B41828: 9170152
`
`Title of Invention
`
`Technological Field
`
`Description
`
`INK JET HEAD
`
`[0001] The present invention relates to the structure of an inkjet head.
`
`Background
`
`[0002]
`
`In recent years, in order to prevent poor ejection due to, for example, thickening of ink and generation of
`
`air bubbles near nozzles in an inkjet head, there is a known technique to collect thickened ink and air bubbles via a
`
`circulation flow path provided near nozzles. For example, Japanese Laid-Open Patent Publication No. 2008-
`
`290292 (PTL l) discloses a mechanism having a circulation flow path in a plate (discharge-hole plate) superposed
`
`on a nozzle plate so as to circulate ink.
`Citation List
`
`Patent Literature
`
`[0003] PTL 1: Japanese Laid-Open Patent Publication No. 2008-290292
`
`Summary
`Technical Problem
`
`[0004]
`
`In the configuration described in the above PTL 1, however, an additional discharge-hole plate is required
`
`to form a circulation flow path, which increases the distance from the pressure chambers to the nozzles by the
`
`thickness of the discharge-hole plate.
`
`The increased distance from the pressure chambers to the nozzles causes
`
`deterioration in ink ejection properties.
`
`[0005] An object of the present invention, which has been made in view of the above problem, is to provide an
`
`inkjet head with a configuration that can prevent deterioration in ink ejection properties.
`Solution to Problem
`
`[0006] This inkjet head comprises: a nozzle plate including a plurality of nozzles; a vibration plate including a
`
`pressure chamber to store ink to be ejected from the nozzle; a spacer plate containing a piezoelectric layer to apply
`
`pressure to the pressure chamber; and a flow path formation substrate between the vibration plate and the nozzle
`
`plate, the flow path formation substrate including a communication flow path that communicates with the nozzle
`
`and the pressure chamber.
`
`[0007] The vibration plate includes a vibration board provided between the pressure chamber and the piezoelectric
`
`layer to transmit deformation of the piezoelectric layer to the pressure chamber.
`
`The nozzle plate includes an
`
`individual circulation flow path provided for each of the plurality of nozzles to discharge ink, and a common
`
`circulation flow path into which a plurality of the individual circulation flow paths merge.
`
`[0008]
`
`In another mode, the nozzle plate includes a nozzle support layer located adjacent to the flow path
`
`formation substrate, and a nozzle layer located opposite to the flow path formation substrate across the nozzle
`
`support layer. The individual circulation flow path and the common circulation flow path are provided in the
`
`nozzle support layer.
`
`[0009]
`
`In another mode, the nozzle plate is an 801 substrate.
`
`In another mode, the common circulation flow path is provided also in the flow path formation substrate.
`
`[0010]
`
`In another mode, a columnar member is disposed in the common circulation flow path.
`
`-1-
`
`

`

`In another mode, a recess is provided at a part of an outer surface of the nozzle plate over which the
`
`common circulation flow path is provided, the recess being recessed toward the common circulation flow path.
`
`[0011]
`
`In another mode, in plan view, the common circulation flow path includes a curved portion.
`
`Advantageous Effects of Invention
`
`[0012] The present invention provides an inkjet head with a configuration that can prevent deterioration in ink
`
`B41828: 9170152
`
`ejection properties.
`
`Brief Description of the Drawings
`
`[0013] Fig. 1 is a cross-sectional view showing the structlne of an inkjet head in embodiment 1.
`
`Fig. 2 is a perspective view showing the configuration of a nozzle plate in embodiment 1.
`
`Fig. 3 is a cross-sectional view showing the structure of an inkjet head in embodiment 2.
`
`Fig. 4 is a perspective view showing the configuration of a nozzle plate in embodiment 3.
`
`Fig. 5 is a cross-sectional view showing the configuration of a nozzle plate in embodiment 4.
`
`Fig. 6 is a plan view showing the configuration of a nozzle plate in embodiment 5.
`
`Fig. 7 is a cross-sectional view showing the structure of an inkjet head in related art.
`
`Fig. 8 shows parameters in an example.
`
`Fig. 9 shows the relation between the communication flow path length and the negative pressure in an
`
`example.
`
`example.
`
`Fig. 10 shows the relation between the communication flow path length and the driving voltage in an
`
`Detailed Description of Embodiments
`
`[0014]
`
`Inkjet heads in embodiments based on the present invention are described hereinafter with reference to the
`
`drawings.
`
`In the embodiments described hereinafter, when reference is made to the number, quantity and the like,
`
`the scope of the present invention is not necessarily limited to the number, quantity and the like, unless otherwise
`
`noted.
`
`Identical or corresponding parts are identically denoted, and the redundant description is not repeated in
`
`some cases.
`
`It is assumed from the start that the features in the embodiments may be combined as appropriate.
`
`Some parts of the drawings are shown not in accordance with the ratio of the actual dimensions but with the ratio
`
`being changed to clarify the structure for easier understanding of the structure.
`
`[0015]
`
`(Embodiment 1: Configlnation of Inkjet Head 1)
`
`With reference to Fig. 1 and Fig. 2, the configuration of an inkjet head 1 according to the present
`
`embodiment is described.
`
`Fig. 1 is a cross-sectional view showing the structure of inkjet head 1.
`
`FIG. 2 is a
`
`perspective view showing the configuration of a nozzle plate 10. The cross section taken along line 1-1 in Fig. 2
`
`corresponds to the cross-sectional view of Fig. 1.
`
`[0016]
`
`In Fig. 1, the plane on which a nozzle N is provided is defined as an X-Y plane. The directions along the
`
`plane and orthogonal to each other are defined as an X direction and a Y direction. The direction orthogonal to the
`
`X-Y plane is defined as a Z direction. The Z—axis direction corresponds to the vertical direction.
`
`[0017] With reference to Fig. 1, inkjet head 1 includes nozzle plate 10 and a head chip 110. Nozzle plate 10 has
`
`nozzle N to eject ink. Nozzle N extends through nozzle plate 10. Nozzle plate 10 includes a nozzle support layer
`
`11 and a nozzle layer 12. Nozzle support layer 11 has a passage 11a, and nozzle layer 12 has nozzle N which
`
`communicates with passage 11a.
`
`

`

`B41828: 9170152
`
`[0018] A plurality of nozzles N and passages 11a are provided in line along the Y-axis direction, for example.
`
`Usually, nozzles N are arranged in a matrix. The number of nozzles (channels) is, for example, 1024 (16 X 64).
`
`[0019] As nozzle plate 10, an SOI substrate may be used, for example. Nozzle plate 10 is not limited to an SOI
`
`substrate but may be made of, for example, SUS, 42Alloy, or polyimide. A water-repellent film may be formed on
`
`the lower face of nozzle plate 10.
`
`[0020] Head chip 110 is formed by stacking a plurality of substrates and the like along the Z direction on the upper
`
`face of nozzle plate 10.
`
`Specifically, head chip 110 is formed by stacking an intermediate substrate 100, a
`
`vibration plate 20 including a pressure chamber 21, a spacer substrate 40, and a wiring substrate 50, on nozzle plate
`10.
`
`[0021] Vibration plate 20 includes a vibration board 30 provided between pressure chamber 21 and a piezoelectric
`
`layer 60 (described later) to transmit deformation of piezoelectric layer 60 to pressure chamber 21.
`
`[0022] Thus, in nozzle plate 10, nozzle support layer 11 is located adjacent to intermediate substrate 100, and
`
`nozzle layer 12 is located opposite to intermediate substrate 100 across nozzle support layer 11.
`
`[0023]
`
`Intermediate substrate 100 has a connection passage 101 which connects nozzle N and pressure chamber 21.
`
`Intermediate substrate 100, vibration plate 20, vibration board 30, spacer substrate 40, and wiring substrate 50 have
`
`ink supply flow paths 22, 31, 41, 51 which communicate with pressure chamber 21. The flow path of ink formed
`
`by the ink supply flow paths connects pressure chamber 21 and an external ink supply flow path provided above
`
`wiring substrate 50.
`
`[0024]
`
`Intermediate substrate 100 is provided for the purpose of providing connection passage 101 between nozzle
`
`plate 10 and vibration plate 20, for example. Connection passage 101 communicates with pressure chamber 21 and
`
`nozzle N and adjusts kinetic energy to be applied to ink when the ink is ejected.
`
`[0025] Providing connection passage 101 makes it possible for the flow path of ink that leads to nozzle N to have
`
`any desired shape.
`
`Intermediate substrate 100 may be made of any material, such as glass, stainless steel, resin, silicon, or the
`
`[0026]
`like.
`
`[0027] Vibration plate 20 is provided on intermediate substrate 100. Vibration plate 20 includes pressure
`
`chamber 21 to store ink.
`
`Pressure chamber 21 communicates with nozzle N via connection passage 101 of
`
`intermediate substrate 100. A plurality of pressure chambers 21 are provided along the Y-axis direction for a
`
`plurality of nozzles N arranged along the Y-axis direction, on a one-to-one basis, so that each pressure chamber 21
`
`communicates with corresponding nozzle N.
`
`Pressure chamber 21 is provided independently of ink supply flow
`
`path 22.
`
`[0028] Vibration board 30 provided in vibration plate 20 covers an opening 42 in spacer substrate 40 in which
`
`piezoelectric layer 60 is contained. Vibration board 30 forms one face (upper face) of pressure chamber 21.
`
`Vibration board 30 can be vibrated by piezoelectric layer 60 provided on vibration board 30. Vibration of
`
`vibration board 30 increases or decreases the pressure in pressure chamber 21.
`
`[0029]
`
`Spacer substrate 40 allows for a space corresponding to the heights of piezoelectric layer 60 and a
`
`connection portion 90 (described later) along the Z direction between vibration board 30 and wiring substrate 50.
`
`Spacer substrate 40 has opening 42 at a location corresponding to the location of piezoelectric layer 60.
`
`[0030] Opening 42 extends through spacer substrate 40 in the Z direction. Opening 42 is provided independently
`
`-3-
`
`

`

`B41828: 9170152
`
`of ink supply flow path 41.
`
`In opening 42, piezoelectric layer 60 is disposed. Opening 42 is covered with wiring
`
`substrate 50. Thus, a closed space S1 is defined around piezoelectric layer 60.
`
`Spacer substrate 40 and wiring
`
`substrate 50 correspond to a sealing portion to seal piezoelectric layer 60.
`
`[0031]
`
`Spacer substrate 40 may be made of any material that allows for the above-described space, such as resin
`
`member, iron, glass, nickel, stainless steel, silicon, or an alloy, for example.
`
`[0032] Wiring substrate 50 includes, for example, an interposer 53, insulating layers 54, 55, a through-substrate
`
`via 56, an interconnection 57, an insulating layer 58, an interconnection 52, an insulating layer 59, and ink supply
`
`flow path 51.
`
`[0033]
`
`lnterposer 53 is in the shape of a plate.
`
`Interposer 53 is the base of wiring substrate 50.
`
`Insulating layer
`
`54 covers the upper face of interposer 53.
`
`Insulating layer 55 covers the lower face of interposer 53.
`
`[0034] Through-substrate via 56 is provided in a through-hole P extending through insulating layer 54, interposer
`
`53, and insulating layer 55.
`
`Interconnection 57 is provided on the upper face of insulating layer 54 and electrically
`
`connected to the upper end of through-substrate via 56.
`
`[0035]
`
`Insulating layer 58 covers the upper face of interconnection 57 and the upper face of the part of insulating
`
`layer 54 where interconnection 57 is not provided.
`
`[0036]
`
`Interconnection 52 is provided on the lower face of insulating layer 55 and electrically connected to the
`
`lower end of through-substrate via 56.
`
`Interconnection 52 is connected to a controller (not shown) to control the
`
`voltage to be applied to piezoelectric layer 60 via through-substrate via 56 and interconnection 57 .
`
`[0037]
`
`Interconnections 52, 57 may be formed by, for example, patterning conductive metal (e. g. Cr, Ti, and Au)
`
`by photolithography. For example, interconnections 52, 57 may be formed by forming films of Cr and Au on the
`
`substrate in this order, then patterning Au, and then patterning Cr. Cr or Ti is used as an adhesion layer for Au.
`
`[0038]
`
`Insulating layer 59 covers the lower face of the part of interconnection 52 where a bump 91 is not formed,
`
`and covers the lower face of the part of insulating layer 55 where interconnection 52 is not provided.
`
`Ink supply
`
`flow path 51 extends through insulating layer 58, insulating layer 54, interposer 53, insulating layer 55, and
`
`insulating layer 59.
`
`[003 9] Piezoelectric layer 60 is electrically connected to interconnection 52 provided in wiring substrate 50 via
`
`connection portion 90 (described later). Each piezoelectric layer 60 is provided for a corresponding one of a
`
`plurality of nozzles N arranged along the Y-axis direction. Piezoelectric layer 60 is provided on vibration board 30.
`
`[0040] Piezoelectric layer 60 includes a piezoelectric portion 61 formed by a piezoelectric layer, a first electrode
`
`62 covering one surface of piezoelectric portion 61, and a second electrode 63 covering the other surface of
`
`piezoelectric portion 61.
`
`[0041] First electrode 62 is electrically connected to interconnection 52 via connection portion 90. Connection
`
`portion 90 connects first electrode 62 and interconnection 52 along the Z direction. Connection portion 90 includes
`
`bump 91 formed on wiring substrate 50.
`
`[0042] Bump 91 is formed by, for example, wire bonding using gold as the material. Bump 91 is formed, for
`
`example, on the lower face of interconnection 52. A conductive material 92 is applied to the lower end of bump 91.
`
`Specifically, conductive material 92 is, for example, a conductive adhesive. The conductive adhesive is an
`
`adhesive that contains conductive powdered metal (e.g. powdered silver).
`
`[0043] Thus, connection portion 90 electrically connects wiring substrate 50 and piezoelectric layer 60 via bump
`
`-4-
`
`

`

`B41828: 9170152
`
`91 formed on wiring substrate 50 and via conductive material 92 applied to bump 91.
`
`[0044]
`
`Second electrode 63 is in contact with an electrode layer (not shown) formed on vibration board 30. The
`
`electrode layer formed on vibration board 30 functions as an electrode that electrically connects second electrode 63
`
`and the above-described controller.
`
`Second electrode 63 is connected to the controller via, for example, an
`
`interconnection (not shown) connected to the electrode layer formed on vibration board 30.
`
`[0045] The electrode layer may be formed by, for example, patteming conductive metal (e. g. Cr, Ti, and Au) by
`
`photolithography on vibration board 30. For example, the electrode layer may be formed by forming films of Cr
`
`and Au on the substrate in this order, then patterning Au, and then patterning Cr. Cr or Ti is used as an adhesion
`
`layer for Au.
`
`[0046] First electrode 62 is connected to the controller via connection portion 90, interconnection 52, through-
`
`substrate via 56, and interconnection 57.
`
`Second electrode 63 is connected to the controller via the electrode layer
`
`formed on vibration board 30. Thus, piezoelectric layer 60 can operate under the control of the controller.
`
`[0047] Operation of piezoelectric layer 60 causes vibration board 30 to vibrate. This causes a change in internal
`
`pressure in pressure chamber 21, thereby allowing the ink that has been supplied to pressure chamber 21 to eject
`from nozzle N.
`
`[0048] An epoxy adhesive is preferably used to bond the above-described intermediate substrate 100 and nozzle
`
`plate 10.
`
`If glass is used as the material of intermediate substrate 100 and silicon is used as the material of nozzle
`
`plate 10, then anodic bonding may be used to bond the glass and the silicon.
`
`[0049]
`
`It is preferable that the differences in coefficient of thermal expansion between the substrates be
`
`sufficiently small. This can prevent the substrates from warping and coming off from one another due to
`
`temperature changes during bonding of the substrates and due to heat generated during operation of inkjet head 1.
`
`[0050] For example, silicon is used as the material of the above-described vibration plate 20, vibration board 30,
`
`and wiring substrate 50; and 42Alloy (alloy containing 42% by weight of nickel, 57% by weight of iron, the balance
`
`including a very small amount of additive [e. g. copper, manganese, or the like]) is used as the material of spacer
`
`substrate 40. This achieves small differences in coefficient of thermal expansion between the substrates.
`
`[0051]
`
`In inkj et head 1 in the above-described embodiment, vibration board 30 is integrated with vibration plate
`
`20. However, inkjet head 1 is not limited to such a configuration. Vibration board 30 and vibration plate 20 may
`
`be separately provided.
`
`[0052]
`
`(Nozzle Plate 10)
`
`With reference to Fig. 2, the configuration of nozzle support layer 11 which constitutes nozzle plate 10 is
`
`described. Nozzle support layer 11 includes individual circulation flow paths 111 each provided for a
`
`corresponding one of a plurality of nozzles N and each communicating with a corresponding passage 11a to
`
`discharge ink.
`
`Further, nozzle support layer 11 has a common circulation flow path 113 into which a plurality of
`
`individual circulation flow paths 111 merge.
`
`In Fig. 2, individual circulation flow paths 111 extend in the X
`
`direction, and common circulation flow path 113 linearly extends in the Y direction.
`
`[0053] As described above, 1024 (16 X 64) nozzles N (channels) are provided, for example.
`
`Individual
`
`circulation flow path 111 is provided for each nozzle N, whereas a single common circulation flow path 113 is
`
`provided for all the nozzles N. Alternatively, nozzles N may be divided into some groups, and a plurality of
`
`common circulation flow paths 113 may be provided for the respective groups.
`
`-5-
`
`

`

`B41828: 9170152
`
`[0054] Thus, inkjet head 1 in the present embodiment includes individual circulation flow path 111 provided for
`
`each of a plurality of nozzles N to discharge ink, and common circulation flow path 113 into which a plurality of
`
`individual circulation flow paths 111 merge. Thus, as shown in Fig. 1, the ink supplied to nozzle N but not ejected
`
`to the outside is discharged through individual circulation flow path 111 to common circulation flow path 113 and is
`
`then supplied again, through a circulation line L1, to ink supply flow paths 22, 31, 41, 51 which comm1micate with
`
`pressure chamber 21.
`
`In this way, deterioration in ink ejection properties can be prevented.
`
`[0055]
`
`Since individual circulation flow path 111 and common circulation flow path 113 are provided in the same
`
`nozzle support layer 11, an additional substrate is not required to manufacture inkjet head 1 in the present
`
`embodiment. Therefore, increase in cost can be prevented.
`
`[0056] The length of individual circulation flow path 111, from pressure chamber 21 to nozzle plate 10, can be
`
`shortened compared with the configuration having an additional substrate for individual circulation flow path 111.
`
`This achieves low-voltage driving. Further, a shortened path from pressure chamber 21 to nozzle plate 10 reduces
`
`the negative pressure, thus preventing increase in negative pressure at pressure chamber 21.
`
`[0057] Further, since there is no need to make nozzle support layer 11 thinner to provide individual circulation
`
`flow path 111 and common circulation flow path 113, it is possible to avoid generation of cracks during bonding of
`
`nozzle support layer 11 and the substrates in head chip 110 in the manufacturing process and also avoid their warps
`
`due to heat. Thus, the productivity of inkjet head 1 can be improved.
`
`[0058] Although the present embodiment discloses a configuration in which the ink discharged from the common
`
`circulation flow path circulates through circulation line L1, it is needless to say that a configuration without
`
`circulation is also possible.
`
`For example, ink may be discharged from common circulation flow path 113 without
`
`passing through circulation line L1.
`
`[0059]
`
`(Embodiment 2: Configlnation of Inkjet Head 1A)
`
`With reference to Fig. 3, the configuration of an inkjet head 1A according to the present embodiment is
`
`described.
`
`Fig. 3 is a cross-sectional view showing the structure of inkjet head 1A. The cross section taken along
`
`line 1-1 in Fig. 2 corresponds to the cross-sectional view of Fig. 1.
`
`[0060] The basic configuration is the same as the configuration of inkjet head 1 in the above-described
`
`embodiment 1. The difference is that common circulation flow path 113 is provided not only in nozzle support
`
`layer 11 but also in intermediate substrate 100.
`
`[0061]
`
`Inkjet head 1A having this configuration can bring about the same advantageous effects as those of inkjet
`
`head 1 in the above-described embodiment 1. Further, common circulation flow path 113 extended into
`
`intermediate substrate 100 allows for an enlarged cross section of common circulation flow path 113 and thus an
`
`increased quantity of flow of circulating ink, without increasing the size of inkjet head 1A in the Z direction.
`
`[0062] Further, a step portion D 1, which is formed at the connecting portion between individual circulation flow
`
`path 111 and common circulation flow path 113, causes a flow from individual circulation flow path 111 drawn into
`
`common circulation flow path 113. Thus, air bubbles in individual circulation flow path 111 can be easily drawn
`
`into the flow in common circulation flow path 113. This can reduce air bubbles staying in passage 11a and more
`
`effectively prevent deterioration in ink ejection properties.
`
`[0063]
`
`(Embodiment 3: Configlnation of Inkjet Head 1B)
`
`With reference to Fig. 4, the configuration of an inkjet head 1B according to the present embodiment is
`
`-6-
`
`

`

`B41828: 9170152
`
`described.
`
`Fig. 4 is a perspective view showing the configuration of nozzle plate 10.
`
`[0064] The basic configuration is the same as the configuration of inkjet head 1 in the above-described
`
`embodiment 1. The difference is that a plurality of columnar members 113P are arranged in common circulation
`
`flow path 113 provided in nozzle plate 10. Columnar members 113P may be disposed at any positions.
`
`In order
`
`not to affect the flow of ink from individual circulation flow path 111 to common circulation flow path 113, each
`
`columnar member 113P is provided preferably at a position that does not face individual circulation flow path 111.
`
`For example, each columnar member 113P may be provided between adjacent individual circulation flow paths 111.
`
`[0065]
`
`Inkjet head 1B haan this configuration can bring about the same advantageous effects as those of inkjet
`
`head 1 in the above-described embodiment 1. Further, nozzle layer 12 in nozzle plate 10 serves as a damper (shock
`
`absorber) by deforming. Columnar members 113P provided in common circulation flow path 113 reinforce nozzle
`
`layer 12. Also, columnar members 113P reduce deformation of nozzle layer 12 if more deformation than is
`
`expected occurs in nozzle layer 12. This can avoid damage to nozzle layer 12.
`
`[0066] Further, the damper, which needs to bend toward intermediate substrate 100, requires a gap between
`
`columnar members 113P and intermediate substrate 100. A possible method includes the following (i) to (iii):
`
`(i) removing a film (e. g. an oxide film) that covers the surface of nozzle support layer 11, only from the
`
`parts of columnar members 113P;
`
`(ii) applying an adhesive to the surface of nozzle support layer 11, other than columnar members 113P, to
`
`bond it to intermediate substrate 100; and
`
`(iii) the adhesive containing beads for controlling the thickness.
`
`[0067]
`
`(Embodiment 4: Configuration of Inkjet Head 1C)
`
`With reference to Fig. 5, the configuration of an inkjet head 1C according to the present embodiment is
`
`described.
`
`Fig. 5 is a cross-sectional view showing the configuration of nozzle plate 10.
`
`[0068] The basic configuration is the same as the configuration of inkjet head 1 in the above-described
`
`embodiment 1.
`
`The difference is that a recess 12r is provided at a part of the outer surface (nozzle surface) 12a of
`
`nozzle plate 10 over which common circulation flow path 113 is provided, the recess 12r being recessed toward
`
`common circulation flow path 113. The area where recess 12r is provided preferably includes the area where
`
`common circulation flow path 113 is provided.
`
`[0069]
`
`Inkjet head 1C haan this configuration can bring about the same advantageous effects as those of inkjet
`
`head 1 in the above-described embodiment 1. Further, during cleaning of outer surface (nozzle surface) 12a of
`
`nozzle plate 10, a blade, made of an elastic body, is made to slide on outer surface (nozzle surface) 12a while being
`
`in contact with the surface 12a. At this time, the moving direction of blade B1 is the Y direction in the drawing,
`
`and the width of the blade in the X direction is broader than the width of recess 12r. Thus, the bottom face of
`
`recess 12r is prevented from being touched by blade B 1.
`
`[0070] This prevents deformation of nozzle layer 12 during cleaning of outer surface (nozzle surface) 12a with
`
`blade B 1, thus avoiding damage to nozzle layer 12.
`
`[0071]
`
`(Embodiment 5: Configuration of Inkjet Head 1D)
`
`With reference to Fig. 6, the configuration of an inkjet head 1D according to the present embodiment is
`
`described.
`
`Fig. 6 is a plan view showing the configuration of nozzle plate 10.
`
`[0072] The basic configuration is the same as the configuration of inkjet head 1 in the above-described
`
`-7-
`
`

`

`B41828: 9170152
`
`embodiment 1. The difference is that a common circulation flow path 113W provided in nozzle plate 10 includes a
`
`curved portion. Common circulation flow path 113 of inkjet head 1 in embodiment 1 shown in Fig. 2 has a linear
`
`shape along the Y direction. On the other hand, common circulation flow path 113W of inkjet head 1C in the
`
`present embodiment has a gentle S—curve in plan view.
`
`Specifically, a side wall 113Q which constitutes common
`
`circulation flow path 113W of nozzle plate 10 has a wavy shape toward circulation flow paths.
`
`[0073]
`
`Inkjet head 1D having this configuration can bring about the same advantageous effects as those of inkjet
`
`head 1 in the above-described embodiment 1. Further, since side wall 113Q which constitutes common circulation
`
`flow path 113W of nozzle plate 10 has a wavy shape toward circulation flow paths, side wall 113Q serves as a
`
`member to reinforce nozzle layer 12. Also, if more deformation (stress) than is expected occurs in nozzle layer 12,
`
`cracks in a plane of cleavage of silicon in nozzle support layer 11 is prevented under stress. Therefore, cracks can
`
`be prevented during assembly and driving of the head.
`
`[0074] The wavy shape of common circulation flow path 113W is preferably a pattern such that individual
`
`circulation flow paths 111 are the longest. This allows thickened fluid and air bubbles to be easily discharged.
`
`[0075]
`
`(Example)
`
`An example is described hereinafter.
`
`Inkjet head 1 having the configuration shown in Fig. 1 and an inkjet
`
`head 1X having the configuration shown in Fig. 7 were compared with each other in performance.
`
`Inkjet head 1X
`
`shown in Fig. 7 includes a circulation plate 70 having common circulation flow path 113 and an ink supply flow
`
`path 71, and nozzle support layer 11 has individual circulation flow path 111. Accordingly, the entire thickness of
`
`inkjet head 1X in the Z direction is larger than that of inkjet head 1.
`
`[0076] Here, the length of the ink flow path from pressure chamber 21 to nozzle layer 12, formed by connection
`
`passage 101, passage 11a, and ink supply flow path 71, is defined as a "communication flow path length". The
`
`"communication flow path length" of inkjet head 1 shown in Fig. 1 is 270 um. On the other hand, the
`
`"communication flow path length" of inkjet head 1X shown in Fig. 6 is 420 pm.
`
`[0077] Fig. 8 shows the relation between the negative pressure (kPa) of pressure chamber 21 and the driving
`
`voltage (V) for driving piezoelectric layer 60 for each communication flow path length. A preferable target value
`
`of the negative pressure (kPa) is -360 (kPa) or more, and a preferable target value of the driving voltage is 25 V or
`less.
`
`[0078] When the "communication flow path length" is 450 pm, the negative pressure is -407 (kPa) and the driving
`
`voltage is 27.8 (V). When the "communication flow path length" is 350 pm, the negative pressure is -368 (kPa)
`
`and the driving voltage is 26.2 (V). When the "communication flow path length" is 300 pm, the negative pressure
`
`is -356 (kPa) and the driving voltage is 25.1 (V). When the "communication flow path length" is 250 pm, the
`
`negative pressure is -339 (kPa) and the driving voltage is 24.2 (V). When the "communication flow path length" is
`
`150 pm, the negative pressure is -312 (kPa) and the driving voltage is 22.8 (V).
`
`Fig. 9 shows the relation between
`
`the "communication flow path length" and the negative pressure.
`
`Fig. 10 shows the relation between the
`
`"communication flow path length" and the driving voltage.
`
`[007 9]
`
`It is shown that a "communication flow path length" of about 300 um or less can achieve a negative
`
`pressure (kPa) of -360 (kPa) or more.
`
`It is shown that a "communication flow path length" of about 300 um or less
`
`can also achieve a driving voltage of 25 V or less.
`
`Inkjet head 1 shown in Fig. 1, whose "communication flow path
`
`length" is 270 um, can satisfy the target values of the negative pressure and the driving voltage. On the other hand,
`
`-8-
`
`

`

`B41828: 9170152
`
`inkjet head 1X shown in Fig. 7, whose "communication flow path length" is 420 um, cannot satisfy the target values
`
`of the negative pressure and the driving voltage.
`
`[0080]
`
`It should be understood that the embodiments and the example disclosed herein are by way of example in
`
`every respect, not by way of limitation. The scope of the present invention is defined not by the above description
`
`but by the terms of the claims.
`
`It is intended that the scope of the present invention includes any modification
`
`within the meaning and the scope equivalent to the terms of the claims.
`
`Reference Signs List
`
`[0081]
`
`1, 1A, 1B, 1C, 1D: inkjet head; 10: nozzle plate; 11: nozzle support layer; 11a: passage; 12: nozzle layer;
`
`12r: recess; 20: vibration plate; 21: pressure chamber; 22, 41, 51, 71, 102: ink supply flow path; 30: vibration board;
`
`40: spacer substrate; 42: opening; 50: wiring substrate; 52, 57: interconnection; 53: interposer; 54, 55, 58, 59:
`
`insulating layer; 56: through-substrate via; 60: piezoelectric layer; 61: piezoelectric portion; 62: first electrode; 63:
`
`second electrode; 90: connection portion; 91: bump; 92: conductive material; 100: intermediate substrate; 101:
`
`connection passage; 110: head chip; 111: individual circulation flow path; 113, 113W: common circulation flow
`
`path; 113P: columnar member; 113Q: side wall; B 1: blade; D1: step portion; N: nozzle
`
`