SUBSTITUTE SPECIFICATION — MARKED UP
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`Title of Invention
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`Description
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`ELK—JE—T—H—EAD
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`w
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`CROSS REFERENCE TO PRIOR APPLICATIONS
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`This is the US. national stage of application No. PCT/JP2017/022682, filed on June 20,
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`2017. Priorit
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`under 35 U.S.C.
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`119 a
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`and 35 U.S.C.
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`365 b
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`is claimed from Ja anese
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`Application No. 2016-147578, filed July 27, 2016, the disclosure of which is also incorporated
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`herein by reference.
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`Technological Field
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`[0001] The present invention relates to the structure of an inkjet head.
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`Background
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`[0002] In recent years, in order to prevent poor ejection due to, for example, thickening of ink
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`and generation of air bubbles near nozzles in an inkjet head, there is a known technique to collect
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`thickened ink and air bubbles via a circulation flow path provided near nozzles. For example,
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`Japanese Laid-Open Patent Publication No. 2008-290292 (PTL 1) discloses a mechanism having
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`a circulation flow path in a plate (discharge-hole plate) superposed on a nozzle plate so as to
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`circulate ink.
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`Citation List
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`Patent Literature
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`[0003] PTL 1: Japanese Laid-Open Patent Publication No. 2008-290292
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`Summary
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`Technical Problem
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`[0004] In the configuration described in the above PTL 1, however, an additional discharge-hole
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`plate is required to form a circulation flow path, which increases the distance from the pressure
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`chambers to the nozzles by the thickness of the discharge-hole plate. The increased distance
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`from the pressure chambers to the nozzles causes deterioration in ink ejection properties.
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`[0005] An object of the present invention, which has been made in view of the above problem, is
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`to provide an inkjet head with a configuration that can prevent deterioration in ink ejection
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`properties.
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`Solution to Problem
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`[0006] This inkjet head comprises: a nozzle plate including a plurality of nozzles; a vibration
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`plate including a pressure chamber to store ink to be ejected from the nozzle; a spacer plate
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`containing a piezoelectric layer to apply pressure to the pressure chamber; and a flow path
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`formation substrate between the vibration plate and the nozzle plate; the flow path formation
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`substrate including a communication flow path that communicates with the nozzle and the
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`pressure chamber.
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`[0007] The vibration plate includes a vibration board provided between the pressure chamber
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`and the piezoelectric layer to transmit deformation of the piezoelectric layer to the pressure
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`chamber. The nozzle plate includes an individual circulation flow path provided for each of the
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`plurality of nozzles to discharge ink; and a common circulation flow path into which a plurality
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`of the individual circulation flow paths merge.
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`[0008] In another mode; the nozzle plate includes a nozzle support layer located adjacent to the
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`flow path formation substrate; and a nozzle layer located opposite to the flow path formation
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`substrate across the nozzle support layer. The individual circulation flow path and the common
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`circulation flow path are provided in the nozzle support layer.
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`[0009] In another mode; the nozzle plate is an $01 substrate.
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`In another mode; the common circulation flow path is provided also in the flow path
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`formation substrate.
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`[0010] In another mode; a columnar member is disposed in the common circulation flow path.
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`In another mode; a recess is provided at a part of an outer surface of the nozzle plate over
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`which the common circulation flow path is provided; the recess being recessed toward the
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`common circulation flow path.
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`[0011] In another mode; in plan view; the common circulation flow path includes a curved
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`portion.
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`Advantageous Effects of Invention
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`[0012] The present invention provides an inkjet head with a configuration that can prevent
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`deterioration in ink ejection properties.
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`Brief Description of the Drawings
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`[0013] Fi—gm. 1 is a cross-sectional view showing the structure of an inkjet head in
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`embodiment 1.
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`Egg}. 2 is a perspective view showing the configuration of a nozzle plate in
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`embodiment 1.
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`Figfl. 3 is a cross-sectional view showing the structure of an inkjet head in
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`embodiment 2.
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`Egg}. 4 is a perspective view showing the configuration of a nozzle plate in
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`embodiment 3.
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`Figfl. 5 is a cross-sectional view showing the configuration of a nozzle plate in
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`embodiment 4.
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`Figfl. 6 is a plan view showing the configuration of a nozzle plate in embodiment 5.
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`Figfl. 7 is a cross-sectional view showing the structure of an inkjet head in related art.
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`Egg}. 8 shows parameters in an example.
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`Figfl. 9 shows the relation between the communication flow path length and the
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`negative pressure in an example.
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`Figfl. 10 shows the relation between the communication flow path length and the
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`driving voltage in an example.
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`Detailed Description of Embodiments
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`[0014] Inkjet heads in embodiments based on the present invention are described hereinafter
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`with reference to the drawings.
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`In the embodiments described hereinafter, when reference is
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`made to the number, quantity and the like, the scope of the present invention is not necessarily
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`limited to the number, quantity and the like, unless otherwise noted. Identical or corresponding
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`parts are identically denoted, and the redundant description is not repeated in some cases.
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`It is
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`assumed from the start that the features in the embodiments may be combined as appropriate.
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`Some parts of the drawings are shown not in accordance with the ratio of the actual dimensions
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`but with the ratio being changed to clarify the structure for easier understanding of the structure.
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`[0015] (Embodiment 1: Configuration of Inkjet Head 1)
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`With reference to Figm}. 1 and Figm}. 2, the configuration of an inkjet head 1
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`according to the present embodiment is described. FigFIG. 1 is a cross-sectional view showing
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`the structure of inkjet head 1. FIG. 2 is a perspective view showing the configuration of a nozzle
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`plate 10. The cross section taken along line H in Figfl. 2 corresponds to the cross-sectional
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`view of Figfl. 1.
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`[0016] In F—igfl. 1, the plane on which a nozzle N is provided is defined as an X-Y plane. The
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`directions along the plane and orthogonal to each other are defined as an X direction and a Y
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`direction. The direction orthogonal to the X-Y plane is defined as a Z direction. The Z-axis
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`direction corresponds to the vertical direction.
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`[0017] With reference to Figfl. 1, inkjet head 1 includes nozzle plate 10 and a head chip 110.
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`Nozzle plate 10 has nozzle N to eject ink. Nozzle N extends through nozzle plate 10. Nozzle
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`plate 10 includes a nozzle support layer 11 and a nozzle layer 12. Nozzle support layer 11 has a
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`passage 11a, and nozzle layer 12 has nozzle N which communicates with passage 11a.
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`[0018] A plurality of nozzles N and passages 11a are provided in line along the Y-axis direction,
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`for example. Usually, nozzles N are arranged in a matrix. The number of nozzles (channels) is,
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`for example, 1024 (16 X 64).
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`[0019] As nozzle plate 10, an $01 substrate may be used, for example. Nozzle plate 10 is not
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`limited to an $01 substrate but may be made of, for example, SUS, 42Alloy, or polyimide. A
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`water-repellent film may be formed on the lower face of nozzle plate 10.
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`[0020] Head chip 110 is formed by stacking a plurality of substrates and the like along the Z
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`direction on the upper face of nozzle plate 10. Specifically, head chip 110 is formed by stacking
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`an intermediate substrate 100, a vibration plate 20 including a pressure chamber 21, a spacer
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`substrate 40, and a wiring substrate 50, on nozzle plate 10.
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`[0021] Vibration plate 20 includes a vibration board 30 provided between pressure chamber 21
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`and a piezoelectric layer 60 (described later) to transmit deformation of piezoelectric layer 60 to
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`pressure chamber 21.
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`[0022] Thus, in nozzle plate 10, nozzle support layer 11 is located adjacent to intermediate
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`substrate 100, and nozzle layer 12 is located opposite to intermediate substrate 100 across nozzle
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`support layer 11.
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`[0023] Intermediate substrate 100 has a connection passage 101 which connects nozzle N and
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`pressure chamber 21. Intermediate substrate 100, vibration plate 20, vibration board 30, spacer
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`substrate 40, and wiring substrate 50 have ink supply flow paths 22, 31, 41, 51 which
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`communicate with pressure chamber 21. The flow path of ink formed by the ink supply flow
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`paths connects pressure chamber 21 and an external ink supply flow path provided above wiring
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`substrate 50.
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`[0024] Intermediate substrate 100 is provided for the purpose of providing connection passage
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`101 between nozzle plate 10 and vibration plate 20, for example. Connection passage 101
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`communicates with pressure chamber 21 and nozzle N and adjusts kinetic energy to be applied to
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`ink when the ink is ejected.
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`[0025] Providing connection passage 101 makes it possible for the flow path of ink that leads to
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`nozzle N to have any desired shape.
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`[0026] Intermediate substrate 100 may be made of any material, such as glass, stainless steel,
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`resin, silicon, or the like.
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`[0027] Vibration plate 20 is provided on intermediate substrate 100. Vibration plate 20 includes
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`pressure chamber 21 to store ink. Pressure chamber 21 communicates with nozzle N via
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`connection passage 101 of intermediate substrate 100. A plurality of pressure chambers 21 are
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`provided along the Y-aXis direction for a plurality of nozzles N arranged along the Y-aXis
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`direction, on a one-to-one basis, so that each pressure chamber 21 communicates with
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`corresponding nozzle N. Pressure chamber 21 is provided independently of ink supply flow path
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`22.
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`[0028] Vibration board 30 provided in vibration plate 20 covers an opening 42 in spacer
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`substrate 40 in which piezoelectric layer 60 is contained. Vibration board 30 forms one face
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`(upper face) of pressure chamber 21. Vibration board 30 can be vibrated by piezoelectric layer
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`60 provided on vibration board 30. Vibration of vibration board 30 increases or decreases the
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`pressure in pressure chamber 21.
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`[0029] Spacer substrate 40 allows for a space corresponding to the heights of piezoelectric layer
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`60 and a connection portion 90 (described later) along the Z direction between vibration board
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`30 and wiring substrate 50. Spacer substrate 40 has opening 42 at a location corresponding to
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`the location of piezoelectric layer 60.
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`[0030] Opening 42 extends through spacer substrate 40 in the Z direction. Opening 42 is
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`provided independently of ink supply flow path 41. In opening 42, piezoelectric layer 60 is
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`disposed. Opening 42 is covered with wiring substrate 50. Thus, a closed space S1 is defined
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`around piezoelectric layer 60. Spacer substrate 40 and wiring substrate 50 correspond to a
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`sealing portion to seal piezoelectric layer 60.
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`[0031] Spacer substrate 40 may be made of any material that allows for the above-described
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`space, such as resin member, iron, glass, nickel, stainless steel, silicon, or an alloy, for example.
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`[0032] Wiring substrate 50 includes, for example, an interposer 53, insulating layers 54, 55, a
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`through-substrate via 56, an interconnection 57, an insulating layer 58, an interconnection 52, an
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`insulating layer 59, and ink supply flow path 51.
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`[0033] Interposer 53 is in the shape of a plate. Interposer 53 is the base of wiring substrate 50.
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`Insulating layer 54 covers the upper face of interposer 53. Insulating layer 55 covers the lower
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`face of interposer 53.
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`[0034] Through-substrate via 56 is provided in a through-hole P extending through insulating
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`layer 54, interposer 53, and insulating layer 55. Interconnection 57 is provided on the upper face
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`of insulating layer 54 and electrically connected to the upper end of through-substrate via 56.
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`[003 5] Insulating layer 58 covers the upper face of interconnection 57 and the upper face of the
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`part of insulating layer 54 where interconnection 57 is not provided.
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`[003 6] Interconnection 52 is provided on the lower face of insulating layer 55 and electrically
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`connected to the lower end of through-substrate via 56. Interconnection 52 is connected to a
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`controller (not shown) to control the voltage to be applied to piezoelectric layer 60 via through-
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`substrate via 56 and interconnection 57.
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`[0037] Interconnections 52, 57 may be formed by, for example, patterning conductive metal (e. g.
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`Cr, Ti, and Au) by photolithography. For example, interconnections 52, 57 may be formed by
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`forming films of Cr and Au on the substrate in this order, then patterning Au, and then patterning
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`Cr. Cr or Ti is used as an adhesion layer for Au.
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`[003 8] Insulating layer 59 covers the lower face of the part of interconnection 52 where a bump
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`91 is not formed, and covers the lower face of the part of insulating layer 55 where
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`interconnection 52 is not provided. Ink supply flow path 51 extends through insulating layer 58,
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`insulating layer 54, interposer 53, insulating layer 55, and insulating layer 59.
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`[0039] Piezoelectric layer 60 is electrically connected to interconnection 52 provided in wiring
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`substrate 50 via connection portion 90 (described later). Each piezoelectric layer 60 is provided
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`for a corresponding one of a plurality of nozzles N arranged along the Y-axis direction.
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`Piezoelectric layer 60 is provided on vibration board 30.
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`[0040] Piezoelectric layer 60 includes a piezoelectric portion 61 formed by a piezoelectric layer,
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`a first electrode 62 covering one surface of piezoelectric portion 61, and a second electrode 63
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`covering the other surface of piezoelectric portion 61.
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`[0041] First electrode 62 is electrically connected to interconnection 52 via connection portion
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`90. Connection portion 90 connects first electrode 62 and interconnection 52 along the Z
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`direction. Connection portion 90 includes bump 91 formed on wiring substrate 50.
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`[0042] Bump 91 is formed by, for example, wire bonding using gold as the material. Bump 91 is
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`formed, for example, on the lower face of interconnection 52. A conductive material 92 is
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`applied to the lower end of bump 91. Specifically, conductive material 92 is, for example, a
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`conductive adhesive. The conductive adhesive is an adhesive that contains conductive powdered
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`metal (e.g. powdered silver).
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`[0043] Thus, connection portion 90 electrically connects wiring substrate 50 and piezoelectric
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`layer 60 via bump 91 formed on wiring substrate 50 and via conductive material 92 applied to
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`bump 91.
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`[0044] Second electrode 63 is in contact with an electrode layer (not shown) formed on vibration
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`board 30. The electrode layer formed on vibration board 30 fiinctions as an electrode that
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`electrically connects second electrode 63 and the above-described controller. Second electrode
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`63 is connected to the controller via, for example, an interconnection (not shown) connected to
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`the electrode layer formed on vibration board 30.
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`[0045] The electrode layer may be formed by, for example, patterning conductive metal (e.g. Cr,
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`Ti, and Au) by photolithography on vibration board 30. For example, the electrode layer may be
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`formed by forming films of Cr and Au on the substrate in this order, then patterning Au, and then
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`patterning Cr. Cr or Ti is used as an adhesion layer for Au.
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`[0046] First electrode 62 is connected to the controller via connection portion 90,
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`interconnection 52, through-substrate via 56, and interconnection 57. Second electrode 63 is
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`connected to the controller via the electrode layer formed on vibration board 30. Thus,
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`piezoelectric layer 60 can operate under the control of the controller.
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`[0047] Operation of piezoelectric layer 60 causes vibration board 30 to vibrate. This causes a
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`change in internal pressure in pressure chamber 21, thereby allowing the ink that has been
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`supplied to pressure chamber 21 to eject from nozzle N.
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`[0048] An epoxy adhesive is preferably used to bond the above-described intermediate substrate
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`100 and nozzle plate 10. If glass is used as the material of intermediate substrate 100 and silicon
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`is used as the material of nozzle plate 10, then anodic bonding may be used to bond the glass and
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`the silicon.
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`[0049] It is preferable that the differences in coefficient of thermal expansion between the
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`substrates be sufficiently small. This can prevent the substrates from warping and coming off
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`from one another due to temperature changes during bonding of the substrates and due to heat
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`generated during operation of inkjet head 1.
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`[0050] For example, silicon is used as the material of the above-described vibration plate 20,
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`vibration board 30, and wiring substrate 50, and 42Alloy (alloy containing 42% by weight of
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`nickel, 57% by weight of iron, the balance including a very small amount of additive [e. g.
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`copper, manganese, or the like]) is used as the material of spacer substrate 40. This achieves
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`small differences in coefficient of thermal expansion between the substrates.
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`[0051] In inkjet head 1 in the above-described embodiment, vibration board 30 is integrated with
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`vibration plate 20. However, inkjet head 1 is not limited to such a configuration. Vibration
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`board 30 and vibration plate 20 may be separately provided.
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`[0052] (Nozzle Plate 10)
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`With reference to Figfl. 2, the configuration of nozzle support layer 11 which
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`constitutes nozzle plate 10 is described. Nozzle support layer 11 includes individual circulation
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`flow paths 111 each provided for a corresponding one of a plurality of nozzles N and each
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`communicating with a corresponding passage 11a to discharge ink. Further, nozzle support layer
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`11 has a common circulation flow path 113 into which a plurality of individual circulation flow
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`paths 111 merge.
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`In F—igfl. 2, individual circulation flow paths 111 extend in the X direction,
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`and common circulation flow path 113 linearly extends in the Y direction.
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`[0053] As described above, 1024 (16 X 64) nozzles N (channels) are provided, for example.
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`Individual circulation flow path 111 is provided for each nozzle N, whereas a single common
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`circulation flow path 113 is provided for all the nozzles N. Alternatively, nozzles N may be
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`divided into some groups, and a plurality of common circulation flow paths 113 may be provided
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`for the respective groups.
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`[0054] Thus, inkjet head 1 in the present embodiment includes individual circulation flow path
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`111 provided for each of a plurality of nozzles N to discharge ink, and common circulation flow
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`path 113 into which a plurality of individual circulation flow paths 111 merge. Thus, as shown
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`in F—i—gfl. 1, the ink supplied to nozzle N but not ejected to the outside is discharged through
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`individual circulation flow path 111 to common circulation flow path 113 and is then supplied
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`

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`again, through a circulation line L1, to ink supply flow paths 22, 31, 41, 51 which communicate
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`with pressure chamber 21. In this way, deterioration in ink ejection properties can be prevented.
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`[0055] Since individual circulation flow path 111 and common circulation flow path 113 are
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`provided in the same nozzle support layer 11, an additional substrate is not required to
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`manufacture inkjet head 1 in the present embodiment. Therefore, increase in cost can be
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`prevented.
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`[0056] The length of individual circulation flow path 111, from pressure chamber 21 to nozzle
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`plate 10, can be shortened compared with the configuration having an additional substrate for
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`individual circulation flow path 111. This achieves low-voltage driving. Further, a shortened
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`path from pressure chamber 21 to nozzle plate 10 reduces the negative pressure, thus preventing
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`increase in negative pressure at pressure chamber 21.
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`[0057] Further, since there is no need to make nozzle support layer 11 thinner to provide
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`individual circulation flow path 111 and common circulation flow path 113, it is possible to
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`avoid generation of cracks during bonding of nozzle support layer 11 and the substrates in head
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`chip 110 in the manufacturing process and also avoid their warps due to heat. Thus, the
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`productivity of inkjet head 1 can be improved.
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`[005 8] Although the present embodiment discloses a configuration in which the ink discharged
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`from the common circulation flow path circulates through circulation line L1, it is needless to
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`say that a configuration without circulation is also possible. For example, ink may be discharged
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`from common circulation flow path 113 without passing through circulation line L1.
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`[0059] (Embodiment 2: Configuration of Inkj et Head 1A)
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`With reference to Figm}. 3, the configuration of an inkjet head 1A according to the
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`present embodiment is described. Figm}. 3 is a cross-sectional view showing the structure of
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`inkjet head 1A. The cross section taken along line H in Figfl. 2 corresponds to the cross-
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`sectional view of Figfl. 1.
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`[0060] The basic configuration is the same as the configuration of inkjet head 1 in the above-
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`described embodiment 1. The difference is that common circulation flow path 113 is provided
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`not only in nozzle support layer 11 but also in intermediate substrate 100.
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`[0061] Inkjet head 1A having this configuration can bring about the same advantageous effects
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`as those of inkjet head 1 in the above-described embodiment 1. Further, common circulation
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`flow path 113 extended into intermediate substrate 100 allows for an enlarged cross section of
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`

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`common circulation flow path 113 and thus an increased quantity of flow of circulating ink,
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`without increasing the size of inkjet head 1A in the Z direction.
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`[0062] Further, a step portion D1, which is formed at the connecting portion between individual
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`circulation flow path 111 and common circulation flow path 113, causes a flow from individual
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`circulation flow path 111 drawn into common circulation flow path 113. Thus, air bubbles in
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`individual circulation flow path 111 can be easily drawn into the flow in common circulation
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`flow path 113. This can reduce air bubbles staying in passage 11a and more effectively prevent
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`deterioration in ink ejection properties.
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`[0063] (Embodiment 3: Configuration of Inkj et Head 1B)
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`With reference to Figm}. 4, the configuration of an inkjet head 1B according to the
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`present embodiment is described. Figfl. 4 is a perspective view showing the configuration of
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`nozzle plate 10.
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`[0064] The basic configuration is the same as the configuration of inkjet head 1 in the above-
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`described embodiment 1. The difference is that a plurality of columnar members 113P are
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`arranged in common circulation flow path 113 provided in nozzle plate 10. Columnar members
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`113P may be disposed at any positions.
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`In order not to affect the flow of ink from individual
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`circulation flow path 111 to common circulation flow path 113, each columnar member 113P is
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`provided preferably at a position that does not face individual circulation flow path 111. For
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`example, each columnar member 113P may be provided between adjacent individual circulation
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`flow paths 111.
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`[0065] Inkjet head 1B having this configuration can bring about the same advantageous effects
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`as those of inkjet head 1 in the above-described embodiment 1. Further, nozzle layer 12 in
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`nozzle plate 10 serves as a damper (shock absorber) by deforming. Columnar members 113P
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`provided in common circulation flow path 113 reinforce nozzle layer 12. Also, columnar
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`members 113P reduce deformation of nozzle layer 12 if more deformation than is expected
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`occurs in nozzle layer 12. This can avoid damage to nozzle layer 12.
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`[0066] Further, the damper, which needs to bend toward intermediate substrate 100, requires a
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`gap between columnar members 113P and intermediate substrate 100. A possible method
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`includes the following (i) to (iii):
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`(i) removing a film (e. g. an oxide film) that covers the surface of nozzle support layer 11,
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`only from the parts of columnar members 113P,
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`(ii) applying an adhesive to the surface of nozzle support layer 11, other than columnar
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`members 113P, to bond it to intermediate substrate 100, and
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`(iii) the adhesive containing beads for controlling the thickness.
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`[0067] (Embodiment 4: Configuration of Inkjet Head 1C)
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`With reference to Figm}. 5, the configuration of an inkjet head 1C according to the
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`present embodiment is described. Figm}. 5 is a cross-sectional view showing the configuration
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`of nozzle plate 10.
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`[0068] The basic configuration is the same as the configuration of inkjet head 1 in the above-
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`described embodiment 1. The difference is that a recess 12r is provided at a part of the outer
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`surface (nozzle surface) 12a of nozzle plate 10 over which common circulation flow path 113 is
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`provided, the recess 12r being recessed toward common circulation flow path 113. The area
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`where recess 12r is provided preferably includes the area where common circulation flow path
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`113 is provided.
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`[0069] Inkjet head 1C having this configuration can bring about the same advantageous effects
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`as those of inkjet head 1 in the above-described embodiment 1. Further, during cleaning of outer
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`surface (nozzle surface) 12a of nozzle plate 10, a blade, made of an elastic body, is made to slide
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`on outer surface (nozzle surface) 12a while being in contact with the surface 12a. At this time,
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`the moving direction of blade B1 is the Y direction in the drawing, and the width of the blade in
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`the X direction is broader than the width of recess 12r. Thus, the bottom face of recess 12r is
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`prevented from being touched by blade B1.
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`[0070] This prevents deformation of nozzle layer 12 during cleaning of outer surface (nozzle
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`surface) 12a with blade B 1, thus avoiding damage to nozzle layer 12.
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`[0071] (Embodiment 5: Configuration of Inkjet Head 1D)
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`With reference to Figm}. 6, the configuration of an inkjet head 1D according to the
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`present embodiment is described. Figm}. 6 is a plan view showing the configuration of nozzle
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`plate 10.
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`[0072] The basic configuration is the same as the configuration of inkjet head 1 in the above-
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`described embodiment 1. The difference is that a common circulation flow path 113W provided
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`in nozzle plate 10 includes a curved portion. Common circulation flow path 113 of inkjet head 1
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`in embodiment 1 shown in Figm}. 2 has a linear shape along the Y direction. On the other
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`hand, common circulation flow path 113W of inkjet head 1C in the present embodiment has a
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`

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`gentle S-curve in plan view. Specifically, a side wall ll3Q which constitutes common
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`circulation flow path 113W of nozzle plate 10 has a wavy shape toward circulation flow paths.
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`[0073] Inkjet head 1D having this configuration can bring about the same advantageous effects
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`as those of inkjet head 1 in the above-described embodiment 1. Further, since side wall 113Q
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`which constitutes common circulation flow path 113W of nozzle plate 10 has a wavy shape
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`toward circulation flow paths, side wall ll3Q serves as a member to reinforce nozzle layer 12.
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`Also, if more deformation (stress) than is expected occurs in nozzle layer 12, cracks in a plane of
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`cleavage of silicon in nozzle support layer 11 is prevented under stress. Therefore, cracks can be
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`prevented during assembly and driving of the head.
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`[0074] The wavy shape of common circulation flow path 113W is preferably a pattern such that
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`individual circulation flow paths 111 are the longest. This allows thickened fluid and air bubbles
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`to be easily discharged.
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`[0075] (Example)
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`An example is described hereinafter. Inkjet head 1 having the configuration shown in
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`F—igfl}. 1 and an inkjet head 1X having the configuration shown in Figli}. 7 were compared
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`with each other in performance. Inkjet head 1X shown in Egg}. 7 includes a circulation plate
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`70 having common circulation flow path 113 and an ink supply flow path 71, and nozzle support
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`layer 11 has individual circulation flow path 111. Accordingly, the entire thickness of inkjet
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`head 1X in the Z direction is larger than that of inkjet head 1.
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`[0076] Here, the length of the ink flow path from pressure chamber 21 to nozzle layer 12,
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`formed by connection passage 101, passage 11a, and ink supply flow path 71, is defined as a
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`"communication flow path length". The "communication flow path length" of inkjet head 1
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`shown in F—igfl. 1 is 270 pm. On the other hand, the "communication flow path length" of
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`inkjet head 1X shown in Figm}. 6 is 420 um.
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`[0077] Fi—gm. 8 shows the relation between the negative pressure (kPa) of pressure chamber 21
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`and the driving voltage (V) for driving piezoelectric layer 60 for each communication flow path
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`length. A preferable target value of the negative pressure (kPa) is -3 60 (kPa) or more, and a
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`preferable target value of the driving voltage is 25 V or less.
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`[0078] When the "communication flow path length" is 450 um, the negative pressure is -407
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`(kPa) and the driving voltage is 27.8 (V). When the "communication flow path length" is 350
`
`um, the negative pressure is -3 68 (kPa) and the driving voltage is 26.2 (V). When the
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`

`

`"communication flow path length" is 300 um, the negative pressure is -3 56 (kPa) and the driving
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`voltage is 25.1 (V). When the "communication flow path length" is 250 um, the negative
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`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).
`
`Egg}. 9 shows the relation between the "communication flow path length" and the negative
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`pressure. Figm}. 10 shows the relation between the "communication flow path length" and the
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`driving voltage.
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`[0079] It is shown that a "communication flow path length" of about 300 um or less can achieve
`
`a negative pressure (kPa) of -3 60 (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 Figm}. 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, inkjet head 1X
`
`shown in Figm}. 7, whose "communication flow path length" is 420 um, cannot satisfy the
`
`target values of the negative pressure and the driving voltage.
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`[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
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`[0081] 1, 1A, 1B, 1C, 1D: inkjet head, 10: nozzle plate, 11: nozzle support layer, 11a: passage,
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`12: nozzle layer, 12r: recess, 20: vibration plate, 21: pressure chamber, 22, 41, 51, 71, 102: ink
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`supply flow path, 30: vibration board, 40: spacer substrate, 42: opening, 50: wiring substrate, 52,
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`57: interconnection, 53: interposer, 54, 55, 58, 59: insulating layer, 56: through-substrate via, 60:
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`piezoelectric layer, 61: piezoelectric portion, 62: first electrode, 63: second electrode, 90:
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`connection portion, 91: bump, 92: conductive material, 100: intermediate substrate, 101:
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`connection passage, 110: head chip, 111: individual circulation flow path, 113, 113W: common
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`circulation flow path, 113P: columnar member, 113Q: side wall, B 1: blade, D1: step portion, N:
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`nozzle
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`