JPH07106653A - Multilayer piezoelectric element - Google Patents

Abstract

PURPOSE:To provide a multilayer piezoelectric element excellent in long term service life test by preventing occurrence of crack and delamination in the element. CONSTITUTION:The multilayer piezoelectric element comprises a multilayer piezoelectric actuator element comprising piezoelectric ceramic sheets 1 and inner electrodes 2 laminated alternately with the inner electrodes being exposed alternately on two side faces out of four side faces in the direction normal to the lamination, and brazing members 8 for laminating a plurality of the actuator elements furthermore and connecting then structurally and electrically.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明はガスの流量制御弁や微動
テーブル等に用いられる積層圧電素子に関するもので、
特に長期連続使用に耐える信頼性の高い積層圧電素子に
関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element used for a gas flow control valve, a fine movement table, etc.
In particular, the present invention relates to a highly reliable laminated piezoelectric element that can withstand long-term continuous use.

【０００２】[0002]

【従来の技術】本発明の対象となる積層圧電素子の従来
構造を示す断面図を図１３に示す。図中１は圧電セラミ
ックス、２は内部電極、３は外部電極である。内部電極
２は一層毎に２つの外部電極３に電気的に接続され、外
部電極３は各々ハンダ７を介してリード線６に接続され
ている。リード線６間に電圧を印加すると、各一対の内
部電極２の間の圧電セラミックス１に電界がかかり積層
方向に伸縮を生じる。従来、このような積層圧電素子に
用いられる圧電材はジルコン酸チタン酸鉛（ＰＺＴ）の
ような鉛系ペロブスカイト構造をもつ複合酸化物より構
成されており、内部電極２は白金または銀パラジウム合
金などに作成されている。また、外部電極３は、金白金
混合粉、銀、あるいは銀パラジウムの混合粉などの金属
粉末をガラス粉末とともにビークル中に分散混合して製
造したペースト状物質をスクリーン印刷法で所望の位置
に塗布したあと、５００〜８００℃で焼成した焼成体よ
りなっている。この従来型積層圧電素子では、外部電極
３の各々に接続された一対の内部電極２が積層方向にみ
て合い重なった領域（図１３中４、電界印加部という）
にある圧電セラミックスには電界が印加されるが、一対
の内部電極２が重なっていない領域（図１３中５、電界
無印加部という）には電界が印加されない。その結果電
界印加部４では変位を生じ、電界無印加部５では変位を
生じないため、この従来の積層圧電素子に電圧を印加す
ると、図１４に示すように太鼓状の変形を生じる。ま
た、この印加する電界は比較的大きいため、電界印加部
４と電界無印加部５との境界部付近に大きな応力が作用
する。この応力は積層圧電素子の積層方向の積層枚数が
多くなればなるほど著しく増大し、この従来型積層圧電
素子にパルス電圧を印加し、繰り返し駆動すると、外部
電極は大きな引っ張り応力を受け、やがては図１４に示
すように素子のセラミックスと内部電極との接合部分か
らクラック１２が入り、外部電極に断裂部１３を生じ、
積層圧電素子が破断してしまうという問題点があった。
これらの問題点を解決するために、特開平３−２７００
８５に示されるように圧電セラミックスの積層枚数を減
らした小型の圧電アクチュエータ単素子を形成し、それ
ら各単素子を中心部で接着し、スタックすることによ
り、電界無印加部の歪を緩和する方法が考案されている
が、この場合、接着工程での接着箇所の管理が困難であ
ることや、あるいは接着剤が素子断面中央部にしか存在
しないため偏荷重に極めて弱いなどの問題点がある。一
方、特開平４ー２７４３７７では、積層圧電アクチュエ
ータ単素子とスタックし、単素子間の接続には接着剤を
用いずに、可とう性を持つ外部電極のみで行う（導電性
接着剤を塗布し、硬化させる）か、あるいは図１５で示
すように銀ペースト等の通常の外部電極を形成した単素
子をスタックし、外部電極間を導電性可とう性を有する
材料１４で構造的かつ電気的に接続し、全体を一体化し
ている。2. Description of the Related Art FIG. 13 is a sectional view showing a conventional structure of a laminated piezoelectric element to which the present invention is applied. In the figure, 1 is a piezoelectric ceramic, 2 is an internal electrode, and 3 is an external electrode. The internal electrodes 2 are electrically connected to two external electrodes 3 for each layer, and the external electrodes 3 are connected to the lead wires 6 via solders 7, respectively. When a voltage is applied between the lead wires 6, an electric field is applied to the piezoelectric ceramics 1 between each pair of internal electrodes 2 to expand and contract in the stacking direction. Conventionally, the piezoelectric material used in such a laminated piezoelectric element is composed of a complex oxide having a lead-based perovskite structure such as lead zirconate titanate (PZT), and the internal electrode 2 is made of platinum or silver-palladium alloy. Has been created in. The external electrode 3 is formed by applying a paste-like substance, which is manufactured by dispersing and mixing metal powder such as gold-platinum mixed powder, silver or silver-palladium mixed powder in a vehicle together with glass powder, to a desired position by screen printing. And then fired at 500 to 800 ° C. In this conventional type laminated piezoelectric element, a region where a pair of internal electrodes 2 connected to each of the external electrodes 3 overlap with each other when viewed in the laminating direction (4 in FIG. 13, referred to as an electric field applying section).
Although an electric field is applied to the piezoelectric ceramics in (1), no electric field is applied to a region where the pair of internal electrodes 2 do not overlap (5 in FIG. 13, referred to as an electric field non-applied portion). As a result, the electric field applying section 4 is displaced and the electric field non-applying section 5 is not displaced. Therefore, when a voltage is applied to this conventional laminated piezoelectric element, a drum-shaped deformation is generated as shown in FIG. Since the applied electric field is relatively large, a large stress acts near the boundary between the electric field applying section 4 and the electric field non-applying section 5. This stress increases significantly as the number of laminated piezoelectric elements in the laminating direction increases, and when a pulse voltage is applied to this conventional laminated piezoelectric element and repeatedly driven, the external electrodes receive a large tensile stress, and eventually the As shown in FIG. 14, cracks 12 are introduced from the joint between the ceramics of the element and the internal electrode, and a fractured portion 13 is generated in the external electrode.
There is a problem that the laminated piezoelectric element is broken.
In order to solve these problems, JP-A-3-2700
As shown in FIG. 85, a method for relaxing strain in an electric field non-applied portion by forming a small piezoelectric actuator single element in which the number of laminated piezoelectric ceramics is reduced, and adhering and stacking each single element at the center portion However, in this case, there are problems that it is difficult to control the bonding location in the bonding process, and that the adhesive is only present in the central portion of the element cross section and is extremely weak against unbalanced load. On the other hand, in Japanese Unexamined Patent Publication No. 4-274377, a laminated piezoelectric actuator is stacked with a single element, and an adhesive is not used for connection between the single elements, and only flexible external electrodes are used (a conductive adhesive is applied). 15), or as shown in FIG. 15, a single element formed by forming an ordinary external electrode such as a silver paste is stacked, and a conductive and flexible material 14 is used between the external electrodes to structurally and electrically Connected and integrated as a whole.

【０００３】[0003]

【発明が解決しようとする課題】この図１５で示した素
子に電圧を印加すると個々の単素子９は図１６のように
太鼓状に変形し、側面の導電性の可とう性を有する材料
１４は伸ばされ、印加電圧をゼロに戻したとき、完全に
は元の長さに復元しにくくなる。従来の場合、この単素
子を積み重ねた後に、図１６に示すように、側面を導電
性可とう性を有する材料で接続しているため、素子に電
圧を印加し素子が伸張すると可とう性を有する材料も伸
び、逆に電圧をゼロに戻すと可とう性を有する材料も収
縮し、元に戻る。しかしながら例えばこのような素子を
交番電圧で長期に渡り駆動した場合、徐々に可とう性を
有する材料の弾性が劣化し、やがては電圧をゼロに戻し
たときに素子の長さは完全には元の状態に復元しにくく
なる。そして、やがては接続された単素子９の間に隙間
ができ、変位量の復元性を失う。可とう性樹脂が長期の
伸縮により伸びきってしまうため、電圧をゼロに戻して
も、素子は元の長さより見かけ上長くなり、単素子間に
隙間が生じてしまっているためと考えられる。さらに
は、このような導電性の可とう性を有する材料の場合、
例えば導電性接着剤を用いた場合など、接着剤には絶縁
性を持つ材料も含まれるため、導電性のフィラを用いて
も比較的電気抵抗が大きく、直流的駆動では問題を生じ
ない場合でも、交流で駆動した場合、誘電体損失により
発熱し、接着強度が劣化する。また、導電性接着剤は、
そのポットライフ管理が難しく、管理状態によって導電
率や接着強度にばらつきを生じるという問題点があっ
た。本発明の目的は、電界印加部と電界無印加部の境界
部付近に作用する応力を小さくでき、さらにその結果、
素子の伸縮による変位量の復元性に優れた信頼性の高い
積層圧電素子を提供することにある。When a voltage is applied to the element shown in FIG. 15, each single element 9 is deformed into a drum shape as shown in FIG. 16, and the conductive material 14 on the side surface is formed. Is stretched, and it becomes difficult to completely restore the original length when the applied voltage is returned to zero. In the conventional case, after stacking the single elements, as shown in FIG. 16, since the side surfaces are connected with a material having a conductive flexibility, the flexibility is obtained when a voltage is applied to the elements and the elements expand. The material that it has also expands, and conversely, when the voltage is returned to zero, the material that has flexibility also contracts and returns to its original state. However, for example, when such an element is driven at an alternating voltage for a long period of time, the elasticity of a flexible material gradually deteriorates, and when the voltage is returned to zero, the element length is not completely restored. It becomes difficult to restore to the state. Then, eventually, a gap is formed between the connected single elements 9, and the resilience of the displacement amount is lost. It is considered that since the flexible resin is stretched out due to the long-term expansion and contraction, even if the voltage is returned to zero, the element is apparently longer than the original length and a gap is formed between the single elements. Furthermore, in the case of a material having such conductive flexibility,
For example, when a conductive adhesive is used, since the adhesive also contains a material having an insulating property, even if a conductive filler is used, the electrical resistance is relatively large and even if direct current driving does not cause a problem. When driven by alternating current, heat is generated due to dielectric loss, and the adhesive strength deteriorates. In addition, the conductive adhesive is
The management of the pot life is difficult, and there is a problem in that conductivity and adhesive strength vary depending on the management state. The object of the present invention is to reduce the stress acting near the boundary between the electric field applying section and the electric field non-applying section, and as a result,
It is an object of the present invention to provide a highly reliable laminated piezoelectric element which is excellent in restoring the displacement amount due to expansion and contraction of the element.

【０００４】[0004]

【課題を解決するための手段】本発明の積層圧電素子
は、シート状に形成された圧電セラミックスと内部電極
を交互に積層し、積層方向に平行な４側面の内２側面
に、前記内部電極を一層毎に交互に露出させて、各側面
上に露出した内部電極の各々を各側面毎に外部電極によ
って接続し、該外部電極に電圧を印加することで積層方
向に伸縮する圧電アクチュエータ単素子を、複数個積層
し、ろう付け材により構造的かつ電気的に接続したこと
を特徴として構成される。本発明において「ろう付け
材」はクリームハンダペースト等のハンダ、銀ロウ材の
ような硬ろう材をいう。In the laminated piezoelectric element of the present invention, a sheet-shaped piezoelectric ceramic and an internal electrode are alternately laminated, and the internal electrode is formed on two of the four side surfaces parallel to the laminating direction. , A piezoelectric actuator single element that expands and contracts in the stacking direction by applying a voltage to the external electrodes by connecting each of the internal electrodes exposed on each side by an external electrode on each side. Are laminated and structurally and electrically connected by a brazing material. In the present invention, "brazing material" refers to solder such as cream solder paste and hard brazing material such as silver brazing material.

【０００５】[0005]

【作用】本発明の積層圧電素子は図１に示すように、従
来の積層圧電素子より相対的に積層枚数が少なく、かつ
高さの低い積層圧電アクチュエータ単素子９を複数個積
み重ねた構造をしている。本発明の積層型圧電素子では
外部電極上にろうづけ材のように、伸びにくく機械的強
度の大きなものを用いるため、各単素子間の密着性が向
上し、かつ伸張する際に各単素子間への与圧が印加さ
れ、極めて安定な変位特性が得られる。また、可とう性
を有する材料とは異なり機械的な耐久性が大きいため、
長期の使用に関しても前述のような問題はなく、変位量
の復元性が確保出来る。なお、ろうづけ材の形成によ
り、単素子を複数個積み重ねた素子の変位量は、従来例
に比べ若干減少するが、外部電極に断裂部を生じること
はない。その結果、本発明の積層圧電素子をパルス電圧
で繰り返し駆動しても破断することがなく、信頼性の高
い素子が提供できる。As shown in FIG. 1, the laminated piezoelectric element of the present invention has a structure in which a plurality of laminated piezoelectric actuator single elements 9 having a relatively smaller number of laminated layers and a lower height than the conventional laminated piezoelectric element are stacked. ing. In the multi-layer piezoelectric element of the present invention, since a material such as a brazing material that is hard to stretch and has high mechanical strength is used on the external electrode, the adhesion between the single elements is improved, and each single element is stretched. A pressurizing force is applied between them, and extremely stable displacement characteristics are obtained. Also, unlike a flexible material, it has high mechanical durability,
Even with long-term use, the above-mentioned problems do not occur and the restoration of displacement can be secured. Although the amount of displacement of the element formed by stacking a plurality of single elements is slightly reduced by the formation of the brazing material as compared with the conventional example, the external electrode does not have a fracture portion. As a result, even if the laminated piezoelectric element of the present invention is repeatedly driven by a pulse voltage, it does not break and a highly reliable element can be provided.

【０００６】[0006]

【実施例】（実施例１）図１は本発明の一実施例の積層
圧電素子の断面図である。まずジルコン酸チタン酸鉛を
主成分とする圧電材料粉末に、有機バインダーとしてＰ
ＶＢ（ポリビニルブチラール）、可塑材としてＢＰＢＧ
（ブチルフタリルブチルグリコレート）、有機溶剤とし
てトリクレンを各々添加して混合し、このスラリーをド
クターブレード法によりキャリアフィルム上に厚さ９０
μｍのシート状に形成した。これをフィルムから剥し、
図３（ａ）または（ｂ）で示すように、一端部に圧電セ
ラミックス１の表面が露出残存するようなパターンでそ
の片面に銀パラジウムあるいは白金ペーストを印刷し内
部電極２を形成した。これを順次数十枚積層して加熱圧
着する。その後、脱バインダーを行い、１１００〜１２
５０℃で１〜５時間、酸素中にて焼成して、図４に示す
ような左右両側面に内部電極２が露出した積層圧電ブロ
ックを形成する。次にこのブロックを任意の大きさに切
断し（図５に示す点線）、さらに内部電極が露出した面
に銀パラジウムあるいは金白金ペーストを塗布、焼成す
ることで外部電極３を形成した（図５−（ａ）〜
（ｄ））。以上の工程により、断面５mm×５mm、積層方
向高さ２mm、積層枚数２０枚の積層圧電アクチュエータ
単素子を得た。次に図１に示すようにこの積層圧電アク
チュエータ単素子９を、内部電極２の露出している側面
をそろえて１０個積み重ねる。この時積層方向両端面か
ら軽い荷重（〜１０ｋｇｆ）をかけ単素子９の位置決め
を行う。積み重ねられたこれら単素子９の外部電極上に
クリームハンダペースト８（液相温度１８０℃）を塗布
した後、２１０℃１０分間の条件で溶融させ、素子長２
０mmの積層圧電素子を作製した。なお、クリームハンダ
は外部電極とのぬれ性を利用することで、ハンダが溶融
した際に外部電極形成面上のみに選択的に塗布できる。
さらにペースト量、加熱温度、加熱時間を最適化するこ
とで各単素子の外部電極間に形成される隙間に、軽度な
ハンダブリッジを生じさせることが出来、その結果積層
方向全面に電気的かつ機械的に接合されたハンダ盛り部
が一様な厚みで塗布できる。この素子の側面のろうづけ
材上に、テフロン被覆のリード線６をハンダペーストと
同様の組成からなるハンダ７でハンダ付けし、外部より
電圧を印加することで、素子が伸張するように構成し
た。上記の積層圧電素子に１５０Ｖ、０．５Ｈｚの交番
電圧を１０，０００回印加し、その変位量の初期特性と
試験後の特性を光学式の接触型変位計で測定した。その
結果を図６（ａ）（ｂ）に示す。同時に従来の図１５に
示した素子も作製し、同様の測定を行った。但し、側面
の接続用可とう性を有する材料として、導電性接着剤
（エポキシ−銀フィラ）を用いた。この結果、従来素子
は初期特性に比較して試験後の変位量が減少しているの
がわかる。また、試験後の変位特性では、およそ０〜１
５Ｖの印加電圧の範囲で素子の変位が得られていない。
これは可とう性樹脂が長期の伸縮により伸びきってしま
うため、電圧をゼロに戻しても、素子は元の長さより見
かけ上長くなり、単素子間に隙間が生じてしまっている
ためと考えられる。従って、０〜１５Ｖの範囲ではその
空隙が素子の変位により補われるまで、実質的な変位量
が減少するのである。一方、本実施例素子は従来素子に
比べて発生変位量が若干少ないものの、初期特性ならび
に試験後の特性いずれにおいても安定した変位特性が得
られていることがわかる。本実施例では単素子９の積み
重ね個数を２０個とし、全長２０mmの単素子積層アクチ
ュエータを作製したが、単素子９の個数を変えることに
より、全長の短いあるいは極めて長尺の積層アクチュエ
ータを容易に作製できる。また、単素子のサイズを上記
のサイズにしたが、セラミックスシートの積層枚数をさ
らに少なくし、外部電極に電圧を印加した際に、各シー
ト間にクラックやデラミネーション（層間剥離）等が発
生しにくい大きさにすれば、より信頼性の高い素子とな
る。なお、外部電極３の形状を図５（ｃ）に示すように
幅広にすることにより、電気的接続の確実性、機械的強
度および変位量の復元性等が向上する。さらに、図５
（ｄ）に示すように外部電極を単素子の上下端近傍まで
延設することにより、単素子間の接続の信頼性も向上す
る。 （実施例２）本実施例では上記実施例１と同様な方法で
アクチュエータ単素子を作製し、その単素子を下記の方
法で接続した。図２は、本実施例の模式的断面図であ
る。まず第１の実施例同様に単素子９を複数個積み重
ね、積層方向両端面から軽い荷重（〜１０ｋｇｆ）をか
け単素子９の位置決めを行う。次に、積み重ねられたこ
れら単素子９の両端部に位置する単素子９の外部電極上
に太さ約０.２mmの導電線（芯材：Ｃｕ、メッキ：Ｎ
ｉ）１１を適当な張力を与えて高温ハンダ（液相温度２
４２℃）７’でハンダ付けする。さらに上記の工程によ
り得られた素子の外部電極３上に液相温度１８０℃のク
リームハンダ８を導電線１１が隠れる程度に塗布し、お
よそ２１０℃の雰囲気中に１０分間入れ、加熱溶融させ
冷却する。これにより、積層圧電単素子はそれぞれ機械
的、かつ電気的に接続され、断面５mm角、積層方向２０
mmの積層圧電アクチュエータが得られた。第２の実施例
の場合、第１の実施例に比較して、クリームハンダ内に
設けられた導電線が、補強材の役を担うため、抗折力や
引っ張り力に対する機械的強度がさらに向上すると同時
に、リード線とハンダのぬれ性の効果により各単素子外
部電極の間隙にもハンダが浸入し、積層方向全長に渡っ
て、ハンダ層が形成される。なお本実施例では導電線を
高温ハンダ７’により最初に固定しているが、この固定
方法として、超音波ボンディングやレーザー溶接等のハ
ンダ以外の方法でもよく、またクリームハンダ８に導電
線が機械的に接続されていれば、例えば、クリームハン
ダペーストを塗布した中に、導電線を埋め込み溶融させ
る方法などで作製してもよい。なお、本実施例において
は積層圧電単素子間の接続にクリームハンダを用いた
が、その他に例えば糸ハンダやプリフォームハンダ等
の、外部電極の焼き付け温度以下の液相温度を持つ電気
的に導電性を持つろうづけ材であれば、これに限定され
ることはない。本実施例２の素子においても実施例１と
同じように電圧−変位量特性を測定したが、実施例１同
様に変位量の復元性が得られた。 （実施例３）第１の実施例で得られたセラミックスシー
ト上に、図７に示すような電極パターンの銀パラジウム
あるいは白金ペーストを印刷し、内部電極２’を形成し
た。これを順次積層し、図８（ａ）に示すような左右両
側面に内部電極端２が露出した積層圧電単素子を得た。
この素子の寸法は他の実施例同様、断面５mm×５mm、積
層方向長さ２mm、積層枚数２０枚である。次にこの単素
子を実施例２と同様の方法で接続し、積層圧電素子を得
た。この素子の場合、素子側面に内部電極がほとんど露
出していないため、側面での水分の付着による絶縁性の
劣化を防ぐことができる。電圧−変位特性も実施例１お
よび２同様に復元性が得られた。さらに、本素子の耐湿
性に関する性能を確かめるために、同素子を２０ヶ試作
し、８５℃，９０％ＲＨの雰囲気に入れ、１５０Ｖ／２
０Ｈｚの矩型波で駆動し、その不良率を測定した。その
結果を、図９に示す。比較のため、従来素子の試験も行
ったが、本実施例素子の耐湿性の向上していることが分
かる。 （実施例４）第３の実施例で用いた積層圧電単素子９を
複数個積み重ね、軽いプリ荷重を印加したままで、図１
０のように外部電極３上に導電線１１の両端部を超音波
ボンディング１５により軽く固定する。この状態で、素
子にフラックスを塗布し、さらにハンダ槽内におよそ２
２０℃で溶融されたろう付け材（液相温度１８２℃）の
中におよそ１０秒程度浸し、素子を取り出す。その結
果、図１１のように導電線１１を中心にろう付け材８が
ブリッジを起こし、各単素子間が接続された素子が得ら
れた。最後に第５の実施例について説明する。上記第
３、第４の実施例で用いた積層圧電単素子９を同様に複
数個積み重ね、軽い荷重を印加したままで、外部電極３
上に薄くろう付け材８（液相温度１８２℃）を塗布し、
その上に導電線（芯材：Ｃｕ、メッキ：Ｎｉ）１１を乗
せる。この際に、導電線１１は塗布したろう付け材８の
粘性あるいは付着性により、仮固定されるが、ろう付け
材８が加熱され、軟化した際の位置ズレを考慮するので
あれば、ろう付け材８を塗布する前に、導電線１１の端
部を第２の実施例、あるい第４の実施例のように固定し
ても構わない。このようにして得られた積層圧電素子を
加熱し、ろう付け材８を溶融固着させると、充分なろう
付け材８の量がないため、図１２のように、積層圧電単
素子９間にろう付け材８がブリッジを生じず、導電線１
１が各単素子間の外部電極３を機械的、電気的に接続す
るような形で積層圧電素子が形成された。この素子につ
いても同様の変位特性を確認したが、前述の実施例と同
様の特性を得ることが出来た。これは、ろう付け材８に
よりテンションを与えられた状態で導電線１１が各単素
子９間に固定され、導電線１１の持つ弾性により素子に
復元性が与えられたためと考えられる。また、導電線１
１を単にハンダ付け（一般的なハンダ鏝を用いて行うも
の）等で各単素子９間に固定したのとは異なり、比較的
広い面積で外部電極にリード線が固定されているため、
単素子間の固定強度も大きくなる。したがって、本実施
例では変位の復元性を得る手段として導電線１１を用い
たが、弾性を有し、かつ電気的に導通する金属であれば
導電線と限らず、たとえば金属薄板や或いは金属箔のよ
うなものでも同様の結果が得られる。なお、第３、第
４、第５の実施例では図７に示す電極パターンの素子を
作製したが、作業能率を上げるため、上記電極パターン
が多数個同時に印刷された大型寸法のシートを作製し、
熱圧着後あるいは焼結後に５mm×５mmになるよう切断し
ても同様の効果が得られる。なお、図８（ｂ）に示すよ
うに通常の外部電極３の他、機械的強度向上用電極３’
を形成して、単素子の接続を４側面で行えば変位量の復
元性がさらに向上する。以上の実施例で作製した素子を
エポキシ系あるいはシリコン系等の樹脂でコーティング
すれば、機械的強度がさらに向上し、かつ感電防止、ほ
こり水分等の付着防止に効果がある。EXAMPLE 1 FIG. 1 is a sectional view of a laminated piezoelectric element according to an example of the present invention. First, a piezoelectric material powder containing lead zirconate titanate as a main component was mixed with P as an organic binder.
VB (polyvinyl butyral), BPBG as a plastic material
(Butylphthalyl butyl glycolate) and trichlene as an organic solvent are added and mixed, and this slurry is formed on a carrier film with a thickness of 90 by a doctor blade method.
It was formed in a sheet shape of μm. Peel it off the film,
As shown in FIG. 3A or FIG. 3B, silver palladium or platinum paste was printed on one surface of the piezoelectric ceramic 1 in a pattern such that the surface of the piezoelectric ceramic 1 was exposed and remained at one end to form the internal electrode 2. Several dozen sheets of this are sequentially laminated and thermocompression bonded. After that, debinding is performed and 1100 to 12
It is fired in oxygen at 50 ° C. for 1 to 5 hours to form a laminated piezoelectric block in which the internal electrodes 2 are exposed on both left and right side surfaces as shown in FIG. Next, this block was cut to an arbitrary size (dotted line in FIG. 5), and silver palladium or gold platinum paste was applied to the surface where the internal electrodes were exposed and baked to form the external electrodes 3 (FIG. 5). -(A) ~
(D)). Through the above steps, a laminated piezoelectric actuator single element having a cross section of 5 mm × 5 mm, a height in the laminating direction of 2 mm, and a laminated number of 20 was obtained. Next, as shown in FIG. 1, ten stacked piezoelectric actuator single elements 9 are stacked with the exposed side surfaces of the internal electrodes 2 aligned. At this time, a light load (-10 kgf) is applied from both end faces in the stacking direction to position the single element 9. After applying the cream solder paste 8 (liquidus temperature 180 ° C.) on the external electrodes of the stacked single elements 9 and melting them under the condition of 210 ° C. for 10 minutes, the element length 2
A 0 mm laminated piezoelectric element was produced. By utilizing the wettability with the external electrode, the cream solder can be selectively applied only on the external electrode formation surface when the solder melts.
Furthermore, by optimizing the amount of paste, heating temperature, and heating time, a slight solder bridge can be created in the gap formed between the external electrodes of each single element, resulting in electrical and mechanical The soldered portion that is mechanically joined can be applied with a uniform thickness. On the brazing material on the side surface of this element, the lead wire 6 coated with Teflon was soldered with the solder 7 having the same composition as the solder paste, and the element was expanded by applying a voltage from the outside. . An alternating voltage of 150 V and 0.5 Hz was applied 10,000 times to the above-mentioned laminated piezoelectric element, and the initial characteristic of the displacement amount and the characteristic after the test were measured by an optical contact displacement meter. The results are shown in FIGS. 6 (a) and 6 (b). At the same time, the conventional device shown in FIG. 15 was prepared and the same measurement was performed. However, a conductive adhesive (epoxy-silver filler) was used as the material having flexibility on the side surface for connection. As a result, it can be seen that the conventional element has a smaller displacement amount after the test as compared with the initial characteristics. The displacement characteristics after the test are about 0 to 1
The displacement of the element is not obtained within the range of applied voltage of 5V.
This is because the flexible resin stretches out due to long-term expansion and contraction, so even if the voltage is returned to zero, the element is apparently longer than the original length and a gap is created between the single elements. To be Therefore, in the range of 0 to 15 V, the substantial displacement amount decreases until the gap is compensated by the displacement of the element. On the other hand, it can be seen that although the element of this example slightly generated a smaller amount of displacement than the conventional element, stable displacement characteristics were obtained in both the initial characteristics and the characteristics after the test. In the present embodiment, the number of stacked single elements 9 was set to 20, and a single element laminated actuator having a total length of 20 mm was manufactured. However, by changing the number of single elements 9, a laminated actuator having a short total length or an extremely long length can be easily manufactured. Can be made. Further, although the size of the single element is set to the above size, when the number of laminated ceramic sheets is further reduced and a voltage is applied to the external electrodes, cracks or delamination (delamination) occur between the sheets. If the size is made difficult, the device becomes more reliable. By widening the shape of the external electrode 3 as shown in FIG. 5C, the reliability of electrical connection, the mechanical strength, and the resilience of the displacement amount are improved. Furthermore, FIG.
By extending the external electrodes to near the upper and lower ends of the single element as shown in (d), the reliability of the connection between the single elements is also improved. (Example 2) In this example, an actuator single element was manufactured by the same method as in Example 1 and the single element was connected by the following method. FIG. 2 is a schematic sectional view of this embodiment. First, similarly to the first embodiment, a plurality of single elements 9 are stacked, and a light load (-10 kgf) is applied from both end faces in the stacking direction to position the single elements 9. Then, a conductive wire (core material: Cu, plating: N) having a thickness of about 0.2 mm is formed on the external electrodes of the single elements 9 located at both ends of the stacked single elements 9.
i) Apply high tension to 11 and apply high temperature solder (liquidus temperature 2
Solder at 42 ° C) 7 '. Further, a cream solder 8 having a liquidus temperature of 180 ° C. is applied on the external electrode 3 of the device obtained by the above process to such an extent that the conductive wire 11 is hidden, placed in an atmosphere of approximately 210 ° C. for 10 minutes, heated and melted, and cooled. To do. As a result, the laminated piezoelectric single elements are mechanically and electrically connected to each other, and the cross section is 5 mm square and the lamination direction is 20 mm.
A mm piezoelectric actuator was obtained. In the case of the second embodiment, as compared with the first embodiment, the conductive wire provided in the cream solder serves as a reinforcing material, so the mechanical strength against bending strength and tensile strength is further improved. At the same time, due to the effect of the wettability of the lead wire and the solder, the solder penetrates into the gaps between the individual element external electrodes, and the solder layer is formed over the entire length in the stacking direction. In this embodiment, the conductive wire is first fixed by the high temperature solder 7 ', but as the fixing method, a method other than solder such as ultrasonic bonding or laser welding may be used. If they are electrically connected, for example, a method may be used in which a conductive wire is embedded and melted while applying a cream solder paste. In this embodiment, cream solder was used for connection between the laminated piezoelectric single elements, but in addition, electrically conductive material having a liquidus temperature equal to or lower than the baking temperature of the external electrode, such as thread solder or preform solder, is used. The brazing material having the property is not limited to this. The voltage-displacement amount characteristic of the element of the present Example 2 was measured in the same manner as in Example 1, but the restoration amount of displacement amount was obtained as in Example 1. Example 3 On the ceramic sheet obtained in the first example, silver palladium or platinum paste having an electrode pattern as shown in FIG. 7 was printed to form an internal electrode 2 '. These were sequentially laminated to obtain a laminated piezoelectric single element in which the internal electrode ends 2 were exposed on both left and right side surfaces as shown in FIG.
Similar to the other embodiments, the size of this element is 5 mm × 5 mm in cross section, 2 mm in length in the stacking direction, and 20 sheets are stacked. Next, this single element was connected in the same manner as in Example 2 to obtain a laminated piezoelectric element. In the case of this element, since the internal electrodes are barely exposed on the side surface of the element, it is possible to prevent the deterioration of the insulating property due to the adhesion of moisture on the side surface. As for the voltage-displacement characteristic, the restorability was obtained as in Examples 1 and 2. Further, in order to confirm the performance of this element with respect to moisture resistance, 20 of the element were made as prototypes and placed in an atmosphere of 85 ° C. and 90% RH, and 150 V / 2.
The defect rate was measured by driving with a rectangular wave of 0 Hz. The result is shown in FIG. For comparison, a conventional device was also tested, but it can be seen that the moisture resistance of the device of this example is improved. (Embodiment 4) A plurality of laminated piezoelectric single elements 9 used in the third embodiment are stacked and a light pre-load is applied to the laminated piezoelectric single element 9 as shown in FIG.
As shown in 0, both ends of the conductive wire 11 are lightly fixed on the external electrode 3 by ultrasonic bonding 15. In this state, apply flux to the element and add about 2 to the solder bath.
The element is taken out by immersing it in a brazing material (liquidus temperature 182 ° C.) melted at 20 ° C. for about 10 seconds. As a result, the brazing material 8 caused a bridge around the conductive wire 11 as shown in FIG. 11, and an element in which the individual elements were connected to each other was obtained. Finally, the fifth embodiment will be described. Similarly, a plurality of laminated piezoelectric single elements 9 used in the third and fourth embodiments are stacked, and the external electrode 3 is applied with a light load applied.
Apply a thin brazing material 8 (liquidus temperature 182 ° C) on top,
A conductive wire (core material: Cu, plating: Ni) 11 is placed on it. At this time, the conductive wire 11 is temporarily fixed due to the viscosity or adhesiveness of the applied brazing material 8. However, if the positional deviation when the brazing material 8 is heated and softened is taken into consideration, brazing is performed. Before applying the material 8, the end of the conductive wire 11 may be fixed as in the second embodiment or the fourth embodiment. When the thus obtained laminated piezoelectric element is heated and the brazing material 8 is melted and fixed, the brazing material 8 does not have a sufficient amount. Therefore, as shown in FIG. The attachment material 8 does not form a bridge, and the conductive wire 1
The laminated piezoelectric element was formed in such a manner that 1 connects mechanically and electrically the external electrodes 3 between the individual elements. The same displacement characteristic was confirmed for this element, but the same characteristic as that of the above-mentioned embodiment could be obtained. It is considered that this is because the conductive wire 11 was fixed between the single elements 9 in a state where tension was applied by the brazing material 8 and the resilience was given to the element by the elasticity of the conductive wire 11. Also, the conductive wire 1
1 is fixed between the single elements 9 simply by soldering (using a general soldering iron) or the like, the lead wires are fixed to the external electrodes in a relatively large area.
The fixing strength between the single elements also increases. Therefore, in this embodiment, the conductive wire 11 is used as a means for obtaining the displacement restoration property, but the metal is not limited to the conductive wire as long as it has elasticity and is electrically conductive. For example, a metal thin plate or a metal foil. Similar results can be obtained with In addition, in the third, fourth and fifth examples, the element having the electrode pattern shown in FIG. 7 was produced. ,
Similar effects can be obtained by cutting into 5 mm × 5 mm after thermocompression bonding or sintering. As shown in FIG. 8B, in addition to the normal external electrode 3, a mechanical strength improving electrode 3 '
If the single element is connected on the four side surfaces by forming, the restoration of the displacement amount is further improved. Coating the elements manufactured in the above examples with an epoxy-based or silicon-based resin further improves the mechanical strength, and is effective in preventing electric shock and adhesion of dust and moisture.

【０００７】[0007]

【発明の効果】以上説明したように本発明は、積層圧電
アクチュエータを複数の積層圧電アクチュエータ単素子
に分割し、これらを導電性ろう付け材で接続した構造を
しているため、単素子単体での高さは相対的に低い。そ
の結果電界印加部と電界無印加部の境界部付近に作用す
る応力が小さく、クラックやデラミネーションの発生し
ない長尺形状の積層圧電アクチュエータが容易に作製で
きる。さらにろう付け材により単素子が密着させられて
いるので、変位量の復元性にも優れる。またろうづけ材
の管理や作業ばらつきも小さいため、特性の再現性がよ
く、かつ作業性に優れた信頼性の高い積層圧電素子を提
供できる。As described above, the present invention has a structure in which a laminated piezoelectric actuator is divided into a plurality of laminated piezoelectric actuator single elements, and these are connected by a conductive brazing material. Is relatively low in height. As a result, it is possible to easily fabricate a long-shaped laminated piezoelectric actuator in which the stress acting near the boundary between the electric field applying portion and the electric field non-applying portion is small and cracks and delamination do not occur. Further, since the single element is brought into close contact with the brazing material, the restoration of the displacement amount is excellent. Further, since the management of the brazing material and the variation in the work are small, it is possible to provide a highly reliable laminated piezoelectric element having good reproducibility of characteristics and excellent workability.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の一実施例の模式的断面図である。FIG. 1 is a schematic sectional view of an embodiment of the present invention.

【図２】本発明の第２の実施例に関する模式的断面図で
ある。FIG. 2 is a schematic sectional view of a second embodiment of the present invention.

【図３】本発明の実施例に関する積層圧電単素子製造上
のグリーンシートの外観を示す図である。FIG. 3 is a diagram showing an appearance of a green sheet for manufacturing a laminated piezoelectric single element according to an example of the present invention.

【図４】本発明の実施例に関する積層圧電単素子製造上
の圧電ブロックの外観図である。FIG. 4 is an external view of a piezoelectric block for manufacturing a laminated piezoelectric single element according to an example of the present invention.

【図５】図４における圧電ブロックの切断部を示す外観
図である。5 is an external view showing a cut portion of the piezoelectric block in FIG.

【図６】本発明の第１の実施例に関する電圧−変位特性FIG. 6 is a voltage-displacement characteristic relating to the first example of the present invention.

【図７】本発明の第３の実施例に関する積層圧電素子製
造上のグリーンシートの外観FIG. 7 is an external view of a green sheet for manufacturing a laminated piezoelectric element according to a third embodiment of the present invention.

【図８】本発明の第３の実施例に関する積層圧電単素子
の模式的外観図である。FIG. 8 is a schematic external view of a laminated piezoelectric single element according to a third embodiment of the present invention.

【図９】本発明の実施例３および従来例の耐湿性繰り返
し寿命試験を示す図である。FIG. 9 is a diagram showing a moisture resistance repeated life test of Example 3 of the present invention and a conventional example.

【図１０】本発明の第４の実施例に関する積層圧電素子
に導電線をボンディングした断面図である。FIG. 10 is a cross-sectional view in which a conductive wire is bonded to the laminated piezoelectric element according to the fourth embodiment of the present invention.

【図１１】本発明の第４の実施例を示す模式的断面図で
ある。FIG. 11 is a schematic sectional view showing a fourth embodiment of the present invention.

【図１２】本発明の第５の実施例を示す模式的断面図で
ある。FIG. 12 is a schematic cross-sectional view showing a fifth embodiment of the present invention.

【図１３】従来の圧電素子の一例を示す模式的断面図で
ある。FIG. 13 is a schematic cross-sectional view showing an example of a conventional piezoelectric element.

【図１４】従来の積層圧電素子に電圧を印加した際の変
形を示す模式的断面図である。FIG. 14 is a schematic cross-sectional view showing deformation when a voltage is applied to a conventional laminated piezoelectric element.

【図１５】従来の可とう性剤により接続された圧電素子
の一例を示す模式的断面図である。FIG. 15 is a schematic cross-sectional view showing an example of a piezoelectric element connected by a conventional flexible agent.

【図１６】従来の可とう性剤により接続された圧電素子
に電圧を印加した際の素子の形状変化を示す図である。FIG. 16 is a diagram showing a change in shape of a conventional piezoelectric element connected to the piezoelectric element when a voltage is applied to the element.

【符号の説明】[Explanation of symbols]

１ 圧電セラミック、２ 内部電極 、３ 外部電極、
４ 電界印加部、５電界無印加部、６ リード線、７
ハンダ、８ ろう付け材、９ 積層圧電単素子、１０
圧電ブロックの切断線、１１ 導電線、１２ クラッ
ク、１３ 外部電極の断裂部、１４ 導電性の可とう性
を有する材料、１５ 超音波ボンディング部1 piezoelectric ceramic, 2 internal electrode, 3 external electrode,
4 electric field applying section, 5 electric field non-applying section, 6 lead wire, 7
Solder, 8 brazing material, 9 laminated piezoelectric single element, 10
Piezoelectric block cutting lines, 11 conductive lines, 12 cracks, 13 external electrode tearing parts, 14 conductive flexible material, 15 ultrasonic bonding parts

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 シート状に形成された圧電セラミックス
と内部電極を交互に積層し、積層方向に平行な４側面の
うち少なくとも１側面に、前記内部電極を一層毎に交互
に露出させて、各側面上に露出した内部電極の各々を各
側面毎に外部電極によって接続し、該外部電極に電圧を
印加することで積層方向に伸縮する圧電アクチュエータ
単素子を、複数個積層し、ろう付け材により構造的かつ
電気的に接続したことを特徴とする積層圧電素子。1. Piezoelectric ceramics and internal electrodes formed in a sheet shape are alternately laminated, and the internal electrodes are alternately exposed for each layer on at least one side surface out of four side surfaces parallel to the laminating direction. Each of the internal electrodes exposed on the side surface is connected by an external electrode for each side surface, and a plurality of piezoelectric actuator single elements that expand and contract in the stacking direction by applying a voltage to the external electrode are stacked and brazed. A laminated piezoelectric element characterized by being structurally and electrically connected. 【請求項２】 前記ろう付け材の液相温度が、該外部電
極の焼成温度よりも低いことを特徴とする請求項１記載
の積層圧電素子。2. The laminated piezoelectric element according to claim 1, wherein a liquidus temperature of the brazing material is lower than a firing temperature of the external electrode.