JP4697517B2 - Piezoelectric thin film resonator and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric thin film resonator in which a thin film portion in which a piezoelectric thin film is sandwiched between a pair of electrodes is acoustically separated and supported from a substrate, and a manufacturing method thereof.

  In the piezoelectric thin film resonator using the bulk acoustic wave (BAW) in the piezoelectric thin film, one (lower electrode) of the pair of electrodes sandwiching the piezoelectric thin film is supported by the substrate.

  Regarding this lower electrode side, for example, in Patent Document 1, each layer of AlN / Al / Mo / Au is arranged in order from the AlN piezoelectric thin film side, and Al arranged between Mo and AlN of the piezoelectric thin film is used as the lower electrode film. The structure which makes it 0.1 times or less of thickness is disclosed.

Patent Document 2 discloses a configuration in which each layer of AlN / Pt / Al is arranged in order from the AlN piezoelectric thin film side. This is because if AlN / Al / Pt layers are arranged from the piezoelectric thin film side, Al is easily oxidized, and non-piezoelectric Al ₂ O ₃ is formed at the AlN / Al boundary, deteriorating the piezoelectricity. Is described.
JP 2003-198319 A JP 2001-156582 A

  When AlN or ZnO, which is a typical piezoelectric thin film of a BAW device, is formed on a normal polycrystalline electrode, it becomes a uniaxially oriented film in which the c-axis that is the polarization axis grows in the normal direction of the substrate.

  Since the c-axis crystallinity of the piezoelectric thin film is strongly influenced by the crystal structure and surface roughness of the base, the base has a small mismatch (degree of lattice constant mismatch) with the crystal structure of the piezoelectric thin film, and the surface roughness. Is required to be small.

  However, on the other hand, characteristics such as piezoelectricity in the entire thin film may not necessarily be as excellent as the c-axis crystallinity (usually expressed by the half-value width of the X-ray rocking curve). This is considered due to the fact that the polarities of the columnar crystals are mixed. Further, the initial growth layer of AlN changes depending on the state of the base surface, and its piezoelectricity also changes.

For example, FIG. 1 shows measured data of frequency characteristics of a piezoelectric thin film resonator in the case of (a) an Al single layer as a lower electrode and (b) a Pt / Al laminated film as a lower electrode. The electromechanical coupling coefficient k ² (%) was 5.7 for the Al single layer and 4.9 for the Pt / Al laminated film.

In recent years, in information communication, as a filter characteristic required for a mobile phone and a wireless LAN system, a wide band, a low loss, and a high acoustic quality factor Q are required. In order to realize this with the BAW resonator, the piezoelectric thin film is required to increase the electromechanical coupling coefficient k ² by extracting the piezoelectricity of the bulk body, and the electrode material has a low resistance and a high Q. (With large acoustic impedance) is required.

  In view of such circumstances, the present invention is intended to provide a piezoelectric thin film resonator that improves the orientation of a piezoelectric thin film, has a large electromechanical coupling coefficient, and has a high acoustic quality factor Q, and a method for manufacturing the same.

  In order to solve the above problems, the present invention provides a piezoelectric thin film resonator having the following configuration.

The piezoelectric thin film resonator includes a substrate, a pair of electrodes arranged along the substrate, and a piezoelectric thin film sandwiched between the pair of electrodes, and one of the electrodes is supported by the substrate, and at least the piezoelectric A portion of the thin film sandwiched between the pair of electrodes is of a type acoustically separated from the substrate. The one electrode is a first conductive layer, a polarity control layer that is disposed between the first conductive layer and the piezoelectric thin film, and is made of a metal having a standard unipolar potential lower than that of the first conductive layer. Including. The polarity control layer has an oxide film on the piezoelectric thin film side. The piezoelectric thin film is an AlN film.

According to the above configuration, the polarity can be improved by aligning the polarity direction of the piezoelectric thin film by the polarity control layer. Since AlN has a high sound velocity, it is suitable for obtaining a piezoelectric thin film resonator having a resonance frequency of 2 GHz to 5 GHz.

Preferably, the thickness of the polarity control layer is 3% or less of the elastic wave wavelength and 5 nm or more .

With the introduction of polarity control layer within the above thickness range, the effect of improving the electromechanical coupling coefficient k ² is obtained.

Preferably, before Symbol polarity control layer is made of a conductive material having a face-centered cubic structure or a hexagonal close-packed structure.

In the above structure, the electrode material of the face-centered cubic structure or a hexagonal close-packed structure, since it is AlN film and the lattice matching, it is possible to improve the orientation of the AlN film formed thereon.

  Preferably, the polarity control layer is Al or Ti.

  According to the above configuration, Al in the polarity control layer is a crystal having a face-centered cubic structure, and Ti has a hexagonal close-packed structure, and lattice matching with the piezoelectric thin film having the hexagonal close-packed structure is better.

  Preferably, the one of the electrodes has a second conductive layer between the first conductive layer and the substrate. The acoustic impedance of the second conductive layer is lower than the acoustic impedance of the first conductive layer. The resistivity of the second conductive layer is smaller than the resistivity of the first conductive layer.

  According to the said structure, the electrode resistance of one electrode supported by the board | substrate can be made small.

  Preferably, the first conductive layer is Pt, and the second conductive layer is Al.

  According to the above configuration, one of the Al / Pt electrodes can improve the piezoelectricity.

  Preferably, at least one between the substrate and the second conductive layer, between the second conductive layer and the first conductive layer, and between the first conductive layer and the polarity control layer. One of them is provided with any adhesion layer selected from Ti, Cr, Ni, NiCr, and Ta.

  According to the above configuration, film peeling can be reduced by the adhesion layer.

  Preferably, the thin film portion is disposed along the substrate with a gap provided between the thin film portion and the substrate. The one electrode is supported by the substrate around the gap.

  According to the above configuration, the thin film portion can be acoustically separated from the substrate by the gap.

  Preferably, the substrate has a recess formed on at least one main surface. The one of the electrodes is supported by the main surface of the substrate around the recess. The thin film portion is disposed away from the substrate via the recess.

  According to the above configuration, the thin film portion can be acoustically separated from the substrate by the recess.

  Preferably, at least one layer each including a relatively low acoustic impedance layer and a relatively high acoustic impedance layer is disposed between the thin film portion and the substrate.

  According to the said structure, the sound from a thin film part is reflected by the layer with a relatively low acoustic impedance and a relatively high layer arrange | positioned alternately. As a result, the thin film portion can be acoustically separated from the substrate.

  The present invention also provides a piezoelectric filter using the piezoelectric thin film resonator having any one of the above configurations. Since this piezoelectric filter uses a piezoelectric thin film resonator that improves the orientation of the piezoelectric thin film, has a large electromechanical coupling coefficient, and has a high acoustic quality factor Q, it is easy to achieve desired resonance characteristics.

  The present invention also provides a duplexer using the piezoelectric thin film resonator piezoelectric filter having any one of the above-described configurations. This duplexer can easily have a desired frequency characteristic.

  The present invention also provides the following method for manufacturing a piezoelectric thin film resonator.

  A method of manufacturing a piezoelectric thin film resonator includes a substrate, a pair of electrodes arranged along the substrate, and a piezoelectric thin film sandwiched between the pair of electrodes, and one of the electrodes is supported by the substrate, In the method of manufacturing a piezoelectric thin film resonator, at least a portion of the piezoelectric thin film sandwiched between the pair of electrodes is acoustically separated from the substrate. The method of manufacturing the piezoelectric thin film resonator includes a first step of forming the one electrode so as to be supported by the substrate, and a second step of forming the piezoelectric thin film on the one electrode. And forming the other electrode on the piezoelectric thin film. The first step includes a step of depositing a first metal to form a first conductive layer, and a second metal having a standard unipolar potential lower than that of the first metal in the first conductive layer. Vapor-depositing and forming a polarity control layer. The second step includes a piezoelectric thin film forming step of forming the piezoelectric thin film on the polarity control layer. After the first step and before the piezoelectric thin film forming step, by heating the substrate under a pressure higher than the pressure before the film formation start in the piezoelectric thin film forming step, the polarity control layer It includes an oxide film forming step of growing an oxide film on the piezoelectric thin film side.

  According to the above method, by growing the oxide layer on the piezoelectric thin film side of the polarity control layer in the oxide film forming step, the polarities of the piezoelectric thin film can be easily uniformed, and the piezoelectricity can be improved. The oxide film formation process can be introduced without complicating the process.

  According to the present invention, it is possible to provide a piezoelectric thin film resonator that improves the orientation of the piezoelectric thin film, has a large electromechanical coupling coefficient, and has a high acoustic quality factor Q, and a manufacturing method thereof.

  Hereinafter, examples of the present invention will be described with reference to FIGS.

Example 1
The piezoelectric thin film resonator 10 according to the first embodiment will be described with reference to FIGS. 3, 9, and 10.

  FIG. 3 is a main part sectional view schematically showing the structure of the piezoelectric thin film resonator 10. In the piezoelectric thin film resonator 10, a lower electrode layer 14, a polarity control layer 15, a piezoelectric thin film 16, an upper electrode 17, an upper thickening electrode (not shown), and a protective layer 18 are sequentially laminated on a substrate 12. .

  As the substrate 12, a Si substrate is used. In the substrate 12, a cavity 13 is formed adjacent to a vibrating portion where the electrodes 14, 15; 17 face each other and sandwich the piezoelectric thin film 16, so that the vibrating portion is acoustically separated from the substrate 12. Yes. The cavity 13 is formed after the layers are stacked on the substrate 12.

  The piezoelectric thin film resonator 10 is manufactured as follows.

  First, the lower electrode layer 14 is formed on the substrate 12 by a film formation method such as vapor deposition or sputtering, and electrode materials (alloy, alloy) such as Pt, Ir, Al, Mo, W, Ti, Cr, Co, and Ru. Including a multilayer film).

  Next, a conductive material (including an alloy) that easily forms an oxide film on the surface of Al, Ti, Ru, Cr, Zn, Fe, Ni, or the like is formed on the lower electrode layer 14 as the polarity control layer 15. . As a patterning method, methods such as lift-off, dry etching, and wet etching are used.

The thickness of the polarity control layer 15 is preferably about 3% or less of the elastic wave wavelength at the operating frequency of the piezoelectric thin film resonator 10. The acoustic wave wavelength; λ is defined by the following equation (1), where v is the speed of sound in the solid (polarity control layer 15) and f is the operating frequency of the piezoelectric thin film resonator 10.
λ = v / f (1)

  For example, when the polarity control layer 15 is Al and the operating frequency of the piezoelectric thin film resonator 10 is f = 5.4 GHz, the sound velocity of Al is V = 6295 m / sec, and the elastic wave wavelength is λ = 1.166 μm. The materials used for the polarity control layer 15 and the sound speed thereof are Ti: 6337 m / sec), Ta: 3965 m / sec, Ni: 5331 m / sec, NiCr (6: 4): 5947 m / sec, except for Al.

When the polarity control layer 15 is Al and the operating frequency of the piezoelectric thin film resonator 10 is f = 5.4 GHz, as shown in FIG. 9, as the film thickness ratio of the polarity control layer 15 to the elastic wave wavelength increases, the piezoelectric thin film resonance The electromechanical coupling coefficient of the child 10 is lowered. If the film thickness of the polarity control layer 15 with respect to the acoustic wave wavelength is about 3%, it is about the same as the maximum electromechanical coupling coefficient (indicated by a dotted line in FIG. 9) when the polarity control layer 15 is not provided. If the thickness of the polarity control layer 15 with respect to the elastic wave wavelength is 3% or less, the electromechanical coupling coefficient can be improved by providing the polarity control layer 15.

  The polarity control layer 15 may be formed on a part of the lower electrode layer 14, but is formed at least on a part that becomes a vibration part.

  The material of the polarity control layer 15 is preferably a material having a standard unipolar potential smaller than that of the electrode material of the lower electrode layer 14. The standard monopolar potential is a monopolar potential when the metal ion concentration is 1 mol / liter, and the temperature is 25 ° C. as a standard. For example, the standard unipolar potential (25 ° C.) of Al is +1.67 volts. The standard unipolar potential of Pt (25 ° C.) is −1.2 volts.

  In a particularly preferred embodiment, after a resist pattern is formed on the substrate 12 with a photoresist, Ti, Pt, Ti, and Al are sequentially deposited as the lower electrode layer 14 and the polarity control layer 15 by an evaporation method. Thereafter, the resist is removed to lift off, and lower electrodes 14 and 15 having desired shapes are formed. Ti is an adhesion layer that reinforces bonding between layers. The Ti film thickness is about 1 nm to 100 nm, the Pt film thickness is about 1 nm to 500 nm, and the Al film thickness is about 1 nm to 5000 nm.

  Next, ZnO, AlN, CdS, lead titanate, lead zirconate titanate, or the like is formed as a piezoelectric thin film 16 on the oxide film of the polarity control layer 15 by a deposition method such as vapor deposition, sputtering, or CVD. Form. In particular, an AlN film is formed using an RF magnetron sputtering method. The AlN film thickness is about 10 nm to about 3000 nm. The piezoelectric thin film 16 is formed on at least the polarity control layer 15.

Next, a window is opened in the piezoelectric thin film 16 in order to take out the pad portion of the lower electrode layer 14 or the polarity control layer 15. As a method for opening the window, wet etching, dry etching, lift-off using a sacrificial layer, or the like is used. For example, in wet etching, strong alkali such as TMAH, KOH, or NaOH is used as an etchant. Cl ₂ may be dry etching using a reactive gas mainly composed of. As the mask material, a single metal such as Ti, Cr, Ni, Au, Pt or the like, a multilayer metal, an alloy, a photoresist, or an organic resin is used. In particular, a lift-off method using ZnO as a sacrificial layer material or a wet etching method using a strong alkaline aqueous solution using a metal or resin as a mask is desirable.

  Next, the upper electrode 17 is formed in the same manner as the lower electrode layer 14.

  Next, in order to lower the resistance of the wiring, a metal mainly composed of Al, Cu or the like is deposited as an upper thickening electrode (not shown) on the wiring part other than the vibration part. The upper thick electrode is multilayered with materials such as Al, Ti, NiCr, Cr, Au, Pt to prevent oxidation and diffusion, and in particular, Al / Ti, Al / Ti / Cu / Ti, Pt / Ti / Cu / A structure such as Ti is desirable.

Next, a film such as SiO ₂ , SiN, or SiON is formed as the protective layer 18 by a film forming method such as sputtering, vapor deposition, or CVD. Thereafter, in order to take out the pad portion, a window is opened using wet etching or dry etching. In particular, SiO ₂ is formed by RF magnetron sputtering, a portion other than the window opening portion is protected with a resist using a photolithography technique, and wet etching is performed with an etchant containing HF as a main component. The film thickness of SiO ₂ is about 10 nm to 3 μm. The SiO ₂ film can be used for improving the moisture resistance of the element, improving the frequency temperature characteristics for having a positive temperature coefficient, and shaving by RIE, milling or wet etching after the element is completed, and adjusting the operating frequency.

Next, a portion adjacent to the vibrating portion of the substrate 12 is removed by a technique such as wet etching or dry etching to form the cavity 13. In the case of wet etching, etching is performed with an etchant such as KOH, TMAH, or hydrofluoric acid using SiO ₂ or SiN as a mask. In the case of dry etching, the _photoresist, SiO 2, SiN, Cr, as a mask such as _Ni, and simple gases such as SF 6, CF _4, a gas mixture of _{O 2} and CHF ₃ in SF ₆ and CF ₄ CCP (Capacitively Coupled Plasma) -RIE, ICP (Inductively Coupled Plasma) -RIE, ECR (Electron Cyclotron Resonance) -RIE, RIBE (Reactive B).

  The cavity 13 is formed by wet etching so as to leave about 20 nm of Si before element formation, etching the remaining Si by dry etching after element formation, and etching Si using ICP-RIE after element formation. As a method, a method in which the element surface is protected with resin or metal after element formation and wet etching with TMAH or KOH is combined with a method in which wet etching and dry etching are combined.

  Next, a method for forming an oxide film on the polarity control layer 15 will be described.

For example, after the Al film of the polarity control layer 15 is formed with a thickness of 10 nm, the AlN film formation start pressure (in the vacuum chamber until the start of film formation of the AlN to be the piezoelectric thin film 16 in the vacuum chamber is started ( Substrate heating is performed at 250 ° C. for about 2 hours in a pressure range of 1 Pa to 5 × 10 ⁻⁴ Pa, which is higher than the back pressure. Thereby, an Al oxide film is grown on the Al film surface of the polarity control layer 15 to a thickness of about 5 nm. Thereafter, vacuuming is performed until a pressure lower than 5 × 10 ⁻⁴ Pa is reached. Next, for example, AlN is deposited at a gas pressure of 0.2 Pa. This Al oxide film forming step is performed while the substrate is put in the vacuum chamber and evacuated to the film formation start pressure, so that a new step need not be introduced.

  FIG. 10 is a TEM photograph of the Al polarity control layer. The Al polarity control layer 15 has an oxide film (film thickness 5 nm) formed on the surface thereof, and an AlN piezoelectric thin film 16 is formed through the oxide film. When Al and N particles (in this case, all of ions, radicals, and neutral particles) flying during the AlN film formation reach the substrate surface, an oxide film of the Al polarity control layer 15 is formed on the surface. Therefore, it is presumed that the Al particles first bind, then the N particles, and then the Al particles, regularly grow easily, and as a result, the polarities are uniform.

  The same effect can be obtained by forming an oxide film on the polarity control layer 15 by another method. For example, heating is performed with a RTA (Rapid Thermal Annealing) apparatus or the like at a low vacuum before forming the AlN film. Alternatively, an AlN load lock type film forming apparatus is used, and after putting a sample into the film forming chamber, the degree of vacuum is lowered and oxygen gas is introduced to perform heating.

  AlN c-axis alignment films do not necessarily exhibit the same orientation even if they have the same rocking curve half-width. This is because the polarities of the columnar crystals constituting the film are mixed in the reverse direction. In Example 1, as a means for aligning the polarities of the columnar crystals, a configuration of AlN / Al / Pt (piezoelectric thin film / base metal / noble metal) was formed from the piezoelectric thin film side on the lower electrode side. In this case, an oxide layer can be formed on the Al surface before forming the AlN film, and the polarity of AlN grown thereon can be made uniform.

By polar c-axis direction of AlN are aligned, for improving the piezoelectricity of the thickness longitudinal electromechanical coupling coefficient k ₂ is large, high acoustic quality factor Q, broadband, resonance characteristics of low loss can be obtained A filter having a wide pass bandwidth can be produced.

(Modification)
A piezoelectric thin film resonator 10a according to a modification of the first embodiment will be described with reference to FIGS.

  The piezoelectric thin film resonator 10a is configured in substantially the same manner as the piezoelectric thin film of Example 1. In the following, the same reference numerals are used for the same components, and differences will be mainly described.

  As shown in FIG. 13, the lower electrode formed on the substrate 12 includes two conductive layers 14a and 14b. A second conductive layer 14b is disposed between the first conductive layer 14a on the piezoelectric thin film 16 side and the Si substrate 12. The resistivity of the second conductive layer 14b is made smaller than the resistivity of the first conductive layer 14a, and the electrode resistance of the lower electrode is reduced. For example, Pt is used for the first conductive layer 14a, Al is used for the second conductive layer 14b, Al is used for the polarity control layer 15, and AlN is used for the piezoelectric thin film 16.

  In a particularly preferred embodiment, after a resist pattern is formed on the substrate 12 with a photoresist, Ti, Al, Ti, Pt, Ti, and Al are sequentially deposited by vapor deposition as the conductive layers 14b and 14a and the polarity control layer 15. Thereafter, the resist is removed to lift off, and lower electrodes 14 and 15 having desired shapes are formed. Ti is an adhesion layer that reinforces bonding between layers. The Ti film thickness is about 1 nm to 100 nm, the Pt film thickness is about 1 nm to 500 nm, and the Al film thickness is about 1 nm to 5000 nm.

  FIG. 2 shows the measurement result of the X-ray rocking curve of the piezoelectric thin film. In FIG. 2C, the curve indicated by reference numeral (a) is a comparative example 2 of the configuration of FIG. 2A, and the curve indicated by reference numeral (b) is a modification of the configuration of FIG. Show. In Comparative Example 2 in FIG. 2A, Al (film thickness 70 nm), Pt (film thickness 30 nm), and AlN (film thickness 500 nm) are formed on the Si substrate. In the modification of FIG. 2B, an Al polarity control layer (10 nm) is added to Comparative Example 2. Although not shown, a 10-nm-thick Ti adhesion layer is formed between the layers. FIG. 2C shows that the half width is 3.5 ° in the comparative example 2 and 2.9 ° in the modified example, and the orientation of AlN is improved by the Al polarity control layer.

  For example, the film configuration of a piezoelectric thin film resonator operating in the 5 GHz band is Al (30 nm) / Ti (10 nm) / Pt (100 nm) / Ti (15 nm) / AlN (500 nm) / Al from the air side to the substrate 12 side. (10 nm) / Ti (10 nm) / Pt (30 nm) / Ti (10 nm) / Al (70 nm) / Ti (10 nm). Ti (10 nm) is used as an adhesion layer.

  Other embodiments will be described below. Also in the following other examples, the same effects as those of the first example can be obtained. Also, in the following embodiments, the lower electrode may be configured as in the modification of the first embodiment.

(Example 2)
The piezoelectric thin film resonator 20 according to the second embodiment will be described with reference to FIG.

The piezoelectric thin film resonator 20 is an air gap type. A sacrificial layer material such as SOG, Ge, porous silicon, polysilicon, Zn0, Cu, and Al is formed on the Si substrate 22, and a portion that becomes the void 23 under the vibration portion is formed by a technique such as wet etching or dry etching. Then, it is planarized using a technique such as etching and polishing, and the lower electrode layer 24, the polarity control layer 25, the piezoelectric thin film 26, the upper electrode 27, and the SiO ₂ film 28 are formed by the same method as in the first embodiment. Finally, the sacrificial layer material is removed by wet etching or dry etching, thereby forming a gap 23 under the vibration part.

(Example 3)
The piezoelectric thin film resonator 30 according to the third embodiment will be described with reference to FIG.

The piezoelectric thin film resonator 30 is a sacrificial layer type. On the Si substrate 32, a concave portion 33 to be a void 33 is formed by a method such as anisotropic etching, dry etching, sand blasting, etc., and SOG, Ge, porous silicon, polysilicon, ZnO, Cu, A sacrificial layer material such as Al is embedded, and is made the same height as the substrate surface by using a polishing method such as CMP. Thereafter, the lower electrode layer 34, the polarity control layer 35, the piezoelectric thin film 36, the upper electrode 37, and the SiO ₂ film 38 are formed by the same method as in the first embodiment. Finally, the material embedded in the recess 33 is removed by wet etching or dry etching, so that the vibration part is floated and acoustically separated from the Si substrate 32.

Example 4
A piezoelectric thin film resonator 40 of Example 4 will be described with reference to FIG.

The piezoelectric thin film resonator 40 is an insulating material acoustic reflection type. On the Si substrate 42, as an acoustic reflection structure that acoustically separates the vibration part from the Si substrate, layers 43a and 43b of a material with high acoustic impedance and layers 43s and 43t of a material with a low acoustic impedance are alternately arranged. One or more layers are formed. In particular, W is used as a material with high acoustic impedance, and SiO ₂ is used as a low material. Thereafter, the lower electrode layer 44, the polarity control layer 45, the piezoelectric thin film 46, the upper electrode 47, and the SiO ₂ film 48 are formed by the same method as in the first embodiment.

(Example 5)
A piezoelectric thin film resonator 50 of Example 5 will be described with reference to FIG.

  The piezoelectric thin film resonator 50 is a conductive material acoustic reflection type. On the Si substrate 52, at least one or more layers of material layers 53a and 53b with high acoustic impedance and material layers 53s and 53t with low acoustic impedance are alternately formed as an acoustic reflection structure. In particular, Pt is used as a material with high acoustic impedance, and Al is used as a low material. The acoustic reflection layers 53a, 53b, 53s, and 53t of the conductive material also serve as a lower electrode. Thereafter, the lower electrode layer 54, the polarity control layer 55, the piezoelectric thin film 56, and the upper electrode 57 are formed by the same method as in the first embodiment.

(Example 6)
The piezoelectric thin film resonator 60 of Example 6 will be described with reference to FIG.

  The piezoelectric thin film resonator 60 is an upper and lower conductive material acoustic reflection type. On the Si substrate 62, at least one or more layers of material layers 63a and 63b with high acoustic impedance and material layers 63s and 63t with low acoustic impedance are alternately formed as an acoustic reflection structure. In particular, Pt is used as a material with high acoustic impedance, and Al is used as a low material. The acoustic reflection layers 63a, 63b, 63s, and 63t of the conductive material also serve as a lower electrode. Thereafter, the lower electrode layer 64, the polarity control layer 65, the piezoelectric thin film 66, and the upper electrode 67 are formed by the same method as in the first embodiment. Next, the conductive material layers 68a and 68b having a high acoustic impedance and the conductive material layers 68s and 68t having a low acoustic impedance are alternately formed at least one each to form an upper acoustic reflection layer.

  The piezoelectric thin film resonators 10, 20, 30, 40, 50, and 60 of Examples 1 to 6 (including modifications) described above improve the orientation of the piezoelectric thin film and increase the electromechanical coupling coefficient. The acoustic quality factor Q can be increased.

(Example 7)
FIG. 11 is a circuit diagram of the piezoelectric filter of the seventh embodiment.

  The piezoelectric filter 70 is configured using the piezoelectric thin film resonators of Examples 1 to 6 (including modifications). As shown in FIG. 11, the piezoelectric filter 70 is an L-type ladder filter in which one series piezoelectric thin film resonator 72 and one parallel piezoelectric thin film resonator 74 are ladder-connected in an L shape.

  Since the filter 70 uses the piezoelectric thin film resonators 72 and 74 that improve the orientation of the piezoelectric thin film, have a large electromechanical coupling coefficient, and have a high acoustic quality factor Q, it is easy to achieve desired resonance characteristics.

(Example 8)
FIG. 12 is a circuit diagram of the duplexer 80 of the eighth embodiment.

  The duplexer 80 is provided with an antenna terminal 82, a reception side terminal 84, and a transmission side terminal 86. The duplexer 80 includes a piezoelectric filter that passes only the reception frequency band and attenuates the transmission frequency band between the reception-side terminal 84 and the antenna terminal 82. In addition, a piezoelectric filter is provided between the transmission side terminal 86 and the antenna terminal 82 to pass only the transmission frequency band and attenuate the reception frequency band. These piezoelectric filters included in the duplexer 80 are constituted by any one of the piezoelectric thin film resonators according to the first to sixth embodiments (including modifications). Since the duplexer 80 uses a piezoelectric filter that can easily achieve a desired resonance characteristic, it is easy to obtain a desired frequency characteristic.

  The present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

It is a graph of a frequency characteristic. (A), (b) is a block diagram of a measuring object, (c) is an X-ray rocking curve. (Comparative example, modified example) It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. Example 1 It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. (Example 2) It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. (Example 3) It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. Example 4 It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. (Example 5) It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. (Example 6) It is a graph which shows the relationship between the film thickness of a polarity control layer, and an electromechanical coupling coefficient. Example 1 It is a TEM photograph near the interface between a piezoelectric thin film and a polarity control layer. Example 1 It is a circuit diagram of a ladder filter. (Example 8) It is a circuit diagram of a duplexer. Example 9 It is principal part sectional drawing which shows the structure of a piezoelectric thin film resonator typically. (Modification)

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric thin film resonator 12 Substrate 13 Cavity 14 Lower electrode layer (one electrode)
15 Polarity control layer (one electrode)
16 Piezoelectric thin film 17 Upper electrode 20 Piezoelectric thin film resonator 22 Substrate 23 Void 24 Lower electrode layer (one electrode)
25 Polarity control layer (one electrode)
26 Piezoelectric thin film 27 Upper electrode 30 Piezoelectric thin film resonator 32 Substrate 33 Recess 34 Lower electrode layer (one electrode)
35 Polarity control layer (one electrode)
36 Piezoelectric thin film 37 Upper electrode 40 Piezoelectric thin film resonator 42 Substrate 43a, 43b, 43s, 43t Acoustic reflection layer 44 Lower electrode layer (one electrode)
45 Polarity control layer (one electrode)
46 Piezoelectric thin film 47 Upper electrode 50 Piezoelectric thin film resonator 52 Substrate 53a, 53b, 53s, 53t Acoustic reflection layer 54 Lower electrode layer (one electrode)
55 Polarity control layer (one electrode)
56 Piezoelectric thin film 57 Upper electrode 60 Piezoelectric thin film resonator 62 Substrate 63a, 63b, 63s, 63t Acoustic reflection layer 64 Lower electrode layer (one electrode)
65 Polarity control layer (one electrode)
66 Piezoelectric thin film 67 Upper electrode 68a, 68b, 68s, 68t Acoustic reflection layer

Claims (13)

A substrate,
A pair of electrodes disposed along the substrate;
A piezoelectric thin film sandwiched between the pair of electrodes,
One of the electrodes is supported by the substrate;
A piezoelectric thin film resonator in which at least a portion between the pair of electrodes of the piezoelectric thin film is acoustically separated from the substrate,
The one of the electrodes is
A first conductive layer;
A polarity control layer disposed between the first conductive layer and the piezoelectric thin film and made of a metal having a standard unipolar potential lower than that of the first conductive layer;
Polar control layer have a oxide film on the piezoelectric thin film side,
The piezoelectric thin-film resonator in which the piezoelectric thin film and said AlN Makudea Rukoto. The piezoelectric thin film resonator according to claim 1, wherein the thickness of the polarity control layer is 3% or less of an elastic wave wavelength and 5 nm or more .   The piezoelectric thin film resonator according to claim 1 or 2, wherein the polarity control layer is made of a conductive material having a face-centered cubic structure or a hexagonal close-packed structure.   4. The piezoelectric thin film resonator according to claim 1, wherein the polarity control layer is made of Al or Ti. The one of the electrodes has a second conductive layer between the first conductive layer and the substrate,
The acoustic impedance of the second conductive layer is lower than the acoustic impedance of the first conductive layer;
5. The piezoelectric thin film resonator according to claim 1, wherein the resistivity of the second conductive layer is smaller than the resistivity of the first conductive layer. 6.   6. The piezoelectric thin film resonator according to claim 1, wherein the first conductive layer is Pt and the second conductive layer is Al.   At least one between the substrate and the second conductive layer, between the second conductive layer and the first conductive layer, and between the first conductive layer and the polarity control layer, 6. The piezoelectric thin film resonator according to claim 1, further comprising an adhesion layer selected from Ti, Cr, Ni, NiCr, and Ta. The thin film portion is disposed along the substrate with a gap between the thin film portion and the substrate.
8. The piezoelectric thin film resonator according to claim 1, wherein the one electrode is supported by the substrate around the gap. 9. The substrate has a recess formed on at least one main surface,
The one electrode is supported by the main surface of the substrate around the recess,
The piezoelectric thin film resonator according to any one of claims 1 to 7, wherein the thin film portion is disposed apart from the substrate via the concave portion.   8. The method according to claim 1, further comprising at least one layer each including a relatively low acoustic impedance layer and a relatively high acoustic impedance layer disposed between the thin film portion and the substrate. The piezoelectric thin film resonator according to any one of the above.   A piezoelectric filter using the piezoelectric thin film resonator according to any one of claims 1 to 10.   A duplexer using the piezoelectric thin film resonator according to claim 1 or the piezoelectric filter according to claim 11. A substrate,
A pair of electrodes disposed along the substrate;
A piezoelectric thin film sandwiched between the pair of electrodes;
Including
One of the electrodes is supported by the substrate;
A method of manufacturing a piezoelectric thin film resonator, wherein at least a portion sandwiched between the pair of electrodes of the piezoelectric thin film is acoustically separated from the substrate,
A first step of forming the one electrode so as to be supported by the substrate;
A second step of forming the piezoelectric thin film on the one electrode;
Forming the other electrode on the piezoelectric thin film,
The first step includes
Depositing a first metal to form a first conductive layer;
Forming a polarity control layer by evaporating a second metal having a lower standard unipolar potential than the first metal on the first conductive layer;
The second step includes a piezoelectric thin film forming step of forming the piezoelectric thin film on the polarity control layer,
After the first step and before the piezoelectric thin film forming step,
Including an oxide film forming step of growing an oxide film on the piezoelectric thin film side of the polarity control layer by heating the substrate under a pressure higher than a pressure before starting the film formation in the piezoelectric thin film forming step. A method for manufacturing a piezoelectric thin film resonator.