JP2014187061A - Piezoelectric element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element in which migration can be prevented in a stress relaxation layer, by lowering the mobility of metal cations or halogen anions, thereby prolonging the time to short-circuit of positive and negative poles.SOLUTION: A laminated piezoelectric element 100 telescoping by application of a voltage includes piezoelectric layers 110 formed of piezoelectric ceramic, internal electrode layers 120 laminated alternately with the piezoelectric layers 110, and a stress relaxation layer 140 formed by calcining a lead titanate paste added with a hardening element for increasing the insulation resistance, and provided in contact with the outer periphery 145 of the element along the same laminate surface as the internal electrode layers 120.

Description

  The present invention relates to a laminated piezoelectric element that expands and contracts by application of a voltage and a method for manufacturing the same.

  Piezoelectric elements are elements in which piezoelectric layers and internal electrodes are alternately stacked and use displacement due to application of voltage. An active piezoelectric layer is displaced between electrodes, and inactive portions are not displaced. Therefore, stress is generated in the piezoelectric element when the piezoelectric element is displaced. Conventionally, various techniques for relieving such stress have been disclosed.

  For example, the piezoelectric element described in Patent Document 1 includes one or more components selected from manganese, iron, chromium, and tungsten in a portion located in the vicinity of the outer peripheral portion of the internal electrode in the piezoelectric ceramic layer more than other portions. The displacement amount of the outer peripheral portion of the internal electrode is continuously reduced from the inside to the outside of this region. And it is trying to prevent stress fracture by such a structure.

  A method of providing a stress relaxation layer on a piezoelectric element is also known. The stress relaxation layer is arranged so as to surround the periphery of the internal electrode on the same plane as the internal electrode, and improves durability by relaxing the stress generated during driving. In recent years, piezoelectric actuators have been used in a high temperature environment exceeding 100 ° C., and there is a demand for improvement in durability at higher temperatures.

JP 2004-158494 A

  However, in the piezoelectric element used in the high temperature environment as described above, a phenomenon has occurred in which a portion with reduced insulation occurs in the stress relaxation layer on the positive electrode side. If such a portion grows, the piezoelectric element will break down and the product will not function.

  The present invention has been made in view of such circumstances, and by reducing the mobility of metal cations and halogen anions and increasing the time until the positive and negative electrodes are short-circuited, insulation deterioration in the stress relaxation layer is achieved. It is an object of the present invention to provide a piezoelectric element capable of preventing the above and a manufacturing method thereof.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a stacked piezoelectric element that expands and contracts by application of voltage, and is alternately formed with piezoelectric layers formed of piezoelectric ceramics and the piezoelectric layers. The internal electrode layer is formed by firing a lead titanate paste added with a hardening element that increases insulation resistance, and is provided in contact with the outer periphery of the element along the same laminated surface as the internal electrode layer. And a stress relaxation layer formed thereon.

  As described above, since the stress relaxation layer is formed on the basis of the lead titanate paste to which the hardening element for increasing the insulation resistance is added, the mobility of the metal cation and the halogen anion in the stress relaxation layer is lowered. be able to. As a result, it is possible to lengthen the time until the positive and negative electrodes are short-circuited, prevent insulation deterioration at high temperatures, and improve durability.

  (2) Moreover, the piezoelectric element of the present invention is characterized in that the hardening element is manganese, iron, chromium, or tungsten. Thereby, by increasing the insulation resistance of the stress relaxation layer, the mobility of metal cations and halogen anions that cause migration can be reduced.

  (3) Further, the piezoelectric element of the present invention is characterized in that the internal electrode layer is formed of a metal having a low ionization tendency such as platinum or palladium. Thus, migration in the internal electrode layer can be prevented by using, for example, platinum or palladium, which has a lower ionization tendency than silver or the like.

  (4) A method for manufacturing a piezoelectric element according to the present invention is a method for manufacturing a stacked piezoelectric element that expands and contracts by application of a voltage, and includes an internal electrode layer paste including a conductive material on a green sheet including piezoelectric ceramics. And a step of applying a stress relaxation layer paste containing lead titanate added with a hardening element that increases insulation resistance, a step of stacking the green sheets to form a molded body, and a step of firing the molded body It is characterized by including.

  Thereby, the insulation resistance of the stress relaxation layer can be increased, the mobility of metal cations and halogen anions in the stress relaxation layer can be lowered, and the time until the positive and negative electrodes are short-circuited can be increased. As a result, it is possible to produce a piezoelectric element suitable for use at high temperatures in which migration of both the internal electrode layer and the stress relaxation layer is prevented.

  According to the present invention, migration in the stress relaxation layer can be prevented by reducing the mobility of metal cations and halogen anions and increasing the time until the positive and negative electrodes are short-circuited.

(A)-(c) It is a perspective view and each plane sectional view showing a piezoelectric element concerning the present invention, respectively.

  Next, embodiments of the present invention will be described with reference to the drawings.

(Configuration of piezoelectric element)
FIGS. 1A to 1C are a perspective view showing the piezoelectric element 100 and a plan sectional view of the stress relaxation layer 140, respectively. The piezoelectric element 100 is a stacked piezoelectric element that expands and contracts when a voltage is applied, and the piezoelectric layers 110 and the internal electrode layers 120 are alternately stacked in the stacking direction Z and formed into a rectangular body.

  The piezoelectric layer 110 is made of, for example, piezoelectric ceramics such as PZT, and is polarized in alternate directions in the respective thickness directions. The internal electrode layer 120 is taken out to the external electrode 130 on the opposite side surface, and is formed so that different voltages can be applied to the adjacent internal electrode layers 120. By applying a voltage to the internal electrode layer 120, each piezoelectric layer 110 is distorted and the entire piezoelectric element expands and contracts.

  The piezoelectric element 100 can be divided into a protective layer provided at both ends in the stacking direction Z and an active layer driven by application of voltage. Furthermore, the active layer can be divided into a central active region where projections in the stacking direction Z of the internal electrode layer 120 overlap and a peripheral region provided so that the internal electrode layer 120 does not short-circuit with the outside. The active region is a region that is actually driven in the piezoelectric element 100. The active region is driven by voltage, but the surrounding region is not deformed by the application of voltage, and stress is generated.

  The piezoelectric element 100 has a stress relaxation layer 140. As shown in FIGS. 1B and 1C, the stress relaxation layer 140 is provided in an axisymmetric manner depending on the direction in which the extraction portion of the internal electrode layer 120 is provided. The stress relaxation layer 140 is provided in an L-shaped cross section along two adjacent side surfaces, and migration resistance is improved because the stress relaxation layer 140 is not provided on the entire outer periphery.

  The stress relaxation layer 140 is formed in a region around the active region. The stress relaxation layer 140 has an insulating property, and is provided in contact with the element outer periphery 145 along the same stacked surface as the internal electrode layer 120 (a plane perpendicular to the stacking direction).

  As described above, the stress relaxation layer 140 is provided around the active region. As a result, the stress generated by driving the piezoelectric element 100 can be dispersed and the stress during driving can be relaxed. Since the stress relaxation layer 140 is formed on the same surface as the internal electrode layer 120, it is not necessary to provide an inactive layer for stress relaxation, and the piezoelectric layer 110 can be used effectively correspondingly.

  The stress relaxation layer 140 is formed of lead titanate powder to which a hardening element that increases insulation resistance is added. Thereby, the mobility of a metal cation or a halogen anion can be reduced by the stress relaxation layer 140. As a result, it is possible to lengthen the time until the positive and negative electrodes are short-circuited, and prevent insulation deterioration. Hardening elements include manganese, iron, chromium, and tungsten. Of the above elements, manganese is particularly preferred as the hardening element. In addition, the stress relaxation layer 140 may include a portion in which the lead titanate powder to which the hardening element is added is detached to form a void.

(Piezoelectric element manufacturing method)
Next, a method for manufacturing the piezoelectric element 100 configured as described above will be described. First, using a slurry containing piezoelectric ceramic, a green sheet is formed by a method such as pulling, doctor blade, or extrusion.

  The green sheet is coated with a pattern for the internal electrode layer 120 containing a conductive material and for the stress relaxation layer 140 containing a lead titanate powder to which a hardening element for increasing insulation resistance is added by screen printing or the like.

For the internal electrode layer 120, an electrode paste is applied and then dried to form a pre-fired electrode film. For the internal electrode layer 120, a paste of platinum, palladium, silver palladium alloy or the like can be used. In particular, in a piezoelectric element used at a high temperature exceeding 100 ° C., migration is accelerated due to the high temperature. For this, it is preferable to use platinum or palladium as the internal electrode layer 120. Silver ions (Ag ⁺ ) are likely to cause migration in the silver-palladium alloy internal electrode, and platinum or palladium having a lower ionization tendency is less likely to cause migration.

  A lead titanate paste to which a hardening element is added is applied as the stress relaxation layer 140. Lead titanate is a material that does not sinter during the firing temperature of the piezoelectric element 100 (non-sintered material). Such a lead titanate paste is obtained by mixing lead titanate powder, a binder, a plasticizer, and an organic solvent to which a hardening element is added at a predetermined ratio. For example, ethyl cellulose is used as the binder, dioctyl phthalate is used as the plasticizer, and butyl carbitol is used as the organic solvent.

  Next, a plurality of green sheets on which the electrode film and the lead titanate film are formed are laminated, press-molded, and then heated to degrease the organic components in the green sheet, the electrode paste, and the lead titanate paste. The organic component is decomposed by heating to become a gas and escapes from the green sheet or paste film.

  The laminated body thus degreased is fired. At this time, the stress relaxation layer 140 is formed at the location where the lead titanate paste is applied. As a result, the insulation resistance of the stress relaxation layer can be increased, and the mobility of metal cations and halogen anions in the stress relaxation layer can be reduced. As a result, it is possible to prevent insulation deterioration due to migration of the piezoelectric element.

  The lead titanate powder to which the hardening element is added does not sinter at the firing temperature of the piezoelectric element 100 but remains as a powder, but a part thereof may be detached to form a void. By appropriately processing after firing, a fired body before polarization is obtained. And the actuator for positioners can be produced by adhere | attaching a sintered compact on the end surface of the lamination direction Z, and making a multiple connection, and polarization-treating the fired body which made the multiple connection.

  In the above embodiment, the piezoelectric element 100 used for the piezoelectric actuator is described, but the present invention is not necessarily limited to such a form. Further, the piezoelectric element is not limited to a rectangular body and can take various forms.

(Examples and comparative examples)
As an example, a paste including a lead titanate powder added with a hardening element to a green sheet is applied as a pattern for a stress relaxation layer, and the piezoelectric as shown in FIGS. 1 (a) to 1 (c). Made the element. As a comparative example, a paste containing lead titanate powder to which no hardening element was added was applied as a pattern for a stress relaxation layer to produce a piezoelectric element (the same form except for the material of the stress relaxation layer).

  These piezoelectric elements were individually driven at 85 ° C. and 90% RH, and the insulation resistance was tested by applying 150 V with DC after a predetermined time. In the test, it was determined that the insulation was poor when it was 10 MΩ or less. As a result, in the example, insulation failure occurred when the insulation resistance was maintained for 60 hours, but in the comparative example, insulation failure occurred in 12 hours.

  Next, a plurality of each of the piezoelectric elements were manufactured, and these were connected in series, sealed with a cap, and subjected to polarization treatment to manufacture a piezoelectric actuator. Each of the piezoelectric actuators of the example and the comparative example was continuously driven under the same 120 ° C. condition, and the insulation resistance was tested by applying 150 V to them. In the example, the insulation was conducted for 730 days until an insulation failure occurred. Although the resistance was maintained, insulation failure occurred in 240 days in the comparative example. From the above experimental results, it was demonstrated that the piezoelectric element in which the stress relaxation layer is formed of the lead titanate powder to which the hardening element is added is less likely to cause insulation failure.

DESCRIPTION OF SYMBOLS 100 Piezoelectric element 110 Piezoelectric layer 120 Internal electrode layer 130 External electrode 140 Stress relaxation layer 145 Element outer periphery Z Lamination direction

Claims (4)

A laminated piezoelectric element that expands and contracts by application of voltage,
A piezoelectric layer formed of piezoelectric ceramic;
Internal electrode layers alternately stacked with the piezoelectric layers;
A stress relaxation layer formed by firing a lead titanate paste added with a hardening element that increases insulation resistance, and provided in contact with the outer periphery of the element along the same laminated surface as the internal electrode layer; A piezoelectric element characterized by that.   The piezoelectric element according to claim 1, wherein the hardening element is manganese, iron, chromium, or tungsten.   The piezoelectric element according to claim 1, wherein the internal electrode layer is made of platinum or palladium. A method for producing a laminated piezoelectric element that expands and contracts by applying a voltage,
Applying an internal electrode layer paste containing a conductive material and a stress relaxation layer paste containing lead titanate to which a hardening element for increasing insulation resistance is added to a green sheet containing piezoelectric ceramics;
Laminating the green sheets to produce a molded body;
And a step of firing the molded body.

Images