JP4158886B2

JP4158886B2 - Multilayer piezoelectric actuator element

Info

Publication number: JP4158886B2
Application number: JP2002196963A
Authority: JP
Inventors: 文雄高尾; 崇行井上
Original assignee: NEC Tokin Corp
Current assignee: Tokin Corp
Priority date: 2002-07-05
Filing date: 2002-07-05
Publication date: 2008-10-01
Anticipated expiration: 2022-07-05
Also published as: JP2004039954A

Description

【０００１】
【発明の属する技術分野】
本発明は、圧電セラミック層と内部電極層を積層した積層型圧電アクチュエータ素子に関し、特に、高温環境下や、高い電界強度で使用される積層型圧電アクチュエータ素子に好適なものである。
【０００２】
【従来の技術】
積層型圧電アクチュエータ素子は、圧電セラミックス層と内部電極層を交互に積層し、内部電極層が一層ずつ対向電極になるように一対の外部電極に接続した構造で、電圧の印加により積層方向に数ミクロンから数１０ミクロンの変位量を発生したり、約３５ＭＰａの力を発生することが出来る。その主な用途は、半導体製造用の微小の位置決め装置や特殊なガスの流量を調整するマスフローコントローラのアクチュエータのような産業機器や、変位量を拡大する機構に積層圧電アクチュエータを組み込み、ワイヤー式ドットプリンターやインチワーム式超音波モータ等の民生機器まで、広い範囲に及んでいる。
【０００３】
近年、自動車のエンジンルーム内や高温蒸着装置内等の１００℃以上の高温環境下で、積層型圧電アクチュエータ素子を使用する用途が増加しているが、繰り返し高温中で、前記積層型圧電アクチュエータ素子を駆動すると、熱履歴による圧電セラミックスと絶縁層の熱膨張係数の異なりが原因で、圧電セラミックス層と絶縁層の境界に応力が生じ、該応力により絶縁層にクラックが生じ、絶縁層と圧電セラミックス層が剥離し絶縁性を失うという問題があり、絶縁性に優れ、高信頼性の積層型圧電アクチュエータ素子が要求されている。
【０００４】
また、積層型圧電アクチュエータ素子を組み込む装置の小型化に伴い、より小型で大きな変位が得られる積層型圧電アクチュエータ素子の開発が必要であり、そのため圧電セラミック層を薄膜化し、従来以上の高い電界強度で駆動が可能な積層型圧電アクチュエータ素子が要求されている。
【０００５】
しかしながら、従来の積層型圧電アクチュエータ素子は、高い電界強度となる電圧を印加して変位量を大きくすると、前記積層型圧電アクチュエータ素子の側面に露出した内部電極層の上の絶縁層に割れを生じ、前記積層型圧電アクチュエータ素子が短絡するため、印加できる電圧には制約（限界電界強度）があり、その結果、目的とする大きな変位量が得られないという問題点があった。
【０００６】
【発明が解決しようとする課題】
したがって、本発明の課題は、１００℃以上の高温環境下や、高い電界強度で大きな変位が長期間に渡って繰り返されるような駆動条件においても、小型で、絶縁層に割れが生じ難い高信頼性の積層型圧電アクチュエータ素子を提供することにある。
【０００７】
【課題を解決する為の手段】
本発明によれば、複数の圧電セラミック層と内部電極層を積層一体化した積層体で、前記内部電極層が対向電極となるよう、前記積層体側面に露出する前記内部電極層を一層おきに絶縁層で被覆し、該絶縁層を覆って一層おきに前記内部電極層と導通する一対の外部電極を形成してなる積層型圧電アクチュエータ素子において、前記絶縁層がホウケイ酸系ガラスと、石英ガラス粉末または溶融石英ガラス粉末、二酸化ケイ素化合物、チタン酸アルミニウムのうち少なくとも１種類からなる低熱膨張フィラーの混合物であることを特徴とする積層型圧電アクチュエータ素子が得られる。
【０００８】
また、本発明によれば、前記積層型圧電アクチュエータの絶縁層に用いられるホウケイ酸系ガラスと二酸化ケイ素等の混合物は、室温から焼き付け温度までの熱膨張係数が前記積層型圧電アクチュエータの前記圧電セラミック層の熱膨張係数の２０％から９５％の範囲にあることを特徴とする積層型圧電アクチュエータ素子が得られる。
【０００９】
積層型圧電アクチュエータ素子の絶縁層の機械的強度向上方法として、絶縁層自体の組織を制御する方法と、絶縁層に加わる応力を減少する二つの方法が考えられる。
【００１０】
前者は、絶縁層の組織に第二相として強度が大きな組成物を混合分散し、絶縁層全体の強度を向上したもので、本発明においては、ホウケイ酸系ガラスの絶縁層を母相として、高強度で、かつ、低熱膨張係数の石英ガラス粉末または溶融石英ガラス粉末、二酸化ケイ素化合物粉末、チタン酸アルミニウム粉末のうち少なくとも１種類を第二相として母相中に混合分散することで、絶縁層の機械的強度を向上し、従来の限界電界強度以上の電界強度でも前記絶縁層が破壊しない積層型圧電アクチュエータ素子を提供するものである。
【００１１】
後者は、積層型圧電アクチュエータ素子の変位時に、積層型圧電アクチュエータ素子から絶縁層に引っ張り応力が加わり、該応力により絶縁層が破壊に至るという破壊のメカニズムから、積層型圧電アクチュエータ素子から絶縁層に、予め圧縮応力を加えておいて、積層型圧電アクチュエータ素子が変位時の絶縁層に加わる引っ張り応力を低減し、絶縁層の強度を向上したものである。
【００１２】
本発明においては、絶縁層の熱膨張係数を積層型圧電アクチュエータ素子の圧電セラミックスの熱膨張係数より小さくすることで、５００℃以上の高温で絶縁層を形成後、室温や１００℃程度の温度に戻した時に、積層型圧電アクチュエータ素子から絶縁層に圧縮応力を加えることが出来、該圧縮応力が前記積層型圧電アクチュエータ素子が変位した時の前記絶縁層へ加わる引っ張り応力を低減し、該絶縁層の破壊を防止することが可能となる。
【００１３】
さらに、絶縁層の熱膨張係数を圧電セラミックスの熱膨張係数の２０〜９５％の範囲内としたのは、２０％未満では絶縁層と圧電セラミックスの熱膨張係数の差が大きくなり過ぎ、室温と１００℃以上の使用温度の熱履歴を繰り返すことにより、該絶縁層と圧電セラミックスの境界部が剥離し、絶縁性が低下してしまうので、前記絶縁層の熱膨張係数の２０〜９５％の範囲内とする必要がある。
【００１４】
【発明の実施の形態】
以下に、本発明の実施の形態を、図を用いて詳細に説明する。
【００１５】
図１は、本発明の実施の形態における積層型圧電アクチュエータ素子の長さ方向の断面図である。図１で、圧電セラミックスは圧電歪定数が大きなジルコン酸チタン酸鉛（ＰＺＴ）系圧電セラミックスを使用し、内部電極は銀／パラジウム電極ペーストを使用して、厚膜の印刷、積層法により、複数の圧電セラミック層２と内部電極層３を積層一体化した積層体１で、前記内部電極層３が対向電極となるよう、前記積層体１の側面に露出する前記内部電極層３を一層おきに絶縁層４で被覆し、該絶縁層４を覆って一層おきに前記内部電極層３と導通する一対の焼き付け銀の外部電極５を形成してなる積層型圧電アクチュエータ素子で、前記絶縁層４はホウケイ酸亜鉛ガラスと溶融石英ガラス粉末の混合体を６００℃で焼き付けたものである。
【００１６】
ここで、使用した圧電セラミックスの３０℃〜５００℃の温度範囲における熱膨張係数は、約４５×１０^-7／ｄｅｇであり、また、絶縁層に用いたホウケイ酸亜鉛ガラスと溶融石英ガラスの熱膨張係数はそれぞれ６３×１０^-7／ｄｅｇと５×１０^-7／ｄｅｇである。本発明で用いる石英ガラスや溶融石英ガラスの３０℃〜５００℃の温度範囲における熱膨張係数は、圧電セラミックスやホウケイ酸系ガラスの約１／１０程度で、ホウケイ酸系ガラスとの混合比率を変えることで、絶縁層の熱膨張係数を小さいほうに変化させることが可能である。
【００１７】
寸法が５ｍｍ×５ｍｍ×１０ｍｍで１０ｍｍの方向に厚さ７５μｍの圧電セラミックス層を１２０層積層一体化し、前記ホウケイ酸亜鉛ガラスと溶融石英ガラス粉末の混合比率を変えて、熱膨張係数の異なる絶縁層を有する積層型圧電アクチュエータを試作した。溶融石英ガラス粉末の混合比率を変えた時の絶縁層の熱膨張係数を測定した。また、該熱膨張係数を測定した試料を用いて曲げ強度を測定した。測定結果を表１に示した。
【００１８】
【表１】

【００１９】
表１から、溶融石英ガラスの混合量が増えるに従い、絶縁層の熱膨張係数が小さくなり、曲げ強度が大きくなることから、絶縁層の機械的強度が向上したことが分かる。
【００２０】
また、試作した積層型圧電アクチュエータを１００℃の高温環境下で、０−１５０Ｖのパルス電圧を印加するエージング試験を実施して、絶縁抵抗の変化を測定した。比較のため、従来使用していたホウケイ酸亜鉛ガラスのみの絶縁層を有する積層型圧電アクチュエータも試作し、同時にエージングを実施し絶縁抵抗の変化を測定した。測定結果を表２に示した。
【００２１】
【表２】

【００２２】
表２の絶縁抵抗の測定結果から、試料Ｎｏ.２から６までは、エージングによる絶縁抵抗の劣化は比較例に比べ、わずかであり、高温環境下で連続駆動した時、高い信頼性が得られることが分かる。試料Ｎｏ.１は絶縁層の熱膨張係数が小さくなり過ぎ、圧電セラミックス層と絶縁層の密着力が低下したため、エージング中に圧電セラミックス層と絶縁層が剥離し、絶縁抵抗が劣化したものである。試料Ｎｏ.２からＮｏ.６の熱膨張率は、圧電セラミックススの熱膨張係数の２０％から９５％の範囲にある。
【００２３】
本発明の実施の形態では、絶縁層として溶融石英ガラス粉末を用いた実施例の説明をしたが、溶融石英ガラス粉末と同様な、高強度で、かつ、低熱膨張係数の、石英ガラス粉末、二酸化ケイ素化合物粉末、チタン酸アルミニウム粉末のうち少なくとも１種類を用いても、２０００時間のエージングで８０ＭΩ以上と同様の効果が得られた。
【００２４】
【発明の効果】
以上説明したように、絶縁層に低熱膨張係数のフィラーを混合することにより、絶縁層の強度を改善し、圧電セラミック層の伸縮に伴う歪の発生に起因する絶縁層のクラックの発生を防止できるため、高電圧の長時間繰り返し印加においても故障が発生しない高信頼性の積層型圧電アクチュエータ素子の提供が可能である。
【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素子の長さ方向の断面図。
【図２】従来の積層型圧電アクチュエータ素子の長さ方向の断面図。
【符号の説明】
１，１１積層体
２，１２圧電セラミック層
３，１３内部電極層
４，１４絶縁層
５，１５外部電極
６，１６リード線[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated piezoelectric actuator element in which a piezoelectric ceramic layer and an internal electrode layer are laminated, and is particularly suitable for a laminated piezoelectric actuator element used in a high temperature environment and with high electric field strength.
[0002]
[Prior art]
A laminated piezoelectric actuator element has a structure in which piezoelectric ceramic layers and internal electrode layers are alternately laminated and connected to a pair of external electrodes so that each internal electrode layer becomes a counter electrode. A displacement amount of several microns to several tens of microns can be generated, and a force of about 35 MPa can be generated. Its main application is the incorporation of laminated piezoelectric actuators into industrial equipment such as micro-positioning devices for semiconductor manufacturing, actuators of mass flow controllers that adjust the flow rate of special gases, and mechanisms that expand displacement, and wire-type dots It covers a wide range of consumer devices such as printers and inchworm type ultrasonic motors.
[0003]
In recent years, the use of laminated piezoelectric actuator elements in a high temperature environment of 100 ° C. or higher such as in an engine room of a car or a high temperature vapor deposition apparatus has increased. When the is driven, stress is generated at the boundary between the piezoelectric ceramic layer and the insulating layer due to the difference in thermal expansion coefficient between the piezoelectric ceramic and the insulating layer due to the thermal history, and the insulating layer and the piezoelectric ceramic are cracked due to the stress. There is a problem that the layers are peeled off and the insulating property is lost, and there is a demand for a laminated piezoelectric actuator element having excellent insulating properties and high reliability.
[0004]
In addition, with the miniaturization of devices incorporating multilayer piezoelectric actuator elements, it is necessary to develop multilayer piezoelectric actuator elements that can be made smaller and obtain larger displacements. For this reason, the piezoelectric ceramic layer is made thinner, and the electric field strength is higher than before. Therefore, there is a demand for a multilayer piezoelectric actuator element that can be driven by the above.
[0005]
However, when the displacement amount is increased by applying a voltage with high electric field strength to the conventional multilayer piezoelectric actuator element, the insulating layer above the internal electrode layer exposed on the side surface of the multilayer piezoelectric actuator element is cracked. Since the laminated piezoelectric actuator element is short-circuited, there is a problem that a voltage that can be applied is limited (limit electric field strength), and as a result, a desired large displacement cannot be obtained.
[0006]
[Problems to be solved by the invention]
Therefore, the problem of the present invention is that it is small in size and high in reliability that is resistant to cracking in an insulating layer even in a high temperature environment of 100 ° C. or higher or in a driving condition in which a large displacement is repeated over a long period with a high electric field strength. It is another object of the present invention to provide a multi-layer piezoelectric actuator element.
[0007]
[Means for solving the problems]
According to the present invention, in the laminated body in which a plurality of piezoelectric ceramic layers and internal electrode layers are laminated and integrated, the internal electrode layers exposed on the side surfaces of the laminated body are provided every other layer so that the internal electrode layer becomes a counter electrode. In a laminated piezoelectric actuator element formed by covering with an insulating layer and covering the insulating layer and forming a pair of external electrodes that are electrically connected to the internal electrode layer, the insulating layer comprises borosilicate glass and quartz glass. A multilayer piezoelectric actuator element characterized in that it is a mixture of at least one kind of powder or fused silica glass powder, silicon dioxide compound, and aluminum titanate is obtained.
[0008]
According to the present invention, the mixture of borosilicate glass and silicon dioxide used for the insulating layer of the multilayer piezoelectric actuator has a coefficient of thermal expansion from room temperature to a baking temperature, and the piezoelectric ceramic of the multilayer piezoelectric actuator. A laminated piezoelectric actuator element characterized by being in the range of 20% to 95% of the thermal expansion coefficient of the layer is obtained.
[0009]
As a method for improving the mechanical strength of the insulating layer of the multilayer piezoelectric actuator element, two methods are conceivable: a method for controlling the structure of the insulating layer itself and a method for reducing the stress applied to the insulating layer.
[0010]
The former is a composition in which the strength of the second phase is mixed and dispersed in the structure of the insulating layer to improve the strength of the entire insulating layer.In the present invention, the insulating layer of borosilicate glass is used as a parent phase. By mixing and dispersing at least one of quartz glass powder or fused silica glass powder, silicon dioxide compound powder, and aluminum titanate powder having high strength and low thermal expansion coefficient as a second phase in the matrix phase, an insulating layer is obtained. The multilayer piezoelectric actuator element is improved so that the insulating layer does not break even when the electric field strength exceeds the conventional limit electric field strength.
[0011]
The latter is based on the mechanism of destruction in which a tensile stress is applied from the multilayer piezoelectric actuator element to the insulating layer when the multilayer piezoelectric actuator element is displaced, and the insulating layer breaks due to the stress. In addition, compressive stress is applied in advance, the tensile stress applied to the insulating layer when the multilayer piezoelectric actuator element is displaced is reduced, and the strength of the insulating layer is improved.
[0012]
In the present invention, by making the thermal expansion coefficient of the insulating layer smaller than the thermal expansion coefficient of the piezoelectric ceramic of the multilayer piezoelectric actuator element, the insulating layer is formed at a high temperature of 500 ° C. or higher, and then the room temperature or 100 ° C. is reached. When returned, compressive stress can be applied to the insulating layer from the laminated piezoelectric actuator element, and the compressive stress reduces the tensile stress applied to the insulating layer when the laminated piezoelectric actuator element is displaced, and the insulating layer Can be prevented.
[0013]
Furthermore, the thermal expansion coefficient of the insulating layer is set within the range of 20 to 95% of the thermal expansion coefficient of the piezoelectric ceramic. If the thermal expansion coefficient is less than 20%, the difference between the thermal expansion coefficients of the insulating layer and the piezoelectric ceramic becomes too large. By repeating the thermal history at a use temperature of 100 ° C. or higher, the boundary between the insulating layer and the piezoelectric ceramic is peeled off and the insulating property is lowered. Therefore, the range of 20 to 95% of the thermal expansion coefficient of the insulating layer It is necessary to be inside.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0015]
FIG. 1 is a cross-sectional view in the length direction of a multilayer piezoelectric actuator element according to an embodiment of the present invention. In FIG. 1, the piezoelectric ceramic is a lead zirconate titanate (PZT) type piezoelectric ceramic having a large piezoelectric strain constant, and the internal electrode is a silver / palladium electrode paste. In the laminated body 1 in which the piezoelectric ceramic layer 2 and the internal electrode layer 3 are laminated and integrated, the internal electrode layers 3 exposed on the side surfaces of the laminated body 1 are formed every other layer so that the internal electrode layer 3 becomes a counter electrode. A laminated piezoelectric actuator element that is covered with an insulating layer 4 and that forms a pair of baked silver external electrodes 5 that cover the insulating layer 4 and is electrically connected to the internal electrode layer 3 every other layer. A mixture of zinc borosilicate glass and fused silica glass powder is baked at 600 ° C.
[0016]
Here, the thermal expansion coefficient in the temperature range of 30 ° C. to 500 ° C. of the used piezoelectric ceramic is about 45 × 10 ⁻⁷ / deg, and the heat of the zinc borosilicate glass and fused quartz glass used for the insulating layer. The expansion coefficients are 63 × 10 ⁻⁷ / deg and 5 × 10 ⁻⁷ / deg, respectively. The thermal expansion coefficient in the temperature range of 30 ° C. to 500 ° C. of quartz glass or fused silica glass used in the present invention is about 1/10 that of piezoelectric ceramics or borosilicate glass, and the mixing ratio with borosilicate glass is changed. As a result, the thermal expansion coefficient of the insulating layer can be changed to a smaller value.
[0017]
Insulating layers with different thermal expansion coefficients by integrating 120 layers of piezoelectric ceramic layers with dimensions of 5 mm x 5 mm x 10 mm and a thickness of 75 μm in the direction of 10 mm, and changing the mixing ratio of the borosilicate glass and fused silica glass powder. A multilayer piezoelectric actuator having The thermal expansion coefficient of the insulating layer when the mixing ratio of the fused silica glass powder was changed was measured. Moreover, bending strength was measured using the sample which measured this thermal expansion coefficient. The measurement results are shown in Table 1.
[0018]
[Table 1]

[0019]
From Table 1, it can be seen that the mechanical strength of the insulating layer is improved because the thermal expansion coefficient of the insulating layer decreases and the bending strength increases as the mixing amount of the fused silica glass increases.
[0020]
In addition, an aging test in which a pulse voltage of 0 to 150 V was applied to the prototype multilayer piezoelectric actuator in a high temperature environment of 100 ° C. was performed to measure a change in insulation resistance. For comparison, a multilayer piezoelectric actuator having an insulating layer made only of zinc borosilicate glass, which was conventionally used, was also prototyped, and at the same time, aging was performed to measure the change in insulation resistance. The measurement results are shown in Table 2.
[0021]
[Table 2]

[0022]
From the measurement results of the insulation resistance shown in Table 2, the deterioration of the insulation resistance due to aging is slight compared with the comparative examples for sample Nos. 2 to 6, and high reliability is obtained when continuously driven in a high temperature environment. I understand that. In sample No. 1, the thermal expansion coefficient of the insulating layer was too small, and the adhesion between the piezoelectric ceramic layer and the insulating layer was reduced, so that the piezoelectric ceramic layer and the insulating layer peeled off during aging and the insulation resistance deteriorated. . The thermal expansion coefficients of samples No. 2 to No. 6 are in the range of 20% to 95% of the thermal expansion coefficient of the piezoelectric ceramics.
[0023]
In the embodiment of the present invention, the example using the fused silica glass powder as the insulating layer has been described. However, the fused silica glass powder, the high strength, and the low thermal expansion coefficient similar to the fused quartz glass powder, Even when at least one of silicon compound powder and aluminum titanate powder was used, the same effect as that of 80 MΩ or more was obtained after aging for 2000 hours.
[0024]
【The invention's effect】
As described above, by mixing a filler with a low thermal expansion coefficient in the insulating layer, the strength of the insulating layer can be improved, and the occurrence of cracks in the insulating layer due to the occurrence of strain accompanying expansion and contraction of the piezoelectric ceramic layer can be prevented. Therefore, it is possible to provide a long repetition multilayer piezoelectric actuator device of high reliability that failure does not occur even in the high voltage application.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a multilayer piezoelectric actuator element of the present invention.
FIG. 2 is a cross-sectional view in the length direction of a conventional multilayer piezoelectric actuator element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,11

Laminated body

2,12 Piezoelectric ceramic layer 3,13 Internal electrode layer 4,14 Insulating

layer

5,15

External electrode

6,16 Lead wire

Claims

A laminated body in which a plurality of piezoelectric ceramic layers and internal electrode layers are laminated and integrated, and the internal electrode layers exposed on the side surfaces of the laminated body are covered with an insulating layer every other layer so that the internal electrode layer becomes a counter electrode, In the laminated piezoelectric actuator element that covers the insulating layer and forms a pair of external electrodes that are electrically connected to the internal electrode layer every other layer, the insulating layer is made of borosilicate glass and quartz glass powder or fused silica glass powder, A laminated piezoelectric actuator element comprising a filler composed of at least one of a silicon dioxide compound and aluminum titanate .

2. The multilayer piezoelectric actuator element according to claim 1, wherein the insulating layer is in a range of 20% to 95% of a thermal expansion coefficient of the piezoelectric ceramic layer .