JP4889200B2 - Multilayer piezoelectric element and injection device - Google Patents

Description

  The present invention relates to a multilayer piezoelectric element, a method for manufacturing the same, and an injection device. For example, the present invention relates to a precision positioning device such as a fuel injection valve for an automobile and an optical device, a driving element for vibration prevention, and the like.

Conventionally, as a laminated piezoelectric element, for example, in order to obtain large displacement using the electrostrictive effect, a laminate of the piezoelectric layers and conductor layers alternately have been proposed. Laminated piezoelectric element has a co-fired type, they are classified into two types of stack type of alternately laminated piezoelectric ceramic and the conductor plate, low voltage, when considered from the viewpoint of production cost reduction, simultaneous sintering type Since the multilayer piezoelectric element is advantageous for thinning, its superiority is being demonstrated.

The multi-layer piezoelectric element of simultaneous sintering type, as shown in FIG. 5, like the multilayer ceramic capacitor, conventionally, the conductive pattern containing green sheets and the conductor material containing piezoelectric material are alternately stacked preparative activity A laminated piezoelectric element has been manufactured by laminating an inactive part formed by laminating a plurality of the ceramic green sheets on the upper and lower surfaces of the part, and degreasing and firing the inactive part (for example, Patent Documents 1 and 2). reference).

By the way, in recent years, for example, in order to ensure a large amount of displacement under a large pressure with a small stacked piezoelectric actuator, a higher electric field is applied to continuously drive for a long time.
JP-A-4-299588 JP-A-5-217796

  However, in the conventional multilayer piezoelectric element of Patent Document 1, the conductor layer contains 10 to 20% of a piezoelectric powder adjusted to a particle size that is 1/2 to 1 times the thickness of the conductor layer. By connecting the piezoelectric layers in a columnar shape, peeling is prevented at the interface between the conductor and the ceramic layer after firing, but because the cooling rate during the heat treatment in the connection process between the conductor layer and the external electrode is fast, As shown in FIG. 5, due to the difference in thermal expansion coefficient between the conductor 102 and the piezoelectric layer 101, the portion where the columnar portion 51 does not exist has a large gap between the conductor layer 102 and the piezoelectric layer 101 over almost the entire interface. A gap 107 was generated. Accordingly, there has been a problem that delamination occurs when a higher electric field is applied and driven continuously for a long period of time.

  Further, in the conventional multilayer electronic component of Patent Document 2, the cut surface (external electrode forming surface) obtained by machining the element is heat-treated at a firing temperature higher than that at the first firing, so that a short circuit caused at the time of cutting can be prevented. The cause of microcracks has been eliminated, but since the cooling rate during heat treatment at a temperature higher than the firing temperature is fast, peeling occurs almost over the entire interface due to the difference in thermal expansion coefficient between the conductor layer and the piezoelectric layer. It has occurred. Accordingly, there has been a problem that delamination occurs when a higher electric field is applied and driven continuously for a long period of time.

Accordingly, the present invention can suppress delamination, cracking or the like, and an object thereof is to provide an injection device using the Re patron Oyo multilayer piezoelectric element obtained is highly reliable.

The multilayer piezoelectric element of the present invention is a multilayer piezoelectric element in which piezoelectric layers and conductor layers are alternately stacked, and a region in which a gap is formed between the piezoelectric layer and the conductor layer , The gap is formed
The ratio of the metal component of the conductor layer in the formed region is larger than the ratio of the metal component of the conductor layer in the other region .

According to the present invention, by increasing the proportion of the metal in the gap portion in the plane of the conductor layer, the rigidity of the metal film in this portion can be lowered. Can be reduced.

  The multilayer piezoelectric element is characterized in that the metal composition in the conductor layer is mainly composed of either a Group VIII metal or a Group Ib metal, or both a Group VIII metal and a Group Ib metal. That is, when the group VIII metal content is M1% by mass and the group Ib metal content is M2% by mass, 0.001 ≦ M1 ≦ 15, 85 ≦ M2 ≦ 99.999, M1 + M2 = 100% by mass Further, the Group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the Group Ib metal is at least one of Cu, Ag, and Au. It is characterized by being.

  That is, in the present invention, by using a combination of the above-described metals as the metal component of the conductor layer, Ag or Cu, which has higher ductility and lower Young's modulus than the other metals, is used as the main component of the conductor layer. Accordingly, the followability to the surface of the piezoelectric layer is enhanced, and delamination and cracks originating from the gap can be suppressed.

  Further, in the present invention, the group VIII metal is at least one of Pt and Pd, the group Ib metal is at least one of Ag, and Au, in particular, the group VIII metal is Ni or the group Ib metal is Cu. It is desirable that

Further, in the stacked piezoelectric device, characterized that you containing an inorganic component to the conductor layer.

  As described above, in the present invention, the conductor layer includes the same common material component as the piezoelectric particles constituting the piezoelectric layer, and the particle diameter on the conductor layer side is smaller than that on the piezoelectric layer side. Piezoelectric particles in contact with the conductor layer are reduced, thereby making it possible to reduce the gap and to suppress the generation of the gap.

  An injection device according to the present invention includes a storage container having an injection port, the laminated piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. It is characterized by becoming.

  In such an injection device, as described above, since the generation of a gap at the interface between the piezoelectric layer and the conductor layer constituting the multilayer piezoelectric element can be suppressed and delamination and cracks can be prevented, the injection device is excellent. The injection characteristics can be obtained and the reliability can be improved.

That is, in the multilayer piezoelectric element of the present invention, the gap is formed because the proportion of the metal component of the conductor layer in the region where the gap is formed is larger than the proportion of the metal component of the conductor layer in the other region . The rigidity of the conductor layer in the region can be reduced , the stress due to the conductor layer can be reduced even in expansion and contraction by piezoelectric driving , and an injection device incorporating this can be provided with high reliability.

  FIG. 1 is a longitudinal sectional view showing an embodiment of a multilayer piezoelectric element composed of a multilayer piezoelectric actuator.

  As shown in FIG. 1, the multilayer piezoelectric element of the present invention is provided with an active portion 8 in which a plurality of piezoelectric layers 1 and a plurality of conductor layers 2 are alternately stacked, and at both ends of the active portion 8 in the stacking direction. It has a quadrangular columnar stacked body 3 composed of the inactive portions 9 formed.

The piezoelectric layer 1 is made of, for example, a piezoelectric ceramic material mainly composed of lead zirconate titanate Pb (Zr, Ti) O3 (hereinafter abbreviated as PZT), but is not limited thereto. Any ceramic having piezoelectricity may be used. As the piezoelectric material, as the piezoelectric strain constant d ₃₃ is high it is preferable.

  The thickness of the piezoelectric layer 1, that is, the distance between the conductor layers 2, is preferably 0.05 to 0.25 mm from the viewpoint of downsizing and applying a high electric field. This is because a method of increasing the number of stacked layers in order to obtain a larger displacement amount by applying a voltage to the stacked piezoelectric element is used, but when the number of stacked layers is increased, the piezoelectric layer 1 in the active portion 8 is used. This is because if the thickness of the piezoelectric layer 1 in the active portion 8 is too thin, dielectric breakdown tends to occur.

  The conductor layer 2 has a rectangular shape as shown in FIG. 2, and as shown in FIG. 1, one side of the conductor layer 2 is exposed on every other side surface (external electrode forming surface) of the columnar laminate 3. In addition, external electrodes 4 for connecting the lead portions 16 via the connection portions 17 are formed on the side surfaces (opposite side surfaces) of the columnar laminate 3 where one side of the conductor layer 2 is exposed. Thereby, the conductor layers 2 are electrically connected to the external electrodes 4 alternately every other layer.

  In the multilayer piezoelectric element of the present invention, a gap 7 is formed between the piezoelectric layer 1 and the conductor layer 2, and when the conductor layer 2 surface is viewed in plan, the area of the gap 7 is It is important that it is 10% or less of the total area of the conductor layer 2, and in particular, 5% or less is more preferable in terms of enhancing piezoelectric characteristics such as capacitance and displacement.

  In the multilayer piezoelectric element of the present invention, it is desirable that the ratio of the metal component in the region where the gap 7 of the conductor layer 2 is larger than the ratio of the metal component in the bonded region.

  Further, this gap is preferably 1 μm or less, particularly 0.8 μm or less, particularly 0.3 μm or less in terms of improving adhesion, while the thermal expansion coefficient with the piezoelectric layer 1 can be relaxed. For the reason, it is preferably 0.01 μm or more, particularly 0.02 μm or more. And the thickness of the conductor layer of this invention is 3 micrometers or less, Especially 2.5 micrometers or less are more preferable.

  In the conductor layer 2 described above, the metal composition constituting the conductor layer 2 is preferably composed mainly of either a Group VIII metal, a Group Ib metal, or both a Group VIII metal and a Group Ib metal. When the content of the Group VIII metal is M1% by mass and the content of the Group Ib metal is M2% by mass, 0.001 ≦ M1 ≦ 15, 85 ≦ M2 ≦ 99.999, and M1 + M2 = 100% by mass. It is desirable to satisfy, and in particular, 3 ≦ M1 ≦ 8 and 92 ≦ M2 ≦ 97 are more desirable. Here, the Group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the Group Ib metal is at least one of Cu, Ag, and Au. It is more desirable that at least one of Pt and Pd, the Group Ib metal is at least one of Ag and Au, and that the Group VIII metal is Ni or that the Group Ib metal is Cu. .

  The conductor layer 2 of the present invention contains an inorganic component, and the inorganic component is preferably the same component as that of the piezoelectric layer 1, and the average particle size of the inorganic component is determined by the piezoelectric layer. It is preferable that the average particle size is smaller than 1.

A manufacturing method of a multilayer piezoelectric actuator, which is a representative example of the multilayer piezoelectric element of the present invention, will be described in detail. The multilayer piezoelectric element of the present invention is first composed of a calcined powder (ceramic powder) of piezoelectric ceramics such as lead zirconate titanate Pb (Zr, Ti) O ₃ and an organic polymer such as acrylic resin and butyral resin. A slurry in which an organic binder and a plasticizer are mixed is prepared, and a ceramic green sheet 21 having a thickness of 50 to 250 μm as shown in FIG. 2 is prepared by, for example, a slip casting method.

  In the present invention, the average particle diameter of the calcined ceramic powder forming the piezoelectric layer 1 is preferably 0.3 to 0.9 μm. By setting the average particle size of the calcined ceramic powder to 0.3 μm or more, a small amount of organic binder necessary for preventing the generation of dry cracks during the production of the green sheet 21 can be achieved.

  On the other hand, by setting the average particle size of the calcined ceramic powder to 0.9 μm or less, sintering during firing can be sufficiently performed, and the ceramic strength can be increased. For example, it is generated by an electric field in a multilayer piezoelectric element. Generation of cracks due to stress can be suppressed.

  Further, the thickness of the green sheet 21 is preferably 90 μm or more, particularly 100 μm or more for the purpose of improving the insulation strength. Moreover, in order to prevent the crack generation at the time of handling the green sheet 21, it is desirable to use a butyral resin having a high tensile strength as the organic binder.

  Next, after the produced green sheet 21 is punched out to a predetermined size, a conductive paste containing Ag—Pd and a solvent to be the conductor layer 2 is screen printed on one side of the green sheet 21 as shown in FIG. Is printed to a thickness of 1 to 10 μm and dried to form the internal conductor pattern 22. In this case, in the present invention, it is important to mix ceramic powder as a co-material in the conductor paste.

  The average particle size of the ceramic powder is desirably smaller than the average particle size of the ceramic powder constituting the green sheet that becomes the piezoelectric layer 1 after firing. And, the average particle size of the ceramic powder in the conductor pattern is desirably in the range of 0.3 to 0.5 when the average particle size of the ceramic powder in the green sheet is 1, and in firing, Although aggregation and grain growth occur, when the average particle diameter of the piezoelectric layer 1 is 1, the gap 7 generated in the conductor layer 2 of the present invention is in the range of 0.5 to 0.9. The concentration (ratio) of the metal component in the region can be maintained high.

  The conductor pattern 22 used in the manufacturing method of the present invention has a rectangular shape and has a smaller area than the rectangular green sheet 21, and one side of the conductor pattern 22 overlaps one side of the green sheet 21. It is formed so as not to overlap the sides.

  Next, as shown in FIG. 3, a predetermined number of green sheets 21 on which the conductor pattern 22 is formed are laminated so that one side of the conductor pattern 22 is alternately exposed on the opposite side surfaces of the laminated molded body 23. The active part laminated molded body 23a is produced, and the inactive part molded body 23b formed by laminating a plurality of green sheets 21 on which the conductive paste is not printed is laminated on the upper and lower surfaces of the active part laminated molded body 23a. The body 23 is produced.

  A plurality of green sheets 21 on which no conductor paste is printed are laminated to produce a lower inactive portion laminated molded body 23b, and then a conductive pattern 22 is formed on the inactive portion laminated molded body 23b. A predetermined number of green sheets 21 are stacked to stack an active portion laminate formed body 23a, and a plurality of green sheets 21 on which no conductor paste is printed are stacked on the active portion stacked formed body 23a. The inactive part laminated molded body 23b may be laminated to produce the laminated molded body 23.

  In addition, it does not specifically limit about the manufacturing method of the laminated molded object 23, What is necessary is just to obtain the laminated molded object 23 by which the green sheet 21 and the conductor pattern 22 were laminated | stacked. Next, pressure is applied while heating the laminated molded body 23 to integrate the laminated molded body 23 to obtain a columnar laminated molded body. Moreover, as a method of pressurizing, pressurization by hydrostatic pressure is desirable in terms of improving the lamination accuracy, and the pressure is desirably 20 to 120 MPa.

  The integrated columnar laminated body is cut to a predetermined size, and then degreased at 400 to 800 ° C. for 5 to 40 hours in the atmosphere, and thereafter at 900 to 1200 ° C. for 2 to 5 hours. The main firing is performed to obtain a columnar laminate 33 as shown in FIG. The columnar laminate 33 has an active portion in which piezoelectric layers 41 and conductor layers 42 are alternately laminated, and one side of the conductor layer 42 is alternately exposed on the opposite side surface.

  Next, an external electrode paste containing Ag-glass is applied to the end face of the columnar laminate 33 and heat-treated at a temperature of 500 to 900 ° C. to form the external electrode 4. In this case, in the heat treatment step, the cooling rate from the maximum temperature of the heat treatment is such that delamination and cracks can be suppressed. In this case, when the Curie temperature of the piezoelectric layer is t (° C.), t / 3 (° C. / Min), and further, when cooling from the heat treatment, when the Curie temperature of the piezoelectric layer is t (° C.), the cooling rate in the temperature range of 0.8 t to 1.2 t is t / 3. It is more desirable that the temperature be (C / min) or less. The piezoelectric layer 1 is cubic at temperatures higher than the Curie temperature, and is rhombohedral or tetragonal at temperatures lower than the Curie temperature. Therefore, the crystal layer changes when the cooling rate is increased in the temperature range where the crystal layer changes. This is because delamination is likely to occur due to internal stress caused by this.

  Here, as a method for confirming the gap between the conductor layer 2 and the piezoelectric layer 1, inspection by ultrasonic flaw detection or SEM of a fracture surface is used. Although it is desirable to use ultrasonic flaw detection in that the distribution of the entire gap of the multilayer piezoelectric element can be easily inspected nondestructively, the actual gap size can also be confirmed by observing the SEM of the fracture surface. Here, when the cross section is finished to be a mirror surface and observed by SEM, the conductor 2 extends into the gap due to the ductility of the conductor 2 even if the gap is actually present. . From the results obtained by observing a surface perpendicular to the stacking direction by inspection by ultrasonic flaw detection, the area ratio between the part where peeling of 2 μm or more occurs and the part where it does not, for example, in the substantially active part To calculate the rate of peeling.

  In the inspection by ultrasonic flaw detection, a plurality of cross sections may be observed at a time. Generally, in the inspection by ultrasonic flaw detection, when the depth of focus is deepened, the sensitivity is lowered. Therefore, for those having a large number of stacked layers and a height of 5 mm or more, cut and split to a height of 2 to 5 mm perpendicular to the stacking direction. Then, it is desirable to calculate the rate of peeling by performing an inspection by ultrasonic flaw detection. The conductor layer 2 and the piezoelectric layer are formed on a part of a portion that is likely to be a starting point of fracture due to a stress due to driving, a stress due to an electric field, a stress due to buckling, and the like. The portion where the gap with the body layer 1 is 1 μm or less may be 10% or less of the total area of the conductor layer 2.

  Further, in the above embodiment, as shown in FIG. 2, one columnar laminated body is produced by one laminated molded body 3, but a plurality of conductor patterns are formed on one green sheet 21, and this green sheet 21 is formed. A mother laminated molded body capable of producing a large number of columnar laminated bodies is produced by cutting a plurality of columnar laminated bodies, and the laminated molded body is cut to a predetermined size to form a large number of columnar laminated bodies as shown in FIG. Of course, the present invention may be applied to a method of manufacturing a laminated piezoelectric element in which a body is manufactured at a time.

  Next, as shown in FIG. 1, a direct current voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 4 to polarize the columnar laminated body, thereby completing a multilayer electronic component as a product. . Here, it is desirable that the rate of change of c / a, which is the ratio of lattice constants, before and after polarization is 0.5% or less. This is because if the rate of change of c / a is greater than 0.5%, peeling occurs between the conductor 2 and the ceramic layer 1 due to stress generated during polarization. In the present invention, in order to prevent peeling due to stress during polarization, the change rate of c / a is more preferably 0.2% or less. Here, the lattice constant ratio c / a is obtained from the peak of the plane index (200) from the XRD diffraction pattern, and similarly, the lattice constant c is obtained from the peak of the plane index (002). Find c / a.

  By using the manufacturing method as described above, the planar view region of the gap at the interface between the conductor layer 2 and the piezoelectric layer 1 can be 10% or less of the total area of the conductor layer 2. If the planar view area of the gap between the conductor layer 2 and the piezoelectric layer 1 is larger than 10% of the total area of the conductor layer 2, cracks may be generated from the gap when a high voltage is applied, or continuous driving for a long period of time. If this is done, cracks are generated from the gaps, reducing reliability. Although the multilayer piezoelectric element of the present invention can prevent peeling, in practice, a gap at the interface may occur due to the mixing of foreign matters in the process, but the planar view region of the gap is the total area of the conductor layer 2. If it is 10% or less, the reliability can be ensured.

  The method for manufacturing a multilayer piezoelectric element of the present invention is suitably used for a method of manufacturing a multilayer electronic component such as a multilayer piezoelectric transformer, a multilayer capacitor, or a multilayer piezoelectric actuator. In particular, in a laminated piezoelectric actuator using piezoelectric ceramics that is continuously driven in a high electric field, the method for producing a laminated piezoelectric element of the present invention is preferably used.

Slurry in which a calcined powder of piezoelectric ceramic having a Curie temperature of 300 ° C. and a particle size of 0.7 μm made of lead zirconate titanate Pb (Zr, Ti) O ₃ , an organic binder made of butyral resin, and a plasticizer are mixed. A green sheet having a thickness of 150 μm was prepared by a slip casting method.

  On one side of the green sheet, as shown in FIG. 2, a predetermined amount of metal powder having a predetermined composition with an Ag—Pd component serving as a conductor layer, a ceramic powder having an average particle size of 0.4 μm, an organic resin, and A conductive paste containing a solvent was printed to a thickness of 4 μm by screen printing to form a conductive pattern 22. The ceramic powder mixed in the conductor paste was used after finely pulverizing the calcined powder used for the green sheet. Next, 30 green sheets on which conductive patterns are formed are stacked, and 5 green sheets to which conductive paste is not applied are stacked on the upper and lower surfaces of the stacked body. The structure shown in FIG. A laminated molded body was produced. Next, this laminated molded body was placed in a mold and integrated by applying a pressure of 100 MPa by a hydrostatic press while heating at 90 ° C. This was cut into a size of 10 mm × 10 mm, and then the binder was removed at 800 ° C. for 10 hours, followed by main firing at 1130 ° C. for 2 hours to obtain a columnar laminate.

  Thereafter, an Ag glass paste mainly composed of silver is applied to the opposite side surfaces of the active part, heated at 750 ° C. for 1 hour, and then subjected to heat treatment at the cooling rates shown in Table 1 to form external electrodes. did.

Then, a 3 kV / mm direct current electric field was applied to the positive electrode and the negative external electrode 4 for 15 minutes to carry out polarization treatment, thereby producing a laminated piezoelectric element. The ratio of the metal and ceramic components in the peeled portion and other portions of the conductor layer was evaluated by an analytical electron microscope. In this case, if the difference exceeds 10%, it is considered that there is a difference. The lattice constant was determined using X-ray diffraction. The evaluation of the effective piezoelectric strain constant is performed by applying a voltage of 0 to 200 V to the laminated piezoelectric element sample fixed on the anti-seismic table with a preload of 150 kgf applied in the laminating direction, and the laminated piezoelectric element at that time. The amount of change in the total length of the element sample was measured, and the amount of change was calculated by dividing by the number of layers and the applied voltage. The Curie temperature was obtained by measuring the temperature characteristics of the capacitance of the piezoelectric ceramic.

  The Curie temperature of the piezoelectric body of the present invention was 330 ° C. From Table 1, Sample No. which is a multilayer piezoelectric element formed by a conductor pattern to which ceramic powder having an average particle size smaller than that of the ceramic powder contained in the green sheet is added. 2-9, the proportion of the metal component in the region that became the gap of the conductor layer is larger than the proportion of the metal component in the bonded region, and the plan view region of the gap between the piezoelectric layer and the conductor layer is The total area of the conductor layer was 10% or less, and the gap was 1 μm or less. As a result, no delamination at the interface was observed.

  On the other hand, Sample No. which is a laminated piezoelectric element produced without adding ceramic powder to the conductor pattern. In No. 1, the planar view region of the gap between the piezoelectric layer and the conductor layer was higher than 10% of the total area of the conductor layer, and delamination was also observed at the interface.

It is a longitudinal cross-sectional view of the multilayer piezoelectric element of the present invention. It is a top view of the ceramic sheet which comprises the lamination type piezoelectric element of this invention. It is an expanded sectional view of a lamination fabrication object which serves as a lamination type piezoelectric element of the present invention. It is sectional drawing of the laminated structure used as the laminated piezoelectric element of this invention. It is a figure which shows the defect between the ceramic layer and conductor of the conventional multilayer electronic component.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 41. Piezoelectric layer 2, 42. Conductor layer 3 .... Columnar laminated body 4 .... External electrode 8 .... Active part 9 .... Inactive part 21 ... Ceramic green sheet 22 ... Conductor pattern 23 ... Laminated molded body

Claims (10)

A laminated piezoelectric element in which piezoelectric layers and conductor layers are alternately laminated, and has a region in which a gap is formed between the piezoelectric layer and the conductor layer , wherein the gap in the region in which the gap is formed A laminated piezoelectric element characterized in that the ratio of the metal component of the conductor layer is larger than the ratio of the metal component of the conductor layer in other regions . Laminate according to claim 1, characterized in that the metal component of the conductive layer is Group VIII metal, either or both of the Group VIII metal and the Ib genera metal, of Ib genus metal mainly Type piezoelectric element. The content of M1 mass% of the Group VIII metal, when the content of the Ib genus metal and M2 mass%, 0.001 ≦ M1 ≦ 15,85 ≦ M2 ≦ 99.999, M1 + M2 = 100 wt% of the relationship the multi-layer piezoelectric element according to claim 2, characterized by satisfying the. The Group VIII metal is Ni, Pt, Pd, Rh, Ir, Ru, at least one of Os, the Ib genus metals Cu, Ag, claim 2 or, characterized in that at least one of a Au 3. The laminated piezoelectric element according to 3. 5. The multilayer piezoelectric element according to claim 4 , wherein the Group VIII metal is at least one of Pt and Pd, and the Group Ib metal is at least one of Ag and Au. The multilayer piezoelectric element according to claim 4, wherein the Group VIII metal is Ni. The multilayer piezoelectric element according to claim 4, wherein the group Ib metal is Cu. Multi-layer piezoelectric element according to any one of claims 1 to 7, characterized by containing an inorganic component to the conductor layer. The inorganic component, multi-layer piezoelectric element according to claim 8, characterized in that the same components as the piezoelectric layer. A container having an injection port, a valve for ejecting the laminated piezoelectric element according to any one of claims 1 to 9 is housed in the container, the liquid from the ejection hole by a drive of the laminated piezoelectric element An injection device comprising:

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