JP4325178B2

JP4325178B2 - Piezoelectric vibration element, piezoelectric vibrator and piezoelectric oscillator

Info

Publication number: JP4325178B2
Application number: JP2002342482A
Authority: JP
Inventors: 浩一岩田
Original assignee: Miyazaki Epson Corp
Current assignee: Miyazaki Epson Corp
Priority date: 2002-11-26
Filing date: 2002-11-26
Publication date: 2009-09-02
Anticipated expiration: 2022-11-26
Also published as: JP2004179879A

Description

【０００１】
【発明の属する技術分野】
本発明は超薄肉の振動板を厚肉の環状部で一体的に包囲した構造の圧電基板に励振電極等の導電パターンを形成した圧電振動素子、圧電振動素子をパッケージ内に気密封止した圧電振動子、更にはこの圧電振動子を用いた圧電発振器の改良に関し、特に１ＧＨｚ以上の共振周波数を出力するために振動板肉厚を超薄肉状に構成した場合においても、該振動板上に形成する励振電極膜の形状、配置方向を種々工夫することによってスプリアスを最小限に抑えることを可能とした技術に関する。
【０００２】
【従来の技術】
水晶振動子の如く、圧電振動素子をパッケージ内に気密封止した構造の表面実装型の圧電デバイスは、携帯電話機、ページャ等の通信機器や、コンピュータ等の電子機器等において、基準周波数発生源、フィルタ等として利用されているが、これらの各種機器の小型化に対応して圧電デバイスに対しても小型化が求められている。
また、表面実装用の圧電デバイスとしての圧電発振器は、例えばセラミック等から成るパッケージ本体の上面に形成された凹所内に、圧電振動素子と、発振回路を構成する回路部品を収納した状態で凹所開口を金属蓋により封止した構成を備えている。
従来から、上記の如き圧電デバイスに使用される圧電振動素子として、基本波周波数が５０ＭＨｚ以上の高周波化に対応できるように圧電基板の片側表面を一部掘削することにより凹陥部を形成してその底面を数μｍ程度の超薄肉の振動板とすると共に、この振動板周縁を厚肉の環状部により一体的に包囲した構造の圧電基板と、この振動板の表裏両面に夫々形成した入出力用の電極と接地電極と、から成る圧電振動素子が知られている（特開平９−５５６３５号公報）。
このような圧電振動素子により例えば１５５ＭＨｚ程度の高周波を出力するためには、振動板の肉厚を１０μｍ程度に薄くする必要があるが、このように薄肉化した場合、インハーモニックスプリアス（非調和振動）が多く発生する。
ところで、現在、実用化可能なレベルの共振周波数は約３００ＭＨｚであり、数ＧＨｚ程度のものは実現可能と言われており実験室では１．６ＧＨｚレベルまで実現されている。しかし、１ＧＨｚ以上２ＧＨｚまでの共振周波数を得ようとした場合には、振動板の肉厚を０．８〜０．４μｍ程度に極薄化する必要があり、その場合にはインハーモニックスプリアスが更に多発することが予想される。
【０００３】
即ち、図７（ａ）及び（ｂ）はＡＴカット水晶基板におけるエネルギー閉込め現象、及び共振周波数スペクトラムを示した図であり、圧電基板１００の振動板１０１の表裏両面に夫々対向配置した励振電極１０２に対して交番電流を印加することによって振動板１０１を励振させる場合に、励振電極１０２間における振動エネルギーの閉込め係数は、次式：（ｎａ／Ｈ）×√Δ［ｎ：次数（基本波はｎ＝１）、ａ：電極のサイズ、Ｈ：圧電基板厚、√Δ：励振電極を係止したことによる共振周波数の低下量］により求められる。
図中Ｓ_０は目的とする周波数帯であり、Ｓ_１、Ｓ_２は夫々インハーモニックスプリアスとなる周波数帯を示している。
そして、図７（ｂ）の横軸に示した閉込め係数が大きくなればなる程、Ｓ_１モードの規格化周波数が小さくなるに連れて、エネルギーの閉込めがより強くなり、その結果Ｓ_１モードが強く励振することとなる。この結果、図７（ａ）に示すようにＳ_１モードのインハーモニックスプリアスが含まれた出力が得られることとなる。
圧電基板厚Ｈが極薄化した場合に多発することが予想されるインハーモニックスプリアスを低減させるためには、上記式によれば、励振電極１０２の面積（電極長ａ）を振動板の肉厚に応じて可能な限り小さくすることが有効な筈であるが、従来、１ＧＨｚ以上の高周波を出力可能な極薄振動板上に、どのような形状の励振電極を、振動板上にどのような状態で配置すればインハーモニックスプリアスを低減できるか、という課題を解決するための具体策は提案されていない。
【特許文献１】
特開平９−５５６３５号公報
【０００４】
【発明が解決しようとする課題】
本発明は上記に鑑みてなされたものであり、１ＧＨｚ以上の共振周波数を出力可能な極薄の振動板を備えた圧電振動素子でありながら、振動板上に形成する励振電極の形状、配置方向を工夫することによって、インハーモニックスプリアスを可能な限り抑圧して目的とする共振周波数を得ることを可能とした圧電振動素子、圧電振動素子、及び圧電発振器を提供することを目的とする。
【０００５】
【課題を解決するための手段】
上記課題を解決するため、請求項１に係る圧電振動素子は、１ＧＨｚ以上の共振周波数を出力可能な薄肉の振動板と、該振動板の外周縁を一体的に包囲する厚肉の環状部と、を備えることにより、少なくとも一方の主面側に凹陥部を形成したＡＴカット水晶から成る圧電基板と、前記圧電基板の振動板の表裏両面に夫々形成した励振電極と、各励振電極から圧電基板の環状部に引き出されるリード電極と、を備えた圧電振動素子であって、少なくとも前記振動板の表裏両面上に夫々位置する２つの励振電極は互いに交差する直線状の細幅帯状電極であり、各励振電極は夫々圧電基板のｘ軸、及びｚ軸と直交しない斜め方向へ延在して両励振電極の交差部を実質的な励振部とし、前記各励振電極は全長に渡って同一幅を有し、且つ両励振電極の幅は同一でないことを特徴とする。
異方性圧電結晶材料から成る圧電基板の平面２軸に対して非平行な方向へ延びる２つの励振電極を振動板の表裏両面上に配置し、且つ両励振電極を振動板上で交差させた場合に、両励振電極の交差部に位置する励振部の形状が、菱形、平行四辺形、或いは不定形としての四辺形となることにより、振動板の超薄肉化による閉込め係数の増大にも拘わらず、非調和振動の励振は僅かとなり、誘導性領域を有するのは主振動のみとすることができる。即ち、各励振電極を延在させる方向が、異方性圧電結晶材料としての圧電基板に励起された波の伝搬方向である２つの軸方向に対して夫々平行な方向でない方がスプリアスが発生しにくく、主振動が効率良く発生することとなる。また、圧電基板の平面２軸方向へ伝搬する厚み振動の振動エネルギーが励振部を除いた励振電極へ漏れることを防止して振動エネルギー分布の不平衡状態を解消し、特に反対称非調和振動の励振を抑圧する上で優れた効果を発揮する。
２つの励振電極が交差する位置に形成される励振部の形状が不定形状としての四辺形になる場合には、励振部の端縁における非調和振動の反射波をランダム化し、定在波の発生を抑制することが可能となる。
【０００６】
請求項２の発明に係る圧電振動素子は、１ＧＨｚ以上の共振周波数を出力可能な薄肉の振動板と、該振動板の外周縁を一体的に包囲する厚肉の環状部と、を備えることにより、少なくとも一方の主面側に凹陥部を形成したＡＴカット水晶から成る圧電基板と、前記圧電基板の振動板の表裏両面に夫々形成した励振電極と、各励振電極から圧電基板の環状部に引き出されるリード電極と、を備えた圧電振動素子であって、少なくとも前記振動板の表裏両面上に夫々位置する２つの励振電極は互いに交差する直線状の細幅帯状電極であり、各励振電極は夫々圧電基板のｘ軸、及びｚ軸と直交しない斜め方向へ延在して両励振電極の交差部を実質的な励振部とし、前記各励振電極のうちの少なくとも一方の幅は、先端へ向かうほど幅が漸増、或いは漸減するテーパー形状であることを特徴とする。
このような励振電極構造を水晶基板に適用した場合には、その効果はさらに顕著となる。
請求項３の発明に係る圧電振動素子は、前記各励振電極同士の交差角度は、非直角であることを特徴とする。
【０００７】
請求項４の発明に係る圧電振動素子は、前記２つの励振電極の交差部に位置する励振部の形状は、菱形形状、或いは非正四辺形状であることを特徴とする。
請求項５の圧電振動子は、請求項１乃至４に記載の圧電振動素子を構成する圧電基板の長手方向一端部を表面実装用のパッケージ内に片持ち状態で接着保持したことを特徴とする。
請求項６の表面実装型の圧電発振器は、請求項５に記載の圧電振動子と、発振回路と、を少なくとも備えたことを特徴とする。
【０００８】
【発明の実施の形態】
以下、本発明を図面に示した実施の形態により詳細に説明する。
図１（ａ）及び（ｂ）は本発明の一実施形態に係る圧電振動素子の一例としてのＡＴカット水晶から成る水晶振動素子１の凹陥部側斜視図、及び平坦面側斜視図である。
この水晶振動素子１は、異方性を有した圧電結晶材料としてのＡＴカット水晶から成る水晶基板２と、水晶基板２の両主面に夫々形成した励振電極１０ａ、１０ｂ、及び各励振電極１０ａ、１０ｂから夫々延びるリード電極１１ａ、１１ｂと、各リード電極端部の接続パッド１２ａ、１２ｂと、を備えている。
この実施形態に係る水晶基板２は、平面２軸方向ｘ、ｚのうちの一方の結晶軸方向（励起された波の伝搬方向）、例えばｘ軸方向に長尺な矩形平板状の基板本体の一方の主面上に凹陥部３をエッチングにより形成することにより、凹陥部３の内底面に超薄肉の振動板４を位置させると共に、振動板４の外周縁を厚肉の環状部５にて一体的に保持した構成を備えている。環状部５のｘ軸方向に位置する一辺５Ａは、ｘ軸方向へ所定長延長形成されて平板状の張り出し部６となっている。張り出し部６の両面上には、各励振電極１０ａ、１０ｂから夫々引き出された各リード電極１１ａ、１１ｂと接続された接続パッド１２ａ、１２ｂが位置している。各電極、パッドは、所定のマスクを用いた蒸着、スパッタリング等により圧電基板上に形成される導体膜である。
この水晶振動子１により例えば２ＧＨｚの周波数を出力せんとする場合には、振動板４の肉厚は０．４μｍ程度となる。
本発明の一実施形態に係る水晶振動素子１の特徴的な構成は、各励振電極１０ａ、１０ｂの形状を、リード電極１１ａ、１１ｂと同幅を有した直線状の細幅帯状体とし、更に各励振電極１０ａ、１０ｂを夫々圧電基板の直交する２つの結晶軸ｘ、ｚと直交しない方向へ延在せしめ、両励振電極１０ａ、１０ｂの交差部を実質的な励振部１５としている点にある。
互いに交差するように振動板４の両面側に対向配置された各励振電極１０ａ、１０ｂは、均一幅の直線状電極としてもよいし、幅の異なる直線状電極としてもよい。或いは、先端へ向かうほど幅が漸増、或いは漸減するテーパー状の直線状電極としてもよい。また、各励振電極１０ａ、１０ｂが交差する角度は９０度である必要はない。
【０００９】
図２は励振電極１０ａ、１０ｂの具体的構成例を示す説明図である。図２（ａ）は０．１ｍｍ幅の励振電極１０ａ、１０ｂを交差させた状態を示す説明図であり、この例では、同じ幅を有した２つの励振電極１０ａ、１０ｂを交差させることにより、交差部に位置する励振部１５の形状が菱形、或いは正方形となっている。このように励振電極１０ａ、１０ｂを、各結晶軸ｘ、ｚと直交しない斜め方向、或いは各結晶軸ｘ、ｚと平行でない方向に延在させ、且つ交差させることにより、交差部に形成される励振部１５は４つの辺の長さが等しい正四辺形となる。
両励振電極１０ａ、１０ｂの交差角度は、９０度であってもよいし、９０度でなくてもよいが。９０度でない方が、インハーモニックスプリアスを減殺する効果が高いことが確認されている。このことは、以下の他の実施形態についても同様に当てはまる。
このような電極構成を備えた水晶振動素子１の共振周波数を測定した結果、超薄肉化した振動板４に励振電極を形成したことによる閉込め係数の増大にも拘わらず、インハーモニックスプリアスの少ない特性が得られることが判明した。
次に、図２（ｂ）は他の実施形態に係る励振電極の構成例を示す図であり、この例では、一方の励振電極１０ａの幅を、他方の励振電極１０ｂの幅よりも狭く設定している。この結果、両励振電極の交差部に位置する励振部１５の形状は、隣接し合う辺の長さが異なる非正四辺形となる。互いに交差するように対向配置された各励振電極１０ａ、１０ｂが延びる方向は、上述の如く、２つの結晶軸ｘ、ｚに対して直交、或いは平行しないように設定する。これにより、励振部１５の非正四辺形は、４辺のみならず、その対角線も結晶軸ｘ、ｚと直交、或いは平行でなくなる。
【００１０】
次に、図２（ｃ）は各励振電極１０ａ、１０ｂの幅が均一ではなく、先端へ向かう程、テーパー状に幅が漸増するように構成した例を示している。この場合、両励振電極の交差部に形成される励振部１５の形状は対向し合う辺の長さが異なるだけでなく、対向する辺が平行でない非正四辺形状となる。
なお、各励振電極１０ａ、１０ｂの形状を、先端へ向かうほど幅が漸減するテーパー形状としてもよい。
また、この例では両励振電極１０ａ、１０ｂの形状を共にテーパー状としたが、何れか一方のみをテーパー状とし、他方の励振電極については均一幅、或いは逆テーパー状としてもよい。
図２（ａ）（ｂ）及び（ｃ）の各実施形態のように、各結晶軸ｘ、ｚと斜め（直交を除く）に交差するように各励振電極１０ａ、１０ｂを配置することにより、振動板４の超薄肉化による閉込め係数の増大にも拘わらず、非調和振動の励振は僅かとなり、誘導性領域を有するのは主振動のみとなった。このことは、各励振電極１０ａ、１０ｂを延在させる方向が、異方性圧電結晶材料としての水晶基板に励起された波の伝搬方向であるｘ軸方向、ｚ軸方向に対して平行な方向でない方がスプリアスが発生しにくく、主振動が効率良く発生することを意味する。また、水晶基板の平面２軸方向へ伝搬する厚み振動の振動エネルギーが励振部１５を除いた励振電極１０ａ、１０ｂへ漏れることを防止して振動エネルギー分布の不平衡状態を解消し、特に反対称非調和振動の励振を抑圧する上で優れた効果を発揮する。
特に、図２（ｂ）及び（ｃ）のように励振部１５の形状が不定形状としての四辺形になる場合には、励振部１５の端縁における非調和振動の反射波をランダム化し、定在波の発生を抑制することが可能となる。
【００１１】
図３（ａ）及び（ｂ）は、図２（ｂ）のように励振部１５の形状が非正四辺形となっている２ＧＨｚ基本波水晶振動素子１の特性を測定した結果を示すグラフであり、（ａ）はアドミタンス特性の実測値を示し、（ｂ）はスミスチャートの実測値を示す図である。
図３（ａ）において横軸は周波数を示し、縦軸はレベルを示す。このグラフから明らかなように本発明の水晶振動素子は矢印Ａで示した共振点が高レベルに出力されており、矢印Ｂで示したインハーモニックスプリアスは減殺されて低いレベルの状態となっている。
また、図３（ｂ）において、水平な直線ｌはインピーダンスの虚部が０となるレベルを示し、直線ｌよりも上側がＬ成分（インダクタンス成分）であり、下側がＣ成分（キャパシタンス成分）である。この図中の矢印Ａで示した位置が図３（ａ）における共振点Ａとほぼ合致しており、主振動（基本波）の特性は直線ｌよりも上側、即ちＬ成分側に位置しているのに対し、振動子の特性として使用しないＣ成分領域内にスプリアスが位置しているため、換言すれば振動子の特性として使用するＬ成分領域内にスプリアスがないため、振動子として優れた特性を有していることが判る。
【００１２】
図４は比較例を示しており、この比較例に係る２ＧＨｚ基本波水晶振動素子１では、図４（ａ）に示すように水晶基板２の凹陥部３内に位置する振動板４の表裏両面上に夫々細線状の励振電極１０ａ、１０ｂを、夫々ｚ軸とｘ軸に対して平行な姿勢、且つ両者が直交するように配置している。図４（ｂ）はこの水晶振動素子１の特性を示す図であり、主振動の共振点Ａの近傍の周波数帯に高いレベルのインハーモニックスプリアスＢが存在しており、実用に耐えない製品であることが明らかである。
この比較例と本発明の実施形態との比較から明らかなように、細幅帯状（線状）の励振電極１０ａ、１０ｂを２つの平面軸ｘ、ｚと非平行な姿勢にて交差するように配置した本発明の実施形態によれば、目的とする主振動の共振点よりも低いレベルのインハーモニックスプリアスしか存在し得なくなる。
【００１３】
次に、図５は上記各実施形態に係る水晶振動素子（圧電振動素子）１を使用した表面実装型圧電デバイスとしての水晶振動子（圧電振動素子）の断面図であり、この水晶振動子３０は、パッケージ３１内に水晶振動素子１を気密封止した構成を備えている。パッケージ３１は、絶縁材料から成る容器本体３２の凹所内に水晶振動素子１を搭載した状態で金属蓋３６により凹所を封止している。容器本体３２の凹所内底面上に接続パッド３３を備え、外底面に外部電極３４を備えている。この接続パッド３３上に導電性接着剤３５を用いて接続パッド１２ａ、１２ｂを固定している。
また、図６は上記各実施形態に係る水晶振動素子（圧電振動素子）１を使用した表面実装型圧電デバイスとしての水晶発振器（圧電発振器）の断面図であり、この水晶発振器４０は、パッケージ３１内に水晶振動素子１と、発振回路等を構成する回路部品４１を収容した構成を備えている。
なお、上記実施形態では、圧電結晶材料として水晶を例示したが、これは一例に過ぎず、本発明はあらゆる圧電結晶材料から成る水晶振動素子に対して適用することができる。
【００１４】
【発明の効果】
以上のように本発明によれば、１ＧＨｚ以上の共振周波数を出力可能な極薄の振動板を備えた圧電振動素子でありながら、振動板上に形成する励振電極の形状、配置方向を工夫することによって、インハーモニックスプリアスを可能な限り抑圧して目的とする共振周波数を得ることができる。
即ち、本発明は、１ＧＨｚ以上、望ましくは２ＧＨｚに達する周波数を出力するための超薄肉の振動板を備えた圧電振動素子において、異方性圧電結晶材料から成る圧電基板の平面２軸に対して非平行な方向へ延びる２つの励振電極を振動板の表裏両面上に配置し、且つ両励振電極を振動板上で交差させて、両励振電極の交差部に位置する励振部の形状を、菱形、平行四辺形、或いは不定形としての四辺形とすることにより、振動板の超薄肉化による閉込め係数の増大にも拘わらず、非調和振動の励振を僅かとすることができ、特性を向上できる。
更に、２つの励振電極が交差する位置に形成される励振部の形状を不定形状としての四辺形にすることにより、励振部の端縁における非調和振動の反射波をランダム化し、定在波の発生を抑制することが可能となる。
【図面の簡単な説明】
【図１】（ａ）及び（ｂ）は本発明の一実施形態に係る圧電振動素子の一例としてのＡＴカット水晶から成る水晶振動素子１の凹陥部側斜視図、及び平坦面側斜視図。
【図２】（ａ）（ｂ）及び（ｃ）は夫々励振電極の具体的構成例を示す説明図。
【図３】（ａ）は本発明の一実施形態に係る水晶振動素子のアドミタンス特性の実測値を示し、（ｂ）はスミスチャートの実測値を示す図。
【図４】（ａ）及び（ｂ）は比較例を示す図、及び特性図。
【図５】本発明の一実施形態に係る圧電振動子の構成を示す断面図。
【図６】本発明の一実施形態に係る圧電発振器の構成を示す断面図。
【図７】（ａ）及び（ｂ）は従来例の説明図。
【符号の説明】
１水晶振動素子、２水晶基板、３凹陥部、４振動板、５環状部、１０ａ、１０ｂ励振電極、１１ａ、１１ｂリード電極、１２ａ、１２ｂ接続パッド、１５励振部、３０水晶振動子、３１パッケージ、３２容器本体、３３接続パッド、３４外部電極、３５導電性接着剤、３６金属蓋、４０水晶発振器、４１回路部品。[0001]
BACKGROUND OF THE INVENTION
In the present invention, a piezoelectric vibration element in which a conductive pattern such as an excitation electrode is formed on a piezoelectric substrate having a structure in which an ultrathin diaphragm is integrally surrounded by a thick annular portion, and the piezoelectric vibration element is hermetically sealed in a package. The present invention relates to an improvement of a piezoelectric vibrator, and further to a piezoelectric oscillator using this piezoelectric vibrator. In particular, even when the diaphragm thickness is configured to be very thin in order to output a resonance frequency of 1 GHz or more, The present invention relates to a technique capable of minimizing spuriousness by devising various shapes and arrangement directions of excitation electrode films to be formed on the substrate.
[0002]
[Prior art]
A surface-mount type piezoelectric device having a structure in which a piezoelectric vibration element is hermetically sealed in a package, such as a crystal resonator, is used as a reference frequency generation source in communication devices such as mobile phones and pagers, and electronic devices such as computers. Although used as a filter or the like, the piezoelectric devices are also required to be miniaturized in response to the miniaturization of these various devices.
In addition, a piezoelectric oscillator as a surface-mounting piezoelectric device has a recess in a state where a piezoelectric vibration element and a circuit component constituting an oscillation circuit are housed in a recess formed on an upper surface of a package body made of, for example, ceramic. The opening is sealed with a metal lid.
Conventionally, as a piezoelectric vibration element used in the piezoelectric device as described above, a concave portion is formed by excavating a part of one surface of a piezoelectric substrate so as to cope with a higher frequency of a fundamental wave frequency of 50 MHz or more. A piezoelectric substrate with a structure in which the bottom surface is an ultra-thin diaphragm with a thickness of several μm and the periphery of the diaphragm is integrally surrounded by a thick annular part, and input and output formed on both sides of the diaphragm. There is known a piezoelectric vibration element comprising a common electrode and a ground electrode (Japanese Patent Laid-Open No. 9-55635).
In order to output a high frequency of, for example, about 155 MHz by such a piezoelectric vibration element, it is necessary to reduce the thickness of the diaphragm to about 10 μm. However, if the thickness is reduced in this way, inharmonic spurious (anharmonic vibration) is required. ) Occur frequently.
By the way, the resonance frequency at a level that can be put into practical use is about 300 MHz, and it is said that a resonance frequency of about several GHz can be realized, and has been realized up to 1.6 GHz level in the laboratory. However, when trying to obtain a resonance frequency from 1 GHz to 2 GHz, it is necessary to make the thickness of the diaphragm as thin as about 0.8 to 0.4 μm. In that case, in-harmonic spurious is further increased. It is expected to occur frequently.
[0003]
7A and 7B are diagrams showing the energy confinement phenomenon and the resonance frequency spectrum in the AT-cut quartz substrate, and the excitation electrodes disposed on both the front and back surfaces of the diaphragm 101 of the piezoelectric substrate 100, respectively. When the diaphragm 101 is excited by applying an alternating current to 102, the confinement coefficient of vibration energy between the excitation electrodes 102 is expressed by the following formula: (na / H) × √Δ [n: order (basic Waves are determined by n = 1), a: electrode size, H: piezoelectric substrate thickness, √Δ: amount of decrease in resonance frequency due to locking of excitation electrode].
In the figure, S ₀ is a target frequency band, and S ₁ and S ₂ indicate frequency bands that become inharmonic spurious, respectively.
Then, as the confinement factor shown in horizontal axis is the greater of FIG. 7 (b), As the normalized frequency of the S ₁ mode becomes smaller, the energy confinement of becomes stronger, the result S ₁ The mode is strongly excited. As a result, an output that includes the inharmonic spurious S ₁ mode as shown in FIG. 7 (a) is obtained.
In order to reduce inharmonic spurs that are expected to occur frequently when the piezoelectric substrate thickness H is extremely thin, according to the above formula, the area of the excitation electrode 102 (electrode length a) is set to the thickness of the diaphragm. It is effective to make it as small as possible according to the conventional method. However, on the ultrathin diaphragm capable of outputting a high frequency of 1 GHz or higher, what kind of excitation electrode is formed on the diaphragm No specific measures have been proposed for solving the problem of whether in-harmonic spurious can be reduced if arranged in a state.
[Patent Document 1]
JP-A-9-55635 [0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above, and although it is a piezoelectric vibration element including an ultrathin diaphragm capable of outputting a resonance frequency of 1 GHz or more, the shape and arrangement direction of excitation electrodes formed on the diaphragm It is an object of the present invention to provide a piezoelectric vibration element, a piezoelectric vibration element, and a piezoelectric oscillator that can suppress inharmonic spurious as much as possible to obtain a target resonance frequency.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a piezoelectric vibration element according to claim 1 includes a thin diaphragm capable of outputting a resonance frequency of 1 GHz or more, and a thick annular portion that integrally surrounds the outer peripheral edge of the diaphragm. , A piezoelectric substrate made of AT-cut quartz having a recess on at least one main surface side, excitation electrodes formed on both front and back surfaces of the diaphragm of the piezoelectric substrate, and each excitation electrode from the piezoelectric substrate A lead electrode drawn out to the annular portion, and at least two excitation electrodes located on both the front and back surfaces of the diaphragm are linear narrow band electrodes intersecting each other, Each excitation electrode extends in an oblique direction that is not orthogonal to the x-axis and z-axis of the piezoelectric substrate, and the intersection of both excitation electrodes serves as a substantial excitation portion, and each excitation electrode has the same width over its entire length. And having both excitation electrodes Characterized in that it is not identical.
Two excitation electrodes extending in a direction not parallel to the two planes of the piezoelectric substrate made of an anisotropic piezoelectric crystal material are arranged on both the front and back surfaces of the diaphragm, and the two excitation electrodes intersect each other on the diaphragm. In this case, the shape of the excitation part located at the intersection of the two excitation electrodes becomes a rhombus, a parallelogram, or a quadrilateral as an indeterminate shape, thereby increasing the confinement factor due to the ultrathinning of the diaphragm. Nevertheless, the excitation of the anharmonic vibration is small and only the main vibration can have the inductive region. That is, spurious is generated when the direction in which each excitation electrode extends is not parallel to the two axial directions that are the propagation directions of waves excited on the piezoelectric substrate as the anisotropic piezoelectric crystal material. It is difficult to generate main vibration efficiently. In addition, the vibration energy of thickness vibration propagating in the plane biaxial direction of the piezoelectric substrate is prevented from leaking to the excitation electrode excluding the excitation part, and the unbalanced state of vibration energy distribution is eliminated. Excellent effect in suppressing excitation.
When the shape of the excitation part formed at the position where the two excitation electrodes intersect is a quadrilateral as an indefinite shape, the reflected wave of the anharmonic vibration at the edge of the excitation part is randomized to generate a standing wave Can be suppressed.
[0006]
According to a second aspect of the present invention, there is provided a piezoelectric vibration element comprising: a thin vibration plate capable of outputting a resonance frequency of 1 GHz or more; and a thick annular portion integrally surrounding an outer peripheral edge of the vibration plate. A piezoelectric substrate made of AT-cut quartz with a concave portion formed on at least one main surface side, excitation electrodes formed on both front and back surfaces of the vibration plate of the piezoelectric substrate, and each excitation electrode drawn out to the annular portion of the piezoelectric substrate. And at least two excitation electrodes positioned on both the front and back surfaces of the diaphragm are linear narrow band electrodes that intersect each other, and each excitation electrode The piezoelectric substrate extends in an oblique direction that is not orthogonal to the x-axis and the z-axis, and the intersection of both excitation electrodes serves as a substantial excitation portion. The width of at least one of the excitation electrodes increases toward the tip. The width gradually increases, or The taper shape gradually decreases .
When such an excitation electrode structure is applied to a quartz substrate, the effect becomes more remarkable.
The piezoelectric vibration element according to a third aspect of the invention is characterized in that the crossing angle between the excitation electrodes is non-right angle.
[0007]
The piezoelectric vibration element according to a fourth aspect of the invention is characterized in that the shape of the excitation portion located at the intersection of the two excitation electrodes is a rhombus shape or a non-regular quadrilateral shape.
The piezoelectric vibrator according to claim 5 is characterized in that one end in the longitudinal direction of the piezoelectric substrate constituting the piezoelectric vibration element according to any one of claims 1 to 4 is held in a cantilevered manner in a surface mounting package. .
According to a sixth aspect of the present invention, there is provided a surface mount piezoelectric oscillator including at least the piezoelectric vibrator according to the fifth aspect and an oscillation circuit.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIGS. 1A and 1B are a perspective view of a concave portion and a flat surface side of a crystal resonator element 1 made of an AT-cut crystal as an example of a piezoelectric resonator element according to an embodiment of the present invention.
The crystal resonator element 1 includes a crystal substrate 2 made of AT cut crystal as an anisotropic piezoelectric crystal material, excitation electrodes 10a and 10b formed on both main surfaces of the crystal substrate 2, and each excitation electrode 10a. 10b, lead electrodes 11a and 11b respectively extending from 10b, and connection pads 12a and 12b at the ends of the lead electrodes.
The quartz crystal substrate 2 according to this embodiment has a rectangular plate-like substrate body that is long in one crystal axis direction (propagation direction of the excited wave) of the two plane biaxial directions x and z, for example, the x-axis direction. By forming the recessed portion 3 on one main surface by etching, the ultrathin diaphragm 4 is positioned on the inner bottom surface of the recessed portion 3, and the outer peripheral edge of the diaphragm 4 is formed into the thick annular portion 5. The structure is held integrally. One side 5 </ b> A located in the x-axis direction of the annular portion 5 is formed by extending a predetermined length in the x-axis direction to form a flat plate-like protruding portion 6. On both surfaces of the projecting portion 6, connection pads 12a and 12b connected to the lead electrodes 11a and 11b respectively drawn from the excitation electrodes 10a and 10b are located. Each electrode and pad is a conductor film formed on the piezoelectric substrate by vapor deposition, sputtering, or the like using a predetermined mask.
For example, when the quartz vibrator 1 outputs a frequency of 2 GHz, for example, the thickness of the diaphragm 4 is about 0.4 μm.
The characteristic configuration of the crystal resonator element 1 according to the embodiment of the present invention is that the shape of each excitation electrode 10a, 10b is a linear narrow band having the same width as the lead electrodes 11a, 11b, and Each excitation electrode 10a, 10b extends in a direction not perpendicular to the two orthogonal crystal axes x, z of the piezoelectric substrate, and the intersection of the two excitation electrodes 10a, 10b is a substantial excitation part 15. .
Each excitation electrode 10a arranged to face both sides of the diaphragm 4 so as to intersect each other, 10b may be a linear electrode with a uniform width, may be different linear electrodes width. Alternatively, it may be a tapered linear electrode whose width gradually increases or decreases toward the tip. Further, the angle at which the excitation electrodes 10a and 10b intersect with each other need not be 90 degrees.
[0009]
FIG. 2 is an explanatory diagram showing a specific configuration example of the excitation electrodes 10a and 10b. FIG. 2A is an explanatory diagram showing a state in which the excitation electrodes 10a and 10b having a width of 0.1 mm are crossed. In this example, by crossing two excitation electrodes 10a and 10b having the same width, The shape of the excitation unit 15 located at the intersection is a rhombus or a square. In this way, the excitation electrodes 10a and 10b are formed in the intersecting portions by extending and intersecting in an oblique direction not orthogonal to the crystal axes x and z or in a direction not parallel to the crystal axes x and z. The excitation unit 15 is a regular quadrilateral having the same length of the four sides.
The crossing angle between the two excitation electrodes 10a and 10b may be 90 degrees or not 90 degrees. It has been confirmed that the effect of reducing inharmonic spurious is higher when the angle is not 90 degrees. The same applies to the other embodiments described below.
As a result of measuring the resonance frequency of the crystal resonator element 1 having such an electrode configuration, in spite of the increase in the confinement coefficient due to the formation of the excitation electrode on the ultrathin diaphragm 4, the inharmonic spurious frequency is increased. It has been found that few properties can be obtained.
Next, FIG.2 (b) is a figure which shows the structural example of the excitation electrode which concerns on other embodiment, In this example, the width | variety of one excitation electrode 10a is set narrower than the width | variety of the other excitation electrode 10b. is doing. As a result, the shape of the excitation unit 15 located at the intersection of the two excitation electrodes is a non-regular quadrilateral with different lengths of adjacent sides. The direction in which the excitation electrodes 10a and 10b arranged to face each other so as to intersect with each other is set so as to be orthogonal to or not parallel to the two crystal axes x and z as described above. As a result, the non-regular quadrilateral of the excitation unit 15 has not only four sides but also a diagonal line that is not orthogonal or parallel to the crystal axes x and z.
[0010]
Next, FIG. 2C shows an example in which the width of each excitation electrode 10a, 10b is not uniform, and the width is gradually increased toward the tip. In this case, the shape of the excitation portion 15 formed at the intersection of both excitation electrodes is not only the length of the opposing sides, but also a non-regular quadrilateral shape in which the opposing sides are not parallel.
Note that the shape of each excitation electrode 10a, 10b may be a tapered shape in which the width gradually decreases toward the tip.
In this example, both the excitation electrodes 10a and 10b are both tapered, but only one of them may be tapered, and the other excitation electrode may have a uniform width or a reverse taper.
As in the embodiments of FIGS. 2A, 2B, and 2C, by arranging the excitation electrodes 10a and 10b so as to intersect each crystal axis x and z obliquely (except orthogonal), Despite the increase in the confinement factor due to the ultrathinning of the diaphragm 4, the excitation of the anharmonic vibration was small and only the main vibration had an inductive region. This is because the direction in which the excitation electrodes 10a and 10b extend is parallel to the x-axis direction and the z-axis direction, which are propagation directions of waves excited on the quartz crystal substrate as the anisotropic piezoelectric crystal material. If it is not, spurious is less likely to occur, which means that the main vibration is efficiently generated. Further, the vibration energy of the thickness vibration propagating in the two axial directions of the quartz substrate is prevented from leaking to the excitation electrodes 10a and 10b excluding the excitation portion 15, and the unbalanced state of the vibration energy distribution is eliminated. Excellent effect in suppressing excitation of anharmonic vibrations.
In particular, as shown in FIGS. 2B and 2C, when the shape of the excitation unit 15 is a quadrilateral as an indefinite shape, the reflected wave of the anharmonic vibration at the edge of the excitation unit 15 is randomized to be constant. It is possible to suppress the occurrence of standing waves.
[0011]
3A and 3B are graphs showing the results of measuring the characteristics of the 2 GHz fundamental wave crystal resonator element 1 in which the shape of the excitation unit 15 is a non-regular quadrilateral as shown in FIG. 2B. Yes, (a) shows the measured value of the admittance characteristic, and (b) shows the measured value of the Smith chart.
In FIG. 3A, the horizontal axis indicates the frequency, and the vertical axis indicates the level. As is apparent from this graph, in the quartz resonator element of the present invention, the resonance point indicated by the arrow A is output at a high level, and the inharmonic spurious indicated by the arrow B is reduced to a low level state. .
In FIG. 3B, a horizontal straight line 1 indicates a level at which the imaginary part of the impedance is 0, the L component (inductance component) is above the straight line 1, and the C component (capacitance component) is below. is there. The position indicated by the arrow A in FIG. 3 substantially coincides with the resonance point A in FIG. 3A, and the characteristic of the main vibration (fundamental wave) is located above the straight line l, that is, the L component side. On the other hand, since the spurious is located in the C component region that is not used as the characteristic of the vibrator, in other words, there is no spurious in the L component area that is used as the characteristic of the vibrator. It can be seen that it has characteristics.
[0012]
FIG. 4 shows a comparative example. In the 2 GHz fundamental wave crystal resonator element 1 according to this comparative example, both the front and back surfaces of the diaphragm 4 located in the recessed portion 3 of the crystal substrate 2 as shown in FIG. The thin line-like excitation electrodes 10a and 10b are respectively arranged on the upper side so as to be parallel to the z-axis and the x-axis and to be orthogonal to each other. FIG. 4B is a diagram showing the characteristics of the crystal resonator element 1, which has a high level of inharmonic spurious B in the frequency band near the resonance point A of the main vibration, and is a product that cannot withstand practical use. It is clear that there is.
As is clear from a comparison between this comparative example and the embodiment of the present invention, the narrow strip (line) excitation electrodes 10a and 10b intersect with the two plane axes x and z in a non-parallel posture. According to the arranged embodiment of the present invention, only inharmonic spurs having a level lower than the resonance point of the intended main vibration can exist.
[0013]
Next, FIG. 5 is a cross-sectional view of a crystal resonator (piezoelectric vibration element) as a surface-mount piezoelectric device using the crystal vibration element (piezoelectric vibration element) 1 according to each of the above embodiments. Has a configuration in which the crystal resonator element 1 is hermetically sealed in the package 31. The package 31 is sealed with a metal lid 36 in a state where the crystal resonator element 1 is mounted in the recess of the container body 32 made of an insulating material. A connection pad 33 is provided on the inner bottom surface of the recess of the container body 32, and an external electrode 34 is provided on the outer bottom surface. The connection pads 12 a and 12 b are fixed on the connection pad 33 using a conductive adhesive 35.
FIG. 6 is a cross-sectional view of a crystal oscillator (piezoelectric oscillator) as a surface-mount type piezoelectric device using the crystal resonator element (piezoelectric resonator element) 1 according to each of the above embodiments. The quartz resonator element 1 and a circuit component 41 constituting an oscillation circuit and the like are accommodated therein.
In the above embodiment, quartz is exemplified as the piezoelectric crystal material. However, this is only an example, and the present invention can be applied to a quartz crystal vibration element made of any piezoelectric crystal material.
[0014]
【The invention's effect】
As described above, according to the present invention, the shape and the arrangement direction of the excitation electrode formed on the diaphragm are devised while being a piezoelectric vibration element including an extremely thin diaphragm capable of outputting a resonance frequency of 1 GHz or more. As a result, in-harmonic spurious can be suppressed as much as possible to obtain a desired resonance frequency.
That is, the present invention relates to a piezoelectric vibration element having an ultrathin diaphragm for outputting a frequency reaching 1 GHz or more, preferably 2 GHz, with respect to two planes of a piezoelectric substrate made of an anisotropic piezoelectric crystal material. The two excitation electrodes extending in a non-parallel direction are arranged on both the front and back surfaces of the diaphragm, and the two excitation electrodes are crossed on the diaphragm, so that the shape of the excitation part located at the intersection of the two excitation electrodes is By adopting a rhombus, parallelogram, or quadrilateral as an indeterminate shape, the excitation of anharmonic vibration can be minimized despite the increase in the confinement factor due to the ultrathinning of the diaphragm. Can be improved.
Furthermore, by making the shape of the excitation part formed at the position where the two excitation electrodes intersect into a quadrilateral as an indefinite shape, the reflected wave of the anharmonic vibration at the edge of the excitation part is randomized, and the standing wave Occurrence can be suppressed.
[Brief description of the drawings]
FIGS. 1A and 1B are a perspective view of a concave portion and a perspective view of a flat surface of a crystal resonator element 1 made of an AT-cut crystal as an example of a piezoelectric resonator according to an embodiment of the present invention.
FIGS. 2A, 2B, and 2C are explanatory diagrams illustrating specific configuration examples of excitation electrodes, respectively.
FIG. 3A is a diagram showing measured values of admittance characteristics of a crystal resonator element according to an embodiment of the present invention, and FIG. 3B is a diagram showing measured values of a Smith chart.
4A and 4B are a diagram showing a comparative example and a characteristic diagram. FIG.
FIG. 5 is a cross-sectional view showing a configuration of a piezoelectric vibrator according to an embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a configuration of a piezoelectric oscillator according to an embodiment of the present invention.
7A and 7B are explanatory diagrams of a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Quartz vibration element, 2 Quartz substrate, 3 Recessed part, 4 Diaphragm, 5 Ring part, 10a, 10b Excitation electrode, 11a, 11b Lead electrode, 12a, 12b Connection pad, 15 Excitation part, 30 Crystal oscillator, 31 Package , 32 Container body, 33 Connection pad, 34 External electrode, 35 Conductive adhesive, 36 Metal lid, 40 Crystal oscillator, 41 Circuit component.

Claims

By forming a thin diaphragm capable of outputting a resonance frequency of 1 GHz or more and a thick annular portion integrally surrounding the outer peripheral edge of the diaphragm, a concave portion is formed on at least one main surface side. A piezoelectric substrate made of AT-cut quartz,
A piezoelectric vibration element comprising: excitation electrodes formed on both front and back surfaces of the diaphragm of the piezoelectric substrate; and lead electrodes drawn from the excitation electrodes to the annular portion of the piezoelectric substrate,
At least two excitation electrodes respectively located on both the front and back surfaces of the diaphragm are linear narrow strip electrodes intersecting each other, and each excitation electrode is in an oblique direction not orthogonal to the x-axis and z-axis of the piezoelectric substrate, respectively. Extending the intersection of both excitation electrodes as a substantial excitation part ,
Each of the excitation electrodes has the same width over its entire length, and the widths of both excitation electrodes are not the same .

By forming a thin diaphragm capable of outputting a resonance frequency of 1 GHz or more and a thick annular portion integrally surrounding the outer peripheral edge of the diaphragm, a concave portion is formed on at least one main surface side. A piezoelectric substrate made of AT-cut quartz,
A piezoelectric vibration element comprising: excitation electrodes formed on both front and back surfaces of the diaphragm of the piezoelectric substrate; and lead electrodes drawn from the excitation electrodes to the annular portion of the piezoelectric substrate,
At least two excitation electrodes respectively located on both the front and back surfaces of the diaphragm are linear narrow strip electrodes intersecting each other, and each excitation electrode is in an oblique direction not orthogonal to the x-axis and z-axis of the piezoelectric substrate, respectively. Extending the intersection of both excitation electrodes as a substantial excitation part,
At least one of the excitation electrodes has a tapered shape in which the width gradually increases or decreases toward the tip .

The intersection angle between the excitation electrodes, the piezoelectric vibrating element according to claim 1 or 2, characterized in that a non-orthogonal.

The shape of the excitation unit positioned at the intersection of the two excitation electrodes, the piezoelectric vibration according to claim 1, 2, or any one of 3, wherein the diamond shape, or a non-positive quadrilateral element.

The piezoelectric vibrator, characterized in that the adhesive held at one longitudinal end cantilevered in a package for surface mounting state of the piezoelectric substrate constituting the piezoelectric vibrating element according to claim 1 to 4.

A surface-mount type piezoelectric oscillator comprising at least the piezoelectric vibrator according to claim 5 and an oscillation circuit.