combining the two. .

Conversely, the small electrode region 2c has a relatively high frequency, the electrode shape is increased with respect to the small electrode region 2c, the electrode film thickness is increased, or a combination of the two is used. The frequency can be adjusted in the lower direction.

  8 and 9 show a substantially trapezoidal shape in which an inclined portion is provided on the long side of the excitation electrode film 2, and FIG. 8 shows a configuration having an inclined portion 2d in which the electrode shape gradually increases toward the right side of the drawing. In the present embodiment, the frequency of a partial region of the excitation electrode film is made different from that of other regions depending on the shape of the excitation electrode film. In the frequency characteristic adjustment, the frequency can be adjusted in the higher direction by reducing the electrode shape with respect to the right electrode region, by reducing the electrode film thickness, or by combining the two. Conversely, the frequency can be adjusted in a lower direction by increasing the electrode shape with respect to the left electrode region, increasing the electrode film thickness, or combining both.

  FIG. 9 shows a configuration having an inclined portion 2e whose electrode shape gradually decreases toward the right side of the drawing. In the present embodiment, the frequency of a partial region of the excitation electrode film is made different from that of other regions depending on the shape of the excitation electrode film. In the frequency characteristic adjustment, the frequency can be adjusted in a higher direction by reducing the electrode shape with respect to the left electrode region, by reducing the electrode film thickness, or by combining the two. Conversely, the frequency can be adjusted in the lower direction by increasing the electrode shape relative to the right electrode region, increasing the electrode film thickness, or combining both.

  In the present invention, the frequency of a partial region where the excitation electrode film is formed may be made different from other regions by deleting a part of the excitation electrode film. For example, in FIG. 10, the excitation electrode film 2 is provided with a plurality of non-electrode portions 2f to vary the frequency of a partial region of the excitation electrode film. In FIG. 10, the non-electrode portion 2f is formed on the left side of the electrode. The frequency of the region is increased by making it unevenly distributed. In the frequency characteristic adjustment, the frequency can be adjusted in the higher direction by reducing the electrode shape with respect to the right electrode region, by reducing the electrode film thickness, or by combining the two. Conversely, the frequency can be adjusted in a lower direction by increasing the electrode shape with respect to the left electrode region, increasing the electrode film thickness, or combining both.

  In the present invention, the frequency of a part of the excitation electrode film may be made different from that of the other areas by making the shapes of the excitation electrode films on the front and back formed on the piezoelectric diaphragm different. FIG. 11 shows an example in which excitation electrode films 2 and 3 having different shapes are formed on the front and back surfaces of the piezoelectric diaphragm. The excitation electrode film 2 on the front surface has a rectangular shape, but the excitation electrode film 3 on the back surface has a large electrode region 3a and a small electrode region 3b similar to the electrode configuration shown in FIG. The large electrode region 3a is set to have a low frequency due to the load mass effect. As described above, the frequency adjustment is performed by reducing the mass of the excitation electrode film in the low frequency region or increasing the mass of the excitation electrode film in the high frequency region.

  By the way, when adjusting the frequency characteristic by reducing the film thickness with respect to the adjustment area of the excitation electrode film formed on the piezoelectric diaphragm, the frequency characteristic adjustment is optimized by making the film thickness decrease amount different in the adjustment area. May be. FIG. 12 shows an example in which the adjustment is performed by changing the film thickness reduction amount in the adjustment region. FIG. 12A is a cross-sectional view of the piezoelectric diaphragm formed with the excitation electrode before the adjustment, and FIG. ) Is a diagram showing an adjustment method by ion milling. As shown in FIG. 12B, when performing ion milling on the adjustment region 2g (electrode thick portion) in which the frequency of a partial region of the excitation electrode film is different from that of the other region, Only a part is configured to be irradiated to the adjustment region 2g. In general, it is known that ion milling has a small etching rate with respect to its central portion. In FIG. 12B, the size of the arrow of the ion milling E indicates the etching rate, and the longer one indicates the higher etching rate. Using such characteristics, the opening M1 of the metal mask M is formed so that only the peripheral part from the central part of the ion milling is irradiated to the adjustment region, and the frequency characteristic is adjusted. As a result, as shown in FIG. 12B, the upper surface of the adjustment region 2g has an inclined shape, and the weight increases toward the vicinity of the outer periphery of the excitation electrode. By adopting a configuration in which the thickness gradually changes in this way, unnecessary spurious vibrations can be suppressed and a piezoelectric vibrator having good characteristics can be obtained.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  It can be applied to mass production of piezoelectric vibration devices such as crystal resonators.

It is a figure which shows the frequency characteristic adjustment by this invention. It is a figure which shows the frequency characteristic adjustment by this invention. It is a figure which shows the frequency characteristic adjustment by this invention. It is a figure which shows the frequency characteristic adjustment by this invention. It is a figure which shows embodiment of this invention. It is a figure which shows the frequency characteristic by embodiment of this invention. It is a figure which shows other embodiment by this invention. It is a figure which shows other embodiment by this invention. It is a figure which shows embodiment of this invention. It is a figure which shows the frequency characteristic by embodiment of this invention. It is a figure which shows other embodiment by this invention. It is a figure which shows other embodiment by this invention. It is a figure which shows a prior art example. It is a figure which shows a prior art example.

Explanation of symbols

1, 7 Quartz diaphragm (piezoelectric diaphragm)
2, 3, 71, 72 Excitation electrode film 2a, 3b Electrode thick layer

Claims (4)

A method for adjusting the frequency characteristics of a piezoelectric vibrator in which an excitation electrode film is formed opposite to the front and back of a piezoelectric diaphragm that operates by thickness shear vibration, and the film thickness is adjusted with respect to the excitation electrode film,
A method for adjusting a frequency characteristic of a piezoelectric vibrator, characterized in that a frequency of a partial region where at least one excitation electrode film is formed is different from that of another region, and the frequency characteristic is adjusted for the partial region. A method for adjusting the frequency characteristics of a piezoelectric vibrator in which an excitation electrode film is formed opposite to the front and back of a piezoelectric diaphragm that operates by thickness shear vibration, and the film thickness is adjusted with respect to the excitation electrode film,
Frequency characteristic adjustment of a piezoelectric vibrator, wherein the thickness or / and shape of a partial region of at least one excitation electrode film is different from that of another region, and the frequency characteristic is adjusted for the partial region Method. The frequency characteristic adjustment method for a piezoelectric vibrator according to claim 1 or 2, wherein the frequency characteristic adjustment is performed by a vacuum deposition method, a sputtering method, or an ion etching method. 4. A method of adjusting the frequency characteristics of a piezoelectric vibrator, comprising performing wet etching on a surface of the excitation electrode film after performing the frequency characteristics adjustment according to claim 1.

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