Abstract:
In order to simplify a step of forming a conductive layer for external connection and improve the reliability thereof, at least either internal individual electrodes or internal common electrodes, which comprise of a piezoelectric vibrator, are connected with each other at through holes situated spaced away from an end face of the piezoelectric vibrator and connected to either a segment electrode of a common electrode, which are formed on one surface in a longitudinal direction of the piezoelectric vibrator. According, it is not necessary to form a conductive layer on the end face or a corner portion where such a layer is hardly formed. Furthermore, even if such portions are slightly broken, the conductivity can be maintained.

Description:
This is a divisional of application Ser. No. 09/394,706 filed Sep. 13, 1999, now U.S. Pat. No. 6,273,558, the disclosure of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a piezoelectric vibrator unit in which internal electrodes are stacked in parallel with the expansion/contraction axis, and more particularly to the structure of internal electrodes, and also to an ink jet recording head. 
   As disclosed in Japanese Patent Publication No. 4-1052A, in an ink jet recording head using a piezoelectric vibrator of the longitudinal vibration mode, an elastic plate is placed via a small gap on the back face of a nozzle plate in which plural nozzles are opened, and piezoelectric vibrators having the piezoelectric constant d31, which are obtained by dividing so as to correspond to respective pressure generating chambers of a channel substrate, abuts against the back face of the elastic plate. Ink in a reservoir is guided into the pressure generating chambers via associated ink supply ports, and the ink is then pressurized by the piezoelectric vibrators which are driven by a recording signal, thereby causing the ink to be ejected from the nozzle orifices. 
   As disclosed in Japanese Patent Publication No. 7-195688A, for example, such a piezoelectric vibrator is configured in the following manner. It is prepared a single piezoelectric diaphragm in which common electrodes and internal individual electrodes are alternately stacked on each other while sandwiching a piezoelectric material therebetween. In the piezoelectric diaphragm, the internal common electrodes are exposed from a rear end face on the side of the fixed end, and the internal individual electrodes are exposed from a front end face on the side of the free end. The piezoelectric diaphragm is divided such that dummy piezoelectric vibrators are arranged in both sides thereof, and driving piezoelectric vibrators are formed into a comb-like shape in the central portion thereof so that their non-vibrating regions are continuous. 
   The internal individual electrodes are connected to a segment electrode which elongates from the front end face to a top face of a non-vibrating region, and the internal common electrodes to a common electrode which elongates from the rear end face to the top face of the non-vibrating region. A driving signal is supplied to the segment electrode and the common electrode via a flexible cable. 
   As described above, the external electrodes, which constitute the segment electrode and the common electrode, are formed in an L-like shape on the two faces, i.e., the end faces and the top face. Therefore, there arise problems in that conductive failure easily occurs in a conductive layer in the interface between the end face and the top face, and hence the formation of the conductive layer requires much labor, and that corner edges tend to be broken and a connection failure thereby occurs, thereby lowering the production yield. 
   SUMMARY OF THE INVENTION 
   The invention has been conducted in view of these problems. It is a first object of the present invention to provide a piezoelectric vibrator unit in which, even when corner edges are slightly broken, the conduction relationship is ensured. 
   It is a second object of the present invention to provide a method of manufacturing such a piezoelectric vibrator unit. 
   It is a third object of the present invention to provide an ink jet recording head incorporating such a piezoelectric vibrator unit. 
   In order to solve the problems, according to the present invention, there are fixed on a fixing substrate a plurality of piezoelectric vibrators in which internal individual electrodes and internal common electrodes are alternately and overlappingly stacked on each other while sandwiching piezoelectric materials therebetween in an area where is to be a vibrating region thereof, comprising: a through hole piercing through the piezoelectric materials in at least one end portions thereof for being filled with a conductive material such that at least either the first conductive layers or the second conductive layers are connected with each other; and an external electrode layer formed on one surface in a longitudinal direction of the piezoelectric vibrators for connecting the conductive material in the through hole. 
   The conductive layers on the internal individual electrodes or the internal common electrodes constituting the piezoelectric vibrators are electrically connected with each other and drawn out to a the top face in the longitudinal direction thereof via the through holes arranged inner than the end faces of the piezoelectric vibrators. Therefore, it is not necessary to form conductive layers on the end faces or the corner edge where such a layer is hardly formed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a view of one embodiment of the ink jet recording head according to the present invention and showing the section structure in a region of piezoelectric vibrators; 
       FIG. 2  is an enlarged section view showing the piezoelectric vibrators of the recording head; 
       FIGS. 3A to 3C  are views showing steps of the first half of a method of manufacturing the piezoelectric vibrators; 
       FIGS. 4A to 4C  are views showing steps of the second half of the method of manufacturing the piezoelectric vibrators; 
       FIG. 5  is a view showing a method of manufacturing the piezoelectric vibrators according to another embodiment of the present invention; 
       FIG. 6  is a view showing a state where breakages are formed in end faces of the piezoelectric vibrators; 
       FIG. 7  is a section view showing another embodiment of the present invention; 
       FIGS. 8A and 8B  are section views showing another embodiment of the present invention. 
       FIGS. 9A and 9B  are section views showing other embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the present invention will be described in detail on the basis of illustrated embodiments. 
     FIG. 1  shows an embodiment of the ink jet recording head according to the present invention. A channel unit  1  is configured by integrally stacking: a nozzle plate  3  in which nozzle orifices  2  are formed at a constant pitch; a channel substrate  7  comprising pressure generating chambers  4  respectively communicating with the associated nozzle orifices  2 , and a reservoir  6  for supplying ink to the respective pressure generating chambers  4  via associated ink supply ports  5 ; and an elastic plate  10  which abuts against front ends of piezoelectric vibrators  9  of the longitudinal vibration mode in a piezoelectric vibrator unit  8 , so as to expand and contract the capacity of each of the pressure generating chambers  4 . 
   The piezoelectric vibrator unit  8  is connected to a flexible cable  11  through which an external driving signal is transmitted, and then housed in and fixed to an unit chamber  13  of a head holder  12 , and the channel unit  1  is fixed to an opening face  14  of the head holder  12 , thereby constituting the recording head. 
   In the piezoelectric vibrator unit  8 , the piezoelectric vibrators  9  of the piezoelectric constant d31 are fixed to a fixing substrate  15  so as to coincide with the arrangement pitch of the pressure generating chambers  4 , and, as required, dummy piezoelectric vibrators which are slightly wider are fixed to the fixing substrate  15  and at both ends in the arrangement direction of the piezoelectric vibrators  9 . 
   As shown in  FIG. 2 , in the piezoelectric vibrators  9 , internal common electrodes  17  and internal individual electrodes  18  are alternately stacked on each other while sandwiching a piezoelectric material  19  therebetween. The internal common electrodes  17  are electrically connected to one another in parallel via a conductive layer filling through holes  20  which are opened in an area on the side of the fixed end. The internal individual electrodes  18  are electrically connected to one another in parallel via a conductive layer filling through holes  21  which are opened in an area on the side of the free end. A segment electrode  22  and a common electrode  23  serving also as the internal individual electrodes are formed on the top face of the piezoelectric vibrator  9 . The flexible cable  11  is connected to the electrodes  22  and  23 . 
   In the embodiment, the through holes  20   a  and  20   b , and  21   a  and  21   b  in adjacent two layers are slightly shifted from each other in a direction of the expansion/contraction axis (hereinafter, axial direction), so that the through holes of alternate layers are positioned on one line. 
     FIGS. 3A–3B  show an embodiment of the method of manufacturing the piezoelectric vibrator unit. A green sheet  32  of a piezoelectric material and having a predetermined thickness is prepared. In the green sheet, through holes  30   a  and  31   a  are opened in the vicinity of both ends thereof so as to coincide with the arrangement pitch of the piezoelectric vibrators ( FIG. 3A ). On the surface of the sheet, a strip-like non-conductive region  33  is formed in a region which is nearer to a center portion than the through holes  31   a  and which coincides with the front ends of the internal common electrodes  17 . Conductive layers  34  and  35  are formed by, for example, printing of a conductive coating material so as to fill the inside of the through holes  30   a  and  31   a  ( FIG. 3B ). 
   A green sheet  32 ′ of a piezoelectric material and having a predetermined thickness is stacked on the green sheet  32 . In the green sheet  32 ′, through holes  30   b  and  31   b  are opened at positions which are slightly different from the through holes  30   a  and  31   a  in the axial direction of the piezoelectric vibrators ( FIG. 3C ). On the surface of the sheet, a strip-like nonconductive region  36  is formed in a region which is nearer to a center portion than the through holes  30   b  and which coincides with the front ends of the internal individual electrodes  18 . Conductive layers  37  and  38  are formed so as to fill the inside of the through holes  30   b  and  31   b  ( FIG. 4A ). 
   When the through holes  30   a ,  30   b ,  31   a , and  31   b  are formed so that the width in at least one direction is larger than the thickness of the green sheet  32  or  32 ′, the conductive coating material which forms the conductive layers can be surely filled into the through holes  30   a ,  30   b ,  31   a , and  31   b.    
   Thereafter, the above-mentioned steps are alternatingly repeated to stack a required number of layers, so that a green sheet  32 ″ in which through holes  30   a  and  31   a  ( 30   b  and  31   b ) are opened in the same manner as described above is stacked, a strip-like non-conductive region  39  is formed in the interface between the segment electrode  22  and the common electrode  23 , and conductive layers  40  and  41  are formed so as to fill the insides of the through holes  30   a  and  31   a  ( 30   b  and  31   b ) ( FIG. 4B ). 
   The green sheets of the piezoelectric material are dried and then baked so as to constitute a single piezoelectric material diaphragm  42 . Slits  44  are formed at a pitch which coincides with the arrangement pitch of the through holes  31   a  ( 31   b ) on the side of the front end serving as the free end, by oblique cutting lines C (see  FIG. 1 ). The cutting lines are formed by a cutting tool  43  such as a wire saw or a dicing saw which is advanced to an area where at least the conductive layer  40  can be split into mutually separated portions, in such a manner that each slit is formed as a slope a top end of which is situated in the rear end side and a bottom end of which is situated in the front end side. As a result, the diaphragm is cut into a comb-like shape so that the rear end side is a continuous portion ( FIG. 4C ). 
   In the embodiment, the slits are formed in the piezoelectric material diaphragm  42 . Alternatively, as shown in  FIG. 5 , the slits  44  may be formed after the non-vibrating regions are fixed to a fixing substrate  45  by means of an adhesive agent or the like. In the alternative, the working efficiency can be improved. 
   In the thus configured ink jet recording head, when a driving signal is supplied through the flexible cable  11 , the driving signal is applied to the internal individual electrodes  18  via the segment electrode  22  and the through holes  21   a  and  21   b  of each layer, and to the internal common electrodes  17  via the common electrode  23  and the through holes  20   a  and  20   b  of each layer, with the result that the layers of the piezoelectric material  19  contract in the axial direction. 
   The capacity of the corresponding one of the pressure generating chambers  4  is thus expanded. Therefore, the ink in the reservoir  6  flows into the pressure generating chamber  4  via the ink supply port  5 . When the supply of the driving signal is stopped after elapse of a predetermined time period, the piezoelectric vibrator  9  returns to its original state to relatively contract the capacity of the pressure generating chamber  4 , whereby an ink droplet is ejected from the nozzle orifice  2 . 
   No external electrode for connection exists on the front end face  9   a  and the rear end face  9   b  of each of the piezoelectric vibrators  9 . Even when minute breakages  9   c  and  9   d  which are not so large and hence does not reach the through holes  20  and  21  exist as shown in  FIG. 6 , therefore, the conduction relationships among the segment electrode  22  or the common electrode  23  and the internal individual electrodes  18  or the internal common electrodes  17  can be maintained. According to this configuration, even when breakages are formed during a process of splitting the single piezoelectric material diaphragm  42  by forming slits into the individual piezoelectric vibrators  9 , or that of mounting the unit into a recording head, there arises no substantial disadvantage and the production yield can be improved. 
   In the above embodiment, the internal common electrodes  17 , the internal individual electrodes  18 , the segment electrode  22 , and the common electrode  23  are formed so that their ends are exposed to the outside from the both end faces of the piezoelectric vibrator  9 . Alternatively, as shown in  FIG. 7 , these electrodes may be formed so that their ends are positioned between the through holes  20  or  21  and the front end face  9   a  or the rear end face  9   b . In the alternative, even when a conductive material abuts against the end faces  9   a  and  9   b , the internal common electrodes  17  and the internal individual electrodes  18  are prevented from being short-circuited. 
   In the above embodiment, the connection among the internal common electrodes  17 , and that among the internal individual electrodes  18  are attained by means of the through holes  20  and  21 , respectively. Alternatively, as shown in  FIGS. 8A and 8B , an external electrode  24  or  25  may be formed on one of the front end face and the rear end face, and the internal common electrodes  17  or the internal individual electrodes  18  may be connected to one another in parallel via the external electrode  24  or  25 , and then connected to the common electrode  23  or the segment electrode  22 . Also in the alternative, the production yield can be improved. 
   In the above embodiment, the through holes  20   a  and  20   b , or  21   a  and  21   b  in the layers are slightly shifted with each other in the axial direction. Alternatively, as shown in  FIG. 9A , the through holes may be formed on the same axial line A or B, or, as shown in  FIG. 9B , the through holes on the side of the fixed end may be formed as a through slit  26 . Also in the alternatives, the same effects can be attained. 
   As described above, according to the present invention, there are fixed on a fixing substrate a plurality of piezoelectric vibrators in which internal individual electrodes and internal common electrodes are alternately and overlappingly stacked on each other while sandwiching piezoelectric materials therebetween in an area where is to be a vibrating region thereof, comprising: a through hole piercing through the piezoelectric materials in at least one end portions thereof for being filled with a conductive material such that at least either the first conductive layers or the second conductive layers are connected with each other; and an external electrode layer formed on one surface in a longitudinal direction of the piezoelectric vibrators for connecting the conductive material in the through hole. Accordingly, the internal individual electrodes constituting the piezoelectric vibrators, or the internal common electrodes can be connected to one another via the through holes which are positioned inside the end face of the piezoelectric vibrators, so as to be drawn to the surface of the longitudinal direction. Therefore, formation of a conductive layer is not required on an end face or an edge where such a layer is hardly formed. As a result, the reliability can be enhanced. 
   Furthermore, no external electrode exists on an end face of each piezoelectric vibrator in which breakages are formed in a relatively easy manner. Even when breakages are formed during a step of splitting the piezoelectric vibrators into a comb-like shape or mounting the vibrator unit into a recording head, therefore, there arises no substantial disadvantage and the production yield can be improved. 
   Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.