JP5141856B2 - Method for manufacturing surface acoustic wave device and surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device manufacturing method and a surface acoustic wave device, and more particularly to a surface acoustic wave device manufacturing method and a surface acoustic wave device suitable for improving frequency temperature characteristics of a surface acoustic wave device. .

  Conventionally, it has been known that among piezoelectric devices, those using an element piece constituted by a quartz substrate have good frequency temperature characteristics (frequency fluctuation characteristics with respect to temperature changes). It is also known that among piezoelectric devices using a crystal resonator element, an AT-cut crystal resonator using an AT-cut crystal substrate as the resonator element has particularly good frequency temperature characteristics.

  In the field of piezoelectric devices, it is desired to increase the frequency of vibration to be excited. Correspondingly, as a resonator element having a configuration capable of exciting a high frequency, a surface acoustic wave using an ST cut quartz substrate is adopted. A surface acoustic wave device (SAW device) using (SAW: surface acoustic wave) element pieces is known. However, the SAW device using the SAW element piece has poor frequency temperature characteristics as compared with the AT vibrator using the AT-cut quartz crystal piece. For this reason, various techniques for improving the frequency temperature characteristics of the SAW device have been proposed.

For example, Patent Document 1 proposes improving the frequency temperature characteristics of the SAW device by giving a specific in-plane rotation angle ψ to the ST cut quartz substrate.
Japanese Patent No. 3622202 JP 2005-57666 A

  As shown in Patent Document 1, by appropriately changing the in-plane rotation angle ψ of the SAW element piece constituted by the ST cut quartz substrate, the frequency temperature characteristic of the SAW element piece can surely be improved. It is considered possible.

  However, while the applicant of the present application intensively researches, even with a SAW element piece in which the in-plane rotation angle of the quartz crystal substrate is adjusted and the frequency temperature characteristics are improved as described above, the resonance frequency is adjusted and It has been found that the frequency temperature characteristic is changed by applying a protective film to an IDT (interdigital transducer) constituting the excitation electrode for the purpose of preventing a short circuit or the like.

  As described above, the provision of a protective film to the excitation electrode is also disclosed in Patent Document 2, but the provision of the protective film in the prior art including Patent Document 2 only gives the resonance frequency of the SAW element piece. The purpose is to adjust, and the influence on the temperature characteristics was not considered. In general, when a protective film is applied to the excitation electrode of the SAW element piece using the ST cut quartz substrate, there is almost no influence on the frequency temperature characteristics in the SAW device. For this reason, conventionally, it has been considered that the SAW element piece using the in-plane rotation ST-cut quartz substrate is not affected by the provision of the protective film.

  For this reason, in the case where the design by the applicant of the present application is such that the frequency temperature characteristic becomes an optimum value within the operating temperature range under the resonance frequency at which the in-plane rotation angle ψ of the ST cut quartz substrate is set. However, it became clear for the first time that the above-described phenomenon that the frequency temperature characteristics deteriorate due to the application of the protective film to the excitation electrode as the final stage of production.

  Accordingly, an object of the present invention is to provide a method for manufacturing a SAW device and a SAW device in which the frequency temperature characteristics of the SAW device are improved when a protective film is applied to the excitation electrode.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
The surface acoustic wave device manufacturing method according to the first embodiment is an in-plane rotation ST cut in the range of (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °) in terms of Euler angles. using a quartz substrate, a method for manufacturing a surface acoustic wave device having a protective film to the excitation electrode, the frequency-temperature of the surface acoustic wave device produced by applying anodic oxide film as the protective film on the excitation electrode The amount of change of the characteristic is obtained, and the amount of change is compensated based on the value of the resonance frequency f set to the upper limit mode of the stop band and the voltage x applied to the excitation electrode when the anodic oxide film is formed. Correction amount Δψ of in-plane rotation angle ψ for


The calculated, to form the plane rotation ST-cut quartz substrate Euler angle calculated to obtain a frequency-temperature characteristic is shifted an angle of only ψ the correction amount Δψ to desired at the set resonant frequency, the surface method of manufacturing an inner rotational ST-cut quartz substrate, surface acoustic wave device characterized by manufacturing a surface acoustic wave device have use the anodic oxide film and the excitation electrode.
The method of manufacturing the surface acoustic wave device according to the second embodiment is the in-plane rotation ST cut in the range of (0 °, 113 ° ≦ θ ≦ 135 °, 40 ° ≦ | ψ | ≦ 49 °) in the Euler angle display. using a quartz substrate, a method for manufacturing a surface acoustic wave device having a protective film to the excitation electrode, the frequency-temperature of the surface acoustic wave device produced by applying anodic oxide film as the protective film on the excitation electrode The amount of change of the characteristic is obtained, and the amount of change is compensated based on the value of the resonance frequency f set to the upper limit mode of the stop band and the voltage x applied to the excitation electrode when the anodic oxide film is formed. Correction amount Δψ of in-plane rotation angle ψ for


The calculated, to form the plane rotation ST-cut quartz substrate Euler angle calculated to obtain a frequency-temperature characteristic is shifted an angle of only ψ the correction amount Δψ to desired at the set resonant frequency, the surface method of manufacturing an inner rotational ST-cut quartz substrate, surface acoustic wave device characterized by manufacturing a surface acoustic wave device have use the anodic oxide film and the excitation electrode.
Moreover, the example of an adaptation for achieving the said objective is as follows.
Method of manufacturing a surface acoustic wave device according to the present invention, in Euler angle display (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °) plane rotation ST-cut in the range of using a quartz substrate, a method for manufacturing a surface acoustic wave device having a protective film to the excitation electrode, the frequency-temperature of the surface acoustic wave device produced by applying anodic oxide film as the protective film on the excitation electrode The amount of change of the characteristic is obtained, the amount of correction Δψ of the in-plane rotation angle ψ to compensate for the amount of change is obtained, and the correction is made from the Euler angle calculated to obtain the desired frequency temperature characteristic at the set resonance frequency. Forming an in- plane rotated ST-cut quartz substrate having an angle of ψ shifted by an amount Δψ, and manufacturing a surface acoustic wave device using the in- plane rotated ST-cut quartz substrate , the excitation electrode, and the anodic oxide film ; Features.

  According to the surface acoustic wave device manufacturing method using the in-plane rotation ST-cut quartz substrate based on the cut angle as described above, the surface acoustic wave device is manufactured by determining the cut angle by the above method. By applying a protective film to the excitation electrode, a curve (temperature characteristic curve) indicating frequency temperature characteristics is shifted so as to approach the desired frequency temperature characteristics by a change amount corresponding to the correction amount Δψ. For this reason, the surface acoustic wave device manufactured using the in-plane rotating ST-cut quartz substrate with the cut angle determined as described above has good frequency temperature characteristics after the protective film is applied to the excitation electrode.

  Further, in the method for manufacturing the surface acoustic wave device according to the present invention for achieving the above object, the cut angle is expressed by Euler angle (0 °, 113 ° ≦ θ ≦ 135 °, 40 ° ≦ | ψ | ≦ 49 °). ) Is a method for manufacturing a surface acoustic wave device having a protective film on an excitation electrode using an in-plane rotating ST-cut quartz substrate that is basically in the range of The amount of change in the frequency temperature characteristic of the surface acoustic wave device caused by this is obtained, and the correction amount Δψ of the in-plane rotation angle ψ to compensate for the amount of change is obtained to obtain the desired frequency temperature characteristic at the set resonance frequency. The cut angle is set by shifting the cut angle by the correction amount Δψ from the cut angle of the in-plane rotation ST cut quartz substrate calculated for the purpose, and the surface acoustic wave device is manufactured using the quartz substrate. To be characterized by It may be a shall.

  Even the surface acoustic wave device using the in-plane rotation ST-cut quartz substrate based on the cut angle as described above has the same characteristics as the surface acoustic wave device based on the cut angle shown in the above-described method. It is. Therefore, the surface acoustic wave device manufactured using the in-plane rotating ST-cut quartz substrate with the cut angle determined as described above has good frequency temperature characteristics after the protective film is applied to the excitation electrode.

In the method of manufacturing the surface acoustic wave device as described above, the protective film applied to the excitation electrode is an anodic oxide film, and the correction amount Δψ constitutes the set resonant frequency f and the anodic oxide film. Based on the value of the voltage x applied to the excitation electrode when
It is desirable to define

  By determining the correction amount using such a coefficient, it is possible to eliminate an unstable factor in which the correction amount is determined only by an experimental rule of thumb. Therefore, it becomes possible to obtain a stable frequency temperature characteristic regardless of experience.

  Further, in the surface acoustic wave device according to the present invention for achieving the above object, the cut angles are in the range of Euler angles (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °). A surface acoustic wave device using an in-plane rotation ST-cut quartz crystal substrate that is based on the in-plane rotation ST, and the in-plane rotation ST required to obtain a desired frequency-temperature characteristic at a set resonance frequency Cut by adding a correction amount Δψ of in-plane rotation angle ψ determined in advance based on the amount of change in frequency temperature characteristics due to the effect of applying a protective film to the excitation electrode configured on the main surface of the quartz substrate to the cut angle of the cut quartz substrate A crystal substrate constituted by corners, an excitation electrode formed on the main surface of the crystal substrate, and a protection applied to the excitation electrode set to a film thickness corresponding to the amount of change in frequency temperature characteristics due to the correction amount Δψ Specially having a membrane To.

  According to the surface acoustic wave device having such a configuration, it is possible to set a frequency temperature characteristic within a use temperature range within a desired range by providing a protective film on the excitation electrode.

  Further, in the surface acoustic wave device according to the present invention for achieving the above object, the cut angle is in the range of Euler angle display (0 °, 113 ° ≦ θ ≦ 135 °, 40 ° ≦ | ψ | ≦ 49 °). A surface acoustic wave device using an in-plane rotation ST-cut quartz crystal substrate that is based on the in-plane rotation ST, and the in-plane rotation ST required to obtain a desired frequency-temperature characteristic at a set resonance frequency Cut by adding a correction amount Δψ of in-plane rotation angle ψ determined in advance based on the amount of change in frequency temperature characteristics due to the effect of applying a protective film to the excitation electrode configured on the main surface of the quartz substrate to the cut angle of the cut quartz substrate A crystal substrate constituted by corners, an excitation electrode formed on the main surface of the crystal substrate, and a protection applied to the excitation electrode set to a film thickness corresponding to the amount of change in frequency temperature characteristics due to the correction amount Δψ Having a membrane It may be one of the symptoms.

  Even in the surface acoustic wave device using the in-plane rotation ST-cut quartz substrate based on the cut angle as described above, similarly to the surface acoustic wave device having the above configuration, by applying a protective film to the excitation electrode, The effect of shifting the frequency temperature characteristics within the operating temperature range to a desired range can be obtained.

In the surface acoustic wave device having the above-described configuration, the protective film applied to the excitation electrode is an anodic oxide film, and the correction amount Δψ constitutes the set resonant frequency f and the anodic oxide film. Based on the value of the voltage x applied to the excitation electrode when
It is desirable that

  By determining the correction amount using such a coefficient, it is possible to eliminate an unstable factor in which the correction amount is determined only by an experimental rule of thumb. Therefore, the manufactured surface acoustic wave device can stably obtain good frequency temperature characteristics regardless of experience or the like.

  Hereinafter, a method for manufacturing a surface acoustic wave device according to the present invention and an embodiment according to the surface acoustic wave device will be described in detail with reference to the drawings. In addition, this invention shall have a various form in the limit which does not change the principal part.

  In the present embodiment, the cut angle of the crystal substrate will be described with reference to the Euler angle display (φ, θ, ψ), which is well known in describing the cut angle of the crystal substrate. In addition, the SAW device according to the present embodiment uses the stopband upper limit mode. The upper limit mode in the stop band of the surface acoustic wave has a smaller absolute value of the secondary temperature coefficient in the frequency temperature characteristics than the lower limit mode, and the change in the absolute value of the secondary temperature coefficient when the thickness of the IDT electrode is increased. Is also small. Further, the upper limit mode in the stop band of the surface acoustic wave also has a feature that the change amount of the oscillation frequency when the thickness of the IDT constituting the excitation electrode is increased is smaller than that in the lower limit mode.

  FIG. 1 shows the configuration of a SAW element piece used in the SAW device manufactured in this embodiment. 1A is a plan view showing the configuration of the SAW element piece, and FIG. 1B is a cross-sectional view taken along the line AA in FIG. 1A.

  The SAW element piece 10 according to the present embodiment basically includes a piezoelectric substrate 12 and an excitation electrode formed on one main surface of the piezoelectric substrate 12. The piezoelectric substrate 12 is made of quartz, and its cut angle and surface acoustic wave propagation direction are expressed in Euler angles (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °). The in-plane rotation angle ψ is determined in detail by the resonance frequency f determined by the configuration of the excitation electrode described later, the setting of the protective film 20 applied to the excitation electrode body 18, and the like. And

  The excitation electrode body 18 can be composed of various conductive materials. In the present embodiment, the case where aluminum (Al) or an alloy mainly composed of Al is used as a constituent material will be described. .

  The excitation electrode is basically composed of an IDT 14 composed of a pair of comb electrodes and a pair of reflectors 16 arranged so as to sandwich the IDT 14. The IDT 14 is configured by connecting a plurality of electrode fingers 14a provided so as to be orthogonal to the propagation direction of the surface acoustic wave by bus bars 14b arranged along the propagation direction of the surface acoustic wave. Composed of two comb electrodes. The arrangement relationship between the two comb-shaped electrodes is that the electrode fingers 14a extending from the two bus bars 14b are arranged so as to alternately engage with each other. The reflector 16 is a grid-like electrode configured by connecting both ends of a plurality of conductor strips 16a arranged in parallel with the electrode fingers 14a of the comb-shaped electrode to a bus bar 16b.

The protective film 20 applied to the excitation electrode body 18 can be variously selected such as an anodic oxide film or SiO ₂ film. In this embodiment, the protective film 20 is obtained by anodizing Al as the protective film. A description will be given by taking an anodic oxide film as an example. Anodization is configured by applying a voltage by immersing the piezoelectric substrate 12 on which the excitation electrode body 18 is formed in an electric field solution (for example, ammonium phosphate). The thickness of the anodic oxide film to be coated (applied) to the excitation electrode body 18, the voltage applied to the excitation electrode body 18 during immersion, and the voltage can be determined by the time such as the application of a. When the voltage is constant, the thickness of the anodic oxide film after a certain time is constant.

  Here, when the applicant of the present invention applies an anodic oxide film (protective film) to the excitation electrode of the SAW element piece using the in-plane rotating ST-cut quartz substrate, a change occurs in the frequency temperature characteristics of the manufactured SAW device. I found. As described above, the phenomenon of the change in the frequency temperature characteristic due to the application of such a protective film is caused by a normal ST-cut quartz substrate (for example, the cut angle is displayed in Euler angle (0 °, 113 ° ≦ θ ≦ 135 °, 0 It was almost impossible to confirm with a SAW device using a quartz substrate), and it was thought that this could not occur in the past.

  The characteristic of the change in frequency temperature characteristics due to the provision of the protective film is that the temperature characteristic curve showing the temperature characteristics by applying the protective film shows a change that rotates counterclockwise around the reference point of the measured temperature. It is. Here, it is known that the frequency temperature characteristics of the SAW device using the in-plane rotation ST-cut quartz substrate can be adjusted by changing the in-plane rotation angle ψ of the substrate. For this reason, the applicant of the present application uses the tendency of the temperature characteristic curve by applying a protective film to the excitation electrode by determining the in-plane rotation angle ψ of the quartz substrate assuming the frequency temperature characteristic after applying the protective film. It was considered that a SAW device that can be optimized in the temperature range can be obtained.

  The applicant of the present application has found that the amount of change in the temperature characteristic curve due to the provision of the protective film is determined by the relative relationship between the thickness of the excitation electrode and the protective film.

The thickness of the anodic oxide film depends on the voltage applied during anodic oxidation and the frequency determined by the film thickness and pitch of the IDT 14. In addition, the relationship between the voltage and the film thickness is proportional, and the relationship between the film thickness and the frequency is that the ratio of the film thickness of the anodized film to the electrode film thickness is relative if the voltage applied during anodization is constant. There is a relationship that changes.

  FIG. 2 shows that the electrode film thickness of the IDT 14 is constant, that is, the resonance frequency to be set is constant, and the voltage for applying the anodic oxide film is changed. The change of the correction amount Δψ of the in-plane rotation angle ψ required for keeping the change amount of the frequency temperature characteristic of the SAW device within a specific range is shown. FIG. 3 shows an in-plane rotation angle ψ when the resonance frequency to be set is changed, specifically, when the electrode film thickness of the IDT 14 is changed when the voltage for applying the anodic oxide film is constant. The change of the correction amount Δψ is shown. 2 and 3, the tendency of the change in the correction amount Δψ of the in-plane rotation angle ψ is due to the manufacture of the SAW element piece 10, the feedback of data acquired at the time of manufacture, and the SAW element piece 10 based on the feedback data. It is empirical gained through an experimental cycle of remanufacturing.

From FIG. 2 and FIG. 3, it can be read that both are proportional to the correction amount Δψ. Further, it is known that the resonance frequency and the film thickness of the protective film 20 applied to the excitation electrode have a mutually affecting relationship. From these relationships, the relationship between the correction amount Δψ of the in-plane rotation angle ψ, the resonance frequency f [MHz], and the anodic oxidation voltage x [V] is
Can be derived.

Next, a specific example of manufacturing a SAW element piece used for the SAW device will be described. For example, when the desired resonance frequency is 314.85 MHz, the relationship between the excitation electrode thickness ratio: H / λ, the line occupancy: η, the wavelength of the IDT portion: λ, and the temperature characteristic curve tend to be optimal. The cut angle indicating is as shown in Table 1.

  Here, when the SAW element piece obtained under the above conditions is coated with an anodic oxide film at a voltage of 60 V, the temperature characteristic curve deviates from the optimum tendency, and the tendency shown by the broken line in FIG. Will be shown.

Therefore, assuming the change in the tendency of the temperature characteristic curve as described above and assuming that the correction amount Δψ obtained in advance is added to the design value based on the relationship shown in Equation 1, the correction amount Δψ is calculated by
It can be calculated to be about 0.6.

  Therefore, when manufacturing the SAW element piece under the above conditions, the cut angle of the quartz substrate for optimizing the tendency of the temperature characteristic curve after applying the protective film is expressed in Euler angles (0 °, 123 °, 42 .6 °). When a SAW element piece is manufactured using a quartz substrate having such a cut angle, the temperature characteristic curve of the SAW device shows a tendency as shown by a one-dot chain line in FIG. 4 before the protective film is applied. Become. Then, the trend of the temperature characteristic curve is improved by applying a voltage of 60 V to the SAW element piece manufactured in the above configuration and covering it with an anodic oxide film serving as a protective film, and the tendency shown by the solid line in FIG. It becomes.

  The above embodiments and examples are described in terms of Euler angle display (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °) in-plane rotation ST cut with a cut angle obtained. It was based on a quartz substrate. However, the SAW device to which the present invention can be applied is not limited to this configuration, and is a range of Euler angles (0 °, 113 ° ≦ θ ≦ 135 °, 40 ° ≦ | ψ | ≦ 49 °). It is also possible to use an in-plane rotated ST-cut quartz substrate with a cut angle obtained in the above. This is because even in such a case, the applicant of the present application has found that the frequency temperature characteristic changes due to the application of the protective film, and the change in the frequency temperature characteristic shows the same tendency.

In the above embodiment, as the protective film, but mentions only the anodic oxide film, SiO ₂ film or the like, be other insulating protective film, the change in frequency temperature characteristics. Therefore, the present invention can be applied even when another protective film such as the SiO ₂ film is applied.

It is a figure which shows the structure of a SAW element piece. It is a figure which shows the relationship between the oxidation amount at the time of protective film formation, and correction amount (DELTA) (psi) of in-plane rotation angle (psi). It is a figure which shows the relationship between the correction amount (DELTA) (psi) of the in-plane rotation angle (psi) required after formation of a protective film and the frequency desired for a SAW apparatus. It is a figure which shows the change of the temperature characteristic curve of a SAW apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... SAW element piece (surface acoustic wave element piece), 12 ......... Piezoelectric substrate, 14 ... IDT, 16 ... Reflector, 18 ... Excitation electrode body, 20 ... Protection film.

Claims (2)

An elastic surface having an in-plane rotated ST-cut quartz substrate in the range of Euler angles (0 °, 95 ° ≦ θ ≦ 155 °, 33 ° ≦ | ψ | ≦ 46 °) and having a protective film on the excitation electrode A method for manufacturing a wave device comprising:
The amount of change in the frequency temperature characteristic of the surface acoustic wave device generated by applying the anodic oxide film as the protective film to the excitation electrode is determined, and the resonance frequency f set in the upper limit mode of the stop band and the anodic oxide film are determined. Based on the value of the voltage x applied to the excitation electrode when configuring, the correction amount Δψ of the in-plane rotation angle ψ to compensate for the change amount,


Sought by
Forming the in- plane rotated ST-cut quartz substrate in which the angle of ψ is shifted by the correction amount Δψ from the Euler angle calculated to obtain a desired frequency temperature characteristic at the set resonance frequency;
Method of manufacturing a surface acoustic wave device characterized by manufacturing a surface acoustic wave device have use the plane rotation ST-cut quartz substrate, and the excitation electrode of the anodic oxide film. Elastic surface with in- plane rotated ST-cut quartz substrate in Euler angle display (0 °, 113 ° ≦ θ ≦ 135 °, 40 ° ≦ | ψ | ≦ 49 °) and a protective film on the excitation electrode A method for manufacturing a wave device comprising:
The amount of change in the frequency temperature characteristic of the surface acoustic wave device generated by applying the anodic oxide film as the protective film to the excitation electrode is determined, and the resonance frequency f set in the upper limit mode of the stop band and the anodic oxide film are determined. Based on the value of the voltage x applied to the excitation electrode when configuring, the correction amount Δψ of the in-plane rotation angle ψ to compensate for the change amount,


Sought by
Forming the in- plane rotated ST-cut quartz substrate in which the angle of ψ is shifted by the correction amount Δψ from the Euler angle calculated to obtain a desired frequency temperature characteristic at the set resonance frequency;
Method of manufacturing a surface acoustic wave device characterized by manufacturing a surface acoustic wave device have use the plane rotation ST-cut quartz substrate, and the excitation electrode of the anodic oxide film.