Patent Application
20120038244
The entire disclosure of Japanese Patent Application No. 2010-181805, filed Aug. 16, 2010 and Japanese Patent Application No. 2011-093343, filed Apr. 19, 2011 are expressly incorporated by reference herein.
1. Technical Field
The present invention relates to a piezoelectric vibration device, a method of manufacturing the piezoelectric vibration device, and a method of adjusting the resonant frequency.
2. Related Art
In various electronic devices such as communication devices, computers, or mobile devices, there is used a piezoelectric vibration device having a surface acoustic wave (SAW) element as an electronic component such as a vibrator, an oscillator, or a filter. The piezoelectric vibration devices assume the role of vibrator/filter for transmitting/receiving sync signals and only the signals with appropriate frequencies of electronic devices, and therefore, the accuracy of the SAW resonant frequency to the base thereof is important.
However, since each SAW element includes production tolerance (e.g., tolerance in the manufacturing dimension or mass of the piezoelectric body, and tolerance in the manufacturing dimension or mass of the electrode), it results that a deviation from the design value is caused in the resonant frequency of each SAW element. Therefore, the manufacturers of quartz crystal devices perform frequency adjustment on each SAW element to thereby tune the frequency to a predetermined value, and further provide airtight sealing so that the frequency does not vary for a long period of time.
Here, the methods of adjusting the frequency of the SAW element can be divided into two major types.
In the first method, a metal film or metal fine particles made of gold (Au) are formed on the surface of the SAW element using a vapor-deposition method or a sputtering method to thereby perform mass attachment to the vibrating body (i.e., the piezoelectric body). Thus, the frequency is lowered (see, e.g., JP-A-2007-53520).
Further, in the second method, a part of the excitation electrode on the surface of the SAW element or a part of the quartz crystal is physically (or chemically) scraped away by sputtering-out (or etching) by irradiating the SAW element with an ion beam or acting the gas plasma on the SAW element to thereby perform mass reduction of the vibrating body. Thus, the frequency is raised (see, e.g., JP-A-2009-141825, JP-A-5-63485).
Incidentally, according to the first method described above, since the frequency can only be lowered, if the frequency is lowered beyond the desired value by chance, it is not possible to restore the production lot, which causes degradation of production yield.
Further, according to the second method, it results that the part of the SAW element is destroyed in the elementary sense. Therefore, it results that the roughness of the excitation electrode surface of the SAW element and the quartz crystal surface is increased, and thus, the possibility of deterioration of the frequency characteristics arises. Further, in some cases, the excitation electrode surface of the SAW element and the quartz crystal surface might be provided with an insulating thin film for preventing the electrical short due to a foreign matter between the excitation electrodes or a thin film for maintaining long-term reliability of the frequency of the SAW oscillator (as such thin films, a water-repellent thin film and an oil-repellent thin film for preventing moisture or organic component from adhering to the SAW chip to decompose or contaminate the SAW chip can be cited). In this case, due to the ion beam irradiation or the plasma etching on the thin film having been formed while taking the trouble, there is a possibility that the thin film causes structural breakage, and fails to sufficiently exert the insulating property, the water repellency, the oil repellency, and so on.
On the other hand, it is also possible to adopt a method of using a combination of the first and second methods as the method of adjusting the frequency. In this case, the problem of the “one-way” property of the frequency adjustment (i.e., the problem that the frequency can only be lowered, or can only be raised) can be avoided. However, as described above, in the case of raising the frequency, there still remains the problem of, for example, the deterioration of the frequency characteristics due to the increase in the surface roughness, and the degradation of the insulating property, the water repellency, and the oil repellency due to the structural breakage.
An advantage of some aspects of the invention is to provide a piezoelectric vibration device arranged to be capable of raising the resonant frequency while preventing the increase in the surface roughness and the structural breakage, a method of manufacturing the piezoelectric vibration device, and a method of adjusting the resonant frequency.
An aspect of the invention is directed to a method of manufacturing a piezoelectric vibration device having a surface acoustic wave element including: forming a functional film adapted to increase a velocity of a wave on a surface of the surface acoustic wave element.
Here, assuming that the velocity of the “wave” is v, the frequency thereof is f, and the wavelength thereof is λ, the relationship of formula 1 is true between these parameters.
f=v/λ (1)
According to such a method, the resonant frequency of the surface acoustic wave element can be raised using the relationship of the formula 1. There is no need for scraping away the surface of the surface acoustic wave element using a physical or chemical measure such as sputtering-out by ion beam irradiation on the surface of the surface acoustic wave element or etching by gas plasma when adjusting the resonant frequency. Therefore, it is possible to raise the resonant frequency while preventing the increase in the surface roughness of the surface acoustic wave element and the structural breakage.
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, a Young's modulus of the functional film is higher than a Young's modulus of each of the excitation electrode and the piezoelectric body, and a density of the functional film is lower than a density of each of the excitation electrode and the piezoelectric body.
Here, the property of the wave excited by the surface acoustic wave element (i.e., the surface acoustic wave) depends on the physical properties of the medium on which the wave propagates, and in particular on the physical properties of the portion near to the surface. Assuming in the surface acoustic wave element that the frequency of the wave to be excited is f, the elastic modulus of the medium is E, and the density of the medium is ρ, the relationship of the formula 2 is true between these parameters.
f∝√(E/ρ) (2)
The inventors have found the fact that the elastic modulus of the medium, on which the surface acoustic wave propagates, rises by forming the film having the Young's modulus higher than that of the piezoelectric body and the excitation electrode on the surface of the surface acoustic wave element, and as a result, and the resonant frequency of the surface acoustic wave element rises in some cases. On the other hand, it is known that, since the film is formed, there arises the phenomenon that the resonant frequency of the surface acoustic element drops due to the mass attachment to the vibrating body as commonly known. Therefore, the inventors have focused attention on the density in order for reduce the drop of the resonant frequency due to the mass attachment.
By forming the functional film having the “high Young's modulus” and the “low density” on the surface of the surface acoustic wave element, it is possible to develop the frequency rise due to the elastic modulus rise while suppressing the influence of the frequency drop due to the mass attachment effect to thereby raise the resonant frequency.
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 50 GPa, and a density of the functional film is one of equal to and lower than 1.0 g/cm3. According to such a method, the resonant frequency of the surface acoustic wave element can be raised as shown in, for example,
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 80 GPa, and a density of the functional film is one of equal to and lower than 2.0 g/cm3. According to such a method, the resonant frequency of the surface acoustic wave element can be raised as shown in, for example,
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 150 GPa, and a density of the functional film is one of equal to and lower than 4.0 g/cm3. According to such a method, the resonant frequency of the surface acoustic wave element can be raised as shown in, for example,
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that there is further provided with measuring, prior to the forming a functional film, a resonant frequency of the surface acoustic wave element with a voltage applied to the excitation electrode, and in the forming a functional film, a thickness of the functional film is adjusted based on a measurement value of the resonant frequency. According to such a method, the resonant frequency of the surface acoustic wave element can be adjusted to a desired value.
Further, in the method of manufacturing a piezoelectric vibration device described above, it is also possible that there is further provided with: forming, prior to the measuring a resonant frequency, one of an insulating film, a water-repellent film, and an oil-repellent film on a surface of the surface acoustic wave element, and in the measuring a resonant frequency, the resonant frequency is measured in a condition in which one of the insulating film, the water-repellent film, and the oil-repellent film is formed, and in the forming a functional film, the functional film is formed on one of the insulating film, the water-repellent film, and the oil-repellent film. According to such a method, the electrical short between the excitation electrodes of the surface acoustic wave element, the corrosion or the contamination due to moisture or an organic component can be prevented. Further, since the sputtering-out by the ion beam irradiation, the etching by the gas plasma, or the like for raising the resonant frequency of the surface acoustic, element is not performed, the structural breakage can also be prevented with respect to this film. It should be noted that “one of the insulating film, the water-repellent film, and the oil-repellent film” corresponds to, for example, a thin film 5 described later.
Another aspect of the invention is directed to a piezoelectric vibration device having a surface acoustic wave element including a functional film formed on a surface of the surface acoustic wave element, wherein the functional film has a function of increasing a velocity of a wave. According to such a configuration, it is possible to raise the resonant frequency while preventing the increase in the surface roughness of the surface acoustic wave element and the structural breakage.
Further, in the piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, a Young's modulus of the functional film is higher than a Young's modulus of each of the excitation electrode and the piezoelectric body, and a density of the functional film is lower than a density of each of the excitation electrode and the piezoelectric body.
Further, in the piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 50 GPa, and a density of the functional film is one of equal to and lower than 1.0 g/cm3.
Further, in the piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 80 GPa, and a density of the functional film is one of equal to and lower than 2.0 g/cm3.
Further, in the piezoelectric vibration device described above, it is also possible that the surface acoustic wave element includes a piezoelectric body and an excitation electrode formed on the piezoelectric body, the excitation electrode is an interdigital transducer made of one of aluminum and aluminum alloy, the piezoelectric body is a quartz crystal substrate, a Young's modulus of the functional film is one of equal to and higher than 150 GPa, and a density of the functional film is one of equal to and lower than 4.0 g/cm3.
Further, in the piezoelectric vibration device described above, it is also possible that there is further provided one of an insulating film, a water-repellent film, and an oil-repellent film formed on a surface of the surface acoustic wave element, and the functional film is formed on one of the insulating film, the water-repellent film, and the oil-repellent film.
Still another aspect of the invention is directed to a method of adjusting a resonant frequency of a surface acoustic wave element, including raising the resonant frequency by forming a functional film adapted to increase a velocity of a wave on a surface of the surface acoustic wave element. According to such a method, it is possible to raise the resonant frequency while preventing the increase in the surface roughness of the surface acoustic wave element and the structural breakage.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
An embodiment of the invention will hereinafter be explained with reference to the accompanying drawings. It should be noted that in the drawings hereinafter explained, the parts having the same configurations are provided with the same reference numerals, and duplicated explanations therefor will be omitted.
As shown in
The excitation electrodes 2 are electrodes for receiving a supply of a drive voltage and applying the voltage to the piezoelectric body 1, and are formed of, for example, interdigital transducers (IDT). The interdigital transducers are each formed of a combination of a plurality of electrode fingers 2a disposed so as to be perpendicular to the propagation direction of the surface acoustic wave and a bus bar 2b disposed along the propagation direction of the surface acoustic wave and for connecting the electrode fingers 2a to each other. Two such interdigital transducers form a pair, and are disposed so that the electrode fingers 2a of one of the pair and the electrode fingers 2a of the other of the pair mesh with each other alternately in a plan view. As shown in
The reflectors 3 are disposed so as to sandwich the excitation electrodes 2 on the both sides thereof in a plan view, and are electrodes for reflecting the SAW (between the reflectors 3) excited by the excitation electrodes 2 to thereby keep the SAW therebetween. The reflectors 3 are each formed of a combination of, for example, a plurality of conductor strips 3a disposed so as to be parallel to the electrode fingers 2a, and bus bars 3b for respectively connecting the both ends of the conductor strips 3a. The excitation electrodes 2 and the reflectors 3 are made of, for example, aluminum or aluminum alloy.
Further, the functional film 4 is a film having a function of increasing the velocity of the SAW. The functional film 4 is formed on the surface of the piezoelectric body 1 so as to entirely cover the electrode fingers 2a of the excitation electrodes 2, for example. Here, the relationship of the formula 1 described above is true between the velocity v of a wave and the frequency f of the wave. By making the SAW propagate to the functional film 4, rising of the resonant frequency of the SAW element 10 is achieved.
Citing an example of the physical properties of the functional film 4, the Young's modulus of the functional film 4 is set higher than the Young' modulus of both of the piezoelectric body 1 and the excitation electrodes 2, and at the same time, the density of the functional film 4 is set lower than the density of both of the piezoelectric body 1 and the excitation electrodes 2. For example, if the piezoelectric body 1 is made of a quartz crystal (the Young's modulus of 73 GPa, the density of 2.6 g/cm3), and the excitation electrodes 2 are made of aluminum (the Young's modulus of 70 GPa, the density of 2.7 g/cm3), a hard carbon film, a beryllium film, and so on described later can be cited as the functional film 4 fulfilling the physical properties described above. As described above, by limiting the material physical properties of the functional film 4 in conjunction with the materials of the piezoelectric body 1 and the excitation electrodes 2, it is possible to develop the rising of the frequency due to the high elastic modulus while suppressing the influence of the frequency drop due to the mass attachment effect to thereby raise the resonant frequency of the SAW element 10.
It should be noted that the SAW element 10 exerts a function of outputting an alternating current with a designed frequency if combined with an oscillator circuit not shown. As shown in
Then, a method of manufacturing the piezoelectric vibration device 100 will be explained.
First of all, in the step S1 of
Alternatively, it is also possible to arrange that the excitation electrodes 2 and the reflectors 3 are formed using the print method in the step S1. For example, it is also possible to arrange that the ink including conductive particles made of, for example, aluminum is sprayed onto the surface of the piezoelectric body 1 to thereby form the excitation electrodes 2 and the reflectors 3.
Subsequently, in the step S2 of
Subsequently, in the step S3 of
Subsequently, in the step S5 of
For the measurement of the resonant frequency in the step S3 of
As shown in
In the deposition device 50, the frequency measuring instrument 56 measures the resonant frequency of the SAW element when measuring the frequency (e.g., the step S3 of
It should be noted that it is also possible for the deposition device 50 to perform the deposition of the functional film 4 on the surface of the SAW element 10 while measuring the resonant frequency of the SAW element 10 with the frequency measuring instrument 56. In other words, it is also possible to simultaneously perform the step S3 and the step S4 of
The material, the size, and so on of the SAW element used in the simulation as a model are substantially the same as those of the SAW element 10 explained in the column of “1. Regarding Configuration Example of Piezoelectric Vibration Device” described above, and are specifically as follows.
As shown in
The material, the size, and so on of the SAW element used in the simulation as a model are substantially the same as those of the SAW element explained in the column of “4-1. Regarding Relationship Between Film Thickness of Functional Film and Resonant Frequency” described above. It should be noted that the physical properties and the thickness of the functional film thus formed are different from those described above, and are specifically set as described below.
As shown in
(a) The Young's modulus of the functional film is equal to or higher than 50 GPa, and the density thereof is equal to or lower than 1.0 g/cm3.
(b) The Young's modulus of the functional film is equal to or higher than 80 GPa, and the density thereof is equal to or lower than 2.0 g/cm3.
(c) The Young's modulus of the functional film is equal to or higher than 150 GPa, and the density thereof is equal to or lower than 4.0 g/cm3.
As the film having such physical properties, the following films, for example, can be cited.
It should be noted that if the type of the functional film is changed, the adjustment amount of the frequency varies in accordance with the density and the Young's modulus of the film thus formed even if the thickness of the film thus formed is the same. Therefore, the adjustment sensitivity of the resonant frequency can be varied by selecting the type of the functional film. For example, the coarse adjustment and the fine adjustment of the resonant frequency can selectively be performed due to the selection of the type of the functional film.
As explained hereinabove, according to the embodiment of the invention, by forming the functional film 4 for increasing the velocity of the wave on the surface of the SAW element 10, the resonant frequency of the SAW element 10 can be raised. As such a functional film 4, there can be cited those having the Young's modulus higher than those of the piezoelectric body 1 and the excitation electrodes 2, and the density lower than those of the piezoelectric body 1 and the excitation electrodes 2. Alternatively, even if the physical properties are slightly different from the physical properties described above, the film having the physical properties of either one of the alternatives (a) through (c) described above can be used as the functional film 4 providing the piezoelectric body 1 consists of a quartz crystal and the excitation electrodes 2 are formed of the interdigital transducers made of aluminum or aluminum alloy. Thus, the resonant frequency of the SAW element 10 can be raised while preventing the increase in the surface roughness and the structural breakage compared to the related art (i.e., the second method explained in the column of the related art).
Specifically, according to the embodiment of the invention, there is no need for partially scraping away the surface of the SAW element 10 with a physical or chemical measure such as sputtering-out by ion beam irradiation on the surface of the SAW element 10 or etching by gas plasma when raising the resonant frequency of the SAW element 10. Therefore, the SAW element 10 with preferable frequency characteristics can be manufactured without causing any deterioration of the frequency characteristics due to the increase in the surface roughness of the piezoelectric body 1 and the excitation electrodes 2 and the structural breakage.
In the description of the above embodiment, the case of forming the functional film 4 so as to cover the entire electrode fingers 2a of the excitation electrodes 2 is explained. However, the invention is not at all limited thereto. It is also possible to form the functional film so as to partially cover the electrode fingers 2a as shown in, for example,
Further, in the description of the above embodiment, the case of forming the functional film 4 directly on the surface of the piezoelectric body 1 provided with the excitation electrodes 2 and the reflectors 3 is explained. However, the invention is not at all limited thereto. It is also possible to form the insulating, water-repellent, or oil-repellent thin film 5 on the surface of the piezoelectric body 1 provided with the excitation electrodes 2, and then form the functional film 4 on the thin film 5. In other words, it is also possible to form the functional film 4 on the surface of the SAW element 10 via the thin film 5.
In this case, the resonant frequency is measured in, for example, the step S3 of
By forming the thin film 5, the electrical short between the excitation electrodes 2 forming a pair, the corrosion or the contamination due to moisture or an organic component can be prevented. Further, since the sputtering-out by the ion beam irradiation, the etching by the gas plasma, or the like for raising the resonant frequency of the SAW element 10 is not performed, the structural breakage of the thin film 5 can also be prevented.
Further, according to the invention, it is also possible to use both of the formation of the functional film 4 explained in the description of the above embodiment and the first method explained in the column of the related art. For example, it is also possible to form the functional film 4 to thereby raise the resonant frequency if the measurement value of the resonant frequency is lower than the target value in the step S4 of
The application range of the invention is not at all limited to the embodiments described hereinabove. The invention can widely be applied within the scope or the spirit described in the present specification. The invention can be applied to, for example, the SAW element using the quarts crystal obtained by cutting another plane, the SAW element using other piezoelectric materials such as aluminum nitride, lithium niobate, or lithium tantalate, and the SAW element using the film made of the materials described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-181805 | Aug 2010 | JP | national |
| 2011-093343 | Apr 2011 | JP | national |
