Patent Publication Number: US-10328698-B2

Title: Liquid discharge apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2017-184830 filed on Sep. 26, 2017 the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates a liquid discharge apparatus. 
     BACKGROUND 
     As a liquid discharge apparatus according to the background art, a liquid jetting head disclosed is known. In an example of the liquid jetting head, a spacer is interposed between an actuator substrate and a sealing plate. The spacer is attached to the actuator substrate through an adhesive so as to surround a bump electrode protruding from the actuator substrate toward the sealing plate. Furthermore, piezoelectric element constituting the actuator substrate is disposed outside the closed space surrounded by the spacer. 
     In another example of the liquid jetting head, a frame-shaped spacer is provided between a sealing plate and an actuator substrate so as to surround a piezoelectric element. The piezoelectric element is displaced to cause a pressure variation of liquid in a pressure chamber formed in the actuator substrate, such that the liquid is jetted from a nozzle communicating with the pressure chamber. 
     SUMMARY 
     In the one example of the liquid jetting head according to background art, the piezoelectric element is disposed outside the closed space surrounded by the spacer. Accordingly, gas generated from the adhesive for attaching the spacer and the actuator to each other may be confined in the closed space and suppressed from reaching the piezoelectric element, which prevents a problem such as deterioration of the piezoelectric element due to the gas. However, since the pressure of the closed space is raised by the gas, the bump electrode may be separated by the pressure. 
     In another example of the liquid jetting head, the piezoelectric element is stored in the closed space surrounded by the spacer. In the closed space, the pressure is raised by the gas of the adhesive, and the displacement of the piezoelectric element is inhibited. Therefore, a desired amount of liquid may not be jetted from the nozzle. 
     This disclosure is to provide a liquid discharge apparatus capable of suppressing reduction in displacement of a piezoelectric element and suppressing a problem due to gas generated from an adhesive. 
     A liquid discharge apparatus of this disclosure includes: a channel substrate, which has a pressure chamber communicating with a nozzle; a first substrate, which is disposed on the channel substrate; a piezoelectric element, which is disposed on the first substrate so as to correspond to the pressure chamber; a spacer, which is provided on a surface of the first substrate on which the piezoelectric element is disposed; a second substrate, which is stacked over the first substrate with the spacer interposed therebetween; and a bump electrode, which communicates with the piezoelectric element and electrically connects a first terminal provided on the first substrate with a second terminal provided on the second substrate. The spacer is provided between the bump electrode and the piezoelectric element and attached to at least one of the first and second substrates by an adhesive. Both a space on a side of the piezoelectric element with respect to the spacer and a space on a side of the bump electrode with respect to the spacer are opened by at least one of a portion other than a portion of the spacer positioned between the piezoelectric element and the bump electrode and an opening provided in at least one of the first and second substrates. 
     According to the configuration, a space on the side of the bump electrode with respect to the spacer is opened by the opening. Therefore, a pressure rise in the space is suppressed, and a problem such as separation of the bump electrode due to the high pressure is suppressed. 
     Since the opening is provided at the portion other than the portion positioned between the piezoelectric element and the bump electrode of the spacer, gas discharged from the opening does not directly flow toward the piezoelectric element from the bump electrode. Accordingly, the gas can be suppressed from reaching the piezoelectric element, whereby a problem of the piezoelectric element due to the gas is suppressed. 
     The space on the side of the piezoelectric element with respect to the spacer is opened by the opening. Therefore, a pressure rise in the space can be suppressed, and displacement reduction of the piezoelectric element due to a high pressure can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed descriptions considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  schematically illustrates a liquid discharge apparatus according to a first embodiment of this disclosure; 
         FIG. 2  is a cross-sectional view of a head taken along the line A-A of  FIG. 1 : 
         FIG. 3  illustrates the head on a first substrate of  FIG. 2 : 
         FIG. 4  illustrates a head on a first substrate of a liquid discharge apparatus according to a first modification of the first embodiment of this disclosure; 
         FIG. 5  illustrates a head on a first substrate of a liquid discharge apparatus according to first and second modifications of the first embodiment of this disclosure; 
         FIG. 6  illustrates a head on a first substrate of a liquid discharge apparatus according to a third modification of the first embodiment of this disclosure; 
         FIG. 7  illustrates a head on a first substrate of a liquid discharge apparatus according to a fourth modification of the first embodiment of this disclosure; 
         FIG. 8  illustrates a head on a first substrate of a liquid discharge apparatus according to a fifth modification of the first embodiment of this disclosure: 
         FIG. 9  illustrates a head on a first substrate of a liquid discharge apparatus according to a sixth modification of the first embodiment of this disclosure: 
         FIG. 10  illustrates a head on a first substrate of a liquid discharge apparatus according to a seventh modification of the first embodiment of this disclosure: 
         FIG. 11  illustrates a head on a first substrate of a liquid discharge apparatus according to an eighth modification of the first embodiment of this disclosure: 
         FIG. 12  illustrates a head on a first substrate of a liquid discharge apparatus according to a second embodiment of this disclosure; 
         FIG. 13  illustrates a head on a first substrate of a liquid discharge apparatus according to a tenth modification of the second embodiment of this disclosure; and 
         FIG. 14  illustrates a head on a first substrate of a liquid discharge apparatus according to an eleventh modification of the second embodiment of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, exemplary embodiments of this disclosure will be described in detail with reference to the accompanying drawings. The same or corresponding elements throughout the whole drawings are represented by like reference numerals, and the duplicated descriptions thereof will be omitted. 
     First Embodiment 
     Liquid Discharge Apparatus 
     As illustrated in  FIG. 1 , a liquid discharge apparatus  10  according to a first embodiment of this disclosure is a printer, for example, that prints a text or image on a recording medium  11  such as paper with liquid such as ink. The liquid discharge apparatus  10  includes a head unit  12 , a platen  13 , a transfer mechanism  14  and a controller  15 . The liquid discharge apparatus  10  is a line-type printer which performs printing while the position of the head unit  12  is fixed in the liquid discharge apparatus  10 . However, the liquid discharge apparatus  10  may include a printer in which the head unit  12  is moved in a direction perpendicular to the transfer direction of the recording medium  11 . 
     The head unit  12  includes a plurality of heads  20 , and the plurality of heads  20  are arranged in parallel to a direction perpendicular to the transfer direction. Each of the heads  20  includes a plurality of nozzles  21  for jetting liquid. The head  20  will be described in detail later. 
     The platen  13  serves as a base on which the recording medium  11  is placed, and is disposed so as to face a nozzle surface to which the nozzles  21  of the heads  20  are opened. The transfer mechanism  14  for transferring the recording medium  11  includes four rollers  14   a  and a transfer motor  14   b  for driving the rollers  14   a . The four rollers  14   a  are set to two pairs of rollers, and the two pairs of rollers  14   a  are disposed so as to interpose the platen  13  therebetween in the transfer direction. Each pair of rollers  14   a  is disposed so as to interpose the recording medium  11  therebetween, and rotated in the opposite direction by the transfer motor  14   b  to transfer the recording medium  11  along the transfer direction. 
     The controller  15  includes an operation unit (not illustrated) and a memory unit (not illustrated). The operation unit is constituted by a processor and the like, and the memory unit is constituted by a memory which the operation unit can access. As a program stored in the memory unit is executed by the operation unit, the respective units of the liquid discharge apparatus  10  are controlled. 
     Head 
     As illustrated in  FIG. 1 , the plurality of nozzles  21  in each of the heads  20  form columns (nozzle columns  21   a ) arranged in a straight line shape in a direction (arrangement direction) having a predetermined angle θ with respect to the transfer direction. Specifically, two nozzle columns  21   a  are provided in parallel to each other, with a space formed therebetween in a direction perpendicular to the arrangement direction. The two nozzle columns  21   a  include an equal number of nozzles  21 . The angle θ of the arrangement direction with respect to the transfer direction is set in the range of 30 to 60 degrees. 
     As illustrated in  FIGS. 2 and 3 , the head  20  includes a channel substrate  30 , a first substrate  40 , a piezoelectric element  50 , a spacer  60 , a second substrate  70  and a bump electrode  80 . The channel substrate  30  includes a pressure chamber  31  communicating with the nozzle  21 , and includes a nozzle plate  32 , a channel plate  33 , a pressure chamber plate  34  and a reservoir member  35 , which are stacked therein. 
     The nozzle plate  32  includes a plurality of nozzles  21  formed therethrough in the stacking direction of the plate. The bottom surface of the nozzle plate  32  is a nozzle surface through which the nozzles  21  are opened. 
     The channel plate  33  is stacked over the nozzle plate  32 , and a descender  36 , a branch channel  37  and a manifold  38  are formed in the channel plate  33 . The descender  36  is formed through the channel plate  33  in the stacking direction so as to communicate with the nozzle  21 . 
     The branch channel  37  is a channel for branching into the plurality of pressure chambers  31  from the manifold  38 . The branch channel  37  is formed through the channel plate  33  in the stacking direction so as to communicate with the manifold  38  and the pressure chamber  31 . The manifold  38  serves as a part of a channel (supply channel) for supplying liquid to the plurality of pressure chambers  31 , and is formed through the channel plate  33  in the stacking direction so as to extend in the arrangement direction. 
     The channel plate  33  includes a damper film  33   a  attached to the bottom surface thereof, such that the damper film  33   a  covers the manifold  38 . The damper film  33   a  defines a part of the manifold  38 . The damper film  33   a  made of a flexible film-shaped member is deformed to suppress a pressure variation of liquid in the manifold  38 . 
     The pressure chamber  31  of the pressure chamber plate  34  is formed through the pressure chamber plate  34  in the stacking direction so as to connect the descender  36  and the branch channel  37 . Accordingly, the pressure chamber  31  communicates with the nozzle  21  through the descender  36 , and communicates with the manifold  38  through the branch channel  37 . 
     The reservoir member  35  is stacked on the channel plate  33  outside the pressure chamber plate  34 , and includes a reservoir  39  formed therein. The reservoir  39  is opened through the bottom surface of the reservoir member  35  so as to communicate with the manifold  38 . Accordingly, the reservoir  39  forms a supply path with the manifold  38 , the supply path being used for supplying liquid to the plurality of pressure chambers  31  through the branch channels  37 . 
     The first substrate  40  is an insulating plate for supporting a first terminal  41 , for example, a vibration plate. The first substrate  40  is stacked over the pressure chamber plate  34  of the channel substrate  30 , and covers the plurality of pressure chambers  31  of the pressure chamber plate  34 . The piezoelectric element  50  is disposed on the first substrate  40  so as to correspond to the pressure chamber  31 . 
     The piezoelectric element  50  includes a common electrode  51 , a piezoelectric body  52  and a discrete electrode  53 . The common electrode  51  serving as a common electrode for the plurality of piezoelectric elements  50  is stacked on the first substrate  40  so as to cover the entire first substrate  40 . The piezoelectric body  52  is disposed on each of the pressure chambers  31 , and the discrete electrode  53  is disposed on the piezoelectric body  52 . Therefore, the discrete electrode  53  is provided for each of the piezoelectric elements  50 . 
     When a voltage is applied to the discrete electrode  53 , the piezoelectric body  52  is deformed to displace the first substrate  40 . As the first substrate  40  is displaced toward the pressure chamber  31 , the volume of the pressure chamber  31  is reduced, and pressure is applied to liquid in the pressure chamber  31 , such that the liquid is discharged from the nozzle  21  communicating with the pressure chamber  31 . 
     A protection film  42  is stacked on the discrete electrode  53  and the common electrode  51 . The protection film  42  is formed of aluminum oxide (alumina: Al 2 O 3 ), for example, and protects the piezoelectric body  52  from moisture in the air. The protection film  42  has a through-hole  43  formed therein, and the through-hole  43  is filled with a conductive material  44 . The protection film  42  includes a plurality of individual conductors  54  provided thereon, the plurality of individual conductors  54  corresponding to the respective discrete electrodes  53 . The individual conductors  54  on the protection film  42  and the discrete electrodes  53  on the protection film  42  are electrically connected to each other through the conductive material  44 . In the present embodiment, the plurality of piezoelectric elements  50  are arranged in the arrangement direction, and form two columns corresponding to the two nozzle columns  21   a . The individual conductor  54  extends from the discrete electrode  53  of the piezoelectric element  50  toward the opposite side (outside) of the center of the two piezoelectric element columns, and electrically connected to the first terminal  41 . 
     The second substrate  70  is an insulating plate for supporting a second terminal  71 , and stacked over the first substrate  40  through the spacer  60 . The second terminal  71  over the second substrate  70  is electrically connected to the first terminal  41  on the first substrate  40  through the bump electrode  80 . The spacer  60  and the bump electrode  80  will be described in detail later. 
     The second substrate  70  includes a driver IC  72  mounted thereon. The driver IC  72  is electrically connected to a wiring connected to the second terminal  71 , and the wiring is electrically connected to the controller  15  ( FIG. 1 ). Accordingly, the controller  15  is connected to the driver IC  72  and the second terminal  71  through the wiring, the second terminal  71  is connected to the first terminal  41  through the bump electrode  80 , and the first terminal  41  is connected to the discrete electrode  53  through the individual conductor  54 . Therefore, the driver IC  72  generates a driving signal for driving the piezoelectric element  50  based on a signal from the controller  15 , and outputs the driving signal to the discrete electrode  53 . 
     Bump Electrode 
     As illustrated  FIG. 2 , the bump electrode  80  includes an elastic internal resin  81  and a conductive film  82  covering the internal resin  81 . The bump electrode  80  protrudes from the first substrate  40  toward the second substrate  70  so as to be elastically deformed between the first and second substrates  40  and  70 . The bump electrode  80  is electrically connected to the first terminal  41  of the first substrate  40  and the second terminal  71  of the second substrate  70 . 
     The first terminal  41  includes a terminal (common terminal  41   a ) communicating with the common electrode  51  of the piezoelectric element  50  and a terminal (power receiving terminal  41   b ) communicating with the discrete electrode  53  of the piezoelectric element  50 . The second terminal  71  includes a ground terminal  71   a  and a terminal (power supply terminal  71   b ) communicating with the driver IC  72 . 
     The common terminal  41   a  is electrically connected to the common electrode  51  through the conductive material  44  filling the through-hole  43  of the protection film  42  which covers the common electrode  51 . For example, the common terminal  41   a  is disposed between the two piezoelectric element columns arranged with a gap formed therebetween in the orthogonal direction. The power receiving terminal  41   b  is electrically connected to the discrete electrode  53  through the conductive material  44  and the individual conductor  54 . For example, the power receiving terminal  41   b  is provided at an end of the discrete electrode  53  extending from the discrete electrode  53  of the piezoelectric element  50  toward the opposite side of the common terminal  41   a.    
     As illustrated in  FIG. 3 , the bump electrode  80  extends in the arrangement direction. For example, a plurality (three) of bump electrodes  80  are arranged in parallel to each other with an interval provided therebetween in the orthogonal direction. The bump electrode  80  may include an electrode (common bump electrode  80   a ) electrically connected to the common terminal  41   a  and the ground terminal  71   a  and an electrode (individual bump electrode  80   b ) electrically connected to the power receiving terminal  41   b  and a power feeding terminal  71   b . For example, two individual bump electrodes  80   b  are provided so as to correspond to two piezoelectric element columns. Between the two piezoelectric element columns, the common bump electrode  80   a  is disposed. 
     Spacer 
     As illustrated in  FIGS. 2 and 3 , the spacer  60  serves to secure a space (holding space) for holding the bump electrode  80  between the first and second substrates  40  and  70 , and is provided between the bump electrode  80  and the piezoelectric elements  50 . The spacer  60  is formed on the surface of the second substrate  70 , facing the first substrate  40 , and protrudes from the second substrate  70  toward the first substrate  40 . The protrusion dimension of the spacer  60  is set to such an extent that the first terminal  41  of the first substrate  40  and the second terminal  71  of the second substrate  70  are electrically connected to the bump electrode  80 . 
     The protruding end of the spacer  60  is connected to the first substrate  40  through an adhesive  61 . As the adhesive  61 , a non-conductive adhesive is used in order to prevent a short circuit between wirings. The adhesive  61  is applied to an adhesion region in which the end of the spacer  60  overlaps the first substrate  40  and a region closer to the bump electrode  80  than the adhesion region. Accordingly, the spacer  60  and the first substrate  40  can be reliably attached to each other, and the adhesive  61  can be suppressed from spreading and adhering to the piezoelectric element  50 . 
     The spacer  60  is formed in a rectangular frame shape to surround the bump electrodes  80 . Therefore, the spacer  60  can secure a space between the first and second substrates  40  and  70  such that the height of the bump electrode  80  becomes more appropriate. The spacer  60  includes a pair of first wall portions  62  extending in the arrangement direction and a pair of second wall portions  63  extending in the orthogonal direction. 
     The pair of first wall portions  62  are disposed with a space formed therebetween so as to interpose the bump electrodes  80  in the orthogonal direction. The pair of first wall portions  62  have the same shape. The first wall portion  62  is continuous from one end to the other end thereof in the arrangement direction, and has no disconnected portions. The pair of first wall portions  62  may include a wall portion positioned on the side of the piezoelectric element  50  with respect to the bump electrode  80  in the orthogonal direction (between the piezoelectric element  50  and the bump electrode  80 ) and a wall portion positioned at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80 . The first wall portion  62  extends longer than the bump electrode  80  in the arrangement direction, such that the end thereof is positioned outside the bump electrode  80  based on the end of the bump electrode  80 . Furthermore, the first wall portion  62  extends longer than the piezoelectric element column in the arrangement direction, such that the end thereof is positioned outside the piezoelectric element  50  positioned at the end of the piezoelectric element column. 
     The pair of second wall portions  63  are disposed with a space formed therebetween so as to interpose the bump electrodes  80  in the arrangement direction. The pair of second wall portions  63  have the same shape. The length of the second wall portion  63  in the orthogonal direction is equal to or larger than the width of the bump electrode  80 , and equal to or smaller than a distance between the outer ends of the pair of first wall portions  62 . The second wall portion  63  is disposed within the interval between the outer ends of the pair of first wall portions  62  in the orthogonal direction. 
     The spacer  60  includes an opening (first opening  64 ) communicating with the outside of the holding space from the holding space therein. Through the first opening  64 , the space (holding space) on the side of the bump electrode  80  inside the spacer  60  is opened. Thus, the holding space surrounded by the first substrate  40 , the second substrate  70  and the spacer  60  is not sealed. Therefore, it possible to suppress a pressure rise in the holding space by gas generated from the adhesive  61  of the holding space and the adhesive  61  of the adhesion region of the spacer  60 , thereby preventing separation of the bump electrode  80  by the pressure rise. 
     For example, the first opening  64  is provided at each corner of the rectangular frame shape. Accordingly, the first opening  64  is provided at portions other than the portion positioned between the piezoelectric element  50  and the bump electrode  80 . Therefore, although the gas generated from the adhesive  61  of the holding space and the adhesive  61  of the adhesion region of the spacer  60  leaks from the holding space with the outside through the first opening  64 , the gas hardly flows toward the piezoelectric element  50 , which prevents a deterioration of the piezoelectric element  50  due to the gas. 
     The first opening  64  is provided at a part of the first wall portion  62  and a part of the second wall portion  63  at the connection position between the first and second wall portions  62  and  63 . Accordingly, the load of the second substrate  70  can be distributed and supported by the first and second wall portions  62  and  63  other than the first opening  64 . 
     The first opening  64  is formed across the entire distance between the first and second substrates  40  and  70  in the stacking direction. Accordingly, since the spacer  60  is divided in the circumferential direction that surrounds the bump electrode  80 , an adhesion defect between the spacer  60  and the first substrate  40  is reduced. In general, since the first substrate  40  is formed of silicon and the spacer  60  is formed of resin, the spacer  60  has a larger linear expansion coefficient than the first substrate  40 . In this case, an adhesion defect may occur due to residual stress caused by a difference between the linear expansion coefficients. 
     However, as the spacer  60  is divided in the circumferential direction by the first opening  64 , the length of the spacer  60  in the circumferential direction is reduced. Accordingly, the residual stress caused by the difference between the linear expansion coefficients can be reduced, and the reduction of the residual stress can suppress an adhesion defect between the spacer  60  and the first substrate  40 . 
     In the present embodiment, three spacers  60  are provided in the head  20  so as to correspond to three bump electrodes  80 . The three spacers  60  include a spacer (first spacer  60   a ) surrounding one of two individual bump electrodes  80   b , a spacer (second spacer  60   a ) surrounding the common bump electrode  80   a , and a spacer (third spacer  60   c ) surrounding the other of the two individual bump electrodes  80   b . The first to third spacers  60   a  to  60   c  are sequentially arranged in the orthogonal direction with a distance provided therebetween. 
     The column of the piezoelectric elements  50  is provided in the space between the spacers  60  adjacent to each other. Therefore, one of the pair of first wall portions  62  of the first spacer  60   a , both of the pair of first wall portions  62  of the second spacer  60   b , and one of the pair of first wall portions  62  of the third spacer  60   c  are arranged between the columns of the piezoelectric elements and the individual bump electrodes  80   b , respectively. 
     Accordingly, the second wall portions  63  of the spacer  60  are provided in the space between the adjacent spacers  60 , that is, the space on the side of the piezoelectric element  50  outside the first wall portion  62  of the spacer  60 . The space between the second wall portions  63  of the adjacent spacers  60  is used as an opening (second opening  65 ) of the spacer  60 , and the space on the side of the piezoelectric elements  50  outside the first wall portion  62  is opened to the outside through the second opening  65 . Since the piezoelectric elements  50  are arranged in the open space, displacement interference of the piezoelectric elements  50  in a closed space does not occur, and a desired amount of liquid can be jetted from the nozzle  21 . 
     First Modified Example 
     In the liquid discharge apparatus  10  of  FIG. 3 , the first opening  64  of the spacer  60  is provided at the corners of the spacer  60 . However, when the first opening  64  is provided at portions other than the position positioned between the piezoelectric element  50  and the bump electrode  80 , the first opening  64  is not limited to the positions illustrated in  FIG. 3 . 
     For example, each spacer  601  of a head  201  illustrated in  FIG. 4  surrounds the bump electrode  80  using first and second wall portions  621  and  631 . In first and third spacers  601   a  and  601   c  among the spacers  601 , a first opening  641  is provided at the first wall portion  621  disposed at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80 . Accordingly, since gas generated from the adhesive  61  flows out to the opposite side of the piezoelectric element  50  through the first opening  641  from the holding space of the spacer  601 , the gas hardly flows toward the piezoelectric element  50 , which prevents a problem of the piezoelectric element  50  due to the gas. 
     In the second spacer  601   b , the first opening  641  is provided at the second wall portion  631  and extends in the arrangement direction. Therefore, the gas generated from the adhesive  61  flows out in the arrangement direction through the first opening  641  from the holding space of the spacer  602 . Accordingly, the gas hardly flows toward the piezoelectric element  50  adjacent to the spacer  602  in the orthogonal direction, which prevents a problem of the piezoelectric element  50  due to the gas. 
     In an example illustrated in  FIG. 5 , each spacer  602  of a head  202  surrounds the bump electrode  80  using first and second wall portions  622  and  632 , and includes a first opening  642  provided at the second wall portion  632 . Therefore, gas generated from the adhesive  61  flows out in the arrangement direction through the first opening  642  from the holding space of the spacer  602 , which prevents a problem of the piezoelectric element  50  due to the gas. 
     Second Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the plurality of first openings  64  are formed in one spacer  60 . However, the number of first openings  64  is not limited thereto. For example, in the example of the head  202  illustrated in  FIG. 5 , one first opening  642  is provided in the spacer  602 . In this case, the first opening  642  is provided at one second wall portion  632  of the pair of second wall portions  632 . In another spacer  602  adjacent to the spacer  602  among the plurality of spacers  602 , the first opening  642  may be provided at the other second wall portion  632  of the pair of second wall portions  632 . 
     That is, the second spacer  602   b  positioned in the center of three spacers  602  arranged in the orthogonal direction includes the first opening  642  formed at one second wall portion  632  of the pair of second wall portions  632 . On the other hand, each of the first and second spacers  602   a  and  602   c  adjacent to the second spacer  602   b  positioned in the center includes the first opening  642  formed at the other second wall portion  632  of the pair of second wall portions  632 . 
     For example, when the adhesive  61  for adhering the spacer  602  and the first substrate  40  hardens and contracts, the first substrate  40  may be warped. Thus, all of the spacers  602  may have the first opening  642  formed at one second wall portion  632  of the pair of the second wall portions  632 . In this case, the first substrate  40  at the one second wall portion  632  having the first opening  642  formed therein is warped more than the first substrate  40  at the other second wall portion  632  having no first opening  642  formed therein. However, since the first openings  642  are formed in the three spacers  602  such that the second wall portion  632  having the first opening  642  formed therein between the pair of second wall portions  632  is alternately disposed, the warpage of the first substrate  40  can be reduced. 
     Third Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the first openings  64  are provided at the same positions in each of the three spacers  60  arranged in the orthogonal direction. However, the positions of the first openings  64  are not limited thereto. As illustrated in an example of a head  302  in  FIG. 6 , an opening  643  may be provided at a position of a second wall portion  633 , which is close to the center of each of a plurality of spacers  603  arranged in the orthogonal direction. 
     That is, each of the spacers  603  surrounds the bump electrode  80  using the first and second wall portions  623  and  633 . The center of the three spacers  604  in the orthogonal direction corresponds to the center position of the second spacer  603   b  disposed in the center of the three spacers  603 . Therefore, the second spacer  603   b  includes the first opening  643  disposed at the center position of the second wall portion in the orthogonal direction. In the first and third spacers  603   a  and  603   c  provided at both ends of the three spacers  603 , however, the first opening  643  is disposed at an end of the second wall portion  633 , which is close to the center position of the second spacer  603   b.    
     Accordingly, in each of the three spacers  603 , the lengths of both of the second wall portions  633  in the orthogonal direction are set to the same value. Furthermore, the lengths of both of the second wall portions  633  in the orthogonal direction are increased. Therefore, a deviation in warpage of the first substrate  40 , caused by thermal contraction of the spacer  603  in the orthogonal direction, can be removed, and the warpage of the first substrate  40  by the thermal contraction of the spacer  603  at the end in the orthogonal direction can be increased, which makes it possible to reduce the warpage of the entire first substrate  40 . 
     Fourth Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the first opening  64  is provided at a part of the first wall portion  62  and a part of the second wall portion  63  in the extension direction. However, the first opening  64  may be provided at one or more of the entire first wall portion  62  and the entire second wall portion  63 . 
     In an example of a head  204  illustrated in  FIG. 7 , a spacer  604  has no first wall portion at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80 , between a pair of first wall portions  624 . The portion where the first wall portion is not provided is used as a first opening  644 . Accordingly, the first opening  64  is provided across the entire first wall portion other than the first wall portion  624  between the bump electrode  80  and the piezoelectric element  50 . 
     The spacer  604  does not have a pair of second wall portions. The portion where the second wall portion is not provided is used as the first opening  644  and the second opening  65 . The first opening  644  is provided across the second wall portion on the side of the bump electrode  80  with respect to the first wall portion  624 , and the second opening  65  is provided across the second wall portion at the piezoelectric element  50  with respect to the first wall portion  624 . 
     As such, only the first wall portion of the bump electrode  80  and the piezoelectric element  50  is provided. Since the first wall portion  624  suppresses gas from flowing toward the piezoelectric element  50  from the adhesive  61  disposed on the side of the bump electrode  80  with respect to the first wall portion  624 , it is possible to prevent a problem of the piezoelectric element  50  due to the gas. 
     Fifth Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the spacer  60  is provided so as to surround the bump electrode  80 . As illustrated in a head  205  of  FIG. 8 , however, a spacer  605  may be provided so as to surround the piezoelectric elements  50  using first and second wall portions  625  and  635 . In this case, the second wall portion  635  may be provided between the two first wall portions  625  adjacent to each other so as to interpose the column of the piezoelectric elements  50  therebetween, and have a second opening  655  provided at a part of the second wall portion  635  in the extension direction thereof. 
     That is, the pair of first wall portions  625  are disposed with a space formed in the orthogonal direction so as to interpose the column of the piezoelectric elements  50  therebetween, and positioned between the piezoelectric elements  50  and the bump electrodes  80 , respectively. Furthermore, the pair of second wall portions  635  are disposed with a space formed in the arrangement direction so as to interpose the column of the piezoelectric elements  50  therebetween, and positioned between the adjacent bump electrodes  80 . 
     Accordingly, no first wall portion is provided at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80  in the orthogonal direction. The portion where no first wall portion is provided is used as a first opening  645 . Therefore, the first opening  645  is provided across the first wall portion at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80 . Since the space of the spacer  625  on the side of the bump electrode  80  with respect to the first wall portion  625  is opened by the first opening  645 , a pressure rise by the gas generated from the adhesive  61  is suppressed, which prevents separation of the bump electrode  80  by a pressure rise. 
     Similarly, in the space on the side of the bump electrode  80  with respect to the first wall portion  625  in the orthogonal direction, no second wall portion is provided outside the bump electrode  80  in the arrangement direction. The portion where no second wall portion is provided is used as the first opening  645 . Therefore, the first opening  645  is provided across the second wall portion on the side of the bump electrode  80  with respect to the first wall portion  625 . Since the space on the side of the bump electrode  80  with respect to the first wall portion  625  is opened by the first opening  645 , a pressure rise by the gas generated from the adhesive  61  is suppressed, which prevents separation of the bump electrode  80  by a pressure rise. 
     The piezoelectric element  50  is surrounded by the first wall portion  625  between the bump electrode  80  and the piezoelectric element  50  and the second wall portion  635  on the side of the piezoelectric element  50  with respect to the bump electrode  80 . Therefore, a gas flow of the adhesive  61  into the piezoelectric element  50  can be reduced, while a problem of the piezoelectric element  50  due to the gas can be suppressed. 
     The space on the side of the piezoelectric element  50  with respect to the bump electrode  80  is opened through the second opening  655  provided in the second wall portion  635  on the side of the piezoelectric element  50  with respect to the first wall portion  625 . Therefore, the piezoelectric element  50  is not held in a closed space, but displacement interference of the piezoelectric element  50  in a closed space is suppressed. 
     The second opening  655  is provided at a part of the second wall portion  635  in the extension direction thereof. Therefore, the load of the second substrate  70  can be distributed and supported by the second wall portion  635  and the first wall portion  625 . 
     In the example of  FIG. 8 , no first and second wall portions are provided on the side of the bump electrode  80  with respect to the first wall portion  625 . However, any one of the first and second wall portions may be provided. Even in this case, the portion where no wall portion is provided is used as the first opening  645 . Therefore, the space on the side of the piezoelectric element  50  with respect to the bump electrode  80  can be opened, thereby preventing a problem due to the gas of the adhesive  61 . 
     Sixth Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the surface of the spacer  60 , parallel to the stacking direction, is formed as the flat surface. However, the surface of the spacer  60  may be formed in a wave shape, or formed as a surface having notches provided thereon. In an example of a head  206  illustrated in  FIG. 9 , notches  66  are provided in a surface of a first wall portion  626 , perpendicular to the orthogonal direction, and a surface of the second wall portion  646 , perpendicular to the arrangement direction. The notches  66  have a triangular cross-sectional shape in a direction perpendicular to the stacking direction and extend in the stacking direction. 
     The surfaces of the first and second wall portions  626  and  636  have a larger length and area than the flat surface due to the notches  66 . Therefore, the adhesive can spread to the respective surfaces of the first and second wall portions  626  and  636  or permeate and accumulate into the notches  66 , thereby reducing a gas flow of the adhesive  61  toward the opposite side (outside) of the bump electrode  80  with respect to the spacer  606 , the adhesive  61  adhering the spacer  606  and the first substrate  40  to each other. Therefore, the spread of the adhesive  61  toward the piezoelectric element  50  can be suppressed, while a problem of the piezoelectric element  50  by the adhesive  61  and the gas of the adhesive  61  is suppressed. 
     In the example of  FIG. 9 , the notches  55  have a triangular cross-sectional shape, but may have a curved cross-sectional shape such as a circular arc. In the example of  FIG. 9 , the notches  66  are provided in the surface (outer surface) of the spacer  606  on the side of the bump electrode  80 . However, the notches  66  may be provided in at least the first wall portion  626  of the spacer  606  on the side of the piezoelectric element  50 . For example, the notches  66  may be provided on the surface (inner surface) of the spacer  606  at the opposite side of the bump electrode  80 . 
     Seventh Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the dimension (width) of the first wall portion  62  (the first wall portion  62  on the side of the piezoelectric element) in the orthogonal direction, which is interposed between the piezoelectric element  50  and the bump electrode  80  in the spacer  60 , is set to the same value as the width of the first wall portion  62  disposed at the opposite side of the piezoelectric element  50  with respect to the bump electrode  80  (the first wall portion  62  at the opposite side). However, the widths of the first wall portions  62  may be different from each other. 
     For example, as in a head  207  illustrated in  FIG. 10 , a first wall portion  627  of a spacer  607  on the side of the piezoelectric element may have a larger width than the first wall portion  627  at the opposite side. Accordingly, an adhesion area between the first substrate  40  and the first wall portion  627  on the side of the piezoelectric element is larger than an adhesion area between the first substrate  40  and the first wall portion  627  at the opposite side. Therefore, the adhesive  61  between the first substrate  40  and the first wall portion  627  on the side of the piezoelectric element is more difficult to spread than the adhesive  61  between the first substrate  40  and the first wall portion  627  at the opposite side, which prevents the adhesive  61  from adhering to the piezoelectric element  50 . 
     Eighth Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 3 , the first wall portion  62  (the first wall portion  62  on the side of the individual bump electrode) interposed between the piezoelectric element  50  and the individual bump electrode  80   b  in the spacer  60  has the same width as the first wall portion  62  (the first wall portion  62  on the side of the common bump electrode) interposed between the piezoelectric element  50  and the common bump electrode  80   a . However, the widths of the first wall portions  62  may be different from each other. 
     For example, as in a head  208  illustrated in  FIG. 11 , the width of a first wall portion  628  of a spacer  608  on the side of the individual bump electrode may be set to a lager value than the width of the first wall portion  628  on the side of the common bump electrode. Since the plurality of individual conductors  54  extend between the first substrate  40  and the first wall portion  628  on the side of the individual bump electrode, a gap is formed therebetween, such that the adhesive  61  easily flows to the outside from the gap. However, since the adhesion area between the first substrate  40  and the first wall portion  628  on the side of the individual bump electrode becomes larger than the adhesion area between the first substrate  40  and the first wall portion  628  on the side of the common bump electrode, the adhesive  61  hardly spreads from the gap, which suppresses the adhesive  61  from adhering to the piezoelectric element  50 . 
     Ninth Modified Example 
     In the liquid discharge apparatus illustrated in  FIG. 3 , the openings  64  and  65  have the same length as the distance between the first and second substrates  40  and  70  in the stacking direction. However, the openings  64  and  65  may have a smaller length than the distance. In this case, within the formation range of the openings  64  and  65 , the spacer  60  extends from the second substrate  70  toward the first substrate  40 , and the openings  64  and  65  are provided at the end of the spacer  60 . Therefore, between the first and second substrates  40  and  70 , the spacer  60  is provided at the second substrate  70 , and the openings  64  and  65  are provided at the first substrate  40 . On the contrary, between the first and second substrates  40  and  70 , the spacer  60  may be provided at the first substrate  40 , and the openings  64  and  65  may be provided at the second substrate  70 . 
     Second Embodiment 
     In the liquid discharge apparatus  10  according to the first embodiment, the space on the side of the bump electrode  80  with respect to the spacer  60  is opened by the first openings  64  provided at portions other than the portions positioned between the piezoelectric elements  50  and the bump electrode  80  in the spacer  60 . In a liquid discharge apparatus  10  according to a second embodiment, however, a head  210  illustrated in  FIG. 12  has a structure in which a space on the side of the bump electrode  80  with respect to a spacer  610  is opened by an opening (third opening  73 ) provided in the second substrate  70  ( FIG. 2 ). In order to promote understandings, the illustration of the second substrate  70  is omitted from  FIG. 12 . 
     Specifically, a pair of first wall portions  6210  in the spacer  610  are disposed so as to interpose the bump electrode  80  therebetween in the orthogonal direction. Furthermore, a pair of second wall portions  6310  are disposed so as to interpose the bump electrode  80  therebetween in the arrangement direction, while connecting the pair of first wall portions  6210  in the orthogonal direction. Since the ends of the first wall portions  6210  and the ends of the second wall portions  6310  are connected to each other, the spacer  610  has a rectangular frame shape to surround the bump electrode  80 . The third opening  73  is provided in the second substrate  70  within the surrounded space (holding space). 
     The third opening  73  is formed through the second substrate  70  in the stacking direction, as a though hole, and connects the holding space with a space outside the holding space. For example, the second substrate  70  may include a substrate through which a through-electrode is provided in the stacking direction. In this case, the third opening  73  can be formed in the second substrate  70  at the same time as the through-electrode, which makes it possible to reduce the number of operation processes. 
     The third opening  73  is provided around the bump electrode  80  in the holding space of the spacer  610 . As the third opening  73  is disposed in the second substrate  70  between the spacer  610  and the bump electrode  80 , the third opening  73  is not interposed between the bump electrode  80  and the second terminal  71  ( FIG. 2 ) of the second substrate  70 , and does not interfere with connection therebetween. 
     In the rectangular holding space of the spacer  610 , one or more third openings  73  (for example, four third openings) are provided. The four third openings  73  are disposed in the four corners of the spacer  610  at which the first wall portion  6210  and the second wall portion  6310  are connected to each other. 
     As such, the holding space formed by the spacer  610  (the space on the side of the bump electrode  80  with respect to the spacer  610 ) is opened through the third openings  73 , and the gas of the adhesive  61  flows to the external space from the holding space through the third openings  73 . Therefore, a pressure rise in the holding space by the gas can be reduced, and an adhesion defect of the bump electrode  80  by the pressure rise can be suppressed. Furthermore, since the gas hardly flows toward the piezoelectric element  50 , it is possible to prevent a problem such as deterioration of the piezoelectric element  50  by the gas. 
     Tenth Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 12 , the space on the side of the bump electrode  80  with respect to the spacer  610  is opened through the third openings  73 . However, a head  211  illustrated in  FIG. 13  may have a structure in which a space on the side of the piezoelectric element  50  with respect to a spacer  611  is opened by third openings  731 . 
     In this case, a pair of first wall portions  6211  of the spacer  611  interpose the column of the piezoelectric elements  50  therebetween in the orthogonal direction, and a pair of second wall portions  6311  interpose the column of the piezoelectric elements  50  therebetween in the arrangement direction. The ends of the first wall portions  6211  and the ends of the second wall portions  6311  are connected to each other, such that the spacer  611  surrounds the column of the piezoelectric elements  50 . The third openings  731  are provided in the second substrate  70  within the surrounded space (holding space). 
     The holding space formed by the spacer  611  (the space on the side of the piezoelectric element  50  with respect to the spacer  611 ) is opened through the third openings  731 , and the gas of the adhesive  61  flows to the external space from the holding space through the third openings  731 . Therefore, a pressure rise in the holding space by the gas can be reduced, and a problem such as displacement interference of the piezoelectric element  50  by the pressure rise can be suppressed. Furthermore, since the gas hardly flows toward the piezoelectric element  50 , it is possible to prevent a defect such as deterioration of the piezoelectric element  50 . 
     The first and second wall portions are not provided on the side of the bump electrode  80  with respect to the first wall portion  6210 , but the portion where the first and second wall portions are not provided is used as a first opening  6411 . Therefore, since the space on the side of the bump electrode  80  with respect to the first wall portion  6211  is opened through the first opening  6411 , it is possible to prevent separation of the bump electrode  80  by a pressure rise. 
     Eleventh Modified Example 
     In the liquid discharge apparatus  10  illustrated in  FIG. 12 , the space on the side of the bump electrode  80  with respect to the spacer  610  is opened through the third openings  73 . Furthermore, in the tenth modification, however, the space on the side of the piezoelectric element  50  with respect to the spacer  611  is opened through the third opening s 731 . However, a head  212  illustrated in  FIG. 14  has a structure in which a spacer  612  surrounds the bump electrode  80  and the column of the piezoelectric elements  50  using first and second wall portions  6212  and  6312 . Furthermore, the space on the side of the bump electrode  80  with respect to the spacer  612  is opened through the third openings  73 , and the space on the side of the piezoelectric element with respect to the spacer  612  may be opened through the third openings  731 . 
     Twelfth Modified Example 
     In the liquid discharge apparatuses  10  of  FIG. 12  and the tenth and eleventh modifications, the third openings  73  and  731  are provided in the second substrate  70 . However, the third openings  73  and  731  may be provided in the first substrate  40  or both of the first and second substrates  40 . 
     Other Embodiments 
     In all of the above-described embodiments, the spacer  611  and the first substrate  40  may be attached through the adhesive  61 . However, the spacer  611  and the second substrate  70  may be attached through the adhesive  61 . In this case, the spacer  611  extends from the first substrate  40  to the second substrate  70 . 
     All of the above-described embodiments may be combined with each other as long as they do not exclude each other. For example, in the liquid discharge apparatus  10  according to any one of the first and second embodiments, the first to fourth modifications and the sixth to ninth modifications, the second opening  655  may be provided at a part of the second wall portion  635  in the extension direction thereof, the second wall portion  635  interposing the piezoelectric element  50  therebetween, as in the fifth modification. In the liquid discharge apparatus  10  according to any one of the first and second embodiments and the first to twelfth modifications, the surface of the spacer  606  may be formed in a wave shape or have the notches  66  provided thereon as in the sixth embodiment. In the liquid discharge apparatus  10  according to any one of the first and second embodiments and the first to twelfth modifications, the first wall portion  627  on the side of the piezoelectric element may have a larger width than the first wall portion  627  at the opposite side as in the seventh modification. In the liquid discharge apparatus  10  according to any one of the first and second embodiments and the first to twelfth modifications, the first wall portion  628  on the side of the individual bump electrode may have a larger width than the first wall portion  628  on the side of the common bump as in the eighth modification. In the liquid discharge apparatus  10  according to any one of the first and second embodiments and the first to eleventh modifications, the openings  64  and  65  may have a smaller length than the distance between the first and second substrates  40  and  70  in the stacking direction as in the ninth modification. 
     From the above descriptions, it is obvious to those skilled in the art that this disclosure can be improved in various manners and modified into other embodiments. Therefore, the above descriptions should be analyzed as examples, and provided to instruct those skilled in the art of the best mode for embodying this disclosure. Furthermore, the details of the structures and/or functions of this disclosure can be substantially changed without departing the spirit of this disclosure.