JP4468510B2 - Piezoelectric element and multilayer piezoelectric actuator - Google Patents

Description

【００２８】
また、印加電圧Ｖ_Ｔは、各誘電体中の電界Ｅ_ｘ，Ｅ_ｐにそれぞれの膜厚ｄ_ｘ，ｄ_ｐを乗じて和をとった値となる（（２）式）。
【００２９】
【数２】

【００３０】
そこで、圧電素子の比誘電率ε_ｐのＫ_ε倍の比誘電率ε_ｘなる低誘電率層を用いたとき、圧電素子に全電圧Ｖ_ＴのＫ_Ｖ倍の電圧が加わるとすると、簡単な計算により、両者は次の（３）式の関係にあることがわかる。
【００３１】
【数３】

【００３２】
ここで、本発明の目的は、積層型圧電アクチュエータにおいて、圧電素子の内部電極層周辺から余白にかけての領域で、圧電素子に印加される電圧の降下が急峻になるのを抑制するものである。
従って、内部電極層４の下部に低誘電率層５が設置された部位の圧電素子に印加される電圧は、全電圧Ｖ_Ｔ０．２５〜０．７５であることが好ましいといえる。
【００３３】
また、上述した圧電素子の好適厚さ０．２〜０．６ｍｍと低誘電率層の厚さ５〜２０μｍを前提として、上記式（３）で計算すると、低誘電率層の比誘電率ε_ｘは、圧電素子の比誘電率ε_ｐの０．５〜６０％の範囲にあることが好ましい。更に、圧電素子としてＰＺＴセラミックスを使用する場合は、その比誘電率は通常２０００〜５０００の範囲にあるので、上述の如く、低誘電率層の比誘電率ε_ｘは、１０〜２０００の範囲にあることが好ましい。
【００３４】
上記誘電率層は、ε_ｘ≦１００の範囲ではＴｉＯ系の微粉末を、ε_ｘ≦２０００の範囲ではＢａＴｉＯ_３系の微粉末を、ガラスフリットに適切な混合比に混合して印刷焼成することにより、作製可能である。
また、誘電体粉末を混合するガラスフリットは、ＰｂＯ−ＳｉＯ_２−Ｂ_２Ｏ_３を主成分とし、軟化点等の耐熱性が６００℃以上のものが好ましい。６００℃未満のものでは、後述するように、上層に内部電極層を印刷焼成する際に、焼成温度（３００〜６００℃）で溶融してしまうからである。
【００３５】
なお、内部電極層の直径は、その周辺部分が低誘電率層上に位置するように、低誘電率層がなす円弧の外径よりも小さく設定されることが好ましい。
内部電極層に使用する導電性接着層用ペーストは、Ａｇ等の金属粉末とガラス粉末を含有し、上記金属板が溶融しない温度（３００〜６００℃程度）でガラス粉末が溶融するものであることが好ましく、該ガラス粉末としてはＺｎＯ−ＳｉＯ_２−Ｂ_２Ｏ_３等が用いられるが、これに限定されるものではない。
【００３６】
次に、本実施形態の積層型圧電アクチュエータの製造方法の一例について説明する。
まず、圧電アクチュエータ用材料として適している円板状のＰＺＴ系焼結体の両面をラッピング研磨して、直径１４ｍｍ、厚さ０．３ｍｍの圧電セラミック板（圧電素子基板１）を製造する。
次に、粒径３μｍ以下のＢａＴｉＯ_３粉末をＰｂＯ、ＺｎＯ、ＳｉＯ_２及びＢ_２Ｏ_３を主成分とするガラス粉末中に、体積含有率４０％となるように混合して、適切な樹脂バインダ溶剤を添加してペーストを作製し、圧電素子基板１の表面に図３（ｂ）に示す形状を７５０℃で印刷・焼成して、厚さ１０μｍの低誘電率層５を形成する。
【００３７】
低誘電率層は、円弧状の形状とし、外径を１３ｍｍ、内径を１１ｍｍ、２個所の円弧状パターンの間隔Ｌを３ｍｍとして、圧電素子基板１のそれぞれの面（表裏面）で９０°回転変位した配置とする（図３（ｂ）、（ｃ）及び（ｄ）参照）。
更に、該圧電素子基板１の両面に、Ａｇ等の金属粉末とガラス粉末を含有するペーストを印刷乾燥して直径１２ｍｍ、厚さ１０μｍの厚膜とし、５２０℃で焼成して内部電極層４を作製する（図３（ｅ）参照）。また、この際、内部電極層４の周辺部幅０．５ｍｍの領域が、低誘電率層５に重なるようにする。
【００３８】
一方、厚さ３０μｍのＡｇ薄板を、２個所に幅２×長さ５．５ｍｍの接続用突起部７を有する直径９ｍｍの円板状に打ち抜き、図３（ａ）に示すような金属板２を製造する。
得られた金属板２を、低誘電率層５ａと５ｂの間隔Ｌに接続用突起７が位置するように、圧電素子基板１上に重ねる（図３（ｅ）参照）。
【００３９】
この圧電素子基板１と金属板２の組み合わせを９９枚用い、図１と図２に示すように、圧電素子基板１と金属板２を交互に積層して、金属板２の接続用突起７が一層おきに同じ位置（真上又は真下）に来るように、９０゜ずつずらして配置された積層体３を組み上げる（図１及び図２参照）。
また、積層体３の上下端部（頂面及び底面）には、内部電極層４の形成に使用したＡｇペーストを予め印刷焼成した不活性板１０を配設する（図１（ａ）参照）。
次いで、上述のようにして組み上げた積層体３を、適切な荷重で加圧しながら、５２０℃、３０分で内部電極層を再溶融させ接合する。
【００４０】
次に、積層体３の外周側面に突出した接続用突起７を積層体の軸方向（積層方向）に折り曲げ、一層おいた隣の接続用突起部７に半田で接合して、外部電極８を形成する（図２参照）。
このように、積層体３の外周側面の４個所に外部電極８を形成することにより、積層体を構成する１００枚の金属板２は、外部電極８ａと８ａ’により電気的に接続された５０枚の金属板２と、外部電極８ｂと８ｂ’により電気的に接続され、上記金属板５０枚とは圧電素子１を隔てて絶縁されている他方の５０枚の金属板２との２組に分けられる（図１（ａ））。
【００４１】
更に、外部電極８ａと８ｂの上にリード線９ａと９ｂを半田により接合し、積層体３の外周側面をシリコーン樹脂で被覆し、脱泡処理を行い、外部電極と積層体側面の間隙に樹脂を完全に充填させた後、硬化させる。そして、積層体３の上下単板（不活性板１０）を研削加工することにより、上下面の平行度を調整する。
しかる後、かかる積層体３を８０℃のシリコーンオイル中に浸漬し、直流電源の正極にリード線９ａを、負極に９ｂを接続し、圧電素子基板１に３ｋＶ／ｍｍの電界を３０分間印加して圧電素子基板１を分極処理し、本実施形態の積層型圧電アクチュエータを得る。
【００４２】
【実施例】
（実施例）
上述の製造工程により得られた積層型圧電アクチュエータに、分極時の電界と同方向に５００Ｖの直流電圧を印加したところ、４０μｍ以上の変位が得られ、アクチュエータとして正常に機能することを確認した。
更に、本実施例の積層型圧電アクチュエータ１０個を、湿度９５％の環境で、０Ｖから５００Ｖの交流電界を５０Ｈｚの周波数で印加し、１×１０^８回連続駆動したが、圧電素子に亀裂は発生せず、全て正常に動作した。
【００４３】
（比較例）
低誘電率層５を設けず、圧電素子基板１の表面に内部電極層４を直接作製した以外は、すべて実施例と同じ構成を採用して本例の積層型圧電アクチュエータを製造した。
得られたアクチュエータに、３ｋＶ／ｍｍの電界を３０分間印加して分極した結果、５００Ｖの直流電圧により４０μｍの変位が得られた。
しかし、実施例と同様の条件下で、０Ｖから５００Ｖの交流電界を５０Ｈｚの周波数で印加して１×１０^７回連続駆動した結果、１０個のうち７個に短絡が発生して駆動しなくなった。
また、短絡したアクチュエータの積層体側面を観察した結果、亀裂が発生している圧電素子が認められ、この部位を切断して観察したところ、内部電極層の周囲に亀裂が発生し、破断面で短絡が発生していた。
【００４４】
以上、本発明を好適実施形態及び実施例により詳細に説明したが、本発明はこれらに限定されるものではなく、本発明の要旨の範囲内において種々の変形実施が可能である。
例えば、金属板の接続用突起７は２本のみならず、３本以上とすることが可能であり、これに対応して、低誘電率層の間隔Ｌの個数を調整すればよい。
また、積層体３の形状は円柱状に限定されるものではなく、多角柱状であってもよく、かかる形状に対応して、低誘電率層のパターン形状や間隔Ｌの個数を調整すればよい。
【００４５】
【発明の効果】
以上説明したように、本発明によれば、圧電素子基板よりも比誘電率の低い低誘電率層が、圧電素子基板と内部電極層の周辺部との間に介在するように、低誘電率層を圧電素子基板上に形成することとしたため、特異な形状の内部電極を用いることなく、圧電素子基板の内部電極周囲部位に印加される電界が、内部電極周辺部で連続的に小さくなり、繰り返し駆動させても圧電素子基板に亀裂が発生しない、信頼性の高い圧電素子及びこれを用いた積層型圧電アクチュエータを提供することができる。
【００４６】
即ち、本発明の積層型圧電アクチュエータは、印刷内部電極層の周辺部と圧電素子基板との間に、圧電素子基板よりも比誘電率の低い低誘電率層が介在するように、低誘電率層を圧電素子基板上に形成したことにより、低誘電率層下部の圧電素子に印加される電界が緩和され、圧電素子の内部電極層周辺部から周囲の余白部へかけての印加電界の変化が穏やかになるため、特異な形状の内部電極層を採用することなく、従来圧電素子に亀裂が発生していたような駆動電圧で長時間駆動させても、圧電素子の内部電極層周囲部に亀裂が発生することのない、信頼性が高い積層型圧電アクチュエータが得られる。
【図面の簡単な説明】
【図１】 本発明の積層型圧電アクチュエータの一実施例を示す斜視図及び上部端面図である。
【図２】図１に示す積層型圧電アクチュエータの部位Ａを軸方向に切断した部分断面図である。
【図３】 図１に示す積層型圧電アクチュエータに使用される部品の形状を示す平面図である。
【図４】比誘電率ε_ｐの誘電体を比誘電率ε_ｘなる誘電体で挟んだ積層構造の誘電体において、各誘電体に印加される電界の分布を示す説明図である。
【図５】従来の積層型圧電アクチュエータの一例を示す斜視図である。
【図６】従来の積層型圧電アクチュエータを構成する圧電素子に電圧が印加された状態を示す横断面図及び縦断面図であって、内部電極層の形状及び印加電圧により電歪が発生した状態を示す。
【図７】図６に示す内部電極層の部位Ａの従来例を示す部分平面図である。
【符号の説明】
１ 圧電素子基板
２ 金属板
３ 積層体
４ 内部電極層
５ 低誘電率層
６ 円板部
７ 接続用突起部
８ａ、８ａ’、８ｂ、８ｂ’ 外部電極
９ａ、９ｂ リード線
１０ 不活性板
１０１ 圧電素子基板
１０２ 金属板
１０３ 舌状片部
１０４ 帯状金属板
１０５ 内部電極層
１０６ 亀裂
Ａ 積層型圧電アクチュエータの部位[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric element and a laminated piezoelectric actuator using the piezoelectric element, and more particularly to a laminated piezoelectric actuator using a longitudinal effect, such as a fuel injection valve of an automobile engine, an optical device, etc. The present invention relates to a laminated piezoelectric actuator used as an actuator for a precision positioning device and a vibration isolation mount for a vibration isolation table.
[0002]
[Prior art]
Conventionally, in order to obtain a large amount of displacement by applying the electrostrictive effect, a structure of a stacked piezoelectric actuator in which piezoelectric ceramic plates and internal electrode layers are alternately stacked has been proposed. A conventional example of such a multilayer piezoelectric actuator is disclosed in Japanese Patent Application Laid-Open No. 62-299093, and its configuration is shown in FIG.
[0003]
In FIG. 5, this multilayer piezoelectric actuator includes a piezoelectric element substrate 101 (FIG. 5 (c)) that has been pre-fired and processed and formed with a fired internal electrode layer 105 such as Ag on both surfaces, and a metal plate 102 (such as stainless steel). It is formed by alternately laminating FIG.
The metal plate 102 has three tongue-shaped pieces 103, and the metal plates 102 adjacent to each other with the piezoelectric element substrate 101 interposed therebetween are arranged with a phase shift of about 60 ° around the vertical axis. That is, the three tongue-like piece portions 103 of a certain metal plate 102 are positioned between the three tongue-like piece portions 103 of other adjacent metal plates 102 (see FIG. 5C). . The metal plates 102 in the same phase among the metal plates 102, that is, the tongue-like pieces 103 of the metal plates 102 arranged every other one, are electrically connected to each other by welding or soldering to the belt-like metal plate 104. They are connected (see FIG. 5A).
In the multilayer piezoelectric actuator having such a configuration, when a voltage is applied to the band-shaped metal plate 104, an electric field is applied to each piezoelectric element substrate 101, and each piezoelectric element generates a strain and functions as an actuator.
[0004]
[Problems to be solved by the invention]
In such a conventional multilayer piezoelectric actuator, the internal electrode layer 105 is formed by printing and firing in order to apply an electric field to both surfaces of each piezoelectric element substrate constituting the multilayer body. It is shown in 6 (a). In this case, it is necessary to cover and form the internal electrode layer leaving a blank portion at the periphery of the piezoelectric element substrate 101 so as not to be in electrical contact with the band-shaped metal plate 104 provided on the side surface of the laminate. is there.
When an electric field is applied to the internal electrode layer having such a shape, electrostriction occurs only in a portion of the piezoelectric element substrate 101 covered with the internal electrode layer 105 (see FIG. 6B).
[0005]
However, when the applied voltage increases in this state, the applied voltage drops sharply in the region from the periphery of the internal electrode layer of the piezoelectric element substrate to the blank portion, and as a result, the blank portion and the internal portion where no electrostriction occurs. Tensile stress is generated at the lower boundary of the electrode layer. Therefore, when such a multilayer piezoelectric actuator is driven for a long time, a stress is repeatedly applied around the internal electrode layer, a crack 106 is generated from this portion, and there is a problem that the piezoelectric element causes fatigue failure (see FIG. 6 (b)).
[0006]
In order to deal with this problem, Japanese Patent Laid-Open No. 2-35785 discloses that the shape around the internal electrode layer is deformed as shown in FIGS. It has been proposed that the internal electrode layer gradually disappears from the periphery to which no electric field is applied.
However, if the periphery of the internal electrode layer 105 has a saw-like shape as shown in FIG. 7A, the electric field toward the periphery of the piezoelectric element 101 is concentrated at the top of the saw, and the metal contained in the internal electrode layer material. There is a problem in that ions cause electromigration toward the periphery of the piezoelectric element substrate, and easily cause a short circuit with the belt-like metal plate 104 installed on the side surface of the laminate.
[0007]
On the other hand, as shown in FIG. 7B, in the case where a two- to three-fold extremely narrow electrode pattern is formed around the internal electrode layer 105b having a width of only about 1 mm, the area of the electrode pattern is set to 0. .5 mm or less, and there is a manufacturing problem that the positions of the internal electrode layers formed on both surfaces of the piezoelectric element substrate 101 must be precisely adjusted. When the area is widened, there is a problem that the area of the internal electrode layer is reduced correspondingly and the effective utilization rate of the piezoelectric element substrate is reduced.
[0008]
The present invention has been made in view of such problems of the prior art, and an electric field applied to a portion around the internal electrode of the piezoelectric element substrate without using an internal electrode having a specific shape is generated around the internal electrode. It is an object of the present invention to provide a highly reliable piezoelectric element and a stacked piezoelectric actuator using the same that are continuously reduced in size and do not crack even when repeatedly driven.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that a low dielectric constant layer having a relative dielectric constant lower than that of the piezoelectric element substrate is interposed between the piezoelectric element substrate and the peripheral portion of the internal electrode layer. as to by Rukoto to form a low dielectric constant layer on the piezoelectric element on the substrate, it found that the above problems can be solved, and have completed the present invention.
[0010]
That is, the piezoelectric element of the present invention is a piezoelectric element formed by sandwiching a piezoelectric element substrate between internal electrode layers, wherein the low dielectric constant layer having a relative dielectric constant lower than that of the piezoelectric element substrate is the piezoelectric element substrate and the internal electrode layer. The low dielectric constant layer is formed on the piezoelectric element substrate so as to be interposed between the peripheral portion and the peripheral portion of the piezoelectric element substrate .
[0011]
In a preferred embodiment of the piezoelectric element of the present invention, the low dielectric constant layer has a relative dielectric constant in the range of 10 to 2,000.
[0012]
Furthermore, the multilayer piezoelectric actuator of the present invention includes a plurality of piezoelectric elements as described above, and a plurality of metal plates having connection protrusions sandwiched between the piezoelectric elements and electrically connected to the piezoelectric elements. A laminate obtained by laminating
A piezoelectric plate bonded to the upper and lower ends of the laminate and having end faces parallel to each other;
The projections for connection of the metal plate are alternately projected in two or more directions from between the piezoelectric elements, and the projections for connection are bent along the stacking direction of the laminated body and protruded in the same direction. It is characterized by being joined to the connection projection.
[0013]
[Action]
In the present invention, the low dielectric constant layer is arranged such that a low dielectric constant layer having a lower relative dielectric constant than the piezoelectric element substrate is interposed between the piezoelectric element substrate of the multilayer piezoelectric actuator and the peripheral portion of the internal electrode layer. Was formed on the piezoelectric element substrate . Therefore, the voltage applied to the piezoelectric element is suitably reduced in the peripheral portion of the internal electrode layer.
[0014]
That is, a low dielectric constant layer having a dielectric constant sufficiently lower than that of the piezoelectric element exists between the peripheral portion of the internal electrode layer and the piezoelectric element substrate surface below the internal electrode layer. Even if the low dielectric constant layer is formed on a film having a thickness of about 10 μm that can be manufactured by a printing and firing method, the low dielectric constant has a low relative dielectric constant so as to have a capacitance equivalent to that of a piezoelectric element having a thickness of several hundred μm. It is what you have. Therefore, the electric field applied to this region is distributed to the low dielectric constant layer and the piezoelectric element, and only about 1/2 of the total voltage is applied to the piezoelectric element.
As described above, by providing the region where the low dielectric constant layer is interposed at the boundary between the internal electrode layer and the margin around the electrode, the electric field applied to the piezoelectric element is temporarily reduced to 1/2 around the internal electrode layer. Since the margin is 0 after the reduction, the tensile stress in this region is relaxed, and the occurrence of fatigue failure can be avoided even when the electric field is repeatedly applied.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a piezoelectric element and a multilayer piezoelectric actuator according to the present invention will be described in detail with reference to the drawings with some embodiments.
[0016]
FIG. 1 is a perspective view showing an embodiment of the multilayer piezoelectric actuator of the present invention, and FIG. 2 is a partial sectional view of this actuator.
In FIG. 2, in this actuator, plate-like piezoelectric element substrates 1 and metal plates 2 are alternately laminated to constitute a laminate 3. An internal electrode layer 4 is provided between the piezoelectric element substrate 1 and the metal plate 2, and both are joined and the surface of the piezoelectric element substrate 1 and the metal plate 2 are electrically joined. Also, a low dielectric constant layer 5 is formed between the peripheral portion of the internal electrode layer 4 and the piezoelectric element substrate 1 to constitute the piezoelectric element of the present invention, and is applied to the piezoelectric element around the internal electrode layer. The voltage is relaxed.
[0017]
FIG. 3 is a plan view showing a configuration of a metal plate or a piezoelectric element in the multilayer piezoelectric actuator of the present invention.
The metal plate 2 has a structure shown in FIG. 3A and includes a disc portion 6 and a connection projection 7.
Further, as shown in FIG. 2B, arc-shaped low dielectric constant layers 5a and 5a ′ are formed on one surface of the piezoelectric element substrate 1 at a portion corresponding to the peripheral portion of the internal electrode layer. An internal electrode layer 4 is formed on the top (see FIG. 3C).
On the other hand, on the other surface of the piezoelectric element substrate 1, low dielectric constant layers 5b and 5b ′ are formed at positions that are rotated and displaced by 90 ° with respect to the low dielectric constant layer formed on one surface. Further, the internal electrode layer is covered (see FIG. 3D).
Further, in this actuator, as shown in FIG. 3 (e), the metal plate 2 and the piezoelectric element substrate 1 are arranged so that the connection protrusions 7 are located at a portion where the low dielectric constant layer is not formed.
[0018]
In the actuator of the present invention, the metal plate or piezoelectric element as described above is laminated to form a laminated body. At that time, as shown in FIG. , 8a ′ and 8b, 8b ′ are positioned 90 ° displaced around the axis of the laminate. By arranging the metal plate 2 in this way, the same voltage can be applied to the stacked metal plates 2 in a single layer.
That is, in FIG. 2, the connection projections 7 of the metal plate 2 protruding from the outer periphery of the laminate 3 are bent along the stacking direction and electrically connected by welding, soldering, etc. every other layer. Constitute. In this case, the “stacking direction” refers to the vertical direction in FIG.
[0019]
Furthermore, in the actuator of the present invention, as shown in FIG. 1A, lead wires 9a and 9b are connected to the external electrodes 8a and 8b, and a voltage is applied to the lead wires, whereby the laminate 3 A voltage is applied to each piezoelectric element.
Note that an inert plate 10 is bonded to the upper and lower ends of the laminate 3 (top and bottom in FIG. 1A) by an adhesive.
[0020]
Next, the materials and dimensions of the various components described above will be described.
Examples of the piezoelectric element substrate 1 include a sintered body mainly composed of lead zirconate titanate Pb (ZrTi) O ₃ and (PZT). However, the piezoelectric element substrate 1 is not limited to this and is made of ceramic having piezoelectricity. sufficient if, it is preferable to use a large piezoelectric constant d _33. The shape of the piezoelectric element substrate 1 may be circular or rectangular.
[0021]
The piezoelectric element substrate preferably has a thickness of 0.2 mm to 0.6 mm.
In the actuator of the present invention, the pre-sintered element substrate is laminated and formed into a plate shape or sintered, or the block body is cut into a plate shape after sintering, but if less than 0.2 mm, It is unrealistic, and if it exceeds 0.6 mm, a high drive voltage is required and the power supply becomes expensive, which is not preferable.
[0022]
The metal plate preferably has a low electric resistance and a melting point higher than the firing temperature of the conductive adhesive described later.
Specific examples of such metals include, but are not limited to, silver, brass, copper, phosphor bronze, and stainless steel.
Further, the metal plate itself does not generate electrostriction. Therefore, the thickness of the metal plate is preferably as thin as possible from the viewpoint of the efficiency of the multilayer piezoelectric actuator. The thickness is preferably 20 μm or more so that the portion having the low dielectric constant layer does not contact the lower layer of the internal electrode layer.
[0023]
The diameter of the disk portion 6 (see FIG. 3A) of the metal plate is preferably as large as possible as long as it does not overlap the low dielectric constant layers 5a and 5a ′ during the production of the laminate. In this case, it is preferable to set the inner diameter of the arc-shaped low dielectric constant layer to be smaller by 0.6 mm or more.
[0024]
Further, in the case where the low dielectric constant layer has a circular arc shape, it is preferable that the outer diameter of the low dielectric constant layer is in a range where a margin of 0.3 mm or more remains around the piezoelectric element substrate 1.
This is to ensure that the side surface of the piezoelectric element substrate is not reached due to a printing error for the convenience of manufacturing by printing and baking.
Note that it is effective that the width of the arc is in the range of 0.5 to 2 mm in order to secure the voltage relaxation region.
[0025]
Further, the connection L is made so that the interval L (see FIG. 3B) between the low dielectric constant layers 5a and 5a ′ installed at two places on the same surface of the piezoelectric element substrate does not overlap with the connection protrusion 7 of the metal plate 2. It is preferable to secure 0.5 mm or more wider than the width of the projection. Furthermore, since the upper internal electrode layer 4 is also produced by printing and firing, the low dielectric constant layer is preferably about 5 to 20 μm thick.
[0026]
Further, the low dielectric constant layer preferably has a relative dielectric constant in the range of 10 to 2000. The reason is as follows.
In FIG. 2, the portion where the low dielectric constant layer 5 is disposed below the internal electrode layer 4 generally has a structure in which a piezoelectric element having a high dielectric constant is sandwiched between the low dielectric constant layers from both sides.
Here, as shown in FIG. 4, when an electric field is applied with three dielectric layers having different relative dielectric constants ε _p and ε _x , the electric flux density D is equal in all dielectric layers. The ratio of the electric fields E _x and E _{p in} the dielectric is equal to the ratio of the reciprocal of each relative dielectric constant, as shown in the following equation (1).
[0027]
[Expression 1]

[0028]
Further, the applied voltage V _T is a value obtained by multiplying the electric fields E _x and E _p in the dielectrics by the film thicknesses d _x and d _p (Equation (2)).
[0029]
[Expression 2]

[0030]
Therefore, when a low dielectric constant layer having a relative dielectric constant ε _{x that} is K _ε times the relative dielectric constant ε _p of the piezoelectric element is used, a voltage of K _V times the total voltage V _T is applied to the piezoelectric element. The calculation shows that both are in the relationship of the following equation (3).
[0031]
[Equation 3]

[0032]
Here, an object of the present invention is to suppress a steep drop in the voltage applied to the piezoelectric element in the region from the periphery of the internal electrode layer of the piezoelectric element to the margin in the multilayer piezoelectric actuator.
Therefore, it can be said that the voltage applied to the piezoelectric element at the portion where the low dielectric constant layer 5 is disposed below the internal electrode layer 4 is preferably the total voltage V _T 0.25 to 0.75.
[0033]
Further, assuming that the above-described piezoelectric element has a preferable thickness of 0.2 to 0.6 mm and a thickness of the low dielectric constant layer of 5 to 20 μm, the relative dielectric constant ε of the low dielectric constant layer is calculated by the above equation (3). _x is preferably in the range of 0.5 to 60% of the relative dielectric constant ε _p of the piezoelectric element. Further, when PZT ceramics are used as the piezoelectric element, the relative dielectric constant is usually in the range of 2000 to 5000, so that the relative dielectric constant ε _x of the low dielectric constant layer is in the range of 10 to 2000 as described above. Preferably there is.
[0034]
The dielectric constant layer is printed and fired by mixing TiO-based fine powder in the range of ε _x ≦ 100 and BaTiO ₃ -based fine powder in the range of ε _x ≦ 2000 in a mixing ratio suitable for the glass frit. Can be produced.
The glass frit mixed with the dielectric powder is preferably composed mainly of PbO—SiO ₂ —B ₂ O _{3 and} having a heat resistance such as a softening point of 600 ° C. or higher. When the temperature is lower than 600 ° C., as will be described later, when the internal electrode layer is printed and fired on the upper layer, it melts at the firing temperature (300 to 600 ° C.).
[0035]
The diameter of the internal electrode layer is preferably set smaller than the outer diameter of the arc formed by the low dielectric constant layer so that the peripheral portion thereof is located on the low dielectric constant layer.
The conductive adhesive layer paste used for the internal electrode layer contains a metal powder such as Ag and glass powder, and the glass powder melts at a temperature at which the metal plate does not melt (about 300 to 600 ° C.). ZnO—SiO ₂ —B ₂ O ₃ or the like is used as the glass powder, but is not limited thereto.
[0036]
Next, an example of a manufacturing method of the multilayer piezoelectric actuator of this embodiment will be described.
First, both sides of a disk-shaped PZT sintered body suitable as a piezoelectric actuator material are lapped and polished to produce a piezoelectric ceramic plate (piezoelectric element substrate 1) having a diameter of 14 mm and a thickness of 0.3 mm.
Next, a BaTiO ₃ powder having a particle size of 3 μm or less is mixed in a glass powder containing PbO, ZnO, SiO ₂ and B ₂ O ₃ as main components so that the volume content is 40%, and an appropriate resin binder is obtained. A paste is prepared by adding a solvent, and the shape shown in FIG. 3B is printed and fired at 750 ° C. on the surface of the piezoelectric element substrate 1 to form a low dielectric constant layer 5 having a thickness of 10 μm.
[0037]
The low dielectric constant layer has an arc shape, an outer diameter of 13 mm, an inner diameter of 11 mm, an interval L between two arc-shaped patterns of 3 mm, and rotated by 90 ° on each surface (front and back surfaces) of the piezoelectric element substrate 1. It is set as the displaced arrangement | positioning (refer FIG.3 (b), (c) and (d)).
Further, a paste containing a metal powder such as Ag and glass powder is printed and dried on both surfaces of the piezoelectric element substrate 1 to form a thick film having a diameter of 12 mm and a thickness of 10 μm, and firing at 520 ° C. to form the internal electrode layer 4. It is manufactured (see FIG. 3 (e)). At this time, a region having a peripheral width of 0.5 mm of the internal electrode layer 4 is overlapped with the low dielectric constant layer 5.
[0038]
On the other hand, an Ag thin plate having a thickness of 30 μm is punched into a disk shape having a diameter of 9 mm and having connecting projections 7 having a width of 2 × length of 5.5 mm at two locations, and a metal plate 2 as shown in FIG. Manufacturing.
The obtained metal plate 2 is overlaid on the piezoelectric element substrate 1 so that the connection protrusions 7 are positioned at the distance L between the low dielectric constant layers 5a and 5b (see FIG. 3E).
[0039]
99 combinations of the piezoelectric element substrate 1 and the metal plate 2 are used, and the piezoelectric element substrates 1 and the metal plates 2 are alternately laminated as shown in FIGS. The laminated bodies 3 arranged so as to be shifted by 90 ° so as to come to the same position (directly above or directly below) every other layer are assembled (see FIGS. 1 and 2).
In addition, on the upper and lower end portions (top surface and bottom surface) of the laminate 3, an inert plate 10 in which the Ag paste used for forming the internal electrode layer 4 is printed and fired in advance is disposed (see FIG. 1A). .
Subsequently, the laminated body 3 assembled as described above is joined by remelting the internal electrode layer at 520 ° C. for 30 minutes while pressing with an appropriate load.
[0040]
Next, the connection protrusions 7 protruding from the outer peripheral side surface of the laminate 3 are bent in the axial direction (stacking direction) of the laminate, and joined to the adjacent connection protrusions 7 by soldering, and the external electrode 8 is attached. Form (see FIG. 2).
Thus, by forming the external electrodes 8 at four locations on the outer peripheral side surface of the multilayer body 3, the 100 metal plates 2 constituting the multilayer body are electrically connected by the external electrodes 8a and 8a ′. The two metal plates 2 are electrically connected by external electrodes 8b and 8b ', and the other 50 metal plates 2 are insulated from the 50 metal plates with the piezoelectric element 1 therebetween. They are divided (FIG. 1 (a)).
[0041]
Furthermore, the lead wires 9a and 9b are joined to the external electrodes 8a and 8b by soldering, the outer peripheral side surface of the laminate 3 is covered with silicone resin, defoaming treatment is performed, and the resin is placed in the gap between the external electrode and the side surface of the laminate Is completely filled and then cured. And the parallelism of an up-and-down surface is adjusted by grinding the upper-and-lower single board (inactive board 10) of the laminated body 3. FIG.
Thereafter, the laminate 3 is immersed in silicone oil at 80 ° C., the lead wire 9a is connected to the positive electrode of the DC power source, the negative electrode 9b is connected, and an electric field of 3 kV / mm is applied to the piezoelectric element substrate 1 for 30 minutes. Then, the piezoelectric element substrate 1 is polarized to obtain the multilayer piezoelectric actuator of this embodiment.
[0042]
【Example】
(Example)
When a DC voltage of 500 V was applied to the laminated piezoelectric actuator obtained by the above manufacturing process in the same direction as the electric field during polarization, a displacement of 40 μm or more was obtained, and it was confirmed that the actuator functions normally.
Furthermore, 10 laminated piezoelectric actuators of this example were continuously driven 1 × 10 ⁸ times by applying an AC electric field of 0 V to 500 V at a frequency of 50 Hz in an environment of 95% humidity. It did not occur and everything worked fine.
[0043]
(Comparative example)
Except that the low dielectric constant layer 5 was not provided and the internal electrode layer 4 was directly formed on the surface of the piezoelectric element substrate 1, the same configuration as that of the example was adopted to manufacture the laminated piezoelectric actuator of this example.
As a result of applying an electric field of 3 kV / mm to the obtained actuator for 30 minutes for polarization, a displacement of 40 μm was obtained with a DC voltage of 500 V.
However, under the same conditions as in the example, an AC electric field of 0 V to 500 V was applied at a frequency of 50 Hz and continuously driven 1 × 10 ⁷ times. As a result, 7 out of 10 were short-circuited and could not be driven. It was.
Also, as a result of observing the side surface of the short-circuited actuator laminate, a cracked piezoelectric element was found, and when this part was cut and observed, a crack occurred around the internal electrode layer, and the fracture surface A short circuit occurred.
[0044]
As mentioned above, although this invention was demonstrated in detail by suitable embodiment and an Example, this invention is not limited to these, A various deformation | transformation implementation is possible within the range of the summary of this invention.
For example, the number of the projections 7 for connecting the metal plate can be not only two but three or more, and the number of the low dielectric constant layer intervals L may be adjusted accordingly.
Moreover, the shape of the laminated body 3 is not limited to a cylindrical shape, and may be a polygonal column shape, and the pattern shape of the low dielectric constant layer and the number of intervals L may be adjusted in accordance with such a shape. .
[0045]
【The invention's effect】
As described above, according to the present invention, as low dielectric constant than the piezoelectric element substrate low dielectric layer is interposed between the peripheral portion of the piezoelectric element substrate and the internal electrode layers, a low dielectric constant Since the layer is formed on the piezoelectric element substrate, the electric field applied to the internal electrode peripheral portion of the piezoelectric element substrate is continuously reduced at the peripheral portion of the internal electrode without using an internal electrode having a specific shape, It is possible to provide a highly reliable piezoelectric element that does not cause cracks in the piezoelectric element substrate even when it is repeatedly driven, and a laminated piezoelectric actuator using the piezoelectric element.
[0046]
That is, the multilayer piezoelectric actuator of the present invention has a low dielectric constant so that a low dielectric constant layer having a lower relative dielectric constant than the piezoelectric element substrate is interposed between the periphery of the printed internal electrode layer and the piezoelectric element substrate. By forming the layer on the piezoelectric element substrate, the electric field applied to the piezoelectric element below the low dielectric constant layer is relaxed, and the applied electric field from the peripheral part of the internal electrode layer of the piezoelectric element to the surrounding margin part is reduced. Because the change is gentle, even if it is driven for a long time with a driving voltage like a crack in a conventional piezoelectric element without adopting an internal electrode layer with a unique shape, the periphery of the internal electrode layer of the piezoelectric element It is possible to obtain a highly reliable stacked piezoelectric actuator that does not crack.
[Brief description of the drawings]
FIG. 1 is a perspective view and an upper end view showing an embodiment of a laminated piezoelectric actuator of the present invention.
FIG. 2 is a partial cross-sectional view of a portion A of the multilayer piezoelectric actuator shown in FIG. 1 cut in the axial direction.
FIG. 3 is a plan view showing the shape of a part used in the multilayer piezoelectric actuator shown in FIG.
In Figure 4 across the dielectric of relative permittivity epsilon _p in the dielectric constant epsilon _x becomes dielectric dielectric laminated structure is an explanatory diagram showing a distribution of an electric field applied to the dielectric.
FIG. 5 is a perspective view showing an example of a conventional multilayer piezoelectric actuator.
FIGS. 6A and 6B are a transverse sectional view and a longitudinal sectional view showing a state in which a voltage is applied to a piezoelectric element constituting a conventional multilayer piezoelectric actuator, in which electrostriction is generated by the shape of the internal electrode layer and the applied voltage. Indicates.
7 is a partial plan view showing a conventional example of a portion A of the internal electrode layer shown in FIG. 6. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piezoelectric element board | substrate 2 Metal plate 3 Laminate body 4 Internal electrode layer 5 Low dielectric constant layer 6 Disc part 7 Projection part 8a, 8a ', 8b, 8b' External electrode 9a, 9b Lead wire 10 Inactive board 101 Piezoelectric Element substrate 102 Metal plate 103 Tongue piece 104 Band-shaped metal plate 105 Internal electrode layer 106 Crack A Location of the laminated piezoelectric actuator

Claims (3)

In the piezoelectric element formed by sandwiching the piezoelectric element substrate in the internal electrode layer, a lower low dielectric layer having a relative dielectric constant than the piezoelectric element substrate is interposed between the peripheral portion of the piezoelectric element substrate and the internal electrode layer As described above, a piezoelectric element comprising the low dielectric constant layer formed on the piezoelectric element substrate . 2. The piezoelectric element according to claim 1, wherein the relative dielectric constant of the low dielectric constant layer is in the range of 10 to 2,000. A laminate in which a plurality of piezoelectric elements according to claim 1 or 2 and a plurality of metal plates having connection protrusions sandwiched between the piezoelectric elements and electrically connected to the piezoelectric elements are laminated,
A piezoelectric plate bonded to the upper and lower ends of the laminate and having end faces parallel to each other;
The projections for connecting the metal plate are alternately projected from between the piezoelectric elements in two or more directions, and the projections for connection are bent along the stacking direction of the laminated body and protruded in the same direction. A laminated piezoelectric actuator characterized in that it is joined to a connecting projection.

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