JP3730893B2 - LAMINATED PIEZOELECTRIC ELEMENT, ITS MANUFACTURING METHOD, AND INJECTION DEVICE - Google Patents

Description

【００８５】
この表１から、収縮調整層中の金属成分量が５体積％より少ない試料では、駆動時に活性部と不活性部の境界で破損が生じてしまっている。一方、収縮調整層中の金属成分量が６０体積％以上の試料では、駆動時に絶縁破壊するか、若しくは初期状態で絶縁不良だった。一方、収縮調整層中の金属成分量が５〜５０体積％の試料では、１×１０⁹まで駆動しても、破損、絶縁破壊等の異常は見られなかった。
【００８６】
【発明の効果】
本発明の積層型圧電素子によれば、焼結性を向上する金属粒子が不活性部の外周部にまで存在することになり、収縮調整層の金属粒子が不活性部の外周部の焼結性を向上し、焼成時の活性部と不活性部の収縮率が実質的に等しくなり、焼成時に活性部と不活性部の界面及びその近傍でのデラミネーションやクラック等の発生をなくし、アクチュエータを駆動させた場合においても活性部と不活性部の界面及びその近傍で破損することがない高信頼性を備えた積層型圧電素子を提供することができる。
【図面の簡単な説明】
【図１】本発明の積層型圧電素子を示すもので、（ａ）は斜視図、（ｂ）は（ａ）のＡ−Ａ’線に沿った縦断面図である。
【図２】本発明の噴射装置を示す説明図である。
【図３】活性部と不活性部の密度差と、不良率の関係を示すグラフである。
【図４】収縮調整層中の金属成分の割合と、活性部と不活性部の密度差及び収縮調整層のシート抵抗の関係を示すグラフである。
【図５】従来の積層型圧電アクチュエータの縦断面図である。
【符号の説明】
１、９ａ・・・圧電体
１ａ・・・柱状積層体
２・・・内部電極
４・・・外部電極
９ｂ・・・収縮調整層
８・・・活性部
９・・・不活性部
３１・・・収納容器
３３・・・噴射孔
３５・・・バルブ
４３・・・圧電アクチュエータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer piezoelectric element, a method for manufacturing the same, and an injection device, for example, a multilayer piezoelectric element used for a precision positioning device such as an automobile fuel injection device and an optical device, a drive element for vibration prevention, and a method for manufacturing the same. The present invention relates to an injection device.
[0002]
[Prior art]
Conventionally, as a multilayer piezoelectric element, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately stacked is known. Multilayer piezoelectric actuators are classified into two types: the simultaneous firing type and the stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Since the multilayer piezoelectric actuator of the type is advantageous for thinning, its superiority is being shown.
[0003]
FIG. 5 shows a conventional multilayer piezoelectric actuator. In this actuator, piezoelectric bodies 51 and internal electrodes 52 are alternately stacked to form active portions 53, and inactive portions are formed on both end surfaces in the stacking direction. 55 is laminated | stacked and the columnar laminated body is comprised by this. The internal electrode 52 is formed so that one end thereof is alternately covered with the insulator 61 on the left and right sides, and the strip-like external electrode 70 is electrically connected to the internal electrode 52 every two layers on the left and right. On the strip-shaped external electrode 70, a lead wire 76 is further fixed with solder 77.
[0004]
In such a multilayer piezoelectric actuator, conventionally, an internal electrode paste is printed on a ceramic green sheet, and a plurality of green sheets coated with the internal electrode paste are stacked to produce an active part molded body, and the internal electrode paste is applied. An inactive part molded body formed by laminating a plurality of ceramic green sheets that are not laminated is laminated on the upper and lower surfaces of the active part molded body to produce a columnar laminated molded body, which is fired to form a columnar laminated body Was making.
[0005]
[Problems to be solved by the invention]
However, in the multilayer piezoelectric actuator, an active part molded body produced by alternately laminating green sheets and internal electrode paste and an inactive part molded body produced by laminating a plurality of green sheets are laminated. Because of the simultaneous firing, there is a problem that delamination, cracks, etc. occur between the active part and the inactive part after firing due to the difference in firing shrinkage between the active part shaped body and the inactive part shaped body. was there.
[0006]
That is, since the green sheet in the active part molded body is sandwiched between internal electrode pastes, sintering is promoted by the catalytic action of noble metals such as silver and palladium in the internal electrode paste, and is not sandwiched between internal electrode pastes. There was a problem that the shrinkage amount at the time of firing was larger than that of the green sheet in the inactive part molded body, and delamination, cracks and the like were generated between the active part and the inactive part. In addition, even if delamination or cracks do not occur, there is a problem that residual stress is generated between the active portion and the inactive portion, causing damage when the actuator is driven.
[0007]
In order to solve such a problem, Japanese Patent Laid-Open No. 63-288074 discloses that silver is added to a green sheet that forms an inactive portion. On the other hand, since the shrinkage behavior of the inactive part is sensitive, it is difficult to completely match the firing shrinkage of the active part and the inactive part.
[0008]
Further, when the amount of the silver component added is large, the insulating property of the inactive part is lowered, and there is a problem that conduction is likely to occur between a pair of external electrodes extending to the inactive part.
[0009]
Furthermore, this method has a problem that two types of green sheets have to be prepared, and the process becomes complicated.
[0010]
In Japanese Patent Laid-Open No. 9-270540, the inactive portion is formed by alternately laminating piezoelectric bodies and metal layers that are not connected to external electrodes. In this method, the metal layer is inactive portions. It is necessary to control the pattern so that it is not exposed to the outer surface of the material, and the process is complicated, and the vicinity of the interface between the active part and the inactive part is substantially the same in the central part but the firing shrinkage rate is substantially the same. Since the metal layer is not formed, the shrinkage rate cannot be made the same, and there is still a problem that residual stress is generated between the active part and the inactive part, causing damage when the actuator is driven. It was.
[0011]
The present invention reduces the residual stress at the time of firing that occurs at the interface between the active part and the inactive part, and suppresses the breakage at the interface between the active part and the inactive part even during driving. And a manufacturing method thereof and an injection device.
[0015]
[Means for Solving the Problems]
The present inventionofThe laminated piezoelectric element is formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and is provided at each of the active portion where the piezoelectric body is displaced and at both ends in the laminating direction of the active portion. A columnar laminate including an active portion; and a pair of external electrodes provided on a side surface of the columnar laminate, the internal electrodes being alternately electrically connected every other layer, and the active portion; A multilayer piezoelectric element in which the inactive part is simultaneously fired, wherein the inactive part is formed by alternately laminating piezoelectric bodies and shrinkage adjustment layers containing metal particles, and the shrinkage adjustment layer Of these, at least one layer end is exposed on the side surface of the inactive part.
[0016]
In such a multilayer piezoelectric element, the metal particles that improve the sinterability are present up to the outer peripheral portion of the inactive portion, and the metal particles of the shrinkage adjusting layer have the sinterability of the outer peripheral portion of the inactive portion. As a result, the shrinkage rate in the vicinity of the interface between the active part and the inactive part can be made substantially the same over the entire region.
[0017]
In the multilayer piezoelectric element of the present invention, the sheet resistance value of the shrinkage adjustment layer is 10⁶It is desirable that it is Ω / □ or more. Thereby, the high insulation of an inactive part can be maintained.
[0018]
Moreover, it is desirable that the shrinkage adjusting layer is composed of 5 to 50% by volume of metal particles and 50 to 95% by volume of piezoelectric particles. By making the metal particles 5 to 50% by volume and the balance being piezoelectric particles, it is possible to maintain high insulation of the inactive part and to improve the sinterability by the metal particles, and the shrinkage rate of the inactive part Can be matched to the contraction rate of the active part.
[0019]
Furthermore, it is desirable that the metal particles constituting the shrinkage adjusting layer are the same as the metal particles constituting the internal electrode. Thereby, the shrinkage behavior during firing of the inactive part can be matched with the shrinkage behavior of the active part, and delamination and cracks can be prevented from occurring at the interface between the active part and the inactive part and in the vicinity thereof.
[0020]
Protruding conductive members are respectively provided at the end of the shrinkage adjustment layer and the end of the internal electrode exposed on the external electrode forming surface of the columnar laminate, and the protruding conductive member is connected to the external electrode. It is desirable that By exposing the edge of the shrinkage adjustment layer to the external electrode formation surface of the columnar laminate, it is effective to generate stress caused by the shrinkage difference between the inactive portion and the active portion even in the vicinity of the external electrode formation surface of the columnar laminate. Therefore, the durability can be greatly improved.
[0021]
Further, by providing a protruding conductive member at each of the end of the shrinkage adjustment layer and the end of the internal electrode exposed on the external electrode forming surface of the columnar laminate, and connecting the protruding conductive member to the external electrode, Since not only the end of the internal electrode exposed on the external electrode formation surface of the columnar laminate but also the end of the shrinkage adjustment layer is connected to the external electrode via the protruding conductive member, the laminated piezoelectric Even when the element is continuously driven under a high electric field, the external electrode and the internal electrode are not disconnected, and the durability can be greatly improved.
[0022]
The manufacturing method of the multilayer piezoelectric element of the present invention is such that a pattern for a shrinkage adjustment layer containing metal powder is formed on both ends in the stacking direction of an active part molded body formed by stacking a plurality of ceramic green sheets on which internal electrode patterns are formed. A step of producing a columnar laminate formed by laminating a plurality of formed ceramic green sheets and providing an inactive part formed body in which at least one end of the shrinkage adjustment layer pattern is exposed on the side surface; Firing the columnar laminated molded body to produce a columnar laminated body, and forming a pair of external electrodes on the side surfaces of the columnar laminated body in which internal electrodes are alternately electrically connected every other layer. It is provided.
[0023]
According to such a manufacturing method, it is possible to approximate the firing shrinkage ratio between the active portion in which a plurality of internal electrodes and piezoelectric bodies are alternately laminated and the inactive portion in which a plurality of shrinkage adjustment layers and piezoelectric bodies are alternately laminated. Therefore, it is possible to prevent problems such as delamination and cracks from occurring at and near the interface between the active part and the inactive part during firing. The metal powder may be an alloy powder of a plurality of metals such as silver-palladium and silver-platinum.
[0024]
An injection device according to the present invention includes a storage container having an injection hole, the laminated piezoelectric element housed in the storage container, and a valve that ejects liquid from the injection hole by driving the laminated piezoelectric element. It has.
[0025]
In such an injection device, as described above, since the residual stress at the time of firing generated at the interface between the active portion and the inactive portion in the multilayer piezoelectric element itself can be eliminated and the durability can be greatly improved, the durability of the injection device can be improved. Can also be improved.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B show an embodiment of a multilayer piezoelectric element comprising a multilayer piezoelectric actuator according to the present invention. FIG. 1A is a perspective view, and FIG. 1B is a longitudinal section along the line AA 'in FIG. FIG.
[0027]
As shown in FIG. 1, the multilayer piezoelectric element of the present invention is configured by forming positive and negative external electrodes 4 on opposite side surfaces of a columnar laminate 1a. The columnar laminate 1a includes an active portion 8 in which a plurality of piezoelectric bodies 1 and internal electrodes 2 are alternately laminated, and inactive portions 9 formed on both end surfaces of the active portion 8 in the stacking direction. Yes.
[0028]
The end portions of the internal electrodes 2 are exposed on the external electrode 4 forming surface of the columnar laminate 1a every other layer, and projecting conductive members 7 are formed on the exposed portions, respectively. The external electrodes 4 made of a metal plate are joined, whereby the internal electrodes 2 are electrically connected to each external electrode 4 every other layer. On the other hand, the end of the internal electrode 2 that is not connected to the external electrode 4 is covered with an insulator 3. Furthermore, a lead wire 6 is connected and fixed to the external electrode 4 with solder or the like.
[0029]
The piezoelectric body 1 is made of, for example, lead zirconate titanate Pb (Zr, Ti) O._Three(Hereinafter abbreviated as PZT) or barium titanate BaTiO_ThreeIt is formed with the piezoelectric ceramic material etc. which have as a main component. This piezoelectric ceramic has a piezoelectric strain constant d indicating its piezoelectric characteristics.₃₃A high value is desirable.
[0030]
The thickness of the piezoelectric body 1 in the active portion 8, that is, the distance between the internal electrodes 2 is preferably 50 to 250 μm. In order to obtain a larger displacement amount by applying a voltage to the stacked piezoelectric actuator, a method of increasing the number of stacked layers is used, but when the number of stacked layers is increased, the piezoelectric body 1 in the active portion 8 is increased. This is because if the thickness is too large, the actuator cannot be reduced in size and height, and if the thickness of the piezoelectric body 1 in the active portion 8 is too thin, dielectric breakdown tends to occur.
[0031]
An internal electrode 2 having a thickness of 0.5 to 10 μm is disposed between the piezoelectric bodies 1 in the active part 8. The internal electrode 2 is formed of a metal material such as silver-palladium, and the active part 8. A predetermined voltage is applied to each of the piezoelectric bodies 1 in the middle, thereby causing the piezoelectric body 1 to be displaced by the inverse piezoelectric effect.
[0032]
In addition, a groove having a depth of 50 to 500 μm and a width of 30 to 200 μm in the stacking direction is formed on the surface of the columnar laminate 1a on the side surface of the active portion 8 where the external electrode 4 is formed. The insulator 3 is formed by filling a resin, a polyimide resin, a polyamideimide resin, a silicone rubber, or the like. Thus, the end portions of the internal electrode 2 are insulated by the insulators 3 alternately filled in the grooves every other layer, and the other non-insulated end portion of the internal electrode 2 is inserted through the projecting conductive member 7. The external electrode 4 is connected.
[0033]
The protruding conductive member 7 is preferably made of silver having a low Young's modulus or an alloy containing silver as a main component from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator. In addition, the protrusion height h of the protruding conductive member 7 is desirably 1/20 or more of the thickness of the piezoelectric body 1 in the active portion 8 from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator. In particular, the protrusion height h is desirably 15 to 50 μm.
[0034]
Further, the thickness t of the plate-like conductive member that constitutes the external electrode 4 follows the expansion and contraction of the actuator, and is disconnected between the external electrode 4 and the protruding conductive member 7 or between the protruding conductive member 7 and the internal electrode 2. It is desirable that the thickness is 50 μm or less from the viewpoint of preventing the occurrence of.
[0035]
The plate-like external electrode 4 is made of a metal having conductivity such as silver, nickel, copper, gold, and aluminum, and an alloy thereof. Among these, the bonding strength with the protruding conductive member 7 is high, and the Young In view of the low rate, silver or an alloy containing silver as a main component is desirable.
[0036]
The insulator 3 is preferably made of a material having a low elastic modulus that follows the displacement of the columnar laminate 1a, specifically, silicone rubber or the like, in order to strengthen the bonding with the columnar laminate 1a. It is.
[0037]
External electrodes 4 made of a plate-like conductive member are connected and fixed to the opposing side surfaces of the columnar laminate 1a via protruding conductive members 7, and the laminated internal electrodes 2 are attached to the external electrodes 4. Every other layer is electrically connected. The external electrode 4 made of this plate-like conductive member serves to commonly supply a voltage necessary for displacing the piezoelectric body 1 by the inverse piezoelectric effect to each internal electrode 2 in the active portion 8 connected thereto.
[0038]
Furthermore, a lead wire 6 is connected and fixed to the external electrode 4 with solder. The lead wire 6 serves to connect the external electrode 4 to an external voltage supply unit.
[0039]
And in this invention, the density of the interface vicinity of the active part 8 and the inactive part 9 is made substantially the same over the interface vicinity whole area. Here, the active portion 9 is a portion in which the piezoelectric body 1 is sandwiched between the internal electrodes 2 and the piezoelectric body 1 is displaced by applying a voltage to the external electrode 4. This refers to a portion that is not displaced even when a voltage is applied to the external electrode 4. Here, “substantially the same” means that the density difference between the active portion 8 and the inactive portion 9 is within 5%. That is, the quotient obtained by dividing the difference between the density of the active part 8 and the density of the inactive part 9 by the density of the active part 8 is within 5%. Further, the density of the active portion 8 refers to the density of a laminate including the piezoelectric body 1 and the internal electrode 2 included in the active portion 8. The density difference between the active portion 8 and the inactive portion 9 is preferably within 2% from the viewpoint of reducing the residual stress during firing. Moreover, it is best that the density of not only the vicinity of the interface between the active portion 8 and the inactive portion 9 but also the entire active portion 8 and the entire inactive portion 9 are substantially the same.
[0040]
That is, by making the density of the active part 8 and the density of the inactive part 9 substantially equal, the shrinkage rate of the active part 8 and the inactive part 9 during firing becomes substantially equal, It is possible to prevent the occurrence of delamination or cracks at the interface of the inactive portion 9 or in the vicinity thereof. Further, since the contraction rate of the active portion 8 and the inactive portion 9 can be made substantially equal, it is possible to prevent the residual stress from being generated at the interface between the active portion 8 and the inactive portion 9 and in the vicinity thereof, thereby driving the actuator. Even in this case, the active portion 8 and the inactive portion 9 are not damaged at the interface and in the vicinity thereof, and high reliability can be obtained.
[0041]
In the present invention, the inactive portion 9 is configured by alternately laminating the same piezoelectric body 9 a as the piezoelectric body of the active portion 8 and the shrinkage adjustment layer 9 b containing metal particles, and all the shrinkage adjustment layers are formed. The outer peripheral end portion of 9b is exposed on the side surface of the inactive portion 9. It should be noted that at least one outer peripheral end portion of the shrinkage adjustment layer 9b may be exposed on the side surface of the inactive portion 9. Further, a part of the outer peripheral end portion of the shrinkage adjustment layer 9b may be exposed on the side surface of the inactive portion 9. For example, the outer peripheral end portion of the shrinkage adjustment layer 9b is the inactive portion 9 where the external electrode 4 is formed. It may be exposed only on the side. From the viewpoint of reducing the stress generation at the interface between the active portion 8 and the inactive portion 9 and in the vicinity thereof, the outer peripheral end portions of all the shrinkage adjusting layers 9b are the four side surfaces of the inactive portion 9 as shown in FIG. It is desirable to be exposed. In addition, although the whole outer peripheral part of the shrinkage | contraction adjustment layer 9b is exposed, it showed with the broken line.
[0042]
The shrinkage adjustment layer 9b constituting the inactive portion 9 has a sheet resistance value of 10⁶It is desirable that it is Ω / □ or more. That is, the inactive portion 9 is formed under the influence of the metal particles in the shrinkage adjusting layer 9b by alternately laminating a plurality of the piezoelectric bodies 9a and the shrinkage adjusting layers 9b in which metal particles are dispersed to form the inactive portion 9. Sintering of the piezoelectric body 9a in 9 is promoted, and the contraction rate of the piezoelectric body 9a in the inactive portion 9 is made substantially equal to the contraction rate of the piezoelectric body 1 sandwiched between the internal electrodes 2 in the active portion 8. be able to.
[0043]
The metal particles of the shrinkage adjustment layer 9b are silver particles or alloy particles of a plurality of metals such as silver-palladium and silver-platinum.
[0044]
The thickness of the piezoelectric body 9 a in the inactive portion 9 is desirably the same as the thickness of the piezoelectric body 1 in the active portion 8. The thickness of the shrinkage adjustment layer 5b is preferably 0.5 to 10 μm.
[0045]
The sheet resistance value of the shrinkage adjustment layer 9b is 10⁶Ω / □ or more. Thereby, high insulation can be maintained, without reducing the insulation of the inactive part 9. The sheet resistance value is obtained by multiplying the resistance value of the measured object by the width of the measured object and dividing the result by the length. In other words, the volume resistivity of the measured object is divided by the thickness of the measured object.
[0046]
Furthermore, in the present invention, the shrinkage adjusting layer 5 is made to have a metal particle content of 5 to 50% by volume in order to match the shrinkage rate of the inactive part 9 with the shrinkage rate of the active part 8 without reducing the insulating property of the inactive part 9. It is desirable that the balance is formed of 50 to 95% by volume of the piezoelectric particles. As a result, the sheet resistance value of the shrinkage adjustment layer 9b is 10.⁶Ω / □ or more.
[0047]
In the present invention, the metal particles constituting the shrinkage adjustment layer 9 b are the same as the metal particles constituting the internal electrode 2. Since the metal particles of the shrinkage adjusting layer 9b are the same as the metal particles constituting the internal electrode 2, the shrinkage behavior of the inactive portion 9 during firing can be matched with the shrinkage behavior of the active portion 8, and the active portion during firing. It is possible to prevent the occurrence of delamination, cracks, and the like at the interface between 8 and the inactive portion 9 and in the vicinity thereof.
[0048]
Furthermore, in the present invention, the end portion of the shrinkage adjustment layer 9b is used in order to prevent generation of stress due to a shrinkage difference during firing of the inactive portion 9 and the active portion 8 even in the vicinity of the formation surface of the external electrode 4 of the columnar laminate 1a. Are exposed on the surface of the columnar laminate 1a where the external electrodes 4 are formed.
[0049]
That is, by exposing the end of the shrinkage adjusting layer 9b to the surface of the columnar laminate 1a where the external electrode 4 is formed, the active portion 8 and the inactive portion 9 are also formed in the vicinity of the surface of the columnar laminate 1a where the external electrode 4 is formed. It is possible to make the firing shrinkage ratios equal to each other, and it is possible to prevent stress from being generated during firing at and near the interface between the active portion 8 and the inactive portion 9 in the vicinity of the surface where the external electrode 4 is formed.
[0050]
Moreover, in this invention, the edge part of the shrinkage | contraction adjustment layer 9b exposed to the external electrode 4 formation surface of the columnar laminated body 1a and the edge part of the internal electrode 2 are respectively separated from the plate-like conductive member via the protruding conductive member 7. Connected to the external electrode 4. Thus, not only the end of the internal electrode 2 of the active part 8 exposed on the surface on which the external electrode 4 of the columnar laminated body 1a is exposed, but also the end of the shrinkage adjustment layer 5 in the inactive part 9. Even when the actuator is continuously driven under a high electric field by being connected and fixed to the plate-like external electrode 4 via the protruding conductive member 7, the internal electrode 2 and the protruding conductive member 7 or the protruding conductive The member 7 and the external electrode 4 are not disconnected, and an actuator having high reliability can be provided.
[0051]
A method for producing the multilayer piezoelectric actuator of the present invention will be described.
[0052]
First, a calcined powder of piezoelectric ceramics such as PZT, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer such as DBP (diethyl phthalate) or DOP (dibutyl phthalate) are mixed. A slurry is prepared, and a ceramic green sheet to be the piezoelectric body 1 is prepared from the slurry by a tape molding method such as a well-known doctor blade method or calendar roll method.
[0053]
Next, an internal electrode paste is prepared by adding and mixing a binder, a plasticizer, and the like to metal powder composed of silver-palladium, and this is printed on the upper surface of each ceramic green sheet to a thickness of 1 to 40 μm by screen printing or the like. An internal electrode pattern is formed on the green sheet.
[0054]
Separately, a binder, a plasticizer, and the like are added to and mixed with a mixture of 5 to 50% by volume of metal powder made of silver-palladium and 50 to 95% by volume of the same ceramic calcined powder as the piezoelectric body 1. A shrinkage adjustment layer paste is prepared, and this is printed on the upper surface of the ceramic green sheet to a thickness of 1 to 40 μm by screen printing or the like to form a shrinkage adjustment layer pattern on the green sheet.
[0055]
Here, the mixing ratio of the metal powder in the shrinkage adjustment layer paste was set to 5 to 50% by volume because when the metal powder was less than 5% by volume, the metal powder was in the inactive portion 9 during firing. 9a is less affected, the sintering promoting effect of the piezoelectric body 9a in the inactive portion 9 is small, and the contraction rate with the piezoelectric body 1 in the active portion 8 tends to be different, whereas the metal powder is 50%. This is because when the amount is more than volume%, the amount of metal particles contained in the shrinkage adjustment layer 5 increases, and the insulating property of the inactive portion 9 tends to decrease.
[0056]
That is, by setting the metal particles contained in the shrinkage adjustment layer paste to 5 to 50% by volume, the shrinkage rate during firing of the inactive part 9 is reduced without reducing the insulating property of the inactive part 9. The shrinkage rate can be adjusted. Furthermore, it is preferable that the shrinkage behavior of the inactive part 9 and the active part 8 at the time of firing is matched to eliminate residual stress at the time of firing and to prevent deterioration of insulation at high temperature. The metal particles contained in the paste are preferably in the range of 10 to 30% by volume.
[0057]
The metal particles contained in the shrinkage adjustment layer paste may be alloy particles composed of a plurality of metal components. In order to effectively match the shrinkage behavior during firing of the piezoelectric body 1 sandwiched between the internal electrodes 2 in the active portion 8 and the piezoelectric body 9a sandwiched between the shrinkage adjustment layers 9b in the inactive portion 9, The metal particles contained in the shrinkage adjustment layer paste are preferably the same as the metal particles contained in the internal electrode paste.
[0058]
Then, a plurality of ceramic green sheets having internal electrode patterns formed on the upper surface are laminated to produce an active part molded body that becomes the active part 8, and a shrinkage adjustment layer pattern is formed on both end surfaces in the stacking direction of the active part molded body. A columnar laminate formed by laminating a plurality of ceramic green sheets each having a layer formed thereon, and laminating inactive part formed bodies on both end surfaces in the stacking direction of the active part formed body. obtain. At this time, the entire outer peripheral end of the internal electrode pattern and the entire outer peripheral end of the shrinkage adjustment layer pattern are exposed on the four side surfaces of the columnar laminated molded body.
[0059]
Then, after debinding at a predetermined temperature for this columnar laminated molded body, by firing at 900 to 1200 ° C., as shown in FIG. 1, the entire outer peripheral end of the internal electrode, the shrinkage adjustment layer 9b A columnar laminate 1a is produced in which the outer peripheral end portions are exposed on the four side surfaces.
[0060]
Thereafter, grooves are formed in every other layer on the side surface of the columnar laminate 1a where the external electrodes 4 are formed using a dicing apparatus or the like. A silver glass paste made of silver powder and glass powder is interposed between the side surface where the external electrode 4 is formed of the columnar laminated body 1a in which the groove is formed and the external electrode 4 made of a plate-like conductive member. By heat-treating the laminated body 1a at 700 to 900 ° C. in a state where the laminated body 1a is pressed at a pressure of 2 to 80 kPa, the glass in the silver glass paste is melted, and the silver component present in the molten glass is A projecting conductive member 7 is formed which gathers at the end and the end of the shrinkage adjustment layer 5 and protrudes from the side surface of the columnar stacked body 1 a. The projecting conductive member 7 has a columnar stacked body 1 a and an external electrode 4. The external electrode 4 made of a plate-like conductive member is joined in a state where a gap is formed therebetween.
[0061]
Thereafter, the insulator 3 is filled in the groove, and the lead wire 6 is connected to the external electrode 4 to complete the multilayer piezoelectric actuator of the present invention.
[0062]
Then, by applying a direct current voltage of 0.1 to 3 kV / mm to the pair of external electrodes 4 via the lead wires 6 to polarize the columnar laminated body 1a, a laminated piezoelectric actuator as a product is completed, When the lead wire 6 is connected to an external voltage supply unit and a voltage is applied to the internal electrode 2 via the lead wire 6 and the external electrode 4, each piezoelectric body 1 is greatly displaced by the reverse piezoelectric effect, and for example, It functions as an automobile fuel injection valve that supplies fuel to the engine.
[0063]
In the multilayer piezoelectric actuator configured as described above, since the densities of the active portion 8 and the inactive portion 9 can be made substantially equal, the contraction rate of the active portion 8 and the inactive portion 9 during firing is substantially reduced. It is possible to prevent the occurrence of problems such as delamination and cracks at and near the interface between the active portion 8 and the inactive portion 9 during firing, and it is active even when the actuator is driven. The durability can be greatly improved without being damaged at the interface between the portion 8 and the inactive portion 9 and in the vicinity thereof.
[0064]
The multilayer piezoelectric element of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the external electrode 4 made of a plate-like conductive member can be changed. A conductive auxiliary member may be formed outside. In this case, by providing a conductive auxiliary member on the outer surface of the plate-like conductive member, a large current can be supplied to the conductive auxiliary member even when a large current is supplied to the actuator and driven at high speed. The current flowing through the electrode 4 can be reduced, the external electrode 4 can be prevented from causing local heat generation and disconnection, and the durability can be greatly improved.
[0065]
Note that the conductive auxiliary member follows the expansion and contraction of the actuator and prevents disconnection of the conductive auxiliary member during driving, so that a flexible conductive adhesive, conductive coil, conductive corrugated plate, or conductive fiber is used. An aggregate (wool shape) is desirable. In particular, a conductive corrugated sheet made of silver is desirable because it has a low resistance value and Young's modulus, is highly stretchable, and can reduce the sectional area of the actuator.
[0066]
FIG. 2 shows an injection device according to the present invention. In the figure, reference numeral 31 denotes a storage container. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 35 that can open and close the injection hole 33 is stored in the storage container 31.
[0067]
A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is formed to be injected into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.
[0068]
Further, the upper end portion of the needle valve 35 has a large diameter, and serves as a piston 41 slidable with a cylinder 39 formed in the storage container 31. In the storage container 31, the piezoelectric actuator 43 described above is stored.
[0069]
In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 so that fuel is injected.
[0070]
【Example】
Example 1
First, on the top surface of a ceramic green sheet containing PZT calcined powder, 300 layers of internal electrode patterns formed by printing an internal electrode paste made of a silver-palladium alloy and a binder were laminated, and an active part molded body was formed. Produced.
[0071]
On the other hand, ten layers of layers on which the shrinkage adjustment layer pattern is formed by printing the shrinkage adjustment layer paste on the upper surface of the ceramic green sheet are laminated to produce two inactive layer formed bodies. Were stacked on both end faces in the stacking direction of the active part molded body to form a quadrangular columnar columnar stacked molded body.
[0072]
The outer peripheral ends of the 10-layer shrinkage adjustment layer pattern were exposed on the four side surfaces of the inactive layer molded body, and the outer peripheral end portions of the 300-layer internal electrode pattern were exposed on the four side surfaces of the active portion molded body.
[0073]
The shrinkage adjustment layer paste is obtained by adding a binder to a solid content composed of 20% by volume of a silver-palladium alloy powder forming an internal electrode and 80% by volume of the same PZT calcined powder contained in the ceramic green sheet. Produced.
[0074]
Thereafter, the columnar laminate was subjected to binder removal treatment at 400 ° C. and fired at 1050 ° C. in the atmosphere to obtain a columnar laminate.
[0075]
The thickness of the piezoelectric body in the active part was 150 μm, and the thickness of the internal electrode was 3 μm. Further, the thickness of the piezoelectric body in the inactive portion was 150 μm, and the thickness of the shrinkage adjustment layer was 3 μm.
[0076]
Thereafter, a groove having a width of 50 μm and a depth of 200 μm was formed in the exposed portion of the internal electrode on the external electrode forming side surface of the active portion every other layer than the dicing apparatus. Then, a silver glass paste made of silver powder and glass powder is interposed between the external electrode forming side surface of the columnar laminate in which the groove is formed and an external electrode made of a plate-like conductive member mainly composed of silver, By performing heat treatment at 900 ° C. in a pressure contact state at a pressure of 30 kPa, a protruding conductive member protruding from the side surface of the columnar laminate is formed at the end of the inner electrode of the active portion and the shrinkage adjustment layer of the inactive portion. While forming, an external electrode was joined to the projecting conductive member.
[0077]
Thereafter, silicone rubber as an insulator was filled in the groove of the active part, and a lead wire was connected to the external electrode.
[0078]
Then, a 3 kV / mm direct current electric field was applied to the positive and negative external electrodes via lead wires for 15 minutes to perform polarization treatment, and a multilayer piezoelectric actuator as shown in FIG. 1 was produced.
[0079]
In the obtained multilayer piezoelectric actuator, the density of the active portion composed of the piezoelectric body and the internal electrode and the density of the inactive portion composed of the piezoelectric body and the shrinkage adjustment layer were substantially the same. Further, when the sheet resistance of the shrinkage adjusting layer was measured with an insulation resistance meter, 8 × 10⁸It was Ω / □.
[0080]
As a result of applying a DC voltage of 150 V to the obtained multilayer piezoelectric actuator, a displacement of 40 μm was obtained in the stacking direction. Furthermore, as a result of conducting a drive test by applying an AC voltage of 0 to +150 V to this actuator at a frequency of 60 Hz at room temperature, 5 × 10 5^TenWhen driven until the cycle, a displacement of 40 μm was obtained, and no abnormalities such as cracks were found at the interface between the active part and the inactive part and in the vicinity thereof.
Example 2
Next, a columnar laminate similar to that of Example 1 was prepared except that the volume ratio of the silver-palladium alloy and the piezoelectric body constituting the shrinkage adjustment layer was changed. About the obtained columnar laminated body, the active part and the inactive part were separated, the density of each was measured by the Archimedes method, and the density difference between the active part and the inactive part was calculated. In addition, the delamination and crack generation conditions at the boundary between the active part and the inactive part and in the vicinity thereof were examined. Furthermore, the sheet resistance of the shrinkage adjustment layer in the inactive part was measured.
[0081]
FIG. 3 shows the relationship between the density difference between the active part and the inactive part, and the delamination and crack defect rate at and near the boundary between the active part and the inactive part. The density difference between the active part and the inactive part is a percentage obtained by dividing the difference in density between the active part and the inactive part by the density of the active part. It can be seen that the larger the density difference between the active part and the inactive part, the more defects due to delamination and cracks.
[0082]
FIG. 4 shows the relationship between the volume% of the silver-palladium alloy in the shrinkage adjustment layer, the density difference, and the sheet resistance of the shrinkage adjustment layer. It can be seen that when the metal component in the shrinkage adjusting layer is smaller than 5% by volume, the bulk density difference becomes larger than 5%, and defects such as delamination and cracks frequently occur. When the metal component in the shrinkage adjustment layer is greater than 50% by volume, the sheet resistance value of the shrinkage adjustment layer is 10⁶It can be seen that it becomes smaller than Ω, and the insulating property of the inactive part is lowered.
[0083]
That is, when the amount of the metal component in the shrinkage adjusting layer is 5 to 50% by volume within the range specified in the present invention, the density of the active part and the inactive part is substantially equal, and the boundary between the inactive part and the active part. It can be seen that defects such as delamination and cracks in the vicinity thereof can be prevented from occurring, and that the insulating properties of the inactive portion are not deteriorated.
Example 3
Further, external electrodes were formed on the columnar laminate obtained by the same method as in Example 2 by the same method as in Example 1 to produce a multilayer piezoelectric actuator. A drive test was performed by applying an AC voltage of 0 to +150 V to the obtained multilayer piezoelectric actuator at a frequency of 60 Hz at room temperature. The obtained results are shown in Table 1.
[0084]
[Table 1]

[0085]
From Table 1, in the sample in which the amount of the metal component in the shrinkage adjusting layer is less than 5% by volume, the breakage occurs at the boundary between the active part and the inactive part during driving. On the other hand, in the sample in which the amount of the metal component in the shrinkage adjustment layer was 60% by volume or more, the dielectric breakdown occurred during driving or the insulation was poor in the initial state. On the other hand, in the sample in which the metal component amount in the shrinkage adjustment layer is 5 to 50% by volume, 1 × 10⁹No abnormality such as breakage or dielectric breakdown was found even when driven up to.
[0086]
【The invention's effect】
According to the multilayer piezoelectric element of the present invention,The metal particles that improve the sinterability are present even on the outer periphery of the inactive part, and the metal particles in the shrinkage adjustment layer improve the sinterability of the outer peripheral part of the inactive part.The shrinkage ratio between the active part and the inactive part during firing became substantially equal, and the occurrence of delamination and cracks at the interface between and in the vicinity of the active part and inactive part during firing was eliminated, and the actuator was driven. Even in this case, it is possible to provide a multilayer piezoelectric element having high reliability that does not break at the interface between the active portion and the inactive portion and in the vicinity thereof.
[Brief description of the drawings]
1A and 1B show a multilayer piezoelectric element of the present invention, in which FIG. 1A is a perspective view and FIG. 1B is a longitudinal sectional view taken along line A-A ′ of FIG.
FIG. 2 is an explanatory view showing an injection device of the present invention.
FIG. 3 is a graph showing a relationship between a density difference between an active part and an inactive part and a defect rate.
FIG. 4 is a graph showing the relationship between the ratio of the metal component in the shrinkage adjustment layer, the density difference between the active part and the inactive part, and the sheet resistance of the shrinkage adjustment layer.
FIG. 5 is a longitudinal sectional view of a conventional multilayer piezoelectric actuator.
[Explanation of symbols]
1, 9a ... Piezoelectric material
1a ... Columnar laminate
2 ... Internal electrode
4 ... External electrode
9b ... Shrinkage adjustment layer
8 ... Active part
9: Inactive part
31 ... Storage container
33 ... Injection hole
35 ... Valve
43 ... Piezoelectric actuator

Claims (7)

A plurality of piezoelectric bodies and a plurality of internal electrodes are alternately stacked, and a columnar stack composed of active portions where the piezoelectric bodies are displaced, and inactive portions that are provided at both ends in the stacking direction of the active portions and are not displaced. And a pair of external electrodes that are provided on the side surface of the columnar laminated body and in which the internal electrodes are alternately electrically connected every other layer, and the active portion and the inactive portion include A multilayer piezoelectric element that is simultaneously fired, wherein the inactive portion is formed by alternately laminating piezoelectric bodies and shrinkage adjustment layers containing metal particles, and at least one end of the shrinkage adjustment layer. The laminated piezoelectric element is characterized in that a portion is exposed on a side surface of the inactive portion. Laminated piezoelectric element according to claim 1, wherein the sheet resistance of the contraction adjustment layer is equal to or is 10 ⁶ Ω / □ or more. 3. The multilayer piezoelectric element according to claim 1, wherein the shrinkage adjustment layer is composed of 5 to 50% by volume of metal particles and 50 to 95% by volume of piezoelectric particles. Shrinkage metal particles constituting the control layer, multi-layer piezoelectric element according to any one of claims 1 to 3, characterized in that it is identical to the metal particles constituting the inner electrode. Protruding conductive members are respectively provided at the ends of the shrinkage adjustment layer and the internal electrodes exposed on the external electrode forming surface of the columnar laminate, and the protruding conductive members are connected to the external electrodes. The multilayer piezoelectric element according to claim 1 , wherein the multilayer piezoelectric element is any one of claims 1 to 4 . A plurality of ceramic green sheets each having a pattern for a shrinkage adjustment layer containing metal powder are laminated on both ends in the stacking direction of an active part molded body formed by stacking a plurality of ceramic green sheets on which internal electrode patterns are formed. A step of producing a columnar laminate formed by providing at least one inactive portion formed from the pattern for shrinkage adjustment layer on the side surface, and firing the columnar laminate for columnar lamination. A laminated type comprising: a step of forming a body; and a step of forming a pair of external electrodes in which internal electrodes are alternately electrically connected every other layer on a side surface of the columnar laminated body. Production method of piezoelectric elements. A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 5 accommodated in the storage container, and a liquid is ejected from the injection hole by driving the multilayer piezoelectric element. An injection device comprising a valve.

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