WO2023190677A1 - 音響多層膜、高周波フィルタデバイス、及びバルク弾性波フィルタデバイス - Google Patents

音響多層膜、高周波フィルタデバイス、及びバルク弾性波フィルタデバイス Download PDF

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WO2023190677A1
WO2023190677A1 PCT/JP2023/012784 JP2023012784W WO2023190677A1 WO 2023190677 A1 WO2023190677 A1 WO 2023190677A1 JP 2023012784 W JP2023012784 W JP 2023012784W WO 2023190677 A1 WO2023190677 A1 WO 2023190677A1
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layer
multilayer film
acoustic
dividing
acoustic multilayer
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French (fr)
Japanese (ja)
Inventor
優津希 青木
大輔 中村
岳 圓岡
愛美 黒瀬
広宣 待永
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Nitto Denko Corp
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Nitto Denko Corp
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Priority to JP2024512672A priority patent/JPWO2023190677A1/ja
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H03H9/02133—Means for compensation or elimination of undesirable effects of stress
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02157—Dimensional parameters, e.g. ratio between two dimension parameters, length, width or thickness
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
    • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
    • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
    • H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/175—Acoustic mirrors

Definitions

  • the present invention relates to an acoustic multilayer film, a high frequency filter device, and a bulk acoustic wave filter device.
  • the 5G mobile communication standard uses a frequency band close to 6 GHz called "sub-6" and a 28 GHz band, and the use of a 100 GHz band is also being considered in the future. Therefore, resonators and bandpass filters suitable for high frequencies exceeding several GHz are required.
  • BAW resonators or BAW filters that utilize bulk acoustic waves (BAW) are used in resonators of electronic devices such as smartphones and high frequency filters of communication devices.
  • a BAW filter filters high frequencies by utilizing the piezoelectric effect of a piezoelectric layer sandwiched between an upper electrode and a lower electrode.
  • the resonance energy leaks to the substrate side during filtering, the waves reflected at the interface of the substrate adversely affect the resonance characteristics.
  • an acoustic multilayer film in which low acoustic impedance layers and high acoustic impedance layers are alternately laminated is used as an acoustic mirror.
  • a method is known in which the acoustic multilayer film is divided into a plurality of regions by dicing in the in-plane direction (for example, see Patent Document 1).
  • a configuration is known in which an acoustic multilayer film is formed on one side of the substrate and a compressive stress film is provided on the opposite side of the substrate to offset the compressive stress generated in the acoustic multilayer film (for example, patented (See Reference 2).
  • acoustic multilayer films metal thin films are used as high acoustic impedance layers.
  • the total thickness of the high acoustic impedance layer is 1 ⁇ m or more, and peeling from the substrate, cracking, etc. occur due to the surface roughness and stress of the metal.
  • Patent Document 1 in order to relieve stress, an acoustic multilayer film is separated into a plurality of regions within a plane by dicing. When a piezoelectric (or resonant) element is formed due to the remaining diced film and the reattachment of generated film pieces, there is a concern that characteristics may be deteriorated due to short-circuiting of electrodes or foreign matter.
  • One aspect of the present invention is to provide an acoustic multilayer film with reduced stress, a high frequency filter device using the same, and a bulk acoustic wave filter device.
  • the acoustic multilayer film includes, on a support substrate, a first layer having a first specific acoustic impedance and a second layer having a specific acoustic impedance lower than the first specific acoustic impedance. Two or more pairs are stacked alternately, At least one of the first layers of the acoustic multilayer film is divided in the stacking direction by dividing layers.
  • the dividing layer included in the first layer has an acoustic impedance lower than the first specific acoustic impedance.
  • An acoustic multilayer film with reduced stress and a high frequency filter device using the same are realized.
  • FIG. 1 is a schematic diagram of a laminate including an acoustic multilayer film of an embodiment.
  • 2 is a schematic diagram of a high frequency filter device using the acoustic multilayer film of FIG. 1.
  • FIG. FIG. 3 is a diagram showing the relationship between the film thickness of a dividing layer and filter characteristics. It is a figure showing the surface roughness of an acoustic multilayer film when there is no dividing layer. It is a figure which shows the surface roughness of the acoustic multilayer film when the thickness of a division layer is 1 nm. It is a figure which shows the surface roughness of the acoustic multilayer film when the thickness of a division layer is 2 nm.
  • FIG. 3 is a diagram showing specifications and filter characteristics of acoustic multilayer films of Examples and Comparative Examples. It is a figure showing film-forming conditions of an acoustic multilayer film.
  • a dividing layer is inserted into at least one of the high acoustic impedance layers constituting the acoustic multilayer film, and the high acoustic impedance layer is divided in the lamination direction.
  • the dividing layer is preferably amorphous.
  • the dividing layer may be formed of metal oxide, metal nitride, metal oxynitride, or the like. From the viewpoint of stress relaxation and maintaining crystallinity of the acoustic multilayer film, it is preferable that the number of dividing layers inserted into the high acoustic impedance layer is two or more.
  • FIG. 1 is a schematic diagram of a laminate 20 including an acoustic multilayer film 18 according to an embodiment.
  • the laminate 20 has a support substrate 11 and an acoustic multilayer film 18 provided on the support substrate 11.
  • the acoustic multilayer film 18 includes two or more pairs of a first layer 16 having a predetermined specific acoustic impedance and a second layer 17 having a lower specific acoustic impedance than the first layer, which are alternately laminated.
  • the first layer 16 has a higher specific acoustic impedance than the second layer 17, for convenience, the first layer will be referred to as the "high acoustic impedance layer 16" and the second layer will be referred to as the "low acoustic impedance layer 17". call.
  • a dividing layer 162 is inserted into at least one of the high acoustic impedance layers 16 to divide the high acoustic impedance layer 16 into a plurality of sublayers 161 in the stacking direction.
  • the main role of the dividing layer 162 is to maintain good surface smoothness of the sublayer 161 and improve the crystal orientation of active elements such as resonators provided in the upper layer. Since high acoustic impedance materials are generally hard and have poor shape conformability, they do not function as a dividing layer, so the specific acoustic impedance of the dividing layer 162 is equal to or smaller than the specific acoustic impedance of the high acoustic impedance layer 16. This is desirable.
  • the sublayer 161 and the dividing layer 162 that constitute the high acoustic impedance layer 16 may be successively formed by sputtering or the like. By inserting the dividing layer 162 into the high acoustic impedance layer 16, the crystal state of the underlying sublayer 161 can be reset, and the laminated high acoustic impedance layer 16 as a whole can maintain a good crystal state.
  • the sublayer 161 of the high acoustic impedance layer 16 is formed of a material with high density or bulk modulus, such as tungsten (W), molybdenum (Mo), tantalum oxide (Ta2O5), and zinc oxide (ZnO).
  • High acoustic impedance layer 16 may have good thermal conductivity.
  • the dividing layer 162 inserted into the high acoustic impedance layer 16 is formed of a material having a lower density or bulk modulus than the high acoustic impedance layer 16 . From the viewpoint of resetting or improving the crystalline state of the sublayer 161, the dividing layer 162 is preferably an amorphous layer.
  • amorphous SiO 2 , Al 2 O 3 , WO 3 , MoO 3 , Si, or the like can be used.
  • the thickness of the dividing layer 162 is determined by the frequency of the elastic wave to be reflected by the acoustic multilayer film 18, that is, the resonant frequency of an active element such as a piezoelectric element or a resonator provided on the top of the acoustic multilayer film 18.
  • the "top" of the acoustic multilayer film 18 is the surface of the acoustic multilayer film 18 opposite to the support substrate 11.
  • the thickness of the splitting layer 162 is 1/3000 or more and I/55 or less of the wavelength ⁇ of the elastic wave, preferably 1/3000 or more and I/66 or less. It is. The basis for this range will be explained in detail later with reference to FIG.
  • the surface roughness Ra of the acoustic multilayer film 18 is 3 nm or less.
  • the surface roughness Ra is a deviation per unit area from the median value of the surface unevenness of the acoustic multilayer film 18.
  • the surface roughness Ra exceeds 3 nm, the orientation of the piezoelectric layer provided on the acoustic multilayer film 18 tends to deteriorate. Due to the disordered orientation of the piezoelectric layer, unnecessary vibration modes in the lateral direction occur, causing noise generation.
  • the basis of this surface roughness Ra will be described later with reference to FIGS. 4A to 4D.
  • the low acoustic impedance layer 17 is made of a material having a lower density or bulk modulus than the high acoustic impedance layer 16, such as SiO 2 , Al 2 O 3 , alumina silicate glass, or the like.
  • the low acoustic impedance layer 17 may be an amorphous layer or a predominantly amorphous oxide film such as SiO 2 or Al 2 O 3 .
  • the support substrate 11 is any substrate that can support the acoustic multilayer film 18.
  • a substrate such as quartz or glass may be used, a semiconductor substrate such as silicon (Si), or an inorganic dielectric substrate such as MgO or sapphire may be used.
  • a plastic substrate may be used.
  • PET polyethylene terephthalate
  • PEN polyethylene naphthalate
  • PC polycarbonate
  • acrylic resin acrylic resin
  • PI polyimide
  • thin film glass etc. May be used.
  • FIG. 2 is a schematic diagram of a high-frequency filter device 10 using the acoustic multilayer film 18 of FIG. 1.
  • the high-frequency filter device 10 is provided on the surface of the acoustic multilayer film 18 opposite to the support substrate 11, including a first electrode layer 12, a second electrode layer 14, and between the first electrode layer 12 and the second electrode layer 14. It has a piezoelectric layer 13.
  • the first electrode layer 12, the second electrode layer 14, and the piezoelectric layer 13 form a resonator 15, which is an active element.
  • the first electrode layer 12 and the second electrode layer 14 are made of a conductive material.
  • a conductive material For example, Mo, W, Pr, Au, Ru, Ir, Al, Cu, etc. may be used as the conductive material.
  • a material for the piezoelectric layer 13 wurtzite crystal, perovskite crystal, etc. can be used. A predetermined amount of an impurity element may be added as a subcomponent using these crystalline materials as the main component.
  • As the wurtzite piezoelectric material zinc oxide (ZnO), aluminum nitride (AlN), gallium nitride (GaN), etc. can be used.
  • the resonance vibration energy is reflected by the acoustic multilayer film 18.
  • the speed at which vibration waves (elastic waves) propagate through the high acoustic impedance layer 16 and the speed at which they propagate through the low acoustic impedance layer 17 are different.
  • the thickness of the film so that the reflected waves strengthen each other due to interference at the interfaces between the layers constituting the acoustic multilayer film 18, the resonance vibration energy is directed to the incident direction of the elastic wave without being affected by the support substrate 11. It can be returned.
  • the resonance energy reflected by the acoustic multilayer film 18 and returned to the resonator 15 is confined between the first electrode layer 12 and the second electrode layer 14, and extracted as an electrical signal by the first electrode layer 12 and the second electrode layer 14. It will be done. Since at least one of the high acoustic impedance layers 16 is divided into a plurality of sublayers 161 by the dividing layer 162, the surface smoothness of the high acoustic impedance layer 16 is improved and the crystal orientation of the piezoelectric layer 13 is improved. The vibration mode in the film thickness direction is maintained, and a high frequency filter device 10 with less noise is realized.
  • FIG. 3 shows the relationship between the thickness of the dividing layer 162 and filter characteristics. If the dividing layer 162 is inserted into the high acoustic impedance layer 16 from the viewpoint of stress relaxation in the acoustic multilayer film 18, the filter characteristics may change, and it is necessary to appropriately determine the thickness of the dividing layer 162. It is desirable that the filter characteristics of the high-frequency filter device 10 not be attenuated, but the passband of commercially available high-frequency filters is defined as a region of about -3 dB or less due to the influence of wiring resistance, etc. Approximately 3 dB is considered to be an acceptable range. The filter characteristics are estimated by simulation while changing the thickness of the dividing layer 162.
  • a high acoustic impedance layer 16 of W with a thickness of 655 nm and a low acoustic impedance layer 17 of SiO 2 with a thickness of 725 nm are placed on a supporting substrate 11 of quartz as an acoustic multilayer film 18.
  • Four dividing layers 162 are inserted into each of the high acoustic impedance layers 16, and the thicknesses of the dividing layers 162 are changed to 0 nm, 1 nm, 2 nm, 40 nm, 45 nm, and 55 nm. When the thickness of the dividing layer 162 is "0 nm", the dividing layer 162 is not provided.
  • the thickness of the dividing layer 162 is 1 nm and 2 nm, the same filter characteristics as the configuration without the dividing layer 162 are maintained, and the surface smoothness of the upper sublayer 161 is improved, so that the piezoelectric layer provided thereon is The crystal orientation of the layer 13 can be improved.
  • the thickness of the dividing layer 162 is 40 nm or 45 nm, the attenuation amount is smaller than 3 dB and does not have much influence on the filter characteristics.
  • the thickness of the dividing layer 162 is 55 nm, the attenuation amount is 3 dB, which is within the allowable limit.
  • the wavelength of a bulk elastic wave propagating in a medium is defined as (propagation sound velocity in the medium V [m/s])/(resonance frequency F [Hz]).
  • V [m/s] propagation sound velocity in the medium
  • F [Hz] resonance frequency
  • the wavelength ⁇ of the bulk elastic wave propagating in the W medium is approximately 2600 nm, and the propagation wave propagates in the SiO2 medium.
  • the wavelength of the bulk elastic wave is approximately 2979 nm.
  • the thickness of the splitting layer 162 is 1/3000 or more and 1/50 or less of the wavelength ⁇ . It is desirable that there be.
  • the thickness range of the dividing layer 162 will be described in more detail with reference to FIGS. 4A to 4D based on actually produced samples.
  • FIGS. 4A to 4D show the relationship between the thickness of the dividing layer 162 and the surface roughness of the acoustic multilayer film 18.
  • the thickness of the dividing layer 162 is 0 nm, 1 nm, 2 nm, and 29 nm, respectively.
  • the surface condition of the acoustic multilayer film 18 at each thickness of the dividing layer 162 is shown.
  • the dividing layer 162 is inserted to improve the surface smoothness of the upper sublayer 161. Therefore, from the viewpoint of surface smoothness, the thickness range of the dividing layer 162 will be examined.
  • acoustic multilayer film 18 is formed.
  • Four dividing layers 162 are inserted into each of the high acoustic impedance layers 16, and the thicknesses of the dividing layers 162 are changed to 0 nm, 1 nm, 2 nm, and 29 nm.
  • the thickness of the dividing layer 162 of "0 nm" corresponds to the configuration in which the dividing layer 162 of FIG. 4A is not provided.
  • the surface of the acoustic multilayer film 18 of each sample produced is observed in the tapping mode of an atomic force microscope (AFM), and the surface roughness Ra (arithmetic mean roughness) is measured.
  • the measurement range is an area of 1.0 ⁇ m ⁇ 1.0 ⁇ m.
  • the thickness of the dividing layer 162 is 1 nm and 2 nm in FIGS. 4B and 4C, surface uniformity is observed from the AFM image, and the surface roughness Ra of the acoustic multilayer film 18 is as small as 2 nm or less.
  • the thickness of the dividing layer 162 is 29 nm in FIG. 4D, the surface roughness Ra slightly exceeds 2 nm, but the surface smoothness is maintained.
  • the surface roughness of the acoustic multilayer film 18 is 3 nm or less.
  • the relationship between the thickness of the dividing layer 162 and the surface roughness Ra of the acoustic multilayer film 18 will be described in more detail with reference to FIG. 5.
  • FIG. 5 shows the specifications and filter characteristics of the acoustic multilayer film 18 of the example and the comparative example.
  • the specifications of the acoustic multilayer film 18 include the center frequency of resonance (GHz), the wavelength (nm) of the elastic wave propagating in the sublayer 161 of the high acoustic impedance layer 16, the material of the sublayer 161, and the thickness of one high acoustic impedance layer 16.
  • Filter characteristics are indicated by attenuation (dB) and crystal orientation (°). Observe the degree of film peeling or cracking as a factor that affects filter characteristics.
  • the crystal orientation is indicated by the FWHM of the peak waveform when the surface of the piezoelectric layer 13 is measured by the XRC method.
  • the piezoelectric layer 13 containing ZnO as a main component is formed on the acoustic multilayer film 18 via a metal electrode layer.
  • the crystal orientation is expressed by the FWHM value of the peak waveform of a rocking curve obtained when the fluctuation of the plane orientation from the (002) plane of the ZnO crystal is measured by the XRC method.
  • ZnO contained in the piezoelectric layer 13 has a wurtzite crystal structure, and the FWHM value indicates the degree of orientation of the crystals constituting the piezoelectric material in the c-axis direction.
  • the FWHM of the peak waveform of the rocking curve obtained by the XRC method is an index of the c-axis orientation of the piezoelectric layer 13.
  • the low acoustic impedance layer 17 was fixed to amorphous SiO 2 with a thickness of 725 nm, and the specifications of the high acoustic impedance layer 16 were variously changed to form a total of 10 samples of Examples 1 to 9 and Comparative Example 1.
  • a low acoustic impedance layer 17 common to all samples is formed by RF magnetron sputtering. After producing each sample, the surface roughness Ra is measured by AFM. Additionally, each sample is connected to a network analyzer to measure the attenuation characteristics.
  • Example 1 a silicon substrate is used as the substrate, the sublayer 161 of the high acoustic impedance layer 16 is made of W, and the dividing layer 162 is made of amorphous SiO 2 .
  • the W layer is formed by RF magnetron sputtering, as shown in FIG. Under these film forming conditions, a polycrystalline W layer is formed.
  • the total thickness of the sublayer 161 is 650 nm.
  • the SiO 2 layer of the dividing layer 162 is formed by RF magnetron sputtering at an O 2 ratio of 15%. This condition makes the SiO 2 layer amorphous.
  • the thickness of the dividing layer 162 is 1 nm, and the total thickness of the high acoustic impedance layer 16 is 650 nm.
  • the center frequency of the applied high frequency is 2 GHz
  • the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm
  • the wavelength of the elastic wave propagating through the SiO 2 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the dividing layer 162 to the wavelength of the elastic wave is 1/2979.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 1 is 1.9 nm, and the attenuation amount of the filter is -1.0 dB.
  • the surface roughness of the acoustic multilayer film 18 is small, and the attenuation of the filter is also small.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.5°. It is presumed that even if the thickness of the dividing layer 162 is less than 1 nm, for example, a few molecular layers thick, surface roughness can be suppressed and high filter characteristics can be obtained. Furthermore, by inserting the dividing layer 162, stress in the high acoustic impedance layer 16 is relaxed, and peeling and cracking of the acoustic multilayer film 18 can be suppressed.
  • the item of film peeling/cracking in Fig. 5 is expressed as “ ⁇ ”. The " ⁇ " mark indicates that film peeling and cracking are suppressed.
  • Example 2 In Example 2, the same conditions as in Example 1 are used except for the thickness of the dividing layer 162. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of W with a total thickness of 650 nm, and the thickness of the dividing layer 162 of amorphous SiO 2 is 2 nm. The conditions for forming the W layer and the SiO 2 layer are the same as in Example 1. Since the center frequency of the applied high frequency is 2 GHz, the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm, and the wavelength of the elastic wave propagating through the SiO 2 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 2/2979.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 2 is 1.9 nm, and the attenuation amount of the filter is -1.0 dB.
  • the surface roughness of the acoustic multilayer film 18 is small, and the attenuation of the filter is also small.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.5°.
  • the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 3 In Example 3, the same conditions as in Examples 1 and 2 are used except for the thickness of the dividing layer 162. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of W with a total thickness of 650 nm, and the thickness of the amorphous SiO 2 dividing layer 162 is 45 nm. The conditions for forming the W layer and the SiO 2 layer are the same as in Examples 1 and 2. Since the center frequency of the applied high frequency is 2 GHz, the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm, and the wavelength of the elastic wave propagating through the SiO 2 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 45/2979, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 3 is 2.0 nm, and the attenuation amount of the filter is -1.8 dB.
  • the surface roughness of the acoustic multilayer film 18 and the attenuation of the filter are well within acceptable limits.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.7°, which is within the permissible range.
  • the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 4 In Example 4, the same conditions as in Example 3 are used except for the material of the dividing layer 162. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of W with a total thickness of 650 nm, and the dividing layer 162 is formed of amorphous Al 2 O 3 with a total thickness of 45 nm. As shown in FIG. 6, the Al 2 O 3 layer is formed by RF magnetron sputtering at an O 2 ratio of 30%. This condition makes the Al 2 O 3 layer amorphous.
  • the center frequency of the applied high frequency is 2 GHz
  • the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm
  • the wavelength of the elastic wave propagating through the Al 2 O 3 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 45/2979, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample in Example 4 is 2.0 nm, which is the same as in Example 3, but the attenuation of the filter is -1.0 dB, and the filter characteristics are better than in Example 3. .
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.7°, which is within the permissible range. Furthermore, by inserting the dividing layer 162, the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 5 In Example 5, the same conditions as in Examples 3 and 4 are used except for the material of the dividing layer 162. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of W with a total thickness of 650 nm, and the dividing layer 162 is formed of amorphous WO 3 with a thickness of 45 nm.
  • the WO 3 layer is formed by RF magnetron sputtering with an O 2 ratio of 25%, as shown in FIG. This condition makes the WO 3 layer amorphous.
  • the center frequency of the applied high frequency is 2 GHz
  • the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm
  • the wavelength of the elastic wave propagating through the Al 2 O 3 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 45/2979, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 5 is 2.0 nm, which is the same as that of Examples 3 and 4.
  • the attenuation amount of the filter is ⁇ 1.1 dB, and filter characteristics comparable to those of the fourth embodiment can be obtained.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.7°, which is within the permissible range. Furthermore, by inserting the dividing layer 162, the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 6 the same conditions as in Example 3 are used except for the material of the sublayer 161 of the high acoustic impedance layer 16. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of Mo, and the dividing layer 162 is formed of amorphous SiO 2 with a thickness of 45 nm. The Mo layer of the sublayer 161 is formed by DC magnetron sputtering, as shown in FIG. A polycrystalline Mo layer is formed under these conditions. The total thickness of the sublayer 161 is 781 nm.
  • the center frequency of the applied high frequency is 2 GHz
  • the wavelength of the elastic wave propagating through the Mo sublayer 161 is approximately 3125 nm
  • the wavelength of the elastic wave propagating through the amorphous SiO 2 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 45/2979, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 6 is 2.1 nm, which is close to that of Examples 3 to 5.
  • the attenuation of the filter is -1.7 dB, which is well within the allowable range.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.7°, which is within the permissible range. Furthermore, by inserting the dividing layer 162, the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 7 the applied frequency is 3 GHz.
  • a silicon substrate is used as the substrate, the sublayer 161 of the high acoustic impedance layer 16 is formed of W, and the dividing layer 162 is formed of amorphous SiO 2 with a thickness of 30 nm.
  • the total film thickness of the W sublayer 161 is 433 nm.
  • the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 1733 nm, and the wavelength of the elastic wave propagating through the amorphous SiO 2 splitting layer 162 is 1986 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 30/1986, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 7 was as small as 1.6 nm.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is as small as 3.1°, and the crystal orientation of the piezoelectric layer 13 is good.
  • the attenuation of the filter is -2.0 dB, which is well within the allowable range.
  • the dividing layer 162 the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Example 8 the applied frequency is 6 GHz.
  • the sublayer 161 of the high acoustic impedance layer 16 is formed of W
  • the dividing layer 162 is formed of amorphous SiO 2 with a thickness of 15 nm.
  • the total film thickness of the W sublayer 161 is 217 nm.
  • the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 867 nm
  • the wavelength of the elastic wave propagating through the amorphous SiO 2 splitting layer 162 is 993 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 15/993, or 5/331.
  • the surface roughness Ra of the acoustic multilayer film 18 of the sample of Example 8 was as small as 1.2 nm.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is as small as 2.9°, and the crystal orientation of the piezoelectric layer 13 is good.
  • the attenuation of the filter is -2.7 dB, which is within the allowable range.
  • Example 9 the same conditions as in Example 1 are used except for the thickness of the dividing layer 162. That is, the sublayer 161 of the high acoustic impedance layer 16 is formed of W with a total thickness of 650 nm, and the thickness of the amorphous SiO 2 dividing layer 162 is 55 nm. The thickness of this dividing layer 162 is under the same conditions as the characteristic f of the simulation in FIG.
  • the center frequency of the applied high frequency is 2 GHz as in the simulation of FIG. 3, the wavelength of the elastic wave propagating through the W sublayer 161 is approximately 2600 nm, and the wavelength of the elastic wave propagating through the SiO 2 splitting layer 162 is 2979 nm.
  • the ratio of the thickness of the splitting layer 162 to the wavelength of the elastic wave is 55/2979, or 1/55.
  • the surface roughness Ra of the sample of Example 9 is 2.0 nm, which is good, and the attenuation of the filter is -3.3 dB, which is within the allowable limit.
  • the XRC FWHM of the piezoelectric layer 13 formed on the acoustic multilayer film 18 is 3.7°, which is close to the allowable limit. It is estimated that if the thickness of the SiO 2 split layer is increased to more than 55 nm when the frequency is 2 GHz, the filter characteristics will deteriorate.
  • the stress in the high acoustic impedance layer is alleviated, and peeling and cracking of the acoustic multilayer film can be suppressed, so the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ ". .
  • Comparative Example 1 In Comparative Example 1, the dividing layer 162 is not provided in the high acoustic impedance layer 16. Other conditions are the same as in Example 1.
  • the high acoustic impedance layer 16 is made of W, and the low acoustic impedance layer 16 is made of SiO2.
  • the center frequency of the applied high frequency is 2 GHz, and the thickness of the high acoustic impedance layer is set to 650 nm.
  • the attenuation of the filter is ⁇ 1.0 dB, which is good, but the surface roughness of the acoustic multilayer film 18 is 3.6 nm.
  • the stress generated in the acoustic multilayer film 18 increases, and there is a high possibility that peeling or cracking will occur.
  • the XRC FWHM of the piezoelectric layer 13 of the active element 15 is 6.1°, which exceeds the allowable range, and the crystal orientation is poor, so good resonance characteristics cannot be expected.
  • the item of film peeling and cracking in FIG. 5 is evaluated as " ⁇ " or "x". The " ⁇ ” mark indicates that the film peeling and cracks are not sufficiently suppressed, and the "x” mark indicates that the film peeling and cracks are not suppressed.
  • At least one high acoustic impedance layer 16 contains 1/3000 or more, 1/55 or less, more preferably 1/3000 or more of the wavelength of the elastic wave corresponding to the frequency used, It can be seen that by inserting the dividing layer 162 with a thickness of 1/66 or less, the surface roughness of the acoustic multilayer film 18 can be reduced and the surface smoothness can be maintained. As shown in FIG.
  • the thickness of the dividing layer 162 inserted into the high acoustic impedance layer 16 is 1 nm or more and 55 nm or less
  • the thickness of the dividing layer 162 is the same as that of the low acoustic impedance layer 17 (SiO2 layer with a thickness of 725 nm). ) is 1/725 to 1/13 of the film thickness.
  • the filter characteristics can be maintained within an acceptable range.
  • the present invention has been described above based on specific embodiments, the present invention is not limited to the above-described configuration example.
  • the number of pairs of the high acoustic impedance layer 16 and the low acoustic impedance layer 17 that are repeatedly stacked is not limited to two, and a larger number of pairs may be stacked.
  • a dividing layer 162 is inserted into one or more of the high acoustic impedance layers 16 .
  • the high acoustic impedance layer may be formed of ZnO, Ta2O5, Ru, Ir, or a composite thereof in addition to W and Mo.
  • a dividing layer is inserted into at least one high acoustic impedance layer.
  • An active element 15 is provided on the side opposite to the support substrate 11 of the acoustic multilayer film having the above-described structure, and the active element 15 is provided on the first electrode layer 12 provided on the acoustic multilayer film 18 and on the first electrode layer 12.
  • an SMR (Solid Mounted Resonator) type bulk acoustic wave filter device may be configured. In this case as well, the stress in the acoustic multilayer film is relaxed and the reliability of device operation is improved.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
PCT/JP2023/012784 2022-03-31 2023-03-29 音響多層膜、高周波フィルタデバイス、及びバルク弾性波フィルタデバイス Ceased WO2023190677A1 (ja)

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