JP3755283B2 - Piezoelectric element and manufacturing method thereof, vibration sensor using piezoelectric element, piezoelectric actuator, optical scanner, strain sensor, piezoelectric vibration gyro - Google Patents

Description

【００３１】
圧電定数が最大となる方向とは、ＰＺＴに印加した電界Ｅ^*と平行な方向における歪み成分ε_//とその電界の強さＥとの比［（ε_//）／Ｅ］が最大となる方向である。いま、座標軸Ｘ₃と平行な方向に強さＥの電界が印加されているとすると、当該電界に平行な方向の歪み成分とはε₃であるから、電界の印加方向における歪み成分と電界の強さの比（すなわち、電界印加方向における圧電定数の大きさ）はｄ₃₃である。
【００３２】
ここで、任意方向の電界Ｅ^*を考えるとともに、座標軸Ｘ₃´が電界Ｅ^*の方向と一致し、元の直交座標軸［座標系］（Ｘ₁，Ｘ₂，Ｘ₃）と原点を共有する新たな直交座標軸［座標系］（Ｘ₁´，Ｘ₂´，Ｘ₃´）を考えると、新たな座標系では、歪みε^*、圧電定数｛ｄij｝及び電界Ｅ^*の関係は、新たな座標系においては、つぎの（２）式のように表わされる。
【００３３】
【数２】

【００３４】
ここで、ダッシュ（´）は、新たな座標系における成分であることを示している。（２）式より、この座標系では、電界Ｅ^*の印加方向における歪み成分と電界の強さの比（すなわち、圧電定数の大きさ）は、新たな座標系における圧電定数の対角成分ｄ₃₃´であることが分かる。よって、圧電定数が最大となる方向を求めるためには、座標系を回転させたときの、圧電定数の対角成分ｄ₃₃の座標変換を考えて最大の対角成分ｄ₃₃´を求めればよいことになる。
【００３５】
新しい座標系における圧電定数ｄ＝｛ｄij´｝は、変換行列Ａ＝｛Ａij｝及びＮ＝｛Ｎij｝を用いて元の座標系における圧電定数ｄ＝｛ｄij｝を一次変換することにより求まる。すなわち、その変換式は、つぎの（３）式で表わされる。ここで、右肩の添字ｔは転置行列を意味する。
【００３６】
【数３】

【００３７】
また、変換行列Ａ＝｛Ａij｝およびＮ＝｛Ｎij｝は、次の行列（４）、（５）で定義される。ここで、｛ｅ₁，ｅ₂，ｅ₃｝は元の座標系（Ｘ₁，Ｘ₂，Ｘ₃）における基底ベクトル、｛ｅ₁´，ｅ₂´，ｅ₃´｝は新しい座標系（Ｘ₁，Ｘ₂，Ｘ₃）における基底ベクトルであって、例えば、ｅ₁・ｅ₂´は座標軸Ｘ1と座標軸Ｘ2´のなす角度の方向余弦を表している。また、行列（５）で用いられている記号ａijはスティフネス定数を表している。
【００３８】
【数４】

【００３９】
【数５】

【００４０】
この計算を実行して任意の方向における圧電定数ｄ₃₃´を具体的に求めるためには、圧電定数ｄのマトリクス成分ｄijの値が必要となる。表１は、定電界下における菱面体晶ＰＺＴ６０／４０［つまり、Ｐｂ（Ｚｒ₀.₆Ｔｉ₀.₄）］の圧電定数ｄ₃₃，ｄ₂₂，ｄ₃₁，ｄ₁₅の値を示す（圧電定数の他のマトリクス成分は０であるとする）。表２は、定電界下における正方晶ＰＺＴ４０／６０［つまり、Ｐｂ（Ｚｒ₀.₄Ｔｉ₀.₆）Ｏ₃］の圧電定数ｄ₃₃，ｄ₃₁，ｄ₁₅の値を示す（圧電定数の他のマトリクス成分は０であるとする）。表１、表２は、M.J.Haun, E.Furman, S.J.Jang and L.E.Cross: Ferroelectrics, 99(1989)63に掲載されているデータを用いて計算したものである。
【００４１】
【表１】

【００４２】
【表２】

【００４３】
座標系が３次元空間で回転すると、回転した新たな座標系（Ｘ₁´，Ｘ₂´，Ｘ3´）における圧電定数ｄの対角成分ｄ₃₃´（以下、変換前の座標系と変換後の座標系を区別するためのダッシュ記号は省略する）は、上記（３）式と表１又は表２から計算される。
【００４４】
菱面体晶ＰＺＴ６０／４０に対する結果を図６（ａ）（ｂ）に示す。図６（ａ）は圧電定数ｄ33の結晶方向依存性を３次元表示したもの、図６（ｂ）は図６（ａ）の３次元表示をＹＺ平面でカットした断面である。なお、Ｚ軸は自発分極の方向である［１１１］方向、Ｘ軸はＰＺＴの鏡面と垂直な方向、Ｙ軸はＺ軸及びＸ軸に垂直な方向であって、座標原点と表示図形上の１点との間の距離は、対応する方向における圧電定数ｄ33の値を表わしている。従来の［１１１］方向（図６のＺ軸）での圧電定数ｄ33は、図６（ａ）の３次元表示とＺ軸との交点にあたり、ちょうど３次元表示の凹みになっている。これに対し、図６（ｂ）によれば、Ｚ軸から５６.７゜傾いた方向で圧電定数ｄ33が最大値［＝１８９×１０-12Ｃ／Ｎ］となっている。この圧電定数ｄ33が最大になる方向は、厳密には菱面体晶ＰＺＴの立方晶系の結晶軸方向を基準とした［１００］方向、［０１０］方向、［００１］方向から２゜ずれているが、実用上はそれぞれ立方晶系の結晶軸方向を基準とした［１００］配向、［０１０］配向、［００１］配向と考えて問題ない。
【００４５】
正方晶ＰＺＴ４０／６０に対して得られた結果を図７に示す。図７（ａ）は正方晶ＰＺＴ４０／６０の圧電定数ｄ₃₃の結晶方向依存性を３次元表示したものであり、図７（ｂ）は図７（ａ）の３次元表示を（０１０）面でカットした断面を示す。正方晶ＰＺＴでは、Ｚ軸から５１.３゜傾いた［００１］方向で圧電定数ｄ₃₃が最大値［＝１６２×１０^-12Ｃ／Ｎ］となっており、菱面体晶の場合の最大値よりも若干小さいものの、やはり［１１１］方向での圧電定数ｄ₃₃よりも大きな値となっている。
【００４６】
従って、大きな圧電定数を有するＰＺＴを得るためには、菱面体晶の組成比を有するペロブスカイト構造のＰＺＴを、（立方晶ペロブスカイト構造の等価な方向の）［１００］方向、［０１０］方向または［００１］方向が電極面とほぼ垂直となるように配向させれば、従来の３倍近い圧電定数を有する圧電素子が得られ、この圧電素子を各種センサ等に適用することにより、その特性を大きく向上させることができる。また、正方晶の組成比を有するペロブスカイト構造のＰＺＴを、（立方晶ペロブスカイト構造の等価な方向の）［００１］方向が電極面とほぼ垂直となるように配向させれば、従来の２倍以上の圧電定数を有する圧電素子が得られ、この圧電素子を各種センサ等に適用することにより、その特性を大きく向上させることができる。よって、従来にない大きな力のとれる圧電アクチュエータや感度の高い歪みセンサ等を実現でき、また、歪みを大きくとれるため、マイクロマシンを用いた超小型センサやアクチュエータ等に適用できる。
【００４７】
（圧電素子の製造方法）
次に、上記のようなＰＺＴ薄膜を用いた圧電素子の製造方法を図８（ａ）〜（ｄ）により説明する。まずは、菱面体晶組成のＰＺＴ薄膜２を用いた圧電素子１を製造する場合について述べる。図８（ａ）に示すように、Ｓｉ基板のような単結晶基板（単結晶基板の表面には、ＳｉＯ2のような酸化膜が形成されていてもよい）６の上に中間金属層としてＴｉ膜７を形成する。ここで、単結晶基板６として（１００）基板、（０１０）基板又は（００１）基板を用いることにより、［１００］方向、［０１０］方向又は［００１］方向が単結晶基板６の表面と垂直な方向を向くようにＴｉ膜７がエピタキシャル成長される。
【００４８】
ついで、図８（ｂ）に示すように、このＴｉ膜７の上に下地金属層としてＰｔ膜８を成膜する。このとき、Ｔｉ膜７は［１００］方向、［０１０］方向又は［００１］方向が膜厚方向を向くように結晶配向しているので、その上にエピタキシャル成長させられたＰｔ膜８も、［１００］方向、［０１０］方向又は［００１］方向が膜厚方向を向くように結晶配向する。こうして、単結晶基板６の上に形成されたＴｉ膜７とＰｔ膜８とによって下面側の電極３ａが形成される。また、Ｐｔ膜８を直接単結晶基板６の上に形成せず、中間にＴｉ膜７を形成しているのは、Ｐｔ膜８と単結晶基板６との密着性を高めて電極３ａの剥離を防止するためである。
【００４９】
さらに、このＰｔ膜８の上には、図８（ｃ）に示すように、菱面体晶組成となるようにＺｒとＴｉの成分組成を制御しながらＰＺＴ薄膜２を形成する。
【００５０】
このとき、上記圧電素子中のＰＺＴ薄膜２には、Ｂａ，Ｓｒ，Ｌａ，Ｂｉ，Ｍｇ，Ｗ，Ｎｂ，Ｚｎ等の添加物のうち少なくとも一種を微量添加することにより、ＰＺＴの温度による特性ばらつきを抑えることができ、圧電素子１の温度特性を安定させることができる。また、このＰＺＴ薄膜２の膜厚は、２μｍ以下とするのが好ましい。膜厚を２μｍ以下にすれば、マイクロマシニング技術で作製される微小なセンサやアクチュエータなどにも用いることができるからである。
【００５１】
こうしてＰｔ膜８の上に形成された菱面体晶組成の未焼成ＰＺＴ薄膜２はアモルファス構造であるので、ついで、焼結（アニール）によってＰＺＴ薄膜２の結晶化を行なう。このとき、焼結方法によってペロブスカイト構造と呼ばれる圧電性を示す結晶構造のＰＺＴ膜２が得られるが、このペロブスカイト構造のＰＺＴ薄膜２は、ＺｒとＴｉの組成比によって決まる結晶の歪みを受ける。すなわち、ＺｒとＴｉの組成比が菱面体晶組成であると、菱面体晶に歪んだぺロブスカイト構造のＰＺＴ薄膜２が得られる。
【００５２】
しかも、この焼結時には、ＰＺＴ薄膜２は下地金属層であるＰｔ膜８の格子によって結晶配向を支配されるので、Ｐｔ膜８の結晶方位に従って［１００］方向、［０１０］方向又は［００１］方向が電極３ａとほぼ垂直な方向を向くように結晶配向する。
【００５３】
従って、ＰＺＴ薄膜２の形成にあたっては、ＰＺＴ薄膜２の結晶配向性を支配する下地金属層の結晶配向を［１００］方向、［０１０］方向又は［００１］方向にしておくことと、その下地金属層上に形成するＰＺＴ薄膜２の組成が菱面体晶となるように組成比を制御することが重要である。
【００５４】
こうして菱面体晶のＰＺＴ薄膜２を得た後、図８（ｄ）に示すように、ＰＺＴ薄膜２の上にＰｔ膜などによって上側の電極３ｂを形成し、圧電素子１の製造を完了する。
【００５５】
なお、ここでは、菱面体晶組成のＰＺＴ薄膜の場合について説明したが、正方晶組成のＰＺＴ薄膜を必要とする場合には、中間金属層であるＴｉ膜と下地金属層であるＰｔ膜の［００１］方向を膜厚方向と垂直な方向を向くように形成し、Ｐｔ膜の上に形成する未焼成のＰＺＴ薄膜を正方晶組成となるように制御すればよい。
【００５６】
上記圧電素子の製造方法では、従来の圧電素子の製造工程におけるプロセス条件を変更するだけでよいので、従来のプロセスをそのまま使用でき、新たな設備を必要とせず、製造プロセスの変更に対するコストが掛からない。従って、圧電アクチュエータや歪みセンサ等を製造する場合にも、コストパフォーマンスの良いものを製造することができる。
【００５７】
また、上記製造方法では、焼結によりＰＺＴを結晶配向させる方法について説明したが、これ以外の製造方法によって本発明の圧電素子を製造することもできる。例えば、ペロブスカイト構造を有する菱面体晶組成〔あるいは、正方晶組成〕のＰＺＴのバルク結晶を製作した後、このバルク結晶を（１００）面、（０１０）面又は（００１）面〔あるいは、正方晶組成の場合には、（００１）面〕で切り出し、その切り出した面に電極を形成するようにしてもよい。あるいは、ＰＺＴ薄膜を下地結晶又は下地金属層の上にエピタキシャル成長させるようにしてもよい。
【００５８】
（応用例）
以下においては、上記圧電素子を応用した装置を説明する。そこでは［１００］方向を電極面と垂直な方向に向けた菱面体晶ＰＺＴを用いた場合を例にとっているが、［０１０］方向や［００１］方向を電極面と垂直な方向に向けた菱面体晶ＰＺＴや［００１］方向を電極面と垂直な方向に向けた正方晶ＰＺＴであってもよい。
【００５９】
（振動センサ）
図９は本発明にかかる圧電素子を利用した振動センサ１１を示す斜視図である。これは、シリコン基板（ウエハ）を加工することにより形成されたものであって、ウエイト部１２がビーム１３によりフレーム１４に片持ち状に支持されている。また、ビーム１３からウエイト部１２にわたる領域の上面には圧電素子１が一体に設けられている。
【００６０】
しかして、この振動センサ１１に振動や加速度が加わると、ウエイト部１２が上下に振動ないし変位するので、ビーム１３が弾性的に屈曲する。ビーム１３が弾性的に屈曲すると、それに応じて圧電素子１も機械的に屈曲させられて圧電素子１の電極３ａ，３ｂ間には電荷が発生する。従って、この発生した電荷による電圧を計測することによってビーム１３の屈曲程度、ひいては振動や加速度を計測することができる。ここで、本発明の圧電素子１を用いると同じ振動や加速度でも、大きな電圧を発生させることが可能になり、検出感度を向上させることができる。
【００６１】
この振動センサ１１の製造プロセスを図１０（ａ）〜（ｊ）に示す。まず、Ｓｉ基板（ウエハ）１５を準備し〔図１０（ａ）〕、Ｓｉ基板１５の表裏両面を熱酸化により酸化させて酸化膜（ＳｉＯ₂）１６を形成する〔図１０（ｂ）〕。ついで、Ｓｉ基板１５の下面において、酸化膜１６をふっ酸でエッチングしてウエイト部１２及びビーム１３となるＳｉ基板領域を部分的に露出させ〔図１０（ｃ）〕、酸化膜１６をエッチング用マスクとしてＳｉ基板１５をエッチングし、ウエイト部１２及びビーム１３となる領域でＳｉ基板１５の厚みを薄くする〔図１０（ｄ）〕。
【００６２】
ついで、Ｓｉ基板１５の厚みを薄くした薄肉領域１７において、酸化膜１６の上にＴｉ膜（中間金属層）７を形成し〔図１０（ｅ）〕、さらにＴｉ膜７の上にＰｔ膜（下地金属層）８を形成して〔図１０（ｆ）〕下側の電極３ａを作った後、Ｐｔ膜８の上に菱面体晶組成のＰＺＴ薄膜２を成膜する〔図１０（ｇ）〕。この後、ＰＺＴ薄膜２を焼結（アニール）することによって、ＰＺＴ薄膜２の［１００］方向を電極３ａの表面と垂直な方向に結晶配向させる〔図１０（ｈ）〕。ついで、ＰＺＴ薄膜２の上にＰｔ膜等によって上側の電極３ｂを形成してＳｉ基板１５の上に高性能の圧電素子１を形成する〔図１０（ｉ）〕。その後、Ｓｉ基板１５及び酸化膜１６をエッチングすることによってＳｉ基板１５のフレーム１４となる部分とウエイト部１２及びビーム１３となる部分を切り離す開口１８を形成して振動センサ１１を完成する〔図１０（ｊ）〕。
【００６３】
（積層型圧電アクチュエータ）
図１１は本発明にかかる圧電素子を利用した積層型の圧電アクチュエータ２１を示す側面図である。この積層型圧電アクチュエータは、ＰＺＴ薄膜２と電極３とを交互に積層したものであり、菱面体晶組成のＰＺＴ薄膜２の［１００］方向が電極３と垂直な方向を向くようにＰＺＴ薄膜２が結晶配向されている。また、各ＰＺＴ薄膜２の自発分極Ｐの方向は電極３と垂直な方向から傾いているが、さらにＰＺＴ薄膜２の分極方向は積層方向に沿って交互に反転している。電極３は、一層おき毎に＋側端子２２と−側端子２３に接続されている。
【００６４】
このような圧電アクチュエータ２１によれば、電圧を印加したときの伸縮量は各ＰＺＴ薄膜２の伸縮量の合計となり、しかも、各ＰＺＴ薄膜２の伸縮量が従来例に比べて大きいので、大きな伸縮量もしくは駆動力を得ることができる。
【００６５】
（光スキャナ）
図１２は本発明にかかる圧電素子を利用した光スキャナ２４を示す斜視図である。この光スキャナ２４は、図１１に示したような構造の積層型圧電アクチュエータ２１の先端（駆動端）に弾性板２５を取り付けたものである。弾性板２５は、Ｓｉ基板を加工することにより形成されており、駆動部２６から延出されたトーションバー２７の先に非対称な形状をしたミラー部２８を設けたものであって、駆動部２６が圧電アクチュエータ２１に固定されている。
【００６６】
しかして、圧電アクチュエータ２１に交流電圧を印加すると、圧電アクチュエータ２１が伸縮して弾性板２５の駆動部２６を振動させる。駆動部２６が微小振動すると、ミラー部２８が非対称で、その重心がトーションバー２７の軸心から偏心しているために、ミラー部２８はトーションバー２７を捩らせることによって一定の周期で回転する。従って、光源から出射されたレーザー光をミラー部２８に照射すると、ミラー部２８で反射された光は往復走査されることになる。
【００６７】
このような光スキャナ２４において、本発明にかかる圧電アクチュエータ２１を用いれば弾性板２５を大きな振幅で振動させることができるので、光の走査幅を大きくすることができる。
【００６８】
（歪みセンサ）
図１３（ａ）は本発明にかかる圧電素子を利用した歪みセンサ３１を示す断面図である。歪みセンサ３１は、ＰＺＴ薄膜２の両面に電極３ａ，３ｂを形成した圧電素子１を歪み検出対象物３２の上に取り付けたものであり、両電極３ａ，３ｂ間の電圧をチャージアンプ等の検出器３３で検出できるようにしている。
【００６９】
しかして、図１３（ｂ）に示すように、歪み検出対象物３２が変形して歪むと、歪み検出対象物３２とともに圧電素子１が歪み、両電極３ａ，３ｂ間には歪み量に応じた電荷が発生するので、この電荷量を電極３ａ，３ｂ間の電圧として検出器３３により計測する。このような歪みセンサ３１に本発明の圧電素子を利用することにより、感度の高い歪みセンサを製作することができる。
【００７０】
（圧電式振動ジャイロ）
図１４は本発明にかかる圧電素子を利用した圧電式振動ジャイロ３４を示す斜視図である。この振動ジャイロ３４は、熱膨張の少ないエリンヴァー合金などで作った音叉３５に発振駆動用の圧電素子１ａを貼り付け、それと直角な面に検出用の圧電振動子１ｂを貼り付けたものである。このような振動ジャイロ３４における両圧電素子１ａ，１ｂとしても本発明の圧電素子を用いることができる。
【図面の簡単な説明】
【図１】ＰＺＴの組成のうちＺｒ，Ｔｉの２成分における、ＰＺＴの相図である。
【図２】本発明の第１の実施形態による圧電素子を示す概略断面図である。
【図３】本発明の第２の実施形態による圧電素子を示す概略断面図である。
【図４】菱面体晶系のペロブスカイト構造を有するＰＺＴの結晶構造を示す図である。
【図５】正方晶系のペロブスカイト構造を有するＰＺＴの結晶構造を示す図である。
【図６】（ａ）は菱面体晶ＰＺＴ６０／４０の圧電定数ｄ₃₃の結晶方向依存性を３次元表示したもの、（ｂ）は（ａ）の３次元表示をＹＺ平面でカットした断面である。
【図７】（ａ）は正方晶ＰＺＴ４０／６０の圧電定数ｄ₃₃の結晶方向依存性を３次元表示したもの、（ｂ）は（ａ）の３次元表示を（０１０）面でカットした断面である。
【図８】（ａ）（ｂ）（ｃ）（ｄ）は、本発明にかかる圧電素子の製造工程を示す断面図である。
【図９】本発明にかかる圧電素子を利用した振動センサを示す斜視図である。
【図１０】（ａ）〜（ｊ）同上の振動センサの製造プロセスを示す断面図である。
【図１１】本発明にかかる圧電素子を利用した積層型の圧電アクチュエータを示す側面図である。
【図１２】本発明にかかる圧電素子を利用した光スキャナを示す斜視図である。
【図１３】（ａ）は本発明にかかる圧電素子を利用した歪みセンサを示す断面図、（ｂ）は歪みセンサに歪みが加わった状態を示す断面図である。
【図１４】本発明にかかる圧電素子を利用した圧電式振動ジャイロを示す斜視図である。
【符号の説明】
１ 圧電素子
２ 菱面体晶組成のＰＺＴ
３ａ，３ｂ 電極
４ 圧電素子
５ 正方晶組成のＰＺＴ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric element such as a strain sensor, a piezoelectric actuator, or a dynamic random access memory (DRAM) using PZT as a piezoelectric material. Moreover, it is related with the manufacturing method.
[0002]
[Prior art]
A piezoelectric material is a substance that generates an electric charge when a strain is applied and generates a strain when a voltage is applied. A strain sensor, a piezoelectric actuator, or the like is manufactured using this property (piezoelectricity). Recently, many researches and developments have been made to apply this voltage-distortion characteristic to DRAMs and the like. In utilizing the properties of this piezoelectric material, it is necessary to obtain a large strain at a low voltage and to obtain a large generated charge with a small strain, and it is desirable that this property is remarkable. For this purpose, it is necessary to use a material having a large piezoelectric constant.
[0003]
PZT [= Pb (Zr_XTi_1-X) O_Three; Lead zirconate titanate] is a well-known piezoelectric material that is relatively well researched and developed among piezoelectric materials, and has a large piezoelectric constant. PZT is a substance composed of Pb, Zr, Ti and O (oxygen), and is a solid solution of lead titanate and lead zirconate.
[0004]
Conventionally, in order to maximize the voltage-strain characteristics of PZT, PZT is sintered in a state where the composition is near the phase boundary between tetragonal and rhombohedral (Morphotropic Phase Boundary; hereinafter referred to as MPB). Therefore, it has been said that it is necessary to orient the crystal in the [111] direction of the perovskite structure. That is, PZT is represented by Pb (Zr shown in FIG._XTi_1-X) O_ThreeAs can be seen from the phase diagram of the system, at room temperature, the crystal structure is divided into tetragonal and rhombohedral crystals depending on the composition ratio of Zr and Ti, and in order to obtain a large piezoelectric constant, PZT was sintered at the phase boundary (MPB). PZT is spontaneously polarized in the [111] direction (hereinafter, this direction is sometimes referred to as the Z-axis direction), and the direction of spontaneous polarization is perpendicular to the electrode surface in order to obtain a large piezoelectric constant. In order to obtain the [111] orientation, the surface of the base metal layer (base electrode) that governs the crystal orientation of PZT is defined as the (111) plane. And the composition ratio of PZT formed on the underlying metal layer is controlled to be in the vicinity of the phase boundary between the tetragonal crystal and the rhombohedral crystal.
[0005]
[Problems to be solved by the invention]
However, as the application field of PZT spreads and strain sensors, piezoelectric actuators, DRAMs and the like using PZT thin films are widely used, development of PZT having a larger piezoelectric constant is required.
[0006]
In addition, since the conventional PZT is formed so that the composition is in the vicinity of the phase boundary between tetragonal and rhombohedral, the structure of the PZT thin film actually formed is a perovskite structure distorted to tetragonal or rhombohedral. One of the perovskite structures distorted in the plane crystal has a problem that the piezoelectric constant varies due to the variation in the structure.
[0007]
The present invention has been made in view of the disadvantages of the conventional examples described above. The purpose of the present invention is to increase the piezoelectric constant of PZT in a piezoelectric element using PZT, and near the phase boundary. It is to make the characteristics of the piezoelectric element stable and favorable by eliminating the variation of the piezoelectric constant derived from the variation of the crystal structure.
[0008]
DISCLOSURE OF THE INVENTION
  The piezoelectric element according to claim 1 is a piezoelectric element including PZT and an electrode, wherein the electrode is oriented in a (100) plane, a (010) plane, or a (001) plane, and the PZT is The perovskite structure having a composition ratio in which Zr and Ti contained in the substrate are rhombohedral at room temperature,Based on cubic crystal axis directionThe crystal orientation is such that the [100] direction, the [010] direction, or the [001] direction is substantially perpendicular to the electrode surface.
[0009]
It was found that PZT having a rhombohedral crystal composition at room temperature has a very large piezoelectric constant in the vicinity of one of the [100], [010], and [001] directions of the perovskite structure. Therefore, if the crystal orientation is made so that any one of the orientation directions is substantially perpendicular to the electrode surface, the electric field direction ( That is, it has a very large piezoelectric constant in the direction perpendicular to the electrode surface. By using such PZT, characteristics of piezoelectric elements such as a strain sensor, a piezoelectric actuator, and a DRAM can be further enhanced.
[0010]
In addition, when the rhombohedral crystal is used, the composition deviation is unlikely to occur as in the conventional PZT using the boundary composition of the tetragonal and rhombohedral crystals, and the characteristic variation due to the composition deviation is suppressed. The characteristics can be stabilized.
[0013]
  And claims2Embodiments described in claim 1 claim1In the described piezoelectric element, at least one of Ba, Sr, La, Bi, Mg, W, Nb, and Zn is added to the PZT.
[0014]
As in this embodiment, by adding any one of Ba, Sr, La, Bi, Mg, W, Nb, and Zn to PZT, the PZT characteristic variation due to temperature can be suppressed.
[0015]
  According to a third aspect of the present invention, there is provided a piezoelectric element manufacturing method comprising:On the surface(100) plane, (010) plane or (001) plane-oriented base metal layer is formed,Next, using a metal different from the intermediate metal layer, a base metal layer having a (100), (010) plane, or (001) plane orientation on the surface of the intermediate metal layer that is not in contact with the single crystal substrate. On the surface of the base metal layer that is not in contact with the intermediate metal layer.After forming the rhombohedral PZT film, the PZT film is sintered,Based on cubic crystal axis directionThe crystal orientation is such that the [100] direction, [010] direction, or [001] direction is substantially perpendicular to the surface of the base metal layer.
[0016]
According to this manufacturing method, the piezoelectric element described in claim 1 can be manufactured, and a PZT film with good crystal orientation can be obtained.
[0017]
  In addition, the piezoelectric element of the present invention can be used by being incorporated in a vibration sensor, a piezoelectric actuator, an optical scanner, a strain sensor, a piezoelectric vibration gyro, or the like as described in claims 4-8.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
(Summary of the Invention)
PZT [= Pb (Zr_XTi_1-X) O_ThreeIn order to obtain a high piezoelectric constant as a result of three-dimensional calculation of the respective piezoelectric constants in the two crystal systems (tetragonal and rhombohedral) of tetragonal and rhombohedral Relative to the composition of the phase boundary (MPB) in the [111] orientation, the rhombohedral composition in the [100] orientation, [010] orientation or [001] orientation has the largest piezoelectric constant. It turns out that it is obtained. It was also found that a piezoelectric constant larger than that of the prior art can be obtained even when the tetragonal composition has a [001] orientation of the perovskite structure.
[0020]
That is, in the composition of PZT, the composition ratio of Zr and Ti is adjusted to a composition region (see FIG. 1) that becomes rhombohedral at normal temperature, and PZT having a perovskite structure distorted to rhombohedral by sintering is fired. For example, PZT spontaneously polarized in the [111] direction, but the piezoelectric constant was found to be maximum in the [100], [010] or [001] direction.
[0021]
  The present invention has been made on the basis of the above knowledge, and as shown in FIG. 2, the piezoelectric element 1 according to the first embodiment comprises PZT2 having a rhombohedral composition perovskite structure.Based on cubic crystal axis directionThe crystal orientation is such that the [100] direction, [010] direction or [001] direction is substantially perpendicular to the surfaces of the electrodes 3a and 3b.
[0022]
Further, when the composition ratio of Zr and Ti in the composition of PZT is adjusted to a composition region (see FIG. 1) that becomes tetragonal at room temperature, and PZT having a perovskite structure distorted to tetragonal by sintering is fired, [111 It was found that the piezoelectric constant was maximum in the [001] direction.
[0023]
The piezoelectric element 4 according to the second embodiment of the present invention has been made based on the above knowledge, and as shown in FIG. 3, a PZT5 having a perovskite structure having a tetragonal composition has a [001] direction. The crystal is oriented so as to be substantially perpendicular to the surfaces of the electrodes 3a and 3b.
[0024]
  According to the piezoelectric element of the present invention, it is possible to use a very large piezoelectric constant as compared with the conventional example without using a special piezoelectric material, and it is possible to manufacture various piezoelectric elements having good characteristics. Specifically, in comparison with the conventional piezoelectric element using the piezoelectric constant in the [111] direction, in the rhombohedral PZTBased on cubic crystal axis directionIn the piezoelectric element of the present invention using the piezoelectric constant in the [100] direction, [010] direction, or [001] direction, the piezoelectric constant is 2.7 times that of the conventional example, and [001] in PZT having a tetragonal composition. ] Of the piezoelectric element of the present invention utilizing the piezoelectric constant in the direction is 2.27 times that of the conventional example.
[0025]
(Theoretical explanation)
Next, the theoretical basis of the present invention will be described. The phase diagram of PZT as shown in FIG. 1 is well known [eg B. Jaffe, WJ Cook and J. Jaffe: Piezoelectric Ceramics (Academic Press, London, 1971)], and PZT is cubic at high temperatures. Although it shows a system paraelectric phase, when the temperature drops to room temperature, it becomes a rhombohedral ferroelectric phase or a tetragonal ferroelectric phase depending on the composition ratio of Zr and Ti. For example, on the Ti rich side, for example, PT [= PbTiO_ThreePZT with lead titanate] of 60% (x = 0.4) is tetragonal PZT exhibits piezoelectricity, and PZT with Zr rich side, for example, PT of 40% (x = 0.6) is rhombohedral PZT exhibits piezoelectricity.
[0026]
Here, the perovskite structure of rhombohedral PZT is a crystal structure as shown in FIG. 4, in which the slanted spheres indicate Pb atoms, the shaded spheres indicate Zr or Ti atoms, and white spheres. Represents an O (oxygen) atom. In addition, the rhombohedral perovskite structure has a form in which the cubic system is stretched or contracted in a diagonal direction (that is, the [111] direction of the cubic system) [100] The direction, [010] direction, and [001] direction have equivalent structures. In this specification, the crystal axis directions of the [100] direction, [010] direction, etc. in both the rhombohedral system and the tetragonal system are cubic crystal system crystal axes as can be seen from FIG. Shows direction.
[0027]
In addition, the perovskite structure of tetragonal PZT is a crystal structure as shown in FIG. 5, in which the lattice extends slightly in the [001] direction, and the lattice constant c in the [001] direction is the [100] direction and [ 010] direction lattice constants a and b (a = b).
[0028]
The purpose of the discussion below is to determine the crystal orientation that maximizes the piezoelectric constant for PZT having the rhombohedral perovskite structure and PZT having the tetragonal perovskite structure as described above.
[0029]
First, the electric field (vector) E is applied to the PZT crystal.^*= (E₁, E₂, E_Three) Is the distortion (vector) of PZT that occurs when^*= (Ε₁, Ε₂, Ε_Three), This strain ε^*Is a matrix of piezoelectric constants d^*= {Dij} is used to express the following equation (1). Here, the electric field component E₁, E₂, E_Three, Distortion component ε₁, Ε₂, Ε_Three, The matrix component dij (i, j = 1, 2, 3) of the piezoelectric constant is represented by a coordinate axis X in an arbitrary orthogonal coordinate system.₁, X₂, X_ThreeThe component in the direction of.
[0030]
[Expression 1]

[0031]
The direction in which the piezoelectric constant is maximum is the electric field E applied to PZT.^*Component ε in the direction parallel to_//And the electric field strength E [(ε_//) / E] is the maximum direction. Coordinate axis X_ThreeIf an electric field of strength E is applied in a direction parallel to the electric field, the distortion component in the direction parallel to the electric field is ε_ThreeTherefore, the ratio of the strain component in the electric field application direction to the electric field strength (that is, the magnitude of the piezoelectric constant in the electric field application direction) is d.₃₃It is.
[0032]
Here, the electric field E in any direction^*And coordinate axis X_Three'Is the electric field E^*The original orthogonal coordinate axis [coordinate system] (X₁, X₂, X_Three) And the new Cartesian coordinate axis [coordinate system] (X₁', X₂', X_Three´), in the new coordinate system, the strain ε^*, Piezoelectric constant {dij} and electric field E^*This relationship is expressed by the following equation (2) in the new coordinate system.
[0033]
[Expression 2]

[0034]
Here, the dash (') indicates that it is a component in a new coordinate system. From this equation (2), in this coordinate system, the electric field E^*The ratio of the distortion component and the electric field strength in the application direction of (ie, the magnitude of the piezoelectric constant) is the diagonal component d of the piezoelectric constant in the new coordinate system.₃₃It turns out that it is'. Therefore, in order to obtain the direction in which the piezoelectric constant becomes maximum, the diagonal component d of the piezoelectric constant when the coordinate system is rotated is used.₃₃Considering the coordinate transformation of the maximum diagonal component d₃₃What is necessary is to obtain '.
[0035]
The piezoelectric constant d = {dij ′} in the new coordinate system is obtained by linearly transforming the piezoelectric constant d = {dij} in the original coordinate system using the transformation matrices A = {Aij} and N = {Nij}. That is, the conversion equation is expressed by the following equation (3). Here, the superscript “t” means a transposed matrix.
[0036]
[Equation 3]

[0037]
The transformation matrices A = {Aij} and N = {Nij} are defined by the following matrices (4) and (5). Where {e₁, E₂, E_Three} Is the original coordinate system (X₁, X₂, X_Three) Basis vectors in {₁', E₂', E_Three'} Is the new coordinate system (X₁, X₂, X_Three), For example, e₁・ E₂'Represents the direction cosine of the angle formed by the coordinate axis X1 and the coordinate axis X2'. The symbol aij used in the matrix (5) represents the stiffness constant.
[0038]
[Expression 4]

[0039]
[Equation 5]

[0040]
Performing this calculation, the piezoelectric constant d in any direction₃₃In order to specifically obtain ', the value of the matrix component dij of the piezoelectric constant d is required. Table 1 shows rhombohedral PZT60 / 40 [that is, Pb (Zr₀.₆Ti₀._Four)] Piezoelectric constant d₃₃, D_{twenty two}, D₃₁, D₁₅(The other matrix components of the piezoelectric constant are assumed to be 0). Table 2 shows tetragonal PZT40 / 60 [that is, Pb (Zr₀._FourTi₀.₆) O_ThreeThe piezoelectric constant d of₃₃, D₃₁, D₁₅(The other matrix components of the piezoelectric constant are assumed to be 0). Tables 1 and 2 are calculated using data published in M.J.Haun, E.Furman, S.J.Jang and L.E.Cross: Ferroelectrics, 99 (1989) 63.
[0041]
[Table 1]

[0042]
[Table 2]

[0043]
When the coordinate system is rotated in 3D space, the new rotated coordinate system (X₁', X₂', X3'), the diagonal component d of the piezoelectric constant d₃₃'(Hereinafter, a dash symbol for distinguishing between the coordinate system before conversion and the coordinate system after conversion is omitted) is calculated from the above equation (3) and Table 1 or Table 2.
[0044]
  The results for rhombohedral PZT 60/40 are shown in FIGS. 6 (a) and 6 (b). FIG. 6A is a three-dimensional representation of the crystal orientation dependence of the piezoelectric constant d33, and FIG. 6B is a cross section of the three-dimensional representation of FIG. 6A cut along the YZ plane. The Z axis is the [111] direction, which is the direction of spontaneous polarization, the X axis is the direction perpendicular to the mirror surface of the PZT, the Y axis is the direction perpendicular to the Z axis and the X axis, The distance between one point represents the value of the piezoelectric constant d33 in the corresponding direction. The conventional piezoelectric constant d33 in the [111] direction (Z-axis in FIG. 6) corresponds to the intersection of the three-dimensional display and Z-axis in FIG. On the other hand, according to FIG. 6B, the piezoelectric constant d33 is the maximum value [= 189 × 10 −12 C / N] in the direction inclined 56.7 ° from the Z axis. Strictly speaking, the direction in which the piezoelectric constant d33 is maximum is that of rhombohedral PZT.Based on cubic crystal axis directionIt is shifted by 2 ° from the [100] direction, [010] direction, and [001] direction.Based on cubic crystal axis directionThere is no problem in considering [100] orientation, [010] orientation, and [001] orientation.
[0045]
The results obtained for tetragonal PZT 40/60 are shown in FIG. FIG. 7A shows the piezoelectric constant d of tetragonal PZT40 / 60.₃₃FIG. 7B shows a cross section obtained by cutting the three-dimensional display of FIG. 7A along the (010) plane. In tetragonal PZT, the piezoelectric constant d in the [001] direction tilted 51.3 ° from the Z-axis.₃₃Is the maximum value [= 162 × 10^-12C / N], which is slightly smaller than the maximum value in the case of rhombohedral crystals, but is still a piezoelectric constant d in the [111] direction.₃₃It is a bigger value.
[0046]
Therefore, in order to obtain PZT having a large piezoelectric constant, PZT of a perovskite structure having a rhombohedral composition ratio can be obtained by changing the [100] direction, [010] direction, or [010] direction (in the equivalent direction of the cubic perovskite structure) If the orientation is such that the 001] direction is substantially perpendicular to the electrode surface, a piezoelectric element having a piezoelectric constant nearly three times that of the conventional one can be obtained. By applying this piezoelectric element to various sensors, the characteristics can be greatly increased. Can be improved. Further, if PZT having a perovskite structure having a tetragonal composition ratio is oriented so that the [001] direction (in the equivalent direction of the cubic perovskite structure) is substantially perpendicular to the electrode surface, the PZT is more than twice the conventional one. A piezoelectric element having a piezoelectric constant of is obtained. By applying this piezoelectric element to various sensors, the characteristics can be greatly improved. Therefore, it is possible to realize a piezoelectric actuator, a strain sensor with high sensitivity, and the like that can take a large force that has not been available conventionally, and because it can take a large strain, it can be applied to a micro sensor or actuator using a micromachine.
[0047]
  (Piezoelectric element manufacturing method)
  Next, a method for manufacturing a piezoelectric element using the PZT thin film as described above will be described with reference to FIGS. First, the case where the piezoelectric element 1 using the PZT thin film 2 having a rhombohedral crystal composition is manufactured will be described. As shown in FIG. 8A, a single crystal substrate such as a Si substrate (an oxide film such as SiO2 may be formed on the surface of the single crystal substrate) 6 is used as an intermediate metal layer. A film 7 is formed. Here, by using a (100) substrate, a (010) substrate or a (001) substrate as the single crystal substrate 6,[100]Ti film 7 is epitaxially grown so that the direction, [010] direction or [001] direction is perpendicular to the surface of single crystal substrate 6.
[0048]
Next, as shown in FIG. 8B, a Pt film 8 is formed on the Ti film 7 as a base metal layer. At this time, since the Ti film 7 is crystal-oriented so that the [100] direction, the [010] direction, or the [001] direction is directed to the film thickness direction, the Pt film 8 epitaxially grown thereon is also [100]. ], [010] direction or [001] direction is oriented in the film thickness direction. Thus, the lower surface side electrode 3 a is formed by the Ti film 7 and the Pt film 8 formed on the single crystal substrate 6. Further, the Pt film 8 is not directly formed on the single crystal substrate 6 but the Ti film 7 is formed in the middle. This is because the adhesion between the Pt film 8 and the single crystal substrate 6 is improved and the electrode 3a is peeled off. It is for preventing.
[0049]
Further, on the Pt film 8, as shown in FIG. 8C, the PZT thin film 2 is formed while controlling the component composition of Zr and Ti so as to have a rhombohedral composition.
[0050]
At this time, the PZT thin film 2 in the piezoelectric element is added with a trace amount of at least one of additives such as Ba, Sr, La, Bi, Mg, W, Nb, Zn, etc., and the characteristic variation due to the temperature of PZT. Can be suppressed, and the temperature characteristics of the piezoelectric element 1 can be stabilized. The thickness of the PZT thin film 2 is preferably 2 μm or less. This is because if the film thickness is 2 μm or less, it can also be used for minute sensors and actuators manufactured by micromachining technology.
[0051]
Since the unfired PZT thin film 2 having a rhombohedral composition formed on the Pt film 8 has an amorphous structure, the PZT thin film 2 is crystallized by sintering (annealing). At this time, a PZT film 2 having a crystal structure having a piezoelectric property called a perovskite structure is obtained by a sintering method. The PZT thin film 2 having the perovskite structure is subjected to crystal distortion determined by the composition ratio of Zr and Ti. That is, when the composition ratio of Zr and Ti is rhombohedral, a PZT thin film 2 having a perovskite structure distorted to rhombohedral is obtained.
[0052]
Moreover, during this sintering, the crystal orientation of the PZT thin film 2 is governed by the lattice of the Pt film 8 that is the base metal layer, so that the [100] direction, [010] direction, or [001] according to the crystal orientation of the Pt film 8 Crystal orientation is performed so that the direction is substantially perpendicular to the electrode 3a.
[0053]
Therefore, in forming the PZT thin film 2, the crystal orientation of the base metal layer that governs the crystal orientation of the PZT thin film 2 is set to the [100] direction, the [010] direction, or the [001] direction, and the base metal It is important to control the composition ratio so that the composition of the PZT thin film 2 formed on the layer is rhombohedral.
[0054]
After obtaining the rhombohedral PZT thin film 2 in this manner, as shown in FIG. 8D, the upper electrode 3b is formed on the PZT thin film 2 by a Pt film or the like, and the manufacture of the piezoelectric element 1 is completed.
[0055]
Here, the case of a PZT thin film having a rhombohedral composition has been described. However, when a PZT thin film having a tetragonal composition is required, a Ti film as an intermediate metal layer and a Pt film as a base metal layer [ The 001] direction may be oriented in a direction perpendicular to the film thickness direction, and the unfired PZT thin film formed on the Pt film may be controlled to have a tetragonal composition.
[0056]
In the above method for manufacturing a piezoelectric element, since it is only necessary to change the process conditions in the manufacturing process of the conventional piezoelectric element, the conventional process can be used as it is, no new equipment is required, and the cost for changing the manufacturing process is increased. Absent. Therefore, even when a piezoelectric actuator, a strain sensor, or the like is manufactured, a product with good cost performance can be manufactured.
[0057]
In the above manufacturing method, the method of crystal orientation of PZT by sintering has been described. However, the piezoelectric element of the present invention can be manufactured by other manufacturing methods. For example, after producing a PZT bulk crystal having a rhombohedral crystal composition [or tetragonal composition] having a perovskite structure, the bulk crystal is converted into a (100) plane, a (010) plane or a (001) plane [or a tetragonal crystal. In the case of a composition, it may be cut out at (001) plane, and an electrode may be formed on the cut out surface. Alternatively, the PZT thin film may be epitaxially grown on the base crystal or the base metal layer.
[0058]
(Application examples)
Below, the apparatus which applied the said piezoelectric element is demonstrated. In this example, a rhombohedral PZT with the [100] direction oriented perpendicular to the electrode surface is used as an example, but the [010] direction and the [001] direction oriented to the direction perpendicular to the electrode surface. It may be a tetragonal PZT or a tetragonal PZT with the [001] direction oriented in a direction perpendicular to the electrode surface.
[0059]
(Vibration sensor)
FIG. 9 is a perspective view showing a vibration sensor 11 using the piezoelectric element according to the present invention. This is formed by processing a silicon substrate (wafer), and the weight portion 12 is supported by the frame 14 in a cantilever manner by the beam 13. The piezoelectric element 1 is integrally provided on the upper surface of the region extending from the beam 13 to the weight portion 12.
[0060]
Therefore, when vibration or acceleration is applied to the vibration sensor 11, the weight portion 12 vibrates or displaces up and down, so that the beam 13 is elastically bent. When the beam 13 is elastically bent, the piezoelectric element 1 is also mechanically bent accordingly, and an electric charge is generated between the electrodes 3a and 3b of the piezoelectric element 1. Therefore, by measuring the voltage due to the generated charges, the degree of bending of the beam 13, and hence vibration and acceleration can be measured. Here, when the piezoelectric element 1 of the present invention is used, a large voltage can be generated even with the same vibration and acceleration, and the detection sensitivity can be improved.
[0061]
The manufacturing process of this vibration sensor 11 is shown in FIGS. First, a Si substrate (wafer) 15 is prepared [FIG. 10A], and both front and back surfaces of the Si substrate 15 are oxidized by thermal oxidation to form an oxide film (SiO 2).₂) 16 is formed [FIG. 10 (b)]. Next, on the lower surface of the Si substrate 15, the oxide film 16 is etched with hydrofluoric acid to partially expose the Si substrate region that becomes the weight portion 12 and the beam 13 (FIG. 10C), and the oxide film 16 is etched. The Si substrate 15 is etched as a mask, and the thickness of the Si substrate 15 is reduced in the regions to be the weight portion 12 and the beam 13 (FIG. 10D).
[0062]
Next, in the thin region 17 where the thickness of the Si substrate 15 is reduced, a Ti film (intermediate metal layer) 7 is formed on the oxide film 16 (FIG. 10E), and a Pt film ( After forming the lower metal layer 8) [FIG. 10 (f)] and forming the lower electrode 3a, the rhombohedral PZT thin film 2 is formed on the Pt film 8 [FIG. 10 (g). ]. Thereafter, the PZT thin film 2 is sintered (annealed) so that the [100] direction of the PZT thin film 2 is oriented in the direction perpendicular to the surface of the electrode 3a [FIG. 10 (h)]. Next, the upper electrode 3b is formed on the PZT thin film 2 by a Pt film or the like to form the high-performance piezoelectric element 1 on the Si substrate 15 [FIG. 10 (i)]. Thereafter, the Si substrate 15 and the oxide film 16 are etched to form an opening 18 that separates the portion that becomes the frame 14 of the Si substrate 15 from the portion that becomes the weight portion 12 and the beam 13 to complete the vibration sensor 11 [FIG. (J)].
[0063]
(Laminated piezoelectric actuator)
FIG. 11 is a side view showing a laminated piezoelectric actuator 21 using the piezoelectric element according to the present invention. This multilayer piezoelectric actuator is obtained by alternately laminating PZT thin films 2 and electrodes 3, and the PZT thin films 2 are arranged so that the [100] direction of the rhombohedral PZT thin film 2 is perpendicular to the electrodes 3. Are crystallographically oriented. Further, the direction of the spontaneous polarization P of each PZT thin film 2 is inclined from the direction perpendicular to the electrode 3, but the polarization direction of the PZT thin film 2 is alternately reversed along the stacking direction. The electrode 3 is connected to the + side terminal 22 and the − side terminal 23 every other layer.
[0064]
According to such a piezoelectric actuator 21, the amount of expansion / contraction when a voltage is applied is the sum of the amount of expansion / contraction of each PZT thin film 2, and the amount of expansion / contraction of each PZT thin film 2 is larger than that of the conventional example. A quantity or driving force can be obtained.
[0065]
(Optical scanner)
FIG. 12 is a perspective view showing an optical scanner 24 using the piezoelectric element according to the present invention. This optical scanner 24 is obtained by attaching an elastic plate 25 to the tip (drive end) of a multilayer piezoelectric actuator 21 having a structure as shown in FIG. The elastic plate 25 is formed by processing a Si substrate, and is provided with a mirror part 28 having an asymmetric shape at the tip of a torsion bar 27 extended from the drive part 26. Is fixed to the piezoelectric actuator 21.
[0066]
Thus, when an AC voltage is applied to the piezoelectric actuator 21, the piezoelectric actuator 21 expands and contracts and vibrates the drive unit 26 of the elastic plate 25. When the drive unit 26 minutely vibrates, the mirror unit 28 is asymmetric and its center of gravity is decentered from the axis of the torsion bar 27, so that the mirror unit 28 rotates at a constant cycle by twisting the torsion bar 27. . Therefore, when the laser beam emitted from the light source is irradiated onto the mirror unit 28, the light reflected by the mirror unit 28 is scanned back and forth.
[0067]
In such an optical scanner 24, if the piezoelectric actuator 21 according to the present invention is used, the elastic plate 25 can be vibrated with a large amplitude, so that the light scanning width can be increased.
[0068]
(Strain sensor)
FIG. 13A is a cross-sectional view showing a strain sensor 31 using a piezoelectric element according to the present invention. The strain sensor 31 is obtained by mounting a piezoelectric element 1 having electrodes 3a and 3b formed on both surfaces of a PZT thin film 2 on a strain detection object 32, and detecting a voltage between the electrodes 3a and 3b by a charge amplifier or the like. The detector 33 can detect it.
[0069]
Thus, as shown in FIG. 13B, when the strain detection target object 32 is deformed and distorted, the piezoelectric element 1 is distorted together with the strain detection target object 32, and the amount of strain between the electrodes 3a and 3b depends on the strain amount. Since charges are generated, this amount of charges is measured by the detector 33 as a voltage between the electrodes 3a and 3b. By using the piezoelectric element of the present invention for such a strain sensor 31, a highly sensitive strain sensor can be manufactured.
[0070]
(Piezoelectric vibratory gyro)
FIG. 14 is a perspective view showing a piezoelectric vibration gyro 34 using the piezoelectric element according to the present invention. The vibrating gyroscope 34 is obtained by attaching a piezoelectric element 1a for oscillation drive to a tuning fork 35 made of an Elinvar alloy or the like having a small thermal expansion, and attaching a piezoelectric vibrator 1b for detection on a surface perpendicular thereto. The piezoelectric element of the present invention can also be used as both the piezoelectric elements 1a and 1b in the vibrating gyroscope 34.
[Brief description of the drawings]
FIG. 1 is a phase diagram of PZT in two components of Zr and Ti in the composition of PZT.
FIG. 2 is a schematic sectional view showing the piezoelectric element according to the first embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a piezoelectric element according to a second embodiment of the present invention.
FIG. 4 is a diagram showing a crystal structure of PZT having a rhombohedral perovskite structure.
FIG. 5 is a diagram showing a crystal structure of PZT having a tetragonal perovskite structure.
6A is a piezoelectric constant d of rhombohedral PZT60 / 40. FIG.₃₃(B) is a cross section obtained by cutting the three-dimensional display of (a) along the YZ plane.
7A is a piezoelectric constant d of tetragonal PZT40 / 60. FIG.₃₃(B) is a cross section obtained by cutting the three-dimensional display of (a) along the (010) plane.
FIGS. 8A, 8B, 8C, and 8D are cross-sectional views showing the manufacturing process of the piezoelectric element according to the present invention. FIGS.
FIG. 9 is a perspective view showing a vibration sensor using a piezoelectric element according to the present invention.
FIGS. 10A to 10J are cross-sectional views showing a manufacturing process of the vibration sensor of the above.
FIG. 11 is a side view showing a laminated piezoelectric actuator using the piezoelectric element according to the present invention.
FIG. 12 is a perspective view showing an optical scanner using the piezoelectric element according to the present invention.
13A is a cross-sectional view showing a strain sensor using a piezoelectric element according to the present invention, and FIG. 13B is a cross-sectional view showing a state in which strain is applied to the strain sensor.
FIG. 14 is a perspective view showing a piezoelectric vibration gyro using the piezoelectric element according to the present invention.
[Explanation of symbols]
1 Piezoelectric element
2 PZT with rhombohedral crystal composition
3a, 3b electrode
4 Piezoelectric elements
5 PZT with tetragonal composition

Claims (8)

A piezoelectric element comprising a PZT and an electrode,
The electrode has a (100) plane, a (010) plane, or a (001) plane orientation,
The PZT is a perovskite structure having a composition ratio in which Zr and Ti contained therein are rhombohedral at room temperature, and the [100] direction, [010] direction or A piezoelectric element characterized in that the crystal orientation is such that the [001] direction is substantially perpendicular to the electrode surface.   2. The piezoelectric element according to claim 1, wherein at least one of Ba, Sr, La, Bi, Mg, W, Nb, and Zn is added to the PZT. An intermediate metal layer having a (100) plane, (010) plane or (001) plane orientation is formed on the surface of the single crystal substrate, and then using a metal different from the intermediate metal layer, the intermediate metal layer A base metal layer having a (100), (010) plane, or (001) plane orientation is formed on the surface not in contact with the single crystal substrate, and then is not in contact with the intermediate metal layer of the base metal layer After forming a rhombohedral composition PZT film on the surface on the side, the PZT film is sintered to obtain a [100] direction, a [010] direction or a [001] direction based on the cubic crystal axis direction. A method for manufacturing a piezoelectric element, characterized by crystal orientation so that the direction is substantially perpendicular to the surface of the underlying metal layer. A vibration sensor using the piezoelectric element according to claim 1. A piezoelectric actuator using the piezoelectric element according to claim 1. An optical scanner using the piezoelectric element according to claim 1. A strain sensor using the piezoelectric element according to claim 1. A piezoelectric vibration gyro using the piezoelectric element according to claim 1.

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