Piezoelectric/electrostrictive element and piezoelectric/electrostrictive device and production method thereof

Abstract

The piezoelectric/electrostrictive element includes: a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes. Since it is of a substantially trapezoidal shape which decreases in width from one of the bottom surfaces to the other bottom surface, the angle which the slant surfaces of both sides make with the other bottom surface is obtuse, thus resulting in an increase in strength of a ridge portion (a corner) defined by the other bottom surface and the slant surfaces. When the other bottom surface of the piezoelectric/electrostrictive element is secured on a movable plate (diaphragm) by adhesive, a recess-shaped (V-groove shaped) gap defined by the movable plate and the slant surfaces of both the sides of the piezoelectric/electrostrictive element can be filled with the adhesive, thereby resulting in a further increase in force (bonding strength) which secures the piezoelectric/electrostrictive element to the movable plate. The existence of the adhesive in the recess-shaped gap offers the effect of avoiding removal of the piezoelectric/electrostrictive element from the movable plate even if the stress arising from a difference in thermal expansion between the piezoelectric/electrostrictive element and the movable plate is produced.

What is claimed is:  
     
         1 . A piezoelectric/electrostrictive element comprising: 
 a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers;    a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and    a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes.    
     
     
         2 . A piezoelectric/electrostrictive element as set forth in  claim 1 , wherein said piezoelectric/electrostrictive layers are decreased in width gradually in one of directions of lamination.  
     
     
         3 . A piezoelectric/electrostrictive element as set forth in  claim 1 , wherein the external electrode layers formed on said side surface portions extend along the wider surface of said laminate.  
     
     
         4 . A piezoelectric/electrostrictive element as set forth in  claim 3 , wherein a width of a portion of said first external electrode layer extending on said wider surface is greater than that of a portion of said second external electrode layer extending on a side of said wider surface.  
     
     
         5 . A piezoelectric/electrostrictive element as set forth in  claim 1 , wherein either of surfaces in said directions of lamination is the piezoelectric/electrostrictive layer.  
     
     
         6 . A piezoelectric/electrostrictive element as set forth in  claim 1 , wherein the number of said internal electrode layers connecting with said first external electrode layer is identical with that of said internal electrode layers connecting with said second external electrode layer.  
     
     
         7 . A piezoelectric/electrostrictive element as set forth in  claim 1 , wherein the number of said internal electrode layers connecting with said first external electrode layer is different from that of said internal electrode layers connecting with said second external electrode layer.  
     
     
         8 . A piezoelectric/electrostrictive device in which a piezoelectric/electrostrictive element includes a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes and in which said piezoelectric/electrostrictive element is bonded to a surface of a movable plate on a side of the narrower surface of said laminate.  
     
     
         9 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said piezoelectric/electrostrictive element is bonded to said movable plate by adhesive disposed within a gap defined by said first surface, said second surface, and said movable plate.  
     
     
         10 . A piezoelectric/electrostrictive device as set forth in  claim 9 , characterized in that a structure made up of said piezoelectric/electrostrictive element and said adhesive is trapezoidal or rectangular parallelepipedic.  
     
     
         11 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein the first and second external electrode layers formed on said first and second surfaces extend on the wider surface of said laminate.  
     
     
         12 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said piezoelectric/electrostrictive element is bonded only to one surface of said movable plate.  
     
     
         13 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said piezoelectric/electrostrictive elements are bonded to both surfaces of the movable plate so as to hold the movable plate therebetween.  
     
     
         14 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said movable plate is made of an insulating material.  
     
     
         15 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said movable plate is made of a conductive material.  
     
     
         16 . A piezoelectric/electrostrictive device as set forth in  claim 15 , wherein said movable plate communicates with one of the external electrode layers of said piezoelectric/electrostrictive element.  
     
     
         17 . A piezoelectric/electrostrictive device as set forth in  claim 16 , wherein said adhesive has conductivity, and wherein said movable plate communicates with one of the external electrode layers of said piezoelectric/electrostrictive elements through the adhesive.  
     
     
         18 . A piezoelectric/electrostrictive device in which a pair of piezoelectric/electrostrictive elements each includes a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes and in which said piezoelectric/electrostrictive elements are bonded to each other on sides of the respective narrower surfaces of said laminates.  
     
     
         19 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said first and second external electrode layers are connected to a voltage applying circuit.  
     
     
         20 . A piezoelectric/electrostrictive device as set forth in  claim 8 , wherein said first and second external electrode layers are connected to a voltage detecting circuit.  
     
     
         21 . A method of producing a piezoelectric/electrostrictive element comprising the steps of: 
 a first step of preparing a ceramic substrate having a given width;    a second step of forming a laminate on said ceramic substrate, said laminate being made up of a first and a second portions laid to overlap each other, the first portion being made by the steps of: 
 printing a first electrode layer and a second electrode layer on said ceramic substrate which are disposed at a given interval away from each other;  
 forming a piezoelectric/electrostrictive layer using a piezoelectric/electrostrictive paste on the first and second electrode layers so as to cover portions of the first and second electrode layers other than edge portions thereof lying outward in a widthwise direction of said ceramic substrate;  
 forming a first electrode layer on an upper surface and a side surface of the piezoelectric/electrostrictive layer so as to establish an electric connection only with the first electrode layer lying immediately beneath the first electrode layer formed in this step,  
 said second portion being made by performing the following set of steps a given number of times which include: 
 forming a piezoelectric/electrostrictive layer using a piezoelectric/electrostrictive paste on an uppermost one of the first electrode layers, the piezoelectric/electrostrictive layer formed in this step having a width smaller than that of the piezoelectric/electrostrictive layer lying immediately beneath the piezoelectric/electrostrictive layer formed in this step;  
 forming a second electrode layer on an upper surface and a side surface of an uppermost one of the piezoelectric/electrostrictive layers so as to establish an electric connection only with the second electrode layer lying immediately beneath the second electrode layer formed in this step;  
 forming a piezoelectric/electrostrictive layer using a piezoelectric/electrostrictive paste on an uppermost one of the second electrode layers, the piezoelectric/electrostrictive layer formed in this step having a width smaller than that of the piezoelectric/electrostrictive layer lying immediately beneath the piezoelectric/electrostrictive layer formed in this step;  
 forming a first electrode layer on an upper surface and a side surface of an uppermost one of the piezoelectric/electrostrictive layers so as to establish an electric connection only with the first electrode layer lying immediately beneath the first electrode layer formed in this step; and  
 a third step of firing said ceramic substrate and said laminate at a given temperature; and  
 a fourth step of removing said laminate from said ceramic substrate.  
 
   
     
     
         22 . A method of producing a piezoelectric/electrostrictive element as set forth in  claim 21 , wherein a width of the second electrode layer disposed on said ceramic substrate at a given interval away from said first electrode layer in an opposed direction is greater than that of the first electrode layer.  
     
     
         23 . A method of producing a piezoelectric/electrostrictive element as set forth in  claim 21 , wherein a film is formed on said ceramic substrate which disappears upon firing.  
     
     
         24 . A method of producing a piezoelectric/electrostrictive device in which a piezoelectric/electrostrictive element includes a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes, and the piezoelectric/electrostrictive element is bonded to a surface of a movable plate by adhesive.  
     
     
         25 . A method of producing a piezoelectric/electrostrictive device as set forth in  claim 24 , wherein said piezoelectric/electrostrictive elements are bonded to surfaces of said movable plate through adhesive.  
     
     
         26 . A method of producing a piezoelectric/electrostrictive device in which a pair of piezoelectric/electrostrictive elements each include a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes, and the piezoelectric/electrostrictive elements are bonded to each other on sides of the respective narrower surfaces of said laminates through adhesive.