JP6360362B2 - Multilayer piezoelectric element - Google Patents

Description

  The present invention relates to a laminated piezoelectric element using piezoelectric ceramics.

  Piezoelectric ceramics having a function of converting electrical energy into mechanical energy or converting mechanical energy into electrical energy (piezoelectric effect) have been applied to many elements (electronic devices). An electronic device using this piezoelectric effect is called a piezoelectric element, and a piezoelectric element having a laminated structure of a layer made of piezoelectric ceramics and an internal electrode layer is called a laminated piezoelectric element.

  Conventionally, among piezoelectric ceramics used in piezoelectric elements, piezoelectric ceramics having an alkali metal-containing niobate-based perovskite structure have been proposed as those containing no lead or low lead.

As an example of such piezoelectric ceramics, Patent Document 1 represents the general formula {Li _y (Na _1−x K _x ) _1−y } _a (Nb _1−zw Ta _z Sb _w ) O ₃ , and 0 .9 ≦ a ≦ 1.2, 0.2 ≦ x ≦ 0.8, 0.0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.5 and 0 ≦ w ≦ 0.1, A ceramic sintered body made of a material in which a compound contains a Mn compound or a Ca compound is disclosed.

JP 2011-144101A

  An object of the present invention is to provide a multilayer piezoelectric element that is less likely to crack even when driven for a long time and is therefore highly reliable.

As a result of intensive studies by the present inventors, the present invention having the following characteristics has been completed.
(1) It has a piezoelectric ceramic layer and an internal electrode layer, and the piezoelectric ceramic layer includes a drive region facing the internal electrode and a peripheral region surrounding the drive region, and the peripheral region is made of glass. A laminated piezoelectric element including a phase.
(2) The laminated piezoelectric element according to (1), wherein the ceramic of the piezoelectric ceramic layer has an alkali metal-containing niobate-based perovskite structure, and the glass phase contains K, Na, and Li.
(3) The laminated piezoelectric element according to (1) or (2), wherein the glass phase has an aspect ratio of 2 or more.
(4) The laminated piezoelectric element according to any one of (1) to (3), wherein the glass phase has an average particle diameter of 1 to 5 μm.

  In the multilayer piezoelectric element, stress generated between a driving region where mechanical displacement occurs during driving and a peripheral region where such a variation does not occur was one of the factors causing cracks. The glass phase scattered in the region has a stress relaxation effect and is not easily cracked. As a result, a laminated piezoelectric element that exhibits high reliability when driven for a long time is provided.

It is a schematic cross section of an example of the laminated piezoelectric element of the present invention. It is a perspective view of the ceramic green sheet manufactured in the manufacturing process of a laminated piezoelectric actuator.

  The present invention will be described in detail with appropriate reference to the drawings. However, the present invention is not limited to the illustrated embodiment, and in the drawings, the characteristic portions of the invention may be emphasized and expressed, so that the accuracy of the scale is not necessarily guaranteed in each part of the drawings. Not.

FIG. 1 is a cross-sectional view of an example of the laminated piezoelectric element of the present invention. This laminated piezoelectric element 1 (hereinafter also simply referred to as element 1) is a laminated body in which a piezoelectric ceramic layer and an internal electrode 22 are laminated, and the lead-out portion of the internal electrode 22 is externally provided on the end face of the laminated body. It is connected to the electrode. A protective layer is formed on one or both surfaces of the laminate. The piezoelectric ceramics 21 sandwiched between the internal electrodes 22 in the layer direction are driven (displaced), and the piezoelectric ceramics 11 around the internal electrodes 22 and the protective layer are not driven (displaced).
The piezoelectric ceramic layer is distinguished into a drive region 21 facing the internal electrode 22 and a peripheral region 11 surrounding the drive region 21.
More specifically, a plurality of internal electrodes 22 and a plurality of piezoelectric ceramic layers (drive region 21) are alternately stacked, and these constitute a stacked region 20. The material of the internal electrode 22 is not particularly limited. If this element 1 is manufactured by ordinary firing in the atmosphere, the material of the internal electrode 22 may be a metal mainly containing Pt, Pd, Ag or the like. Prior art etc. can be referred to for the specific laminated structure in the laminated region 20 as appropriate.

  Around the laminated region 20, there is a peripheral region 11 that does not have the above-described laminated structure. The peripheral region 11 is mainly a piezoelectric ceramic layer, and the material thereof is generally the same material as that of the above-described piezoelectric ceramic layer (drive region 21). The peripheral region 11 existing above and below the laminated region 20 in FIG. 1 can be obtained, for example, by stacking only piezoelectric ceramic layers without providing an internal electrode layer. Thus, the peripheral region 11 existing above and below the laminated region 20 (here, the laminated direction is regarded as the vertical direction) can also be called a protective layer. 1 can be obtained by, for example, forming a piezoelectric ceramic layer wider than a portion where an internal electrode layer is provided when the stacked region 20 is formed. Thus, in the layer in which the peripheral regions 11 existing on the left and right sides of the stacked region 20 are stacked, it can also be called a side margin. In FIG. 1, the internal electrode layer 22 may reach the outer surface of the element 1 to form a take-out electrode in the front and back direction of the drawing. Therefore, the stacked region 20 does not need to be completely covered by the peripheral region 11, and even if a part of the stacked region 20 reaches the surface of the element 1 as in the portion where the extraction electrode is formed as described above. Good.

  The piezoelectric ceramic layers 11 and 21 can be made of any known material without particular limitation, and preferably ceramics having an alkali metal-containing niobic acid-based perovskite structure can be used. Preferably, as the ceramic material in the drive region 21 and the peripheral region 11, the same ceramic material can be used for both.

The ceramic having the above-mentioned alkali metal-containing niobate-based perovskite structure has a general ABO ₃ type perovskite structure, and typically, an alkali metal element such as K, Na, Li is coordinated to the A site, By adopting a structure in which Nb conforms to the B site, 6 Os coordinate around the B site, and 12 Os coordinate around the A site. , Forming crystals.

  Regarding the alkali metal-containing niobate-based perovskite structure, the crystal system is preferably a monoclinic system whose Z value (the number of composition units contained in the crystal lattice) can be evaluated as 1, and is extremely low such as Pm in the space group. It has a symmetric crystal structure. Therefore, the A-site element, B-site element and O (oxygen) can be displaced without restriction in the plane direction of the mirror surface (m) defined by the space group, It has become.

The piezoelectric ceramic layer having an alkali metal-containing niobate-based perovskite structure needs to contain elements of niobium, oxygen, and alkali metal, and preferably Li _x Na _y K _1-xy ) _a (Nb _1-z Ta _z ) O ₃ , where 0.04 <x ≦ 0.1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0.98 ≦ a ≦ 1.01 It is.

  The peripheral region 11 is mainly made of a ceramic material, and the glass phase 12 is scattered in the ceramic material. Here, the glass phases 12 are scattered because the ceramic material has a continuous structure, and there are a plurality of discrete glass phases 12 in the continuous structure. Means. The ceramic material and the glass phase 12 dispersed therein can be clearly discriminated from the difference in contrast in the SEM observation image of the peripheral region 11. Due to the presence of the glass phase 12 in the peripheral region, stress relaxation is achieved in the glass phase 12, and as a result, the occurrence of cracks in the element 1 is prevented, and high reliability when the element 1 is driven for a long time is achieved.

  Preferably, the ceramic material (peripheral region 11) has the above-described alkali metal-containing niobate-based perovskite structure, and the glass phase 12 contains K, Na, and Li. More preferably, the glass phase 12 consists of only elements of K, Na, Li, Si and O. Separately, preferably, among the three of K, Na and Li in the glass phase 12, the molar ratio of K is the largest. The presence of these elements and the ratio of the existing elements can be known by elemental analysis accompanying SEM observation. Moreover, since the composition of the glass powder added at the time of manufacture becomes the composition of the glass phase 12 as it is, it is possible to adjust the kind and ratio of the elements present in the glass phase 12 from the composition of the glass powder added as a raw material. . When the composition of the ceramic material and the glass phase 12 is as described above, the closeness of the element distribution of the ceramic material (peripheral region 11) and the glass phase 12 is high, and it is separated at the interface between the piezoelectric ceramic and the glass phase even when fired. Without doing so, the stress relaxation effect described above becomes more prominent.

  The size of the glass phase 12 is measured by SEM observation. Specifically, the average particle diameter of the glass phase 12 can be obtained by finding about 500 glass phases 12, measuring the length in a certain direction for each, and calculating the number average. Further, the aspect ratio can be obtained by measuring the length of the major axis and the minor axis of each glass phase 12 found. Preferably, more than half of the glass phases 12 (number basis) have an aspect ratio of 2 or more, more preferably 2-5. Separately, preferably, the average particle diameter of the glass phase 12 is 1 to 5 μm. If it is smaller than 1 μm, the stress relaxation effect is difficult to obtain, and if it exceeds 5 μm, there is a risk of peeling at the interface between the glass phase and the ceramic. Due to the presence of the glass phase 12 having these shapes and sizes, the above-described stress relaxation effect can be more effectively achieved.

Preferably, the glass phase 12 is unevenly distributed near the surface side of the element 1 in the peripheral region 11. Specifically, it is preferably present in a portion of 50 to 200 μm from the surface side of the element 1 in the peripheral region 11, and more preferably present in a portion of 100 to 150 μm. More preferably, it exists in the said part with the frequency of 10-50 pieces / 100 micrometer < ² > or more. The distance from the surface side of the element 1 in the peripheral region 10 is the length indicated by the symbols L and W in FIG. The glass phase 12 may be present in at least a part of the peripheral region 11 and is preferably present in the entire region of the peripheral region 11 (however, on the surface side of the element 1). For example, the glass phase 12 may be scattered only in the portion corresponding to the protective layer, or the glass phase 12 may be scattered only in the portion corresponding to the side margin. Preferably, the glass phase 12 is interspersed in both the portion corresponding to the protective layer and the portion corresponding to the side margin.

  According to the present invention, the laminated piezoelectric element is particularly limited in its specific component form as long as it is an electronic device using a function (piezoelectric effect) for converting electrical energy into mechanical energy or mechanical energy into electrical energy. Not.

  According to the manufacturing method of the present invention, a conventional manufacturing method for a piezoelectric element can be applied mutatis mutandis, and a desired glass phase 12 can be obtained by adding glass powder to a so-called protective layer or side margin. it can.

  As an example of the manufacture of the piezoelectric element in the present invention, a manufacturing method related to a multilayer piezoelectric actuator which is a multilayer ceramic component will be described below. The following description is only an example of a manufacturing method and does not limit the present invention.

  First, a piezoelectric ceramic having an alkali metal-containing niobate-based perovskite structure, which is the main composition constituting the piezoelectric ceramic layer, is synthesized.

  As a raw material for a piezoelectric ceramic having an alkali metal-containing niobate-based perovskite structure, a raw material containing potassium (K), a raw material containing sodium (Na), a raw material containing lithium (Li), and niobium (Nb) A raw material containing and a raw material containing tantalum (Ta) are prepared.

In that case, as a raw material containing potassium, potassium carbonate (K ₂ CO ₃ ) or potassium hydrogen carbonate (KHCO ₃ ) is preferable. As a raw material containing sodium, sodium carbonate (Na ₂ CO ₃ ) or sodium hydrogen carbonate (NaHCO ₃ ) is preferable. As a raw material containing lithium, lithium carbonate (Li ₂ CO ₃ ) is preferable.

Further, niobium pentoxide (Nb ₂ O ₅ ) is preferable as a raw material containing niobium, and tantalum pentoxide (Ta ₂ O ₅ ) is preferable as a raw material containing tantalum.

  After the above raw materials are finally weighed to a predetermined target composition, they are wet-stirred with a partially stabilized zirconia (PSZ) ball and an organic solvent such as ethanol for 10 to 60 hours using a ball mill. Is evaporated and dried to obtain a stirring raw material.

  The obtained stirring raw material is calcined for 1 hour to 10 hours at a temperature of 700 ° C. to 950 ° C. and then crushed by a ball mill to obtain calcined powder.

  And as an optional component, a raw material containing a desired element that can be selected from Mn, Ni, Si, Ca, Ba, Sr, Zr, etc. is prepared as necessary, and each of the predetermined amounts is added to the calcined powder. The raw materials were weighed, and again wet-stirred for 10 to 60 hours using a ball mill with an organic solvent such as PSZ balls and ethanol, and then the organic solvent was evaporated and dried to obtain a calcined powder mixture.

  An organic binder and a dispersant are added to the obtained calcined powder mixture and wet mixed in a ball mill using an organic solvent such as pure water or ethanol to obtain a ceramic slurry. A ceramic green sheet is produced by molding the ceramic slurry by a doctor blade method or the like.

  In the production of the ceramic green sheet, glass powder serving as a source of the glass phase 12 is added to the portion corresponding to the side margin and the portion corresponding to the protective layer. Since the composition and shape of the glass powder are substantially the same as the composition and shape of the glass phase 12 in the finally obtained device, the composition, shape, etc. of the glass phase 12 can be designed by selecting the raw glass powder. .

  FIG. 2 is a perspective view of a ceramic green sheet manufactured in the manufacturing process of the multilayer piezoelectric actuator. A conductive paste mainly composed of Pt, Pd, Ag, etc. is prepared, and as shown in FIG. 2, the internal electrode pattern consisting of a half array shape (502a) and an array shape (502b) is formed on a ceramic green sheet (501a- g) Screen print on top.

  The ceramic green sheets (501a to 501g) on which the internal electrode patterns are formed are alternately stacked, and further sandwiched between the ceramic green sheets (503a and 503b) on which the internal electrode patterns are not formed to be bonded to each other. A ceramic laminate having a shape in which a pattern and ceramic green sheets (501a to 501g) are stacked on each other is obtained. The ceramic green sheets indicated by reference numerals 503a and 503b correspond to the protective layer described above. Therefore, it is particularly preferable to add glass powder to the ceramic green sheets 503a and 503b.

  Then, after cutting the inner electrode pattern (502a, 502b) of the obtained ceramic laminate and the arrayed internal electrode pattern (502b) in the middle of the constricted portion, it is accommodated in, for example, an alumina sheath. After performing the binder removal treatment at 300 ° C. to 500 ° C., a sintered laminate can be obtained by firing in an air atmosphere at 900 ° C. to 1050 ° C.

  A terminal electrode is formed by applying a conductive paste mainly composed of Ag or the like to both ends where the internal electrodes of the sintered laminate are exposed, and performing baking treatment at 750 ° C. to 850 ° C. A laminated piezoelectric actuator can be manufactured by applying an electric field to the internal piezoelectric ceramic layer using the terminal electrode formed in the above and performing polarization treatment to form a piezoelectric ceramic layer. In forming the terminal electrode, it is sufficient that the adhesion is good and the current supply to the internal electrode is good. As another method, a thin film forming method by a sputtering method or a vacuum evaporation method may be used.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the embodiments described in these examples.

In the example,
100Li _0.06 Na _0.52 K _0.42 NbO ₃ +0.6 MnO + 0.6NiO + 0.8Li ₂ O + 1.3SiO ₂ + 0.5SrO + 0.5ZrO ₂ (a)
A calcined powder mixture blended according to the composition formula (a) was used.

The calcined powder was obtained as follows.
Weigh potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), lithium carbonate (Li ₂ CO ₃ ) and niobium pentoxide (Nb ₂ O ₅ ) so as to have the composition of the above composition formula (a). Then, after partially stirring with a partially stabilized zirconia (PSZ) ball and an organic solvent for 24 hours by a ball mill, the organic solvent was evaporated and dried to obtain a stirring raw material. The obtained stirring raw material was calcined at 900 ° C. for 3 hours, and then crushed by a ball mill. Then, Mn, Ni, Li, Si, Sr, and Zr oxides were weighed and added so as to have the composition of the above composition formula (a), and again using a ball mill with PSZ balls and an organic solvent, After 24 hours of wet stirring, the organic solvent was evaporated and dried to obtain a calcined powder.

The following were used as the glass powder.
-Composition: More specifically, glass containing K, Na and Li as a main component is glass having more K compared to Na and Li, thereby further absorbing displacement.

  This calcined powder is charged into a ball mill together with an organic binder and ethanol and mixed thoroughly, and the resulting slurry (first slurry) is obtained using a doctor blade method to obtain a ceramic green sheet having a thickness of 20 μm. It was.

  Separately from the above, a second slurry containing 100 parts by weight of the calcined powder and 0.1 parts by weight of the glass powder was prepared.

  The second slurry was applied to an outer peripheral portion (a portion constituting a side margin) surrounding a portion where printing of the paste for the internal electrode of the finally obtained element was planned. Moreover, the ceramic green sheet for a protective layer was manufactured using the 2nd slurry.

  Next, a conductive layer having a predetermined pattern was formed on the ceramic green sheet by using a conductive paste using Pt as the internal electrode paste. And after sandwiching the ceramic green sheet on which the conductive layer is formed and the ceramic green sheet on which the internal electrode is not formed to form a laminated state, the upper and lower sides of the ceramic green sheet for the protective layer on which the internal electrode is not formed The sheet was sandwiched between ceramic green sheets, pressed with a pressure of about 50 MPa, and pressed to obtain a plate-shaped formed body of a ceramic laminate.

  Next, the plate-shaped molded body is cut so as to satisfy a predetermined size, and then accommodated in an alumina sheath, subjected to a binder removal treatment at 300 ° C. to 500 ° C., and then fired for each piezoelectric ceramic. Firing was performed in an air atmosphere at a temperature to obtain a laminated ceramic sintered body.

  After that, a conductive paste made of Ag was applied to both end portions where the internal electrodes of the multilayer ceramic sintered body were exposed, and baked at 800 ° C. to obtain a positive electrode and a negative electrode. Thereafter, 200 V was applied at 100 ° C. for 10 minutes for polarization treatment to obtain a laminated piezoelectric actuator (Example). When the obtained laminated piezoelectric element was observed, it was confirmed that the glass layer having an aspect ratio of 2 or more and an average particle diameter of 1 to 5 μm was present in the cover layer and the side margin.

  The laminated piezoelectric actuator of the comparative example was obtained in the same manner as in the example except that the first slurry was used without preparing the second slurry.

The laminated piezoelectric actuators of the examples and comparative examples were subjected to an acceleration test for reliability when a DC voltage was applied. The measurement environment is as follows: drive voltage (400 V), ambient temperature (150 ° C.), 2 hr.
In the accelerated test, a sample that was not dielectrically broken was judged as a good product, and a sample that was broken down was judged as a defective product. Here, it was assumed that a sample having a resistance lower than 1 MΩ was broken down.
In the comparative example, the non-defective product was 0/5 pieces, whereas in the example, the non-defective product was 5/5 pieces. As described above, the improvement in the lifetime in the examples is presumed to be due to the difficulty of generating cracks in the peripheral region of the element.

1: laminated piezoelectric element 11: peripheral region 12: glass phase 20: laminated region 21: driving region 22: internal electrode layers 501a to 501g: ceramic green sheets 502a, 502b: internal electrode patterns 503a, 503b: ceramics for a protective layer Green sheet

Claims (4)

Having a laminate formed by laminating a piezoelectric ceramic layer and an internal electrode layer;
The piezoelectric ceramic layer includes a drive region facing the internal electrode layer , and a peripheral region surrounding the drive region, and the peripheral region includes a side margin parallel to the stacking direction of the stacked body. A laminated piezoelectric element having a protective layer perpendicular to the laminating direction, wherein both the side margin and the protective layer contain a glass phase.   The multilayer piezoelectric element according to claim 1, wherein the ceramic of the piezoelectric ceramic layer has an alkali metal-containing niobate-based perovskite structure, and the glass phase contains K, Na, and Li.   The multilayer piezoelectric element according to claim 1, wherein the glass phase has an aspect ratio of 2 or more.   The laminated piezoelectric element according to claim 1, wherein the glass phase has an average particle diameter of 1 to 5 μm.

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