Patent Publication Number: US-2022227134-A1

Title: Inkjet head, method for manufacturing same, and image formation device

Description:
TECHNICAL FIELD 
     The present invention relates to an inkjet head, a method for manufacturing the same, and an image formation device. 
     BACKGROUND ART 
     As an inkjet head used in an inkjet printer and the like, an inkjet head provided with a pressure chamber a volume of which fluctuates by actuation of a piezoelectric body and provided with an ink flow path communicating from an ink chamber to a nozzle opening via the pressure chamber is known. 
     Patent Literature 1 discloses a method for manufacturing the above-described inkjet head by fabricating a piezoelectric body on one surface of a diaphragm, fabricating a pressure chamber member formed of a partition wall that divides a plurality of pressure chambers on the other surface of the diaphragm, and thereafter adhering the above-described partition wall of the above-described pressure chamber member to an ink flow path member and a nozzle plate. Note that Patent Literature 1 discloses that, by forming a resist pattern of a photoresist on the other surface described above of the diaphragm and thereafter fabricating the pressure chamber member (partition wall) by electroplating, the piezoelectric body and the pressure chamber member may be integrally fabricated on both surfaces of the diaphragm, so that alignment between the piezoelectric body and the pressure chamber is facilitated. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2009-045871 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In order to cause sufficiently large volume fluctuation for discharging ink in a pressure chamber, it is desirable that a volume of the pressure chamber itself be sufficiently large. Therefore, when the pressure chambers are to be arranged at a higher density in order to enable high-definition pattern formation, it is required to secure the volume of the pressure chamber a width of which is narrowed due to high-density arrangement by increasing a height of the pressure chamber. In order to increase the height of the pressure chamber, it is required to increase a height of a partition wall, and for this purpose, it is required to increase an aspect ratio of the partition wall (ratio (t/W) of the height (t) of the partition wall to the width (W) of the partition wall). In contrast, in order to increase the width of the pressure chamber to decrease the height of the partition wall, it is required to form an ink flow path between the pressure chambers, and the width of the partition wall becomes thinner, so that the aspect ratio of the partition wall also needs to be increased. 
     Such partition wall with the high aspect ratio has been conventionally fabricated by a method for performing photolithography and performing deep etching (Deep-DIE) on a support layer of a silicon on insulator (SOI) substrate, a method for performing wet etching on the support layer of the SOI substrate having an active layer plane orientation of ( 110 ) and the like. However, Si being a single crystal in which a fracture easily proceeds along a cleavage surface when a bending stress is concentrated on a defect portion is very fragile and easily broken. Especially, when forming a diaphragm to be thinner to improve compliance of the diaphragm in order to secure a volume discharging performance of the pressure chamber while arranging the pressure chambers at a high density and the like, it is required to etch the support layer deeper, and to perform processing so that a remaining thickness of the support layer becomes thinner. In a silicon wafer, generally, a wafer end is subjected to beveling processing to suppress stress concentration on a defect portion; however, when the support layer is made thinner, there is a case where breakage cannot be sufficiently suppressed even by beveling. Therefore, when fabricating the partition wall having a high aspect ratio by a conventional method, breakage is likely to occur during manufacture, and production efficiency is unlikely to be improved. 
     In contrast, as disclosed in Patent Document 1, it is possible to fabricate a partition wall without a cleavage surface when fabricating the partition wall on a surface of a substrate such as Si by electroplating of nickel (Ni) and the like using a resist pattern of a photoresist, so that the breakage due to a bending stress and the like is less likely to occur. However, the aspect ratio of the pattern that may be formed of the photoresist is limited to about 1/1, and it is difficult to fabricate the partition wall having the aspect ratio higher than this. 
     The present invention has been achieved on the basis of the above-described findings, and an object thereof is to provide an inkjet head including a pressure chamber in which an aspect ratio of a partition wall is higher, the inkjet head less likely to be broken at the time of fabrication, a method for manufacturing the same, and an image formation device provided with the inkjet head. 
     Solution to Problem 
     The above-described problem is solved by an inkjet head including a diaphragm that vibrates by actuation of a piezoelectric body, and a pressure chamber a volume of which fluctuates by vibration of the diaphragm, in which the pressure chamber is divided from an adjacent pressure chamber or flow path by a partition wall in which a region in contact with the diaphragm is formed of metal, and the partition wall has an aspect ratio of 1.3 or higher. 
     The above-described problem is solved by an image formation device including the above-described inkjet head. 
     Advantageous Effects of Invention 
     According to the present invention, provided is an inkjet head including a pressure chamber in which an aspect ratio of a partition wall is higher, the inkjet head less likely to be broken at the time of fabrication, a method for manufacturing the same, and an image formation device provided with the inkjet head. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of an inkjet image formation device. 
         FIG. 2  is an exploded perspective view illustrating an outline of an inkjet head in a first embodiment of the present invention used in the image formation device illustrated in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line A-A in  FIG. 2  illustrating an outline of a head chip included in the inkjet head of the first embodiment of the present invention. 
         FIG. 4  is a cross-sectional view taken along line B-B in  FIG. 2  illustrating the outline of the head chip included in the inkjet head of the first embodiment of the present invention. 
         FIG. 5  is a conceptual diagram illustrating an interval (P) between adjacent pressure chambers, a width (W) of a partition wall, and a height (t) of the partition wall regarding the inkjet head in the first embodiment of the present invention. 
         FIG. 6A  to  FIG. 6C  are a first flowchart illustrating steps of manufacturing the inkjet head in the first embodiment of the present invention. 
         FIG. 7A  to  FIG. 7D  are a second flowchart illustrating steps of manufacturing the inkjet head in the first embodiment of the present invention. 
         FIG. 8A  to  FIG. 8D  are a third flowchart illustrating steps of manufacturing the inkjet head in the first embodiment of the present invention. 
         FIG. 9  is a cross-sectional view taken along line B-B in  FIG. 2  illustrating an outline of a head chip included in an inkjet head of a second embodiment of the present invention. 
         FIG. 10A  to  FIG. 10C  are a first flowchart illustrating steps of manufacturing the inkjet head in the second embodiment of the present invention. 
         FIG. 11A  to  FIG. 11E  are a second flowchart illustrating steps of manufacturing the inkjet head in the second embodiment of the present invention. 
         FIG. 12A  to  FIG. 12C  are a third flowchart illustrating steps of manufacturing the inkjet head in the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are hereinafter described in detail with reference to the drawings. Note that a member common in the respective drawings is assigned with the same reference sign. The present invention is not limited to the following embodiments. 
     First Embodiment 
     (Image Formation Device and Inkjet Head) 
     An image formation device according to a first embodiment of the present invention may be configured similarly to a well-known inkjet image formation device except that this includes an inkjet head according to this embodiment to be described later. 
     As illustrated in  FIG. 1 , an image formation device  100  includes an inkjet head  1 , an ink supply device  120 , a conveyance device  130 , and a main tank  140 . 
     The inkjet head  1  includes a plurality of nozzles for discharging ink droplets onto a recording medium  150  such as paper being a printed matter. For example, the inkjet head  1  is configured so that a plurality of types of ink of different colors are supplied to specific nozzles, respectively. The inkjet head  1  is arranged so as to be scannable in a direction crossing a conveyance direction X of the recording medium  150  on which an image should be formed, for example. A configuration of the inkjet head  1  is described later. 
     The conveyance device  130  is a device for conveying the recording medium  150  with respect to the inkjet head  1 . The conveyance device  130  is provided with, for example, a belt conveyor  131  and a rotatable feed roller  132 . The belt conveyor  131  is formed of rotatable pulleys  133   a  and  133   b  and an endless belt  134  stretched around the pulleys  133   a  and  133   b . The feed roller  132  is arranged in a position facing the pulley  133   a  on an upstream side in the conveyance direction X of the recording medium  150  so as to interpose the belt  134  and the recording medium  150  between the same and the pulley  133   a  to feed the recording medium  150  onto the belt  134 . 
     The ink supply device  120  is integrally arranged with the inkjet head  1 . The ink supply device  120  is arranged for each type of ink. For example, when using the inks of four colors of yellow (Y), magenta (M), cyan (C), and black (K), four ink supply devices  120  are arranged on the inkjet head  1 . 
     Each ink supply device  120  is supplied with the ink in the main tank  140  via a pipe  161  and a valve  164  connected to the main tank  140 . Each ink supply device  120  is communicated with a common ink chamber  2  to be described later of the inkjet head  1  via a pipe  162 , and is connected so that the ink of each color may be supplied to an ink supply port  2   a  of a desired common ink chamber  2 . 
     The inkjet head  1  is also connected to the main tank  140  by a bypass pipe  163  branching from the above-described pipe  161 . At a branching point between the pipe  161  and the bypass pipe  163 , the valve  164  capable of switching and setting an ink flow path to one of or both the pipe  161  and the bypass pipe  163  is arranged. Each of the pipe  161 , the pipe  162 , and the bypass pipe  163  is, for example, a flexible pipe. The valve  164  is, for example, a three-way valve. 
     The main tank  140  is a tank for accommodating the ink that should be supplied to the inkjet head  1 . The main tank  140  is arranged separately from the inkjet head  1 . The main tank  140  includes, for example, a stirring device not illustrated. The main tank  140  may be appropriately determined according to an image forming performance, a size and the like of the image formation device  100 . For example, in a case where an image forming speed of the image formation device is 1 to 3 m 2 /min, a capacity of the main tank  140  is, for example, 1 L. 
       FIG. 2  is an exploded perspective view illustrating an outline of the inkjet head  1  used in the image formation device  100  described above. As illustrated in  FIG. 2 , the inkjet head  1  includes the common ink chamber  2 , a holder  3 , a head chip  4 , and a flexible wiring board  5 . 
     The common ink chamber  2  is formed into a hollow substantially rectangular parallelepiped shape with one surface facing the holder  3  opened. The ink supply port  2   a  for supplying the ink of the ink supply device  120  and an ink discharge port  2   b  for discharging the ink to the ink supply device  120  are provided on one surface opposed to the above-described opening of the common ink chamber  2 . The common ink chamber  2  is provided with a filter therein, removes foreign matters from the ink supplied from the ink supply port  2   a , and finely crushes bubbles contained in the ink by the above-described filter. 
     The holder  3  is formed into a substantially flat plate shape with an opening  3   a  at substantially the center, and is arranged so as to cover the above-described opening of the common ink chamber  2 . As a result, the common ink chamber  2  is connected to one surface of the holder  3  so as to cover the opening  3   a . The head chip  4  is connected to the other surface of the holder  3  so as to cover the opening  3   a . The holder  3  allows the common ink chamber  2  and the head chip  4  to be communicated with each other via the opening  3   a.    
     An insertion hole  3   b  is provided on an outer periphery of the holder  3 . The flexible wiring board  5  is inserted through the insertion hole  3   b . One end of the flexible wiring board  5  is connected to a wiring board  50  of the head chip  4  to be described later. The other end of the flexible wiring board  5  is inserted through the insertion hole  3   b  provided on the holder  3  from the other surface of the holder  3  to be pulled out toward the common ink chamber  2 . 
       FIG. 3  is a cross-sectional view taken along line A-A in  FIG. 2  illustrating an outline of the head chip  4  included in the inkjet head  1  described above, and  FIG. 4  is a cross-sectional view taken along line B-B in  FIG. 2  illustrating the outline of the head chip  4  included in the inkjet head  1  described above. 
     The head chip  4  includes a nozzle plate  10 , an intermediate plate  20 , a pressure chamber forming plate  30 , a drive plate  40 , and the wiring board  50 . The head chip  4  is obtained by stacking the nozzle plate  10 , the intermediate plate  20 , the pressure chamber forming plate  30 , the drive plate  40 , and the wiring board  50  in this order from an ink discharge surface side. 
     A plurality of nozzle holes  11  is formed in the nozzle plate  10 . The nozzle hole  11  penetrates from one surface to the other surface of the nozzle plate  10 . The nozzle hole  11  has a cross-sectional shape narrowed so that a tip end side thereof serving as a discharge port has a small diameter, and discharges the ink supplied from the common ink chamber  2  from the discharge port to the outside. A plurality of (for example, 500 to 2000) nozzle holes  11  is provided in the nozzle plate  10  to be arranged in a matrix pattern. The nozzle holes  11  are communicated with a pressure chamber  31  formed in the pressure chamber forming plate  30  via the intermediate plate  20  stacked on the nozzle plate  10 . 
     The intermediate plate  20  is arranged between the nozzle plate  10  and the pressure chamber forming plate  30 . The intermediate plate  20  is provided with a first communication hole  21  that allows the nozzle hole  11  and the pressure chamber  31  provided in the pressure chamber forming plate  30  to be described later to be communicated with each other. The first communication hole  21  is provided in a position corresponding to the nozzle hole  11  of the nozzle plate  10  and penetrates from one surface to the other surface of the intermediate plate  20 . 
     The pressure chamber forming plate  30  includes a plurality of pressure chambers  31  and a diaphragm  32 . The pressure chamber  31  is provided in a position corresponding to the nozzle hole  11  of the nozzle plate  10  and the first communication hole  21  of the intermediate plate  20 . The pressure chamber  31  penetrates from one surface to the other surface of the pressure chamber forming plate  30 . The pressure chamber  31  applies a discharge pressure to the ink discharged from the nozzle hole  11  by volume fluctuation thereof. A partition wall  33  is formed between a plurality of pressure chambers  31 . In this embodiment, an entire partition wall  33  is formed of metal capable of electroplating such as nickel (Ni). As a result, rigidity of the partition wall  33  may be improved, and the inkjet head  1  may have a stable structure that is hardly broken by vibration. 
     The diaphragm  32  is arranged so as to cover an opening on a side opposite to the intermediate plate  20  of the pressure chamber  31 . The diaphragm  32  is provided with a second communication hole  34  communicated with the pressure chamber  31 . The drive plate  40  is arranged on one surface on a side opposite to one surface on the pressure chamber  31  side of the diaphragm  32 . 
     The drive plate  40  includes a space  41  and a third communication hole  42  communicated with the second communication hole  34 . The space  41  is arranged in a position facing the pressure chamber  31  with the diaphragm  32  interposed therebetween. An actuator  60  is accommodated in the space  41 . 
     The actuator  60  includes a piezoelectric element  61 , a first electrode  62 , and a second electrode  63 . The first electrode  62  is stacked on one surface of the diaphragm  32 . Note that an insulating layer may be arranged between the first electrode  62  and the diaphragm  32 . The piezoelectric element  61  is stacked on the first electrode  62 , and is arranged for each pressure chamber  31  (each channel) in a position facing the pressure chamber  31  with the diaphragm  32  and the first electrode  62  interposed therebetween. 
     The piezoelectric element  61  is formed of a material deformed by application of a voltage, and is formed of a ferroelectric material such as lead zirconate titanate (PZT), for example. The second electrode  63  is stacked on a surface on the side opposite to the first electrode  62  of the piezoelectric element  61 . The second electrode  63  is connected to a wiring layer  51  provided on the wiring board  50  to be described later via a bump  64 . A film thickness of the piezoelectric element  61  is, for example, 10 μm or less. 
     The wiring board  50  includes the wiring layer  51  and a silicon layer  52  on one surface of which the wiring layer  51  is formed. The wiring layer  51  is connected to the bump  64  provided on the second electrode  63  via a solder Ma. An outer edge of the wiring layer  51  is connected to the flexible wiring board  5 . Furthermore, the silicon layer  52  is arranged on one surface on a side opposite to the drive plate  40  of the wiring layer  51 . The silicon layer  52  is joined to the holder  3 . 
     The wiring board  50  is provided with a fourth communication hole  53  that penetrates the wiring layer  51  and the silicon layer  52 . The fourth communication hole  53  is communicated with the common ink chamber  2  via the third communication hole  42  of the drive plate  40  and the opening  3   a  of the holder  3 . 
     In this embodiment, an inlet that serves as a flow path for supplying the ink in the common ink chamber  2  to the pressure chamber  31  is formed of the fourth communication hole  53  of the wiring board  50 , the third communication hole  42  of the drive plate  40 , and the second communication hole  34  of the diaphragm  32  communicated with one another. The inlet serves to decrease flow path resistance (flow rate) of the ink that flows from the common ink chamber  2  into the pressure chamber  31 . An outlet for discharging the ink in the pressure chamber  31  toward the recording medium  150  is formed of the first communication hole  21  of the intermediate plate  20  and the nozzle hole  11  of the nozzle plate  10  communicated with each other. 
     In the inkjet head  1  having such a configuration, the ink accommodated in the common ink chamber  2  passes through the inlet (that is, the fourth communication hole  53 , the third communication hole  42 , and the second communication hole  34 ) and flows into the pressure chamber  31 . When a voltage is applied between the first electrode  62  and the second electrode  63 , the piezoelectric element  61  is actuated to be deformed (vibrates), and the diaphragm  32  is deformed (vibrates) as the piezoelectric element  61  is deformed. When the diaphragm  32  is deformed (vibrates), a pressure for discharging the ink is generated in the pressure chamber  31 . Due to generation of such pressure, the ink in the pressure chamber  31  is pushed out to the outlet (that is, the first communication hole  21  and the nozzle hole  11 ), and is discharged from the tip end (nozzle opening) of the nozzle hole  11  toward the recording medium  150 . 
     In the inkjet head  1  described above, in order to enable high-definition pattern formation, the pressure chambers  31  are arranged at a high density; for example, the pressure chambers  31  are arranged in a pattern of 300 dpi (an interval (P) between adjacent pressure chambers  31  is about 85 μm). At that time, in order to secure a volume of the pressure chamber  31  enabling sufficiently large volume fluctuation for discharging the ink, a width (W) of the partition wall  33  is desirably about 25 μm to 30 μm, and a height (t) of the partition wall  33  is desirably about 60 μm to 180 μm. 
     When the inkjet head  1  has such a configuration, a ratio of the height (t) of the partition wall to the width (W) of the partition wall is (t/W), and an aspect ratio of the partition wall is about 2.0 to 8.0. 
     Note that, in order to increase a width of the pressure chamber  31  and decrease the height of the partition wall  33  to suppress an increase in size of the inkjet head  1 , the pressure chambers  31  may be arranged in a pattern of 75 dpi (the interval (P) between the adjacent pressure chambers  31  is about 320 μm). At that time, the height (t) of the partition wall  33  is about 50 μm to 180 μm. However, at that time, in order to form a common flow path (reservoir) of the ink between the pressure chambers  31  and arrange the pressure chambers at a higher density, the width (W) of the partition wall  33  is desirably about 25 μm. 
     When the inkjet head  1  has such configuration, the ratio of the height (t) of the partition wall to the width (W) of the partition wall is (t/W), and the aspect ratio of the partition wall is about 1.3 to 4.5. 
     In this manner, this embodiment is intended to achieve both the arrangement of the pressure chambers at a high density and securement of the volume of the pressure chamber by setting the aspect ratio of the partition wall to 1.3 or higher. 
     Note that, in this specification, as illustrated in  FIG. 5 , the interval (P) between the adjacent pressure chambers  31  means an interval between the centers of the adjacent pressure chambers  31 , the width (W) of the partition wall  33  means a minimum value of a distance between one surface facing the pressure chamber of the partition wall  33  and the other surface thereof facing an adjacent space (pressure chamber or flow path) in the inkjet head  1 , and the height (t) of the partition wall  33  means a length in a direction in which the discharged ink flies (in this embodiment, a distance between an end on a piezoelectric element  61  side (contact surface in contact with the diaphragm  32 ) and an end on an outlet side (contact surface in contact with the intermediate plate  20 )) of the partition wall  33 . The height (t) of the partition wall  33  is substantially equal to the length (height) of the pressure chamber  31  in the direction in which the discharged ink flies. Note that the adjacent space means, out of a plurality of pressure chambers or flow paths arranged around a certain pressure chamber, a space having a smallest distance from the center of the pressure chamber to the center thereof (pressure chamber of flow path). 
     (Fabrication of Inkjet Head) 
       FIGS. 6A - FIG. 6C  to  FIG. 8A - FIG. 8D  are explanatory views illustrating an example of a method for fabricating the inkjet head according to this embodiment. Note that scales of some members are changed for facilitating understanding in  FIGS. 6A - FIG. 6C  to  FIG. 8A - FIG. 8D . 
     First, as illustrated in  FIG. 6A , an adhesion layer  612 , a second electrode layer  663 , a piezoelectric layer  661 , a first electrode layer  662 , and a diaphragm layer  632  are formed on a substrate  610 . 
     The substrate  610  may be a well-known substrate such as a silicon wafer, a glass substrate, a metal substrate, and a ceramic substrate. 
     The adhesion layer  612  is a layer for enhancing adhesion of the second electrode layer  663  to the substrate  610 , and may be deposited on a surface of the substrate  610  by sputtering a target made of titanium (Ti), tantalum (Ta), iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), an alloy thereof and the like. It is sufficient that a film thickness of the adhesion layer  612  is, for example, 0.005 μm or more and 0.2 μm or less. 
     The second electrode layer  663  may be deposited on a surface of the adhesion layer  612  by sputtering a target made of platinum (Pt), iridium (Ir), palladium (Pd), ruthenium (Ru), an alloy thereof and the like. It is sufficient that a film thickness of the second electrode layer  663  is, for example, 0.005 μm or more and 0.2 μm or less. 
     The piezoelectric layer  661  may be deposited on a surface of the second electrode layer  663  by sputtering a target made of a ferroelectric material such as lead zirconate titanate (PZT), applying a sol solution containing a PZT material to the surface of the second electrode layer  663  with a spin coater and the like to gelate the same, and then burning the same. It is sufficient that a film thickness of the piezoelectric layer  661  is, for example, 1 μm or more and 10 μm or less. 
     The first electrode layer  662  may be deposited on a surface of the piezoelectric layer  661  by sputtering a target made of a conductive material such as platinum (Pt). It is sufficient that a film thickness of the first electrode layer  662  is, for example, 0.1 μm or more and 0.5 μm or less. Note that an insulating layer may be formed on a surface of the first electrode layer  662  by applying a photosensitive polyimide and the like and exposing the same, or sputtering a target made of an inorganic material such as SiO 2 . 
     The diaphragm layer  632  may be deposited on the surface of the first electrode layer  662  or a surface of the insulating layer by sputtering a target made of copper (Cu), chromium (Cr), nickel (Ni), aluminum (Al), tantalum (Ta), tungsten (W), silicon (Si) and oxides and nitrides thereof. It is sufficient that a film thickness of the diaphragm layer  632  is, for example, 1 μm or more and 10 μm or less. 
     Thereafter, as illustrated in  FIG. 6B , a first resist  635  is applied to a surface of the diaphragm layer  632 . For example, a dry film resist having a film thickness of about 30 μm may be adhered to the surface of the diaphragm layer  632 . 
     Next, as illustrated in  FIG. 6C , the first resist  635  is exposed and developed to form a first resist pattern  636 . The first resist pattern  636  may be formed so that a cured film having a pattern having a shape corresponding to a cross-sectional shape in a width direction (direction parallel to the diaphragm  32 ) of the pressure chamber to be fabricated remains on the surface of the diaphragm layer  632 , and a resist having a shape corresponding to a cross-sectional shape in a width direction of the partition wall and having a shape with an aspect ratio of 1.3 or higher is removed. In this embodiment, the first resist pattern  636  is formed so that the cured film having a width of 60 μm remains on the surface of the diaphragm layer  632 , and the resist having a width of 30 μm is removed in a cross-sectional view illustrated in  FIG. 6C . 
     In this embodiment, thereafter, a second resist  637  is adhered to a surface of the formed first resist pattern  636  as illustrated in  FIG. 7A , and this is exposed and developed to form a second resist pattern  638  as illustrated in  FIG. 7B . Specifically, a dry film resist having a film thickness of about 30 μm is further adhered to the surface of the first resist pattern  636 , and this is exposed and developed so that a cured film having the same shape as that of the first resist pattern  636  is formed on a surface of the cured film that forms the first resist pattern  636 . 
     Next, as illustrated in  FIG. 7C , metal  633  capable of electroplating such as nickel (Ni) is deposited by electroplating on portions from which the resist is removed of the first resist pattern  636  and the second resist pattern  638 . Specifically, first, nickel sulfamate is formed in a nickel electroforming bath at a concentration of 300 to 700 g/L. The above-described electroforming bath is formed by stirring 10 to 30 g/L of boric acid and nickel chloride in pure water in advance. After pH is adjusted to about 4 and temperature is adjusted from normal temperature to about 60° C., a current of 1 to 10 A/dm 2  is allowed to flow through an anode in the electroforming bath, and the metal is deposited on the portion from which the resist is removed of the substrate immersed in the electroforming bath. A deposition rate increases as the temperature of a bath and current density of the anode increase. For example, in order to surely perform deposition inside the resist pattern, it is possible to adjust to suppress the deposition rate at an initial stage of deposition. 
     Thereafter, as illustrated in  FIG. 7D , by grinding the metal  633  and the second resist pattern  638  according to the height of the partition wall  33  to be fabricated and removing the first resist pattern  636  and the second resist pattern  638 , the pressure chamber forming plate  30  including the space  631  to become the pressure chamber and the partition wall  33  derived from the metal  633  is formed. 
     Subsequently, as illustrated in  FIG. 8A  (in  FIG. 8A , upper and lower sides are reversed with respect to previous drawings), the substrate  610  and the adhesion layer  612  are removed by grinding, etching and the like, and the second electrode layer  663  and the piezoelectric layer  661  are individualized by a well-known method such as photolithography and etching. As a result, the piezoelectric element  61  and the second electrode  63  are formed in corresponding positions in the space  631  to become the pressure chamber. The first electrode layer  662  may be made the first electrode  62 , and the diaphragm layer  632  may be made the diaphragm  32 . At that time, the first electrode layer  662  may be further processed to form the ink flow path, or the diaphragm layer  632  may be further processed to further form the second communication hole  34  (not illustrated in  FIG. 8A - FIG. 8D ). 
     Next, as illustrated in  FIG. 8B , the intermediate plate  20  in which the first communication hole  21  is formed and the nozzle plate  10  in which the nozzle hole  11  is formed are prepared, and the intermediate plate  20  and the nozzle plate  10  are adhered with an adhesive and the like to be joined to each other while aligning the first communication hole  21  and the nozzle hole  11 . Then, as illustrated in  FIG. 8C , the joined intermediate plate  20  and nozzle plate  10  described above are adhered to the partition wall  33  to be joined. As a result, the pressure chamber forming plate  30  including the pressure chamber  31  is formed. 
     Finally, the drive plate  40  that divides a plurality of piezoelectric elements  61  and the wiring board  50  are adhered to obtain the head chip  4 . The head chip  4  thus fabricated, the flexible wiring board  5  of which is connected to the wiring board  50 , is connected to the common ink chamber  2  via the holder  3  to become the inkjet head  1 . 
     By the above-described method, the partition wall  33  having the aspect ratio of 1.3 or higher may be fabricated using the photoresist, and the inkjet head  1  including such partition wall  33  may be fabricated. 
     Second Embodiment 
     (Image Formation Device and Inkjet Head) 
     An image formation device according to a second embodiment of the present invention is different from that of the first embodiment in that a partition wall  33  having an aspect ratio of 1.3 or higher included in an inkjet head  1  is formed by joining a plurality of partition wall members. 
       FIG. 9  is a cross-sectional view taken along line B-B in  FIG. 2  illustrating an outline of a head chip  4  included in the inkjet head  1  according to this embodiment. 
     In this embodiment, the partition wall  33  is formed by joining a first partition wall member  33   a  in contact with a diaphragm  32  and a second partition wall member  33   b  in contact with an intermediate plate  20  to each other. 
     The first partition wall member  33   a  is made of metal capable of electroplating such as nickel (Ni) from the viewpoint of improving rigidity of the partition wall  33  to make a structure of the inkjet head less likely to be broken by vibration and stable. 
     The second partition wall member  33   b  may be formed of a material of the same type as that of the first partition wall member  33   a , or may be formed of a different material. For example, the second partition wall member  33   b  may be formed of nickel (Ni) having high ink resistance from the viewpoint of improving durability of the inkjet head  1 . In contrast, the second partition wall member  33   b  is preferably formed of silicon, glass, or stainless steel microfabrication of which is easy from the viewpoint of manufacturing the inkjet head  1  at a lower cost in a shorter time. 
     A method for joining the first partition wall member  33   a  and the second partition wall member  33   b  is not particularly limited, and they may be adhered by an adhesive or by diffusion joining between metals. 
     In this embodiment, the first partition wall member  33   a  and the second partition wall member  33   b  have joint surfaces of different widths (refer to  FIG. 12C ). As a result, as is to be described later, the joint surface having a larger width may absorb misalignment between the first partition wall member  33   a  and the second partition wall member  33   b  at the time of alignment, so that alignment when joining is easy. 
     (Fabrication of Inkjet Head) 
       FIGS. 10A - FIG. 10C  to  FIG. 12A  to  FIG. 12C  are explanatory views illustrating an example of a method for fabricating the inkjet head according to the second embodiment of the present invention. Note that scales of some members are changed for facilitating understanding in  FIGS. 10A - FIG. 10C  to  FIG. 12A  to  FIG. 12C . 
     In this embodiment, as in the first embodiment, a first resist pattern  636  is formed on a substrate  610  on which an adhesion layer  612 , a second electrode layer  663 , a piezoelectric layer  661 , a first electrode layer  662 , and a diaphragm layer  632  are formed (refer to  FIG. 6A  to  FIG. 6C ). 
     Next, as illustrated in  FIG. 10A , metal  933   a  such as nickel (Ni) is deposited by electroplating on a portion from which the resist is removed of the first resist pattern  636 . Specifically, first, nickel sulfamate is formed in a nickel electroforming bath at a concentration of 300 to 700 g/L. The above-described electroforming bath is formed by stirring 10 to 30 g/L of boric acid and nickel chloride in pure water in advance. After pH is adjusted to about 4 and temperature is adjusted from normal temperature to about 60° C., a current of 1 to 10 A/dm 2  is allowed to flow through an anode in the electroforming bath, and the metal is deposited on the portion from which the resist is removed of the substrate immersed in the electroforming bath. A deposition rate increases as the temperature of a bath and current density of the anode increase. For example, in order to surely perform deposition inside the resist pattern, it is possible to adjust to suppress the deposition rate at an initial stage of deposition. 
     Thereafter, as illustrated in  FIG. 10B , by grinding the metal  933   a  and the first resist pattern  636  and removing the first resist pattern  636 , the first partition wall member  33   a  is formed. 
     Subsequently, as illustrated in  FIG. 10C  (in  FIG. 10C , upper and lower sides are reversed with respect to previous drawings), the substrate  610  and the adhesion layer  612  are removed by grinding, etching and the like, and the second electrode layer  663  and the piezoelectric layer  661  are individualized by a well-known method such as photolithography and etching. As a result, the piezoelectric element  61  and the second electrode  63  are formed in corresponding positions in the space  631  to become the pressure chamber. The first electrode layer  662  may be made the first electrode  62 , and the diaphragm layer  632  may be made the diaphragm  32 . At that time, the first electrode layer  662  may be further processed to form the ink flow path, or the diaphragm layer  632  may be further processed to further form the second communication hole  34  (not illustrated in  FIG. 10C ). 
     Note that, hereinafter, a member including the first partition wall member  33   a , the diaphragm  32 , the first electrode  62 , the piezoelectric element  61 , and the second electrode  63  fabricated in this manner is also referred to as a first chip member  941 . 
     Subsequently, as illustrated in  FIG. 11A , a silicon (Si) substrate  920  that becomes a material of the intermediate plate  20  is prepared. 
     Next, a third resist  935  is applied to one surface of the Si substrate  920  with a spin coater and the like as illustrated in  FIG. 11B , and this is exposed and developed to form a third resist pattern  936  as illustrated in  FIG. 11C . The third resist pattern  936  may be formed so that a cured film having a pattern having a shape corresponding to a cross-sectional shape in a width direction (direction parallel to the intermediate plate  20 ) of the particle wall to be fabricated remains on the surface of intermediate plate  20 , and a resist having a shape corresponding to a cross-sectional shape in a width direction of the pressurization chamber is removed. In this embodiment, the third resist pattern  936  is formed so that the cured film having a width of 29 μm remains on the surface of the intermediate plate  20 , and the resist having a width of 56 μm is removed in a cross-sectional view illustrated in  FIG. 11B . 
     Next, as illustrated in  FIG. 11D , the Si substrate  920  is etched using the third resist pattern  936  as a mask. The etching may be dry etching using CHF 3  (trifluoromethane) gas, CH 4  (methane) gas and the like, or may be wet etching. In this embodiment, the second partition wall member  33   b  having a width of 29 μm and a depth of 29 μm is formed on the Si substrate  920  by the etching. 
     Furthermore, as illustrated in  FIG. 11E , by forming a resist pattern and etching the Si substrate  920 , a first communication hole  21  that communicates a bottom of the Si substrate  920  on a side on which the second partition wall member  33   b  is formed with the other surface of the Si substrate  920  is formed. As a result, the intermediate plate  20  including the second partition wall member  33   b  is fabricated. 
     Subsequently, as illustrated in  FIG. 12A , the nozzle plate  10  in which the nozzle hole  11  is formed is prepared, and the intermediate plate  20  and the nozzle plate  10  are adhered with an adhesive and the like to be joined to each other while aligning the first communication hole  21  and the nozzle hole  11 . Note that, hereinafter, a member including the second partition wall member  33   b , the intermediate plate  20 , and the nozzle plate  10  fabricated in this manner is also referred to as a second chip member  942 . 
     Next, as illustrated in  FIG. 12B , the first chip member  941  (refer to  FIG. 10C ) and the second chip member  942  fabricated above are joined to each other while aligning the first partition wall member  33   a  of the first chip member  941  and the second partition wall member  33   b  of the second chip member  942 . 
       FIG. 12C  is an enlarged view illustrating a joint portion between the first partition wall member  33   a  and the second partition wall member  33   b  at that time. In this embodiment, the first partition wall member  33   a  and the second partition wall member  33   b  are formed so that a width on a joint surface of the first partition wall member  33   a  is larger than a width on a joint surface of the second partition wall member  33   b . As a result, the joint surface of the first partition wall member  33   a  may absorb misalignment between the first partition wall member  33   a  and the second partition wall member  33   b  at the time of alignment, so that alignment when joining is easy. 
     Note that, in this specification, the width on the joint surface of the partition wall member means a minimum value of a distance between one side facing the pressure chamber and the other side facing the adjacent pressure chamber on the joint surface of the partition wall member. 
     Thereafter, the drive plate  40  that divides a plurality of piezoelectric elements  61  and the wiring board  50  are adhered and joined to form the head chip  4  as in the first embodiment. The head chip  4  thus fabricated, the flexible wiring board  5  of which is connected to the wiring board  50 , is connected to the common ink chamber  2  via the holder  3  to become the inkjet head  1 . 
     By the above-described method, the partition wall  33  having the aspect ratio of 1.3 or higher may be fabricated by joining a plurality of partition wall members, and the inkjet head  1  including such partition wall  33  may be fabricated. 
     Note that, although the first partition wall member  33   a  and the second partition wall member  33   b  are formed of different materials in the above-described method, but the first partition wall member  33   a  and the second partition wall member  33   b  may be formed of the same type of material. For example, the second partition wall member  33   b  may be formed of metal by photoresist and electroplating. 
     The second partition wall member  33   b  including a region in contact with the intermediate plate  20  may be formed not only by silicon etching but also by blast treatment on a glass substrate or diffusion joining of the second partition wall member  33   b  made of stainless steel and the like to the intermediate plate  20 . Microfabrication of these materials is easier than the electroplating of nickel (Ni) and the like, so that the inkjet head  1  may be manufactured at a lower cost in a shorter time. 
     In the above-described method, the width on the joint surface of the first partition wall member  33   a  is made larger than the width on the joint surface of the second partition wall member  33   b , but the width on the joint surface of the second partition wall member  33   b  may be made larger than the width on the joint surface of the first partition wall member  33   a . In any case, by making the width on the joint surface of the first partition wall member  33   a  different from the width on the joint surface of the second partition wall member  33   b , alignment when joining may be facilitated. 
     Note that, in this embodiment, the first partition wall member  33   a  in contact with the diaphragm  32  and the second partition wall member  33   b  in contact with the intermediate plate  20  are joined to form the partition wall  33  including the two partition wall members; however, the first partition wall member  33   a  and the second partition wall member  33   b  may be joined to each other via another partition wall member to form the partition wall  33  including three or more partition wall members. 
     INDUSTRIAL APPLICABILITY 
     According to the inkjet head of the present invention, it is possible to achieve both the arrangement of the pressure chambers at high density and the securement of the volume of the pressure chamber. Therefore, according to the inkjet head of the present invention, it is possible to further improve definition of an image to be formed and further reduce a cost of fabricating the inkjet head, and it is expected to further contribute to spread of the inkjet head to fields such as image formation and pattern formation. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Inkjet head 
               2  Common ink chamber 
               2   a  Ink supply port 
               2   b  Ink discharge port 
               3  Holder 
               3   a  Opening 
               4  Head chip 
               5  Flexible wiring board 
               10  Nozzle plate 
               11  Nozzle hole 
               20  Intermediate plate 
               21  First communication hole 
               30  Pressure chamber forming plate 
               31  Pressure chamber 
               32  Diaphragm 
               33  Partition wall 
               33   a  First partition wall member 
               33   b  Second partition wall member 
               34  Second communication hole 
               40  Drive plate 
               41  Space 
               42  Third communication hole 
               50  Wiring board 
               51  Wiring layer 
               51   a  Solder 
               52  Silicon layer 
               53  Fourth communication hole 
               60  Actuator 
               61  Piezoelectric element 
               62  First electrode 
               63  Second electrode 
               100  Image formation device 
               120  Ink supply device 
               130  Conveyance device 
               131  Belt conveyor 
               132  Feed roller 
               133   a ,  133   b  Pulley 
               134  Belt 
               140  Main tank 
               161 ,  162  Pipe 
               163  Bypass pipe 
               164  Valve 
               610  Substrate 
               612  Adhesion layer 
               631  Space to become pressure chamber 
               632  Diaphragm layer 
               633 ,  933   a  Metal 
               635  First resist 
               636  First resist pattern 
               637  Second resist 
               638  Second resist pattern 
               661  Piezoelectric layer 
               662  First electrode layer 
               663  Second electrode layer 
               920  Silicon (Si) substrate 
               935  Third resist 
               936  Third resist pattern 
               941  First chip member 
               942  Second chip member