JP2008211047A - Piezoelectric element and its manufacturing method, vibrating plate, as well as vibration wave driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element made by forming a through hole electrode excellent in reliability in piezoelectric ceramics, and also to provide its manufacturing method. <P>SOLUTION: A piezoelectric element 10 is manufactured by a process to prepare a through hole in a predetermined position of a green sheet made by shape forming a piezoelectric material, to fill up the through hole with a first conductive paste, after that, to bond in piles a plurality of the green sheets so that the through holes are superposed, and to calcinate them; a process to planarize simultaneously two opposite planes in which a through hole electrode 15 formed by the through hole in the obtained calcinated body is exposed; and a process to apply respectively a second conductive paste to the thus planarized planes, and to prepare surface electrodes 13a, 13b, 14 in this planarized plane by calcinating them at the temperature lower than calcinating temperature in the calcinating process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric element that is an electro-mechanical energy conversion element, a manufacturing method thereof, a diaphragm including the piezoelectric element, and a vibration wave driving device.

  Piezoelectric elements having an electro-mechanical energy conversion function capable of converting electrical energy into mechanical energy and vice versa can be used in various fields. Piezoelectric ceramics such as barium titanate and lead zirconate titanate, and polyvinylidene fluoride-based piezoelectric polymers are known as piezoelectric materials, but piezoelectric ceramics are widely used as structural parts and mechanical parts.

  In a piezoelectric element as an electro-mechanical energy conversion element using piezoelectric ceramics, in general, electrodes are formed on two opposing surfaces of piezoelectric ceramics, and a predetermined voltage is applied between these electrodes to cause spontaneous polarization. Piezoelectricity is expressed by performing a polarization process for aligning the directions in a certain direction. Applying force or strain to the piezoelectric element from the outside to generate a voltage between the electrodes provided on the piezoelectric element, or applying a voltage between the electrodes provided on the piezoelectric element to generate vibration in the piezoelectric element. can do.

  Specific examples of the piezoelectric element that generates vibration include a vibration element incorporated in a piezoelectric buzzer or an ultrasonic motor. These have a structure in which a piezoelectric element is attached to a diaphragm using an adhesive in order to transmit the vibration of the piezoelectric element to a diaphragm made of metal or the like.

  FIG. 6 shows a perspective view of a general piezoelectric buzzer. In the piezoelectric buzzer 120, a piezoelectric element 123 having electrodes 122 (the back side is not shown) on the front and back surfaces of the piezoelectric ceramic plate 121 is attached to a vibration plate 124 made of metal, and the piezoelectric element 123 is exposed. A lead wire 126 is connected to the electrode 122 and the diaphragm 124 formed on the surface by solder 125 respectively. In FIG. 6, the electrodes 122 are hatched with dots to distinguish the piezoelectric ceramic plate 121 from the electrodes 122.

  The lead wire 126 is attached to the diaphragm 124 because an electrode (not shown) on the diaphragm 124 side of the piezoelectric element 123 is in partial contact with the diaphragm 124, and conduction is ensured between them. Therefore, by using the diaphragm 124 for conduction, the structure for feeding power to the piezoelectric element 123 can be made simple and space-saving.

  However, when the diaphragm is an insulating material, it is necessary to provide routing means for exposing the electrode located on the diaphragm side to the outside. Accordingly, a piezoelectric element having the structure shown in FIG. 7 has been proposed (see, for example, Patent Document 1). 7A is a top view of the piezoelectric element 130, FIG. 7B is a bottom view thereof, and FIG. 7C is a cross-sectional view taken along line AA shown in FIG. 7A.

  In the piezoelectric element 130, surface electrodes 132 and 133 are respectively formed on two opposing surfaces (that is, front and back surfaces) of the piezoelectric ceramic 131, and the surface on which the surface electrode 132 is formed is changed to the surface on which the surface electrode 133 is formed. The lead electrode 134 extending from the surface electrode 132 via the end face of the piezoelectric ceramic 131 is formed. When the surface provided with the surface electrode 132 is bonded to an insulator, it is possible to connect to an external power source (not shown) using the surface electrode 133 and the routing electrode 134. In FIG. 7A, the surface electrode 133 and the routing electrode 134 are hatched with dots in order to distinguish them from the surface electrode 133, the routing electrode 134, and the piezoelectric ceramic 131. In FIG. 7B, the entire lower surface is an electrode. In order to show this, the surface electrode 132 and the leading electrode 134 are hatched with dots.

  However, the lead-out electrode generally has a problem that the film thickness tends to be thin at the edge portion of the piezoelectric ceramic, and there is a problem that the resistance becomes large or disconnection easily occurs at this portion. Further, when the piezoelectric ceramic has a thin plate shape of, for example, 0.5 mm or less, there is no appropriate coating method for forming a lead electrode with a uniform film thickness. In order to make the thickness of the lead-out electrode constant, a means of providing a taper at the edge may be considered, but there is a problem that the processing cost is increased and the productivity is lowered, and particularly for a thin plate-shaped piezoelectric ceramic. Providing such a taper does not guarantee that the film thickness of the routing electrode can be made constant.

  A through-hole electrode can be considered as an electrode for avoiding such a problem. In the production of piezoelectric ceramics, a powder press molding method is generally used, but it is not easy to form a through hole by the press molding method. Further, the press molding method has a defect that defects such as minute voids and holes are likely to remain in the obtained piezoelectric ceramic, and corner portions are not easily cracked and the piezoelectric body is easily cracked.

  On the other hand, the through-hole electrode is used in a laminated piezoelectric element manufactured by simultaneously firing a green sheet together with an internal electrode and a surface electrode (see, for example, Patent Document 2). Since piezoelectric ceramics generally need to be fired at a high temperature of 1000 ° C. or higher, silver / palladium electrode materials and platinum electrode materials that can withstand such firing temperatures are used for the through-hole electrodes and internal electrodes.

  However, the co-firing method tends to warp and deform, and the surface electrodes and through-holes are likely to have small irregularities. When the thickness of the piezoelectric element is increased, it becomes difficult for the vibration of the piezoelectric element to be transmitted to the diaphragm, and when the piezoelectric element is pressed to adhere to the diaphragm, the piezoelectric element is broken. Therefore, the surface of the piezoelectric ceramic is ground or polished, and a silver paste is applied to the processed surface and baked to form a surface electrode.

However, when silver is used for the surface electrode, the silver / palladium electrode filled in the through hole or applied to the inner wall of the through hole reacts with the silver of the surface electrode to blacken, and the through hole portion has a convex shape. I understood. For example, in a thin piezoelectric element having a thickness of 0.5 mm or less, if there is such a convex portion, there arises a problem that the desired vibration characteristics described above cannot be obtained because the adhesive layer becomes thick.
JP 2001-298344 A JP-A-6-120580

  This invention is made | formed in view of this situation, and it aims at providing the piezoelectric element by which the through-hole electrode excellent in reliability was formed in piezoelectric ceramic, and its manufacturing method. It is another object of the present invention to provide a diaphragm and a vibration wave driving device including such a piezoelectric element.

  According to the first aspect of the present invention, a piezoelectric element having a through-hole electrode for obtaining electrical conduction from one surface to the other surface of a piezoelectric body having two opposing surfaces is manufactured. A method is provided in which a through hole is provided at a predetermined position of a green sheet formed by molding a piezoelectric material, the first conductive paste is filled in the through hole, and then the plurality of green sheets are connected to the through hole. The steps of bonding, baking, and flattening the two opposing surfaces where the through-hole electrodes formed by the through-holes are exposed in the obtained fired body, and the surfaces thus flattened, respectively. And applying a conductive paste of No. 2 and firing at a temperature lower than the firing temperature in the firing step to provide a surface electrode that is electrically connected to the through-hole electrode on the planarized surface. Method for manufacturing a piezoelectric element characterized by is provided.

In this method of manufacturing a piezoelectric element, the first conductor paste contains silver and palladium, and 10% ≦ W ₁ ≦ 30% when the weight percentage of palladium in the total weight of these is W ₁ Is preferably used, and the second conductor paste contains silver and palladium. When the weight percentage of palladium in the total weight of these is W ₂ , the relationship of 0 ≦ W ₁ −W ₂ <20 is satisfied. What has been used is preferably used.

  Moreover, it is also preferable to use the first conductor paste containing silver and palladium as a conductive material and the second conductor paste containing silver and platinum as a conductive material. In this case, the weight percentage of palladium in the total weight of silver and palladium in the first conductor paste is preferably 10% or more and 30% or less, and the second conductor paste accounts for the total weight of silver and platinum. The weight percentage of platinum is preferably 0.2% or more and 3% or less.

  When stacking a plurality of green sheets so that the through-holes are connected, a predetermined number of green sheets with through-holes are stacked on the green sheet with no through-holes, and these are bonded together. When the obtained laminate is fired, it is preferable to fire by placing a green sheet having no through-holes on the lower side in the vertical direction. In such a processing method, after a predetermined number of green sheets having through holes formed thereon are stacked on a green sheet having no through holes, green sheets having no through holes are further stacked thereon. It is also preferable that these are bonded and fired.

  According to the second aspect of the present invention, the piezoelectric element manufactured by the method for manufacturing a piezoelectric element, that is, has a plate shape, and is electrically connected from one main surface to the other main surface. A piezoelectric body having a through-hole electrode, a first surface electrode provided on one main surface of the piezoelectric body so as to be electrically connected to the through-hole electrode, and a through-hole electrode on the other main surface of the piezoelectric body A first surface electrode having a second surface electrode provided so as to be electrically connected to the hall electrode and a third surface electrode provided so as to be insulated from the second surface electrode; The piezoelectric element is characterized in that the projection height of the portion joined to the through-hole electrode is 5 μm or less.

  The through-hole electrode is formed of a first conductive paste, and the first, second, and third surface electrodes are formed of a second conductive paste.

  According to a third aspect of the present invention, there is provided a diaphragm characterized in that such a piezoelectric element is attached to an insulator.

  Further, according to a fourth aspect of the present invention, there is provided a vibration wave driving device comprising the vibration plate and moving an object in contact with the vibration plate by driving the vibration plate.

  According to the present invention, a through hole electrode having a high conduction reliability is formed by forming a through hole electrode when a piezoelectric ceramic is manufactured using a green sheet, and the surface where the through hole is exposed and the through hole are flattened. Then, by forming the surface electrode using an electrode material containing platinum or palladium, it is possible to prevent the through-hole electrode from becoming convex. This makes it possible to increase the vibration transmission efficiency from the piezoelectric element to the vibrating body by thinning the adhesive layer when the piezoelectric element is attached to the bonded body such as a vibration plate. Destruction can be prevented. Further, by using a firing method using a green sheet, it is possible to obtain a piezoelectric ceramic having a small number of defects such as holes and a large specific gravity, so that chipping and cracking are less likely to occur. Further, since an expensive electrode material having a small content of palladium or platinum can be used for the surface electrode as compared with the electrode material used for the through-hole electrode, the cost can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a perspective view of the piezoelectric element 10, and FIG. 2 shows a cross-sectional view of the piezoelectric element 10 with a flexible printed wiring board 21 attached thereto. FIG. 3 is a schematic perspective view of a vibration wave driving device 30 in which the piezoelectric element 10 to which the flexible printed wiring board 21 is attached is attached to the diaphragm 22.

  The piezoelectric element 10 includes a piezoelectric body 12 made of piezoelectric ceramics, surface electrodes 13a and 13b provided on one of two opposing faces (here, the front and back surfaces), and the other face. And a through-hole electrode 15 that electrically connects the surface electrode 13b and the surface electrode 14 to each other.

  The surface electrodes 13a and 13b are electrically insulated, and a portion of the piezoelectric body 12 sandwiched between the surface electrodes 13a and 14 is polarized.

  As will be described later, the piezoelectric body 12 is obtained by laminating and integrating a plurality of green sheets. Therefore, in FIG. 2, a layer derived from one green sheet is indicated by a broken line in the piezoelectric body 12. However, the piezoelectric layers in the piezoelectric body 12 are integrated and densified so that they cannot be distinguished.

  The flexible printed wiring board 21 is formed by forming a copper wiring on a base material made of polyimide, for example, and can be electrically connected to an external power source (not shown) independently of the surface electrodes 13a and 13b. Wiring (not shown) is provided. By applying a predetermined voltage to the surface electrodes 13a and 13b, a predetermined voltage is applied between the surface electrodes 13a and 14 as a result. A resin adhesive is used for bonding the flexible printed wiring board 21 to the piezoelectric element 10.

  A resin adhesive is also used for bonding the piezoelectric element 10 to the diaphragm 22. By applying a predetermined high-frequency voltage to the surface electrodes 13a and 13b from an external power source (not shown), the high-frequency voltage is applied to the surface electrodes 13a and 14 as a result, and the piezoelectric body 12 can be vibrated. Due to this vibration, a force is applied to the moving body 23 in contact with the diaphragm 22, and the moving body 23 can be moved in the plane of the diaphragm 22 or moved on the diaphragm 22. it can.

  Specifically, the piezoelectric element 10 has a shape of length 30 mm × width 4 mm × thickness 0.25 mm. The diaphragm 22 is made of an insulating inorganic material with little vibration damping, such as ceramics or glass such as alumina. Examples of the diaphragm 22 to which the piezoelectric element 10 having the above-described shape is attached include those having a shape of 40 mm long × 60 mm wide × 0.5 mm thick. However, these dimensions are not limited to such values.

  Next, a method for manufacturing the piezoelectric element 10 will be described. Here, it is assumed that the piezoelectric element 10 having a shape of length 30 mm × width 4 mm × thickness 0.25 mm is manufactured.

  First, a piezoelectric ceramic powder (for example, lead zirconate titanate-based piezoelectric ceramic powder) is formed using a known sheet forming method such as a doctor blade method or a calender roll method, and the thickness is about 40 to 150 μm. Manufacture a green sheet.

  From this long green sheet, taking into account the firing shrinkage and cutting margin until the piezoelectric element 10 is manufactured, a plurality of green sheets of appropriate sizes are obtained by punching etc. A through hole having a diameter of 0.2 mm is formed at a predetermined position.

  Here, the size of the green sheet may be set such that a plurality of piezoelectric elements can be obtained by performing a cutting process later. In that case, the position where the through hole is provided is determined in consideration of the shape and size of the finally obtained piezoelectric element. For example, a laser can be used to form the through hole. The diameter of the through hole is not limited to φ0.2 mm, and is set in consideration of shrinkage of the first conductor paste described later, and can be set to φ0.05 mm to φ0.5 mm.

  Subsequently, the first conductor paste for forming the through-hole electrode 15 is filled into the through-hole formed in the green sheet by a method such as screen printing, inkjet printing, or cylinder injection. At this time, it is preferable to form a coating film of the first conductor paste in a certain range around the through hole. In order to perform such a coating film simultaneously with the filling of the first conductor paste into the through hole, a screen printing method is suitable. By forming such a coating film, even if the positions of the through holes are slightly shifted when a plurality of green sheets are stacked, a through hole formed from this first conductive paste It is possible to prevent the electrode 15 from being broken.

  This first conductive paste is later fired simultaneously with the green sheet. In general, the firing temperature of a green sheet formed from piezoelectric ceramics is almost determined by the chemical composition of the piezoelectric ceramics and the powder particle size. For example, zirconic acid having an average particle size of about 0.4 μm to 1.2 μm. In lead titanate-based piezoelectric ceramics, the temperature is generally 1000 ° C. to 1200 ° C. For the first conductive paste, it is necessary to use an electrode material that can withstand such a firing temperature, and preferably a material containing silver (Ag) and palladium (Pd) as a conductive substance.

Silver and palladium dissolve in the entire composition range, so-called so-called solid solution characteristics. From the state diagram (phase diagram) of silver and palladium, it does not melt at the firing temperature and is possible considering the production cost. A composition with as little palladium content as possible can be expected. When the firing temperature is 1000 ° C. to 1200 ° C., the weight percentage of palladium in the total weight of silver and palladium is 10% when W ₁ {= [Pd / (Ag + Pd)] × 100 (%)}. A composition satisfying ≦ W ₁ ≦ 30% is preferably used.

  The first conductive paste is composed of silver and palladium as conductive materials, ethyl cellulose as an organic binder, and piezoelectric ceramic powder for adjusting the shrinkage during firing (the same as that used for forming the green sheet). , And α-terpineol as a solvent can be produced by kneading with three rolls. As the silver powder and the palladium powder, for example, a spherical coprecipitation powder having an average particle diameter of about 1 μm can be used. However, the organic binder and the solvent are not limited to such materials.

  The weight percentage of each material constituting the first conductor paste is, for example, 65% of the total amount of silver and palladium, 10% of the piezoelectric ceramic powder, 5% of the organic binder, and 20% of the solvent. If necessary, fine adjustment such as re-kneading by adding a solvent in order to adjust the viscosity to facilitate filling of the through-holes is performed. The organic binder and the solvent are burned off when the temperature is raised during firing. When the piezoelectric ceramic powder contained in the first conductor paste is sintered and bonded to the wall surface of the through-hole formed in the green sheet, an anchor effect is brought about on the through-hole electrode.

  Subsequently, a plurality of green sheets are aligned at the position of the through hole, and are laminated to a thickness in consideration of firing shrinkage so that the thickness after firing becomes, for example, 0.36 mm. At this time, it is preferable that a green sheet in which no through hole is formed is stacked on one or both of the ends in the stacking direction. The green sheets stacked in this way are integrated using a hot press device. As is well known, this process, generally called thermocompression bonding, is one of the techniques for bonding green sheets together. The method is not limited as long as the green sheets can be bonded to each other.

  FIG. 4 shows a cross-sectional view of a laminate obtained by thermocompression bonding of a green sheet. The laminated body 20 shown in FIG. 4 is obtained by stacking a predetermined number of green sheets 16a having through holes 17 on a green sheet 16b having no through holes 17 and then thermocompression bonding them. is there. The first conductive paste 18 is filled in the through holes 17 connected to each other.

  When the coating film of the first conductor paste 18 is formed in a certain range around the through hole 17, the portion becomes the flange portion 19 of the first conductor paste 18. In FIG. 4, the collar portion 19 is drawn thick and clearly. For example, the thickness of the green sheet 16 a is 40 μm to 150 μm, whereas the thickness of the collar portion 19 is about 1 to 10 μm.

  The green sheet 16b in which the through-hole 17 is not further formed may be stacked on the uppermost green sheet 16a of the stacked body 20 and may be thermocompression bonded. In addition, in each green sheet before lamination, when the first conductor paste is filled in the through holes so as to be exposed extremely higher than the surface of the green sheets, the green sheets in the vicinity of the through holes are not bonded to each other at the time of thermocompression bonding. There is a risk that the adhesion of the material will be hindered. It is preferable to control the upper limit of the filling amount of the first conductor paste so as not to be in such a state.

  The laminated molded body thus obtained is fired at a predetermined temperature. By this firing treatment, a piezoelectric body 12 made of piezoelectric ceramics in which a plurality of green sheets are integrated is obtained. Also, the through holes formed in the green sheet communicate with each other to form through holes, and the first conductor pastes filled in the through holes are joined and baked to form continuous through hole electrodes 15. The through-hole electrode 15 is exposed on the front and back surfaces of the piezoelectric body 12.

  When only one green sheet having no through hole is stacked, in this firing step, the green sheet is placed on the lower side and fired. By using the green sheet not provided with the through hole, it is possible to prevent the first conductor paste filled in the through hole from dripping or flowing down from the lower opening of the through hole during firing.

  During this firing, the entire laminated molded body contracts three-dimensionally, and at the same time, the hole diameter and length of the through hole are shortened, and the electrode material derived from the first conductor paste filled in the through hole contracts. As described above, the shrinkage rate of the electrode material can be adjusted by adding the piezoelectric ceramic powder to the first conductive paste or changing the blending composition. The lower limit of the filling amount of the first conductor paste that fills the through-hole formed in the green sheet needs to be set so that a cavity or an unfilled portion is not formed inside). .

  FIG. 5 shows a cross-sectional view of the piezoelectric body 12 obtained by firing. FIG. 5 shows that the through-hole electrode 15 is exposed in a fired body obtained by laminating only one green sheet not provided with a through hole in the previous thermocompression bonding process, thermocompression bonding, and firing. The structure in the vicinity of the through-hole electrode 15 on the surface side is shown.

  Although the surface of the piezoelectric body 12 has some unevenness after firing, the end surface of the through-hole electrode 15 is convex so as to be exposed on the surface, and its height h is 0 <h ≦ 0. It is preferable that the relationship of 1 mm is satisfied. The electrode material derived from the first conductive paste is a green sheet in order to prevent filling of the green sheets at the time of thermocompression bonding, which does not hinder the adhesion between the green sheets described above, and to prevent electrode breakage during firing. It is preferable that firing shrinkage is smaller (that is, it does not shrink).

  The method for manufacturing piezoelectric ceramics by stacking, integrating and firing green sheets as described above is conventionally used for manufacturing piezoelectric elements having internal electrodes such as stacked piezoelectric actuators. In this case, since the piezoelectric ceramic layer is bonded via the internal electrode, the bonding strength between the piezoelectric ceramic layers is not so high, and the density of each piezoelectric ceramic layer is not high. Also, the powder press molding method and extrusion molding method, which are general methods for producing piezoelectric ceramics, have defects such as minute voids and voids remaining in the interior, resulting in low specific gravity and low mechanical strength. There are drawbacks such as chipping at the corners of the body and cracks in the piezoelectric body.

  On the other hand, as described above, in the method of manufacturing piezoelectric ceramics by stacking, integrating, and firing green sheets without providing internal electrodes, the green sheets are bonded to each other and the boundary between them can be determined. Piezoelectric ceramics with such a high density that the density is so small that there are few microscopic voids and pores inside can be obtained. For example, the powder press molding method has a limit of obtaining a specific gravity of about 7.6, whereas the method of laminating, integrating and firing green sheets is to produce a piezoelectric ceramic having a specific gravity of about 7.8. This difference, which can be obtained, indicates that a piezoelectric ceramic with few voids and holes is obtained.

  A dense piezoelectric ceramic with few defects is extremely less likely to have a problem of corners being cut during cutting or handling. As a result, the production yield can be improved and the production cost can be reduced. In addition, a piezoelectric ceramic with few defects has a feature that, when a predetermined high frequency voltage is applied and vibrated, the occurrence of cracking can be suppressed even when a larger amount of power is applied.

  A method for producing a plate-shaped piezoelectric ceramic by laminating a large number of thin green sheets in this way and firing them is not only easy to form a through hole but also a dense and highly reliable piezoelectric ceramic. Suitable for manufacturing.

  The front and back surfaces of the piezoelectric body 12 thus obtained are simultaneously lapped (polished) by, for example, a double-sided lapping machine using loose abrasive grains, and the thickness of the piezoelectric body 12 is about 0.36 mm. Grind to 0.25mm. In the case where a green sheet having no through-holes is used first, all parts derived from the green sheet are removed by lapping. By performing such double-sided lapping, the piezoelectric body 12 having a uniform thickness can be obtained in a short time. In addition, such thickness adjustment processing of the piezoelectric body 12 may be performed one side at a time, and a grinding machine may be used at that time.

  A broken line BB shown in FIG. 5 indicates the height of the surface appearing by the lapping process. Since the through-hole electrode 15 is also lapped by double-sided lapping, the end surface (exposed surface) of the through-hole electrode 15 is located on the same plane as the front and back surfaces of the piezoelectric body 12.

  Using a cutting machine, taking out the position of the through-hole, it is cut out with a length of 30 mm and a width of 4 mm. A second conductor paste for forming the surface electrodes 13a, 13, and 14 is printed on the front and back surfaces of the piezoelectric body 12 thus cut out in a pattern as shown in FIG. Since the front and back surfaces of the piezoelectric body 12 are flattened by double-sided lapping, the printed film thickness can be made constant, and the contact with the through-hole electrode 15 can be reliably performed.

  As shown in FIG. 1, the second conductor paste print area is set a certain distance from the outer periphery of the piezoelectric body 12 when the second conductor paste is applied to the entire outer periphery of the piezoelectric body 12. This is because the paste may flow out to the side surface of the piezoelectric body 12 and may be electrically connected to the printed electrode on the opposite side, thus eliminating the trouble of removing the paste attached to the side surface.

  After the printed second conductor paste is dried at a predetermined temperature, the solid component contained in the second conductor paste is baked onto the piezoelectric body 12 by heating to the predetermined temperature. The thickness of the surface electrodes 13a, 13b, and 14 formed in this way is, for example, 3 μm to 5 μm.

The second conductive paste used here contains silver and palladium, and the weight percentage of palladium in the total weight of these is W ₂ {= [Pd / (Ag + Pd)] × 100 (%)}. , 0 ≦ W ₁ −W ₂ <20 is preferably used, whereby the projection height of the through-hole electrode 15 can be kept low.

  In addition, the second conductor paste contains glass frit for baking silver and palladium on the surface of the piezoelectric body 12 as a solid component, which means that the piezoelectric bodies 12 of the surface electrodes 13a, 13b, and 14 to be formed. This is preferable from the viewpoint of increasing the adhesion strength. The baking temperature of the conductive paste containing glass frit is determined by the composition of the glass frit. By using lead borosilicate glass as the glass frit, the baking temperature can be set to 650 ° C to 800 ° C.

  In addition, since the cost of palladium is 20 to 30 times that of silver, from the viewpoint of keeping the electrode material cost low, the palladium content should be as low as possible without causing any problem in adhesion to the diaphragm. It is preferable to do. For this purpose, it is preferable to adjust the composition of the glass frit so that baking at a low temperature is possible. Furthermore, since palladium undergoes an oxidation / reduction reaction in the air, reducing the palladium content is advantageous in that it suppresses the occurrence of unevenness due to the oxidation / reduction reaction on the surface electrode and lowers the electrical resistance of the electrode. It is.

  Specifically, the second conductive paste comprises, as a conductive material, silver and palladium alloy powder, glass frit powder, ethyl cellulose as an organic binder, and α-terpineol as a solvent in weight percentage. Is 70%, the glass frit is 5%, the organic binder is 5%, and the solvent is 20%. Silver and palladium alloy powder with an average particle diameter of about 1 μm can be used, and glass frit powder with an average particle diameter of several μm can be used. Instead of silver and palladium alloy powder, silver and palladium can be used. You may mix and use each powder. The viscosity of the paste can be finely adjusted by adjusting the amount of the solvent.

As the second conductive paste, one containing platinum (Pt) instead of palladium can be used, and the weight percentage of platinum in the total weight of silver and platinum is expressed as W ₃ {= [Pt / (Ag + Pt)] × 100 (%)}, a material satisfying the relationship of W ₃ = 0.3% to 3% is preferably used. When W ₃ <0.3%, the projection height of the through-hole electrode 15 cannot be kept low. On the other hand, when W ₃ > 3%, platinum is extremely expensive compared to silver. The problem that the paste cost becomes high arises.

  The method for preparing the second conductor paste containing silver and platinum is the same as the method for preparing the conductor paste containing silver and palladium described above. That is, a powder in which silver and platinum are mixed (for example, a silver powder having an average particle diameter of 0.5 μm and a platinum powder having an average particle diameter of 0.3 μm), a glass frit, an organic binder (for example, ethyl cellulose), A solvent (for example, α-terpineol) is weighed so as to have a predetermined ratio, and can be produced by kneading them with a three-roll or the like.

  The cost of platinum is several tens to one hundred times that of silver, but the mixing ratio with respect to silver can be extremely reduced as compared with palladium, so that the cost is not higher than when palladium is used. In addition, unlike palladium, platinum does not cause an oxidation / reduction reaction, so that a smooth surface electrode with few irregularities can be formed. This is a preferable characteristic when the flexible printed wiring board is attached to the piezoelectric element or the piezoelectric element is attached to the diaphragm. In addition, platinum does not increase the electrical resistance unlike palladium, so generation of unnecessary heat at the surface electrode can be suppressed, and the input power can be efficiently converted into vibration energy. The diaphragm can be vibrated more greatly.

  After forming the surface electrodes 13a, 13b, and 14 using such a second conductor paste, the piezoelectric body 12 is subjected to polarization treatment. This polarization process is performed by immersing the piezoelectric body 12 in an insulating oil or the like maintained at a predetermined temperature equal to or lower than its Curie temperature, and applying a predetermined voltage between the surface electrode 13a and the surface electrode 14 for a predetermined time, For example, the temperature of the insulating oil is 120 ° C., the applied voltage is 3 kV / mm, and the voltage application time is 30 minutes. The polarization treatment of the piezoelectric body 12 can also be performed in air using a high-temperature dryer or the like. Thus, the piezoelectric element 10 is obtained by causing the piezoelectric body 12 to exhibit piezoelectricity. The flexible printed wiring board 21 is bonded to the manufactured piezoelectric element 10 using a resin adhesive, and the piezoelectric element 10 is bonded to the vibration plate 22 using a resin adhesive, whereby the vibration wave driving device 30 is manufactured. can do.

  Next, the relationship between the composition of the first conductor paste and the composition of the second conductor paste will be described in detail with reference to examples.

The case where a silver / palladium paste of W ₁ = 30% is used as the first conductor paste will be described. On the condition that the method for manufacturing the piezoelectric element 10 described above was followed, the firing temperature of the green sheet laminated molded body was set to 1200 ° C., and a predetermined number of samples obtained by performing double-sided lapping on the obtained piezoelectric body were manufactured. The lapping surface of each _{sample, W 2 = 0%, 10} %, 20%, the second conductor paste prepared with 30% by screen printing, followed by firing at 750 ° C., to form a surface electrode. Table 1 shows the results of measurement using a contact surface roughness meter to determine how much the portion where the through-hole electrode is formed protrudes from other flat regions.

The protrusion height of the through-hole electrode is 7 to 12 μm in the sample 1 with W ₂ = 0%, 4 to 9 μm in the sample 2 with W ₂ = 10%, 2 to 5 μm in the sample 3 with W ₂ = 20%, and W _2. In the sample 4 of 30%, it was 0 to 2 μm.

  As described above, it was confirmed that the protrusion of the through-hole electrode was suppressed by using the second conductive paste containing a predetermined amount of palladium. This is probably because the baking temperature of the second conductor paste is lower than the firing temperature of the green sheet, and the diffusion of silver is suppressed by increasing the palladium content.

  When a vibration wave drive device is configured by bonding a piezoelectric element to a diaphragm, it is usually bonded so that vibration is efficiently transmitted from the piezoelectric element to the diaphragm and the bonding strength between them is secured. The layer thickness is about 5 μm.

For this reason, in the vibration wave driving device configured using the piezoelectric element of Sample 1 where W ₂ = 0%, the adhesive layer is usually used because the projection height of the through-hole electrode formed on the piezoelectric element is 7 to 12 μm. The vibration attenuation of the diaphragm became larger than usual. Further, in the vibration wave driving device configured using the piezoelectric element of sample 2 where W ₂ = 10%, the protrusion height of the through-hole electrode formed on the piezoelectric element is 4 to 9 μm, and thus the adhesive layer is usually used. In some cases, the thickness of the vibration plate becomes thicker, and the vibration attenuation of the diaphragm may be larger than usual.

On the other hand, in the vibration wave driving device configured using the piezoelectric elements of samples 3 and 4 where W ₂ = 20% and 30%, the protrusion height of the through-hole electrode formed in the piezoelectric element is 5 μm or less. For this reason, the thickness of the adhesive layer can be set to a normal thickness, so that the vibration attenuation of the diaphragm is at a level with no problem.

The case where a silver / palladium paste of W ₁ = 20% is used as the first conductor paste will be described. On the condition that the method for manufacturing the piezoelectric element 10 described above was followed, the firing temperature of the green sheet laminated molded body was set to 1100 ° C., and a predetermined number of samples obtained by performing double-sided lapping on the obtained piezoelectric body were manufactured. On the lapping surface of each sample, a second conductive paste prepared with W ₂ = 0%, 5%, 10%, and 20% is screen-printed and fired at 750 ° C. to form a surface electrode. The protrusion height of the through-hole electrode was measured. The results are also shown in Table 1.

The protrusion height of the through-hole electrode is 4 to 8 μm in the sample 5 with W ₂ = 0%, 3 to 6 μm in the sample 6 with W ₂ = 5%, 1 to 4 μm in the sample 7 with W ₂ = 10%, and W _2. = 20% for Sample 8 0-2 μm.

In the vibration wave driving device configured using the piezoelectric elements of Samples 5 and 6 where W ₂ = 0,5%, the protrusion height of the through-hole electrode formed on the piezoelectric element may exceed 5 μm, and hence the bonding As the layer becomes thicker, the vibration attenuation of the diaphragm may be larger than usual. On the other hand, in the vibration wave driving device configured using the piezoelectric elements of Samples 7 and 8 where W ₂ = 10, 20%, the adhesive layer can have a normal thickness, and therefore, vibration attenuation of the diaphragm is also a problem. There was no level.

The case where a silver / palladium paste of W ₁ = 10% is used as the first conductor paste will be described. On the condition that the method for manufacturing the piezoelectric element 10 described above was followed, the firing temperature of the green sheet laminated molded body was set to 1000 ° C., and a predetermined number of samples obtained by subjecting the obtained piezoelectric body to double-sided lapping were prepared. On the lapping surface of each sample, a second conductive paste prepared with W ₂ = 0%, 5% and 10% was screen-printed and baked at 750 ° C. to form a surface electrode, and a through-hole electrode The height of the protrusion was measured. The results are also shown in Table 1.

The protrusion height of the through-hole electrode was 3 to 5 μm for the sample 9 with W ₂ = 0%, 1 to 3 μm with the sample 10 with W ₂ = 5%, and 0 to ₂ μm with the sample 11 with W ₂ = 10%. . In the vibration wave driving device configured using the piezoelectric elements of these samples 9 to 11, the adhesive layer can be set to a normal thickness, and therefore the vibration attenuation of the vibration plate is at a level with no problem.

As described above, it was confirmed that if the relationship of 0 ≦ W ₁ −W ₂ <20 is satisfied, the protrusion height of the through-hole electrode is suppressed to be low.

On condition that the method for manufacturing the piezoelectric element 10 described above is followed, a silver / palladium paste of W ₁ = 30% is used as the first conductor paste, the firing temperature of the laminated molded body is 1200 ° C., and the obtained piezoelectric body A predetermined number of samples subjected to double-sided lapping were prepared. On the other hand, when the weight percentage of platinum in the total weight of silver and platinum is W ₃ {= [Pt / (Ag + Pt)] × 100 (%)}, W ₃ = 0%, 0.1%,. Second conductor pastes having 2%, 0.3%, 0.5%, 1.0%, and 3.0% were prepared. A surface electrode was formed on the lapping surface of each sample by screen printing the paste prepared in the predetermined weight percentage W ₃ and baked at 750 ° C., and the protrusion height of the through-hole electrode was measured. . The results are shown in Table 2.

The protrusion height of the through-hole electrode is 8 to 11 μm for the sample 12 with W ₃ = 0%, 7 to 9 μm with the sample 13 with W ₃ = 0.1%, and 2 with the sample 14 with W ₃ = 0.2%. Sample 15 with 4 μm, W ₃ = 0.3%, 1-3 μm, Sample 16 with W ₃ = 0.5%, 1-2 μm, Sample 17 with W ₃ = 1.0%, 1-2 μm, W ₃ = In the sample 18 of 3.0%, it was 0 to 1 μm.

As described above, since the thickness of the adhesive layer when the piezoelectric element is bonded to the diaphragm is about 5 μm, in order to obtain a piezoelectric element in which the protrusion height of the through-hole electrode is lower than this, 0 It can be seen that a paste of .2% ≦ W ₃ ≦ 3% may be used. However, this condition is a result obtained when W ₁ = 30% in the through-hole electrode, and when W ₁ <30% in the through-hole electrode, W ₃ <0.2%. It can also be used.

  Thus, it was confirmed that even if the content of platinum is small, the reaction and diffusion between the through-hole electrode and silver are suppressed and the effect of suppressing the protrusion of the through-hole electrode is reduced. In addition, it is easier to mix and disperse the silver powder and the platinum powder having a small particle diameter as long as the average particle diameter is 0.2 μm to 1.2 μm, but there is no practical problem.

  While the embodiments and examples of the present invention have been described with specific examples, the present invention is not limited to such embodiments. For example, since the surface electrode 13a is not electrically connected to the through-hole electrode 15, a conductive paste made of 100% silver can be used to form the surface electrode 13a, thereby reducing the electrode material cost. However, work such as changing the plate used for screen printing is required.

  Moreover, you may add metal oxides, such as bismuth oxide, lead oxide, and copper oxide which promote the adhesiveness to a piezoelectric material to the 2nd conductor paste for forming a surface electrode. The organic binder and the solvent for producing the conductor paste are not limited to ethyl cellulose and α-terpineol, respectively, as long as they can produce the paste and disappear when firing or baking. When the organic binder and the solvent are changed, the composition ratio of various raw materials used for paste production is appropriately changed in order to obtain a paste having a desired viscosity.

The perspective view of the piezoelectric element which concerns on embodiment of this invention. Sectional drawing of the piezoelectric element shown in FIG. The perspective view of the vibration wave drive device using the piezoelectric element shown in FIG. Sectional drawing which shows the lamination | stacking state of a green sheet. Sectional drawing of the through-hole vicinity in the manufacture stage of the piezoelectric element shown in FIG. The perspective view of a well-known piezoelectric buzzer. The top view of a well-known piezoelectric element. FIG. 7B is a bottom view of the piezoelectric element shown in FIG. 7A. FIG. 7B is a cross-sectional view of the piezoelectric element shown in FIG. 7A.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Piezoelectric element, 12 ... Piezoelectric body, 13a, 13b, 14 ... Surface electrode, 15 ... Through-hole electrode, 16a ... Green sheet (with through-hole), 16b ... Green sheet (without through-hole), 17 ... Through-hole, DESCRIPTION OF SYMBOLS 18 ... 1st conductor paste, 19 ... The collar part of 1st conductor paste, 20 ... Laminated body, 21 ... Flexible printed wiring board, 22 ... Vibration plate, 23 ... Moving body, 30 ... Vibration wave drive device.

Claims (11)

A piezoelectric element manufacturing method in which a through-hole electrode for obtaining electrical conduction from one surface to the other surface of a piezoelectric body having two opposing surfaces is provided,
A through hole is provided at a predetermined position of the green sheet formed by forming the piezoelectric material, the first conductive paste is filled in the through hole, and then a plurality of green sheets are stacked and bonded so that the through hole is connected, A firing step;
Flattening two opposing surfaces in which the through-hole electrodes formed by the through-holes are exposed in the obtained fired body;
A surface electrode which is electrically connected to the through-hole electrode on the planarized surface by applying the second conductor paste to the planarized surface and firing at a temperature lower than the firing temperature in the firing step. And a step of providing the piezoelectric element. The first conductive paste contains silver and palladium, and the weight percentage of palladium in the total weight of these is W ₁ , and 10% ≦ W ₁ ≦ 30%,
The second conductive paste contains silver and palladium, and the weight percentage of palladium in the total weight of these is W _2, and the relationship of 0 ≦ W ₁ −W ₂ <20 is satisfied. The method for manufacturing a piezoelectric element according to claim 1.   2. The piezoelectric element according to claim 1, wherein the conductive material contained in the first conductive paste is silver and palladium, and the conductive material contained in the second conductive paste is silver and platinum. Method. In the first conductive paste, the weight percentage of palladium in the total weight of silver and palladium is 10% or more and 30% or less,
4. The method of manufacturing a piezoelectric element according to claim 3, wherein the second conductive paste has a weight percentage of platinum in a total weight of silver and platinum of 0.2% to 3%. When stacking the plurality of green sheets so that the through-holes are connected, a predetermined number of green sheets with the through-holes are stacked on the green sheet without the through-holes and bonded together And
When firing the laminated body obtained in this way, the green sheet in which the through-hole is not formed is disposed on the lower side in the vertical direction and fired. A method for manufacturing the piezoelectric element according to the above.   A predetermined number of green sheets with through-holes are stacked on a green sheet without through-holes, and green sheets without through-holes are further stacked thereon and bonded together. The method of manufacturing a piezoelectric element according to claim 5. A piezoelectric body having a plate-like shape and having a through-hole electrode electrically conducting from one main surface to the other main surface;
A first surface electrode provided on one main surface of the piezoelectric body so as to be electrically connected to the through-hole electrode;
A second surface electrode provided to be electrically connected to the through-hole electrode and a third surface electrode provided to be insulated from the second surface electrode on the other main surface of the piezoelectric body; Have
The piezoelectric element according to claim 1, wherein a protrusion height of a portion of the first and second surface electrodes joined to the through-hole electrode is 5 μm or less. The through-hole electrode contains silver and palladium, and the weight percentage of palladium in the total weight of these is W ₁ , and 10% ≦ W ₁ ≦ 30%,
The first and second surface electrodes contain silver and palladium, and the relationship of 0 ≦ W ₁ −W ₂ <20 is satisfied when the weight percentage of palladium in the total weight of these is W _2. The piezoelectric element according to claim 7. The through-hole electrode contains silver and palladium, and the weight percentage of palladium in the total weight of these is 10% or more and 30% or less,
8. The piezoelectric element according to claim 7, wherein the first and second surface electrodes contain silver and platinum, and a weight percentage of platinum in a total weight of these is 0.2% or more and 3% or less. .   A diaphragm comprising the insulator and the piezoelectric element according to any one of claims 7 to 9 attached thereto.   11. A vibration wave driving device comprising the vibration plate according to claim 10 and moving an object in contact with the vibration plate by driving the vibration plate.

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