JP4299807B2 - Multilayer piezoelectric element and injection device - Google Patents

Description

The present invention relates to a laminated piezoelectric element and an injection device used for a precision positioning device such as a fuel injection valve for an automobile and an optical device, a drive element for vibration prevention, and the like.

Conventionally, in order to obtain a large amount of displacement using the electrostrictive effect, multilayer piezoelectric elements in which piezoelectric bodies and internal electrodes are alternately stacked have been proposed. Multilayer piezoelectric elements are classified into two types: simultaneous firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Since the multilayer piezoelectric element is advantageous for thinning, its superiority is being shown.

  Conventionally, the co-fired multilayer piezoelectric element has conventionally been made by first placing the green sheet on the upper and lower surfaces of an active part molded body in which green sheets containing piezoelectric materials and internal electrode patterns containing internal electrode materials are alternately laminated. An element body molded body in which a plurality of inactive part molded bodies formed by laminating is laminated is manufactured. In the end portion of the internal electrode pattern exposed on the side surface of the element body molded body, the concave grooves are alternately formed, and the end portions of the internal electrode pattern are alternately exposed on the opposite side surface of the element body molded body, An insulator is filled in the concave groove and baked to produce an element body.

  Thereafter, a paste containing metal powder and glass frit is applied and baked on the side surface of the element body where the internal electrodes are alternately exposed and on the side surface of the inactive portion, and the external electrodes alternately connected to the internal electrodes are connected to the element body. To the side surfaces (side surfaces of the active portion and the inactive portion).

  This external electrode is formed by diffusing and joining the metal powder constituting the external electrode and the internal electrode material, and diffusing Si in the glass frit constituting the external electrode into the active part piezoelectric body and the inactive part. It was joined to the element body.

  However, in the conventional multilayer piezoelectric element, since there is no internal electrode in the inactive part, Si in the glass frit constituting the external electrode diffuses into the inactive part when joining the inactive part to the external electrode. The bonding strength between the external electrode and the inactive portion is weaker than the bonding strength between the external electrode and the active portion, and peeling occurs from the inactive portion side end of the external electrode during driving. There was a problem that it was easy to do.

  That is, when the stacked piezoelectric element is driven, the active portion is displaced by the reverse piezoelectric effect, but the inactive portion is not displaced by the reverse piezoelectric effect, so that stress is applied in the vicinity of the boundary between the active portion and the inactive portion. Separation occurs from the edge of the external electrode, which is concentrated and weak in bonding strength, that is, the inactive part side end of the external electrode, and the active part and the external electrode are separated from this as the starting point. There was a problem that the connection was cut and the characteristics deteriorated.

  Further, it is conceivable that Si in the glass frit in the external electrode is increased to diffuse a large amount of Si in the external electrode into the active part and the inactive part, but excessive diffusion of Si is caused by the active part and the inactive part. There is a problem that the surface of the piezoelectric body to which the external electrode is bonded becomes brittle and the bonding strength of the external electrode is decreased. In particular, there is a problem that the bonding strength between the inactive portion where no internal electrode is present and the external electrode is significantly reduced.

  The present invention solves the above-described problems, and can provide a laminated piezoelectric element and an injection device that can prevent the external electrode from peeling from the end portion on the inactive portion side, have excellent durability, and high reliability. The purpose is to provide.

The multilayer piezoelectric element of the present invention includes a plurality of piezoelectric bodies and a plurality of internal electrodes that are alternately stacked, an active portion that is displaced, and an inactive portion that is provided at both ends of the active portion in the stacking direction and is not displaced. And a pair of external electrodes which are joined to the side surfaces of the element body extending from the active portion to the inactive portion and having the internal electrodes alternately connected to each other. And the said external electrode has glass containing Si, and Si content of the said inactive part is more than the said active part, It is characterized by the above-mentioned.

In addition, an element body including a plurality of piezoelectric bodies and a plurality of internal electrodes that are alternately stacked, and an active portion that is displaced, and an inactive portion that is provided at both ends in the stacking direction of the active portion and is not displaced, wherein the said active portion on the side face of the element body are joined to extend in the inactive portion, wherein the inner electrode is a laminated piezoelectric element comprising a pair of external electrodes connected alternately, the device body The inactive part contains more Si than the active part, the external electrode has a glass containing Si, and the Si diffusion distance from the external electrode to the inactive part is It is shorter than the Si diffusion distance from the external electrode to the active part.

  In such a laminated piezoelectric element, Si in the external electrode diffuses from the external electrode formation surface of the element body to the inside during heat treatment, but by adding more Si to the inactive part than in the active part. Although the bonding strength between the active part and the external electrode does not change, the glass frit Si in the external electrode is less likely to diffuse into the inactive part than the active part, and the diffusion distance of Si into the inactive part is short. However, although the effect of improving the bonding strength due to the diffusion of Si between the inactive portion and the external electrode is reduced, the embrittlement of the side surface of the inactive portion can be suppressed and the decrease in the bonding strength due to this can be remarkably suppressed. The bonding strength between the side surface of the active part and the external electrode can be remarkably improved.

  In such a multilayered piezoelectric element, the bonding strength between the external electrode and the inactive portion can be made larger than the bonding strength between the external electrode and the active portion, and the inactive portion of the external electrode due to driving stress Peeling from the end is prevented, and durability and reliability can be improved.

  Moreover, in this invention, since it is not necessary to increase the amount of Si contained in an external electrode, weakening of the external electrode formation surface of an active part and an inactive part can be suppressed to the minimum.

  Si in the external electrode is determined to have the highest bonding strength from the viewpoint of weakening of the side surface of the element body due to Si diffusion and improvement of the bonding strength. . In the present invention, Si is preliminarily contained in the inactive part to minimize the diffusion of Si into the inactive part, minimize the weakening of the side surface of the inactive part, and improve the bonding strength than before. be able to.

  An injection device of the present invention includes a storage container having an injection hole, the stacked piezoelectric element stored in the storage container, and a valve for ejecting liquid from the injection hole by driving the stacked piezoelectric element. It is made.

  In the injection device of the present invention, since the bonding strength between the inactive portion and the external electrode can be improved in the multilayer piezoelectric element and the peeling from the end of the external electrode can be suppressed, the durability and reliability of the injection device are improved. it can.

  As described above in detail, in the multilayer piezoelectric element of the present invention, the bonding strength between the external electrode and the inactive portion can be improved, and the bonding strength between the external electrode and the active portion can be made higher than that. For this reason, even when the laminated piezoelectric element (actuator) is driven, it is possible to prevent peeling of the external electrode due to stress generated in the vicinity of the boundary between the active part and the inactive part, and the reliability can be improved.

  FIG. 1A is a perspective view showing an embodiment of a multilayer piezoelectric element comprising the multilayer piezoelectric actuator of the present invention, and FIG. 1B is a longitudinal sectional view taken along line AA ′ of FIG. .

  As shown in FIG. 1, the multilayer piezoelectric actuator of the present invention is provided on an active portion 8 in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately stacked, and on the outer side of the active portion 8 in the stacking direction. Further, the element main body 3 having a quadrangular prism shape composed of the inactive portion 9 is provided.

  The end portions of the internal electrodes 2 are exposed on the opposite side surfaces (external electrode forming surfaces) of the element body 3, and conductive portions 4a are formed on the exposed portions of the internal electrodes 2, respectively. The metal plate 4b is joined to the part 4a, and the external electrode 4 is configured.

  Thereby, the internal electrodes 2 are electrically connected to the respective external electrodes 4 every other layer, while the end portions of the internal electrodes 2 not connected to the external electrodes 4 are covered with the insulator 10. . Furthermore, a lead wire 16 is connected and fixed to the external electrode 4 with solder or the like.

As the piezoelectric body 1, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly composed of barium titanate BaTiO ₃ is used. It is not limited, and any ceramics 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 body 1, that is, the distance between the internal electrodes 2, is preferably 0.05 to 0.25 mm from the viewpoint of downsizing and applying a high electric field. In order to obtain a larger amount of displacement by applying a voltage to the stacked piezoelectric element, 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.

  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 element body 3 on the side of the active portion 8 where the external electrode 4 is formed. Insulator 10 is formed by being filled with polyimide resin, polyamideimide resin, silicone rubber, or the like. In this way, the end portions of the internal electrode 2 are insulated by the insulators 10 alternately filled in the groove every other layer, and the other end portion of the internal electrode 2 that is not insulated is connected to the metal plate via the conductive portion 4a. It is connected.

  The conductive portion 4 a needs to contain silver or an alloy containing silver as a main component for bonding by diffusion bonding with the internal electrode 2 and a glass component for bonding by diffusion bonding with the piezoelectric body 1. In order to provide conductivity as the external electrode 4, it is desirable that silver or an alloy containing silver as a main component is 40 to 90% by volume in the total amount of the external electrode 4.

  The thickness t of the metal plate 4b constituting the external electrode 4 follows the expansion and contraction of the actuator, and no disconnection occurs between the metal plate 4b and the conductive portion 4a or between the conductive portion 4a and the internal electrode 2. Therefore, it is desirable that it is 50 μm or less.

  The plate-like metal plate 4b 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 conductive portion 4a is strong, and the Young's modulus is high. From the viewpoint of low, silver or an alloy containing silver as a main component is desirable.

  The insulator 10 is preferably made of a material having a low elastic modulus that follows the displacement of the element body 3, specifically, silicone rubber or the like in order to strengthen the bonding with the element body 3. .

  A metal plate 4b is connected and fixed to at least one side surface of the element body 3 via a conductive portion 4a, and the stacked internal electrodes 2 are electrically connected to the external electrode 4 every other layer. ing. The metal plate 4b serves to supply in common 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.

  Further, the lead wire 16 is connected and fixed to the external electrode 4 by soldering. The lead wire 16 serves to connect the external electrode 4 to an external voltage supply unit.

  In the present invention, the inactive portion 9 contains more Si than the active portion 8, thereby reducing the distance of the concentration gradient of diffusion of Si in the external electrode 4 to the inactive portion 9, It is possible to prevent a decrease in bonding strength due to embrittlement of the piezoelectric body of the inactive portion 9 due to excessive diffusion of Si, and improve the bonding strength between the external electrode 4 and the inactive portion 9. As a result, the bonding strength between the external electrode 4 and the inactive portion 9 can be made higher than the bonding strength between the external electrode 4 and the active portion 8, and in the vicinity of the boundary between the active portion 8 and the inactive portion 9 during driving. It is possible to prevent peeling from the end portion of the external electrode 4 due to the stress generated in step 1, and high reliability can be obtained.

The content of Si in the inactive part 9 is 0.1 to 3 of the piezoelectric ceramic constituting the inactive part 9 in terms of SiO _{2 in} terms of preventing a decrease in strength of the piezoelectric body 1 due to diffusion of Si. % By weight is desirable. In particular, it is preferably 0.1 to 1% by weight from the viewpoint of reducing the Si diffusion distance and improving the bonding strength.

The multi-layer piezoelectric element configured as described above is manufactured by the following process. First, a slurry is prepared by mixing a calcined powder of a piezoelectric ceramic such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer, and by slip casting method, A ceramic green sheet having a thickness of 50 to 250 μm is prepared.

  A conductive paste mainly composed of silver-palladium serving as the internal electrode 2 is printed on one side of the green sheet to a thickness of 1 to 10 μm by screen printing.

  After the conductive paste is dried, a predetermined number of green sheets coated with the conductive paste are stacked to form an active part molded body of the active part 8.

Separately, a predetermined amount of SiO ₂ , a calcined powder of piezoelectric ceramic such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer were mixed. A slurry is prepared, and a ceramic green sheet having a thickness of 50 to 250 μm is prepared by a slip casting method.

  A predetermined number of the green sheets are laminated at both ends in the lamination direction of the active part molded body, and the inactive part molded body is laminated.

  Next, pressure is applied while heating the laminated body at 50 to 200 ° C. to integrate the laminated body. After the integrated laminate is cut to a predetermined size, the binder is removed at 400 to 800 ° C. for 5 to 40 hours, and main firing is performed at 900 to 1200 ° C. for 2 to 5 hours. A laminated sintered body to be the main body 3 is obtained. The end of the internal electrode 2 is exposed on the side surface of the element body 3.

  Thereafter, a groove is formed in every other layer on the side surface of the element body 3 where the external electrode 4 is formed by a dicing apparatus or the like. A silver glass paste made of silver powder and Pb-Si-based or B-Si-based glass powder is interposed between the side surface of the element body 3 in which the concave grooves are formed and the metal plate 4b. Then, Si in the silver glass paste is transferred to the piezoelectric body 1 and the inactive portion 9 of the active portion 8 by heat-treating the metal plate 4b and the element main body 3 at a pressure of 2 to 80 kPa at 500 to 900 ° C. In addition, the silver in the silver glass paste diffuses to the internal electrode 2, and a conductive portion 4a is formed on the side surface of the element body 3, and a metal plate 4b made of a plate-like conductive member is formed on the conductive portion 4a. Are joined.

  Thereafter, the lead wire 16 is connected to the external electrode 4 and the outer peripheral surface of the element is coated with an exterior resin by a method such as dipping by vacuum defoaming, and then a polarization voltage of 0.1 to 3 kV is applied to the entire element. Is subjected to polarization treatment to obtain a final laminated piezoelectric element.

  In the multilayer piezoelectric actuator configured as described above, the bonding strength between the external electrode 4 and the inactive portion 9 increases, and even when the actuator is driven, the vicinity of the boundary between the active portion 8 and the inactive portion 9 The external electrode 4 can be prevented from being peeled off from the end of the inactive portion due to the stress generated in the above, and an actuator having high reliability can be provided.

  The multilayer piezoelectric element of the present invention may be any column body such as a quadrangular column, a hexagonal column, or a cylinder, but a quadrangular column shape is desirable for ease of cutting.

  Moreover, although the metal plate 4b is used as the external electrode 4, the same effect can be obtained even if it is formed only by a paste.

  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.

  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.

  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.

  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.

A slurry is prepared by mixing a calcined powder of piezoelectric ceramics such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer, and a thickness of 150 μm is obtained by a slip casting method. A ceramic green sheet was prepared.

  A conductive paste mainly composed of silver-palladium serving as an internal electrode is printed on one side of the green sheet to a thickness of 5 μm by a screen printing method, and the conductive paste is dried. 100 green sheets were laminated to produce an active part molded body.

On the other hand, a predetermined amount of SiO ₂ is added to the slurry, ceramic green sheets are produced by a slip casting method, 10 ceramic green sheets are laminated at both ends in the laminating direction of the active part molded body, and active body molding is performed. An inactive part molded body was formed on both end faces of the body to prepare a device body molded body.

  Next, the element body molded body was pressed and integrated while being heated at 100 ° C., cut into a size of 10 mm × 10 mm, debindered at 800 ° C. for 10 hours, and then at 1130 ° C. for 2 hours. Was fired to obtain a laminated sintered body to be the element body.

  Thereafter, concave grooves having a width of 50 μm and a depth of 200 μm were formed on the side surface of the active part where the external electrodes were formed by a dicing apparatus. And, between the external electrode forming side surface of the element body in which this concave groove is formed and the metal plate mainly composed of silver, a silver glass paste made of silver powder and B-Si glass powder is interposed, By heat-treating the external electrode in a pressure contact state at a pressure of 30 kPa, a conductive portion was formed on the side surface of the element body, the conductive portion was bonded to a metal plate, and the external electrode was bonded to the element body. Thereafter, silicone rubber was filled into the concave groove to form the insulator 10.

  The diffusion distance of Si into the element body of the obtained sample was measured by electron probe microanalysis (EPMA). The result is shown in FIG. In addition, in order to measure the bonding strength of the external electrode of the obtained multilayer piezoelectric element, the bonded portion of the external electrode with the inactive portion and the bonded portion with the active portion are cut and separated, A metal plate was bonded to the plate with an epoxy resin, and the strength was measured by pulling the plate. The result of the tensile strength ratio between the active part and the inactive part is shown in FIG.

FIG. 3 shows that the Si diffusion distance decreases as the amount of SiO ₂ in the inactive portion increases. As a result, excessive diffusion of Si into the inactive part is suppressed, and it becomes possible to prevent weakening of the surface of the piezoelectric body of the inactive part, and the bonding strength between the external electrode and the inactive part is improved. Recognize.

Further, when the amount of SiO ₂ in the inactive part is 0.1 to 3% by weight, the diffusion distance is shortened and a large bonding strength ratio is obtained. In particular, the amount of SiO _{2 in the} inactive part is 0.1 to 1%. It turns out that it is desirable to set it as 0.0 weight%.

Using a green sheet in which 2% by weight of SiO ₂ is added to the inert part, lead wires are connected to the laminated piezoelectric element manufactured in the same manner as in Example 1, and silicone is formed on the outer peripheral surface of the element by a method such as dipping. The laminated piezoelectric element of the present invention was obtained by coating the resin, applying a polarization voltage of 1 kV, and polarizing the entire element.

  For comparison, a similar sample was prepared for the inactive part except that the same green sheet as that for the active part was used.

  As a result of applying a DC voltage of 200 V to the obtained multilayer piezoelectric actuator, a displacement of 10 μm was obtained for each actuator.

In order to compare the durability of the obtained actuator, a driving durability test was performed up to 5 × 10 ⁸ cycles of a DC electric field of 200 V at room temperature. In the driving test, the actuator was driven, the displacement was measured, and the variation from the initial displacement was examined. The displacement is measured with the average value of the values measured at the center part and the peripheral part of the element with a laser displacement meter by fixing the sample on the vibration isolation table, attaching an aluminum foil to the upper surface of the sample, and using a laser displacement meter. evaluated. The results are shown in Table 1.

  From Table 1, the conventional product in which Si is not contained in the inactive part has a weak bonding strength between the external electrode and the inactive part, and the external electrode is also seen from the vicinity of the boundary between the active part and the inactive part in the driving test. The voltage was not supplied to the internal electrode after peeling, and the displacement characteristics deteriorated when the number of cycles was less than a predetermined number. On the other hand, the displacement of the product of the present invention was not observed after the driving test.

The laminated piezoelectric element of this invention is shown, (a) is a perspective view, (b) is a longitudinal cross-sectional view along the A-A 'line of (a). It is explanatory drawing which shows the injection apparatus of this invention. Diffusion length of SiO ₂ amount and Si in the inactive portion, which is a graph showing the bonding strength ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 2 ... Internal electrode 3 ... Element main body 4 ... External electrode 8 ... Active part 9 ... Inactive part 10 ... Exterior resin 16 ... Lead wire 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator (multilayer piezoelectric element)

Claims (4)

An element body comprising a plurality of piezoelectric bodies and a plurality of internal electrodes which are alternately stacked and displaceable active parts, and non-displaceable inactive parts provided at both ends of the active parts in the stacking direction, and the element A laminated piezoelectric element comprising a pair of external electrodes that are joined to the side surface of the main body by extending from the active portion to the inactive portion, and wherein the internal electrodes are alternately connected, wherein the external electrodes are: A laminated piezoelectric element having glass containing Si and having an Si content in the inactive part larger than that in the active part. An element body comprising a plurality of piezoelectric bodies and a plurality of internal electrodes which are alternately stacked and displaceable active parts, and non-displaceable inactive parts provided at both ends of the active parts in the stacking direction, and the element joined from the active portion to the side surface of the main body extends in the inactive portion, wherein the inner electrode is a laminated piezoelectric element comprising a pair of external electrodes connected alternately, the element body wherein The inactive part contains more Si than the active part, and the external electrode has glass containing Si, and the Si diffusion distance from the external electrode to the inactive part is A laminated piezoelectric element characterized by being shorter than the Si diffusion distance from the active part to the active part. Laminated piezoelectric element according to claim 1 or 2, wherein the Si content of the inert portion is characterized in that 0.1 to 3 wt% more in terms of SiO ₂ than the active part. A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 3 accommodated in the storage container, and liquid is ejected from the injection hole by driving the multilayer piezoelectric element. An injection device comprising a valve.

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