JP2005011913A

JP2005011913A - Ceramic multilayered electromechanical transducing element and its manufacturing method

Info

Publication number: JP2005011913A
Application number: JP2003172834A
Authority: JP
Inventors: Sadayuki Takahashi; 貞行高橋
Original assignee: Shoei Chemical Inc
Current assignee: Shoei Chemical Inc
Priority date: 2003-06-18
Filing date: 2003-06-18
Publication date: 2005-01-13

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic multilayered electromechanical transducing element which can be industrially easily manufactured and can be prevented from cracking when an electric field is applied. <P>SOLUTION: The ceramic multilayered electromechanical transducing element 1 comprises a plurality of ceramic layers 2 which are displaced by application of an electric field, a plurality of internal electrode layers 3 which are stacked alternately with the ceramic layers 2 and form a laminate 4 together with the ceramic layers 2, and grooves 10 for reducing stress. Each of the internal electrode layers 3 has a partial electrode 7 and a non-electrode portion 8. External electrodes 9 for applying a prescribed electric field to each ceramic layer 2 are connected to every other partial electrode 7. The grooves 10 are formed in side edges 4a and 4b along the lamination direction of the laminate 4. A length L1 in the lamination direction of an absence-of-groove region where no groove 10 is formed in the side edges 4a and 4b is set shorter than a minimum breaking length at which cracking occurs in the absence-of-groove region when a prescribed electric field is applied from the external electrodes 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、セラミック積層型電気機械変換素子とその製造方法に関する。
【０００２】
【従来の技術】
セラミック積層型電気機械変換素子は、一般に、複数のセラミックス層と複数の内部電極層とが交互に重ねられて一体に焼結された積層体と、１対の外部電極と、を備え、各内部電極層は、内部電極としての部分電極を有する。外部電極は、積層体の２つの側面上にそれぞれ配置され、部分電極に一層おきに電気的に接続される。
【０００３】
各部分電極は、電極面積が素子（積層体）の断面積よりも小さく、その縁端面は、２つの外部電極が配置された積層体の２つの側面の少なくとも一方で露出している。各部分電極は、自身の縁端面が露出する積層体の側面においてこの側面上に配置された外部電極とは電気的に接続するが、縁端面が露出しない積層体の側面上に配置された外部電極とは電気的に接続していない。
【０００４】
セラミックス層は、圧電又は電歪セラミックスを主成分とし、外部電極間に電圧が印加されることにより機械的に変位する。各内部電極層の部分電極が設けられていない領域（以下、無電極部という）の存在により、１対の隣り合う内部電極層間のセラミックス層には、当該２つの内部電極層の部分電極に挟まれた部分と挟まれない部分とが存在する。外部電極間に電圧が印加されたとき、上記２つの部分のうち部分電極に挟まれた部分は変位するが、部分電極に挟まれない部分は変位せず、両者の境界付近に応力が発生する。そして、発生する最大応力がセラミックス層の破壊強度を超えてしまうと、き裂が発生して破損を生じる恐れがある。また、き裂は、耐湿特性を著しく劣化させる原因となる。このため、高湿度雰囲気中で素子に電界を印加して駆動すると、き裂を通して内部電極を形成する金属がマイグレーションを起こし、絶縁性が要求される部位において部分電極と外部電極とが電気的に導通してしまう恐れがある。
【０００５】
このような不都合を回避することを目的とした構造として、素子の積層方向と平行な側面上に、幅０．１ｍｍ、深さ０．１ｍｍの溝を、素子の周囲全体に２ｍｍの間隔で形成したものがある（例えば、特許文献１参照）。
【０００６】
【特許文献１】
特公平６−５７９４号公報
【０００７】
【発明が解決しようとする課題】
しかし、特許文献１の構造では、素子（積層体）の長さに対して形成する溝の数が多い。例えば、素子の長さが３０ｍｍの場合には、１４本の溝を形成しなければならず、製造上の負担となり、工数及びコストの増大を招く。また、溝を素子の周囲全体に形成することも、製造上の負担となり、工数及びコストの増大を招く。
【０００８】
そこで、本発明は、工業的に生産が容易で、電界印加時のき裂の発生を防止することが可能なセラミック積層型電気機械変換素子とその製造方法の提供を目的とする。
【０００９】
【課題を解決するための手段】
上記目的を達成するため、本発明に係るセラミック積層型電気機械変換素子は、積層体と１対の外部電極とを備えている。積層体は、電界の印加により変位する材質よりなる複数のセラミックス層と、複数の内部電極層と、が交互に重ねられ、両者が一体に焼結されたものである。１対の外部電極は、積層体の側面に配置されている。各内部電極層は、部分電極と無電極部とからなり、部分電極は、１対の外部電極と一層おきに交互に電気的に接続されている。
【００１０】
積層体の積層方向に沿った側部には、応力を緩和する溝が形成されている。この溝は、積層体の側部のうち溝を含まない溝不存在領域の積層方向に連続する最大長さを、セラミックス層に所定の電界が印加されたときに溝不存在領域においてき裂が発生する最小破壊長さよりも小さく抑えている。セラミックス層は、いわゆる圧電セラミックスや電歪セラミックスを主成分とする。
【００１１】
上記構成では、外部電極に電圧が印加されたとき、セラミックス層のうち積層方向で隣り合って対となる２つの部分電極に挟まれた部分は変位するが、この２つの部分電極に挟まれない部分は変位しない。このため、両者の境界（隣り合う２つの部分電極に挟まれる部分と挟まれない部分との境界）に応力が発生する。発生する応力の大きさは、積層体の積層方向の両端から中央部に向かって増大し、所定位置で最大応力となる。この最大応力は、積層体の側部において応力を緩和する溝を含まない領域（以下、溝不存在領域と称する）の積層方向の長さの増減に応じて増減する。
【００１２】
これに対し、本発明では、セラミックス層に所定の電界が印加されたときにき裂が発生する溝不存在領域の積層方向の最小の長さ（以下、最小破壊長さと称する）を実験的に又は計算によって予め求め、各溝不存在領域の積層方向の長さがこの最小破壊長さよりも小さくなるように、応力を緩和するための溝を配置している。
【００１３】
この最小破壊長さは、印加する電界の強さ、セラミックス層の材質や寸法形状、部分電極の寸法形状等の諸条件によって決定される。従って、溝不存在領域の積層方向の長さが最小破壊長さよりも小さくなるように溝を配置することによって、き裂の発生及び成長を確実に防止することができる。
【００１４】
また、溝の数は、溝不存在領域の積層方向の長さを最小破壊長さよりも小さくする最少数で済み、多数の溝を形成する必要がない。従って、製造上の負担が少なくて済み、工業的に生産が容易である。
【００１５】
溝不存在領域においてセラミックス層に所定の電界が印加されたときに発生する応力がセラミックス層の破壊強度を超えて最大となる部分（最大応力発生部）の近傍に、応力を緩和する溝を配置しても良い。
【００１６】
これにより、溝不存在領域に発生する最大応力を、セラミックス層の破壊強度よりも小さくなるように効果的に低減させることができ、き裂の発生をより確実に抑えることができる。
【００１７】
応力を緩和する溝を、積層体の積層方向の全体の長さをほぼ等分割する位置に配置しても良い。
【００１８】
発生する最大応力の大きさが溝不存在領域の積層方向の長さによって一律に決定される場合、各溝不存在領域の積層方向の長さがほぼ等しくなるように溝を配置することによって、各溝不存在領域における最大応力がセラミックス層の破壊強度を超えないように、発生する応力を効率的に分散させることができる。従って、積層体の全域において、最大応力を効率良く低減させて、き裂の発生を抑えることができる。
【００１９】
溝を、積層体の積層方向に沿った側面から積層方向と略直交する方向へ延びるように、セラミックス層に形成しても良い。
【００２０】
上記構成では、外部電極が溝内へ侵入している場合であっても、溝が内部電極層と異なった別の平面内のセラミックス層内に存在するため、絶縁性が要求される部分における外部電極と部分電極との導通を確実に防止することができる。
【００２１】
溝が形成されたセラミックス層の厚さを、他のセラミックス層の厚さよりも大きく形成しても良い。
【００２２】
上記構成では、溝を有さないセラミックス層の厚さを小さく設定して、印加する電圧の大きさを小さく抑えつつ素子の変位量を増大させることができると共に、溝を形成するセラミックス層の厚さを大きく設定して、溝の加工作業を容易に行うことができ、工業的生産が一段と容易となる。
【００２３】
溝の先端を、湾曲面状としても良い。
【００２４】
例えば、溝の先端が角部を有する場合には、この角部をきっかけとしてき裂が発生し成長する可能性がある。これに対し、溝の先端を湾曲面状とすれば、き裂の発生のきっかけとなる角部が存在しないので、き裂の発生をより確実に防止することができる。
【００２５】
積層方向と略直交し且つ溝を含む断面において、セラミックス層のほぼ全ての領域が、セラミックス層と隣り合って対となる部分電極によって挟まれるように、溝を形成しても良い。
【００２６】
上記構成では、積層方向と略直交し且つ溝を含むセラミックス層の断面において、そのほぼ全ての領域が電界の印加によってほぼ均一に変位するので、積層体に発生する応力が良好に緩和され、最大応力の低減をより確実に図ることができる。
【００２７】
積層体を、略角柱状とし、内部電極層を、セラミックス層を挟んで交互に重ねられた第１内部電極層と第２内部電極層とから構成しても良い。第１内部電極層と第２内部電極層とを、矩形板形状のうち一つの角部が切除された部分電極と、前記切除された角部に配置された無電極部と、を備えた略矩形板形状としても良い。第１内部電極層の無電極部と第２内部電極層の無電極部とを、積層体の相対向する２つの側辺部にそれぞれ配置し、溝を、２つの側辺部にそれぞれ形成しても良い。
【００２８】
また、第１内部電極層と第２内部電極層とを、矩形板形状の一辺に切り欠き部を有する部分電極と、切り欠き部に配置された無電極部と、を備えた略矩形板形状としても良い。第１内部電極層の無電極部と第２内部電極層の無電極部とを、積層体の相対向する２つの側面にそれぞれ面して配置し、溝を、２つの側面にそれぞれ形成しても良い。
【００２９】
また、第１内部電極層と第２内部電極層とを、矩形板形状の三辺に連続する切り欠き部を有する部分電極と、切り欠き部に配置された無電極部と、を備えた略矩形板形状としても良い。第１内部電極層の部分電極と第２内部電極層の部分電極とを、積層体の相対向する２つの側面にそれぞれ面して配置し、溝を、積層体の４つの側面に亘って環状に形成しても良い。
【００３０】
本発明に係るセラミック積層型電気機械変換素子は、セラミック粉末と有機バインダとを含むグリーンシートの表面に、内部電極層を形成する金属ペーストを塗布し、このグリーンシートを積層し、積層されたグリーンシートの集合体を焼結して積層体を生成し、焼結後の積層体に溝を形成することにより製造しても良い。
【００３１】
また、セラミック粉末と有機バインダとを含むグリーンシートの表面に、内部電極層を形成する金属ペーストを塗布し、このグリーンシートを積層し、積層されたグリーンシートの集合体に溝を形成し、溝を有する集合体を焼結して積層体を生成することにより製造しても良い。
【００３２】
このように焼結前のグリーンシートの集合体に対して溝を形成する方法は、溝を形成する作業を容易に行うことができる点と、溝を形成する際に生じた残留歪みが焼結時に解消するという点で優れている。
【００３３】
【発明の実施の形態】
本発明の一実施形態を、図面に基づいて説明する。
【００３４】
図１は本発明に係るセラミック積層型電気機械変換素子の一実施形態を示す斜視図、図２は図１の積層体の一部のセラミックス層を透視した斜視図、図３は図１のＩＩＩ−ＩＩＩ矢視断面図、図４は図１のＶＩ−ＶＩ矢視断面図、図５は図１のＶ−Ｖ矢視断面図図である。
【００３５】
図１〜図５に示すように、セラミック積層型電気機械変換素子１は、電界の印加により変位する複数のセラミックス層２と、複数の内部電極層３と、一対の外部電極９と、応力を緩和するための溝１０と、を備えている。セラミックス層２と内部電極層３とは、交互に重ねられて一体化され、積層体４を形成する。内部電極層３は一層おきに２つの外部電極９にそれぞれ接続され、外部電極９からの電圧印加によって各セラミックス層２に所定の電界が印加される。セラミックス層２及び内部電極層３は共に矩形板形状であり、積層体４は角柱状である。各セラミックス層２は、ほぼ同じ厚さを有している。なお、積層体４の形状は、角柱状に限定されず、例えば円柱状や中空円筒状等、様々な形状に設定することができる。
【００３６】
内部電極層３は、第１内部電極層５と第２内部電極層６とに分けられる。セラミックス層２と内部電極層３とは、セラミックス層２、第１内部電極層５、セラミックス層２、第２内部電極層６、セラミックス層２…の順に積層されている。すなわち、第１内部電極層５と第２内部電極層６とは、セラミックス層２を挟んで交互に重ねられている。
【００３７】
各内部電極層３（５，６）は、部分電極７と無電極部８とを有し、無電極部８では、隣接するセラミックス層２同士が一体化している。各部分電極７は、矩形板形状のうち一つの角部が切除された形状であり、この切除された角部が無電極部８を構成する。第１内部電極層５の無電極部８と第２内部電極層６の無電極部８とは、積層体４の相対向する２つの側辺部４ａ，４ｂにそれぞれ配置されている。すなわち、第１内部電極層５の無電極部８と第２内部電極層６の無電極部８とは、積層方向と略平行な２つの積層軸（側辺部４ａ近傍の第１積層軸及び側辺部４ｂ近傍の第２積層軸）上にそれぞれ配置されている。２つの外部電極９は、この側辺部４ａ，４ｂ上にそれぞれ配置され、固定されている。これにより、一方の外部電極９は、第１内部電極層５の部分電極７に電気的に接続され、第２内部電極層６の部分電極７とは絶縁状態に維持される。また、他方の外部電極９は、第２内部電極層６の部分電極７に電気的に接続され、第１内部電極層５の部分電極７とは絶縁状態に維持される。
【００３８】
溝１０は、積層体４の側辺部（側部）４ａ，４ｂのセラミックス層２にそれぞれ形成されている。溝１０の先端１０ａは、湾曲面状に形成されている。溝１０の幅（積層方向の高さ）は、数１０μｍ程度である。外部電極９には、焼き付け金属ペーストが使用され、溝１０の部分において、外部電極９はブリッジを形成し、分断されることない。また、仮に外部電極９が溝１０の内部まで侵入したとしても、溝１０は部分電極７と異なった平面内に存在するため、絶縁性が要求される部分における外部電極９と部分電極７との導通（例えば、図３において、外部電極９とその下方の第２内部電極層６の部分電極７との導通）を確実に防止することができる。
【００３９】
溝１０は、積層方向と略直交し且つ溝１０を含む断面において、セラミックス層２のほぼ全ての領域が、セラミックス層２と隣り合って対となる部分電極７によって挟まれるような寸法形状を有している。換言すると、積層方向から視た状態で、部分電極７の無電極部８の端縁が溝１０の先端とほぼ完全に重なるか又は溝１０の先端１０ａが無電極部８の端縁８ａよりも僅かに内側に配置される（図５参照）ように、無電極部８及び溝１０が設定されている。
【００４０】
溝１０を有するセラミックス層２の厚さは、溝１０を有さない他のセラミックス層２の厚さよりも大きく形成されている。
【００４１】
セラミックス層２は、いわゆる圧電セラミックス又は電歪セラミックスからなる。圧電セラミックス及び電歪セラミックスは、共に電界（電圧）を印加すると歪む（変位する）という特性を有する。圧電セラミックスの代表的な材料としては、Ｐｂ（Ｚｒ，Ｔｉ）Ｏ_３やＢａＴｉＯ_３などがある。電歪セラミックスの代表的な材料としては、Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３ −ＰｂＴｉＯ_３やＰｂ（Ｎｉ_１／３Ｎｂ_２／３）Ｏ_３ −ＰｂＴｉＯ_３や（Ｐｂ，Ｌａ）（Ｚｒ，Ｔｉ）Ｏ_３などがある。なお、圧電セラミックスの場合、分極の向きを一方向に揃えるためのいわゆる分極処理を施す必要がある。また、Ｐｂ（Ｚｒ，Ｔｉ）Ｏ_３はＰＺＴと、ＢａＴｉＯ_３はＢＴと、Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３ −ＰｂＴｉＯ_３はＰＭＮ−ＰＴと、Ｐｂ（Ｎｉ_１／３Ｎｂ_２／３）Ｏ_３ −ＰｂＴｉＯ_３はＰＮＮ−ＰＴと、（Ｐｂ，Ｌａ）（Ｚｒ，Ｔｉ）Ｏ_３はＰＬＺＴと、それぞれ略称される。
【００４２】
溝１０を有さないセラミックス層２では、隣り合った対の部分電極７に挟まれる部分は電界の印加によって積層方向へ変位（伸張）するが、部分電極７に挟まれない部分は変位せず、この両者の境界付近に応力が発生する。溝１０を有するセラミックス層２では、そのほぼ全域が隣り合った対の部分電極７に挟まれる。このため、電界の印加により層全域に亘って均一に変位が生じ、積層方向への歪み（変位）が拘束されることがないので、積層方向への応力は基本的に発生せず、また発生したとしてもその大きさは極めて小さい。
【００４３】
電界の印加に起因して積層体４に発生する積層方向の応力の大きさは、積層体４の積層方向の両端から中央部に向かって増大し、所定位置で最大応力となる。この最大応力は、積層体４の側辺部４ａ，４ｂのうち溝１０を含まない領域（以下、溝不存在領域と称する）の積層方向の長さの増減に応じて増減する。
【００４４】
また、本実施形態のように、溝１０を有さないセラミックス層２の形状及び配置方向が積層方向において一様であり、無電極部８が積層方向に沿って交互に配置され、各セラミックス層２がほぼ同じ厚さを有している場合、溝不存在領域における最大応力は、溝不存在領域の積層方向のほぼ中央部分で生じ、その最大応力の大きさは、溝不存在領域の積層方向の長さＬ１の増減に応じて増減する。そして、電界を印加した際に、溝不存在領域の積層方向の長さＬ１が所定値（最小破壊長さ）Ｌｍ以上であるとき、最大応力発生部においてセラミックス層２にき裂が発生する。この最小破壊長さＬｍは、印加する電界の強さ（外部電極９間の電圧の大きさ）、セラミックス層２の材質や寸法形状、部分電極７の寸法形状等の諸条件によって一義的に決定される。本実施形態では、溝１０が設けられていない場合（積層体４の側辺部４ａ，４ｂの全域を溝不存在領域とした場合）に最大応力が発生する積層体４の積層方向の中央部分に、溝１０が形成されている。また、溝不存在領域の積層方向の長さ（積層体４の端から溝１０まで長さ）Ｌ１は、最小破壊長さＬｍよりも小さく設定されている。
【００４５】
例えば、全長Ｌが３０ｍｍ、積層方向と直交する断面が７ｍｍ×７ｍｍの略正方形、セラミックス層と内部電極層とを合わせた１層の長さ（高さ）が８０μｍ、積層数が３７５層であり、応力緩和のための溝を有さない積層体（素子）に対し、印加する電圧の強さを徐々に上昇させると、９６０Ｖ／ｍｍの電界を印加したときに、積層方向の略中央付近において、積層体の側面に、部分電極の端から無電極部へ向けて内部電極層に沿った小さなき裂が発生する。このような結果は、破壊実験を行ったり、有限要素法等を用いた計算などを行うことによって得ることができる。すなわち、上記積層体では、９６０Ｖ／ｍｍの電界印加時の最小破壊長さＬｍが３０ｍｍであり、積層体の全長が３０ｍｍ以上となる場合に、溝不存在領域の積層方向の長さが３０ｍｍ未満となるように、応力緩和のための溝１０を設ければ良い。
【００４６】
積層方向における溝１０の数は、溝不存在領域の積層方向の長さＬ１が最小破壊長さＬｍよりも小さく設定されるように決定すれば良い。この場合、溝１０の形成は製造作業の煩雑化を招くため、積層方向における溝１０の数はできるだけ少ない方が好ましい。具体的には、積層体４の全長Ｌと最小破壊長さＬｍと積層方向における溝１０の配置個所の数ｎとの関係が、Ｌ／ｎ＜Ｌｍを満たす最小整数値のｎを求め、ｎ箇所の溝１０を、積層体４の全長Ｌを（ｎ＋１）等分する位置に配置すれば良い。例えば、２カ所に溝１０を配置する場合には積層体４の積層方向の全長Ｌをほぼ３等分する位置に、３カ所に配置する場合にはほぼ４等分する位置にそれぞれ配置すれば良い。
【００４７】
本実施形態に係る素子１は、例えばセラミックコンデンサ等の製造に用いられるセラミックグリーンシートの積層体を焼結する方法によって得ることができる。具体的には、圧電あるいは電歪セラミックス粉末を作成する工程と、粉末に有機バインダ等を加えて混練しグリーンシート化する工程と、得られたグリーンシートの表面に部分電極７となる金属電極ペーストを印刷する工程と、印刷後のグリーンシートを積層する工程と、この積層体（生積層体）を焼結して一体化する工程と、部分電極７を並列接続するように外部電極９を形成する工程と、によって製造される。なお、圧電セラミックスの場合には、最後に、外部電極間に直流電圧を印加する分極処理工程が加えられる。
【００４８】
溝１０は、焼結後の積層体４に形成しても良く、焼結前の生積層体に形成しても良い。溝１０の形成は、ダイシングソーやワイヤーソーやレーザ加工機などを用いて行う。焼結前の生積層体に対して溝１０を形成する方法は、溝１０を形成する作業を容易に行うことができる点と、溝１０を形成する際に生じた残留歪みが焼結時に解消するという点で優れている。
【００４９】
本実施形態によれば、溝不存在領域の積層方向の長さＬ１は、外部電極９に所定の電圧が印加されたときに溝不存在領域においてき裂が発生する最小破壊長さＬｍよりも小さく設定されているので、応力を緩和する溝１０によって、き裂の発生及び／又は成長を確実に防止することができる。
【００５０】
また、溝１０の数は、溝不存在領域の積層方向の長さＬ１を最小破壊長さＬｍよりも小さくさせる最少数で済み、多数の溝１０を形成する必要がない。従って、製造上の負担が少なくて済み、工業的に生産が容易である。
【００５１】
各溝不存在領域の積層方向の長さＬ１がほぼ等しくなるように溝１０が配置されているので、発生する応力を各溝不存在領域に均等に分散させることができる。従って、積層体４の全域において効率良く最大応力の低減を図ることができる。
【００５２】
溝１０を、積層体４に溝１０が設けられていない場合（積層体４の側辺部４ａ，４ｂの全域を溝不存在領域とした場合）に最大応力が発生する積層体４の積層方向の中央部分に配置したので、発生する最大応力をより効果的に低減させることができる。
【００５３】
溝１０を、セラミックス層２に、積層方向と略直交するように配置したので、外部電極９が溝１０内へ侵入している場合であっても、溝１０が内部電極層と異なった別の平面内のセラミックス層２内に存在する。このため、絶縁性が要求される部分における外部電極９と部分電極７との導通を確実に防止することができる。
【００５４】
溝１０の先端１０ａを湾曲面状としたので、溝１０の存在がき裂の発生を助長することが抑えられ、き裂の発生をより確実に防止することができる。
【００５５】
また、一般に、印加する電圧の大きさを小さく抑えつつ素子１の変位量を増大させるためには、セラミックス層２の厚さをできるだけ小さく設定する方が有利である。一方、溝１０の形成作業性の点からは、セラミックス層２の厚さを大きく設定する方が有利である。ここで、本実施形態では、溝１０を有するセラミックス層２の数は溝１０を有さない他のセラミックス層２の数に比して極めて少なく、且つ、溝１０を有するセラミックス層２の厚さは、他のセラミックス層２の厚さよりも大きく形成している。従って、製造の煩雑化を招くことなく、低電圧による変位量の増大化を図ることができる。
【００５６】
図６〜図１０に、上記実施形態の変形例を、図１１〜図１５に、上記実施形態の他の変形例をそれぞれ示す。これらの変形例は、部分電極の形状が上記実施形態と相違し、これに合わせて溝の形状が相違するものであり、その他の基本構成は上記実施形態と同様である。なお、図７及び図１２では、便宜上セラミックス層を透視して部分電極を示している。
【００５７】
図６〜図１０の内部電極層１２は、矩形板形状の一辺に切り欠き部を有する（矩形板形状の四辺のうち一辺部分が切除された形状を有する）部分電極１３と、この切り欠き部に配置された無電極部１４と、を備えた略矩形板形状であり、第１内部電極層１５の無電極部１４と第２内部電極層１６の無電極部１４とは、積層体４の相対向する２つの側面（側部）４ｃ，４ｄにそれぞれ面して配置されている。外部電極９は、積層体４の２つの側面４ｃ，４ｄ上に配置されている。溝１７の先端１７ａは、湾曲面状に形成されている。溝１７は、積層体４の２つの側面４ｃ，４ｄ上にそれぞれ配置され、積層体４の積層方向の中央部分のセラミック層２に形成されている。溝不存在領域の積層方向の長さＬ１は、最小破壊長さＬｍよりも小さく設定されている。
【００５８】
溝１７は、積層方向と略直交し且つ溝１７を含む断面において、セラミックス層２のほぼ全ての領域が、セラミックス層２と隣り合って対となる部分電極１３によって挟まれるような寸法形状を有している。換言すると、積層方向から視た状態で、部分電極１３の無電極部１４の先端が溝１７の先端１７ａとほぼ完全に重なるか又は溝１７の先端１７ａが無電極部１４の先端１４ａよりも僅かに内側に配置される（図１０参照）ように、無電極部１４及び溝１７が設定されている。溝１７を有するセラミックス層２の厚さは、溝１７を有さない他のセラミックス層２の厚さよりも大きく形成されている。
【００５９】
図１１〜図１５の内部電極層２０は、矩形板形状の三辺に連続する切り欠き部を有する（矩形板形状の四辺のうち三辺部分が略Ｕ状に切除された形状を有する）部分電極２１と、この切り欠き部に配置された無電極部２２と、を備えた略矩形板形状であり、第１内部電極層２３の部分電極２１と第２内部電極層２４の部分電極２１とは、積層体４の相対向する２つの側面（側部）４ｃ，４ｄにそれぞれ交互に面して配置されている。外部電極９は、積層体４の２つの側面４ａ，４ｂ上に配置されている。溝２５は、この２つの側面４ｃ，４ｄを含む積層体４の４つの側面に亘って環状に配置され、積層体４の積層方向の中央部分のセラミック層２に形成されている。溝不存在領域の積層方向の長さＬ１は、最小破壊長さＬｍよりも小さく設定されている。
【００６０】
溝２５、積層方向と略直交し且つ溝２５を含む断面において、セラミックス層２のほぼ全ての領域が、セラミックス層２と隣り合って対となる部分電極２１によって挟まれるような寸法形状を有している。換言すると、積層方向から視た状態で、部分電極２１の無電極部２２の先端２２ａが溝２５の先端２５ａとほぼ完全に重なるか又は溝２５の先端２５ａが無電極部２２の先端２２ａよりも僅かに内側に配置される（図１５参照）ように、無電極部２２及び溝２５が設定されている。溝２５を有するセラミックス層２の厚さは、溝２５を有さない他のセラミックス層２の厚さよりも大きく形成されている。
【００６１】
このような変形例においても、上記実施形態と同様の作用効果を得ることができる。
【００６２】
【実施例】
図１に示す本実施形態に係るセラミック積層型電気機械変換素子と比較サンプルとを、下記の方法にそれぞれ従って作製し、比較試験を行った。
【００６３】
ＰＺＴ系圧電セラミックス粉末を準備し、粉末１００重量部に対してアクリル樹脂５重量部、テルピネオールを主成分とした有機溶剤２０重量部とを混合したスラリーを作製し、これをＰＥＴフィルム上にキャスティング後乾燥して、厚さが約０．１ｍｍのセラミックグリーンシートとした。内部電極材料用金属ペーストには白金ペーストを使用し、上記グリーンシートの片面上に印刷塗布を施した。部分電極構造を有するグリーンシート１０１枚を、ペースト印刷面を上に積み重ね、その上にペーストを印刷していないグリーンシートを重ねて、熱プレスを用いて圧着した。得られた生積層体に溝を形成し、４００℃の温度で４８時間熱処理して脱脂し、その後１２００℃の温度で１時間焼結し一体化した。焼結後の各内部電極の層間は約０．０８ｍｍであった。この焼結体を、断面７ｍｍ×７ｍｍ、長さ１０ｍｍの寸法に加工した。外部電極ペーストを素子側辺に塗布して乾燥させ、各内部電極（部分電極）を電気的に並列接続した。
【００６４】
得られた素子に対して２つの外部電極間に１６０Ｖ（電界強度約２ｋＶ／ｍｍ）の直流電圧を１分間印加して分極処理を施したが、素子にき裂が生じることはなかった。その後再び分極時と同方向に１６０Ｖの直流電圧を印加したところ、素子は長さ方向（積層方向）で０．０１２ｍｍの伸び変位を発生していることが確認された。また、最大変位が０．０１２ｍｍとなるように変調したパルス電圧を印加して間歇駆動を行ったが、素子が機械的に破壊することはなかった。
【００６５】
他方、上記と同じ寸法形状で溝を有さない素子（比較サンプル）を作製し、１６０Ｖの直流電圧を印加して分極処理を施したところ、長さ方向（積層方向）の中央部分の側面に内部電極層に沿ったき裂が生じた。この状態で、上記条件で間歇駆動を行ったところ、数万サイクル程度で素子はき裂部分から機械的に破壊した。
【００６６】
本発明は、一例として説明した上述の実施形態、その変形例、及び実施例に限定されることはない。すなわち、上述の実施形態等以外であっても、本発明に係る技術的思想を逸脱しない範囲であれば、設計等に応じて種々の変更が可能であることは勿論である。
【００６７】
【発明の効果】
以上説明したように、本発明によれば、工業的に生産が容易で、且つ電界印加時のき裂の発生を防止することが可能なセラミック積層型電気機械変換素子を提供することができる。
【図面の簡単な説明】
【図１】本発明に係るセラミック積層型電気機械変換素子の一実施形態を示す斜視図である。
【図２】図１の積層体の一部のセラミックス層を透視した斜視図である。
【図３】図１のＩＩＩ−ＩＩＩ矢視断面図である。
【図４】図１のＶＩ−ＶＩ矢視断面図である。
【図５】図１のＶ−Ｖ矢視断面図図である。
【図６】変形例を示す斜視図である。
【図７】図６の積層体の一部のセラミックス層を透視した斜視図である。
【図８】図６のＶＩＩＩ−ＶＩＩＩ矢視断面図である。
【図９】図６のＩＸ−ＩＸ矢視断面図である。
【図１０】図６のＸ−Ｘ矢視断面図図である。
【図１１】他の変形例を示す斜視図である。
【図１２】図１１の積層体の一部のセラミックス層を透視した斜視図である。
【図１３】図１１のＸＩＩＩ−ＸＩＩＩ矢視断面図である。
【図１４】図１１のＩＸＶ−ＩＸＶ矢視断面図である。
【図１５】図１１のＸＶ−ＸＶ矢視断面図図である。
【符号の説明】
１セラミック積層型電気機械変換素子
２セラミックス層
３、１２、２０内部電極層
４積層体
４ａ，４ｂ積層体の側辺部（側部）
４ｃ，４ｄ積層体の側面（側部）
５、１５、２３第１内部電極層
６、１６、２４第２内部電極層
７、１３、２１部分電極
８、１４、２２無電極部
９外部電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic laminated electromechanical transducer and a method for manufacturing the same.
[0002]
[Prior art]
A ceramic laminated electromechanical transducer generally includes a laminate in which a plurality of ceramic layers and a plurality of internal electrode layers are alternately stacked and integrally sintered, and a pair of external electrodes, and each internal The electrode layer has a partial electrode as an internal electrode. The external electrodes are respectively disposed on the two side surfaces of the laminate, and are electrically connected to the partial electrodes every other layer.
[0003]
Each partial electrode has an electrode area smaller than the cross-sectional area of the element (stacked body), and its edge surface is exposed at least one of the two side surfaces of the stacked body in which two external electrodes are arranged. Each partial electrode is electrically connected to the external electrode disposed on the side surface of the laminate at which the edge surface of the partial electrode is exposed, but is externally disposed on the side surface of the laminate at which the edge surface is not exposed. It is not electrically connected to the electrode.
[0004]
The ceramic layer is mainly composed of piezoelectric or electrostrictive ceramics, and is mechanically displaced when a voltage is applied between the external electrodes. Due to the presence of a region where no partial electrode of each internal electrode layer is provided (hereinafter referred to as an electrodeless portion), a ceramic layer between a pair of adjacent internal electrode layers is sandwiched between the partial electrodes of the two internal electrode layers. There is a part that is not sandwiched and a part that is not sandwiched. When a voltage is applied between the external electrodes, the portion sandwiched between the partial electrodes of the two portions is displaced, but the portion not sandwiched between the partial electrodes is not displaced, and stress is generated near the boundary between the two electrodes. . If the maximum stress generated exceeds the fracture strength of the ceramic layer, there is a risk that a crack will occur and damage will occur. In addition, cracks cause the moisture resistance to deteriorate significantly. For this reason, when an electric field is applied to the device in a high-humidity atmosphere, the metal forming the internal electrode migrates through the crack, and the partial electrode and the external electrode are electrically connected at the site where insulation is required. There is a risk of conduction.
[0005]
As a structure for the purpose of avoiding such inconvenience, grooves having a width of 0.1 mm and a depth of 0.1 mm are formed at intervals of 2 mm on the entire periphery of the element on a side surface parallel to the stacking direction of the element. (For example, refer to Patent Document 1).
[0006]
[Patent Document 1]
Japanese Examined Patent Publication No. 6-5794 [0007]
[Problems to be solved by the invention]
However, in the structure of Patent Document 1, the number of grooves formed with respect to the length of the element (laminated body) is large. For example, in the case where the length of the element is 30 mm, 14 grooves must be formed, which is a burden on manufacturing, and increases man-hours and costs. In addition, forming the groove around the entire periphery of the element also becomes a manufacturing burden, and increases man-hours and costs.
[0008]
Accordingly, an object of the present invention is to provide a ceramic laminated electromechanical transducer that can be easily produced industrially and that can prevent the occurrence of cracks when an electric field is applied, and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a ceramic laminated electromechanical transducer according to the present invention includes a laminated body and a pair of external electrodes. In the laminate, a plurality of ceramic layers made of a material that is displaced by application of an electric field and a plurality of internal electrode layers are alternately stacked, and both are integrally sintered. The pair of external electrodes is disposed on the side surface of the stacked body. Each internal electrode layer consists of a partial electrode and a non-electrode part, and the partial electrode is electrically connected alternately with a pair of external electrodes every other layer.
[0010]
Grooves that relieve stress are formed in side portions along the stacking direction of the stacked body. This groove has a maximum length continuous in the stacking direction of the groove-free region that does not include the groove in the side portion of the laminate, and a crack is generated in the groove-free region when a predetermined electric field is applied to the ceramic layer. It is kept smaller than the minimum fracture length. The ceramic layer is mainly composed of so-called piezoelectric ceramics or electrostrictive ceramics.
[0011]
In the above configuration, when a voltage is applied to the external electrode, a portion of the ceramic layer sandwiched between two paired partial electrodes adjacent to each other in the stacking direction is displaced, but is not sandwiched between the two partial electrodes. The part is not displaced. For this reason, stress is generated at the boundary between them (the boundary between the portion sandwiched between two adjacent partial electrodes and the portion not sandwiched). The magnitude of the generated stress increases from both ends in the stacking direction of the stacked body toward the central portion, and becomes maximum stress at a predetermined position. This maximum stress increases or decreases according to the increase or decrease in the length in the stacking direction of a region that does not include a groove that relaxes stress (hereinafter referred to as a groove-free region) in the side portion of the stacked body.
[0012]
On the other hand, in the present invention, the minimum length in the stacking direction (hereinafter referred to as the minimum fracture length) of the groove-free region where a crack is generated when a predetermined electric field is applied to the ceramic layer is experimentally determined. Or the groove | channel for relieving stress is arrange | positioned so that it may obtain | require beforehand by calculation and the length of the lamination direction of each groove | channel absence area | region may become smaller than this minimum fracture length.
[0013]
This minimum breakdown length is determined by various conditions such as the strength of the applied electric field, the material and size of the ceramic layer, and the size and shape of the partial electrode. Therefore, by arranging the grooves so that the length in the stacking direction of the groove-free region is smaller than the minimum fracture length, the generation and growth of cracks can be reliably prevented.
[0014]
Further, the number of grooves may be the minimum number that makes the length of the groove-free region in the stacking direction smaller than the minimum fracture length, and it is not necessary to form a large number of grooves. Therefore, the manufacturing burden is small and industrial production is easy.
[0015]
A groove to relieve stress is placed in the vicinity of the part where the stress generated when a predetermined electric field is applied to the ceramic layer in the absence of groove exceeds the fracture strength of the ceramic layer (maximum stress generating part). You may do it.
[0016]
As a result, the maximum stress generated in the groove-free region can be effectively reduced so as to be smaller than the fracture strength of the ceramic layer, and the generation of cracks can be suppressed more reliably.
[0017]
You may arrange | position the groove | channel which relieves stress in the position which divides | segments the whole length of the lamination direction of a laminated body substantially equally.
[0018]
When the magnitude of the maximum stress generated is uniformly determined by the length of the groove-free region in the stacking direction, by arranging the grooves so that the length of each groove-free region in the stacking direction is substantially equal, The generated stress can be efficiently dispersed so that the maximum stress in each groove absence region does not exceed the fracture strength of the ceramic layer. Therefore, it is possible to efficiently reduce the maximum stress and suppress the generation of cracks in the entire area of the laminate.
[0019]
You may form a groove | channel in a ceramic layer so that a groove | channel may be extended in the direction substantially orthogonal to a lamination direction from the side surface along the lamination direction of a laminated body.
[0020]
In the above configuration, even when the external electrode penetrates into the groove, the groove exists in the ceramic layer in a different plane different from the internal electrode layer, so that the external portion in the portion where insulation is required Conductivity between the electrode and the partial electrode can be reliably prevented.
[0021]
You may form the thickness of the ceramic layer in which the groove | channel was formed larger than the thickness of another ceramic layer.
[0022]
In the above configuration, the thickness of the ceramic layer that does not have a groove can be set small to increase the amount of displacement of the element while keeping the applied voltage small, and the thickness of the ceramic layer that forms the groove The groove can be easily worked by setting the length large, and industrial production becomes easier.
[0023]
The tip of the groove may be curved.
[0024]
For example, when the tip of the groove has a corner, a crack may be generated and grow by using the corner as a trigger. On the other hand, if the tip of the groove is curved, there is no corner that triggers the generation of cracks, so that the generation of cracks can be prevented more reliably.
[0025]
The groove may be formed so that substantially all the region of the ceramic layer is sandwiched between the pair of partial electrodes adjacent to the ceramic layer in a cross section that is substantially orthogonal to the stacking direction and includes the groove.
[0026]
In the above configuration, in the cross section of the ceramic layer substantially perpendicular to the stacking direction and including the groove, almost all of the region is displaced almost uniformly by the application of an electric field, so that the stress generated in the stack is relieved well and the maximum The stress can be reduced more reliably.
[0027]
The laminated body may have a substantially prismatic shape, and the internal electrode layer may be composed of first internal electrode layers and second internal electrode layers that are alternately stacked with a ceramic layer interposed therebetween. The first internal electrode layer and the second internal electrode layer, each having a partial electrode with one corner cut out of a rectangular plate shape, and a non-electrode portion arranged at the cut corner It may be a rectangular plate shape. The non-electrode portion of the first internal electrode layer and the non-electrode portion of the second internal electrode layer are respectively arranged on two opposite side portions of the laminate, and grooves are formed on the two side portions, respectively. May be.
[0028]
Further, the first internal electrode layer and the second internal electrode layer are each formed in a substantially rectangular plate shape including a partial electrode having a cutout portion on one side of the rectangular plate shape and an electrodeless portion disposed in the cutout portion. It is also good. The non-electrode portion of the first internal electrode layer and the non-electrode portion of the second internal electrode layer are arranged so as to face two opposite side surfaces of the laminate, and grooves are respectively formed on the two side surfaces. Also good.
[0029]
Further, the first internal electrode layer and the second internal electrode layer are each provided with a partial electrode having a cutout portion continuous on three sides of a rectangular plate shape, and an electrodeless portion arranged in the cutout portion. It may be a rectangular plate shape. The partial electrode of the first internal electrode layer and the partial electrode of the second internal electrode layer are arranged so as to face two opposite side surfaces of the multilayer body, respectively, and the groove is annular over the four side surfaces of the multilayer body. You may form in.
[0030]
The ceramic laminated electromechanical transducer according to the present invention is obtained by applying a metal paste that forms an internal electrode layer on the surface of a green sheet containing ceramic powder and an organic binder, laminating the green sheet, It may be manufactured by sintering a sheet assembly to form a laminate and forming grooves in the sintered laminate.
[0031]
In addition, a metal paste for forming an internal electrode layer is applied to the surface of a green sheet containing ceramic powder and an organic binder, the green sheet is laminated, and a groove is formed in an assembly of the laminated green sheets. You may manufacture by sintering the aggregate | assembly which has and producing | generating a laminated body.
[0032]
As described above, the method of forming the groove in the green sheet aggregate before sintering can easily perform the operation of forming the groove and the residual strain generated when forming the groove is sintered. It is excellent in that it is resolved at times.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0034]
FIG. 1 is a perspective view showing an embodiment of a ceramic laminated electromechanical transducer according to the present invention, FIG. 2 is a perspective view showing a part of the ceramic layer of the laminated body of FIG. 1, and FIG. FIG. 4 is a cross-sectional view taken along arrow VI-VI in FIG. 1, and FIG. 5 is a cross-sectional view taken along arrow V-V in FIG.
[0035]
As shown in FIGS. 1 to 5, the ceramic laminated electromechanical transducer 1 includes a plurality of ceramic layers 2 that are displaced by application of an electric field, a plurality of internal electrode layers 3, a pair of external electrodes 9, and stress. And a groove 10 for relaxing. The ceramic layers 2 and the internal electrode layers 3 are alternately stacked and integrated to form a laminate 4. The internal electrode layers 3 are connected to two external electrodes 9 every other layer, and a predetermined electric field is applied to each ceramic layer 2 by applying a voltage from the external electrodes 9. Both the ceramic layer 2 and the internal electrode layer 3 have a rectangular plate shape, and the laminate 4 has a prismatic shape. Each ceramic layer 2 has substantially the same thickness. In addition, the shape of the laminated body 4 is not limited to prismatic shape, For example, it can set to various shapes, such as a column shape and a hollow cylinder shape.
[0036]
The internal electrode layer 3 is divided into a first internal electrode layer 5 and a second internal electrode layer 6. The ceramic layer 2 and the internal electrode layer 3 are laminated in the order of the ceramic layer 2, the first internal electrode layer 5, the ceramic layer 2, the second internal electrode layer 6, the ceramic layer 2. That is, the first internal electrode layers 5 and the second internal electrode layers 6 are alternately stacked with the ceramic layer 2 interposed therebetween.
[0037]
Each internal electrode layer 3 (5, 6) has a partial electrode 7 and a non-electrode portion 8, and the adjacent ceramic layers 2 are integrated in the non-electrode portion 8. Each partial electrode 7 has a shape in which one corner is cut out of a rectangular plate shape, and the cut-out corner constitutes an electrodeless portion 8. The electrodeless portion 8 of the first internal electrode layer 5 and the electrodeless portion 8 of the second internal electrode layer 6 are respectively disposed on the two opposite side portions 4 a and 4 b of the stacked body 4. That is, the non-electrode portion 8 of the first internal electrode layer 5 and the non-electrode portion 8 of the second internal electrode layer 6 include two stacking axes (the first stacking axis near the side portion 4a and the first stacking axis substantially parallel to the stacking direction). The second laminated axis in the vicinity of the side portion 4b). The two external electrodes 9 are disposed and fixed on the side portions 4a and 4b, respectively. Thereby, one external electrode 9 is electrically connected to the partial electrode 7 of the first internal electrode layer 5 and is kept in an insulated state from the partial electrode 7 of the second internal electrode layer 6. The other external electrode 9 is electrically connected to the partial electrode 7 of the second internal electrode layer 6 and is maintained in an insulated state from the partial electrode 7 of the first internal electrode layer 5.
[0038]
The groove 10 is formed in each of the ceramic layers 2 of the side portions (side portions) 4 a and 4 b of the laminate 4. The tip 10a of the groove 10 is formed in a curved surface shape. The width of the groove 10 (height in the stacking direction) is about several tens of μm. A baked metal paste is used for the external electrode 9, and the external electrode 9 forms a bridge in the groove 10 and is not divided. Even if the external electrode 9 penetrates to the inside of the groove 10, the groove 10 exists in a different plane from the partial electrode 7, so that the external electrode 9 and the partial electrode 7 in a portion where insulation is required It is possible to reliably prevent conduction (for example, conduction between the external electrode 9 and the partial electrode 7 of the second internal electrode layer 6 below the external electrode 9 in FIG. 3).
[0039]
The groove 10 has a dimension and shape so that almost all the region of the ceramic layer 2 is sandwiched between the pair of partial electrodes 7 adjacent to the ceramic layer 2 in a cross section that is substantially orthogonal to the stacking direction and includes the groove 10. is doing. In other words, when viewed from the stacking direction, the edge of the electrodeless portion 8 of the partial electrode 7 almost completely overlaps the tip of the groove 10 or the tip 10a of the groove 10 is more than the edge 8a of the electrodeless portion 8. The electrodeless portion 8 and the groove 10 are set so as to be disposed slightly inside (see FIG. 5).
[0040]
The thickness of the ceramic layer 2 having the groove 10 is formed larger than the thickness of the other ceramic layer 2 not having the groove 10.
[0041]
The ceramic layer 2 is made of so-called piezoelectric ceramics or electrostrictive ceramics. Piezoelectric ceramics and electrostrictive ceramics both have the property of being distorted (displaced) when an electric field (voltage) is applied. Typical materials for piezoelectric ceramics include Pb (Zr, Ti) O ₃ and BaTiO ₃ . Typical materials for electrostrictive ceramics include Pb (Mg _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ , Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbTiO _3, and (Pb, La). (Zr, Ti) O ₃ and the like. In the case of piezoelectric ceramics, it is necessary to perform a so-called polarization process for aligning the direction of polarization in one direction. Pb (Zr, Ti) O ₃ is PZT, BaTiO ₃ is BT, Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ is PMN-PT, Pb (Ni _1/3 Nb _{2 /} _₃₎ O 3 -PbTiO 3 is a PNN-PT, (Pb, La ) (Zr, Ti) O 3 is a PLZT, abbreviated respectively.
[0042]
In the ceramic layer 2 that does not have the groove 10, a portion sandwiched between adjacent pairs of partial electrodes 7 is displaced (stretched) in the stacking direction by application of an electric field, but a portion not sandwiched between the partial electrodes 7 is not displaced. Stress is generated near the boundary between the two. In the ceramic layer 2 having the groove 10, almost the entire region is sandwiched between a pair of adjacent partial electrodes 7. For this reason, the application of an electric field causes uniform displacement throughout the entire layer, and distortion (displacement) in the stacking direction is not constrained, so stress in the stacking direction is basically not generated or generated. Even so, the size is extremely small.
[0043]
The magnitude of the stress in the stacking direction generated in the stacked body 4 due to the application of the electric field increases from both ends in the stacking direction of the stacked body 4 toward the center, and becomes the maximum stress at a predetermined position. This maximum stress increases / decreases in accordance with increase / decrease of the length in the stacking direction of a region not including the groove 10 (hereinafter referred to as a groove non-existing region) of the side portions 4a, 4b of the stacked body 4.
[0044]
In addition, as in the present embodiment, the shape and arrangement direction of the ceramic layer 2 that does not have the grooves 10 are uniform in the stacking direction, and the electrodeless portions 8 are alternately arranged along the stacking direction. 2 have approximately the same thickness, the maximum stress in the groove non-existing region is generated at the substantially central portion in the stacking direction of the groove non-existing region. Increase / decrease according to the increase / decrease of the direction length L1. When an electric field is applied, if the length L1 in the stacking direction of the groove-free region is equal to or greater than a predetermined value (minimum fracture length) Lm, a crack is generated in the ceramic layer 2 at the maximum stress generation portion. This minimum breakdown length Lm is uniquely determined by various conditions such as the strength of the electric field applied (the magnitude of the voltage between the external electrodes 9), the material and dimensions of the ceramic layer 2, and the dimensions of the partial electrode 7. Is done. In the present embodiment, when the groove 10 is not provided (when the entire region of the side portions 4a and 4b of the laminated body 4 is a groove-free region), the central portion of the laminated body 4 in the stacking direction in which the maximum stress is generated. In addition, a groove 10 is formed. In addition, the length in the stacking direction of the groove-free region (the length from the end of the stacked body 4 to the groove 10) L1 is set to be smaller than the minimum fracture length Lm.
[0045]
For example, the overall length L is 30 mm, the cross section orthogonal to the stacking direction is a substantially square of 7 mm × 7 mm, the length (height) of one layer including the ceramic layer and the internal electrode layer is 80 μm, and the number of stacks is 375 layers When the strength of the applied voltage is gradually increased with respect to a laminate (element) having no grooves for stress relaxation, when an electric field of 960 V / mm is applied, in the vicinity of the approximate center in the lamination direction. A small crack along the internal electrode layer is generated on the side surface of the laminated body from the end of the partial electrode toward the non-electrode portion. Such a result can be obtained by performing a destructive experiment or performing a calculation using a finite element method or the like. That is, in the laminate, when the minimum breakdown length Lm when an electric field of 960 V / mm is applied is 30 mm and the overall length of the laminate is 30 mm or more, the length in the stacking direction of the groove-free region is less than 30 mm. A groove 10 for stress relaxation may be provided so that
[0046]
The number of grooves 10 in the stacking direction may be determined so that the length L1 in the stacking direction of the groove-free region is set to be smaller than the minimum fracture length Lm. In this case, since the formation of the grooves 10 complicates the manufacturing work, the number of the grooves 10 in the stacking direction is preferably as small as possible. Specifically, the relationship between the total length L and the minimum fracture length Lm of the laminate 4 and the number n of the locations where the grooves 10 are arranged in the stacking direction is determined as a minimum integer value n satisfying L / n <Lm. What is necessary is just to arrange | position the groove | channel 10 of the location in the position which divides the full length L of the laminated body 4 into (n + 1) equally. For example, when the grooves 10 are arranged at two locations, the total length L in the stacking direction of the laminate 4 is divided into approximately three equal parts, and when arranged at three locations, the grooves 10 are arranged at approximately four equal positions. good.
[0047]
The element 1 according to the present embodiment can be obtained, for example, by a method of sintering a laminate of ceramic green sheets used for manufacturing a ceramic capacitor or the like. Specifically, a step of creating a piezoelectric or electrostrictive ceramic powder, a step of adding an organic binder or the like to the powder and kneading to form a green sheet, and a metal electrode paste that becomes the partial electrode 7 on the surface of the obtained green sheet Forming the external electrode 9 so as to connect the partial electrodes 7 in parallel, the step of laminating the green sheets after printing, the step of sintering and integrating the laminate (raw laminate) And the process of manufacturing. In the case of piezoelectric ceramics, finally, a polarization process step for applying a DC voltage between the external electrodes is added.
[0048]
The groove 10 may be formed in the laminated body 4 after sintering, or may be formed in the raw laminated body before sintering. The groove 10 is formed using a dicing saw, a wire saw, a laser processing machine, or the like. The method of forming the groove 10 on the green laminate before sintering is that the operation of forming the groove 10 can be easily performed, and the residual strain generated when forming the groove 10 is eliminated during sintering. It is excellent in that it does.
[0049]
According to the present embodiment, the length L1 in the stacking direction of the groove-free region is greater than the minimum fracture length Lm at which a crack is generated in the groove-free region when a predetermined voltage is applied to the external electrode 9. Since it is set to be small, the occurrence of cracks and / or growth can be reliably prevented by the grooves 10 that relieve stress.
[0050]
In addition, the number of grooves 10 may be the minimum number that makes the length L1 in the stacking direction of the groove-free region smaller than the minimum fracture length Lm, and it is not necessary to form a large number of grooves 10. Therefore, the manufacturing burden is small and industrial production is easy.
[0051]
Since the grooves 10 are arranged so that the length L1 in the stacking direction of each groove non-existing region is substantially equal, the generated stress can be evenly distributed in each groove non-existing region. Therefore, the maximum stress can be efficiently reduced in the entire area of the laminate 4.
[0052]
The stacking direction of the stacked body 4 in which the maximum stress is generated when the groove 10 is not provided in the stacked body 4 (when the entire sides 4a and 4b of the stacked body 4 are defined as groove-free regions). Therefore, the maximum stress generated can be more effectively reduced.
[0053]
Since the groove 10 is arranged in the ceramic layer 2 so as to be substantially orthogonal to the stacking direction, even if the external electrode 9 has penetrated into the groove 10, the groove 10 is different from the internal electrode layer. It exists in the ceramic layer 2 in the plane. For this reason, it is possible to reliably prevent conduction between the external electrode 9 and the partial electrode 7 in a portion where insulation is required.
[0054]
Since the tip 10a of the groove 10 has a curved surface, the presence of the groove 10 can suppress the generation of cracks, and the generation of cracks can be more reliably prevented.
[0055]
In general, it is advantageous to set the thickness of the ceramic layer 2 as small as possible in order to increase the amount of displacement of the element 1 while keeping the applied voltage small. On the other hand, it is advantageous to set the thickness of the ceramic layer 2 large from the viewpoint of workability of forming the groove 10. Here, in this embodiment, the number of the ceramic layers 2 having the grooves 10 is extremely smaller than the number of the other ceramic layers 2 not having the grooves 10, and the thickness of the ceramic layers 2 having the grooves 10. Is formed larger than the thickness of the other ceramic layer 2. Therefore, it is possible to increase the amount of displacement due to a low voltage without causing complication of manufacturing.
[0056]
6 to 10 show modifications of the above embodiment, and FIGS. 11 to 15 show other modifications of the above embodiment. In these modified examples, the shape of the partial electrode is different from that of the above-described embodiment, and the shape of the groove is different according to this, and other basic configurations are the same as those of the above-described embodiment. 7 and 12 show the partial electrodes through the ceramic layer for convenience.
[0057]
The internal electrode layer 12 in FIGS. 6 to 10 includes a partial electrode 13 having a cutout portion on one side of a rectangular plate shape (having a shape in which one side portion is cut out of four sides of the rectangular plate shape), and the cutout portion. The non-electrode portion 14 of the first internal electrode layer 15 and the non-electrode portion 14 of the second internal electrode layer 16 are formed on the laminated body 4. Two opposing side surfaces (side portions) 4c and 4d are arranged so as to face each other. The external electrode 9 is disposed on the two side surfaces 4 c and 4 d of the multilayer body 4. The tip 17a of the groove 17 is formed in a curved surface shape. The groove 17 is disposed on each of the two side surfaces 4 c and 4 d of the multilayer body 4, and is formed in the ceramic layer 2 in the center portion of the multilayer body 4 in the stacking direction. The length L1 in the stacking direction of the groove absence region is set to be smaller than the minimum fracture length Lm.
[0058]
The groove 17 has a dimension and shape so that almost all the region of the ceramic layer 2 is sandwiched by the pair of partial electrodes 13 adjacent to the ceramic layer 2 in a cross section that is substantially orthogonal to the stacking direction and includes the groove 17. is doing. In other words, when viewed from the stacking direction, the tip of the electrodeless portion 14 of the partial electrode 13 overlaps the tip 17a of the groove 17 almost completely, or the tip 17a of the groove 17 is slightly smaller than the tip 14a of the electrodeless portion 14. The electrodeless portion 14 and the groove 17 are set so as to be disposed inside (see FIG. 10). The thickness of the ceramic layer 2 having the grooves 17 is formed larger than the thickness of the other ceramic layer 2 not having the grooves 17.
[0059]
The internal electrode layer 20 in FIGS. 11 to 15 has a cutout portion that is continuous with three sides of a rectangular plate shape (having a shape in which three sides of the four sides of the rectangular plate shape are cut into a substantially U shape). The electrode 21 and the non-electrode portion 22 arranged in the notch are substantially rectangular plate shapes, and the partial electrode 21 of the first internal electrode layer 23 and the partial electrode 21 of the second internal electrode layer 24 Are arranged alternately facing two opposite side surfaces (side portions) 4c, 4d of the laminate 4. The external electrode 9 is disposed on the two side surfaces 4 a and 4 b of the multilayer body 4. The groove 25 is annularly arranged over the four side surfaces of the multilayer body 4 including the two side surfaces 4c and 4d, and is formed in the ceramic layer 2 in the central portion of the multilayer body 4 in the stacking direction. The length L1 in the stacking direction of the groove absence region is set to be smaller than the minimum fracture length Lm.
[0060]
Groove 25, in a cross section substantially perpendicular to the stacking direction and including groove 25, has a size and shape such that almost all regions of ceramic layer 2 are sandwiched between paired partial electrodes 21 adjacent to ceramic layer 2. ing. In other words, the tip 22a of the electrodeless portion 22 of the partial electrode 21 is almost completely overlapped with the tip 25a of the groove 25 when viewed from the stacking direction, or the tip 25a of the groove 25 is more than the tip 22a of the electrodeless portion 22. The electrodeless portion 22 and the groove 25 are set so as to be disposed slightly inside (see FIG. 15). The thickness of the ceramic layer 2 having the groove 25 is formed larger than the thickness of the other ceramic layer 2 not having the groove 25.
[0061]
Also in such a modification, the same effect as the said embodiment can be acquired.
[0062]
【Example】
A ceramic laminated electromechanical transducer according to this embodiment shown in FIG. 1 and a comparative sample were produced according to the following methods, respectively, and a comparative test was performed.
[0063]
PZT-based piezoelectric ceramic powder was prepared, and a slurry was prepared by mixing 5 parts by weight of an acrylic resin and 20 parts by weight of an organic solvent containing terpineol as a main component with respect to 100 parts by weight of the powder. After casting this onto a PET film It was dried to obtain a ceramic green sheet having a thickness of about 0.1 mm. A platinum paste was used as the metal paste for the internal electrode material, and printing was applied on one side of the green sheet. 101 green sheets having a partial electrode structure were stacked on top of the paste printing surface, and green sheets on which no paste was printed were stacked on top of each other, and pressure bonded using a hot press. Grooves were formed in the obtained green laminate, heat treated at a temperature of 400 ° C. for 48 hours, degreased, and then sintered at a temperature of 1200 ° C. for 1 hour to be integrated. The interlayer between each internal electrode after sintering was about 0.08 mm. This sintered body was processed into dimensions of a cross section of 7 mm × 7 mm and a length of 10 mm. The external electrode paste was applied to the side of the element and dried, and the internal electrodes (partial electrodes) were electrically connected in parallel.
[0064]
The obtained device was subjected to polarization treatment by applying a direct current voltage of 160 V (electric field strength of about 2 kV / mm) between the two external electrodes for 1 minute, but no crack was generated in the device. After that, when a DC voltage of 160 V was applied again in the same direction as that during polarization, it was confirmed that the device had an elongation displacement of 0.012 mm in the length direction (stacking direction). In addition, intermittent drive was performed by applying a pulse voltage modulated so that the maximum displacement was 0.012 mm, but the element was not mechanically destroyed.
[0065]
On the other hand, when an element (comparative sample) having the same size and shape as described above and having no groove was produced and subjected to polarization treatment by applying a DC voltage of 160 V, it was found on the side surface of the central portion in the length direction (stacking direction). Cracks along the internal electrode layer occurred. In this state, intermittent driving was performed under the above conditions, and the device was mechanically broken from the cracked portion in about tens of thousands of cycles.
[0066]
The present invention is not limited to the above-described embodiment described as an example, modifications thereof, and examples. That is, it is needless to say that various modifications can be made according to the design and the like as long as the technical idea according to the present invention is not deviated from other than the above-described embodiment.
[0067]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a ceramic laminated electromechanical transducer that is industrially easy to produce and can prevent the occurrence of cracks when an electric field is applied.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a ceramic multilayer electromechanical transducer according to the present invention.
2 is a perspective view of a part of the ceramic body of FIG. 1 seen through. FIG.
3 is a cross-sectional view taken along the line III-III in FIG. 1;
4 is a cross-sectional view taken along the line VI-VI in FIG. 1;
5 is a cross-sectional view taken along line VV in FIG. 1;
FIG. 6 is a perspective view showing a modification.
7 is a perspective view of a part of the ceramic body of FIG. 6 seen through. FIG.
8 is a cross-sectional view taken along arrow VIII-VIII in FIG. 6;
9 is a cross-sectional view taken along arrow IX-IX in FIG. 6;
10 is a cross-sectional view taken along arrow XX in FIG. 6;
FIG. 11 is a perspective view showing another modification.
12 is a perspective view of a part of the ceramic layer of FIG. 11 seen through. FIG.
13 is a cross-sectional view taken along arrow XIII-XIII in FIG.
14 is a cross-sectional view taken along arrow IXV-IXV in FIG.
15 is a cross-sectional view taken along arrow XV-XV in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic laminated type electromechanical conversion element 2 Ceramic layer 3, 12, 20 Internal electrode layer 4 Laminated body 4a, 4b Side part (side part) of laminated body
4c, 4d Laminated body side face (side part)
5, 15, 23 First internal electrode layers 6, 16, 24 Second internal electrode layers 7, 13, 21 Partial electrodes 8, 14, 22 No electrode portion 9 External electrodes

Claims

A laminate in which a plurality of ceramic layers and a plurality of internal electrode layers made of a material that is displaced by application of an electric field are alternately stacked and sintered together, and a pair of external electrodes disposed on the side surface of the laminate Each internal electrode layer is composed of a partial electrode and a non-electrode portion, and the partial electrode is a ceramic laminated electromechanical transducer that is electrically connected alternately to the pair of external electrodes every other layer. And
On the side portion along the stacking direction of the stacked body, a groove for relaxing stress is formed,
The groove has a maximum continuous length in the stacking direction of the groove-free region that does not include the groove in the side portion in the groove-free region when a predetermined electric field is applied to the ceramic layer. A ceramic laminated electromechanical transducer, characterized by being suppressed to be smaller than a minimum fracture length at which a crack occurs.

The ceramic laminated electromechanical transducer according to claim 1,
The groove is disposed in the vicinity of a portion where the stress generated when a predetermined electric field is applied to the ceramic layer exceeds the fracture strength of the ceramic layer and is maximized in the groove non-existing region where the groove is removed. A ceramic laminated electromechanical transducer characterized by being made.

The ceramic laminated electromechanical transducer according to claim 1 or 2,
2. The ceramic laminated electromechanical transducer according to claim 1, wherein the groove is arranged at a position that substantially divides the entire length of the laminated body in the lamination direction.

A ceramic multilayer electromechanical transducer according to any one of claims 1 to 3,
2. The ceramic laminated electromechanical transducer according to claim 1, wherein the groove is formed in the ceramic layer and extends in a direction substantially perpendicular to the laminating direction from a side surface along the laminating direction of the laminated body.

The ceramic laminated electromechanical transducer according to claim 4,
The ceramic layered electromechanical transducer according to claim 1, wherein the thickness of the ceramic layer in which the groove is formed is larger than the thickness of the other ceramic layers.

The ceramic laminated electromechanical transducer according to claim 4 or 5,
In a cross section that includes the groove and is substantially perpendicular to the stacking direction, almost all the region of the ceramic layer is sandwiched between a pair of partial electrodes adjacent to the ceramic layer. Mechanical conversion element.

The ceramic laminated electromechanical transducer according to claim 6,
The laminate is substantially prismatic,
The internal electrode layer comprises a first internal electrode layer and a second internal electrode layer that are alternately stacked with the ceramic layer interposed therebetween,
The first internal electrode layer and the second internal electrode layer include a partial electrode with one corner portion cut out of a rectangular plate shape, and an electrodeless portion disposed at the cut corner portion. It has a substantially rectangular plate shape,
The electrodeless portion of the first internal electrode layer and the electrodeless portion of the second internal electrode layer are respectively disposed on two opposite side portions of the laminate,
2. The ceramic laminated electromechanical transducer according to claim 1, wherein the groove is formed in each of the side portions.

The ceramic laminated electromechanical transducer according to claim 6,
The laminate is substantially prismatic,
The internal electrode layer comprises a first internal electrode layer and a second internal electrode layer that are alternately stacked with the ceramic layer interposed therebetween,
The first internal electrode layer and the second internal electrode layer each have a substantially rectangular plate shape including a partial electrode having a cutout portion on one side of a rectangular plate shape and an electrodeless portion disposed in the cutout portion. And
The non-electrode portion of the first internal electrode layer and the non-electrode portion of the second internal electrode layer are respectively arranged facing two opposite side surfaces of the laminate,
2. The ceramic multilayer electromechanical transducer according to claim 1, wherein the groove is formed on each of the side surfaces.

The ceramic laminated electromechanical transducer according to claim 6,
The laminate is substantially prismatic,
The internal electrode layer comprises a first internal electrode layer and a second internal electrode layer that are alternately stacked with the ceramic layer interposed therebetween,
The first internal electrode layer and the second internal electrode layer each include a partial electrode having a cutout portion that is continuous with three sides of a rectangular plate shape, and a non-electrode portion disposed in the cutout portion. A rectangular plate,
The partial electrode of the first internal electrode layer and the partial electrode of the second internal electrode layer are respectively disposed facing two opposite side surfaces of the laminate,
2. The ceramic laminated electromechanical transducer according to claim 1, wherein the groove is formed in an annular shape over four side surfaces of the laminated body.

A ceramic laminated electromechanical transducer according to any one of claims 1 to 9,
The ceramic laminated electromechanical transducer according to claim 1, wherein the tip of the groove has a curved surface.

A method for producing a ceramic laminated electromechanical transducer according to any one of claims 1 to 10,
Apply a metal paste to form an internal electrode layer on the surface of the green sheet containing ceramic powder and organic binder,
Laminating green sheets coated with the metal paste,
Sintering an assembly of laminated green sheets to produce the laminate,
A method for producing a ceramic laminated electromechanical transducer, comprising forming the groove in the laminated body after sintering.

A method for producing a ceramic laminated electromechanical transducer according to any one of claims 1 to 10,
Apply a metal paste to form an internal electrode layer on the surface of the green sheet containing ceramic powder and organic binder,
Laminating green sheets coated with the metal paste,
Forming the groove in an assembly of laminated green sheets,
A method for producing a ceramic laminated electromechanical transducer, comprising producing the laminated body by sintering an aggregate having the grooves.