Patent Publication Number: US-11031538-B2

Title: Liquid ejection apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 16/257,252, filed Jan. 25, 2019, now issued U.S. Pat. No. 10,727,392, which is a continuation of U.S. patent application Ser. No. 16/055,291, filed Aug. 6, 2018, now issued U.S. Pat. No. 10,236,434, which is a continuation of U.S. patent application Ser. No. 15/472,056, filed Mar. 28, 2017, now issued U.S. Pat. No. 10,069,058, which further claims priority from Japanese Patent Application No. 2016-189997, filed on Sep. 28, 2016, the disclosure of all of which is herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The following disclosure relates to an actuator device, a liquid ejection apparatus, and a connection structure of a wire member. 
     There is known a charge plate for selectively charging ink to be ejected by an ink-jet head through its orifices. An insulated base of the charge plate is provided with charge electrodes and lead wires corresponding to the respective charge electrodes. Contacts are provided on end portions of the respective lead wires. A wire member including wires (conduction bands) are joined to an end portion of the insulated base on which the contacts provided on the lead wires are disposed. 
     The wire member and the insulated base of the charge plate are connected to each other with a conductive adhesive formed of an anisotropic conductive material, for example. The conductive adhesive is a thermosetting adhesive containing conductive particles. Portions of the wire member and the insulated base of the charge plate which are to be joined to each other are heated and pressurized in a state in which the conductive adhesive having not been hardened yet is interposed between the wire member and the insulated base of the charge plate. In this process, the contacts provided on the charge plate and the wires provided on the wire member are electrically connected to each other through the conductive particles. Also, the adhesive is hardened by heating, which mechanically joins the wire member to the charge plate. 
     SUMMARY 
     In the joining with the conductive adhesive, the contacts of the two components are electrically connected to each other through the conductive particles contained in the thermosetting adhesive. In this process, however, the conductive particles contained in the conductive adhesive in some cases flow out to areas around the contacts together with the adhesive, leading to shorts between adjacent contacts due to the conductive particles having flowed out. Decreased density of the conductive particles may reduce occurrences of the shorts. However, the smaller number of the conductive particles easily causes a situation in which no conductive particles are provided between two contacts, which may lead to poor connection. 
     Accordingly, an aspect of the disclosure relates to a technique of increasing reliability of electric connection between two contacts without increase in density of conductive particles in connection of the two contacts using a conductive adhesive. 
     In one aspect of the disclosure, an actuator device includes: an actuator including at least one first contact; and a wire member including at least one second contact respectively connected to the at least one first contact with a conductive adhesive including a conductive particle. One of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one particular contact, and another of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one specific contact. At least two protrusions and at least one recess are formed on and in the at least one particular contact. The at least two protrusions are arranged in a first direction parallel with a placement surface of each of the at least one particular contact. The at least one recess is interposed between the at least two protrusions. The at least one particular contact is respectively joined to the at least one specific contact with the conductive adhesive provided in the at least one recess, in a state in which each of the at least two protrusions is in contact with a corresponding one of the at least one specific contact. 
     In another aspect of the disclosure, a liquid ejection apparatus includes: a passage definer defining therein at least one pressure chamber; a vibration layer covering the at least one pressure chamber; at least one piezoelectric element disposed on the vibration layer so as to respectively overlap the at least one pressure chamber; at least one first contact respectively drawn from the at least one piezoelectric element; and a wire member including at least one second contact respectively connected to the at least one first contact with a conductive adhesive including a conductive particle. One of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one particular contact, and another of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one specific contact. At least two protrusions and at least one recess are formed on and in the at least one particular contact. The at least two protrusions are arranged in a first direction parallel with a placement surface of each of the at least one particular contact, the at least one recess being interposed between the at least two protrusions. The at least one particular contact is respectively joined to the at least one specific contact with the conductive adhesive provided in the at least one recess, in a state in which each of the at least two protrusions is in contact with a corresponding one of the at least one specific contact. 
     Yet another aspect of the disclosure relates to a connection structure for connecting at least one first contact and at least one second contact of a wire member respectively to each other with a conductive adhesive. One of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one particular contact. Another of (i) each of the at least one first contact and (ii) each of the at least one second contact is each of at least one specific contact. At least two protrusions and at least one recess are formed on and in the at least one particular contact. The at least two protrusions are arranged in a first direction parallel with a placement surface of each of the at least one particular contact. The at least one recess is interposed between the at least two protrusions. The at least one particular contact is respectively joined to the at least one specific contact with the conductive adhesive provided in the at least one recess, in a state in which each of the at least two protrusions is in contact with a corresponding one of the at least one specific contact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of the embodiment, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic plan view of a printer according to the present embodiment; 
         FIG. 2  is a plan view of an ink-jet head; 
         FIG. 3  is an enlarged view of a rear end portion of the ink-jet head in  FIG. 2 ; 
         FIG. 4  is an enlarged view of an area A in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 4 ; 
         FIG. 7  is a plan view of a driving contact of a piezoelectric actuator; 
         FIG. 8A  is a cross-sectional view of joined portions of the piezoelectric actuator and a COF, taken along line A-A in  FIG. 7 , and  FIG. 8B  is a cross-sectional view of the joined portions, taken along line B-B in  FIG. 7 ; 
         FIG. 9  is a plan view of a ground contact of the piezoelectric actuator; 
         FIG. 10A  is a cross-sectional view of the joined portions of the piezoelectric actuator and the COF, taken along line A-A in  FIG. 9 , and  FIG. 10B  is a cross-sectional view of the joined portions, taken along line B-B in  FIG. 9 ; 
         FIGS. 11A-11F  are views illustrating a first portion of a process of producing the ink-jet head; 
         FIGS. 12G-12I  are views illustrating a second portion of the process of producing the ink-jet head; 
         FIGS. 13A and 13B  are cross-sectional views each illustrating joined portions of a piezoelectric actuator and a COF of an ink-jet head in a corresponding modification; 
         FIGS. 14A-14D  are cross-sectional views each illustrating joined portions of a piezoelectric actuator and a COF of an ink-jet head in a corresponding modification; and 
         FIG. 15  is a cross-sectional view illustrating joined portions of a piezoelectric actuator and a COF of an ink-jet head in another modification. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Hereinafter, there will be described an embodiment by reference to the drawings. First, there will be explained an overall configuration of an ink-jet printer  1  with reference to  FIG. 1 . The direction in which a recording sheet  100  is conveyed in  FIG. 1  is defined as the front and rear direction of the printer  1 . The widthwise direction of the recording sheet  100  is defined as the right and left direction of the printer  1 . The direction orthogonal to the front and rear direction and the right and left direction and perpendicular to the sheet surface of  FIG. 1  is defined as the up and down direction of the printer  1 . 
     Overall Configuration of Printer 
     As illustrated in  FIG. 1 , the ink-jet printer  1  includes a carriage  3 , an ink-jet head  4 , a conveying mechanism  5 , and a controller  6 . 
     The carriage  3  is mounted on guide rails  10 ,  11  extending in the right and left direction (hereinafter may also be referred to as “scanning direction”). The carriage  3  is joined to a carriage driving motor  15  via an endless belt  14 . The carriage  3  is driven by the motor  15  and reciprocated in the scanning direction over the recording sheet  100  conveyed on a platen  2 . 
     The ink-jet head  4  is mounted on the carriage  3 . Inks of four colors, namely, black, yellow, cyan, and magenta, are supplied to the ink-jet head  4  respectively via tubes, not illustrated, from four ink cartridges  17  held by a holder  7 . While moving in the scanning direction with the carriage  3 , the ink-jet head  4  ejects the inks from a multiplicity of nozzles  24  (see FIGS.  2 - 6 ) onto the recording sheet  100  conveyed on the platen  2 . 
     The conveying mechanism  5  includes two conveying rollers  18 ,  19  configured to convey the recording sheet  100  on the platen  2  in the front direction (hereinafter may also be referred to as “conveying direction”). 
     The controller  6  controls devices including the ink-jet head  4  and the carriage driving motor  15  to print an image on the recording sheet  100  based on a print instruction received from an external device such as a personal computer (PC). 
     Detailed Configuration of Ink-Jet Head 
     There will be next explained a configuration of the ink-jet head  4  with reference to  FIGS. 2-6 . It is noted that  FIGS. 3 and 4  omit illustration of a protector  23  illustrated in  FIG. 2 . 
     In the present embodiment, the ink-jet head  4  ejects the inks of the four colors (black, yellow, cyan, and magenta). As illustrated in  FIGS. 2-6 , the ink-jet head  4  includes a nozzle plate  20 , a passage definer  21 , and an actuator device  25  including a piezoelectric actuator  22 . In the present embodiment, the actuator device  25  does not indicate only the piezoelectric actuator  22  but includes not only the piezoelectric actuator  22  but also the protector  23  and chip-on-films (COFs)  50  disposed on the piezoelectric actuator  22 . Each of the COFs  50  is one example of a wire member. 
     Nozzle Plate 
     The nozzle plate  20  is formed of silicon, for example. The nozzle plate  20  has the nozzles  24  arranged in the conveying direction. That is, the front and rear direction coincides with a direction in which the nozzles  24  are arranged (hereinafter also referred to as “nozzle arrangement direction”). 
     More specifically, as illustrated in  FIGS. 2 and 3 , the nozzle plate  20  has four nozzle groups  27  arranged in the scanning direction. The four nozzle groups  27  are for ejection of the different inks, respectively. Each of the nozzle groups  27  is constituted by right and left nozzle rows  28 . In each of the nozzle rows  28 , the nozzles  24  are arranged at intervals P. Positions of the nozzles  24  are displaced by P/2 in the conveying direction between the two nozzle rows  28 . That is, the nozzles  24  are arranged in two rows in a staggered configuration in each nozzle group  27 . 
     In the following explanation, one of suffixes k, y, c, and m may be selectively added to the reference numbers of components of the ink-jet head  4  to indicate their respective correspondences with one of the black, yellow, cyan, and magenta inks. For example, the wording “nozzle groups  27   k ” indicates the nozzle group  27  for the black ink. 
     Passage Definer 
     The passage definer  21  is a base plate formed of silicon single crystal. As illustrated in  FIGS. 3-6 , the passage definer  21  has pressure chambers  26  communicating with the respective nozzles  24 . Each of the pressure chambers  26  has a rectangular shape elongated in the scanning direction in plan view. The pressure chambers  26  are arranged in the conveying direction so as to correspond to the arrangement of the nozzles  24 . The pressure chambers  26  are arranged in eight pressure chamber rows, each two of which correspond to one of the four ink colors. A lower surface of the passage definer  21  is covered with the nozzle plate  20 . An outer end portion of each of the pressure chambers  26  in the scanning direction overlaps a corresponding one of the nozzles  24 . 
     A vibration layer  30  of the piezoelectric actuator  22 , which will be described below, is disposed on an upper surface of the passage definer  21  so as to cover the pressure chambers  26 . The vibration layer  30  is not limited in particular as long as the vibration layer  30  is an insulating layer covering the pressure chambers  26 . In the present embodiment, the vibration layer  30  is formed by oxidation or nitriding of a surface of the base plate formed of silicon. The vibration layer  30  has ink supply holes  30   a  at areas each covering an end portion of a corresponding one of the pressure chambers  26  in the scanning direction (which end portion is located on an opposite side of the pressure chamber  26  from the nozzle  24 ). 
     For each ink color, the ink is supplied from a corresponding one of four reservoirs  23   b  formed in the protector  23  to the pressure chambers  26  through the respective ink supply holes  30   a . When ejection energy is applied to the ink in each of the pressure chambers  26  by a corresponding one of piezoelectric elements  31  of the piezoelectric actuator  22  which will be described below, an ink droplet is ejected from the nozzle  24  communicating with the pressure chamber  26 . 
     Actuator Device 
     The actuator device  25  is disposed on the upper surface of the passage definer  21 . The actuator device  25  includes: the piezoelectric actuator  22  including the piezoelectric elements  31 ; the protector  23 ; and the two COFs  50 . 
     The piezoelectric actuator  22  is disposed on the entire upper surface of the passage definer  21 . As illustrated in  FIGS. 3 and 4 , the piezoelectric actuator  22  includes the piezoelectric elements  31  arranged so as to overlap the respective pressure chambers  26 . The piezoelectric elements  31  are arranged in the conveying direction so as to correspond to the arrangement of the pressure chambers  26  and constitute eight piezoelectric element rows  38 . A plurality of driving contacts  46  and two ground contacts  47  are drawn out leftward from left four of the piezoelectric element rows  38 , and as illustrated in  FIGS. 2 and 3  the contacts  46 ,  47  are disposed on a left end portion of the passage definer  21 . A plurality of driving contacts  46  and two ground contacts  47  are drawn out rightward from right four of the piezoelectric element rows  38 , and the contacts  46 ,  47  are disposed on a right end portion of the passage definer  21 . The structure of the piezoelectric actuator  22  will be described below in detail. 
     The protector  23  is disposed on an upper surface of the piezoelectric actuator  22  so as to cover the piezoelectric elements  31 . Specifically, the protector  23  includes eight recessed protecting portions  23   a  respectively covering the eight piezoelectric element rows  38 . As illustrated in  FIG. 2 , the protector  23  does not cover right and left end portions of the piezoelectric actuator  22 , so that the driving contacts  46  and the ground contacts  47  are exposed from the protector  23 . The protector  23  has the reservoirs  23   b  connected to the respective ink cartridges  17  held by the holder  7 . The ink in each of the reservoirs  23   b  is supplied to the pressure chambers  26  through respective ink supply passages  23   c  and the respective ink supply holes  30   a  formed in the vibration layer  30 . 
     Each of the COFs  50  illustrated in  FIGS. 2-5  is a flexible wire (lead) member including a base  56  formed of insulating material such as a polyimide film. A driver IC  51  is mounted on the base  56 . One end portions of the respective two COFs  50  are connected to the controller  6  (see  FIG. 1 ) of the printer  1 . The other end portions of the respective two COFs  50  are respectively joined to right and left end portions of the piezoelectric actuator  22 . As illustrated in  FIG. 4 , each of the COFs  50  includes ground wires  53  and a plurality of individual wires  52  connected to the respective driver ICs  51 . Individual contacts  54  are provided on distal end portions of the respective individual wires  52  and connected to the respective driving contacts  46  of the piezoelectric actuator  22 . Ground contacts  55  are provided on distal end portions of the respective ground wires  53  and connected to the respective ground contacts  47  of the piezoelectric actuator  22 . Each of the driver ICs  51  outputs a drive signal to a corresponding one of the piezoelectric elements  31  of the piezoelectric actuator  22  via a corresponding one of the individual contacts  54  and a corresponding one of the driving contacts  46 . While the two ground contacts  47  are provided for each of the COFs  50  in the present embodiment, the following explanation will be given for one of the ground contacts  47  for simplicity unless otherwise required. 
     Detailed Structure of Piezoelectric Actuator 
     The piezoelectric actuator  22  includes: the vibration layer  30  formed on the upper surface of the passage definer  21 ; and the piezoelectric elements  31  disposed on an upper surface of the vibration layer  30 . For simplicity,  FIGS. 3 and 4  omit illustration of a protecting layer  40 , an insulating layer  41 , and a wire protecting layer  43  illustrated in  FIGS. 5 and 6 . 
     As illustrated in  FIGS. 3-6 , the piezoelectric elements  31  are arranged on the upper surface of the vibration layer  30  so as to overlap the respective pressure chambers  26 . That is, the piezoelectric elements  31  are arranged in the conveying direction so as to correspond to the arrangement of the pressure chambers  26 . As a result, in accordance with the arrangement of the nozzles  24  and the pressure chambers  26 , the piezoelectric elements  31  constitute the eight piezoelectric element rows  38 , each two of which correspond to one of the four ink colors. It is noted that a group of the piezoelectric elements  31  of the two piezoelectric element rows  38  corresponding to each of the four ink colors will be referred to as “piezoelectric element group  39 ”. As illustrated in  FIG. 3 , the four piezoelectric element groups  39   k ,  39   y ,  39   c ,  39   m  respectively corresponding to the four ink colors are arranged in the scanning direction. 
     Each of the piezoelectric elements  31  includes a first electrode  32 , a piezoelectric layer  33 , and a second electrode  34  disposed in this order from a lower side over the vibration layer  30 . 
     As illustrated in  FIGS. 5 and 6 , the first electrode  32  is formed at an area opposed to the pressure chamber  26  formed in the vibration layer  30 . As illustrated in  FIG. 6 , each adjacent two of the first electrodes  32  of the respective piezoelectric elements  31  are connected to each other by an electrically conductive portion  35  disposed between the piezoelectric elements  31 . In other words, the first electrodes  32  and the electrically conductive portions  35  connecting the first electrodes  32  to each other constitute a common electrode  36  that covers substantially the entire upper surface of the vibration layer  30 . The common electrode  36  is formed of platinum (Pt), for example. The thickness of the common electrode  36  is 0.1 μm, for example. It is noted that the wording “conduct” and “conductive” in the present specification principally means “electrically conduct” and “electrically conductive”. 
     The piezoelectric layer  33  is formed of a piezoelectric material such as lead zirconate titanate (PZT), for example. The piezoelectric layer  33  may be formed of a non-lead piezoelectric material not containing lead. The thickness of the piezoelectric layer  33  is ranged between 1.0 μm and 2.0 μm, for example. 
     As illustrated in  FIGS. 3, 4, and 6 , in the present embodiment, the piezoelectric layers  33  of the respective piezoelectric elements  31  are connected to each other in the conveying direction to form a rectangular piezoelectric member  37  elongated in the conveying direction. That is, the eight piezoelectric members  37  constituted by the piezoelectric layers  33  respectively corresponding to the eight pressure chamber rows are disposed on the common electrode  36  covering the vibration layer  30 . 
     The second electrodes  34  are disposed on upper surfaces of the respective piezoelectric layers  33 . Each of the second electrodes  34  has a rectangular shape in plan view which is one size smaller than each of the pressure chambers  26 . The second electrodes  34  respectively overlap central portions of the respective pressure chambers  26 . Unlike the first electrodes  32 , the second electrodes  34  of the respective piezoelectric elements  31  are separated and spaced apart from each other. That is, the second electrodes  34  are individual electrodes provided for individually for the respective piezoelectric elements  31 . The second electrodes  34  are formed of iridium (Ir) or platinum (Pt), for example. The thickness of each of the second electrodes  34  is 0.1 μm, for example. 
     As illustrated in  FIGS. 5 and 6 , the piezoelectric actuator  22  includes the protecting layer  40 , the insulating layer  41 , wires  42 , and the wire protecting layer  43 . 
     As illustrated in  FIG. 5 , the protecting layer  40  is disposed so as to cover a surface of the piezoelectric member  37  except central portions of the respective second electrodes  34 . One of main purposes of the protecting layer  40  is preventing ingress of water from air into the piezoelectric layers  33 . The protecting layer  40  is formed of a material having low permeability such as oxides and nitrides, for example. Examples of the oxides include alumina (Al 2 O 3 ), silicon oxide (SiOx), and tantalum oxide (TaOx). Examples of the nitrides include silicon nitride (SiN). 
     The insulating layer  41  is formed on an upper side of the protecting layer  40 . A material of the insulating layer  41  is not limited in particular. For example, the insulating layer  41  is formed of silicon dioxide (SiO2). This insulating layer  41  is provided for increasing insulation between the common electrode  36  and the wires  42  connected to the respective second electrodes  34 . 
     The wires  42  are formed on the insulating layer  41 . The wires  42  are drawn out from the respective second electrodes  34  of the piezoelectric elements  31 . Each of the wires  42  is formed of aluminum (Al), for example. As illustrated in  FIG. 5 , one end portion of each of the wires  42  is disposed so as to overlap an end portion of the second electrode  34  disposed on a corresponding one of the piezoelectric layers  33 . Each of the wires  42  is conductive with the corresponding second electrode  34  by a through electrically-conductive portion  48  that extends through the protecting layer  40  and the insulating layer  41 . 
     Each of the wires  42  corresponding to the respective piezoelectric elements  31  extends rightward or leftward. That is, a direction in which each of the wires  42  extends (hereinafter may be referred to as “wire extending direction”) is orthogonal to the nozzle arrangement direction. Specifically, as illustrated in  FIG. 3 , the wires  42  extend rightward from the respective piezoelectric elements  31  constituting the right two piezoelectric element groups  39   k ,  39   y  of the four piezoelectric element groups  39 , and the wires  42  extend leftward from the respective piezoelectric elements  31  constituting the left two piezoelectric element groups  39   c ,  39   m  of the four piezoelectric element groups  39 . 
     Each of the driving contacts  46  is provided on an end portion of a corresponding one of the wires  42 , which end portion is located on an opposite side of the wire  42  from its portion on which the second electrode  34  is disposed. The driving contacts  46  are arranged in a row in the front and rear direction at each of a right end portion and a left end portion of the piezoelectric actuator  22 . That is, the direction in which the driving contacts  46  are arranged (hereinafter may also referred to as “contact arrangement direction”) is parallel with the nozzle arrangement direction. In the present embodiment, the nozzles  24  forming the nozzle group  27  of each color are arranged at intervals of 600 dpi (=42 μm). Also, each of the wires  42  extends rightward or leftward from the piezoelectric element  31  corresponding to the nozzle groups  27  associated with corresponding two colors. Accordingly, at each of the right end portion and the left end portion of the piezoelectric actuator  22 , the driving contacts  46  are arranged at very short intervals of a half of those of the nozzles  24  of each nozzle group  27 , that is, the driving contacts  46  are arranged at the intervals of about 21 μm. 
     The two ground contacts  47  are respectively disposed in front of and at a rear of the driving contacts  46  arranged in a row in the front and rear direction. Each of the ground contacts  47  has a larger contacting area than each of the driving contacts  46 . Each of the ground contacts  47  is connected to the common electrode  36  via a corresponding one of conducting portions  49  (see  FIGS. 10A and 10B ) which extends through the protecting layer  40  and the insulating layer  41  located just under the ground contact  47 . 
     As described above, the driving contacts  46  and the ground contacts  47  disposed on the right end portion and the left end portion of the piezoelectric actuator  22  are exposed from the protector  23 . The two COFs  50  are respectively joined to the right end portion and the left end portion of the piezoelectric actuator  22 . Each of the driving contacts  46  is connected to a corresponding one of the driver ICs  51  via a corresponding one of the individual contacts  54  and a corresponding one of the individual wires  52  of the COFs  50 . A drive signal is supplied from the driver IC  51  to the driving contacts  46 . Each of the ground contacts  47  is connected to a corresponding one of the ground contacts  55  of the COFs  50 . A ground potential is applied from the ground contact  55  to the ground contact  47 . Detailed constructions of the driving contacts  46  and the ground contacts  47  of the piezoelectric actuator  22  and electric connection of these contacts  46 ,  47  and the contacts  54 ,  55  of the COF  50  will be described later. 
     As illustrated in  FIG. 5 , the wire protecting layer  43  is disposed so as to cover the wires  42 . The wire protecting layer  43  increases insulation between the wires  42 . Also, the wire protecting layer  43  inhibits oxidation of a material, e.g., Al, of the wires  42 . The wire protecting layer  43  is formed of silicon nitride (SiNx), for example. 
     As illustrated in  FIGS. 5 and 6 , in the present embodiment, each of the second electrodes  34  is exposed from the protecting layer  40 , the insulating layer  41 , and the wire protecting layer  43  except its peripheral portion. That is, deformation of the piezoelectric layers  33  is not hindered by the protecting layer  40 , the insulating layer  41 , and the wire protecting layer  43 . 
     Joined Portions of Piezoelectric Actuator and COF 
     There will be next explained a detailed construction of the joined portions of the piezoelectric actuator  22  and each of the COFs  50 . 
     As described above, the driving contacts  46  and the two ground contacts  47  are arranged in the front and rear direction at each of the right end portion and the left end portion of the piezoelectric actuator  22 . The end portions of the respective COFs  50  are respectively joined to the right end portion and the left end portion of the piezoelectric actuator  22  with a conductive adhesive  60 . 
     As illustrated in  FIGS. 8A and 10A , the conductive adhesive  60  is formed by mixing conductive particles  62  into a thermosetting adhesive  61  formed of epoxy resin, for example. The epoxy resin is used for the thermosetting adhesive  61 . Each of the conductive particles  62  is a spherical particle with a diameter D ranged between 3-5 μm, for example. The conductive adhesive  60  is generally used in the form of a film or a paste. One example of the film is an anisotropic conductive film (ACF), and one example of the paste is an anisotropic conductive paste (ACP). The conductive adhesive  60  is provided between the piezoelectric actuator  22  and each of the COFs  50  at an area elongated in the front and rear direction across the contacts  46 ,  47  (the contacts  54 ,  55 ). The COFs  50  are pressed against the piezoelectric actuator  22  in this state while heating the conductive adhesive  60 . As a result, the thermosetting adhesive  61  is hardened, so that the piezoelectric actuator  22  and each of the COFs  50  is mechanically joined to each other, and the contacts are electrically connected between the piezoelectric actuator  22  and each of the COFs  50  by the conductive particles  62  contained in the adhesive  60 . 
     In some cases, incidentally, the conductive particles  62  may flow out to areas around the contacts together with the adhesive at heating in the joining using the conductive adhesive  60 , leading to poor connection. To improve reliability of electric connection, the present embodiment employs a structure for preventing an outflow of the conductive particles  62  contained in the adhesive  60 . 
     Specifically, as illustrated in  FIGS. 7-8B , each of the driving contacts  46  is provided with two protrusions  63  arranged in the front and rear direction and a recess  64  interposed between the two protrusions  63 . Each of the protrusions  63  is elongated in the right and left direction. Accordingly, the recess  64  interposed between the two protrusions  63  also has an elongated shape with its length in the right and left direction is longer than its width in the front and rear direction. 
     Each of the driving contacts  46  is joined to a corresponding one of the individual contacts  54  of the COF  50  with the conductive adhesive  60  located in the recess  64  in a state in which the two protrusions  63  are in direct contact with the individual contact  54  of the COF  50 . The conductive particles  62  located in the conductive adhesive  60  are caught by the recess  64  of the driving contact  46 , and the contacts  46 ,  47  conduct each other also by the conductive particles  62  located in the recess  64 . 
     There will be specifically explained constructions of the protrusions  63  and the recess  64  of the driving contact  46 . As illustrated in  FIGS. 7-8B , a distal end portion of each of the wires  42  extending from the respective second electrodes  34  is bifurcated into two portions. That is, the distal end portion of the wire  42  has two electrically conductive portions  42   a  spaced apart from in the front and rear direction and each extending in the right and left direction. The two electrically conductive portions  42   a  are connected to each other by coupling portions  42   b ,  42   c  respectively provided at a basal end portion of the driving contact  46  and a central portion of the driving contact  46  in its longitudinal direction. The wire protecting layer  43  covering the wire  42  also covers the two electrically conductive portions  42   a.    
     Each of the driving contacts  46  is formed of, e.g., gold (Au) and overlaps the two electrically conductive portions  42   a  of the corresponding wire  42  via the wire protecting layer  43 . More specifically, each driving contact  46  is disposed so as to overlap the entire two electrically conductive portions  42   a  and a region located between the two electrically conductive portions  42   a . As illustrated in  FIG. 8B , the driving contact  46  conducts with the coupling portion  42   b  by a conducting portion  67  extending through the wire protecting layer  43 . That is, the driving contact  46  is connected to the wire  42  via the conducting portion  67 , the coupling portion  42   b , and the two electrically conductive portions  42   a.    
     In the above-described construction, each of the protrusions  63  is formed by a corresponding one of the electrically conductive portions  42   a , a portion of the wire protecting layer  43  which covers the electrically conductive portion  42   a , and a portion the driving contact  46  which covers the electrically conductive portion  42   a . The recess  64  is formed by a portion of the driving contact  46  which is located between the two electrically conductive portions  42   a . As is apparent from  FIGS. 8A and 8B , the recess  64  is partially shallow at its region overlapping the coupling portion  42   c.    
     Like the driving contact  46 , as illustrated in  FIGS. 9-10B , each of the ground contacts  47  includes two protrusions  65  and a recess  66 . Each of the ground contacts  47  is joined to a corresponding one of the ground contacts  55  of the COF  50  with the conductive adhesive  60  located in the recess  66  in a state in which the two protrusions  65  are in contact with the ground contact  55  of the COF  50 . While the ground contact  47  is a contact with what is called a solid pattern expanding in plan view in  FIG. 9 , the ground contact  47  may be divided into a plurality of small contacts arranged at the same intervals as those of the driving contacts  46 . A strength of joining between the ground contact  47  and the ground contact  55  of the COF  50  is increased by the adhesive  60  having entered regions each between adjacent two of the small contacts. 
     There will be next explained constructions of the protrusions  65  and the recess  66  of the ground contact  47 . Drawn-out wires  58  for the common electrode  36  are formed on the insulating layer  41  with the wires  42 . Each of the drawn-out wires  58  conducts with the common electrode  36  located under the protecting layer  40 , by a corresponding one of the conducting portions  49  which extends through the insulating layer  41  and the protecting layer  40 . Two electrically conductive portions  58   a  are formed on a distal end portion of each of the drawn-out wires  58 . The two electrically conductive portions  58   a  are connected to each other by coupling portions  58   b ,  58   c . The two electrically conductive portions  58   a  are also covered with the wire protecting layer  43  on which the ground contact  47  formed of, e.g., gold (Au) is disposed. The ground contact  47  conducts with the coupling portion  58   b  by a conducting portion  68  extending through the wire protecting layer  43 . That is, the ground contact  47  is connected to the common electrode  36  via the conducting portion  68 , the coupling portion  58   b , the two electrically conductive portions  58   a , the drawn-out wires  58 , and the conducting portion  49 . 
     In the above-described construction, each of the protrusions  65  is formed by a corresponding one of the electrically conductive portions  58   a , a portion of the wire protecting layer  43  which covers the electrically conductive portion  58   a , and a portion of the ground contact  47  which covers the electrically conductive portion  58   a . The recess  66  is formed by a portion of the ground contact  47  which is located between the two electrically conductive portions  58   a.    
     The area of each of the protrusions  65  of the ground contact  47  is larger than that of each of the protrusions  63  of the driving contact  46 . The area of the recess  66  of the ground contact  47  is also larger than the area of the recess  64  of the driving contact  46 . Specifically, the width Wa′ of the protrusion  65  of the ground contact  47  in the front and rear direction is greater than the width Wa of the protrusion  63  of the driving contact  46  in the front and rear direction. The width Wb′ of the recess  66  of the ground contact  47  in the front and rear direction is greater than the width Wb of the recess  64  of the driving contact  46  in the front and rear direction. 
     As described above, the ground contact  47  is connected to the common electrode  36 . A large current may temporarily flow in the common electrode  36  when a plurality of the piezoelectric elements  31  are driven at the same time. In this case, a difference in length among passages connected to the common electrode  36  increases a difference in drop of voltage in the passages connected to the common electrode  36  among the piezoelectric elements  31 , resulting in increase in difference in amount of displacement among the piezoelectric elements  31 . To suppress this phenomenon, the resistance of the passages connected to the common electrode  36  is preferably made as small as possible. Thus, a resistance of connection between the ground contact  47  and the ground contact  55  is also preferably made small. That is, the area of the protrusion  65  of the ground contact  47  which contacts the ground contact  55  of the COF  50  is preferably large, and the area of the recess  66  of the ground contact  47  in which the conductive particles  62  are caught is also preferably large. 
     In the present embodiment as described above, each of the driving contacts  46  and the ground contacts  47  has the protrusions and the recess. However, although the contacting area, etc, is different in some degree between the driving contacts  46  and the ground contacts  47 , there is no large difference in electric connection between the contacts of the piezoelectric actuator  22  and the contacts of the COF  50 . Thus, the following explanation will be provided, taking the driving contacts  46  as an example except cases which requires references to the ground contacts  47 , in particular. 
     There will be explained a process of producing the ink-jet head  4  with reference to  FIGS. 11A-12I , mainly focusing on forming of the driving contacts  46  and joining of the COF  50 . It is noted that the following steps A-I respectively correspond to  FIGS. 11A-12I . 
     In step A, the vibration layer  30  is formed by performing an oxidation processing or a nitriding processing on a surface of a silicon single crystal base that is to become the passage definer  21 . In step B, the first electrodes  32  (the common electrode  36 ), the piezoelectric layers  33 , and the second electrodes  34  are formed on the vibration layer  30  by deposition and etching to form the piezoelectric elements  31 . In step C, the protecting layer  40  and the insulating layer  41  are formed so as to cover the piezoelectric layers  33 , and patterning is performed by etching. 
     In step D, the wires  42  formed of, e.g., aluminum (Al) are formed on the insulating layer  41 . Specifically, step D is performed by forming an Al layer on the insulating layer  41  and then patterning and etching this Al layer. In this patterning, the two electrically conductive portions  42   a  are formed on the distal end portion of each wire  42 . In step E, the wire protecting layer  43  is formed on the wires  42  and patterned. The wire protecting layer  43  is also formed so as to cover the two electrically conductive portions  42   a  of the distal end portion of each wire  42 . In step F, the driving contacts  46  formed of, e.g., gold (Au) is formed by plating on the wire protecting layer  43  covering the electrically conductive portions  42   a . As a result, each of the driving contacts  46  is shaped to have the two protrusions  63  and the recess  64  (see  FIGS. 8A and 8B ). 
     In step G, the protector  23  is joined to the piezoelectric actuator  22  so as to cover the piezoelectric elements  31 . In step H, the passage definer  21  is polished to reduce its thickness to an appropriate thickness, and then the pressure chambers  26  are formed by etching. In step I, the COF  50  is joined with the conductive adhesive  60  to the end portion of the piezoelectric actuator  22  on which the driving contacts  46  and the ground contacts  47  are disposed. Specifically, the conductive adhesive  60  (ACF or ACP) is provided between the piezoelectric actuator  22  and the COF  50 , and then the COF  50  is pressed against the conductive adhesive  60  using a heater plate  58  placed on an upper surface of the COF  50 . 
     This pressing of the COF  50  using the heater plate  58  heats and compresses the conductive adhesive  60  between each of the driving contacts  46  and the corresponding individual contact  54 . In this process, as illustrated in  FIGS. 8A and 8B , the thermosetting adhesive  61  is partly melted and pushed to an outside from an area located between each pair of contacts, and the two protrusions  63  of each driving contact  46  and the corresponding individual contact  54  of the COF  50  are brought into contact with each other. The thermosetting adhesive  61  is hardened in this state, whereby the COF  50  is mechanically joined to the piezoelectric actuator  22  in a state in which each driving contact  46  and the corresponding individual contact  54  conduct with each other. The conductive particles  62  contained in the conductive adhesive  60  are caught in the recess  64  interposed between the two protrusions  63 . With this construction, the number of the conductive particles  62  contained in the conductive adhesive  60  need not be increased so much to catch the conductive particles  62  in the area between the two contacts  46 ,  47 . This construction is particularly effective to increase electric reliability while preventing shorts between adjacent contacts in the construction in which intervals of the arrangement of the driving contacts  46  is very short as in the present embodiment. 
     In the present embodiment, each driving contact  46  and the corresponding individual contact  54  of the actuator device  25  are in contact with each other in two configurations (i) and (ii). The configuration (i) is direct contact of the protrusions  63  with the individual contacts  54 . The configuration (ii) is contact of the conductive particles  62  caught in the recess  64  with the individual contacts  54 . 
     If each driving contact  46  and the corresponding individual contact  54  conduct with each other only in the configuration (i) (the direct contact of the protrusions  63 ), when a mechanically bonding force of the adhesive  61  is lowered due to time-dependent deterioration of the adhesive  61  around the driving contacts  46 , a conduction failure may occur due to separation of the protrusions  63  from the individual contact  54 . In this regard, in the present embodiment, conduction is caused not only by the direct contact of the protrusions  63  but also by the conductive particles  62  located in the recess  64 . Thus, even if the protrusions  63  are separated from the individual contact  54 , the conducting state is maintained by the conductive particles  62 . That is, the actuator device has a long useful life with high resistance to the time-dependent deterioration. 
     If each driving contact  46  and the corresponding individual contact  54  conduct with each other only by the conductive particles  62  as in the configuration (ii), the conduction ceases when the conductive particles  62  flow out from between the two contacts  46 ,  47 . In this regard, in the present embodiment, conduction is caused not only by the direct contact of the protrusions  63  but also by the conductive particles  62 , resulting in improved reliability of electric connection. Also, connection resistance is reduced. 
     In the present embodiment, the following configurations are employed from the viewpoint of improving reliability of electric connection between the contacts. 
     In the case where the number of the conductive particles  62  contained in the conductive adhesive  60  interposed between the piezoelectric actuator  22  and the COF  50  per area A is defined as n, and the base area of each recess  64  is defined as Al, a relationship “Al A/n” is established. In the case where the area of the recess  64  is greater than or equal to the value A/n, one or more conductive particles  62  are held in each recess  64  based on a simple calculation. That is, the conductive particle or particles  62  are more easily caught in the recess  64 . 
     Specifically, in the case where the conductive adhesive  60  is an anisotropic conductive film (ACF), the number of the conductive particles  62  contained in the film per area A only needs to be n. In the case where the conductive adhesive  60  is an anisotropic conductive paste (ACP), the number of the conductive particles  62  contained in the paste per area A in a state in which the paste is applied to the surface of the contact only needs to be n. 
     As illustrated in  FIGS. 8A and 8B , the two protrusions  63  of the driving contact  46  are in contact with the individual contact  54 . In this construction, the driving contact  46  is in direct contact with the individual contact  54  at two positions, resulting in improved reliability of conduction. Also, the recess  64  located between the two protrusions  63  is closed by the individual contact  54 , making it difficult for the conductive particles  62  to flow out from the recess  64 . 
     The width W 0  of the individual contact  54  in the front and rear direction is greater than the width W 1  of the driving contact  46  in the front and rear direction for reliable contact of the two protrusions  63  of the driving contact  46  with the individual contact  54 . More specifically, the width W 0  of the individual contact  54  is preferably greater than or equal to twice the width W 1  of the driving contact  46 . Even in the case where the width W 0  of the individual contact  54  is slightly shorter than the width W 1 , the individual contact  54  is in reliable contact with the two protrusions  63  in the case where the width W 0  is greater than the distance Wp between outer ends of the two protrusions  63  of the driving contact  46 . 
     In the case where the width of the recess  64  is less than the diameter of the conductive particle  62 , there is a higher possibility that the conductive particle  62  is pushed out from the recess  64  at joining without being caught in the recess  64 . In order to reliably catch the conductive particle  62  in the recess  64 , the width Wb of the recess  64  in the front and rear direction is greater than or equal to the diameter D of the conductive particle  62  before joining in the present embodiment. Specifically, the width Wb of the recess  64  is preferably greater than or equal to twice the diameter D of the conductive particle  62 . This sufficient width of the recess  64  can catch the conductive particle  62  more reliably. Also, it is possible to catch two or more conductive particles  62  in each recess  64 . 
     In the case where the area of each protrusion  63  is too large with respect to the recess  64  in  FIGS. 8A and 8B , the conductive particle  62  may be located on the protrusion  63 , making it difficult for the conductive particle  62  to contact the contacts  46 ,  47  in the recess  64 . From this viewpoint, the width Wa of the protrusion  63  is preferably less than the width Wb of the recess  64 . This discussion is true to the ground contacts  47  illustrated in  FIGS. 10A and 10B , the width Wa′ of the protrusion  65  is preferably less than the width Wb′ of the recess  66 . 
     If the width Wb of the recess  64  is made too large, the width W 1  of the driving contact  46  including the recess  64  is also increased. In this case, a distance between the driving contact  46  and another driving contact  46  next to the driving contact  46  is short, which may lead to shorts therebetween. If the distance is made large in order to prevent shorts, the size of the actuator  22  increases in the front and rear direction. Accordingly, the width Wb of the recess  64  in the front and rear direction is preferably less than or equal to ten times the diameter D of the conductive particle  62 . Furthermore, the width W 1  of the driving contact  46  in the front and rear direction is also preferably less than or equal to ten times the diameter D of the conductive particle  62 . 
     The conductive particle  62  caught in the recess  64  is preferably compressed between the driving contact  46  and the individual contact  54  and in contact with both of the driving contact  46  and the individual contact  54  by elastic resilience. From this viewpoint, in the present embodiment, the depth d of the recess  64  is less than the diameter D of the conductive particle  62 . Specifically, in the case where the depth d of the recess  64  is less than or equal to three fifths of the diameter D of the conductive particle  62 , the conductive particle  62  is compressed in an appropriate degree. In  FIG. 8A , the two-dot chain line indicates the conductive particle  62  at a time before joining (before compression), and the solid line indicates the conductive particle  62  at a time after joining (after compression). The above-described diameter D of the conductive particle  62  indicates the diameter of the conductive particle  62  before the conductive particle  62  is compressed. In the above-described construction, the conductive particle  62  located in the recess  64  is reliably compressed between the driving contact  46  and the individual contact  54  and reliably in contact with both of the driving contact  46  and the individual contact  54 , resulting in increased reliability of electric connection. 
     However, if the depth d of the recess  64  is too small, the conductive particle  62  easily flows out from the recess  64 . Accordingly, the depth d of the recess  64  is preferably greater than or equal to one fifth of the diameter D of the conductive particle  62 . 
     While the relationship between the width Wb of the recess  64  and the diameter D of the conductive particle  62  is described above in relation to the catch of the conductive particle  62 , there is another problem in which in the case where the width Wb of the recess  64  is not large enough with respect to the diameter D of the conductive particle  62 , when the COF  50  is pressed against the conductive particle  62 , the conductive particle  62  cannot be widened laterally and is not easily compressed vertically. That is, the width Wb of the recess  64  is preferably large enough with respect to the diameter of the conductive particle  62  also from the viewpoint of reliably compressing the conductive particle  62 . Specifically, the width Wb of the recess  64  is preferably greater than or equal to twice the diameter D of the conductive particle  62 . 
     In the present embodiment, the recess  64  has an elongated shape whose length in the right and left direction is longer than its width in the front and rear direction. Also, only one recess  64  is formed for each of the driving contacts  46  in the front and rear direction. With these constructions, the width Wb of the recess  64  is short in the front and rear direction in which the driving contacts  46  are arranged, so that the width W 1  of the driving contact  46  is small. Since the recess  64  is long in the right and left direction, it is possible to catch many conductive particles  62  in the recess  64 . Also, although the recess  64  is formed in each of the driving contacts  46 , intervals at which the driving contacts  46  are arranged can be made short. In particular, the present embodiment employs the above-described construction because the driving contacts  46  need to be arranged in a row though the nozzles  24  of the two nozzle groups  27  corresponding to the driving contacts  46  are arranged at the high density of 600 dpi. 
     In the present embodiment, the driving contact  46  of the piezoelectric actuator  22  is formed with the protrusions  63  and the recess  64 . However, effects similar to the above-described effects are obtained even in a construction in which protrusions and a recess are formed on and in each of the individual contacts  54  of the COF  50 . However, forming of the protrusions and the recess on and in each of the contacts requires patterning at intervals shorter than the intervals at which the contacts are arranged. Specifically, in the present embodiment, the two electrically conductive portions  42   a  for forming the two protrusions  63  are formed on the distal end portion of each of the wires  42 . The two electrically conductive portions  42   a  are formed at a considerably small distance of a half of the intervals in which the wires  42  are arranged. 
     Focusing on achieving fine pitches, patterning is in general more easily performed on a silicon single crystal base than a wire base such as the COF  50  at the current technological level. That is, fine patterns are more easily formed on the silicon base than on the wire base. Accordingly, if the recess and the protrusions may be formed in and on any of each contact of the piezoelectric actuator  22  and each contact of the COF  50 , the protrusions  63  and the recess  64  are more easily formed on and in each of the driving contacts  46  of the piezoelectric actuator  22 . 
     As described in the explanation for the producing process, each wire  42  having the two electrically conductive portions  42   a  is formed of aluminum (Al) and patterned by etching of the Al layer in the present embodiment. The patterning using etching enables formation of wire patterns at a high definition. In contrast, the driving contacts  46  are formed of gold (Au) and are generally formed by plating. The precision of patterning by plating is less than that of patterning by etching. That is, in the present embodiment, the driving contact  46  formed of a material unsuitable for fine pitches is formed over the electrically conductive portions  42   a  formed by etching at fine pitches, whereby the two protrusions  63  and the recess  64  are formed. 
     However, aluminum is subject to oxidation when compared with gold. Thus, in the present embodiment, the two electrically conductive portions  42   a  are covered with the wire protecting layer  43 , and the driving contact  46  is formed thereon. This construction inhibits oxidation of the electrically conductive portions  42   a.    
     In the embodiment described above, the ink-jet head  4  is one example of a liquid ejection apparatus. The piezoelectric actuator  22  is one example of an actuator. The front and rear direction, i.e., each of the nozzle arrangement direction and the contact arrangement direction is one example of a first direction. The right and left direction, i.e., the wire extending direction parallel with the upper surface of the piezoelectric actuator  22  on which the contacts  46  are disposed and orthogonal to the contact arrangement direction is one example of a second direction. The COF  50  is one example of a wire member. Each of the driving contacts  46  and the ground contacts  47  of the piezoelectric actuator  22  is one example of a first contact. Each of the individual contacts  54  and the ground contacts  55  of the COF  50  is one example of a second contact. The wire protecting layer  43  covering the two electrically conductive portions  42   a  is one example of an insulating layer. 
     There will be next explained modifications of the embodiment. It is noted that the same reference numerals as used in the above-described embodiment are used to designate the corresponding elements of the modifications, and an explanation of which is dispensed with. 
     In the above-described embodiment, each of the driving contacts  46  and the ground contacts  47  of the piezoelectric actuator  22  has the protrusions and the recess. However, only one of each of the driving contacts  46  and each of the ground contacts  47  may have the protrusions and the recess. 
     In the above-described embodiment, the three insulating layers, namely, the protecting layer  40 , the insulating layer  41 , and the wire protecting layer  43 , are formed on the piezoelectric layers  33 , but these layers may be removed as needed. For example, in the case where the wires connected to the second electrodes  34  are formed of a highly stable material such as gold (Au), the insulating layer  41  and the protecting layer  43  may not be provided. 
     The shapes of the protrusions and the recess formed on and in each contact are not limited to those in the above-described embodiment. For example, the following first-fourth modifications may be provided. 
     In the first modification, three or more protrusions and two or more recesses may be formed on and in each contact. Increase in the number of protrusions increases the direct contact area, resulting in higher reliability of electric connection. Also, the connection resistance is reduced. Furthermore, increase in the number of recesses increases the number of the conductive particles  62  to be caught, resulting in higher reliability of electric connection. 
     In the above-described embodiment, as illustrated in  FIGS. 8A and 8B , the width of the individual contact  54  of the COF  50  is greater than the width of the driving contact  46  of the piezoelectric actuator  22 . In a second modification, as illustrated in  FIG. 13A , the width of an individual contact  54 A of the COF  50 A may be less than that of the driving contact  46  of the piezoelectric actuator  22 . Alternatively, as illustrated in  FIG. 13B , only one of the two protrusions  63  of the driving contact  46  may be in contact with the individual contact  54 B. Also in this construction, most of the recess  64  located between the two protrusions  63  is closed by a COF  50 B, making it difficult for the conductive particles  62  to flow out from the recess  64 . 
     In the above-described embodiment, the depth of the recess  64  is less than the diameter of the conductive particle  62 . In a third modification, however, the depth of the recess may be greater than the diameter of the conductive particle  62 . Also in this construction, it is possible to compress the conductive particles  62  in the recess as long as two or more conductive particles  62  are caught in the recess. 
     In the above-described embodiment, as illustrated in  FIG. 7 , no protrusion is formed to the right of the recess  64  (i.e., on one of opposite sides of the recess  64  which is located nearer to a distal end of the contact  46  than the other), and a right end of the recess  64  is open. In a fourth modification, however, a protrusion may be formed on one of opposite sides of the recess which is located nearer to a distal end of the contact than the other. In this construction, the recess is surrounded by the protrusions, making it difficult for the conductive particles to flow out from the recess. 
     While the two protrusions  63  are formed by the bifurcated shape of the distal end portion of the wire  42  in the above-described embodiment, protrusions and a recess may be formed on and in the contact in other methods. 
     In a modification illustrated in  FIG. 14A , a recessed layer portion  70  is formed by etching an upper surface of a vibration layer  30 C. A driving contact  46 C is disposed so as to cover the recessed layer portion  70 . In this construction, a portion of the driving contact  46 C which overlaps the recessed layer portion  70  serves as a recess  64 C. Protrusions  63 C are constituted by (i) portions of the vibration layer  30 C which are located in front of and at a rear of the layer portion  70  and (ii) portions of the driving contact  46 C which are respectively located just above the portions of the vibration layer  30 C. 
       FIG. 14B  illustrates yet another modification in which a recessed layer portion is formed by etching the piezoelectric layer instead of the vibration layer. In this modification, a piezoelectric layer  33 D located over the vibration layer  30  extends to an end portion of the passage definer  21 . The piezoelectric layer  33 D is etched to form a recessed layer portion  71 . A driving contact  46 D is disposed so as to cover the recessed layer portion  71 . In this construction, a portion of the driving contact  46 D which overlaps the recessed layer portion  71  serves as a recess  64 D. Protrusions  63 D are constituted by (i) portions of the piezoelectric layer  33 D which are located in front of and at a rear of the layer portion  71  and (ii) portions of the driving contact  46 D which are respectively located just above the portions of the piezoelectric layer  33 D. 
       FIG. 14C  illustrates yet another modification in which a driving contact  46 E disposed on the vibration layer  30  includes a conductive layer  72  and two conductors  73 . The two conductors  73  are disposed on the conductive layer  72  so as to be spaced apart from each other in the front and rear direction. In this modification, protrusions  63 E are constituted by the conductors  73  and portions of the conductive layer  72  which are located just below the respective conductors  73 . A portion of the conductive layer  72  which is interposed between the two conductors  73  serves as a recess  64 E. 
       FIG. 14D  illustrates yet another modification in which etching, plasma processing, and/or other similar processings may be performed on a surface of a driving contact  46 F, to which the individual contact  54  is connected, such that the driving contact  46 F has a rough surface  74  with a surface roughness enough to catch the conductive particles  62 . For example, a desired surface roughness of the surface of the driving contact may be achieved by changes of an etch rate of wet etching (see Japanese Patent Application Publication No. 2012-222025). 
     Protrusions  63 F and recesses  64 F having various shapes are formed on and in the rough surface  74 . The surface roughness (arithmetic average roughness) Ra of the rough surface  74  is preferably less than the diameter D of the conductive particle  62  in order to compress the conductive particles  62  in the recesses  64 F of the rough surface  74 . If the surface roughness Ra is too small, the recesses  64 F cannot catch the conductive particles  62 . Thus, the surface roughness Ra is preferably greater than or equal to one fifth of the diameter D of the conductive particle  62 . 
     In the above-described embodiment, the two protrusions  63  of each of the driving contacts  46  are arranged in the front and rear direction coinciding with the direction in which the driving contacts  46  are arranged. However, two or more protrusions may be arranged in a direction orthogonal to the direction in which the driving contacts are arranged. In this construction, the width of each of the contacts in the contact arrangement direction is large in many cases, leading to increase in intervals at which the contacts are arranged. However, the larger width of each contact results in higher peel strength of the COF. 
     In the above-described embodiment, the protrusions  63  and the recess  64  are formed on and in each of the driving contacts  46  of the piezoelectric actuator  22 , but protrusions and a recess are formed on and in each contact of the COF. For example, in a modification illustrated in  FIG. 15 , an individual contact  54 G of a COF  50 G which is connected to a driving contact  46 G of a piezoelectric actuator  22 G includes a conductive layer  76  and two conductors  77 . The two conductors  77  are disposed on the conductive layer  76  so as to be spaced apart from each other in the front and rear direction. In this construction, protrusions  63 G are constituted by the conductors  77  and portions of the conductive layer  76  which are located just below the respective conductors  77 . Also, a portion of the conductive layer  76  which is located between the two conductors  77  serves as a recess  64 G. 
     The arrangement of the driving contacts and the ground contacts in one ink-jet head is not limited to the arrangement in the above-described embodiment. For example, the ink-jet head may be configured such that all the wires of the piezoelectric elements are drawn in one direction, and all the driving contacts are arranged in a row at one end portion of the piezoelectric actuator. The ink-jet head may be configured such that all the wires of the piezoelectric elements are drawn toward a central portion of the piezoelectric actuator in the scanning direction, and all the driving contacts are arranged in a row at the central portion of the piezoelectric actuator. The number of the ground contacts is not limited to two and may be one, or three or more. 
     The ink-jet head  4  in the above-described embodiment is a serial head configured to eject the ink while moving in the widthwise direction of the recording sheet  100 . However, the present disclosure may be applied to a line head having nozzles arranged in the widthwise direction of the sheet. 
     While the present disclosure is applied to the ink-jet head configured to eject the ink onto the recording sheet to record an image in the above-described embodiment, the present disclosure may be applied to actuator devices used for purposes other than liquid ejection. Also, the actuator is not limited to the piezoelectric actuator including a plurality of piezoelectric elements. For example, the actuator may be an actuator including a heater as a drive element which causes driving by utilizing a heat generated when a current passes through the heater.