Patent Publication Number: US-8118412-B2

Title: Liquid ejecting head, liquid ejecting apparatus, and actuator

Description:
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2008-082877, filed Mar. 27, 2008 and Japanese Patent Application No. 2009-006324, filed Jan. 15, 2009, the entire disclosures of which are expressly incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a liquid ejecting head for ejecting droplets from a nozzle in response to the displacement of a piezoelectric element, a liquid ejecting apparatus, and an actuator that includes a piezoelectric element. 
     2. Related Art 
     A representative example of liquid ejecting heads for ejecting droplets is an ink jet recording head. A typical ink jet recording head includes a piezoelectric element disposed on a flow passage forming substrate with a diaphragm interposed therebetween. The flow passage forming substrate includes a pressure generating chamber. The piezoelectric element includes a lower electrode, a piezoelectric layer, and an upper electrode. A displacement of the piezoelectric element generates pressure in the pressure generating chamber, allowing the ink jet recording head to eject ink droplets from a nozzle. It is known that the displacement characteristics of a piezoelectric element used in such an ink jet recording head depend greatly on the crystalline orientation of a piezoelectric layer. Thus, in some proposed piezoelectric elements, the crystals of a piezoelectric layer are appropriately orientated to improve the displacement characteristics (see, for example, JP-A-2004-66600). 
     In some piezoelectric elements that include a lower electrode, a piezoelectric layer, and an upper electrode, the piezoelectric layer tapers downward at its ends (tapered surfaces) (see, for example, JP-A-2007-118193). 
     In a piezoelectric element described in JP-A-2007-118193, although no upper electrode is formed on inclined end faces (hereinafter referred to as a tapered portion) of a piezoelectric layer, a lower electrode is continuously disposed across a plurality of piezoelectric elements. Thus, the tapered portion of the piezoelectric layer undergoes a strong driving electric field and may be damaged. 
     In piezoelectric elements described in JP-A-2004-66600 and JP-A-2007-118193, a lower electrode is continuously disposed across a plurality of piezoelectric elements. In other piezoelectric elements, a lower electrode is patterned for each piezoelectric element, and a piezoelectric layer extends to the outside of the lower electrode (for example, JP-A-2000-32653). 
     In a piezoelectric element described in JP-A-2000-32653, a tapered portion of a piezoelectric layer does not undergo a strong driving electric field and may not be damaged by the driving electric field. However, when a piezoelectric layer described in JP-A-2004-66600 is applied to a piezoelectric element described in JP-A-2000-32653 to improve the displacement characteristics of the piezoelectric element, the piezoelectric layer may be damaged around an end of a lower electrode during the operation of the piezoelectric element probably because of a difference in crystallinity between one portion of the piezoelectric layer on the lower electrode and the other portion of the piezoelectric layer outside the lower electrode (on a diaphragm). Furthermore, the piezoelectric element may have a low response speed and may be difficult to drive at a high speed. 
     Such problems may occur not only in ink jet recording heads for ejecting ink droplets, but also in other liquid ejecting heads for ejecting droplets and actuators that include a piezoelectric element. 
     SUMMARY 
     An advantage of some aspects of the invention is that it provides a liquid ejecting head that includes a piezoelectric element having improved displacement characteristics, can be driven at a high speed, and includes a piezoelectric layer having improved durability to resist damage, a liquid ejecting apparatus, and an actuator. 
     According to one aspect of the invention, a liquid ejecting head includes a flow passage forming substrate that includes a plurality of pressure generating chambers juxtaposed to each other and each in communication with a nozzle for ejecting droplets, and piezoelectric elements disposed on the flow passage forming substrate with a diaphragm interposed therebetween, the piezoelectric elements including a lower electrode, a piezoelectric layer, and an upper electrode, wherein the piezoelectric layer tapers downward at its ends, the lower electrode has a width smaller than the width of each of the pressure generating chambers, the piezoelectric layer has a larger width than the lower electrode to cover end faces of the lower electrode, the diaphragm has a top layer formed of a titanium oxide (TiO x ) insulator film, the lower electrode has a top layer formed of a lanthanum nickel oxide (LaNi y O x ) orientation control layer, and the orientation control layer and at least part of the piezoelectric layer disposed on the orientation control layer are formed of perovskite crystals having a (113) preferred orientation. In such a liquid ejecting head, the piezoelectric layer has high crystallinity. Thus, the piezoelectric element can be driven at a high speed, and the piezoelectric layer has high durability to resist damage. 
     Preferably, the liquid ejecting head further includes a metal layer between the diaphragm and the piezoelectric layer, the metal layer being separated from the lower electrode and having a top layer at least partly formed of the orientation control layer. The metal layer can increase the crystallinity of the piezoelectric layer even in an inactive region in which no lower electrode is formed. This allows the entire piezoelectric layer to be displaced harmoniously, ensuring proper displacement of the piezoelectric element. Thus, the piezoelectric element can be driven at a high speed, and the piezoelectric layer has high durability to resist damage. 
     Preferably, the piezoelectric layer has a rhombohedral, tetragonal, or monoclinic crystal structure. Preferably, at least part of the piezoelectric layer disposed on the orientation control layer is formed of columnar crystals. Preferably, part of the piezoelectric layer disposed on the insulator film is also formed of columnar crystals. These ensure the high speed operation of the piezoelectric element and more securely protect the piezoelectric layer from damage associated with repeated operation of the piezoelectric element. 
     Preferably, the end faces of the lower electrode covered with the piezoelectric layer taper downward. This further increases the crystallinity of the piezoelectric layer at the end faces of the lower electrode. This ensures the high speed operation of the piezoelectric element and more securely protects the piezoelectric layer from damage associated with repeated operation of the piezoelectric element. 
     Preferably, the lower electrode further includes an electroconductive layer under the orientation control layer, the electroconductive layer being formed of a material having a resistivity lower than that of the orientation control layer. Through the electroconductive layer, a sufficient electric current can be supplied to a plurality of piezoelectric elements even when the piezoelectric elements are driven simultaneously. This allows for uniform displacement characteristics of the piezoelectric elements juxtaposed to each other. 
     Preferably, the electroconductive layer is covered with the orientation control layer. Thus, only the orientation control layer of the lower electrode is in contact with the piezoelectric layer. This can more reliably increase the crystallinity of the piezoelectric layer. 
     Preferably, the electroconductive layer is formed of a metallic material, an oxide of a metallic material, or an alloy thereof. Preferably, the metallic material contains at least one element selected from the group consisting of copper, aluminum, tungsten, platinum, iridium, ruthenium, silver, nickel, osmium, molybdenum, rhodium, titanium, magnesium, and cobalt. With these materials, a sufficient electric current can be supplied to the piezoelectric element with higher reliability. 
     Preferably, the piezoelectric layer is mainly composed of lead zirconium titanate (PZT). With such a piezoelectric layer, the piezoelectric element can have excellent displacement characteristics. 
     Preferably, the end faces of the piezoelectric layer are covered with a moisture-resistant protective film. Preferably, the end faces of the piezoelectric layer are covered with the upper electrode. These can prevent the piezoelectric layer from being damaged by atmospheric water. 
     While the electrodes in the piezoelectric element may have any structure, the lower electrodes may be individually disposed on each of the pressure generating chambers as individual electrodes of the piezoelectric element, and the upper electrode may be continuously disposed over the pressure generating chambers as a common electrode of the piezoelectric element. This can improve the displacement characteristics of the piezoelectric element independently of the electrode structure and prevent the piezoelectric layer from being damaged, thus improving the durability of the piezoelectric layer. 
     According to another aspect of the invention, a liquid ejecting apparatus includes a liquid ejecting head according to the invention. Such a liquid ejecting apparatus can include a highly reliable liquid ejecting head. 
     According to still another aspect of the invention, an actuator includes a diaphragm disposed on a substrate, and a piezoelectric element disposed on the diaphragm, the piezoelectric element including a lower electrode, a piezoelectric layer, and an upper electrode, wherein the piezoelectric layer tapers downward at its ends, the piezoelectric layer has a larger width than the lower electrode to cover end faces of the lower electrode, the diaphragm has a top layer formed of a titanium oxide (TiO x ) insulator film, the lower electrode has a top layer formed of a lanthanum nickel oxide (LaNi y O x ) orientation control layer, and the orientation control layer and at least part of the piezoelectric layer disposed on the orientation control layer are formed of perovskite crystals having a (113) preferred orientation. 
     In such an actuator, the piezoelectric layer has high crystallinity. Thus, the actuator can be driven at a high speed, and the piezoelectric layer has high durability to resist damage. In other words, the actuator has both high-speed responsivity and high durability. 
     Preferably, the actuator further includes a metal layer between the diaphragm and the piezoelectric layer, the metal layer being separated from the lower electrode and having a top layer at least partly formed of the orientation control layer. The metal layer can increase the crystallinity of the piezoelectric layer even in an inactive region in which no lower electrode is formed. This allows the entire piezoelectric layer to be displaced harmoniously, ensuring proper displacement of the actuator. In such an actuator, the piezoelectric element can be driven at a high speed, and the piezoelectric layer has higher durability to resist damage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is an exploded perspective view of a recording head according to a first embodiment of the invention. 
         FIG. 2A  is a plan view of the recording head according to the first embodiment. 
         FIG. 2B  is a cross-sectional view of the recording head according to the first embodiment. 
         FIG. 3  is a cross-sectional view of a principal portion of the recording head according to the first embodiment. 
         FIGS. 4A to 4C  are cross-sectional views illustrating a process of manufacturing the recording head according to the first embodiment. 
         FIGS. 5A to 5C  are cross-sectional views illustrating a process of manufacturing the recording head according to the first embodiment. 
         FIGS. 6A to 6C  are cross-sectional views illustrating a process of manufacturing the recording head according to the first embodiment. 
         FIGS. 7A to 7C  are cross-sectional views illustrating a process of manufacturing the recording head according to the first embodiment. 
         FIG. 8  is a cross-sectional view of a principal portion of a recording head according to a second embodiment of the invention. 
         FIG. 9  is an exploded perspective view of a recording head according to a third embodiment of the invention. 
         FIG. 10A  is a plan view of the recording head according to the third embodiment. 
         FIG. 10B  is a cross-sectional view of the recording head according to the third embodiment. 
         FIG. 11  is a cross-sectional view of a principal portion of the recording head according to the third embodiment. 
         FIG. 12A  is a plan view of a recording head according to a fourth embodiment of the invention. 
         FIG. 12B  is a cross-sectional view of the recording head according to the fourth embodiment. 
         FIG. 13  is a schematic view of a recording apparatus according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will be described in detail below. 
     First Embodiment 
       FIG. 1  is an exploded perspective view of an ink jet recording head, which is an example of a liquid ejecting head, according to a first embodiment of the invention. FIG.  2 A is a plan view of the ink jet recording head according to the first embodiment.  FIG. 2B  is a cross-sectional view of the ink jet recording head taken along the line IIB-IIB of  FIG. 2A . 
     A flow passage forming substrate  10  is a single-crystal silicon substrate having a (110) crystal plane orientation. An elastic oxide film  51  is disposed on the flow passage forming substrate  10 . The flow passage forming substrate  10  includes a plurality of pressure generating chambers  12  juxtaposed to each other in the width direction. The pressure generating chambers  12  are divided by partitions  11  and are covered with the elastic film  51 . 
     The flow passage forming substrate  10  further includes ink feed channels  13  defined by the partitions  11  and in communication with respective ends of the pressure generating chambers  12  in the longitudinal direction. The flow passage forming substrate  10  further includes communication paths  14  and a communication portion  15  in communication with the communication paths  14 . The communication portion  15 , together with a reservoir portion  32  in a protective substrate  30  described below, constitutes a reservoir  100 , which is a common ink chamber (liquid chamber) of the pressure generating chambers  12 . 
     The ink feed channels  13  have a cross-sectional area smaller than that of the pressure generating chambers  12  to maintain a constant flow resistance against ink flowing from the communication portion  15  to the pressure generating chambers  12 . For example, flow passages between the reservoir  100  and the pressure generating chambers  12  are narrowed in the proximity of the pressure generating chambers  12  to form the ink feed channels  13  having a width smaller than the pressure generating chambers  12 . While each of the flow passages is narrowed at one side thereof in the present embodiment, each of the flow passages may be narrowed at both sides thereof to form the ink feed channels  13 . Alternatively, instead of reducing the width of the flow passages, the thickness of the flow passages may be reduced to form the ink feed channels  13 . The partitions  11  on opposite sides of each of the pressure generating chambers  12  are extended to the communication portion  15  to define spaces between the ink feed channels  13  and the communication portion  15 , thus forming the communication paths  14 . 
     While the flow passage forming substrate  10  is a single-crystal silicon substrate in the present embodiment, the flow passage forming substrate  10  may be formed of glass ceramic or stainless steel. 
     The bottom surface of the flow passage forming substrate  10  is attached to a nozzle plate  20  with an adhesive or a heat-seal film. The nozzle plate  20  has nozzles  21  near the ends of the pressure generating chambers  12  opposite the ink feed channels  13 . The nozzle plate  20  may be formed of glass ceramic, single-crystal silicon, or stainless steel. 
     The top surface of the flow passage forming substrate  10  is attached to a diaphragm  50 , on which piezoelectric elements  300  are disposed. The piezoelectric elements  300  and the diaphragm  50  constitute an actuator. The operation of the piezoelectric elements  300  causes displacements of the diaphragm  50 . The diaphragm  50  includes the elastic film  51  on the flow passage forming substrate  10  and an insulator film  52  on the elastic film  51 . The insulator film  52  is formed of titanium oxide (TiO x ). 
     The piezoelectric elements  300  disposed on the diaphragm  50  (insulator film  52 ) include a lower electrode film  60 , a piezoelectric layer  70 , and an upper electrode film  80 . The piezoelectric elements  300  may be portions that include at least the piezoelectric layer  70 , as well as the portions composed of the lower electrode film  60 , the piezoelectric layer  70 , and the upper electrode film  80 . In general, one of the lower electrode film  60  and the upper electrode film  80  is a common electrode, and the other is an individual electrode. The individual electrode, together with the piezoelectric layer  70 , is patterned for each of the pressure generating chambers  12 . A region that is composed of the patterned electrode and the piezoelectric layer  70  and in which the application of a voltage between the common electrode and the individual electrode causes a piezoelectric strain is referred to as a piezoelectric active portion  320 . 
     The structure of a piezoelectric element  300  according to the present embodiment will be described in detail below. As illustrated in  FIG. 3 , a lower electrode film  60  is formed as an individual electrode in a region opposite a pressure generating chamber  12 . The lower electrode film  60  has a smaller width than the pressure generating chamber  12 . The lower electrode film  60  tapers downward at its ends. The lower electrode film  60  extends from a portion corresponding to one end of the pressure generating chamber  12  in the longitudinal direction onto a protrusion of a partition  11  defining an ink feed channel  13  (hereinafter referred to as “surrounding wall”) and is connected to a lead electrode  90 , for example, formed of gold (Au) outside the pressure generating chamber  12 . A voltage is selectively applied to each piezoelectric element  300  through the lead electrode  90  (see  FIG. 2 ). 
     A region in which no patterned lower electrode film  60  is formed is referred to as an inactive region  330 . 
     The lower electrode film  60  is composed of an electroconductive layer  61  disposed on the insulator film  52  and an orientation control layer  62  disposed on the electroconductive layer  61 . The orientation control layer  62  is formed of lanthanum nickel oxide (LaNi y O x ). The electroconductive layer  61  is formed of a material having a lower resistivity than the orientation control layer  62 , for example, a metallic material, an oxide of a metallic material, or an alloy thereof. Preferred examples of the metallic material of the electroconductive layer  61  include metallic materials that contain at least one element selected from the group consisting of copper, aluminum, tungsten, platinum, iridium, ruthenium, silver, nickel, osmium, molybdenum, rhodium, titanium, magnesium, and cobalt. 
     Lanthanum nickel oxide (LaNi y O x ) used in the orientation control layer  62  according to the present embodiment is LaNiO 3  (x=3 and y=1). The orientation control layer  62  formed of such a lanthanum nickel oxide is substantially unaffected by the plane orientation of the underlying electroconductive layer  61 . The orientation control layer  62  is formed of perovskite crystals having a (113) preferred orientation. 
     The orientation control layer  62  having such crystallinity may be formed by any method, including sputtering, a sol-gel method, and metal organic deposition (MOD), under appropriate conditions. 
     The piezoelectric layer  70  has a larger width than the lower electrode film  60  and a smaller width than the pressure generating chamber  12 . Thus, the piezoelectric layer  70  is continuously formed on the lower electrode film  60  and the insulator film  52  outside the lower electrode film  60 . The both ends of the piezoelectric layer  70  in the longitudinal direction extend beyond the pressure generating chamber  12  (see  FIG. 2 ). The lower electrode film  60  in a region opposite the pressure generating chamber  12  is covered with the piezoelectric layer  70 . An end of the piezoelectric layer  70  in the longitudinal direction is disposed in the vicinity of one end of the pressure generating chamber  12 . The lower electrode film  60  extends beyond the end of the piezoelectric layer  70  (see  FIG. 2 ). 
     A piezoelectric layer  70   a  disposed on the orientation control layer  62  (lower electrode film  60 ) is formed of perovskite crystals. The piezoelectric layer  70   a  has a (113) crystal plane orientation under the influence of the crystalline orientation of the orientation control layer  62 . More specifically, crystals grow epitaxially on the orientation control layer  62  to form the piezoelectric layer  70  having a (113) crystal plane orientation. Preferably, a piezoelectric layer  70   b  disposed on the insulator film  52  outside the orientation control layer  62  is also formed of perovskite crystals having the (113) crystal plane orientation. 
     The piezoelectric element  300  that includes such a piezoelectric layer  70  having high crystallinity has an improved response speed and high durability. The piezoelectric element  300  can be driven at a high speed, and the reduction in displacement of the piezoelectric element  300  during its repeated operation can be minimized. In general, the displacement of a piezoelectric element is reduced during its repeated operation because of degradation of the piezoelectric element. However, the piezoelectric layer  70  having high crystallinity can minimize the reduction in displacement. 
     Preferably, the piezoelectric layer  70  is entirely formed of perovskite crystals having a (113) crystal plane orientation. However, since the piezoelectric layer  70   b  disposed on the insulator film  52  does not have a substantial effect on the displacement of the piezoelectric element  300 , the piezoelectric layer  70   b  is not necessarily formed of perovskite crystals having a (113) crystal plane orientation. In other words, at least the piezoelectric layer  70   a  disposed on the orientation control layer  62  may be formed of perovskite crystals having a (113) crystal plane orientation. 
     Preferably, the piezoelectric layer  70 , particularly the piezoelectric layer  70   a  disposed on the orientation control layer  62 , has a rhombohedral, tetragonal, or monoclinic crystal structure. Preferably, the piezoelectric layer  70  is formed of columnar crystals. These can minimize the reduction in displacement of the piezoelectric element  300  and allow the piezoelectric element  300  to be driven at a high speed. In the present embodiment, the top layer of the lower electrode film  60  is the orientation control layer  62  formed of lanthanum nickel oxide, the top layer of the diaphragm  50  is the insulator film  52  formed of titanium oxide, and the crystals of the piezoelectric layer  70  are grown from the underlying orientation control layer  62  and insulator film  52 . Thus, the piezoelectric layer  70  having any of the crystal structures described above and formed of columnar crystals can be formed relatively easily. 
     Preferably, the piezoelectric layer  70  is formed of a material that is mainly composed of lead zirconium titanate [Pb(Zr,Ti)O 3 : PZT]. The piezoelectric layer  70  may be formed of a solid solution of lead magnesium niobate and lead titanate [Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3 : PMN-PT] or a solid solution of lead zinc niobate and lead titanate [Pb(Zn 1/3 Nb 2/3 )O 3 —PbTiO 3 : PZN-PT]. The piezoelectric layer  70  may be composed of any material formed of perovskite crystals. 
     The piezoelectric layer  70  may be produced by any method, including a sol-gel method and MOD. The production conditions of the piezoelectric layer  70 , such as deposition conditions and heating (firing) conditions, may be appropriately controlled to form the piezoelectric layer  70  having the crystallinity as described above. 
     As described above, the end faces of the lower electrode film  60  are not perpendicular but are inclined relative to the surface of the diaphragm  50  (see  FIG. 3 ). Preferably, the end faces of the lower electrode film  60  form an angle in the range of 10° to 30° with the surface of the diaphragm  50 . Within this angle range, the piezoelectric layer  70  can be satisfactorily formed on the end faces of the lower electrode film  60 . This ensures more uniform crystallinity across the piezoelectric layer  70 . Thus, the reduction in displacement of the piezoelectric element  300  and the diaphragm  50  can be more properly minimized. 
     Since the lower electrode film  60  includes the electroconductive layer  61  having a lower resistivity than the orientation control layer  62 , as described above, a sufficient electric current can be supplied to a plurality of piezoelectric elements  300  even when the piezoelectric elements  300  are driven simultaneously. Thus, even when a plurality of piezoelectric elements  300  juxtaposed to each other are driven simultaneously, each of the piezoelectric elements  300  consistently has substantially the same displacement characteristics. 
     The upper electrode film  80  is continuously formed in a region opposite the pressure generating chambers  12  and extends from the other end of the pressure generating chambers  12  in the longitudinal direction onto the surrounding wall. Thus, the upper electrode film  80  almost entirely covers the top and end faces of the piezoelectric layers  70  in the region opposite the pressure generating chambers  12 . The upper electrode film  80  therefore substantially prevents atmospheric water (moisture) from entering the piezoelectric layers  70 . This protects the piezoelectric elements  300  (piezoelectric layers  70 ) from damage caused by water (moisture), thus significantly improving the durability of the piezoelectric elements  300 . 
     The protective substrate  30  is attached with an adhesive  35  to the flow passage forming substrate  10 , on which the actuator composed of the diaphragm  50  and the piezoelectric elements  300  is formed. The protective substrate  30  includes a piezoelectric element holding portion  31  in a region opposite the piezoelectric elements  300 . The piezoelectric element holding portion  31  has a space so as not to prevent the displacement of the piezoelectric elements  300 . The piezoelectric element holding portion  31  houses the piezoelectric elements  300  to protect the piezoelectric elements  300  from the effects of the external environment. The protective substrate  30  includes the reservoir portion  32  in correspondence with the communication portion  15  in the flow passage forming substrate  10 . The reservoir portion  32  is opened at the top of the protective substrate  30  and extends in the width direction. As described above, the reservoir portion  32  and the communication portion  15  in the flow passage forming substrate  10  constitute the reservoir  100 , which serves as a common ink chamber for the pressure generating chambers  12 . 
     A through-hole  33  in the protective substrate  30  is disposed between the piezoelectric element holding portion  31  and the reservoir portion  32 . An end of the lower electrode film  60  and an end of the lead electrode  90  are exposed in the through-hole  33 . The lower electrode film  60  and the lead electrode  90  are connected to a driving IC (not shown) for driving the piezoelectric elements  300  via interconnecting wiring in the through-hole  33 . 
     The protective substrate  30  may be formed of glass, a ceramic material, metal, or resin. Preferably, the material of the protective substrate  30  has substantially the same thermal expansion coefficient as the flow passage forming substrate  10 . In the present embodiment, the protective substrate  30  is formed of the same material as the flow passage forming substrate  10 , that is, silicon single crystals. 
     The protective substrate  30  is attached to a compliance substrate  40 , which includes a sealing film  41  and a fixing plate  42 . The sealing film  41  is formed of a flexible material and seals one side of the reservoir portion  32 . The fixing plate  42  is formed of a hard material, such as metal. The fixing plate  42  has an opening  43  on top of the reservoir  100 . Thus, one side of the reservoir  100  is sealed with the flexible sealing film  41  alone. 
     In the ink jet recording head according to the present embodiment, the reservoir  100  to the nozzles  21  are filled with ink supplied from an external ink supply unit (not shown). A voltage is applied to piezoelectric elements  300  in response to a recording signal from the driving IC (not shown) to deform the piezoelectric elements  300 . The deformation increases the pressure in the corresponding pressure generating chambers  12 , allowing the ink jet recording head to eject ink droplets from the corresponding nozzles  21 . 
     A method for manufacturing an ink jet recording head will be described below with reference to  FIGS. 4 to 7 .  FIGS. 4 to 7  are cross-sectional views illustrating processes for manufacturing an ink jet recording head. 
     As illustrated in  FIG. 4A , a diaphragm  50  is formed on a wafer  110  for a flow passage forming substrate. The wafer  110  is formed of silicon single crystals having a (110) crystal plane orientation. More specifically, first, an elastic film  51  of a silicon dioxide film  53  is formed. For example, the surface of the wafer  110  is thermally oxidized to form the elastic film  51  (silicon dioxide film  53 ). The elastic film  51  may be formed by another method. An insulator film  52  formed of titanium oxide (TiO x ) is formed on the elastic film  51  (silicon dioxide film  53 ) by any method, for example, sputtering. 
     The insulator film  52  of the diaphragm  50  also serves to prevent a lead component in a piezoelectric layer  70  of a piezoelectric element  300  from diffusing into the elastic film  51  and the flow passage forming substrate  10 . 
     As illustrated in  FIG. 4B , a lower electrode film  60  is formed on the diaphragm  50  (insulator film  52 ). The lower electrode film  60  includes an electroconductive layer  61  and an orientation control layer  62 . The lower electrode film  60  is patterned into a predetermined shape. More specifically, for example, a metallic material, such as platinum (Pt), is deposited on the insulator film  52  by sputtering to form the electroconductive layer  61 . The orientation control layer  62  formed of lanthanum nickel oxide is formed on the electroconductive layer  61 . The orientation control layer  62  and the electroconductive layer  61  are then successively patterned. 
     As described above, the orientation control layer  62  may be formed by sputtering, a sol-gel method, or MOD. The deposition conditions can be appropriately controlled to form the orientation control layer  62  having the crystallinity described above. 
     As illustrated in  FIG. 4C , a piezoelectric layer  70 , for example, formed of lead zirconium titanate (PZT) is formed over the entire surface of the wafer  110  for a flow passage forming substrate on which the lower electrode film  60  has been formed. The piezoelectric layer  70  may be formed by any method. In the present embodiment, the piezoelectric layer  70  is formed by a sol-gel method in the following manner. First, an organometallic compound is dissolved or dispersed in a solvent to prepare a so-called sol. The sol is applied over the wafer  110 , is dried for gelation, and is fired at a high temperature to form the piezoelectric layer  70  formed of metal oxide. Alternatively, the piezoelectric layer  70  may be formed by MOD or sputtering. 
     The production conditions of the piezoelectric layer  70 , such as deposition conditions and heating (firing) conditions, may be appropriately controlled to form the piezoelectric layer  70  having the crystallinity as described above. 
     The piezoelectric layer  70  is then patterned into a predetermined shape. More specifically, as illustrated in  FIG. 5A , a resist is applied to the piezoelectric layer  70 , is exposed, and is developed to form a resist film  200  having a predetermined pattern. For example, a negative resist is applied to the piezoelectric layer  70  by spin coating, is exposed through a mask, is developed, and is baked to form the resist film  200 . The negative resist may be replaced by a positive resist. The resist film  200  has end faces inclined with a predetermined angle. 
     As illustrated in  FIG. 5B , the piezoelectric layer  70  is patterned into a predetermined shape by ion milling using the resist film  200  as a mask. The piezoelectric layer  70  is patterned along the inclined end faces of the resist film  200 . Thus, the piezoelectric layer  70  also has inclined end faces. 
     As illustrated in  FIG. 5C , the resist film  200  is removed from the piezoelectric layer  70  by any method, for example, using an organic stripping solution. The piezoelectric layer  70  is washed, for example, with a cleaning liquid to completely remove the resist film  200 . 
     As illustrated in  FIG. 6A , an upper electrode film  80  is formed over the entire surface of the wafer  110  for a flow passage forming substrate and is patterned into a predetermined shape to produce a piezoelectric element  300 . The upper electrode film  80  may be formed of any material having relatively high electrical conductivity, preferably, a metallic material, such as iridium, platinum, or palladium. The upper electrode film  80  has such a thickness that the upper electrode film  80  does not interfere with the displacement of the piezoelectric element  300 . However, it is desirable that the upper electrode film  80  has a relatively large thickness because the upper electrode film  80  also functions as a moisture-resistant protective film that protects the piezoelectric layer  70  from damage caused by water. 
     As illustrated in  FIG. 6B , a gold (Au) lead electrode  90  is formed over the entire surface of the wafer  110  for a flow passage forming substrate and is patterned for each of the piezoelectric elements  300 . As illustrated in  FIG. 6C , a wafer  130  for a protective substrate, in which a plurality of protective substrates  30  are integrated, is attached to the wafer  110  for a flow passage forming substrate with an adhesive  35 . The wafer  130  for a protective substrate includes a preformed piezoelectric element holding portion  31 , a preformed reservoir portion  32 , and a preformed through-hole  33 . 
     As illustrated in  FIG. 7A , the thickness of the wafer  110  for a flow passage forming substrate is reduced. As illustrated in  FIG. 7B , a protective film  55 , for example, formed of silicon nitride (SiN x ) is formed on the wafer  110  for a flow passage forming substrate and is patterned into a predetermined shape using a mask. As illustrated in  FIG. 7C , the wafer  110  for a flow passage forming substrate is anisotropically etched (wet-etched), for example, with an alkaline solution, such as KOH, using the protective film  55  as a mask to form pressure generating chambers  12 , ink feed channels  13 , communication paths  14 , and a communication portion  15 . 
     Although not shown in the drawings, unnecessary portions on the periphery of the wafer  110  for a flow passage forming substrate and the wafer  130  for a protective substrate are removed, for example, by dicing. A nozzle plate  20  is then attached to the wafer  110  for a flow passage forming substrate. A compliance substrate  40  is then attached to the wafer  130  for a protective substrate. The wafer  110  for a flow passage forming substrate is finally divided into chips as illustrated in  FIG. 1  to manufacture ink jet recording heads. 
     Second Embodiment 
       FIG. 8  is a cross-sectional view of a principal portion of an ink jet recording head according to a second embodiment. 
     An ink jet recording head according to the present embodiment has the same structure as in the first embodiment except for the lower electrode film  60 . In the first embodiment, the orientation control layer  62  is formed on the electroconductive layer  61  (top surface). In the present embodiment, as illustrated in  FIG. 8 , an orientation control layer  62 A is formed on the top and end faces of an electroconductive layer  61 ; that is, the orientation control layer  62 A covers the electroconductive layer  61 , in the lower electrode film  60 . 
     Thus, a piezoelectric layer  70  is formed on the orientation control layer  62 A even at the end faces of the lower electrode film  60 . This further increases the crystallinity of the piezoelectric layer  70  at the ends of the lower electrode film  60 . 
     Third Embodiment 
       FIG. 9  is an exploded perspective view of an ink jet recording head according to a third embodiment of the invention.  FIG. 10A  is a plan view of the ink jet recording head.  FIG. 10B  is a cross-sectional view of the ink jet recording head taken along the line XB-XB of  FIG. 10A . FIG.  11  is a cross-sectional view of a principal portion of the ink jet recording head. The same components in  FIGS. 9 to 11  as in  FIGS. 1 to 3  are denoted by the same reference numerals and will not be further described. 
     An ink jet recording head according to the present embodiment has the same structure as in the first embodiment except that a lower electrode film  60 A constitutes a common electrode and upper electrode films  80 A constitute individual electrodes in a piezoelectric element  300 . 
     As illustrated in  FIG. 9 , a lower electrode film  60 A constitutes a common electrode of the piezoelectric elements  300 . Branches of the lower electrode film  60 A extend from each end of pressure generating chambers  12  in the longitudinal direction onto surrounding walls in regions opposite the pressure generating chambers  12 . The branches of the lower electrode film  60 A have a smaller width than the pressure generating chambers  12 . The branches of the lower electrode film  60 A are connected to lead electrodes  91  on the surrounding walls. The ends of the branches of the lower electrode film  60 A adjacent the other ends of the pressure generating chambers  12  in the longitudinal direction are disposed in regions opposite the pressure generating chambers  12 . 
     As illustrated in  FIG. 10B , a piezoelectric layer  70  extends beyond both ends of a pressure generating chamber  12  in the longitudinal direction, thus completely covering the top and end faces of a lower electrode film  60 A in a region opposite the pressure generating chamber  12 . The lower electrode film  60 A extends beyond the piezoelectric layer  70  at one end of the pressure generating chamber  12  in the longitudinal direction. 
     The upper electrode films  80 A have a larger width than the piezoelectric layers  70  and are disposed separately in a region opposite each of the pressure generating chambers  12 . Thus, the upper electrode films  80 A are divided by partitions  11  between the pressure generating chambers  12 , thus constituting individual electrodes of the piezoelectric elements  300 . The upper electrode films  80 A extend from the other ends of the pressure generating chambers  12  in the longitudinal direction onto the surrounding walls. 
     The upper electrode films  80 A extend beyond the ends of the piezoelectric layers  70  at the other ends of the pressure generating chambers  12  in the longitudinal direction. The upper electrode films  80 A are connected to the lead electrodes  91 . A voltage is selectively applied to each of the piezoelectric elements  300  through the corresponding lead electrodes  90 . 
     Also in the structure according to the present embodiment, the piezoelectric layers  70  having high crystallinity allow the piezoelectric elements  300  to be driven at a high speed and prevent the piezoelectric layers  70  from being damaged, thus improving the durability of the piezoelectric layers  70 . Furthermore, the upper electrode films  80 A covering the piezoelectric layers  70  protect the piezoelectric elements  300  from damage caused by water and other foreign substances. Hence, the ink jet recording head can be securely protected against damage of the piezoelectric layers  70  and have improved durability, independently of the structure of electrodes in the piezoelectric elements  300 . 
     Fourth Embodiment 
       FIG. 12A  is a plan view of an ink jet recording head according to a fourth embodiment of the invention.  FIG. 12B  is a cross-sectional view of a principal portion of the ink jet recording head taken along the line XIIB-XIIB of  FIG. 12A . The same components in  FIGS. 12A and 12B  as in  FIGS. 1 to 3  in the first embodiment are denoted by the same reference numerals and will not be further described. 
     An ink jet recording head according to the present embodiment has the same structure as in the first embodiment except that, in addition to the lower electrode film  60 , a metal layer  65  separated from the lower electrode film  60  is disposed between the diaphragm  50  and the piezoelectric layer  70 . 
     In  FIG. 12B , the metal layer  65  is disposed between the diaphragm  50  and the piezoelectric layer  70  in a region in which no lower electrode film  60  is formed. The metal layer  65  is separated from and is not electrically connected to the lower electrode film  60 . 
     While the metal layer  65  has a rectangular top surface in the present embodiment, the metal layer  65  may have a top surface of any shape provided that the metal layer  65  is separated from the lower electrode film  60 . Likewise, the metal layer  65  may have a trapezoidal cross section as in the lower electrode film  60 , as well as the rectangular cross section in the present embodiment. 
     The metal layer  65  has a two-layer structure, in which a orientation control layer  62  is disposed on an electroconductive layer  61 , as in the lower electrode film  60 . The electroconductive layer  61  and the orientation control layer  62  may be formed of the same material as in the first embodiment. The electroconductive layer  61  may be formed of another material. The orientation control layer  62  improves the crystallinity of the piezoelectric layer  70   b  even in an inactive region  330  in which no lower electrode film  60  is formed. This allows the entire piezoelectric layer  70  to be displaced harmoniously, ensuring proper displacement of the piezoelectric layer  70 . Thus, the piezoelectric element  300  can be driven at a high speed, and the piezoelectric layer  70  has higher durability to resist damage. 
     As in the lower electrode film  60  illustrated in  FIG. 8  in the second embodiment, the orientation control layer  62  may cover the electroconductive layer  61 . 
     Thus, the piezoelectric layer  70  is formed on the orientation control layer  62  even at the end faces of the metal layer  65 . This further increases the crystallinity of the piezoelectric layer  70 . 
     Other Embodiments 
     While the embodiments of the invention have been described, the invention is not limited to these embodiments. 
     For example, while the lower electrode film  60  has a two-layer structure composed of the electroconductive layer  61  and the orientation control layer  62  in the embodiments described above, the lower electrode film  60  may have another structure. The electroconductive layer  61  may have any structure, for example, a multilayer structure, provided that the top layer is an orientation control layer  62  formed of lanthanum nickel oxide. 
     Likewise, while the diaphragm  50  has a two-layer structure composed of the elastic film  51  and the insulator film  52  in the embodiments described above, the diaphragm  50  may have another structure. For example, an additional layer may be disposed between the elastic film  51  and the insulator film  52  or between the elastic film  51  and the flow passage forming substrate  10  provided that the top layer is the insulator film  52  formed of titanium oxide. 
     Furthermore, while the upper electrode film  80  covers the piezoelectric layer  70  to protect the piezoelectric layer  70  from damage caused by water in the first embodiment, the upper electrode film  80  may have another structure. For example, the upper electrode film  80  may be disposed only in a region opposite the lower electrode film  60 . In this case, a portion of the piezoelectric layer  70  not covered with the upper electrode film  80  may be covered with a protective film formed of a moisture-resistant material, such as aluminum oxide, to protect the piezoelectric layer  70  from damage caused by water. 
     The ink jet recording head according to any one of the embodiments described above can be installed in an ink jet recording apparatus, which is an example of liquid ejecting apparatuses, as one component of a recording head unit that includes an ink path in communication with an ink cartridge.  FIG. 13  is a schematic view of an ink jet recording apparatus according to an embodiment of the invention. Recording head units  1 A and  1 B, which include an ink jet recording head, house removable cartridges  2 A and  2 B, which constitute an ink supply unit. A carriage  3 , which includes the recording head units  1 A and  1 B, is mounted on a carriage shaft  5  attached to a main body  4  of the apparatus. The carriage  3  can move in the axial direction. For example, the recording head units  1 A and  1 B eject a black ink composition and a color ink composition, respectively. When the driving force of a drive motor  6  is transferred to the carriage  3  via a plurality of gears (not shown) and a timing belt  7 , the carriage  3  including the recording head units  1 A and  1 B is moved along the carriage shaft  5 . The main body  4  of the apparatus includes a platen  8  along the carriage shaft  5 . A recording sheet S, which is a recording medium, such as paper, fed by a feed roller (not shown) is transported over the platen  8 . 
     While ink jet recording heads have been described in the embodiments described above as liquid ejecting heads according to the invention, the liquid ejecting head may be of any other type. The invention is directed to a wide variety of liquid ejecting heads and may be applied to the ejection of liquid other than ink. Examples of the liquid ejecting heads include recording heads for use in image recording apparatuses, such as a printer, coloring material ejecting heads for use in the manufacture of color filters for a liquid crystal display, electrode material ejecting heads for use in the formation of electrodes for an organic EL display and a field emission display (FED), and bioorganic compound ejecting heads for use in the manufacture of biochips. 
     The invention can be applied not only to an actuator installed in a liquid ejecting head, such as an ink jet recording head, but also to actuators installed in other apparatuses.