WO2015182228A1 - Piezoelectric actuator, piezoelectric actuator manufacturing method, inkjet head, and inkjet printer - Google Patents

Piezoelectric actuator, piezoelectric actuator manufacturing method, inkjet head, and inkjet printer Download PDF

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Publication number
WO2015182228A1
WO2015182228A1 PCT/JP2015/058710 JP2015058710W WO2015182228A1 WO 2015182228 A1 WO2015182228 A1 WO 2015182228A1 JP 2015058710 W JP2015058710 W JP 2015058710W WO 2015182228 A1 WO2015182228 A1 WO 2015182228A1
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Prior art keywords
film
thin film
piezoelectric thin
piezoelectric
upper electrode
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PCT/JP2015/058710
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French (fr)
Japanese (ja)
Inventor
三嘉 宮井
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コニカミノルタ株式会社
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Priority to JP2016523361A priority Critical patent/JPWO2015182228A1/en
Publication of WO2015182228A1 publication Critical patent/WO2015182228A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/06—Forming electrodes or interconnections, e.g. leads or terminals
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/09—Forming piezoelectric or electrostrictive materials
    • H10N30/093—Forming inorganic materials
    • H10N30/097—Forming inorganic materials by sintering
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/88—Mounts; Supports; Enclosures; Casings

Definitions

  • the present invention relates to a piezoelectric actuator having a lower electrode, a piezoelectric thin film and an upper electrode on a substrate, a method for manufacturing the piezoelectric actuator, an inkjet head, and an inkjet printer.
  • piezoelectric materials such as lead zirconate titanate (PZT) have been used as electromechanical conversion elements such as drive elements and sensors.
  • MEMS Micro Electro Mechanical Systems
  • Si silicon
  • high-precision processing using semiconductor process technology such as film formation and photolithography can be performed, and miniaturization and high density can be realized.
  • the elements can be collectively processed on a large-area wafer, the cost can be reduced.
  • there is an advantage that the conversion efficiency of mechanical electricity is improved and the characteristics of the drive element and the sensitivity of the sensor are improved.
  • An inkjet printer is known as an application example of a device using such a MEMS element.
  • a two-dimensional image is recorded on a recording medium by controlling the ejection of ink while moving an inkjet head having a plurality of channels for ejecting liquid ink relative to the recording medium such as paper or cloth. Formed.
  • the ink can be ejected by using a pressure actuator (piezoelectric, electrostatic, thermal deformation, etc.) or by generating bubbles in the ink inside the tube by heat.
  • a pressure actuator piezoelectric, electrostatic, thermal deformation, etc.
  • the piezoelectric actuator has advantages such as high output, modulation, high responsiveness, and choice of ink, and has been frequently used in recent years.
  • it is suitable to use an inkjet head using a thin film piezoelectric body.
  • the ink jet head is required to be capable of ejecting ink having a high viscosity of 10 cp (0.01 Pa ⁇ s) or more.
  • the piezoelectric thin film (ferroelectric thin film) requires high piezoelectric characteristics (piezoelectric constant d 31 ) and displacement generation force (film thickness of 1 ⁇ m or more).
  • methods for forming a piezoelectric material such as PZT on a substrate such as Si include chemical film formation methods such as CVD (Chemical Vapor Deposition), physical methods such as sputtering and ion plating, and sol-gel.
  • CVD Chemical Vapor Deposition
  • physical methods such as sputtering and ion plating
  • sol-gel sol-gel
  • the growth method in the liquid phase such as the method is known.
  • the upper limit of the thickness of the thin film obtained by these manufacturing methods is about 10 ⁇ m. If the film thickness exceeds that, cracks and film peeling occur, and desired characteristics cannot be obtained.
  • the deposited PZT exhibits a good piezoelectric effect when the crystal has a perovskite structure.
  • the perovskite structure ideally has a cubic unit cell, and is arranged at each vertex of the cubic A, metal B arranged at the body center, and arranged at each face center of the cubic crystal. It is an ABO 3 type crystal structure composed of oxygen O. Crystals having a perovskite structure include tetragonal crystals, orthorhombic crystals, rhombohedral crystals and the like in which cubic crystals are distorted.
  • the PZT thin film formed on the electrode on the Si substrate becomes a polycrystal composed of an aggregate of a plurality of crystals due to a difference in lattice constant from the crystal of the electrode.
  • this polycrystal is composed of granular crystals (granular crystals) with a particle size of several hundreds of nanometers, or a width of several hundreds of nanometers and one elongated crystal grain in the film thickness direction. A certain columnar crystal is gathered together.
  • Patent Document 1 an insulator layer is formed on the lower electrode so as to cover the piezoelectric thin film and the upper electrode. Since the side surface of the piezoelectric thin film is shielded from the atmosphere by the insulator layer, it is possible to prevent the occurrence of side leakage due to the intake of moisture in the atmosphere. However, in the configuration in which the piezoelectric thin film is covered with the insulator layer, the piezoelectric layer is deteriorated because displacement (stretching) of the piezoelectric thin film is inhibited by the insulator layer.
  • Patent Document 2 the surface of the piezoelectric thin film is polished and smoothed, thereby eliminating the location where the electric field concentrates between the upper electrode and the lower electrode (the recessed area on the surface of the piezoelectric thin film). The withstand voltage is improved without deteriorating the piezoelectric characteristics.
  • the piezoelectric thin film is composed of a polycrystalline body in which crystals having different particle sizes are mixed. By mixing small crystal grains with large crystal grains, gaps are prevented from forming at the grain boundaries between the large crystal grains, and the insulation and piezoelectric characteristics of the piezoelectric thin film are improved. ing.
  • Patent Document 4 by forming a low dielectric material in a region where the grain boundary of the piezoelectric thin film is exposed, leakage current flowing through the grain boundary of the piezoelectric thin film is reduced and voltage resistance is improved. Yes.
  • the low dielectric material is such that the surplus composition generated in the crystal growth process due to the firing of the piezoelectric thin film is driven to the grain boundary as the crystal grain of the piezoelectric thin film grows, and is finally passed through the grain boundary. It is thought that it was pushed to the surface layer.
  • JP-A-10-226071 see claims 1 and 6, paragraphs [0006], [0023], [0025], [0038], FIG. 2, FIG. 3 etc.
  • JP-A-10-264385 (refer to claim 1, paragraphs [0032], [0034], [0054], FIG. 3, etc.)
  • Japanese Patent Laid-Open No. 2002-084012 see claims 1 and 2, paragraphs [0004], [0006], [0034], [0065], FIG. 3, FIG. 6, FIG. 7, etc.
  • Japanese Patent Laid-Open No. 10-217458 (refer to claim 1, paragraphs [0007] and [0035], FIG. 2, FIG. 3, and FIG. 5)
  • the present invention has been made in order to solve the above-described problems, and its purpose is to prevent dielectric breakdown and leakage current (side leakage) of the piezoelectric thin film without impairing the displacement of the piezoelectric thin film and deteriorating the piezoelectric characteristics.
  • the present invention provides a piezoelectric actuator and a method for manufacturing the same, an ink jet head provided with the piezoelectric actuator, and an ink jet printer.
  • a piezoelectric actuator is a piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode in this order on a substrate, wherein the piezoelectric thin film includes a polycrystalline film including a plurality of crystals, and a plurality of piezoelectric films. And an altered film in which grain boundaries have disappeared due to integral alteration of the crystal, and the altered film is formed at least in a region protruding from the outer shape of the upper electrode in the piezoelectric thin film on the lower electrode. And is exposed on the surface opposite to the substrate in the region.
  • a method of manufacturing a piezoelectric actuator includes a step of forming a lower electrode on a substrate, and forming a piezoelectric thin film by forming a polycrystalline film including a plurality of crystals on the lower electrode.
  • a plurality of crystals contained in the polycrystalline film are integrally modified to form a modified film in which the grain boundaries disappear, on at least the surface of the region.
  • FIG. 1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention.
  • FIG. FIG. 2 is a plan view showing a schematic configuration of an actuator of an ink jet head provided in the ink jet printer, and a cross-sectional view taken along line A-A ′ in the plan view. It is sectional drawing of the said inkjet head. It is sectional drawing which shows the detailed structure of the said actuator. It is explanatory drawing which shows typically the horizontal cross section of the polycrystalline film and alteration film which comprise the piezoelectric thin film of the said actuator. It is sectional drawing of the piezoelectric actuator which does not have the said altered film. It is sectional drawing which shows the manufacturing process of the said inkjet head.
  • the numerical value range includes the values of the lower limit A and the upper limit B.
  • FIG. 1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer 1 according to the present embodiment.
  • the ink jet printer 1 is a so-called line head type ink jet recording apparatus in which an ink jet head 21 is provided in a line shape in the width direction of a recording medium in the ink jet head unit 2.
  • the ink jet printer 1 includes an ink jet head unit 2, a feed roll 3, a take-up roll 4, two back rolls 5 and 5, an intermediate tank 6, a liquid feed pump 7, a storage tank 8, and a fixing tank. And a mechanism 9.
  • the inkjet head unit 2 ejects ink from the inkjet head 21 toward the recording medium P to perform image formation (drawing) based on image data, and is disposed in the vicinity of one back roll 5. Details of the inkjet head 21 will be described later.
  • the feeding roll 3, the take-up roll 4 and the back rolls 5 are members each having a cylindrical shape that can rotate around its axis.
  • the feeding roll 3 is a roll that feeds the long recording medium P wound around the circumferential surface toward the position facing the inkjet head unit 2.
  • the feeding roll 3 is rotated by driving means (not shown) such as a motor, thereby feeding the recording medium P in the X direction in FIG.
  • the take-up roll 4 is taken out from the take-out roll 3 and takes up the recording medium P on which the ink is ejected by the inkjet head unit 2 around the circumferential surface.
  • Each back roll 5 is disposed between the feed roll 3 and the take-up roll 4.
  • One back roll 5 located on the upstream side in the conveyance direction of the recording medium P is opposed to the inkjet head unit 2 while winding the recording medium P fed by the feeding roll 3 around and supporting the recording medium P.
  • Transport toward The other back roll 5 conveys the recording medium P from a position facing the inkjet head unit 2 toward the take-up roll 4 while being wound around and supported by a part of the peripheral surface.
  • the intermediate tank 6 temporarily stores the ink supplied from the storage tank 8.
  • the intermediate tank 6 is connected to a plurality of ink tubes 10, adjusts the back pressure of ink in each inkjet head 21, and supplies ink to each inkjet head 21.
  • the liquid feed pump 7 supplies the ink stored in the storage tank 8 to the intermediate tank 6, and is arranged in the middle of the supply pipe 11.
  • the ink stored in the storage tank 8 is pumped up by the liquid feed pump 7 and supplied to the intermediate tank 6 through the supply pipe 11.
  • the fixing mechanism 9 fixes the ink ejected to the recording medium P by the inkjet head unit 2 on the recording medium P.
  • the fixing mechanism 9 includes a heater for heat-fixing the discharged ink on the recording medium P, a UV lamp for curing the ink by irradiating the discharged ink with UV (ultraviolet light), and the like. Yes.
  • the recording medium P fed from the feeding roll 3 is conveyed to the position facing the inkjet head unit 2 by the back roll 5, and ink is ejected from the inkjet head unit 2 to the recording medium P. Thereafter, the ink ejected onto the recording medium P is fixed by the fixing mechanism 9, and the recording medium P after ink fixing is taken up by the take-up roll 4.
  • the line head type inkjet printer 1 ink is ejected while the recording medium P is conveyed while the inkjet head unit 2 is stationary, and an image is formed on the recording medium P.
  • the ink jet printer 1 may be configured to form an image on a recording medium by a serial head method.
  • the serial head method is a method of forming an image by ejecting ink by moving an inkjet head in a direction orthogonal to the transport direction while transporting a recording medium.
  • FIG. 2 is a plan view showing a schematic configuration of the actuator 21a (piezoelectric actuator) of the inkjet head 21 and a cross-sectional view taken along the line AA ′ in the plan view.
  • FIG. 3 is a cross-sectional view of the inkjet head 21 in which the nozzle substrate 31 is joined to the actuator 21a of FIG.
  • the inkjet head 21 has a thermal oxide film 23, a lower electrode 24, a piezoelectric thin film 25, and an upper electrode 26 in this order on a substrate 22 having a plurality of pressure chambers 22a (openings).
  • the substrate 22 is composed of a semiconductor substrate made of a single crystal Si (silicon) alone having a thickness of, for example, about 300 to 750 ⁇ m, or an SOI (Silicon On Insulator) substrate.
  • FIG. 2 shows a case where the substrate 22 is configured by an SOI substrate.
  • the SOI substrate is obtained by bonding two Si substrates through an oxide film.
  • the upper wall of the pressure chamber 22a in the substrate 22 (the wall positioned on the side where the piezoelectric thin film 25 is formed with respect to the pressure chamber 22a) constitutes a vibration plate 22b serving as a driven film. Along with this displacement (vibration), pressure is applied to the ink in the pressure chamber 22a.
  • the thermal oxide film 23 is made of, for example, SiO 2 (silicon oxide) having a thickness of about 0.1 ⁇ m, and is formed for the purpose of protecting and insulating the substrate 22.
  • the lower electrode 24 is a common electrode provided in common to the plurality of pressure chambers 22a, and is configured by laminating a Ti (titanium) layer and a Pt (platinum) layer.
  • the Ti layer is formed in order to improve the adhesion between the thermal oxide film 23 and the Pt layer.
  • the thickness of the Ti layer is, for example, about 0.02 ⁇ m, and the thickness of the Pt layer is, for example, about 0.1 ⁇ m.
  • the piezoelectric thin film 25 is composed of a ferroelectric thin film made of, for example, PZT (lead zirconate titanate), and is provided corresponding to each pressure chamber 22a.
  • the film thickness of the piezoelectric thin film 25 is, for example, not less than 1 ⁇ m and not more than 10 ⁇ m.
  • the upper electrode 26 is an individual electrode provided corresponding to each pressure chamber 22a, and is configured by laminating a Ti layer and a Pt layer.
  • the Ti layer is formed in order to improve the adhesion between the piezoelectric thin film 25 and the Pt layer.
  • the thickness of the Ti layer is, for example, about 0.02 ⁇ m, and the thickness of the Pt layer is, for example, about 0.1 to 0.2 ⁇ m.
  • the upper electrode 26 is provided so as to sandwich the piezoelectric thin film 25 from the film thickness direction with the lower electrode 24. Note that a layer made of gold (Au) may be formed instead of the Pt layer.
  • the lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 constitute a thin film piezoelectric element 27 for discharging ink in the pressure chamber 22a to the outside.
  • the thin film piezoelectric element 27 is driven based on a voltage (drive signal) applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26.
  • the ink jet head 21 is formed by arranging the thin film piezoelectric element 27 and the pressure chamber 22a vertically and horizontally.
  • a nozzle substrate 31 is bonded to the opposite side of the pressure chamber 22a from the diaphragm 22b.
  • the nozzle substrate 31 is formed with ejection holes (nozzle holes) 31a for ejecting ink stored in the pressure chambers 22a to the outside as ink droplets.
  • Ink supplied from the intermediate tank 6 is stored in the pressure chamber 22a.
  • the piezoelectric thin film 25 when a voltage is applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is in a direction perpendicular to the thickness direction (substrate) according to the potential difference between the lower electrode 24 and the upper electrode 26. (Direction parallel to the surface of 22). Then, due to the difference in length between the piezoelectric thin film 25 and the diaphragm 22b, a curvature is generated in the diaphragm 22b, and the diaphragm 22b is displaced (curved or vibrated) in the thickness direction.
  • the inkjet head 21a of the present embodiment since the voltage resistance of the piezoelectric thin film 25 of the piezoelectric actuator 21a is high, a high electric field can be applied to the piezoelectric thin film 25. As a result, it is possible to discharge ink using high-viscosity ink, and it is possible to realize the inkjet printer 1 that is advantageous for high-speed and high-definition drawing.
  • FIG. 4 is a cross-sectional view showing a detailed configuration of the piezoelectric actuator 21a.
  • the thermal oxide film 23 is not shown for convenience.
  • the piezoelectric thin film 25 of the piezoelectric actuator 21a has a polycrystalline film 25p and an altered film 25m.
  • the polycrystalline film 25p is a film made of an aggregate of a plurality of crystals (for example, columnar crystals).
  • the altered film 25m is a film in which grain boundaries disappear due to integral alteration of a plurality of crystals, and is, for example, an amorphous structure (amorphous) film.
  • alteration refers to a change in the properties of a substance, but here, an aggregate of a plurality of crystals having a grain boundary (polycrystalline structure) is integrated into a structure having no grain boundary (for example, By changing to an (amorphous structure), it means eliminating the property of allowing moisture in the atmosphere to permeate through grain boundaries.
  • alteration can be realized by irradiating a laser beam of a predetermined wavelength to a film having a polycrystalline structure and heating it to melt and solidify the irradiated portion.
  • FIG. 5 schematically shows a horizontal cross section of the polycrystalline film 25p and the altered film 25m observed with a scanning electron microscope (SEM). As shown in the figure, in the polycrystalline film 25p, there are grain boundaries between the crystals, but in the altered film 25m, there is no grain boundary as seen in the polycrystalline film 25p. It has a crystalline structure.
  • the piezoelectric thin film 25 has a terrace region R1 (a portion where the piezoelectric thin film 25 protrudes without being covered by the upper electrode 26) protruding from the outer shape of the upper electrode 26 on the lower electrode 24. That is, the piezoelectric thin film 25 is sandwiched between the lower electrode 24 and the upper electrode 26 in portions other than the terrace region R1.
  • the above-described altered film 25m is formed at least in the terrace region R1. More specifically, in the terrace region R1 of the piezoelectric thin film 25, the polycrystalline film 25p and the altered film 25m are laminated in this order from the substrate 22 side. As a result, the altered film 25m is exposed on the surface opposite to the substrate 22 in the terrace region R1.
  • the side surface (end surface) of the upper electrode 26 is separated from the side surface (end surface) of the piezoelectric thin film 25, and these side surfaces are not located on the same plane.
  • FIG. 6 is a cross-sectional view of the piezoelectric actuator 21a 'when the altered film 25m is not formed in the terrace region R1.
  • the terrace region R1 moisture in the atmosphere is taken into the inside from the surface opposite to the substrate 22 of the piezoelectric thin film 25 through the crystal grain boundary of the polycrystalline film 25p. It is considered that dielectric breakdown of the piezoelectric thin film 25 occurs and a leak current is likely to occur between the end portion of the upper electrode 26 and the lower electrode 24.
  • a modified film 25m is formed in the terrace region R1, and the modified film 25m is exposed on the surface opposite to the substrate 22 in the terrace region R1. It is possible to suppress the moisture from being taken into the inside of the piezoelectric thin film 25 by the altered film 25m having no grain boundary. Thereby, dielectric breakdown of the piezoelectric thin film 25 caused by the moisture and generation of leakage current can be suppressed, and voltage resistance can be improved. That is, it is possible to suppress the occurrence of a leak current other than the side surface of the piezoelectric thin film 25.
  • the piezoelectric thin film 25 is covered with an insulating layer or the like and cut off from the atmosphere, for example, the insulator Unlike the conventional case where the layer is provided, the piezoelectric characteristics are not deteriorated due to the inhibition of the displacement of the piezoelectric thin film 25.
  • the altered film 25m has an amorphous structure having no grain boundary, it is possible to reliably suppress moisture in the atmosphere from being taken into the multilayer film 25a via the altered film 25m. As a result, it is possible to reliably obtain the above-described effects such as the improvement of the voltage resistance by suppressing the occurrence of dielectric breakdown and leakage current due to the moisture.
  • the lower electrode 24 and the substrate 22 exist on the substrate 22 side of the piezoelectric thin film 25, and do not come into contact with the atmosphere.
  • the opposite side of the piezoelectric thin film 25 from the substrate 22 is in direct contact with the atmosphere.
  • the altered film 25m is formed by alteration of PZT constituting the polycrystalline film 25p, and the material itself is the same as the polycrystalline film 25p. Therefore, since the polycrystalline film 25p and the altered film 25m are formed in this order from the substrate 22 side and have a laminated structure of the same material, it is possible to ensure high adhesion between these films.
  • the above-described altered film 25m is formed by altering the polycrystalline structure by laser light irradiation as described above (the entire manufacturing method of the piezoelectric actuator 21a will be described later).
  • the altered film 25m is thickened, there is a concern that the lower electrode 24 and the substrate 22 located in the lower layer of the polycrystalline film 25p may be deteriorated by high heat during laser light irradiation.
  • the thickness of the altered film 25m is preferably thinner than the thickness of the polycrystalline film 25p (formed on the substrate 22 side of the altered film 25m) below that.
  • the total thickness of the piezoelectric thin film 25 is 1 to 10 ⁇ m.
  • the thickness of the altered film 25 m is desirably 1/10 or less of the total thickness of the piezoelectric thin film 25. / 50 or less is more desirable.
  • the altered film 25m is surely thinner than the underlying polycrystalline film 25p, so that deterioration of the lower electrode 24 and the substrate 22 due to high heat during the formation of the altered film 25 can be suppressed.
  • the thickness of the altered film 25m is preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more. In order to ensure that the altered film 25m has a function of exhibiting a moisture-proof effect, it is desirable to secure at least 5 nm as the thickness of the altered film 25m.
  • FIG. 7 is a cross-sectional view showing the manufacturing process of the inkjet head 21.
  • the substrate 22 is prepared.
  • crystalline silicon (Si) often used in MEMS (Micro Electro Mechanical Systems) can be used.
  • MEMS Micro Electro Mechanical Systems
  • two Si substrates 22 c and 22 d are joined via an oxide film 22 e.
  • An SOI structure is used.
  • the substrate 22 is put in a heating furnace and held at about 1500 ° C. for a predetermined time, and thermal oxide films 23a and 23b made of SiO 2 are formed on the surfaces of the Si substrates 22c and 22d, respectively.
  • thermal oxide films 23a and 23b made of SiO 2 are formed on the surfaces of the Si substrates 22c and 22d, respectively.
  • Ti and Pt layers are sequentially formed on one thermal oxide film 23a by a sputtering method to form the lower electrode 24.
  • the substrate 22 is reheated to about 600 ° C., and a PZT layer 25a serving as a displacement film is formed by sputtering.
  • the layer 25a made of PZT is a polycrystalline film 25p made of an aggregate of a plurality of crystals.
  • a photosensitive resin 35 is applied to the substrate 22 by a spin coating method, and unnecessary portions of the photosensitive resin 35 are removed by exposure and etching through a mask, and the shape of the piezoelectric thin film 25 to be formed is transferred. . Thereafter, using the photosensitive resin 35 as a mask, the shape of the layer 25 a is processed using a reactive ion etching method to form the piezoelectric thin film 25.
  • Ti and Pt layers are sequentially formed by sputtering on the lower electrode 24 so as to cover the piezoelectric thin film 25 to form a layer 26a.
  • a photosensitive resin 36 is applied onto the layer 26a by a spin coating method, and unnecessary portions of the photosensitive resin 36 are removed by exposure and etching through a mask, and the shape of the upper electrode 26 to be formed is transferred. To do.
  • the shape of the layer 26a is processed using a reactive ion etching method to form the upper electrode 26.
  • the upper electrode 26 is formed on the piezoelectric thin film 25 so that the terrace region R ⁇ b> 1 that protrudes from the outer shape of the upper electrode 26 is formed in the piezoelectric thin film 25.
  • the surface of the piezoelectric thin film 25 opposite to the substrate 22 in the terrace region R1 is heated by laser light irradiation, so that the plurality of crystals constituting the polycrystalline film 25p are integrally altered to thereby change the terrace region.
  • an altered film 25m having a grain boundary disappeared is formed on the surface of R1.
  • a photosensitive resin 37 is applied to the back surface (thermal oxide film 23b side) of the substrate 22 by a spin coat method, and unnecessary portions of the photosensitive resin 37 are removed by exposure and etching through a mask.
  • the shape of the pressure chamber 22a to be formed is transferred.
  • the substrate 22 is removed using a reactive ion etching method to form a pressure chamber 22a to be an actuator 21a.
  • the substrate 22 of the actuator 21a and the nozzle substrate 31 having the discharge holes 31a are bonded using an adhesive or the like. Thereby, the inkjet head 21 is completed.
  • an intermediate glass having a through hole at a position corresponding to the discharge hole 31a is used, the thermal oxide film 23b is removed, and the substrate 22 and the intermediate glass, and the intermediate glass and the nozzle substrate 31 are anodic bonded to each other. Also good. In this case, the three parties (substrate 22, intermediate glass, nozzle substrate 31) can be joined without using an adhesive.
  • the piezoelectric thin film 25 by forming the terrace region R1 that protrudes from the outer shape of the upper electrode 26, the side surface of the upper electrode 26 and the side surface of the piezoelectric thin film 25 are separated, so that an electric field is applied to the side surface of the piezoelectric thin film. There is nothing. Thereby, generation
  • the altered film 25m is formed by heating the surface opposite to the substrate 22 in the terrace region R1 of the piezoelectric thin film 25
  • moisture in the atmosphere is taken into the inside from the surface of the piezoelectric thin film 25.
  • Can be suppressed it is possible to suppress the dielectric breakdown due to the moisture and the occurrence of leak currents other than the side surfaces of the piezoelectric thin film 25.
  • the insulator layer which covers the piezoelectric thin film 25 is not formed, the problem of deterioration of the piezoelectric characteristics due to the insulator layer does not occur.
  • the altered film 25m can be formed by performing local heating for heating only the surface of the piezoelectric thin film 25. Such local heating can prevent excessive high heat from being applied to the substrate 22 and the lower electrode 24 under the piezoelectric thin film 25, so that deterioration of these members can be prevented.
  • FIG. 8 is a graph showing the spectral transmittance of PZT which is a constituent material of the piezoelectric thin film 25.
  • the laser beam used for local heating of the piezoelectric thin film 25 may be any wavelength that does not transmit PZT but can be absorbed by PZT and heat its surface. If laser light having a wavelength that passes through the piezoelectric thin film 25 is irradiated, the laser light may pass through the piezoelectric thin film 25 and damage the base (the lower electrode 24 and the substrate 22). From this viewpoint, it is desirable that the wavelength of the laser beam to be used is a wavelength at which the transmittance when transmitting through the piezoelectric thin film 25 is 50% or less.
  • heating PZT when heating PZT, as shown in FIG. 8, it is desirable to use laser light having a wavelength of 400 nm or less, and more desirably, laser light having a wavelength of 360 nm or less. Note that ovens and hot plates should not be used because instantaneous local heating is difficult.
  • FIG. 9 is a cross-sectional view showing another configuration of the piezoelectric actuator 21a.
  • the altered film 25m may be formed over the entire film thickness direction of the terrace region R1. That is, the altered film 25m may be formed over the entire film thickness direction of the terrace region R1, and the surface of the terrace region R1 opposite to the substrate 22 may be exposed.
  • the lower layer (the lower electrode 24 and the substrate 22) of the altered film 25m may be deteriorated due to high heat when the altered film 25m is formed, but in the atmosphere in the terrace region R1.
  • the alteration film 25m prevents the moisture from being absorbed, thereby preventing the occurrence of dielectric breakdown and leakage current, thereby improving the withstand voltage.
  • FIG. 10 is a cross-sectional view showing still another configuration of the piezoelectric actuator 21a.
  • the altered film 25m may be formed on the entire surface of the piezoelectric thin film 25 opposite to the substrate 22. That is, in addition to the terrace region R1, also in the drive region R2 sandwiched between the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is formed by laminating the polycrystalline film 25p and the altered film 25m in this order from the substrate 22 side. It may be configured as.
  • the entire surface of the piezoelectric thin film 25 is irradiated with laser light to form the altered film 25m on the entire surface, and then the terrace region R1 is formed.
  • This can be realized by forming the upper electrode 26 as described above. Even with this configuration, the alteration film 25m in the terrace region R1 prevents moisture from being absorbed in the atmosphere, so that dielectric breakdown and generation of leakage current can be prevented, and the voltage resistance can be improved.
  • the piezoelectric thin film 25 is more excellent in piezoelectric characteristics when it is polycrystalline. Therefore, when the altered film 25m is formed in the drive region R2, it is desirable that the altered film 25m is thinner than the polycrystalline film 25p on the substrate side. Specifically, the thickness of the altered film 25m in the drive region R2 is desirably 1/10 or less of the total thickness of the piezoelectric thin film 25, as in the case of forming in the terrace region R1, and is 1/50 or less. Is more desirable. In addition, the thickness of the altered film 25m in the drive region R2 is preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more.
  • FIG. 11 is a cross-sectional view of the piezoelectric actuator 21a when the piezoelectric thin film 25 includes the foreign matter Q.
  • an electric field is applied between the upper electrode 26 and the lower electrode 24 in a state where the piezoelectric thin film 25 contains the foreign matter Q, current easily leaks through the foreign matter Q, the interface of the foreign matter Q, or the grain boundary around the foreign matter Q. Therefore, dielectric breakdown is likely to occur.
  • the foreign material Q exists in the piezoelectric thin film 25, since a part of upper electrode 26 protrudes in the location with the foreign material Q, the presence or absence of the foreign material Q can be confirmed by the external appearance inspection of the piezoelectric actuator 21a.
  • the foreign material Q exists in the piezoelectric thin film 25
  • a part inside the outer shape of the upper electrode 26 is irradiated with laser light. Remove by heating with.
  • an electric field is not applied around the foreign material Q.
  • the surface of the piezoelectric thin film 25 in the region exposed by removing a part of the upper electrode 26 (exposed region R3) is heated (locally heated) by laser light irradiation, and a plurality of crystals are integrally altered.
  • the altered film 25m is further formed on the surface.
  • FIG. 12 is a cross-sectional view of the piezoelectric actuator 21a in which the upper electrode 26 around the foreign material Q is removed and the altered film 25m is formed in the exposed region R3 of the piezoelectric thin film 25.
  • the piezoelectric thin film 25 is configured by laminating the polycrystalline film 25p and the altered film 25m in this order from the substrate 22 side.
  • the range (upper limit and lower limit) of the altered film 25 in the exposed region R3 can be considered in the same manner as the thickness range of the altered film 25 in the terrace region R1 and the drive region R2.
  • the exposed region R3 by forming the altered film 25m on the surface of the piezoelectric thin film 25 on the atmosphere side, it is possible to prevent moisture in the atmosphere from being taken into the piezoelectric thin film 25. Thereby, even when a part of the upper electrode 26 is removed due to the presence of the foreign matter Q and the lower piezoelectric thin film 25 is exposed, the dielectric breakdown and leakage current of the piezoelectric thin film 25 in the exposed region R3 due to the moisture are caused. Occurrence can be suppressed.
  • the piezoelectric actuator 21a of FIG. 12 a part of the upper electrode 26 is removed on the inner side of the outer shape, and the altered film 25m has a piezoelectric thin film formed by removing a part of the upper electrode 26. It is further formed in the exposed exposed region R3, and in the exposed region R3, it can be said that the piezoelectric thin film 25 may have the polycrystalline film 25p and the altered film 22m in this order from the substrate 22 side.
  • the example in which the piezoelectric thin film 25 has the terrace region R ⁇ b> 1 has been described. Preventing the current can be applied to a piezoelectric thin film having no terrace region R1, that is, a configuration in which the side surface of the piezoelectric thin film and the side surface of the upper electrode are flush with each other.
  • Example 1 After the lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 are sequentially formed on the substrate 22 by the method shown in FIG. 7, the altered region 25m is formed by irradiating the terrace region R1 of the piezoelectric thin film 25 with laser light.
  • the piezoelectric actuator 21a having the configuration shown in FIG. 4 was manufactured. At this time, the thickness of the diaphragm 22b made of Si is 5 ⁇ m, the thickness of the lower electrode 24 containing Pt is 0.1 ⁇ m, the thickness of the piezoelectric thin film 25 made of PZT is 5 ⁇ m, and the thickness of the upper electrode containing Au is 0 ⁇ m. 3 ⁇ m.
  • the piezoelectric thin film 25 formed on the lower electrode 24 by sputtering is a polycrystalline film 25p in which columnar crystals extending upward from the lower electrode 24 are gathered (grain size: about several tens of nm to 1 ⁇ m, crystal orientation: ⁇ 100
  • the PZT surface of the terrace region R1 that is not covered with the upper electrode 26 has an amorphous PZT, that is, a region having no grain boundary (modified film 25m). ) was confirmed from SEM images and the like.
  • the thickness of the altered film 25m was 20 nm.
  • the altered film 25m is formed by locally heating the polycrystalline film 25p of PZT (only the surface is heated).
  • the local heating at this time is performed by a YAG laser irradiator (LR-3100SUV) manufactured by HOYA.
  • LR-3100SUV YAG laser irradiator
  • the wavelength of the laser beam was 266 nm
  • the pulse width was 5 nsec
  • the light amount was 0.1 mJ.
  • the melting point of PZT is generally said to be 1300 to 1600 ° C.
  • the PZT surface is surely melted and solidified by local heating, and the grain boundary on the PZT surface is changed. I was able to lose it.
  • the wavelength of laser light that can be used for local heating of PZT is desirably 400 nm or less as described above. Examples of such laser light include the following.
  • YAG laser (a type of solid-state laser with a fundamental wavelength of 1064 nm)
  • YAG third harmonic Wavelength 355 nm (YAG fundamental wave converted to 1/3 wavelength)
  • YAG fourth harmonic wavelength 266 nm (YAG fundamental wave converted to a quarter wavelength)
  • YAG fifth harmonic Wavelength 213 nm (YAG fundamental wave converted to 1/5 wavelength)
  • Excimer laser (a type of gas laser with different wavelengths depending on the medium used)
  • Medium N 2 wavelength 337 nm
  • Medium XeCl wavelength 308 nm
  • Medium KrF wavelength 248 nm
  • Medium KrCl wavelength 222 nm
  • Medium ArF wavelength 193 nm
  • the withstand voltage property of the piezoelectric actuator 21a thus manufactured was examined as follows. That is, a test was performed to check whether or not dielectric breakdown occurred by applying a voltage of 20 V with a rectangular wave with a frequency of 100 kHz for 30 minutes between the upper electrode 26 and the lower electrode 24. When dielectric breakdown did not occur, the test was performed by further increasing the applied voltage by 5 V and increasing it to a maximum of 50 V.
  • the test environment was 23 ° C. and humidity 50% RH.
  • Example 1 the one in which the altered film 25m was not formed was used as the piezoelectric actuator of Comparative Example 1 (see FIG. 6), and the voltage resistance of this piezoelectric actuator was also examined in the same manner as described above.
  • dielectric breakdown did not occur in Example 1 even when the applied voltage was increased to 50V, but dielectric breakdown occurred in Comparative Example 1 when the applied voltage was 35V. Therefore, it can be said that with the configuration in which the altered film 25m is formed in the terrace region R1 as in Example 1, the withstand voltage is improved by 15 V or more compared to the case where the altered film 25m is not formed.
  • the piezoelectric displacement was the same value in Example 1 and Comparative Example 1, and it was confirmed that there was no influence on the piezoelectric displacement due to the formation of the altered film 25m.
  • Example 2 After the completion of the piezoelectric actuator 21a, when it is confirmed by appearance inspection that the foreign matter Q is mixed in the piezoelectric thin film 25, the upper electrode 26 around the foreign matter Q is removed by irradiating laser light, The exposed surface of the PZT was also irradiated with laser light to form an altered film 25m having no PZT grain boundaries (see FIG. 12). By doing in this way, generation
  • the removal of the upper electrode 26 and the formation of the altered film 25m on the PZT surface were performed by irradiating a pulse laser using a YAG laser irradiator (LR-3100SUV) manufactured by HOYA.
  • the wavelength of the laser beam was 266 nm
  • the pulse width was 5 nsec
  • the amount of light was 0.5 mJ.
  • Example 2 As a result of the treatment as described above, in Example 2, it was confirmed that even when the applied voltage was increased to 50 V, dielectric breakdown did not occur and good voltage resistance was obtained.
  • the piezoelectric actuator, the manufacturing method of the piezoelectric actuator, the ink jet head, and the ink jet printer of the present embodiment described above can be expressed as follows, and thereby have the following effects.
  • the piezoelectric actuator of this embodiment is a piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode in this order on a substrate.
  • the piezoelectric thin film includes a polycrystalline film including a plurality of crystals and a plurality of crystals.
  • An alteration film in which grain boundaries disappear due to integral alteration, and the alteration film is formed at least in a region protruding from the outer shape of the upper electrode in the piezoelectric thin film on the lower electrode, And in the said area
  • the piezoelectric thin film has a region protruding from the outer shape of the upper electrode on the lower electrode.
  • the side surface (end surface) of the upper electrode is not flush with the side surface (end surface) of the piezoelectric thin film, it is separated from the piezoelectric thin film when an electric field is applied between the upper electrode and the lower electrode. No electric field is applied to the side surface. For this reason, even if moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film, it is possible to suppress the occurrence of side surface leakage due to the moisture.
  • an altered film in which the grain boundaries have disappeared due to integral alteration of a plurality of crystals is formed in at least the above-described region of the piezoelectric thin film, and this altered film is exposed on the surface opposite to the substrate in the above-described region. ing. If the altered film is exposed on the surface, the altered film may be formed in the entire region of the piezoelectric thin film in the region, or may be formed only on the surface side (on the substrate side). It may be a polycrystalline film).
  • the altered film may have an amorphous structure. In this case, since the altered film does not have grain boundaries, the above effect can be obtained with certainty.
  • the piezoelectric thin film may have the polycrystalline film and the altered film in this order from the substrate side.
  • the substrate side of the piezoelectric thin film is not in contact with the atmosphere (because the lower electrode and the substrate are present), and the opposite side of the substrate is in contact with the atmosphere. Therefore, in the above region, even if the entire film thickness direction of the piezoelectric thin film is not formed by the altered film, that is, the substrate side is a polycrystalline film, and the opposite side of the substrate is the altered film, The effects described above can be obtained.
  • the upper electrode is partially removed inside the outer shape, and the altered film is further formed in an exposed region where the piezoelectric thin film is exposed by removing a part of the upper electrode.
  • the piezoelectric thin film may have the polycrystalline film and the altered film in this order from the substrate side.
  • a part of the upper electrode may be removed inside the outer shape of the upper electrode. is there.
  • the polycrystalline film is positioned on the substrate side, and the altered film is positioned on the atmospheric side, so that moisture in the atmosphere is contained inside the piezoelectric thin film. Can be prevented from being taken in. Thereby, it is possible to suppress dielectric breakdown and generation of leakage current in the exposed region of the piezoelectric thin film.
  • the thickness of the altered film is preferably thinner than the thickness of the polycrystalline film formed on the substrate side than the altered film.
  • the altered film is formed by, for example, altering a plurality of crystals integrally (for example, making them amorphous) by irradiation with laser light, for example.
  • the altered film is thickened, there is a concern that the lower layer (lower electrode, substrate) of the polycrystalline film may be deteriorated by high heat during laser light irradiation. Therefore, it is desirable that the altered film be thinner than the polycrystalline film. .
  • the thickness of the altered film is preferably 5 nm or more. If the thickness of the altered film is at least 5 nm, the altered film can reliably function as a film that prevents moisture from entering the atmosphere.
  • the inkjet head includes the above-described piezoelectric actuator and a nozzle substrate having a nozzle hole for ejecting ink accommodated in an opening formed in the substrate of the piezoelectric actuator to the outside.
  • the above-described piezoelectric actuator since the withstand voltage can be improved, it is possible to eject ink by applying a high electric field. As a result, ink discharge using high-viscosity ink becomes possible.
  • the ink jet printer includes the above ink jet head, and ejects ink from the ink jet head toward a recording medium.
  • an inkjet printer advantageous for high-speed and high-definition drawing can be realized.
  • the method for manufacturing a piezoelectric actuator of this embodiment includes a step of forming a lower electrode on a substrate, a step of forming a polycrystalline film including a plurality of crystals on the lower electrode, and forming a piezoelectric thin film, In the piezoelectric thin film, the step of forming the upper electrode on the piezoelectric thin film so as to form a region protruding from the outer shape of the upper electrode, and heating the surface of the region opposite to the substrate to Forming a denatured film having the grain boundaries disappeared on at least the surface of the region by integrally modifying a plurality of crystals contained in the crystal film.
  • the piezoelectric thin film In the piezoelectric thin film, a region protruding from the outer shape of the upper electrode is formed, and the side surface of the upper electrode is separated from the side surface of the piezoelectric thin film, so that no electric field is applied to the side surface of the piezoelectric thin film. For this reason, even if moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film, the occurrence of side leakage due to the moisture can be suppressed.
  • a modified film with the grain boundaries disappearing is formed on the surface of the piezoelectric thin film opposite to the substrate, so that moisture in the atmosphere can be prevented from being taken into the surface from the surface of the piezoelectric thin film. it can. Therefore, it is possible to improve the voltage resistance while suppressing the occurrence of dielectric breakdown and leakage current due to the moisture. That is, it is possible to suppress the dielectric breakdown of the piezoelectric thin film between the end portion of the upper electrode and the lower electrode, and it is possible to suppress the occurrence of a leakage current other than on the side surface of the piezoelectric thin film.
  • the above-described insulator layer inhibits the displacement of the piezoelectric thin film, and the piezoelectric characteristics are deteriorated. Can't happen.
  • the method may further include a step of forming, on the surface, a modified film in which the grain boundaries have disappeared by integrally modifying a plurality of crystals contained in the polycrystalline film.
  • the piezoelectric thin film By applying laser light, the piezoelectric thin film (polycrystalline film) is locally heated, that is, a part of the piezoelectric thin film in the film thickness direction (for example, only the surface) is instantaneously heated to form an altered film. be able to.
  • laser light By applying laser light, the piezoelectric thin film (polycrystalline film) is locally heated, that is, a part of the piezoelectric thin film in the film thickness direction (for example, only the surface) is instantaneously heated to form an altered film. be able to.
  • By such local heating it is possible to prevent excessive heat from being applied to the substrate and the lower electrode, which are constituent members, so that deterioration of these members can be prevented.
  • the wavelength of the laser beam is preferably such that the transmittance when transmitting through the piezoelectric thin film is 50% or less.
  • the piezoelectric actuator of the present invention can be used for an inkjet head and an inkjet printer.
  • Inkjet Printer 21 Inkjet Head 21a Actuator (Piezoelectric Actuator) 22 Substrate 22a Pressure chamber (opening) 24 Lower electrode 25 Piezoelectric thin film 25p Polycrystalline film 25m Altered film 26 Upper electrode 31 Nozzle substrate 31a Discharge hole (nozzle hole) R1 Terrace area R3 Exposed area

Abstract

A piezoelectric actuator (21a) has a lower electrode (24), a piezoelectric thin film (25), and an upper electrode (26) in this order on a substrate (22). The piezoelectric thin film (25) has: a polycrystalline film (25p) containing a plurality of kinds of crystals; and a degenerated film (25m) wherein grain boundaries are disappeared due to integral degeneration of the crystals. In the piezoelectric thin film (25) on the lower electrode (24), the degenerated film (25m) is formed at least in a terrace region (R1) that is protruding from the outer shape of the upper electrode (26), said degenerated film being exposed from a terrace region (R1) surface that is on the reverse side of the substrate (22).

Description

圧電アクチュエータ、圧電アクチュエータの製造方法、インクジェットヘッドおよびインクジェットプリンタPiezoelectric actuator, method for manufacturing piezoelectric actuator, inkjet head, and inkjet printer
　本発明は、基板上に、下部電極、圧電薄膜および上部電極を有する圧電アクチュエータと、その圧電アクチュエータの製造方法と、インクジェットヘッドと、インクジェットプリンタとに関するものである。 The present invention relates to a piezoelectric actuator having a lower electrode, a piezoelectric thin film and an upper electrode on a substrate, a method for manufacturing the piezoelectric actuator, an inkjet head, and an inkjet printer.
　従来から、駆動素子やセンサなどの電気機械変換素子として、チタン酸ジルコン酸鉛（ＰＺＴ）などの圧電体が用いられている。また、近年、装置の小型化、高密度化、低コスト化などの要求に応えて、シリコン（Ｓｉ）基板を用いたＭＥＭＳ（Micro  Electro　Mechanical　Systems）素子が増加している。ＭＥＭＳ素子に圧電体を応用するには、圧電体を薄膜化することが望ましい。圧電体を薄膜化することで、成膜、フォトリソグラフィーなど半導体プロセス技術を用いた高精度な加工が可能となり、小型化、高密度化を実現できる。また、大面積のウェハに素子を一括加工できるため、コストを低減できる。さらに、機械電気の変換効率が向上し、駆動素子の特性や、センサの感度が向上する等の利点がある。 Conventionally, piezoelectric materials such as lead zirconate titanate (PZT) have been used as electromechanical conversion elements such as drive elements and sensors. In recent years, MEMS (Micro Electro Mechanical Systems) elements using a silicon (Si) substrate are increasing in response to demands for downsizing, high density, and low cost of devices. In order to apply a piezoelectric body to a MEMS element, it is desirable to make the piezoelectric body thin. By reducing the thickness of the piezoelectric body, high-precision processing using semiconductor process technology such as film formation and photolithography can be performed, and miniaturization and high density can be realized. Further, since the elements can be collectively processed on a large-area wafer, the cost can be reduced. Furthermore, there is an advantage that the conversion efficiency of mechanical electricity is improved and the characteristics of the drive element and the sensitivity of the sensor are improved.
　このようなＭＥＭＳ素子を用いたデバイスの応用例として、インクジェットプリンタが知られている。インクジェットプリンタでは、液体インクを吐出する複数のチャネルを有するインクジェットヘッドを、用紙や布などの記録メディアに対して相対的に移動させながらインクの吐出を制御することで、二次元の画像が記録メディアに形成される。 An inkjet printer is known as an application example of a device using such a MEMS element. In an inkjet printer, a two-dimensional image is recorded on a recording medium by controlling the ejection of ink while moving an inkjet head having a plurality of channels for ejecting liquid ink relative to the recording medium such as paper or cloth. Formed.
　インクの吐出は、圧力式のアクチュエータ（圧電式、静電式、熱変形など）を利用したり、熱によって管内のインクに気泡を発生させることで行うことができる。中でも、圧電式のアクチュエータは、出力が大きい、変調が可能、応答性が高い、インクを選ばない、などの利点を有しており、近年よく利用されている。特に、高解像度（小液滴で良い）で小型、低コストのプリンタを実現するには、薄膜の圧電体を用いたインクジェットヘッドの利用が適している。 The ink can be ejected by using a pressure actuator (piezoelectric, electrostatic, thermal deformation, etc.) or by generating bubbles in the ink inside the tube by heat. Among them, the piezoelectric actuator has advantages such as high output, modulation, high responsiveness, and choice of ink, and has been frequently used in recent years. In particular, in order to realize a small-sized and low-cost printer with high resolution (small droplets may be used), it is suitable to use an inkjet head using a thin film piezoelectric body.
　さらに近年、インクジェットプリンタには、より高速に高精細な画像を形成することが求められている。そのためには、インクジェットヘッドに対して、１０ｃｐ（０．０１Ｐａ・ｓ）以上の高粘度のインクを吐出する性能が求められる。高粘度のインクの吐出を実現するためには、圧電薄膜（強誘電体薄膜）に高い圧電特性（圧電定数ｄ31）と変位発生力（膜厚１μｍ以上）が必要となる。 In recent years, inkjet printers are required to form high-definition images at higher speeds. For this purpose, the ink jet head is required to be capable of ejecting ink having a high viscosity of 10 cp (0.01 Pa · s) or more. In order to realize high-viscosity ink ejection, the piezoelectric thin film (ferroelectric thin film) requires high piezoelectric characteristics (piezoelectric constant d 31 ) and displacement generation force (film thickness of 1 μm or more).
　一方、ＰＺＴなどの圧電体をＳｉなどの基板上に成膜する方法としては、ＣＶＤ（Chemical　Vapor  Deposition）法などの化学的成膜法、スパッタ法やイオンプレーティング法といった物理的な方法、ゾルゲル法などの液相での成長法が知られている。これらの製法により得られる薄膜の膜厚の上限は１０μｍ程度である。それ以上の膜厚になると、クラックや膜剥がれが生じてしまい、所望の特性が得られない。 On the other hand, methods for forming a piezoelectric material such as PZT on a substrate such as Si include chemical film formation methods such as CVD (Chemical Vapor Deposition), physical methods such as sputtering and ion plating, and sol-gel. The growth method in the liquid phase such as the method is known. The upper limit of the thickness of the thin film obtained by these manufacturing methods is about 10 μm. If the film thickness exceeds that, cracks and film peeling occur, and desired characteristics cannot be obtained.
　成膜されたＰＺＴは、結晶がペロブスカイト構造となるときに良好な圧電効果を発揮する。なお、ペロブスカイト構造とは、理想的には立方晶系の単位格子を有し、立方晶の各頂点に配置される金属Ａ、体心に配置される金属Ｂ、立方晶の各面心に配置される酸素Ｏとから構成されるＡＢＯ3型の結晶構造である。ペロブスカイト構造の結晶には、立方晶が歪んだ正方晶、斜方晶、菱面体晶等も含まれるものとする。 The deposited PZT exhibits a good piezoelectric effect when the crystal has a perovskite structure. The perovskite structure ideally has a cubic unit cell, and is arranged at each vertex of the cubic A, metal B arranged at the body center, and arranged at each face center of the cubic crystal. It is an ABO 3 type crystal structure composed of oxygen O. Crystals having a perovskite structure include tetragonal crystals, orthorhombic crystals, rhombohedral crystals and the like in which cubic crystals are distorted.
　Ｓｉ基板上の電極の上に成膜されたＰＺＴの薄膜は、電極の結晶との格子定数の違いから、複数の結晶の集合体からなる多結晶となる。この多結晶は、製法にもよるが、粒径が数百ｎｍの粒状の結晶（粒状結晶）が寄り集まって構成されたり、幅は数百ｎｍで膜厚方向には１つの細長い結晶粒である柱状結晶が寄り集まって構成される。 The PZT thin film formed on the electrode on the Si substrate becomes a polycrystal composed of an aggregate of a plurality of crystals due to a difference in lattice constant from the crystal of the electrode. Depending on the production method, this polycrystal is composed of granular crystals (granular crystals) with a particle size of several hundreds of nanometers, or a width of several hundreds of nanometers and one elongated crystal grain in the film thickness direction. A certain columnar crystal is gathered together.
　ところで、基板上に、下部電極、圧電薄膜、上部電極を有する圧電式のアクチュエータでは、圧電薄膜の側面（端面）が露出していると、大気中の水分が圧電薄膜の上記側面から内部に取り込まれる。このため、圧電薄膜の端部では、上記水分によって絶縁破壊が生じてリーク電流が発生しやすくなる。つまり、圧電薄膜の側面と上部電極の側面とを面一（同一平面上）に構成した場合は、上部電極と下部電極との間に電界を印加したときに、圧電薄膜の側面を介して上部電極と下部電極との間でリーク電流（側面リーク）が発生しやすくなる。 By the way, in a piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode on a substrate, when the side surface (end surface) of the piezoelectric thin film is exposed, moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film. It is. For this reason, at the end of the piezoelectric thin film, dielectric breakdown occurs due to the moisture, and a leak current is likely to occur. In other words, when the side surface of the piezoelectric thin film and the side surface of the upper electrode are configured to be flush with each other (on the same plane), when the electric field is applied between the upper electrode and the lower electrode, Leakage current (side leakage) is likely to occur between the electrode and the lower electrode.
　そこで、特許文献１では、下部電極上に、圧電薄膜および上部電極を覆うように絶縁体層を形成している。絶縁体層により、圧電薄膜の側面が大気と遮断されるため、大気中の水分の取り込みによる側面リークの発生を防止することができる。しかし、絶縁体層で圧電薄膜を覆う構成では、絶縁体層によって圧電薄膜の変位（伸縮）が阻害されるため、圧電特性が低下する。 Therefore, in Patent Document 1, an insulator layer is formed on the lower electrode so as to cover the piezoelectric thin film and the upper electrode. Since the side surface of the piezoelectric thin film is shielded from the atmosphere by the insulator layer, it is possible to prevent the occurrence of side leakage due to the intake of moisture in the atmosphere. However, in the configuration in which the piezoelectric thin film is covered with the insulator layer, the piezoelectric layer is deteriorated because displacement (stretching) of the piezoelectric thin film is inhibited by the insulator layer.
　一方、特許文献２では、圧電薄膜の表面を研磨し、平滑化することで、上部電極と下部電極との間で電界が集中する箇所（圧電薄膜の表面の凹部領域）を無くし、これによって、圧電特性を低下させずに耐電圧性を向上させるようにしている。 On the other hand, in Patent Document 2, the surface of the piezoelectric thin film is polished and smoothed, thereby eliminating the location where the electric field concentrates between the upper electrode and the lower electrode (the recessed area on the surface of the piezoelectric thin film). The withstand voltage is improved without deteriorating the piezoelectric characteristics.
　また、特許文献３では、圧電薄膜を、粒径の異なる結晶が混在した多結晶体で構成している。大粒径の結晶に小粒径の結晶を混在させることにより、大粒径の結晶間の粒界に隙間が形成されることを防止し、圧電薄膜の絶縁性および圧電特性を向上させるようにしている。 Also, in Patent Document 3, the piezoelectric thin film is composed of a polycrystalline body in which crystals having different particle sizes are mixed. By mixing small crystal grains with large crystal grains, gaps are prevented from forming at the grain boundaries between the large crystal grains, and the insulation and piezoelectric characteristics of the piezoelectric thin film are improved. ing.
　さらに、特許文献４では、圧電薄膜の粒界が露出する領域に低誘電性物質を形成することで、圧電薄膜の粒界を介して流れるリーク電流を減らし、耐電圧性を向上させるようにしている。なお、上記の低誘電性物質は、圧電薄膜の焼成による結晶成長過程で生じた余剰組成物が、圧電薄膜の結晶粒が成長するにしたがって粒界へと追いやられ、上記粒界を介して最終的に表層面に押し出されたものと考えられている。 Further, in Patent Document 4, by forming a low dielectric material in a region where the grain boundary of the piezoelectric thin film is exposed, leakage current flowing through the grain boundary of the piezoelectric thin film is reduced and voltage resistance is improved. Yes. In addition, the low dielectric material is such that the surplus composition generated in the crystal growth process due to the firing of the piezoelectric thin film is driven to the grain boundary as the crystal grain of the piezoelectric thin film grows, and is finally passed through the grain boundary. It is thought that it was pushed to the surface layer.
特開平１０－２２６０７１号公報（請求項１、６、段落〔０００６〕、〔００２３〕、〔００２５〕、〔００３８〕、図２、図３等参照）JP-A-10-226071 (see claims 1 and 6, paragraphs [0006], [0023], [0025], [0038], FIG. 2, FIG. 3 etc.) 特開平１０－２６４３８５号公報（請求項１、段落〔００３２〕、〔００３４〕、〔００５４〕、図３等参照）JP-A-10-264385 (refer to claim 1, paragraphs [0032], [0034], [0054], FIG. 3, etc.) 特開２００２－０８４０１２号公報（請求項１、２、段落〔０００４〕、〔０００６〕、〔００３４〕、〔００６５〕、図３、図６、図７等参照）Japanese Patent Laid-Open No. 2002-084012 (see claims 1 and 2, paragraphs [0004], [0006], [0034], [0065], FIG. 3, FIG. 6, FIG. 7, etc.) 特開平１０－２１７４５８号公報（請求項１、段落〔０００７〕、〔００３５〕、図２、図３、図５等参照）Japanese Patent Laid-Open No. 10-217458 (refer to claim 1, paragraphs [0007] and [0035], FIG. 2, FIG. 3, and FIG. 5)
　ところが、特許文献２～４は、いずれも、圧電薄膜の側面が露出し、かつ、圧電薄膜の側面と上部電極の側面とが面一（同一平面上）となっている構成である。この構成では、前述のように、取り込んだ大気中の水分に起因して側面リークが発生する。 However, in each of Patent Documents 2 to 4, the side surface of the piezoelectric thin film is exposed, and the side surface of the piezoelectric thin film and the side surface of the upper electrode are flush with each other (on the same plane). In this configuration, as described above, side leakage occurs due to the moisture in the taken-in air.
　また、側面リークの発生を抑えるために、例えば、下部電極上で圧電薄膜を上部電極から張り出すように形成する構成が考えられる（圧電薄膜の側面に電界がかからないため）。しかし、この場合は、圧電薄膜の張り出し部分の表面（下部電極とは反対側の表面）から、大気中の水分が内部に取り込まれるため、上部電極と下部電極との間に電界がかかったときに、上部電極の端部と下部電極との間で圧電薄膜の絶縁破壊が起こりやすくなり、この部分でリーク電流が発生しやすくなる。 In order to suppress the occurrence of side leakage, for example, a configuration in which a piezoelectric thin film is formed on the lower electrode so as to protrude from the upper electrode (because an electric field is not applied to the side surface of the piezoelectric thin film) is conceivable. However, in this case, moisture in the atmosphere is taken in from the surface of the overhanging portion of the piezoelectric thin film (the surface opposite to the lower electrode), so when an electric field is applied between the upper electrode and the lower electrode In addition, the dielectric breakdown of the piezoelectric thin film is likely to occur between the end portion of the upper electrode and the lower electrode, and a leak current is likely to occur in this portion.
　本発明は、上記の問題点を解決するためになされたもので、その目的は、圧電薄膜の変位を阻害して圧電特性を低下させることなく、圧電薄膜の絶縁破壊およびリーク電流（側面リークを含む）の発生を抑えて、耐電圧性を向上させることができる圧電アクチュエータおよびその製造方法と、その圧電アクチュエータを備えたインクジェットヘッドと、インクジェットプリンタとを提供することにある。 The present invention has been made in order to solve the above-described problems, and its purpose is to prevent dielectric breakdown and leakage current (side leakage) of the piezoelectric thin film without impairing the displacement of the piezoelectric thin film and deteriorating the piezoelectric characteristics. The present invention provides a piezoelectric actuator and a method for manufacturing the same, an ink jet head provided with the piezoelectric actuator, and an ink jet printer.
　本発明の一側面に係る圧電アクチュエータは、基板上に、下部電極、圧電薄膜および上部電極をこの順で有する圧電アクチュエータであって、前記圧電薄膜は、複数の結晶を含む多結晶膜と、複数の結晶の一体的な変質によって粒界が消滅した変質膜とを有しており、前記変質膜は、前記下部電極上の前記圧電薄膜において、前記上部電極の外形からはみ出した領域に少なくとも形成されており、かつ、前記領域において前記基板とは反対側の表面に露出している。 A piezoelectric actuator according to one aspect of the present invention is a piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode in this order on a substrate, wherein the piezoelectric thin film includes a polycrystalline film including a plurality of crystals, and a plurality of piezoelectric films. And an altered film in which grain boundaries have disappeared due to integral alteration of the crystal, and the altered film is formed at least in a region protruding from the outer shape of the upper electrode in the piezoelectric thin film on the lower electrode. And is exposed on the surface opposite to the substrate in the region.
　本発明の他の側面に係る圧電アクチュエータの製造方法は、基板上に下部電極を形成する工程と、前記下部電極上に、複数の結晶を含む多結晶膜を成膜して圧電薄膜を形成する工程と、前記圧電薄膜において、上部電極の外形からはみ出す領域が形成されるように、前記圧電薄膜上に前記上部電極を形成する工程と、前記領域の前記基板とは反対側の表面を加熱して、前記多結晶膜に含まれる複数の結晶を一体的に変質させることにより、粒界が消滅した変質膜を、前記領域の少なくとも前記表面に形成する工程とを有している。 A method of manufacturing a piezoelectric actuator according to another aspect of the present invention includes a step of forming a lower electrode on a substrate, and forming a piezoelectric thin film by forming a polycrystalline film including a plurality of crystals on the lower electrode. A step of forming the upper electrode on the piezoelectric thin film so that a region protruding from the outer shape of the upper electrode is formed in the piezoelectric thin film; and heating a surface of the region opposite to the substrate. A plurality of crystals contained in the polycrystalline film are integrally modified to form a modified film in which the grain boundaries disappear, on at least the surface of the region.
　上記の構成および製造方法によれば、圧電薄膜の変位を阻害して圧電特性を低下させることなく、絶縁破壊およびリーク電流の発生を抑えて、耐電圧性を向上させることができる。 According to the above-described configuration and manufacturing method, it is possible to suppress dielectric breakdown and generation of a leakage current without impeding the displacement of the piezoelectric thin film and deteriorating the piezoelectric characteristics, thereby improving the withstand voltage.
本発明の実施の一形態に係るインクジェットプリンタの概略の構成を示す説明図である。1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention. FIG. 上記インクジェットプリンタが備えるインクジェットヘッドのアクチュエータの概略の構成を示す平面図、およびその平面図におけるＡ－Ａ’線矢視断面図である。FIG. 2 is a plan view showing a schematic configuration of an actuator of an ink jet head provided in the ink jet printer, and a cross-sectional view taken along line A-A ′ in the plan view. 上記インクジェットヘッドの断面図である。It is sectional drawing of the said inkjet head. 上記アクチュエータの詳細な構成を示す断面図である。It is sectional drawing which shows the detailed structure of the said actuator. 上記アクチュエータの圧電薄膜を構成する多結晶膜および変質膜の水平断面を模式的に示す説明図である。It is explanatory drawing which shows typically the horizontal cross section of the polycrystalline film and alteration film which comprise the piezoelectric thin film of the said actuator. 上記変質膜を持たない圧電アクチュエータの断面図である。It is sectional drawing of the piezoelectric actuator which does not have the said altered film. 上記インクジェットヘッドの製造工程を示す断面図である。It is sectional drawing which shows the manufacturing process of the said inkjet head. ＰＺＴの分光透過率を示すグラフである。It is a graph which shows the spectral transmittance of PZT. 上記変質膜を有する圧電アクチュエータの他の構成を示す断面図である。It is sectional drawing which shows the other structure of the piezoelectric actuator which has the said altered film. 上記圧電アクチュエータのさらに他の構成を示す断面図である。It is sectional drawing which shows other structure of the said piezoelectric actuator. 圧電薄膜に異物が含まれた圧電アクチュエータの断面図である。It is sectional drawing of the piezoelectric actuator in which the foreign material was contained in the piezoelectric thin film. 上記異物の周辺の上部電極を除去した圧電アクチュエータの断面図である。It is sectional drawing of the piezoelectric actuator which removed the upper electrode of the periphery of the said foreign material.
　本発明の実施の一形態について、図面に基づいて説明すれば、以下の通りである。なお、本明細書において、数値範囲をＡ～Ｂと表記した場合、その数値範囲に下限Ａおよび上限Ｂの値は含まれるものとする。 An embodiment of the present invention will be described below with reference to the drawings. In this specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B.
　〔インクジェットプリンタの構成〕
　図１は、本実施形態のインクジェットプリンタ１の概略の構成を示す説明図である。インクジェットプリンタ１は、インクジェットヘッド部２において、インクジェットヘッド２１が記録媒体の幅方向にライン状に設けられた、いわゆるラインヘッド方式のインクジェット記録装置である。 [Configuration of inkjet printer]
FIG. 1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer 1 according to the present embodiment. The ink jet printer 1 is a so-called line head type ink jet recording apparatus in which an ink jet head 21 is provided in a line shape in the width direction of a recording medium in the ink jet head unit 2.
　インクジェットプリンタ１は、上記のインクジェットヘッド部２と、繰り出しロール３と、巻き取りロール４と、２つのバックロール５・５と、中間タンク６と、送液ポンプ７と、貯留タンク８と、定着機構９とを備えている。 The ink jet printer 1 includes an ink jet head unit 2, a feed roll 3, a take-up roll 4, two back rolls 5 and 5, an intermediate tank 6, a liquid feed pump 7, a storage tank 8, and a fixing tank. And a mechanism 9.
　インクジェットヘッド部２は、インクジェットヘッド２１から記録媒体Ｐに向けてインクを吐出させ、画像データに基づく画像形成（描画）を行うものであり、一方のバックロール５の近傍に配置されている。なお、インクジェットヘッド２１の詳細については後述する。 The inkjet head unit 2 ejects ink from the inkjet head 21 toward the recording medium P to perform image formation (drawing) based on image data, and is disposed in the vicinity of one back roll 5. Details of the inkjet head 21 will be described later.
　繰り出しロール３、巻き取りロール４および各バックロール５は、軸回りに回転可能な円柱形状からなる部材である。繰り出しロール３は、周面に幾重にも亘って巻回された長尺状の記録媒体Ｐを、インクジェットヘッド部２との対向位置に向けて繰り出すロールである。この繰り出しロール３は、モータ等の図示しない駆動手段によって回転することで、記録媒体Ｐを図１のＸ方向へ繰り出して搬送する。 The feeding roll 3, the take-up roll 4 and the back rolls 5 are members each having a cylindrical shape that can rotate around its axis. The feeding roll 3 is a roll that feeds the long recording medium P wound around the circumferential surface toward the position facing the inkjet head unit 2. The feeding roll 3 is rotated by driving means (not shown) such as a motor, thereby feeding the recording medium P in the X direction in FIG.
　巻き取りロール４は、繰り出しロール３より繰り出されて、インクジェットヘッド部２によってインクが吐出された記録媒体Ｐを周面に巻き取る。 The take-up roll 4 is taken out from the take-out roll 3 and takes up the recording medium P on which the ink is ejected by the inkjet head unit 2 around the circumferential surface.
　各バックロール５は、繰り出しロール３と巻き取りロール４との間に配設されている。記録媒体Ｐの搬送方向上流側に位置する一方のバックロール５は、繰り出しロール３によって繰り出された記録媒体Ｐを、周面の一部に巻き付けて支持しながら、インクジェットヘッド部２との対向位置に向けて搬送する。他方のバックロール５は、インクジェットヘッド部２との対向位置から巻き取りロール４に向けて、記録媒体Ｐを周面の一部に巻き付けて支持しながら搬送する。 Each back roll 5 is disposed between the feed roll 3 and the take-up roll 4. One back roll 5 located on the upstream side in the conveyance direction of the recording medium P is opposed to the inkjet head unit 2 while winding the recording medium P fed by the feeding roll 3 around and supporting the recording medium P. Transport toward The other back roll 5 conveys the recording medium P from a position facing the inkjet head unit 2 toward the take-up roll 4 while being wound around and supported by a part of the peripheral surface.
　中間タンク６は、貯留タンク８より供給されるインクを一時的に貯留する。また、中間タンク６は、複数のインクチューブ１０と接続され、各インクジェットヘッド２１におけるインクの背圧を調整して、各インクジェットヘッド２１にインクを供給する。 The intermediate tank 6 temporarily stores the ink supplied from the storage tank 8. The intermediate tank 6 is connected to a plurality of ink tubes 10, adjusts the back pressure of ink in each inkjet head 21, and supplies ink to each inkjet head 21.
　送液ポンプ７は、貯留タンク８に貯留されたインクを中間タンク６に供給するものであり、供給管１１の途中に配設されている。貯留タンク８に貯留されたインクは、送液ポンプ７によって汲み上げられ、供給管１１を介して中間タンク６に供給される。 The liquid feed pump 7 supplies the ink stored in the storage tank 8 to the intermediate tank 6, and is arranged in the middle of the supply pipe 11. The ink stored in the storage tank 8 is pumped up by the liquid feed pump 7 and supplied to the intermediate tank 6 through the supply pipe 11.
　定着機構９は、インクジェットヘッド部２によって記録媒体Ｐに吐出されたインクを当該記録媒体Ｐに定着させる。この定着機構９は、吐出されたインクを記録媒体Ｐに加熱定着するためのヒータや、吐出されたインクにＵＶ（紫外線）を照射することによりインクを硬化させるためのＵＶランプ等で構成されている。 The fixing mechanism 9 fixes the ink ejected to the recording medium P by the inkjet head unit 2 on the recording medium P. The fixing mechanism 9 includes a heater for heat-fixing the discharged ink on the recording medium P, a UV lamp for curing the ink by irradiating the discharged ink with UV (ultraviolet light), and the like. Yes.
　上記の構成において、繰り出しロール３から繰り出される記録媒体Ｐは、バックロール５により、インクジェットヘッド部２との対向位置に搬送され、インクジェットヘッド部２から記録媒体Ｐに対してインクが吐出される。その後、記録媒体Ｐに吐出されたインクは定着機構９によって定着され、インク定着後の記録媒体Ｐが巻き取りロール４によって巻き取られる。このようにラインヘッド方式のインクジェットプリンタ１では、インクジェットヘッド部２を静止させた状態で、記録媒体Ｐを搬送しながらインクが吐出され、記録媒体Ｐに画像が形成される。 In the above configuration, the recording medium P fed from the feeding roll 3 is conveyed to the position facing the inkjet head unit 2 by the back roll 5, and ink is ejected from the inkjet head unit 2 to the recording medium P. Thereafter, the ink ejected onto the recording medium P is fixed by the fixing mechanism 9, and the recording medium P after ink fixing is taken up by the take-up roll 4. As described above, in the line head type inkjet printer 1, ink is ejected while the recording medium P is conveyed while the inkjet head unit 2 is stationary, and an image is formed on the recording medium P.
　なお、インクジェットプリンタ１は、シリアルヘッド方式で記録媒体に画像を形成する構成であってもよい。シリアルヘッド方式とは、記録媒体を搬送しながら、その搬送方向と直交する方向にインクジェットヘッドを移動させてインクを吐出し、画像を形成する方式である。 The ink jet printer 1 may be configured to form an image on a recording medium by a serial head method. The serial head method is a method of forming an image by ejecting ink by moving an inkjet head in a direction orthogonal to the transport direction while transporting a recording medium.
　〔インクジェットヘッドの構成〕
　次に、上記したインクジェットヘッド２１の構成について説明する。図２は、インクジェットヘッド２１のアクチュエータ２１ａ（圧電アクチュエータ）の概略の構成を示す平面図と、その平面図におけるＡ－Ａ’線矢視断面図とを併せて示したものである。また、図３は、図２のアクチュエータ２１ａにノズル基板３１を接合してなるインクジェットヘッド２１の断面図である。 [Configuration of inkjet head]
Next, the configuration of the inkjet head 21 will be described. FIG. 2 is a plan view showing a schematic configuration of the actuator 21a (piezoelectric actuator) of the inkjet head 21 and a cross-sectional view taken along the line AA ′ in the plan view. FIG. 3 is a cross-sectional view of the inkjet head 21 in which the nozzle substrate 31 is joined to the actuator 21a of FIG.
　インクジェットヘッド２１は、複数の圧力室２２ａ（開口部）を有する基板２２上に、熱酸化膜２３、下部電極２４、圧電薄膜２５、上部電極２６をこの順で有している。 The inkjet head 21 has a thermal oxide film 23, a lower electrode 24, a piezoelectric thin film 25, and an upper electrode 26 in this order on a substrate 22 having a plurality of pressure chambers 22a (openings).
　基板２２は、厚さが例えば３００～７５０μｍ程度の単結晶Ｓｉ（シリコン）単体からなる半導体基板またはＳＯＩ（Silicon  on  Insulator）基板で構成されている。なお、図２では、基板２２をＳＯＩ基板で構成した場合を示している。ＳＯＩ基板は、酸化膜を介して２枚のＳｉ基板を接合したものである。基板２２における圧力室２２ａの上壁（圧力室２２ａよりも圧電薄膜２５の形成側に位置する壁）は、従動膜となる振動板２２ｂを構成しており、圧電薄膜２５の駆動（伸縮）に伴って変位（振動）し、圧力室２２ａ内のインクに圧力を付与する。 The substrate 22 is composed of a semiconductor substrate made of a single crystal Si (silicon) alone having a thickness of, for example, about 300 to 750 μm, or an SOI (Silicon On Insulator) substrate. Note that FIG. 2 shows a case where the substrate 22 is configured by an SOI substrate. The SOI substrate is obtained by bonding two Si substrates through an oxide film. The upper wall of the pressure chamber 22a in the substrate 22 (the wall positioned on the side where the piezoelectric thin film 25 is formed with respect to the pressure chamber 22a) constitutes a vibration plate 22b serving as a driven film. Along with this displacement (vibration), pressure is applied to the ink in the pressure chamber 22a.
　熱酸化膜２３は、例えば厚さが０．１μｍ程度のＳｉＯ2（酸化シリコン）からなり、基板２２の保護および絶縁の目的で形成されている。 The thermal oxide film 23 is made of, for example, SiO 2 (silicon oxide) having a thickness of about 0.1 μm, and is formed for the purpose of protecting and insulating the substrate 22.
　下部電極２４は、複数の圧力室２２ａに共通して設けられるコモン電極であり、Ｔｉ（チタン）層とＰｔ（白金）層とを積層して構成されている。Ｔｉ層は、熱酸化膜２３とＰｔ層との密着性を向上させるために形成されている。Ｔｉ層の厚さは例えば０．０２μｍ程度であり、Ｐｔ層の厚さは例えば０．１μｍ程度である。 The lower electrode 24 is a common electrode provided in common to the plurality of pressure chambers 22a, and is configured by laminating a Ti (titanium) layer and a Pt (platinum) layer. The Ti layer is formed in order to improve the adhesion between the thermal oxide film 23 and the Pt layer. The thickness of the Ti layer is, for example, about 0.02 μm, and the thickness of the Pt layer is, for example, about 0.1 μm.
　圧電薄膜２５は、例えばＰＺＴ（チタン酸ジルコン酸鉛）からなる強誘電体薄膜で構成されており、各圧力室２２ａに対応して設けられている。圧電薄膜２５の膜厚は、例えば１μｍ以上１０μｍ以下である。 The piezoelectric thin film 25 is composed of a ferroelectric thin film made of, for example, PZT (lead zirconate titanate), and is provided corresponding to each pressure chamber 22a. The film thickness of the piezoelectric thin film 25 is, for example, not less than 1 μm and not more than 10 μm.
　上部電極２６は、各圧力室２２ａに対応して設けられる個別電極であり、Ｔｉ層とＰｔ層とを積層して構成されている。Ｔｉ層は、圧電薄膜２５とＰｔ層との密着性を向上させるために形成されている。Ｔｉ層の厚さは例えば０．０２μｍ程度であり、Ｐｔ層の厚さは例えば０．１～０．２μｍ程度である。上部電極２６は、下部電極２４との間で圧電薄膜２５を膜厚方向から挟むように設けられている。なお、Ｐｔ層の代わりに、金（Ａｕ）からなる層を形成してもよい。 The upper electrode 26 is an individual electrode provided corresponding to each pressure chamber 22a, and is configured by laminating a Ti layer and a Pt layer. The Ti layer is formed in order to improve the adhesion between the piezoelectric thin film 25 and the Pt layer. The thickness of the Ti layer is, for example, about 0.02 μm, and the thickness of the Pt layer is, for example, about 0.1 to 0.2 μm. The upper electrode 26 is provided so as to sandwich the piezoelectric thin film 25 from the film thickness direction with the lower electrode 24. Note that a layer made of gold (Au) may be formed instead of the Pt layer.
　下部電極２４、圧電薄膜２５および上部電極２６は、圧力室２２ａ内のインクを外部に吐出させるための薄膜圧電素子２７を構成している。この薄膜圧電素子２７は、駆動回路２８から下部電極２４および上部電極２６に印加される電圧（駆動信号）に基づいて駆動される。インクジェットヘッド２１は、薄膜圧電素子２７および圧力室２２ａを縦横に並べることにより形成される。 The lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 constitute a thin film piezoelectric element 27 for discharging ink in the pressure chamber 22a to the outside. The thin film piezoelectric element 27 is driven based on a voltage (drive signal) applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26. The ink jet head 21 is formed by arranging the thin film piezoelectric element 27 and the pressure chamber 22a vertically and horizontally.
　圧力室２２ａの振動板２２ｂとは反対側には、ノズル基板３１が接合されている。ノズル基板３１には、圧力室２２ａに収容されるインクをインク滴として外部に吐出するための吐出孔（ノズル孔）３１ａが形成されている。圧力室２２ａには、中間タンク６より供給されるインクが収容される。 A nozzle substrate 31 is bonded to the opposite side of the pressure chamber 22a from the diaphragm 22b. The nozzle substrate 31 is formed with ejection holes (nozzle holes) 31a for ejecting ink stored in the pressure chambers 22a to the outside as ink droplets. Ink supplied from the intermediate tank 6 is stored in the pressure chamber 22a.
　上記の構成において、駆動回路２８から下部電極２４および上部電極２６に電圧を印加すると、圧電薄膜２５が、下部電極２４と上部電極２６との電位差に応じて、厚さ方向に垂直な方向（基板２２の面に平行な方向）に伸縮する。そして、圧電薄膜２５と振動板２２ｂとの長さの違いにより、振動板２２ｂに曲率が生じ、振動板２２ｂが厚さ方向に変位（湾曲、振動）する。 In the above configuration, when a voltage is applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is in a direction perpendicular to the thickness direction (substrate) according to the potential difference between the lower electrode 24 and the upper electrode 26. (Direction parallel to the surface of 22). Then, due to the difference in length between the piezoelectric thin film 25 and the diaphragm 22b, a curvature is generated in the diaphragm 22b, and the diaphragm 22b is displaced (curved or vibrated) in the thickness direction.
　したがって、圧力室２２ａ内にインクを収容しておけば、上述した振動板２２ｂの振動により、圧力室２２ａ内のインクに圧力波が伝搬され、圧力室２２ａ内のインクが吐出孔３１ａからインク滴として外部に吐出される。 Therefore, if ink is accommodated in the pressure chamber 22a, a pressure wave is propagated to the ink in the pressure chamber 22a by the vibration of the vibration plate 22b described above, and the ink in the pressure chamber 22a is ejected from the ejection hole 31a. Is discharged to the outside.
　本実施形態のインクジェットヘッド２１ａにおいては、後述するように、圧電アクチュエータ２１ａの圧電薄膜２５の耐電圧性が高いため、圧電薄膜２５に高い電界を印加することが可能となる。これにより、高粘度のインクを用いたインク吐出が可能となり、高速で高精細な描画に有利なインクジェットプリンタ１を実現することが可能となる。 In the inkjet head 21a of the present embodiment, as described later, since the voltage resistance of the piezoelectric thin film 25 of the piezoelectric actuator 21a is high, a high electric field can be applied to the piezoelectric thin film 25. As a result, it is possible to discharge ink using high-viscosity ink, and it is possible to realize the inkjet printer 1 that is advantageous for high-speed and high-definition drawing.
　〔圧電アクチュエータの詳細について〕
　次に、上記した圧電アクチュエータ２１ａの詳細について説明する。図４は、圧電アクチュエータ２１ａの詳細な構成を示す断面図である。なお、同図では、便宜上、熱酸化膜２３の図示を省略している。 [Details of piezoelectric actuator]
Next, the details of the piezoelectric actuator 21a will be described. FIG. 4 is a cross-sectional view showing a detailed configuration of the piezoelectric actuator 21a. In the figure, the thermal oxide film 23 is not shown for convenience.
　圧電アクチュエータ２１ａの圧電薄膜２５は、多結晶膜２５ｐと、変質膜２５ｍとを有している。多結晶膜２５ｐは、複数の結晶（例えば柱状結晶）の集合体からなる膜である。変質膜２５ｍは、複数の結晶の一体的な変質によって粒界が消滅した膜であり、例えば非晶質構造（アモルファス）の膜である。なお、変質とは、一般的に、物質の性質が変わることを言うが、ここでは、粒界を持つ複数の結晶の集合（多結晶構造）を一体的に、粒界を持たない構造（例えば非晶質構造）に変化させることにより、粒界を介して大気中の水分を透過させる性質を無くすことを指す。このような変質は、後述するように、所定波長のレーザー光を多結晶構造の膜に照射して加熱し、照射部分を溶融、固化させることによって実現できる。 The piezoelectric thin film 25 of the piezoelectric actuator 21a has a polycrystalline film 25p and an altered film 25m. The polycrystalline film 25p is a film made of an aggregate of a plurality of crystals (for example, columnar crystals). The altered film 25m is a film in which grain boundaries disappear due to integral alteration of a plurality of crystals, and is, for example, an amorphous structure (amorphous) film. In general, alteration refers to a change in the properties of a substance, but here, an aggregate of a plurality of crystals having a grain boundary (polycrystalline structure) is integrated into a structure having no grain boundary (for example, By changing to an (amorphous structure), it means eliminating the property of allowing moisture in the atmosphere to permeate through grain boundaries. As will be described later, such alteration can be realized by irradiating a laser beam of a predetermined wavelength to a film having a polycrystalline structure and heating it to melt and solidify the irradiated portion.
　図５は、走査型電子顕微鏡（ＳＥＭ：Scanning　Electron　Microscope）により観察される多結晶膜２５ｐおよび変質膜２５ｍの水平断面を模式的に示している。同図のように、多結晶膜２５ｐにおいては、結晶と結晶との間に粒界が存在しているが、変質膜２５ｍにおいては、多結晶膜２５ｐで見られたような粒界のない非晶質構造となっている。 FIG. 5 schematically shows a horizontal cross section of the polycrystalline film 25p and the altered film 25m observed with a scanning electron microscope (SEM). As shown in the figure, in the polycrystalline film 25p, there are grain boundaries between the crystals, but in the altered film 25m, there is no grain boundary as seen in the polycrystalline film 25p. It has a crystalline structure.
　また、圧電薄膜２５は、下部電極２４上において、上部電極２６の外形からはみ出したテラス領域Ｒ１（圧電薄膜２５が上部電極２６に覆われずに張り出した部分）を有している。すなわち、圧電薄膜２５は、テラス領域Ｒ１以外の部分において下部電極２４と上部電極２６とで挟まれている。 The piezoelectric thin film 25 has a terrace region R1 (a portion where the piezoelectric thin film 25 protrudes without being covered by the upper electrode 26) protruding from the outer shape of the upper electrode 26 on the lower electrode 24. That is, the piezoelectric thin film 25 is sandwiched between the lower electrode 24 and the upper electrode 26 in portions other than the terrace region R1.
　上記の変質膜２５ｍは、少なくともテラス領域Ｒ１に形成されている。より詳しくは、圧電薄膜２５のテラス領域Ｒ１では、基板２２側から多結晶膜２５ｐと変質膜２５ｍとがこの順で積層されている。この結果、変質膜２５ｍは、テラス領域Ｒ１において、基板２２とは反対側の表面に露出している。 The above-described altered film 25m is formed at least in the terrace region R1. More specifically, in the terrace region R1 of the piezoelectric thin film 25, the polycrystalline film 25p and the altered film 25m are laminated in this order from the substrate 22 side. As a result, the altered film 25m is exposed on the surface opposite to the substrate 22 in the terrace region R1.
　このように、圧電薄膜２５がテラス領域Ｒ１を有している場合、上部電極２６の側面（端面）が圧電薄膜２５の側面（端面）から離れ、これらの側面が同一面上に位置しない。これにより、上部電極２６と下部電極２４との間に電界をかけたときに、圧電薄膜２５の側面に電界がかかることはない。このため、たとえ大気中の水分が圧電薄膜２５の側面から内部に取り込まれても、圧電薄膜２５の側面をリーク電流が流れることはない。 Thus, when the piezoelectric thin film 25 has the terrace region R1, the side surface (end surface) of the upper electrode 26 is separated from the side surface (end surface) of the piezoelectric thin film 25, and these side surfaces are not located on the same plane. Thereby, when an electric field is applied between the upper electrode 26 and the lower electrode 24, an electric field is not applied to the side surface of the piezoelectric thin film 25. For this reason, even if moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film 25, no leak current flows through the side surface of the piezoelectric thin film 25.
　また、図６は、テラス領域Ｒ１に変質膜２５ｍが形成されていない場合の圧電アクチュエータ２１ａ’の断面図である。この構成では、テラス領域Ｒ１において、大気中の水分が圧電薄膜２５の基板２２とは反対側の表面から、多結晶膜２５ｐの結晶粒界を介して内部に取り込まれるため、取り込まれた水分によって圧電薄膜２５の絶縁破壊が生じ、上部電極２６の端部と下部電極２４との間でリーク電流が発生しやすくなると考えられる。 FIG. 6 is a cross-sectional view of the piezoelectric actuator 21a 'when the altered film 25m is not formed in the terrace region R1. In this configuration, in the terrace region R1, moisture in the atmosphere is taken into the inside from the surface opposite to the substrate 22 of the piezoelectric thin film 25 through the crystal grain boundary of the polycrystalline film 25p. It is considered that dielectric breakdown of the piezoelectric thin film 25 occurs and a leak current is likely to occur between the end portion of the upper electrode 26 and the lower electrode 24.
　これに対して、図４のように、テラス領域Ｒ１に変質膜２５ｍが形成されており、この変質膜２５ｍがテラス領域Ｒ１において基板２２とは反対側の表面に露出する構成では、大気中の水分が圧電薄膜２５の上記表面から内部に取り込まれるのを、粒界を持たない変質膜２５ｍによって抑えることができる。これにより、上記水分に起因する圧電薄膜２５の絶縁破壊およびリーク電流の発生を抑えて、耐電圧性を向上させることができる。つまり、圧電薄膜２５の側面以外におけるリーク電流の発生も抑えることができる。 On the other hand, as shown in FIG. 4, a modified film 25m is formed in the terrace region R1, and the modified film 25m is exposed on the surface opposite to the substrate 22 in the terrace region R1. It is possible to suppress the moisture from being taken into the inside of the piezoelectric thin film 25 by the altered film 25m having no grain boundary. Thereby, dielectric breakdown of the piezoelectric thin film 25 caused by the moisture and generation of leakage current can be suppressed, and voltage resistance can be improved. That is, it is possible to suppress the occurrence of a leak current other than the side surface of the piezoelectric thin film 25.
　また、例えば絶縁体層などで圧電薄膜２５を覆って大気と遮断する構成を採らなくても、大気中の水分の吸収に起因してリーク電流が発生するのを抑えることができるため、絶縁体層を設ける従来のように、圧電薄膜２５の変位の阻害による圧電特性の低下が生じることはない。 In addition, since it is possible to suppress the occurrence of a leakage current due to the absorption of moisture in the atmosphere without adopting a configuration in which the piezoelectric thin film 25 is covered with an insulating layer or the like and cut off from the atmosphere, for example, the insulator Unlike the conventional case where the layer is provided, the piezoelectric characteristics are not deteriorated due to the inhibition of the displacement of the piezoelectric thin film 25.
　また、変質膜２５ｍは、粒界を持たない非晶質構造であるため、大気中の水分が変質膜２５ｍを介して多層膜２５ａ側に取り込まれるのを確実に抑えることができる。その結果、上記水分に起因する絶縁破壊およびリーク電流の発生を抑えて耐電圧性を向上させるなどの上記の効果を確実に得ることができる。 Further, since the altered film 25m has an amorphous structure having no grain boundary, it is possible to reliably suppress moisture in the atmosphere from being taken into the multilayer film 25a via the altered film 25m. As a result, it is possible to reliably obtain the above-described effects such as the improvement of the voltage resistance by suppressing the occurrence of dielectric breakdown and leakage current due to the moisture.
　また、下部電極２４上のテラス領域Ｒ１においては、圧電薄膜２５の基板２２側には下部電極２４および基板２２が存在し、大気と接触しない。一方、圧電薄膜２５の基板２２とは反対側は、大気と直接接触する。このため、テラス領域Ｒ１では、圧電薄膜２５において大気と接触する表面側にのみ変質膜２５ｍを形成する構成とすることで、変質膜２５ｍの基板２２側に多層膜２５ａが形成されていても、リーク電流の発生を抑える上述の効果を得ることができる。したがって、テラス領域Ｒ１全体を変質膜２５ｍで構成する必要がなくなる。 Further, in the terrace region R1 on the lower electrode 24, the lower electrode 24 and the substrate 22 exist on the substrate 22 side of the piezoelectric thin film 25, and do not come into contact with the atmosphere. On the other hand, the opposite side of the piezoelectric thin film 25 from the substrate 22 is in direct contact with the atmosphere. For this reason, in the terrace region R1, by adopting a configuration in which the altered film 25m is formed only on the surface side in contact with the atmosphere in the piezoelectric thin film 25, even if the multilayer film 25a is formed on the substrate 22 side of the altered film 25m, The above-described effect of suppressing the generation of leakage current can be obtained. Therefore, it is not necessary to configure the entire terrace region R1 with the altered film 25m.
　また、変質膜２５ｍは、多結晶膜２５ｐを構成するＰＺＴの変質によって形成されるものであり、材料自体は多結晶膜２５ｐと同じである。したがって、基板２２側から多結晶膜２５ｐと変質膜２５ｍとがこの順で構成され、同じ材料の積層構造となるため、これらの膜の密着性を高く確保することが可能となる。 The altered film 25m is formed by alteration of PZT constituting the polycrystalline film 25p, and the material itself is the same as the polycrystalline film 25p. Therefore, since the polycrystalline film 25p and the altered film 25m are formed in this order from the substrate 22 side and have a laminated structure of the same material, it is possible to ensure high adhesion between these films.
　ところで、上記した変質膜２５ｍは、上述のように、レーザー光の照射によって多結晶構造を変質させることによって形成される（圧電アクチュエータ２１ａの全体の製造方法については後述する）。このとき、変質膜２５ｍを厚くする場合は、多結晶膜２５ｐの下層に位置する下部電極２４や基板２２が、レーザー光の照射時の高熱により劣化することが懸念される。このため、変質膜２５ｍの厚みは、その下層の（変質膜２５ｍよりも基板２２側に形成される）多結晶膜２５ｐの厚みよりも薄いことが望ましい。 By the way, the above-described altered film 25m is formed by altering the polycrystalline structure by laser light irradiation as described above (the entire manufacturing method of the piezoelectric actuator 21a will be described later). At this time, when the altered film 25m is thickened, there is a concern that the lower electrode 24 and the substrate 22 located in the lower layer of the polycrystalline film 25p may be deteriorated by high heat during laser light irradiation. For this reason, the thickness of the altered film 25m is preferably thinner than the thickness of the polycrystalline film 25p (formed on the substrate 22 side of the altered film 25m) below that.
　具体的には、圧電薄膜２５の全体厚さは１～１０μｍであるが、このうち、変質膜２５ｍの厚さは、圧電薄膜２５の全体厚さの１／１０以下であることが望ましく、１／５０以下であることがより望ましい。これにより、変質膜２５ｍはその下層の多結晶膜２５ｐよりも確実に薄くなるため、変質膜２５の形成時の高熱によって、下部電極２４および基板２２が劣化するのを抑えることができる。 Specifically, the total thickness of the piezoelectric thin film 25 is 1 to 10 μm. Among these, the thickness of the altered film 25 m is desirably 1/10 or less of the total thickness of the piezoelectric thin film 25. / 50 or less is more desirable. As a result, the altered film 25m is surely thinner than the underlying polycrystalline film 25p, so that deterioration of the lower electrode 24 and the substrate 22 due to high heat during the formation of the altered film 25 can be suppressed.
　また、変質膜２５ｍの厚みは、５ｎｍ以上であることが望ましく、１０ｎｍ以上であることがより望ましく、２０ｎｍ以上であることがさらに望ましい。変質膜２５ｍに防湿効果を発揮する機能を確実に持たせるためには、変質膜２５ｍの厚みとして少なくとも５ｎｍを確保することが望まれる。 Further, the thickness of the altered film 25m is preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more. In order to ensure that the altered film 25m has a function of exhibiting a moisture-proof effect, it is desirable to secure at least 5 nm as the thickness of the altered film 25m.
　〔インクジェットヘッドの製造方法〕
　次に、上記の圧電アクチュエータ２１ａを備えたインクジェットヘッド２１の製造方法について以下に説明する。図７は、インクジェットヘッド２１の製造工程を示す断面図である。 [Inkjet head manufacturing method]
Next, the manufacturing method of the inkjet head 21 provided with said piezoelectric actuator 21a is demonstrated below. FIG. 7 is a cross-sectional view showing the manufacturing process of the inkjet head 21.
　まず、基板２２を用意する。基板２２としては、ＭＥＭＳ（Micro  Electro　Mechanical　Systems）に多く利用されている結晶シリコン（Ｓｉ）を用いることができ、ここでは、酸化膜２２ｅを介して２枚のＳｉ基板２２ｃ・２２ｄが接合されたＳＯＩ構造のものを用いている。 First, the substrate 22 is prepared. As the substrate 22, crystalline silicon (Si) often used in MEMS (Micro Electro Mechanical Systems) can be used. Here, two Si substrates 22 c and 22 d are joined via an oxide film 22 e. An SOI structure is used.
　基板２２を加熱炉に入れ、１５００℃程度に所定時間保持して、Ｓｉ基板２２ｃ・２２ｄの表面にＳｉＯ2からなる熱酸化膜２３ａ・２３ｂをそれぞれ形成する。次に、一方の熱酸化膜２３ａ上に、ＴｉおよびＰｔの各層をスパッタ法で順に成膜し、下部電極２４を形成する。 The substrate 22 is put in a heating furnace and held at about 1500 ° C. for a predetermined time, and thermal oxide films 23a and 23b made of SiO 2 are formed on the surfaces of the Si substrates 22c and 22d, respectively. Next, Ti and Pt layers are sequentially formed on one thermal oxide film 23a by a sputtering method to form the lower electrode 24.
　続いて、基板２２を６００℃程度に再加熱し、変位膜となるＰＺＴの層２５ａをスパッタ法で成膜する。なお、ＰＺＴからなる層２５ａは、複数の結晶の集合体からなる多結晶膜２５ｐである。次に、基板２２に感光性樹脂３５をスピンコート法で塗布し、マスクを介して露光、エッチングすることによって感光性樹脂３５の不要な部分を除去し、形成する圧電薄膜２５の形状を転写する。その後、感光性樹脂３５をマスクとして、反応性イオンエッチング法を用いて層２５ａの形状を加工し、圧電薄膜２５とする。 Subsequently, the substrate 22 is reheated to about 600 ° C., and a PZT layer 25a serving as a displacement film is formed by sputtering. The layer 25a made of PZT is a polycrystalline film 25p made of an aggregate of a plurality of crystals. Next, a photosensitive resin 35 is applied to the substrate 22 by a spin coating method, and unnecessary portions of the photosensitive resin 35 are removed by exposure and etching through a mask, and the shape of the piezoelectric thin film 25 to be formed is transferred. . Thereafter, using the photosensitive resin 35 as a mask, the shape of the layer 25 a is processed using a reactive ion etching method to form the piezoelectric thin film 25.
　次に、圧電薄膜２５を覆うように下部電極２４上に、ＴｉおよびＰｔの各層をスパッタ法で順に成膜し、層２６ａを形成する。続いて、層２６ａ上に感光性樹脂３６をスピンコート法で塗布し、マスクを介して露光、エッチングすることによって感光性樹脂３６の不要な部分を除去し、形成する上部電極２６の形状を転写する。その後、感光性樹脂３６をマスクとして、反応性イオンエッチング法を用いて層２６ａの形状を加工し、上部電極２６を形成する。このとき、圧電薄膜２５において、上部電極２６の外形からはみ出すテラス領域Ｒ１が形成されるように、圧電薄膜２５上に上部電極２６を形成する。 Next, Ti and Pt layers are sequentially formed by sputtering on the lower electrode 24 so as to cover the piezoelectric thin film 25 to form a layer 26a. Subsequently, a photosensitive resin 36 is applied onto the layer 26a by a spin coating method, and unnecessary portions of the photosensitive resin 36 are removed by exposure and etching through a mask, and the shape of the upper electrode 26 to be formed is transferred. To do. Thereafter, using the photosensitive resin 36 as a mask, the shape of the layer 26a is processed using a reactive ion etching method to form the upper electrode 26. At this time, the upper electrode 26 is formed on the piezoelectric thin film 25 so that the terrace region R <b> 1 that protrudes from the outer shape of the upper electrode 26 is formed in the piezoelectric thin film 25.
　次に、圧電薄膜２５におけるテラス領域Ｒ１の基板２２とは反対側の表面を、レーザー光の照射によって加熱することにより、多結晶膜２５ｐを構成する複数の結晶を一体的に変質させ、テラス領域Ｒ１の表面に、粒界が消滅した変質膜２５ｍを形成する。 Next, the surface of the piezoelectric thin film 25 opposite to the substrate 22 in the terrace region R1 is heated by laser light irradiation, so that the plurality of crystals constituting the polycrystalline film 25p are integrally altered to thereby change the terrace region. On the surface of R1, an altered film 25m having a grain boundary disappeared is formed.
　次に、基板２２の裏面（熱酸化膜２３ｂ側）に感光性樹脂３７をスピンコート法で塗布し、マスクを介して露光、エッチングすることによって、感光性樹脂３７の不要な部分を除去し、形成しようとする圧力室２２ａの形状を転写する。そして、感光性樹脂３７をマスクとして、反応性イオンエッチング法を用いて基板２２の除去加工を行い、圧力室２２ａを形成してアクチュエータ２１ａとする。 Next, a photosensitive resin 37 is applied to the back surface (thermal oxide film 23b side) of the substrate 22 by a spin coat method, and unnecessary portions of the photosensitive resin 37 are removed by exposure and etching through a mask. The shape of the pressure chamber 22a to be formed is transferred. Then, using the photosensitive resin 37 as a mask, the substrate 22 is removed using a reactive ion etching method to form a pressure chamber 22a to be an actuator 21a.
　その後、アクチュエータ２１ａの基板２２と、吐出孔３１ａを有するノズル基板３１とを、接着剤等を用いて接合する。これにより、インクジェットヘッド２１が完成する。なお、吐出孔３１ａに対応する位置に貫通孔を有する中間ガラスを用い、熱酸化膜２３ｂを除去して、基板２２と中間ガラス、および中間ガラスとノズル基板３１とをそれぞれ陽極接合するようにしてもよい。この場合は、接着剤を用いずに３者（基板２２、中間ガラス、ノズル基板３１）を接合することができる。 Thereafter, the substrate 22 of the actuator 21a and the nozzle substrate 31 having the discharge holes 31a are bonded using an adhesive or the like. Thereby, the inkjet head 21 is completed. It should be noted that an intermediate glass having a through hole at a position corresponding to the discharge hole 31a is used, the thermal oxide film 23b is removed, and the substrate 22 and the intermediate glass, and the intermediate glass and the nozzle substrate 31 are anodic bonded to each other. Also good. In this case, the three parties (substrate 22, intermediate glass, nozzle substrate 31) can be joined without using an adhesive.
　上記のように、圧電薄膜２５において、上部電極２６の外形からはみ出すテラス領域Ｒ１を形成することにより、上部電極２６の側面と圧電薄膜２５の側面とが離れるため、圧電薄膜の側面に電界がかかることはない。これにより、圧電薄膜の側面でリーク電流が発生するのを抑えることができる。 As described above, in the piezoelectric thin film 25, by forming the terrace region R1 that protrudes from the outer shape of the upper electrode 26, the side surface of the upper electrode 26 and the side surface of the piezoelectric thin film 25 are separated, so that an electric field is applied to the side surface of the piezoelectric thin film. There is nothing. Thereby, generation | occurrence | production of a leakage current can be suppressed on the side surface of a piezoelectric thin film.
　また、圧電薄膜２５のテラス領域Ｒ１において基板２２とは反対側の表面を加熱することにより変質膜２５ｍを形成しているので、大気中の水分が圧電薄膜２５の上記表面から内部に取り込まれるのを抑えることができる。これにより、上記水分に起因する絶縁破壊、および圧電薄膜２５の側面以外でのリーク電流の発生を抑えることができる。なお、圧電薄膜２５を覆う絶縁体層を形成しないので、上記の絶縁体層による圧電特性の低下の問題は発生しない。 In addition, since the altered film 25m is formed by heating the surface opposite to the substrate 22 in the terrace region R1 of the piezoelectric thin film 25, moisture in the atmosphere is taken into the inside from the surface of the piezoelectric thin film 25. Can be suppressed. Thereby, it is possible to suppress the dielectric breakdown due to the moisture and the occurrence of leak currents other than the side surfaces of the piezoelectric thin film 25. In addition, since the insulator layer which covers the piezoelectric thin film 25 is not formed, the problem of deterioration of the piezoelectric characteristics due to the insulator layer does not occur.
　また、圧電薄膜２５の表面の加熱を、レーザー光の照射によって行っているので、圧電薄膜２５を表面のみ加熱する局所加熱を行って、変質膜２５ｍを形成することができる。このような局所加熱により、圧電薄膜２５の下層の基板２２や下部電極２４に余分な高熱がかからないようにできるため、これらの部材の劣化を防ぐことができる。 Further, since the surface of the piezoelectric thin film 25 is heated by laser light irradiation, the altered film 25m can be formed by performing local heating for heating only the surface of the piezoelectric thin film 25. Such local heating can prevent excessive high heat from being applied to the substrate 22 and the lower electrode 24 under the piezoelectric thin film 25, so that deterioration of these members can be prevented.
　ここで、図８は、圧電薄膜２５の構成材料であるＰＺＴの分光透過率を示すグラフである。圧電薄膜２５（テラス領域Ｒ１）の局所加熱に用いるレーザー光としては、ＰＺＴを透過せず、ＰＺＴに吸収されてその表面を加熱できる波長であればよい。なお、圧電薄膜２５を透過する波長のレーザー光を照射すると、レーザー光が圧電薄膜２５を透過して下地（下部電極２４、基板２２）を破損させてしまうおそれがある。この観点では、用いるレーザー光の波長は、圧電薄膜２５を透過するときの透過率が５０％以下となる波長であることが望ましい。したがって、ＰＺＴを加熱する場合は、図８より、４００ｎｍ以下の波長のレーザー光を用いることが望ましく、３６０ｎｍ以下の波長のレーザー光を用いることがより望ましい。なお、オーブンやホットプレートは、瞬間的な局所加熱が難しいため、用いないほうがよい。 Here, FIG. 8 is a graph showing the spectral transmittance of PZT which is a constituent material of the piezoelectric thin film 25. The laser beam used for local heating of the piezoelectric thin film 25 (terrace region R1) may be any wavelength that does not transmit PZT but can be absorbed by PZT and heat its surface. If laser light having a wavelength that passes through the piezoelectric thin film 25 is irradiated, the laser light may pass through the piezoelectric thin film 25 and damage the base (the lower electrode 24 and the substrate 22). From this viewpoint, it is desirable that the wavelength of the laser beam to be used is a wavelength at which the transmittance when transmitting through the piezoelectric thin film 25 is 50% or less. Therefore, when heating PZT, as shown in FIG. 8, it is desirable to use laser light having a wavelength of 400 nm or less, and more desirably, laser light having a wavelength of 360 nm or less. Note that ovens and hot plates should not be used because instantaneous local heating is difficult.
　〔圧電アクチュエータの他の構成〕
　図９は、圧電アクチュエータ２１ａの他の構成を示す断面図である。同図のように、変質膜２５ｍは、テラス領域Ｒ１の膜厚方向の全体にわたって形成されていてもよい。つまり、変質膜２５ｍが、テラス領域Ｒ１の膜厚方向の全体にわたって形成されて、テラス領域Ｒ１の基板２２とは反対側の表面が露出していてもよい。ただし、この場合は、上述したように、変質膜２５ｍの形成時の高熱によって変質膜２５ｍの下層（下部電極２４、基板２２）が劣化することが懸念されるが、テラス領域Ｒ１での大気中の水分の吸収を変質膜２５ｍにより防止して、絶縁破壊およびリーク電流の発生を防止し、これによって耐電圧性が向上することに変わりはない。 [Other configurations of piezoelectric actuator]
FIG. 9 is a cross-sectional view showing another configuration of the piezoelectric actuator 21a. As shown in the figure, the altered film 25m may be formed over the entire film thickness direction of the terrace region R1. That is, the altered film 25m may be formed over the entire film thickness direction of the terrace region R1, and the surface of the terrace region R1 opposite to the substrate 22 may be exposed. However, in this case, as described above, there is a concern that the lower layer (the lower electrode 24 and the substrate 22) of the altered film 25m may be deteriorated due to high heat when the altered film 25m is formed, but in the atmosphere in the terrace region R1. The alteration film 25m prevents the moisture from being absorbed, thereby preventing the occurrence of dielectric breakdown and leakage current, thereby improving the withstand voltage.
　また、図１０は、圧電アクチュエータ２１ａのさらに他の構成を示す断面図である。同図のように、変質膜２５ｍは、圧電薄膜２５における基板２２とは反対側の表面全体に形成されていてもよい。つまり、テラス領域Ｒ１に加えて、下部電極２４と上部電極２６とで挟まれる駆動領域Ｒ２においても、圧電薄膜２５は、基板２２側から、多結晶膜２５ｐと変質膜２５ｍとをこの順で積層して構成されていてもよい。なお、この構成は、下部電極２４上に圧電薄膜２５を形成した後、圧電薄膜２５の表面全体にレーザー光を照射して表面全体に変質膜２５ｍを形成し、その後、テラス領域Ｒ１が形成されるように上部電極２６を形成することで実現することができる。この構成であっても、テラス領域Ｒ１の変質膜２５ｍによって大気中の水分の吸収を防止するため、絶縁破壊およびリーク電流の発生を防止して、耐電圧性を向上させることができる。 FIG. 10 is a cross-sectional view showing still another configuration of the piezoelectric actuator 21a. As shown in the figure, the altered film 25m may be formed on the entire surface of the piezoelectric thin film 25 opposite to the substrate 22. That is, in addition to the terrace region R1, also in the drive region R2 sandwiched between the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is formed by laminating the polycrystalline film 25p and the altered film 25m in this order from the substrate 22 side. It may be configured as. In this configuration, after the piezoelectric thin film 25 is formed on the lower electrode 24, the entire surface of the piezoelectric thin film 25 is irradiated with laser light to form the altered film 25m on the entire surface, and then the terrace region R1 is formed. This can be realized by forming the upper electrode 26 as described above. Even with this configuration, the alteration film 25m in the terrace region R1 prevents moisture from being absorbed in the atmosphere, so that dielectric breakdown and generation of leakage current can be prevented, and the voltage resistance can be improved.
　また、圧電薄膜２５は、多結晶であるほうが圧電特性に優れている。したがって、駆動領域Ｒ２に変質膜２５ｍを形成する場合は、変質膜２５ｍの厚みは、その基板側の多結晶膜２５ｐの厚みよりも薄いことが望ましい。具体的には、駆動領域Ｒ２における変質膜２５ｍの厚さは、テラス領域Ｒ１に形成する場合と同様に、圧電薄膜２５の全体厚さの１／１０以下であることが望ましく、１／５０以下であることがより望ましい。また、駆動領域Ｒ２における変質膜２５ｍの厚さは、５ｎｍ以上であることが望ましく、１０ｎｍ以上であることがより望ましく、２０ｎｍ以上であることがさらに望ましい。 Moreover, the piezoelectric thin film 25 is more excellent in piezoelectric characteristics when it is polycrystalline. Therefore, when the altered film 25m is formed in the drive region R2, it is desirable that the altered film 25m is thinner than the polycrystalline film 25p on the substrate side. Specifically, the thickness of the altered film 25m in the drive region R2 is desirably 1/10 or less of the total thickness of the piezoelectric thin film 25, as in the case of forming in the terrace region R1, and is 1/50 or less. Is more desirable. In addition, the thickness of the altered film 25m in the drive region R2 is preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more.
　ところで、図１１は、圧電薄膜２５に異物Ｑが含まれる場合の圧電アクチュエータ２１ａの断面図である。圧電薄膜２５に異物Ｑが含まれた状態で、上部電極２６および下部電極２４の間に電界をかけると、異物Ｑや異物Ｑの界面、または異物Ｑの周辺の粒界を電流がリークしやすくなり、絶縁破壊が発生しやすい。なお、圧電薄膜２５に異物Ｑが存在すると、上部電極２６の一部が異物Ｑのある箇所で隆起するため、異物Ｑの有無は、圧電アクチュエータ２１ａの外観検査によって確認できる。 Incidentally, FIG. 11 is a cross-sectional view of the piezoelectric actuator 21a when the piezoelectric thin film 25 includes the foreign matter Q. When an electric field is applied between the upper electrode 26 and the lower electrode 24 in a state where the piezoelectric thin film 25 contains the foreign matter Q, current easily leaks through the foreign matter Q, the interface of the foreign matter Q, or the grain boundary around the foreign matter Q. Therefore, dielectric breakdown is likely to occur. In addition, when the foreign material Q exists in the piezoelectric thin film 25, since a part of upper electrode 26 protrudes in the location with the foreign material Q, the presence or absence of the foreign material Q can be confirmed by the external appearance inspection of the piezoelectric actuator 21a.
　そこで、圧電薄膜２５に異物Ｑが存在することが確認された場合は、上部電極２６の形成後、上部電極２６の外形よりも内側の一部（異物Ｑによって隆起した部分）をレーザー光の照射による加熱によって除去する。異物Ｑの周辺部の上部電極２６を蒸散させて除去することにより、異物Ｑの周辺に電界がかからなくなる。その後、上部電極２６の一部の除去によって露出する領域（露出領域Ｒ３）の圧電薄膜２５の表面を、レーザー光の照射によって加熱（局所加熱）して、複数の結晶を一体的に変質させることにより、上記表面に変質膜２５ｍをさらに形成する。 Therefore, when it is confirmed that the foreign material Q exists in the piezoelectric thin film 25, after the formation of the upper electrode 26, a part inside the outer shape of the upper electrode 26 (a portion raised by the foreign material Q) is irradiated with laser light. Remove by heating with. By removing the upper electrode 26 around the foreign material Q by evaporation, an electric field is not applied around the foreign material Q. Thereafter, the surface of the piezoelectric thin film 25 in the region exposed by removing a part of the upper electrode 26 (exposed region R3) is heated (locally heated) by laser light irradiation, and a plurality of crystals are integrally altered. Thus, the altered film 25m is further formed on the surface.
　図１２は、異物Ｑの周辺の上部電極２６を除去して、圧電薄膜２５の露出領域Ｒ３に変質膜２５ｍを形成した圧電アクチュエータ２１ａの断面図である。露出領域Ｒ３では、圧電薄膜２５は、基板２２側から、多結晶膜２５ｐと変質膜２５ｍとがこの順で積層された形で構成される。なお、露出領域Ｒ３における変質膜２５の厚みの範囲（上限、下限）については、テラス領域Ｒ１および駆動領域Ｒ２における変質膜２５の厚みの範囲と同様に考えることができる。 FIG. 12 is a cross-sectional view of the piezoelectric actuator 21a in which the upper electrode 26 around the foreign material Q is removed and the altered film 25m is formed in the exposed region R3 of the piezoelectric thin film 25. In the exposed region R3, the piezoelectric thin film 25 is configured by laminating the polycrystalline film 25p and the altered film 25m in this order from the substrate 22 side. The range (upper limit and lower limit) of the altered film 25 in the exposed region R3 can be considered in the same manner as the thickness range of the altered film 25 in the terrace region R1 and the drive region R2.
　露出領域Ｒ３において、圧電薄膜２５の大気側の表面に変質膜２５ｍを形成することにより、大気中の水分が圧電薄膜２５の内部に取り込まれるのを抑えることができる。これにより、異物Ｑの存在によって上部電極２６の一部を除去し、下層の圧電薄膜２５が露出する場合でも、上記水分に起因する、露出領域Ｒ３での圧電薄膜２５の絶縁破壊およびリーク電流の発生を抑えることができる。 In the exposed region R3, by forming the altered film 25m on the surface of the piezoelectric thin film 25 on the atmosphere side, it is possible to prevent moisture in the atmosphere from being taken into the piezoelectric thin film 25. Thereby, even when a part of the upper electrode 26 is removed due to the presence of the foreign matter Q and the lower piezoelectric thin film 25 is exposed, the dielectric breakdown and leakage current of the piezoelectric thin film 25 in the exposed region R3 due to the moisture are caused. Occurrence can be suppressed.
　以上のことから、図１２の圧電アクチュエータ２１ａにおいては、上部電極２６は、その外形よりも内側で一部が除去されており、変質膜２５ｍは、上部電極２６の一部の除去によって圧電薄膜が露出する露出領域Ｒ３にさらに形成されており、露出領域Ｒ３において、圧電薄膜２５は、基板２２側から多結晶膜２５ｐと変質膜２２ｍとをこの順で有していてもよいと言える。 From the above, in the piezoelectric actuator 21a of FIG. 12, a part of the upper electrode 26 is removed on the inner side of the outer shape, and the altered film 25m has a piezoelectric thin film formed by removing a part of the upper electrode 26. It is further formed in the exposed exposed region R3, and in the exposed region R3, it can be said that the piezoelectric thin film 25 may have the polycrystalline film 25p and the altered film 22m in this order from the substrate 22 side.
　図１２においては、圧電薄膜２５がテラス領域Ｒ１を有する例で説明したが、上部電極２６の一部を除去し、露出領域Ｒ３に変質膜２５ｍを形成して圧電薄膜上部からの水分吸着によるリーク電流を防止することは、テラス領域Ｒ１を持たない圧電薄膜、すなわち圧電薄膜の側面と上部電極の側面とが面一になっている構成においても適用できる。 In FIG. 12, the example in which the piezoelectric thin film 25 has the terrace region R <b> 1 has been described. Preventing the current can be applied to a piezoelectric thin film having no terrace region R1, that is, a configuration in which the side surface of the piezoelectric thin film and the side surface of the upper electrode are flush with each other.
　〔実施例〕
　次に、図４および図１２で示した構成において、変質膜２５ｍを形成する具体的な実施例を、それぞれ実施例１および２として説明する。 〔Example〕
Next, specific examples of forming the altered film 25m in the configuration shown in FIGS. 4 and 12 will be described as Examples 1 and 2, respectively.
　（実施例１）
　図７で示した方法で、基板２２上に、下部電極２４、圧電薄膜２５、上部電極２６を順に形成した後、圧電薄膜２５のテラス領域Ｒ１にレーザー光を照射して変質膜２５ｍを形成し、図４で示した構成の圧電アクチュエータ２１ａを製造した。このとき、Ｓｉからなる振動板２２ｂの厚みを５μｍとし、Ｐｔを含む下部電極２４の厚みを０．１μｍとし、ＰＺＴからなる圧電薄膜２５の厚みを５μｍとし、Ａｕを含む上部電極の厚みを０．３μｍとした。 Example 1
After the lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 are sequentially formed on the substrate 22 by the method shown in FIG. 7, the altered region 25m is formed by irradiating the terrace region R1 of the piezoelectric thin film 25 with laser light. The piezoelectric actuator 21a having the configuration shown in FIG. 4 was manufactured. At this time, the thickness of the diaphragm 22b made of Si is 5 μm, the thickness of the lower electrode 24 containing Pt is 0.1 μm, the thickness of the piezoelectric thin film 25 made of PZT is 5 μm, and the thickness of the upper electrode containing Au is 0 μm. 3 μm.
　下部電極２４上にスパッタ法で成膜される圧電薄膜２５は、下部電極２４から上側に伸びる柱状の結晶が集まった多結晶膜２５ｐ（粒径：数十ｎｍ～１μｍ程度、結晶配向：＜１００＞方向）を有しており、また、圧電薄膜２５において、上部電極２６で覆われていないテラス領域Ｒ１のＰＺＴ表面には、アモルファスの状態のＰＺＴ、すなわち、粒界のない領域（変質膜２５ｍ）が形成されていることが、ＳＥＭ画像等から確認された。なお、変質膜２５ｍの厚みは、２０ｎｍであった。 The piezoelectric thin film 25 formed on the lower electrode 24 by sputtering is a polycrystalline film 25p in which columnar crystals extending upward from the lower electrode 24 are gathered (grain size: about several tens of nm to 1 μm, crystal orientation: <100 In the piezoelectric thin film 25, the PZT surface of the terrace region R1 that is not covered with the upper electrode 26 has an amorphous PZT, that is, a region having no grain boundary (modified film 25m). ) Was confirmed from SEM images and the like. The thickness of the altered film 25m was 20 nm.
　ここで、変質膜２５ｍは、ＰＺＴの多結晶膜２５ｐを局所加熱（表面のみを加熱）することにより形成されるが、このときの局所加熱は、ＨＯＹＡ製のＹＡＧレーザー照射機（ＬＲ－３１００ＳＵＶ）を用い、パルスレーザーを照射して行った。レーザー光の波長は２６６ｎｍであり、パルス幅は５ｎｓｅｃであり、光量は０．１ｍＪであった。ＰＺＴの融点は、一般的には１３００～１６００℃と言われているが、上記のレーザー光を用いることにより、局所加熱によってＰＺＴ表面を確実に融解し、固化させて、ＰＺＴ表面の粒界を無くすことができた。 Here, the altered film 25m is formed by locally heating the polycrystalline film 25p of PZT (only the surface is heated). The local heating at this time is performed by a YAG laser irradiator (LR-3100SUV) manufactured by HOYA. Was performed by irradiating a pulse laser. The wavelength of the laser beam was 266 nm, the pulse width was 5 nsec, and the light amount was 0.1 mJ. The melting point of PZT is generally said to be 1300 to 1600 ° C. However, by using the above laser beam, the PZT surface is surely melted and solidified by local heating, and the grain boundary on the PZT surface is changed. I was able to lose it.
　ＰＺＴ透過率の高い波長（吸収の少ない波長）での加工は、光のほとんどがＰＺＴを透過して、ＰＺＴの表面にかかる熱が非常に小さくなるので好適ではない。ＰＺＴの局所加熱に使用できるレーザー光の波長は、上述のように４００ｎｍ以下であることが望ましい。このようなレーザー光の例としては、以下のものが挙げられる。
　（１）ＹＡＧレーザー（固体レーザーの一種で、波長１０６４ｎｍを基本波とするレーザー）
　ＹＡＧ第３高調波：波長３５５ｎｍ（ＹＡＧ基本波を３分の１の波長に変換したもの）
　ＹＡＧ第４高調波：波長２６６ｎｍ（ＹＡＧ基本波を４分の１の波長に変換したもの）
　ＹＡＧ第５高調波：波長２１３ｎｍ（ＹＡＧ基本波を５分の１の波長に変換したもの）
　（２）エキシマレーザー（気体レーザーの一種で、使う媒質により波長が異なる）
　媒質Ｎ2    ：波長３３７ｎｍ
　媒質ＸｅＣｌ：波長３０８ｎｍ
　媒質ＫｒＦ　：波長２４８ｎｍ
　媒質ＫｒＣｌ：波長２２２ｎｍ
　媒質ＡｒＦ　：波長１９３ｎｍ Processing at a wavelength with a high PZT transmittance (a wavelength with little absorption) is not preferable because most of the light passes through the PZT and the heat applied to the surface of the PZT becomes very small. The wavelength of laser light that can be used for local heating of PZT is desirably 400 nm or less as described above. Examples of such laser light include the following.
(1) YAG laser (a type of solid-state laser with a fundamental wavelength of 1064 nm)
YAG third harmonic: Wavelength 355 nm (YAG fundamental wave converted to 1/3 wavelength)
YAG fourth harmonic: wavelength 266 nm (YAG fundamental wave converted to a quarter wavelength)
YAG fifth harmonic: Wavelength 213 nm (YAG fundamental wave converted to 1/5 wavelength)
(2) Excimer laser (a type of gas laser with different wavelengths depending on the medium used)
Medium N 2 : wavelength 337 nm
Medium XeCl: wavelength 308 nm
Medium KrF: wavelength 248 nm
Medium KrCl: wavelength 222 nm
Medium ArF: wavelength 193 nm
　また、ＰＺＴ表面に十分な熱が加わるように照射光量を上げると、ＰＺＴ表面だけでなく、その下地（下部電極２４、振動板２２ｂ等）および照射エリア周辺が、加熱の影響を受けて、素子性能が劣化する場合がある。このため、照射光量についても適切に設定する必要がある。 Further, when the amount of irradiation light is increased so that sufficient heat is applied to the PZT surface, not only the PZT surface but also the base (the lower electrode 24, the diaphragm 22b, etc.) and the periphery of the irradiation area are affected by heating, Performance may be degraded. For this reason, it is necessary to appropriately set the irradiation light quantity.
　このようにして作製した圧電アクチュエータ２１ａの耐電圧性を以下のようにして調べた。すなわち、上部電極２６と下部電極２４との間に、周波数１００ｋＨｚの矩形波で２０Ｖの電圧を３０分印加して、絶縁破壊が発生するかどうかのテストを行った。絶縁破壊が発生しなかった場合は、印加電圧をさらに５Ｖ上げてテストを行い、最大５０Ｖまで上げてテストを行った。なお、テスト環境は、２３℃湿度５０％ＲＨであった。 The withstand voltage property of the piezoelectric actuator 21a thus manufactured was examined as follows. That is, a test was performed to check whether or not dielectric breakdown occurred by applying a voltage of 20 V with a rectangular wave with a frequency of 100 kHz for 30 minutes between the upper electrode 26 and the lower electrode 24. When dielectric breakdown did not occur, the test was performed by further increasing the applied voltage by 5 V and increasing it to a maximum of 50 V. The test environment was 23 ° C. and humidity 50% RH.
　また、実施例１において、変質膜２５ｍを形成しなかったものを比較例１の圧電アクチュエータ（図６参照）とし、この圧電アクチュエータについても上記と同様にして耐電圧性を調べた。その結果、実施例１では、印加電圧を５０Ｖまで上げても絶縁破壊は発生しなかったが、比較例１では、印加電圧が３５Ｖのときに絶縁破壊が発生した。したがって、実施例１のようにテラス領域Ｒ１に変質膜２５ｍを形成する構成では、変質膜２５ｍを形成しない場合に比べて、耐電圧性が１５Ｖ以上向上すると言える。 Further, in Example 1, the one in which the altered film 25m was not formed was used as the piezoelectric actuator of Comparative Example 1 (see FIG. 6), and the voltage resistance of this piezoelectric actuator was also examined in the same manner as described above. As a result, dielectric breakdown did not occur in Example 1 even when the applied voltage was increased to 50V, but dielectric breakdown occurred in Comparative Example 1 when the applied voltage was 35V. Therefore, it can be said that with the configuration in which the altered film 25m is formed in the terrace region R1 as in Example 1, the withstand voltage is improved by 15 V or more compared to the case where the altered film 25m is not formed.
　なお、圧電変位については、実施例１と比較例１とで同じ値であり、変質膜２５ｍを形成したことによる圧電変位への影響はないことが確認された。 The piezoelectric displacement was the same value in Example 1 and Comparative Example 1, and it was confirmed that there was no influence on the piezoelectric displacement due to the formation of the altered film 25m.
　（実施例２）
　圧電アクチュエータ２１ａの完成後、圧電薄膜２５に異物Ｑは混入していることが外観検査で確認されたときに、レーザー光を照射して、異物Ｑの周辺の上部電極２６を除去し、その後、むき出しとなったＰＺＴの表面にもレーザー光を照射して、ＰＺＴの粒界を無くした変質膜２５ｍを形成した（図１２参照）。このようにすることで、異物起因のリーク電流の発生を抑えることができる。 (Example 2)
After the completion of the piezoelectric actuator 21a, when it is confirmed by appearance inspection that the foreign matter Q is mixed in the piezoelectric thin film 25, the upper electrode 26 around the foreign matter Q is removed by irradiating laser light, The exposed surface of the PZT was also irradiated with laser light to form an altered film 25m having no PZT grain boundaries (see FIG. 12). By doing in this way, generation | occurrence | production of the leakage current resulting from a foreign material can be suppressed.
　上部電極２６の除去およびＰＺＴ表面における変質膜２５ｍの形成は、ＨＯＹＡ製のＹＡＧレーザー照射機（ＬＲ－３１００ＳＵＶ）を用い、パルスレーザーを照射して行った。レーザー光の波長は２６６ｎｍであり、パルス幅は５ｎｓｅｃであり、光量は０．５ｍＪであった。レーザー光の照射光量を実施例１よりも上げることにより、異物Ｑの周辺の上部電極２６の除去と、ＰＺＴ表面の変質膜２５の形成（粒界をなくす処理）とを一括して（連続して）行うことができる。なお、上部電極２６の除去と、ＰＺＴ表面の変質膜２５の形成とを非連続的に（時間を空けて）行ってもよい。 The removal of the upper electrode 26 and the formation of the altered film 25m on the PZT surface were performed by irradiating a pulse laser using a YAG laser irradiator (LR-3100SUV) manufactured by HOYA. The wavelength of the laser beam was 266 nm, the pulse width was 5 nsec, and the amount of light was 0.5 mJ. By increasing the amount of laser light irradiation more than in Example 1, the removal of the upper electrode 26 around the foreign matter Q and the formation of the altered film 25 on the PZT surface (treatment for eliminating the grain boundary) are collectively performed (continuously). Can do). The removal of the upper electrode 26 and the formation of the altered film 25 on the PZT surface may be performed discontinuously (with a time interval).
　上記のように処理することで、実施例２では、印加電圧を５０Ｖまで上げても絶縁破壊は発生せず、良好な耐電圧性が得られることが確認された。 As a result of the treatment as described above, in Example 2, it was confirmed that even when the applied voltage was increased to 50 V, dielectric breakdown did not occur and good voltage resistance was obtained.
　以上で説明した本実施形態の圧電アクチュエータ、圧電アクチュエータの製造方法、インクジェットヘッドおよびインクジェットプリンタは、以下のように表現することができ、これによって以下の作用効果を奏する。 The piezoelectric actuator, the manufacturing method of the piezoelectric actuator, the ink jet head, and the ink jet printer of the present embodiment described above can be expressed as follows, and thereby have the following effects.
　本実施形態の圧電アクチュエータは、基板上に、下部電極、圧電薄膜および上部電極をこの順で有する圧電アクチュエータであって、前記圧電薄膜は、複数の結晶を含む多結晶膜と、複数の結晶の一体的な変質によって粒界が消滅した変質膜とを有しており、前記変質膜は、前記下部電極上の前記圧電薄膜において、前記上部電極の外形からはみ出した領域に少なくとも形成されており、かつ、前記領域において前記基板とは反対側の表面に露出している。 The piezoelectric actuator of this embodiment is a piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode in this order on a substrate. The piezoelectric thin film includes a polycrystalline film including a plurality of crystals and a plurality of crystals. An alteration film in which grain boundaries disappear due to integral alteration, and the alteration film is formed at least in a region protruding from the outer shape of the upper electrode in the piezoelectric thin film on the lower electrode, And in the said area | region, it exposes on the surface on the opposite side to the said board | substrate.
　圧電薄膜は、下部電極上で上部電極の外形からはみ出した領域を有している。この構成では、上部電極の側面（端面）が、圧電薄膜の側面（端面）と同一面上になく、離れているため、上部電極と下部電極との間に電界をかけたときに、圧電薄膜の側面に電界がかかることはない。このため、たとえ大気中の水分が圧電薄膜の側面から内部に取り込まれても、その水分に起因して側面リークが発生するのを抑えることができる。 The piezoelectric thin film has a region protruding from the outer shape of the upper electrode on the lower electrode. In this configuration, since the side surface (end surface) of the upper electrode is not flush with the side surface (end surface) of the piezoelectric thin film, it is separated from the piezoelectric thin film when an electric field is applied between the upper electrode and the lower electrode. No electric field is applied to the side surface. For this reason, even if moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film, it is possible to suppress the occurrence of side surface leakage due to the moisture.
　また、圧電薄膜の少なくとも上記の領域に、複数の結晶の一体的な変質によって粒界が消滅した変質膜が形成されており、この変質膜が上記領域において基板とは反対側の表面に露出している。なお、変質膜が上記表面に露出するのであれば、変質膜は上記領域において圧電薄膜の膜厚方向全体に形成されていてもよいし、表面側にのみ形成されていてもよい（基板側は多結晶膜であってもよい）。 In addition, an altered film in which the grain boundaries have disappeared due to integral alteration of a plurality of crystals is formed in at least the above-described region of the piezoelectric thin film, and this altered film is exposed on the surface opposite to the substrate in the above-described region. ing. If the altered film is exposed on the surface, the altered film may be formed in the entire region of the piezoelectric thin film in the region, or may be formed only on the surface side (on the substrate side). It may be a polycrystalline film).
　圧電薄膜の表面に多結晶膜が存在する場合は、大気中の水分が多結晶膜の粒界を介して内部に取り込まれる。しかし、変質膜は粒界を持たないため、大気中の水分が圧電薄膜の上記表面から内部に取り込まれるのを抑えることができる。これにより、上記水分に起因して圧電薄膜に絶縁破壊が生じてリーク電流が発生するのを抑えることができ、耐電圧性を向上させることができる。つまり、上部電極と下部電極との間に電界をかけたときに、上部電極の端部と下部電極との間で圧電薄膜の絶縁破壊が発生するのを抑えて、圧電薄膜の側面以外におけるリーク電流の発生も抑えることができる。しかも、従来のように、絶縁体層で圧電薄膜を覆うことなく、リーク電流の発生を抑えることができるので、上記の絶縁体層によって圧電薄膜の変位が阻害され、圧電特性が低下するということは起こり得ない。 When a polycrystalline film is present on the surface of the piezoelectric thin film, moisture in the atmosphere is taken into the interior through the grain boundary of the polycrystalline film. However, since the altered film does not have a grain boundary, it is possible to prevent moisture in the atmosphere from being taken into the inside from the surface of the piezoelectric thin film. Thereby, it is possible to suppress the occurrence of a leakage current due to dielectric breakdown in the piezoelectric thin film due to the moisture, and to improve the voltage resistance. In other words, when an electric field is applied between the upper electrode and the lower electrode, the dielectric breakdown of the piezoelectric thin film is prevented from occurring between the end portion of the upper electrode and the lower electrode, so that leakage occurs on the side other than the side surface of the piezoelectric thin film. Generation of current can also be suppressed. Moreover, unlike the conventional case, since the generation of leakage current can be suppressed without covering the piezoelectric thin film with the insulator layer, the above-described insulator layer inhibits the displacement of the piezoelectric thin film, and the piezoelectric characteristics are deteriorated. Can't happen.
　前記変質膜は、非晶質構造を持っていてもよい。この場合、変質膜は確実に粒界を持たないため、上記の効果を確実に得ることができる。 The altered film may have an amorphous structure. In this case, since the altered film does not have grain boundaries, the above effect can be obtained with certainty.
　前記領域において、前記圧電薄膜は、前記基板側から前記多結晶膜と前記変質膜とをこの順で有していてもよい。 In the region, the piezoelectric thin film may have the polycrystalline film and the altered film in this order from the substrate side.
　下部電極上の上記領域においては、圧電薄膜の基板側は大気と接触せず（下部電極および基板が存在するため）、基板とは反対側が大気と接触する。このため、上記領域では、圧電薄膜の膜厚方向全体を変質膜で形成しなくても、つまり、基板側を多結晶膜とし、基板とは反対側を変質膜とした構成であっても、上述の効果を得ることができる。 In the above region on the lower electrode, the substrate side of the piezoelectric thin film is not in contact with the atmosphere (because the lower electrode and the substrate are present), and the opposite side of the substrate is in contact with the atmosphere. Therefore, in the above region, even if the entire film thickness direction of the piezoelectric thin film is not formed by the altered film, that is, the substrate side is a polycrystalline film, and the opposite side of the substrate is the altered film, The effects described above can be obtained.
　前記上部電極は、その外形よりも内側で一部が除去されており、前記変質膜は、前記上部電極の一部の除去によって前記圧電薄膜が露出する露出領域にさらに形成されており、前記露出領域において、前記圧電薄膜は、前記基板側から前記多結晶膜と前記変質膜とをこの順で有していてもよい。 The upper electrode is partially removed inside the outer shape, and the altered film is further formed in an exposed region where the piezoelectric thin film is exposed by removing a part of the upper electrode. In the region, the piezoelectric thin film may have the polycrystalline film and the altered film in this order from the substrate side.
　例えば、圧電薄膜に存在する異物を介してリーク電流が発生するのを防止するために、上部電極の外形よりも内側で、上部電極の一部（異物の上方の箇所）が除去される場合がある。上部電極の一部の除去によって圧電薄膜が露出する領域（露出領域）では、基板側に多結晶膜を位置させ、大気側に変質膜を位置させることで、大気中の水分が圧電薄膜の内部に取り込まれるのを抑えることができる。これにより、圧電薄膜の上記露出領域での絶縁破壊およびリーク電流の発生を抑えることができる。 For example, in order to prevent leakage current from being generated through foreign matter existing in the piezoelectric thin film, a part of the upper electrode (a portion above the foreign matter) may be removed inside the outer shape of the upper electrode. is there. In the region where the piezoelectric thin film is exposed by removing a part of the upper electrode (exposed region), the polycrystalline film is positioned on the substrate side, and the altered film is positioned on the atmospheric side, so that moisture in the atmosphere is contained inside the piezoelectric thin film. Can be prevented from being taken in. Thereby, it is possible to suppress dielectric breakdown and generation of leakage current in the exposed region of the piezoelectric thin film.
　前記変質膜の厚みは、該変質膜よりも前記基板側に形成される前記多結晶膜の厚みよりも薄いことが望ましい。変質膜は、例えばレーザー光の照射により、複数の結晶を一体的に変質させる（例えば非晶質化させる）ことによって形成される。変質膜を厚くする場合は、多結晶膜の下層（下部電極、基板）がレーザー光の照射時の高熱により劣化することが懸念されるため、変質膜は多結晶膜よりも薄くすることが望ましい。 The thickness of the altered film is preferably thinner than the thickness of the polycrystalline film formed on the substrate side than the altered film. The altered film is formed by, for example, altering a plurality of crystals integrally (for example, making them amorphous) by irradiation with laser light, for example. When the altered film is thickened, there is a concern that the lower layer (lower electrode, substrate) of the polycrystalline film may be deteriorated by high heat during laser light irradiation. Therefore, it is desirable that the altered film be thinner than the polycrystalline film. .
　前記変質膜の厚みは、５ｎｍ以上であることが望ましい。変質膜の厚みが少なくとも５ｎｍあれば、変質膜を、大気中の水分の侵入を防ぐ膜として確実に機能させることができる。 The thickness of the altered film is preferably 5 nm or more. If the thickness of the altered film is at least 5 nm, the altered film can reliably function as a film that prevents moisture from entering the atmosphere.
　本実施形態のインクジェットヘッドは、上述した圧電アクチュエータと、前記圧電アクチュエータの前記基板に形成される開口部に収容されるインクを外部に吐出するためのノズル孔を有するノズル基板とを備えている。上述した圧電アクチュエータでは、耐電圧性を向上させることができるため、高い電界を印加してインク吐出を行うことが可能となる。これにより、高粘度のインクを用いたインク吐出が可能となる。 The inkjet head according to the present embodiment includes the above-described piezoelectric actuator and a nozzle substrate having a nozzle hole for ejecting ink accommodated in an opening formed in the substrate of the piezoelectric actuator to the outside. In the above-described piezoelectric actuator, since the withstand voltage can be improved, it is possible to eject ink by applying a high electric field. As a result, ink discharge using high-viscosity ink becomes possible.
　本実施形態のインクジェットプリンタは、上記のインクジェットヘッドを備え、前記インクジェットヘッドから記録媒体に向けてインクを吐出させる。上記のインクジェットヘッドを備えていることにより、高速で高精細な描画に有利なインクジェットプリンタを実現できる。 The ink jet printer according to the present embodiment includes the above ink jet head, and ejects ink from the ink jet head toward a recording medium. By including the above-described inkjet head, an inkjet printer advantageous for high-speed and high-definition drawing can be realized.
　本実施形態の圧電アクチュエータの製造方法は、基板上に下部電極を形成する工程と、前記下部電極上に、複数の結晶を含む多結晶膜を成膜して圧電薄膜を形成する工程と、前記圧電薄膜において、上部電極の外形からはみ出す領域が形成されるように、前記圧電薄膜上に前記上部電極を形成する工程と、前記領域の前記基板とは反対側の表面を加熱して、前記多結晶膜に含まれる複数の結晶を一体的に変質させることにより、粒界が消滅した変質膜を、前記領域の少なくとも前記表面に形成する工程とを有している。 The method for manufacturing a piezoelectric actuator of this embodiment includes a step of forming a lower electrode on a substrate, a step of forming a polycrystalline film including a plurality of crystals on the lower electrode, and forming a piezoelectric thin film, In the piezoelectric thin film, the step of forming the upper electrode on the piezoelectric thin film so as to form a region protruding from the outer shape of the upper electrode, and heating the surface of the region opposite to the substrate to Forming a denatured film having the grain boundaries disappeared on at least the surface of the region by integrally modifying a plurality of crystals contained in the crystal film.
　圧電薄膜には、上部電極の外形からはみ出した領域が形成されており、上部電極の側面と圧電薄膜の側面とが離れるため、圧電薄膜の側面に電界がかかることはない。このため、たとえ大気中の水分が圧電薄膜の側面から内部に取り込まれても、その水分に起因する側面リークの発生を抑えることができる。 In the piezoelectric thin film, a region protruding from the outer shape of the upper electrode is formed, and the side surface of the upper electrode is separated from the side surface of the piezoelectric thin film, so that no electric field is applied to the side surface of the piezoelectric thin film. For this reason, even if moisture in the atmosphere is taken into the inside from the side surface of the piezoelectric thin film, the occurrence of side leakage due to the moisture can be suppressed.
　また、圧電薄膜の上記領域の基板とは反対側の表面に、粒界が消滅した変質膜が形成されるので、大気中の水分が圧電薄膜の上記表面から内部に取り込まれるのを抑えることができる。したがって、上記水分に起因する絶縁破壊およびリーク電流の発生を抑えて、耐電圧性を向上させることができる。つまり、上部電極の端部と下部電極との間で圧電薄膜の絶縁破壊が発生するのを抑えて、圧電薄膜の側面以外におけるリーク電流の発生も抑えることができる。しかも、従来のように、絶縁体層で圧電薄膜を覆うことなく、リーク電流の発生を抑えることができるので、上記の絶縁体層によって圧電薄膜の変位が阻害され、圧電特性が低下するということは起こり得ない。 In addition, a modified film with the grain boundaries disappearing is formed on the surface of the piezoelectric thin film opposite to the substrate, so that moisture in the atmosphere can be prevented from being taken into the surface from the surface of the piezoelectric thin film. it can. Therefore, it is possible to improve the voltage resistance while suppressing the occurrence of dielectric breakdown and leakage current due to the moisture. That is, it is possible to suppress the dielectric breakdown of the piezoelectric thin film between the end portion of the upper electrode and the lower electrode, and it is possible to suppress the occurrence of a leakage current other than on the side surface of the piezoelectric thin film. Moreover, unlike the conventional case, since the generation of leakage current can be suppressed without covering the piezoelectric thin film with the insulator layer, the above-described insulator layer inhibits the displacement of the piezoelectric thin film, and the piezoelectric characteristics are deteriorated. Can't happen.
　上記の製造方法は、前記上部電極の形成後、前記上部電極の外形よりも内側の一部を加熱によって除去し、その後、前記上部電極の一部の除去によって露出する前記圧電薄膜の表面を加熱して、前記多結晶膜に含まれる複数の結晶を一体的に変質させることにより、粒界が消滅した変質膜を前記表面に形成する工程をさらに有していてもよい。 In the above manufacturing method, after the formation of the upper electrode, a part inside the outer shape of the upper electrode is removed by heating, and then the surface of the piezoelectric thin film exposed by removing a part of the upper electrode is heated. In addition, the method may further include a step of forming, on the surface, a modified film in which the grain boundaries have disappeared by integrally modifying a plurality of crystals contained in the polycrystalline film.
　この場合、上部電極の一部の除去によって露出した圧電薄膜の内部に大気中の水分が取り込まれるのを、表面の変質膜で抑えることができる。これにより、上部電極の一部の除去によって露出した領域での圧電薄膜の絶縁破壊およびリーク電流の発生を抑えることができる。 In this case, it is possible to suppress the moisture in the atmosphere from being taken into the piezoelectric thin film exposed by removing a part of the upper electrode with the altered film on the surface. Thereby, it is possible to suppress the dielectric breakdown of the piezoelectric thin film and the occurrence of leakage current in the region exposed by removing a part of the upper electrode.
　前記圧電薄膜の表面の加熱を、レーザー光の照射によって行うことが望ましい。レーザー光の照射により、圧電薄膜（多結晶膜）を局所的に加熱して、つまり、圧電薄膜の膜厚方向の一部（例えば表面のみ）を瞬間的に加熱して、変質膜を形成することができる。このような局所加熱により、構成部材である基板や下部電極に余分な高熱がかからないようにできるため、これらの部材の劣化を防ぐことができる。 It is desirable to heat the surface of the piezoelectric thin film by laser light irradiation. By applying laser light, the piezoelectric thin film (polycrystalline film) is locally heated, that is, a part of the piezoelectric thin film in the film thickness direction (for example, only the surface) is instantaneously heated to form an altered film. be able to. By such local heating, it is possible to prevent excessive heat from being applied to the substrate and the lower electrode, which are constituent members, so that deterioration of these members can be prevented.
　前記レーザー光の波長は、前記圧電薄膜を透過するときの透過率が５０％以下となる波長であることが望ましい。圧電薄膜が吸収する波長のレーザー光を照射することにより、圧電薄膜を確実に局所加熱できる。 The wavelength of the laser beam is preferably such that the transmittance when transmitting through the piezoelectric thin film is 50% or less. By irradiating laser light having a wavelength that is absorbed by the piezoelectric thin film, the piezoelectric thin film can be reliably heated locally.
　本発明の圧電アクチュエータは、インクジェットヘッドおよびインクジェットプリンタに利用可能である。 The piezoelectric actuator of the present invention can be used for an inkjet head and an inkjet printer.
　　　１　　　インクジェットプリンタ
　　２１　　　インクジェットヘッド
　　２１ａ　　アクチュエータ（圧電アクチュエータ）
　　２２　　　基板
　　２２ａ　　圧力室（開口部）
　　２４　　　下部電極
　　２５　　　圧電薄膜
　　２５ｐ　　多結晶膜
　　２５ｍ　　変質膜
　　２６　　　上部電極
　　３１　　　ノズル基板
　　３１ａ　　吐出孔（ノズル孔）
　　Ｒ１　　　テラス領域
　　Ｒ３　　　露出領域 1 Inkjet Printer 21 Inkjet Head 21a Actuator (Piezoelectric Actuator)
22 Substrate 22a Pressure chamber (opening)
24 Lower electrode 25 Piezoelectric thin film 25p Polycrystalline film 25m Altered film 26 Upper electrode 31 Nozzle substrate 31a Discharge hole (nozzle hole)
R1 Terrace area R3 Exposed area

Claims (12)

  1. 　基板上に、下部電極、圧電薄膜および上部電極をこの順で有する圧電アクチュエータであって、
    　前記圧電薄膜は、複数の結晶を含む多結晶膜と、複数の結晶の一体的な変質によって粒界が消滅した変質膜とを有しており、
    　前記変質膜は、前記下部電極上の前記圧電薄膜において、前記上部電極の外形からはみ出した領域に少なくとも形成されており、かつ、前記領域において前記基板とは反対側の表面に露出している、圧電アクチュエータ。     A piezoelectric actuator having a lower electrode, a piezoelectric thin film, and an upper electrode in this order on a substrate,
    The piezoelectric thin film has a polycrystalline film containing a plurality of crystals and a modified film in which grain boundaries have disappeared due to integral modification of the plurality of crystals,
    In the piezoelectric thin film on the lower electrode, the altered film is formed at least in a region protruding from the outer shape of the upper electrode, and is exposed on the surface opposite to the substrate in the region. Piezoelectric actuator.
  2. 　前記変質膜は、非晶質構造を持つ、請求項１に記載の圧電アクチュエータ。 The piezoelectric actuator according to claim 1, wherein the altered film has an amorphous structure.
  3. 　前記領域において、前記圧電薄膜は、前記基板側から前記多結晶膜と前記変質膜とをこの順で有している、請求項１または２に記載の圧電アクチュエータ。 3. The piezoelectric actuator according to claim 1, wherein in the region, the piezoelectric thin film has the polycrystalline film and the altered film in this order from the substrate side.
  4. 　前記上部電極は、その外形よりも内側で一部が除去されており、
    　前記変質膜は、前記上部電極の一部の除去によって前記圧電薄膜が露出する露出領域にさらに形成されており、
    　前記露出領域において、前記圧電薄膜は、前記基板側から前記多結晶膜と前記変質膜とをこの順で有している、請求項３に記載の圧電アクチュエータ。     The upper electrode has been partially removed inside its outer shape,
    The altered film is further formed in an exposed region where the piezoelectric thin film is exposed by removing a part of the upper electrode,
    4. The piezoelectric actuator according to claim 3, wherein in the exposed region, the piezoelectric thin film has the polycrystalline film and the altered film in this order from the substrate side.
  5. 　前記変質膜の厚みは、該変質膜よりも前記基板側に形成される前記多結晶膜の厚みよりも薄い、請求項３または４に記載の圧電アクチュエータ。 5. The piezoelectric actuator according to claim 3, wherein a thickness of the altered film is thinner than a thickness of the polycrystalline film formed on the substrate side than the altered film.
  6. 　前記変質膜の厚みは、５ｎｍ以上である、請求項１から５のいずれかに記載の圧電アクチュエータ。 The piezoelectric actuator according to any one of claims 1 to 5, wherein the thickness of the altered film is 5 nm or more.
  7. 　請求項１から６のいずれかに記載の圧電アクチュエータと、
    　前記圧電アクチュエータの前記基板に形成される開口部に収容されるインクを外部に吐出するためのノズル孔を有するノズル基板とを備えている、インクジェットヘッド。     A piezoelectric actuator according to any one of claims 1 to 6,
    An inkjet head comprising: a nozzle substrate having a nozzle hole for discharging ink accommodated in an opening formed in the substrate of the piezoelectric actuator.
  8. 　請求項７に記載のインクジェットヘッドを備え、前記インクジェットヘッドから記録媒体に向けてインクを吐出させる、インクジェットプリンタ。 An inkjet printer comprising the inkjet head according to claim 7, wherein ink is ejected from the inkjet head toward a recording medium.
  9. 　基板上に下部電極を形成する工程と、
    　前記下部電極上に、複数の結晶を含む多結晶膜を成膜して圧電薄膜を形成する工程と、
    　前記圧電薄膜において、上部電極の外形からはみ出す領域が形成されるように、前記圧電薄膜上に前記上部電極を形成する工程と、
    　前記領域の前記基板とは反対側の表面を加熱して、前記多結晶膜に含まれる複数の結晶を一体的に変質させることにより、粒界が消滅した変質膜を、前記領域の少なくとも前記表面に形成する工程とを有している、圧電アクチュエータの製造方法。     Forming a lower electrode on the substrate;
    Forming a piezoelectric thin film by forming a polycrystalline film containing a plurality of crystals on the lower electrode;
    Forming the upper electrode on the piezoelectric thin film such that a region protruding from the outer shape of the upper electrode is formed in the piezoelectric thin film;
    The surface of the region opposite to the substrate is heated to integrally modify a plurality of crystals contained in the polycrystalline film, thereby causing a modified film in which grain boundaries have disappeared to form at least the surface of the region. A method of manufacturing a piezoelectric actuator.
  10. 　前記上部電極の形成後、前記上部電極の外形よりも内側の一部を加熱によって除去し、その後、前記上部電極の一部の除去によって露出する前記圧電薄膜の表面を加熱して、前記多結晶膜に含まれる複数の結晶を一体的に変質させることにより、粒界が消滅した変質膜を前記表面に形成する工程をさらに有している、請求項９に記載の圧電アクチュエータの製造方法。 After the formation of the upper electrode, a part inside the outer shape of the upper electrode is removed by heating, and then the surface of the piezoelectric thin film exposed by the removal of a part of the upper electrode is heated to form the polycrystal The method for manufacturing a piezoelectric actuator according to claim 9, further comprising a step of forming, on the surface, a modified film in which grain boundaries have disappeared by integrally modifying a plurality of crystals contained in the film.
  11. 　前記圧電薄膜の表面の加熱を、レーザー光の照射によって行う、請求項９または１０に記載の圧電アクチュエータの製造方法。 The method for manufacturing a piezoelectric actuator according to claim 9 or 10, wherein the surface of the piezoelectric thin film is heated by laser light irradiation.
  12. 　前記レーザー光の波長は、前記圧電薄膜を透過するときの透過率が５０％以下となる波長である、請求項１１に記載の圧電アクチュエータの製造方法。 12. The method of manufacturing a piezoelectric actuator according to claim 11, wherein the wavelength of the laser beam is a wavelength at which the transmittance when transmitting through the piezoelectric thin film is 50% or less.
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