JP2004296772A - Electrical drive method for multilayer piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the electrically driving method of a stacked piezoelectric element which suppresses the migration of silver. <P>SOLUTION: When an intermittent voltage is applied to the stacked piezoelectric element 10, the applied voltage respectively includes a positive polarity voltage and a negative polarity voltage in every intermittent driving. The total amount of an electric charge flowed into the stacked piezoelectric element 10 in every respective intermittent driving is preferably set to a substantial zero. Further preferably, the larger absolute value out of the positive polarity voltage or the negative polarity voltage is determined as a main voltage. The voltage opposed to the main voltage in polarity is set to a sub-voltage. The absolute value of the sub-voltage is not more than 1/4 of the absolute value of the main voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for electrically driving a laminated piezoelectric element.
[0002]
[Prior art]
Laminated piezoelectric elements having a structure in which piezoelectric ceramic layers and electrode layers (internal electrodes) are alternately laminated, and the internal electrodes are connected alternately, can be broadly classified into an adhesive type and an integral firing type. Among them, the monolithic firing type laminated piezoelectric element is obtained by printing an electrode paste on a green sheet having a predetermined shape manufactured using piezoelectric ceramic powder, laminating a predetermined number of the pastes, integrating and firing. It is made. In the multilayer piezoelectric element thus manufactured, the thickness of the piezoelectric ceramic layer is generally several tens μm to one hundred and several tens μm. In addition, as the internal electrode, a relatively inexpensive silver / palladium alloy among metals having a high melting point that can withstand a high temperature at which piezoelectric ceramics can be fired is generally used.
[0003]
As described above, since silver is contained in the internal electrode in the multilayer piezoelectric element, it is important from the viewpoint of improving reliability to suppress dielectric breakdown due to migration of silver. As is well known, silver migration occurs in a device in which a silver electrode is formed via an insulator. FIG. 4 is an explanatory view schematically showing the deposition of silver by migration of silver. Silver is combined with oxygen to form silver oxide, and when moisture (or water vapor) is present in the insulator 91, silver oxide becomes an ion. When there is a gradient in the electric field, the ion moves from the positive electrode 92a side to the negative electrode 92b side. As a result, silver is deposited in a dendritic manner. In FIG. 4, silver deposited (grown) in a tree shape is indicated by reference numeral 93.
[0004]
As described above, in the integrally fired multilayer piezoelectric element, since the thickness of the piezoelectric ceramic layer is as thin as about 100 μm, a short circuit between the electrodes is likely to occur due to dendritic silver. In practical use, before the deposited silver reaches the opposing electrodes and short-circuits between the electrodes, the deposited silver lowers the withstand voltage, so the silver deposited when a predetermined voltage is applied between the internal electrodes A discharge occurs between the electrode and the opposite electrode, and dielectric breakdown occurs.
[0005]
For example, Japanese Patent Application Laid-Open No. 5-291641 (Patent Document 1) discloses a laminated piezoelectric element in which silver migration is suppressed, in which a silver-based material is removed from an internal electrode, an external electrode, a lead wire, and solder. A piezoelectric element is disclosed. Japanese Patent Application Laid-Open No. 5-160458 (Patent Document 2) discloses a laminated piezoelectric element whose surface is coated with a silicon resin in which acrylic and urethane are combined.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 5-291641 (Paragraph 6, FIG. 1)
[Patent Document 2]
JP-A-5-160458 (paragraphs 28 to 31; FIG. 1)
[0007]
[Problems to be solved by the invention]
However, the multi-layer piezoelectric element disclosed in Japanese Patent Application Laid-Open No. 5-291641 has a problem that the production cost (element unit price) increases because expensive platinum is used as the internal electrode material. Further, the invention disclosed in Japanese Patent Application Laid-Open No. 5-160458 discloses that moisture in the air is attracted to the element by avoiding the resin film formed on the surface of the multilayer piezoelectric element from containing a chlorine component. It is from the viewpoint of preventing the situation.
[0008]
However, even when such a resin film does not contain a chlorine component, the difficulty of passage of water vapor through the resin film is related to the degree of crosslinking of the resin, and the degree of crosslinking is further increased by the degree of crosslinking of the resin. Because of the relationship with the hardness, it is necessary to increase the degree of crosslinking of the resin in order to reduce the water vapor permeability of the resin. In this case, the hardness of the resin increases, and the displacement of the multilayer piezoelectric element is reduced. A new problem of suppression occurs. Conversely, if the hardness of the resin is reduced so as not to hinder the displacement of the laminated piezoelectric element, the water vapor permeability cannot be reduced.
[0009]
The present invention has been made in view of such circumstances, and has as its object to provide a method for electrically driving a multilayer piezoelectric element that suppresses migration of silver.
[0010]
[Means for Solving the Problems]
According to the present invention, in an electric driving method for intermittently applying a voltage to a multilayer piezoelectric element,
A method of electrically driving a multi-layer piezoelectric element, wherein the voltage applied intermittently to the multi-layer piezoelectric element includes a positive polarity voltage and a negative polarity voltage for each intermittent drive. Provided.
[0011]
According to the electric driving method of the multilayer piezoelectric element of the present invention, when an electric field that causes silver to grow into a resin state is applied, an electric field opposite to the electric field is continuously applied. Migration is suppressed, whereby the insulating properties can be kept constant.
[0012]
In such a method for electrically driving a multilayer piezoelectric element, the voltage applied intermittently to the multilayer piezoelectric element includes a voltage of a positive polarity and a voltage of a negative polarity for each intermittent drive. It is preferable that the sum of the charges flowing into the piezoelectric element at each intermittent drive is substantially zero. Thus, it is possible to suppress the deterioration of the insulation characteristics due to the accumulation of minute migration of silver when the intermittent driving is repeatedly performed.
[0013]
Further, in the method for electrically driving the multilayer piezoelectric element of the present invention, the voltage applied intermittently to the multilayer piezoelectric element includes a positive polarity voltage and a negative polarity voltage for each intermittent drive, At this time, when a voltage having a larger absolute value of a positive polarity voltage or a negative polarity voltage is used as a main voltage, and a voltage having a polarity opposite to the main voltage is used as a sub voltage, an absolute value of the sub voltage is used. It is preferable that the value be 1/4 or less of the absolute value of the main voltage. Thereby, it is possible to suppress a change in the polarization state of the piezoelectric body constituting the multilayer piezoelectric element, to maintain the driving characteristics of the multilayer piezoelectric element, and to suppress the destruction of the multilayer piezoelectric element. it can.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic structure of a laminated piezoelectric element. In the laminated piezoelectric element 10, the piezoelectric ceramic layers 11 and the internal electrodes 12 are alternately laminated, and the internal electrodes 12 are alternately provided by the insulator 13 on a pair of opposing side surfaces (side surfaces in the X direction in FIG. 1). The external electrodes 14 extending in the laminating direction are provided on the X-direction side surface on which the insulator 13 is provided, so that the internal electrodes 12 are electrically connected every other layer. It has a structure.
[0015]
Such a so-called full-electrode-type multilayer piezoelectric element 10 is manufactured by, for example, firstly manufacturing a multilayer capacitor-type multilayer piezoelectric element by an integral firing method (simultaneous firing method) using a known ceramic green sheet. Subsequently, a charged colloid of a glass component is deposited on the exposed portion of the internal electrode 12 by an electrophoresis method or the like, and then the laminated piezoelectric element is fired at a predetermined temperature to form an insulator 13 made of glass. Alternatively, it can be manufactured by cutting off a portion where adjacent electrodes do not overlap with each other, and applying and baking an external electrode 14 on the side surface on which the insulator 13 is formed.
[0016]
An electric field is generated between the internal electrodes 12 by applying a predetermined driving voltage to the pair of external electrodes 14 of the laminated piezoelectric element 10, and the electric field causes the piezoelectric ceramic layer 11 to generate polarization and the piezoelectric ceramics. stretching displacement in the Z direction by the effect (longitudinal effect piezoelectric constant d ₃₃₎ occurs. FIG. 5 is a graph schematically showing the relationship between the amount of displacement of the laminated piezoelectric element 10 and the drive voltage, and is a so-called butterfly curve.
[0017]
A point P in FIG. 5 indicates a state (initial state) after the external electrode 14 is burned. When a voltage is applied to the multilayer piezoelectric element 10 from this state and the applied voltage is increased, the displacement of the multilayer piezoelectric element 10 increases. Reduced and lowered gradually applied voltage from the voltage V ₁ was displacement of the laminated piezoelectric element 10, the displacement of the laminated piezoelectric element 10 at the time the applied voltage becomes zero to return to the point P'without returning to zero . This is due to the influence of remanent polarization. When the applied voltage is further reduced, the laminated piezoelectric element 10 contracts. However, when the applied voltage reaches −V ₂ , polarization reversal occurs in which the contracted displacement is reversed to the extended displacement. The absolute value of the voltage V ₂ is called the polarization inversion voltage, an electric field across the piezoelectric ceramic layer 11 in this case is referred to as the coercive field. The value of the voltage V ₂ is the type of piezoelectric ceramic material (composition), determined by the thickness of the piezoelectric layer 11.
[0018]
Displacement of the laminated piezoelectric element 10 then furthermore decrease the applied voltage is increased, but when we increased the applied voltage polarity is reversed applied voltage after reaching the voltage -V _1, the stacked piezoelectric element 10 The displacement decreases, and when the applied voltage value becomes zero, the displacement of the multilayer piezoelectric element 10 returns to the point P '. Although further and raising the applied voltage multilayer piezoelectric element 10 is contracted, occur poled displacement the applied voltage had been contracted to reach V ₂ is reversed to the displacement extending and then is further raised to the applied voltage The displacement of the multilayer piezoelectric element 10 increases. When the applied voltage lowers the applied voltage after reaching the voltage V _1, the displacement of the stacked piezoelectric element 10 as described above becomes smaller towards the point P'.
[0019]
Conventionally, in the case of intermittently driving the multilayer piezoelectric element 10, after being subjected to a polarization treatment at a greater voltage than the polarization inversion voltage V _2, as shown in FIG. 6, the polarity of the positive voltage (polarization voltage and (Voltages of the same polarity). However, according to such a method, silver ions are generated from silver or the like which is a component of the internal electrode 12 or the external electrode 14 due to moisture that has penetrated into the multilayer piezoelectric element 10 or moisture that has adhered to the surface of the multilayer piezoelectric element 10. In this case, the migration of silver occurs and proceeds because the electric field is always applied in the same direction.
[0020]
Therefore, when the multilayer piezoelectric element 10 is intermittently driven using the characteristics shown in FIG. 5, a positive voltage is applied to the piezoelectric ceramic layer 11 every time the intermittent driving is performed, and then a negative voltage (positive voltage) is applied. A voltage having the opposite polarity to the voltage). FIG. 2A is an example of a graph showing the relationship between drive voltage and time when such intermittent drive is performed. FIG. 2B shows a displacement generated in the multilayer piezoelectric element 10 by the driving voltage shown in FIG. With such a driving method, migration of silver can be suppressed. This is because, even when silver ions are generated, the silver ions are alternately applied with electric fields in opposite directions, so that movement in the piezoelectric ceramic layer 11 is suppressed.
[0021]
When the laminated piezoelectric element 10 is driven intermittently and a positive voltage and a negative voltage are applied every intermittent driving as described above, a desired displacement is obtained with a positive voltage. For this purpose, the absolute value of the maximum value Vmax of the positive voltage is made larger than the absolute value of the minimum value Vmin of the negative voltage (that is, the lowest voltage value). In addition, from the viewpoint of preventing the destruction of the multilayer piezoelectric element 10 due to repeated polarization inversion, as shown in FIG. 2A, the absolute value of the minimum value Vmin of the negative voltage is equal to the polarization inversion voltage V _2. Is preferably not larger than the absolute value of.
[0022]
When the multilayer piezoelectric element 10 is driven so that a positive voltage and a negative voltage are included at each intermittent drive, the total sum of electric charges flowing into the multilayer piezoelectric element 10 at each intermittent drive is substantially zero. It is preferable that In FIG. 2 (a), the charge due to the positive voltage is indicated by an area S _1, the charge due to the negative voltage since represented by area S _2, so that this area S ₁ and the area S ₂ equal. This is because, when the area S ₁ is different from the area S ₂ , when intermittent driving is repeatedly performed, accumulation of minute silver migration due to driving of the larger area occurs, thereby causing the multilayer piezoelectric element 10 This is because the insulation characteristics may deteriorate.
[0023]
As described above, when the multilayer piezoelectric element 10 is driven so that a positive voltage and a negative voltage are included for each intermittent drive, the absolute value of the maximum value Vmax of the positive voltage is set to the minimum value of the negative voltage. Vmin is made larger than the absolute value. At this time, assuming that a positive voltage having a large absolute value for obtaining a target displacement is a main voltage and a negative voltage having a small absolute value for the main purpose of suppressing silver migration is a sub-voltage, It is preferable that the absolute value is not more than 1/4 of the absolute value of the main voltage. In the case of FIG. 2A, the absolute value of Vmin is set to １ ／ or less of the absolute value of Vmax.
[0024]
Application is applied unnecessarily large voltage polarization direction opposite to the direction, polarization characteristics of the piezoelectric ceramic layer 11 is changed without voltage value reaches the polarization inversion voltage V _2, thereby, a constant positive voltage In this case, the displacement characteristics of the laminated piezoelectric element 10 change. Therefore, by providing such a limitation on the magnitude of the main voltage and the sub-voltage in the intermittent drive of the multilayer piezoelectric element 10, the drive characteristics of the multilayer piezoelectric element 10 can be kept constant.
[0025]
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments. For example, as is well known, it is preferable to provide a resin film on the side surface of the multilayer piezoelectric element 10 shown in FIG. At this time, a resin film having a hardness that does not suppress the displacement of the multilayer piezoelectric element 10 can be used. The multilayer piezoelectric element 10 may be used in a form sealed in a metal can.
[0026]
Further, the multilayer electrode 10 of the full-electrode type shown in FIG. 1 is merely an example of the multilayer piezoelectric element manufactured by the integral firing method. For example, the driving method according to the present invention described above is applied to a well-known multilayer piezoelectric element 10a having a multilayer capacitor type structure shown in FIG. 3A and a stress relaxation type multilayer piezoelectric element 10b shown in FIG. It goes without saying that it can be applied. Reference numeral 15 in FIG. 3B denotes a slit (gap), and other reference numerals in FIG. 3 denote members equivalent to those in FIG.
[0027]
Furthermore, the driving method according to the present invention is also applied to a laminated piezoelectric element in which a plurality of piezoelectric veneers are stacked by bonding with an adhesive, and a Langevin-type piezoelectric actuator in which a plurality of piezoelectric veneers are tightened by bolting or the like. be able to. The voltage waveform when the multilayer piezoelectric element is driven intermittently is not limited to the rectangular wave shown in FIG. 2A, but may be a triangular wave or the like.
[0028]
【The invention's effect】
As described above, according to the method for electrically driving the multilayer piezoelectric element of the present invention, migration of silver is suppressed. Thereby, the insulation characteristics of the multilayer piezoelectric element are maintained for a long time, and the reliability is improved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an embodiment of a laminated piezoelectric element.
FIG. 2 is an explanatory diagram showing a driving method of the multilayer piezoelectric element according to the present invention and a displacement of the multilayer piezoelectric element.
FIG. 3 is a schematic cross-sectional view showing another embodiment of the multilayer piezoelectric element.
FIG. 4 is an explanatory diagram showing the progress of silver migration.
FIG. 5 is an explanatory diagram showing a relationship between a displacement amount of a multilayer piezoelectric element and an applied voltage.
FIG. 6 is an explanatory diagram showing a conventional driving method of a multilayer piezoelectric element and a displacement of the multilayer piezoelectric element.
[Explanation of symbols]
10; laminated piezoelectric element 11; piezoelectric ceramic layer 12; internal electrode 13; insulator 14; external electrode 15;

Claims (3)

In an electric driving method of intermittently applying a voltage to a laminated piezoelectric element,
A method of electrically driving a multilayer piezoelectric element, wherein the voltage intermittently applied to the multilayer piezoelectric element includes a positive polarity voltage and a negative polarity voltage for each intermittent drive. The voltage applied intermittently to the multilayer piezoelectric element includes a positive polarity voltage and a negative polarity voltage for each intermittent drive,
2. The method for electrically driving a multilayer piezoelectric element according to claim 1, wherein the sum of electric charges flowing into the multilayer piezoelectric element at each intermittent drive is set to substantially zero. . The voltage applied intermittently to the multilayer piezoelectric element includes a positive polarity voltage and a negative polarity voltage for each intermittent drive,
When the positive polarity voltage or the negative polarity voltage is a voltage having a larger absolute value as a main voltage, and a voltage having a polarity opposite to the main voltage is a sub voltage, the absolute value of the sub voltage is 3. The method according to claim 1, wherein the value is not more than 1/4 of the absolute value of the main voltage.

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