Patent Publication Number: US-7210769-B2

Title: Liquid jet head and liquid jet apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid jet head and a liquid jet apparatus, and more particularly, to an inkjet recording head and an inkjet recording apparatus, in which a part of pressure generating chambers which communicate with nozzle orifices ejecting ink droplets is formed of a vibration plate, piezoelectric elements are formed on a surface of this vibration plate, and the ink droplets are ejected by displacement of the piezoelectric elements. 
     2. Description of the Related Art 
     In an inkjet recording head, a part of pressure generating chambers communicating with nozzle orifices ejecting ink droplets is formed of a vibration plate, this vibration plate is deformed by piezoelectric elements, ink in pressure generating chambers is pressurized and thus ink droplets are ejected from nozzle orifices. There are two types of inkjet recording heads which have been put to practical use, which include: one using a piezoelectric actuator of a longitudinal vibration mode, which extends and contracts in an axial direction of a piezoelectric element; and one using a piezoelectric actuator of a flexure vibration mode. 
     As the one using the actuator of the flexure vibration mode, there is one, for example, in which a uniform piezoelectric material layer is formed across an entire surface of a vibration plate by use of a deposition technology, this piezoelectric material layer is cut into a shape corresponding to pressure generating chambers by use of a lithography method, and piezoelectric elements are formed so as to be independent for each of the pressure generating chambers (for example, see Patent Document 1) Moreover, the piezoelectric element used in the above-described actuator of the flexure vibration mode includes a lower electrode that is a common electrode, a piezoelectric layer formed on the lower electrode and an upper electrode that is an individual electrode formed on the piezoelectric layer. 
     In such a conventional inkjet recording head, the lower electrode is provided so as to be common to a plurality of piezoelectric elements. Thus, when a number of ink droplets are ejected all at once by simultaneously driving a number of piezoelectric elements, a voltage drop occurs and a displacement amount of the piezoelectric elements becomes unstable. Consequently, there arises a problem that an ink ejecting property is deteriorated. Moreover, if the piezoelectric elements are arranged densely, for example, it is required to narrow a width of wiring drawn out from the lower electrode between the piezoelectric elements. Accordingly, when the Wiring width is narrowed, wiring resistance (resistance value) is increased, thus causing such problem as described above. 
     Moreover, since the lower electrode formed of a thin film has a thin film thickness, the wiring resistance is increased as in the case of narrowing the wiring width. Thus, there arises a problem that the ink ejecting property is deteriorated. Note that this problem can be solved by forming the lower electrode to have a large film thickness. However, the lower electrode serves also as a vibration plate in a region facing the pressure generating chambers. Accordingly, when the film thickness of the lower electrode is increased, there arises a problem that a displacement amount of the vibration plate due to drive of the piezoelectric element is lowered. Note that, needless to say, such problems as described above similarly arise not only in the inkjet recording head ejecting ink droplets but also in other liquid jet heads ejecting liquid droplets other than ink. 
     [Patent Document 1] 
     Japanese Patent Laid-Open No. 2002-225290 (Page 5, FIGS. 1 and 2) 
     SUMMARY OF THE INVENTION 
     In consideration of the circumstances as described above, an object of the present invention is to provide a liquid jet head and a liquid jet apparatus, which can obtain a good and stable liquid ejecting property while preventing lowering of a displacement amount of a vibration plate. 
     A first aspect of the present invention for achieving the foregoing object is a liquid jet head which includes: a passage-forming substrate in which pressure generating chambers communicating with nozzle orifices ejecting liquids are formed; and piezoelectric elements provided on one side of the passage-forming substrate with a vibration plate interposed between the elements and the substrate, and each of the piezoelectric elements includes a lower electrode, a piezoelectric layer and an upper electrode. In the liquid jet head, a plurality of pressure generating chambers are arranged in a width direction thereof, and the lower electrode is continuously provided from a region facing the pressure generating chambers to a region facing compartment walls at both sides in the width direction of the pressure generating chambers. The liquid jet head includes a lead electrode for lower electrode, which is drawn out from the lower electrode in the region facing the compartment walls. The lead electrode for lower electrode at least includes a first lead electrode having a width which is either equivalent to or narrower than that of the compartment wall and a second lead electrode which is formed on the first lead electrode and is wider than the first lead electrode. 
     In the first aspect, since the second lead electrode is formed to be wider than the first lead electrode, a wiring resistance (resistance value) is surely lowered, compared to the case where the second lead electrode is formed to have the same width as that of the first lead electrode. Moreover, the width of the first lead electrode is equivalent to or narrower than that of the compartment wall, and the first lead electrode is never formed in the region facing a pressure generating chamber. Thus, lowering of a displacement amount of the vibration plate due to drive of piezoelectric elements is surely prevented. 
     A second aspect of the present invention is the liquid jet head according to the first aspect, characterized in that the second lead electrode is wider than the compartment wall. 
     In the second aspect, since the second lead electrode is wider than the compartment wall, the wiring resistance (resistance value) is surely lowered. 
     A third aspect of the present invention is the liquid jet head according to one of the first and second aspects, characterized in that at least the piezoelectric elements and the lead electrode for lower electrode are covered with an insulating film made of an insulating material, and a width of the second lead electrode on its upper surface side is wider than a width thereof on the first lead electrode side. 
     In the third aspect, since the width of the second lead electrode on the first lead electrode side is formed to be narrower than that on the upper surface side, the insulating material easily enters into a periphery of the first lead electrode. Accordingly, the periphery of the first lead electrode is surely covered with the insulating film. Thus, destruction of the piezoelectric element (the piezoelectric layer) attributable to moisture and the like is surely prevented. 
     A fourth aspect of the present invention is the liquid jet head according to any one of the first to third aspects, characterized in that the first lead electrode serves also as an adhesion layer made of adherent metal for closely bonding at least the lower electrode and the second lead electrode. 
     In the fourth aspect, adhesion at least between the lower electrode and the second lead electrode is enhanced. 
     A fifth aspect of the present invention is the liquid jet head according to the fourth aspect, characterized in that the first lead electrode is formed by side etching in a state where the second lead electrode is closely bonded on the first lead electrode. 
     In the fifth aspect, the width of the first lead electrode can be relatively easily and surely formed to be narrower than that of the second lead electrode. 
     A sixth aspect of the present invention is the liquid jet head according to any one of the first to fifth aspects, characterized in that the pressure generating chambers are formed in a single crystal silicon substrate by anisotropic etching and respective layers of the piezoelectric element are formed by deposition and a lithography method. 
     In the sixth aspect, even if the lower electrode is thinly formed, the wiring resistance is surely lowered by forming the second lead electrode to be wider than the first lead electrode drawn out from the lower electrode. Moreover, if the lower electrode is set to function as the vibration plate, the resistance value can be lowered without forming the lower electrode to be thick. Thus, lowering of the displacement amount of the vibration plate due to drive of piezoelectric elements is surely prevented. 
     A seventh aspect of the present invention is a liquid jet apparatus including the liquid jet head according to any one of the first to sixth aspects. 
     In the seventh aspect, a liquid jet apparatus with improved reliability is relatively easily realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a recording head according to Embodiment 1. 
         FIGS. 2(A) and 2(B)  are a plan and cross-sectional view of the recording head according to Embodiment 1. 
         FIGS. 3(A) and 3(B)  are a plan and cross-sectional view showing a main part of the recording head according to Embodiment 1. 
         FIGS. 4(A) to 4(D)  are cross-sectional views showing steps of manufacturing the recording head according to Embodiment 1. 
         FIGS. 5(A) to 5(C)  are cross-sectional views showing steps of manufacturing the recording head according to Embodiment 1. 
         FIG. 6  is a cross-sectional view showing a step of manufacturing the recording head according to Embodiment 1. 
         FIG. 7  is a cross-sectional view showing a main part of a recording head according to Embodiment 2. 
         FIG. 8  is a schematic view of a recording apparatus according to an embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described in detail below based on embodiments. 
     Embodiment 1 
       FIG. 1  is an exploded perspective view showing an inkjet recording head according to Embodiment 1 of the present invention.  FIGS. 2(A) and 2(B)  are a plan and cross-sectional view of  FIG. 1 . As shown in  FIG. 1 , a passage-forming substrate  10  is made of a single crystal silicon substrate of plane orientation (110) in this embodiment and, on one surface thereof, an elastic film  50  with a thickness of 1 to 2 μm, which is made of silicon dioxide previously formed by thermal oxidation, is formed. In this passage-forming substrate  10 , pressure generating chambers  12  are arranged in a width direction thereof by performing anisotropic etching of the single crystal silicon substrate from the other surface thereof. Moreover, on the outside in a longitudinal direction of the pressure generating chambers  12  in the passage-forming substrate  10 , a communicating portion  13  is formed, which communicates with a reservoir portion in a protective plate to be described later and constitutes a part of a reservoir to be a common ink chamber of the respective pressure generating chambers  12 . The communicating portion  13  and the respective pressure generating chambers  12  are communicated with each other through ink supply paths  14 , each of which is provided for each of the pressure generating chambers  12 . 
     Here, anisotropic etching is performed by utilizing a difference in an etching rate of the single crystal silicon substrate. For example, in this embodiment, when the single crystal silicon substrate is dipped in an alkaline solution such as KOH, the substrate is gradually eroded and there appear a first plane (111) perpendicular to the plane (110) and a second plane (111) positioned at about a 70-degree angle with this first plane (111) and at about a 35-degree angle with the foregoing plane (110). Thus, the anisotropic etching is performed by utilizing a characteristic that an etching rate of the planes (111) is about 1/180 as compared with that of the plane (110). By use of the anisotropic etching, high-precision processing can be performed on the basis of a depth processing in a parallelogram shape, which is formed by two of the first planes (111) and two of the oblique second planes (111). The pressure generating chambers  12  can be arranged with high density. 
     In this embodiment, long sides of each pressure generating chamber  12  are formed of first planes (111) and short sides thereof are formed of second planes (111). This pressure generating chamber  12  is formed by performing etching up to the elastic film  50  while nearly penetrating the passage-forming substrate  10 . Here, an extremely small part of the elastic film  50  is dipped in the alkaline solution used for etching the single crystal silicon substrate. Moreover, each of the ink supply paths  14  is formed to have a width narrower than that of a pressure generating chamber  12 . Accordingly, a passage resistance of ink flowing into the pressure generating chamber  12  from the communicating portion  13  is maintained constant. 
     Moreover, on the open face side of the passage-forming substrate  10 , a nozzle plate  20  having nozzle orifices  21  drilled therein is fixed by use of an adhesive agent, a thermowelding film or the like, with an insulating film  51  interposed therebetween. Specifically, the insulating film  51  is used as a mask in the formation of the pressure generating chambers  12 , and the nozzle orifices  21  communicate with the vicinity of end portions of the pressure generating chambers  12  at the opposite side to the ink supply paths  14 . Note that the nozzle plate  20  is made of glass ceramics, stainless steel, or the like having a thickness of, for example, 0.01 to 1 mm and a linear expansion coefficient of, for example, 2.5 to 4.5 [×10 −6 /degree C.] at 300 degree C. or less. 
     Meanwhile, on the side opposite to the open face of the passage-forming substrate  10  as described above, the elastic film  50  having a thickness of, for example, about 1.0 μm is formed as described above. On this elastic film  50 , an insulation film  55  having a thickness of, for example, about 0.4 μm is formed. Furthermore, on this insulation film  55 , a lower electrode film  60  having a thickness of, for example, about 0.2 μm, a piezoelectric layer  70  having a thickness of, for example, about 1.0 μm and an upper electrode film  80  having a thickness of, for example, about 0.05 μm are laminated by a process to be described later to constitute a piezoelectric element  300 . Here, the piezoelectric element  300  means a part including the lower electrode film  60 , the piezoelectric layer  70  and the upper electrode film  80 . In general, the piezoelectric element  300  is formed by using any one of the electrodes thereof as a common electrode and patterning the other electrode and the piezoelectric layer  70  for each of the pressure generating chambers  12 . Consequently, here, a part which includes the patterned electrodes and the piezoelectric layer  70  and in which piezoelectric strain is caused by voltage application to both the electrodes is called a piezoelectric active portion. In this embodiment, the lower electrode film  60  is used as the common electrode of the piezoelectric element  300  and the upper electrode film  80  is used as an individual electrode thereof. However, there is no harm in reversing this order for convenience of a drive circuit and wiring. In either case, the piezoelectric active portion comes to be formed in each of the pressure generating chambers  12 . Moreover, here, the piezoelectric element  300  and the vibration plate undergoing displacement by drive of the piezoelectric element  300  are collectively referred to as a piezoelectric actuator. Note that, in the example described above, the elastic film  50 , the insulation film  55  and the lower electrode film  60  function as the vibration plate. 
     Furthermore, in this embodiment, as shown in  FIGS. 2A ,  3 (A) and  3 (B), a lead electrode for upper electrode  90  is connected in the vicinity of one end of the upper electrode film  80 . In this embodiment, the lead electrode for upper electrode  90  is extended to the vicinity of the communicating portion  13  from above a piezoelectric inactive portion on the outside of the pressure generating chamber  12 . A tip of the lead electrode for upper electrode  90  is set to be a connection portion  90   a  to which a connection wiring  130  is connected, as in the case of the lower electrode film  60 . Meanwhile, the lower electrode film  60  is formed in a region facing a pressure generating chamber  12  in the longitudinal direction of the pressure generating chamber  12  and is continuously provided in a region corresponding to the plurality of pressure generating chambers  12 . Moreover, the lower electrode film  60  is extended to the vicinity of the communicating portion  13  from the outside of the array of the pressure generating chambers  12 . A tip of the lower electrode film  60  is set to be a connection portion  60   a  to which the connection wiring  130  is connected, the connection wiring  130  being extended from a drive IC  120  to be described later. Furthermore, a lead electrode for lower electrode  100  to be electrically connected to the lower electrode film  60  is extended from a space between the piezoelectric elements  300  in which the lower electrode film  60  is provided. A tip of this lead electrode for lower electrode  100  is set to be a connection portion  100   a  with the connection wiring  130 . 
     The lead electrode for lower electrode  100  is provided in a region facing compartment walls  11  and includes: a first lead electrode  101  which is made of, for example, adherent metal such as titanium tungsten (TiW) and has one end extended to a region facing the ink supply path  14 ; and a second lead electrode  102  which is formed on the first lead electrode  101  and is made of, for example, gold (Au). The first lead electrode  101  as described above serves as an adhesion layer for closely bonding the second lead electrode  102  and the insulation film  55  or the like. 
     In this embodiment, as shown in  FIG. 3(B) , the first lead electrode  101  is formed to have a width narrower than that of each of the compartment walls  11  at both sides in the width direction of the pressure generating chamber  12 . Moreover, the second lead electrode  102  is formed to be wider than the first lead electrode  101  and, in this embodiment, to be wider than the width of the compartment wall  11 . Thus, although the second lead electrode  102  protrudes into the region facing the pressure generating chamber  12 , the second lead electrode  102  is formed to be closely bonded only on the first lead electrode  101 . Thus, the second lead electrode  102  does not come into contact with the vibration plate, and has absolutely no effect on the vibration plate. Consequently, by forming the second lead electrode  102  to be wide, a wiring resistance can be lowered and reduction in a displacement amount of the vibration plate can be prevented. Therefore, a good and stable ink ejecting property can be obtained. Moreover, since the second lead electrode  102  can be formed so as not to come into contact with the vibration plate as described above, the thickness of the second lead electrode may be increased so as to further lower the wiring resistance. 
     Furthermore, in this embodiment, when the first lead electrode  101  is formed to have the width narrower than that of the compartment wall  11 , there is also an effect in-that a positional shift of the first lead electrode  101  in a width direction can be tolerated to some extent in the region facing the compartment wall  11 . 
     Note that, in this embodiment, the second lead electrode  102  is formed to be wider than the compartment wall  11 . However, needless to say, without being limited thereto, the second lead electrode may be narrower than the compartment wall  11  as long as the second lead electrode is wider than the first lead electrode. This is because, the wiring resistance can be surely lowered, at least compared to the case where the second lead electrode  102  has the same width as that of the first lead electrode  101 . 
     Moreover, on the surface of the passage-forming substrate  10  at the piezoelectric element  300  side, the protective plate  30  is bonded by use of an adhesive agent  35 . Specifically, the protective plate  30  has a piezoelectric element holding portion  31  capable of securing a space without interfering with movement of the piezoelectric element  300  in a region facing the piezoelectric element  300 . Since the piezoelectric element  300  is formed inside this piezoelectric element holding portion  31 , the piezoelectric element  300  is protected in a state of being hardly influenced by the external environment. Furthermore, in the protective plate  30 , the reservoir portion  32  is provided in a region corresponding to the communicating portion  13  in the passage-forming substrate  10 . In this embodiment, this reservoir portion  32  is provided along the arrangement direction of the pressure generating chambers  12  while penetrating the protective plate  30  in its thickness direction. As described above, the reservoir portion  32  constitutes the reservoir  110  to be the common ink chamber of the respective pressure generating chambers  12  by communicating with the communicating portion  13  in the passage-forming substrate  10 . 
     Moreover, in a region between the piezoelectric element holding portion  31  and the reservoir portion  32  in the protective plate  30 , a through-hole  33  is provided, which penetrates the protective plate  30  in its thickness direction. Inside this through-hole  33 , the connection portion  60   a  of the lower electrode film  60 , the connection portion  90   a  of the lead electrode for upper electrode  90  and the connection portion  100   a  of the lead electrode for lower electrode  100 , all of which are described above, are exposed. Accordingly, to these connection portions  60   a ,  90   a  and  100   a , one end of the connection wiring  130  extended from the drive IC  120  mounted on the protective plate  30  is connected. The through-hole  33 , in which the connection wiring  130  described above is extended, is filled with a sealer  140  that is an organic insulating material, for example, a potting material in this embodiment. The connection portion  60   a  of the lower electrode film  60 , the connection portion  90   a  of the lead electrode for upper electrode  90 , the connection portion  100   a  of the lead electrode for lower electrode  100  and the connection wiring  130  are completely covered with the sealer  140 . 
     Note that, as a material of the protective plate  30 , for example, glass, a ceramic material, metal, resin and the like are cited. However, it is more preferable that the protective plate  30  is formed of a material having approximately the same thermal expansion coefficient as that of the passage-forming substrate  10 . In this embodiment, the protective plate  30  is formed by use of a single crystal silicon substrate, which is the same material as that of the passage-forming substrate  10 . 
     Moreover, on the protective plate  30 , a compliance plate  40  including a sealing film  41  and a fixing plate  42  is bonded. The sealing film  41  is made of a material having low stiffness and flexibility (for example, a polyphenylene sulfide (PPS) film with a thickness of 6 μm) and this sealing film  41  seals one side of the reservoir portion  32 . Moreover, the fixing plate  42  is formed by use of a hard material such as metal (for example, stainless-steel (SUS) with a thickness of 30 μm or the like). A region of this fixing plate  42 , the region corresponding to the reservoir  110 , is set to be an opening portion  43  which is obtained by entirely removing the fixing plate  42  in the region in its thickness direction. Thus, one side of the reservoir  110  is sealed only by the sealing film  41  having flexibility. 
     The inkjet recording head of this embodiment as described above takes in ink from unillustrated external ink supply means and fills the inside thereof from the reservoir  110  to the nozzle orifices  21  with ink. Thereafter, in accordance with a recording signal from the drive IC  120 , a voltage is applied between the respective lower and upper electrode films  60  and  80  which correspond to the respective pressure generating chambers  12 . Subsequently, the elastic film  50 , the insulation film  55 , the lower electrode film  60  and the piezoelectric layer  70  undergo flexible deformations. Thus, pressures in the respective pressure generating chambers  12  are increased and ink droplets are ejected the nozzle orifices  21 . 
     Here, with reference to  FIGS. 4(A) to 4(D) ,  FIGS. 5(A) to 5(D)  and  FIG. 6 , a method for manufacturing such an inkjet recording head will be described. Note that  FIGS. 4(A) to 4(D)  and  FIGS. 5(A) to 5(C)  are cross-sectional views in the longitudinal direction of the pressure generating chamber. Moreover,  FIG. 6  is a cross-sectional view in the width direction of the pressure generating chamber. First, as shown in  FIG. 4(A) , a passage-forming substrate  10  that is a single crystal silicon substrate is thermally oxidized in a diffusion furnace heated to about 1100 degree C. Thus, a silicon dioxide film  52  to form an elastic film  50  and mask film  51  is formed all over the passage-forming substrate  10 . Next, as shown in  FIG. 4(B) , on the elastic film  50  (the silicon dioxide film  52 ), an insulation film  55  is formed, which is made of zirconium oxide (ZrO 2 ) obtained by thermally-oxidizing a zirconium (Zr) layer formed on the elastic film in a diffusion furnace heated to about 500 to 1200 degree C., for example. Next, as shown in  FIG. 4(C) , after a lower electrode film  60  is formed by laminating platinum and iridium, for example, on the insulation film  55 , this lower electrode film  60  is patterned to have a predetermined shape. Next, as shown in  FIG. 4(D)  a piezoelectric layer  70  made of, for example, lead zirconate titanate (PZT) or the like and an upper electrode film  80  made of, for example, iridium are formed on the entire surface of the passage-forming substrate  10 . 
     Subsequently, as shown in  FIG. 5(A) , the piezoelectric layer  70  and the upper electrode film  80  are patterned in a region facing each of the pressure generating chambers  12 , thus forming a piezoelectric element  300 . Next, a lead electrode for upper electrode  90  and a lead electrode for lower electrode  100  are formed. To be more specific, as shown in  FIG. 5(B)  and  FIG. 6 , a first metal film made of adherent metal, for example, titanium tungsten (TiW) is formed on the entire surface of the passage-forming substrate  10 . Thereafter, on the entire surface of the first metal film, a second metal film made of, for example, gold (Au) or the like is formed. Subsequently, for example, by means of a mask pattern (not shown) which is made of resist or the like, the second metal film is etched by using a potassium iodide solution and patterned into a predetermined shape for each of the piezoelectric elements  300  and a predetermined shape in the lower electrode film  60  between the piezoelectric elements  300  provided thereon. Furthermore, by means of the same mask pattern, the first metal film is etched by using a hydrogen peroxide solution and patterned into a predetermined shape. Thus, the lead electrode for upper electrode  90  including a first and second lead electrode  91  and  92 , and the lead electrode for lower electrode  100  including a first and second lead electrode  101  and  102  are formed. In this embodiment, in etching of the first metal film, the first metal film is side-etched (over-etched) to form the first lead electrodes  91  and  101  to be narrower than the second lead electrodes  92  and  102 . In this event, the first metal film is side-etched in a state of being closely bonded to the second metal film in the middle of the width direction. Note that this side-etching is performed by controlling an etching time. Next, as shown in  FIG. 5(C) , a protective plate  30  is bonded to the piezoelectric element  300  side of the passage-forming substrate  10  by use of an adhesive agent  35 , and the passage-forming substrate  10  is subjected to anisotropic etching by means of the mask film  51  patterned into a predetermined shape. Thus, the pressure generating chamber  12  and the like are formed. 
     Note that, in practice, a number of chips are simultaneously formed on a piece of wafer by performing the above-described series of film formation and anisotropic etching. After the above-described process is completed, the wafer is divided into chip-size pieces for each passage-forming substrate  10  as shown in  FIG. 1 . Thereafter, a nozzle plate  20  is bonded to the passage-forming substrate  10  with the mask film  51  interposed therebetween, a drive IC  120  is mounted on the protective plate  30  and a compliance plate  40  is bonded to the protective plate  30 . Furthermore, a connection wiring  130  is formed between the drive IC  120  and the connection portions  60   a  and  90   a  of the lower electrode film  60  and the lead electrode for upper electrode  90 . Thereafter, these connection portions  60   a  and  90   a  and the connection wiring  130  are covered with a sealer  140 . Thus, the inkjet recording head of this embodiment is obtained. 
     (Embodiment 2) 
       FIG. 7  is a cross-sectional view showing a main part of an inkjet recording head according to Embodiment 2 of the present invention. In this embodiment, as shown in  FIG. 7 , a lead electrode for lower electrode  100 A and a piezoelectric element  300  are covered with an insulating film  200  made of aluminum oxide, for example, so as to prevent destruction of the piezoelectric element  300  attributable to moisture. This embodiment is similar to Embodiment 1 except that a second lead electrode  102 A of the lead electrode for lower electrode  100 A is formed to become narrower toward a first lead electrode  101 A. 
     Here, the insulating film  200  provided to cover the piezoelectric element  300  is formed, for example, by use of a CVD method or the like. Thus, it is difficult to form the insulating film  200  around the lead electrode for lower electrode  100 A having the second lead electrode  102 A wider than the first lead electrode  101 A. However, as in the case of this embodiment, when the second lead electrode  102 A is formed to become narrower toward the first lead electrode  101 A, an insulating material easily enters into a periphery of the first lead electrode  101 A and the insulating film  200  is formed well also in a periphery of the lead electrode for lower electrode  100 A. Thus, the piezoelectric element  300  can be surely covered with the insulating film  200  and destruction of the piezoelectric element  300  (a piezoelectric layer  70 ) attributable to moisture and the like can be surely prevented. Moreover, it is needless to say that the configuration as described above can obtain the same effects as those of Embodiment 1. 
     (Other Embodiments) 
     Although the respective embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. For example, in Embodiment 1 described above, the first lead electrode  101  is formed to be narrower than the compartment wall  11 . However, without being limited thereto, the first lead electrode may be formed to have the same width as that of the compartment wall. Moreover, in Embodiment  1  described above, the description was given by exemplifying the lead electrode for lower electrode  100  with a two-layer structure including the first and second lead electrodes  101  and  102 . However, without being limited thereto, the lead electrode for lower electrode may have a structure with three layers or more. Note that the inkjet recording head of the embodiments described above constitutes a part of a recording head unit including an ink passage communicating with an ink cartridge and the like and is mounted on an inkjet recording apparatus.  FIG. 8  is a schematic view showing an example of the inkjet recording apparatus. As shown in  FIG. 8 , in recording head units  1 A and  1 B having inkjet recording heads, cartridges  2 A and  2 B included in ink supply means are detachably provided. A carriage  3  having these recording head units  1 A and  1 B mounted thereon is movably provided in an axial direction on a carriage shaft  5  attached to an apparatus main body  4 . These recording head units  1 A and  1 B are, for example, ones which eject a black ink composition and a color ink composition, respectively. Drive force of a drive motor  6  is transmitted to the carriage  3  via a plurality of unillustrated gears and a timing belt  7 . Thus, the carriage  3  having the recording head units  1 A and  1 B mounted thereon is moved along the carriage shaft  5 . Meanwhile, a platen  8  is provided along the carriage shaft  5  in the apparatus main body  4 , and a recording sheet S that is a recording medium such as paper fed by an unillustrated feed roller or the like is carried on the platen  8 . 
     Moreover, in the above-described embodiments, the inkjet recording heads were described as an example of the liquid jet head of the present invention. However, basic configurations of a liquid jet head are not limited to the one described above. The present invention is aimed widely at general liquid jet heads and, needless to say, can also be applied to ones ejecting liquids other than ink. As the other liquid jet heads, cited are, for example: various kinds of recording heads used in an image recording apparatus such as a printer; a coloring material jet head used for manufacturing color filters of a liquid crystal display and the like; an electrode material jet head used for forming electrodes of an organic EL display, a field emission display (FED) and the like; a bio-organic matter jet head used for manufacturing biochips; and the like.