JP2005109702A - Thin film piezo-electric resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid a deterioration of resonance characteristics peculiar to a convex cavity structure. <P>SOLUTION: A thin film piezo-electric resonator includes a substrate 2 having a flat surface, a piezo-electric film 8 having a flat part 8a opposed in substantially parallel with the front surface of the substrate via a cavity 12 and an oblique part 8b lowered to the front surface of the substrate to support the flat part and substantially forming a cavity together with the front surface of the substrate and the flat part, a lower part electrode 6 provided on the front surface side of the flat part at the cavity side, and an upper electrode 10 provided on the front surface substantially parallel to the opposite side to the front surface of the flat part at the cavity side and opposed to the lower electrode via the flat part. A region in which the lower electrode and the upper electrode of the piezo-electric film are opposed is limited within the flat part, and an end of the opposed region is separated by 1 μm or more from a boundary between the flat part and the oblique part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thin film piezoelectric resonator, and is particularly used for a filter and an oscillator of a high frequency circuit.

  With the development of wireless communication technology and the shift to a new system, the demand for communication devices compatible with a plurality of transmission / reception systems is increasing. In addition, the number of parts has increased significantly with the improvement in performance and functionality of mobile radio terminals, and the importance of downsizing and modularization of parts is increasing. Among passive components in a wireless circuit, since the ratio occupied by the filter circuit is particularly large, in order to downsize the wireless circuit and reduce the number of components, downsizing and modularization of the filter are essential.

  Conventionally used filters include dielectric filters, SAW (Surface Acoustic Wave) filters, LC filters, and the like. In recent years, a filter using a thin film bulk acoustic wave resonator (also referred to as a thin film piezoelectric resonator) is considered most promising for downsizing and modularization. Since this type of filter utilizes the resonance phenomenon of piezoelectric vibration, it does not interfere like an electromagnetic wave even when placed close to each other, and is easy to miniaturize compared to a dielectric filter or an LC filter. In addition, since the frequency band used for wireless communication has become higher, SAW filters that use surface waves require sub-micron level microfabrication, making it difficult to manufacture at low cost.

  On the other hand, since the filter using the thin film piezoelectric resonator uses the longitudinal vibration of the piezoelectric body, if the thickness of the piezoelectric body is reduced, the operating band can be easily increased in frequency, and the level in the plane direction is 1 μm level. Since the processing dimensions are sufficient, there is no increase in manufacturing costs associated with higher frequencies. Further, the substrate for manufacturing the thin film piezoelectric resonator does not need to be a piezoelectric substrate like a SAW filter, and can be manufactured on a Si substrate or a GaAs substrate, which is a semiconductor, so that the filter is formed monolithically with an LSI chip. It is also possible.

  In such a thin film piezoelectric resonator, in order to confine the energy of the excited elastic vibration, it is desirable that the upper part and the lower part of the resonance part are in contact with the air layer. This is because the acoustic impedance of the piezoelectric body and electrodes constituting the resonator and the acoustic impedance of the air differ by several orders of magnitude, so that the elastic vibration is efficiently reflected at the interface and the energy of the elastic wave is confined in the resonance portion. Since the upper air layer is naturally formed, how to form the lower air layer is a point of the process of the thin film piezoelectric resonator.

  Several processes are known for forming a hollow air resonator by forming a lower air layer.

The first known method is a method of creating an air layer below the resonator by etching from the back side of the substrate after the resonator is formed (see, for example, Non-Patent Document 1). According to this method, a silicon nitride film is formed on the Si (100) substrate as an etching stop layer by a known CVD method or the like. Next, an Al electrode film is formed by sputtering or the like, and the Al electrode film is patterned using lithography and RIE to form an Al electrode. Next, an AlN piezoelectric film is formed and patterned by lithography and RIE. An Al upper electrode is formed thereon and patterned by lithography and RIE. Subsequently, Si is anisotropically etched from the lower surface side of the substrate to form a via hole. In this way, a thin film piezoelectric resonator in which the top and bottom of the resonator portion are in contact with the air layer can be produced.

  The biggest problem with the above structure is that a via hole must be formed by anisotropic etching from the lower surface side of the substrate. Creating a via hole requires a long etching time in a strong acid containing hydrofluoric acid. In addition, the thin film piezoelectric resonator has an advantage that the size of the resonator can be reduced to several tens of μm. However, if a via hole formed by anisotropic etching with an angle is used, the element size increases due to the via hole. There is a problem. Furthermore, it cannot be manufactured monolithically with an LSI chip.

A conventionally known second method is a method in which a resonator is formed on a SiO ₂ -based sacrificial layer, and finally the sacrificial layer is removed by selective etching (see, for example, Patent Document 1). In this method, first, a recess is formed on an Si substrate by anisotropic etching. Further, the surface of the depression is thermally oxidized to prevent diffusion of the glass doping component formed in the next step into the Si substrate. Next, a sacrificial layer (for example, silicate glass doped with phosphorus, PSG) is formed on the substrate. The surface is polished to the Si substrate surface using CMP. A lower electrode, a piezoelectric film, and an upper electrode are sequentially deposited thereon. Next, a hole is made until the sacrificial layer is reached, and the sacrificial layer is removed by selective etching using hydrofluoric acid to form a cavity. This process completes the thin film resonator.

  The problem with the above process is that hydrofluoric acid must be used to remove the sacrificial layer. Hydrofluoric acid is a violent acid with an oxidizing action and dissolves all metals except Au and Pt. Therefore, there is a problem that the electrode, the piezoelectric film, and the like are easily peeled off during the sacrifice layer etching. In addition, since a resonator must be formed on the surface flattened by CMP, an AlN film having good crystallinity cannot be formed by taking over the orientation from the substrate.

A conventionally known third method is a method in which a resonator is formed on a sacrificial layer formed in a convex shape on a substrate, and finally the sacrificial layer is removed by selective etching (see, for example, Patent Document 2). . In this method, first, a sacrificial layer is formed without digging a substrate, a lower electrode, a piezoelectric body, and an upper electrode are sequentially laminated thereon, and finally the sacrificial layer is removed by etching. Since this method does not require planarization by CMP, the manufacturing process can be simplified, and if the oriented sacrificial layer is formed on the substrate, the lower electrode and the piezoelectric body can be oriented. It is better than other methods.
“Film Bulk Acoustic Wave Resonator Technology”, SV Krishnaswany, J. Rosenbaum, S. Horwitz, C. Vale and RA Moore, Ultrasonic Symposium 1990, p529-536 JP 2000-69594 A US Pat. No. 606,0818

  As described above, a method of forming a hollow structure (cavity) by first forming a convex sacrificial layer on a substrate, forming an electrode and a resonator made of a piezoelectric material, and then etching away the sacrificial layer This is an advantageous structure from the viewpoint of improving the orientation of the piezoelectric body and simplifying the manufacturing process, but has a problem that the stepped portion of the cavity adversely affects the resonance characteristics. Incomplete vibration of the piezoelectric body formed on the cavity step portion and reflection / absorption of the vibration in the lateral direction of the step portion cause a decrease in the Q value.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thin film piezoelectric resonator capable of avoiding deterioration of resonance characteristics peculiar to a convex cavity structure.

  A thin film piezoelectric resonator according to an aspect of the present invention includes a substrate having a flat surface, a flat portion that is substantially parallel to the substrate surface through a cavity, and descends to the substrate surface so as to support the flat portion. A piezoelectric film having the substrate surface and an inclined part that substantially forms the cavity together with the flat part, a lower electrode provided on the cavity side surface of the flat part, and the cavity side surface of the flat part The lower electrode and an upper electrode facing each other through the flat portion, and the region where the lower electrode and the upper electrode of the piezoelectric film face each other is in the flat portion. It is limited, and the end of the facing area is 1 μm or more away from the boundary between the flat part and the inclined part.

  The piezoelectric film may be aluminum nitride.

  The area where the lower electrode is provided on the flat part may be larger than the area where the upper electrode is provided on the flat part.

  An amorphous metal layer provided on the substrate surface may exist under the flat portion of the piezoelectric film that is not in contact with the lower electrode.

  According to the present invention, it is possible to avoid the resonance characteristic deterioration peculiar to the convex cavity structure.

  The inventors of the present invention have studied in detail the structure of a thin film piezoelectric resonator having a convex cavity structure from both experimental and theoretical viewpoints. As a result, it was found that a resonator having a high Q value and less spurious vibration can be obtained by optimizing the size and size relationship of the cavity and the upper and lower electrodes.

  Hereinafter, the principle of the present invention will be described in detail.

  First, the inventors examined the electrode structure of a thin film piezoelectric resonator having a convex cavity structure in detail. In the conventional method of forming a sacrificial layer in the recess dug in the substrate and the resonator in which the substrate is etched from the back surface to form a hollow structure, the lower electrode has a conventional structure that extends beyond the entire cavity surface. As a result, the structure has the strongest strength, and the step of the piezoelectric film is not formed inside the cavity, so that unnecessary spurious vibrations are not generated in the resonance characteristics. However, in this structure, at least on one side of the electrode, a region where the upper and lower electrodes face each other extends beyond the cavity, and a parallel parasitic capacitance is formed outside the cavity.

  On the other hand, in a resonator with a convex cavity structure, if the opposing part of the upper and lower electrodes hits the step part of the slope of the piezoelectric film, incomplete piezoelectric vibration induced by the piezoelectric film of the step part with poor crystallinity and morphology The inventors have experimentally found that spurious is induced and the Q value of the antiresonance point is deteriorated. Therefore, when adopting the convex cavity structure, it is necessary to make the structure in which the opposing region of the upper and lower electrodes is contained in the cavity. Such a structure is said to be weak in terms of structure as described above. However, if the stresses of the piezoelectric film and the upper and lower electrodes are optimally designed, a sufficiently high yield can be obtained practically.

  In addition, even if there is a step in the piezoelectric film within the cavity, the convex cavity structure efficiently absorbs vibration on the slope of the piezoelectric film, so it does not cause unnecessary spurious vibration. The inventors have found for the first time. Note that the decrease in the Q value accompanying the absorption of vibration becomes a very serious problem when the electrode size is comparable to the film thickness, but is almost negligible for practically used electrode sizes.

  In addition, the inventors theoretically and experimentally studied the problem of how far the opposing portion of the upper and lower electrodes should be separated from the upper end of the slope of the piezoelectric film. When the end portion of the electrode is in contact with the upper end of the inclined surface of the piezoelectric film, the antiresonance Q value decreases, and in addition, a large spurious vibration is observed near the antiresonance frequency. Such a phenomenon is suppressed as the electrode end is moved away from the inclined surface of the piezoelectric film, and it is seen that the resonance characteristics necessary for obtaining a sufficiently small insertion loss can be obtained if an interval of at least 1 μm is provided. It was issued. As a result of a simulation using the finite element method, some evanescent elastic vibration is radiated from the electrode to the periphery, and when the electrode and the slope of the piezoelectric film are close to each other, the transverse mode of vibration is low order. It has been clarified that the Q value phenomenon and spurious increase due to strong resonance and vibration being absorbed by the slope of the piezoelectric film. Therefore, if the distance is increased, the radiated vibration is attenuated and does not affect the characteristics.

  The inventors of the present invention have also found for the first time that AlN (aluminum nitride) having a high-frequency cutoff type dispersion relationship behaves like a piezoelectric body having a low-frequency cutoff type dispersion relationship. Based on the above experimental and theoretical considerations, the present inventors have made the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
The configuration of the thin film piezoelectric resonator according to the first embodiment of the present invention is shown in FIGS. FIG. 1 is a cross-sectional view of the thin film piezoelectric resonator according to the first embodiment, and FIG. 2 is a plan view of the thin film piezoelectric resonator according to the first embodiment.

The thin film piezoelectric resonator 1 according to the first embodiment includes a substrate 2 having a flat surface, a flat portion 8a opposed to the surface of the substrate 2 via a cavity (cavity) 12 substantially in parallel, and the flat portion 8a. A piezoelectric film 8 having an inclined portion 8b that descends to the surface of the substrate 2 so as to support and forms a cavity 12 substantially together with the surface of the substrate 2 and the flat portion 8a, and a cavity-side surface of the flat portion 8a. The lower electrode 6 and the upper electrode 10 provided on the substantially parallel surface opposite to the cavity-side surface of the flat portion 8a and facing the lower electrode 6 via the flat portion 8a.

  The cavity 12 has a main body portion 12a and an outlet portion 12b. The main body portion 12 a of the cavity 12 is substantially formed by the flat portion 8 a and the inclined portion 8 b of the piezoelectric film 8 and the surface of the substrate 2. The exit 12b of the cavity 12 is a hole that connects the main body 12a and the outside, and is provided on the side of the thin film piezoelectric resonator 1 according to the present embodiment. And this exit part 12c is used as a hole for discharging | emitting the sacrificial layer for forming the cavity 12 used when manufacturing the thin film piezoelectric resonator 1 by this embodiment outside.

  Further, the region 14 of the lower electrode 6 and the upper electrode 10 facing each other through the piezoelectric film 8 is configured to be located in the flat portion 8 a of the piezoelectric film 8. The ends of the facing regions 14 are configured to be separated from the boundary between the flat portion 8a and the inclined portion 8b of the piezoelectric film 8 by a predetermined distance x. The predetermined distance x is preferably 1 μm or more, and more preferably 3 μm or more.

  Next, the manufacturing process of the thin film piezoelectric resonator 1 of the present embodiment will be described with reference to FIGS. 3 to 5 are manufacturing process cross-sectional views of the thin film piezoelectric resonator 1 of the first embodiment.

  First, as shown in FIG. 3, a sacrificial layer 4 made of Mo (molybdenum) having a film thickness of 1 μm is formed on a Si substrate 2 having an oxide film formed on the outermost surface by RF (Radio Frequency) magnetron sputtering, and lithography is performed. Then, the sacrificial layer 4 is patterned using chemical dry etching (CDE) using a fluoride gas.

  Next, as shown in FIG. 4, an amorphous underlayer (not shown) made of TaAl having a thickness of 0.05 μm and a film made of Al (aluminum) having a thickness of 0.2 μm are formed by RF magnetron sputtering. The lower electrode 6 was formed by sequentially forming the Al film and the amorphous underlayer using lithography and RIE (Reactive Ion Etching) using a fluoride-based gas. Subsequently, a film made of AlN having a film thickness of 1.2 μm is formed by a reactive RF magnetron sputtering method, and then a film made of AlN is patterned by lithography and RIE using a chloride-based gas to form a piezoelectric film 8. did. Further, a film made of Al was formed by RF magnetron sputtering, and the film made of Al was patterned by lithography and RIE to form the upper electrode 10 (see FIG. 4).

  Next, as shown in FIG. 5, 50% hydrogen peroxide water heated to 70 ° C. is exposed from the portion where the sacrificial layer 4 made of Mo is exposed on the substrate 2 (the portion corresponding to the outlet portion 12b in FIG. 2). Using this, selective etching was performed to form a cavity 12 below the resonator composed of the lower electrode 6, the piezoelectric film 8, and the upper electrode 10. Although all of the sacrificial layer 4 was dissolved by selective etching using hydrogen peroxide, the upper electrode 10, the lower electrode 6, and the piezoelectric film 8 were not damaged at all, and no peeling was observed.

  Among the thin film piezoelectric resonators produced by the above process, the frequency characteristics of the thin film piezoelectric resonator, in which the size relationship between the electrode and the cavity is schematically shown in FIG. 2, were evaluated. The distance x (see FIG. 2) between the end of the region 14 where the upper and lower electrodes face each other and the boundary between the flat portion 8a and the inclined portion 8b of the piezoelectric film 8 was 3 μm. Evaluation was performed using a vector network analyzer (HP8510C). As a result, the resonance frequency was about 1.9 GHz, the electromechanical coupling constant was 6.4%, the resonance Q value was 850, and the anti-resonance Q value was 750. Also, almost no spurious vibration was observed.

(First comparative example)
Next, as a first comparative example, as shown in FIG. 6, a thin film piezoelectric resonator in which the opposed region 14 of the upper and lower electrodes 6 and 10 extends to the outside of the cavity 12 was prepared, and the resonance characteristics were examined. The manufacturing process of the thin film piezoelectric resonator of this comparative example is the same as the process described in the first embodiment. In FIG. 6, a region 14 where the upper and lower electrodes 6 and 10 face each other extends to the outside of the cavity 12. As can be seen from FIG. 6, the region 14 where the upper and lower electrodes 6, 10 face each other in the inclined portion 8 b of the piezoelectric film 8, so that the piezoelectric vibration excited by the piezoelectric film 8 made of AlN having incomplete piezoelectricity is generated. It adversely affects the characteristics such as deterioration of Q value and increase of spurious. When the frequency characteristics of this resonator were evaluated, the coupling constant and the resonance frequency were 6.4% and 800, respectively, which were almost the same as in the first embodiment, but the antiresonance Q value was greatly reduced to 270. In addition, strong spurious vibrations were observed around the anti-resonance point.

(Second comparative example)
Next, as a second comparative example, as shown in FIG. 7, a thin film piezoelectric resonator in which the region 14 where the upper and lower electrodes 6 and 10 face each other is in contact with the boundary between the flat portion 8a and the inclined portion 8b of the piezoelectric film 8 is used. The resonance characteristics were prepared. The manufacturing process of the thin film piezoelectric resonator of this comparative example is the same as the process described in the first embodiment. As can be seen from FIG. 7, the electrode ends of the upper and lower electrodes 6, 10 substantially overlap the boundary between the flat portion 8 a and the inclined portion 8 b of the piezoelectric film 8. In such a structure, since the vibration radiated from the electrode end portion is not sufficiently attenuated and absorbed by the inclined portion 8a of the piezoelectric film 8 made of imperfect AlN, the Q value decreases. When the frequency characteristics of this resonator were evaluated, the coupling constant and the resonance frequency were almost the same as in the first embodiment, but the antiresonance Q value was greatly reduced to 400, and the antiresonance point was the center. Spurious vibrations were observed.

  As described above, according to the present embodiment, it is possible to avoid the deterioration of resonance characteristics peculiar to the convex cavity structure.

  In the present embodiment, AlN is used for the piezoelectric film 8. Since AlN is a low-frequency confining piezoelectric material, spurious due to the electrode is below the resonance frequency, and the influence on the filter characteristics can be minimized. In addition, since the standing wave outside the electrode is hardly generated as described above in the convex cavity structure, the spurious between the resonance and the anti-resonance is very small. Furthermore, if it is AlN, it can be produced by a normal process used in the current LSI process, and is particularly valuable in practice.

(Second Embodiment)
Next, a thin film piezoelectric resonator according to a second embodiment of the invention will be described with reference to FIG. The thin film piezoelectric resonator according to this embodiment has a configuration in which an amorphous metal layer 5 is formed on a substrate 2 in the thin film piezoelectric resonator according to the first embodiment.

  The reason for forming the amorphous metal layer 5 on the substrate 2 is to form the piezoelectric film 8 having good crystallinity. Therefore, in this embodiment, as a means for improving the c-axis orientation of the piezoelectric film 8 used in the thin film piezoelectric resonator, the piezoelectric film, electrode layer, and sacrificial material formed on the amorphous metal layer are used. This is because the layer uses the property of causing highly oriented growth on the crystal habit plane.

  The present inventors have extensively studied theoretically and experimentally the conditions under which a hexagonal piezoelectric film such as AlN or ZnO grows in a high orientation without using an epitaxial growth technique from the substrate. It has been found that the orientation of the piezoelectric film is dramatically improved by sandwiching an amorphous metal layer between the films.

  When the amorphous metal layer 5 is compared with, for example, a polycrystalline metal layer, the surface of the polycrystalline metal is composed of crystal planes having various orientations, and there are many irregularities depending on crystal grains. On the other hand, since the amorphous metal layer is formed with a uniform amorphous surface and is flat and uniform, it is oriented to the c-plane which is the original crystal habit plane of hexagonal crystals such as AlN and ZnO. It is thought that it is easy to grow and the orientation is improved.

In addition, compared with the case of using an amorphous insulating layer such as SiO ₂ conventionally used as an underlayer or sacrificial layer on the substrate surface, the surface energy of the amorphous metal layer is generally higher than that of the amorphous insulating layer. It is considered that the orientation is further improved because the crystal growing on the layer grows in layers and tends to lower the surface energy.

  The portion where the piezoelectric film 8 needs to obtain good crystallinity is at least the region of the substrate 2 corresponding to the region indicated by reference numeral 16 in FIG. 8, that is, the flat portion 8a of the piezoelectric film 8 to the lower electrode 6. And the region of the substrate 2 under the region excluding the region where the flat portion 8a of the piezoelectric film 8 overlaps.

  When such a structure of the second embodiment is used, the film strength is improved because the piezoelectric film 8 is oriented in both the region where the lower electrode 6 is present and the region where the lower electrode 6 is not present in the cavity 12. As a result, a fracture mode such as a crack at the step portion of the piezoelectric film 8 or a hollow structure is less likely to occur, and the margin of the film stress that can stably manufacture the hollow structure is increased, yield. Is further improved. When Al or Al alloy is used as a sacrificial layer, a non-oxidizing acid can be used as an etchant for the sacrificial layer, and an extremely stable manufacturing process can be established without dissolving the piezoelectric film and electrodes. This is very useful industrially.

  Next, the manufacturing method of the thin film piezoelectric resonator according to the present embodiment will be explained with reference to FIG. First, as shown in FIG. 8, an amorphous metal layer 5 made of, for example, an alloy of Ta and Al is formed on the surface of the Si substrate 2. Thereafter, a sacrificial layer (not shown) made of Al having a film thickness of 1 μm is formed on the amorphous metal layer 5 by RF magnetron sputtering, and reactive ion etching (RIE) using lithography and a chloride-based gas. Thus, the sacrificial layer was patterned.

  Next, a film made of Mo having a thickness of 0.2 μm was formed by RF magnetron sputtering, and the film made of Mo was patterned by RIE using lithography and a fluoride-based gas, whereby the lower electrode 6 was formed.

  Next, a film made of AlN having a thickness of 1.2 μm is formed by a reactive RF magnetron sputtering method, and the film made of AlN is patterned by lithography and RIE using a chloride-based gas to form a piezoelectric film 8. did. Further, a film made of Mo was formed by the RF magnetron sputtering method, and the film made of Mo was patterned by lithography and RIE to form the upper electrode 10.

  Next, selective etching is performed from a portion (not shown) where the Al sacrificial layer is exposed on the substrate using hydrochloric acid having a concentration of 10%, and from the lower electrode 6, the piezoelectric film, and the upper electrode 10. A cavity 12 was created at the bottom of the resonator. The sacrificial layer was completely dissolved by selective etching using hydrochloric acid, but the upper and lower electrodes 6, 10, the piezoelectric film 8, and the amorphous metal layer 5 were not damaged at all, and no peeling was observed. .

  The thin film piezoelectric resonator produced by the above process was evaluated. In the region indicated by reference numeral 16 in FIG. 8, the orientation of the piezoelectric film 8 made of AlN is improved as compared with the resonator not using the oriented sacrificial layer as in the first embodiment, and the loss is further reduced. Resonance characteristics with less can be expected. Actually, when the frequency characteristics of this resonator were evaluated, the coupling constant was 6.4%, the resonance Q value was 1200, and the anti-resonance Q value was 1100. In addition, unnecessary spurious vibrations were hardly observed.

  The orientation of the piezoelectric film 8 made of AlN was measured by X-ray diffraction, and the orientation half-width was 2 degrees or less.

  Similar to the first embodiment, this embodiment can avoid the deterioration of resonance characteristics peculiar to the convex cavity structure.

  As described above, according to each embodiment of the present invention, the Q value is high, and unnecessary spurious vibrations can be minimized.

Here, each embodiment of the present invention has been described by taking AlN having the highest compatibility as an LSI process as an example of the piezoelectric material, but PbTiO ₃ (lead titanate), BaTiO ₃ (titanic acid) are used as the piezoelectric material. Any material may be used as long as the Lamb wave dispersion relationship is a high-frequency cutoff type, such as barium), and is not limited to AlN.

Further, here, the description has been made taking an alloy of Ta and Al as an example of the amorphous metal layer, but other materials such as TiB ₂ may be used. Further, the oriented sacrificial layer material formed on the amorphous underlayer may be Au, Mo, W, or the like other than Al, and the orientation is improved in the same manner as Al. Therefore, the amorphous metal layer and the sacrificial layer material are not limited to the materials shown here.

1 is a cross-sectional view showing a configuration of a thin film piezoelectric resonator according to a first embodiment of the present invention. 1 is a plan view showing a configuration of a thin film piezoelectric resonator according to a first embodiment of the present invention. Sectional drawing of the manufacturing process of the thin film piezoelectric resonator of 1st Embodiment. Sectional drawing of the manufacturing process of the thin film piezoelectric resonator of 1st Embodiment. Sectional drawing of the manufacturing process of the thin film piezoelectric resonator of 1st Embodiment. Sectional drawing which shows the structure of the 1st comparative example in 1st Embodiment. Sectional drawing which shows the structure of the 2nd comparative example in 1st Embodiment. Sectional drawing which shows the structure of the thin film piezoelectric resonator by 2nd Embodiment of this invention.

Explanation of symbols

2 Si substrate 4 Sacrificial layer 5 Amorphous metal layer 6 Lower electrode 8 Piezoelectric film 8a Flat part 8b Inclined part 10 Upper electrode 12 Cavity 12a Body part 12b Outlet part 14 Regions where the upper electrode and the lower electrode face each other

Claims (4)

A substrate with a flat surface;
A flat portion opposed to the substrate surface through a cavity substantially parallel to the substrate surface, and an inclined portion that descends to the substrate surface to support the flat portion and substantially forms the cavity together with the substrate surface and the flat portion. A piezoelectric film having
A lower electrode provided on the cavity side surface of the flat part;
Provided on a substantially parallel surface opposite to the cavity-side surface of the flat portion, and comprising the lower electrode and an upper electrode facing each other through the flat portion,
The region where the lower electrode and the upper electrode of the piezoelectric film face each other is limited within the flat portion,
The thin film piezoelectric resonator according to claim 1, wherein an end of the facing region is separated by 1 μm or more from a boundary between the flat portion and the inclined portion.   2. The thin film piezoelectric resonator according to claim 1, wherein the piezoelectric film is aluminum nitride.   3. The thin film piezoelectric resonator according to claim 1, wherein an area where the lower electrode is provided on the flat portion is larger than an area where the upper electrode is provided on the flat portion.   4. The amorphous metal layer provided on the substrate surface is present under the flat portion of the piezoelectric film that is not in contact with the lower electrode. 5. Thin film piezoelectric resonator.

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