Patent Publication Number: US-8967775-B2

Title: Ink jet head and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-192550; filed on Aug. 31, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an ink jet head and an image forming device. 
     BACKGROUND 
     On-demand type ink jet recording methods are known in which discharge ink droplets are discharged from a nozzle according to an image signal to form an image on a recording paper. In connection with the on-demand type ink jet recording method, a heating element type ink jet recording method and a piezoelectric element type ink jet recording method are known. 
     In the heating element type ink jet recording method, air bubbles are generated in ink by heat provided by a heat source in an ink flow channel. The ink pressed by the air bubbles is discharged from a nozzle. 
     In the piezoelectric element type ink jet recording method, a pressure change occurs in an ink chamber, where ink is stored, due to the deformation of a piezoelectric element. Thus the ink is discharged from a nozzle. 
     A piezoelectric element is an electromechanical conversion element, undergoes expansion or shear deformation when an electric field is applied thereto. Lead zirconate titanate is used as a representative piezoelectric element. 
     With respect to an ink jet head using a piezoelectric element, a configuration using a nozzle plate formed of a piezoelectric material is known. The nozzle plate of the ink jet head includes an actuator. The actuator includes, for example, a piezoelectric film having a nozzle for discharging ink, and a metal electrode film formed on both surfaces of the piezoelectric film surrounding the nozzle. 
     The ink jet head includes a pressure chamber that is connected to the nozzle. Ink enters the pressure chamber and the nozzle of the nozzle plate and forms a meniscus within the nozzle, and thus the ink is maintained within the nozzle. When a driving waveform (voltage) is applied to the two electrodes provided around the nozzle on either side of the piezoelectric film, an electric field in the same direction as a polarization direction is applied to the piezoelectric film through the electrodes. Thereby, the actuator expands and contracts in a direction perpendicular to the direction of the electric field. The nozzle plate deforms by virtue of the expansion and the contraction of the actuator. A pressure change occurs in the ink within the pressure chamber due to the deformation of the nozzle plate, and thus the ink within the nozzle is discharged. 
     When a nozzle plate is formed, film stress occurs. There is a concern that a uniform deformation of the nozzle plate through an actuator may be obstructed by the film stress of the nozzle plate. When the deformation of the nozzle plate becomes non-uniform, there is a concern that a discharge direction of ink may become unstable. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an ink jet head of an ink jet printer, according to a first embodiment. 
         FIG. 2  is a plane view of the ink jet head according to the first embodiment. 
         FIG. 3  is a cross-sectional view of the ink jet head of the first embodiment taken along line F 3 -F 3  of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of a part of the ink jet head of the first embodiment taken along line F 4 -F 4  of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a part of an ink jet head of the first embodiment in which a nozzle plate is deformed. 
         FIG. 6  is a cross-sectional view of a part of an ink jet head according to a second embodiment. 
         FIG. 7  is a cross-sectional view of a part of an ink jet head according to a third embodiment. 
         FIG. 8  is a cross-sectional view of a part of an ink jet head according to a fourth embodiment. 
         FIG. 9  is a cross-sectional view of a part of an ink jet head according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An ink jet head according to an embodiment comprises a substrate including amounting surface and a pressure chamber open to the mounting surface. The ink jet head further comprises a nozzle plate including an inner surface fixed to the mounting surface and covering the pressure chamber, a nozzle open to the pressure chamber, and a piezoelectric element surrounding the nozzle and configured to deform to thereby change a volume of the pressure chamber. The ink jet head further comprises a deformation control unit disposed on and extending from the inner surface of the nozzle plate and surrounding the nozzle, the deformation control unit configured to cause deformation of the piezoelectric element to be substantially symmetric with respect to the nozzle. 
     Hereinafter, a first embodiment will be described with reference to  FIG. 1  through  FIG. 5 . 
       FIG. 1  is an exploded perspective view of an ink jet head  10  of an ink jet printer  1  according to a first embodiment.  FIG. 2  is a plane view of the ink jet head  10 .  FIG. 3  is a schematic cross-sectional view of the ink jet head  10  taken along line F 3 -F 3  of  FIG. 2 . 
     As shown in  FIG. 1 , the ink jet head  10  is mounted on the ink jet printer  1 . The ink jet printer  1  is an example of an image forming device. The image forming device is not limited thereto, and may be any other image forming device such as a copy machine. 
     The ink jet head  10  includes a nozzle plate  100 , a pressure chamber structure  200 , a separate plate  300 , and an ink feed passage structure  400 . The pressure chamber structure  200  can be formed from a substrate. The pressure chamber structure  200 , the separate plate  300 , and the ink feed passage structure  400  are joined with, for example, an epoxy-based adhesive. 
     The nozzle plate  100  is formed in a rectangular plate shape. The nozzle plate  100  is formed on the pressure chamber structure  200  by using a film-forming process, described below. As a result of the film-forming process, the nozzle plate  100  is firmly fixed to the pressure chamber structure  200 . 
     A plurality of nozzles  101  for discharging ink are provided in the nozzle plate  100 . Each nozzle  101  is a circular hole that extends through the nozzle plate  100  in the thickness direction. 
     The pressure chamber structure  200  is formed of a silicon wafer having a rectangular plate shape. The thickness of the pressure chamber structure  200  is, for example, 725 μm. Heating and thin-film formation are repeatedly performed on the pressure chamber structure  200  during a manufacturing process of the ink jet head  10 . For this reason, the silicon wafer has a heat resistance property and is smoothed according to an SEMI (Semiconductor Equipment and Materials International) standard. However, the pressure chamber structure  200  is not limited to the above description, and may be formed of any of other semiconductors such as a silicon carbide (SiC) germanium substrate. 
     The pressure chamber structure  200  includes a mounting surface  200   a  that faces the nozzle plate  100 , and a plurality of pressure chambers  201 . The nozzle plate  100  is firmly fixed to the mounting surface  200   a.    
     The pressure chamber  201  is comprised of a circular hole, for example having a diameter of 240 μm. However, the pressure chamber  201  may be a hole having any of other shapes such as a rectangular shape or a rhombic shape. The pressure chambers  201  open on the mounting surface  200   a  and are covered by the nozzle plate  100 . 
     The plurality of pressure chambers  201  are arranged to correspond to the plurality of nozzles  101 , and are disposed coaxially with the plurality of nozzles  101 , respectively. For this reason, each nozzle  101  is in direct communication with a corresponding pressure chamber  201 . 
     The separate plate  300  is formed of stainless steel having a rectangular plate shape. The separate plate  300  covers the plurality of pressure chambers  201  on the side opposite of the nozzle plate  100 . 
     A plurality of ink apertures  301  are provided in the separate plate  300 . Each of the plurality of ink apertures  301  are disposed so as to respectively correspond to one of the pressure chambers  201 . For this reason, each ink aperture  301  opens in one of the pressure chambers  201 . The ink apertures  301  are formed such that the ink flow path resistance to each of the respective pressure chambers  201  is approximately the same. 
     The ink feed passage structure  400  is formed of stainless steel having a rectangular plate shape. The ink feed passage structure  400  includes an ink supply port  401  and an ink supply passage  402 . 
     The ink supply port  401  is disposed in a central portion of the ink supply passage  402 . The ink supply port  401  is connected to an ink tank  11  in which ink for forming an image is stored. The ink tank  11  supplies the ink to the ink supply passage  402 . 
     The ink supply passage  402  is recessed from the surface of the ink feed passage structure  400 , and extends outwardly beyond the perimeter of the array of ink apertures  301 . In other words, each of the ink apertures  301  open into the ink supply passage  402 . Thus, the ink supply port  401  supplies ink to all the pressure chambers  201  through the ink apertures  301 . In addition, the ink supply port  401  is formed such that the ink flow path resistance to each of the respective pressure chambers  201  is approximately the same. 
     As described above, the separate plate  300  and the ink feed passage structures  400  may be formed of stainless steel. However, the materials of such components are not limited to stainless steel. The separate plate  300  and the ink feed passage structure  400  may be formed of any of other materials such as a ceramic, a resin, or a metal alloy so long as a difference in expansion coefficient between the separate plate  300  and the ink feed passage structure  400  on the one hand, and the nozzle plate  100 , on the other hand does not affect the generation of ink discharge pressure. The ceramic used may be a nitride or an oxide such as alumina ceramic, zirconia, silicon carbide, silicon nitride, or barium titanate. The resin used may be a plastic material such as ABS (acrylonitrile.butadiene.styrene), polyacetal, polyamide, polycarbonate, or polyethersulfone. The metal used may be, for example, aluminum or titanium. 
     The pressure chamber  201  holds the supplied ink. When a pressure change occurs in the ink within each pressure chamber  201  by the deformation of the nozzle plate  100 , the ink within the pressure chamber  201  is discharged from each nozzle  101 . The separate plate  300  confines pressure generated within the pressure chambers  201  so as to prevent the pressure from escaping to the ink supply passage  402 . For this reason, the diameter of the ink aperture  301  is, for example, equal to or less than ¼ of the diameter of the pressure chamber  201 . 
     Next, the nozzle plate  100  will be described. As shown in  FIG. 2 , the nozzle plate  100  includes the above-mentioned plurality of nozzles  101 , a plurality of actuators  102 , two shared electrode terminal portions  105 , a shared electrode  106 , a plurality of wiring electrode terminal portions  107 , and a plurality of wiring electrodes  108 . As shown in  FIG. 3 , the nozzle plate  100  further includes a vibration plate  109 , a protective film  113 , and an ink-repellent film  116 . The actuator  102  is an example of a piezoelectric element. 
     The vibration plate  109  has a rectangular shape and is formed on the mounting surface  200   a  of the pressure chamber structure  200 . The vibration plate  109  includes a first surface  501  and a second surface  502 . The first surface  501  is an example of an inner surface of the nozzle plate. 
     The first surface  501  is firmly fixed to the mounting surface  200   a  of the pressure chamber  200  and covers the pressure chambers  201 , except in the location of the nozzle  101  extending therethrough. The second surface  502  is located on the opposite side of the first surface  501 . The actuators  102 , the shared electrode  106 , and the wiring electrodes  108  are formed on the second surface  502  of the vibration plate  109 . 
     The plurality of actuators  102  are arranged so that each corresponds to one of the plurality of pressure chambers  201  and one of the plurality of nozzles  101 . The actuator  102  generates pressure for discharging ink in the pressure chamber  201  from the nozzle  101 . 
     As shown in  FIG. 2 , the actuator  102  is formed in an annular shape. The actuator  102  is disposed coaxially with the corresponding nozzle  101 . In other words, the center of the actuator  102  and the center of the nozzle  101  are aligned. The actuator  102  surrounds the nozzle  101 . However, the center of the actuator  102  and the center of the nozzle  101  may deviate from each other. 
     In order to arrange the nozzles  101  with higher density, the nozzles  101  are disposed in a zigzag shape. In other words, the plurality of nozzles  101  are arranged linearly in an X-axis direction of  FIG. 2 . Two aligned rows of the nozzles  101  are provided in a Y-axis direction. 
     As shown in  FIG. 3 , the actuator  102  includes a piezoelectric film  111 , an electrode portion  106   a  of the shared electrode  106 , an electrode portion  108   a  of the wiring electrode  108 , and an insulating film  112 . 
     The piezoelectric film  111  may be formed of lead zirconate titanate (PZT) in a film shape. The piezoelectric film  111  is not limited to that material, and may be formed of any of various materials such as PTO (PbTiO 3 : lead titanate), PMNT (Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3 ), PZNT (Pb(Zn 1/3 Nb 2/3 )O 3 —PbTiO 3 ), ZnO, and AlN. 
     The piezoelectric film  111  is formed in an annular shape. The piezoelectric film  111  is disposed coaxially with the nozzle  101  and the pressure chamber  201 . In other words, the piezoelectric film  111  surrounds the nozzle  101 . An inner circumferential portion of the piezoelectric film  111  is slightly separated from the nozzle  101 . 
     The piezoelectric film  111  is sandwiched between the electrode portion  108   a  of the wiring electrode  108  and the electrode portion  106   a  of the shared electrode  106 . In other words, the electrode portion  108   a  of the wiring electrode  108  and the electrode portion  106   a  of the shared electrode  106  are disposed on either side of the piezoelectric film  111 . 
     The formed piezoelectric film  111  generates polarization in the thickness direction. When an electric field is applied to the piezoelectric film  111  in the same direction as the polarization direction through the wiring electrode  108  and the shared electrode  106 , the actuator  102  expands and contracts in a direction perpendicular to the direction of the electric field. The vibration plate  109  is deformed in the thickness direction of the nozzle plate  100  by the expansion and the contraction of the actuator  102 . The capacity of the pressure chamber  201  is changed, and a pressure change occurs in the ink within the pressure chamber  201 . 
     The electrode portion  108   a  of the wiring electrode  108  is one of two electrodes connected to the opposed sides of the piezoelectric film  111 . The electrode portion  108   a  of the wiring electrode  108  is formed in an annular shape larger than that of the piezoelectric film  111 , and is formed on the discharge side (the side facing the outside of the ink jet head  10 ) of the piezoelectric film  111 . 
     The electrode portion  106   a  of the shared electrode  106  is one of the two electrodes connected to the piezoelectric film  111 . The electrode portion  106   a  of the shared electrode  106  is formed in an annular shape smaller than that of the piezoelectric film  111 , and is formed on the second surface  502  of the vibration plate  109 . The electrode portion  106   a  of the shared electrode  106  is formed on the second surface  502  of the vibration plate  109 . 
     The insulating film  112  is sandwiched between the shared electrode  106  and the wiring electrode  108  on the outside of a region in which the piezoelectric film  111  is formed. That is, the shared electrode  106  and the wiring electrode  108  are insulated from each other by the piezoelectric film  111  or the insulating film  112 . The insulating film  112  may be formed of, for example, SiO 2  (silicon oxide). The insulating film  112  may be formed of any of other materials. 
     A driving circuit is connected to the shared electrode terminal portions  105  and the wiring electrode terminal portions  107 . The driving circuit may be, for example, a flexible printed circuit board or a tape carrier package (TCP). 
     The wiring electrode terminal portion  107  is provided at an end of the wiring electrode  108 . The wiring electrode terminal portion  107  is connected to the driving circuit and transmits a signal for driving the actuator  102 . 
     As shown in  FIG. 2 , an interval between the wiring electrode terminal portions  107  is the same as an interval between the nozzles  101  in the X-axis direction. The width of the wiring electrode terminal portion  107  in the X-axis direction is wider than the width of the wiring electrode  108 . For this reason, the wiring electrode terminal portion  107  is easily connected to the driving circuit. 
     For example, the shared electrode terminal portions  105  are provided on the second surface  502  of the vibration plate  109 . The shared electrode terminal portion  105  is an end of the shared electrode  106  and is connected to a GND (ground=0 V) provided in the driving circuit. 
     The wiring electrodes  108  are each individually connected to the piezoelectric films  111  of the corresponding actuators  102  and each transmit a signal for driving the respective actuators  102 . Each wiring electrode  108  is used as an individual electrode for operating the piezoelectric film  111  independently of other piezoelectric films  111  on the nozzle plate  100 . Each of the plurality of wiring electrodes  108  includes the above-mentioned electrode portion  108   a , a wiring portion, and the above-mentioned wiring electrode terminal portion  107 . 
     The wiring portion of the wiring electrode  108  extends toward the wiring electrode terminal portion  107  from the electrode portion  108   a . The electrode portion  108   a  of the wiring electrode  108  is disposed coaxially with the nozzle  101 . An inner circumferential portion of the electrode portion  108   a  is slightly separated from the nozzle  101 . 
     The wiring electrodes  108  are formed of, for example, a Pt (platinum) thin film. However, the wiring electrodes  108  may be formed of any of other materials such as Ni (nickel), Cu (copper), Al (aluminum), Ag (silver), Ti (titanium), W (tantalum), No (molybdenum), or Au (gold). 
     The shared electrode  106  is connected to the plurality of piezoelectric films  111 . The shared electrode  106  includes the above-mentioned plurality of electrode portions  106   a , a plurality of wiring portions, and the above-mentioned two shared electrode terminal portions  105 . 
     The wiring portion of the shared electrode  106  extends from the electrode portion  106   a  to the opposite side of the wiring portion of the wiring electrode  108 . The wiring portions of the shared electrode  106  join at an end of the nozzle plate  100  in the Y-axis direction shown in  FIG. 2 , and extend to both ends of the nozzle plate  100  in the X-axis direction. The electrode portion  106   a  is provided coaxially around the nozzle  101 . An inner circumferential portion of the electrode portion  106   a  is spaced separated from the outer circumference of nozzle  101 . The shared electrode terminal portions  105  are respectively disposed at opposed ends of the nozzle plate  100  in the X-axis direction. 
     The shared electrode  106  may be formed of, for example, a Pt (platinum)/Ti (titanium) thin film. However, the shared electrode  106  may be formed of any of other materials such as Ni, Cu, Al, Ti, W, Mo, or Au. 
     As shown in  FIG. 3 , the protective film  113  is provided on the second surface  502  of the vibration plate  109 . The protective film  113  covers the second surface  502  of the vibration plate  109 , the shared electrode  106 , the wiring electrode  108 , and the piezoelectric film  111 . 
     The protective film  113  may be formed of polyimide. The protective film  113  is not limited thereto, and may be formed of any of other materials such as a resin, a ceramic, or a metal (alloy). The resin used is a plastic material such as ABS (acrylonitrile.butadiene.styrene), polyacetal, polyamide, polycarbonate, or polyethersulfone. The ceramic used is a nitride or an oxide such as zirconia, silicon carbide, silicon nitride, or barium titanate. The metal used is, for example, aluminum, SUS, or titanium. Meanwhile, when the protective film  113  is formed of a conductive material, the shared electrode  106 , the wiring electrode  108 , and the piezoelectric film  111  are insulated from each other, for example, by a resin. 
     The material of the protective film  113  has a Young&#39;s modulus that is greatly different from that of the material of the vibration plate  109 . A deformation amount of a plate shape is affected by the Young&#39;s modulus and a plate thickness of a material. Even when the same force is applied, the deformation amount increases as the Young&#39;s modulus decreases and the plate thickness decreases. 
     The ink-repellent film  116  covers the surface of the protective film  113 . The ink-repellent film  116  may be formed of a silicone-based water repellent material with a water repellent property. However, the ink-repellent film  116  may be formed of any of other materials such as a fluoride-containing organic material. 
     The ink-repellent film  116  does not cover the shared electrode terminal portions  105 , the wiring electrode terminal portions  107 , and the protective film  113  around the shared electrode terminal portions  105  and the wiring electrode terminal portions  107 , so as to expose such components. 
     The nozzles  101  extend through the vibration plate  109 , the protective film  113 , and the ink-repellent film  116 . In other words, the nozzles  101  are provided in the vibration plate  109 , the protective film  113 , and the ink-repellent film  116 . 
     The vibration plate  109  may be formed of SiO 2 . However, the vibration plate  109  is not limited thereto, and may be formed of any of other materials such as SiN (silicon nitride), Al 2 O 3  (aluminum oxide), HfO 2  (hafnium oxide), ZrO 2  (zirconium oxide), or DLC (Diamond Like Carbon). 
     The material of the vibration plate  109  is selected in consideration of, for example, a heat resistance property, an insulation property (e.g., when ink with high conductivity is used, the influence of ink alteration due to the driving of the actuator  102  is considered), an expansion coefficient, smoothness, and wettability with respect to ink. 
     As shown in  FIG. 3 , a plurality of deformation control units  505  are provided in the pressure chamber  201 . However, only one deformation control unit  505  may be provided in the pressure chamber  201 . The deformation control units  505  protrude from the first surface  501  of the vibration plate  109  of the nozzle plate  100 . 
     The deformation control units  505  are now further described, with reference to a single deformation control unit  505 . The description is applicable to each of the plurality of deformation control units  505 , if more than one deformation control unit  505  is provided. The deformation control unit  505  is formed of silicon which is the same material as the pressure chamber structure  200 . However, the deformation control unit  505  may be formed of a different material from the pressure chamber structure  200 . In addition, the deformation control unit  505  may be formed out of a portion of the vibration plate  109 . 
       FIG. 4  is a cross-sectional view of a part of the ink jet head  10  taken along line F 4 -F 4  of  FIG. 3 . As shown in  FIG. 4 , the deformation control unit  505  is formed in an annular shape. The deformation control unit  505  is disposed coaxially with the nozzle  101 . In other words, the deformation control unit  505  surrounds the nozzle  101  so that the center of the deformation control unit  505  and the center of the nozzle  101  are substantially the same. However, the center of the deformation control unit  505  and the center of the nozzle  101  may deviate from each other. 
     The deformation control unit  505  is disposed at a position overlapping the actuator  102  on the nozzle plate  100 . In other words, the deformation control unit  505  is disposed inside a region D on the nozzle plate that is defined by an outer edge of the actuator  102 . An external diameter of the actuator  102  having an annular shape is, for example, 174 μm. 
     A distance between an inner edge of the deformation control unit  505  and an outer edge thereof is smaller than a distance between an inner edge of the actuator  102  and the outer edge thereof. In other words, an annular width of the deformation control unit  505  is smaller than an annular width of the actuator  102 . The annular width of the deformation control unit  505  is, for example, 10 μm to 30 μm. The annular width of the deformation control unit  505  is, for example, 10 μm to 100 μm. 
     Considering the plurality of deformation control units  505 , the deformation control unit  505  on the innermost side of the nozzle plate  100  is separated from the nozzle  101 . The plurality of deformation control units  505  are arranged at equal intervals. However, the innermost deformation control unit  505  may be adjacent to the nozzle  101 . Also, the deformation control units  505  may be arranged at different intervals. 
     The above-described inkjet printer  1  performs printing (i.e., image formation) as follows. Ink is supplied to the ink supply port  401  of the ink feed passage structure  400  from the ink tank  11 . The ink is supplied to the plurality of pressure chambers  201  via the plurality of ink apertures  301 . The ink supplied to the pressure chamber  201  is then supplied into the corresponding nozzle  101  and forms a meniscus in the nozzle  101 . The ink supplied from the ink supply port  401  is held with an appropriate negative pressure, so that the ink within the nozzle  101  is held without leaking from the nozzle  101 . 
     A printing instruction signal is input to the driving circuit, for example, by a user&#39;s operation. The driving circuit that received the printing instruction outputs the signal to the actuator  102  through the wiring electrode  108 . In other words, the driving circuit applies a voltage to the electrode portion  108   a  of the wiring electrode  108 . Thereby, an electric field is applied to the piezoelectric film  111  in the same direction as a polarization direction, and the actuator  102  expands and contracts in a direction perpendicular to the direction of the electric field. 
     The actuator  102  is sandwiched between the vibration plate  109  and the protective film  113 . Thus, when the actuator  102  extends in the direction perpendicular to the direction of the electric field, force for deforming in a concave shape with respect to the pressure chamber  201  side is applied to the vibration plate  109 . Furthermore, a force for deforming in a convex shape with respect to the pressure chamber  201  side is applied to the protective film  113 . When the actuator  102  contracts in the direction perpendicular to the direction of the electric field, a force for deforming in a convex shape with respect to the pressure chamber  201  side is applied to the vibration plate  109 . In addition, a force for deforming in a concave shape with respect to the pressure chamber  201  side is applied to the protective film  113 . 
       FIG. 5  is a cross-sectional view of a part of the ink jet head  10  in which the nozzle plate  100  is deformed. In  FIG. 5 , the nozzle plate  100  and the actuator  102  are shown. In addition,  FIG. 5  shows only one deformation control unit  505 , although, as explained above, more than one may be used. 
     The polyimide film of the protective film  113  has a Young&#39;s modulus smaller than that of the vibration plate  109 . For this reason, the protective film  113  has a greater deformation amount with respect to the same force. When the actuator  102  extends in the direction perpendicular to the direction of the electric field, the nozzle plate  100  is deformed in a convex shape with respect to the pressure chamber  201  side, as shown in  FIG. 5 . Thereby, the capacity of the pressure chamber  201  is reduced because the protective film  113  has a greater deformation amount in a convex shape with respect to the pressure chamber  201  side. Conversely, when the actuator  102  contracts in the direction perpendicular to the direction of the electric field, the nozzle plate  100  is deformed in a concave shape with respect to the pressure chamber  201  side. Thereby, the capacity of the pressure chamber  201  is increased because the protective film  113  has a greater deformation amount in a concave shape with respect to the pressure chamber  201  side. In this manner, the actuator  102  changes the capacity of the pressure chamber  201  by deforming the nozzle plate  100 . 
     When the volume of the pressure chamber  201  is increased or reduced by the deformation of the nozzle plate  100 , a pressure change occurs in the ink of the pressure chamber  201 . The ink supplied to the nozzles  101  is discharged by the pressure change. In  FIG. 5 , the discharged ink droplets are shown as a dashed-two dotted line. 
     As a difference in the Young&#39;s modulus between the vibration plate  109  and the protective film  113  increases, a difference in deformation amount of the vibration plate  109  when the same voltage is applied to the actuator  102  increases. For this reason, as the difference in the Young&#39;s modulus between the vibration plate  109  and the protective film  113  increases, ink can be discharged at a lower voltage. 
     When a voltage is applied to the actuator  102  in a case where the vibration plate  109  and the protective film  113  have the same film thickness and Young&#39;s modulus, forces that cause the deformation by the same amount in the directly opposite directions are applied to the vibration plate  109  and the protective film  113 , and thus the vibration plate  109  is not deformed. 
     Meanwhile, as described above, a deformation amount of a plate is affected by not only the Young&#39;s modulus of a material but also a plate thickness. For this reason, when a difference occurs in the deformation amount between the vibration plate  109  and the protective film  113 , both the Young&#39;s modulus of each material and the film thicknesses of each material are considered. Even when the materials of the vibration plate  109  and the protective film  113  have the same Young&#39;s modulus, if there is a difference between the film thicknesses, ink can be discharged. 
     Next, an example of a method of manufacturing the ink jet head  10  will be described. First, the vibration plate  109  is formed in the pressure chamber structure  200  (which is formed from a silicon wafer) before the pressure chamber  201  is formed. The SiO 2  film for forming the vibration plate  109  is formed on the entirety of the mounting surface  200   a  of the pressure chamber structure  200  by using, for example, a CVD method. The SiO 2  film may also be formed by thermal oxidation. In addition, if the vibration plate  109  is formed of SiN, the vibration plate may be formed using a sputtering method. 
     Next, the vibration plate  109  is patterned to form the nozzles  101 . The patterning is performed by forming an etching mask on the vibration plate  109  and removing the unmasked portions of the vibration plate  109  through etching. 
     Next, the shared electrode  106  is formed on the second surface  502  of the vibration plate  109 . For example, Ti and Pt are sequentially deposited using a sputtering method. The shared electrode  106  may be formed by any of other manufacturing methods such as deposition or plating. 
     After the shared electrode  106  is formed, the plurality of electrode portions  106   a , the wiring portion, and the two shared electrode terminal portions  105  are formed through patterning. The patterning is performed by forming an etching mask on an electrode film and removing the unmasked portions of electrode material through etching. 
     Since the nozzle  101  is formed at the center of the electrode portion  106   a  of the shared electrode  106 , a portion of the electrode portion  106   a  having no electrode film, concentric with the center of the electrode portion  106   a , is formed. The shared electrode  106  is patterned, and thus the vibration plate  109  is exposed at positions other than at the electrode portion  106   a  of the shared electrode  106 , the wiring portion, and the shared electrode terminal portion  105 . 
     Next, the piezoelectric film  111  is formed on the shared electrode  106 . The piezoelectric film  111  is formed using, for example, an RF magnetron sputtering method. After the formation of the piezoelectric film, the piezoelectric film  111  is heated at a temperature of 500° C. for three hours in order to impart piezoelectricity to the piezoelectric film  111 . Thereby, the piezoelectric film  111  obtains a good piezoelectric performance. The piezoelectric film  111  may be formed using any of various manufacturing methods such as a CVD (chemical vapor deposition) method, a sol-gel method, an AD (aerosol deposition) method, or a hydrothermal synthesis method. The piezoelectric film  111  is patterned by etching. 
     Since the nozzle  101  is formed at the center of the piezoelectric film  111 , a portion having no piezoelectric film is formed which is concentric with the nozzle  101 . The vibration plate  109  is exposed in the portion not including the piezoelectric film  111 . The piezoelectric film  111  covers the electrode portion  106   a  of the shared electrode  106 . 
     Next, the insulating film  112  is formed on a part of the piezoelectric film  111  and apart of the shared electrode  106 . The insulating film  112  is formed using a CVD method capable of realizing a good insulation property through low-temperature film formation. The insulating film  112  is patterned after the film formation. In order to prevent defects from occurring due to patterning process variations, the insulating film  112  covers a part of the piezoelectric film  111 . The insulating film  112  covers the piezoelectric film  111  to the extent that a deformation amount of the piezoelectric film  111  is not obstructed. 
     Next, the wiring electrode  108  is formed on the vibration plate  109 , the piezoelectric film  111 , and the insulating film  112 . The wiring electrode  108  may be formed using a sputtering method. The wiring electrode  108  may also be formed using any of various manufacturing methods such as vacuum deposition or plating. 
     The electrode portion  108   a , the wiring portion, and the wiring electrode terminal portion  107  are formed by patterning the formed wiring electrode  108 . The patterning is performed by forming an etching mask on an electrode film and removing unmasked portions of electrode material through etching. 
     Since the nozzle  101  is formed at the center of the electrode portion  108   a  of the wiring electrode  108 , a portion of the wiring electrode  108  having no electrode film is formed concentric with the electrode portion  108   a . The electrode portion  108   a  of the wiring electrode  108  covers the piezoelectric film  111 . 
     Next, the protective film  113  is formed on the vibration plate  109 , the wiring electrode  108 , the shared electrode  106 , and the insulating film  112 . The protective film  113  is formed by depositing a solution containing a polyimide precursor through spin coating, and performing thermal polymerization and removal of the solution through baking. The protective film may be formed through spin coating, and thus a film having a smooth surface is formed. The protective film  113  may also be formed using any of various manufacturing methods such as CVD, vacuum deposition, plating, or spin on methods. 
     Next, patterning is performed to expose the shared electrode terminal portion  105  and the wiring electrode terminal portion  107  and to open the nozzles  101 . When non-photosensitive polyimide is used for the protective film  113 , patterning is performed by forming an etching mask on the non-photosensitive polyimide film and removing unmasked portions of the polyimide film through etching. 
     Next, a protective film cover tape is adhered onto the protective film  113 . The pressure chamber structure  200  to which the protective film cover tape is adhered is inverted vertically, and the plurality of pressure chambers  201  are formed in the pressure chamber structure  200 . 
     In detail, first, the protective film cover tape is attached onto the protective film  113 . For example, the protective film cover tape is a rear surface protection tape for chemical mechanical polishing (CMP) of a silicon wafer. 
     An etching mask is formed on the pressure chamber structure  200  which is a silicon wafer, and the unmasked portions of the silicon wafer are removed using a so-called vertical deep dry etching method exclusively for a silicon substrate, and thus the pressure chambers  201  are formed. 
     For example, a halftone mask is used as the etching mask. The halftone mask includes a transmissive portion and a semi-transmissive portion. The semi-transmissive portion is provided at a position corresponding to the deformation control unit  505 , and thus the pressure chambers  201  and the plurality of deformation control units  505  are formed by a single etching. In this manner, the deformation control units  505  are formed by etching the silicon wafer for forming the pressure chamber structure  200 . 
     SF6 gas used for the above-mentioned etching does not have an etching effect on the SiO 2  film and the SiN film of the vibration plate  109  and the polyimide film of the protective film  113 . For this reason, the progression of the dry etching of the silicon wafer for forming the pressure chambers  201  is stopped at the vibration plate  109 . 
     Meanwhile, the above-described etching may use any of various methods such as a wet etching method using a chemical solution or a dry etching method using plasma. The etching method and the etching conditions may be changed using a material such as an insulating film, an electrode film, or a piezoelectric film. After an etching process using a photosensitive resist film is finished, the remaining photosensitive resist film is removed using a solution. 
     In addition, the deformation control unit  505  may be formed using methods other than etching. For example, after the pressure chambers  201  are formed by etching, the deformation control units  505  may be formed using a sputtering method. In this case, the deformation control unit  505  may be formed of a material—for example, SiO 2 —which is different from the material of the pressure chamber structure  200 . 
     Next, the separate plate  300  and the ink feed passage structure  400  are attached to the pressure chamber structure  200 . That is, the separate plate  300 , which is adhered to the ink feed passage structure  400 , is adhered to the pressure chamber structure by using an epoxy resin agent. 
     Next, a cover tape is attached to the protective film  113  so as to cover the shared electrode terminal portions  105  and the wiring electrode terminal portions  107 . The cover tape is formed of a resin, and can be easily desorbed from the protective film  113 . The cover tape prevents dust and the ink-repellent film  116  to be described below from adhering to the shared electrode terminal portion  105  and the wiring electrode terminal portion  107 . 
     Next, the ink-repellent film  116  is formed on the protective film  113 . The ink-repellent film  116  is formed on the protective film  113  by spin coating a liquid ink-repellent film material. During the spin coating process, positive pressure air is injected from the ink supply port  401 , so that the positive pressure air is discharged from the nozzles  101  connected to the ink supply passage  402 . In this state, when the liquid ink-repellent film material is applied, the ink-repellent film material is prevented from adhering to inner walls of the nozzles  101 . 
     After the ink-repellent film  116  is formed, the cover tape is peeled off from the protective film  113 . Thereby, the ink jet head  10  shown in  FIG. 3  is formed. The ink jet head  10  is mounted inside the ink jet printer  1 . The driving circuit is then connected to the shared electrode terminal portions  105  and the wiring electrode terminal portions  107 . 
     According to the ink jet printer  1  of the first embodiment, the deformation control units  505  surrounding the nozzle  101  protrude from the first surface  501  of the vibration plate  109  of the nozzle plate  100 . The deformation control units  505  surround the nozzle, and thus there is a tendency for the deformation of the nozzle plate  100  through the actuator  102  to become uniform (i.e., symmetric) in the region surrounded by the deformation control units  505 . 
     Specifically, the nozzle plate  100  is deformed by the actuator  102  as shown in  FIG. 5 . Non-uniform (i.e., asymmetric) deformation of the nozzle plate  100  occurs when, for example, a portion located on the right side of the nozzle  101  is deformed further than a portion located on the left side of the nozzle  101 . The non-uniformity of the deformation is reduced by the stiffness of the deformation control units  505  surrounding the nozzle  101 . Thereby, it is possible to prevent the deformation of the nozzle plate  100  from becoming non-uniform, and to prevent an ink discharge direction from becoming unstable. 
     The first surface  501  of the vibration plate  109  of the nozzle plate  100  applies pressure to the ink supplied to the pressure chambers  201 . The deformation control units  505  are provided in the vibration plate  109 , and thus non-uniform deformation of the nozzle plate  100  is prevented. 
     The deformation control units  505  are disposed inside the region D that is defined by the outer edge of the actuator  102 . Accordingly, deformation of the nozzle plate  100  is made substantially uniform due to the deformation control units  505 . 
     The annular width of the deformation control unit  505  is smaller than the annular width of the actuator  102 . Thus, the deformation control unit  505  does not obstruct deformation of the nozzle plate  100  through the actuator  102 . 
     The center of the deformation control unit  505  is aligned with the center of the nozzle  101 . Thereby, the deformation of the nozzle plate  100  is uniform (i.e., symmetric) in a region centered around the nozzle  101 . This arrangement prevents ink discharge from becoming unstable. 
     However, the center of each of the plurality of deformation control units  505  may be different from the center of the nozzle  101 . In this case, the nozzle plate  100  is uniformly deformed by adjusting the position of each of the deformation control units  505 . 
     Next, a second embodiment will be described with reference to  FIG. 6 . Components in the second embodiment having the same function as the ink jet printer  1  of the first embodiment are denoted by the same reference numerals. Further, the description of the component may be partially or totally omitted. 
       FIG. 6  is a cross-sectional view of a part of the ink jet head  10  according to the second embodiment. As shown in  FIG. 6 , a plurality of slits  506  are provided in the deformation control units  505  of the second embodiment. In other words, the plurality of deformation control units  505  are arc-like ribs that are adjacent to each other, separated by the slits  506 . 
     The plurality of slits  506  are radially located around the nozzle  101 . In other words, the plurality of slits  506  are located from an inner edge the deformation control unit  505  to an outer edge thereof. The slits  506  of an outer deformation control unit  505  are arranged alternately with the slits  506  of a deformation control unit  505  located inside the outer deformation control unit  505 . 
     The depth of the slit  506  is equal to the thickness of the deformation control unit  505 . In other words, in a portion where the slit  506  is provided, the deformation control unit  505  is removed. Thus the first surface  501  of the vibration plate  109  is exposed at each slit  506 . However, the depth of the slit  506  is not limited thereto, and may be, for example, half the thickness of the deformation control unit  505 . 
     According to the ink jet printer  1  of the second embodiment, the slits  506  are provided in the deformation control unit  505 . Thereby, ink can pass through the slits  506 , and thus it is possible to prevent the ink from pooling inside the deformation control unit  505 . 
     Next, a third embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a cross-sectional view of a part of the ink jet head  10  according to the third embodiment. As shown in  FIG. 7 , the deformation control unit  505  of the third embodiment is formed in a spiral shape. Thereby, it is possible for the ink to flow to the nozzle  101 , and to prevent the ink from pooling inside the deformation control unit  505 . 
     Next, fourth and fifth embodiments will be described with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a cross-sectional view of a part of the ink jet head  10  according to the fourth embodiment. As shown in  FIG. 8 , the pressure chamber  201  of the fourth embodiment is formed in a rectangular shape. The actuator  102  and the deformation control units  505  correspond to the pressure chamber  201 , and are also formed in a rectangular shape. 
       FIG. 9  is a cross-sectional view of a part of the ink jet head  10  according to the fifth embodiment. As shown in  FIG. 9 , the pressure chamber  201  of the fifth embodiment is formed in a rhombic shape. The pressure chamber  201  is formed in a rhombic shape, and thus there is a tendency for the nozzles  101  to be arranged in a zigzag manner. The actuator  102  and the deformation control unit  505  correspond to the pressure chamber  201 , and are also formed in a rhombic shape. 
     In the fourth and fifth embodiments, the shapes of the actuator  102  and the deformation control unit  505  are similar to the shape of the pressure chamber  201 . Meanwhile, the shapes of the actuator  102  and the deformation control unit  505  may be flat or inclined with respect to the shape of the pressure chamber  201 . 
     The center of the deformation control unit  505  is aligned with the center of the nozzle  101 . In other words, the shape of the actuator  102  is formed so as to be point-symmetrical with respect to the center of the nozzle  101 . 
     As in the above-described embodiment, the deformation control unit  505  is not limited to an annular shape, and may have any of various shapes. Likewise, the shape of the deformation control unit  505  may be different from the shapes of the pressure chamber  201  and the actuator  102 . 
     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.