WO2023017780A1 - Elastic wave device - Google Patents

Elastic wave device Download PDF

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WO2023017780A1
WO2023017780A1 PCT/JP2022/029970 JP2022029970W WO2023017780A1 WO 2023017780 A1 WO2023017780 A1 WO 2023017780A1 JP 2022029970 W JP2022029970 W JP 2022029970W WO 2023017780 A1 WO2023017780 A1 WO 2023017780A1
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layer
elastic wave
wave device
silicon nitride
piezoelectric layer
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French (fr)
Japanese (ja)
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泰伸 林
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株式会社村田製作所
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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 devices; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves

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  • the present invention relates to an acoustic wave device in which a dielectric film is provided between a piezoelectric layer and an IDT electrode.
  • Acoustic wave devices are conventionally known in which a dielectric film is provided between an IDT electrode and a piezoelectric layer.
  • a dielectric film is provided between an IDT electrode and a piezoelectric layer.
  • a thin silicon nitride film or aluminum nitride film is formed on a piezoelectric layer made of LiTaO 3 .
  • An IDT electrode is provided on the silicon nitride film or the aluminum nitride film.
  • An object of the present invention is to provide an elastic wave device whose characteristics are less likely to deteriorate.
  • An acoustic wave device includes a piezoelectric layer, a silicon nitride film provided on the piezoelectric layer, and an IDT electrode provided on the silicon nitride film, wherein the IDT electrode is made of Cu
  • the silicon nitride film has a metal layer made of a Cu alloy
  • the refractive index of the silicon nitride film is 2.15 or more
  • the film thickness of the silicon nitride film is 10 nm or more and 75 nm or less.
  • FIG. 1 is a front cross-sectional view of an elastic wave device according to a first embodiment of the invention.
  • FIG. 2 is a partially cutaway front cross-sectional view showing an enlarged main part of the elastic wave device according to the first embodiment of the present invention.
  • FIG. 3 is a circuit diagram of a ladder-type filter as an elastic wave filter having the elastic wave device of the first embodiment of the present invention.
  • FIG. 4 is a diagram showing the relationship between the film thickness of the silicon nitride film and the fractional bandwidth of the acoustic wave device.
  • FIG. 5 is a diagram showing the relationship between the refractive index of a silicon nitride film and the amount of characteristic variation in a moisture resistance test.
  • FIG. 6 is a front cross-sectional view of an elastic wave device according to a second embodiment of the invention.
  • FIG. 7 is a front cross-sectional view of an elastic wave device according to a third embodiment of the invention.
  • FIG. 8 is a front cross-sectional view of an elastic wave device according to a fourth embodiment of the invention.
  • FIG. 1 is a front cross-sectional view of an elastic wave device according to the first embodiment of the present invention.
  • An elastic wave device 1 has a support substrate 2 .
  • the support substrate 2 is made of Si.
  • the material of the support substrate 2 is not limited to Si, and various insulators and semiconductors can be used.
  • the intermediate layer 3 is laminated on the support substrate 2 .
  • the intermediate layer 3 has a high acoustic velocity film 4 as a high acoustic velocity material layer laminated on the support substrate 2 and a low acoustic velocity film 5 laminated on the high acoustic velocity film 4 .
  • a piezoelectric layer 6 is laminated on the intermediate layer 3 .
  • the piezoelectric layer 6 is made of LiTaO 3 . Therefore, the supporting substrate 2 is laminated on the surface of the intermediate layer 3 opposite to the side on which the piezoelectric layer 6 is provided.
  • the piezoelectric layer 6 has first and second main surfaces 6a and 6b facing each other.
  • the second main surface 6b is located on the intermediate layer 3 side.
  • a silicon nitride film 7 is laminated on the first main surface 6a.
  • the silicon nitride film 7 is represented by SiNx . where x is a positive number. Therefore, the intermediate layer 3 is provided on the side of the second main surface 6b opposite to the side of the piezoelectric layer 6 on which the silicon nitride film 7 is laminated.
  • An IDT electrode 8 is provided on the silicon nitride film 7 .
  • the IDT electrode 8 has an adhesion layer 8b and a metal layer 8a made of Cu as a main electrode layer provided on the adhesion layer 8b.
  • the adhesion layer 8b is made of Ti. However, instead of Ti, other metals or alloys such as NiCr may be used.
  • the metal layer 8 a is made of Cu and is the main electrode layer of the IDT electrode 8 . It should be noted that the main electrode layer refers to a predominant electrode layer among portions functioning as electrodes.
  • the metal layer 8a may be made of a copper alloy mainly containing Cu instead of Cu.
  • Reflectors 10 and 11 are provided on both sides of the IDT electrode 8 in the elastic wave propagation direction. An elastic wave resonator is thereby configured.
  • a protective layer 9 is laminated so as to cover the IDT electrodes 8 .
  • the protective layer 9 is provided not only on the top and side surfaces of the electrode finger portions of the IDT electrodes 8 but also on the regions between the electrode fingers.
  • the protective layer 9 is made of suitable insulating ceramics.
  • the protective layer 9 is made of silicon oxide.
  • the intermediate layer 3 is provided to confine the energy of elastic waves in the piezoelectric layer 6 .
  • the high acoustic velocity film 4 described above is made of a high acoustic velocity material.
  • a high acoustic velocity material is a material in which the acoustic velocity of a propagating bulk wave is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric layer 6 .
  • Such high sonic materials include aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, fort.
  • the high acoustic velocity film 4 is made of silicon nitride.
  • the low sound velocity film 5 is made of a low sound velocity material.
  • a low sound velocity material is a material in which a propagating bulk wave has a lower acoustic velocity than a bulk wave propagating through the piezoelectric layer 6 .
  • Such low sound velocity materials include silicon oxide, glass, silicon oxynitride, tantalum oxide, compounds obtained by adding fluorine, carbon, boron, hydrogen, or silanol groups to silicon oxide, and media containing the above materials as main components. and various other materials.
  • the low sound velocity film 5 is made of silicon oxide.
  • the low sound velocity film 5 is laminated on the second main surface 6 b of the piezoelectric layer 6 .
  • a high acoustic velocity film 4 is laminated on the surface of the low acoustic velocity film 5 opposite to the piezoelectric layer 6 . Therefore, the energy of the elastic wave can be effectively confined on the piezoelectric layer 6 side.
  • the silicon nitride film 7 is provided between the piezoelectric layer 6 and the IDT electrode 8 .
  • the refractive index of the silicon nitride film 7 is 2.15 or more, and the film thickness of the silicon nitride film 7 is in the range of 10 nm or more and 75 nm or less. Therefore, deterioration of the characteristics of the acoustic wave device is less likely to occur. That is, in the elastic wave resonator, deterioration of resonance characteristics such as a fractional bandwidth is less likely to occur. This will be explained more specifically.
  • a silicon nitride film 7 of SiNx was formed on the piezoelectric layer 6 by sputtering.
  • the refractive index was adjusted by adjusting the SiN 2 gas flow rate during film formation.
  • the film thickness of the silicon nitride film 7 was set to 15 nm.
  • a copper alloy of Cu-0.02Ag was used for the metal layer 8a of the IDT electrode 8 .
  • Cu-0.02Ag means a Cu alloy containing Ag in a proportion of 2% by weight.
  • the adhesion layer 8b was a Ti film with a thickness of 10 nm.
  • FIG. 4 is a diagram showing the relationship between the film thickness (nm) of the silicon nitride film 7 and the fractional bandwidth of the acoustic wave device 1 as a resonator.
  • the specific bandwidth is required to be 2% or more. Therefore, as is clear from FIG. 4, a sufficiently large fractional bandwidth can be realized if the film thickness of the silicon nitride film 7 is 75 nm or less.
  • the film thickness of the silicon nitride film 7 is required to be 10 nm or more in order to obtain a sufficient anti-diffusion effect. As described above, in the present embodiment, the thickness of the silicon nitride film 7 is 10 nm or more and 75 nm or less.
  • FIG. 5 is a diagram showing the relationship between the refractive index of the silicon nitride film 7 and the amount of characteristic variation in a moisture resistance test.
  • the elastic wave device 1 was maintained in an environment of 93° C. and 81% RH for 1200 hours.
  • the amount of characteristic variation (%) after this moisture resistance test was determined.
  • the amount of variation in the center frequency of the passband of the elastic wave filter using a plurality of elastic wave devices 1 shown in FIG. 1 was defined as the amount of characteristic variation (%).
  • the refractive index of the silicon nitride film 7 is 2.15 or more.
  • the refractive index is 2.8 or less. If the refractive index exceeds 2.8, filter characteristics may deteriorate.
  • Optical constants refractive index, extinction coefficient
  • film thickness is calculated by fitting with the model formula from the change in the polarization state due to the incidence and reflection of light (ratio of amplitude reflectance tan ( ⁇ ) and phase difference ⁇ ). Method. Specifically, the refractive index was determined using an ellipsometer.
  • the refractive index can be increased when the SiNx becomes rich in Si.
  • the value of the refractive index can be controlled.
  • FIG. 3 is a circuit diagram of a ladder-type filter as an elastic wave filter having the elastic wave device according to the first embodiment of the present invention.
  • the acoustic wave filter 12 has a plurality of series arm resonators S1-S4 and a plurality of parallel arm resonators P1-P3.
  • the acoustic wave device 1 of the present embodiment for at least one of the series arm resonators S1 to S4 and the parallel arm resonators P1 to P3, deterioration of filter characteristics can be suppressed.
  • the elastic wave device according to the present invention can be used not only for such ladder-type filters having a plurality of elastic wave resonators, but also for various band-pass filters.
  • the supporting substrate 2A is a high acoustic velocity supporting substrate made of the above high acoustic velocity material.
  • FIG. 7 is a front cross-sectional view of an elastic wave device according to a third embodiment of the invention.
  • the support substrate 2A is laminated on the second main surface 6b of the piezoelectric layer 6 with the bonding layer 22 interposed therebetween.
  • the support substrate 2A is made of Si. However, it may be made of other semiconductors or insulators.
  • the support substrate 2A has a concave portion 2a open on the upper surface. This concave portion 2 a is positioned below the IDT electrode 8 . Therefore, the excitation region having the IDT electrodes 8 is positioned above the recess 2a.
  • the second main surface 6b of the piezoelectric layer 6, the inner side surface of the bonding layer 22, and the concave portion 2a of the support substrate 2A form a cavity 23 for preventing vibration. No protective layer is provided.
  • FIG. 8 is a front cross-sectional view of an elastic wave device according to a fourth embodiment of the invention.
  • the intermediate layer 32 has a structure in which high acoustic impedance layers 32a, 32c, 32e and low acoustic impedance layers 32b, 32d, 32f are alternately laminated.
  • the high acoustic impedance layers 32a, 32c, 32e are made of a high acoustic impedance material with relatively high acoustic impedance.
  • the low acoustic impedance layers 32b, 32d, 32f are made of a low acoustic impedance material with relatively low acoustic impedance.
  • the elastic wave device 31 is configured in the same manner as the elastic wave device 1 except that the intermediate layer 32 is different from the intermediate layer 3 and no protective layer is provided.
  • the intermediate layer for confining the energy of elastic waves may be an acoustic reflection layer having high acoustic impedance layers 32a, 32c, 32e and low acoustic impedance layers 32b, 32d, 32f. good.
  • the silicon nitride film 7 is formed on the piezoelectric layer 6, so that deterioration of characteristics hardly occurs.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

Provided is an elastic wave device that is not prone to deterioration of device characteristics.　The elastic wave device 1 has: a silicon nitride membrane 7 provided upon a piezoelectric layer 6; and an IDT electrode 8 provided upon the silicon nitride membrane 7. The IDT electrode 8 has a metal layer 8a comprising Cu or a Cu alloy. The refractive index of the silicon nitride membrane 7 is at least 2.15 and the thickness of the silicon nitride membrane 7 is 10–75 nm,

Description

弾性波装置Acoustic wave device
　本発明は、圧電体層とＩＤＴ電極との間に誘電体膜が設けられている、弾性波装置に関する。 The present invention relates to an acoustic wave device in which a dielectric film is provided between a piezoelectric layer and an IDT electrode.
　従来、ＩＤＴ電極と、圧電体層との間に誘電体膜が設けられている弾性波装置が知られている。例えば下記の特許文献１に記載されている弾性波装置では、ＬｉＴａＯ３からなる圧電体層上に、薄い窒化ケイ素膜や窒化アルミニウム膜が形成されている。この窒化ケイ素膜や窒化アルミニウム膜上に、ＩＤＴ電極が設けられている。 Acoustic wave devices are conventionally known in which a dielectric film is provided between an IDT electrode and a piezoelectric layer. For example, in an elastic wave device described in Patent Document 1 below, a thin silicon nitride film or aluminum nitride film is formed on a piezoelectric layer made of LiTaO 3 . An IDT electrode is provided on the silicon nitride film or the aluminum nitride film.
ＷＯ２０２０／２０９１８９WO2020/209189
　特許文献１に記載のような弾性波装置では、圧電体層とＩＤＴ電極との間に配置された誘電体膜の厚みが薄いと、耐湿特性やフィルタ特性などが劣化するおそれがあった。 In the acoustic wave device as described in Patent Document 1, if the dielectric film disposed between the piezoelectric layer and the IDT electrode is thin, there is a risk of deterioration in moisture resistance and filter characteristics.
　本発明の目的は、特性の劣化が生じ難い、弾性波装置を提供することにある。 An object of the present invention is to provide an elastic wave device whose characteristics are less likely to deteriorate.
　本発明に係る弾性波装置は、圧電体層と、前記圧電体層上に設けられた窒化ケイ素膜と、前記窒化ケイ素膜上に設けられたＩＤＴ電極と、を備え、前記ＩＤＴ電極が、ＣｕまたはＣｕ合金からなる金属層を有し、前記窒化ケイ素膜の屈折率が、２．１５以上であり、かつ該窒化ケイ素膜の膜厚が１０ｎｍ以上、７５ｎｍ以下である。 An acoustic wave device according to the present invention includes a piezoelectric layer, a silicon nitride film provided on the piezoelectric layer, and an IDT electrode provided on the silicon nitride film, wherein the IDT electrode is made of Cu Alternatively, the silicon nitride film has a metal layer made of a Cu alloy, the refractive index of the silicon nitride film is 2.15 or more, and the film thickness of the silicon nitride film is 10 nm or more and 75 nm or less.
　本発明によれば、特性の劣化が生じ難い弾性波装置を提供することができる。 According to the present invention, it is possible to provide an elastic wave device whose characteristics are less likely to deteriorate.
図１は、本発明の第１の実施形態に係る弾性波装置の正面断面図である。FIG. 1 is a front cross-sectional view of an elastic wave device according to a first embodiment of the invention. 図２は、本発明の第１の実施形態の弾性波装置の要部を拡大して示す部分切欠き正面断面図である。FIG. 2 is a partially cutaway front cross-sectional view showing an enlarged main part of the elastic wave device according to the first embodiment of the present invention. 図３は、本発明の第１の実施形態の弾性波装置を有する弾性波フィルタとしてのラダー型フィルタの回路図である。FIG. 3 is a circuit diagram of a ladder-type filter as an elastic wave filter having the elastic wave device of the first embodiment of the present invention. 図４は、窒化ケイ素膜の膜厚と、弾性波装置の比帯域との関係を示す図である。FIG. 4 is a diagram showing the relationship between the film thickness of the silicon nitride film and the fractional bandwidth of the acoustic wave device. 図５は、窒化ケイ素膜の屈折率と、耐湿試験の特性変動量との関係を示す図である。FIG. 5 is a diagram showing the relationship between the refractive index of a silicon nitride film and the amount of characteristic variation in a moisture resistance test. 図６は、本発明の第２の実施形態に係る弾性波装置の正面断面図である。FIG. 6 is a front cross-sectional view of an elastic wave device according to a second embodiment of the invention. 図７は、本発明の第３の実施形態に係る弾性波装置の正面断面図である。FIG. 7 is a front cross-sectional view of an elastic wave device according to a third embodiment of the invention. 図８は、本発明の第４の実施形態に係る弾性波装置の正面断面図である。FIG. 8 is a front cross-sectional view of an elastic wave device according to a fourth embodiment of the invention.
　以下、図面を参照しつつ、本発明の具体的な実施形態を説明することにより、本発明を明らかにする。 Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.
　なお、本明細書に記載の各実施形態は、例示的なものであり、異なる実施形態間において、構成の部分的な置換または組み合わせが可能であることを指摘しておく。 It should be noted that each embodiment described in this specification is an example, and partial replacement or combination of configurations is possible between different embodiments.
　図１は、本発明の第１の実施形態に係る弾性波装置の正面断面図である。弾性波装置１は、支持基板２を有する。支持基板２は、Ｓｉからなる。もっとも、支持基板２の材料は、Ｓｉに限定されず、様々な絶縁体や半導体を用いることができる。 FIG. 1 is a front cross-sectional view of an elastic wave device according to the first embodiment of the present invention. An elastic wave device 1 has a support substrate 2 . The support substrate 2 is made of Si. However, the material of the support substrate 2 is not limited to Si, and various insulators and semiconductors can be used.
　支持基板２上に、中間層３が積層されている。中間層３は、支持基板２上に積層された高音速材料層としての高音速膜４と、高音速膜４上に積層された低音速膜５とを有する。 An intermediate layer 3 is laminated on the support substrate 2 . The intermediate layer 3 has a high acoustic velocity film 4 as a high acoustic velocity material layer laminated on the support substrate 2 and a low acoustic velocity film 5 laminated on the high acoustic velocity film 4 .
　中間層３上に、圧電体層６が積層されている。圧電体層６は、ＬｉＴａＯ３からなる。従って、支持基板２は、中間層３の圧電体層６が設けられている側とは反対側の面に積層されている。 A piezoelectric layer 6 is laminated on the intermediate layer 3 . The piezoelectric layer 6 is made of LiTaO 3 . Therefore, the supporting substrate 2 is laminated on the surface of the intermediate layer 3 opposite to the side on which the piezoelectric layer 6 is provided.
　圧電体層６は、対向し合う第１及び第２の主面６ａ及び６ｂを有する。第２の主面６ｂが、中間層３側に位置している。 The piezoelectric layer 6 has first and second main surfaces 6a and 6b facing each other. The second main surface 6b is located on the intermediate layer 3 side.
　第１の主面６ａ上に、窒化ケイ素膜７が積層されている。窒化ケイ素膜７は、ＳｉＮｘで表される。ここで、ｘは、正の数である。従って、圧電体層６の窒化ケイ素膜７が積層されている側とは反対側の第２の主面６ｂ側に中間層３が設けられている。 A silicon nitride film 7 is laminated on the first main surface 6a. The silicon nitride film 7 is represented by SiNx . where x is a positive number. Therefore, the intermediate layer 3 is provided on the side of the second main surface 6b opposite to the side of the piezoelectric layer 6 on which the silicon nitride film 7 is laminated.
　窒化ケイ素膜７上に、ＩＤＴ電極８が設けられている。 An IDT electrode 8 is provided on the silicon nitride film 7 .
　図２に拡大して示すように、ＩＤＴ電極８は、密着層８ｂと、密着層８ｂ上に設けられた主電極層としてのＣｕからなる金属層８ａとを有する。密着層８ｂは、Ｔｉからなる。もっとも、Ｔｉに代えて、ＮｉＣｒなどの他の金属もしくは合金を用いてもよい。 As shown enlarged in FIG. 2, the IDT electrode 8 has an adhesion layer 8b and a metal layer 8a made of Cu as a main electrode layer provided on the adhesion layer 8b. The adhesion layer 8b is made of Ti. However, instead of Ti, other metals or alloys such as NiCr may be used.
　金属層８ａは、Ｃｕからなり、ＩＤＴ電極８の主電極層である。なお、主電極層とは、電極として機能する部分のうち支配的な電極層をいうものとする。金属層８ａは、Ｃｕに代えて、Ｃｕを主体とする銅合金からなるものであってもよい。 The metal layer 8 a is made of Cu and is the main electrode layer of the IDT electrode 8 . It should be noted that the main electrode layer refers to a predominant electrode layer among portions functioning as electrodes. The metal layer 8a may be made of a copper alloy mainly containing Cu instead of Cu.
　ＩＤＴ電極８の弾性波伝搬方向両側には、反射器１０，１１が設けられている。それによって、弾性波共振子が構成されている。 Reflectors 10 and 11 are provided on both sides of the IDT electrode 8 in the elastic wave propagation direction. An elastic wave resonator is thereby configured.
　ＩＤＴ電極８を覆うように、保護層９が積層されている。保護層９は、ＩＤＴ電極８の電極指部分の上面及び側面だけでなく、電極指間の領域にも至るように設けられている。 A protective layer 9 is laminated so as to cover the IDT electrodes 8 . The protective layer 9 is provided not only on the top and side surfaces of the electrode finger portions of the IDT electrodes 8 but also on the regions between the electrode fingers.
　保護層９は、適宜の絶縁性セラミックスからなる。本実施形態では、保護層９は酸化ケイ素からなる。 The protective layer 9 is made of suitable insulating ceramics. In this embodiment, the protective layer 9 is made of silicon oxide.
　中間層３は、弾性波のエネルギーを圧電体層６に閉じ込めるために設けられている。前述した高音速膜４は、高音速材料からなる。高音速材料とは、伝搬するバルク波の音速が、圧電体層６を伝搬する弾性波の音速よりも高い材料をいう。このような高音速材料としては、酸化アルミニウム、炭化ケイ素、窒化ケイ素、酸窒化ケイ素、シリコン、サファイア、タンタル酸リチウム、ニオブ酸リチウム、水晶、アルミナ、ジルコニア、コ－ジライト、ムライト、ステアタイト、フォルステライト、マグネシア、ＤＬＣ（ダイヤモンドライクカーボン）膜またはダイヤモンド、上記材料を主成分とする媒質、上記材料の混合物を主成分とする媒質等の様々な材料を挙げることができる。本実施形態では、高音速膜４は窒化ケイ素からなる。 The intermediate layer 3 is provided to confine the energy of elastic waves in the piezoelectric layer 6 . The high acoustic velocity film 4 described above is made of a high acoustic velocity material. A high acoustic velocity material is a material in which the acoustic velocity of a propagating bulk wave is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric layer 6 . Such high sonic materials include aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, fort. Various materials such as stellite, magnesia, a DLC (diamond-like carbon) film or diamond, a medium containing the above materials as a main component, and a medium containing a mixture of the above materials as a main component can be used. In this embodiment, the high acoustic velocity film 4 is made of silicon nitride.
　低音速膜５は、低音速材料からなる。低音速材料とは、伝搬するバルク波の音速が、圧電体層６を伝搬するバルク波の音速よりも低い材料である。このような低音速材料としては、酸化ケイ素、ガラス、酸窒化ケイ素、酸化タンタル、また、酸化ケイ素にフッ素や炭素やホウ素、水素、あるいはシラノール基を加えた化合物、上記材料を主成分とする媒質等の様々な材料が挙げられる。本実施形態では、低音速膜５は、酸化ケイ素からなる。 The low sound velocity film 5 is made of a low sound velocity material. A low sound velocity material is a material in which a propagating bulk wave has a lower acoustic velocity than a bulk wave propagating through the piezoelectric layer 6 . Such low sound velocity materials include silicon oxide, glass, silicon oxynitride, tantalum oxide, compounds obtained by adding fluorine, carbon, boron, hydrogen, or silanol groups to silicon oxide, and media containing the above materials as main components. and various other materials. In this embodiment, the low sound velocity film 5 is made of silicon oxide.
　中間層３では、圧電体層６の第２の主面６ｂに、低音速膜５が積層されている。また、低音速膜５の圧電体層６とは反対側の面に高音速膜４が積層されている。従って、圧電体層６側に弾性波のエネルギーを効果的に閉じ込めることができる。 In the intermediate layer 3 , the low sound velocity film 5 is laminated on the second main surface 6 b of the piezoelectric layer 6 . A high acoustic velocity film 4 is laminated on the surface of the low acoustic velocity film 5 opposite to the piezoelectric layer 6 . Therefore, the energy of the elastic wave can be effectively confined on the piezoelectric layer 6 side.
　弾性波装置１では、窒化ケイ素膜７が圧電体層６とＩＤＴ電極８との間に設けられている。そして、窒化ケイ素膜７の屈折率が２．１５以上であり、かつ該窒化ケイ素膜７の膜厚が１０ｎｍ以上、７５ｎｍ以下の範囲にある。そのため、弾性波装置の特性の劣化が生じ難い。すなわち、弾性波共振子では、比帯域などの共振特性の劣化が生じ難い。これを、より具体的に説明する。 In the elastic wave device 1 , the silicon nitride film 7 is provided between the piezoelectric layer 6 and the IDT electrode 8 . The refractive index of the silicon nitride film 7 is 2.15 or more, and the film thickness of the silicon nitride film 7 is in the range of 10 nm or more and 75 nm or less. Therefore, deterioration of the characteristics of the acoustic wave device is less likely to occur. That is, in the elastic wave resonator, deterioration of resonance characteristics such as a fractional bandwidth is less likely to occur. This will be explained more specifically.
　弾性波装置１の製造に際しては、圧電体層６上に、スパッタリングによりＳｉＮｘである窒化ケイ素膜７を成膜した。この場合、成膜に際してのＳｉＮ２ガス流量などを調整することにより、屈折率を調整した。 In manufacturing the elastic wave device 1, a silicon nitride film 7 of SiNx was formed on the piezoelectric layer 6 by sputtering. In this case, the refractive index was adjusted by adjusting the SiN 2 gas flow rate during film formation.
　窒化ケイ素膜７の膜厚は１５ｎｍとした。ＩＤＴ電極８の金属層８ａは、Ｃｕ－０．０２Ａｇの銅合金を用いた。Ｃｕ－０．０２Ａｇは、２重量％の割合でＡｇを含むＣｕ合金であることを意味する。また、密着層８ｂは、１０ｎｍの厚みのＴｉ膜とした。 The film thickness of the silicon nitride film 7 was set to 15 nm. A copper alloy of Cu-0.02Ag was used for the metal layer 8a of the IDT electrode 8 . Cu-0.02Ag means a Cu alloy containing Ag in a proportion of 2% by weight. The adhesion layer 8b was a Ti film with a thickness of 10 nm.
　図４は、窒化ケイ素膜７の膜厚（ｎｍ）と、弾性波装置１の共振子としての比帯域との関係を示す図である。一般に帯域通過型フィルタなどに弾性波共振子を用いる場合、比帯域は２％以上であることが求められる。従って、図４から明らかなように、窒化ケイ素膜７の膜厚が７５ｎｍ以下であれば、十分大きな比帯域を実現することができる。 FIG. 4 is a diagram showing the relationship between the film thickness (nm) of the silicon nitride film 7 and the fractional bandwidth of the acoustic wave device 1 as a resonator. In general, when an acoustic wave resonator is used in a band-pass filter or the like, the specific bandwidth is required to be 2% or more. Therefore, as is clear from FIG. 4, a sufficiently large fractional bandwidth can be realized if the film thickness of the silicon nitride film 7 is 75 nm or less.
　他方、窒化ケイ素膜７の厚みが薄すぎると、Ｃｕの圧電体層６側への拡散防止効果が低下する。従って、窒化ケイ素膜７の膜厚は、拡散防止効果を十分に得るには、１０ｎｍ以上であることが求められる。上記のように、本実施形態では、窒化ケイ素膜７の膜厚が１０ｎｍ以上、７５ｎｍ以下であるため、弾性波装置１の特性劣化が生じ難いための、必要十分な厚みとなっている。 On the other hand, if the thickness of the silicon nitride film 7 is too thin, the effect of preventing Cu from diffusing toward the piezoelectric layer 6 decreases. Therefore, the film thickness of the silicon nitride film 7 is required to be 10 nm or more in order to obtain a sufficient anti-diffusion effect. As described above, in the present embodiment, the thickness of the silicon nitride film 7 is 10 nm or more and 75 nm or less.
　図５は、窒化ケイ素膜７の屈折率と、耐湿試験における特性変動量との関係を示す図である。ここで、耐湿試験では、弾性波装置１を、９３℃及び８１％ＲＨの環境下に１２００時間維持した。この耐湿試験後の特性変動量（％）を求めた。なお、図１に示した弾性波装置１を複数用いた弾性波フィルタの通過帯域の中心周波数の変動量を、特性変動量（％）とした。 FIG. 5 is a diagram showing the relationship between the refractive index of the silicon nitride film 7 and the amount of characteristic variation in a moisture resistance test. Here, in the moisture resistance test, the elastic wave device 1 was maintained in an environment of 93° C. and 81% RH for 1200 hours. The amount of characteristic variation (%) after this moisture resistance test was determined. The amount of variation in the center frequency of the passband of the elastic wave filter using a plurality of elastic wave devices 1 shown in FIG. 1 was defined as the amount of characteristic variation (%).
　図５から明らかなように、屈折率が２．１５以上であれば、耐湿試験後の特性変動量の絶対値が１．５（％）以下となる。従って、特性変化を抑制し得ることがわかる。よって、弾性波装置１では、窒化ケイ素膜７の屈折率は、２．１５以上である。好ましくは、屈折率は、２．８以下である。屈折率が２．８を超えると、フィルタ特性が悪化することがある。 As is clear from FIG. 5, when the refractive index is 2.15 or more, the absolute value of the amount of characteristic variation after the humidity resistance test is 1.5 (%) or less. Therefore, it can be seen that the characteristic change can be suppressed. Therefore, in the elastic wave device 1, the refractive index of the silicon nitride film 7 is 2.15 or more. Preferably, the refractive index is 2.8 or less. If the refractive index exceeds 2.8, filter characteristics may deteriorate.
　なお、上記屈折率の値の測定方法としては、以下の方法を用いた。 In addition, the following method was used as a method for measuring the above refractive index value.
　光の入反射による偏光状態の変化（振幅反射率の比ｔａｎ（Ψ）と、位相差Δ）から、光学定数（屈折率、消衰係数）及び膜厚を、モデル式とのフィッティングにより算出する方法。具体的には、エリプソメータを用いて、屈折率を求めた。 Optical constants (refractive index, extinction coefficient) and film thickness are calculated by fitting with the model formula from the change in the polarization state due to the incidence and reflection of light (ratio of amplitude reflectance tan (Ψ) and phase difference Δ). Method. Specifically, the refractive index was determined using an ellipsometer.
　なお、窒化ケイ素膜７では、ＳｉＮｘにおいてＳｉがリッチになると、屈折率を高めることができる。そして、窒化ケイ素膜７を成膜する際のガス流量をコントロールすることにより、屈折率の値をコントロールすることができる。 In addition, in the silicon nitride film 7, the refractive index can be increased when the SiNx becomes rich in Si. By controlling the gas flow rate when forming the silicon nitride film 7, the value of the refractive index can be controlled.
　図３は、本発明の第１の実施形態に係る弾性波装置を有する弾性波フィルタとしてのラダー型フィルタの回路図である。弾性波フィルタ１２は、複数の直列腕共振子Ｓ１～Ｓ４及び複数の並列腕共振子Ｐ１～Ｐ３を有する。これらの直列腕共振子Ｓ１～Ｓ４及び並列腕共振子Ｐ１～Ｐ３の少なくとも１つに、本実施形態の弾性波装置１を用いることにより、フィルタ特性の劣化を抑制することができる。 FIG. 3 is a circuit diagram of a ladder-type filter as an elastic wave filter having the elastic wave device according to the first embodiment of the present invention. The acoustic wave filter 12 has a plurality of series arm resonators S1-S4 and a plurality of parallel arm resonators P1-P3. By using the acoustic wave device 1 of the present embodiment for at least one of the series arm resonators S1 to S4 and the parallel arm resonators P1 to P3, deterioration of filter characteristics can be suppressed.
　なお、本発明に係る弾性波装置は、このような複数の弾性波共振子を有するラダー型フィルタに限らず、様々な帯域通過型フィルタに用いることができる。 It should be noted that the elastic wave device according to the present invention can be used not only for such ladder-type filters having a plurality of elastic wave resonators, but also for various band-pass filters.
　なお、図６に示す第２の実施形態の弾性波装置４１では、高音速膜が省略されている。低音速膜４２が、支持基板２Ａに直接積層されている。支持基板２Ａは、上記高音速材料からなる高音速支持基板である。 Note that the high acoustic velocity film is omitted in the elastic wave device 41 of the second embodiment shown in FIG. A low sound velocity film 42 is directly laminated on the support substrate 2A. The supporting substrate 2A is a high acoustic velocity supporting substrate made of the above high acoustic velocity material.
　図７は、本発明の第３の実施形態に係る弾性波装置の正面断面図である。弾性波装置２１では、圧電体層６の第２の主面６ｂに、接合層２２を介して支持基板２Ａが積層されている。支持基板２Ａは、Ｓｉからなる。もっとも、他の半導体や絶縁体からなるものであってもよい。支持基板２Ａは、上面に開いた凹部２ａを有する。この凹部２ａは、ＩＤＴ電極８の下方に位置している。従って、ＩＤＴ電極８を有する励振領域は、凹部２ａの上方に位置している。 FIG. 7 is a front cross-sectional view of an elastic wave device according to a third embodiment of the invention. In the elastic wave device 21, the support substrate 2A is laminated on the second main surface 6b of the piezoelectric layer 6 with the bonding layer 22 interposed therebetween. The support substrate 2A is made of Si. However, it may be made of other semiconductors or insulators. The support substrate 2A has a concave portion 2a open on the upper surface. This concave portion 2 a is positioned below the IDT electrode 8 . Therefore, the excitation region having the IDT electrodes 8 is positioned above the recess 2a.
　圧電体層６の第２の主面６ｂと、接合層２２の内側側面と、支持基板２Ａの凹部２ａとにより、振動を阻害しないためのキャビティ２３が構成されている。なお、保護層は設けられていない。 The second main surface 6b of the piezoelectric layer 6, the inner side surface of the bonding layer 22, and the concave portion 2a of the support substrate 2A form a cavity 23 for preventing vibration. No protective layer is provided.
　その他の構造は、弾性波装置２１は、弾性波装置１と同様である。従って、弾性波装置２１においても、特性の劣化が生じ難い。 Other structures of the elastic wave device 21 are the same as those of the elastic wave device 1 . Accordingly, deterioration of characteristics is less likely to occur in the elastic wave device 21 as well.
　図８は、本発明の第４の実施形態に係る弾性波装置の正面断面図である。弾性波装置３１では、中間層３２が、高音響インピーダンス層３２ａ，３２ｃ，３２ｅと、低音響インピーダンス層３２ｂ，３２ｄ，３２ｆを交互に積層した構造を有する。なお、高音響インピーダンス層３２ａ，３２ｃ，３２ｅは、音響インピーダンスが相対的に高い高音響インピーダンス材料からなる。低音響インピーダンス層３２ｂ，３２ｄ，３２ｆは、音響インピーダンスが相対的に低い低音響インピーダンス材料からなる。中間層３２が中間層３と異なること及び保護層が設けられていないことを除いては、弾性波装置３１は弾性波装置１と同様に構成されている。 FIG. 8 is a front cross-sectional view of an elastic wave device according to a fourth embodiment of the invention. In the elastic wave device 31, the intermediate layer 32 has a structure in which high acoustic impedance layers 32a, 32c, 32e and low acoustic impedance layers 32b, 32d, 32f are alternately laminated. The high acoustic impedance layers 32a, 32c, 32e are made of a high acoustic impedance material with relatively high acoustic impedance. The low acoustic impedance layers 32b, 32d, 32f are made of a low acoustic impedance material with relatively low acoustic impedance. The elastic wave device 31 is configured in the same manner as the elastic wave device 1 except that the intermediate layer 32 is different from the intermediate layer 3 and no protective layer is provided.
　このように、本発明では、弾性波のエネルギーを閉じ込めるための中間層は、高音響インピーダンス層３２ａ，３２ｃ，３２ｅと、低音響インピーダンス層３２ｂ，３２ｄ，３２ｆとを有する音響反射層であってもよい。本実施形態においても、弾性波装置１と同様に、圧電体層６上に窒化ケイ素膜７が構成されているため、特性の劣化が生じ難い。 Thus, in the present invention, the intermediate layer for confining the energy of elastic waves may be an acoustic reflection layer having high acoustic impedance layers 32a, 32c, 32e and low acoustic impedance layers 32b, 32d, 32f. good. Also in this embodiment, similarly to the elastic wave device 1, the silicon nitride film 7 is formed on the piezoelectric layer 6, so that deterioration of characteristics hardly occurs.
１…弾性波装置
２，２Ａ…支持基板
２ａ…凹部
３…中間層
４…高音速膜
５…低音速膜
６…圧電体層
６ａ，６ｂ…第１，第２の主面
７…窒化ケイ素膜
８…ＩＤＴ電極
８ａ…金属層
８ｂ…密着層
９…保護層
１０，１１…反射器
１２…弾性波フィルタ
２１，３１，４１…弾性波装置
２２…接合層
２３…キャビティ
３２…中間層
３２ａ，３２ｃ，３２ｅ…高音響インピーダンス層
３２ｂ，３２ｄ，３２ｆ…低音響インピーダンス層
４２…低音速膜
Ｐ１～Ｐ３…並列腕共振子
Ｓ１～Ｓ４…直列腕共振子 REFERENCE SIGNS LIST 1 elastic wave device 2, 2A support substrate 2a concave portion 3 intermediate layer 4 high acoustic velocity film 5 low acoustic velocity film 6 piezoelectric layers 6a, 6b first and second main surfaces 7 silicon nitride film 8... IDT electrode 8a... Metal layer 8b... Adhesion layer 9... Protective layers 10, 11... Reflector 12... Elastic wave filter 21, 31, 41... Elastic wave device 22... Bonding layer 23... Cavity 32... Intermediate layers 32a, 32c , 32e... High acoustic impedance layers 32b, 32d, 32f... Low acoustic impedance layers 42... Low acoustic velocity films P1 to P3... Parallel arm resonators S1 to S4... Series arm resonators

Claims (11)

  1. 　圧電体層と、
    　前記圧電体層上に設けられた窒化ケイ素膜と、
    　前記窒化ケイ素膜上に設けられたＩＤＴ電極と、
    を備え、前記ＩＤＴ電極が、ＣｕまたはＣｕ合金からなる金属層を有し、
    　前記窒化ケイ素膜の屈折率が、２．１５以上であり、かつ該窒化ケイ素膜の膜厚が１０ｎｍ以上、７５ｎｍ以下である、弾性波装置。     a piezoelectric layer;
    a silicon nitride film provided on the piezoelectric layer;
    an IDT electrode provided on the silicon nitride film;
    wherein the IDT electrode has a metal layer made of Cu or a Cu alloy,
    The elastic wave device, wherein the silicon nitride film has a refractive index of 2.15 or more and a thickness of 10 nm or more and 75 nm or less.
  2. 　前記窒化ケイ素膜の屈折率が、２．８以下である、請求項１に記載の弾性波装置。 The elastic wave device according to claim 1, wherein the silicon nitride film has a refractive index of 2.8 or less.
  3. 　前記ＩＤＴ電極が、前記ＣｕまたはＣｕ合金からなる金属層と、前記窒化ケイ素膜との間に積層されており、ＴｉまたはＮｉＣｒからなる密着層をさらに備える、請求項１または２に記載の弾性波装置。 The elastic wave according to claim 1 or 2, wherein the IDT electrode is laminated between the metal layer made of Cu or Cu alloy and the silicon nitride film, and further includes an adhesion layer made of Ti or NiCr. Device.
  4. 　前記ＩＤＴ電極を覆うように設けられた保護層をさらに備える、請求項１～３のいずれか１項に記載の弾性波装置。 The elastic wave device according to any one of claims 1 to 3, further comprising a protective layer provided to cover the IDT electrodes.
  5. 　前記保護層が、絶縁性セラミックスからなる、請求項４に記載の弾性波装置。 The elastic wave device according to claim 4, wherein the protective layer is made of insulating ceramics.
  6. 　前記圧電体層の前記窒化ケイ素膜が積層されている側とは反対側の面に設けられた中間層と、前記中間層の前記圧電体層が設けられている側の面とは反対側の面に積層された支持基板とをさらに備える、請求項１～５のいずれか１項に記載の弾性波装置。 An intermediate layer provided on the side of the piezoelectric layer opposite to the side on which the silicon nitride film is laminated, and an intermediate layer provided on the side opposite to the side on which the piezoelectric layer is provided of the intermediate layer. The elastic wave device according to any one of claims 1 to 5, further comprising a supporting substrate laminated on the surface.
  7. 　前記中間層が、前記圧電体層を伝搬するバルク波の音速よりも、伝搬するバルク波の音速が低い低音速材料からなる低音速膜と、
    　前記圧電体層を伝搬する弾性波の音速よりも、伝搬するバルク波の音速が高い高音速材料からなる高音速材料層とを備える、請求項６に記載の弾性波装置。     a low-temperature-velocity film in which the intermediate layer is made of a low-temperature-velocity material whose acoustic velocity is lower than that of the bulk wave propagating through the piezoelectric layer;
    7. The elastic wave device according to claim 6, further comprising a high acoustic velocity material layer made of a high acoustic velocity material whose acoustic velocity of bulk waves propagating is higher than that of acoustic waves propagating through said piezoelectric layer.
  8. 　前記中間層が、伝搬するバルク波の音速が、前記圧電体層を伝搬するバルク波の音速よりも低い低音速材料からなる低音速膜を有し、
    　前記支持基板が、伝搬するバルク波の音速が、前記圧電体層を伝搬する弾性波の音速よりも高い高音速材料からなる高音速支持基板である、請求項６に記載の弾性波装置。     The intermediate layer has a low-temperature-velocity film made of a low-temperature-velocity material in which the acoustic velocity of the propagating bulk wave is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer,
    7. The elastic wave device according to claim 6, wherein said supporting substrate is a high acoustic velocity supporting substrate made of a high acoustic velocity material in which the acoustic velocity of propagating bulk waves is higher than the acoustic velocity of elastic waves propagating through said piezoelectric layer.
  9. 　前記中間層が、音響インピーダンスが相対的に低い低音響インピーダンス材料からなる低音響インピーダンス層と、音響インピーダンスが相対的に高い高音響インピーダンス材料からなる高音響インピーダンス層とを有する、請求項６に記載の弾性波装置。 7. The intermediate layer of claim 6, wherein the intermediate layer comprises a low acoustic impedance layer made of a low acoustic impedance material with a relatively low acoustic impedance and a high acoustic impedance layer made of a high acoustic impedance material with a relatively high acoustic impedance. elastic wave device.
  10. 　前記圧電体層の前記窒化ケイ素膜が積層されている側とは反対側の面に積層された支持基板をさらに備え、前記支持基板に、前記圧電体層側に向かって開いた凹部が設けられており、該凹部が前記圧電体層と前記支持基板とにより囲まれたキャビティを構成している、請求項１～５のいずれか１項に記載の弾性波装置。 A support substrate laminated on a side of the piezoelectric layer opposite to the side on which the silicon nitride film is laminated is further provided, and the support substrate is provided with a recess opening toward the piezoelectric layer. 6. The elastic wave device according to claim 1, wherein said recess forms a cavity surrounded by said piezoelectric layer and said support substrate.
  11. 　前記支持基板と、前記圧電体層とが接合されている部分において、前記支持基板と前記圧電体層を接合している接合層をさらに備える、請求項１０に記載の弾性波装置。 11. The elastic wave device according to claim 10, further comprising a bonding layer bonding said supporting substrate and said piezoelectric layer at a portion where said supporting substrate and said piezoelectric layer are bonded.
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