Patent Publication Number: US-8991985-B2

Title: Method of manufacturing a liquid jet head and a liquid jet apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 13/253,896 filed Oct. 5, 2011, which is a continuation application of Ser. No. 12/391,910 filed Feb. 24, 2009, which claims priority to Japanese Patent Application No. 2008-043652, filed Feb. 25, 2008. The entire contents of the aforementioned applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a liquid jet head and a liquid jet apparatus. 
     2. Description of the Related Art 
     A piezoelectric element for use in a liquid jet head has a problem of susceptibility to damage resulting from, for example, exposure to an external environment such as moisture. To solve this problem, the periphery of a piezoelectric layer covered with an upper electrode, for example, is disclosed in Japanese Unexamined Patent Application Publication No. 2005-88441. If a piezoelectric element is formed by depositing and patterning a lower electrode film, a piezoelectric layer, and an upper electrode film individually as described above, the piezoelectric layer is subject to damage during manufacturing processes, resulting in deterioration of displacement properties of the piezoelectric element. Specifically, a piezoelectric layer is etched via, for example, a protective film consisting of a resist and patterned into a predetermined pattern. After the piezoelectric layer is patterned, peeling off such a protective film of a resist followed by washing the surface of the piezoelectric layer is performed. An acid or alkaline solution may be used as a peeling solution for use in the peeling step or a cleaning solution for use in the washing step. However, such a solution adhering to the piezoelectric layer may damage the piezoelectric layer, resulting in deterioration of various properties including displacement properties of the piezoelectric element. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been achieved to solve at least some of the above-described problems and can be realized as an embodiment described below. 
     An embodiment to which the present invention is applicable is a method of manufacturing a liquid jet head, including forming a pressure generating chamber in a passage forming substrate, forming a lower electrode film having a smaller width than the pressure generating chamber in a region opposite to the pressure generating chamber, forming a piezoelectric layer so as to cover the top and end faces of the lower electrode film in a region opposite to the pressure generating chamber, forming an upper electrode film so as to cover top and end faces of the piezoelectric layer in a region opposite to the pressure generating chamber, forming an intermediate film made of a conductive material on the piezoelectric layer, forming a protective film on the intermediate film and, using the protective film as a mask, patterning by etching the piezoelectric layer together with the intermediate film into a predetermined pattern, and peeling off the protective film and depositing the upper electrode film on the passage forming substrate and the intermediate film. 
     The above as well as additional features and objectives of the present invention will become apparent in the following description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions in conjunction with the accompanying drawings. 
         FIG. 1  is an exploded perspective view of a recording head according to Embodiment 1 of the present invention. 
         FIG. 2  is a plan view and a cross-sectional view of a recording head according to Embodiment 1 of the present invention. 
         FIG. 3  is a cross-sectional view showing a structure of a piezoelectric element of a recording head according to Embodiment 1 of the present invention. 
         FIG. 4  is a plan view and a cross-sectional view showing modifications to a recording head according to Embodiment 1 of the present invention. 
         FIG. 5  is a cross-sectional view showing a manufacturing process of a recording head according to the present invention. 
         FIG. 6  is a cross-sectional view showing a manufacturing process of a recording head according to the present invention. 
         FIG. 7  is a cross-sectional view showing a manufacturing process of a recording head according to the present invention. 
         FIG. 8  is a cross-sectional view showing a manufacturing process of a recording head according to the present invention. 
         FIG. 9  is a cross-sectional view showing a structure of a piezoelectric element of a recording head according to Embodiment 2 of the present invention. 
         FIG. 10  is an exploded perspective view of a recording head according to Embodiment 3 of the present invention. 
         FIG. 11  is a plan view and a cross-sectional view of a recording head according to Embodiment 3 of the present invention. 
         FIG. 12  is a cross-sectional view showing a structure of a piezoelectric element according to Embodiment 3 of the present invention. 
         FIG. 13  is a modified structure of a piezoelectric element according to Embodiment 3 of the present invention. 
         FIG. 14  is a modified structure of a piezoelectric element according to Embodiment 3 of the present invention. 
         FIG. 15  is an illustration showing an example of a recording apparatus. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     At least the following will become apparent from the following descriptions and the accompanying drawings. 
     As an embodiment of a liquid jet head, a method of manufacturing a liquid jet head includes forming a pressure generating chamber in a passage forming substrate, forming a lower electrode film having a smaller width than the pressure generating chamber in a region opposite to the pressure generating chamber, forming a piezoelectric layer so as to cover the top and end faces of the lower electrode film in a region opposite to the pressure generating chamber, forming an upper electrode film so as to cover top and end faces of the piezoelectric layer in a region opposite to the pressure generating chamber, forming an intermediate film made of a conductive material on the piezoelectric layer, forming a protective film on the intermediate film and, using the protective film as a mask, patterning by etching the piezoelectric layer together with the intermediate film into a predetermined pattern, and peeling off the protective film and depositing the upper electrode film on the passage forming substrate and the intermediate film. 
     Since the piezoelectric layer is patterned together with the intermediate film, the intermediate film, for example, plays a role as a barrier when the protective film is peeled off, resulting in almost no peeling solution adhering to the piezoelectric layer. This prevents damage to the piezoelectric layer caused by the peeling solution, which leads to the manufacture of a liquid jet head provided with a piezoelectric element having good displacement properties. Also, the intermediate film is formed of a conductive material and comes into contact with the upper electrode, thereby complementing conductive properties as the upper electrode. 
     Furthermore, as another embodiment of a liquid jet head, a method of manufacturing a liquid jet head uses a metallic material having an ionization tendency equal to or smaller than a material of the upper electrode film. 
     In particular, it is preferable to use any one selected from among groups including iridium, platinum, and palladium as the material of the intermediate film. 
     This allows the intermediate film to securely function as a protective film against an acid solution, thereby more securely preventing damage to the piezoelectric layer. 
     Furthermore, the upper electrode film is formed so as to be thicker than the intermediate film and have a thickness of 30 μm or more. 
     This more securely prevents water content (moisture) from penetrating into the piezoelectric layer. 
     In addition, a liquid jet apparatus provided with a liquid jet head manufactured by the above described manufacturing method is provided. 
     Use of this liquid jet head ensures that a highly reliable liquid jet apparatus is provided. 
     A preferred embodiment of the present invention will now be described below with reference to the accompanying drawings. The embodiment to be described below is described as an example of the present invention, and not all of the components to be presented below constitute the essential components of the present invention. 
     Best Mode for Carrying Out the Invention 
     An embodiment of the present invention is described below on the basis of the accompanying drawings. 
     (Embodiment 1) 
       FIG. 1  is an exploded perspective view showing a structure of an ink jet recording head as an example of a liquid jet head manufactured by the manufacturing method according to Embodiment 1 of the present invention.  FIG. 2  is a plan view of an ink jet recording head shown in  FIG. 1  and a cross-sectional view taken along the line A-A′. 
     As shown in figures, in this embodiment a passage forming substrate  10  is made of a silicon single crystal substrate having a crystal face orientation of ( 110 ) and has an elastic film  50  made of an oxide film formed at one face thereof. The passage forming substrate  10  includes a plurality of pressure generating chambers  12  disposed in parallel with each other in the breadthwise direction thereof, each of the plurality of pressure generating chambers  12  being defined by a partition wall and constructed at one face thereof with the elastic film  50 . 
     The passage forming substrate  10  includes an ink supply passage  13  and a communicating passage  14  formed at one lengthwise end of the pressure generating chamber  12 , the ink supply passage  13  and the communicating passage  14  being defined with the partition wall  11  and communicating with the pressure generating chamber  12 . A communicating section  15  communicating with the communicating passage  14  is provided outside of the communicating passage  14 . The communicating section  15  communicates with a reservoir section  32  of a protective substrate  30  to be mentioned later to form part of a reservoir  100 , which constitutes an ink chamber (liquid chamber) common to each of the pressure generating chambers  12 . 
     The ink supply passage  13  is designed to have a smaller cross section than the pressure generating chamber  12  in order to allow ink flowing from the communicating section  15  into the pressure generating chamber  12  to have a constant flow resistance. For example, the ink supply passage  13  is formed so as to have a smaller width than the pressure generating chamber  12  by narrowing a passage going through the reservoir  100  and the pressure generating chamber  12  at a position on the side of the pressure generating chamber  12 . In this embodiment, the ink supply passage is formed by narrowing the passage at one breadthwise side thereof, but may be formed by narrowing the passage at both breadthwise sides thereof. Also, the ink supply passage may be formed by narrowing the passage in the thickwise direction, instead of narrowing the passage in the breadthwise direction. The communicating passage  14  is formed by extending the partition walls  11  at both breadthwise sides of the pressure generating chamber  12  to the communicating section  15  and thereby defining a space between the ink supply passage  13  and the communicating section  15 . 
     In this embodiment, the passage forming substrate  10  uses a silicon single crystal substrate as a material. Needless to say, the material is not limited to this, and another material such as a glass ceramic or stainless steel may be used. 
     The passage forming substrate  10  has a nozzle plate  20  mounted at an open side thereof by an adhesive or a hot melt film or the like, the nozzle plate  20  having a nozzle  21  communicating with the end of the pressure generating chamber  12  opposite the ink supply passage  13 . The nozzle plate  20  is made of, for example, a glass ceramic, a silicon single crystal substrate, stainless steel or the like. 
     Meanwhile, the passage forming substrate  10  has the above mentioned elastic film  50  formed at the side opposite to the open side, and an insulator film  55  made of an oxide film of a different material from the elastic film  50  is formed on the elastic film  50 . In addition, a piezoelectric element  300  consisting of a lower electrode film  60 , a piezoelectric layer  70 , and an upper electrode film  80  is formed on the insulator film  55 . The piezoelectric element  300  includes portions having at least the piezoelectric layer  70 , in addition to portions having the lower electrode film  60 , the piezoelectric layer  70 , and the upper electrode film  80 . Generally, any one electrode of the piezoelectric element  300  is used as a common electrode, while an individual electrode is formed by patterning the other electrode together with the piezoelectric layer  70  for each of the pressure generating chambers  12 . As used herein, the piezoelectric element  300  together with a vibration plate producing a displacement by operation of the piezoelectric element  300  is called an actuator unit. 
     The structure of the piezoelectric element  300  according to this embodiment is detailed below. As shown in  FIG. 3 , the lower electrode film  60  constituting the piezoelectric element  300  is formed so as to have a smaller width than the pressure generating chamber  12  in a region opposite to the pressure generating chamber  12 , thereby forming an individual electrode of the piezoelectric element  300 . Also, the lower electrode film  60  extends onto a peripheral wall from one lengthwise end of the pressure generating chamber  12 . The lower electrode film  60  is connected to a lead electrode  90  made of, for example, gold (Au) in a region outside of the pressure generating chamber  12 . The piezoelectric element  300  is subjected to a selective voltage application through the lead electrode  90 . Meanwhile, the end of the lower electrode film  60  at the side of the other lengthwise end of the pressure generating chamber  12  is located in a region opposite to the pressure generating chamber  12 . 
     The piezoelectric layer  70  is formed so as to have a larger width than the lower electrode film  60  and a smaller width than the pressure generating chamber  12 . Both ends of the piezoelectric layer  70  extend outside of the ends of the pressure generating chamber  12  in the lengthwise direction of the pressure generating chamber  12 . In other words, the piezoelectric layer  70  is formed so as to completely cover the top and end faces of the lower electrode film  60  in a region opposite to the pressure generating chamber  12 . The end of the piezoelectric layer  70  at the side of one lengthwise end of the pressure generating chamber  12  is located close to the end of the pressure generating chamber  12 , and the lower electrode film  60  further extends outside the end. 
     The upper electrode film  80  is formed in a continuous manner in regions opposite to a plurality of the pressure generating chambers  12 , and extends onto a peripheral wall from the other lengthwise end of the pressure generating chamber  12 . In other words, the upper electrode film  80  is formed so as to completely cover the top and end faces of the piezoelectric layer  70  in a region opposite to the pressure generating chamber  12 . This substantially prevents water content (moisture) of the atmosphere from penetrating into the piezoelectric layer  70 . Accordingly, this prevents damage to the piezoelectric element  300  (piezoelectric layer  70 ) caused by water content (moisture), resulting in a significant improvement in the durability of the piezoelectric element  300 . 
     The end of the upper electrode film  80  at the side of the other lengthwise end of the pressure generating chamber  12  is located in a region opposite to the pressure generating chamber  12 , and a substantial driving section for the piezoelectric element  300  is provided in a region opposite to the pressure generating chamber  12 . In other words, a section of the piezoelectric element  300  between the end of the lower electrode film  60  and the end of the upper electrode film  80 , which is located inside the pressure generating chamber  12 , is a substantial driving section. Accordingly, the piezoelectric element  300 , when driven, causes a vibration plate (elastic film  50 , insulator film  55 ) to produce no large deformation at positions close to both lengthwise ends of the pressure generating chamber  12 , thereby preventing a crack from occurring at such positions of the vibration plate. In this arrangement, a small part of the surface of the piezoelectric layer  70  is exposed in a region opposite to the pressure generating chamber  12 . However, since such a part is not a substantial driving section and has a very small area, and there is a large distance between the peripheral portion of the upper electrode film  80  and the lower electrode film  60 , as mentioned later, damage to the piezoelectric layer  70  caused by moisture can be prevented. 
     An intermediate film  85  is provided between the upper electrode film  80  and the piezoelectric layer  70 . The intermediate film  85  is made of a conductive material, and substantially functions as part of the upper electrode film  80 . In other words, due to being made of a conductive material the intermediate film  85  can supplement the conductive property as the upper electrode film  80  when being in contact with the upper electrode film  80 . As detailed later, the intermediate film  85  is patterned at the same time as the piezoelectric layer  70  so as to prevent damage to the piezoelectric layer  70  in a manufacturing process. For this reason, the intermediate film  85  is formed only on the upper surface of the piezoelectric layer  70 . 
     It is preferable that the piezoelectric layer  70  constituting the piezoelectric element  300  meets the following relationship regarding thickness. Specifically, the thickness of the piezoelectric layer  70  formed on the upper surface of the lower electrode film  60 , namely the distance D 1  between the upper surface of the lower electrode film  60  and the upper surface of the piezoelectric layer  70 , and the thickness of the piezoelectric layer  70  formed on the slanted end surface of the lower electrode film  60 , namely, the distance D 2  between the end surface of the lower electrode film  60  and the end surface of the piezoelectric layer  70  preferably have the relationship of D 2 □D 1  (see  FIG. 3 ). In other words, it is preferable that the thickness D 2  of the piezoelectric layer  70  on the end surface of the lower electrode film  60  is more than the thickness D 1  of the piezoelectric layer  70  formed on the upper surface of the lower electrode film  60 , which contributes to driving of the piezoelectric element  300 . 
     This arrangement ensures that a sufficient clearance is maintained between the upper electrode film  80  (intermediate film  85 ) on the end surface of the piezoelectric layer  70  and the lower electrode film  60 , thereby preventing dielectric breakdown from occurring between the upper electrode film  80  and the lower electrode film  60 . Accordingly, damage to the piezoelectric element  300  can be prevented, which will lead to the implementation of an ink jet recording head having improved durability. 
     As shown in  FIG. 4 , a protective film  150  made of a material having moisture-absorption characteristics, such as aluminum oxide or the like, may be provided so as to cover the surface of the piezoelectric layer  70  exposed to the peripheral portion of the upper electrode film  80  and a region opposite to the pressure generating chamber  12 . This arrangement more securely prevents damage to the piezoelectric layer  70  caused by moisture. 
     A protective substrate  30  having a piezoelectric element retaining section  31  is joined with an adhesive  35  onto the passage forming substrate  10  having the piezoelectric element  300  formed thereon, the piezoelectric element retaining section  31  being in a region opposite to the piezoelectric element  300  and having a space large enough to allow the piezoelectric element  300  to move without any difficulties. The piezoelectric element  300  is provided inside the piezoelectric element retaining section  31 , and therefore is negligibly subject to the effects of the outside environment. The protective substrate  30  includes a reservoir section  32  formed in a region corresponding to the communicating section  15  in the passage forming substrate  10 . In this embodiment, the reservoir section  32  penetrates through the protective substrate  30  in the thickwise direction so as to extend along the pressure generating chambers  12  disposed in parallel, and, as described above, communicates with the communicating section  15  in the passage forming substrate  10 , thereby constituting the reservoir  100  which is an ink chamber shared by each of the pressure generating chambers  12 . 
     Furthermore, a through hole  33  penetrating through the protective substrate  30  in the thicknesswise direction is provided in a region between the piezoelectric element retaining section  31  and the reservoir  32  in the protective substrate  30 . The ends of the upper electrode film  80  and the lead electrode  90  are exposed to the through hole  33 . In addition, the lower electrode film  60  and the lead electrode  90  (not illustrated) are connected to a driving IC for driving the piezoelectric element  300  through a connecting wire provided to extend into the through hole  33 . 
     The protective substrate  30  uses, for example, glass, a ceramic material, metal, a resin or the like as a material, and is preferably made of a material substantially equal in terms of coefficient of thermal expansion to the passage forming substrate  10 . In this embodiment, the protective substrate  30  is formed of the same silicon single crystal substrate as the passage forming substrate  10 . 
     A compliance substrate  40  consisting of a sealing film  41  and a fixed plate  42  is joined onto the protective substrate  30 . The sealing film  41  is made of a flexible material having low stiffness, and is used to seal one side of the reservoir section  32 . The fixed plate  42  is made of a hard metallic material. The fixed plate  42  includes an opening  43  formed therein, which is formed by removing a region opposite to the reservoir  100  from the fixed plate  42 . Accordingly, one side of the reservoir  100  is sealed only by the flexible sealing film  41 . 
     An ink jet recording head according to this embodiment takes in an ink from an external ink supply unit (not illustrated), fills the reservoir  100  through the nozzle  21  with the ink, and then applies a voltage to the respective piezoelectric element  300  corresponding to each of the pressure generating chambers  12  in accordance with a recording signal from an driving IC (not illustrated) to deform the piezoelectric element  300 , which raises a pressure in the pressure generating chamber  12 , thereby jetting ink droplets through the nozzle  21 . 
     A method of manufacturing the ink jet recording head is described below with reference to  FIGS. 5 through 8 .  FIGS. 5 through 8  are cross-sectional views showing the manufacturing processes of the ink jet recording head. 
     As shown in  FIG. 5(   a ), a silicon dioxide film  51  constituting the elastic film  50  is formed on a surface of a passage forming substrate wafer  110 , a silicon wafer of a silicon single crystal substrate having a crystal face orientation of ( 110 ), and the insulator film  55  consisting of zirconium oxide is formed on the elastic film  50  (silicon dioxide film  51 ). Then, as shown in  FIG. 5(   b ), the lower electrode film  60  is formed by laminating, for example, platinum (Pt) and iridium (Ir) on the insulator film  55  by sputtering, and is patterned into a predetermined pattern. 
     Then, as shown in  FIG. 5(   c ), the piezoelectric layer  70  made of, for example, lead zirconate titanate (PZT) or the like is deposited on the entire surface of the passage forming substrate wafer  110  having the lower electrode film  60  formed thereon. The piezoelectric layer  70  constituting the piezoelectric element  300  uses as a material, for example, a ferroelectric material such as lead zirconate titanate (PZT), or a relaxor ferroelectric to which a metal such as niobium, nickel, magnesium, bismuth or yttrium is added. Selection of its composition depends on the characteristics and applications of the piezoelectric element  300 . Although no limitations are placed on a forming method of the piezoelectric layer  70 , this embodiment forms the piezoelectric layer  70  by using, for example, a so-called sol-gel method where a so-called sol including a metal organic substance dissolved and dispersed in a solvent is coated and dried into a gel which is then calcined at high temperatures to form a metallic oxide which constitutes the piezoelectric layer  70 . Needless to say, a method of forming the piezoelectric layer  70  is not limited to the sol-gel method, and the MOD method or sputtering method, for example, may be used. 
     Then, as shown in  FIG. 5(   d ), the intermediate film  85  made of a conductive material is deposited on the entire surface of the piezoelectric layer  70 . 
     In addition, the piezoelectric layer  70  is patterned together with the intermediate film  85  into a predetermined pattern. Specifically, as shown in  FIG. 6(   a ), a resist is coated on the intermediate film  85 , and the resist is exposed and developed to form a resist film  200  having a predetermined pattern. In other words, a negative resist, for example, is coated on the intermediate film  85  by means of the spin coat method and then exposed, developed, and baked using a predetermined mask to form the resist film  200 . Needless to say, a positive resist may be used instead of the negative resist. In this embodiment, the resist film  200  is formed so as to have its end surface slanted at a predetermined angle. 
     Then, as shown in  FIG. 6(   b ), using the resist film  200  of a protective film as a mask, the piezoelectric layer  70  is patterned together with the intermediate film  85  by ion milling into a predetermined pattern. At this time, the piezoelectric layer  70  and the intermediate film  85  are patterned along the slanted end surface of the resist film  200 . Part of the lower electrode film  60  is exposed, and the exposed portion of the lower electrode film  60  is slightly etched together with the piezoelectric layer  70  and the intermediate film  85 , causing the exposed portion to be somewhat thinner than the other portion of the lower electrode film  60 . 
     Then, as shown in  FIG. 6(   c ), the resist film  200  on the intermediate film  85  is caused to be peeled off. Although no limitations are placed on a method for peeling off the resist film  200 , an organic peeling solution, for example, may be used for this peeling purpose. After that, the resist film  200  is completely removed by washing the surface of the intermediate film  85  with a predetermined cleaning solution. 
     The piezoelectric layer  70  constituting the piezoelectric element  300  can be properly formed by patterning the piezoelectric layer  70  according to these procedures. In the present invention, the resist film  200  is formed on the piezoelectric layer  70  via the intermediate film  85  instead of forming the resist film  200  directly on the piezoelectric layer  70 , and then the piezoelectric layer  70  is patterned using the resist film  200  as a mask. Accordingly, when the resist film  200  is peeled off and washed with an organic peeling solution or a cleaning solution or the like, the intermediate film, for example, plays a role as a barrier layer, resulting in almost no organic peeling solution adhering to the piezoelectric layer  70 . This prevents damage to the piezoelectric layer  70  caused by, for example, an organic peeling solution, a cleaning solution or the like. If the organic peeling solution is an acid or alkaline solution, such an organic peeling solution or a cleaning solution adheres to the piezoelectric layer  70 , which may cause the piezoelectric layer  70  to suffer from, for example, lead deficiency or oxygen defect formation. However, the intermediate film  85  formed on the piezoelectric layer  70  prevents damage to the piezoelectric layer  70 , as described above. 
     No limitations are placed on a material of the intermediate film  85  as long as such a material has a conductive property. More preferably, a metallic material having an ionization tendency equal to or smaller than the upper electrode film  80 , such as iridium, platinum, palladium or the like is used. Most preferably, a metallic material having an ionization tendency smaller than hydrogen, such as iridium, platinum or the like is used. Even if an acid solution is used to peel off and wash the resist film  200 , use of such a material does not allow the acid solution to remove the intermediate film  85 , securely protecting the piezoelectric layer  70 . 
     Since the intermediate film  85  substantially doubles as the upper electrode film  80 , it is preferable that the intermediate film  85  is made of a relatively highly conductive material. Also, preferably the intermediate film  85  is formed to be thin to such a degree that the piezoelectric layer  70  is securely protected. A thickness of, for example, not less than 5 μm and not more than 50 μm is more preferable. This arrangement allows the piezoelectric element  300  to be properly displaced even if the intermediate film  85  is formed on the piezoelectric layer  70 . 
     After the resist film  200  is removed from the intermediate film  85 , the upper electrode film  80  is formed on the entire surface of the passage forming substrate wafer  110 , and then the upper electrode film  80  is patterned into a predetermined pattern to form the piezoelectric element  300 , as shown in  FIG. 7(   a ). 
     No limitations are placed on a material of the upper electrode film  80  as long as such a material has a relatively high conductive property. Preferably, a metallic material, such as iridium, platinum, palladium or the like is used. Also, the upper electrode film  80  should be formed to be thick to such a degree that a displacement of the piezoelectric element  300  is not impeded. Since the upper electrode film  80  doubles as a moisture-resistant protective film for preventing damage to the piezoelectric element  300  caused by water content, it is preferably formed to be relatively thick. Specifically, the upper electrode film  80  is more preferably formed to have a thickness of 30 μm or more. 
     Then, as shown in  FIG. 7(   b ), a gold (Au) lead electrode  90  is formed on the entire surface of the passage forming substrate wafer  110  and patterned for each of the piezoelectric elements  300 . Then, as shown in  FIG. 7(   c ), a protective substrate wafer  130  having a plurality of protective substrates  30  formed in an integral manner is joined to the passage forming substrate wafer  110  with the adhesive  35 . The protective substrate wafer  130  has the piezoelectric element retaining section  31 , the reservoir section  32 , and the through hole  33  formed in advance therein. 
     Then, as shown in  FIG. 8(   a ), the passage forming substrate wafer  110  is thinned into a predetermined thickness. Then, as shown in  FIG. 8(   b ), a protective film  52  of, for example, silicon nitride (SiN) is newly formed on the passage forming substrate wafer  110 , and the protective film  52  is patterned via a predetermined mask into a predetermined pattern. As shown in  FIG. 8(   c ), using the protective film  52  as a mask, the passage forming substrate wafer  110  is anisotropically etched (wet etching) with an alkaline solution such as KOH or the like to form the pressure generating chamber  12 , the ink supply passage  13 , the communicating passage  14 , and the communicating section  15  in the passage forming substrate wafer  110 . 
     After that, unwanted parts (not illustrated) on the peripheral edge of the passage forming substrate wafer  110  and the protective substrate wafer  130  are removed by, for example, die cutting, and the nozzle plate  20  and the compliance substrate  40  are joined to the passage forming substrate wafer  110  and the protective substrate wafer  130 , respectively. Then the passage forming substrate wafer  110  is divided into chips each having a size shown in  FIG. 1  to form an ink jet recording head. 
     An exemplary method of manufacturing an ink jet recording head according to the present invention is described above. The present invention is applicable to an ink jet recording head having a structure where a piezoelectric layer is covered at its top and end surfaces with an upper electrode film. 
     A structure of an ink jet recording head to which the present invention can be applied is described below as another embodiment. 
     (Embodiment 2) 
       FIG. 9  is a cross-sectional view showing a piezoelectric element constituting an ink jet recording head according to Embodiment 2. As shown in  FIG. 9 , in this embodiment, piezoelectric layers  70  are formed in a continuous manner in regions opposite to a plurality of pressure generating chambers  12  provided in parallel. In other words, an ink jet recording head according to Embodiment 2 is the same as that according to Embodiment 1, except that piezoelectric layers  71  thinner than a piezoelectric layer  70  constituting the piezoelectric element  300  are provided among piezoelectric elements  300  formed in parallel. No limitations are placed on the thickness of the piezoelectric layer  71 , which may be determined depending on the amount of displacement of the piezoelectric element  300 . 
     The piezoelectric layers  70  formed in a continuous manner as described above prevent a vibration plate, namely an elastic film  50  and an insulator film  55 , from being subject to damage when the piezoelectric element  300  is driven. Portions of the vibration plate close to the both breadthwise ends of the pressure generating chamber  12  are prone to cracks due to their significant deformation when the piezoelectric element  300  is driven. However, the piezoelectric layers  70  formed in a continuous manner substantially enhance the rigidity of the vibration plate, preventing the vibration plate from cracking 
     As described above, it is preferable that the peripheral edge of the upper electrode film  80  and an exposed surface of the piezoelectric layer  70  are covered with a protective film  150 . 
     (Embodiment 3) 
       FIG. 10  is an exploded perspective view showing the structure of an ink jet recording head according to Embodiment 3.  FIG. 11  is a plan view of an ink jet recording shown in  FIG. 10  and a cross-sectional view taken along the line C-C′.  FIG. 12  is a cross-sectional view showing the structure of a piezoelectric element according to Embodiment 3. The reference numerals and symbols in  FIGS. 10 through 12  refer to the same components as those with the reference numerals and symbols in  FIGS. 1 through 3 , and repeated descriptions of the same components are omitted. 
     An ink jet recording head according to this embodiment is the same as that according to Embodiment 1, except that a lower electrode film  60  constituting the piezoelectric element  300  constitutes a common electrode of the piezoelectric elements  300 , and an upper electrode film  80  constitutes an individual electrode. 
     As shown in figures, in this embodiment, the lower electrode films  60  each having width smaller than that of the pressure generating chambers  12  extend from one lengthwise ends of the pressure generating chambers  12  onto their peripheral walls in regions opposite to the pressure generating chambers  12 , and are coupled together on the peripheral walls to form an electrode common to each of the piezoelectric elements  300 . The end of the lower electrode film  60  at the side of the other lengthwise end of the pressure generating chamber  12  is located in a region opposite to the pressure generating chamber  12 . 
     A piezoelectric layer  70  extends outside of the end of the pressure generating chamber  12  along its lengthwise direction, and completely covers the top and end surfaces of the lower electrode film  60  in a region opposite to the pressure generating chamber  12 . Also, the lower electrode film  60  extends outside of the piezoelectric layer  70  at one lengthwise end of the pressure generating chamber  12 . 
     Each of the upper electrode films  80  having a larger width than the piezoelectric layer  70  is separately provided in a region opposite to each of the pressure generating chambers  12 . In other words, the upper electrode film  80  is divided on partition walls among the pressure generating chambers  12  to form an electrode for each of the piezoelectric elements  300 . Also, the upper electrode film  80  extends from the other lengthwise end of the pressure generating chamber  12  onto the peripheral wall. Accordingly, the top and end surfaces of the piezoelectric layer  70  in a region opposite to the pressure generating chamber  12  are completely covered with the upper electrode film  80 . 
     In this embodiment, the upper electrode film  80  extends outside of the end of the piezoelectric layer  70  at the other lengthwise end of the pressure generating chamber  12 . The end of the upper electrode film  80  is connected to a lead wire  91 , through which a voltage is selectively applied to each of the piezoelectric elements  300 . 
     In a structure according to this embodiment, the distance D 1  between the upper surface of the lower electrode film  60  and the upper surface of the piezoelectric layer  70  and the distance D 2  between the end surface of the lower electrode film  60  and the end surface of the piezoelectric layer  70  also have the relationship of D 2 □D 1  (see  FIG. 12 ). In other words, the thickness D 2  of the piezoelectric layer  70  on the end surface of the lower electrode film  60  is more than the thickness D 1  of the piezoelectric layer  70  formed on the upper surface of the lower electrode film  60 . 
     Needless to say, this arrangement also prevents damage to the piezoelectric element  300  caused by water content or the like. In other words, damage to the piezoelectric layer can securely be prevented irrespective of the structure of the piezoelectric element electrode, which leads to the implementation of an ink jet recording head having improved durability. 
     Furthermore in this embodiment, as shown in  FIG. 13 , piezoelectric layers  70  may be formed in a continuous manner in regions opposite to a plurality of pressure generating chambers  12  provided in parallel, while piezoelectric layers  71  thinner than a piezoelectric layer  70  may be left among piezoelectric elements  300  formed in parallel. 
     In this structure, the end of the upper electrode film  80  and an exposed surface of the piezoelectric layer  70  are preferably covered with a protective film  150 , as described above. Also, in this embodiment, as shown in  FIG. 14 , the surface of the piezoelectric layer  71  exposed on the partition walls among the pressure generating chambers  12  are preferably covered with the protective film  150 . Since part of the piezoelectric layer  71  on the partition wall, namely outside of the pressure generating chamber  12  does not directly contribute to displacement of the piezoelectric element  300 , the surface of the piezoelectric layer  71  exposed on the partition wall is not necessarily covered with the protective film  150 . However, damage to the piezoelectric layer  70  constituting the piezoelectric element  300  can securely be prevented by covering the surface of the piezoelectric layer  71  exposed on the partition wall with the protective film  150 , thereby allowing the piezoelectric element  300  to be properly displaced on a constant basis. 
     An ink jet recording head according to each embodiment described above constitutes part of a recording head unit provided with an ink passage communicating with an ink cartridge or the like, which is then installed to a ink jet recording apparatus.  FIG. 15  is an illustration showing an example of such a recording apparatus. As shown in  FIG. 15 , recording head units  1 A and  1 B each having an ink jet recording head include cartridges  2 A and  2 B constituting an ink supply means removably mounted thereon, and a carriage  3  having the recording head units  1 A and  2 B mounted thereon is provided on a carriage shaft  5  mounted to the apparatus body  4  so as to be movable in the axial direction of the carriage shaft  5 . The recording head units  1 A and  1 B eject, for example, a black ink composition and a color ink composition, respectively. A driving force from a driving motor  6  is transmitted to the carriage  3  via a gear and a timing belt not illustrated, whereby the carriage  3  having the recording head units  1 A and  2 B mounted thereon moves along the carriage shaft  5 . Meanwhile, a platen  8  is provided in the apparatus body  4  along the carriage shaft  5 , and a recording sheet S of recording media such as paper fed by a paper feeding roller not illustrated is transported over the platen  8 . 
     The present invention is detailed above. Needless to say, the present invention is not limited to the embodiments described above. Although an ink jet recording head is described in the embodiments above as an example of a liquid jet head according to the present invention, a fundamental structure of a liquid jet head is not limited to a structure described above. The present invention is applicable to a wide range of liquid jet heads and, needless to say, can be applied to a head for jetting a liquid other than an ink. Other liquid jet heads include, for example, various types of recording heads for use in an image recording apparatus such as a printer, a color material jet head for use in the manufacture of a color filter such as a liquid crystal display, an electrode material jet head for use in the electrode formation of an organic EL display or FED (Field Emission Display) or the like, and a bioorganic compound jet head for use in biochip fabrication.