Abstract:
An electrostatic inkjet head is constructed to operate such that a large margin is provided to a drive voltage and a deviation in the drive characteristic is significantly reduced. A vibration plate defines a part of an ink chamber connected to an inkjet nozzle. The vibration plate is elastically deformed so as to eject a droplet of ink from the inkjet nozzle. An individual electrode is located opposite to the vibration plate with a predetermined gap therebetween, the individual electrode being formed by processing a single crystal silicon substrate. Gap spacers are formed on the single crystal silicon substrate. The gap spacers are formed of insulating films so as to define a gap between the individual electrode and the vibration plate. The individual electrode is formed of a silicon film containing impurity atoms providing one of an n-type conductivity and a p-type conductivity to the individual electrode. The individual electrode is surrounded by the gap spacers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to an inkjet head and a manufacturing method thereof and, more particularly, to an electrostatic inkjet head having an individual electrode structure in which a vibration plate is driven by an electrostatic force generated by the individual electrode, and also relates to a method of manufacturing such an inkjet head.  
           [0003]    2. Description of the Related Art  
           [0004]    Japanese Laid-Open patent application No. 6-71882 discloses an electrostatic inkjet head used for an on-demand inkjet printer. The inkjet head disclosed in this patent application has a vibration plate and an individual electrode located opposite to the vibration plate. The individual electrode is formed by an n-type or p-type diffusion layer formed in a single crystal silicon (Si) substrate. The individual electrode is isolated from the Si substrate by a p-n junction. In such an inkjet head structure, the vibration plate is deformed by supplying a voltage to the individual electrode so as to discharge droplets of ink from a nozzle connected to a space defined by the vibration plate.  
           [0005]    In the above-mentioned electrostatic inkjet head, the individual electrode is isolated from the Si substrate via the p-n junction. Accordingly, a leak current flowing through the p-n junction area varies due to a deviation in a process of forming the p-n junction. Thus, a problem such as an increased power consumption, an unstable operation of the inkjet head or an insufficient drive power generated by a drive circuit may be caused by the p-n junction leakage or generation of a p-n junction capacitance.  
           [0006]    Additionally, in the above-mentioned inkjet head, the individual electrode comprises a diffusion layer formed by doping n-type or p-type impurities into the Si substrate, and a drive voltage is provided to the individual electrode. Accordingly, the drive voltage is limited by a width of a depletion layer, and, thereby, the drive voltage must be a relatively low voltage. Usually, the drive voltage has a sufficient margin relative to a junction destruction voltage. However, in the above-mentioned inkjet head, since a relatively low voltage must be provided to the individual electrode, there is a problem in that a margin in the drive voltage provided to the individual electrode is small.  
           [0007]    Further, the above-mentioned patent application describes an example of the inkjet head in which an individual electrode is provided in a groove formed in a glass substrate, which groove defines a gap between the individual electrode and the vibration plate. Since the groove is formed via a dry or wet etching method, the gap between the individual electrode and the vibration plate cannot be precisely controlled. Accordingly, when a plurality of grooves are formed on a wafer substrate, a uniform gap cannot be reliably achieved. The gap is an important design parameter which determines a drive characteristic of the inkjet head. Thus, if the gap is not uniform, a uniform characteristic of the inkjet head cannot be achieved.  
         SUMMARY OF THE INVENTION  
         [0008]    To overcome the problems described above, the preferred embodiments of the present invention provide an improved inkjet head and a manufacturing method thereof wherein the inkjet head achieves a large margin in a drive voltage and prevents deviation in a drive characteristic of the inkjet head.  
           [0009]    According to one preferred embodiment of the present invention, an electrostatic inkjet head has at least one ink chamber connected to an inkjet nozzle and is formed of a silicon substrate, the electrostatic inkjet nozzle includes a vibration plate defining a part of the ink chamber, the vibration plate being elastically deformable so as to eject a droplet of ink from the inkjet nozzle, an individual electrode located opposite to the vibration plate with a predetermined gap therebetween, the individual electrode including a single crystal silicon substrate, and gap spacers disposed on the single crystal silicon substrate, the gap spacers being made of an insulating film so as to define the gap between the individual electrode and the vibration plate, wherein the individual electrode is made of a silicon film containing impurity atoms providing one of an n-type conductivity and a p-type conductivity to the individual electrode, and the individual electrode is surrounded by the gap spacers.  
           [0010]    According to the above-mentioned preferred embodiment of the present invention, the individual electrode is surrounded by the gap spacers which are made of insulating films. Thus, the individual electrode is electrically insulated from other parts of the inkjet head such as the single crystal silicon substrate or other individual electrodes. As a result, a leak current from the individual electrode is significantly reduced which results in a low-power consumption inkjet head. Additionally, a margin of voltage between the individual electrodes is increased, which results in an increase in freedom of a driving voltage used to drive the inkjet head. Further, since the individual electrode is formed of the silicon film containing impurity atoms which provide an n-type conductivity or a p-type conductivity to the individual electrode, a resistance of the individual electrode is reduced, which results in a high-speed operation of the inkjet head.  
           [0011]    In the electrostatic inkjet head according to preferred embodiments of the present invention, the silicon film forming the individual electrode may contain impurity atoms at a concentration of more than about 1E18/cm 3 . Accordingly, an ohmic contact can be easily obtained which increases reliability. Additionally, since a resistance of the individual electrode is reduced, a high-speed operation can be achieved.  
           [0012]    The impurity atoms contained in the silicon film forming the individual electrode may be phosphorus atoms or arsenic atoms. Additionally, the impurity atoms contained in the silicon film forming the individual electrode may be boron atoms. This enables use of a manufacturing line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.  
           [0013]    Additionally, there is provided according to another preferred embodiment of the present invention, an electrostatic inkjet head having at least one ink chamber connected to an inkjet nozzle, the electrostatic inkjet head including a silicon substrate, the electrostatic inkjet nozzle including a vibration plate defining a part of the ink chamber, the vibration plate being elastically deformable by an electrostatic force so as to eject a droplet of ink from the inkjet nozzle, an individual electrode located opposite to the vibration plate with a predetermined gap therebetween, the individual electrode being made of a single crystal silicon substrate, and gap spacers formed on the single crystal silicon substrate, the gap spacers including an insulating film arranged to define the gap between the individual electrode and the vibration plate, wherein the individual electrode includes a silicon film and a silicide film formed on the silicon film, the silicon film lacking impurity atoms providing one of an n-type conductivity and a p-type conductivity to the individual electrode, and the individual electrode is surrounded by the gap spacers.  
           [0014]    According to the preferred embodiment described in the preceding paragraph, the individual electrode is surrounded by the gap spacers which are made of insulating films. Thus, the individual electrode is electrically insulated from other parts of the inkjet head such as the single crystal silicon substrate or other individual electrodes. Thus, a leak current from the individual electrode can be reduced which results in a low-power consumption inkjet head. Additionally, a margin of voltage tolerance between the individual electrodes is increased, which results in an increase in freedom of a driving voltage for driving the inkjet head. Further, since the individual electrode is made of the silicon film and the silicide film formed on the silicon film, a resistance of the individual electrode can be reduced without introducing impurity atoms into the silicon film, which results in a high-speed operation of the inkjet head.  
           [0015]    Additionally, in the electrostatic inkjet head according to preferred embodiments of the present invention, the individual electrode may include a silicide film formed on the silicon film containing the impurity atoms. Accordingly, a resistance of the individual electrode can be greatly reduced, which results in a high-speed operation of the inkjet head.  
           [0016]    In the electrostatic inkjet head according to preferred embodiments of the present invention, the silicide film may be made of titanium silicide. Since the titanium silicide has excellent heat resistance, there is less limitation in the subsequent heat treatment and a freedom in process design is increased. Additionally, this enables use of a process line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.  
           [0017]    The electrostatic inkjet head according to preferred embodiments of the present invention may further include an insulating film formed on the silicon film of the individual electrode. The insulating film prevents the vibration plate from contacting the individual electrode during operation. Thus, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be prevented.  
           [0018]    Additionally, in the electrostatic inkjet head according to preferred embodiments of the present invention, the insulating film may be made of silicon nitride. Since the silicon nitride has excellent insulation characteristics, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be reliably prevented. Additionally, use of the silicon nitride enables allows a manufacturing line of a conventional LSI semiconductor device to be used, which results in reduction in a manufacturing cost of the inkjet head. Further, since the silicon nitride film used as a mask for forming the individual electrode can be used as an insulating film on the individual electrode, a number of process steps required for manufacturing the inkjet head is reduced.  
           [0019]    Alternatively, the insulating film may be made of silicon oxide. Since the silicon oxide has excellent insulation characteristics, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be reliably prevented. Additionally, use of the silicon oxide enables use of a process line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.  
           [0020]    Additionally, according to another preferred embodiment of the present invention, methods for manufacturing the above-mentioned electrostatic inkjet heads are provided.  
           [0021]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1A is a plan view of an inkjet head according to a first preferred embodiment of the present invention;  
         [0023]    [0023]FIG. 1B is a cross-sectional view of the inkjet head shown in FIG. 1A taken along a line I-I of FIG. 1A;  
         [0024]    [0024]FIG. 1C is a cross-sectional view of the inkjet head shown in FIG. 1A taken along a line II-II of FIG. 1A;  
         [0025]    [0025]FIGS. 2A, 2B,  2 C,  2 D,  2 E,  2 F,  2 G,  2 H,  21 ,  2 J,  2 K,  2 L,  2 M and  2 N are cross-sectional views for explaining a manufacturing process of the inkjet head according to the first preferred embodiment of the present invention;  
         [0026]    [0026]FIG. 3A is a plan view of an inkjet head according to a second preferred embodiment of the present invention;  
         [0027]    [0027]FIG. 3B is a cross-sectional view of the inkjet head shown in FIG. 3A taken along a line I-I of FIG. 3A;  
         [0028]    [0028]FIG. 3C is a cross-sectional view of the inkjet head shown in FIG. 3A taken along a line II-II of FIG. 3A;  
         [0029]    [0029]FIGS. 4A, 4B,  4 C,  4 D,  4 E,  4 F,  4 G,  4 H,  41 ,  4 J,  4 K,  4 L,  4 M,  4 N,  4 O and  4 P are cross-sectional views for explaining a manufacturing process of the inkjet head according to the second preferred embodiment of the present invention;  
         [0030]    [0030]FIG. 5A is a plan view of an inkjet head according to a third preferred embodiment of the present invention;  
         [0031]    [0031]FIG. 5B is a cross-sectional view of the inkjet head shown in FIG. 5A taken along a line I-I of FIG. 5A;  
         [0032]    [0032]FIG. 5C is a cross-sectional view of the inkjet head shown in FIG. 5A taken along a line II-II of FIG. 5A;  
         [0033]    [0033]FIGS. 6A, 6B,  6 C,  6 D,  6 E,  6 F,  6 G,  6 H,  61 ,  6 J,  6 K,  6 L,  6 M,  6 N,  6 O,  6 P,  6 Q,  6 R,  6 S and  6 T are cross-sectional views for explaining a manufacturing process of the inkjet head according to the third preferred embodiment of the present invention;  
         [0034]    [0034]FIG. 7A is a cross-sectional view of a first example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B;  
         [0035]    [0035]FIG. 7B is a cross-sectional view of the first example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C;  
         [0036]    [0036]FIG. 8A is a cross-sectional view of a second example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 1B;  
         [0037]    [0037]FIG. 8B is a cross-sectional view of the second example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 1C;  
         [0038]    [0038]FIG. 9A is a cross-sectional view of a third example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B;  
         [0039]    [0039]FIG. 9B is a cross-sectional view of the third example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C;  
         [0040]    [0040]FIG. 10A is a cross-sectional view of a fourth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B;  
         [0041]    [0041]FIG. 10B is a cross-sectional view of the fourth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C;  
         [0042]    [0042]FIG. 11A is a cross-sectional view of a fifth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B;  
         [0043]    [0043]FIG. 11B is a cross-sectional view of the fifth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C;  
         [0044]    [0044]FIG. 12A is a cross-sectional view of a sixth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B;  
         [0045]    [0045]FIG. 12B is a cross-sectional view of the sixth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C;  
         [0046]    [0046]FIG. 13A is a cross-sectional view of a seventh example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B;  
         [0047]    [0047]FIG. 13B is a cross-sectional view of the seventh example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C;  
         [0048]    [0048]FIG. 14A is a cross-sectional view of an eighth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B; and  
         [0049]    [0049]FIG. 14B is a cross-sectional view of the eighth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0050]    A description will now be given, with reference to FIGS. 1A, 1B and  1 C, of a first preferred embodiment of the present invention. FIG. 11A is a plan view of an inkjet head according to the first preferred embodiment of the present invention. FIG. 1B is a cross-sectional view of the inkjet head shown in FIG. 1A taken along a line I-I of FIG. 1A, and FIG. 1C is a cross-sectional view of the inkjet head shown in FIG. 1A taken along a line II-II of FIG. 1A.  
         [0051]    The inkjet head according to the present preferred embodiment includes an ink-chamber substrate  10  and an electrode substrate  20 . The ink-chamber substrate  10  is preferably formed of a single crystal silicon (Si) substrate. A plurality of inkjet nozzles are formed on the ink-chamber substrate  10  via an anisotropic etching method. A plurality of individual ink-chambers are formed inside of the ink-chamber substrate  10  so that each of the inkjet nozzles is provided for a respective one of the individual ink-chambers. A common ink-chamber is also formed inside of the ink-chamber substrate  10 . The common ink-chamber is connected to each of the individual ink-chambers by passages formed via an anisotropic etching method so that ink is supplied to each of the individual ink-chambers from the common ink-chamber. A part of a wall constituting each of the individual ink-chambers defines a thin silicon film vibration plate which is driven by an electrostatic force. The thin silicon film vibration plate is located opposite to an individual electrode provided on the electrode substrate  20 .  
         [0052]    The electrode substrate  20  is also formed of a single crystal silicon (Si) substrate  21  which contains n-type or p-type impurity atoms. Normally, a single crystal Si substrate having a plane orientation (100) is used for the substrate  21 . However, a-single crystal Si substrate having a plane orientation (110) or (111) may be used depending on a process or method to be used. A silicon oxide film  22  is formed on the Si substrate  21 , and individual electrodes  23   b  are formed on the silicon oxide film  22  which defines an insulating layer. The individual electrodes  23   b  are made of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The individual electrodes  23   b  contain impurity atoms implanted by an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method. The individual electrodes  23   b  preferably contain impurity atoms of more than about 1E18/cm 3 . Additionally, insulating gap spacers  23   a  are formed on the silicon oxide film  22  so that each of the individual electrodes  23   b  is located inside a space defined by the insulating gap spacers  23   a.    
         [0053]    The insulating gap spacers  23   a  are preferably made of a silicon (Si) oxidation film formed via a thermal oxidation method. The insulating gap spacers  23   a  define a gap between the vibration plates formed in the ink-chamber substrate  10  and the individual electrodes  23   b  formed in the electrode substrate  20 . That is, an electrostatic force is generated between each of the vibration plates and the respective one of the individual electrodes  23   b  separated by the gap defined by the gap spacers  23   a.    
         [0054]    Insulating films  24  are formed on walls of the insulating gap spacers  23   a  and the individual electrodes  23   b  so as to maintain insulation between each of the individual electrodes  23   b  and the respective one of the vibration plates formed in the ink-chamber substrate  10 . The insulating films  24  are silicon nitride films preferably formed by a chemical vapor deposition (CVD) method or a sputtering method. It should be noted that the insulating films  24  may be omitted if an insulation is not necessary. A voltage applying pad  25  is formed on each of the insulating films  24 . A part of each of the voltage applying pads  25  is connected to a respective one of the individual electrodes  23   b  so as to apply a voltage to the respective one of the individual electrodes  23   b.    
         [0055]    In FIGS. 1A, 1B and  1 C, an area indicated by an arrow b is an opening through which a flexible printed circuit board (FPC) or a bonding wire is connected to each of the voltage applying pads  25 . Additionally, arrows X and Y shown in FIG. 1B are directions of a droplet of ink projected from each of the inkjet nozzles provided on the ink-chamber substrate  10 . That is, when the inkjet nozzles are provided on a side surface of the ink-chamber substrate  10 , the droplet of ink is projected in the direction indicated by the arrow X. When the inkjet nozzles are provided on a top surface of the ink-chamber substrate  10 , the droplet of ink is projected in the direction indicated by the arrow Y.  
         [0056]    A description will now be given, with reference to FIGS. 2A through 2N, of an example of method of manufacturing an inkjet head according to the above-mentioned first preferred embodiment shown in FIGS. 1A, 1B and  1 C. It should be noted that FIGS. 2B, 2D,  2 F,  2 H,  2 J,  2 L and  2 N are cross-sectional views taken along a line I-I of FIGS. 2A, 2C,  2 E,  2 G,  21 ,  2 K and  2 M, respectively.  
         [0057]    First, as shown in FIGS. 2A and 2B, the insulating film  22  is formed on the single crystal silicon substrate  21  via a thermal oxidation method, a chemical vapor deposition method or a sputtering method. The single crystal silicon substrate  21  is of an n-type or a p-type, and preferably has a thickness of about 400 μm to about 700 μm and an electrical resistivity of about 5 Ω-cm 3  to about 30 Ω-cm 3 . Plane orientation of the single crystal silicon substrate  21  is preferably (100), (111) or (110). The insulating film  22  provides insulation between the individual electrodes and the single crystal silicon substrate  21 .  
         [0058]    Thereafter, as shown in FIGS. 2C and 2D, a silicon film  23  is formed on the insulating film  22 . The silicon film  23  can be formed of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The silicon film  23  preferably contains impurity atoms of about 1E18/cm 3  which can be implanted via an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method.  
         [0059]    Thereafter, as shown in FIGS. 2E and 2F, the insulating film  24  is formed on the silicon film  23  via a chemical vapor deposition (CVD) method or a sputtering method. The insulating film is preferably made of a silicon nitride film so as to prevent diffusion of oxygen. Then, the insulating film  24  is patterned via a regular photolithography process and a dry or wet etching method so as to form parts corresponding to the individual electrodes  23   b.    
         [0060]    Thereafter, the silicon film  23  is oxidized by being placed in an oxygen atmosphere in an electric oven. At this time, a first area of the silicon film  23 , at which first area the insulating film  24  for preventing oxygen diffusion is not formed, is oxidized. Thus, a thick silicon oxidation film  23   a  is formed as shown in FIGS. 2G and 2H. On the other hand, a second area of the silicon film  23 , at which second area the insulating film  24  for preventing oxygen diffusion is formed, is not oxidized. Thus, the thickness of the silicon film  23  in the second area remains unchanged as shown in FIGS. 2G and 2H. Since the silicon oxidation film  23   a  and the silicon film  23   b  have different thicknesses, a step is formed between the silicon oxidation film  23   a  and the silicon film  23   b.  This step corresponds to the gap between the individual electrodes and the vibration plates in the inkjet head according to preferred embodiments of the present embodiment. Although the insulating film is not removed in the present preferred embodiment after the silicon oxidation film  23   a  is formed, the insulating film  24  may be removed after the silicon oxidation film  23   a  is formed, if desired.  
         [0061]    Thereafter, as shown in FIGS. 2I and 2J, a single crystal silicon substrate  11  (corresponding to the ink-chamber substrate  10 ) is joined to the electrode substrate  20  which is in an intermediate state as shown in FIGS. 2I and 2J. The single crystal silicon substrate  11  is of an n-type or a p-type, and has a plane orientation (110). A diffusion layer  12  and single crystal silicon etching mask patterns  13  are previously formed on the single crystal silicon substrate  11 . The diffusion layer  12  contains n-type or p-type having impurities of more than about 1E19/cm 3 . A thickness of the diffusion layer  12  is preferably substantially equal to a thickness of the vibration plate. The single crystal silicon etching patterns  13  are formed on a surface of the single crystal silicon substrate  11 , which surface is opposite to the surface on which the diffusion layer  12  is formed. The etching mask patterns  13  are preferably formed of a silicon oxide film, a silicon nitride film or a tantalum peroxide film. The etching mask patterns  13  are provided so as to define areas in which ink chambers and inkjet nozzles are formed. It should be noted that the substrate  11  can be a silicon on insulator (SOI) substrate which is constituted by a single crystal silicon substrate and a single crystal thin silicon film formed on the single crystal silicon substrate via a silicon oxide film.  
         [0062]    The ink-chamber substrate  10  can be joined to the electrode substrate  20  via a direct bonding method or an anode bonding method. In the direct bonding method, the bonding is performed preferably at a temperature of more than about 800° C. within an oxygen atmosphere at a normal pressure or a reduced pressure. In the anode bonding method, an insulating film containing mobile ions such as Na ions or H ions is formed on the single crystal silicon substrate preferably via a sputtering method, and, thereafter, the bonding is performed by applying an electric field at a temperature ranging from about 200° C. to about 500° C., and preferably from about 350° C. to about 450° C. Additionally, it is preferable that before the bonding is performed, the silicon oxidation film  23   a  of the electrode substrate  20  is polished via a chemical mechanical polishing process so as to planarize the surface to be bonded.  
         [0063]    After the ink-chamber substrate  10  is bonded to the electrode substrate  20 , the ink-chamber substrate  10  (the single crystal silicon substrate  11 ) is etched preferably via an anisotropic etching method on the surface provided with the etching mask patterns  13 . The anisotropic etching is performed by using KOH or TMAH. The etching is stopped by the diffusion layer  12  which contains impurities at a high concentration. Accordingly, the diffusion layer  12  remains as the vibration plate as shown in FIGS. 2K and 2L. If the SOI substrate is used, the etching is stopped by the silicon oxide film. In such a case, the silicon oxide film on the SOI substrate may be removed after the etching.  
         [0064]    Thereafter, an ink-chamber cover  14  is bonded to the substrate  11  so as to form the individual ink-chambers  18  and the common ink-chamber  16  as shown in FIG. 2M. The ink-chamber cover  14  is preferably formed of a glass plate or a metal plate. A passage  15  for supplying ink to the common ink-chamber  16  is previously formed in the ink-chamber cover  14  preferably via sand blasting or laser machining. Additionally, the crystal silicon thin film  12  corresponding to a pad area (an area indicated by arrow b) is removed by etching. Then, the voltage applying pads  25  are formed on the individual electrodes  23   b.    
         [0065]    As shown in FIG. 2M, each of the inkjet nozzles  19  is provided for a respective one of the individual ink-chambers  18 . Each of the individual ink-chambers  18  is connected to the common ink-chamber  16  by the passage  17 .  
         [0066]    When a predetermined voltage is applied to the voltage applying pad  25  which is connected to the individual electrode  23   b,  an electrostatic force is generated between the vibration plate  12  and the individual electrode  23   b  which results in warpage of the vibration plate  12  toward the individual electrode  23   b.  Accordingly, ink is introduced into the individual ink-chamber  18  via the passage  15 , the common ink-chamber  16  and the passage  17 . When the supply of the voltage is stopped, the vibration plate  12  returns to the original position due to its elasticity. At this time, the ink in the individual ink-chamber  18  is pressurized, and a droplet of the ink is discharged from the inkjet nozzle  19  in a direction indicated by an arrow X in FIG. 2M so that the droplet of the ink is projected onto a recording paper.  
         [0067]    In the present preferred embodiment, although the inkjet nozzle  19  is formed so that a droplet of ink is projected in the direction (horizontal direction) indicated by the arrow X, the droplet of ink may be projected in a vertical direction by changing the position of the inkjet nozzle  19 . Additionally, the inkjet nozzle  19  may be formed after the ink-chamber substrate  10  and the electrode substrate  20  are bonded to each other.  
         [0068]    A description will now be given, with reference to FIGS. 3A, 3B and  3 C, of a second preferred embodiment of the present invention. FIG. 3A is a plan view of an inkjet head according to the second preferred embodiment of the present invention. FIG. 3B is a cross-sectional view of the inkjet head shown in FIG. 3A taken along a line I-I of FIG. 3A, and FIG. 3C is a cross-sectional view of the inkjet head shown in FIG. 3A taken along a line II-II of FIG. 3A.  
         [0069]    The inkjet head according to the present preferred embodiment includes an ink-chamber substrate  30  and an electrode substrate  40 . The ink-chamber substrate  30  is preferably formed of a single crystal silicon (Si) substrate. A plurality of inkjet nozzles are formed on the ink-chamber substrate  30  preferably via an anisotropic etching method. A plurality of individual ink-chambers are formed inside of the ink-chamber substrate  30  so that each of the inkjet nozzles is provided for a respective one of the individual ink-chambers. A common ink-chamber is also formed inside of the ink-chamber substrate  30 . The common ink-chamber is connected to each of the individual ink-chambers via passages formed preferably via an anisotropic etching method so that ink is supplied to each of the individual ink-chambers from the common ink-chamber. A part of a wall constituting each of the individual ink-chambers defines a thin silicon film vibration plate which is driven by an electrostatic force. The thin silicon film vibration plate is located opposite to an individual electrode formed on the electrode substrate  40 .  
         [0070]    The electrode substrate  20  is also formed of a single crystal silicon (Si) substrate  41  which contains n-type or p-type impurity atoms. Normally, a single crystal Si substrate having a plane orientation (100) is used for the substrate  41 . However, a single crystal Si substrate having a plane orientation (110) or (111) may be used depending on a process or method to be used. A silicon oxide film  42  is formed on the Si substrate  41 , and individual electrodes  43   b  are formed on the silicon oxide film  42  which defines an insulating layer. The individual electrodes  43   b  are made of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The individual electrodes  43   b  contain impurity atoms implanted by an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method. The individual electrodes  43   b  preferably contain impurity atoms of more than about 1E18/cm 3 . Additionally, insulating gap spacers  43   a  are arranged on the silicon oxide film  42  so that each of the individual electrodes  43   b  is located inside a space defined by the insulating gap spacers  43   a.    
         [0071]    The insulating gap spacers  43   a  are preferably made of a silicon (Si) oxide film formed by a thermal oxidation method. The insulating gap spacers  43   a  define a gap between the vibration plates formed in the ink-chamber substrate  30  and the individual electrodes  43   b  formed in the electrode substrate  40 . That is, an electrostatic force is generated between each of the vibration plates and the respective one of the individual electrodes  43   b  separated by the gap defined by the gap spacers  43   a.    
         [0072]    A silicon oxide insulating film  45  is formed on each of the individual electrodes  43   b  so as to maintain insulation between each of the individual electrodes  43   b  and the respective one of the vibration plates formed in the ink-chamber substrate  30 . A voltage applying pad  46  is formed on the silicon oxide insulating film  45 . A part of the voltage applying pad  46  is connected to the individual electrode  43   b  so as to apply a voltage to the individual electrode  43   b.    
         [0073]    In FIGS. 3A, 3B and  3 C, an area indicated by an arrow b is an opening through which a flexible printed circuit board (FPC) or a bonding wire is connected to each of the voltage applying pads  46 . Additionally, arrows X and Y shown in FIG. 3B are directions of a droplet of ink projected from each of the inkjet nozzles formed on the ink-chamber substrate  30 . That is, when the inkjet nozzles are provided on a side surface of the ink-chamber substrate  30 , the droplet of ink is projected in the direction indicated by the arrow X. When the inkjet nozzles are provided on a top surface of the ink-chamber substrate  30 , the droplet of ink is projected in the direction indicated by the arrow Y.  
         [0074]    A description will now be given, with reference to FIGS. 4A through 4P, of an example of a method of manufacturing of the inkjet head according to the above-mentioned second preferred embodiment shown in FIGS. 3A, 3B and  3 C. FIGS. 4A through 4P are cross-sectional views for explaining the manufacturing process of the inkjet head according to the second preferred embodiment of the present invention. It should be noted that FIGS. 4B, 4D,  4 F,  4 H,  4 J,  4 L,  4 N and  4 P are cross-sectional views taken along a line I-I of FIGS. 4A, 4C,  4 E,  4 G,  4 I,  4 K,  4 M and  4 O, respectively.  
         [0075]    First, as shown in FIGS. 4A and 4B, the insulating film  42  is formed on the single crystal silicon substrate  41  preferably via a thermal oxidation method, a chemical vapor deposition method or a sputtering method. The single crystal silicon substrate  41  is an n-type or a p-type, and preferably has a thickness of about 400 μm to about 700 μm and an electrical resistivity of about 5 Ω-cm 3  to about 30 Ω-cm 3 . Plane orientation of the single crystal silicon substrate  41  is preferably (100), (111) or (110). The insulating film  42  provides an insulation between the individual electrodes and the single crystal silicon substrate  41 .  
         [0076]    Thereafter, as shown in FIG. 4C and 4D, a silicon film  43  is formed on the insulating film  42 . The silicon film  43  can be formed of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The silicon film  43  preferably contains impurity atoms of about 1E18/cm 3  which can be implanted via an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method.  
         [0077]    Thereafter, as shown in FIGS. 4E and 4F, the insulating film  44  is formed on the silicon film  43  by a chemical vapor deposition (CVD) method or a sputtering method. The insulating film  44  is made of a silicon nitride film so as to prevent diffusion of oxygen. Then, the insulating film  44  is patterned via a regular photolithography and a dry or wet etching method so as to form parts corresponding to the individual electrodes  23   b.    
         [0078]    Thereafter, the silicon film  43  is oxidized by being placed in an oxygen atmosphere in an electric furnace. At this time, a first area of the silicon film  43  in which first area the insulating film  44  for preventing oxygen diffusion is not formed is oxidized. Thus, a thick silicon oxidation film  43   a  is formed as shown in FIGS. 4G and 4H. On the other hand, a second area of the silicon film  43  in which the insulating film  44  for preventing oxygen diffusion is formed is not oxidized. Thus, the thickness of the silicon film  43  in the second area remains unchanged as shown in FIGS. 4G and 4H. Since the silicon oxidation film  43   a  and the silicon film  43   b  have different thicknesses, a step is formed between the silicon oxide film  43   a  and the silicon film  43   b.  This step corresponds to the gap between the individual electrodes and the vibration palates in the inkjet head according to the present preferred embodiment. The insulating film  44  is removed after the silicon oxide film  43   a  is formed. Then, a silicon oxide film  45  is formed on the silicon film  43   b,  as shown in FIGS. 4I and 4J, by placing the substrate  41  in an oxygen atmosphere in an electric furnace.  
         [0079]    Thereafter, as shown in FIGS. 4K and 4L, a single crystal silicon substrate  31  (corresponding to the ink-chamber substrate  30 ) is joined to the electrode substrate  40  which is in an intermediate state. The single crystal silicon substrate  31  is an n-type or a p-type, and has a plane orientation (110). A diffusion layer  32  and single crystal silicon etching mask patterns  33  are previously formed on the single crystal silicon substrate  31 . The diffusion layer  32  contains n-type or p-type impurities of more than about 1E19/cm 3 . A thickness of the diffusion layer  32  is preferably substantially equal to a thickness of the vibration plate. The single crystal silicon etching patterns  33  are formed on a surface of the single crystal silicon substrate  31 , which surface is opposite to the surface on which the diffusion layer  32  is formed. The etching mask patterns  33  are formed of a silicon oxide film, a silicon nitride film or a tantalum peroxide film. The etching mask patters  33  are arranged so as to define areas in which ink chambers and inkjet nozzles are formed. It should be noted that the substrate  31  can be a silicon on insulator (SOI) substrate which is constituted by a single crystal silicon substrate and a single crystal thin silicon film formed on the single crystal silicon substrate via a silicon oxidation film.  
         [0080]    The ink-chamber substrate  30  can be joined to the electrode substrate  40  preferably via a direct bonding method or an anode bonding method. In the direct bonding method, the bonding is performed preferably at a temperature of more than about 800° C. within an oxygen atmosphere at a normal pressure or a reduced pressure. In the anode bonding method, an insulating film containing mobile ions such as Na ions or H ions is formed on the single crystal silicon substrate via a sputtering method, and, thereafter, the bonding is performed by applying an electric field at a temperature ranging from about 200° C. to about 500° C., and preferably from about 350° C. to about 450° C. Additionally, it is preferable that before the bonding is performed, the silicon oxide film  23   a  of the electrode substrate  20  is polished via a chemical mechanical polishing process so as to planarize the surface to be bonded.  
         [0081]    After the ink-chamber substrate  30  is bonded to the electrode substrate  40 , the ink-chamber substrate  30  (the single crystal silicon substrate  31 ) is etched via an anisotropic etching method on the surface provided with the etching mask patterns  33 . The anisotropic etching is performed by using KOH or TMAH. The etching is stopped by the diffusion layer  32  which contains impurities at a high concentration. Accordingly, the diffusion layer  32  remains as the vibration plate as shown in FIGS. 4M and 4N. If the SOI substrate is used, the etching is stopped by the silicon oxide film. In such a case, the silicon oxide film on the SOI substrate may be removed after the etching.  
         [0082]    Thereafter, an ink-chamber cover  34  is bonded to the substrate  31  so as to form the individual ink-chambers  38  and the common ink-chamber  36  as shown in FIG. 4O. The ink-chamber cover  34  is preferably formed of a glass plate or a metal plate. A passage  35  for supplying ink to the common ink-chamber  36  is previously formed in the ink-chamber cover  34  preferably via sand blasting or laser machining.  
         [0083]    Additionally, the single crystal silicon thin film  32  corresponding to a pad area (an area indicated by arrow b) is removed by etching. Then, the voltage applying pads  46  are formed on the individual electrodes  43   b.    
         [0084]    As shown in FIG. 4O, each of the inkjet nozzles  39  is provided for a respective one of the individual ink-chambers  38 . Each of the individual ink-chambers  38  is connected to the common ink-chamber  36  via the passage.  
         [0085]    When a predetermined voltage is applied to the voltage applying pad  46  which is connected to the individual electrode  43   b,  an electrostatic force is generated between the vibration plate  32  and the individual electrode  43   b  which results in warpage of the vibration plate  32  toward the individual electrode  43   b.  Accordingly, ink is introduced into the individual ink-chamber  38  via the passage  35 , the common ink-chamber  36  and the passage  37 . When the supply of the voltage is stopped, the vibration plate  32  returns to the original position due to its elasticity. At this time, the ink in the individual ink-chamber  38  is pressurized, and a droplet of the ink is discharged from the inkjet nozzle  39  in a direction indicated by an arrow X in FIG. 4O so that the droplet of the ink is projected onto a recording paper.  
         [0086]    In the present preferred embodiment, although the inkjet nozzle  39  is formed so that a droplet of ink is projected in the direction (horizontal direction) indicated by the arrow X, the droplet of ink may be projected in a vertical direction by changing the position of the inkjet nozzle  39 . Additionally, the inkjet nozzle  39  may be formed after the ink-chamber substrate  30  and the electrode substrate  40  are bonded to each other.  
         [0087]    A description will now be given, with reference to FIGS. 5A, 5B and  5 C, of a third preferred embodiment of the present invention. FIG. 5A is a plan view of an inkjet head according to the third preferred embodiment of the present invention. FIG. 5B is a cross-sectional view of the inkjet head shown in FIG. 5A taken along a line I-I of FIG. 5A, and FIG. 5C is a cross-sectional view of the inkjet head shown in FIG. 5A taken along a line II-II of FIG. 5A.  
         [0088]    The inkjet head according to the present preferred embodiment includes an ink-chamber substrate  50  and an electrode substrate  60 . The ink-chamber substrate  40  is preferably made of a single crystal silicon (Si) substrate. A plurality of inkjet nozzles are provided on the ink-chamber substrate  50  preferably via an anisotropic etching method. A plurality of individual ink-chambers are formed inside of the ink-chamber substrate  50  so that each of the inkjet nozzles is provided for a respective one of the individual ink-chambers. A common ink-chamber is also formed inside of the ink-chamber substrate  50 . The common ink-chamber is connected to each of the individual ink-chambers by passages formed preferably by an anisotropic etching method so that ink is supplied to each of the individual ink-chambers from the common ink-chamber. A part of a wall constituting each of the individual ink-chambers defines a thin silicon film vibration plate which is driven by an electrostatic force. The thin silicon film vibration plate is located opposite to an individual electrode formed on the electrode substrate  60 .  
         [0089]    The electrode substrate  60  is also made of a single crystal silicon (Si) substrate  61  which contains n-type or p-type impurity atoms. The single crystal silicon substrate  61  preferably contains impurity atoms of about 1E14/cm 3 . Normally, a single crystal Si substrate having a plane orientation (100) is used for the substrate  61 . However, a single crystal Si substrate having a plane orientation (110) or (111) may preferably be used depending on a processing method to be used. A silicon oxide film  62  is formed on the Si substrate  61 , and individual electrodes  63   b  are formed on the silicon oxide film  62  which defines an insulating layer. The individual electrodes  63   b  are made of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The individual electrodes  63   b  contain impurity atoms implanted via an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method. The individual electrodes  63   b  preferably contain more than about 1E18/cm 3  of impurity atoms. Additionally, a silicide film  67  is formed on the individual electrodes  63   b.  The silicide film  67  is preferably made of titanium silicide. Insulating gap spacers  63   a  are formed on the silicon oxide film  62  so that each of the individual electrodes  63   b  is located inside of a space defined by the insulating gap spacers  63   a.    
         [0090]    The insulating gap spacers  63   a  are made of a silicon (Si) oxidation film formed via a thermal oxidation method. The insulating gap spacers  63   a  define a gap between the vibration plates formed in the ink-chamber substrate  50  and the individual electrodes  63   b  formed in the electrode substrate  60 . That is, an electrostatic force is generated between each of the vibration plates and the respective one of the individual electrodes  63   b  separated by the gap defined by the insulating gap spacers  63   a.    
         [0091]    A silicon nitride insulating film  68  is formed on the silicide film  67  of each of the individual electrodes  63   b  so as to maintain insulation between each of the individual electrodes  63   b  and the respective one of the vibration plates formed in the ink-chamber substrate  50 . A voltage applying pad  69  is formed on the silicon nitride insulating film  68 . A part of the voltage applying pad  69  is connected to the silicide film  67  of each of the individual electrodes  63   b  so as to apply a voltage to the individual electrode  63   b.    
         [0092]    In FIGS. 5A, 5B and  5 C, an area indicated by an arrow b is an opening through which a flexible printed circuit board (FPC) or a bonding wire is connected to each of the voltage applying pads  69 . Additionally, arrows X and Y shown in FIG. 5B are directions of a droplet of ink projected from each of the inkjet nozzles formed on the ink-chamber substrate  50 . That is, when the inkjet nozzles are provided on a side surface of the ink-chamber substrate  50 , the droplet of ink is projected in the direction indicated by the arrow X. When the inkjet nozzles are provided on a top surface of the ink-chamber substrate  50 , the droplet of ink is projected in the direction indicated by the arrow Y.  
         [0093]    A description will now be given, with reference to FIGS. 6A through 6T, of an example of a method of manufacturing the inkjet head according to the above-mentioned third preferred embodiment shown in FIGS. 5A, 5B and  5 C. FIGS. 6A through 6T are cross-sectional views for explaining the manufacturing process of the inkjet head according to the third preferred embodiment of the present invention. It should be noted that FIGS. 6B, 6D,  6 F,  6 H,  6 J,  6 L,  6 N,  6 P,  6 R and  6 T are cross-sectional views taken along a line I-I of FIGS. 6A, 6C,  6 E,  6 G,  61 ,  6 K,  6 M,  6 O,  6 Q and  6 S, respectively.  
         [0094]    First, as shown in FIGS. 6A and 6B, the insulating film  62  is formed on the single crystal silicon substrate  61  via a thermal oxidation method, a chemical vapor deposition method or a sputtering method. The single crystal silicon substrate  61  is an n-type or a p-type, and preferably has a thickness of about 400 μm to about 700 μm and an electrical resistivity of about 5 Ω-cm 3  to about 30 Ω-cm 3 . Plane orientation of the single crystal silicon substrate  61  is (100), (111) or (110). The insulating film  62  provides insulation between the individual electrodes and the single crystal silicon substrate  21 .  
         [0095]    Thereafter, as shown in FIGS. 6C and 6D, a silicon film  63  is formed on the insulating film  22 . The silicon film  63  can be formed of an n-type or p-type polycrystalline silicon or an n-type or p-type single crystal silicon. The silicon film  63  preferably contains impurity atoms of about 1E18/cm 3  which can be implanted by an impurity introducing method such as an ion implantation method, a coating diffusion method or a solid diffusion method.  
         [0096]    Thereafter, as shown in FIGS. 6E and 6F, the insulating film  64  is formed on the silicon film  63  by a chemical vapor deposition (CVD) method or a sputtering method. The insulating film  64  is preferably made of a silicon nitride film so as to prevent diffusion of oxygen. Then, the insulating film  64  is patterned by a regular photolithography process and a dry or wet etching method so as to form parts corresponding to the individual electrodes  63   b.    
         [0097]    Thereafter, the silicon film  63  is oxidized by being placed in an oxygen atmosphere in an electric furnace. At this time, a first area of the silicon film  23  in which first area, the insulating film  64  for preventing oxygen diffusion is not formed is oxidized. Thus, a thick silicon oxidation film  63   a  is formed as shown in FIGS. 6G and 6H. On the other hand, a second area of the silicon film  63  in which second area the insulating film  64  for preventing oxygen diffusion is formed is not oxidized. Thus, the thickness of the silicon film  63  in the second area remains unchanged as shown in FIGS. 6G and 6H. Since the silicon oxide film  62   a  and the silicon film  63   b  have different thicknesses, a step is formed between the silicon oxide film  63   a  and the silicon film  63   b.  This step corresponds to the gap between the individual electrodes and the vibration plates in the inkjet head according to the present preferred embodiment.  
         [0098]    Thereafter, an insulating layer  64  for preventing oxygen diffusion is removed, and a metal film  66  is formed on the silicon films  63   a  and  63   b.  The metal film  66  is preferably made of titanium. After the metal film  66  is formed, annealing is performed within a nitrogen atmosphere by using an RTA apparatus or a furnace. In the annealing process, a silicide reaction occurs in the silicon film  63   b  (corresponding to the individual electrode) since the surface of the silicon film  63   b  is pure silicon. Accordingly, a silicide layer (titanium silicide film)  67  is formed on the silicon film  63   b.  On the other hand, since the silicon film  63   a  is oxidized, a silicide reaction does not occur. Accordingly, a silicide film is not formed on the silicon film  63   a  as shown in FIG. 6M.  
         [0099]    Thereafter, the metal film  66  is removed by wet etching so that the silicide layer  67  remains on the silicon film  63   b  as shown in FIGS. 6K and 6L. When titanium is used as the metal film  66 , a mixture of an ammonium solution and a hydrogen peroxide solution is used for removing the metal film  66 .  
         [0100]    Thereafter, an insulating film such as a silicon nitride film is formed on the entire surface of the electrode substrate  60  via a chemical vapor deposition method or a sputtering method. After that, the insulating film  68  is subjected to a patterning so that the insulating film  68  remains only on the silicide layer  67  as shown in FIGS. 6M and 6N. It should be noted that the insulating film  68  is not necessarily formed.  
         [0101]    Thereafter, as shown in FIGS. 6O and 6P, a single crystal silicon substrate  51  (corresponding to the ink-chamber substrate  50 ) is joined to the electrode substrate  60  which is in an intermediate state. The single crystal silicon substrate  51  is an n-type or a p-type, and has a plane orientation (110). A diffusion layer  52  and single crystal silicon etching mask patterns  53  are previously formed on the single crystal silicon substrate  51 . The diffusion layer  52  contains n-type or p-type impurities of more than about 1E19/cm 3 . A thickness of the diffusion layer  52  is preferably substantially equal to a thickness of the vibration plate. The single crystal silicon etching patterns  53  are formed on a surface of the single crystal silicon substrate  51  which surface is opposite to the surface on which the diffusion layer  52  is formed. The etching mask patterns  53  are preferably formed of a silicon oxide film, a silicon nitride film or a tantalum peroxide film. The etching mask patterns  53  are provided so as to define areas in which ink chambers and inkjet nozzles are formed. It should be noted that the substrate  51  can be a silicon on insulator (SOI) substrate which is constituted by a single crystal silicon substrate and a single crystal thin silicon film formed on the single crystal silicon substrate via a silicon oxide film.  
         [0102]    The ink-chamber substrate  50  can be joined to the electrode substrate  60  via a direct bonding method or an anode bonding method. In the direct bonding method, the bonding is performed at a temperature of more than about 800° C. within an oxygen atmosphere at a normal pressure or a reduced pressure. In the anode bonding method, an insulating film containing mobile ions such as Na ions or H ions is formed on the single crystal silicon substrate preferably via a sputtering method, and, thereafter, the bonding is performed by applying an electric field at a temperature ranging from about 200° C. to about 500° C., and preferably about 350° C. to about 450° C. Additionally, it is preferable that before the bonding is performed, the silicon oxidation film  63   a  of the electrode substrate  60  is polished via a chemical mechanical polishing process so as to planarize the surface to be bonded.  
         [0103]    After the ink-chamber substrate  50  is bonded to the electrode substrate  60 , the ink-chamber substrate  50  (the single crystal silicon substrate  51 ) is etched by an anisotropic etching method on the surface provided with the etching mask patterns  53 . The anisotropic etching is performed by using KOH or TMAH. The etching is stopped by the diffusion layer  52  which contains impurities at a high concentration. Accordingly, the diffusion layer  52  remains as the vibration plate as shown in FIGS. 6Q and 6R. If the SOI substrate is used, the etching is stopped by the silicon oxide film. In such a case, the silicon oxide film on the SOI substrate may be removed after the etching.  
         [0104]    Thereafter, an ink-chamber cover  14  is bonded to the substrate  51  so as to form the individual ink-chambers  58  and the common ink-chamber  56  as shown in FIG. 6S. The ink-chamber cover  54  is preferably formed of a glass plate or a metal plate. A passage  55  for supplying ink to the common ink-chamber  56  is previously formed in the ink-chamber cover  54  preferably via sand blasting or laser machining. Additionally, the crystal silicon thin film  52  corresponding to a pad area (an area indicated by arrow b) is removed by etching. Then, the voltage applying pads  69  are formed on the individual electrodes  63   b.    
         [0105]    As shown in FIG. 6S, each of the inkjet nozzles  59  is provided for a respective one of the individual ink-chambers  58 . Each of the individual ink-chambers  58  is connected to the common ink-chamber  55  via the passage  57 .  
         [0106]    When a predetermined voltage is applied to the voltage applying pad  69  which is connected to the individual electrode  63   b,  an electrostatic force is generated between the vibration plate  52  and the individual electrode  63   b  which results in warpage of the vibration plate  52  toward the individual electrode  63   b.  Accordingly, ink is introduced into the individual ink-chamber  58  via the passage  55 , the common ink-chamber  56  and the passage  57 . When the supply of the voltage is stopped, the vibration plate  52  returns to the original position due to its elasticity. At this time, the ink in the individual ink-chamber  58  is pressurized, and a droplet of the ink is discharged from the inkjet nozzle  59  in a direction indicated by an arrow X in FIG. 6S so that the droplet of the ink is projected onto a recording paper.  
         [0107]    In the present preferred embodiment, although the inkjet nozzle  59  is formed so that a droplet of ink is projected in the direction (horizontal direction) indicated by the arrow X, the droplet of ink may be projected in a vertical direction by changing the position of the inkjet nozzle  59 . Additionally, the inkjet nozzle  59  may be formed after the ink-chamber substrate  50  and the electrode substrate  60  are bonded to each other.  
         [0108]    A description will now be given, with reference to FIGS. 7A and 7B, of a first example of the inkjet head according to preferred embodiments of the present invention. The first example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 4A through 4P. FIG. 7A is a cross-sectional view of the first example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B. FIG. 7B is a cross-sectional view of the first example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C.  
         [0109]    In the inkjet head shown in FIGS. 7A and 7B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of 10 Ω-cm 3  was used to form the substrate  41 . The insulating film  42  having a thickness of about 300 nm was formed on the silicon substrate  41  by oxidizing a surface of the substrate  41 . The individual electrode  43   b  having a thickness of about 500 nm was formed on the insulating film  42 . The gap spacers  43   a  which are silicon oxide films were formed by being placed within an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The thickness of the silicon oxidation film formed on the individual electrode  43   b  is preferably about 200 nm. The gap between the vibration plate  32  and the individual electrode  43   b  is preferably about 0.5 μm. The individual electrode  43   b  was formed by n-type polycrystalline silicon. Phosphorus atoms were implanted into the n-type polycrystalline silicon by an ion implantation method so that the impurity concentration becomes about 1E20/cm 3 . The voltage applying pad  46  was formed by using gold (Au) via a sputtering method.  
         [0110]    The vibration plate  32  was formed by etching the single crystal silicon substrate  31  having a plane orientation (110) via an anisotropic etching method using KOH. The vibration plate  32  contained boron impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  32  was about 3 μm. The vibration plate  32  was bonded to the gap spacers  43   a  (silicon oxide film) via a direct bonding method. The individual ink-chamber  38  and the common ink-chamber  36  were formed in the single crystal silicon substrate  31  via an anisotropic etching method using KOH. The passage  37  was also formed between the individual ink-chamber  38  and the common ink-chamber  36 . Additionally, the ink-chamber cover  34  was made of a glass plate. The ink-chamber cover  34  had the passage  35  for supplying ink which passage  35  was formed by a sand blasting process. The thus-formed ink-chamber cover  34  was bonded to the single crystal silicon substrate  31 .  
         [0111]    The vibration plate  32  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  43   b  via the voltage applying pad  46  at a predetermined frequency. When the voltage is applied, an electrostatic force was generated between the vibration plate  32  and the individual electrode  43   b.  As a result, the vibration plate  32  was attracted toward the individual electrode  32 . Accordingly, a negative pressure was generated in the individual ink chamber  38 , and ink was supplied from the common ink-chamber  36  to the individual ink-chamber  38 . When the voltage applied to the individual electrode  43   b  was cut, the vibration plate  32  returned to its original position, and, thus, the ink in the individual ink-chamber  38  was pressurized. Thereby, a droplet of the ink was discharged from the inkjet nozzle  39  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0112]    A description will now be given, with reference to FIGS. 8A and 8B, of a second example of the inkjet head according to preferred embodiments of the present invention. The second example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 2A through 2N. FIG. 8A is a cross-sectional view of the second example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 1B. FIG. 8B is a cross-sectional view of the second example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 1C.  
         [0113]    In the inkjet head shown in FIGS. 8A and 8B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  was used to form the substrate  21 . The insulating film  22  having a thickness of about 300 nm was formed on the silicon substrate  21  by oxidizing the silicon substrate  21 . The individual electrode  23   b  was formed on the insulating film  22 . The gap spacers  23   a  which are silicon oxide films were formed by being placed within an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The gap between the vibration plate  12  and the individual electrode  23   b  was about 0.5 μm. The individual electrode  23   b  having a thickness of about 500 nm was formed of p-type polycrystalline silicon. Boron atoms were implanted into the p-type polycrystalline silicon via an ion implantation method so that the impurity concentration becomes about 1E20/cm 3 . The silicon nitride film  24  having a thickness of about 100 nm was formed on the individual electrode  23   b  by an LPCVD method. The voltage applying pad  25  was formed by using gold (Au) via a sputtering method.  
         [0114]    The vibration plate  12  was formed by etching the single crystal silicon substrate  11  having a plane orientation (110) by an anisotropic etching method using KOH. The vibration plate  12  contained phosphorus impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  12  was about 3 μm. The vibration plate  12  was bonded to the gap spacers  23   a  (silicon oxide film) by a direct bonding method. The individual ink-chamber  18  and the common ink-chamber  16  were formed in the single crystal silicon substrate  11  via an anisotropic etching method using KOH. The passage  17  was also formed between the individual ink-chamber  18  and the common ink-chamber  16 . Additionally, the ink-chamber cover  14  was formed by a glass plate. The ink-chamber cover  14  had the passage  15  for supplying ink which passage  15  was formed by a sand blasting. The thus-formed ink-chamber cover  14  was bonded to the single crystal silicon substrate  11 .  
         [0115]    The vibration plate  12  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  23   b  via the voltage applying pad  25  at a predetermined frequency. When the voltage is applied, an electrostatic force was generated between the vibration plate  12  and the individual electrode  23   b.  Thereby, the vibration plate  12  was attracted toward the individual electrode  23   b.  Accordingly, a negative pressure was generated in the individual ink-chamber  18 , and ink was supplied from the common ink-chamber  16  to the individual ink-chamber  18 . When the voltage applied to the individual electrode  23   b  was cut, the vibration plate  12  returned to its original position, and, thus, the ink in the individual ink-chamber  18  was pressurized. Thereby, a droplet of the ink was ejected from the inkjet nozzle  19  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0116]    A description will now be given, with reference to FIGS. 9A and 9B, of a third example of the inkjet head according to preferred embodiments of the present invention. The third example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 6A through 6T. FIG. 9A is a cross-sectional view of the third example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B. FIG. 9B is a cross-sectional view of the third example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C.  
         [0117]    In the inkjet head shown in FIGS. 9A and 9B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  to about 20 Ω-cm 3  was used to form the substrate  61 . The insulating film  62  having a thickness of about 300 nm was formed on the silicon substrate  61  by oxidizing the silicon substrate  61 . The individual electrode  63   b  was formed on the insulating film  62 . The gap spacers  63   a  which are silicon oxide films were formed by being placed within an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The gap between the vibration plate  52  and the individual electrode  63   b  was about 0.5 μm. The individual electrode  63   b  was formed by a p-type or n-type polycrystalline silicon which does not contain impurity atoms. The titanium silicide film  67  having a thickness of about 60 nm was formed on the individual electrode  63   b.  The titanium silicide film  67  defined a part of the individual electrode  63   b.  Additionally, the silicon oxide film  68  having a thickness of about 100 nm was formed on the titanium silicide film  67  by an LPCVD method. The voltage applying pad  69  was formed by using gold (Au) by a sputtering method.  
         [0118]    The vibration plate  52  was formed by etching the single crystal silicon substrate  51  having a plane orientation (110) via an anisotropic etching method using KOH. The vibration plate  52  contained phosphorus impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  52  was about 3 μm. The vibration plate  52  was bonded to the gap spacers  63   a  (silicon oxide film) by an anode bonding method which uses an electric field. The individual ink-chamber  58  and the common ink-chamber  56  were formed in the single crystal silicon substrate  51  by an anisotropic etching method using KOH. The passage  57  was also formed between the individual ink-chamber  58  and the common ink-chamber  56 . Additionally, the ink-chamber cover  54  was formed of a glass plate. The ink-chamber cover  54  had the passage  55  for supplying ink which passage  55  was formed via sand blasting. The thus-formed ink-chamber cover  54  was bonded to the single crystal silicon substrate  51 .  
         [0119]    The vibration plate  52  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  63   b  via the voltage applying pad  65  at a predetermined frequency. When the voltage was applied, an electrostatic force was generated between the vibration plate  52  and the individual electrode  63   b.  Thereby, the vibration plate  52  was attracted toward the individual electrode  63   b.  Accordingly, a negative pressure was generated in the individual ink-chamber  58 , and ink was supplied from the common ink-chamber  56  to the individual ink-chamber  58 . When the voltage applied to the individual electrode  63   b  was cut, the vibration plate  52  returned to its original position, and, thus, the ink in the individual ink-chamber  58  was pressurized. Thereby, a droplet of the ink was ejected from the inkjet nozzle  59  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0120]    A description will now be given, with reference to FIGS. 10A and 10B, of a fourth example of the inkjet head according to preferred embodiments of the present invention. The fourth example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 4A through 4P. FIG. 10A is a cross-sectional view of the fourth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B. FIG. 10B is a cross-sectional view of the fourth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C.  
         [0121]    In the inkjet head shown in FIGS. 10A and 10B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  to about 20 Ω-cm 3  was used to form the substrate  41 . The insulating film  42  having a thickness of about 300 nm was formed on the silicon substrate  41  by oxidizing a surface of the substrate  41 . The individual electrode  43   b  having a thickness of about 300 nm was formed on the insulating film  42 . The gap spacers  43   a  which are silicon oxide films were formed by being placed in an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The gap between the vibration plate  32  and the individual electrode  43   b  was about 0.5 μm. The individual electrode  43   b  was formed by p-type polycrystalline silicon. Phosphorus atoms were implanted into the p-type polycrystalline silicon by an ion implantation method so that the impurity concentration becomes 1E20/cm 3 . A silicon oxide film was not formed on the individual electrode  43   b.  The voltage applying pad  46  was formed by using gold (Au) via a sputtering method.  
         [0122]    The vibration plate  32  was formed by etching the single crystal silicon substrate  31  having a plane orientation (110) via an anisotropic etching method using KOH. In the vibration plate  32 , a silicon oxide film  32   a  having a thickness of about 3 μm was formed on the single crystal vibration plate  32   b  having a thickness of about 150 nm. The silicon oxide film  32   a  of the vibration plate  32  was bonded to the gap spacers  43   a  (silicon oxide film) via a direct bonding method. The individual ink-chamber  38  and the common ink-chamber  36  were formed in the single crystal silicon substrate  31  by an anisotropic etching method using KOH. The passage  37  was also formed between the individual ink-chamber  38  and the common ink-chamber  36 . Additionally, the ink-chamber cover  34  was formed of a glass plate. The ink-chamber cover  34  included the passage  35  for supplying ink which passage  35  was formed by sand blasting. The thus-formed ink-chamber cover  34  was bonded to the single crystal silicon substrate  31 .  
         [0123]    The vibration plate  32  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  43   b  via the voltage applying pad  46  at a predetermined frequency. When the voltage was applied, an electrostatic force was generated between the vibration plate  32  and the individual electrode  43   b.  Thereby, the vibration plate  32  was attracted toward the individual electrode  32 . Accordingly, a negative pressure was generated in the individual ink-chamber  38 , and ink was supplied from the common ink-chamber  36  to the individual ink-chamber  38 . When the voltage applied to the individual electrode  43   b  was cut, the vibration plate  32  returned to its original position, and, thus, the ink in the individual ink-chamber  38  was pressurized. As a result, a droplet of the ink was ejected from the inkjet nozzle  39  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0124]    A description will now be given, with reference to FIGS. 11A and 11B, of a fifth example of the inkjet head according to preferred embodiments of the present invention. The fifth example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 6A through 6T. FIG. 11A is a cross-sectional view of the fifth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B. FIG. 11B is a cross-sectional view of the fifth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C.  
         [0125]    In the inkjet head shown in FIGS. 11A and 11B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  to about 20 Ω-cm 3  was used to form the substrate  61 . The insulating film  62  having a thickness of about 300 nm was formed on the silicon substrate  61  by oxidizing the silicon substrate  61 . The individual electrode  63   b  was formed on the insulating film  62 . The gap spacers  63   a  which are silicon oxide films were formed by being placed within an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The gap between the vibration plate  52  and the individual electrode  63   b  was about 0.5 μm. The individual electrode  63   b  was formed by an n-type single crystal silicon containing phosphorus atoms at an impurity concentration of more than about 1E20/cm 3 . The phosphorus atoms were implanted by an ion implantation method. The titanium silicide film  67  having a thickness of about 100 nm was formed on the individual electrode  63   b.  The titanium silicide film  67  served as a part of the individual electrode  63   b.  A silicon oxide film serving as a protective film was not formed on the titanium silicide film  67 . The voltage applying pad  69  was formed by using gold (Au) via a sputtering method.  
         [0126]    The vibration plate  52  was formed by etching the single crystal silicon substrate  51  having a plane orientation (110) via an anisotropic etching method using KOH. The vibration plate  52  contained boron impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  52  was about 3 μm. The vibration plate  52  was bonded to the gap spacers  63   a  (silicon oxide film) via a direct bonding method. The individual ink-chamber  58  and the common ink-chamber  56  were formed in the single crystal silicon substrate  51  via an anisotropic etching method using KOH. The passage  57  was also formed between the individual ink-chamber  58  and the common ink-chamber  56 . Additionally, the ink-chamber cover  54  was formed of a glass plate. The ink-chamber cover  54  had the passage  55  for supplying ink which passage  55  was formed by sand blasting. The thus-formed ink-chamber cover  54  was bonded to the single crystal silicon substrate  51 .  
         [0127]    The vibration plate  52  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  63   b  via the voltage applying pad  65  at a predetermined frequency. When the voltage was applied, an electrostatic force was generated between the vibration plate  52  and the individual electrode  63   b.  Thereby, the vibration plate  52  was attracted toward the individual electrode  63   b.  Accordingly, a negative pressure was generated in the individual ink-chamber  58 , and ink was supplied from the common ink-chamber  56  to the individual ink-chamber  58 . When the voltage applied to the individual electrode  63   b  was cut, the vibration plate  52  returned to its original position, and, thus, the ink in the individual ink-chamber  58  was pressurized. Thereby, a droplet of the ink was ejected from the inkjet nozzle  59  in a direction indicated by an arrow Y, and landed on a recording paper.  
         [0128]    A description will now be given, with reference to FIGS. 12A and 12B, of a sixth example of the inkjet head according to preferred embodiments of the present invention. The sixth example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 6A through 6T. FIG. 12A is a cross-sectional view of the sixth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5B. FIG. 12B is a cross-sectional view of the sixth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 5C.  
         [0129]    In the inkjet head shown in FIGS. 12A and 12B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  to about 20 Ω-cm 3  was used to form the substrate  61 . The insulating film  62  having a thickness of about 300 nm was formed on the silicon substrate  61  by oxidizing the silicon substrate  61 . The individual electrode  63   b  was formed on the insulating film  62 . The gap spacers  63   a  which are silicon oxide films were formed by being placed within an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The gap between the vibration plate  52  and the individual electrode  63   b  was about 0.5 μm. The individual electrode  63   b  was formed by a p-type or n-type single crystal silicon which does not contain impurity atoms. The titanium silicide film  67  having a thickness of about 50 nm was formed on the individual electrode  63   b.  The titanium silicide film  67  defined a part of the individual electrode  63   b.  Additionally, the silicon nitride film  68  having a thickness of about 150 nm was formed on the titanium silicide film  67  by an LPCVD method. The voltage applying pad  69  was formed by using gold (Au) via a sputtering method.  
         [0130]    The vibration plate  52  was formed by etching the single crystal silicon substrate  51  having a plane orientation (110) via an anisotropic etching method using KOH. The vibration plate  52  contained phosphorus impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  52  was about 3 μm. The vibration plate  52  was bonded to the gap spacers  63   a  (silicon oxide film) by an anode bonding method which uses an electric field. The individual ink-chamber  58  and the common ink-chamber  56  were formed in the single crystal silicon substrate  51  by an anisotropic etching method using KOH. The vibration plate  52  included a single crystal silicon film  52   a  having a thickness of about 2 μm and a silicon oxide film  52   b  having a thickness of about 150 nm. The vibration plate was formed by etching the single crystal silicon substrate  51  by an anisotropic etching method. The passage  57  was also formed between the individual ink-chamber  58  and the common ink-chamber  56 . Additionally, the ink-chamber cover  54  was formed of a glass plate. The ink-chamber cover  54  had the passage  55  for supplying ink which passage  55  was formed by sand blasting. The thus-formed ink-chamber cover  54  was bonded to the single crystal silicon substrate  51 .  
         [0131]    The vibration plate  52  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  63   b  via the voltage applying pad  65  at a predetermined frequency. When the voltage is applied, an electrostatic force was generated between the vibration plate  52  and the individual electrode  63   b.  Thereby, the vibration plate  52  was attracted toward the individual electrode  63   b.  Accordingly, a negative pressure was generated in the individual ink-chamber  58 , and ink was supplied from the common ink-chamber  56  to the individual ink-chamber  58 . When the voltage applied to the individual electrode  63   b  was cut, the vibration plate  52  returned to its original position, and, thus, the ink in the individual ink-chamber  58  was pressurized. Thereby, a droplet of the ink was ejected from the inkjet nozzle  59  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0132]    A description will now be given, with reference to FIGS. 13A and 13B, of a seventh example of the inkjet head according to preferred embodiments of the present invention. The seventh example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 4A through 4P. FIG. 13A is a cross-sectional view of the seventh example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B. FIG. 13B is a cross-sectional view of the seventh example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C.  
         [0133]    In the inkjet head shown in FIGS. 13A and 13B, an n-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  to about 20 Ω-cm 3  was used to form the substrate  41 . The insulating film  42  having a thickness of about 300 nm was formed on the silicon substrate  41  by oxidizing a surface of the substrate  41 . The individual electrode  43   b  having a thickness of about 300 nm was formed on the insulating film  42 . The gap spacers  43   a  which are silicon oxide films were formed by being placed in an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The thickness of the silicon oxide film formed on the individual electrode  43   b  was about 200 nm. The gap between the vibration plate  32  and the individual electrode  43   b  was about 0.5 μm. The individual electrode  43   b  was formed by n-type polycrystalline silicon. Phosphorus atoms were implanted into the n-type polycrystalline silicon by an ion implantation method so that the impurity concentration becomes about 1E20/cm 3 . The voltage applying pad  46  was formed by using gold (Au) via a sputtering method.  
         [0134]    The vibration plate  32  was formed by etching the single crystal silicon substrate  31  having a plane orientation (110) by an anisotropic etching method using KOH. The vibration plate  32  contained boron impurity atoms at a concentration of more than about 1E20/cm 3 . The thickness of the vibration plate  32  was about 2 μm. The vibration plate  32  was bonded to the gap spacers  43   a  (silicon oxide film) by a direct bonding method. The individual ink-chamber  38  and the common ink-chamber  36  were formed in the single crystal silicon substrate  31  by an anisotropic etching method using KOH. The passage  37  was also formed between the individual ink-chamber  38  and the common ink-chamber  36 . Additionally, the ink-chamber cover  34  was formed of a glass plate. The ink-chamber cover  34  had the passage  35  for supplying ink which passage  35  was formed by sand blasting. The thus-formed ink-chamber cover  34  was bonded to the single crystal silicon substrate  31 .  
         [0135]    The vibration plate  32  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  43   b  via the voltage applying pad  46  at a predetermined frequency. When the voltage was applied, an electrostatic force was generated between the vibration plate  32  and the individual electrode  43   b.  Thereby, the vibration plate was attracted toward the individual electrode  32 . Accordingly, a negative pressure was generated in the individual ink-chamber  38 , and ink was supplied from the common ink-chamber  36  to the individual ink-chamber  38 . When the voltage applied to the individual electrode  43   b  was cut, the vibration plate  32  returned to its original position, and, thus, the ink in the individual ink-chamber  38  was pressurized. Thereby, a droplet of the ink was discharged from the inkjet nozzle  39  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0136]    A description will now be given, with reference to FIGS. 14A and 14B, of an eighth example of the inkjet head according to preferred embodiments of the present invention. The eighth example of the inkjet head according to preferred embodiments of the present invention was produced by the manufacturing process shown in FIGS. 4A through 4P. FIG. 14A is a cross-sectional view of the eighth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3B. FIG. 14B is a cross-sectional view of the eighth example of the inkjet head which cross-sectional view corresponds to the cross-sectional view of FIG. 3C.  
         [0137]    In the inkjet head shown in FIGS. 14A and 14B, a p-type single crystal silicon substrate having a plane orientation (100) and an electric resistivity of about 10 Ω-cm 3  was used to form the substrate  41 . The insulating film  42  having a thickness of about 300 nm was formed on the silicon substrate  41  by oxidizing a surface of the substrate  41 . The individual electrode  43   b  having a thickness of about 300 nm was formed on the insulating film  42 . The gap spacers  43   a  which are silicon oxide films were formed by being placed in an H 2  and O 2  atmosphere in a pyrogenic oxidation furnace. The thickness of the silicon oxide film formed on the individual electrode  43   b  was about 200 nm. The gap between the vibration plate  32  and the individual electrode  43   b  was about 0.5 μm. The individual electrode  43   b  was formed by p-type amorphous silicon. Boron atoms were implanted into the p-type amorphous silicon by an ion implantation method so that the impurity concentration becomes about 1E20/cm 3 . A silicon oxide film serving as a protective film was not formed on the individual electrode  43   b.  The voltage applying pad  46  was formed by using gold (Au) via a sputtering method.  
         [0138]    The vibration plate  32  was formed by etching the single crystal silicon substrate  31  having a plane orientation (110) by an anisotropic etching method using KOH. The vibration plate  32  included a silicon oxide film  32   b  having a thickness of about 150 nm and a single crystal silicon film having a thickness of about 2 μm. The vibration plate  32  was bonded to the gap spacers  43   a  (silicon oxide film) by an anode bonding method in which the bonding is performed by applying a static electric field. The individual ink-chamber  38  and the common ink-chamber  36  were formed in the single crystal silicon substrate  31  by an anisotropic etching method using KOH. The passage  37  was also formed between the individual ink-chamber  38  and the common ink-chamber  36 . Additionally, the ink-chamber cover  34  was formed by a glass plate. The ink-chamber cover  34  had the passage  35  for supplying ink which passage  35  was formed by a sand blasting. The thus-formed ink-chamber cover  34  was bonded to the single crystal silicon substrate  31 .  
         [0139]    The vibration plate  32  of the thus-formed inkjet head was grounded and a predetermined positive voltage was applied to the individual electrode  43   b  via the voltage applying pad  46  at a predetermined frequency. When the voltage is applied, an electrostatic force was generated between the vibration plate  32  and the individual electrode  43   b.  Thereby, the vibration plate  32  was attracted toward the individual electrode  32 . Accordingly, a negative pressure was generated in the individual ink-chamber  38 , and ink was supplied from the common ink-chamber  36  to the individual ink-chamber  38 . When the voltage applied to the individual electrode  43   b  was cut, the vibration plate  32  returned to its original position, and, thus, the ink in the individual ink-chamber  38  was pressurized. Thereby, a droplet of the ink was discharged from the inkjet nozzle  39  in a direction indicated by an arrow X, and landed on a recording paper.  
         [0140]    The present invention is not limited to the specifically disclosed preferred embodiments, and variations and modifications may be made without departing from the scope of the present invention.  
         [0141]    The present application is based on Japanese priority application No. 10-220541 filed on Aug. 4, 1998, the entire contents of which are hereby incorporated by reference.