BACKGROUND OF THE INVENTION 
     The invention relates to a method for manufacturing a piezoelectric actuator employing a piezoelectric element which becomes deformed upon receipt of a supplied drive signal, and to a liquid ejecting head equipped with the actuator, as well as to an actuator mother member from which the piezoelectric actuator is originated. 
     A piezoelectric actuator is a member having a piezoelectric element which becomes deformed upon receipt of supplied electrical energy. The piezoelectric actuator is in widespread use as a drive element for, e.g., a liquid ejecting head, a micropump, and a sounding body (a speaker or the like). Here, the piezoelectric element is formed from piezoelectric ceramics made by compacting and sintering metal oxide powder, such as BaTiO 3 , PbZrO 3 , or PbTiO 3 , which are piezoelectric materials and exhibit a piezoelectric effect, or from a piezoelectric macromolecular film utilizing a high molecular compound. 
     Here, the liquid ejecting head ejects a droplet from a nozzle orifice by inducing pressure fluctuations in a liquid stored in a pressure chamber. The liquid ejecting head is embodied as, e.g., a recording head to be used in an image recording apparatus such as a printer, a liquid-crystal ejecting head for use in manufacturing a liquid-crystal display, or a coloring material ejecting head to be used for manufacturing a color filter. Here, the micropump is an ultrasmall pump capable of ejecting a very small volume of liquid and used at the time of, e.g., delivery of a trace amount of chemical. 
     The piezoelectric actuator is mounted on a pressure chamber formation substrate having a void which is to serve as a pressure chamber, and a portion of the pressure chamber is partitioned by the vibration plate. When ejection of a droplet or delivery of liquid is to be performed, a drive pulse is supplied to the piezoelectric element, to thereby deform the piezoelectric element and the vibration plate (i.e., the deformed portion of the pressure chamber) and vary the volume of the pressure chamber. 
     In the field of the liquid ejecting head and that of the micropump, strong demand exists for high-frequency driving of the piezoelectric element. This demand is intended for implementing high-frequency ejection of a droplet and enhancing liquid delivery capability. In order to implement high-frequency driving of the piezoelectric element, the compliance of the deformed portion must be made smaller than that of a related-art piezoelectric element and the extent to which the piezoelectric element is deformed must be made greater than that to which the related-art piezoelectric element is deformed. The reason for this is that a reduction in the compliance of the deformed portion results in enhancement of responsiveness, thereby enabling driving of the piezoelectric element at a frequency higher than that required conventionally. Another reason is that an increase in the extent to which the piezoelectric element is deformed results in an increase in volumetric change in the pressure chamber, and hence the volume of droplet to be ejected or the volume of droplet to be delivered can be increased. 
     A piezoelectric element of multilayer structure is proposed for sufficing for a characteristic pertaining to the compliance of the deformed portion and a characteristic pertaining to the extent to which the piezoelectric element becomes deformed, the characteristics being mutually contradictory. For example, a piezoelectric element disclosed in Japanese Patent Publication No. 2-289352A is formed from a piezoelectric layer having a two-layer structure; that is, an upper layer piezoelectric substance and a lower layer piezoelectric substance. Drive electrodes (individual electrodes) are formed at a boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. A common electrode is formed on an outer surface of the upper layer piezoelectric substance, and another common electrode is formed on an outer surface of the lower layer piezoelectric substance. Similarly, Japanese Patent Publication No. 10-34924A discloses a piezoelectric element of multilayer structure. 
     In the case of the piezoelectric element of multilayer structure, the drive electrodes are provided at the boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. Hence, an electric field, whose intensity is determined by an interval between the drive electrodes and the respective common electrodes (i.e., the thickness of each piezoelectric substance) and by a potential difference between the drive electrodes and the common electrodes, is imparted to the piezoelectric substances of respective layers. Therefore, in contrast with a piezoelectric element of monolayer structure formed by interposing a single layer piezoelectric substance between the common electrode and the drive electrodes, the piezoelectric element can be deformed at the same drive voltage as that conventionally required, even when the compliance of the deformed portion is reduced by increasing the total thickness of the piezoelectric element to some extent. 
     However, characteristics capable of responding to recently-growing demand cannot be achieved by mere use of the piezoelectric element of multilayer structure. Therefore, users are forced to use, as an actual product, a piezoelectric element of monolayer structure formed by interposing a single layer piezoelectric substance between a common electrode and drive electrodes. Various factors are conceivable as being responsible for this, including insufficient efficiency of deformation of the piezoelectric element. 
     For example, on the occasion of mass production of the piezoelectric actuator, manufacturing piezoelectric actuators on an individual basis deteriorates efficiency. Pressure chambers, piezoelectric elements, and feed terminals are provided in number equal to a plurality of units on a ceramic sheet, and the ceramic sheet is cut. When piezoelectric actuators are cut off from the ceramic sheet, electrode material may adhere to a cutting blade. When the electrode material has adhered to the cutting blade, sharpness of the cutting blade will be deteriorated, and there may arise a necessity for cleaning the electrode material adhering to the cutting blade, or a drop in manufacturing efficiency. Further, chips (cuttings) which have arisen during cutting of the ceramic sheet may cause a short-circuit. 
     The electrode materials adhere to the cutting blade because a feed terminal to be used for supplying an electric signal to the piezoelectric element is set to the maximum size. More specifically, on the occasion of fabricating the piezoelectric element, measurement of electrostatic capacitance is performed as a part of quality control operation, and the feed terminal is used for measuring electrostatic capacitance. In order to bring a probe of a measurement instrument into reliable contact with the feed terminal, the feed terminal must be made as large as possible. A portion of the feed terminal is formed so as to extend beyond a predetermined cutting line (i.e., a contour line of the piezoelectric actuator) provided on the ceramic sheet. Since the feed terminal is for feeding a drive signal to respective piezoelectric elements, the feed terminal remains conductive with a contact terminal of a wiring member; that is, remains electrically connected to the contact terminal. Therefore, when a configuration in which the feed terminal is to be cut is employed, the feed terminal is laid so as to extend up to the contour line of the piezoelectric actuator, thus ensuring electrical connection with the contact terminal. However, as mentioned previously, provision of the contact terminal in this manner is not preferable in terms of manufacturing efficiency. 
     SUMMARY OF THE INVENTION 
     The present invention is conceived in view of the foregoing circumstances and aims at providing a method for manufacturing a piezoelectric actuator and a liquid ejecting head equipped with the actuator, which enables enhancement of manufacturing efficiency. Further, the invention aims at providing an actuator mother member having a structure suitable for the manufacturing method. 
     In order to achieve the above object, according to the invention, there is provided a method of manufacturing a piezoelectric actuator, comprising steps of:
         preparing a substrate, which is to be a vibration plate actuated by a piezoelectric element;   defining a plurality of chip regions on the substrate;   forming a first common electrode of the piezoelectric element on the substrate, so as not to extend beyond an outline of each of the chip regions;   forming a first piezoelectric layer of the piezoelectric element on the first common electrode;   forming a drive electrode of the piezoelectric element on the first piezoelectric layer, so as not to extend beyond the outline of each of the chip regions;   forming a second piezoelectric layer of the piezoelectric element on the drive electrode;   forming a second common electrode of the piezoelectric element on the second piezoelectric layer, so as not to extend beyond the outline of each of the chip regions; and   cutting the substrate so as to divide the chip regions from one another.       

     Here, the term “chip region” represents an area corresponding to a piezoelectric actuator serving as a unit; namely, an area which is to become one piezoelectric actuator. For instance, the chip regions correspond to areas which are partitioned (defined) with predetermined cutting lines to be used for cutting piezoelectric actuators from an actuator mother member. Here, the term “mother member” implies a member which is to be cut into piezoelectric actuators. 
     Preferably, the manufacturing method further comprises a step of forming a terminal electrically connected to the drive electrode, so as not to extend beyond the outline of each of the chip regions, the terminal forming step being performed after the second common electrode is formed and before the substrate is cut. 
     In the above configurations, the range within which the electrodes are to be formed is set inward of the chip region. Hence, no electrode material adheres to a cutting blade during a process for cutting the ceramic sheet, and hence good sharpness can be maintained over a long time period. As a result, efficiency of mass production of piezoelectric actuators can be enhanced. Moreover, the piezoelectric actuators can also be cut with superior dimensional accuracy. 
     According to the invention, there is also provided a manufacturing method of a liquid ejecting head, comprising a step of joining the piezoelectric actuator manufactured by the above method with a substrate in which a pressure chamber communicated with a nozzle orifice is formed, such that the piezoelectric element opposes to the pressure chamber. 
     According to the invention, there is also provided a mother member which is to be a plurality of piezoelectric actuators, comprising:
         a substrate, on which a plurality of chip regions are defined; and   a piezoelectric element, formed in each of the chip regions, the piezoelectric element including:
           a first common electrode, formed on the substrate so as not to extend beyond an outline of each of the chip regions;   a first piezoelectric layer, formed on the first common electrode;   a drive electrode, formed on the first piezoelectric layer so as not to extend beyond the outline of each of the chip regions;   a second piezoelectric layer, formed on the drive electrode; and   a second common electrode, formed on the second piezoelectric layer so as not to extend beyond the outline of each of the chip regions.   
               

     Preferably, the mother member further comprises a terminal electrically, connected to the drive electrode so as not to extend beyond the outline of each of the chip regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, 
         FIG. 1  is a cross-sectional view showing the basic structure of a head main body; 
         FIG. 2  is a plan view of the head main body when viewed from a nozzle plate; 
         FIG. 3  is a cross-sectional view of an actuator unit taken along a longitudinal direction of a pressure chamber; 
         FIG. 4  is a cross-sectional view of an actuator unit taken along a transverse direction of the pressure chamber; 
         FIG. 5  is a cross-sectional view showing an end structure of a drive electrode; 
         FIG. 6  is a cross-sectional view showing the end structure of a common electrode; 
         FIG. 7A  is a plan view of an upper common electrode; 
         FIG. 7B  is a plan view of a lower common electrode; 
         FIGS. 8A to 8F  are views showing processes for fabricating a piezoelectric element; 
         FIG. 9  is a view showing polarization processing of the piezoelectric element; 
         FIG. 10  is a view showing a positional relationship between a ceramic sheet and chip regions; and 
         FIG. 11  is a plan view showing a recording head equipped with a plurality of head main bodies. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention will be described hereinbelow by reference to the accompanying drawings. Here, a liquid ejecting head will be described by taking, as an example, a recording head to be mounted on an image recording apparatus such as a printer or a plotter. As shown in  FIG. 11 , for example, the recording head has a plurality of head main bodies  1 , and the head main bodies  1  are mounted on a mount base  61 . 
     The basic structure of the head main body  1  will first be described by reference to  FIGS. 1 and 2 . The head main body  1  is essentially formed from a flow passage unit  2  and an actuator unit  3 . 
     The flow passage unit  2  is fabricated from a supply port formation substrate  6  having formed therein through holes which are to serve as ink supply ports  4 , and through holes which are to constitute portions of nozzle communication ports  5 ; a reservoir formation substrate  8  having formed therein through holes which are to serve as a common ink reservoir  7 , and through holes which are to constitute portions of the nozzle communication ports  5 ; and a nozzle plate  10  having formed therein nozzle orifices  9  oriented in a secondary scanning direction. 
     The supply port formation substrate  6 , the reservoir formation substrate  8 , and the nozzle plate  10  are formed by pressing, for example, a stainless steel plate. The flow passage unit  2  is fabricated by placing the nozzle plate  10  on one surface of the reservoir formation substrate  8  (e.g., the lower side in the drawing) and the supply port formation substrate  6  on the other surface of the same (e.g., the upper side in the drawing), and bonding together the supply port formation substrate  6 , the reservoir formation substrate  8 , and the nozzle plate  10 . For instance, the flow passage unit  2  is fabricated by bonding together the members  6 ,  8 , and  10  by use of, e.g., a sheet-shaped adhesive. 
     As shown in  FIG. 2 , the nozzle orifices  9  are formed in a plurality of rows at predetermined pitches. Rows of nozzles  11  are formed from the plurality of nozzle orifices  9  arranged in rows. For example, a row of nozzles  11  is formed from  92  nozzle orifices  9 . Two rows of nozzles  11  are formed side by side. 
     The actuator unit  3  is a member also called a head chip. The actuator unit  3  comprises a pressure chamber formation substrate  13  having formed therein through holes which are to constitute pressure chambers  12 ; a vibration plate  14  for defining a part of each pressure chamber  12 ; a cover member  16  having formed therein through holes which are to constitute portions of supply-side communication ports  15 , and through holes which are to constitute portions of the nozzle communication ports  5 ; and a piezoelectric element  17  formed on the surface of the vibration plate  14  opposite the pressure chamber  12 . 
     With regard to the thicknesses of the members  13 ,  14 , and  16 , the pressure chamber formation substrate  13  and the cover member  16  preferably assume a thickness of 50 μm or more, more preferably 100 μm or more. The vibration plate  14  preferably assumes a thickness of 50 μm or less, more preferably 3 to 12 μm or thereabouts. In the actuator unit  3 , the vibration plate  14  and the piezoelectric element  17  constitute a kind of piezoelectric actuator of the invention. 
     The actuator unit  3  is made by placing the cover member  16  onto one surface of the pressure chamber formation substrate  13 , and the vibration plate  14  onto the other surface of the same, and forming the piezoelectric elements  17  on the surface of the vibration plate  14  opposite the pressure chamber  12 . Of these members, the pressure chamber formation substrate  13 , the vibration plate  14 , and the cover member  16  are made from ceramics such as alumina or zirconia and are integrated together by sintering (to be described later). 
     The pressure chamber  12  is a hollow section which is elongated in the direction orthogonal to the row of nozzles  11 , and a plurality of pressure chambers  12  are formed so as to correspond to the nozzle orifices  9 . Specifically, as shown in  FIG. 2 , the pressure chambers  12  are arranged in rows in line with the row of nozzles. One end of each pressure chamber  12  is in communication with the corresponding nozzle orifice  9  by way of the nozzle communication port  5 . The other end on the side of the pressure chamber  12  opposite the nozzle communication port  5  is in communication with the common ink reservoir  7  by way of the supply-side communication port  15  and the ink supply port  4 . A part of the pressure chamber  12  is partitioned by the vibration plate  14 . 
     Here, the piezoelectric element  17  is a piezoelectric element of so-called flexural vibration mode and is provided, for each pressure chamber  12 , on the surface of the vibration plate  14 . As shown in  FIGS. 3 and 4 , the piezoelectric element  17  is substantially identical in width with the pressure chamber  12  and somewhat greater in length than the same. Both longitudinal ends of the piezoelectric element  17  project beyond the pressure chamber  12  to the outside; namely, the piezoelectric element  17  is formed so as to cover the pressure chamber  12  in the longitudinal direction thereof. 
     The piezoelectric element  17  has a multilayer structure formed from a piezoelectric layer  31 , a common electrode  32 , a drive electrode  33 , and other elements. The piezoelectric layer  31  is sandwiched between the drive electrode  33  and the common electrode  32 . The structure of the piezoelectric element  17  will be described later in detail. 
     A drive signal supply source (not shown) is electrically continuous with or connected to the drive electrode  33 . The common electrode  32  is controlled to, e.g., a ground potential. When a drive signal is supplied to the drive electrode  33 , an electric field whose intensity is related to a potential difference between the drive electrode  33  and the common electrode  32  is induced. Since the electric field is imparted to the piezoelectric layer  31 , the piezoelectric layer  31  becomes deformed in response to supply of the drive signal. In this case, as the electric potential of the drive electrode  33  increases, the piezoelectric layer  31  contracts in the direction orthogonal to the electric field, thereby deforming the vibration plate  14  such that the volume of the pressure chamber  12  is reduced. Conversely, as the electric potential of the drive electrode  33  is lowered, the piezoelectric layer  31  expands in the direction orthogonal to the electric field, thereby deforming the vibration plate  14  such that the volume of the pressure chamber  12  is increased. 
     The actuator unit  3  and the flow passage unit  2  are bonded together in a unit bonding process whose processing is to be performed subsequent to a cutting process which will be described later. For instance, a sheet-shaped adhesive is interposed between the supply port formation substrate  6  and the cover member  16 . In this state, pressure is applied to the actuator unit  3  toward the flow passage unit  2 , whereupon the actuator unit  3  and the flow passage unit  2  are bonded together. 
     As shown in  FIG. 1 , in the head main body  1 , a continuous ink flow passage is formed for each nozzle orifice  9  so as to extend from the common ink reservoir  7  to the nozzle orifice  9  by way of the ink supply port  4 , the supply-side communication port  15 , the pressure chamber  12 , and the nozzle communication port  5 . When the actuator unit is in use, the interior of the ink flow passage is filled with ink. When an ink droplet is ejected from the nozzle orifice  9 , ink is supplied from the common ink reservoir  7  to the ink flow passage, thereby deforming the piezoelectric element  17 . As a result, a corresponding pressure chamber  12  is subjected to contraction or expansion, thereby causing pressure fluctuations in the ink stored in the pressure chamber  12 . 
     By controlling the ink pressure, the nozzle orifice  9  can be caused to eject an ink droplet. For instance, if the pressure chamber  12  having a stationary volume is subjected to rapid expansion once having been contracted, the pressure chamber  12  is filled with ink in association with expansion of the pressure chamber  12 . By subsequent rapid contraction, the ink stored in the pressure chamber  12  is pressurized, whereupon an ink droplet is ejected. 
     Here, high-speed recording operation involves a necessity for ejecting a larger number of ink droplets within a short time period. In order to satisfy this requirement, the compliance of a deformed portion of the pressure chamber  12  (i.e., the portion of the pressure chamber partitioned by the vibration plate  14  and the piezoelectric element  17 ) and the amount of deformation of the piezoelectric element  17  must be taken into consideration. More specifically, as the compliance of the deformed portion becomes greater, responsiveness of the pressure chamber to deformation is deteriorated, whereby driving of the recording head at a high frequency becomes difficult. In contrast, as the compliance of the deformed portion becomes smaller, the amount of deformation of the pressure chamber  12  becomes smaller, whereby the volume of one ink droplet is also decreased. 
     From this viewpoint, in the case of a recording head employing a piezoelectric element of flexural vibration mode which has already become commercially practical, there is employed a piezoelectric element of monolayer structure formed by interposing a single layer of piezoelectric substance between a common electrode and a drive electrode. The piezoelectric element has a maximum response frequency of about 25 kHz and a maximum ink droplet volume of about 13 pL (picoliters). 
     In the embodiment, the compliance of the vibration plate  14  is reduced by use of the piezoelectric element  17  of multilayer structure. Further, the piezoelectric element  17  is improved. Thus, the recording head of the invention can eject the required volume of ink droplet at a frequency higher than that at which an ink droplet has hitherto been ejected. The following description explains this point. 
     First, the structure of the piezoelectric element  17  is described in detail. As shown in  FIGS. 3 and 4 , the piezoelectric layer  31  is formed from an upper layer piezoelectric substance (i.e., an outer piezoelectric substance)  34  and a lower layer piezoelectric substance (i.e., an inner piezoelectric substance)  35 . The common electrode  32  is formed from an upper common electrode (i.e., an outer common electrode)  36  and a lower common electrode (i.e., an inner common electrode)  37 . The common electrode  32  and a drive electrode (individual electrodes)  33  constitute an electrode layer. 
     Here, the terms “upper (or outer)” and “lower (or inner)” denote a positional relationship with reference to the vibration plate  14 . In other words, the term “upper (outer)” denotes the surface of the piezoelectric element distant from the vibration plate  14 , and the term “lower (inner)” denotes the surface of the same close to the vibration plate  14 . 
     The drive electrode  33  is formed at a boundary between the upper layer piezoelectric substance  34  and the lower layer piezoelectric substance  35  such that the entire width of the drive electrode  33  is covered with the upper layer piezoelectric substance  34 . The lower common electrode  37  is formed in a lower portion of the lower layer piezoelectric substance  35 ; that is, at a position between the lower layer piezoelectric substance  35  and the vibration plate  14 , such that the entire width of the lower common electrode  37  is covered with the lower layer piezoelectric substance  35 . Further, the upper common electrode  36  is formed on the surface of the upper layer piezoelectric substance  34  opposite the lower layer piezoelectric substance  35 . Accordingly, the piezoelectric element  17  has a multilayer structure comprising, in order from the vibration plate  14 , the lower common electrode  37 , the lower layer piezoelectric substance  35 , the drive electrode  33 , the upper layer piezoelectric substance  34 , and the upper common electrode  36 . The thickness of the piezoelectric layer  31  is equal to a total thickness of the upper layer piezoelectric substance  34  and the lower layer piezoelectric substance  35 ; that is, about 17 μm. Further, the total thickness of the piezoelectric element  17 , including the common electrode  32 , is about 20 μm. The total thickness of the conventional piezoelectric element  17  of monolayer structure is about 15 μm. As the thickness of the piezoelectric element  17  is increased, the compliance of the vibration plate  14  becomes smaller correspondingly. 
     The upper common electrode  36  and the lower common electrode  37  are controlled to a given potential regardless of the drive signal and serve as common electrodes as mentioned above. In the embodiment, the upper common electrode  36  and the lower common electrode  37  are electrically connected together and controlled to the earth potential. The drive electrode  33  is electrically connected to the drive signal supply source and changes a potential in accordance with a supplied drive signal. Accordingly, supply of the drive signal induces an electric field between the drive electrode  33  and the upper common electrode  36  and between the drive electrode  33  and the lower common electrode  37 , wherein the electric fields are opposite in direction to each other. 
     Various conductors; e.g., a single metal substance, a metal alloy, or a mixture consisting of electrically insulating ceramics and metal, are selected as materials which constitute the electrodes  33 ,  36 , and  37 . The materials are required not to cause any deterioration at a sintering temperature. In the embodiment, gold is used for the upper common electrode  36 , and platinum is used for the lower common electrode  37  and the drive electrode  33 . 
     The upper layer piezoelectric substance  34  and the lower layer piezoelectric substance  35  are formed from piezoelectric material containing, e.g., lead zirconate titanate (PZT) as the main ingredient. The direction of polarization of the upper layer piezoelectric substance  34  is opposite that of the lower layer piezoelectric substance  35 . Therefore, when the drive signal is applied to the upper layer piezoelectric substance  34  and the lower layer piezoelectric substance  35 , the substances expand and contract in the same direction and can become deformed without any problem. The upper layer piezoelectric substance  34  and the lower layer piezoelectric substance  35  deform the vibration plate  14  such that the volume of the pressure chamber  12  is reduced with an increase in the potential of the drive electrode  33  and such that the volume of the pressure chamber  12  is increased with a decrease in the potential of the drive electrode  33 . 
     In the embodiment, in order to efficiently deform the piezoelectric element  17  of multilayer structure, the thickness tp  1  of the upper layer piezoelectric substance  34  is set to three-fourths or less the thickness tp  2  of the lower layer piezoelectric substance  35 , thereby rendering the degree of deformation of the upper layer piezoelectric substance  34  stemming from supply of the drive signal greater than that of the lower piezoelectric substance  35 . In short, when the same drive signal is supplied, the upper layer piezoelectric substance  34  is deformed to a greater extend than is the lower layer piezoelectric substance  35 . In this way, when the upper layer piezoelectric substance  34  has become deflected to a greater extent than the lower layer piezoelectric substance  35 , the upper layer piezoelectric substance  34  is spaced farther from the vibration plate  14  than is the lower layer piezoelectric substance  35 , and hence, deformation of the upper layer piezoelectric  34  acts on the vibration plate  14  while the amount of deformation is amplified. Thus, the amount of deformation of the vibration plate  14  can be increased. 
     The vibration plate  14  can be deformed to a great extent, and hence the volume of the pressure chamber  12 , which would be achieved at the time of contraction of the piezoelectric element, can be made smaller. Accordingly, a volumetric difference between the expanded pressure chamber  12  and the contracted pressure chamber  12  can be made greater than when the piezoelectric element  17  of multilayer structure is simply used, thereby increasing the quantity of ink droplet to be ejected. 
     An electrode material which is thinner and more flexible than those of the other electrodes (i.e., the drive electrode  33  and the lower common electrode  37 ) is used for the upper common electrode  36 , in view that the upper common electrode  36  deforms to a greater extent than the other electrodes. Specifically, the upper common electrode  36  is formed on the surface of the upper layer piezoelectric substance  34  and becomes deformed to a greater extent than the other electrodes. For this reason, a material which is softer than those used for the other electrodes is used for the upper common electrode  36  and/or in a small thickness. As a result, there can be prevented occurrence of a rupture, which would otherwise be caused by repeated deformation. In order to prevent an excessive increase in electrical resistance, which would otherwise arise when the thickness of the upper common electrode is reduced, an electrode material having superior conductivity like gold is preferably used. 
     More specifically, as mentioned above, in relation to the material of an electrode, the upper common electrode  36  is formed from gold, and the drive electrode  33  and the lower common electrode  37  are formed from platinum. In relation to the thicknesses of the electrodes, the lower common electrode  37  and the drive electrode  33  assume a thickness of 2 to 3 μm, and the upper common electrode  36  assumes a thickness (te1) which is about one-tenth the value of 2 to 3 μm (e.g., 0.3 μm). By such a configuration, the upper common electrode  36  can be deformed so as to follow the piezoelectric element  17 , thereby preventing occurrence of a problem; that is, impairment of the amount of deformation of the piezoelectric element  17 . Further, even when being deformed repeatedly, the piezoelectric element  17  is less susceptible to a break in wiring. Moreover, an electric current can be caused to efficiently flow through the upper common electrode  36 . 
     For example, as shown in  FIG. 5 , the drive electrode  33  becomes exposed outside at one longitudinal end of the piezoelectric element  17  and is electrically connected to a conduction electrode  39  at the end face of the piezoelectric element  17 . The drive electrode  33  is brought into electrical conduction with the feed terminal  40  by way of the conduction electrode  39 . The feed terminal  40  is a contact terminal to be used for supplying a drive signal. A plurality of feed terminals  40  are formed for each drive electrode  33 . In the embodiment, the feed terminals  40  are formed by sintering a silver paste. 
     Contact terminals (not shown) to be used for feeding a drive signal provided in a flexible flat cable (FFC) are electrically connected to the respective feed terminals  40 . Accordingly, the drive signal is supplied to a corresponding drive electrode  33  by way of the feed terminal  40  and the conduction electrode  39 . 
     The conduction electrode  39  is continuously formed on the end face of the piezoelectric element  17 , the surface of the vibration plate  14 , and the surface of a terminal substrate  41  on which the feed terminal  40  is to be provided. As mentioned above, the lower common electrode  37  is also formed on the surface of the vibration plate  14 . However, a disconnection region X where no electrode is to be formed is set between the conduction electrode  39  and the lower common electrode  37 . Hence, the conduction electrode  39  and the lower common electrode  37  are electrically isolated from each other. 
     As mentioned above, the piezoelectric element  17  is provided for each nozzle orifice  9 . Hence, the number of piezoelectric elements  17  to be provided for one row of nozzles  11  is  92 . Although the upper common electrode  36  and the lower common electrode  37  are brought into conduction; that is, they are electrically connected together, a working efficiency will be deteriorated if the common electrodes  36 ,  37  are electrically connected together for each piezoelectric element  17 , thereby resulting in a failure to improve productivity. 
     In view of the circumstances, in the embodiment, the upper common electrode  36  and the lower common electrode  37  are formed from a pectinated electrode consisting of a trunk electrode and a plurality of prong electrodes. After having been subjected to predetermined inspection and polarization processing, the trunk electrodes are electrically connected together. The following description will explain this point. 
     As shown in  FIG. 7A , the upper common electrode  36  is formed from a swath trunk electrode (proximal electrode)  42  which is elongated in the direction of a nozzle row; and a plurality of prong electrodes  43  which are continuously formed on one side of the trunk electrode  42  so as to cover the surface of the piezoelectric element  17  (i.e., the upper layer piezoelectric substance  34 ). The upper common electrode  36  is formed in a pectinated pattern. 
     The trunk electrode  42  is formed on the surface of the vibration plate  14 , and the width of the trunk electrode  42  is set so as to become sufficiently greater than the width of the prong electrode  43  so that an electric current can be caused to flow to the prong electrodes without a problem even when the drive signals are simultaneously supplied to all the piezoelectric elements  17 . As indicated by dashed lines in  FIG. 7A , a conduction area  42   a  is provided at the longitudinal end of the trunk electrode  42 . The conduction area  42   a  is used for bringing the upper common electrode  36  and the lower common electrode  37  into conduction with each other (to be described later). As shown in  FIG. 6 , the respective prong electrodes  43  are formed on the surface of the upper layer piezoelectric substance  34  so as to run over a slope surface formed at one end of the piezoelectric layer  31  (i.e., an end section of the piezoelectric layer  31  close to the trunk electrode  42 ). 
     As shown in  FIG. 5 , the extremities of the respective prong electrodes  43  (i.e., extremities of the same opposite the trunk electrode  42 ) are located at positions inward of the end face of the upper layer piezoelectric substance  34  (i.e., the end face close to the feed terminals  40 ). This is intended for preventing occurrence of a failure due to a short which would arise between the prong electrodes  43  and the drive electrode  33 . More specifically, there can be prevented occurrence of a failure, which would otherwise be caused when a short-circuit arises between the prong electrodes  43  and the drive electrode  33  by atmospheric discharge as a result of the extremities of the prong electrodes  43  having been spaced from the drive electrode  33 . 
     The entirety of the lower common electrode  37  is formed on the surface of the vibration plate  14 . As shown in  FIG. 7B , the lower common electrode  37  is formed into a pectinated pattern from a swath trunk electrode (proximal electrode)  44  which is elongated in the direction of the nozzle row; a plurality of prong electrodes  45  on one side of the trunk electrode  44  for respective piezoelectric elements  17  (i.e., the lower layer piezoelectric substance  35 ); and a conduction strip section  46  extending from one end of the trunk electrode  44  in the direction opposite the prong electrodes  45 . 
     The width of the trunk electrode  44  is set so as to become sufficiently greater than the width of the prong electrode  45  so that an electric current can be caused to flow to the prong electrodes without a problem even when the drive signals are simultaneously supplied to all the piezoelectric elements  17 . The prong electrodes  45  are located between the piezoelectric layer  31  (i.e., the lower layer piezoelectric substance  35 ) and the vibration plate  14 , and the positions of extremities of the prong electrodes  45  (i.e., ends of the prong electrodes opposite the trunk electrode  44 ) in the longitudinal direction of the piezoelectric element are aligned with extremities of the upper common electrodes  36 , as shown in  FIG. 5 . 
     The conduction strip section  46  is used for bringing the lower common electrode  37  into conduction with the upper common electrode  36 . For this reason, the conduction strip section  46  is formed at a position close to the conduction area  42   a . As shown in  FIG. 8F , a conduction member  47 , such as solder, is provided so as to extend across the conduction area  42   a  and the conduction strip section  46 . Consequently, electrical connection of the common electrodes  36 ,  37  can be achieved by merely forming the conduction member  47  so as to extend across the conduction area  42   a  and the conduction strip section  46 , thereby enabling simplification of work. This structure is suitable for automating operations for assembling piezoelectric elements. 
     In relation to the method for manufacturing a recording head, a method for manufacturing the actuator unit  3  will be chiefly described. The actuator unit  3  is manufactured through, in the sequence given, a mother member manufacturing process for forming an actuator mother member, and a process for cutting the actuator mother member into the chip regions  19  (see  FIG. 10 ). In the embodiment, the actuator unit  3  is not manufactured individually. After the mother member is prepared, a plurality of actuator units  3  are cut from the mother member, in order to improve manufacturing efficiency. 
     Here, the term “actuator mother member” means a member which is to be cut into a piezoelectric actuator (e.g., the vibration plate  14  and the piezoelectric element  17 ). The actuator mother member comprises a sheet-shaped ceramic body which is to become the vibration plate  14  (hereinafter also called a “vibration plate base”); the piezoelectric elements  17  to be provided on the surface of the vibration plate base; and the feed terminals  40 . In the base member manufacturing process, the ceramic sheet  18  including the actuator mother member is prepared. More specifically, the mother member preparation process comprises a sheet preparation process for preparing a ceramic sheet base member; an element formation process for forming the plurality of piezoelectric elements  17  on the surface of the sheet base member for each chip region  19 ; and a feed terminal formation process for preparing the ceramic sheet  18  by forming the plurality of feed terminals  40  on each piezoelectric element  17 . Processing pertaining to these processes is performed in sequence. 
     In the sheet preparation process, first, a ceramic slurry is prepared from ceramic material, a binder, a liquid medium, or the like. Next, a green sheet (i.e., a sheet material which has not yet been sintered) is formed from the slurry through use of a commonly employed apparatus such as a doctor blade apparatus or a reverse roll coater. Subsequently, the green sheet is subjected to processing, such as cutting or punching, thereby forming required through holes. Thus, sheet-shaped precursors for the pressure chamber formation substrate  13 , the vibration plate  14 , and the cover member  16  are formed. The sheet-shaped precursors are laminated and sintered, thereby integrating the sheet-shaped precursors and producing a single sheet-shaped member. Specifically, the sheet base member comprises a sheet-shaped member which is to become a pressure chamber formation plate  13  (a formation plate base); the vibration plate member; and the sheet-shaped member which is to become the cover member  16  (a cover base). In this case, since the sheet-shaped precursors are formed integrally, special bonding operation is not necessary. Moreover, a high sealing characteristic can also be achieved at cemented surfaces of the respective sheet-shaped precursors. 
     As shown in  FIG. 10 , a plurality of rectangular chip regions  19  are set in a matrix pattern on one sheet mother member. Here, the “chip region” means an area which is to become one actuator unit  3 ; that is, an area which is to become a piezoelectric actuator. For instance, areas partitioned (surrounded) by predetermined cutting lines Y 1 , Y 2  to be used for cutting the actuator units  3  from the actuator mother member correspond to the chip regions. Accordingly, the pressure chambers  12 , the nozzle communication ports  5 , and the like are provided within each of the partitioned chip region  19 . 
     In the embodiment, after production of the sheet base member, the terminal substrate  41  is first formed. The terminal substrate  41  is formed on the surface of the vibration plate base member opposite the pressure chamber  12 . For instance, the terminal substrate  41  is formed from ceramics. Specifically, after a ceramic paste is applied over the sheet base member in a predetermined pattern, the sheet base member is sintered, thereby forming the terminal substrate  41 . After the terminal substrate  41  is formed, processing proceeds to the element formation process. 
     In the element formation process, the respective piezoelectric elements  17  are formed on the surface of the vibration plate base member. By reference to  FIGS. 8A to 8E , the element formation process will be described. As shown in  FIG. 8A , a lower common electrode  37  is first formed on the surface of a vibration plate base member  14 ′ in the element formation process. In the embodiment, the lower common electrode  37  is formed through printing. Accordingly, a mask is placed at a predetermined location on the vibration plate base member  14 ′. A platinum paste is applied over the vibration plate base member  14 ′ via the mask. So long as the platinum paste is applied over the surface of the vibration plate base member  14 ′, the platinum paste is sintered. More specifically, the vibration plate base member  14 ′ to which the platinum paste is applied is sintered in a baking furnace at a predetermined temperature over a predetermined time period. By sintering operation, the lower common electrode  37  is formed on the surface of the vibration plate base member  14 ′. 
     In the process, portions of the conduction electrode  39  are also formed simultaneously. As shown in  FIG. 5 , a vibration plate surface portion of the conduction electrode  39  (i.e., a vibration plate section)  39   a  and a terminal substrate surface portion (i.e., a terminal substrate section)  39   b  are formed. Accordingly, a mask used in the first process is provided with a pattern to be used for forming the lower common electrode  37  and a pattern to be used for forming the vibration plate section  39   a  and the terminal substrate section  39   b  in the conduction electrode  39 . 
     As shown in  FIG. 8B , when the lower common electrode  37  is formed, the lower layer piezoelectric substance  35  is formed. Namely, after a mask is placed at a predetermined location on the vibration plate base member  14 ′, a piezoelectric material (e.g., lead zirconate titanate) paste is applied over the lower common electrode  37 . The thus-applied piezoelectric material paste is sintered. 
     Subsequently, as shown in  FIGS. 8C to 8E , the drive electrode  33 , the upper layer piezoelectric substance  34 , and the upper common electrode  36  are formed, in this sequence, through the same procedures. In the process shown in  FIG. 8C , the drive electrodes  33  are stacked on the lower piezoelectric substances  35 . In the process shown in  FIG. 8D , the upper layer piezoelectric substances  34  are formed on the lower layer piezoelectric substances  35  so as to cover the drive electrodes  33 . In the process shown in  FIG. 8E , the upper common electrode  36  is formed on the surface of the upper piezoelectric substances  34 . 
     In the third process, portions of the conduction electrode are formed simultaneously. Specifically, the same electrode material as that of the drive electrode  33  is continuously applied over the side face (end face) at one side of the lower layer piezoelectric substance  35 . As a result, an element end face portion (element section)  39   c  of the conduction electrode  39  is formed. A portion of the element section  39   c  comes into contact and conduction with the vibration plate section  39   a.    
     In the element formation process, the range within which the lower common electrode  37 , the lower piezoelectric substances  35 , the drive electrodes  33 , the upper layer piezoelectric substances  34 , and the upper common electrode  36  are to be formed is set inward of the chip regions  19  as indicated by reference symbol R shown in  FIG. 10 . 
     When the elements have been fabricated up to the upper common electrode  36 , processing proceeds to the feed terminal formation process, where the feed terminals  40  are formed. In the feed terminal formation process, the feed terminal  40  is formed in close proximity to the side of the piezoelectric element  17  facing the conduction electrode  39 . The feed terminals  40  are formed by application and sintering of a paste. For example, the mask pattern formed in alignment with the feed terminals  40  is placed on the terminal substrate  41  on which the conduction electrodes  39  are formed. 
     After the mask pattern is placed on the terminal substrate  41 , a silver paste is applied over the terminal substrate  41  via the mask pattern. After application of the silver paste, the silver paste is sintered, thereby forming a plurality of feed terminals  40 . Similarly, the feed terminals  40  are also formed within the chip regions  19 , as in the case of the layers constituting the piezoelectric element  17 . Specifically, the feed terminals  40  are formed within the formation range R shown in  FIG. 10 . 
     Here, the respective feed terminals  40  are formed at positions spaced from the edge of the chip region  19  by about 10 μm. At these positions, the geometries of the thus-formed feed terminals are substantially identical with those obtained by cutting the feed terminals along the edge of the chip region  19  after portions of the respective feed terminals  40  have been formed outside the chip region  19 . 
     When the feed terminals  40  have been formed, processing proceeds to the cutting process. In the cutting process, the ceramic sheet  18  is cut along cutting lines Y 1 , Y 2  (see  FIG. 11 ) running along the edges of the chip regions  19 , thereby producing actuator units  3 . In this case, as mentioned above, the formation region R, in which the electrode layers  33 ,  36 ,  37 , the upper and lower piezoelectric substances,  34 ,  35 , and the conduction electrode  39  and the feed terminal  40  are to be formed, is set inward of the chip region  19 . Therefore, electrode material does not adhere to the cutting blade, and hence the cutting blade can be maintained sharp over a long time period. Moreover, the respective actuator units  3  can be cut with superior dimensional accuracy. Since the chips are non-conductive, occurrence of a short-circuit hardly arises even when the chips have adhered to the electrode layer or the like on the vibration plate  14 . There can be prevented generation of burrs, which would otherwise be caused by cutting of a metal layer. Hence, ease of assembly of a recording head is achieved in a subsequent process. 
     After the ceramic sheet is cut into the actuator units  3 , an inspection is performed as to whether or not the respective layers constituting the piezoelectric element  17  are formed properly. In the embodiment, the electrostatic capacitance relevant to the dimension (e.g., the thickness or width) of the piezoelectric layer can be measured for each of the piezoelectric substances  34 ,  35 . Since the common electrodes  36 ,  37  are not electrically connected together, the electrostatic capacitance can be measured for each of the piezoelectric layers  34 ,  35 . 
     After all the piezoelectric elements  17  have finished undergoing inspection, a determination is made as to whether or not the thus-inspected actuator unit  3  is non-defective. The actuator units  3  that have been determined to be non-defective are classified according to the measured electrostatic capacitance. For instance, the actuator units  3  are ranked according to a mean electrostatic capacitance or on the basis of the range of variation in electrostatic capacitance. 
     After having been classified, the actuator units  3  are subjected to a polarization process, where the produced piezoelectric elements  17  are polarized. As shown in, e.g.,  FIG. 9 , in the polarization process the upper common electrode  36  and the lower common electrode  37  are connected to the ground, whereby the drive electrodes  33  are connected to the power source. 
     In this case, polarization is effected at a voltage which is sufficiently higher than a drive voltage to be used. In the embodiment, the drive voltage is about 30 V, and hence the polarization voltage is set to 70 V or thereabouts. When the polarization voltage is applied to the actuator units over a predetermined time period, the polarization process is completed. 
     After completion of the polarization process, processing proceeds to a conduction process. As shown in  FIG. 8F , in the conduction process, the actuator units  3  that have been subjected to polarization processing are subjected to conduction processing, such as soldering, thereby bringing the upper common electrode  36  into conduction with the lower common electrode  37 . For instance, the conduction member  47 , such as solder or wire bonding, is provided so as to spread across the conduction area  42   a  and the conduction strip section  46 . 
     The invention is not limited to the embodiment and is susceptible to various modifications on the basis of the scope of the invention defined by claims. 
     First, the terminal board  41  of the embodiment may be formed from a conductive material. For instance, the terminal board  41  may be formed from a silver paste which is the same conductive material as that of the supply terminals  40 . In this case, the terminal board section  39   b  of the conduction electrode  39  is also formed on the surface of the vibration plate substrate  14 ′. Further, the feed terminals  40  are formed from a silver paste so as to be laid over the terminal board  41 . By such a configuration, the feed terminals  40  and the terminal board  41  are formed from conductive material, and hence electrical resistance can be diminished. 
     The invention is described by taking, as an example, a recording head which is a kind of a liquid ejecting head. The invention can also be applied to another liquid ejecting head, such as a liquid-crystal ejecting head or a coloring material ejecting head. Moreover, the invention can also be applied to a piezoelectric actuator used in a micropump or a sounding member.
Methods for manufacturing a piezoelectric actuator and a liquid ejecting head. In particular, a substrate, which is to be a vibration plate actuated by a piezoelectric element is prepared. A plurality of chip regions are defined on the substrate. A first common electrode of the piezoelectric element is formed on the substrate. A first piezoelectric layer of the piezoelectric element is formed on the first common electrode. A drive electrode of the piezoelectric element is formed on the first piezoelectric layer. A second piezoelectric layer of the piezoelectric element is formed on the drive electrode. A second common electrode of the piezoelectric element is formed on the second piezoelectric layer. Then, the substrate is cut so as to divide the chip regions from one another. In the aforementioned aspects of the invention, the first and second common electrodes as well as the drive electrode are formed so as not to extend beyond the outline of each of the chip regions.