JP6199757B2 - Multilayer piezoelectric element, piezoelectric actuator, and mass flow controller including the same - Google Patents

Description

  The present invention relates to a multilayer piezoelectric element such as a piezoelectric actuator used in a fuel injection device for an automobile engine, a mass flow controller device such as a semiconductor manufacturing device, a liquid injection device such as an ink jet, a precision positioning device for an XY table, a piezoelectric actuator, and the like. It is related with the mass flow controller provided with.

  As a laminated piezoelectric element, a laminated body in which a piezoelectric ceramic layer, a first internal electrode layer, and a second internal electrode layer are laminated, an end of the first internal electrode layer in the laminated body, and the second internal electrode The thing of the structure containing the piezoelectric ceramic coating layer provided in the side surface from which both the edge parts of the electrode layer were derived | led-out is known (for example, refer patent document 1).

  Here, in the above configuration, a piezoelectric ceramic coating layer (ceramic coating) is provided to prevent migration on the side surface from which the end portion of the internal electrode layer is derived.

JP 2001-135872 A

  However, in such a multilayer piezoelectric element, when a DC bias is applied for a long time under severe conditions, the piezoelectric ceramic coating layer is close to the first internal electrode layer and the second internal electrode layer due to the influence of the leakage electric field. Is gradually polarized, extending in the direction in which the multilayer piezoelectric element is displaced. Therefore, even when the applied voltage is turned off, the stacked piezoelectric element does not return to its original length by the amount of extension of the piezoelectric ceramic coating layer, and there is a possibility that the amount of displacement is reduced.

  There is a need for a multilayer piezoelectric element that can withstand a harsh use environment in which a DC bias is applied for a long period of time.

  Similarly, a piezoelectric actuator provided with the above-described multilayer piezoelectric element and a mass flow controller provided with the piezoelectric actuator are also required to be able to withstand severe use environments.

  The present invention has been made in view of the above circumstances, and even when used in a harsh DC environment, when the applied voltage is turned off, it returns to its original length and the displacement type piezoelectric element is suppressed from being lowered in displacement. An object of the present invention is to provide a piezoelectric actuator and a mass flow controller including the same.

Multi-layer piezoelectric element of the present invention, the piezoelectric ceramic layer, the first and laminate the internal electrode layer and the second inner electrode layers are stacked, the in the laminate the first inner electrode layer and the second and a piezoelectric ceramic coating layer both ends of the internal electrode layer is provided near contact side, the ends of both of said first internal electrode layer and the second inner electrode layer is the piezoelectric ceramic coating layer internal of than provided sides are located inside, the piezoelectric ceramic particle size of the ceramic particles constituting the coating layer is rather smaller than the particle size of the ceramic particles constituting the piezoelectric ceramic layer, said first The particle size of the ceramic particles existing in the region between the end portion of the electrode layer and the end portion of the second internal electrode layer and the side surface provided with the piezoelectric ceramic coating layer constitutes the piezoelectric ceramic layer. SE And it is characterized in smaller Ikoto than the particle size of the electrochromic particles.

  In the multilayer piezoelectric element of the present invention, the piezoelectric ceramic layer and the piezoelectric ceramic coating layer are made of a piezoelectric material having the same composition in the above configuration.

Further, the multi-layer piezoelectric element of the present invention, in the above configuration, the side surface which the an end piezoelectric ceramic coating layer is provided before Symbol first inner electrode layer end and the second inner electrode layers There is a void between the two.

  In addition, a piezoelectric actuator of the present invention includes the above-described multilayer piezoelectric element and a case that accommodates the multilayer piezoelectric element therein.

  The mass flow controller of the present invention includes a flow path, a flow rate sensor unit that detects the flow rate of the fluid flowing in the flow path, a flow rate control valve that controls the flow rate of the fluid including the piezoelectric actuator, and a control circuit. The flow rate control valve performs flow rate control by expansion and contraction of the piezoelectric actuator.

  According to the multilayer piezoelectric element of the present invention, the ceramic particles of the piezoelectric ceramic coating layer are hardly polarized by making the particle size of the piezoelectric ceramic coating layer smaller than the ceramic particles of the piezoelectric ceramic layer. Thereby, even if it uses in a severe DC environment, if an applied voltage is turned off, an element will return to the original length and a displacement amount fall will be suppressed.

  Moreover, also in the piezoelectric actuator of this invention and a mass flow controller provided with the same, the amount of displacement can be stabilized for a long period of time.

(A) is a schematic perspective view which shows an example of embodiment of the laminated piezoelectric element of this invention, (b) is a principal part enlarged view of an example of the cross section cut | disconnected by the AA line shown to (a). (A) is the cross-sectional view cut | disconnected by the BB line shown to Fig.1 (a), (b) is the cross-sectional view cut | disconnected by the CC line | wire shown to Fig.1 (a). It is a principal part enlarged view of the other example of the cross section cut | disconnected by the AA line shown to Fig.1 (a). It is a principal part enlarged view of the other example of the cross section cut | disconnected by the AA line shown to Fig.1 (a). (A) is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this invention, (b) is the cross-sectional view cut | disconnected by the BB line shown to (a), (c) is ( It is the cross-sectional view cut | disconnected by CC line shown to a). It is a schematic sectional drawing which shows an example of embodiment of the piezoelectric actuator of this invention. It is a block diagram of an example of embodiment of the massflow controller of this invention.

  Hereinafter, the laminated piezoelectric element of the present invention will be described in detail with reference to the drawings.

  FIG. 1 (a) is a schematic perspective view showing an example of an embodiment of the multilayer piezoelectric element of the present invention, and FIG. 1 (b) is an example of an example of a cross section taken along line AA shown in FIG. 1 (a). It is a part (area | region X) enlarged view. 2A is a cross-sectional view taken along the line BB shown in FIG. 1A, and FIG. 2B is a cross-sectional view taken along the line CC shown in FIG. 1A. is there.

  The laminated piezoelectric element 1 of the present invention shown in FIGS. 1 and 2 includes a laminated body 13 in which the piezoelectric ceramic layer 11, the first internal electrode layer 121 and the second internal electrode layer 122 are laminated, and the laminated body 13. The piezoelectric ceramic coating layer 14 includes both the end portion of the first internal electrode layer 121 and the end portion of the second internal electrode layer 122 that are led out or provided on the side surfaces close to each other. The particle diameter of the ceramic particles 14a constituting the ceramic particles 11a is smaller than the particle diameter of the ceramic particles 11a constituting the piezoelectric ceramic layer 11.

  In the multilayer body 13 constituting the multilayer piezoelectric element 1, a plurality of piezoelectric ceramic layers 11 are laminated, and one first internal electrode layer 121 and one second internal electrode layer 122 are provided between the piezoelectric ceramic layers 11. It is formed alternately. The laminated body 13 is formed in a rectangular parallelepiped shape having a length of 4 to 7 mm, a width of 4 to 7 mm, and a height of about 20 to 50 mm, for example.

The plurality of piezoelectric ceramic layers 11 constituting the laminated body 13 are composed of piezoelectric ceramics (piezoelectric ceramics) having piezoelectric characteristics, and the ceramic particles 11a constituting the piezoelectric ceramic layer 11 have an average particle diameter of, for example, 1.7 to 4.0 μm. It is formed. As this piezoelectric ceramic, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) or the like, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. 1 and FIG. 2 has a quadrangular prism shape, but may have a hexagonal column shape, an octagonal column shape, or the like.

  The first internal electrode layer 121 and the second internal electrode layer 122 are made of, for example, silver, silver-palladium (Ag—Pd) alloy, silver-platinum, copper, or the like, and are alternately provided between the layers of the piezoelectric ceramic layer 11. And are alternately arranged in the order of lamination, whereby a drive voltage is applied to the piezoelectric ceramic layers 11 sandwiched between them. Specifically, one of the first internal electrode layer 121 and the second internal electrode layer 122 is a positive electrode and the other is a negative electrode (or a ground electrode). In other words, a part of the end face is exposed. That is, the end portion of the first internal electrode layer 121 is led out to one of the pair of side surfaces facing each other, and the end portion of the second internal electrode layer 122 is led out to the other side.

  Conductive layers 15 are respectively provided on the side surfaces from which one end of the first internal electrode layer 121 and the second internal electrode layer 122 is led out, and the first internal electrode layer 121 or the second internal electrode layer The electrode layer 122 is electrically connected. The conductor layer 15 is formed by applying and baking a conductor paste made of, for example, silver and glass. The thickness of the conductor layer 15 is 5 to 500 μm, for example.

  Although not shown, an external electrode plate is preferably attached on the surface of the conductor layer 15 via a conductive bonding material.

The external electrode plate is a plate-like body made of copper, iron, stainless steel, phosphor bronze or the like, and is formed to have a width of 0.5 to 10 mm and a thickness of 0.01 to 1.0 mm, for example. The shape having a high effect of relieving the stress generated by the expansion and contraction of the laminate 13 may be, for example, a shape having slits in the width direction perpendicular to the longitudinal direction (lamination direction), a metal plate processed into a mesh shape, or the like. . Moreover, the structure provided with the hole extended especially in the width direction with the slit instead of the slit may be sufficient. It is preferable that a plurality of slits and holes are arranged in the stacking direction of the stacked body 13. In particular, the first internal electrode layer 121 and the second internal electrode layer 121 are interposed between the piezoelectric ceramic layers 11.
It is preferable that a plurality of internal electrode layers 122 are arranged at positions corresponding to regions (active portions) formed by alternately forming every other layer.

  The conductive bonding material is preferably an epoxy resin or polyimide resin containing solder or conductive particles having good conductivity such as Ag particles and Cu particles. The conductive bonding material is formed to a thickness of, for example, 5 to 500 μm.

  In addition, when the external electrode plate is attached, the conductor layer 15 may not be provided.

  Lead wires or lead pins are respectively attached to the pair of conductor layers 15 or the external electrode plates with solder or the like, and a drive voltage is applied thereto.

  In addition, both ends of the first internal electrode layer 121 and the second internal electrode layer 122 are led out or in close proximity to another set of side surfaces facing each other. Here, both end portions of the first internal electrode layer 121 and the second internal electrode layer 122 are led out to the side surface when the first internal electrode layer 121 and the second internal electrode layer 122 are inside. Means that the end portions of both the first internal electrode layer 121 and the second internal electrode layer 122 are close to the side surface. 121 and the second internal electrode layer 122 are formed to extend from the inside to the vicinity of the side surface. On this side surface, the piezoelectric ceramic coating layer 14 is provided in order to prevent migration between the first internal electrode layer 121 and the second internal electrode layer 122 through the side surface.

  The piezoelectric ceramic coating layer 14 can follow the driving deformation (expansion and contraction) of the multilayer body 13 when the multilayer piezoelectric element 1 is driven, and the piezoelectric ceramic coating layer 14 can be applied by stress so that the piezoelectric ceramic coating layer 14 may not peel off and cause creeping discharge. A deformable material is preferred.

Specifically, stress occurs when locally phase transformation to volume change to deformable partially stabilized _{zirconia, Ln 1-X Si X AlO} 3 + 0.5X (Ln is, Sn, Y, La, Ce, A ceramic material such as Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, at least one selected from x = 0.01 to 0.3), Alternatively, piezoelectric materials such as barium titanate and lead zirconate titanate (lead zirconate titanate) in which the distance between ions in the crystal lattice changes so as to relieve the generated stress can be used.

  Here, the particle size of the ceramic particles 14 a constituting the piezoelectric ceramic coating layer 14 is smaller than the particle size of the ceramic particles 11 a constituting the piezoelectric ceramic layer 11.

  By making the particle diameter of the ceramic particles 14a constituting the piezoelectric ceramic coating layer 14 smaller than the particle diameter of the ceramic particles 11a constituting the piezoelectric ceramic layer 11, the ceramic particles 14a constituting the piezoelectric ceramic coating layer 14 are polarized. It becomes difficult. This is because as the ceramic particles 14a become smaller, the ferroelectricity decreases due to the size effect (increase in the ratio of the low dielectric constant layer on the surface, phase transition of the crystal phase, and crystal distortion). Thus, by reducing the ceramic particles 14a of the piezoelectric ceramic coating layer 14, even when used in a harsh DC environment, when the applied voltage is turned off, the multilayer piezoelectric element 1 returns to its original length, and the amount of displacement decreases. Is suppressed.

  For example, the average particle diameter of the ceramic particles 11a constituting the piezoelectric ceramic layer 11 is in the range of 1.7 μm to 4.0 μm, whereas the average particle diameter of the ceramic particles 14a constituting the piezoelectric ceramic coating layer 14 is low in cost. The range of 0.5 μm to 1.6 μm is preferable from the viewpoint of suppressing the formation and ferroelectricity.

  The average particle size of the ceramic particles is determined by specular polishing of the surface of the measurement sample, for example, etching using phosphoric acid to dissolve the grain boundary, and then, for example, a predetermined image of a 1000 times image by SEM (scanning electron microscope). It can be obtained by a so-called intercept method in which a plurality of lines are drawn for a region and the number of intersections with the grain boundaries of each line is counted.

  About the thickness of the piezoelectric ceramic coating layer 14, 5 micrometers-30 micrometers are preferable at the point which prevents the defect and ensures the displacement amount at the time of a drive.

  Furthermore, the piezoelectric ceramic layer 11 and the piezoelectric ceramic coating layer 14 are preferably made of a piezoelectric material having the same composition. By using these piezoelectric materials having the same composition, the piezoelectric characteristics are the same, so that the polarization can be easily controlled. Further, since the composition is the same, the adhesion is improved, and further, the compositional deviation of the piezoelectric ceramic layer 11 does not occur, so that the generation of oxygen vacancies is suppressed and the durability is improved.

  Further, as shown in FIG. 3, both end portions of the first internal electrode layer 121 and the second internal electrode layer 122 are close to the side surface on which the piezoelectric ceramic coating layer 14 is provided and inside the side surface. In the case where it is located, the ceramic particles 13a and the second internal electrode layer existing in the region (region Y) between the end of the first internal electrode layer 121 and the side surface on which the piezoelectric ceramic coating layer 14 is provided. The particle size of the ceramic particles 13 a existing in the region (region Y) between the end of 122 and the side surface provided with the piezoelectric ceramic coating layer 14 is larger than the particle size of the ceramic particles 11 a constituting the piezoelectric ceramic layer 11. Small is preferable. The piezoelectric ceramic layer 11 is placed between the end portion of the first internal electrode layer 121 and the end portion of the second internal electrode layer 122 where the displacement stress is concentrated, and the side surface on which the piezoelectric ceramic coating layer 14 is provided. By providing a region (region Y) made of ceramic particles 13a having a particle size smaller than the particle size of the constituting ceramic particles 11a, an end portion of the first internal electrode layer 121 and an end portion of the second internal electrode layer 122 are provided. As a result, the stress is reduced and the durability is improved.

  Further, as shown in FIG. 4, both end portions of the first internal electrode layer 121 and the second internal electrode layer 122 are close to the side surface on which the piezoelectric ceramic coating layer 14 is provided and inside the side surface. In the case where it is located, there is a void 13b between each of the end portion of the first internal electrode layer 121 and the end portion of the second internal electrode layer 122 and the side surface on which the piezoelectric ceramic coating layer 14 is provided. Is preferred. Since the stress can be relieved by the presence of the void 13b, the durability is further improved.

  In the multilayer piezoelectric element 1 shown in FIGS. 1 and 2, the conductor layer 15 is formed on the side surface where both end portions of the first internal electrode layer 121 and the second internal electrode layer 122 are led out or close to each other. As shown in FIG. 5, the first internal electrode layer 121 is not electrically connected to a region where the conductor layer 15 is not formed on the side surface where the conductor layer 15 is formed. Both the end of the second internal electrode layer 122 and the end of the second internal electrode layer 122 may be led out or close to each other. In the case of the form of FIG. 5, the piezoelectric ceramic coating layer 14 is provided up to a region where the conductor layer 15 is not formed on the same side surface as the conductor layer 15. The laminated piezoelectric element 1 in the present invention may have such a form.

  Next, an example of an embodiment of the piezoelectric actuator of the present invention will be described. FIG. 6 is a schematic cross-sectional view showing an example of an embodiment of the piezoelectric actuator of the present invention. The piezoelectric actuator 10 of the example shown in FIG. 6 includes the multilayer piezoelectric element 1 and the multilayer piezoelectric element 1 inside. A case 2 is provided.

Case 2 is, for example, SUS304 (JIS standard for austenitic stainless steel) or S
It is formed of a metal material such as US316L (JIS standard for austenitic stainless steel). Specifically, a base body 21 whose upper surface is in contact with the lower surface of the piezoelectric element 1, a lid body 22 whose upper surface is in contact with the upper surface of the piezoelectric element 1, and a cylinder bonded to the base body 21 and the lid body 22. And a body 23.

  The base 21 (lower lid) is made of a metal material such as SUS304 or SUS316L in the shape of a disk, and in the drawing, the peripheral edge has a thin flange shape. The base 21 has two through holes 211 through which the lead pins 31 can be inserted. The lead pins 31 electrically connected to the lead wires 32 are inserted into the through holes 211 to connect the conductor layer 15 and the outside. It is electrically connected. The gap between the through holes 211 is filled with soft glass 34 to fix the lead pins 31 and prevent the outside air from entering. For example, an annular protrusion may be provided on the upper surface of the base body 21 for welding with the cylindrical body 23.

  The lid body 22 is made of a metal material such as SUS304 or SUS316L, like the base body 21. And the cover body 22 is formed so that the outer diameter is the same as the inner diameter of the cylinder body 23. The lid body 22 is fitted into one end side opening of the cylinder body 23, which will be described later, and its outer periphery is, for example, on the inner wall near the one end side opening. Joined by welding such as laser welding. The lid 22 has a recess, and the upper end of the piezoelectric element 1 is in contact with the recess. Here, an insulating material may be provided so as to cover the inner peripheral wall surface of the concave portion, and a short circuit between the conductor layers 15 may be prevented.

  Further, the cylindrical body 23 is made of a metal material such as SUS304 or SUS316L like the base body 21 and the lid body 22, and after producing a seamless tube having a predetermined shape, for example, a bellows by a rolling process or an isostatic press. It is formed in a shape having a plurality of circumferential grooves 231 such as a (bellows) shape. Specifically, the cylindrical body 23 shown in the drawing is formed to be curved inward so that the outer diameter and the inner diameter become smaller at the groove 231 portion. The cylindrical body 23 has a predetermined spring constant so that it can follow the expansion and contraction of the piezoelectric element 1 (laminated body 13) when a voltage is applied to the piezoelectric element 1, and depends on the thickness, groove shape, and number of grooves. The spring constant is adjusted. For example, when the thickness of the cylindrical body 23 is 0.1 to 0.2 mm and the height of the laminated body 13 is 20 mm, the number of grooves is about 3 when the height of the laminated body 13 is 40 mm. is there.

  The one end side opening of the cylindrical body 23 is formed in a cylindrical shape, and the other end side opening of the cylindrical body 23 is formed in a so-called trumpet shape that expands radially outward. Thus, the other end side opening of the cylinder body 23 has a trumpet shape, so that the cylinder body 23 has a structure having a flange 232 at the lower end.

  The cylindrical body 23 and the base body 21 are welded in a state where a compressive load is applied to the piezoelectric element 1, and the piezoelectric element 1 is put together with an inert gas in a storage space formed by the cylindrical body 23, the base body 21 and the lid body 22. The piezoelectric actuator 10 is configured by being enclosed.

  Since the multilayer piezoelectric element 1 is sealed in such a case 2, it can be used, for example, in corrosive gas or in water. Further, in order to suppress ion migration of the first internal electrode layer 121 and the second internal electrode layer 122, sealing may be performed using an inert gas.

  With the above configuration, since the laminated piezoelectric element in which the displacement amount is suppressed from being lowered is mounted, a piezoelectric actuator having a stable displacement amount for a long time can be obtained.

  Next, a method for manufacturing the multilayer piezoelectric element 1 and the piezoelectric actuator 10 of the present embodiment will be described.

  First, the ceramic green sheet used as the piezoelectric ceramic layer 11 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. The piezoelectric ceramic may be any piezoelectric ceramic, and for example, a perovskite oxide made of lead zirconate titanate can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the first internal electrode layer 121 and the second internal electrode layer 122 is manufactured. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in a pattern of the first internal electrode layer 121 and the second internal electrode layer 122 by using a screen printing method. Furthermore, after laminating a plurality of ceramic green sheets on which this conductive paste is printed, after performing a binder removal treatment at a predetermined temperature, firing at a temperature of 850 to 1100 ° C., and using a surface grinder or the like, By performing a grinding process so as to have a shape, the laminated body 13 including the piezoelectric ceramic layers 11, the first internal electrode layers 121, and the second internal electrode layers 122 that are alternately stacked is manufactured.

  The laminate 13 is not limited to the one produced by the above manufacturing method, and is formed by laminating a plurality of piezoelectric ceramic layers 11, first internal electrode layers 121, and second internal electrode layers 122. As long as the laminated body 13 can be manufactured, it may be manufactured by any manufacturing method.

  Next, an oxide ink to be the piezoelectric ceramic coating layer 14 is applied to another pair of opposing side surfaces where the first internal electrode layer 121 and the second internal electrode layer 122 (both electrodes) of the laminate 13 are exposed. For example, it is formed by dipping or screen printing. At this time, in order to further strengthen the adhesion after firing, the surface of the side surface of the laminated body 13 is preferably roughened by polishing or the like. Then, it bakes at 850-1100 degreeC, and forms the piezoelectric ceramic coating layer 14 which consists of an oxide on the side surface of the laminated body 13. FIG.

  Here, the oxide ink is obtained by, for example, dispersing oxide powder composed of stabilized zirconia, barium titanate, lead zirconate titanate, or the like in a solvent, a dispersant, a plasticizer, and a binder solution. By passing three rolls several times, it is possible to disintegrate the powder and to disperse the powder. It can also be produced by a method in which a ball mill containing a powder of a solvent, a dispersant, and an oxide is rotated, the powder is pulverized and crushed, a binder and a plasticizer are added, and the powder is further rotated.

  Here, as a method of making the particle size of the ceramic particles 14 a constituting the piezoelectric ceramic coating layer 14 smaller than the particle size of the ceramic particles 11 a constituting the piezoelectric ceramic layer 11, the pulverized particle size of the piezoelectric ceramic coating layer 14 before sintering is as follows. Is made larger than the pulverized particle diameter of the piezoelectric ceramic layer 11 before sintering, the sintering activity is lowered, and the particle diameter after sintering can be reduced.

In the dipping, the piezoelectric ceramic coating layer 14 is soaked in the oxide ink by immersing the side surfaces of the laminate 13 where the first internal electrode layer 121 and the second internal electrode layer 122 (both electrodes) are exposed. And then dried to form. At this time, the thickness of the piezoelectric ceramic coating layer 14 can be controlled by appropriately adjusting the viscosity and the lifting speed of the ink. Further, in screen printing, a printing opening is provided in the plate making in accordance with the size of the laminate 13, ink is filled therein, ink is applied to the side surface of the laminate 13, and dried. At this time, the thickness of the piezoelectric ceramic coating layer 14 can be controlled by appropriately adjusting the viscosity of the ink, the number of plate making meshes, the printing speed, and the like.

  3 and FIG. 4, first, the end of the first internal electrode layer 121, the end of the second internal electrode layer 122, and the side surface on which the piezoelectric ceramic coating layer 14 is provided. In order to form a recess in this region so as to provide an intermediate region, the end of the first internal electrode layer 121 exposed to the side surface of the laminate 13 and the second internal electrode layer 122 are immersed in an etching solution. Etch the edge. At this time, it is preferable to use an alkaline (such as sodium cyanide) etching solution that does not dissolve the piezoelectric ceramic layer 11 as the etching solution. Further, since the etching depth varies when abrupt etching is performed, it is preferable that the concentration of the etching solution is 30% or less and the solution temperature is 30 ° C. or less.

  Then, after etching the end portion of the first internal electrode layer 121 and the end portion of the second internal electrode layer 122 to form a recess, dipping or screen printing is performed. For example, in order to obtain the structure shown in FIG. 3, an ink having a particle size similar to that of the piezoelectric ceramic coating layer 14 is adjusted to an ink having a low ink rheology yield value, and the inner electrode end of the recess is It suffices that the ink penetrates to the part. In order to form the void 13b between the end of the first internal electrode layer 121 and the end of the second internal electrode layer 122 shown in FIG. 4 and the side surface on which the piezoelectric ceramic coating layer 14 is provided. It is sufficient to adjust the ink to have a high yield value of ink rheology so that the ink does not easily penetrate into the recess.

  Note that the step of forming the piezoelectric ceramic coating layer 14 may be a method in which an oxide ink is applied to the laminated molded body (raw state of the laminated body 13) and then fired at the same time. A method may be employed in which the oxide ink is applied to the post-condensation state and then fired again.

  Next, if necessary, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly composed of silver and glass is laminated in a pattern of the conductor layer 15. After printing on the side surface of the body 13 by a screen printing method or the like and drying, a baking process is performed at a temperature of 650 to 750 ° C. to form the conductor layer 15.

  Then, the lead wires 32 are respectively attached to the conductor layers 15 with the solder 33 to complete the multilayer piezoelectric element 1.

  Next, the through hole 211 is formed, and the laminated piezoelectric element 1 is fixed to the upper surface of the base 21 to which the lead pin 31 is fixed by the soft glass 34 so as to penetrate the through hole 211, and the lead wire 32. And the lead pin 31 are connected by soldering.

  Next, by rolling a seamless cylinder made of SUS304, the cylindrical body 23 having a bellows shape and the lid body 22 made of SUS304 are welded by laser welding.

  Next, a welded body of the cylinder body 23 and the lid body 22 is placed on the multilayer piezoelectric element 1 bonded to the base 21, the cylinder body 23 is pulled with a predetermined load, and a load is applied to the multilayer piezoelectric element 1.

  Next, the place where the cylindrical body 23 and the base 21 are overlapped is welded by laser welding, and the multilayer piezoelectric element 1 is sealed (case 2 is sealed).

Next, a hole for injecting an inert gas is drilled at a predetermined position of the case 2 and evacuated in a vacuum chamber to release oxygen in the case 2, and then nitrogen gas is injected into the vacuum chamber. The case 2 is purged with nitrogen. Thereafter, the hole for nitrogen purge is welded by laser welding to close the hole, and the injection of the inert gas into the case 2 is completed.

  Thereafter, the piezoelectric actuator 10 of the present embodiment is completed by applying a DC electric field of 0.1 to 3 kV / mm to the lead pins 31 attached to the base body 21 to polarize the laminate 13 (piezoelectric ceramic layer 11). To do.

  The completed piezoelectric actuator 10 is connected to an external power supply via the lead pin 31 and applies a voltage to the piezoelectric ceramic layer 11 so that each piezoelectric ceramic layer 11 can be largely displaced by the inverse piezoelectric effect. This makes it possible to function as a mass flow controller for the purpose of gas control of a semiconductor manufacturing apparatus.

  The multilayer piezoelectric element of the present embodiment is not limited to a mass flow controller such as a semiconductor manufacturing apparatus, but can also be used as a fuel injector for an automobile engine, a liquid injector such as an ink jet, a precision positioning device such as an optical device, or the like. Can do.

  Next, a mass flow controller including the piezoelectric actuator described so far will be described. FIG. 7 is a configuration diagram of an example of an embodiment of a mass flow controller.

  The mass flow controller 4 shown in FIG. 7 includes a flow path 41, a flow rate sensor unit 42 that detects the flow rate of the fluid flowing in the flow path 41, and a flow rate control valve 43 that controls the flow rate of the fluid including the piezoelectric actuator 10 described above. And the control circuit unit 44, and the flow rate control valve 43 performs flow rate control by expansion and contraction of the piezoelectric actuator 10.

  For example, a fluid such as a gas flows through the flow path 41, and flows in from the inflow port 411 and flows out from the outflow port 412.

  A flow rate sensor unit 42 is connected to a part of the flow channel 41 in a bypass shape, for example, and the flow rate sensor unit 42 detects the flow rate (mass flow rate) of the fluid flowing in the flow channel 41. .

  The flow rate signal detected by the flow rate sensor unit 42 is transmitted to the control circuit unit 44 after being amplified by an amplification circuit.

  In the control circuit unit 44, the flow rate signal transmitted to the control circuit unit 44 is compared with a preset flow rate signal.

  Then, a drive signal (drive voltage) that eliminates the difference between the transmitted flow rate signal and a preset flow rate signal is input to the piezoelectric actuator 10 that forms the flow rate control valve 43.

  The piezoelectric actuator 10 expands and contracts according to the input drive voltage, and the opening / closing amount of the flow control valve 43 is controlled by the expansion and contraction, thereby controlling the flow rate of the fluid flowing through the flow path 41.

  As described above, since the piezoelectric actuator equipped with the laminated piezoelectric element in which the displacement amount reduction is suppressed is provided, a mass flow controller in which the displacement amount is stable for a long period of time can be obtained.

  The piezoelectric actuator of the example of the present invention was manufactured as follows.

First, a ceramic slurry was prepared by mixing a binder ceramic and a plasticizer with a piezoelectric ceramic powder mainly composed of lead zirconate titanate (PbZrTiO ₃ ) having an average particle size of 0.4 μm, and having a thickness of 150 μm by a doctor blade method. A ceramic green sheet to be a piezoelectric ceramic layer was produced.

  Next, 260 conductive prints obtained by adding a binder to a silver-palladium alloy and forming an internal electrode layer were printed on a ceramic green sheet by a screen printing method. A laminated molded body in which 20 ceramic green sheets were laminated was produced.

  Next, after cutting with a dicing saw machine so as to have a predetermined size, the laminated molded body was degreased at 400 ° C. and fired at 1000 ° C. for 3 hours to produce a laminated sintered body. The obtained laminated sintered body had a rectangular parallelepiped shape, and the size thereof was 5 mm in length, 5 mm in width, and 35 mm in height.

  Next, the laminated body obtained by firing is ground on the side surface so as to have a predetermined shape using a surface grinder or the like, and then the laminated piezoelectric element 1 is added to a sodium cyanide-based alkaline etching solution. After soaking for 30 minutes, the multilayer piezoelectric element was washed with pure water for 30 minutes.

  Next, an ink is prepared by adding a binder and a plasticizer to a calcined powder of piezoelectric ceramic mainly composed of lead zirconate titanate having an average particle diameter of 0.8 μm, and the thickness of the piezoelectric ceramic coating layer becomes 20 μm. As described above, by screen printing, printing is performed on a pair of opposing side surfaces of the laminate in which both electrodes of the internal electrode layer are exposed, and then baking is performed at 1000 ° C. to coat the opposing pair of side surfaces of the laminate. Formed.

  Next, a silver glass-containing conductive paste is prepared by adding a binder to the silver particles and the glass powder, and this is printed on the other pair of side surfaces of the laminate by screen printing, at a temperature of about 700 ° C. After forming a conductor layer by baking, lead wires were connected thereto by soldering.

  Next, a disk-shaped lid body was made of SUS304. Similarly, after making a disk with SUS304, a substrate was made with holes drilled in two locations and lead pins attached with soft glass.

  Next, the laminated piezoelectric element was fixed to the upper surface of the base with an adhesive, and the lead wire soldered to the conductor layer and the lead pin attached to the base were electrically connected by soldering.

  Next, a SUS304 seamless tube is rolled to produce a bellows-shaped cylindrical body, the cylindrical body and the lid are welded by laser welding, and this is covered with a laminated piezoelectric element adhered to a substrate. The cylindrical body was pulled to the substrate side with a predetermined load, and a load was applied to the multilayer piezoelectric element. Then, the portion where the cylindrical body and the substrate overlapped was welded by laser welding to seal the multilayer piezoelectric element.

  Next, a hole for injecting an inert gas is drilled at a predetermined position of the case composed of the cylinder, the lid, and the base, and a vacuum chamber is evacuated to release oxygen in the case. After injecting high-purity nitrogen gas into the chamber and purging the inside of the case with nitrogen, holes for nitrogen purging are welded by laser welding to close the holes and complete the nitrogen purging, as shown in FIG. A piezoelectric actuator according to an embodiment of the invention was produced.

In the piezoelectric actuator of the example of the present invention, the average particle size of the ceramic particles constituting the piezoelectric ceramic coating layer was 1.2 μm. The average particle size of the ceramic particles constituting the piezoelectric ceramic layer was 2.4 μm.

  In addition, as a comparative example, a ceramic particle having an average particle diameter of 2.4 μm and a ceramic particle constituting the piezoelectric ceramic layer were prepared.

  A poling process was performed by applying a DC electric field of 3 kV / mm to these piezoelectric actuators via a lead wire and a lead pin for 15 minutes. When a DC voltage of 150 V was applied to the laminated piezoelectric element, a displacement amount (initial displacement amount) of 50 μm was obtained in the lamination direction.

  Furthermore, as a result of confirming the displacement amount after 500 hours under the test conditions of DC 150 V and 55 ° C., the displacement amount of the piezoelectric actuator of the comparative example was 47 μm, whereas the displacement amount of the piezoelectric actuator of the example was It was 49 μm, and almost no change was seen.

DESCRIPTION OF SYMBOLS 1 ... Multilayer piezoelectric element 10 ... Piezoelectric actuator 11 ... Piezoelectric ceramic layer 11a ... Ceramic particle 121 ... 1st internal electrode layer 122 ... 2nd internal electrode layer 13 ... -Laminated body 13a ... Ceramic particles 13b ... Void 14 ... Piezoelectric ceramic coating layer 14a ... Ceramic particles 15 ... Conductor layer 2 ... Case 21 ... Base 22 ... Lid 23 ... Cylinder 211 ... Through hole 31 ... Lead pin 32 ... Lead wire 33 ... Solder 34 ... Soft glass 4 ... Mass flow controller 41 ... Flow path 411 ... Inlet 412 ... Outlet 42 ... Flow rate sensor 43 ... Flow rate control valve 44 ... Control circuit part

Claims (5)

Piezoelectric ceramic layer, and the laminate first inner electrode layers and second inner electrode layers are laminated, the ends of both of said first internal electrode layer and the second inner electrode layers in the laminate and a piezoelectric ceramic coating layer provided on the side surface near contact,
Both ends of the first internal electrode layer and the second internal electrode layer are located on the inner side than the side surface on which the piezoelectric ceramic coating layer is provided,
The piezoelectric ceramic particle size of the ceramic particles constituting the coating layer is rather smaller than the particle size of the ceramic particles constituting the piezoelectric ceramic layer,
The particle size of the ceramic particles present in the region between the end portion of the first internal electrode layer and the end portion of the second internal electrode layer and the side surface on which the piezoelectric ceramic coating layer is provided is laminated piezoelectric element characterized smaller Ikoto than the particle size of the ceramic particles constituting the ceramic layers.   2. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric ceramic layer and the piezoelectric ceramic coating layer are made of a piezoelectric material having the same composition. Claim 1 or, characterized in that there is a void between each said piezoelectric ceramic coating layer is provided side end of the end portion and the second inner electrode layer of said first internal electrode layer The multilayer piezoelectric element according to claim 2 . A piezoelectric actuator comprising: the laminated piezoelectric element according to any one of claims 1 to 3 ; and a case for housing the laminated piezoelectric element therein. A flow rate sensor unit that detects a flow rate of a fluid flowing in the flow channel, a flow rate control valve that controls a flow rate of the fluid including the piezoelectric actuator according to claim 4 , and a control circuit unit. The mass flow controller is characterized in that the flow rate control valve performs flow rate control by expansion and contraction of the piezoelectric actuator.

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