JP7343991B2 - Piezoelectric thin film resonators, acoustic wave devices, filters and multiplexers - Google Patents

Description

The present invention relates to piezoelectric thin film resonators, acoustic wave devices, filters, and multiplexers.

Acoustic wave devices using piezoelectric thin film resonators are used, for example, as filters and multiplexers for wireless devices such as mobile phones. A piezoelectric thin film resonator has a laminated structure in which a lower electrode and an upper electrode face each other with a piezoelectric film in between. The region where the lower electrode and the upper electrode face each other with the piezoelectric film in between is the resonance region. An air gap is provided below the lower electrode in the resonance region so as not to limit vibrations in the resonance region. It is known to provide a protective film on the upper electrode in order to prevent the upper electrode from being exposed to air or moisture (for example, Patent Document 1).

Japanese Patent Application Publication No. 2004-64785

However, deterioration of the laminated film may occur, such as separation between the lower electrode and the piezoelectric film.

The present invention was made in view of the above problems, and an object of the present invention is to suppress deterioration of laminated films.

The present invention provides a substrate , a lower electrode which is provided with a gap between the substrate and is a single layer film or a laminated film mainly composed of ruthenium, chromium, titanium, molybdenum, tungsten and tantalum, and the lower electrode. a piezoelectric film provided on the piezoelectric film; and an upper electrode provided on the piezoelectric film so as to overlap the gap and form a resonance region facing the lower electrode with at least a portion of the piezoelectric film in between. , an adsorption film provided in the void and spaced apart from the lower electrode, the adsorption film containing at least one of titanium, zirconium, vanadium, niobium, tantalum, nickel, and palladium as a main component; It is a vessel.

In the above structure, the adsorption film may have a structure containing at least one of titanium, zirconium, vanadium, niobium , and tantalum as a main component.

In the above structure, the piezoelectric film may have aluminum nitride as a main component, and the metal film of at least one of the lower electrode and the upper electrode in contact with the piezoelectric film may have ruthenium as a main component.

In the above structure, the piezoelectric film may have aluminum nitride as a main component, and the metal film of the lower electrode in contact with the piezoelectric film may have ruthenium as a main component.

In the above structure, the lower electrode may be provided with a hole that communicates with the void from the outside.

The present invention is an acoustic wave device including the piezoelectric thin film resonator described above and a sealing portion that seals the piezoelectric thin film resonator in a closed space, which is a gap.

In the above configuration, the substrate is mounted on the base body such that the upper electrode faces the base body with the gap being the closed space in between, the sealing portion is provided so as to surround the substrate, and the sealing portion is provided to surround the substrate, and the sealing portion is provided so as to surround the substrate. The stop portion may be made of metal.

The present invention is a filter including the piezoelectric thin film resonator described above.

The present invention is a multiplexer including the above filter.

According to the present invention, deterioration of the laminated film can be suppressed.

1(a) and 1(b) are plan views of an acoustic wave device according to Example 1. FIG. FIGS. 2(a) and 2(b) are a sectional view taken along line AA and sectional view taken along line BB in FIG. 1(a), respectively. FIG. 3 is a sectional view corresponding to the BB cross section of the piezoelectric thin film resonator according to Comparative Example 1. FIGS. 4A and 4B are cross-sectional views of piezoelectric thin film resonators according to Modifications 1 and 2 of Example 1, respectively. FIG. 5 is a cross-sectional view of an acoustic wave device according to Example 2. 6A is a circuit diagram of a filter according to a third embodiment, and FIG. 6B is a circuit diagram of a duplexer according to a first modification of the third embodiment.

Embodiments of the present invention will be described below with reference to the drawings.

1(a) and 1(b) are plan views of the acoustic wave device according to Example 1, and FIGS. 2(a) and 2(b) are respectively AA in FIG. 1(a). They are a sectional view and a BB sectional view. 1(a) mainly shows the substrate 10, the lower electrode 12, and the upper electrode 16, and FIG. 1(b) mainly shows the substrate 10, the adsorption film 25, and the void 30.

As shown in FIGS. 1A to 2B, a lower electrode 12 is provided on a substrate 10 with a gap 30 in between. The substrate 10 is, for example, a silicon substrate. The void 30 has a dome-shaped bulge. The dome-shaped bulge is, for example, a bulge having a shape such that the height of the void 30 is small around the void 30 and becomes larger toward the inside of the void 30. The void 30 functions as an acoustic reflection layer that reflects the elastic waves excited in the piezoelectric film 14. The lower electrode 12 includes a lower layer 12a and an upper layer 12b. The lower layer 12a is, for example, a chromium (Cr) film, and the upper layer 12b is, for example, a ruthenium (Ru) film.

A piezoelectric film 14 mainly composed of aluminum nitride (AlN) whose main axis is in the (0001) direction (that is, has C-axis orientation) is provided on the lower electrode 12 . An upper electrode 16 is provided on the piezoelectric film 14 so as to form a resonance region 50 facing the lower electrode 12 with at least a portion of the piezoelectric film 14 sandwiched therebetween. The resonance region 50 has an elliptical shape, and is a region where elastic waves in the thickness longitudinal vibration mode resonate. In plan view, the air gap 30 overlaps the resonance region 50 and is provided larger than the resonance region 50 . As a result, the elastic waves excited in the piezoelectric film 14 are reflected by the air gap 30. Upper electrode 16 includes a lower layer 16a and an upper layer 16b. The lower layer 16a is, for example, a ruthenium film, and the upper layer 16b is, for example, a chromium film.

A mass load membrane 20 is provided between the lower layer 16a and the upper layer 16b of the upper electrode 16. The mass load film 20 is, for example, a titanium (Ti) film. The mass load membrane 20 sets the difference in resonance frequency between the piezoelectric thin film resonators. A protective film 24 is provided on the upper electrode 16. The protective film 24 is, for example, a silicon oxide film. The protective film 24 protects the lower electrode 12, the upper electrode 16, and the piezoelectric film 14 from the outside air. Laminated film 18 within resonant region 50 includes lower electrode 12 , piezoelectric film 14 , upper electrode 16 , mass-loading film 20 , and protective film 24 . A metal layer 26 is provided on the lower electrode 12 and the upper electrode 16, respectively. The metal layer 26 is, for example, a titanium (Ti) film and gold (Au) from the substrate 10 side. The metal layer 26 is, for example, a wiring connected to the lower electrode 12 and the upper electrode 16.

As shown in FIGS. 1(a) and 2(b), a hole 34 penetrating the lower electrode 12 is provided outside the resonance region 50. The hole 34 communicates with the cavity 30 via an introduction path 35. The hole 34 and the introduction passage 35 are passages into which an etching solution is introduced when etching the sacrificial layer within the gap 30. The holes 34 may be covered with the protective film 24 or may not be covered.

An adsorption film 25 is provided on the substrate 10 within the gap 30 . The adsorption film 25 has titanium as a main component, for example. The adsorption film 25 adsorbs hydrogen gas within the voids 30. The adsorption film 25 is electrically insulated from the lower electrode 12, and has a floating potential, for example.

As the substrate 10, in addition to a silicon substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used. As the lower electrode 12 and the upper electrode 16, in addition to ruthenium and chromium, aluminum (Al), titanium, copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium ( A single layer film of Rh) or iridium (Ir) or a laminated film of these can be used.

In addition to aluminum nitride, the piezoelectric film 14 can be made of zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), or the like. Further, for example, the piezoelectric film 14 mainly contains aluminum nitride, and may also contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 is improved by using scandium (Sc), two elements, a group 2 element and a group 4 element, or two elements, a group 2 element and a group 5 element, as additive elements. do. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. Group 2 elements are, for example, calcium (Ca), magnesium (Mg), strontium (Sr) or zinc (Zn). Group 4 elements are, for example, titanium, zirconium (Zr) or hafnium (Hf). Group 5 elements are, for example, tantalum, niobium (Nb) or vanadium (V). Furthermore, the piezoelectric film 14 mainly contains aluminum nitride and may also contain boron (B).

As the mass load film 20, in addition to the titanium film, the metal film illustrated as the lower electrode 12 and the upper electrode 16, or an insulating film such as silicon nitride or silicon oxide can also be used. As the protective film 24, in addition to the silicon oxide film, a silicon nitride film, an aluminum nitride film, or the like can be used.

The adsorption film 25 mainly contains zirconium, vanadium (V), niobium (Nb), tantalum (Ta), nickel (Ni), or palladium (Pd) as a material for adsorbing or storing hydrogen, in addition to titanium. A film, a titanium alloy film, a nickel alloy film, or a laminated film of these can be used.

[Comparative example 1]
FIG. 3 is a sectional view corresponding to the BB cross section of the piezoelectric thin film resonator according to Comparative Example 1. As shown in FIG. 3, in Comparative Example 1, no adsorption film was provided. The other configurations are the same as those in Example 1, and their explanation will be omitted.

A piezoelectric thin film resonator according to Comparative Example 1 was manufactured. The manufacturing conditions are as follows.
Substrate 10: Silicon substrate Lower layer 12a of lower electrode 12: Chromium film with a thickness of 70 nm Upper layer 12b of lower electrode 12: Ruthenium film with a thickness of 250 nm Piezoelectric film 14: Aluminum nitride film with a thickness of 970 nm Lower layer of the upper electrode 16 16a: Ruthenium film with a thickness of 120 nm Upper layer 16b of the upper electrode 16: Chromium film with a thickness of 5 nm Mass load film 20: Titanium film with a thickness of 15 nm Protective film 24: Silicon oxide film with a thickness of 70 nm

In Comparative Example 1, the lower electrode 12 and the piezoelectric film 14 may peel off. Therefore, the piezoelectric thin film resonator according to Comparative Example 1 was exposed to an atmosphere containing 100% hydrogen gas, a pressure of 20 MPa, and room temperature for 6 hours. As a result, it was found that peeling occurred between the lower electrode 12 and the piezoelectric film 14.

From the above experimental results, it is considered that the peeling between the lower electrode 12 and the piezoelectric film 14 is caused by hydrogen gas. For example, metals such as solder, gold and/or copper are present within the package that mounts the piezoelectric thin film resonator. When these metals adsorb or contain hydrogen, it is thought that hydrogen gas is generated from the metals. In particular, metals formed by plating may contain a large amount of hydrogen.

In the piezoelectric thin film resonator of Comparative Example 1, the reason why the lower electrode 12 and the piezoelectric film 14 are separated by hydrogen gas is not clear, but it is thought to be as follows, for example. As indicated by an arrow 60, hydrogen gas in the external atmosphere is introduced into the cavity 30 through the hole 34 and the introduction path 35. Although the holes 34 may be blocked by the protective film 24, hydrogen easily passes through the protective film 24 because the protective film 24 above the holes 34 has poor film quality. The chromium film and ruthenium film that are the lower electrode 12 easily absorb hydrogen. Therefore, hydrogen in the gap 30 passes through the lower electrode 12 as indicated by an arrow 62. Since hydrogen is difficult to be taken into the piezoelectric film 14, it is stored at the interface between the lower electrode 12 and the piezoelectric film 14. Hydrogen at the interface between the lower electrode 12 and the piezoelectric film 14 reduces the adhesion between the lower electrode 12 and the piezoelectric film 14 . For example, hydrogen in metals is known to cause hydrogen embrittlement. When the lower electrode 12 near the interface with the piezoelectric film 14 becomes hydrogen embrittled, peeling occurs between the lower electrode 12 and the piezoelectric film 14 .

The reason why similar peeling does not occur between the upper electrode 16 and the piezoelectric film 14 is not clear, but it is thought to be as follows, for example. An inorganic insulating film such as a silicon oxide film or a silicon nitride film is more difficult for hydrogen to pass through than a metal film such as the lower electrode 12. Therefore, hydrogen is not stored between the upper electrode 16 and the piezoelectric film 14, and no peeling occurs between the upper electrode 16 and the piezoelectric film 14.

According to the first embodiment, the adsorption film 25 that adsorbs or stores hydrogen is provided within the gap 30 with a space between it and the lower electrode 12 . As a result, since the adsorption film 25 adsorbs hydrogen gas in the void 30, hydrogen is not accumulated in the lower electrode 12, and deterioration of the laminated film 18, such as separation of the lower electrode 12 and the piezoelectric film 14, can be suppressed. Furthermore, by providing the adsorption film 25 within the void 30, it is possible to suppress an increase in chip size. Furthermore, the adsorption film 25 can enhance the heat exhaust effect from the void 30 to the substrate 10.

In Comparative Example 1, peeling between the lower electrode 12 and the piezoelectric film 14 was a problem, but the adsorption film 25 within the gap 30 is also effective in preventing peeling between the upper electrode 16 and the piezoelectric film 14. That is, if the adsorption film 25 adsorbs or stores hydrogen in the void 30, the hydrogen concentration in the space in which the piezoelectric thin film resonator is sealed decreases. Therefore, it is also effective in preventing peeling between the upper electrode 16 and the piezoelectric film 14. In this way, the adsorption film 25 is effective against deterioration of the laminated film 18 caused by hydrogen.

The adsorption film 25 has at least one of titanium, zirconium, vanadium, niobium, tantalum, nickel, and palladium as a main component. Thereby, the adsorption membrane 25 can adsorb or store hydrogen. Note that the adsorption film 25 containing a certain element as a main component means that the adsorption film 25 contains a certain element to the extent that it can adsorb or store hydrogen, for example, contains 50 atomic % or more of a certain element.

The piezoelectric film 14 has aluminum nitride as its main component, and the upper layer 12b or the lower layer 16a (metal film) in contact with the piezoelectric film 14, which is at least one of the lower electrode 12 and the upper electrode 16, has ruthenium as its main component. In this case, separation between the upper layer 12b or the lower layer 16a and the piezoelectric film 14 is likely to occur. Therefore, it is effective to provide the adsorption film 25 within the void 30. Note that the piezoelectric film 14 is mainly composed of aluminum nitride and the metal film is mainly composed of ruthenium. This means that the piezoelectric film 14 is made of aluminum nitride to the extent that the piezoelectric film 14 and the lower electrode 12 will separate if the adsorption film 25 is not provided. The metal film contains ruthenium; for example, the total concentration of nitrogen and aluminum in the piezoelectric film 14 is 50 atomic % or more, and the ruthenium concentration in the metal film is 50 atomic % or more.

Furthermore, when the piezoelectric film 14 is mainly composed of aluminum nitride and the upper layer 16b in contact with the piezoelectric film of the lower electrode 12 is mainly composed of ruthenium, since the adsorption film 25 adsorbs or stores hydrogen in the void 30, the lower electrode Peeling between the piezoelectric film 12 and the piezoelectric film 14 can be suppressed.

The lower electrode 12 is provided with a hole 34 and an introduction path 35 that communicate with the cavity 30 from the outside. Thereby, hydrogen is easily introduced into the void 30 from the outside. Therefore, it is effective to provide the adsorption film 25 within the void 30.

[Modification 1 of Example 1]
FIG. 4A is a cross-sectional view of a piezoelectric thin film resonator according to Modification 1 of Example 1. As shown in FIG. 4(a), a depression is formed on the upper surface of the substrate 10. The lower electrode 12 is formed flat on the substrate 10. As a result, a void 30 is formed in the depression of the substrate 10. The adsorption film 25 is provided on the bottom surface of the recess forming the void 30. The adsorption film 25 may be provided on the side surface of the recess forming the void 30. The other configurations are the same as those in Example 1, and their explanation will be omitted. The void 30 may be formed to penetrate the substrate 10. In this case, the adsorption film 25 may be provided on the side surface of the penetrating hole forming the void 30.

[Modification 2 of Example 1]
FIG. 4(b) is a cross-sectional view of a piezoelectric thin film resonator according to a second modification of the first embodiment. The piezoelectric film 14 has a lower piezoelectric film 14a and an upper piezoelectric film 14b provided on the lower piezoelectric film 14a. An insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The insertion film 28 is not provided in the central region of the resonant region 50, but is provided in at least a part of the region surrounding the resonant region 50 and including the outer periphery of the resonant region 50. In the region where the lower electrode 12 is drawn out from the resonance region 50, the end surface of the lower piezoelectric film 14a is located outside the end surface of the upper piezoelectric film 14b. The other configurations are the same as in Example 1, and the explanation will be omitted. As in the second modification of the first embodiment, an insertion membrane 28 may be provided.

In the first embodiment and its modified examples, the planar shape of the resonance region 50 has been described as an elliptical shape, but the planar shape of the resonance region 50 may also be a polygonal shape such as a quadrangular shape or a pentagonal shape.

FIG. 5 is a cross-sectional view of an acoustic wave device according to Example 2. As shown in FIG. 5, the substrate 10 is flip-chip mounted on the substrate 32. The substrate 32 has laminated insulating layers 32a and 32b. Insulating layers 32a and 32b are, for example, ceramic layers or resin layers. Wirings 33c and 33d are provided on the upper surfaces of insulating layers 32a and 32b, respectively. A terminal 39 is provided on the lower surface of the insulating layer 32a. The terminal 39 is a foot pad for connecting the piezoelectric thin film resonator 31 to the outside. Via wiring 33a and 33b are provided that penetrate through insulating layers 32a and 32b. Via wiring 33a, 33b and wiring 33c form internal wiring 33. The internal wiring 33 electrically connects the wiring 33d and the terminal 39. An annular metal layer 37 is provided on the periphery of the upper surface of the substrate 32 . The via wirings 33a, 33b, the wirings 33c, 33d, the terminals 39, and the annular metal layer 37 are, for example, metal layers such as a copper layer, a gold layer, an aluminum layer, and/or a nickel layer.

A piezoelectric thin film resonator 31 and wiring 43 are provided on the lower surface of the substrate 10. The piezoelectric thin film resonator 31 is the piezoelectric thin film resonator of the first embodiment and its modification. A gap 30 is provided between the laminated film 18 and the substrate 10, and an adsorption film 25 is provided on the lower surface of the substrate 10 within the gap 30. The wiring 43 is the metal layer 26 of the piezoelectric thin film resonator.

The board 10 is flip-chip mounted (face-down mounted) on the upper surface of the board 32 via bumps 36. The bumps 36 are, for example, gold bumps, solder bumps, or copper bumps. Bump 36 is connected to wirings 33d and 43. The piezoelectric thin film resonator 31 faces the upper surface of the substrate 32 with a gap 38 in between.

A sealing section 44 is provided to surround the substrate 10. The sealing portion 44 is made of, for example, metal such as solder or resin. It is bonded to the annular metal layer 37. A lid 45 is provided on the sealing part 44 and the upper surface of the substrate 10. The lid 45 is, for example, a metal plate such as a Kovar plate or an insulating plate. A protective film 46 is provided to cover the lid 45 and the sealing part 44. The protective film 46 is, for example, a metal film such as a nickel film or an insulating film.

In the second embodiment, the sealing portion 44 and the like seal the piezoelectric thin film resonator 31 within the void 38, which is a closed space. If the member in contact with the void 38 adsorbs or contains hydrogen, the hydrogen concentration within the void 38 increases. This may cause the laminated film 18 to deteriorate. Therefore, in the piezoelectric thin film resonator 31, an adsorption film 25 is provided in the gap 30, like the piezoelectric thin film resonator of the first embodiment and the first modification thereof. Thereby, deterioration of the laminated film 18 can be suppressed.

In particular, the substrate 10 is mounted on a substrate 32 (substrate) so that the laminated film 18 faces the substrate 32 with a gap 38 in between, and the sealing part 44 is provided so as to surround the substrate 10. In this case, if the sealing part 44 is made of metal, it is possible that the sealing part 44 generates a large amount of hydrogen. In particular, if the sealing part 44 is formed by a plating method, the sealing part 44 contains a large amount of hydrogen. Therefore, it is preferable to use the piezoelectric thin film resonator 31 as Example 1 and its examples.

The acoustic wave device may have a structure in which the piezoelectric thin film resonator 31 is sealed in a void 38 which is a closed space. For example, the substrate 10 may be a piezoelectric substrate, and a surface acoustic wave element may be provided on the piezoelectric substrate. The upper surface of the substrate 10 and the lower surface of the substrate 10 may be bonded via an annular metal layer, and the annular metal layer may seal the piezoelectric thin film resonator in the gap.

Example 3 is an example of a filter and a duplexer using the piezoelectric thin film resonator of Example 1 and its modification. FIG. 6(a) is a circuit diagram of a filter according to the third embodiment. As shown in FIG. 6(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. The piezoelectric thin film resonator of Example 1 and its modifications can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P4. The number of resonators of the ladder filter can be set as appropriate.

FIG. 6(b) is a circuit diagram of a duplexer according to a first modification of the third embodiment. As shown in FIG. 6(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes signals in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as transmission signals, and suppresses signals at other frequencies. The reception filter 42 passes signals in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as reception signals, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Substrate 12 Lower electrode 14 Piezoelectric film 16 Upper electrode 18 Laminated film 24 Protective film 25 Adsorption film 30 Gap 34 Hole 35 Introduction path 40 Transmission filter 42 Reception filter 44 Sealing part

Claims (9)

A substrate and
a lower electrode which is provided with a gap between the substrate and is a single layer film or a laminated film mainly containing ruthenium, chromium, titanium, molybdenum, tungsten and tantalum;
a piezoelectric film provided on the lower electrode;
an upper electrode provided on the piezoelectric film so as to form a resonance region that overlaps the gap and faces the lower electrode with at least a portion of the piezoelectric film in between;
an adsorption film provided in the void and spaced apart from the lower electrode, the adsorption film containing at least one of titanium, zirconium, vanadium, niobium, tantalum, nickel, and palladium as a main component ;
A piezoelectric thin film resonator comprising: The piezoelectric thin film resonator according to claim 1, wherein the adsorption film contains at least one of titanium, zirconium, vanadium, niobium, and tantalum as a main component. 3. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric film has aluminum nitride as a main component, and a metal film in contact with the piezoelectric film of at least one of the lower electrode and the upper electrode has ruthenium as a main component. 3. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric film has aluminum nitride as a main component, and the metal film of the lower electrode in contact with the piezoelectric film has ruthenium as a main component. The piezoelectric thin film resonator according to any one of claims 1 to 4, wherein the lower electrode is provided with a hole that communicates with the void from the outside. A piezoelectric thin film resonator according to any one of claims 1 to 5,
a sealing part that seals the piezoelectric thin film resonator in a void that is a closed space;
An elastic wave device equipped with The substrate is mounted on the substrate such that the upper electrode faces the substrate across the gap, which is a closed space, the sealing portion is provided to surround the substrate, and the sealing portion is made of metal. The elastic wave device according to claim 6, comprising: A filter comprising the piezoelectric thin film resonator according to any one of claims 1 to 5. A multiplexer comprising a filter according to claim 8.

Images