JP6323863B2 - Piezoelectric element, piezoelectric actuator, and method of manufacturing piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric element, a piezoelectric actuator using the same, and a method for manufacturing the piezoelectric element.

  A stacked piezoelectric element extends in the stacking direction (polarization direction) by applying a voltage, but contracts in the plane direction. At this time, the inactive portion is not deformed, including the protective layers on both end surfaces of the piezoelectric element and the electrode concealed structure portion on the side surface, and only the active portion sandwiched between the internal electrodes is deformed. When such a piezoelectric element is driven repeatedly, stress concentrates on the boundary between the active part and the inactive part, cracks may occur, and a failure may occur.

  On the other hand, in the piezoelectric element described in Patent Document 1, the density of the non-electrode portion formed as a region without an electrode layer composed of only a piezoelectric layer (region with a piezoelectric layer in which no electrode layer is formed) It is formed so as to be 94% or more and 97% or less of the density of the electrode portion formed as a region where the electrode layer is overlapped (region where the electrode layer is formed on the piezoelectric layer). By determining an appropriate firing temperature, such a structure is formed, and cracks at the boundary between the electrode portion and the non-electrode portion are suppressed.

JP 2012-191733 A

  However, although the piezoelectric element as described above prevents stress from concentrating on the boundary between the active part and the inactive part, it is made insulating by adding a sintering aid and sintering at a low temperature. There are difficulties, and high piezoelectric properties cannot always be exhibited.

  The present invention has been made in view of such circumstances, has high piezoelectric characteristics, and repetitively drives to relieve stress concentrated on the boundary between the active part and the inactive part, thereby causing a failure that causes cracks. It is an object of the present invention to provide a piezoelectric element, a piezoelectric actuator, and a method for manufacturing a piezoelectric element that can prevent a large displacement.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a piezoelectric element in which piezoelectric layers and internal electrode layers are alternately stacked, and the piezoelectric element is sandwiched between the internal electrode layer and the internal electrode layer. An active portion formed of a body layer and formed as a region where projections in the stacking direction of the internal electrode layers overlap each other, and provided around the side surface direction and the end surface direction of the active portion. 94% or more and 97% or less inactive part with respect to the sintered density of the piezoelectric layer of the active part, and the internal electrode layer is made of Ag or Ag / Pd, and the active part and the inactive part The piezoelectric layer is made of a PZT-PZN material.

  As a result, it has high piezoelectric characteristics, relieves stress concentrated on the boundary between the active part and the inactive part by repeated driving, prevents the occurrence of cracks, and enables large displacement.

  (2) Moreover, the piezoelectric element of the present invention is characterized in that the PZT-PZN material has a molar ratio of PZN to PZT of 0.1 or more and 0.3 or less. Thereby, it becomes easy to form an inactive part having a predetermined sintered density ratio with respect to the active part.

  (3) Moreover, the piezoelectric actuator of the present invention is characterized by being configured by connecting the above piezoelectric elements in series. Thereby, a piezoelectric actuator can be comprised with a piezoelectric element with a high piezoelectric characteristic and it is hard to produce a crack in an inactive part.

  (4) Moreover, the ultrasonic motor element of this invention is characterized by the said internal electrode being divided and formed in 4 divisions on a lamination surface as an ultrasonic motor element. As a result, an ultrasonic motor element having high piezoelectric characteristics and hardly causing cracks in the inactive portion can be configured.

  (5) Further, the method for manufacturing a piezoelectric element of the present invention is a method for manufacturing a piezoelectric element in which piezoelectric layers and internal electrode layers are alternately laminated, and printed with an electrode paste of Ag or Ag / Pd. The step of producing a molded body by laminating green sheets of PZN-based material, the molded body so that the printed electrode paste forms an internal electrode layer, and the PZT-PZN-based material forms a piezoelectric layer. In the firing step, the region where the projection of the internal electrode layer in the stacking direction overlaps the active portion, and the region provided around the side surface direction and the end surface direction of the active portion is the inactive portion. The firing temperature of the compact is controlled so that the sintered density of the piezoelectric layer of the inactive part is 94% or more and 97% or less with respect to the sintered density of the piezoelectric layer of the active part. It is characterized by.

  As a result, it is possible to manufacture a piezoelectric element that has high piezoelectric characteristics, relieves stress concentrated on the boundary between the active part and the inactive part by repeated driving, prevents a failure that causes cracks, and enables large displacement. .

  According to the present invention, the piezoelectric element has high piezoelectric characteristics, prevents stress from concentrating on the boundary between the active part and the inactive part by repeated driving, and enables large displacement.

It is a sectional side view which shows the piezoelectric element of this invention. It is a plane sectional view showing the piezoelectric element of the present invention. It is a plane sectional view showing the piezoelectric element of the present invention. It is a top view which shows an active part and an inactive part. It is a side view which shows an active part and an inactive part. It is sectional drawing which shows the piezoelectric actuator of this invention. It is a perspective view which shows the ultrasonic motor element of this invention. It is a figure which shows schematic structure of an ultrasonic motor apparatus.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Piezoelectric element)
1A is a side sectional view showing the piezoelectric element 100, and FIGS. 1B and 1C are plan sectional views showing the piezoelectric element 100. The piezoelectric element 100 is formed by alternately stacking piezoelectric layers 110 and internal electrode layers 120a and 120b, and includes external electrodes 125a and 125b connected to the internal electrode layers 120a and 120b, respectively. The piezoelectric element 100 expands and contracts by applying different voltages to the adjacent internal electrode layers 120a and 120b via the external electrodes 125a and 125b.

  1D and 1E are a plan view and a side view showing the active part 130 and the inactive part 140, respectively. The piezoelectric element 100 can divide a region into an active part 130 and an inactive part 140. The active portion 130 is formed of an internal electrode layer and a piezoelectric layer sandwiched between the internal electrode layers, and is formed as a region where projections in the stacking direction of the internal electrode layers overlap. The inactive part 140 is provided around the side and end faces of the active part, and the sintered density of the piezoelectric layer is 94% or more and 97% or less with respect to the sintered density of the piezoelectric layer of the active part. Therefore, the rigidity of the active part is low. Thereby, the stress which concentrates on the boundary of an active part and an inactive part is relieve | moderated by repeated drive, and the failure which a crack produces can be prevented. The inactive portion 140 includes not only a side surface layer portion provided by the electrode concealment structure but also so-called protective layers provided on both end surfaces in the stacking direction.

A PZT-PZN material is used for the piezoelectric layer 110 of the active part 130 and the inactive part 140. PZT-PZN is a material represented by xPb (Zr _0.52 Ti _0.48 ) O ₃ − (x−1) Pb (Zn _1/3 Nb _2/3 ) O ₃ . Thereby, a high piezoelectric characteristic can be exhibited. In order to perform sintering so that the sintered density of the piezoelectric layer is 94% or more and 97% or less with respect to the sintered density of the piezoelectric layer of the active portion at a predetermined temperature, 0.7 ≦ x ≦ 0.9. It is preferable that That is, the piezoelectric element 100 preferably has a composition in which the molar ratio of PZN to PZT is 0.1 or more and 0.3 or less. By using a PZT-PZN-based material, grain boundaries in which Zn elements are unevenly distributed are formed in the gaps between crystal grains as the main component, and the sinterability is improved even at a low temperature of 1050 ° C. or lower.

(Piezoelectric element manufacturing method)
A method for manufacturing the piezoelectric element 100 configured as described above will be described. First, a compact is produced using a PZT-PZN material as the material of the piezoelectric layer 110. The PZT-PZN-based material is represented by xPb (Zr _0.52 Ti _0.48 ) O _3- (x-1) Pb (Zn _1/3 Nb _2/3 ) O ₃ , and 0.7 ≦ x ≦ 0 It is preferable to mix the materials so that. Such a PZT-PZN-based material is a low-temperature fired piezoelectric material, and is fired at 850 ° C. or higher and 1050 ° C. or lower, so that the piezoelectric layer of the inactive portion 140 with respect to the sintered density of the piezoelectric layer 110 of the active portion 130 is obtained. The sintered density of 110 is 94% or more and 97% or less.

  A green sheet is formed with such a material of the piezoelectric layer 110, and an electrode paste of Ag or Ag / Pd is printed on the sheet as a material of the internal electrode layers 120a and 120b. An electrode paste containing Ag in a molar ratio of 0.8 to 1.0 with respect to Pd is used. As a result, due to the effect of Ag during firing, the active portion 130 in which the piezoelectric layer 110 is sandwiched between the Ag or Ag / Pd internal electrode layers 120a and 120b is sufficiently sintered, and the Ag or Ag / Pd internal electrode layer The sintered density of the inactive portion 140 not sandwiched between 120a and 120b is 94% or more and 97% or less. On the other hand, if it is the range of the said composition, it can prevent that an electrode melt | dissolves at the time of baking. The obtained sheet is laminated and pressed to produce a molded body. When the firing temperature is relatively high, it is preferable that Pd be included in the material of the internal electrodes 120a and 120b.

  The molded body is fired while controlling the temperature within the above temperature range. Then, the obtained piezoelectric element 100 is polarized. In the piezoelectric element 100 manufactured in this way, the rigidity of the inactive part 140 is lower than the rigidity of the active part 130. Therefore, the stress generated between them can be relieved, and failure due to cracks can be reduced. Moreover, since the inactive part 140 does not inhibit the displacement of the active part 130, a large amount of displacement can be obtained.

(Piezoelectric actuator)
FIG. 2 is a cross-sectional view showing the piezoelectric actuator 200. The piezoelectric actuator 200 includes a piezoelectric actuator main body 205, a shim plate 231, a hemisphere 230, a seat 240, and a cap 260.

  The piezoelectric actuator main body 205 includes a plurality of piezoelectric elements 100 and lead members 208. The plurality of piezoelectric elements 100 are connected to each other in series (stretching direction due to voltage application) by bonding the piezoelectric elements 100 at the end faces. In the piezoelectric element 100, since the sintered density of the inactive portion 140 formed around the active portion 130 in the side surface direction and the end surface direction is 94% or more and 97% or less, the active portion 130 has rigidity. Low. Accordingly, the piezoelectric actuator 200 can be configured with the piezoelectric element 100 that has high piezoelectric characteristics and hardly causes cracks in the inactive portion 140.

  The piezoelectric actuator body 205 has a shim plate 231 and a hemisphere 230 at one end, and the other end is bonded to the seat 240 as a bottom, and expands and contracts when a voltage is applied to the multiple piezoelectric elements 100.

  The lead member 208 is made of metal and formed in a plate shape, and is bonded to external electrodes 125 a formed on both side surfaces of the piezoelectric element 100. The pair of lead members 208 are connected to the pair of terminals 250 at the seat 240.

  The shim plate 231 is bonded to the end of the piezoelectric actuator body 205 on the displacement side, and the hemisphere 233 is bonded to the shim plate 231. The cap 260 is made of metal, is formed in a cylindrical shape, covers the piezoelectric actuator main body 205, the shim plate 231, and the hemisphere 233, and is sealed in the seat 240 in a state where these are accommodated.

  The seat 240 is formed in a substantially disk shape and supports the other end of the piezoelectric actuator main body 205. The seat 240 is joined to the open end of the cap 260. A terminal 250 is inserted into the seat 240 from the outside.

(Ultrasonic motor element)
FIG. 3 is a perspective view showing the ultrasonic motor element 300. The ultrasonic motor element 300 is formed of piezoelectric ceramics, and the polarization direction coincides with the z-axis direction of the coordinate axis shown in FIG. The expansion / contraction direction when the ultrasonic motor element 1 vibrates in the primary longitudinal vibration mode is parallel to the x-axis, and the length of the ultrasonic motor element 1 in the x-axis direction is L. Further, the shear direction when the ultrasonic motor element 1 vibrates in the secondary bending vibration mode is parallel to the y-axis, and the length (thickness) of the ultrasonic motor element 1 in the y-axis direction is d. .

  The primary longitudinal vibration is generated by repeatedly expanding and contracting in the longitudinal direction (x-axis direction) of the ultrasonic motor element 300. The secondary bending vibration is generated by repeatedly bending in the thickness direction (y-axis direction) of the ultrasonic motor element 1 with shearing forces having different directions. By synthesizing (degenerate) these primary longitudinal vibrations and secondary bending vibrations, the chip 302 provided in the ultrasonic motor element 300 performs an elliptical motion to generate a driving force.

  The value of d / L is substantially 0.6. Therefore, the length in the longitudinal direction is reduced, and downsizing can be achieved. Moreover, since it becomes thick, it becomes difficult to produce the damage by fatigue and excessive input, and it becomes possible to improve durability.

  FIG. 4 is a diagram showing a schematic configuration of the ultrasonic motor device 400. The ultrasonic motor element 300 is formed in a rectangular shape, and is provided with a pair of laminated electrodes 304a and a pair of laminated electrodes 304b that are diagonally opposed to each other so that one main surface is divided into four. In each of the stacked electrodes 304a and 304b, one of the electrodes adjacent in the stacking direction is grounded. These laminated electrodes 304a and 304b are individually provided in an insulated state, and then the non-grounded electrodes of the laminated electrodes 304a and 304b located diagonally to each other are connected to each other by the connecting portions 304c and 304d, respectively. Are electrically connected to each other to form two sets of stacked electrodes 304a and 304b.

  The sintered density of the inactive portion formed in the periphery in the side surface direction and the end surface direction is 94% or more and 97% or less with respect to the active portion formed with respect to the four sections constituted by the two sets of laminated electrodes 304a and 304b. Therefore, the rigidity of the active part 130 is low. Thereby, a crack can be made hard to produce in the inactive part of an ultrasonic motor element.

  In addition, the ultrasonic motor device 400 includes an AC power source 405 and a switching unit 406. The AC power source 405 outputs to the ultrasonic motor device 400 a sinusoidal voltage having a frequency that excites the vibration of the primary longitudinal vibration mode that expands and contracts in the longitudinal direction and the vibration of the secondary bending vibration mode that flexes in the shear direction. Is done. When the ultrasonic motor device 400 is driven, the switching unit 406 applies a voltage output from the AC power source 405 to an electrode that is not grounded of one of the stacked electrode 304a and the stacked electrode 304b.

  As described above, when an AC voltage is applied to one of the laminated electrodes 304a and 304b of the ultrasonic motor element 300, the ultrasonic motor element 300 has a primary longitudinal vibration mode that expands and contracts in the longitudinal direction. Vibration and vibration of the second bending vibration mode that bends in the shear direction are generated. When these resonance frequencies are equal, both vibration modes are combined (degenerated), elliptic vibration is generated in the sliding tip 302 of the ultrasonic motor element 300, and the driven body 415 is driven.

DESCRIPTION OF SYMBOLS 100 Piezoelectric element 110 Piezoelectric layer 120a Internal electrode layer 125a External electrode 130 Active part 140 Inactive part 160 Cap 200 Piezoelectric actuator 205 Piezoelectric actuator body 208 Lead member 230 Hemisphere 231 Shim plate 233 Hemisphere 240 Seat 250 Terminal 260 Cap 300 Ultrasonic motor Element 302 Chip 302 Sliding chip 304a, b Stacked electrode 304c, d Connection unit 400 Ultrasonic motor device 405 AC power source 406 Switching unit 415 Driven body

Claims (4)

A piezoelectric element in which piezoelectric layers and internal electrode layers are alternately stacked,
An active portion formed of an internal electrode layer and a piezoelectric layer sandwiched between the internal electrode layers, and formed as a region where projections in the stacking direction of the internal electrode layers overlap;
An inactive part that is provided around the side surface direction and the end surface direction of the active part, and the sintered density of the piezoelectric layer is 94% or more and 97% or less with respect to the sintered density of the piezoelectric layer of the active part; Prepared,
The internal electrode layer is made of Ag / Pd having a molar ratio of Ag to Pd of 0.8 or more and 1.0 or less, and the piezoelectric layer of the active part and the inactive part has a molar ratio of PZN to PZT of 0. A piezoelectric element comprising a PZT-PZN material that is 1 or more and 0.3 or less . A piezoelectric actuator comprising the piezoelectric elements according to claim 1 connected in series. 2. The piezoelectric element according to claim 1 , wherein the ultrasonic motor element is formed by dividing the internal electrode into four sections on the laminated surface. A method of manufacturing a piezoelectric element in which piezoelectric layers and internal electrode layers are alternately stacked,
A step of producing a molded body by laminating green sheets of PZT-PZN materials printed with an Ag / Pd electrode paste having a molar ratio of Ag to Pd of 0.8 to 1.0 ;
The molded electrode is fired so that the printed electrode paste forms an internal electrode layer, and a PZT-PZN material having a molar ratio of PZN to PZT of 0.1 to 0.3 forms a piezoelectric layer. Including the steps of:
In the firing step, when the area where projections in the stacking direction of the internal electrode layers overlap is an active part, and the area provided around the side surface direction and the end surface direction of the active part is an inactive part, the molded body, A method for manufacturing a piezoelectric element, wherein a firing temperature is controlled so that a sintered density of the piezoelectric layer of the inactive part is 94% to 97% with respect to a sintered density of the piezoelectric layer of the active part .

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