Piezoelectric thin film device having a drive section with a weighted portion

There is provided a piezoelectric thin film device with its frequency impedance characteristic unsusceptible to spuriousness.A film bulk acoustic resonator has a configuration where an adhesive layer, a lower electrode, a piezoelectric thin film, and an upper electrode are laminated in this order on a support substrate. A drive section of the upper electrode and a drive section of the lower electrode are opposed to each other with the piezoelectric thin film interposed therebetween. The respective drive section has a slender two-dimensional shape, with magnitude in its longitudinal direction being not less than twice, more desirably four times, and further desirably ten times, as large as magnitude in its widthwise direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric thin film device including a single or a plurality of film bulk acoustic resonators (FBAR).

2. Description of the Background Art

FIG. 59is an oblique view showing a schematic configuration of a main part of a conventional film bulk acoustic resonator9.

As shown inFIG. 59, the film bulk acoustic resonator9includes a piezoelectric thin film91, and an upper electrode92and a lower electrode93formed on respective main surfaces of the piezoelectric thin film91. In the film bulk acoustic resonator9, a square drive section921of the upper electrode92and a square drive section931of the lower electrode93are opposed to each other with the piezoelectric thin film91interposed therebetween, and when an excitation signal is applied to pads923and933electrically connected to the drive sections921and931, an electric field is generated to excite vibrations inside the piezoelectric thin film91in an excitation region911where the drive sections921and931are opposed to each other. It is to be noted that the shapes of the drive sections921and931may not be square but may alternatively be circular.

In such a film bulk acoustic resonator9, in order to prevent leakage of the excited vibrations from the excitation region911leading to generation of sub-resonance due to the outline of the piezoelectric thin film91, an energy trapping structure is often adopted in which a cutoff frequency of acoustic waves is displaced by a means for partially changing a film thickness of the piezoelectric thin film91, to prevent leakage of vibrations from the excitation region911.

It should be noted that Japanese Patent Application Laid-Open No. 8 (1996)-242026 is a prior art document on the conventional film bulk acoustic resonator.

However, with the conventional film bulk acoustic resonator, there has been a problem in that in the case of using a piezoelectric material having a large electromechanical coupling factor, such as lithium niobate or lithium tantalite, a sufficient energy trapping effect cannot be obtained, and hence a frequency impedance characteristic becomes susceptible to spuriousness.

SUMMARY OF THE INVENTION

The present invention relates to a piezoelectric thin film device including a single or a plurality of film bulk acoustic resonators.

According to the present invention, a piezoelectric thin film device including a single or a plurality of film bulk acoustic resonators, the device includes: a piezoelectric thin film; and electrodes formed on respective main surfaces of the piezoelectric thin film and having drive sections opposed to each other with the piezoelectric thin film interposed therebetween, wherein the respective drive section has a slender two-dimensional shape with magnitude in a longitudinal direction being not less than twice as large as magnitude in a widthwise direction.

Accordingly, a frequency impedance characteristic of the film bulk acoustic resonator becomes insusceptible to spuriousness.

It is preferable that at least one of the drive sections has a weighted portion with a larger mass per unit area than that of a central portion, only along inner sides of a pair of opposite sides extending in the longitudinal direction.

Accordingly, the frequency impedance characteristic of the film bulk acoustic resonator can be unsusceptible to spuriousness while the influence exerted by a resonance waveform of the resonator formed by the weighted portion is avoided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, desired embodiments of piezoelectric thin film devices of the present invention are described by taking as examples a single film bulk acoustic resonator and a ladder-type filter (hereinafter referred to as “piezoelectric thin film filter”) formed by combination of two film bulk acoustic resonators. However, the following embodiments do not mean that the piezoelectric thin film device of the present invention is not limited to the single film bulk acoustic resonator and the piezoelectric thin film filter. Namely, in the present invention, the piezoelectric thin film device typically means piezoelectric thin film devices in general which include a single or a plurality of film bulk acoustic resonators. Such piezoelectric thin film devices include an oscillator, a trap and the like, each including a single film bulk acoustic resonator, and a filter, a duplexer, a triplexer, a trap, and the like, each including a plurality of film bulk acoustic resonators. Here, the film bulk acoustic resonator is a resonator using an electrical response by means of bulk acoustic waves piezoelectrically excited by a thin film that cannot stand up under its own weight without a support.

1. First Embodiment

FIG. 1is an oblique view showing a schematic configuration of a film bulk acoustic resonator (FBAR)1according to a first embodiment of the present invention.FIG. 2is a sectional view showing a cross section of the film bulk acoustic resonator1along a cutting-plane line II-II ofFIG. 1. InFIGS. 1 and 2, an XYZ orthogonal coordinate system is defined for the sake of explanation where the right-and-left direction is the X-axis direction, the front-and-back direction is the Y-axis direction, and the top-and bottom-direction is the Z-axis direction. This also applies to each of later-described figures. The film bulk acoustic resonator1is a resonator using an electrical response by means of thickness extension vibrations excited by a piezoelectric thin film14.

As shown inFIGS. 1 and 2, the film bulk acoustic resonator1has a configuration where an adhesive layer12, a lower electrode13, the piezoelectric thin film14, and an upper electrode15are laminated in this order on a support substrate11. In the film bulk acoustic resonator1, the piezoelectric thin film14has a size smaller than that of the support substrate11, and part of the lower electrode13is in the state of being exposed.

In the manufacture of the film bulk acoustic resonator1, the piezoelectric thin film14is obtained by performing removal processing on a piezoelectric substrate that can independently stand up under its own weight, but the piezoelectric thin film14obtained by removal processing cannot independently stand up under its own weight. For this reason, prior to removal processing in manufacture of the film bulk acoustic resonator1, a predetermined member including a piezoelectric substrate is previously bonded to the support substrate11as a support.

Support Substrate

When the piezoelectric substrate is subjected to removal processing during manufacture of the film bulk acoustic resonator1, the support substrate11serves as a support to support, via the adhesive layer12, the piezoelectric substrate with the lower electrode13formed on its lower surface. In addition, after the manufacture of the film bulk acoustic resonator1, the support substrate11also serves as a support to support, via the adhesive layer12, the piezoelectric thin film14with the lower electrode13formed on its under surface and the upper electrode15on its upper surface. Therefore, the support substrate11is required to be able to stand force applied at the time of removal processing on the piezoelectric substrate, and also required not to reduce its strength after manufacture of the film bulk acoustic resonator1.

The material for and the thickness of the support substrate11can be selected as appropriate so as to satisfy the above-mentioned requirements. However, if the material for the support substrate11is a material having a thermal expansion coefficient close to that of the piezoelectric material constructing the piezoelectric thin film14, more desirably a material having a thermal expansion coefficient equivalent to that of the piezoelectric material constructing the piezoelectric thin film14, e.g. the same material as the piezoelectric material constructing the piezoelectric thin film14, it is possible to suppress warpage and damage caused by a difference in thermal expansion coefficient during manufacture of the film bulk acoustic resonator1. It is further possible to suppress characteristic variations and damage caused by a difference in thermal expansion coefficient after manufacture of the film bulk acoustic resonator1. It is to be noted that in the case of using a material having an anisotropic thermal expansion coefficient, it is desirable to see that the thermal expansion coefficients in all different directions are made the same. Moreover, the same material as the piezoelectric material may be used in the same orientation as the piezoelectric material.

A depression (concave portion or groove)111is formed in a predetermined region of the support substrate11opposed to an excitation region141of the piezoelectric thin film14. The depression111forms a cavity below the excitation region141of the piezoelectric thin film14to separate the excitation region141of the piezoelectric thin film14from the support substrate11so as to prevent vibrations excited by the excitation region141from interfering with the support substrate11.

Adhesive Layer

The adhesive layer12serves to bond and fix the piezoelectric substrate with the lower electrode13formed on its bottom surface to the support substrate11when the piezoelectric substrate is subjected to removal processing during manufacture of the film bulk acoustic resonator1. Additionally, the adhesive layer12also serves to bond and fix the piezoelectric thin film14with the lower electrode13formed on its lower surface and the upper electrode15on its upper surface to the support substrate11after manufacture of the film bulk acoustic resonator1. Therefore, the adhesive layer12is required to be able to stand force applied at the time of removal processing on the piezoelectric substrate, and also required not to reduce its adhesive force after manufacture of the film bulk acoustic resonator1.

A desirable example of the adhesive layer12satisfying such requirements may be an adhesive layer12formed of an organic adhesive agent, desirably an epoxy adhesive agent (adhesive layer made of an epoxy resin using thermosetting properties) or an acrylic adhesive agent (adhesive layer made of an acrylic resin using both thermosetting and photocuring properties), which has a filling effect and exerts sufficient adhesive force even when an object to be bonded is not completely flat. Adoption of such a resin allows prevention of unexpected formation of an air space between the piezoelectric substrate and the support substrate11, thereby to prevent occurrence of cracking or the like at the time of removal processing on the piezoelectric substrate due to the air space. However, this does not prevent the piezoelectric thin film14and the support substrate11from being bonded and fixed to each other by an adhesive layer12different from the above-mentioned adhesive layer12.

Piezoelectric Thin Film

The piezoelectric thin film14is obtained by performing removal processing on the piezoelectric substrate. More specifically, the piezoelectric thin film14is obtained by reducing the piezoelectric substrate in thickness from a thickness (e.g. not smaller than 50 μm) with which the substrate can independently stand up under its own weight, to a thickness (e.g. not larger than 10 μm) with which the substrate cannot independently stand up under its own weight.

As a piezoelectric material constructing the piezoelectric thin film14, a piezoelectric material having a desired piezoelectric property can be selected, and it is desirable to select a single crystal material including no grain boundary, such as quartz crystal (SiO2), lithium niobate (LiNbO3), lithium tantalite (LiTaO3), lithium tetraborate (Li2B4O7), zinc oxide (ZnO), potassium niobate (KNbO3), or langasite (La3Ga3SiO14). This is because the use of the single crystal material as the piezoelectric material constructing the piezoelectric thin film14can lead to improvement in electromechanical coupling factor as well as mechanical quality factor of the piezoelectric thin film14.

Further, a crystal orientation in the piezoelectric thin film14can be selected to be a crystal orientation having a desired piezoelectric characteristic. Here, the crystal orientation in the piezoelectric thin film14is desirably a crystal orientation that leads to favorable temperature characteristics of a resonance frequency and an antiresonance frequency of the film bulk acoustic resonator1, and is further desirably a crystal orientation in which a resonance frequency temperature coefficient is “0”.

Removal processing on the piezoelectric substrate15is performed by mechanical processing such as cutting, grinding or polishing, or chemical processing such as etching. Here, if the piezoelectric substrate is subjected to removal processing where a plurality of removal processing methods are combined and the removal processing method is shifted in stages from one performed at high processing speed to one with small process degradation in an object to be processed, it is possible to improve the quality of the piezoelectric thin film14while maintaining high productivity, so as to improve the characteristics of the film bulk acoustic resonator1. For example, the piezoelectric substrate is subjected to grinding where the substrate is brought into contact with fixed abrasive grains for grinding, and is then subjected to polishing where the substrate is brought into contact with free abrasive grains for grinding. Thereafter, a processing degradation layer generated on the piezoelectric substrate by above-mentioned polishing is removed by finish-polishing. If such processing is executed, the piezoelectric substrate can be ground at faster speed so as to improve productivity of the film bulk acoustic resonator1, and also, the quality of the piezoelectric thin film14is improved so as to improve the characteristics of the film bulk acoustic resonator1. It is to be noted that more specific methods for removal processing on the piezoelectric substrate is described in later-described examples.

In the film bulk acoustic resonator1as thus described, different from the case of forming the piezoelectric thin film14by sputtering or the like, since the piezoelectric material constructing the piezoelectric thin film14and the crystal orientation in the piezoelectric thin film14are free from constraints of the substrate, the degree of flexibility is high in selection of the piezoelectric material constructing the piezoelectric thin film14and the crystal orientation in the piezoelectric thin film14. This facilitates realization of a desired characteristic in the film bulk acoustic resonator1.

Upper Electrode and Lower Electrode

In the following, the upper electrode15and the lower electrode13are described with reference toFIGS. 3A and 3B.FIGS. 3A and 3Brespectively show patterns of the upper electrode15and the lower electrode13when seen from above.

The upper electrode15and the lower electrode13are conductive thin films obtained by formation of films of a conductive material.

The thicknesses of the upper electrode15and the lower electrode13are determined in consideration of adhesiveness to the piezoelectric thin film14, electric resistance, withstand power, and the like. It is to be noted that in order to suppress variations in resonance frequencies and antiresonance frequencies of the film bulk acoustic resonator1caused by variations in acoustic velocity and film thickness of the piezoelectric thin film14, the thicknesses of the upper electrode15and the lower electrode13may be adjusted as appropriate.

Although a conductive material constituting the upper electrode15and the lower electrode13is not particularly limited, the material is desirably selected from metals such as aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), tungsten (W), and tantalum (Ta). Naturally, an alloy may be used as the conductive material constituting the upper electrode15and the lower electrode13. Further, a plurality of conductive materials may be laminated to form the upper electrode15and the lower electrode13.

The upper electrode15has a drive section151, a pull-out line152, and a pad153. Similarly, the lower electrode13has a drive section131, a pull-out section132, and a pad133. The drive section151of the upper electrode15and the drive section131of the lower electrode13are opposed to each other with the piezoelectric thin film14interposed therebetween.

The upper electrode15formed on the upper surface of the piezoelectric thin film14is pulled out in the −X direction from the drive section151by the pull-out line152, and the end of the upper electrode15is a pad153for connection with external wiring electrically connected to the outside of the film bulk acoustic resonator1.

The lower electrode13formed on the lower surface of the piezoelectric thin film14is pulled out in the +X direction from the drive section131by the pull-out line132, and the end of the lower electrode13is a pad133for connection with external wiring electrically connected to the outside of the film bulk acoustic resonator1.

In the film bulk acoustic resonator1, in order to make the pad133connectable with the external wire, the piezoelectric thin film14in the vicinity of the pad133(portion indicated by a doffed line inFIG. 1) has been removed, to bring the pad133into an exposed state. In the film bulk acoustic resonator1, with the upper electrode15and the lower electrode13in the above described state, when the excitation signals are applied to the upper electrode15and the lower electrode13via the pads153and133, an electric field E is generated inside the piezoelectric thin film14in the excitation region141where the upper electrode151and the lower electrode131are opposed to each other, to excite vibrations.

The drive sections151and131each have a slender two-dimensional shape (rectangular inFIGS. 1,2,3A and3B) with magnitude in its longitudinal direction being not less than twice, more desirably four times, and further desirably ten times, as large as magnitude in its widthwise direction.

Here, “a slender two-dimensional shape with magnitude in its longitudinal direction being not less than n (n=2, 4, 10) times as large as magnitude in its widthwise direction” typically means a rectangular with its long-side length La as magnitude in its longitudinal direction being larger than its short-side length Lb as magnitude in its widthwise direction, and an aspect ratio La/Lb being not less than n (see a figure drawn with a solid line inFIG. 4), or may mean an oval with its long-axis length La as magnitude in its longitudinal direction being longer than its short-axis length Lb as magnitude in its widthwise direction, and an aspect ratio La/Lb being not less than n (see a figure drawn with a solid line inFIG. 5).

More generally speaking, here, “the slender two-dimensional shape with magnitude in its longitudinal direction being not less than n times as large as magnitude in its widthwise direction” means a two-dimensional shape having a circumscribed rectangle with the smallest area (see a figure drawn by a dotted line in each ofFIGS. 5 to 7) with its long-side length La being not less than n times as large as its short-side length Lb, and also a two dimensional shape in which, when the two-dimensional shape is symmetric with respect to both symmetric axes Sa and Sb that are orthogonal to each other, magnitude in the direction of the one symmetric axis Sa in its longitudinal direction is not less than n times as large as magnitude in the direction of the other symmetric axis Sb.

Therefore, the drive sections151and131may be in obround shape drawn by a solid line inFIG. 6, or may be a rectangular with its vertexes rounded, drawn by a solid line inFIG. 7, or may be a rectangular with its vertexes cut off to form oblique lines, drawn by a solid line inFIG. 8.

2. Second Embodiment

FIG. 9is an oblique view showing a schematic configuration of a film bulk acoustic resonator2according to a second embodiment of the present invention. The film bulk acoustic resonator2is also a resonator using an electrical response by means of thickness extension vibrations excited by a piezoelectric thin film24.

As shown inFIG. 9, the film bulk acoustic resonator2has a configuration where an adhesive layer22, a lower electrode23, the piezoelectric thin film24, and an upper electrode25are laminated in this order on a support substrate21. The film bulk acoustic resonator2of the second embodiment has a similar structure to that of the film bulk acoustic resonator1of the first embodiment, and the support substrate21, the adhesive layer22, the lower electrode23, the piezoelectric thin film24, and the upper electrode25of the film bulk acoustic resonator2are respectively the same as the support substrate11, the adhesive layer12, the lower electrode13, the piezoelectric thin film14, and the upper electrode15of the film bulk acoustic resonator1except for the patterns of the lower electrode23and the upper electrode25. It is to be noted that, in the following, repeated description on the same points as those of the film bulk acoustic resonator1is not given, but the patterns of the lower electrode23and the upper electrode25, which are different from those in the film bulk acoustic resonator1, are particularly described.

FIGS. 10A and 10Brespectively show patterns of the upper electrode25and the lower electrode23when seen from above.

The upper electrode25has a drive section251, a pull-out line252, and a pad253. Similarly, the lower electrode23has a drive section231, a pull-out section232, and a pad233. The drive section251of the upper electrode25and the lower electrode231of the lower electrode23are opposed to each other with the piezoelectric thin film24interposed therebetween.

The upper electrode25formed on the upper surface of the piezoelectric thin film24is pulled out in the −X direction from the drive section251by the pull-out section252, and the end of the upper electrode25is a pad253for connection with external wiring electrically connected to the outside of the film bulk acoustic resonator2.

The lower electrode23formed on the lower surface of the piezoelectric thin film24is pulled out in the +X direction from the drive section231by the pull-out section232, and the end of the lower electrode23is a pad233for connection with external wiring electrically connected to the outside of the film bulk acoustic resonator2.

Also in the film bulk acoustic resonator2, the drive sections251and231each have a slender rectangular shape with its long-side length being not less than twice, more desirably four times, and further desirably ten times, as large as its short-side length.

The pull-out section252is connected to a long side251sof the drive section251, and the width of the upper electrode25in the ±Y direction from the drive section251to the pad253through the pull-out section252is kept constant. Similarly, the pull-out section232is connected to a long side213sof the drive section231, and the width of the lower electrode23in the ±Y direction from the drive section231to the pad233through the pull-out section232is kept constant. Namely, in the film bulk acoustic resonator2, the rectangular band-shaped upper electrode25and lower electrode23, which extend in the same direction (±X direction), are respectively formed on the upper and lower surfaces of the piezoelectric thin film24, and the ends of the upper electrode25and the lower electrode23are opposed to each other with the piezoelectric thin film24interposed therebetween, to obtain an excitation region241.

It should be noted that, since an outline of the excitation region241where the drive sections251and231are opposed to each other with the piezoelectric thin film24interposed therebetween reflects acoustic waves of a transverse mode propagated in the spreading direction of the piezoelectric thin film24, the state of the outline of the excitation region241has an influence on a spurious characteristic of the film bulk acoustic resonator2. However, different from the film bulk acoustic resonator1, in the film bulk acoustic resonator2, the pull-out section252is arranged so as to be connected to the whole of the long side251sof the drive section251, and the pull-out section232is arranged so as to be connected to the whole of the long side213sof the drive section231. For this reason, in the film bulk acoustic resonator2, uniform reflection of the acoustic waves occurs on the long sides251sand213s, and hence generation of a large number of spuriousness caused by nonuniformity of the reflection can be effectively prevented, compared with the film bulk acoustic resonator1in which reflection of the acoustic waves occurs nonuniformly in the portions connected with the pull-out lines152and132and portions not connected with those lines.

Further, if such patterns of the upper electrode25and the lower electrode23are adopted, as shown inFIG. 11, the shape of the excitation region241where the upper electrode25and the lower electrode23are opposed remains rectangular even when positions where the upper electrode25and the lower electrode23are displaced in directions indicated by allows A25and A23from positions they should be. Namely, in the film bulk acoustic resonator2, even when the positions where the upper electrode25and the lower electrode23are formed are displaced from positions they should be, the excitation region241, the outline of which reflects the acoustic waves of the transverse mode propagating in the spreading direction of the piezoelectric thin film24, remains simple rectangular. Therefore, even when the positions where the upper electrode25and the lower electrode23are formed are displaced from positions where they should be, a large number of spuriousness are not generated caused by such displacement. This is apparent by comparison with the case, as shown inFIGS. 1 and 2, in which the shape of the excitation region141where the upper electrode15and the lower electrode13are opposed to each other becomes complicated when the positions where the upper electrode15and the lower electrode13of the film bulk acoustic resonator1of the first embodiment are displaced in directions indicated by arrows A15and A13from positions where they should be, which might cause generation of a large number of spuriousness.

In addition, in the foregoing description, the example was shown as a desirable example in which the width in the ±Y direction from the drive section251to the pad253through the pull-out section252is kept uniform and the width in the ±Y direction from the drive section231to the pad233through the pull-out section232is also kept uniform. However, when energy trapping into the excitation region241is sufficiently performed, with distance from the excitation region241, the influence exerted by the upper electrode25and the lower electrode23on a frequency impedance characteristic of the film bulk acoustic resonator2decreases. Therefore, for example, as shown inFIGS. 13A and 13B, it is allowable to make the width in the ±Y direction of only a portion of the pull-out section252which is close to the drive section251the same as the width of the drive section251, and make the width in the ±Y direction of only a portion of the pull-out section232which is close to the drive section231the same as the width of the drive section231. Here,FIGS. 13A and 13Bshow patterns of the upper electrode25and the lower electrode23when seen from above.

FIG. 14is an oblique view showing a schematic configuration of a film bulk acoustic resonator3according to a third embodiment of the present invention. Further,FIG. 15is a sectional view showing a cross section of the film bulk acoustic resonator3along a cutting plane line XV-XV ofFIG. 14. The film bulk acoustic resonator3is also a resonator using an electrical response by means of thickness extension vibrations excited by a piezoelectric thin film34.

As shown inFIGS. 14 and 15, the film bulk acoustic resonator3has a configuration where an adhesive layer32, a lower electrode33, the piezoelectric thin film34, and an upper electrode35are laminated in this order on a support substrate31. The film bulk acoustic resonator3of the third embodiment has a similar structure to that of the film bulk acoustic resonator2of the second embodiment, and the support substrate31, the adhesive layer32, the lower electrode33, the piezoelectric thin film34, and the upper electrode35of the film bulk acoustic resonator3are respectively the same as the support substrate21, the adhesive layer22, the lower electrode23, the piezoelectric thin film24, and the upper electrode25of the film bulk acoustic resonator2except that a drive section351of the upper electrode35has a weighted portion351W. It is to be noted that, in the following, repeated description on the same points as those of the film bulk acoustic resonator2is not given, but the weighted portion351W, which is an element differentiating from the film bulk acoustic resonator2, is particularly described.

FIGS. 16A and 16Brespectively show patterns of the upper electrode35and the lower electrode33when seen from above.

The upper electrode35has a drive section351, a pull-out section352, and a pad353. Similarly, the lower electrode33has a drive section331, a pull-out section332, and a pad333. The drive section351of the upper electrode35and the lower electrode331of the lower electrode33are opposed to each other with the piezoelectric thin film34interposed therebetween. The patterns of the upper electrode35and the lower electrode33of the film bulk acoustic resonator3are the same as those of the upper electrode25and the lower electrode23of the film bulk acoustic resonator2except that the drive section351has the weighted portion351W.

In the film bulk acoustic resonator3, the lower electrode33is a conductive thin film with a substantially uniform film thickness, whereas the upper electrode35has a structure where, on the conductive thin film with a substantially uniform film thickness, a conductive thin film is further superposed in regions RG31along the inner sides of a long sides351L as a pair of opposite sides extending in the longitudinal direction of the drive section351. The weighted portion351W, hatched inFIG. 16A, is formed by partially increasing the thickness of the upper electrode35in the region RG31beyond unavoidable variation.

The weighted portion351W is larger than the central portion of the drive section351with a substantially uniform film thickness in mass per unit area, thereby serving to reduce a cutoff frequency of the acoustic waves in the region RG31. In the film bulk acoustic resonator3, the reduction in cutoff frequency leads to prevention of leakage of vibration energy of vibrations excited in an opposing region341where the drive sections351and331are opposed to each other with the piezoelectric thin film34interposed therebetween, thereby to suppress sub-resonance which depends upon the outline shape of the piezoelectric thin film34.

It is to be noted that the reason why the weighted portion351W is provided only along the inner side of the long side351L whereas the weighted portion351W is not provided along the inner side of a pair of short sides351S is because such a configuration makes the frequency impedance characteristic of the film bulk acoustic resonator3unsusceptible to spuriousness while avoiding the influence exerted by a resonance waveform of the resonator formed by the weighted portion351W. Namely, a active reason is that the area of the region RG31, occupied by the weighted portion351W which forms a resonator with a lower resonance frequency than a resonator formed by the central portion, can be reduced so as to suppress strength of another resonance waveform superposed on the low frequency side of the resonance waveform of the resonator formed by the central portion. Further, a passive reason is that in the case of adopting the drive sections351and331each having a slender two-dimensional shape, the acoustic waves of the transverse mode are propagated mainly in a direction crossing the long side351L, thereby allowing sufficient prevention of leakage of vibration energy from the opposing region341even without provision of the weighted portion351W along the inner side of the short side351S.

A width W31of the region RG31is desirably not less than 1% and not more than 30%, further desirably not less than 5% and not more than 20%, of a width W32of the drive section351. This is because the width W31falling out of this range would cause reduction in vibration energy trapping effect. Here, the width W31of the drive section351is a length of the short side351S when the drive section351is formed in rectangular shape.

The film thicknesses of the upper electrode35and the lower electrode33should be determined according to the conductive material constituting the electrodes, and when tungsten is selected as the conductive material, its thickness is desirably not less than 700 angstroms. This is because, if tungsten has a film thickness below 700 angstroms, its electric resistance increases, to significantly increase resonance resistance of the film bulk acoustic resonator3. Further, typically, when a difference in film thickness between the weighted portion351W and a portion other than351W is about 500 angstroms, sub-resonance of the film bulk acoustic resonator3can be favorably suppressed.

The upper electrode35can be formed such that a conductive thin film with a substantially uniform film thickness is formed and a conductive thin film is further formed as superposed on the weighted portion351W, or that a conductive thin film with a substantially uniform film thickness is formed and a portion other than a portion to become the weighted portion351W is reduced in thickness.

In addition, although the example was shown inFIG. 15where the weighted portion351W is arranged in the drive section351of the upper electrode35, the weighted portion may be arranged on the drive section331of the lower electrode33in place of the drive section351of the upper electrode35, or the weighted portion may be arranged on both the drive section351of the upper electrode35and the drive section331of the lower electrode33. Further, although the weighted portion351W can be readily formed by partially increasing the film thickness of the drive section351to form the weighted portion351W, this does not prevent another method of forming the weighted portion351W by partially increasing a mass of the drive section351instead of partially increasing the film thickness of the drive section351or in addition to partially increasing the film thickness of the drive section351.

Further, it is desirable to increase the film thickness of the pull-out section352adjacent to the drive section351to match the film thickness of the weighted portion351W, since the electric resistance of the pull-out section352can be reduced.

Moreover, as shown inFIGS. 17A and 17B, it is considered that another drive section351may be arranged on the inner side of the weighted portion351W shown inFIGS. 14,15,16A and16B.

In addition to these, it is also possible to favorably suppress sub-resonance of the film bulk acoustic resonator3even when it is arranged that the film thickness of the weighted portion351W increases with distance from the central portion of the drive section351so as to increase the mass per unit area of the weighted portion351W. Further, there is an advantage in that such a weighted portion351W does not have a large influence on the suppression effect of the sub-resonance even with a slight change in shape of the weighted portion351W.

For example, in a sectional view ofFIG. 18, an example is shown in which the weighted portion351W is in the shape of steps having a portion with a relatively large film thickness and a portion with a relatively small film thickness. It is to be noted that, althoughFIG. 18shows the example where the weighted portion351W has the shape of a two step staircase, the weighted portion351W may have the shape of a staircase of three or more steps. Or, as shown in a sectional view ofFIG. 19, the weighted portion371W in slope shape, having a continuously increasing film thickness, may be arranged on the upper electrode371.

FIGS. 20 to 22are schematic views showing a configuration of a film bulk acoustic resonator4according to a fourth embodiment of the present invention. Further,FIG. 20is an oblique view of the film bulk acoustic resonator4seen obliquely from above,FIG. 21is a plan view of the film bulk acoustic resonator4seen from above, andFIG. 22is a sectional view showing a cross section of the film bulk acoustic resonator4along a cutting plane line XXII-XXII ofFIG. 20. InFIG. 20, an XYZ orthogonal coordinate system is defined for the sake of explanation where the right-and-left direction is the X-axis direction, the front-and-back direction is the Y-axis direction, and the top-and bottom-direction is the Z-axis direction.

As shown inFIGS. 20 to 22, the film bulk acoustic resonator4has a configuration where an adhesive layer42, a cavity formation film43, a lower electrode45, a piezoelectric thin film46, and an upper electrode47are laminated in this order on a support substrate41. In manufacture of the film bulk acoustic resonator4, the piezoelectric thin film46is obtained by performing removal processing on a piezoelectric substrate that can independently stand up under its own weight, but the piezoelectric thin film46obtained by removal processing cannot independently stand up under its own weight. For this reason, prior to removal processing in manufacture of the film bulk acoustic resonator4, a piezoelectric substrate on which the lower electrode45and the cavity formation film43are formed is previously bonded to the support substrate41as a support.

Support Substrate

When a piezoelectric substrate is subjected to removal processing during manufacture of the film bulk acoustic resonator4, the support substrate41serves as a support to support, via the adhesive layer42, the piezoelectric substrate with the lower electrode45and the cavity formation film43formed on its lower surface. In addition, after manufacture of the film bulk acoustic resonator4, the support substrate41also serves as a support to support, via the adhesive layer42, the piezoelectric thin film46with the lower electrode45and the cavity formation film43formed on its under surface and the upper electrode47on its upper surface. Therefore, the support substrate41is required to be able to stand force applied at the time of removal processing on the piezoelectric substrate, and also required not to reduce its strength after manufacture of the film bulk acoustic resonator4.

The material for and the thickness of the support substrate41can be selected as appropriate so as to satisfy the above-mentioned requirements. However, if the material for the support substrate41is a material having a thermal expansion coefficient close to that of the piezoelectric material constructing the piezoelectric thin film46, more desirably a material having a thermal expansion coefficient equivalent to that of the piezoelectric material constructing the piezoelectric thin film46, e.g. the same material as the piezoelectric material constructing the piezoelectric thin film46, it is possible to suppress warpage and damage caused by a difference in thermal expansion coefficient during manufacture of the film bulk acoustic resonator4. It is further possible to suppress characteristic variations and damage caused by a difference in thermal expansion coefficient after manufacture of the film bulk acoustic resonator4. In addition, in the case of using a material having an anisotropic thermal expansion coefficient, it is desirable to see that the thermal expansion coefficients in all different directions are made the same. Moreover, in the case of using the same material for the support substrate41and the piezoelectric thin film46, it is desirable to match the crystal orientations of the support substrate41and the piezoelectric thin film46.

Adhesive Layer

The adhesive layer42serves to bond and fix the piezoelectric substrate with the lower electrode45and the cavity formation film43formed on its bottom surface to the support substrate41when the piezoelectric substrate is subjected to removal processing during manufacture of the film bulk acoustic resonator4. Additionally, the adhesive layer42also serves to bond and fix the piezoelectric thin film46with the lower electrode45and the cavity formation film43formed on its lower surface and the upper electrode47on its upper surface to the support substrate41after manufacture of the film bulk acoustic resonator4. Therefore, the adhesive layer42is required to be able to stand force applied at the time of removal processing on the piezoelectric substrate, and also required not to reduce its adhesive force after manufacture of the film bulk acoustic resonator4.

A desirable example of the adhesive layer42satisfying such requirements may be an adhesive layer42formed of an organic adhesive agent, desirably an epoxy adhesive agent (adhesive layer made of an epoxy resin using thermosetting properties) or an acrylic adhesive agent (adhesive layer made of an acrylic resin using both thermosetting and photocuring properties), which has a filling effect and exerts sufficient adhesive force even when an object to be bonded is not completely flat. Adoption of such a resin allows prevention of unexpected formation of an air space between the piezoelectric substrate and the support substrate41, thereby to prevent occurrence of cracking or the like at the time of removal processing on the piezoelectric substrate due to the air space. However, this does not prevent the piezoelectric thin film46and the support substrate41from being bonded and fixed to each other by an adhesive layer42different from the above-mentioned adhesive layer42.

Cavity Formation Film

The cavity formation film43is an insulating film obtained by forming a film of an insulating material. The cavity formation film43is formed on the lower surface of a region other than an opposing region E4of the piezoelectric thin film46, to form a cavity C4which separates the opposing region E4of the piezoelectric thin film46from the scanner section41. Arrangement of such a cavity formation film43which serves as a spacer allows the opposing region E4of the piezoelectric thin film46not to interfere with the support substrate41, thereby preventing inhibition of vibrations excited in the opposing region E4.

The insulating material for constituting the cavity formation film43is not particularly limited, but desirably selected from insulating materials such as silica dioxide (SiO2).

Piezoelectric Thin Film

The piezoelectric thin film46is obtained by performing removal processing on the piezoelectric substrate. More specifically, the piezoelectric thin film46is obtained by reducing the piezoelectric substrate in thickness from a thickness (e.g. not smaller than 50 μm) with which the substrate can independently stand up under its own weight, to a thickness (e.g. not larger than 10 μm) with which the substrate cannot independently stand up under its own weight.

As a piezoelectric material constructing the piezoelectric thin film46, a piezoelectric material having a desired piezoelectric property can be selected, and it is desirable to select a single crystal material including no grain boundary, such as quartz crystal (SiO2), lithium niobate (LiNbO3), lithium tantalite (LiTaO3), lithium tetraborate (Li2B4O7), zinc oxide (ZnO), potassium niobate (KNbO3), or langasite (La3Ga3SiO14). This is because the use of the single crystal material as the piezoelectric material constructing the piezoelectric thin film46can lead to improvement in electromechanical coupling factor as well as mechanical quality factor of the piezoelectric thin film46.

Further, a crystal orientation in the piezoelectric thin film46can be selected to be a crystal orientation having a desired piezoelectric characteristic. Here, the crystal orientation in the piezoelectric thin film46is desirably a crystal orientation that leads to favorable temperature characteristics of a resonance frequency and an antiresonance frequency of the film bulk acoustic resonator4, and is further desirably a crystal orientation in which a resonance frequency temperature coefficient is “0”.

Removal processing on the piezoelectric substrate is performed by mechanical processing such as cutting, grinding or polishing, or chemical processing such as etching. Here, if the piezoelectric substrate is subjected to removal processing where a plurality of removal processing methods are combined and the removal processing method is shifted in stages from one performed at high processing speed to one with small process degradation in an object to be processed, it is possible to improve the quality of the piezoelectric thin film46while maintaining high productivity, so as to improve the characteristics of the film bulk acoustic resonator4. For example, the piezoelectric substrate is subjected to grinding where the substrate is brought into contact with fixed abrasive grains for grinding, and is then subjected to polishing where the substrate is brought into contact with free abrasive grains for grinding. Thereafter, a processing degradation layer generated on the piezoelectric substrate by above-mentioned polishing is removed by finish-polishing. If such processing is executed, the piezoelectric substrate can be ground at faster speed so as to improve productivity of the film bulk acoustic resonator4, and also, the quality of the piezoelectric thin film46is improved so as to improve the characteristics of the film bulk acoustic resonator4. It is to be noted that more specific methods for removal processing on the piezoelectric substrate is described in later-described examples.

In the film bulk acoustic resonator4as thus described, different from the case of forming the piezoelectric thin film46by sputtering or the like, since the piezoelectric material constructing the piezoelectric thin film46and the crystal orientation in the piezoelectric thin film46are free from constraints of the substrate, the degree of flexibility is high in selection of the piezoelectric material constructing the piezoelectric thin film46and the crystal orientation in the piezoelectric thin film46. This facilitates realization of a desired characteristic in the film bulk acoustic resonator4.

In a region other than the opposing region E4of this piezoelectric thin film46, a via hole VH4is formed for penetrating through the piezoelectric thin film46between its upper and lower surfaces, and conducting an upper electrode472and the lower electrode45which are opposed to each other with the piezoelectric thin film46interposed therebetween. The via hole VH4short-circuits, by a conductive thin film formed on its inner surface, the upper electrode472and the lower electrode45for direct conduction.

Upper Electrode and Lower Electrode

The upper electrode47and the lower electrode45are conductive thin films formed by forming films of a conductive material on the upper and lower surfaces of the piezoelectric thin film46which have been polished and flattened. Here, the upper and lower surfaces of the piezoelectric thin film46being “flat” means that those surfaces are in the state of not having roughness larger than roughness that unavoidably remains after polishing.

Although the conductive material constituting the upper electrode47and the lower electrode45is not particularly limited, the material is desirably selected from metals such as aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), tungsten (W), and tantalum (Ta). Naturally, an alloy may be used as the conductive material constituting the upper electrode47and the lower electrode45. Further, a plurality of kinds of conductive materials may be laminated to form the upper electrode47and the lower electrode45.

Out of the upper electrode47, an upper electrode471is opposed to the lower electrode45with the piezoelectric thin film46interposed therebetween in the opposing region E4. The upper electrode471is pulled out from the opposing region E4in the −X direction, and the pulled-out portion serves as a feeding section for feeding the excitation signal to the upper electrode471.

Meanwhile, in the lower electrode45, the lower electrode45is pulled out from the opposing region E4in the +X direction, and the pulled-out portion serves as a feeding section for feeding the excitation signal to the lower electrode45.

Further, out of the upper electrode47, the upper electrode472is opposed to the feeding section of the lower electrode45with the piezoelectric thin film46interposed therebetween in a region other than the opposing region E4. Since the via hole VH4conducts the upper electrode472and the lower electrode45, the excitation signal is fed to the lower electrode45through the externally exposed upper electrode472in the film bulk acoustic resonator4.

In the film bulk acoustic resonator4, the upper electrode472and the lower electrode45are conductive thin films with a substantially uniform film thickness, whereas the upper electrode471has a structure where, on the conductive thin film with a substantially uniform film thickness, a conductive thin film is further superposed across a frame-like region RG41along the inner side of the outer periphery of the opposing region E4(periphery section of the opposing region) and a rectangular region RG42of the feeding section adjacent to the opposing region E4. The upper electrode471also has a configuration where a weighted portion471W for adding a mass is arranged across both sides of a portion which is the outer periphery of the opposing region E4and a projected outline border PL41drawn by projecting the outline border OL41of the lower electrode45on the upper electrode471. The weighted portion471W, hatched inFIG. 21, is formed by partially increasing the thickness of the upper electrode471in the regions RG41and42beyond unavoidable variations.

The weighted portion471W is larger than the central portion of the opposing region E4with a substantially uniform film thickness in mass per unit area, thereby serving to reduce a cutoff frequency of the acoustic waves in the regions RG41and RG42. In the film bulk acoustic resonator4, the reduction in cutoff frequency leads to prevention of leakage of vibration energy of vibrations excited in the opposing region E4, thereby to suppress sub-resonance which depends upon the outline shape of the piezoelectric thin film46.

Further, in the film bulk acoustic resonator4, the upper and lower surfaces of the piezoelectric thin film46are flat, and the lower electrode45is not formed outside the opposing region E4except for the feeding section. Therefore, in the film bulk acoustic resonator4, a difference in thickness of a laminated body including the upper electrode47, the piezoelectric thin film46and the lower electrode45, namely, a difference in mass per unit area, between the periphery of the opposing region E4and the outside of the opposing region E4can be made large, thereby to prevent acoustic waves slightly leaked from the opposing region E4toward the outside of the opposing region E4from reflecting on the end face of the piezoelectric thin film46and returning to the opposing region E4. Further, in the film bulk acoustic resonator4, since both the upper electrode471and the lower electrode45are partial electrodes which covers part of the main surface, excitation of vibrations or reflection of acoustic waves on the end surface of the piezoelectric thin film46can be prevented. Additionally, that the upper and lower surfaces of the piezoelectric thin film46are flat also has the advantage of allowing performance of patterning on the upper electrode47and the lower electrode45with high accuracy in size.

These advantages of the film bulk acoustic resonator4cannot be realized by the conventional film bulk acoustic resonator formed by sequentially film-forming the lower electrode, the piezoelectric thin film and the upper electrode since it is impossible that both the upper and lower electrodes are made to be partial electrodes while both main surfaces of the piezoelectric thin film are made flat.

Meanwhile, in the film bulk acoustic resonator4, since the weighted portion471W is part of the upper electrode471, it is possible to avoid exertion of an influence by the weighted portion471W on the main resonance and deterioration in its characteristic. Here, the periphery of the film bulk acoustic resonator4means a portion in contact with the outer periphery of the opposing region E4, and the central portion of the opposing region E4means a portion apart from the outer periphery of the opposing region E4and surrounded by the periphery of the opposing region E4.

The width W41of the region RG41which rims the central portion of the opposing region E4with a substantially uniform film thickness is desirably not less than 1% and not more than 30%, further desirably not less than 5% and not more than 20%, of a width W42of the opposing region E4. This is because the width W41falling out of this range causes reduction in vibration energy trapping effect. Here, the width W42of the opposing region E4is a short-side length when the opposing region E4is formed in rectangular shape, and a length of the diameter when formed in circular shape.

Although the film thicknesses of the upper electrode45and the upper electrode47should be determined according to a conductive material constituting the electrodes, when tungsten is selected as the conductive material, its thickness is desirably not less than 700 angstroms. This is because, if tungsten has a film thickness below 700 angstroms, its electric resistance increases, to significantly increase resonance resistance of the film bulk acoustic resonator, its electric resistance increases, to significantly increase resonance resistance of the film bulk acoustic resonator4. Further, typically, when a difference in film thickness between the weighted portion471W and a portion other than471W is about 500 angstroms, sub-resonance of the film bulk acoustic resonator4can be favorably suppressed.

The upper electrode471with the portion of the opposing region E4formed in tray shape can be formed such that a conductive thin film with a substantially uniform film thickness is formed and a conductive thin film is further formed as superposed on the weighted portion471W, or that a conductive thin film with a substantially uniform film thickness is formed and a portion other than a portion to become the weighted portion451W is reduced in thickness.

Although as the example was shown inFIGS. 20 to 22, where the weighted portion471W is arranged on the lower electrode45of the upper electrode45, the weighted portion may be arranged on the lower electrode45in place of the upper electrode471, or the weighted portion may be arranged on both the upper electrode471and the lower electrode45. Further, although the weighted portion471W can be readily formed by partially increasing the film thickness of the upper electrode471to form the weighted portion471W, this does not prevent formation of the weighted portion471W by partially increasing a mass of the upper electrode471instead of partially increasing the film thickness of the upper electrode471or in addition to partially increasing the film thickness of the upper electrode471.

Another Example of Weighted Portion

Subsequently, another example of the weighted portion471W is described. However, the weighted portion471W described below is just an example and thus not aimed at limiting the range of the present invention.

InFIGS. 20 to 22, the weighted portion471W is arranged to surround the central portion of the opposing region E4for effectively suppressing sub-resonance of the film bulk acoustic resonator4. However, this does not prevent arrangement of the weighted portion471W across the region RG41along the inner side of part of the outer periphery of the opposing region E4and the rectangular region RG42of the feeding portion adjacent to the opposing region E4, for example, arrangement of the weighted portion471W across the region RG41along the inner side of one of the opposite sides of the opposing region E4and the rectangular region RG42of the feeding portion adjacent to the opposing region E4, as shown in a plan view ofFIG. 23.

Further, constant arrangement of a width W41of the region RG41in the weighted portion471W is not essential. For example, as shown in a plan view ofFIG. 24, the weighted portion471W may be arranged across the region RG41along the inner side of the outer periphery of the opposing region E4, having a circular opening, and the rectangular region RG42of the feeding section adjacent to the opposing region E4, as shown in a plan view ofFIG. 24.

Further, as shown in a plan view ofFIG. 25, the weighted portion471W is located across the region RG41along the inner side of the outer periphery of the opposing region E4and the rectangular region RG42making up the whole of the feeding section adjacent to the opposing region E4.

Further, as shown inFIG. 26, it is considered that another weighted portion471W may be further arranged on the inner side of the weighted portion471W shown inFIGS. 20 to 22.

Other than these, even when the weighted portion471W is arranged such that its film thickness becomes larger and its mass per unit area becomes larger with distance from the central portion of the opposing region E4, sub-resonance of the film bulk acoustic resonator4can be favorably suppressed. Further, such a weighted portion471W has the advantage of not having a large influence on the sub-resonance suppressing effect even when the shape of the weighted portion471W is slightly changed.

For example, a plan view ofFIG. 27and a sectional view ofFIG. 28show an example of the weighted portion471W in staircase shape having a portion with a relatively small film thickness and a portion with a relatively large film thickness. It should be noted thatFIGS. 27 and 28show the example where the weighted portion471W has the shape of a two step staircase, the weighted portion471W may have the shape of a staircase of three or more steps. Or, as shown in a sectional view ofFIG. 29, the weighted portion471W in slope shape, having a continuously increasing film thickness, may be arranged on the upper electrode471.

FIGS. 30 to 33are schematic views showing a configuration of a piezoelectric thin film filter5according to a fifth embodiment of the present invention.FIG. 30is an oblique view of the piezoelectric thin film filter5seen obliquely from above,FIG. 31is a plan view of the piezoelectric thin film filter5seen from above,FIG. 32is a sectional view showing a cross section of the piezoelectric thin film filter5along a cutting plane line XXXII-XXXII ofFIG. 30, andFIG. 33is a circuit diagram showing electrical connection between two film bulk acoustic resonators R51and R52included in the piezoelectric thin film filter5. It is to be noted that inFIG. 30, an XYZ orthogonal coordinate system is defined for the sake of explanation where the right-and-left direction is the X-axis direction, the front-and-back direction is the Y-axis direction, and the top-and bottom-direction is the Z-axis direction.

As shown inFIGS. 30 to 33, in the same manner as the case of the film bulk acoustic resonator4of the fourth embodiment, the piezoelectric thin film filter5has a configuration where an adhesive layer52, a cavity formation film53, a lower electrode55, a piezoelectric thin film56, and an upper electrode57are laminated in this order on a support substrate51. The support substrate51, the adhesive layer52, the cavity formation film53, the lower electrode55, the piezoelectric thin film56and the upper electrode57can be respectively constituted using the same materials of those of the support substrate41, the adhesive layer42, the cavity formation film43, the lower electrode45, the piezoelectric thin film46and the upper electrode47of the fourth embodiment.

Here, patterns of the upper electrode57and the lower electrode55are described, which are different from the case of the film bulk acoustic resonator4of the fourth embodiment.

Out of the upper electrode57, the upper electrode571is opposed to the lower electrode55with the piezoelectric thin film56interposed therebetween in an opposing region E51, to constitute a film bulk acoustic resonator (serial resonator) R52. After pulled out from the opposing region E51in the +Y direction, the upper electrode571is bent in the +X direction and the −Y direction sequentially in its extending direction, and the pulled-out portion is a feeding section for feeding the excitation signal to the upper electrode571. Part of the feeding portion is a pad53connected with external wiring.

The upper electrode572is opposed to the lower electrode55with the piezoelectric thin film56interposed therebetween in an opposing region E52, to constitute a film bulk acoustic resonator (parallel resonator) R51. After pulled out from the opposing region E52in the −Y direction, the upper electrode572is bent in the −X direction and the +Y direction sequentially in its extending direction, and the pulled-out portion is a feeding section for feeding the excitation signal to the upper electrode572. Parts of the feeding portions are pads P52and P54which are connected with external wiring.

The upper electrode573is opposed to the lower electrode55with the piezoelectric thin film56interposed therebetween in a region other than the opposing regions E51and E52. Since a via hole VH5conducts the upper electrode573and the lower electrode55, in the piezoelectric thin film filter5, the excitation signal is fed to the lower electrode55via the upper electrode572exposed to the outside. Part of the upper electrode572is the pad P51connected with external wiring.

As shown in the sectional view ofFIG. 32, cavities C51and C52for separating the opposing regions E51and E52from the support substrate51are formed below the opposing regions E51and E52.

With the upper electrode57and the lower electrode55as thus arranged, the piezoelectric thin film filter5is a ladder-type band-pass filter obtained by monolithically unifying film bulk acoustic resonators R51and R52.

In the film bulk acoustic filter5, as in the case of the film bulk acoustic resonator4of the fourth embodiment, the upper electrode571has a structure where a conductive thin film is further superposed on the conductive thin film with a substantially uniform film thickness across a frame-like region RG511along the inner side of the outer periphery of the opposing region E51and a region RG512of the feeding section making up the whole of the feeding section adjacent to the opposing region E51. The upper electrode572has a structure where a conductive thin film is further superposed on the conductive thin film with a substantially uniform film thickness across a frame-like region RG521along the inner side of the outer periphery of the opposing region E52and a region RG522making up the whole of the feeding section adjacent to the opposing region E52. The upper electrode571also has a structure where, due to the presence of the conductive thin films superposed on the regions RG511and RG512, the weighted portions571W and572W for adding a mass are arranged across both sides of a portion which are the outer peripheries of the opposing regions E51and E52and projected outline borders PL511and PL512drawn by projecting the outline border OL51of the lower electrode55on the upper electrodes571and572. Naturally, the weighted potions571W and572W as described in “Another example of weighted potion” in the fourth embodiment may be adopted to the piezoelectric thin film filter5.

In the piezoelectric thin film filter5as thus described, since sub-resonance which depends upon the outline shape of the piezoelectric thin film56can be suppressed, a filtering characteristic is unsusceptible to spuriousness.

It is to be noted that the present invention includes the following inventions [1] to [5].

[1] A piezoelectric thin film device including a single or a plurality of film bulk acoustic resonators, which includes: a piezoelectric thin film having flat first and second main surfaces; a first portion electrode which covers part of the first main surface; a second portion electrode which covers part of the second main surface, wherein the first potion electrode has a weighted portion with a mass per unit larger than that of the central portion of an opposing region where the first electrode and the second electrode are opposed to each other with the piezoelectric thin film interposed therebetween, across both sides of a portion which is the outer periphery of the opposing region and a projected outline border drawn by projecting the outline border of the second portion electrode on the first portion electrode.

[2] The piezoelectric thin film device according to [1], wherein the weighted portion surrounds the central portion.

[3] The piezoelectric thin film device according to [2], wherein the first portion electrode further has another weighted portion on the inner side of the weighted portion surrounding the central portion.

[4] The piezoelectric thin film device according to any of [1] to [3], wherein the weighted portion is formed by increasing a film thickness of the electrode.

[5] The piezoelectric thin film device according to any of [1] to [4], wherein the weighted portion increases its mass per unit area with distance from the central portion.

EXAMPLES

In the following described are examples according to the desired embodiments of the present invention, and comparative examples out of the range of the present invention.

Example 1 is an example regarding the film bulk acoustic resonator1where the drive sections151and the drive section131each have a rectangular shape with its long-side length La being twice as large as its short-side length Lb.

In Example 1, the film bulk acoustic resonator1was produced using: a single crystal of lithium niobate as the piezoelectric material constructing the support substrate11and the piezoelectric thin film14; an epoxy adhesive agent as a material constituting the adhesive layer12; molybdenum and tantalum as the conductive materials constituting the lower electrode13; and chromium and gold as the conductive materials constituting the upper electrode15.

As shown in a sectional view ofFIG. 34, in order to reduce manufacturing cost, the film bulk acoustic resonator1of Example 1 is obtained in the following manner. After production of an assembly U1by integration of a large number of film bulk acoustic resonators1, the assembly U1is cut using a dicing saw into individual film bulk acoustic resonators1. It is to be noted that, although the example of including three film bulk acoustic resonators1in the assembly U1is shown inFIG. 8, the number of film bulk acoustic resonators1included in the assembly U1may be four or larger, and typically, several hundreds to several thousands of film bulk acoustic resonators1are included in the assembly U1.

Although description is made with focus on one film bulk acoustic resonator1included in the assembly U1for the sake of simplicity, the other film bulk acoustic resonators1included in the assembly are produced simultaneously with the focused film bulk acoustic resonator1.

Subsequently, the method for manufacturing the film bulk acoustic resonator1of Example 1 is described with reference toFIGS. 35A to 35Dand36E to36G. It is to be noted thatFIGS. 35A to 35DandFIG. 36E to 36Gare sectional views along the cutting-plane line II-II ofFIG. 1of the film bulk acoustic resonator1during manufacture.

In manufacture of the film bulk acoustic resonator1, first, a circular wafer (36-degree-cut Y plate) of a single crystal of lithium niobate with a film thickness of 0.5 mm and a diameter of 3 inches was prepared as the support substrate11and a piezoelectric substrate17.

Subsequently, a mask (laminated film included of a chromium film and a gold film) M1in which a region to form the depression111is an opening is formed on the upper surface of the support substrate11(FIG. 35A), and the support substrate11is immersed in a 1:1 buffered hydrofluoric acid aqueous solution at 60° C., to obtain the support substrate11with the depression111formed therein (FIG. 35B).

Thereafter, a molybdenum film with a film thickness of 0.057 μm and a tantalum film with a film thickness of 0.02 μm were formed on the lower surface of the piezoelectric substrate17by sputtering, and the lower electrode13having the pattern shown inFIG. 3Bwas obtained by photolithography (FIG. 35C).

Thereafter, an epoxy adhesive agent to be the adhesive layer12was applied to the upper surface of the support substrate11, to bond the upper surface of the support substrate11with the lower surface of the piezoelectric substrate17. Pressure was then applied to the support substrate11and the piezoelectric substrate17for press pressure bonding, to make the adhesive layer12have a thickness of 0.5 μm. Thereafter, the support substrate11and the piezoelectric substrate17, bonded to each other, were left to stand in a 200° C. environment for one hour for curing the epoxy adhesive agent, so as to bond the support substrate11with the piezoelectric substrate17(FIG. 35D).

After completion of bonding of the support substrate11with the piezoelectric substrate17, while the piezoelectric substrate17was kept in the state of being bonded to the support substrate11, the lower surface of the support substrate11was fixed to a polishing jig made of silicon carbide (SiC), and the upper surface of the piezoelectric substrate17was subjected to grinding processing using a grinding machine with fixed abrasive grains, to reduce the thickness of the piezoelectric substrate17down to 50 μm. Further, the upper surface of the piezoelectric substrate17was subjected to polishing processing using diamond abrasive grains, to reduce the thickness of the piezoelectric substrate17down to 2 μm. Finally, for removing a process degradation layer generated on the piezoelectric substrate17by polishing processing using the diamond abrasive grains, free abrasive grains and a non-woven polishing pad were used to perform finish-polishing on the piezoelectric substrate17so as to obtain the piezoelectric thin film14with a film thickness of 1 μm (FIG. 36E).

Subsequently, the upper surface (polished surface) of the piezoelectric thin film14was washed using an organic solvent, and a chromium film with a film thickness of 0.02 μm and a gold film with a film thickness of 0.0515 μm were formed by sputtering, and the upper electrode15having the pattern shown inFIG. 3Awas obtained by photolithography (FIG. 36F).

Further, a portion of the piezoelectric thin film14which covers the pad133of the lower electrode13was removed by etching using hydrofluoric acid, to obtain the film bulk acoustic resonator1with the pad133exposed (FIG. 36G).

A frequency impedance characteristic of the film bulk acoustic resonator1as thus obtained was estimated using a network analyzer and a prober, to obtain a resonance waveform, on which a small influence is exerted by spuriousness, as shown inFIG. 37.

Moreover, a distribution of the amplitude of the vibrations in the drive section was measured using a laser displacement gauge, to find that, as shown inFIG. 40, the amplitude is large in the vicinity of the center of the drive section shown by the range D1, and become smaller with distance from the center of the drive section, and the range of diffusion of vibrations in the long side direction is only about as large as the short side length Lb of the drive section.

It is considered that the amplitude distribution as thus described is obtained such that a two-dimensional wave surface of acoustic waves spread from the center of the drive section is strongly influenced by a distribution of an electric field in the short side direction of the drive section151, to generate a strong effect of energy trapping into the vicinity of the center of the drive section so as to strongly suppress leakage of the vibrations.

Example 2 is an example regarding the film bulk acoustic resonator1where the drive sections151and the drive section131each have a rectangular shape with its long-side length La being four times as large as its short-side length Lb. In Example 2, the film bulk acoustic resonator1was manufactured in the same process as in Example 1 except that the patterns of the upper electrode15and the lower electrode13were changed.

A frequency impedance characteristic of the film bulk acoustic resonator1as thus obtained was estimated using a network analyzer and a prober, and thereby a single resonance waveform could be observed on which almost no influence was exerted by spuriousness, as shown inFIG. 38.

Comparative Example 1

Comparative Example 1 is an example regarding a film bulk acoustic resonator out of the range of the present invention, with the drive sections151and the drive section131each having a circular shape. In Comparative Example 1, the film bulk acoustic resonator was produced in the same practice as in Example 1 except that the patterns of the upper electrode and the lower electrode were changed.

A frequency impedance characteristic of the film bulk acoustic resonator1as thus obtained was estimated using the network analyzer and the prober, and thereby only a resonance waveform formed by a large number of laminated spuriousness could be observed. as shown inFIG. 39.

Further, a distribution of the amplitude of the vibrations in the drive section was measured using the laser displacement gauge, to find that the vibrations are distributed broadly throughout the drive section shown by the range D2, as shown inFIG. 41.

Comparison Among Examples 1 to 2 and Comparative Example 1

As apparent from Examples 1 and 2 and Comparative Example 1, making the shape of the drive section slender enables suppression of propagation of vibrations in its longitudinal direction of the drive section so that an energy trapping-type film bulk acoustic resonator can be realized in which most of energy is concentrated on the vicinity of the center of the drive section. Due to such strong energy trapping, in those film bulk acoustic resonators1, generation of sub-resonance caused by the outline of the piezoelectric thin film14is suppressed to make the frequency impedance characteristic unsusceptible to spuriousness despite a disadvantageous condition of the use of piezoelectric material with a large electromechanical coupling factor as lithium niobate and undesirable propagation of acoustic waves to the end of the piezoelectric thin film14.

It is to be noted that such a spuriousness suppressing effect is obtained so long as the drive section is in slender shape, and adoption of the shape illustrated inFIGS. 4 to 8is not necessarily essential.

Example 3 is an example regarding the film bulk acoustic resonator3where the drive sections351and331each have a rectangular shape with its long-side length La being ten times as large as its short-side length Lb. In Example 3, the weighted portion351W is formed such that a conductive thin film with a substantially uniform film thickness is formed and then a conductive thin film is further formed as superposed on a portion to become the weighted portion351W.

In Example 3, the film bulk acoustic resonator3was produced using: a single crystal of lithium niobate as the piezoelectric material constructing the piezoelectric thin film34and the support substrate31; an epoxy adhesive agent as a material constituting the adhesive layer32; and tungsten as the conductive materials constituting the upper electrode35and the lower electrode33.

The film bulk acoustic resonator3of Example 3 can be manufactured in a manufacturing method similar to that for the film bulk acoustic resonator1of Example 1. However, in manufacture of the film bulk acoustic resonator3, the film bulk acoustic resonator3is different from the film bulk acoustic resonator1in that tungsten films are formed as the upper electrode35and the lower electrode33, and the weighted portion351W is formed on the upper electrode35.

In formation of the weighted portion351W, first, a tungsten film with a film thickness of 500 angstroms was formed all over the upper surface of the piezoelectric thin film34by sputtering, and then subjected to patterning by means of a typical photolithography process, to leave a tungsten film351aonly on a portion to become the weighted portion351W of the upper electrode35(FIG. 42).

Further, a tungsten film with a film thickness of 1000 angstroms was formed all over the upper surface of the piezoelectric thin film34by sputtering, and then subjected to patterning by means of the typical photolithography process, to obtain the upper electrode35having the pattern shown inFIGS. 14,15,16A and16B and provided with the weighted portion351W (FIG. 43).

A frequency impedance characteristic of the film bulk acoustic resonator3as thus obtained was estimated using the network analyzer and the prober, and thereby a resonance waveform could be observed in proximity to main resonance at about 2.2 GHz, on which a small influence is exerted by spuriousness, as shown inFIG. 44.

Example 4 is an example regarding a film bulk acoustic resonator obtained by adding the weighted portion351W to the film bulk acoustic resonator3of Example 3, along the inner side of the short side351S of the drive section351.

A frequency impedance characteristic of the film bulk acoustic resonator of Example 4 was estimated using the network analyzer and the prober, and thereby a resonance waveform could be obtained in proximity to main resonance at about 2.0 GHz, on which a small influence is exerted by spuriousness, as shown inFIG. 45. However, in the film bulk acoustic resonator of Example 4, the resonance waveform of the resonator formed by the weighted portion351W was superposed at about 1.6 GHz.

In Example 5, in the film bulk acoustic resonator3of Example 3, when a side ratio La/Lb of the long-side length La to the short-side length Lb was changed in the range from 1 to 100, changes were checked in strength (hereinafter referred to as spurious strength) Ia of a resonance waveform of spuriousness in proximity to the main resonance, and in strength (hereinafter referred to as low-frequency resonance waveform strength) Lb of a low-frequency resonance waveform of a resonator formed by the weighted portion351W. The results are shown inFIGS. 46 and 47.

It is to be noted that as shown inFIG. 48, the “spurious strength Ia” indicates a width between a resonance resistance and an antiresonance resistance of the resonance waveform of spuriousness. As shown inFIG. 49, the “spurious strength Ib” indicates a width between a resonance resistance and an antiresonance resistance of the low-frequency resonance waveform. Further, inFIGS. 46 and 47, in the film bulk acoustic resonator of Example 4 with the side ratio La/Lb of one (four sides of the rectangular zone) as a reference, relative values of the spurious strength Ia and the low-frequency resonance waveform strength Ib are indicated with the side ratio La/Lb changed in the range of 1 to 10 (two sides of the rectangular zone)

As apparent fromFIGS. 46 and 47, when the side ratio La/Lb is one, provision of the weighted portion351W only along the inner side of the long side351L cannot lead to reduction in spurious strength Ia. However, when the side ratio La/Lb is not less than two, desirably not less than four, and further desirably not less than ten, the provision of the weighted portion351W only along the inner side of the long side351L can lead to sufficient reduction in spurious strength Ia. Meanwhile, when the side ratio La/Lb is not less than one and not more than 40, the provision of the weighted portion351W only along the inner side of the long side351L can lead to sufficient reduction in low-frequency resonance waveform Ib.

In the following described is Example 6 regarding the film bulk acoustic resonator4according to the fourth embodiment of the present invention. In Example 6, the weighted portion471W is formed such that a conductive thin film with a substantially uniform film thickness is formed and then a conductive thin film is further formed as superposed on a portion to become the weighted portion471W.

In Example 6, the film bulk acoustic resonator4was produced using: a single crystal of lithium niobate as the piezoelectric material constructing the piezoelectric thin film46and the support substrate41; tungsten as the conductive material constituting the upper electrode47and the lower electrode45; silicon dioxide as the insulating material constituting the cavity formation film43; and an epoxy adhesive agent as the material constituting the adhesive layer42.

As shown inFIG. 50, in order to reduce manufacturing cost, the film bulk acoustic resonator4of Example 6 is obtained in the following manner. After production of an assembly U4by integration of a large number (typically, several hundreds to several thousands) of film bulk acoustic resonators4, the assembly U4is cut using the dicing saw into individual film bulk acoustic resonators4.

Although description is made with focus on one film bulk acoustic resonator4included in the assembly U4for the sake of simplicity, the other film bulk acoustic resonators4included in the assembly U4are produced simultaneously with the focused film bulk acoustic resonator4.

Subsequently, the method for manufacturing the film bulk acoustic resonator4of Example 6 is described with reference toFIGS. 51A to 51Dand52E to52H.

In manufacture of the film bulk acoustic resonator4, first, a circular wafer (45-degree-cut Y plate) of a single crystal of lithium niobate with a film thickness of 0.5 mm and a diameter of 3 inches was prepared as the piezoelectric substrate49and the support substrate41.

Further, a tungsten film with a film thickness of 1000 angstroms was formed all over the lower surface of the piezoelectric substrate49by sputtering, and then subjected to patterning by means of the typical photolithography process, to obtain the lower electrode45having the pattern shown inFIGS. 20 and 21(FIG. 51A).

Subsequently, a silicon dioxide film with a film thickness of 0.5 μm all over the lower surface of the piezoelectric substrate49by sputtering, and the silicon dioxide film formed in a region to become the opposing region E4in the piezoelectric thin film46obtained by removal processing on the piezoelectric substrate49was removed by wet-etching using hydrofluoric acid. Thereby, the cavity formation film43was formed in a region other than the region to become the opposing region E4in the piezoelectric thin film46(FIG. 51B).

Further, the epoxy adhesive layer to be the adhesive layer42was applied to the upper surface of the support substrate41, to bond the upper surface of the support substrate41with the lower surface of the piezoelectric substrate49where the lower electrode45and the cavity formation film43are formed. Pressure was then applied to the support substrate41and the piezoelectric substrate49for press pressure bonding, to make the adhesive layer42have a thickness of 0.5 μm. Thereafter, the support substrate41and the piezoelectric substrate49were left to stand in a 200° C. environment for one hour for curing the epoxy adhesive agent, so as to bond the support substrate41with the piezoelectric substrate49. Thereby, a cavity C4with a depth of about 0.5 μm was formed below the region to become the opposing region E4in the piezoelectric thin film46of the piezoelectric thin film device49(FIG. 51C).

After completion of bonding of the support substrate41with the piezoelectric substrate49, while the piezoelectric substrate49was kept in the state of being bonded to the support substrate41, the lower surface of the support substrate41was fixed to a polishing jig, and the upper surface of the piezoelectric substrate49was subjected to grinding processing using a grinding machine with fixed abrasive grains, to reduce the thickness of the piezoelectric substrate49down to 50 μm. Further, the upper surface of the piezoelectric substrate49was subjected to polishing processing using diamond abrasive grains, to reduce the thickness of the piezoelectric substrate49down to 2 μm. Finally, for removing a process degradation layer generated on the piezoelectric substrate49by polishing processing using the diamond abrasive grains, free abrasive grains and a non-woven polishing pad were used to perform finish-polishing on the piezoelectric substrate49so as to obtain the piezoelectric thin film46with a film thickness of 1.00 μm (FIG. 51D).

Subsequently, the upper surface (polished surface) of the piezoelectric thin film46was washed using an organic solvent, and a chromium film with a film thickness of 200 angstroms and a gold film with a film thickness of 2000 angstroms were sequentially formed on the upper surface of the piezoelectric thin film46, and the obtained laminated films were then patterned by pattering by means of the typical photolithography process, to obtain an etching mask M4with only a portion to form the via hole VH4is exposed. (FIG. 52E)

After formation of the etching mask M4, the piezoelectric thin film46was etched by buffered hydrofluoric acid heated to 65° C., to form the via hole VH4which penetrates through the piezoelectric thin film46between its upper and lower surfaces, and thereby the lower electrode45is exposed and the etching mask M4was removed by etching (FIG. 52F).

In the subsequent formation process for the upper electrode47, first, a tungsten film with a film thickness of 500 angstroms was formed all over the upper surface of the piezoelectric thin film46by sputtering, and then subjected to patterning by means of the typical photolithography process, to leave a tungsten film471aonly on a portion to become the weighted portion471W of the upper electrode47(FIG. 52G).

Further, a tungsten film with a film thickness of 1000 angstroms was formed all over the upper surface of the piezoelectric thin film46by sputtering, and then subjected to patterning by means of the typical photolithography process, to obtain the upper electrode47having the pattern shown inFIGS. 20 and 21and provided with the weighted portion471W (FIG. 52H). At this time, the tungsten film was formed also on the inner side surface of the via hole VH4, so as to secure conduction between the upper electrode472and the lower electrode45.

A frequency impedance characteristic of the film bulk acoustic resonator4as thus obtained was measured for estimating resonance characteristic of thickness extension vibrations, to observe waveform as shown inFIG. 54, and an antiresonance resistance was 1326 ohms.

In the following described is Example 7 regarding the piezoelectric thin film filter5according to the fifth embodiment of the present invention. In Example 7, a conductive thin film with a substantially uniform film6thickness is formed and then a portion other than the portions to become the weighted portions571W and572W are reduced in thickness, to form the weighted potions571W and572W. It is to be noted that in Example 7, the piezoelectric thin film filter5is produced in the same practice as in Example 6 except for the formation process for the upper electrode57, and hence the formation process for the upper electrode57is described below.

With reference to a sectional view ofFIGS. 53A and 53B, the formation process of the upper electrode57is described. First, a tungsten film with a film thickness of 1200 angstroms was formed all over the upper surface of the piezoelectric thin film56by sputtering, and then subjected to patterning by means of the typical photolithography process, to obtain the upper electrode57having the patterns shown inFIGS. 30 and 31(FIG. 53A). At this time, the tungsten film was formed also on the inner side surface of the via hole VH5, so as to secure conduction between the upper electrode573and the lower electrode55.

Further, portions to become the weighted portions571W and572W of the upper electrodes571and572were protected by a metal mask, and the remnant portion was etched using an ion beam IB, to form the weighted portions571W and572W (FIG. 53B).

A frequency-attenuation characteristic of the piezoelectric thin film filter5obtained after the formation process for the upper electrode57as thus described was measured for estimating a filter wave form, to observe a waveform indicated by a solid line inFIG. 56.

In Example 8, the film bulk acoustic resonator was produced in the same practice as in Example 6 except that the weighed portion471W was not arranged on the upper electrode471, namely, the film thickness of the upper electrode471was made substantially uniform. A frequency impedance characteristic of the film bulk acoustic resonator as thus obtained was measured for estimating a resonance characteristic of the thickness extension vibrations, to observe a waveform as shown inFIG. 55, and an antiresonance resistance was 617 ohms.

In Example 9, the piezoelectric thin film filter was produced in the same practice as in Example 7 except that the weighed portions571W and572W were not arranged on the upper electrode571, namely, the film thicknesses of the upper electrodes571and572are made substantially uniform. A frequency-attenuation characteristic of the piezoelectric thin film filter as thus obtained was measured for estimating a filter waveform, to observe a waveform as indicated by a dotted line inFIG. 56.

Comparison Among Examples 6 to 9

As apparent fromFIGS. 54 and 55, arrangement of a weighed portion on an upper electrode of a film bulk acoustic resonator allows reduction in spuriousness superposed on a resonance waveform of the film bulk acoustic resonator and also an increase in an antiresonance resistance to increase a Q value in an antiresonance frequency, while no influence is exerted on main resonance.

Further, as apparent fromFIG. 56, arrangement of a weighted portion on the upper electrode of a piezoelectric thin film filter allows reduction in ripples within a band as indicated by arrows inFIG. 56, so as to reduce a passage loss.

Such improvement in characteristics of the piezoelectric thin film device can be obtained in the case of arranging a weighed portion on a lower electrode instead of the upper electrode and also in the case of arranging weighed portions on both the upper and lower electrodes, not to mention in a variety of weighted portions shown in “other examples of weighted portion” and in weighed portions further modified from those.

Moreover, in the fourth embodiment, the film bulk acoustic resonator4was described in which the width of the cavity C4is larger than the width W41of the opposing region E4, and the outer periphery of the cavity C4is located outside the opposing region E4, as shown inFIG. 22. However, this does not prevent adoption of a configuration where part or the whole of the outer periphery of the cavity C4is located inside the opposing region E4in the film bulk acoustic resonator4.

For example, as shown in a sectional view ofFIG. 57, even when the weighted portion471W is arranged on the upper electrode47in the film bulk acoustic resonator4where one of opposite sides of the rectangular cavity C4is located inside the opposing region E4or in the film bulk acoustic resonator4where both of the opposite sides of the rectangular cavity C4are located inside the opposing region E4, it is possible to effectively suppress sub resonance.

In the film bulk acoustic resonator4where the cavity formation film43is formed across both sides of the outer periphery of the opposing region E4, a continuous range from the edge along the inner side of the outer periphery of the opposing region E4to the outer edge portion along the outer side of the outer periphery of the opposing region E4is fixed to the support substrate41via the cavity formation film43and the adhesive layer42. In the film bulk acoustic resonator4, in addition to the upper electrode471, the weight corresponding to film thicknesses of the cavity formation film43, the adhesive layer42and the like is also applied to the lower electrode45, to allow effective suppression of sub-resonance. It is to be noted that in a case where the end surface of the lower electrode45is included in the range, a continuous range from the edge portion along the inner side of the outer periphery of the opposing region E4to the outer edge portion along the outside of the outer periphery of the opposing region E4through the end surface of the lower electrode45is fixed to the support substrate41in a three-dimensional manner, which also contributes to effective suppression of sub resonance in the film bulk acoustic resonator4.

Modified Examples

Further, although the film bulk acoustic resonator using an electrical response by means of thickness extension vibrations excited by the piezoelectric thin film was described above, a mode other than the thickness extension vibrations, e.g. thickness shear vibrations, is also available.

The technical constitution described in the first to fifth embodiments can be used in combination as appropriate. For example, the pull-out portion of the lower electrode13may be replaced by a via hole in the film bulk acoustic resonator1, or the cavity configuration of the film bulk acoustic resonator1may be adopted to the piezoelectric thin film filter5.