Patent Publication Number: US-2022216393-A1

Title: Piezoelectric actuator, liquid ejecting head, and recording apparatus

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-000275, filed Jan. 4, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure relate to a piezoelectric actuator, a liquid ejecting head, and a recording apparatus. 
     2. Related Art 
     A liquid ejecting apparatus equipped with a liquid ejecting head configured to eject liquid such as ink is known. A liquid ejecting head disclosed in JP2012-161958 includes piezoelectric actuators configured to drive a diaphragm disposed over pressure compartments. The piezoelectric actuators include a plurality of individual electrodes, a piezoelectric layer disposed in such a way as to cover the plurality of individual electrodes, and a common electrode disposed in such a way as to cover the piezoelectric layer. 
     In a piezoelectric actuator, the portion, of a piezoelectric layer, sandwiched between an individual electrode and a common electrode behaves as a drive region. A non-drive region is formed around the drive region. There is a risk that the individual electrode might be damaged due to stress concentration that occurs at an end portion of the individual electrode near the boundary between the drive region and the non-drive region. 
     SUMMARY 
     A piezoelectric actuator according to a certain aspect of the present disclosure includes a plurality of individual electrodes, a piezoelectric layer, and a common electrode that are stacked in layers on a diaphragm. The plurality of individual electrodes each extending in a first direction are arranged in a second direction intersecting with the first direction. The piezoelectric actuator has a drive region where the individual electrode, the piezoelectric layer, and the common electrode overlap as viewed in a stack direction (Z) and a non-drive region, adjacent to the drive region, where the individual electrode, the piezoelectric layer, and the common electrode do not overlap as viewed in the stack direction. The individual electrode has a first portion included in the drive region and a second portion included in the non-drive region and located adjacent to the first portion in the first direction. The first portion includes a narrower portion whose width is less than a width in the second direction at a boundary between the first portion and the second portion. 
     A liquid ejecting head according to a certain aspect of the present disclosure includes the above piezoelectric actuator and a pressure compartment forming substrate, inside which pressure compartments are formed. The drive region is located over the pressure compartment. 
     A recording apparatus according to a certain aspect of the present disclosure includes the above liquid ejecting head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram that illustrates a liquid ejecting apparatus according to a first embodiment. 
         FIG. 2  is a cross-sectional view of a liquid ejecting head. 
         FIG. 3  is an enlarged cross-sectional view of an essential part of the liquid ejecting head. 
         FIG. 4  is a cross-sectional view of the liquid ejecting head taken along a Y-Z plane at an end of an upper electrode in the X-axis direction. 
         FIG. 5  is a cross-sectional view of the liquid ejecting head taken along an X-Y plane, wherein lower electrodes arranged over pressure compartments are illustrated. 
         FIG. 6  is a schematic cross-sectional view of a drive region and a non-drive region of a piezoelectric actuator. 
         FIG. 7  is a cross-sectional view of an end portion of a lower electrode disposed near a boundary between the drive region and the non-drive region. 
         FIG. 8  is a plan view of an end structure of a lower electrode according to a first modification example. 
         FIG. 9  is a plan view of an end structure of a lower electrode according to a second modification example. 
         FIG. 10  is a plan view of an end structure of a lower electrode according to a third modification example. 
         FIG. 11  is a plan view of an end structure of a lower electrode according to a fourth modification example. 
         FIG. 12  is a plan view of lower electrodes and lead electrodes according to a fifth modification example. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     With reference to the accompanying drawings, an exemplary embodiment of the present disclosure will now be explained. In the drawings, the dimensions and scales of components may be made different from those in actual implementation. Since the embodiment described below shows some preferred examples of the present disclosure, they contain various technically-preferred limitations. However, the scope of the present disclosure shall not be construed to be limited to the examples described below unless and except where any intention of restriction is mentioned explicitly. 
     In the description below, three directions that are orthogonal to one another will be referred to as X-axis direction, Y-axis direction, and Z-axis direction. The X-axis direction includes X1 direction and X2 direction, which are the opposite of each other. The Y-axis direction includes Y1 direction and Y2 direction, which are the opposite of each other. The Z-axis direction includes Z1 direction and Z2 direction, which are the opposite of each other. The Z1 direction is the direction going down. The Z2 direction is the direction going up. In this specification, the terms “upper” and “lower” will be used. The terms “upper” and “lower” as used herein correspond to the ordinary meaning of “upper” and “lower” in a normal state of use, in which nozzles are directed vertically downward, of a liquid ejecting apparatus  1 . 
     The X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to one another. In an ordinary configuration, the Z-axis direction is along the vertical direction. However, the Z-axis direction is not necessarily along the vertical direction. 
       FIG. 1  is a schematic diagram that illustrates an example of the configuration of a liquid ejecting apparatus  1  according to a first embodiment. The liquid ejecting apparatus  1  is an ink-jet-type printing apparatus that ejects droplets of ink, which is an example of “liquid”, onto a medium P. The liquid ejecting apparatus  1  according to the present embodiment is a head-scan-type printing apparatus also called as a serial-type printer that reciprocates a plurality of nozzles, from which ink is ejected, in the direction of the width of the medium P. The medium P is, typically, printing paper such as plain paper, coated paper, glossy paper, etc. The medium P is not limited to printing paper. The medium P may be a print target made of any material such as, for example, a resin film or a cloth. The liquid ejecting apparatus  1  is an example of a recording apparatus. 
     As illustrated in  FIG. 1 , the liquid ejecting apparatus  1  includes a liquid container  2  that contains ink. Some specific examples of the liquid container  2  are: a cartridge that can be detachably attached to the liquid ejecting apparatus  1 , a bag-type ink pack made of a flexible film material, an ink tank which can be refilled with ink, etc. Any type of ink may be contained in the liquid container  2 . The liquid container  2  is an example of a liquid containing unit. 
     In an ordinary configuration, the liquid container  2  includes a first liquid container and a second liquid container, though not illustrated. The liquid container  2  may be a single liquid container instead. The first liquid container contains first ink. The second liquid container contains second ink, the type of which is different from the type of the first ink. For example, the color of the first ink and the color of the second ink are different from each other. The first ink and the second ink may be the same type of ink. 
     The liquid ejecting apparatus  1  includes a control unit  3 , a medium transportation mechanism  4 , a carriage  5 , a carriage transportation mechanism  6 , and a plurality of liquid ejecting heads  10 . The control unit  3  controls the operation of each component of the liquid ejecting apparatus  1 . The control unit  3  includes a processing circuit, for example, a CPU (central processing unit) or an FPGA (field programmable gate array), and a storage circuit such as a semiconductor memory. Various kinds of program and data are stored in the storage circuit. The processing circuit realizes various kinds of control by running the program and using the data. 
     The medium transportation mechanism  4  is controlled by the control unit  3  and transports the medium P in a transportation direction DM. The transportation direction DM is, for example, the Y1 direction. The transportation direction DM is not limited to the Y1 direction. The transportation direction DM may be the Y2 direction or any other direction. The medium transportation mechanism  4  includes a transportation roller that is elongated in the X-axis direction and a motor that causes the transportation roller to rotate. The configuration of the medium transportation mechanism  4  is not limited to the illustrated example in which the transportation roller is used. For example, a drum that transports the medium P in a state in which the medium P is attracted to the circumferential surface of the drum due to an electrostatic force, etc., or an endless belt, may be used instead. 
     The plurality of liquid ejecting heads  10  is mounted on the carriage  5 . The carriage transportation mechanism  6  is controlled by the control unit  3  and reciprocates the carriage  5  in the X-axis direction. The carriage transportation mechanism  6  includes, for example, an endless belt tensioned around and between plural rollers distanced from each other in the X-axis direction. 
     Ink flows from the liquid container  2  through an ink flow passage and is then supplied to the liquid ejecting head  10 . The liquid ejecting head  10  is controlled by the control unit  3  and ejects ink from each of the plurality of nozzles toward the medium P. 
     Next, with reference to  FIG. 2 , ink flow passages  11  formed inside the liquid ejecting head  10  will now be explained.  FIG. 2  is a cross-sectional view of the liquid ejecting head  10  taken along an X-Z plane. The X-Z plane is a plane that is along the X-axis direction and the Z-axis direction. In  FIG. 2 , the direction in which ink flows inside the liquid ejecting head  10  is indicated by arrows. Flow passages  11  through which ink flows are formed inside the liquid ejecting head  10 . The flow passage  11  leads from a supply inlet  12  to a nozzle N. The flow passages  11  are line-symmetric with respect to a center line O extending in the Z-axis direction. 
     The flow passage  11  includes the supply inlet  12 , a common reservoir  13 , a common reservoir  14 , a relay flow passage  15 , a relay flow passage  16 , a pressure compartment  17 , a communication flow passage  18 , and the nozzle N. The supply inlet  12  is provided on both sides in the X-axis direction of the liquid ejecting head  10 . The supply inlet  12  is in communication with the common reservoir  13  in the Z-axis direction. The common reservoir  13  is in communication with the common reservoir  14  in the Z-axis direction. The common reservoirs  13  and  14  are formed in different members respectively. The common reservoir  13 ,  14  extends in the Y-axis direction. The common reservoir  13 ,  14  is a common space that is in communication with the plurality of pressure compartments  17 . The plural pressure compartments  17  are arranged next to one another in the Y-axis direction. 
     A plurality of relay flow passages  15 ,  16  is connected to the common reservoir  14 . The plurality of relay flow passages  15 ,  16  is provided such that they correspond to the plurality of pressure compartments  17  respectively. The plural relay flow passages  15  are arranged next to one another in the Y-axis direction. The relay flow passage  15  extends from the outside toward the inside in the X-axis direction. The relay flow passage  16  is connected to the downstream end of the relay flow passage  15 . The relay flow passage  16  extends in the Z2 direction from the relay flow passage  15  and is in communication with the pressure compartment  17 . 
     Each of the plurality of pressure compartments  17  extends inward in the X-axis direction. The communication flow passage  18  is connected to the downstream end of the pressure compartment  17  and extends in the Z1 direction. The plurality of communication flow passages  18  is connected to the plurality of pressure compartments  17  respectively. The plurality of communication flow passages  18  is connected to the plurality of nozzles N respectively. 
     The communication flow passage  18  is located downstream of the pressure compartment  17 . The communication flow passage  18  is located at an inner side in the X-axis direction in comparison with the relay flow passage  16 . The communication flow passage  18  provides communication between the pressure compartment  17  and the nozzle N. The communication flow passage  18  extends in the Z-axis direction. 
     Next, the flow of ink inside the liquid ejecting head  10  will now be explained. Ink flows into the liquid ejecting head  10  through the supply inlet  12 . The ink having passed through the supply inlet  12  flows into the common reservoir  13  and next into the common reservoir  14 . The flow path of the ink from the common reservoir  14  branches into the plurality of relay flow passages  15 . The ink in the relay flow passage  15  flows through the relay flow passage  16  into the pressure compartment  17 . The pressure of the ink in the pressure compartment  17  is raised by a piezoelectric actuator  31 , which will be described later. Due to the rise in pressure, the ink in the pressure compartment  17  flows through the communication flow passage  18  to be ejected from the nozzle N. 
     Next, the structure of the liquid ejecting head  10  will now be explained. The liquid ejecting head  10  includes a nozzle plate  21 , a bottom plate  22 , a flow passage forming substrate  23 , a pressure compartment forming substrate  24 , a diaphragm  25 , and the piezoelectric actuators  31 . The liquid ejecting head  10  further includes a sealing plate  40  for sealing the piezoelectric actuators  31 , a COF  60  coupled to the piezoelectric actuators  31  electrically, and a cover  70  enclosing the sealing plate  40 . COF is an acronym for Chip On Film. The sealing plate  40  is an example of a protective substrate. 
     The supply inlet  12  and the common reservoir  13  are formed in the cover  70 . The cover  70  has a cavity for housing the pressure compartment forming substrate  24 , the diaphragm  25 , the piezoelectric actuators  31 , and the sealing plate  40 . The cover  70  encloses the sealing plate  40  from the Z1-directional side. The common reservoir  13  is located on both sides outside the sealing plate  40  in the X-axis direction. The cover  70  has an opening  75  at a position corresponding to the opening  50  of the sealing plate  40 . 
     The nozzle plate  21  has the plurality of nozzles N. The nozzle N is a through hole going in a plate-thickness direction. The plate-thickness direction of the nozzle plate  21  is along the Z axis. The nozzles N constitute each nozzle row, that is, a row of nozzles arranged linearly in the Y-axis direction. Plural nozzle rows distanced from each other in the X-axis direction are formed in the nozzle plate  21 . The nozzle plate  21  is bonded to the bottom surface of the flow passage forming substrate  23  and covers the communication flow passages  18  from below. The nozzles N are located at respective positions corresponding to the communication flow passages  18 . 
     The bottom plate  22  is disposed outside the nozzle plate  21  in the X-axis direction. The bottom plate  22  is bonded to the bottom surface of the flow passage forming substrate  23  and covers the common reservoir  14  and the relay flow passages  15 ,  16  from below. 
     The common reservoir  14 , the relay flow passages  15 ,  16 , and the communication flow passages  18  are formed in the flow passage forming substrate  23 . The common reservoir  14 , the relay flow passages  16 , and the communication flow passages  18  are openings going through the flow passage forming substrate  23  in the plate-thickness direction. The plate-thickness direction of the flow passage forming substrate  23  is along the Z axis. The relay flow passage  15  is a groove formed in the bottom surface of the flow passage forming substrate  23 . 
     The pressure compartments  17  are formed in the pressure compartment forming substrate  24 . The pressure compartments  17  are openings going through the pressure compartment forming substrate  24  in the plate-thickness direction. The length of the pressure compartment forming substrate  24  in the X-axis direction is less than the length of the flow passage forming substrate  23  in the X-axis direction. The pressure compartment forming substrate  24  is bonded to the top surface of the flow passage forming substrate  23 . 
       FIG. 3  is an enlarged cross-sectional view of an essential part of the liquid ejecting head  10 .  FIG. 4  is a cross-sectional view of the liquid ejecting head  10  taken along a Y-Z plane at an end of an upper electrode in the X-axis direction. As illustrated in  FIGS. 3 and 4 , the diaphragm  25  is disposed on the top surface of the pressure compartment forming substrate  24 . The plate-thickness direction of the diaphragm  25  is along the Z axis. The diaphragm  25  covers the openings of the pressure compartment forming substrate  24 . The portion, of the diaphragm  25 , covering the openings of the pressure compartment forming substrate  24  constitutes the ceiling of the pressure compartments  17 . The diaphragm  25  includes a plurality of insulation layers. More specifically, the diaphragm  25  includes an insulation layer  25   a  made of silicon dioxide (SiO 2 ) and an insulation layer  25   b  made of zirconium dioxide compartment forming substrate  24 . The insulation layer  25   b  is formed on the insulation layer  25   a . The diaphragm  25  is driven by the piezoelectric actuator  31  and vibrates in the Z-axis direction. 
     The plurality of piezoelectric actuators  31  is disposed on the diaphragm  25 . The plurality of piezoelectric actuators  31  is provided such that they correspond to the plurality of pressure compartments  17  respectively. The piezoelectric actuator  31  includes a lower electrode  32 , a piezoelectric layer  33 , and an upper electrode  34 . The lower electrode  32 , the piezoelectric layer  33 , and the upper electrode  34  are stacked in this order on the diaphragm  25 . The lower electrode  32  is an individual electrode(s). The upper electrode  34  is a common electrode. The common electrode may be the lower electrode. The individual electrode may be the upper electrode. 
       FIG. 5  is a cross-sectional view of the liquid ejecting head  10  taken along an X-Y plane, wherein the lower electrodes  32  arranged over the pressure compartments  17  are illustrated. As illustrated in  FIG. 5 , the lower electrodes  32  are arranged at predetermined intervals in the Y-axis direction. Each of the plurality of lower electrodes  32  is located at a position overlapping with the corresponding one of the plurality of pressure compartments  17  as viewed in the Z-axis direction. The lower electrode  32  has a predetermined length in the X-axis direction, and extends inward toward the center line O from the position over the pressure compartment  17 . The center line O is illustrated in  FIG. 2 . 
     The lower electrode  32  includes, for example, an electrode layer containing a conductive material having a low resistance such as platinum (Pt) or iridium (Ir), etc., and a ground layer containing titanium (Ti). The electrode layer may be made of oxide such as, for example, strontium ruthenate (SrRuO 3 ), lanthanum nickelate (LaNiO 3 ), etc. 
     As illustrated in  FIGS. 3 and 4 , the piezoelectric layer  33  is formed on the lower electrodes  32 . The piezoelectric layer  33  is disposed in such a way as to cover the plurality of lower electrodes  32 . The piezoelectric layer  33  is a band-shaped dielectric film extending in the Y-axis direction. 
     The upper electrode  34  is formed on the piezoelectric layer  33 . The upper electrode  34  extends in the Y-axis direction in such a way as to cover the plurality of lower electrodes  32 , with the piezoelectric layer  33  sandwiched therebetween. The upper electrode  34  includes, for example, an electrode layer containing a conductive material having a low resistance such as Pt or Ir, etc., and a ground layer containing Ti. The electrode layer may be made of oxide such as, for example, SrRuO 3 , LaNiO 3 , etc. 
       FIG. 6  is a schematic cross-sectional view of a drive region  33   a  and a non-drive region  33   b  of the piezoelectric actuator  31 . As illustrated in  FIG. 6 , the portion, of the piezoelectric layer  33 , sandwiched between the lower electrode  32  and the upper electrode  34  in the Z-axis direction is the drive region  33   a . The drive region  33   a  overlaps with the pressure compartment  17  as viewed in the Z-axis direction. The non-drive region  33   b  is formed around the drive region  33   a  as viewed in the Z-axis direction. The lower electrode  32  and the upper electrode  34  do not overlap with each other at the non-drive region  33   b.    
     In  FIGS. 3 to 6 , a boundary  36  between the drive region  33   a  and the non-drive region  33   b  is illustrated. In  FIGS. 3 and 4 , the boundary  36  is shown by a broken line. In  FIG. 5 , the boundary  36  is shown by a two-dot chain line. In  FIG. 6 , the boundary  36  is shown by a solid line. The boundary  36  includes boundaries  36   a  and  36   b . The boundary  36   a  is the boundary in the X-axis direction. The boundary  36   b  is the boundary in the Y-axis direction. The boundary  36   a  is along an end surface  34   a  of the upper electrode  34  as viewed in the Z-axis direction. The end surface  34   a  is the X2-side end surface of the upper electrode  34  and extends in the Y-axis direction. The structure of the lower electrode  32  near the boundary  36   a  will be described later. 
     As illustrated in  FIG. 2 , the liquid ejecting head  10  includes a plurality of lead electrodes  35  coupled to the plurality of lower electrodes  32  electrically. Each of the plurality of lead electrodes  35  is coupled to the corresponding one of the plurality of lower electrodes  32 . The lead electrode  35  extends in the X-axis direction and is wired to reach the inside of the opening  50  of the sealing plate  40 . The opening  50  goes through the sealing plate  40  in the Z-axis direction. The lead electrode  35  is electrically coupled to the COF  60  inside the opening  50 . 
     The lead electrode  35  is made of a conductive material having a lower resistance than that of the lower electrode  32 . For example, the lead electrode  35  is a conductive pattern having a layered structure obtained by forming a conductive film made of gold (Au) on the surface of a conductive film made of nichrome (NiCr). 
     The sealing plate  40  is disposed in such a way as to cover the plurality of piezoelectric actuators  31  from the Z1-directional side. The sealing plate  40  has a rectangular shape as viewed in the Z-axis direction. The sealing plate  40  protects the plurality of piezoelectric actuators  31  and enhances the mechanical strength of the pressure compartment forming substrate  24  and the diaphragm  25 . 
     The sealing plate  40  has a recessed portion  43 . The recessed portion  43  is located on both sides with respect to the opening  50  in the X-axis direction. The recessed portion  43  is recessed from the Z1-side surface in the Z2 direction. The recessed portion  43  extends in the Y-axis direction in such a way as to overlap with the plurality of piezoelectric actuators  31  arranged next to one another in the Y-axis direction. As illustrated in  FIG. 3 , the sealing plate  40  is bonded to the piezoelectric layer  33  by means of an adhesive. 
     The COF  60  is inserted in the opening  50  and is electrically coupled to the piezoelectric actuator  31  via the lead electrode  35 . The COF  60  includes a flexible wiring board  61  and a driver IC  62 . The flexible wiring board  61  is a wiring board that has flexibility. The flexible wiring board  61  is, for example, an FPC (Flexible Printed Circuit). The flexible wiring board  61  may be, for example, an FFC (Flexible Flat Cable). 
     The flexible wiring board  61  is bonded to the diaphragm  25  by means of an adhesive applied to the inside of the opening  50 . The driver IC  62  is mounted on the flexible wiring board  61 . The driver IC  62  is electrically coupled to the control unit  3  via the flexible wiring board  61 . The driver IC  62  receives a command signal outputted from the control unit  3 . In response to the command signal, the driver IC  62  supplies a drive signal to each piezoelectric actuator  31  to cause the diaphragm  25  to vibrate. 
     Next, with reference to  FIGS. 5, 6, and 7 , the structure of the lower electrode  32  near the boundary  36   a  will now be explained. As described earlier, the boundary  36   a  extends along the end surface  34   a  of the upper electrode  34  in the Y-axis direction. 
     The lower electrode  32  includes a part  32   a  and another part  32   b . The part  32   a  is a portion that overlaps with the drive region  33   a  of the piezoelectric layer  33  as viewed in the Z-axis direction. The part  32   b  is a portion that overlaps with the non-drive region  33   b  of the piezoelectric layer  33  as viewed in the Z-axis direction. The part  32   b  is located adjacent to the part  32   a  in the X-axis direction. The region that is closer to the lead electrode  35  than the boundary  36   a  is in the X-axis direction is defined as the part  32   b . The region that is farther from the lead electrode  35  than the boundary  36   a  is in the X-axis direction is defined as the part  32   b . In  FIGS. 5, 6, and 7 , the part  32   b  exists on the X2-directional side with respect to the boundary  36   a , and the part  32   a  exists on the X1-directional side with respect to the boundary  36   a . The part  32   a  is an example of a first portion. The part  32   b  is an example of a second portion. 
     As illustrated in  FIG. 7 , the lower electrode  32  includes a body portion  131 , a boundary base portion  132 , and a lead-out portion  133 . The body portion  131  has a strip shape and extends in the X-axis direction. The body portion  131  is included in the part  32   a . The body portion  131  is demarcated by a side  131   a  and another side  131   b . The sides  131   a  and  131   b  are at a distance from each other in the Y-axis direction. Each of the sides  131   a  and  131   b  extends in the X-axis direction. The region located between the sides  131   a  and  131   b  in the Y-axis direction is the body portion  131 . The body portion  131  has a width W 1 , which is a length in the Y-axis direction. The width W 1  is the length from the side  131   a  to the side  131   b.    
     The boundary base portion  132  is located adjacent to the body portion  131  in the X2 direction. The boundary base portion  132  is arranged in such a way as to overlap with the boundary  36   a  as viewed in the Z-axis direction. The boundary base portion  132  includes a region demarcated by sides  132   a ,  132   b ,  132   c ,  132   d ,  132   e , and  132   f . The sides  132   a  and  132   c  are at a distance from each other in the X-axis direction. Each of the sides  132   a  and  132   c  extends in the Y-axis direction. The sides  132   a  and  132   c  are located relatively on the Y1-directional side, as compared with the side  131   a . The sides  132   d  and  132   f  are at a distance from each other in the X-axis direction. Each of the sides  132   d  and  132   f  extends in the Y-axis direction. The sides  132   d  and  132   f  are located relatively on the Y2-directional side, as compared with the side  131   b.    
     The sides  132   b  and  132   e  are at a distance from each other in the Y-axis direction. Each of the sides  132   b  and  132   e  extends in the X-axis direction. The side  132   b  is a straight line segment connecting the Y1-side end of the side  132   a  and the Y1-side end of the side  132   c  to each other. The side  132   e  is a straight line segment connecting the Y2-side end of the side  132   d  and the Y2-side end of the side  132   f  to each other. The region located between the sides  132   b  and  132   e  in the Y-axis direction is the boundary base portion  132 . The boundary base portion  132  has a width W 2 , which is a length in the Y-axis direction. The width W 2  is the length from the side  132   b  to the side  132   e.    
     In addition, the width W 2  is the length of the boundary  36   a  in the Y-axis direction. The point P 1  is the point where the boundary  36   a  and the side  132   b  cross each other as viewed in the Z-axis direction. The point P 2  is the point where the boundary  36   a  and the side  132   e  cross each other as viewed in the Z-axis direction. The distance between the point P 1  and the point P 2  is equal to the width W 2 . 
     The lead-out portion  133  is demarcated by a side  133   a  and another side  133   b . The lead-out portion  133  is included in the part  32   b . The sides  133   a  and  133   b  are at a distance from each other in the Y-axis direction. Each of the sides  133   a  and  133   b  extends in the X-axis direction. The region located between the sides  133   a  and  133   b  in the Y-axis direction is the lead-out portion  133 . The lead-out portion  133  has a width W 3 , which is a length in the Y-axis direction. The width W 3  is the length from the side  133   a  to the side  133   b . The lead-out portion  133  is an example of another narrower portion having the width W 3 , which is less than the width W 2 . 
     The lower electrode  32  includes a narrower portion  134  having the width W 1 . The narrower portion  134  is located on the X1-directional side with respect to the boundary base portion  132 . The narrower portion  134  includes, of the body portion  131 , a part located adjacent to the boundary base portion  132 . The narrower portion  134  is, in the X-axis direction, located relatively on the X1-directional side in comparison with the sides  132   a  and  132   d . The narrower portion  134  has a predetermined length L 2  in the X-axis direction. The length of the narrower portion  134  in the X-axis direction may be equal to or approximately equal to the length of the boundary base portion  132  in the X-axis direction. 
     In the liquid ejecting head  10  having the above structure, the boundary base portion  132  is formed in the lower electrode  32  along the boundary  36   a . The width W 2  of the boundary base portion  132  is greater than the width W 1  of the body portion  131 . In addition, the non-drive region  33   b  of the piezoelectric layer  33  is formed in such a way as to surround the point P 1 , P 2 . The range of the drive region  33   a  existing around the point P 1 , P 2  is less than that of related art. Therefore, it is possible to reduce stress concentration near the point P 1 , P 2 , of the lower electrode  32 . Consequently, it is possible to prevent or reduce the occurrence of cracking that starts from a position corresponding to the boundary  36   a  of the lower electrode  32 . The structure of the liquid ejecting head  10  makes it possible to prevent or reduce damage near the boundary  36   a  of the lower electrode  32 , thereby improving the reliability of the liquid ejecting head  10 . 
     In the lower electrode  32 , the side  132   a  of the boundary base portion  132  forms a right angle with the side  131   a . Similarly, the side  132   d  of the boundary base portion  132  forms a right angle with the side  131   b . Therefore, it is easier to increase the width of the boundary base portion  132  in relation to the body portion  131 . This makes it easier to reduce stress concentration. 
     In the lower electrode  32 , the width W 3  of the lead-out portion  133  is less than the width W 2  of the boundary base portion  132 . Because of this structure, it is possible to make a leading-out wire thinner. Such a thinner wire makes wire routing easier. 
     In the liquid ejecting head  10 , the lower electrode  32  is configured as an individual electrode(s). It is easy to form a precise individual electrode pattern on the diaphragm  25 . Therefore, in the liquid ejecting head  10 , it is possible to easily form the lower electrode  32  that is a precise individual electrode. 
     In the liquid ejecting head  10 , the sealing plate  40  for protecting the piezoelectric actuators  31  is bonded to, of the pressure compartment forming substrate  24  on which the diaphragm  25  is formed, the surface over which the piezoelectric actuators  31  are formed. For example, when wires are thin, it is easier to widen the gap between the wires. This makes it difficult for an applied adhesive to spread through the gap between the wires. Therefore, it is possible to bond the sealing plate  40  well. Consequently, it is possible to protect the piezoelectric actuators  31  securely by the sealing plate  40 , thereby improving the reliability of the liquid ejecting head  10 . 
     In the liquid ejecting head  10 , the ratio of the protruding length L 3  of the boundary base portion  132  to the distance L 4  between two lower electrodes  32  located adjacent to each other in the Y-axis direction may be 5% or more and 30% or less. This makes it possible to form the boundary base portion  132  well while maintaining the intervals between the lower electrodes  32  in the Y-axis direction. It is possible to make the width W 2  of the boundary base portion  132  greater than the width W 1  of the body portion  131 . Consequently, it is possible to prevent or reduce damage near the boundary  36   a  of the lower electrode  32 . 
     Next, with reference to  FIG. 8 , an end structure of a lower electrode  32 B according to a first modification example will now be explained.  FIG. 8  is a plan view of an end structure of a lower electrode  32 B according to a first modification example. In  FIG. 8 , the lower electrode  32 B is viewed in the Z1 direction. The end structure of the lower electrode  32 B means its structure near the boundary  36   a . In the description of the first modification example below, the same explanation as that of the foregoing embodiment will not be given. 
     The lower electrode  32 B according to the first modification example is different from the lower electrode  32  according to the foregoing embodiment in that its boundary base portion  132 B has a curved side  132   g  and another curved side  132   h . The sides  132   g  and  132   h  are at a distance from each other in the Y-axis direction. The side  132   g  is a curve connecting the Y1-side end of the side  132   a  and the Y1-side end of the side  132   c  to each other. The side  132   g  is curved in such a way as to bulge in the Y1 direction. The side  132   h  is a curve connecting the Y2-side end of the side  132   d  and the Y2-side end of the side  132   f  to each other. The side  132   h  is curved in such a way as to bulge in the Y2 direction. 
     The point P 1  is located at the outermost position in the Y1 direction on the side  132   g . The point P 2  is located at the outermost position in the Y2 direction on the side  132   h . The width W 1  of the body portion  131  is less than the width W 2  of the boundary base portion  132 . The boundary base portion  132 B protrudes outward in the Y-axis direction beyond the sides  131   a  and  131   b  of the body portion  131 . 
     As described above, the sides  132   g  and  132   h  of the boundary base portion  132 B according to the first modification example may be curved in an arc shape. The liquid ejecting head  10  having the lower electrode  32 B described above produces the same operational effects as those of the liquid ejecting head  10  according to the foregoing embodiment. 
     In the lower electrode  32 B, the sides  132   g  and  132   h  of the boundary base portion  132 B are curved. There is a possibility that the lower electrode  32  and the upper electrode  34  might be misaligned from each other in the processes of manufacturing the piezoelectric actuator  31 . If the sides  132   g  and  132   h  are curved, as compared with a case where the sides  132   g  and  132   h  are straight, the possibility that the sides  132   g  and  132   h  and the boundary  36   a  will overlap will be high, which is desirable. 
     Next, with reference to  FIG. 9 , an end structure of a lower electrode  32 C according to a second modification example will now be explained.  FIG. 9  is a plan view of an end structure of a lower electrode  32 C according to a second modification example. In the description of the second modification example below, the same explanation as that of the foregoing embodiment will not be given. 
     The lower electrode  32 C according to the second modification example is different from the lower electrode  32  according to the foregoing embodiment in that, firstly, a width W 6  between sides  135   a  and  135   b  of a body portion  135  is approximately equal to the width W 2  of the boundary base portion  132 , and, secondly, sides  136   a  and  136   b  of a narrower (narrowing) portion  136  are inclined with respect to the X-axis direction. 
     The sides  135   a  and  135   b  are at a distance from each other in the Y-axis direction. Each of the sides  135   a  and  135   b  extends in the X-axis direction. The sides  136   a  and  136   b  are at a distance from each other in the Y-axis direction. The side  136   a  extends from the X2-side end of the side  135   a  toward the X2-directional side. The X2-side end of the side  136   a  is located relatively on the Y2-directional side, as compared with the X1-side end of the side  136   a . The side  136   b  extends from the X2-side end of the side  135   b  toward the X2-directional side. The X2-side end of the side  136   b  is located relatively on the Y1-directional side, as compared with the X1-side end of the side  136   b.    
     The point P 3  is located at the X2-side end of the side  136   a . The point P 3  is the intersection of the side  136   a  and the side  132   a . The point P 4  is located at the X2-side end of the side  136   b . The point P 4  is the intersection of the side  136   b  and the side  132   d . The narrower portion  136  is located on the X1-directional side with respect to the boundary base portion  132 . The narrower portion  136  has a predetermined length L 2  in the X-axis direction. The width W 5 , from the point P 3  to the point P 4 , of the narrower portion  136  is less than the width W 2  of the boundary base portion  132 . 
     A region  111  between the sides  135   a  and  135   b , within the body portion  135 , is an example of a first region. The region  111  has a width W 6  going in the Y-axis direction. The width W 6  is an example of a first width. The narrower portion  136  is an example of a second region. The width W 5  is an example of a second width. A region  113  located on the X1-directional side with respect to the boundary  36   a , within the boundary base portion  132 , is an example of a third region. The width W 2  is an example of a third width. The width W 5  is less than the width W 6 . The width W 2  is greater than the width W 5 . 
     The liquid ejecting head  10  having the lower electrode  32 C according to the second modification example described above produces the same operational effects as those of the liquid ejecting head  10  according to the foregoing embodiment. 
     In the lower electrode  32 C, the region  111  having the width W 6 , the narrower portion  136  having the width W 5 , and the region  113  having the width W 2  are arranged in this order in the X2 direction. In other words, when each width is defined as a length in the Y-axis direction, an area having a relatively large width, an area having a relatively small width, and an area having a relatively large width are arranged in this order. Since the lower electrode  32 C has the structure described above, it is possible to reduce a decrease in the area size of the lower electrode disposed over the pressure compartment  17 . Consequently, it is possible to reduce damage to the lower electrode without sacrificing the performance of the piezoelectric actuator  31 . 
     Next, with reference to  FIG. 10 , an end structure of a lower electrode  32 D according to a third modification example will now be explained.  FIG. 10  is a plan view of an end structure of a lower electrode  32 D according to a third modification example. In the description of the third modification example below, the same explanation as that of the foregoing embodiment will not be given. 
     The lower electrode  32 D according to the third modification example is different from the lower electrode  32 C according to the second modification example described above in that a lead-out portion  137  has a width W 7  that is approximately equal to the width W 2  of the boundary base portion  132 . The lead-out portion  137  leads in the X2 direction from the boundary base portion  132 . 
     The lead-out portion  137  has sides  137   a  and  137   b . The sides  137   a  and  137   b  are at a distance from each other in the Y-axis direction. Each of the sides  137   a  and  137   b  extends in the X-axis direction. Specifically, the side  137   a  extends from the X2-side end of the side  132   b  in the X2 direction and the side  137   b  extends from the X2-side end of the side  132   e  in the X2 direction. The width W 7 , which is the length from the side  137   a  to the side  137   b , is approximately equal to the width W 2  of the boundary base portion  132 . 
     The liquid ejecting head  10  having the lower electrode  32 D according to the third modification example described above produces the same operational effects as those of the liquid ejecting head  10  according to the foregoing embodiment. 
     Next, with reference to  FIG. 11 , an end structure of a lower electrode  32 E according to a fourth modification example will now be explained.  FIG. 11  is a plan view of an end structure of a lower electrode  32 E according to a fourth modification example. In the description of the fourth modification example below, the same explanation as that of the foregoing embodiment will not be given. 
     The lower electrode  32 E according to the fourth modification example is different from the lower electrode  32 D according to the third modification example described above in that, firstly, sides  138   a  and  138   b  of a boundary base portion  138  are inclined with respect to the X-axis direction, and, secondly, a lead-out portion  139  has a width W 9  that is greater than the width W 8  of the boundary base portion  138 . 
     The sides  138   a  and  138   b  of the boundary base portion  138  are at a distance from each other in the Y-axis direction. The side  138   a  extends from the X2-side end of the side  136   a  toward the X2-directional side. The X2-side end of the side  138   a  is located relatively on the Y1-directional side, as compared with the X1-side end of the side  138   a . The side  138   b  extends from the X2-side end of the side  136   b  toward the X2-directional side. The X2-side end of the side  138   b  is located relatively on the Y2-directional side, as compared with the X1-side end of the side  138   b.    
     The lead-out portion  139  is located adjacent to the boundary base portion  132  in the X2 direction. Sides  139   a  and  139   c  of the lead-out portion  139  are at a distance from each other in the Y-axis direction. The side  139   a  extends along the line of extension of the side  138   a . The X2-side end of the side  139   a  is located relatively on the Y1-directional side, as compared with the X1-side end of the side  139   a . The side  139   c  extends along the line of extension of the side  138   b . The X2-side end of the side  139   c  is located relatively on the Y2-directional side, as compared with the X1-side end of the side  139   c.    
     Sides  139   b  and  139   d  of the lead-out portion  139  are at a distance from each other in the Y-axis direction. Each of the sides  139   b  and  139   b  extends in the X-axis direction. The side  139   b  extends from the X2-side end of the side  139   a  in the X2 direction. The side  139   d  extends from the X2-side end of the side  139   c  in the X2 direction. 
     The point P 5  is located at the intersection of the side  138   a  and the boundary  36   a  as viewed in the Z-axis direction. The point P 6  is located at the intersection of the side  138   b  and the boundary  36   a  as viewed in the Z-axis direction. The boundary base portion  138  is located on the X2-directional side with respect to the narrower portion  136 . The boundary base portion  138  has a predetermined length L 1  in the X-axis direction. The width W 8 , from the point P 5  to the point P 6 , of the boundary base portion  138  is greater than the width W 5 . 
     A region  114  located on the X1-directional side with respect to the boundary  36   a , within the boundary base portion  138 , is an example of a third region. The width W 8  is an example of a third width. 
     The width W 9  of the lead-out portion  139  is the length from the side  139   b  to the side  139   d . The lead-out portion  139  is an example of a wider portion. 
     The liquid ejecting head  10  having the lower electrode  32 E according to the fourth modification example described above produces the same operational effects as those of the liquid ejecting head  10  according to the foregoing embodiment. 
     Since the lower electrode  32 E includes the lead-out portion  139  whose width W 9  is relatively large, it is easier to reduce stress concentration at the boundary base portion  138 . 
     Next, with reference to  FIG. 12 , a lead electrode  35 B according to a fifth modification example will now be explained.  FIG. 12  is a plan view of lower electrodes  32  and lead electrodes  35 B according to a fifth modification example. The lead electrode  35 B according to the fifth modification example is different from the lead electrode  35  according to the foregoing embodiment in that it is inclined with respect to the X-axis direction as viewed in the Z-axis direction. 
     The lead electrode  35 B is bent with respect to the X-axis direction. The bent portion  35   a  includes a curved portion. The lead electrode  35 B may have the curved structure at the portion narrowed from the lower electrode  32 . 
     The foregoing embodiment merely discloses typical examples of the present disclosure. The scope of the present disclosure is not limited to the foregoing embodiment. Various modifications and additions, etc. can be made within a range not departing from the gist of the present disclosure. 
     The lower electrode  32  of the piezoelectric actuator  31  may have a curved structure at the portion narrowed from the boundary base portion  132 . For example, a part of the sides of the body portion  131  may be curved, or a part of the sides of the lead-out portion  133  may be curved. With this structure, it is possible to relax stress acting on the lower electrode  32  near the boundary  36   a , thereby preventing the occurrence of cracking in the lower electrode  32 . 
     In the foregoing embodiment, the liquid ejecting apparatus  1  that is a so-called serial-type device configured to reciprocate the carriage  5  on which the liquid ejecting head  10  is mounted has been described to show some examples. However, the present disclosure may be applied to a so-called line-type liquid ejecting apparatus in which the plural nozzles N are arranged throughout the entire width of the medium P. 
     The liquid ejecting apparatus  1  disclosed as examples in the foregoing embodiment can be applied to not only print-only machines but also various kinds of equipment such as facsimiles and copiers, etc. The scope of application of a liquid ejecting apparatus according to the present disclosure is not limited to printing. For example, a liquid ejecting apparatus that ejects a colorant solution can be used as an apparatus for manufacturing a color filter of a display device such as a liquid crystal display panel. A liquid ejecting apparatus that ejects a solution of a conductive material can be used as a manufacturing apparatus for forming wiring lines and electrodes of a wiring substrate. A liquid ejecting apparatus that ejects a solution of a living organic material can be used as a manufacturing apparatus for, for example, production of biochips. 
     The actuator  31  disclosed as examples in each embodiment may be used for devices such as, for example, an ultrasonic wave transmitter, an ultrasonic motor, a piezoelectric transformer, a piezoelectric speaker, a piezoelectric pump, a pressure-electricity converter, and the like.