Patent Publication Number: US-9833993-B2

Title: Ink jet head and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-137736, filed Jul. 9, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an ink jet head and a manufacturing method thereof. 
     BACKGROUND 
     Generally, an ink jet head of one type has an actuator including a diaphragm and a plurality of piezoelectric elements to eject ink from a plurality of pressure chambers. In such an ink jet head, the diaphragm is deformed by a piezoelectric element to pressurize ink inside a corresponding pressure chamber, and then the ink is ejected. 
     Depending on a method to form the actuator, especially when using photolithography, compressive stress may remain in the diaphragm of the actuator. 
     When the compressive stress in the diaphragm is excessively great, upon driving of the actuator, the actuator may undergo buckling distortion due to the compressive stress of the diaphragm. When there is variation in the compressive stress of the diaphragms among the plurality of actuators, the degree of buckling distortion may differ among the actuators, which lead to uneven deformation characteristics among the actuators. As a result, the ink ejection characteristics may become uneven. Also, durability of the actuators may decrease due to the buckling distortion. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an ink jet head according to a first embodiment. 
         FIG. 2  is a plan view of an end portion of a pressure chamber plate of the ink jet head according to the first embodiment. 
         FIG. 3  is a cross-sectional view of the ink jet head of  FIG. 2  taken along line F 3 -F 3 . 
         FIG. 4  is an enlarged plan view of a pressure chamber of the ink jet head shown in  FIG. 2 . 
         FIG. 5  is a cross-sectional view of the ink jet head of  FIG. 4  taken along line F 5 -F 5 . 
         FIGS. 6A-12A, 6B-12B, and 6C-12C  are cross-sectional diagrams of a portion of the inkjet head of  FIG. 4  taken along an A-A line, a B-B line, and a C-C line, respectively, at different manufacturing stages. 
         FIG. 13  is an exploded perspective view of an ink jet head according to a second embodiment. 
         FIG. 14  is a plan view of an end portion of a pressure chamber plate of the ink jet head according to the second embodiment. 
         FIG. 15  is an enlarged plan view of a pressure chamber of the ink jet head according to the second embodiment. 
         FIGS. 16A and 16B  are cross-sectional views of the pressure chamber of the ink jet head of  FIG. 15  according to the second embodiment, where  FIGS. 16A and 16B  correspond to a portion taken along a D-D line and an E-E line, respectively. 
         FIGS. 17A-23A and 17B-23B  are cross-sectional diagrams of a portion of the ink jet head of  FIG. 15  taken along the D-D line, and the E-E line, respectively, at different manufacturing stages. 
         FIGS. 24A to 24C  illustrate a pressure chamber plate according to first, second, and third modification examples, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments provide an ink jet head and a manufacturing method thereof capable of releasing the compressive stress of diaphragms and suppressing or reducing the buckling distortion of actuators when the actuators are driven, capable of making the deformation characteristics among the actuators to be more uniform and the ink ejection characteristics to be more uniform, and capable of preventing damage to the actuators. 
     In general, according to an embodiment, an ink jet head includes a base member having a plurality of openings, a diaphragm formed on a surface of the base member covering each of the openings, a pressure chamber being formed at each of the openings, and a plurality of piezoelectric elements formed at locations on the diaphragm corresponding to the pressure chambers, each of the piezoelectric elements being configured to eject liquid from a corresponding pressure chamber by causing deformation of the diaphragm. The diaphragm includes a plurality of stress release portions that reduces compressive residual stress in the diaphragm, each of the stress release portions corresponding to one of the piezoelectric elements. 
     First Embodiment 
       FIGS. 1 to 12C  illustrate an ink jet head according to a first embodiment. 
     Structure of Ink Jet Head 
     Hereinafter, a structure of an ink jet head  5  according to the first embodiment will be described.  FIG. 1  is an exploded perspective view of the ink jet head  5 ,  FIG. 2  is a plan view of an end portion of a pressure chamber plate  2  of the ink jet head  5 , and  FIG. 3  is a cross-sectional view of the ink jet head  5  taken along line F 3 -F 3  of  FIG. 2 . 
     As illustrated in  FIG. 1 , the ink jet head  5  according to the present embodiment has a structure in which a nozzle plate  1 , the pressure chamber plate  2 , ink supply plates  3 A and  3 B, and reservoir plates  4 A and  4 B are stacked together. In the present embodiment, the stack of these elements is formed such that a plan shape of each element as viewed from above is rectangular. 
     As illustrated in  FIG. 3 , the pressure chamber plate  2  includes a silicon substrate (base member)  22  which is covered with a diaphragm  21  of silicon (Si) thermal oxide. A plurality of pressure chambers  23 , paths  24 , and ink supply chambers  25  are formed in the inner portion of the pressure chamber plate  2 . As illustrated in  FIG. 1 , the plurality of pressure chambers  23  is formed to have a rectangular plan shape when viewed from above. In the present embodiment, two rows of pressure chambers  23  are arranged in a short direction of the rectangular pressure chamber plate  2 . The plurality of the pressure chambers  23  is formed in the longitudinal direction in each row of the pressure chambers  23 . 
     Normally, the thickness of the pressure chamber plate  2  is 50 μm to 500 μm, and the thickness of the silicon thermal oxide film is 0.2 μm to 10 μm. For the diaphragm  21 , a zirconium oxide film, an iridium oxide film, a ruthenium oxide film, or the like may be used instead of a silicon thermal oxide film. For example, when the zirconium oxide film is used, it is possible to form the zirconium oxide film by thermally oxidizing a zirconium film after the zirconium film is formed on the silicon substrate  22  by sputtering. 
     Openings of the pressure chambers  23  are formed on a side of the pressure chamber plate  2  that is opposite to a side of the pressure chamber plate  2  covered with the diaphragm  21 . The nozzle plate  1  is adhered to the side of the pressure chamber plate  2  with the openings. Nozzles  11  are formed in the nozzle plate  1  corresponding to the pressure chambers  23 . A polyimide is an example of the material of the nozzle plate  1 , and the nozzles  11  of the nozzle plate  1  may be formed by laser machining. 
     Piezoelectric elements  7  are disposed on positions of the diaphragm  21  corresponding to the pressure chambers  23 . The piezoelectric element  7  has a structure in which a bottom electrode  71 , a piezoelectric material  72 , and a top electrode  73  are stacked together. 
     On the side of the pressure chamber plate  2  that has the piezoelectric element  7 , ink supply plates  3 A and  3 B and reservoir plates  4 A and  4 B are stacked via an epoxy adhesive, for example. An ink supply path  31  to communicate with the ink supply chamber  25  is formed in the ink supply plates  3 A and  3 B. A reservoir  41  connected to the ink supply path  31  is formed in the reservoir plate  4 A. An ink inlet  42  for supplying the ink to the reservoir  41  is formed in the reservoir plate  4 B. 
     For the materials of the ink supply plates  3 A and  3 B, and the reservoir plates  4 A and  4 B, alumina, zirconia, silicon carbide, silicon nitride, barium titanate, and the like are examples of ceramic materials. Stainless steel, aluminum, titanium, and the like are examples of metal materials. ABS, polyacetal, polyamide, polycarbonate, polyether sulfone, and the like are examples of resin materials. 
     As illustrated in  FIGS. 2 and 3 , the bottom electrode  71  is connected to individual wiring  74   a , which extends to the end portion of the pressure chamber plate  2 . The top electrode  73  is connected to common wiring  74   b  via an opening  75   b  of an insulating film  75  of silicon oxide, and the common wiring  74   b  also extends to the end portion of the pressure chamber plate  2 . A wiring  74  which includes the individual wiring  74   a  and the common wiring  74   b  is connected to connection terminals of a drive circuit section (not illustrated) at the end portion of the pressure chamber plate  2 . 
       FIG. 4  is an enlarged plan view of a pressure chamber  23  of  FIG. 2 , and  FIG. 5  is a cross-sectional view of the pressure chamber  23  taken along line F 5 -F 5  of  FIG. 4 . As illustrated in  FIGS. 4 and 5 , stress release sections  26  for releasing and reducing compressive stress of the diaphragm  21  are formed in a region of the diaphragm  21  which does not face the pressure chamber  23 . In the present embodiment, the region which does not face the pressure chamber  23  is a region outside the pressure chamber  23 , surrounding the pressure chamber  23 , and excluding the portion corresponding to the constricting path  24  and the wiring  74 . A pair of through holes (removed sections)  26   a  having a groove shape (slit shape) are formed alongside portions of the pressure chamber  23  in a region surrounding the pressure chamber  23  in the stress release section  26 . For each of the piezoelectric elements  7 , a pair of through holes  26   a  is formed in the same shape with respect to each of the piezoelectric elements  7 . Here, a pull-out position and a pull-out direction of the wiring  74  in relation to each of the piezoelectric elements  7  are matched such that it is easy to render the shape of each of the through holes  26   a  corresponding to each of the piezoelectric elements  7  to be the same shape. 
     Manufacture of Pressure Chamber Plate  2  and Piezoelectric Element  7   
     Hereinafter, a manufacturing process of the pressure chamber plate  2  and the piezoelectric element  7  will be described.  FIGS. 6A, 7A, 8A, 9A, and 10A  are cross-sectional diagrams of the pressure chamber plate  2  taken along the A-A line of  FIG. 4 . Similarly,  FIGS. 6B, 7B, 8B, 9B, and 10B  are cross-sectional diagrams of the pressure chamber plate  2  taken along the B-B line of  FIG. 4 , and  FIGS. 6C, 7C, 8C, 9C, and 10C  are cross-sectional diagrams of the pressure chamber plate  2  taken along the C-C line of  FIG. 4 . 
     First, as illustrated in  FIG. 6A , the through holes  26   a  are formed using dry etching in the diaphragm  21  of silicon thermal oxide, which is formed on the silicon substrate  22 . As a result, the surface of the silicon substrate  22  is exposed in the through holes  26   a  except for the portions corresponding to the formation positions of the constricting path  24  and the wiring  74  which are formed in later processes. In  FIGS. 6B and 6C , the through holes  26   a  are not formed in the diaphragm  21 . 
     The film of silicon thermal oxide has compressive stress in the intra-surface direction as internal stress. In the present embodiment, since a portion of the internal stress of the diaphragm  21  is released by forming the stress release sections  26  of the through holes  26   a  in the diaphragm  21 , the internal stress of the diaphragm  21  is reduced in comparison with a case in which no stress release sections  26  is formed in the diaphragm  21 . 
     Next, as illustrated in  FIGS. 7A to 7C , a bottom conductive film  71   a  serving as the bottom electrode  71 , a piezoelectric layer  72   a  serving as the piezoelectric material  72 , and a top conductive film  73   a  serving as the top electrode  73  are sequentially formed on the diaphragm  21  by sputtering. For example, it is possible to use the CVD, a sol gel method, aerodeposition (AD), a hydrothermal method or the like as another method of producing the piezoelectric layer  72   a . At this time, as illustrated in  FIG. 7A , even in the through hole  26   a  of the diaphragm  21 , the bottom conductive film  71   a , the piezoelectric layer  72   a , and the top conductive film  73   a  are formed in the same manner on the surface of the silicon substrate  22 . 
     Examples of materials of the bottom conductive film  71   a  and the top conductive film  73   a  include Pt, Ir, Ni, Cu, Al, Ti, W, Mo, and Au. Examples of materials of the piezoelectric layer  72   a  include PZT, PTO (lead titanate), PMNT, PZNT, ZnO, and AlN. Normally, thicknesses of the bottom conductive film  71   a  and the top conductive film  73   a  are 0.01 μm to 1 μm, and the thickness of the piezoelectric layer  72   a  is 0.1 μm to 10 μm. 
     Next, as illustrated in  FIGS. 8A to 8C , the top conductive film  73   a , the piezoelectric layer  72   a , and the bottom conductive film  71   a  are subjected to dry etching to form the piezoelectric element  7  in the region surrounded by the stress release section  26 . During the formation of the piezoelectric element  7 , when the bottom conductive film  71   a  is patterned to form the bottom electrode  71 , the individual wiring  74   a  is also formed as illustrated in  FIGS. 8B and 8C . When the bottom conductive film  71   a  is subjected to dry etching to form the bottom electrode  71 , since the silicon substrate  22  may also be etched when the bottom conductive film  71   a  on the bottom surface of the stress release sections  26  is etched, the etching of the bottom conductive film  71   a  is performed using a pattern such that the bottom conductive film  71   a  remains on the bottom surface of the stress release sections  26  as illustrated in  FIG. 8A . 
     Next, as illustrated in  FIGS. 9A to 9C , the insulating film  75  of the silicon oxide film is formed by CVD using TEOS to cover the diaphragm  21  entirely. Next, as illustrated in  FIGS. 9A and 9C , the opening  75   b  ( FIG. 9A ) which exposes a portion of the top electrode  73  and a first opening section  25   b  ( FIG. 9C ) serving as an opening section of the ink supply chamber  25  are formed by dry etching the insulating film  75 . It is possible to use silicon nitride, aluminum oxide, hafnium oxide, or diamond-like carbon (DLC) instead of silicon oxide as the material of the insulating film  75 . The thickness of the insulating film  75  is 0.1 μm to 2 μm. 
     Next, as illustrated in  FIGS. 10A to 10C , the conductive film is formed to cover the diaphragm  21  entirely, and the formed conductive film is subjected to wet etching. As a result, the common wiring  74   b  ( FIG. 10A ) which is connected to the top electrode  73  via the opening  75   b  is formed. Examples of materials of the conductive film include Au, Ir, Ni, Cu, Al, Ti, W, and Mo. The thickness of the common wiring  74   b  is 0.01 μm to 1 μm. 
     Next, as illustrated in  FIG. 11C , the portion of the diaphragm  21  corresponding to the ink supply chamber  25  is removed from the diaphragm  21  using dry etching, and a second opening section  25   b  which serves as a portion of the ink supply chamber  25  is formed in the diaphragm  21 . 
     Next, as illustrated in  FIG. 12A , the silicon substrate  22  is subjected to dry etching, using the diaphragm  21  as an etch stop, from the side opposite to the diaphragm  21  side of the silicon substrate  22 . As a result, the pressure chamber  23  is formed in a position corresponding to the piezoelectric element  7 . At the same time, as illustrated in  FIG. 12B , the silicon substrate  22  is subjected to dry etching using the diaphragm  21  as an etch stop in the same manner, and the constricting path  24  is also formed. At the same time, as illustrated in  FIG. 12C , a third opening section  25   c  which communicates with the second opening section  25   b  of the diaphragm  21  is formed in the silicon substrate  22  using dry etching. In such a way, the ink supply chamber  25  is formed. 
     When the pressure chamber  23  is formed, an actuator  8  (including the piezoelectric element  7  and the diaphragm  21 ) deforms to protrude toward the pressure chamber  23  due to the internal stress in the intra-surface direction of the insulating film  75 , the piezoelectric element  7 , and the diaphragm  21 . At this time, since the stress release sections  26  are formed in the diaphragm  21  of the present embodiment, a portion of the compressive stress of the diaphragm  21  is released by the stress release sections  26  and the compressive stress of the diaphragm  21  is reduced. Therefore, the initial deformation of the actuator  8  is small in comparison to a case in which no stress release sections are formed. 
     Operations of Ink Jet Head 
     Hereinafter, an operation of the ink jet head  5  will be described. During the operation of the ink jet head  5 , electrical power is supplied from the drive circuit section (not illustrated) to the bottom electrode  71  and the top electrode  73 . At this time, when an electric field is generated inside the piezoelectric material  72  to distort the piezoelectric element  7 , the actuator  8  (the piezoelectric element  7  and the diaphragm  21 ) deforms due to the interaction between the piezoelectric element  7  and the diaphragm  21 . In this case, since the compressive stress of the diaphragm  21  is released by the stress release sections  26 , the actuator  8  either does not undergo buckling distortion or the degree of buckling distortion is small, if any. Therefore, variation in the deformation characteristics among the plurality of actuators  8  caused by the buckling distortion of the actuators  8  is suppressed. 
     When the actuator  8  deforms, the ink inside the pressure chamber  23  is pressurized, and ejected from the nozzle  11 . At this time, since the variation in the deformation characteristics among the plurality of actuators  8  is suppressed in the present embodiment, the variation in the ink ejection characteristics among the actuators  8  is low. When the ink is consumed through the ejection, ink (new ink) is supplied to the pressure chamber  23  sequentially via the reservoir  41 , the ink supply path  31 , the ink supply chamber  25 , and the constricting path  24  according to the consumption amount. 
     Advantages 
     In the ink jet head  5  according to the present embodiment, the stress release sections  26  for releasing and reducing the compressive stress of the diaphragm  21  are formed in a region of the diaphragm  21  which does not face the pressure chamber  23 . Since the compressive stress of the diaphragm  21  is released by the stress release section  26  during the manufacture of the ink jet head  5 , it is possible to suppress or reduce the buckling distortion of the actuator  8  when the actuator  8  is driven. Therefore, it is possible to render the deformation characteristics among the plurality of actuators  8  formed in the single ink jet head  5  to be uniform and to render the ink ejection characteristics to be uniform. Therefore, it is possible to provide an ink jet head capable of preventing damage to the actuators  8 . 
     During the manufacturing of the ink jet head  5 , the diaphragm  21  is formed on one end surface of the silicon substrate  22 . Thereafter, the stress release sections  26  are formed by removing a portion of the diaphragm  21  by forming the through holes  26   a  in a region which does not face the pressure chamber  23  to be formed on the inside of the silicon substrate  22 . After forming the stress release sections  26 , the piezoelectric element  7  is formed by sequentially stacking the bottom electrode  71 , the piezoelectric material  72 , and the top electrode  73  on the diaphragm  21 . Subsequently, the pressure chamber  23  is formed inside the silicon substrate  22  by etching the silicon substrate  22  from the other end surface side of the silicon substrate  22  which is opposite the one end surface. At this time, the compressive stress of diaphragms  21  is released by the stress release sections  26 , the buckling distortion of the actuators  8  when the actuators  8  are driven is suppressed or reduced. As a result, the deformation characteristics among the actuators  8  become more uniform and the ink ejection characteristics become more uniform. It is possible to provide a manufacturing method of an ink jet head capable of preventing damage to the actuators  8  by suppressing or reducing the buckling distortion of the actuators  8 . 
     Second Embodiment 
       FIGS. 13 to 23B  illustrate an ink jet head according to a second embodiment. The present embodiment is a modification example in which the structure of the ink jet head  5  according to the first embodiment (refer to  FIGS. 1 to 12C ) is modified in the following manner. 
     Hereinafter, a structure of an ink jet head  105  according to the present embodiment will be described.  FIG. 13  is an exploded perspective view of the ink jet head  105 . As illustrated in  FIG. 13 , the ink jet head  105  according to the present embodiment has a structure in which a pressure chamber plate  102 , and reservoir plates  104 A and  104 B are stacked together. In the present embodiment, the stack of these elements is formed such that a plan shape of each element as viewed from above is rectangular. 
       FIG. 14  is a plan view of an end portion of the pressure chamber plate  102  of the ink jet head  105 . A plurality of pressure chambers  123  is formed in the pressure chamber plate  102 . As illustrated in  FIGS. 14 and 15 , the pressure chamber  123  according to the present embodiment is cylindrical. 
       FIG. 15  is an enlarged view of one of the pressure chambers  123  of  FIG. 14 ,  FIG. 16A  is a cross-sectional view of the pressure chamber  123  taken along the line D-D of  FIG. 15 , and  FIG. 16B  is a cross-sectional view of the pressure chamber  123  taken along the line E-E of  FIG. 15 . As illustrated in  FIGS. 16A and 16B , the pressure chamber plate  102  includes a silicon substrate  122  which is covered with a diaphragm  121  of silicon thermal oxide. 
     Normally, the thickness of the pressure chamber plate  102  is 50 μm to 500 μm, and the thickness of the silicon thermal oxide film (the diaphragm  121 ) is 0.2 μm to 10 μm. For the diaphragm  121 , a zirconium oxide film, an iridium oxide film, a ruthenium oxide film, or the like may be used instead of a silicon thermal oxide film. For example, when the zirconium oxide film is used, it is possible to form the zirconium oxide film by thermally oxidizing a zirconium film after the zirconium film is formed on the silicon substrate  122  by sputtering. 
     On a surface of the pressure chamber plate  102  on which the pressure chambers  123  are opened, the reservoir plates  104 A and  104 B are stacked via an epoxy adhesive, for example. A reservoir  141  which is joined to the pressure chambers  123  by the reservoir plate  104 A is formed, and an ink inlet  142  for supplying the ink to the reservoir  141  is formed in the reservoir plate  104 B. For the materials of the reservoir plates  104 A and  104 B, alumina, zirconia, silicon carbide, silicon nitride, barium titanate, and the like are given as examples of ceramic materials, stainless steel, aluminum, and titanium are given as examples of metal materials, and ABS, polyacetal, polyamide, polycarbonate, polyether sulfone, and the like are examples of resin materials. 
     A piezoelectric element  107  is disposed at a position of the diaphragm  121  corresponding to the pressure chamber  123 . The piezoelectric element  107  has a structure in which a bottom electrode  171 , a piezoelectric body  172 , and a top electrode  173  are stacked together. A through hole penetrating through the diaphragm  121  and the piezoelectric element  107  is formed at axial centers thereof, and the through hole forms a nozzle  127  which is connected to the pressure chamber  123 . 
     As illustrated in  FIGS. 14, 15, and 16A , the bottom electrode  171  is connected to individual wiring  174   a , and the individual wiring  174   a  extends to the end portion of the pressure chamber plate  102 . The top electrode  173  is connected to common wiring  174   b  via an opening  175   b  of an insulating film  175  of the silicon oxide film, and the common wiring  174   b  also extends to the end portion of the pressure chamber plate  102 . A wiring  174  which includes the individual wiring  174   a  and the common wiring  174   b  is connected to connection terminals of a drive circuit section (not illustrated) at the end portion of the pressure chamber plate  102 . 
     As illustrated in  FIGS. 15 and 16B , a pair of substantially semicircular stress release sections  126  is formed in a groove shape in the diaphragm  121  for each of the piezoelectric elements  107  so as to surround the pressure chamber  123 . The stress release sections  126  are formed in the same shape as the piezoelectric elements  107  except for the portion corresponding to the wiring  174 . Here, the pull-out position and the pull-out direction of the wiring  174  corresponding to each of the piezoelectric elements  107  are matched such that it is easy to render the shape of each of the stress release sections  126  corresponding to each of the piezoelectric elements  107  to be the same shape. 
     Manufacture of Pressure Chamber Plate  102  and Piezoelectric Element  107   
     Hereinafter, a manufacturing process of the pressure chamber plate  102  and the piezoelectric element  107  will be described.  FIGS. 17A, 18A, 19A, 20A, 21A, 22A, and 23A  are cross-sectional diagrams of the pressure chamber plate  102  and the piezoelectric element  107  taken along the D-D line of  FIG. 15 . In the same manner,  FIGS. 17B, 18B, 19B, 20B, 21B, 22B , and  23 B are cross-sectional diagrams of the pressure chamber plate  102  and the piezoelectric element  107  taken along the E-E line of  FIG. 15 . 
     First, as illustrated in  FIG. 17B , through holes  126   a  are formed using dry etching in the diaphragm  121  of silicon thermal oxide. As a result, the surface of the silicon substrate  122  is exposed in the through holes  126   a  except for the portions corresponding to positions of the wiring  174  to be formed in a later process. In  FIG. 17A , the through holes  126   a  are not formed in the diaphragm  121 . 
     The silicon thermal oxide film (diaphragm  121 ) has compressive stress in the intra-surface direction as internal stress. In the present embodiment, since a portion of the internal stress of the diaphragm  121  is released by forming the stress release sections  126  of the through holes  126   a  in the diaphragm  121 , the internal stress of the diaphragm  121  is reduced in comparison with a case in which no stress release section is formed in the diaphragm  121 . 
     Next, as illustrated in  FIGS. 18A and 18B , a bottom conductive film  171   a  serving as the bottom electrode  171 , a piezoelectric layer  172   a  serving as the piezoelectric body  172 , and a top conductive film  173   a  serving as the top electrode  173  are sequentially formed on the diaphragm  121  by sputtering. It is possible to use the CVD, a sol gel method, aerodeposition (AD), a hydrothermal method or the like as another method for forming the piezoelectric layer  172   a . At this time, as illustrated in  FIG. 18B , even in the through hole  126   a , the bottom conductive film  171   a , the piezoelectric layer  172   a , and the top conductive film  173   a  are formed in the same manner on the surface of the silicon substrate  122 . 
     Examples of materials of the bottom conductive film  171   a  and the top conductive film  173   a  include Pt, Ir, Ni, Cu, Al, Ti, W, Mo, and Au. Examples of materials of the piezoelectric layer  172   a  include PZT, PTO (lead titanate), PMNT, PZNT, ZnO, and AlN. Normally, the thicknesses of the bottom conductive film  171   a  and the top conductive film  173   a  are 0.01 μm to 1 μm, and the thickness of the piezoelectric layer  172   a  is 0.1 μm to 10 μm. 
     Next, as illustrated in  FIGS. 19A and 19B , the top conductive film  173   a , the piezoelectric layer  172   a , and the bottom conductive film  171   a  are subjected to dry etching to form the donut-shaped piezoelectric element  107  having a through hole  107   a  in the region surrounded by the stress release section  126 . During the formation of the piezoelectric element  107 , when the bottom conductive film  171   a  is patterned to form the bottom electrode  171 , the individual wiring  174   a  is also formed. If the bottom conductive film  171   a  of the stress release sections  126  is etched while the bottom conductive film  171   a  is subjected to dry etching to form the bottom electrode  171 , the silicon substrate  122  may also be etched. To prevent the etching of the silicon substrate  122 , the etching of the bottom conductive film  171   a  is performed using a pattern such that the bottom conductive film  171   a  remains on the bottom surface of the stress release sections  126 . 
     Next, as illustrated in  FIGS. 20A and 20B , the insulating film  175  of silicon oxide is formed by CVD using TEOS so as to cover the diaphragm  121  entirely. Next, as illustrated in  FIG. 20A , the opening  175   b  which exposes a portion of the top electrode  173  is formed by dry etching the insulating film  175 . It is possible to use silicon nitride, aluminum oxide, hafnium oxide, or diamond-like carbon (DLC) instead of the silicon oxide film as the material of the insulating film  175 . The thickness of the insulating film  175  is 0.1 μm to 2 μm. 
     Next, as illustrated in  FIG. 21A , the conductive film is formed to cover the diaphragm  121  entirely, and the formed conductive film is subjected to wet etching. As a result, the common wiring  174   b  which is connected to the top electrode  173  via the opening  175   b  is formed. Examples of materials of the conductive film include Au, Ir, Ni, Cu, Al, Ti, W, and Mo. The thickness of the common wiring  174   b  is 0.01 μm to 1 μm. 
     Next, as illustrated in  FIGS. 22A and 22B , a through hole  121   a  connected to the through hole  107   a  of the piezoelectric element  107  is formed in the diaphragm  121  by dry etching, and the nozzle  127  is formed as a result. 
     Next, as illustrated in  FIGS. 23A and 23B , the silicon substrate  122  is subjected to dry etching, using the diaphragm  121  as an etch stop, from the side opposite to the diaphragm  121  of the silicon substrate  122 , and the pressure chamber  123  is formed in a position corresponding to the piezoelectric element  107 . When the pressure chamber  123  is formed, an actuator  108  (the piezoelectric element  107  and the diaphragm  121 ) deforms to protrude toward the pressure chamber  123  due to the internal stress in the intra-surface direction of the insulating film  175 , the piezoelectric element  107 , and the diaphragm  121 . At this time, the stress release sections  126  are formed in the diaphragm  121  in the present embodiment, a portion of the compressive stress of the diaphragm  121  is released by the stress release sections  126  and the compressive stress of the diaphragm  121  is reduced. Therefore, the initial deformation of the actuator  108  is small in comparison to a case in which no stress release section is formed. 
     Operations of Ink Jet Head 
     Hereinafter, an operation of the ink jet head  105  will be described. During the operation of the ink jet head  105 , electrical power is supplied from the drive circuit section (not illustrated) to the bottom electrode  171  and the top electrode  173 . At this time, when an electric field is generated inside the piezoelectric body  172  to distort the piezoelectric element  107 , the actuator  108  (the piezoelectric element  107  and the diaphragm  121 ) deforms due to the interaction between the piezoelectric element  107  and the diaphragm  121 . In this case, since the compressive stress of the diaphragm  121  is released by the stress release sections  126 , the actuator  108  either does not undergo buckling distortion or the degree of buckling distortion is small, if any. Therefore, variation in the deformation characteristics among the plurality of actuators  108  caused by the buckling distortion is suppressed. 
     When the actuator  108  deforms, the ink inside the pressure chamber  123  is pressurized and ejected from the nozzle  127 . At this time, since the variation in the deformation characteristics among the plurality of actuators  108  is suppressed in the present embodiment, the variation in the ink ejection characteristics among the actuators  108  is low. When the ink is consumed through the ejection, ink (new ink) is supplied to the pressure chamber  123  from the reservoir  141  according to the consumption amount. 
     Advantages and Effects 
     According to the present embodiment, a pair of substantially semicircular stress release sections  126  is formed in a groove shape in the diaphragm  121  for each of the piezoelectric elements  107  so as to surround the pressure chambers  123 . Since a portion of the internal stress of the diaphragm  121  is released, the internal stress of the diaphragm  121  is reduced in comparison with a case in which the stress release sections  126  are not formed in the diaphragm  121 . Therefore, it is possible to suppressor to reduce the buckling distortion of the actuator  108  when the compressive stress of the diaphragm  121  is released and the actuator  108  is driven. Accordingly, it is possible to cause the deformation characteristics among the plurality of actuators  108  to be more uniform and the ink ejection characteristics to be more uniform. As a result, it is possible to provide the ink jet head  105  capable of preventing damage to the actuators  108 . 
     During the manufacturing of the ink jet head  105 , the diaphragm  121  is formed on one end surface of the silicon substrate  122 . Thereafter, the stress release sections  126  are formed by removing a portion of the diaphragm  121  by forming the through holes  126   a  in a region which does not face the pressure chamber  123  to be formed on the inside of the silicon substrate  122 . After forming the stress release sections  126  of the diaphragm  121 , the piezoelectric element  107  is formed by sequentially stacking the bottom electrode  171 , the piezoelectric body  172 , and the top electrode  173  on the diaphragm  121 . Subsequently, the pressure chamber  123  is formed inside the silicon substrate  122  by etching the silicon substrate  122  from the other end surface of the silicon substrate  122  which is opposite the one end surface. At this time, the compressive stress of diaphragms  121  is released by the stress release sections  126 , the buckling distortion of the actuators  108  when the actuators  108  are driven is suppressed or reduced, and thus, the deformation characteristics among the actuators  108  become more uniform and the ink ejection characteristics become more uniform. It is possible to provide a manufacturing method of an ink jet head capable of preventing damage to the actuators  108  by suppressing or reducing the buckling distortion of the actuators  108 . 
     Modification Example 
       FIG. 24A  illustrates a pressure chamber plate according to a first modification example of the first embodiment (refer to  FIGS. 1 to 12C ). In the first embodiment, during the formation of the stress release section  126 , the through hole  26   a  is formed in the diaphragm  21 , and the surface of the silicon substrate  22  is exposed from the bottom surface of the stress release section (the removed section)  26 . In the present modification example, by half etching the diaphragm  21 , a non-penetrating recessed section  226   a  is formed in the diaphragm  21  as illustrated in  FIG. 24A , and a stress release section  226  (a removed section) in which a portion of the diaphragm  21  is removed is formed. In this case, it is possible to ensure that the surface of the silicon substrate  22  is not exposed from the bottom surface of the stress release section  226 . 
     When the silicon oxide film remains on the bottom surface of the stress release section  26  according to the first modification example, in the dry etching of the bottom conductive film  71   a , the silicon oxide film serves as a protective film of the silicon substrate  122 . Therefore, when the bottom conductive film  71   a  remains on the bottom surface of the stress release section  26  as in the first embodiment, during the dry etching of the bottom conductive film  71   a , the bottom conductive film  71   a  on the bottom surface of the stress release section  26  can be removed, and the bottom conductive film  71   a  may not remain on the bottom surface of the stress release section  26 . 
       FIG. 24B  illustrates a pressure chamber plate according to a second modification example of the first embodiment. In the ink jet head  5  according to the first embodiment, the stress release section  26  is not formed on the portion of the diaphragm  21  corresponding to the wiring  74  (the wiring  74  is not formed on the stress release section  26 ). 
     In comparison, in the present modification example, a tapered section  26   b  is provided on the circumferential wall surface of the through hole  26   a  of the diaphragm  21  as illustrated in  FIG. 24B . The tapered section  26   b  is shaped such that an outside opening edge  26   a   1  of the through hole  26   a  is opened wider than an inside opening edge  26   a   2  of the through hole  26   a . The tapered section  26   b  is provided on the circumferential wall surface of the through hole  26   a  in this manner, and the wiring  74  is provided on a portion of the tapered section  26   b  of the through hole  26   a . Accordingly, it is possible to reduce the risk of disconnection caused by the level difference in the wiring  74  in comparison to a case in which the tapered section  26   b  is not provided on the circumferential wall surface of the through hole  26   a.    
     When the non-penetrating recessed section  226   a  is formed in the diaphragm  21  as illustrated in  FIG. 24A , the tapered section  26   b  may be provided on the circumferential wall surface of the recessed section  226   a  and the wiring  74  may be provided on a portion of the tapered section  26   b  of the recessed section  226   a.    
       FIG. 24C  illustrates a pressure chamber plate according to a third modification example of the first embodiment. In the first embodiment, the stress release section  26  is a space. In the present modification example, after forming the stress release section  26 , the stress release section  26  is filled with a filler capable of forming a filler section  26   c  in which the internal stress is tensile stress. The filler is formed of, for example, polyimide. The filler section  26   c  that has the tensile stress is formed by, for example, applying a layer of photosensitive polyimide, and exposing and developing the layer of polyimide so that the filler remains in the stress release section  26 . In this case, an end surface  21   p  of the diaphragm  21  is pulled by the tensile stress of the filler section  26   c . Therefore, the internal compressive stress of the diaphragm  21  is released further and the internal stress of the diaphragm  21  is further reduced in comparison to a case in which the stress release section  26  is a space. Since the stress release section  26  is filled with the filler, even when the stress release section  26  is formed in a portion of the diaphragm  21  corresponding to the wiring  74 , level differences are less likely to be formed in the wiring  74 . Therefore, there is few risk of disconnection. 
     In the first embodiment, the stress release section  26  has a groove shape; however, as long as it is possible to release the internal stress of the diaphragm  21  facing the piezoelectric element  7 , it is possible to freely set the number, position, shape, and the like of the stress release section  26 . For example, in the second embodiment (refer to  FIGS. 13  to  23 B), it is possible to remove portions of the diaphragm  121  except for the portion corresponding to the wiring  174  and the pressure chamber  123 . 
     According to the above embodiments, the compressive stress of diaphragms is released by the stress release sections, and the buckling distortion of the actuators when the actuators are driven is suppressed or reduced. As a result, the deformation characteristics among the actuators become more uniform and the ink ejection characteristics become more uniform. It is possible to provide an ink jet head and a manufacturing method thereof capable of preventing damage to the actuators by suppressing or reducing the buckling distortion of the actuators. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.