JP2004273506A

JP2004273506A - Stacked piezoelectric ceramic element

Info

Publication number: JP2004273506A
Application number: JP2003058204A
Authority: JP
Inventors: Nobuhiko Toshitsuna; 信彦年綱; Hideo Komamura; 秀雄駒村
Original assignee: NEC Tokin Corp
Current assignee: Tokin Corp
Priority date: 2003-03-05
Filing date: 2003-03-05
Publication date: 2004-09-30

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked piezoelectric ceramic element which is capable of preventing a corner internal electrode layer from being exposed after it is sheathed and protected against deterioration caused by an electric discharge occurring between the ends of internal electrode layers. <P>SOLUTION: The stacked piezoelectric ceramic element is equipped with a laminate composed of a plurality of laminated square piezoelectric ceramic layers 1 and internal electrode layers 3 each interposed between the piezoelectric ceramic layers 1, external electrodes 4 where every other internal electrode layers 3 are connected so as to form counter electrodes formed on each of opposed sides of the laminating direction of the laminate, layers 6 provided on the side faces of the laminate, and an external cover 5. A rounded corner having a radius of 1 mm or above is provided to at least a part of corners formed by the two sides of the laminate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、アクチュエータ等に用いられる積層型圧電セラミック素子に係り、特に流体などのインジェクタの駆動源として好適な積層型圧電セラミック素子に関する。
【０００２】
【従来の技術】
従来この分野では、例えば下記の特許文献１に開示されているように、積層型圧電セラミック素子の積層方向の二つの側面で挟まれた角部の少なくとも一部にコーナー部角取り処理（Ｃ面加工の角取り処理）のみを施したり、半径１ｍｍ未満の角部丸め処理（Ｒ面加工の処理）を施していた。
【０００３】
その場合、コーナー部角取り処理のみを施したり、半径１ｍｍ未満の角部丸め処理を施した角部では、内部電極の端部の突起が大きかった。よって外装を施した際、コーナー部角取り処理あるいは角部丸め処理を行った角部の外装が薄くなり、内部電極の端部が十分に外装に覆われずに、外気に露出しやすい状態となっていた。
【０００４】
【特許文献１】
特開２００１−３３９１０５号公報
【０００５】
【発明が解決しようとする課題】
既に一部を説明したように、従来技術においては、積層型圧電セラミック素子の積層方向の二つの側面で挟まれた角部の少なくとも一部に、コーナー部角取り処理のみを施したり、半径１ｍｍ未満の角部丸め処理を施していたが、その角部で外装の厚みが薄くなり、セラミック面よりも５〜１０μｍ突起した内部電極が角部で外気に露出しやすい状態となり、その角部の露出した内部電極間にて放電が発生し、その結果、素子の破壊に至るという問題点があった。
【０００６】
したがって、本発明の技術的課題は、外装後に角部の内部電極が露出せず、内部電極の端部間での放電による劣化が発生しない積層型圧電セラミック素子を提供することにある。
【０００７】
【課題を解決するための手段】
本発明の積層型圧電セラミック素子は、積層された多角形の複数の圧電セラミック層及び前記圧電セラミック層の間に形成された内部電極からなる積層体と、前記積層体の積層方向に対する側面のうち２つの側面で前記内部電極が１層おきに接続されて対向電極を形成するように、前記側面の各々に前記積層方向に延在して形成された外部電極とを備える積層型圧電セラミック素子であって、前記積層方向に対する側面で挟まれた角部の少なくとも一部に半径１ｍｍ以上の角部丸め処理が施されたことを特徴とする。
【０００８】
また、本発明の積層型圧電セラミック素子は、積層された多角形の複数の圧電セラミック層及び前記圧電セラミック層の間に形成された内部電極からなる積層体と、前記積層体の積層方向に対する側面のうち２つの側面で前記内部電極が１層おきに接続されて対向電極を形成するように、前記側面の各々に前記積層方向に延在して形成された外部電極とを備える積層型圧電セラミック素子であって、前記積層方向に対する２つの側面で挟まれた角部の少なくとも一部にコーナー部角取り処理が施され、前記コーナー部角取り処理により新たに形成された角部の各々に半径１ｍｍ以上の角部丸め処理が施されたことを特徴とする。
【０００９】
【発明の実施の形態】
以下に本発明の実施の形態を、図面を参照してさらに説明する。
【００１０】
図１（ａ）は、本発明の実施の形態１での、外部電極を形成した後に、研磨により各角部に半径１ｍｍ以上の角部丸め処理が施された外装後の積層型圧電セラミック素子における上面に平行な切断面によるＢ−Ｂ線断面図であり、図１（ｂ）はその正面に平行な切断面によるＡ−Ａ線断面図である。
【００１１】
図２（ａ）は、本発明の実施の形態２での、外部電極の形成後に、各角部にコーナー部角取り処理が施され、その後に、コーナー部角取り処理によって発生した各角部に、研磨により半径１ｍｍ以上の角部丸め処理が施された外装後の積層型圧電セラミック素子のＤ−Ｄ線断面図であり、図２（ｂ）はそのＣ−Ｃ線断面図である。
【００１２】
図１及び図２を参照すると、本発明における積層型圧電セラミック素子は、圧電セラミック層１と、内部電極層３とを、上下面が圧電セラミック層１となるように、交互に積層された積層体を形成している。
【００１３】
この積層体は圧電セラミック層及び導電層の各グリーンシートまたはペーストを積層して、所定の大きさに切断の後、焼成されたものからなる。その積層体の積層方向の側面の対向面には、積層方向に交互に絶縁層６が形成されている。さらに、絶縁層６が形成された対向面の各々の上に、積層方向に延在する外部電極４が形成されており、内部電極層３の一端と積層方向で交互に接続されている。
【００１４】
ここで、図１に示される実施の形態１の積層型圧電セラミック素子は、外部電極を形成した後に、研磨により各角部に半径２ｍｍと半径３ｍｍの角部丸め処理（Ｒ面加工）が施されている。
【００１５】
また、図２に示される実施の形態２の積層型圧電セラミック素子は、外部電極を形成した後に、各角部にコーナー部角取り処理（Ｃ面加工）が施され、その後に、コーナー部角取り処理によって発生した各角部に、研磨により半径２ｍｍと半径３ｍｍの角部丸め処理が施されている。
【００１６】
しかる後に、信号入力または出力用のリード線２を半田を介して接続し、その上に外装５を施した。
【００１７】
このように本発明の実施の形態１及び実施の形態２の積層型圧電セラミック素子によれば、角部での内部電極の突起を抑制し、外装後の角部での外装厚みを十分に厚くすることができる。したがって、角部の内部電極が露出することがなく、内部電極間での放電の発生を防止することができる。
【００１８】
また、比較のために、従来技術による積層型圧電セラミック素子も製造した。
【００１９】
図４（ａ）は、従来例１による、外部電極を形成した後に、研磨により各角部に半径１ｍｍ未満の角部丸め処理が施された外装後の積層型圧電セラミック素子のＦ−Ｆ線断面図であり、図４（ｂ）は、そのＥ−Ｅ線断面図である。
【００２０】
図５（ａ）は、従来例２による、外部電極を形成した後に、各角部にコーナー部角取り処理のみを施した積層型圧電セラミック素子のＨ−Ｈ線断面図であり、図５（ｂ）はそのＧ−Ｇ線断面図である。
【００２１】
ここで従来例１は、外部電極形成後、各角部に研磨により半径０．５ｍｍ未満の角部丸め処理（Ｒ面加工）を施したものであり、従来例２は、各角部にコーナー部角取り処理（Ｃ面加工）のみを施したものである。
【００２２】
この従来例１または２の場合、図６に角部の断面図を示すように、角部では、圧電セラミック層１のセラミック面よりも７．５μｍ突起した内部電極層３が存在していた。
【００２３】
下記の表１は、図１、図２、図４及び図５の積層型圧電セラミック素子、各々１０本を電界強度３．０ｋＶ／ｍｍ、周波数２００Ｈｚにて、１×１０^９回駆動させる耐久試験を行った結果で、１×１０^９回に到達するまでに、放電が発生した本数を示す。
【００２４】
【表１】

【００２５】
また、この耐久試験とは別に、外部電極を形成した後の積層型圧電セラミック素子において研磨による角部丸め処理の半径を、０．１、０．５、１．０、２．０、３．０ｍｍと変化させ、その時の二つの側面で挟まれた角部での内部電極の突起量と、外装厚みを測定した。その結果を図３に示す。
【００２６】
この図３に示されているように、角部丸め処理の半径が１．０ｍｍ以上において、内部電極の突起量が５μｍ以下となり、外装厚みが５μｍ以上となった。
【００２７】
この結果は、次のように考察することができる。すなわち、（１）角部丸め処理の半径が１．０ｍｍ未満のときには、内部電極層と圧電セラミック層の角部丸め処理（研磨）に対する機械的な性質の違いにより、内部電極層の突起量が５μｍを超えるが、角部丸め処理の半径が大きくなるとともに、内部電極層の研磨面と、圧電セラミック層の研磨面が次第に一致する。また、（２）角部丸め処理の半径が小さいときには、この角部における外装部の厚みが、他の部分より薄くなるが、角部丸め処理の半径が大きくなると、この角部における外装部の厚みが他の部分の厚みに近づく。
【００２８】
表１及び図３の結果から分かるように、角部丸め処理の半径が１．０ｍｍ以上の場合に、内部電極層の端面を外装で十分に覆うことにより、耐久性を向上させることができる。
【００２９】
【発明の効果】
以上に説明したように、本発明によれば、積層型圧電セラミック素子の、二つの側面で挟まれた角部の一部またはすべてにおいて、半径１ｍｍ以上の角部丸め処理を施すことにより、また、積層型圧電セラミック素子の二つの側面で挟まれた角部の一部またはすべてにおいて、コーナー部角取り処理を施し、さらにそのコーナー部角取り処理を施して生じた角部に、半径１ｍｍ以上の角部丸め処理を施すことにより、その角部での内部電極の突起を抑制することができ、外装した後で、その角部での外装の厚みが薄くならず、よって角部の内部電極が露出せず、内部電極間での放電の発生を防止した積層型圧電セラミック素子を提供することが可能となった。
【図面の簡単な説明】
【図１】実施の形態１の積層型圧電セラミック素子を示す図。図１（ａ）はそのＢ−Ｂ線断面図、図１（ｂ）はそのＡ−Ａ線断面図。
【図２】実施の形態２の積層型圧電セラミック素子を示す図。図２（ａ）はそのＤ−Ｄ線断面図、図２（ｂ）はそのＣ−Ｃ線断面図。
【図３】角部丸め処理において、角部の半径を変化させた場合の、角部の内部電極突起量と外装厚みを示す図。
【図４】従来例１の積層型圧電セラミック素子を示す図。図４（ａ）はそのＦ−Ｆ線断面図、図４（ｂ）はそのＥ−Ｅ線断面図。
【図５】従来例２の積層型圧電セラミック素子を示す図。図５（ａ）はそのＨ−Ｈ線断面図、図５（ｂ）はそのＧ−Ｇ線断面図。
【図６】従来例における角部の断面図。
【符号の説明】
１圧電セラミック層
２リード線
３内部電極層
４外部電極
５外装
６絶縁層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laminated piezoelectric ceramic element used for an actuator or the like, and more particularly to a laminated piezoelectric ceramic element suitable as a drive source for an injector such as a fluid.
[0002]
[Prior art]
Conventionally, in this field, as disclosed in, for example, Patent Document 1 below, at least a part of a corner portion sandwiched between two side surfaces in a stacking direction of a multilayer piezoelectric ceramic element is subjected to a corner chamfering process (C surface In this case, only the processing (squaring processing) or the rounding of a corner having a radius of less than 1 mm (R surface processing) is performed.
[0003]
In this case, the protrusion at the end of the internal electrode was large in the corner portion where only the corner portion corner removal processing was performed or the corner rounding process with a radius of less than 1 mm was performed. Therefore, when the exterior is applied, the corner exterior that has been subjected to the corner corner rounding process or the corner rounding process is thinned, and the end of the internal electrode is not sufficiently covered with the exterior, and is easily exposed to the outside air. Had become.
[0004]
[Patent Document 1]
JP 2001-339105 A
[Problems to be solved by the invention]
As described above, in the related art, at least a part of a corner portion sandwiched between two side surfaces in the stacking direction of the multilayer piezoelectric ceramic element is subjected to only a corner chamfering process or a radius of 1 mm. Although the corner was rounded, the thickness of the exterior was reduced at the corner, and the internal electrode protruding 5 to 10 μm from the ceramic surface was easily exposed to outside air at the corner, and the corner was rounded. Discharge occurs between the exposed internal electrodes, resulting in a problem that the device is destroyed.
[0006]
Therefore, a technical problem of the present invention is to provide a laminated piezoelectric ceramic element in which the internal electrodes at the corners are not exposed after the packaging and the deterioration due to the discharge between the ends of the internal electrodes does not occur.
[0007]
[Means for Solving the Problems]
The multilayer piezoelectric ceramic element according to the present invention includes a multilayer body including a plurality of stacked polygonal piezoelectric ceramic layers and internal electrodes formed between the piezoelectric ceramic layers, and a side surface in a stacking direction of the multilayer body. A laminated piezoelectric ceramic element comprising an external electrode formed on each of the side surfaces so as to extend in the laminating direction such that the internal electrodes are connected every other layer on two side surfaces to form a counter electrode. In addition, at least a part of the corner sandwiched between the side surfaces in the laminating direction is subjected to a corner rounding process with a radius of 1 mm or more.
[0008]
Further, the multilayer piezoelectric ceramic element of the present invention is a multilayer piezoelectric ceramic element comprising: a multilayer polygonal piezoelectric ceramic layer and internal electrodes formed between the piezoelectric ceramic layers; and a side surface in the stacking direction of the multilayer body. A multi-layer piezoelectric ceramic comprising external electrodes formed on each of the side surfaces so as to extend in the laminating direction such that the internal electrodes are connected every other layer on two sides to form a counter electrode. An element, wherein at least a part of a corner sandwiched between two side surfaces with respect to the stacking direction is subjected to a corner chamfering process, and each of the corners newly formed by the corner chamfering process has a radius. A corner rounding process of 1 mm or more is performed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be further described with reference to the drawings.
[0010]
FIG. 1A shows a laminated piezoelectric ceramic element according to Embodiment 1 of the present invention, in which an external electrode is formed, and each corner is rounded to have a radius of 1 mm or more by polishing after forming an external electrode. FIG. 1B is a cross-sectional view taken along a line BB of a cross section parallel to the upper surface, and FIG. 1B is a cross-sectional view taken along a line AA of FIG.
[0011]
FIG. 2A is a view showing a state in which each corner is subjected to a corner chamfering process after the external electrode is formed in the second embodiment of the present invention, and thereafter, each corner generated by the corner chamfering process. FIG. 2B is a cross-sectional view taken along line DD of the laminated piezoelectric ceramic element after the packaging, which has been subjected to a corner rounding process with a radius of 1 mm or more by polishing, and FIG. 2B is a cross-sectional view taken along line CC of FIG.
[0012]
Referring to FIG. 1 and FIG. 2, a multilayer piezoelectric ceramic element according to the present invention has a multilayer structure in which a piezoelectric ceramic layer 1 and an internal electrode layer 3 are alternately stacked such that the upper and lower surfaces are the piezoelectric ceramic layer 1. Forming the body.
[0013]
This laminated body is formed by laminating green sheets or pastes of a piezoelectric ceramic layer and a conductive layer, cutting the green sheet or paste into a predetermined size, and then firing. Insulating layers 6 are alternately formed in the stacking direction on opposite sides of the stack in the stacking direction. Further, external electrodes 4 extending in the stacking direction are formed on each of the opposing surfaces on which the insulating layer 6 is formed, and are alternately connected to one ends of the internal electrode layers 3 in the stacking direction.
[0014]
Here, in the laminated piezoelectric ceramic element of the first embodiment shown in FIG. 1, after forming the external electrodes, each corner is rounded (R-face processing) with a radius of 2 mm and a radius of 3 mm by polishing. Have been.
[0015]
Further, in the laminated piezoelectric ceramic element according to the second embodiment shown in FIG. 2, after forming the external electrodes, each corner is subjected to a corner chamfering process (C-plane processing). Each corner generated by the removing process is subjected to a rounding process of a radius of 2 mm and a radius of 3 mm by polishing.
[0016]
Thereafter, the lead wires 2 for signal input or output were connected via solder, and the exterior 5 was provided thereon.
[0017]
As described above, according to the multilayer piezoelectric ceramic elements of the first and second embodiments of the present invention, the protrusion of the internal electrode at the corner is suppressed, and the thickness of the exterior at the corner after the exterior is sufficiently increased. can do. Therefore, the internal electrodes at the corners are not exposed, and the occurrence of discharge between the internal electrodes can be prevented.
[0018]
For comparison, a multilayer piezoelectric element according to the prior art was also manufactured.
[0019]
FIG. 4A shows an FF line of a laminated piezoelectric ceramic element after packaging, in which, after forming an external electrode, each corner is rounded to have a radius of less than 1 mm according to Conventional Example 1. FIG. 4B is a cross-sectional view taken along the line EE.
[0020]
FIG. 5A is a cross-sectional view taken along the line HH of the laminated piezoelectric ceramic element according to Conventional Example 2, in which each corner is subjected to only the corner chamfering process after the external electrodes are formed. (b) is a sectional view taken along line GG.
[0021]
Here, in Conventional Example 1, after the external electrode was formed, each corner was subjected to a rounding process (R surface processing) with a radius of less than 0.5 mm by polishing, and in Conventional Example 2, a corner was formed at each corner. Only the corner chamfering process (C surface processing) is performed.
[0022]
In the case of the conventional example 1 or 2, as shown in the sectional view of the corner portion in FIG. 6, the internal electrode layer 3 projecting 7.5 μm from the ceramic surface of the piezoelectric ceramic layer 1 was present at the corner portion.
[0023]
Table 1 below shows a durability test in which ten laminated piezoelectric ceramic elements shown in FIGS. 1, 2, 4 and 5 were driven 1 × 10 ⁹ times at an electric field strength of 3.0 kV / mm and a frequency of 200 Hz. The number of discharges occurring before the number of discharges reaches 1 × 10 ⁹ is shown.
[0024]
[Table 1]

[0025]
Separately from the durability test, the radius of the corner rounding treatment by polishing in the laminated piezoelectric ceramic element after forming the external electrode is 0.1, 0.5, 1.0, 2.0, 3.. The thickness was changed to 0 mm, and the amount of protrusion of the internal electrode at the corner between the two side surfaces and the thickness of the exterior were measured. The result is shown in FIG.
[0026]
As shown in FIG. 3, when the radius of the corner rounding process was 1.0 mm or more, the protrusion amount of the internal electrode was 5 μm or less, and the thickness of the outer package was 5 μm or more.
[0027]
This result can be considered as follows. That is, (1) when the radius of the corner rounding process is less than 1.0 mm, the protrusion amount of the internal electrode layer is reduced due to a difference in mechanical properties of the internal electrode layer and the piezoelectric ceramic layer with respect to the corner rounding process (polishing). Although it exceeds 5 μm, the radius of the corner rounding process increases, and the polished surface of the internal electrode layer and the polished surface of the piezoelectric ceramic layer gradually match. (2) When the radius of the corner rounding process is small, the thickness of the exterior portion at this corner is thinner than other portions, but when the radius of the corner rounding process is large, the thickness of the exterior portion at this corner is large. The thickness approaches the thickness of other parts.
[0028]
As can be seen from the results in Table 1 and FIG. 3, when the radius of the corner rounding treatment is 1.0 mm or more, the end face of the internal electrode layer is sufficiently covered with the exterior, so that the durability can be improved.
[0029]
【The invention's effect】
As described above, according to the present invention, a part or all of the corners sandwiched between two side surfaces of the multilayer piezoelectric ceramic element is subjected to a corner rounding process with a radius of 1 mm or more, and In some or all of the corners sandwiched between the two side surfaces of the multilayer piezoelectric ceramic element, a corner portion is beveled, and the corner formed by performing the corner beveling process has a radius of 1 mm or more. By performing the rounding process of the corner, the protrusion of the internal electrode at the corner can be suppressed, and after the exterior is covered, the thickness of the exterior at the corner does not become thin, and thus the internal electrode at the corner is removed. , And the occurrence of discharge between the internal electrodes is prevented, thereby making it possible to provide a laminated piezoelectric ceramic element.
[Brief description of the drawings]
FIG. 1 is a diagram showing a laminated piezoelectric ceramic element according to a first embodiment. FIG. 1A is a sectional view taken along line BB, and FIG. 1B is a sectional view taken along line AA.
FIG. 2 is a diagram showing a laminated piezoelectric ceramic element according to a second embodiment. FIG. 2A is a sectional view taken along line DD, and FIG. 2B is a sectional view taken along line CC.
FIG. 3 is a diagram showing the amount of internal electrode projections and the thickness of an outer package at the corner when the radius of the corner is changed in the corner rounding process.
FIG. 4 is a diagram showing a multilayer piezoelectric ceramic element of Conventional Example 1. 4A is a sectional view taken along line FF, and FIG. 4B is a sectional view taken along line EE.
FIG. 5 is a diagram showing a multilayer piezoelectric ceramic element of Conventional Example 2. FIG. 5A is a sectional view taken along line HH, and FIG. 5B is a sectional view taken along line GG.
FIG. 6 is a sectional view of a corner portion in a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic layer 2 Lead wire 3 Internal electrode layer 4 External electrode 5 Exterior 6 Insulating layer

Claims

A laminated body including a plurality of laminated polygonal piezoelectric ceramic layers and internal electrodes formed between the piezoelectric ceramic layers; and one of the internal electrodes on one of two side surfaces out of the side surfaces in the stacking direction of the laminated body. In a multilayer piezoelectric ceramic element having an external electrode formed on each of the side surfaces so as to extend in the stacking direction so as to be connected every other so as to form a counter electrode, the piezoelectric device is sandwiched between the side surfaces in the stacking direction. A laminated piezoelectric ceramic element, wherein at least a part of a corner is subjected to a corner rounding process with a radius of 1 mm or more.

A laminated body including a plurality of laminated polygonal piezoelectric ceramic layers and internal electrodes formed between the piezoelectric ceramic layers; and one of the internal electrodes on one of two side surfaces out of the side surfaces in the stacking direction of the laminated body. A multi-layer piezoelectric ceramic element having an external electrode formed on each of the side surfaces so as to extend in the laminating direction so as to be connected to each other so as to form a counter electrode. At least a part of the corners formed is subjected to corner corner shaving processing, and each of the newly formed corners by the corner corner shaving processing is subjected to corner rounding processing with a radius of 1 mm or more. Laminated piezoelectric ceramic element.