JP2014192676A - Acoustic wave element - Google Patents

Acoustic wave element Download PDF

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JP2014192676A
JP2014192676A JP2013065869A JP2013065869A JP2014192676A JP 2014192676 A JP2014192676 A JP 2014192676A JP 2013065869 A JP2013065869 A JP 2013065869A JP 2013065869 A JP2013065869 A JP 2013065869A JP 2014192676 A JP2014192676 A JP 2014192676A
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idt electrode
medium
electrode
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dielectric film
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JP5716050B2 (en
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Toshihiro Sakamoto
俊裕 坂本
Hiroyuki Nakamura
弘幸 中村
Tomoya Komatsu
禎也 小松
Rei Goto
令 後藤
Masahiro Yasumi
正博 安見
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Panasonic Corp
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Abstract

PROBLEM TO BE SOLVED: To provide an acoustic wave element capable of reducing spurious in the vicinity of resonant frequency and anti-resonant frequency.SOLUTION: The acoustic wave element comprises: a comb-like medium which is formed over a piezoelectric substrate in a pattern shape identical to that of an IDT electrode; the IDT electrode laminated over the medium with the upper surface thereof facing an excitation space; and a dielectric film which is formed between the medium and the IDT electrode to fill the space therebetween. The density of the IDT electrode can be set to be larger than the density of the piezoelectric substrate, the medium and the dielectric film. With this, SH wave can be transmitted while being convergent to the inside of the IDT electrode. Since the acoustic velocity of the SH wave is lowered, the difference in acoustic velocity between the SH wave and a Rayleigh wave transmitting on the surface of the board can be increased. As a result, an acoustic wave element can be achieved, in which the spurious is extremely small in the vicinity of resonant frequency of undesired spurious and major wave.

Description

本発明は、圧電効果を利用した弾性波素子に関するものである。   The present invention relates to an acoustic wave element using a piezoelectric effect.

近年誘電体膜を具備し温度特性を改善された弾性波素子が盛んに開発されている。従来の弾性波素子１１を図７（ａ）〜（ｃ）に示す。図７（ａ）は、ＩＤＴ電極パターン図、図７（ｂ）は図７（ａ）におけるＢ−Ｂ’線の断面図、図７（ｃ）は図７（ｂ）の要部拡大図である。   In recent years, elastic wave elements having a dielectric film and improved temperature characteristics have been actively developed. A conventional acoustic wave element 11 is shown in FIGS. 7A is an IDT electrode pattern diagram, FIG. 7B is a cross-sectional view taken along line BB ′ in FIG. 7A, and FIG. 7C is an enlarged view of a main part of FIG. 7B. is there.

図７（ａ）〜（ｃ）において、弾性波素子１１は、圧電基板１２とＩＤＴ電極１３と反射器電極１４と誘電体膜１５と励振空間１６を有する。ＩＤＴ電極１３は、圧電基板１２の上に形成された電極であり、間隙を介して互いに噛みあうように配置された一対の櫛歯状の電極からなる。反射器電極１４は、圧電基板１２の上でＩＤＴ電極１３を挟むように形成された一対の格子状の電極である。誘電体膜１５は、圧電基板１２とＩＤＴ電極１３と反射器電極１４を覆う誘電体の保護膜である。励振空間１６は、ＩＤＴ電極１３が励振するための空間である。このような構成を有する弾性波素子１１は、封止体（図示せず）によって励振空間１６を密封されて電子部品を構成する。   7A to 7C, the acoustic wave element 11 includes a piezoelectric substrate 12, an IDT electrode 13, a reflector electrode 14, a dielectric film 15, and an excitation space 16. The IDT electrode 13 is an electrode formed on the piezoelectric substrate 12 and is composed of a pair of comb-like electrodes arranged so as to engage with each other through a gap. The reflector electrode 14 is a pair of grid-like electrodes formed on the piezoelectric substrate 12 so as to sandwich the IDT electrode 13. The dielectric film 15 is a dielectric protective film that covers the piezoelectric substrate 12, the IDT electrode 13, and the reflector electrode 14. The excitation space 16 is a space for exciting the IDT electrode 13. The acoustic wave element 11 having such a configuration forms an electronic component by sealing the excitation space 16 with a sealing body (not shown).

このような弾性波素子１１を直列腕共振器と並列腕共振器として用いて、直列腕の共振周波数と並列腕の***振周波数がほぼ一致するようにして作製したラダー型弾性波フィルタにおいて、通過帯域内にリップルを生じないようにするためには、ラダー型弾性波フィルタの動作原理から直列腕共振器の共振周波数近傍において不要波によるスプリアスが十分に小さいこと、および並列腕共振器の***振周波数近傍においてスプリアスが十分小さいことが必要である。   In such a ladder-type acoustic wave filter manufactured using such an acoustic wave element 11 as a series arm resonator and a parallel arm resonator so that the resonance frequency of the series arm and the anti-resonance frequency of the parallel arm substantially coincide with each other. In order to prevent ripples in the band, spurious due to unnecessary waves is sufficiently small near the resonance frequency of the series arm resonator from the principle of operation of the ladder-type elastic wave filter, and anti-resonance of the parallel arm resonator. The spurious must be sufficiently small near the frequency.

従来の弾性波素子１１は、共振周波数近傍または***振周波数近傍に出現する不要波スプリアスを抑圧する手段として、図７（ｂ）、（ｃ）に示すように、圧電基板１２上に誘電体膜１５を堆積し、さらに電極上方に誘電体膜１５の突起を形成することで不要波を抑圧する手法が用いられている。   As shown in FIGS. 7B and 7C, the conventional acoustic wave element 11 is a dielectric film on the piezoelectric substrate 12 as means for suppressing unwanted wave spurious appearing near the resonance frequency or near the anti-resonance frequency. 15 is used, and a projection of the dielectric film 15 is formed above the electrode to suppress unwanted waves.

なお、この出願の発明に関する先行技術情報としては、例えば、特許文献１、非特許文献１が知られている。   For example, Patent Document 1 and Non-Patent Document 1 are known as prior art information relating to the invention of this application.

国際公開第２０１１／０５２２１８号International Publication No. 2011/052218

Ｈ．ｎａｋａｍｕｒａ著、Ｓｕｐｐｒｅｓｓｉｏｎ ｏｆ Ｔｒａｎｓｖｅｒｓｅ Ｍｏｄｅ Ｓｐｕｒｉｏｕｓ ｉｎ ＳＡＷ ＲＥＳＯＮＡＴＯＲＳｏｎ ａｎ ＳｉＯ2／Ａｌ／ＬｉＮｂＯ3 Ｓｔｒｕｃｔｕｒｅ ｆｏｒ Ｗｉｄｅｂａｎｄ ＣＤＭＡ Ａｐｐｌｉｃａｔｉｏｎｓ、Ｐｒｏｃ． ＩＥＥＥ ＩＵＳ ２００８、５９４−５９７H. by Nakamura, Suppression of Transverse Mode Spurious in SAW RESONATORSon an SiO2 / Al / LiNbO3 Structure for Wideband CDMA Applications, Proc. IEEE IUS 2008, 594-597

しかしながら、従来の弾性波素子は誘電体膜上の不要波スプリアスの抑圧条件となる突起の形状制御が容易ではないため、スプリアスを十分に抑圧した弾性波素子を容易に製造することが難しいという課題があった。   However, since the conventional elastic wave device is not easy to control the shape of the protrusion, which is a condition for suppressing unwanted wave spurious on the dielectric film, it is difficult to easily manufacture an elastic wave device with sufficiently suppressed spurious. was there.

そこで、本発明では作製が容易で、共振周波数近傍または***振周波数近傍の不要波スプリアスを十分に小さくすることができる弾性波素子の提供を目的とするものである。   Accordingly, an object of the present invention is to provide an elastic wave element that can be easily manufactured and can sufficiently reduce unnecessary wave spurious near the resonance frequency or the anti-resonance frequency.

上記目的を達成するために本発明の弾性波素子は、圧電基板の上方に形成されたＩＤＴ電極と、圧電体基板と前記ＩＤＴ電極に挟まれるように形成された媒質と、媒質およびＩＤＴ電極間に形成された誘電体膜とを備え、ＩＤＴ電極の上面は、誘電体膜の上面より圧電基板上方に高く形成され、ＩＤＴ電極の密度は、圧電基板の密度および媒質の密度および誘電体膜の密度のいずれよりも大きいことを特徴としたものである。   In order to achieve the above object, an acoustic wave device of the present invention includes an IDT electrode formed above a piezoelectric substrate, a medium formed so as to be sandwiched between the piezoelectric substrate and the IDT electrode, and between the medium and the IDT electrode. The upper surface of the IDT electrode is formed higher than the upper surface of the dielectric film above the piezoelectric substrate, and the density of the IDT electrode is the density of the piezoelectric substrate, the density of the medium, and the dielectric film. It is characterized by being larger than any of the densities.

上記構成により、レイリー波の音速に対し、ＳＨ波の音速は遅くなり、主要波と不要波の音速差を広げることができる。この結果、共振周波数近傍または***振周波数近傍の不要波スプリアスが十分に小さい弾性波素子が実現できる。またこのような弾性波素子を用いてラダー型弾性波フィルタを構成することで通過帯域内のリップルが小さいラダー型弾性波フィルタを得ることができる。   With the above configuration, the sound speed of the SH wave becomes slower than the speed of the Rayleigh wave, and the difference in sound speed between the main wave and the unnecessary wave can be widened. As a result, it is possible to realize an acoustic wave device having sufficiently small unnecessary wave spurious near the resonance frequency or anti-resonance frequency. Moreover, a ladder-type elastic wave filter having a small ripple in the passband can be obtained by configuring a ladder-type elastic wave filter using such an elastic wave element.

（ａ）本発明の一実施の形態における弾性波素子の上面模式図、（ｂ）同弾性波素子の断面模式図、（ｃ）同弾性波素子の要部拡大図(A) Schematic top view of acoustic wave element in one embodiment of the present invention, (b) Schematic cross-sectional view of the acoustic wave element, (c) Enlarged view of essential parts of the acoustic wave element 比較例の弾性波素子のアドミッタンス特性図Admittance characteristics of elastic wave device of comparative example 本発明の構造の実施例１の弾性波素子のアドミッタンス特性図Admittance characteristic diagram of elastic wave device of embodiment 1 having structure of the present invention 本発明の構造の実施例１の弾性波素子を用いたラダー型フィルタの通過特性とアドミッタンス特性を示す図The figure which shows the passage characteristic and admittance characteristic of the ladder type filter using the elastic wave element of Example 1 of the structure of this invention 本発明の構造の実施例２の弾性波素子のアドミッタンス特性図Admittance characteristic diagram of elastic wave device of embodiment 2 of structure of the present invention 本発明の構造の実施例２の弾性波素子を用いたラダー型フィルタの通過特性とアドミッタンス特性を示す図The figure which shows the passage characteristic and admittance characteristic of the ladder type filter using the elastic wave element of Example 2 of the structure of this invention （ａ）従来の弾性波素子の上面模式図、（ｂ）同弾性波素子の断面模式図、（ｃ）同弾性波素子の断面要部拡大図(A) A schematic top view of a conventional acoustic wave element, (b) a schematic sectional view of the acoustic wave element, and (c) an enlarged cross-sectional view of the principal part of the acoustic wave element. 比較例の弾性波素子の断面要部拡大図Cross-sectional main part enlarged view of the acoustic wave device of the comparative example 本発明の一実施の形態における弾性波素子を用いた高周波フィルタの回路図The circuit diagram of the high frequency filter using the elastic wave element in one embodiment of the present invention

以下、本発明の一実施の形態における弾性波素子１について、図面を参照しながら説明する。   Hereinafter, an acoustic wave device 1 according to an embodiment of the present invention will be described with reference to the drawings.

図１（ａ）は本発明の一実施の形態における弾性波素子１の上面模式図、図１（ｂ）は図１（ａ）におけるＡ−Ａ’線の断面模式図、図１（ｃ）は図１（ｂ）の要部拡大図である。   1A is a schematic top view of the acoustic wave device 1 according to an embodiment of the present invention, FIG. 1B is a schematic cross-sectional view taken along the line AA ′ in FIG. 1A, and FIG. These are the principal part enlarged views of FIG.1 (b).

図１（ａ）〜（ｃ）において、本発明の一実施の形態における弾性波素子１は、圧電基板２と媒質３とＩＤＴ（ＩｎｔｅｒＤｉｇｉｔａｌ Ｔｒａｎｓｄｕｃｅｒ）電極４と誘電体膜５と反射器電極６と励振空間７を有する。圧電基板２は、タンタル酸リチウム（ＬｉＴａＯ3）やニオブ酸リチウム（ＬｉＮｂＯ3）のような圧電性の単結晶基板である。媒質３は、圧電基板２の表面において、ＩＤＴ電極４と反射器電極６の下に配置した層である。ＩＤＴ電極４および反射器電極６は、媒質３を介して圧電基板２の上に形成された電極であり、その上面は励振空間７に面している。ＩＤＴ電極４は、間隙を介して互いに噛みあうように配置された一対の櫛歯状の電極からなる。反射器電極６は、圧電基板２の上でＩＤＴ電極４を挟むように形成された一対の格子状の電極である。誘電体膜５は、圧電基板２の表面に形成された誘電体からなる膜であり、ＩＤＴ電極４と反射器電極６の側面方向の電極指間を埋めるように形成したものである。励振空間７は、ＩＤＴ電極４が励振するための空間である。このような構成を有する弾性波素子１は、封止体（図示せず）によってＩＤＴ電極４と励振空間７を密封されて電子部品を構成する。 1A to 1C, an acoustic wave device 1 according to an embodiment of the present invention includes a piezoelectric substrate 2, a medium 3, an IDT (InterDigital Transducer) electrode 4, a dielectric film 5, and a reflector electrode 6. It has an excitation space 7. The piezoelectric substrate 2 is a piezoelectric single crystal substrate such as lithium tantalate (LiTaO 3 ) or lithium niobate (LiNbO 3 ). The medium 3 is a layer disposed below the IDT electrode 4 and the reflector electrode 6 on the surface of the piezoelectric substrate 2. The IDT electrode 4 and the reflector electrode 6 are electrodes formed on the piezoelectric substrate 2 through the medium 3, and the upper surfaces thereof face the excitation space 7. The IDT electrode 4 is composed of a pair of comb-like electrodes arranged so as to mesh with each other through a gap. The reflector electrode 6 is a pair of grid-like electrodes formed on the piezoelectric substrate 2 so as to sandwich the IDT electrode 4. The dielectric film 5 is a film made of a dielectric formed on the surface of the piezoelectric substrate 2, and is formed so as to fill the gap between the electrode fingers in the side surface direction of the IDT electrode 4 and the reflector electrode 6. The excitation space 7 is a space for exciting the IDT electrode 4. The acoustic wave device 1 having such a configuration constitutes an electronic component by sealing the IDT electrode 4 and the excitation space 7 with a sealing body (not shown).

そして、本発明の一実施の形態における弾性波素子１は、ＩＤＴ電極４の密度が、圧電基板２の密度と媒質３の密度と誘電体膜５の密度のいずれよりも大きく、かつＩＤＴ電極４の上面は、誘電体膜５の上面より圧電基板２の上方に高く形成されたことを特徴とするものである。   In the acoustic wave device 1 according to the embodiment of the present invention, the density of the IDT electrode 4 is larger than any of the density of the piezoelectric substrate 2, the density of the medium 3, and the density of the dielectric film 5, and the IDT electrode 4. The upper surface is formed higher than the upper surface of the dielectric film 5 above the piezoelectric substrate 2.

上記構成において、密度の大きい媒体に集中して伝搬するＳＨ（Ｓｈｅａｒ−Ｈｏｒｉｚｏｎｔａｌ）波は、ＩＤＴ電極４の上面に近い表面付近に振幅分布が集中するためＩＤＴ電極４のグレーティング構造による音速低下が圧電基板２の表面付近に集中して伝搬するレイリー波より大きく、ＳＨ波とレイリー波の音速差を拡大することができる。これにより、ＳＨ波とレイリー波の一方を弾性波素子１の主要波として選択した場合、不要波となる他方の周波数を主要波の周波数から遠ざけて必要とする周波数帯域から外すことができ、必要周波数帯域における不要波スプリアスを十分に小さくすることができる。ＩＤＴ電極４の上面が、誘電体膜５の上面より圧電基板２の上方に高く形成された構成とすることでＳＨ波をより遅くしレイリー波との音速差を大きくでき、不要波スプリアスをより遠ざけることができる。更に、媒質３の膜厚を増やすことによってＳＨ波が圧電基板２の表面から離れるため、音速差をより拡大でき、不要波スプリアスの現れる周波数を調整することができる。   In the above configuration, SH (Shear-Horizontal) waves concentratedly propagating in a medium having a high density are concentrated in the vicinity of the surface near the upper surface of the IDT electrode 4, so that the sound speed reduction due to the grating structure of the IDT electrode 4 is piezoelectric. The sound speed difference between the SH wave and the Rayleigh wave is larger than the Rayleigh wave that is concentrated and propagated near the surface of the substrate 2. Thereby, when one of the SH wave and the Rayleigh wave is selected as the main wave of the elastic wave element 1, the other frequency that becomes an unnecessary wave can be removed from the required frequency band away from the frequency of the main wave. Unwanted wave spurious in the frequency band can be sufficiently reduced. By making the upper surface of the IDT electrode 4 higher than the upper surface of the dielectric film 5 above the piezoelectric substrate 2, the SH wave can be made slower, the sound speed difference from the Rayleigh wave can be increased, and unnecessary wave spurious can be further increased. You can keep away. Furthermore, since the SH wave is separated from the surface of the piezoelectric substrate 2 by increasing the film thickness of the medium 3, the difference in sound speed can be further increased, and the frequency at which the unwanted wave spurious appears can be adjusted.

次に、本発明の一実施の形態における弾性波素子を用いた高周波フィルタであるラダー型弾性波フィルタの回路図を図９に示す。図９は、上記構成の弾性波素子１を直列腕共振器８および並列腕共振器９として用いてラダー型弾性波フィルタ１０を構成した回路図であり、直列腕共振器８の共振周波数と並列腕共振器９の***振周波数がほぼ一致するようにして設計したもので、並列腕共振器９の共振周波数と直列腕共振器８の***振周波数の間に通過帯域が形成されるとともに、並列腕共振器９の共振周波数と直列腕共振器８の***振周波数により通過帯域の下端および上端に減衰極が形成され、バンドパスフィルタが形成できる。   Next, FIG. 9 shows a circuit diagram of a ladder-type acoustic wave filter that is a high-frequency filter using an acoustic wave element according to an embodiment of the present invention. FIG. 9 is a circuit diagram in which a ladder-type elastic wave filter 10 is configured using the elastic wave element 1 having the above configuration as the series arm resonator 8 and the parallel arm resonator 9, and in parallel with the resonance frequency of the series arm resonator 8. It is designed so that the antiresonance frequencies of the arm resonators 9 substantially coincide with each other, and a pass band is formed between the resonance frequency of the parallel arm resonator 9 and the antiresonance frequency of the series arm resonator 8, and in parallel. Attenuation poles are formed at the lower end and upper end of the pass band by the resonance frequency of the arm resonator 9 and the anti-resonance frequency of the series arm resonator 8, and a band-pass filter can be formed.

本発明の一実施の形態による弾性波素子１は、主要波の共振周波数および***振周波数に対し不要波の共振周波数および***振周波数を通過帯域から外すことによって、主要波の共振周波数の近傍および***振周波数の近傍から主要なスプリアスを排除することができ、ラダー型弾性波フィルタ１０の通過帯域内におけるリップルを十分に低減することができ、良好なフィルタ特性を実現できる。   The elastic wave device 1 according to one embodiment of the present invention removes the resonance frequency and the antiresonance frequency of the unnecessary wave from the passband with respect to the resonance frequency and the antiresonance frequency of the main wave. Main spurious can be eliminated from the vicinity of the anti-resonance frequency, ripple in the passband of the ladder-type elastic wave filter 10 can be sufficiently reduced, and good filter characteristics can be realized.

ここで、共振器の共振周波数ｆｒと***振周波数ｆａの差をΔｆとしたとき、共振周波数ｆｒの近傍とはｆｒ±０．９×Δｆの周波数範囲を指し、***振周波数ｆａの近傍とはｆａ±０．９×Δｆの周波数範囲を指すことと定義する。共振器のＱ値（尖鋭度）が有限な値であることを考慮すると、この定義で規定された直列腕共振器８の共振周波数の近傍および並列腕共振器９の***振周波数の近傍がすなわちバンドパスフィルタの通過帯域であり、この通過帯域においてスプリアスを十分に低減できればラダー型弾性波フィルタ１０の通過帯域内のリップルを十分に低減することができる。   Here, when the difference between the resonance frequency fr and the antiresonance frequency fa of the resonator is Δf, the vicinity of the resonance frequency fr indicates a frequency range of fr ± 0.9 × Δf, and the vicinity of the antiresonance frequency fa is It is defined to indicate a frequency range of fa ± 0.9 × Δf. Considering that the Q value (sharpness) of the resonator is a finite value, the vicinity of the resonance frequency of the series arm resonator 8 and the vicinity of the antiresonance frequency of the parallel arm resonator 9 defined by this definition are If the spurious is sufficiently reduced in the pass band of the band-pass filter, the ripple in the pass band of the ladder-type elastic wave filter 10 can be sufficiently reduced.

なお、本発明の一実施の形態における弾性波素子１はＩＤＴ電極４の上面が励振空間７に面している。このような構造は、圧電基板２上にＩＤＴ電極４と反射器電極６を形成後、誘電体膜をスパッタやＣＶＤなどの方法で成膜した後、誘電体膜を研磨することで得られる。誘電体膜に比べＩＤＴ電極４を構成する金属材料のほうが硬い材料を選択すれば、ＩＤＴ電極４を構成する金属材料が化学機械研磨等の機械的研磨法におけるストッパーの役割を果たす。このため、弾性波素子１の上面の平坦化が容易かつ安定的に製造できる。また、機械的研磨法の条件を選択することにより、ＩＤＴ電極４の上面は、誘電体膜５の上面より圧電基板２の上方に高く形成された構造を安定的に作製することができる。   In the elastic wave device 1 according to the embodiment of the present invention, the upper surface of the IDT electrode 4 faces the excitation space 7. Such a structure can be obtained by forming the IDT electrode 4 and the reflector electrode 6 on the piezoelectric substrate 2, forming the dielectric film by a method such as sputtering or CVD, and then polishing the dielectric film. If a metal material constituting the IDT electrode 4 is selected to be harder than the dielectric film, the metal material constituting the IDT electrode 4 serves as a stopper in a mechanical polishing method such as chemical mechanical polishing. For this reason, the upper surface of the acoustic wave device 1 can be easily and stably manufactured. Further, by selecting the conditions of the mechanical polishing method, it is possible to stably produce a structure in which the upper surface of the IDT electrode 4 is formed higher than the upper surface of the dielectric film 5 above the piezoelectric substrate 2.

圧電基板２は例えばニオブ酸リチウム（ＬｉＮｂＯ3）のような主要波と不要波の音速が近い圧電単結晶基板からなる。より具体的には、ＳＨ波とレイリー波の近い１１８〜１３８°回転ＹカットＸ伝搬ＬｉＮｂＯ3などがある。 The piezoelectric substrate 2 is composed of a piezoelectric single crystal substrate in which the speed of sound of the main wave and the unnecessary wave is close, such as lithium niobate (LiNbO 3 ). More specifically, there are 118-138 ° rotated Y-cut X-propagating LiNbO 3 that is close to the SH wave and Rayleigh wave.

媒質３は、例えばＳｉＯ2（酸化珪素）やアルミニウムを主成分とするが、媒質３の密度が圧電基板２およびＩＤＴ電極４の密度より小さい材料であれば構わない。特に媒質３としてＳｉＯ2を用いた場合、ＳｉＯ2の音速の温度特性が圧電基板２の音速の温度特性と異なり高温で音速が速くなる性質を有するため、共振周波数および***振周波数の温度特性が弾性波素子１の温度特性改善ができる。また媒質３にアルミニウムを用いた場合、電気機械結合係数を大きくできる。 The medium 3 is mainly composed of, for example, SiO 2 (silicon oxide) or aluminum, but may be any material as long as the density of the medium 3 is smaller than the density of the piezoelectric substrate 2 and the IDT electrode 4. In particular, when SiO 2 is used as the medium 3, the temperature characteristics of the sound speed of SiO 2 are different from the temperature characteristics of the sound speed of the piezoelectric substrate 2, and the sound speed increases at high temperatures. The temperature characteristics of the acoustic wave device 1 can be improved. When aluminum is used for the medium 3, the electromechanical coupling coefficient can be increased.

ＩＤＴ電極４は、櫛形電極が交差する様に形成された金属電極であり、例えば、銅、銀、金、チタン、タングステン、白金、クロム、若しくはモリブデンからなる単体金属、又はこれらを主成分とする合金又はそれらの金属が積層された構成である。特に、タングステンやモリブデンを用いると、媒質３や誘電体膜５より密度を大きくすることが容易であり、硬さも大きい材料であるので、本発明の一実施の形態における弾性波素子１のＩＤＴ電極４として好ましい。   The IDT electrode 4 is a metal electrode formed so that the comb-shaped electrodes intersect with each other. For example, the IDT electrode 4 is a single metal made of copper, silver, gold, titanium, tungsten, platinum, chromium, or molybdenum, or the main component thereof. It is the structure by which the alloy or those metals were laminated | stacked. In particular, when tungsten or molybdenum is used, it is easier to increase the density than the medium 3 or the dielectric film 5 and the material has a higher hardness. Therefore, the IDT electrode of the acoustic wave device 1 according to the embodiment of the present invention. 4 is preferable.

なお、図１（ａ）では、ＩＤＴ電極４は、ＩＤＴ電極４の電極指の交差幅が一定の正規型の構成を示したが、高次横モードスプリアス抑圧のために、ＩＤＴ電極４の中央から反射器電極６に近づくに従って交差幅が小さくなるようなアポタイズ重み付けが施されていても良い。   In FIG. 1A, the IDT electrode 4 has a regular configuration in which the crossing width of the electrode fingers of the IDT electrode 4 is constant. However, in order to suppress higher-order transverse mode spurious, the IDT electrode 4 is centered. To the reflector electrode 6, the apodization weighting may be applied so that the crossing width becomes smaller.

誘電体膜５は、例えばＳｉＯ2を主成分とするが、誘電体膜５の密度がＩＤＴ電極４の密度より小さい材料であれば構わない。 The dielectric film 5 is mainly composed of, for example, SiO 2 , but may be any material as long as the density of the dielectric film 5 is smaller than the density of the IDT electrode 4.

ＩＤＴ電極４の主成分をモリブデンとし、媒質３の主成分をＳｉＯ2とした場合、携帯電話などの通信システムに対応したフィルタ特性を得るために実用的な７％以上の電気機械結合係数を得るためにモリブデンの膜厚は０．０３７５λ以上である必要がある。ここで、λは図１（ｃ）に示すようにＩＤＴ電極４の１波長分の周期で決まる長さである。一方、媒質３の主成分をアルミニウムとした場合、ＩＤＴ電極４の膜厚を０．０１２５λ以上とすることで、主要波の共振周波数より低周波数側に不要波スプリアスを離すことができ、主要波の共振周波数近傍から不要波スプリアスを排除することができる。このような構成とすることで、本実施の形態の弾性波素子を直列腕共振器と並列腕共振器としたラダー型弾性波フィルタ１０を作製した際、通過帯域内リップルの小さなフィルタ特性を得ることができる。 When the main component of the IDT electrode 4 is molybdenum and the main component of the medium 3 is SiO 2 , a practical electromechanical coupling coefficient of 7% or more is obtained to obtain filter characteristics corresponding to a communication system such as a mobile phone. Therefore, the film thickness of molybdenum needs to be 0.0375λ or more. Here, λ is a length determined by the period of one wavelength of the IDT electrode 4 as shown in FIG. On the other hand, when the main component of the medium 3 is aluminum, by setting the film thickness of the IDT electrode 4 to 0.0125λ or more, unnecessary wave spurious can be separated to a lower frequency side than the resonance frequency of the main wave. Unnecessary wave spurious can be eliminated from the vicinity of the resonance frequency. With this configuration, when the ladder-type elastic wave filter 10 using the elastic wave element according to the present embodiment as a series arm resonator and a parallel arm resonator is manufactured, a filter characteristic with small ripple in the passband is obtained. be able to.

（比較例）
以下、図７（ａ）、図８の構成を有する比較例の弾性波素子１１について説明する。比較例の弾性波素子１１は、図７の従来の弾性波素子１１から誘電体膜１５の突起を取り除いたものである。 (Comparative example)
Hereinafter, the elastic wave element 11 of the comparative example having the configurations of FIGS. 7A and 8 will be described. The elastic wave element 11 of the comparative example is obtained by removing the protrusion of the dielectric film 15 from the conventional elastic wave element 11 of FIG.

比較例の弾性波素子１１において、圧電基板１２は１２８°回転ＹカットＸ伝搬のニオブ酸リチウム基板、ＩＤＴ電極１３の電極指周期はλ＝４．０μｍ、ＩＤＴ電極１３および反射器電極１４の主成分はモリブデンで膜厚は０．０７５λ、誘電体膜１５の主成分はＳｉＯ2である。ＩＤＴ電極１３の設計は、電極指の交差幅が２０λ、電極指対数が１００対、電極指のデューティ比（電極指幅／（λ／２））が０．５であり、反射器電極１４の電極指本数は３０本である。圧電基板１２の表面からの誘電体膜１５の膜厚は０．０８８１λである。 In the acoustic wave element 11 of the comparative example, the piezoelectric substrate 12 is a 128 ° rotated Y-cut X-propagation lithium niobate substrate, the electrode finger period of the IDT electrode 13 is λ = 4.0 μm, and the IDT electrode 13 and the reflector electrode 14 are main. The component is molybdenum, the film thickness is 0.075λ, and the main component of the dielectric film 15 is SiO 2 . The IDT electrode 13 is designed such that the crossing width of electrode fingers is 20λ, the number of electrode finger pairs is 100, the duty ratio of electrode fingers (electrode finger width / (λ / 2)) is 0.5, and the reflector electrode 14 The number of electrode fingers is 30. The film thickness of the dielectric film 15 from the surface of the piezoelectric substrate 12 is 0.0881λ.

次に比較例の弾性波素子のアドミッタンス特性を図２に示す。図２において、縦軸はアドミッタンス特性を示し、横軸は共振周波数での規格化された規格化周波数を示す。   Next, FIG. 2 shows the admittance characteristics of the acoustic wave device of the comparative example. In FIG. 2, the vertical axis represents the admittance characteristics, and the horizontal axis represents the normalized frequency normalized at the resonance frequency.

図２において、主要波であるレイリー波の共振周波数の規格化周波数ｆｒは１．０００、***振周波数の規格化周波数ｆａは１．０５９であり、***振周波数と共振周波数の規格化周波数の差Δｆは０．０５９である。一方、不要波であるＳＨ波スプリアスの規格化周波数ｆｘは１．０１１である。本明細書において共振周波数の近傍とはｆｒ±０．９×Δｆと定義しているので、ＳＨ波スプリアスは共振周波数近傍に存在することになる。このような比較例の弾性波素子をラダー型フィルタの直列腕共振器として用いた場合には、フィルタの通過帯域にＳＨ波スプリアスに起因するリップルを生じてしまう。   In FIG. 2, the normalized frequency fr of the resonance frequency of the Rayleigh wave as the main wave is 1.000, the normalized frequency fa of the anti-resonance frequency is 1.059, and the difference between the normalized frequency of the anti-resonance frequency and the resonance frequency. Δf is 0.059. On the other hand, the normalized frequency fx of the SH wave spurious which is an unnecessary wave is 1.011. In this specification, the vicinity of the resonance frequency is defined as fr ± 0.9 × Δf, so that the SH wave spurious exists near the resonance frequency. When such an elastic wave element of the comparative example is used as a series arm resonator of a ladder type filter, a ripple due to SH wave spurious is generated in the pass band of the filter.

（実施例１）
以下、図１（ａ）〜（ｃ）の構成を有する本発明の弾性波素子１の実施例１について説明する。 Example 1
Hereinafter, Example 1 of the acoustic wave device 1 of the present invention having the configuration shown in FIGS.

実施例１の弾性波素子１において、圧電基板２は１２８°回転ＹカットＸ伝搬のニオブ酸リチウム基板、ＩＤＴ電極４の電極指周期はλ＝４．０μｍ、媒質３および誘電体膜５の主成分はＳｉＯ2、媒質３の規格化膜厚は０．０１１４λ、誘電体膜５の規格化膜厚は０．０８１４λ、ＩＤＴ電極４および反射器電極６の主成分はモリブデン、ＩＤＴ電極４および反射器電極６の規格化膜厚は０．０７５λである。ＩＤＴ電極４の設計は、電極指の交差幅が２０λ、電極指対数が１００対、電極指のデューティ比（電極指幅／（λ／２））が０．５であり、反射器電極６の電極指本数は３０本である。ここで、ＩＤＴ電極４の規格化膜厚と媒質３の規格化膜厚の比は、１対０．１５２である。ＩＤＴ電極４の上面と、誘電体膜５の上面の凹部との高さの差Ｈｄｉｆは２０ｎｍであり、電極周期で規格化すると０．００５λである。誘電体膜５の上面はＩＤＴ電極４に接する側において高く、ＩＤＴ電極４とＩＤＴ電極４の中間位置において低くなるように高さが変化しており、前述のＨｄｉｆは高さの最大差の値を示す。なお、規格化膜厚とは、電極周期で規格化した膜厚をいう。 In the acoustic wave device 1 of Example 1, the piezoelectric substrate 2 is a 128 ° rotated Y-cut X-propagation lithium niobate substrate, the electrode finger period of the IDT electrode 4 is λ = 4.0 μm, the medium 3 and the dielectric film 5 The component is SiO 2 , the normalized film thickness of the medium 3 is 0.0114λ, the normalized film thickness of the dielectric film 5 is 0.0814λ, the main components of the IDT electrode 4 and the reflector electrode 6 are molybdenum, the IDT electrode 4 and the reflective film. The normalized film thickness of the device electrode 6 is 0.075λ. The design of the IDT electrode 4 is such that the crossing width of the electrode fingers is 20λ, the number of electrode finger pairs is 100 pairs, the duty ratio of the electrode fingers (electrode finger width / (λ / 2)) is 0.5, The number of electrode fingers is 30. Here, the ratio of the normalized film thickness of the IDT electrode 4 to the normalized film thickness of the medium 3 is 1 to 0.152. The height difference Hdif between the upper surface of the IDT electrode 4 and the concave portion of the upper surface of the dielectric film 5 is 20 nm, and is 0.005λ when normalized by the electrode period. The upper surface of the dielectric film 5 is high on the side in contact with the IDT electrode 4, and the height changes so as to be low at the intermediate position between the IDT electrode 4 and the IDT electrode 4, and the aforementioned Hdif is a value of the maximum difference in height. Indicates. Note that the normalized film thickness refers to a film thickness normalized by the electrode period.

このとき、ＳｉＯ2を主成分とする媒質３および誘電体膜５の密度は２．２０×１０3ｋｇ／ｍ3であり、１２８°ＹカットＸ伝搬のニオブ酸リチウム基板からなる圧電基板２の密度は２．７０×１０3ｋｇ／ｍ3であり、ＩＤＴ電極４であるモリブデンの密度は１０．２８×１０3ｋｇ／ｍ3である。 At this time, the density of the medium 3 and the dielectric film 5 mainly composed of SiO 2 is 2.20 × 10 3 kg / m 3 , and the piezoelectric substrate 2 made of a 128 ° Y-cut X-propagation lithium niobate substrate is used. The density is 2.70 × 10 3 kg / m 3 , and the density of molybdenum as the IDT electrode 4 is 10.28 × 10 3 kg / m 3 .

次に、本発明の弾性波素子１の実施例１のアドミッタンス特性を図３に示す。   Next, FIG. 3 shows the admittance characteristics of Example 1 of the acoustic wave device 1 of the present invention.

図３において、主要波であるレイリー波の共振周波数の規格化周波数ｆｒは１．０００、***振周波数の規格化周波数ｆａは１．０３３であるため、Δｆは０．０３３である。一方、不要波であるＳＨ波スプリアスの規格化周波数ｆｘは０．９６８であり、共振周波数近傍ｆｒ±０．９×Δｆおよび***振周波数近傍ｆａ±０．９×Δｆに大きなスプリアスはない。媒質３のＳｉＯ2の膜厚が０．０１１４λより厚い条件においてはＳＨ波の音速がより遅くなるためＳＨスプリアスの規格化周波数ｆｘがより低くなり、さらに共振周波数の近傍より離れる。ＩＤＴ電極４と、誘電体膜５の上面の凹部の高さの差Ｈｄｉｆを０．００５λ以上とするとＳＨ波の音速がより遅くなるためＳＨスプリアスの規格化周波数ｆｘがより低くなり、さらに共振周波数の近傍より離れる。なお、媒質３の主成分としてＳｉＯ2を用いることにより、電気機械結合係数が９％程度から７％程度に低下したが、共振周波数の温度特性が−６４ｐｐｍ／℃から−５６ｐｐｍ／℃に、***振周波数の温度特性が−５６ｐｐｍ／℃から−３９ｐｐｍ／℃に改善した。 In FIG. 3, since the normalized frequency fr of the resonance frequency of the Rayleigh wave as the main wave is 1.000 and the normalized frequency fa of the anti-resonance frequency is 1.033, Δf is 0.033. On the other hand, the normalized frequency fx of the SH wave spurious which is an unnecessary wave is 0.968, and there is no large spurious in the vicinity of the resonance frequency fr ± 0.9 × Δf and the anti-resonance frequency vicinity fa ± 0.9 × Δf. Under the condition that the SiO 2 film thickness of the medium 3 is thicker than 0.0114λ, the sound speed of the SH wave becomes slower, so the normalized frequency fx of SH spurious becomes lower and further away from the vicinity of the resonance frequency. When the height difference Hdif between the IDT electrode 4 and the concave portion on the upper surface of the dielectric film 5 is 0.005λ or more, the sound speed of the SH wave becomes slower, so the SH spurious normalized frequency fx becomes lower and the resonance frequency further decreases. Away from the vicinity of. Although the electromechanical coupling coefficient was reduced from about 9% to about 7% by using SiO 2 as the main component of the medium 3, the temperature characteristic of the resonance frequency was increased from −64 ppm / ° C. to −56 ppm / ° C. The temperature characteristic of the resonance frequency was improved from −56 ppm / ° C. to −39 ppm / ° C.

図４は、上記実施例１の構成を有する弾性波素子１を直列腕共振器８および並列腕共振器９に用い、その直列腕共振器８の共振周波数ｆSｒとその並列腕共振器９の***振周波数ｆPａがほぼ一致するようにＩＤＴ電極周期を異ならせて作製したラダー型弾性波フィルタ１０の通過特性と直列腕共振器８および並列腕共振器９のアドミッタンス特性を示した図である。 FIG. 4 shows that the elastic wave element 1 having the configuration of the first embodiment is used for the series arm resonator 8 and the parallel arm resonator 9, and the resonance frequency f S r of the series arm resonator 8 and the parallel arm resonator 9 are used. The pass characteristic of the ladder-type elastic wave filter 10 produced by making the IDT electrode period different so that the anti-resonance frequencies f Pa of the two substantially coincide, and the admittance characteristic of the series arm resonator 8 and the parallel arm resonator 9 It is.

図４において、実線Ａがラダー型弾性波フィルタ１０の通過特性、点線Ｂが直列腕共振器８のアドミッタンス特性、破線Ｃが並列腕共振器９のアドミッタンス特性である。図４において、並列腕共振器９の共振周波数ｆPｒにより通過帯域の低域側に減衰極が生成され、直列腕共振器８の***振周波数ｆSａにより、通過帯域の高域側に減衰極が生成され、バンドパスフィルタが形成される。ここで、並列腕共振器９の共振周波数ｆPｒと直列腕共振器８の不要波スプリアスの周波数ｆSｘをほぼ一致させたことにより、直列腕共振器８のＳＨ波スプリアスは通過帯域の低域側の減衰極により減衰しており、通過帯域内にリップルを生じさせない。また、並列腕共振器９のＳＨ波スプリアスの周波数ｆPｘは直列腕共振器８のＳＨ波スプリアスの周波数ｆSｘより更に低い位置に現れるためフィルタの通過帯域内特性に悪影響を与えない。そして、媒質３の膜厚を０．０１１４λより厚くすることにより、ＳＨ波の音速をより遅くすることができ、ＳＨ波のスプリアスにより生ずるリップルを通過帯域内からより遠ざけることができる。以上より、ＩＤＴ電極４の主成分をモリブデン、媒質３の主成分をＳｉＯ2としたときに、電極周期で規格化したＩＤＴ電極４の規格化膜厚と媒質３の規格化膜厚の比を、１対０．１５２以上とすることにより、フィルタの通過帯域内のリップルが小さいラダー型弾性波フィルタ１０が実現できる。 In FIG. 4, the solid line A is the pass characteristic of the ladder-type acoustic wave filter 10, the dotted line B is the admittance characteristic of the series arm resonator 8, and the broken line C is the admittance characteristic of the parallel arm resonator 9. 4, the attenuation pole on the low frequency side of the pass band by the resonance frequency f P r of the parallel arm resonator 9 is generated by the anti-resonant frequency f S a series arm resonator 8, the high-frequency side of the pass band An attenuation pole is generated and a bandpass filter is formed. Here, by making the resonance frequency f P r of the parallel arm resonator 9 substantially coincide with the frequency f S x of the unwanted wave spurious of the series arm resonator 8, the SH wave spurious of the series arm resonator 8 has a pass band. It is attenuated by the attenuation pole on the low frequency side and does not cause ripples in the passband. Further, since the frequency f P x of the SH wave spurious of the parallel arm resonator 9 appears at a position lower than the frequency f S x of the SH wave spurious of the series arm resonator 8, there is no adverse effect on the in-pass characteristics of the filter. By making the thickness of the medium 3 thicker than 0.0114λ, the sound speed of the SH wave can be made slower, and the ripple caused by the spurious of the SH wave can be further away from the passband. From the above, when the main component of the IDT electrode 4 is molybdenum and the main component of the medium 3 is SiO 2 , the ratio between the normalized film thickness of the IDT electrode 4 normalized by the electrode period and the normalized film thickness of the medium 3 is obtained. By setting it to 1: 0.152 or more, the ladder-type elastic wave filter 10 with a small ripple in the passband of the filter can be realized.

（実施例２）
以下、図１（ａ）〜（ｃ）の構成を有する本発明の弾性波素子１の実施例２について説明する。 (Example 2)
Hereinafter, Example 2 of the acoustic wave device 1 of the present invention having the configuration shown in FIGS.

実施例２の弾性波素子１において、圧電基板２は１２８°ＹカットＸ伝搬のニオブ酸リチウム基板、ＩＤＴ電極４の電極指の周期はλ＝４．０μｍ、媒質３の主成分はアルミニウム、媒質３の膜厚は０．０６０３λ、ＩＤＴ電極４および反射器電極６の主成分はモリブデン、ＩＤＴ電極４および反射器電極６の膜厚は０．０５λ、誘電体膜５の主成分はＳｉＯ2、誘電体膜５の膜厚は０．１０５３λである。ＩＤＴ電極４の設計は、電極指交差幅が２０λ、電極指の対数は１００対、電極指のデューティ比（電極指幅／ピッチ）は０．５であり、反射器電極６の電極指本数は３０本である。ここで、ＩＤＴ電極４の規格化膜厚と媒質３の規格化膜厚の比は、１対１．２０６である。ＩＤＴ電極４の上面と、誘電体膜５の上面の凹部との高さの差Ｈｄｉｆは２０ｎｍであり、電極周期で規格化すると０．００５λである。 In the acoustic wave device 1 of Example 2, the piezoelectric substrate 2 is a 128 ° Y-cut X-propagation lithium niobate substrate, the electrode finger period of the IDT electrode 4 is λ = 4.0 μm, the main component of the medium 3 is aluminum, the medium 3 is 0.0603λ, the main component of the IDT electrode 4 and the reflector electrode 6 is molybdenum, the thickness of the IDT electrode 4 and the reflector electrode 6 is 0.05λ, and the main component of the dielectric film 5 is SiO 2 . The film thickness of the dielectric film 5 is 0.1053λ. The IDT electrode 4 is designed such that the electrode finger crossing width is 20λ, the number of electrode finger pairs is 100, the duty ratio of electrode fingers (electrode finger width / pitch) is 0.5, and the number of electrode fingers of the reflector electrode 6 is 30. Here, the ratio of the normalized film thickness of the IDT electrode 4 to the normalized film thickness of the medium 3 is 1: 1.206. The height difference Hdif between the upper surface of the IDT electrode 4 and the concave portion of the upper surface of the dielectric film 5 is 20 nm, and is 0.005λ when normalized by the electrode period.

このとき、アルミニウムを主成分とする媒質３の密度は２．７０×１０3ｋｇ／ｍ3であり、ＳｉＯ2を主成分とする誘電体膜５の密度は２．２０×１０3ｋｇ／ｍ3であり、１２８°ＹカットＸ伝搬のニオブ酸リチウムからなる圧電基板２の密度は２．７０×１０3ｋｇ／ｍ3であり、モリブデンを主成分とするＩＤＴ電極４の密度は１０．２８×１０3ｋｇ／ｍ3である。 At this time, the density of the medium 3 whose main component is aluminum is 2.70 × 10 3 kg / m 3 , and the density of the dielectric film 5 whose main component is SiO 2 is 2.20 × 10 3 kg / m 3. 3 , the density of the piezoelectric substrate 2 made of 128 ° Y-cut X-propagating lithium niobate is 2.70 × 10 3 kg / m 3 , and the density of the IDT electrode 4 whose main component is molybdenum is 10.28. × 10 3 kg / m 3

次に、本発明の弾性波素子１の実施例２のアドミッタンス特性を図５に示す。   Next, FIG. 5 shows the admittance characteristics of Example 2 of the acoustic wave device 1 of the present invention.

図５において、主要波であるレイリー波の共振周波数の規格化周波数ｆｒは１．０００、***振周波数の規格化周波数ｆａは１．０４５であるため、Δｆ＝０．０４５となる。一方、不要波であるＳＨ波スプリアスの規格化周波数ｆｘは０．９５７であり、共振周波数近傍ｆｒ±Δｆおよび***振周波数近傍ｆａ±ΔｆにＳＨ波スプリアスはない。媒質３のアルミニウムの膜厚が０．０６０３λより厚い条件においてはＳＨ波の音速がより遅くなるためＳＨ波スプリアスの周波数が低くなり、主要波の共振周波数近傍より周波数の低い側へより離れる。なお、このとき媒質３をアルミニウムにすることで、電気機械結合係数は９％程度と大きい値が得られる。   In FIG. 5, since the normalized frequency fr of the resonance frequency of the Rayleigh wave which is the main wave is 1.000 and the normalized frequency fa of the anti-resonance frequency is 1.045, Δf = 0.045. On the other hand, the normalized frequency fx of the SH wave spurious that is an unnecessary wave is 0.957, and there is no SH wave spurious in the vicinity of the resonance frequency fr ± Δf and the anti-resonance frequency near fa ± Δf. Under the condition that the film thickness of the aluminum of the medium 3 is thicker than 0.0603λ, the sound speed of the SH wave becomes slower, so the frequency of the SH wave spurious becomes lower, and it is further away from the vicinity of the resonance frequency of the main wave toward the lower frequency side. At this time, if the medium 3 is made of aluminum, the electromechanical coupling coefficient can be as large as about 9%.

図６は、上記実施例２の構成を有する弾性波素子１を直列腕共振器８および並列腕共振器９に用いて、その直列腕共振器８の共振周波数ｆSｒとその並列腕共振器９の***振周波数ｆPａがほぼ一致するようにＩＤＴ電極周期を異ならせて作製したラダー型弾性波フィルタ１０の通過特性と直列腕共振器８および並列腕共振器９のアドミッタンス特性を示した図である。 FIG. 6 shows a case where the acoustic wave device 1 having the configuration of the second embodiment is used for the series arm resonator 8 and the parallel arm resonator 9, and the resonance frequency f S r of the series arm resonator 8 and its parallel arm resonator. anti-resonance frequency f P a nine showed admittance characteristic of the pass characteristics and the series arm resonator 8 and the parallel arm resonator 9 of the ladder-type acoustic wave filter 10 produced with different IDT electrode period to match almost FIG.

図６において、実線Ｄがラダー型弾性波フィルタ１０の通過特性、点線Ｅが直列腕共振器８のアドミッタンス特性、破線Ｆが並列腕共振器９のアドミッタンス特性である。図６において、並列腕共振器９の共振周波数ｆPｒと直列腕共振器８のＳＨ波スプリアスの周波数ｆSｘがほぼ同じであるため、直列腕共振器８側のＳＨ波スプリアスは通過帯域の低域側の減衰極により減衰している。媒質３の膜厚を０．０６０３λより厚くすることにより、ＳＨ波の音速をより遅くすることができ、ＳＨ波のスプリアスにより生ずるリップルをフィルタの通過帯域内から排除できる。以上より、ＩＤＴ電極４の主成分をモリブデン、媒質３の主成分をアルミニウムとしたときに、電極周期で規格化したＩＤＴ電極４の規格化膜厚と媒質３の規格化膜厚の比を１対１．２０６以上とすることにより、フィルタの帯域内のリップルが小さいラダー型弾性波フィルタ１０が実現できる。 In FIG. 6, the solid line D is the pass characteristic of the ladder-type elastic wave filter 10, the dotted line E is the admittance characteristic of the series arm resonator 8, and the broken line F is the admittance characteristic of the parallel arm resonator 9. In FIG. 6, since the resonance frequency f P r of the parallel arm resonator 9 and the frequency f S x of the SH wave spurious of the series arm resonator 8 are substantially the same, the SH wave spurious on the series arm resonator 8 side is in the passband. It is attenuated by the attenuation pole on the low frequency side. By making the film thickness of the medium 3 thicker than 0.0603λ, the sound speed of the SH wave can be made slower, and the ripple caused by the spurious wave of the SH wave can be excluded from the pass band of the filter. From the above, when the main component of the IDT electrode 4 is molybdenum and the main component of the medium 3 is aluminum, the ratio of the normalized film thickness of the IDT electrode 4 normalized by the electrode period to the normalized film thickness of the medium 3 is 1. By setting it to 1.206 or more, the ladder-type acoustic wave filter 10 with small ripple in the filter band can be realized.

本発明にかかる弾性波素子は、移動体通信機器に用いられる高周波フィルタなどの電子機器に適用可能である。   The acoustic wave device according to the present invention can be applied to electronic devices such as a high frequency filter used in mobile communication devices.

１、１１ 弾性波素子
２、１２ 圧電基板
３ 媒質
４、１３ ＩＤＴ電極
５、１５ 誘電体膜
６、１４ 反射器電極
７、１６ 励振空間
８ 直列腕共振器
９ 並列腕共振器
１０ ラダー型弾性波フィルタ DESCRIPTION OF SYMBOLS 1,11 Elastic wave element 2,12 Piezoelectric substrate 3 Medium 4,13 IDT electrode 5,15 Dielectric film 6,14 Reflector electrode 7,16 Excitation space 8 Series arm resonator 9 Parallel arm resonator 10 Ladder type elastic wave filter

Claims (11)

圧電基板と、
前記圧電基板の上方に形成されたＩＤＴ電極と、
前記圧電体基板と前記ＩＤＴ電極に挟まれるように形成された媒質と、
前記媒質および前記ＩＤＴ電極間に形成された誘電体膜とを備え、
前記ＩＤＴ電極の上面は、前記誘電体膜の上面より前記圧電基板の上方高く形成され、
前記ＩＤＴ電極の密度は、前記圧電基板の密度と、前記媒質の密度と、前記誘電体膜の密度のいずれよりも大きいことを特徴とする弾性波素子。 A piezoelectric substrate;
An IDT electrode formed above the piezoelectric substrate;
A medium formed so as to be sandwiched between the piezoelectric substrate and the IDT electrode;
A dielectric film formed between the medium and the IDT electrode,
The upper surface of the IDT electrode is formed higher above the piezoelectric substrate than the upper surface of the dielectric film,
The density of the IDT electrode is larger than any of the density of the piezoelectric substrate, the density of the medium, and the density of the dielectric film. 前記ＩＤＴ電極の上面と、前記誘電体膜の上面との高さの差が０．００５λ以上であることを特徴とする請求項１に記載の弾性波素子。 The acoustic wave device according to claim 1, wherein a difference in height between the upper surface of the IDT electrode and the upper surface of the dielectric film is 0.005λ or more. 前記誘電体膜の密度が前記媒質の密度以下であることを特徴とする請求項１に記載の弾性波素子。 The acoustic wave device according to claim 1, wherein a density of the dielectric film is equal to or less than a density of the medium. 前記誘電体膜の主成分が前記媒質の主成分と同じであることを特徴とする請求項１に記載の弾性波素子。 2. The acoustic wave device according to claim 1, wherein a main component of the dielectric film is the same as a main component of the medium. 前記ＩＤＴ電極が励振する主要弾性波がレイリー波である請求項１に記載の弾性波素子。 The elastic wave device according to claim 1, wherein the main elastic wave excited by the IDT electrode is a Rayleigh wave. 前記ＩＤＴ電極が励振する主要弾性波がＳＨ波である請求項１に記載の弾性波素子。 The acoustic wave device according to claim 1, wherein the main acoustic wave excited by the IDT electrode is an SH wave. 前記ＩＤＴ電極の主成分がモリブデンであり、前記ＩＤＴ電極の電極周期での規格化膜厚が３．７５％以上であり、前記媒質および前記誘電体膜の主成分が酸化珪素である請求項１に記載の弾性波素子。 The main component of the IDT electrode is molybdenum, the normalized film thickness in the electrode period of the IDT electrode is 3.75% or more, and the main component of the medium and the dielectric film is silicon oxide. The elastic wave device described in 1. 前記ＩＤＴ電極の主成分がモリブデンであり、前記ＩＤＴ電極の電極周期での規格化膜厚が１．２５％以上であり、前記媒質の主成分がアルミニウムである請求項１に記載の弾性波素子。 2. The acoustic wave device according to claim 1, wherein a main component of the IDT electrode is molybdenum, a normalized film thickness in an electrode period of the IDT electrode is 1.25% or more, and a main component of the medium is aluminum. . 前記圧電基板がニオブ酸リチウムであり、前記ＩＤＴ電極の主成分がモリブデンであり、前記媒質および前記誘電体膜の主成分が酸化珪素であり、前記ＩＤＴ電極と前記媒質の電極周期での規格化膜厚比が１対０．１５２以上である請求項１に記載の弾性波素子。 The piezoelectric substrate is lithium niobate, the main component of the IDT electrode is molybdenum, the main component of the medium and the dielectric film is silicon oxide, and is normalized by the electrode period of the IDT electrode and the medium The elastic wave device according to claim 1, wherein the film thickness ratio is 1 to 0.152 or more. 前記圧電基板が１２８°回転Ｙカットニオブ酸リチウムであり、前記媒質の主成分がアルミニウムであり、前記誘電体膜の主成分が酸化珪素であり、前記ＩＤＴ電極と前記媒質の電極周期での規格化膜厚比が１対１．２０６以上である請求項１に記載の弾性波素子。 The piezoelectric substrate is 128 ° rotated Y-cut lithium niobate, the main component of the medium is aluminum, the main component of the dielectric film is silicon oxide, and the standard of the electrode period of the IDT electrode and the medium The elastic wave device according to claim 1, wherein the chemical film thickness ratio is 1: 1 to 1.206 or more. 前記ＩＤＴ電極は、アポタイズ重み付けを施した請求項１に記載の弾性波素子。 The elastic wave device according to claim 1, wherein the IDT electrode is subjected to apodization weighting.
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