JP2004228901A - Surface wave device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface wave device with an excellent frequency temperature characteristic, a large electromechanical coupling coefficient, and a low propagation loss. <P>SOLUTION: The surface wave device 1 includes a piezoelectric substrate 2 composed of LiTaO<SB>3</SB>of an Euler angle (0±2, 90°-160°, 0±2°), an IDT 3 formed on the piezoelectric substrate 2 and composed of platinum, for which a normalized film thickness H/λ is in the range of 0.005-0.054 at the time of defining a film thickness as H and the wavelength of a surface wave as λ, and an SiO<SB>2</SB>film 4 formed on the piezoelectric substrate 2 so as to cover the IDT 3, for which the normalized film thickness Hs/λ is in the range of 0.10-0.40. An attenuation constant becomes small and thus the surface wave device of the excellent frequency temperature characteristic, the large electromechanical coupling coefficient and the small propagation loss is obtained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００１２】
本発明に係る表面波装置のさらに他の特定の局面では、前記圧電基板のオイラー角が（０±２°，１０２°〜１５０°，０±２°）であり、前記ＩＤＴの規格化膜厚Ｈ／λが０．０１３〜０．０３３の範囲にあり、それによって、電気機械結合係数を高めることができる。
【００１３】
本発明に係る表面波装置のさらに限定的な局面では、前記ＬｉＴａＯ_３からなる圧電基板のオイラー角と、前記ＳｉＯ_２膜の規格化膜厚Ｈｓ／λが下記の表４に示すいずれかの組み合わせであり、それによって、減衰定数αを０．０５ｄＢ／λ以下、また、表４中の好ましいオイラー角の場合には、減衰定数αを０．０２５ｄＢ／λ以下とすることができる。
【００１４】
【表４】

【００１５】
本発明に係る表面波装置のさらに他の特定の局面では、白金からなる電極層に積層された白金以外の金属からなる少なくとも１つの電極層をさらに備えていてもよく、ＩＤＴの全体の平均密度が白金の密度±２０％の範囲であれば、本発明の効果を得ることができる。
【００１６】
本発明の別の広い局面によれば、オイラー角（０±２°，９０°〜１６０°，０±２°）のＬｉＴａＯ_３からなる圧電基板を用意する工程と、前記圧電基板上に、白金からなる電極層を少なくとも有する少なくもと１つのＩＤＴを形成する工程と、前記ＩＤＴを形成した後に周波数調整を行う工程と、前記周波数調整後に、ＩＤＴを被覆するようにＳｉＯ_２膜を前記圧電基板上に形成する工程とを備える、本発明の表面波装置の製造方法が提供される。
【００１７】
【発明の実施の形態】
以下、図面を参照しつつ、発明の具体的な実施例を説明することにより、本発明を明らかにする。
【００１８】
図１は、本発明の一実施形態に係る表面波装置の模式的平面図である。表面波装置１は、縦結合共振子型表面波フィルタであり、オイラー角で（０±２°，９０°〜１６０°，０±２°）のＬｉＴａＯ_３すなわち、０°〜７０°回転Ｙ板ＬｉＴａＯ_３からなる圧電基板２を有する。
【００１９】
圧電基板２上に、白金膜よりなるＩＤＴ３ａ，３ｂ及び反射器５ａ，５ｂが形成されている。ＩＤＴ３ａ，３ｂの規格化膜厚Ｈ／λは０．００５〜０．０５４の範囲とされている。
【００２０】
なお、ＩＤＴの規格化膜厚Ｈ／λにおいて、ＨはＩＤＴの厚みを、λは表面波の波長を示す。
【００２１】
また、ＩＤＴ３ａ，３ｂを覆うように、圧電基板２上には、ＳｉＯ_２膜４が形成されている。ＳｉＯ_２膜４の規格化膜厚Ｈｓ／λは、０．１０〜０．４０の範囲とされている。なお、ＨｓはＳｉＯ_２膜の厚みを示し、λは表面波の波長を示す。
【００２２】
本実施例では上記のように、オイラー角（０±２°，９０°〜１６０°，０±２°）のＬｉＴａＯ_３からなる圧電基板２と、Ｈ／λ＝０．００５〜０．０５４である白金よりなるＩＤＴ３ａ，３ｂと、Ｈｓ／λ＝０．１０〜０．４０の範囲にあるＳｉＯ_２膜４とを用いているため、周波数温度係数ＴＣＦが小さく、電気機械結合係数Ｋ^２が大きく、かつ伝搬損失が小さい表面波装置を提供することができる。これを、以下の具体的な実験例に基づき説明する。
【００２３】
ＬｉＴａＯ_３基板を伝搬する表面波としては、レイリー波の他に、漏洩弾性表面波が存在する。漏洩弾性表面波は、レイリー波に比べて音速が速く、電気機械結合係数が大きい。しかしながら、漏洩弾性表面波は、エネルギーを基板内部に放射しながら伝搬する波である。従って、漏洩弾性表面波は、伝搬損失の原因となる減衰定数を有する。
【００２４】
図２は、回転Ｙ板Ｘ伝搬ＬｉＴａＯ_３におけるオイラー角（０，θ，０）のθと、基板表面が電気的に短絡された場合の減衰定数（伝搬損失）αとの関係を示す。なお、回転角＝θ−９０度の関係である。
【００２５】
図２から明らかなように、オイラー角のθが１２４〜１２６°の範囲で減衰定数αは小さい。この範囲を外れると、減衰定数αは大きくなる。
また、比較的膜厚が厚いＡｌからなるＩＤＴを形成した場合には、θ＝１３０°〜１３２°で減衰定数が小さくなることが知られている（例えば、前述した非特許文献１）。従って、従来、ＡｌからなるＩＤＴと、ＬｉＴａＯ_３基板とを組み合わせた構成では、θ＝１３０°〜１３２°の回転Ｙ板Ｘ伝搬のＬｉＴａＯ_３基板が用いられていた。
【００２６】
図３は、回転Ｙ板Ｘ伝搬ＬｉＴａＯ_３基板におけるオイラー角（０，θ，０）のθと電気機械結合係数Ｋ^２との関係を示す。オイラー角のθが１００°〜１２０°の範囲で大きな電気機械結合係数Ｋ^２が得られることがわかる。しかしながら、θ＝１００°〜１２０°の範囲では、前述の図２から明らかなように減衰定数αが大きい。従って、このようなオイラー角のＬｉＴａＯ_３基板を用いることはできないことがわかる。
【００２７】
図４は、３６°回転Ｙ板Ｘ伝搬［オイラー角で（０°，１２６°，０°）］のＬｉＴａＯ_３基板上に、電極膜として、白金膜またはアルミニウム膜を形成した場合の該電極膜の規格化膜厚Ｈ／λ（Ｈは膜厚を、λは表面波の波長を示す）と、電気機械結合係数Ｋ^２との関係を示す。白金膜の規格化膜厚Ｈ／λ＝０．００５〜０．０５４の範囲では、電気機械結合係数Ｋ^２は、Ｈ／λ＝０（成膜しなかった場合）の場合の電気機械結合係数の１．５倍以上となり、Ｈ／λ＝０．０１〜０．０４では、１．７５倍以上となり、Ｈ／λ＝０．０１３〜０．０３３では、１．８５倍以上となることがわかる。
【００２８】
従って、Ｈ／λ＝０．００５〜０．０５４とすることにより、電気機械結合係数Ｋ^２を高めることができることがわかる。
【００２９】
図５は、白金膜またはアルミニウム膜からなる電極膜の規格化膜厚Ｈ／λと、電極指１本あたりの反射係数との関係を示す図である。従来、ＡｌからなるＩＤＴでは、十分な反射係数と電気機械結合係数を得るためには、規格化膜厚Ｈ／λは０．０８以上であることが必要であった。これに対して、白金膜からなるＩＤＴでは、Ｈ／λが０．０８以上のＡｌ膜の場合と同等の反射係数を得るには、Ｈ／λは０．０１以上であればよいことがわかる。
【００３０】
よって、白金膜からなるＩＤＴの規格化膜厚Ｈ／λは、０．００５〜０．０５４の範囲、好ましくは０．０１〜０．０４の範囲、より好ましくは０．０１３〜０．０３３の範囲とすればよいことがわかる。
【００３１】
次に、ＳｉＯ_２膜をＬｉＴａＯ_３基板上に形成した場合の周波数温度係数ＴＣＦの改善効果を説明する。図６は、θ＝１１３°、１２６°及び１２９°の（０，θ，０）の各ＬｉＴａＯ_３基板上にＳｉＯ_２膜を成膜した場合の周波数温度係数ＴＣＦの変化を示す図である。
【００３２】
図６から明らかなように、θが１１３°，１２６°及び１２９°のいずれの場合においても、ＳｉＯ_２の規格化膜厚Ｈｓ／λ（ＨｓはＳｉＯ_２膜の膜厚を、λは表面波の波長を示す）が０．１０〜０．４５の範囲において、ＴＣＦが−２４〜＋１７ｐｐｍ／℃の範囲にはいることがわかる。もっとも、ＳｉＯ_２膜の成膜には時間を要するため、ＳｉＯ_２膜の規格化膜厚Ｈｓ／λは０．４０以下であることが望ましい。従って、好ましくは、ＳｉＯ_２膜の規格化膜厚Ｈｓ／λは、０．１０〜０．４０の範囲であり、それによって、短時間で成膜でき、かつＴＣＦを−２０〜＋１７ｐｐｍ／℃の範囲とすることができる。
【００３３】
従来、ＬｉＴａＯ_３基板上に、Ａｌ電極を形成し、さらにＳｉＯ_２膜を形成することにより、レイリー波などのＴＣＦが改善されるという報告がいくつか存在する（例えば、特許文献１など）。しかしながら、ＬｉＴａＯ_３基板−白金からなる電極−ＳｉＯ_２膜の積層構造において、電極の膜厚や漏洩弾性表面波の減衰定数を考慮にいれて実験が行われた報告は存在しない。
【００３４】
図７及び図８は、オイラー角（０°，１２５°，０°）と、（０°，１４０°，０°）の各ＬｉＴａＯ_３基板上に、種々の膜厚の白金からなるＩＤＴと、種々の膜厚のＳｉＯ_２膜とを形成した場合の減衰定数を示す図である。
【００３５】
図７から明らかなように、θ＝１２５°では、ＳｉＯ_２の膜厚Ｈｓ／λが０．１〜０．４０かつ白金よりなる電極の規格化膜厚Ｈ／λが０．００５〜０．０６の範囲において、減衰定数が小さいことがわかる。他方、図８から明らかなように、θ＝１４０°では、白金からなる電極の規格化膜厚Ｈ／λが０．００５〜０．０６の範囲では、ＳｉＯ_２膜の膜厚の如何に係わらず、減衰定数が大きくなっていることがわかる。
【００３６】
すなわち、ＴＣＦの絶対値を小さくし、大きな電気機械結合係数を得、かつ減衰定数を小さくするには、ＬｉＴａＯ_３基板のカット角、ＳｉＯ_２膜の厚み及び白金からなる電極の膜厚の３つの条件を考慮しなければならないことがわかる。
【００３７】
図９〜図１４は、ＳｉＯ_２膜の規格化膜厚Ｈｓ／λ及び白金からなる電極膜の規格化膜厚Ｈ／λを変化させた場合の、θ（度）と減衰定数との関係を示す。
図９〜図１４から明らかなように、白金からなる電極の規格化膜厚Ｈ／λが０．００５〜０．０５４では、θは９０°〜１６０°の範囲とすることが望ましいことがわかる。また、白金からなる電極の規格化膜厚Ｈ／λが０．０１〜０．０４及び０．０１３〜０．０３３においては、ＳｉＯ_２膜の膜厚と、最適なθとの関係は、減衰定数αを低下させることも考慮すると、下記の表５及び表６に示す通りとなる。ここで、表５及び表６における「ＬｉＴａＯ_３のオイラー角」の範囲は、減衰定数が０．０５ｄＢ／λ以下の範囲を規定したものである。また、表５及び表６におけるＬｉＴａＯ_３のオイラー角の「より好ましい」範囲は、減衰定数が０．０２５ｄＢ／λ以下の範囲を規定したものである。なお、この最適θは、白金電極の電極指幅のばらつきや単結晶基板のばらつきにより−２°〜＋４°程度ばらつくことがある。
【００３８】
【表５】

【００３９】
【表６】

【００４０】
すなわち、表５及び表６から明らかなように、白金よりなる電極の規格化膜厚Ｈ／λが、０．００５〜０．０５４の場合、温度特性を改善するために、ＳｉＯ_２膜の膜厚を０．１〜０．４の範囲とした場合、ＬｉＴａＯ_３のオイラー角におけるθは、９０°〜１６０°の範囲、すなわち、回転角で０°〜７０°の範囲を選択すればよいことがわかる。
【００４１】
同様に、表５から明らかなように、白金膜からなる電極の規格化膜厚Ｈ／λが０．０１〜０．０４であり、周波数温度特性を改善するために、ＳｉＯ_２膜の規格化膜厚Ｈｓ／λを０．１〜０．４の範囲とした場合には、ＬｉＴａＯ_３基板のオイラー角のθは９０°〜１４５°の範囲とすればよく、より好ましくはＳｉＯ_２膜の膜厚に応じて表５のオイラー角を選択すればよいことがわかる。
【００４２】
同様に、白金膜からなる電極の規格化膜厚Ｈ／λが０．０１３〜０．０３３であり、周波数温度特性を改善するために、ＳｉＯ_２膜の規格化膜厚Ｈｓ／λを０．１〜０．４の範囲とした場合には、ＬｉＴａＯ_３基板のオイラー角のθは、１０２°〜１５０°の範囲とすればよく、より好ましくは、ＳｉＯ_２膜の膜厚に応じて表６のオイラー角を選択すればよいことがわかる。
【００４３】
また、白金からなる電極膜の規格化膜厚が０．０１３〜０．０３３である場合のＳｉＯ_２膜の膜厚とオイラー角の関係は、図９〜図１４に示す白金からなる電極膜の規格化膜厚から換算して求めたものであり、それによって、表５及び表６のＳｉＯ_２膜の膜厚とオイラー角の値を求めている。
【００４４】
また、図１６（ａ）〜（ｃ）は、上記実施例の弾性表面波フィルタにおける表面の走査型電子顕微鏡写真である。ここでは、Ｈ／λ＝０．０２の規格化膜厚の白金からなるＩＤＴ上に、規格化膜厚Ｈｓ／λ＝０．３のＳｉＯ_２膜が形成される前後の結果が示されている。図１６（ｂ）の成膜後の写真から明らかなように、ＳｉＯ_２膜の表面にクラックは見られず、従って、クラックによる特性の劣化も生じ難いことがわかる。Ａｌ電極に比べ白金電極では、薄い膜厚で大きな電気機械結合係数と反射係数が得られる。そのため、薄い白金電極の上にＳｉＯ_２が成膜されていても、図１６（ｂ），（ｃ）に示すように、ＳｉＯ_２に大きな段差やクラックが生じないという利点がある。
【００４５】
本発明に係る弾性表面波装置の製造に際しては、回転Ｙ板Ｘ伝搬ＬｉＴａＯ_３基板上に白金を主成分とする金属からなるＩＤＴを形成した後、その状態において周波数調整を行い、しかる後減衰定数αを小さくし得る範囲の膜厚のＳｉＯ_２膜を成膜することが望ましい。これを、図１７及び図１８を参照して説明する。図１７は、オイラー角（０°，１２６°，０°）の回転Ｙ板Ｘ伝搬ＬｉＴａＯ_３基板上に、種々の厚みＨ／λの白金からなるＩＤＴ上に種々の膜厚Ｈｓ／λのＳｉＯ_２膜を形成した場合のＳｉＯ_２膜厚に対する漏洩弾性表面波の音速の変化を示す。また、図１８は、同じオイラー角のＬｉＴａＯ_３基板上に、種々の膜厚Ｈ／λの白金からなるＩＤＴとその上にＳｉＯ_２膜を形成した場合の白金の膜厚に対する漏洩弾性表面波の音速の変化を示す。図１７と図１８を比較すれば明らかなように、白金の膜厚を変化させた場合の方が、ＳｉＯ_２膜の膜厚を変化させた場合よりも表面波の音速の変化がはるかに大きい。従って、ＳｉＯ_２膜の形成に先立ち、周波数調整が、行われることが望ましく、白金からなるＩＤＴを形成した後に、例えば、レーザーエッチングやイオンエッチングなどにより周波数調整を行うことが望ましい。
【００４６】
なお、本発明は、上記のように、オイラー角（０±２°，９０°〜１６０°，０±２°）のＬｉＴａＯ_３からなる圧電基板、Ｈ／λ＝０．００５〜０．０５４である白金よりなるＩＤＴと、Ｈｓ／λ＝０．１０〜０．４０であるＳｉＯ_２膜とを有することを特徴とするものであり、従って、ＩＤＴの数及び構造等については特に限定されない。すなわち、本発明は、図１に示した表面波装置だけでなく、上記条件を満たす限り、様々な表面波共振子や表面波フィルタ等のデバイスに適用することができる。
【００４７】
また、白金からなる電極層の下や上に電極の密着強度を向上させるためやボンディングを容易とするために、ＴｉやＣｒ，Ａｌ等の他の金属からなる電極層を薄く成膜してもよく、その場合、ＩＤＴ全体の平均密度が、白金の密度±２０％以内であれば、上記実施形態と同様の効果を得ることができる。
【００４８】
【発明の効果】
本発明に係る表面波装置では、オイラー角（０±２°，９０°〜１６０°，０±２°）のＬｉＴａＯ_３からなる圧電基板上に、規格化膜厚Ｈ／λが０．００５〜０．０５４であり、かつ白金よりなるＩＤＴが形成されており、ＩＤＴを覆うように、Ｈｓ／λ＝０．１０〜０．４０のＳｉＯ_２膜が形成されている、ＳｉＯ_２膜により周波数温度係数ＴＣＦが改善され、白金膜よりなるＩＤＴの膜厚Ｈ／λが上記特定の範囲とされているため、電気機械結合係数と反射係数が大きく、さらにＬｉＴａＯ_３基板の回転角が上記特定の範囲とされているため、減衰定数が小さくされる。よって、周波数温度特性に優れ、大きな電気機械結合係数を有し、かつ伝搬損失が少ない表面波装置を提供することが可能となる。
【００４９】
特に、ＩＤＴの膜厚Ｈ／λが０．０１０〜０．４０、より好ましくは０．０１３〜０．０３３の範囲にある場合には、電気機械結合係数を効果的に高めることができる。
【００５０】
また、白金電極が薄いため、この白金電極からなるＩＤＴ上にＳｉＯ_２が成膜されてもＳｉＯ_２に大きな段差やクラックができないため、Ａｌ電極の場合に生じるそれらに起因した挿入損失等の特性の劣化もない。
【図面の簡単な説明】
【図１】本発明の一実施例に係る表面波装置を示す模式的平面図。
【図２】オイラー角（０，θ，０）のＬｉＴａＯ_３基板のθと、減衰定数αとの関係を示す図。
【図３】オイラー角（０，θ，０）のＬｉＴａＯ_３基板におけるθと電気機械結合係数Ｋ^２との関係を示す図。
【図４】オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に白金またはアルミニウムからなる電極膜を形成した構造における電極膜の規格化膜厚Ｈ／λと、電気機械結合係数Ｋ^２との関係を示す図。
【図５】オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金またはアルミニウムによりなる電極を形成した場合の電極の規格化膜厚と、電極指１本あたりの反射係数との関係を示す図。
【図６】オイラー角（０°，１１３°，０°）、（０°，１２６°，０°）及び（０°，１２９°０，０°）の各ＬｉＴａＯ_３基板上にＳｉＯ_２膜を形成した場合のＳｉＯ_２膜の規格化膜厚Ｈｓ／λと、周波数温度係数ＴＣＦとの関係を示す図。
【図７】オイラー角（０°，１２５°，０°）のＬｉＴａＯ_３基板上に、様々な厚みのＳｉＯ_２膜及び様々な厚みの白金からなるＩＤＴを形成した構造における減衰定数αの変化を示す図。
【図８】オイラー角（０°，１４０°，０°）のＬｉＴａＯ_３基板上に、様々な厚みのＳｉＯ_２膜及び様々な厚みの白金からなるＩＤＴを形成した構造における減衰定数αの変化を示す図。
【図９】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．１のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１０】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．１５のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１１】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．２のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１２】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．２５のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１３】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．３のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１４】オイラー角（０°，θ，０°）のＬｉＴａＯ_３基板上に、様々な厚みの白金よりなる電極膜を形成し、さらに規格化膜厚Ｈｓ／λ＝０．４のＳｉＯ_２膜を形成した表面波装置におけるθと、白金よりなる電極膜の規格化厚みＨ／λと、減衰定数αとの関係を示す図。
【図１５】（ａ）は、オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に、膜厚Ｈ／λ＝０．０８のアルミニウム電極からなるＩＤＴが形成された表面、（ｂ）は、その上に厚みＨｓ／λ＝０．３のＳｉＯ_２が成膜された表面、（ｃ）は、その断面を示す各走査型電子顕微鏡写真を示す図。
【図１６】（ａ）は、オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に、厚みＨ／λ＝０．０２の白金からなるＩＤＴが形成された表面、（ｂ）は、その上に厚みＨｓ／λ＝０．３のＳｉＯ_２が成膜された表面、（ｃ）は、その断面を示す各走査型電子顕微鏡写真を示す図。
【図１７】オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に白金からなるＩＤＴを形成し、さらにＳｉＯ_２膜を形成した場合のＳｉＯ_２膜の膜厚と、音速との関係を示す図。
【図１８】オイラー角（０°，１２６°，０°）のＬｉＴａＯ_３基板上に白金からなるＩＤＴを形成し、さらにＳｉＯ_２膜を形成した場合の白金膜の膜厚と、音速との関係を示す図。
【符号の説明】
１…表面波装置
２…圧電基板
３ａ，３ｂ…ＩＤＴ
４…ＳｉＯ_２膜
５ａ，５ｂ…反射器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave device used for, for example, a surface acoustic wave filter, and more particularly, to a surface acoustic wave device using a piezoelectric substrate made of LiTaO ₃ .
[0002]
[Prior art]
Conventionally, a surface wave device using a 40 ° to 42 ° rotating Y-plate X-propagation LiTaO ₃ substrate has been known as a bandpass filter (for example, the following Non-Patent Document 1). In the band filter in the RF band, the IDT is formed on the 40 ° to 42 ° rotating Y plate X-propagating LiTaO ₃ substrate by using an Al film having a thickness H / λ of 0.08 to 0.10. Was formed.
[0003]
As described above, in the conventional surface acoustic wave device using the 40 ° to 42 ° rotating Y-plate X-propagation LiTaO ₃ substrate, the frequency-temperature characteristic TCF is relatively large at −33 ppm / ° C., so that the temperature characteristic is further improved. Certain specifications could not be fully met. Conventionally, as a method of improving the frequency temperature characteristic TCF of the surface acoustic wave device, a method of forming an IDT made of Al on a LiTaO ₃ substrate and then forming an SiO ₂ layer is known (see Patent Document 1 below). ).
[0004]
[Non-patent document 1]
Proceedings of the 1997 IEICE General Conference: SA-10-6, pp. 500-501 [Patent Document 1]
JP-A-2-295212
[Problems to be solved by the invention]
However, when forming a resonator or a filter using an IDT made of Al, in order to obtain a large electromechanical coupling coefficient K _saw and a reflection coefficient, as shown in FIG. 4 and FIG. H / λ (H is the film thickness, λ is the wavelength of the surface wave) must be considerably thick, 0.08 to 0.10. As described above, since the IDT made of Al is considerably thick, a SiO ₂ film is formed on the portion where the IDT shown in FIG. 15A is formed in order to improve the frequency-temperature characteristics. Once formed, as shown in FIG. 15 (b), (c) , a large step in the SiO ₂ film occurs, there is a crack occurs in the SiO ₂ film. For this reason, the filter characteristics of the surface acoustic wave filter tend to deteriorate due to the occurrence of cracks.
[0006]
In addition, since the thickness of the electrode of the IDT made of Al is large, the effect of covering the unevenness of the electrode surface of the IDT by the formation of the SiO ₂ film is not sufficient, so that the frequency temperature characteristic may not be sufficiently improved. Was.
[0007]
An object of the present invention is to provide a surface acoustic wave device using a rotating Y-plate X-propagation LiTaO ₃ substrate in view of the above-mentioned state of the art, and not only to improve the frequency-temperature characteristics by forming a SiO ₂ film, By reducing the thickness of the electrode of the IDT, cracks in the SiO ₂ film can be prevented and the attenuation constant can be significantly reduced. Therefore, electrical characteristics such as desired filter characteristics can be obtained. It is an object of the present invention to provide a surface acoustic wave device and a method of manufacturing the same in which the electromechanical coupling coefficient and the reflection coefficient are sufficiently large.
[0008]
[Means for Solving the Problems]
According to a broad aspect of the present invention, a piezoelectric substrate made of LiTaO _{3 having} an Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °), and at least platinum formed on the piezoelectric substrate And an IDT having a normalized thickness H / λ in the range of 0.005 to 0.054, wherein the thickness is H and the wavelength of the surface wave is λ. As described above, when the film thickness is Hs, the SiO ₂ film having a normalized thickness Hs / λ in the range of 0.10 to 0.40 at the wavelength λ of the surface wave is formed on the piezoelectric substrate. There is provided a surface acoustic wave device comprising:
[0009]
In a specific aspect of the surface acoustic wave device according to the present invention, the piezoelectric substrate has an Euler angle of (0 ± 2 °, 90 ° to 155 °, 0 ± 2 °), and the normalized film thickness H / λ is in the range of 0.01 to 0.04, whereby the electromechanical coupling coefficient can be increased.
[0010]
In another specific aspect of the surface acoustic wave device according to the present invention, the Euler angle of the piezoelectric substrate made of LiTaO ₃ and the normalized thickness Hs / λ of the SiO ₂ film are one of the combinations shown in Table 3 below. Accordingly, the attenuation constant α can be set to 0.05 dB / λ or less, and in the case of the preferable Euler angle shown in Table 3, the attenuation constant α can be set to 0.025 dB / λ or less.
[0011]
[Table 3]

[0012]
In still another specific aspect of the surface acoustic wave device according to the present invention, the piezoelectric substrate has an Euler angle of (0 ± 2 °, 102 ° to 150 °, 0 ± 2 °), and the normalized film thickness of the IDT. H / λ is in the range of 0.013 to 0.033, whereby the electromechanical coupling coefficient can be increased.
[0013]
In a further limited aspect of the surface acoustic wave device according to the present invention, the Euler angle of the piezoelectric substrate made of LiTaO ₃ and the normalized thickness Hs / λ of the SiO ₂ film are any combination shown in Table 4 below. Accordingly, the attenuation constant α can be set to 0.05 dB / λ or less, and in the case of the preferable Euler angle shown in Table 4, the attenuation constant α can be set to 0.025 dB / λ or less.
[0014]
[Table 4]

[0015]
In still another specific aspect of the surface acoustic wave device according to the present invention, the surface acoustic wave device may further include at least one electrode layer made of a metal other than platinum laminated on the electrode layer made of platinum, and the overall average density of the IDT Is within the range of the density of platinum ± 20%, the effect of the present invention can be obtained.
[0016]
According to another broad aspect of the present invention, there is provided a step of preparing a piezoelectric substrate made of LiTaO _{3 having} an Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °), and forming platinum on the piezoelectric substrate. Forming at least one IDT having at least an electrode layer consisting of: a step of adjusting the frequency after forming the IDT; and, after adjusting the frequency, forming a SiO ₂ film on the piezoelectric substrate so as to cover the IDT. And a method of manufacturing a surface acoustic wave device according to the present invention.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be clarified by describing specific embodiments of the invention with reference to the drawings.
[0018]
FIG. 1 is a schematic plan view of a surface acoustic wave device according to one embodiment of the present invention. The surface acoustic wave device 1 is a longitudinally coupled resonator type surface acoustic wave filter, and has a LiTaO ₃ having an Euler angle of (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °), that is, a 0 ° to 70 ° rotating Y plate. It has a piezoelectric substrate 2 made of LiTaO ₃ .
[0019]
On the piezoelectric substrate 2, IDTs 3a and 3b and reflectors 5a and 5b made of a platinum film are formed. The normalized film thickness H / λ of the IDTs 3a and 3b is in the range of 0.005 to 0.054.
[0020]
In the standardized film thickness H / λ of the IDT, H represents the thickness of the IDT, and λ represents the wavelength of the surface wave.
[0021]
Further, an SiO ₂ film 4 is formed on the piezoelectric substrate 2 so as to cover the IDTs 3a and 3b. The normalized thickness Hs / λ of the SiO ₂ film 4 is in the range of 0.10 to 0.40. Hs indicates the thickness of the SiO ₂ film, and λ indicates the wavelength of the surface wave.
[0022]
In this embodiment, as described above, the piezoelectric substrate 2 made of LiTaO ₃ having the Euler angles (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °) and H / λ = 0.005 to 0.054 are used. and IDT3a, 3b made of certain platinum, the use and the SiO ₂ film 4 is in a range of Hs / lambda = 0.10 to 0.40, the temperature coefficient of frequency TCF is small, a large electromechanical coupling coefficient ^{K 2} And a surface acoustic wave device having a small propagation loss. This will be described based on the following specific experimental examples.
[0023]
As surface waves propagating through the LiTaO ₃ substrate, there are leaky surface acoustic waves in addition to Rayleigh waves. Leaky surface acoustic waves have a higher sound speed and a larger electromechanical coupling coefficient than Rayleigh waves. However, leaky surface acoustic waves are waves that propagate while radiating energy into the interior of the substrate. Therefore, the leaky surface acoustic wave has an attenuation constant that causes a propagation loss.
[0024]
FIG. 2 shows the relationship between θ of the Euler angles (0, θ, 0) in the rotating Y plate X-propagation LiTaO ₃ and the attenuation constant (propagation loss) α when the substrate surface is electrically short-circuited. It should be noted that the rotation angle has a relationship of θ-90 degrees.
[0025]
As is clear from FIG. 2, the attenuation constant α is small when the Euler angle θ is in the range of 124 to 126 °. Outside this range, the attenuation constant α increases.
It is also known that when an IDT made of Al having a relatively large thickness is formed, the attenuation constant decreases when θ = 130 ° to 132 ° (for example, Non-Patent Document 1 described above). Thus, conventionally, the IDT composed of Al, the structure of a combination of a LiTaO ₃ substrate, LiTaO ₃ substrate of rotated Y-plate X-propagation of θ = 130 ° ~132 ° has been used.
[0026]
FIG. 3 shows the relationship between the Euler angle (0, θ, 0) θ and the electromechanical coupling coefficient K ² in the rotating Y-plate X-propagation LiTaO ₃ substrate. Euler angle θ is understood that a large electromechanical coupling coefficient K ² can be obtained in the range of 100 ° to 120 °. However, in the range of θ = 100 ° to 120 °, the attenuation constant α is large as is apparent from FIG. Therefore, it is understood that a LiTaO ₃ substrate having such an Euler angle cannot be used.
[0027]
FIG. 4 shows a case where a platinum film or an aluminum film is formed as an electrode film on a LiTaO ₃ substrate having a 36 ° rotation Y plate X propagation [Euler angle (0 °, 126 °, 0 °)]. (a is H film thickness, lambda denotes the wavelength of the surface wave) of the normalized thickness H / lambda and shows the relationship between the electromechanical coupling coefficient K ^2. In the range of the normalized thickness H / λ of the platinum film in the range of 0.005 to 0.054, the electromechanical coupling coefficient K ² is the electromechanical coupling coefficient in the case of H / λ = 0 (when no film is formed). 1.5 times or more of H / λ = 0.01 to 0.04, and more than 1.75 times of H / λ = 0.013 to 0.033. Understand.
[0028]
Therefore, by the H / lambda = from 0.005 to 0.054, it is understood that it is possible to increase the electromechanical coupling coefficient ^{K 2.}
[0029]
FIG. 5 is a diagram showing the relationship between the normalized film thickness H / λ of the electrode film made of a platinum film or an aluminum film and the reflection coefficient per electrode finger. Conventionally, in the IDT made of Al, the normalized film thickness H / λ needs to be 0.08 or more in order to obtain a sufficient reflection coefficient and electromechanical coupling coefficient. On the other hand, in the IDT made of a platinum film, H / λ is required to be 0.01 or more to obtain a reflection coefficient equivalent to that of the Al film having H / λ of 0.08 or more. .
[0030]
Therefore, the normalized thickness H / λ of the IDT made of a platinum film is in the range of 0.005 to 0.054, preferably in the range of 0.01 to 0.04, and more preferably in the range of 0.013 to 0.033. It is understood that the range should be set.
[0031]
Next, the effect of improving the frequency temperature coefficient TCF when the SiO ₂ film is formed on the LiTaO ₃ substrate will be described. FIG. 6 is a diagram showing a change in the frequency temperature coefficient TCF when an SiO ₂ film is formed on each (0, θ, 0) LiTaO ₃ substrate at θ = 113 °, 126 °, and 129 °.
[0032]
As apparent from FIG. 6, theta is 113 °, in either case of 126 ° and 129 °, the film thickness of the SiO ₂ normalized thickness Hs / λ (Hs is SiO ₂ film, lambda surface waves It can be seen that the TCF falls within the range of −24 to +17 ppm / ° C. in the range of 0.10 to 0.45. However, since the formation of the SiO ₂ film it takes time, it is desirable that the normalized thickness Hs / lambda of the SiO ₂ film is 0.40 or less. Therefore, preferably, the normalized film thickness Hs / λ of the SiO ₂ film is in the range of 0.10 to 0.40, whereby the film can be formed in a short time and the TCF is in the range of −20 to +17 ppm / ° C. Range.
[0033]
Conventionally, there have been some reports that forming an Al electrode on a LiTaO ₃ substrate and further forming an SiO ₂ film can improve TCF such as Rayleigh waves (for example, Patent Document 1). However, there is no report that an experiment has been performed in the layered structure of the LiTaO ₃ substrate, the electrode composed of platinum, and the SiO ₂ film in consideration of the film thickness of the electrode and the attenuation constant of the leaky surface acoustic wave.
[0034]
FIGS. 7 and 8 show an Euler angle (0 °, 125 °, 0 °), an IDT made of platinum of various thicknesses on each LiTaO ₃ substrate at (0 °, 140 °, 0 °), FIG. 3 is a diagram showing attenuation constants when SiO ₂ films having various thicknesses are formed.
[0035]
As is clear from FIG. 7, when θ = 125 °, the thickness Hs / λ of SiO ₂ is 0.1 to 0.40 and the normalized thickness H / λ of the electrode made of platinum is 0.005 to 0.5. It can be seen that the attenuation constant is small in the range of 06. On the other hand, as is clear from FIG. 8, when θ = 140 °, the normalized thickness H / λ of the platinum electrode is in the range of 0.005 to 0.06 regardless of the thickness of the SiO ₂ film. It can be seen that the damping constant is large.
[0036]
That is, in order to reduce the absolute value of TCF, obtain a large electromechanical coupling coefficient, and reduce the damping constant, there are _three cut angles of the LiTaO ₃ substrate, the thickness of the SiO ₂ film, and the thickness of the electrode made of platinum. It turns out that conditions must be considered.
[0037]
9 to 14 show the relationship between θ (degree) and the attenuation constant when the normalized thickness Hs / λ of the SiO ₂ film and the normalized thickness H / λ of the electrode film made of platinum are changed. Show.
As is clear from FIGS. 9 to 14, when the normalized film thickness H / λ of the electrode made of platinum is 0.005 to 0.054, θ is desirably in the range of 90 ° to 160 °. . When the normalized thickness H / λ of the electrode made of platinum is 0.01 to 0.04 and 0.013 to 0.033, the relationship between the thickness of the SiO ₂ film and the optimal θ is attenuated. Taking into account the reduction of the constant α, the results are as shown in Tables 5 and 6 below. Here, the range of “Eulerian angle of LiTaO ₃ ” in Tables 5 and 6 defines a range where the attenuation constant is 0.05 dB / λ or less. In Tables 5 and 6, the “more preferable” range of the Euler angle of LiTaO ₃ is a range in which the attenuation constant is 0.025 dB / λ or less. Note that this optimum θ may vary from about −2 ° to + 4 ° due to variations in the electrode finger width of the platinum electrode and variations in the single crystal substrate.
[0038]
[Table 5]

[0039]
[Table 6]

[0040]
That is, as is clear from Tables 5 and 6, when the normalized thickness H / λ of the electrode made of platinum is 0.005 to 0.054, in order to improve the temperature characteristics, the SiO ₂ film is formed. When the thickness is in the range of 0.1 to 0.4, θ in the Euler angle of LiTaO ₃ may be in the range of 90 ° to 160 °, that is, in the range of 0 ° to 70 ° in the rotation angle. I understand.
[0041]
Similarly, as is apparent from Table 5, the normalized film thickness H / λ of the platinum film electrode is 0.01 to 0.04, and in order to improve the frequency temperature characteristics, the normalized SiO ₂ film is used. When the film thickness Hs / λ is in the range of 0.1 to 0.4, the Euler angle θ of the LiTaO ₃ substrate may be in the range of 90 ° to 145 °, and more preferably a SiO ₂ film. It can be seen that the Euler angles in Table 5 should be selected according to the thickness.
[0042]
Similarly, the normalized thickness H / λ of the electrode made of a platinum film is 0.013 to 0.033, and the normalized thickness Hs / λ of the SiO ₂ film is set to 0.1 to improve the frequency temperature characteristics. When the thickness is in the range of 1 to 0.4, the Euler angle θ of the LiTaO ₃ substrate may be in the range of 102 ° to 150 °, and more preferably, according to the thickness of the SiO ₂ film. It can be seen that the Euler angle should be selected.
[0043]
When the normalized thickness of the electrode film made of platinum is 0.013 to 0.033, the relationship between the thickness of the SiO ₂ film and the Euler angle is as shown in FIG. 9 to FIG. The values are obtained by conversion from the normalized film thickness, and the values of the film thickness and the Euler angle of the SiO ₂ film in Tables 5 and 6 are obtained accordingly.
[0044]
FIGS. 16A to 16C are scanning electron micrographs of the surface of the surface acoustic wave filter of the above embodiment. Here, the results before and after the formation of the SiO ₂ film having the normalized thickness Hs / λ = 0.3 on the IDT made of platinum having the normalized thickness of H / λ = 0.02 are shown. . As is clear from the photograph after the film formation shown in FIG. 16B, no crack is observed on the surface of the SiO ₂ film, and therefore, it is understood that deterioration of the characteristics due to the crack hardly occurs. Compared with the Al electrode, the platinum electrode provides a large electromechanical coupling coefficient and a large reflection coefficient with a thin film thickness. Therefore, even if SiO ₂ is formed on a thin platinum electrode, there is an advantage that large steps and cracks do not occur in SiO _{2 as} shown in FIGS. 16 (b) and 16 (c).
[0045]
In manufacturing the surface acoustic wave device according to the present invention, an IDT made of a metal containing platinum as a main component is formed on a rotating Y-plate X-propagation LiTaO ₃ substrate, the frequency is adjusted in that state, and then the attenuation constant is set. It is desirable to form a SiO ₂ film having a thickness in a range where α can be reduced. This will be described with reference to FIGS. FIG. 17 shows that a rotating Y-plate X-propagation LiTaO ₃ substrate having an Euler angle (0 °, 126 °, 0 °) is formed on a platinum IDT having various thicknesses H / λ on an IDT made of various thicknesses Hs / λ. The change of the sound speed of the leaky surface acoustic wave with respect to the SiO ₂ film thickness when _two films are formed is shown. FIG. 18 shows an IDT made of platinum having various film thicknesses H / λ on a LiTaO ₃ substrate having the same Euler angle and a leakage surface acoustic wave with respect to the film thickness of platinum when an SiO ₂ film is formed thereon. Shows the change in sound speed. As is clear from a comparison between FIG. 17 and FIG. 18, the change in the sound velocity of the surface wave is much greater when the thickness of the platinum is changed than when the thickness of the SiO ₂ film is changed. . Therefore, it is desirable to adjust the frequency before forming the SiO ₂ film, and it is preferable to adjust the frequency by, for example, laser etching or ion etching after forming the IDT made of platinum.
[0046]
Note that, as described above, the present invention provides a piezoelectric substrate made of LiTaO ₃ having an Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °), wherein H / λ = 0.005 to 0.054. It is characterized by having an IDT made of a certain platinum and a SiO ₂ film with Hs / λ = 0.10 to 0.40, and therefore the number and structure of the IDTs are not particularly limited. That is, the present invention can be applied not only to the surface acoustic wave device shown in FIG. 1 but also to various devices such as surface acoustic wave resonators and surface acoustic wave filters as long as the above conditions are satisfied.
[0047]
Further, in order to improve the adhesion strength of the electrode below or above the electrode layer made of platinum and to facilitate bonding, an electrode layer made of another metal such as Ti, Cr, or Al may be formed as a thin film. In this case, if the average density of the entire IDT is within ± 20% of the density of platinum, the same effect as in the above embodiment can be obtained.
[0048]
【The invention's effect】
In the surface acoustic wave device according to the present invention, the normalized film thickness H / λ is 0.005 to 0.005 on a piezoelectric substrate made of LiTaO ₃ having an Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °). is 0.054, and is formed with an IDT made of platinum, so as to cover the IDT, the SiO ₂ film of Hs / lambda = 0.10 to 0.40 is formed, the frequency temperature by SiO ₂ film Since the coefficient TCF is improved and the thickness H / λ of the IDT made of a platinum film is in the above specific range, the electromechanical coupling coefficient and the reflection coefficient are large, and the rotation angle of the LiTaO ₃ substrate is in the above specific range. Therefore, the attenuation constant is reduced. Therefore, it is possible to provide a surface acoustic wave device having excellent frequency-temperature characteristics, a large electromechanical coupling coefficient, and a small propagation loss.
[0049]
In particular, when the thickness H / λ of the IDT is in the range of 0.010 to 0.40, more preferably 0.013 to 0.033, the electromechanical coupling coefficient can be effectively increased.
[0050]
Furthermore, since the platinum electrodes is thin, the characteristics of this for SiO ₂ on the IDT composed of platinum electrode can not be a large step or cracks SiO ₂ be deposited, insertion loss or the like due to their occurring when the Al electrode There is no deterioration.
[Brief description of the drawings]
FIG. 1 is a schematic plan view showing a surface acoustic wave device according to one embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between θ of a LiTaO ₃ substrate having an Euler angle (0, θ, 0) and an attenuation constant α.
[3] Euler angles (0, θ, 0) shows the relationship between the LiTaO ₃ and the theta in the substrate electromechanical coefficient ^{K 2} of.
FIG. 4 is a diagram illustrating a normalized film thickness H / λ and an electromechanical coupling coefficient of an electrode film in a structure in which an electrode film made of platinum or aluminum is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °). diagram showing the relationship between K ^2.
FIG. 5 shows the normalized film thickness of electrodes formed of platinum or aluminum electrodes of various thicknesses on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °), and one electrode finger. FIG. 5 is a diagram showing a relationship between the reflection coefficient and the reflection coefficient.
FIG. 6 shows a SiO ₂ film formed on each LiTaO ₃ substrate having Euler angles (0 °, 113 °, 0 °), (0 °, 126 °, 0 °) and (0 °, 129 ° 0, 0 °). shows the normalized thickness Hs / lambda of the SiO ₂ film in the case of forming, the relation between the temperature coefficient of frequency TCF.
FIG. 7 is a graph showing changes in attenuation constant α in a structure in which an IDT made of various thicknesses of SiO ₂ films and various thicknesses of platinum is formed on a LiTaO ₃ substrate having Euler angles (0 °, 125 °, 0 °). FIG.
FIG. 8 shows changes in attenuation constant α in a structure in which IDTs made of various thicknesses of SiO ₂ films and various thicknesses of platinum are formed on a LiTaO ₃ substrate having Euler angles (0 °, 140 °, 0 °). FIG.
FIG. 9 shows that an electrode film made of platinum having various thicknesses is formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and SiO _{2 having a} normalized film thickness Hs / λ = 0.1. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 10 shows an example in which electrode films made of platinum having various thicknesses are formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and SiO _{2 having a} normalized film thickness Hs / λ = 0.15. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 11 shows that an electrode film made of platinum having various thicknesses is formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and SiO _{2 having a} normalized film thickness Hs / λ = 0.2. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 12 shows an example in which electrode films made of platinum having various thicknesses are formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and SiO _{2 having a} normalized film thickness Hs / λ = 0.25 is formed. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 13 shows a method of forming electrode films made of platinum of various thicknesses on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and further forming SiO _{2 having a} normalized film thickness Hs / λ = 0.3. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 14 shows an example in which electrode films made of platinum having various thicknesses are formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and SiO _{2 having a} normalized film thickness Hs / λ = 0.4. The figure which shows the relationship between (theta) in the surface acoustic wave device which formed the film, the normalized thickness H / (lambda) of the electrode film which consists of platinum, and the attenuation constant (alpha).
FIG. 15A shows a surface on which an IDT made of an aluminum electrode having a film thickness of H / λ = 0.08 is formed on a LiTaO ₃ substrate having an Euler angle (0 °, 126 °, 0 °); (b) is a surface on which a SiO ₂ film having a thickness of Hs / λ = 0.3 is formed, and (c) is a view showing each scanning electron micrograph showing a cross section thereof.
FIG. 16 (a) is a surface in which an IDT made of platinum having a thickness of H / λ = 0.02 is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °); Is a surface on which a SiO ₂ film having a thickness of Hs / λ = 0.3 is formed, and (c) is a view showing each scanning electron micrograph showing a cross section thereof.
FIG. 17 shows the relationship between the thickness of a SiO ₂ film and the sound velocity when an IDT made of platinum is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °), and a SiO ₂ film is further formed. The figure which shows a relationship.
FIG. 18 shows the relationship between the thickness of a platinum film and the sound speed when an IDT made of platinum is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °) and a SiO ₂ film is further formed. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Surface wave device 2 ... Piezoelectric substrates 3a, 3b ... IDT
4. SiO ₂ films 5a, 5b reflector

Claims (7)

A piezoelectric substrate made of LiTaO _{3 having an} Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °);
It is formed on the piezoelectric substrate, has an electrode layer made of platinum, and when the film thickness is H and the wavelength of the surface wave is λ, the normalized film thickness H / λ is 0.005 to 0.054. IDT in the range of
The SiO 2 is formed on the piezoelectric substrate so as to cover the IDT and has a normalized thickness Hs / λ in the range of 0.10 to 0.40 at a wavelength λ of a surface wave when the thickness is Hs. _A surface acoustic wave device, comprising: _two films. The Euler angles of the piezoelectric substrate are (0 ± 2 °, 90 ° to 155 °, 0 ± 2 °), and the normalized thickness H / λ of the IDT is in the range of 0.01 to 0.04. The surface acoustic wave device according to claim 1. _3. The surface acoustic wave device according to claim 1, wherein the Euler angle of the LiTaO ₃ piezoelectric substrate and the normalized thickness Hs / λ of the SiO ₂ film are any of the combinations shown in Table 1 below. 4.

The Euler angle of the piezoelectric substrate is (0 ± 2 °, 102 ° to 150 °, 0 ± 2 °), and the normalized thickness H / λ of the IDT is in the range of 0.013 to 0.033. Item 2. A surface acoustic wave device according to item 1. 5. The surface acoustic wave device according to claim 4, wherein the Euler angle of the LiTaO ₃ piezoelectric substrate and the normalized thickness Hs / λ of the SiO ₂ film are any combination shown in Table 2 below. 6.

6. The device according to claim 1, further comprising at least one electrode layer made of a metal other than platinum laminated on the electrode layer made of platinum, wherein the average density of the entire IDT is in the range of ± 20% of the density of platinum. A surface acoustic wave device according to claim 1. A step of preparing a piezoelectric substrate made of LiTaO _{3 having an} Euler angle (0 ± 2 °, 90 ° to 160 °, 0 ± 2 °);
Forming at least one IDT having at least an electrode layer made of platinum on the piezoelectric substrate;
Performing frequency adjustment after forming the IDT;
7. The method of manufacturing a surface acoustic wave device according to claim 1, further comprising: after the frequency adjustment, forming a SiO ₂ film on the piezoelectric substrate so as to cover the IDT. 8.

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