Patent Description:
An inkjet printing head is known as an actuator that uses a piezoelectric film. An example of such an inkjet printing head is disclosed in Patent Literature <NUM>. The inkjet printing head disclosed in Patent Literature <NUM> includes a nozzle substrate, a pressure chamber substrate, a movable film (vibrating film), and a piezoelectric element bonded to the movable film. A pressure chamber, into which ink is introduced, is formed in the pressure chamber substrate and the movable film faces the pressure chamber. The piezoelectric element is arranged by laminating a lower electrode, a piezoelectric film, and an upper electrode in that order from the movable film side.

Patent Literature <NUM>: <CIT>
Further, document <CIT>relates to a piezoelectric element which includes in a laminated state a piezoelectric layer, a first electrode formed on a first surface of the piezoelectric layer, and a second electrode formed on a second surface of the piezoelectric layer which is opposite to the first surface. The piezoelectric layer has a film thickness of <NUM> or less, and has a flat portion formed as a second surface in parallel with the first surface, and a lateral portion inclined downwardly from the flat portion towards the first surface. The second electrode has a central portion formed in parallel with the flat portion, and a slope portion inclined downwardly from the central portion towards the flat portion. The inclination angle of the slope portion to the flat portion is gentle as compared with the inclination angle of the lateral portion to the first surface.

Document <CIT> relates to a piezoelectric element which includes: a base substrate; a lower electrode formed above the base substrate; a ferroelectric layer formed above the lower electrode; and an upper electrode formed above the ferroelectric layer, wherein an angle of a corner defined by a side surface of the ferroelectric layer and a top surface of the base substrate is between <NUM>° and <NUM>°.

Document <CIT>relates to an inkjet printing head which includes a hydrogen barrier film, covering side surfaces of upper electrodes and piezoelectric films, a portion of an upper surface of each upper electrode, and a portion of an upper surface of a lower electrode, an insulating film, formed above the hydrogen barrier film, upper wiring, formed above the insulating film, connects the upper electrode to a drive circuit, and a lower wiring, formed above the insulating film, connects the lower electrode to the drive circuit. First contact holes, each exposing an upper electrode, and second contact holes, each exposing an extension portion, are formed in the hydrogen barrier film and the insulating film. The upper wirings are connected to the upper surfaces of the upper electrodes via the first contact holes and the lower wiring is connected to an upper surface of the extension portion via the second contact holes.

Document <CIT> relates to a piezoelectric element which includes a vibration plate; a lower electrode; a piezoelectric film; and an upper electrode, which are laminated in the stated order. An electric field is applied to the piezoelectric film by the lower electrode and the upper electrode. A shape of the piezoelectric film near a boundary face between the piezoelectric film and the upper electrode as viewed from a lamination direction of the piezoelectric film and the upper electrode, is substantially the same as a shape of the upper electrode. A width of the piezoelectric film precipitously extends from an end of the boundary face. A thickness of the piezoelectric film in an area in the width of the piezoelectric film where the upper electrode is not formed, is formed to be proportionate to the precipitous extension of the width of the piezoelectric film.

Document <CIT> shows a ferroelectric element which comprises a diaphragm, a lower electrode, a ferroelectric layer, and an upper laminated and tapered electrode formed in this order on a silicon substrate for an ink jet head.

With the arrangement described in Patent Literature <NUM>, the upper electrode is formed to have a uniform thickness. To make a displacement amount of the movable film large, it is preferable for the upper electrode to be thinner in thickness. However, if the upper electrode is made thin in thickness, it increases in electrical resistance and it may not be possible to apply an electric field uniformly to the piezoelectric film. If an applied voltage is then increased, the piezoelectric film may be put in a so-called fatigue state in which the displacement amount decreases or response becomes slow.

An object of the present invention is to provide a piezoelectric film utilization device with which a normal electric field can be applied to a piezoelectric film and a movable film can be made large in displacement amount.

A piezoelectric film utilization device according to the present invention is defined in independent claim <NUM>.

With this arrangement, a central portion of the upper electrode besides the peripheral edge portion and a portion of the peripheral edge portion besides the thin portion are thick portions. The thick portions are low in electrical resistance value in comparison to the thin portion and therefore, charges can be injected into the piezoelectric film without causing a large voltage drop. On the other hand, in comparison to the thick portions, the thin portion is high in electrical resistance value but is short in distance to a peripheral edge of the upper electrode and short in distance through which charges pass and therefore, an amount of current flowing through the peripheral edge portion is low. A large voltage drop thus does not occur in the thin portion as well.

Consequently, in comparison to a case where an entirety of the upper electrode is of the same thickness as the thick portions, a normal electric field can be applied to the piezoelectric film even if an average thickness is decreased. Since the average thickness can be decreased in comparison to the case where the entirety of the upper electrode is of the same thickness as the thick portions, a displacement amount of the movable film can be increased.

In a preferred embodiment of the present invention, the upper electrode has the thin portion across an entirety of the peripheral edge portion.

In the preferred embodiment of the present invention, the upper electrode has a rectangular shape that is long in one direction in plan view and the upper electrode has thin portions at both side portions.

In the preferred embodiment of the present invention, the upper electrode also has thin portions at both end portions.

According to the present invention, the thin portion has a tapered upper surface with which a distance to an upper surface of the piezoelectric film decreases gradually toward the outside.

In the preferred embodiment of the present invention, a length in an inside/outside direction of the thin portion is not less than <NUM> in plan view.

In the preferred embodiment of the present invention, an inclination angle of the tapered upper surface with respect to the upper surface of the piezoelectric film is not less than <NUM> degree and within <NUM> degrees.

In the preferred embodiment of the present invention, an outer edge portion of the tapered upper surface is formed to a curved surface that is outwardly convex.

In the preferred embodiment of the present invention, the upper electrode is constituted of a laminated film of an IrO<NUM> film that is formed on the upper surface of the piezoelectric film and an Ir film that is laminated on the IrO<NUM> film and the Ir film is present on the IrO<NUM> film at an outer edge portion of the thin portion.

In the preferred embodiment of the present invention, the upper electrode is constituted of a laminated film of an IrO<NUM> film that is formed on the upper surface of the piezoelectric film and an Ir film that is laminated on the IrO<NUM> film and the Ir film is not present on the IrO<NUM> film at an outer edge portion of the thin portion.

In the preferred embodiment of the present invention, the upper electrode is constituted of a laminated film of an IrO<NUM> film that is formed on an upper surface of the piezoelectric film and an Ir film that is laminated on the IrO<NUM> film.

In the preferred embodiment of the present invention, the piezoelectric film is constituted of a material having PZT as a main component.

In the preferred embodiment of the present invention, the lower electrode is constituted of a material having Pt as a main component.

In the preferred embodiment of the present invention, a thickness of the thin portion is constant and the thin portion has an upper surface that is parallel to an upper surface of the piezoelectric film.

The aforementioned as well as yet other objects, features, and effects of the present invention will be made clear by the following description of the preferred embodiments made with reference to the accompanying drawings.

<FIG> is a schematic plan view of an inkjet printing head to which a piezoelectric film utilization device is applied. <FIG> is a schematic enlarged sectional view taken along line II-II in <FIG>. <FIG> is a schematic enlarged sectional view taken along line III-III in <FIG>. <FIG> is a partially enlarged view of an actual shape of mainly a peripheral edge portion of an upper electrode of <FIG>. A hydrogen barrier film and an insulating film indicated by the reference signs <NUM> and <NUM> in <FIG> and <FIG> are omitted in <FIG> and <FIG>.

Referring to <FIG> and <FIG>, the inkjet printing head <NUM> includes a silicon substrate <NUM> and a nozzle substrate <NUM> having discharge ports 31a that discharge ink. A movable film formation layer <NUM> is laminated on the silicon substrate <NUM>. In the laminate of the silicon substrate <NUM> and the movable film formation layer <NUM>, pressure chambers (cavities) <NUM> are formed as ink flow passages (ink reservoirs).

The nozzle substrate <NUM> is constituted, for example, of a silicon plate, is adhered to a rear surface of the silicon substrate <NUM>, and, together with the silicon substrate <NUM> and the movable film formation layer <NUM>, defines the pressure chambers <NUM>. Ink discharge passages <NUM> are formed in the nozzle substrate <NUM>. Each ink discharge passage <NUM> penetrates through the nozzle substrate <NUM> and has the discharge port 31a at an opposite side from the pressure chamber <NUM>. Therefore, when a volume change occurs in the pressure chamber <NUM>, the ink retained in the pressure chamber <NUM> passes through the ink discharge passage <NUM> and is discharged from the discharge port 31a.

Each pressure chamber <NUM> is formed by digging into the silicon substrate <NUM> (or the silicon substrate <NUM> and the movable film formation layer <NUM>) from the rear surface side of the silicon substrate <NUM>. Ink supply passages <NUM> (see <FIG> and <FIG> together), in communication with the pressure chambers <NUM>, are further formed in the silicon substrate <NUM> (or the silicon substrate <NUM> and the movable film formation layer <NUM>). The ink supply passages <NUM> are in communication with the pressure chambers <NUM> and are formed to guide ink from an ink tank (for example, an ink cartridge) that is an ink supply source to the pressure chambers <NUM>.

Each pressure chamber <NUM> is formed to be elongate along an ink flow direction <NUM>, which is a right/left direction in <FIG>. A portion of the movable film formation layer <NUM> that is a top roof portion of the pressure chamber <NUM> constitutes a movable film 10A. The movable film 10A (movable film formation layer <NUM>) is constituted, for example, of a silicon oxide (SiO<NUM>) film formed on the silicon substrate <NUM>. The movable film 10A (movable film formation layer <NUM>) may instead be constituted of a laminate, for example, of a silicon (Si) layer formed on the silicon substrate <NUM>, a silicon oxide (SiO<NUM>) layer formed on the silicon layer, and a silicon nitride (SiN) layer formed on the silicon oxide layer. In the present description, the movable film 10A refers to the portion of the movable film formation layer <NUM> that is the top roof portion defining the pressure chamber <NUM>. Therefore, portions of the movable film formation layer <NUM> besides the top roof portion of the pressure chamber <NUM> do not constitute the movable film 10A.

The movable film 10A has a thickness of, for example, approximately <NUM> to <NUM>. In the present preferred embodiment, the thickness of the movable film 10A is approximately <NUM>.

The pressure chamber <NUM> is defined by the movable film 10A, the silicon substrate <NUM>, and the nozzle substrate <NUM> and is formed to a substantially rectangular parallelepiped shape in the present preferred embodiment. A length of the pressure chamber <NUM> is, for example, approximately <NUM>, a width thereof is approximately <NUM>, and a depth thereof is approximately <NUM>. The ink supply passages <NUM> are formed to be in communication with one end portion (an end portion positioned at an opposite side from the discharge port 31a in a long direction of the pressure chamber <NUM>. The discharge port 31a of the nozzle substrate <NUM> is disposed near another end portion related to the long direction of the pressure chamber <NUM>.

The pressure chamber <NUM> has the rectangular parallelepiped shape and therefore, the movable film 10A has a rectangular shape that is long in the ink flow direction <NUM> in plan view. The movable film 10A has a length in a long direction of approximately <NUM> and a length in a short direction of approximately <NUM>.

A piezoelectric element <NUM> is disposed on a front surface of each movable film 10A. The piezoelectric element <NUM> includes a lower electrode <NUM> formed on the movable film formation layer <NUM>, a piezoelectric film <NUM> formed on the lower electrode <NUM>, and an upper electrode <NUM> formed on the piezoelectric film <NUM>. In other words, the piezoelectric element <NUM> is arranged by sandwiching the piezoelectric film <NUM> from above and below by the upper electrode <NUM> and the lower electrode <NUM>.

The lower electrode <NUM> is constituted, for example, of a single film that is a Pt (platinum) layer. Besides this, the lower electrode <NUM> can instead be formed of a single film that is an Au (gold) film, a Cr (chromium) layer, or an Ni (nickel) layer, etc. Also, the lower electrode <NUM> may instead be formed of a laminated film in which a Ti (titanium) layer and a Pt (platinum) layer are laminated in that order from the movable film 10A side. A film thickness of the lower electrode <NUM> is, for example, approximately <NUM>.

The lower electrode <NUM> has a rectangular portion <NUM> that is disposed on the movable film 10A and has substantially the same shape and size as the movable film 10A, a lead-out electrode portion <NUM> that is led out from one end side of the rectangular portion <NUM>, and a common connection portion <NUM> that connects the lower electrodes <NUM> of a plurality of piezoelectric elements <NUM> in common. A portion of the rectangular portion <NUM> that is in contact with a lower surface of the piezoelectric film <NUM> is a main electrode portion 71A that constitutes the piezoelectric element <NUM>.

Referring to <FIG> and <FIG>, each lead-out electrode portion <NUM> is led out to a downstream side from a width central portion of a downstream side end in the ink flow direction <NUM> of the rectangular portion <NUM>. At a further downstream side than the rectangular portions <NUM>, the common connection portion <NUM> extends in a direction orthogonal to the ink flow direction <NUM>. Downstream side ends of a plurality of lead-out electrode portions <NUM> are connected to the common connection portion <NUM>.

Returning to <FIG> and <FIG>, as the piezoelectric film <NUM>, for example, a PZT (PbZrxTi<NUM>-xO<NUM>: lead zirconate titanate) film formed by a sol-gel method or a sputtering method can be applied. Such a piezoelectric film <NUM> is constituted of a sintered body of a metal oxide crystal. The piezoelectric film <NUM> preferably has a thickness of <NUM> to <NUM>. In the present preferred embodiment, the thickness of the piezoelectric film <NUM> is approximately <NUM>. An overall thickness of the movable film 10A is preferably approximately the same as the thickness of the piezoelectric film <NUM> or approximately <NUM>/<NUM> the thickness of the piezoelectric film <NUM>.

In plan view, the piezoelectric film <NUM> has a rectangular shape that is long in the ink flow direction <NUM>. Each side surface of the piezoelectric film <NUM> is formed to an inclined surface that spreads outward toward a lower side. The piezoelectric film <NUM> is formed with a length in a long direction thereof being shorter than the length in the long direction of the movable film 10A (pressure chamber <NUM>) and both end edges thereof are disposed inwardly at predetermined first intervals from corresponding both end edges of the movable film 10A. A length in a long direction of an upper surface of the piezoelectric film <NUM> is approximately <NUM>.

The piezoelectric film <NUM> is formed with a length in a short direction thereof being shorter than the length in the short direction of the movable film 10A (pressure chamber <NUM>) and both side edges thereof are disposed inwardly at predetermined second intervals from corresponding both side edges of the movable film 10A. A length in a short direction of the upper surface of the piezoelectric film <NUM> is approximately <NUM>.

The upper electrodes <NUM> are formed to be of substantially the same pattern as the upper surfaces of the piezoelectric films <NUM>. That is, each upper electrode <NUM> has a rectangular shape that is long in the ink flow direction <NUM>. The upper electrode <NUM> has, for example, a two-layer structure in which an IrO<NUM> (iridium oxide) film 9A and an Ir (iridium) film 9B are laminated in that order from the piezoelectric film <NUM> side as shown in <FIG>.

In plan view, the upper electrode <NUM> is constituted of a thick central portion <NUM> and a thin peripheral edge portion <NUM> at outer sides of the central portion <NUM>. In plan view, the central portion <NUM> has a rectangular shape that is long in the ink flow direction <NUM>. A film thickness of the central portion <NUM> is constant and an upper surface of the central portion <NUM> is formed to a flat surface that is substantially parallel to the upper surface of the piezoelectric film <NUM>.

The peripheral edge portion <NUM> has a rectangular annular shape in plan view. In the present preferred embodiment, the peripheral edge portion <NUM> is formed to a thin portion of tapered shape with which a film thickness decreases gradually towards the outside (outer peripheral edges). In other words, the peripheral edge portion <NUM> has a tapered upper surface 92a with which a distance to the piezoelectric film <NUM> upper surface decreases gradually toward the outside.

In the present preferred embodiment, a length in a long direction of the central portion <NUM> is approximately <NUM> and a length in a short direction of the central portion <NUM> is approximately <NUM>. Also, in plan view, a length in an inside/outside direction of the peripheral edge portion <NUM> (width of the peripheral edge portion) is approximately <NUM>. The length in the inside/outside direction of the peripheral edge portion <NUM> is preferably not less than <NUM>. In the present preferred embodiment, an inclination angle of the tapered upper surface 92a with respect to the upper surface of the piezoelectric film <NUM> is approximately <NUM> degrees. The inclination angle of the tapered upper surface 92a with respect to the upper surface of the piezoelectric film <NUM> is preferably not less than <NUM> degree and not more than <NUM> degrees.

As shown in <FIG>, an outer edge portion 92b of the tapered upper surface 92a of the peripheral edge portion <NUM> is formed to a curved surface that is outwardly convex. In <FIG>, the Ir film 9B is present on the IrO<NUM> film 9A at the outer edge portion 92b of the peripheral edge portion <NUM>. However, as shown in <FIG>, the Ir film 9B does not have to be present on the IrO<NUM> film 9A at the outer edge portion 92b of the peripheral edge portion <NUM>.

A front surface of the movable film formation layer <NUM>, front surfaces of the piezoelectric elements <NUM>, and front surfaces of portions of the lower electrodes <NUM> besides the main electrode portions 71A are covered with a hydrogen barrier film <NUM>. The hydrogen barrier film <NUM> is constituted, for example, of Al<NUM>O<NUM> (alumina). Degradation of characteristics of the piezoelectric films <NUM> due to hydrogen reduction can thereby be prevented. A film thickness of the hydrogen barrier film <NUM> is approximately <NUM>.

An insulating film <NUM> is laminated on the hydrogen barrier film <NUM>. The insulating film <NUM> is constituted, for example, of SiO<NUM>. Wirings <NUM> are formed on the insulating film <NUM>. The wirings <NUM> are constituted of a metal material that includes Al (aluminum).

One end portion of each wiring <NUM> is disposed above one end portion of the upper electrode <NUM>. A penetrating hole <NUM> penetrating continuously through the hydrogen barrier film <NUM> and the insulating film <NUM> is formed between the wiring <NUM> and the upper electrode <NUM>. The one end portion of the wiring <NUM> enters into the penetrating hole <NUM> and is connected to the upper electrode <NUM> inside the penetrating hole <NUM>. Also, the hydrogen barrier film <NUM> and the insulating film <NUM> have a cutout portion <NUM> at a position corresponding to a region surrounded by a peripheral edge portion of a front surface of the central portion <NUM> of each upper electrode <NUM>. The cutout portions <NUM> are portions at which the hydrogen barrier film <NUM> and the insulating film <NUM> are cut out.

Also, although not illustrated, an opening that penetrates continuously through the hydrogen barrier film <NUM> and the insulating film <NUM> is formed at a position corresponding to a predetermined region on the common connection portion <NUM> of the lower electrodes <NUM> and a front surface of the common connection portion <NUM> is exposed via the opening. The exposed portion constitutes a pad portion that is arranged to connect the lower electrode <NUM> to the exterior.

Each piezoelectric element <NUM> is formed at a position facing the pressure chamber <NUM> across the movable film 10A. That is, the piezoelectric element <NUM> is formed to contact a surface of the movable film 10A at the opposite side from the pressure chamber <NUM>. The pressure chamber <NUM> is filled with ink supplied from an unillustrated ink tank through the ink supply passages <NUM>. The movable film 10A defines a top surface portion of the pressure chamber <NUM> and faces the pressure chamber <NUM>. The movable film 10A is supported by portions of the laminate of the movable film formation layer <NUM> and the silicon substrate <NUM> at a periphery of the pressure chamber <NUM> and has flexibility enabling deformation in a direction facing the pressure chamber <NUM> (in other words, in a thickness direction of the movable film 10A).

The wirings <NUM> and the common connection portion <NUM> of the lower electrodes <NUM> are connected to a drive circuit <NUM>. The drive circuit <NUM> may be formed in a region of the silicon substrate <NUM> separate from the pressure chambers <NUM> or may be formed outside the silicon substrate <NUM>. When a drive voltage is applied from the drive circuit <NUM> to a piezoelectric element <NUM>, the piezoelectric film <NUM> deforms due to an inverse piezoelectric effect. The movable film 10A is thereby made to deform together with the piezoelectric element <NUM> to bring about a volume change of the pressure chamber <NUM> and the ink inside the pressure chamber <NUM> is pressurized. The pressurized ink passes through the ink discharge passage <NUM> and is discharged as microdroplets from the discharge port 31a.

Referring to <FIG>, a plurality of the pressure chambers <NUM> are formed as stripes extending parallel to each other in the silicon substrate <NUM> (or the laminate of the silicon substrate <NUM> and the movable film formation layer <NUM>). The plurality of pressure chambers <NUM> are formed at equal intervals that are minute intervals (for example, of approximately <NUM> to <NUM>) in a width direction thereof.

In plan view, each pressure chamber <NUM> has an oblong shape that is elongate along the ink flow direction <NUM> directed from the ink supply passages <NUM> to the ink discharge passage <NUM>. That is, the top surface portion of the pressure chamber <NUM> has two side edges 5c and 5d along the ink flow direction <NUM> and two end edges 5a and 5b along the direction orthogonal to the ink flow direction <NUM>.

At the one end portion of each pressure chamber <NUM>, the ink supply passages <NUM> are divided and formed as two passages and are in communication with a common ink passage <NUM>. The common ink passage <NUM> is in communication with the ink supply passages <NUM> corresponding to the plurality of pressure chambers <NUM> and is formed to supply the ink from the ink tank to the ink supply passages <NUM>.

Each wiring <NUM> is constituted of a lead-out portion 13A having one end portion connected to one end portion of the upper electrode <NUM> at an upstream side in the ink flow direction <NUM> and extending in a direction opposite to the ink flow direction <NUM> and a pad portion 13B of rectangular shape in plan view that is made integral to the lead-out portion 13A and connected to a tip of the lead-out portion 13A. With the exception of the portion connected to the upper electrode <NUM>, the lead-out portion 13A is formed on a front surface of the insulating film <NUM> that covers one end portion of the upper surface of the piezoelectric element <NUM>, an end surface of the piezoelectric element <NUM> continuous thereto, and the front surface of the movable film formation layer <NUM>. The pad portion 13B is formed on the insulating layer <NUM> that covers the front surface of the movable film formation layer <NUM>.

An annular region (a rectangular annular region that is long in the ink flow direction <NUM> of each movable film 10A between peripheral edges of the movable film 10A and peripheral edges of the piezoelectric element <NUM> is a region that is not constrained by the piezoelectric element <NUM> or a peripheral wall of the pressure chamber <NUM> and is a region in which a large deformation occurs. That is, a peripheral edge portion of the movable film 10A is a region in which a large deformation occurs. Therefore, when the piezoelectric element <NUM> is driven, the peripheral edge portion of the movable film 10A bends such that an inner peripheral edge side of the peripheral edge portion of the movable film 10A is displaced in a thickness direction of the pressure chamber <NUM> and an entirety of a central portion surrounded by the peripheral edge portion of the movable film 10A is thereby displaced in the thickness direction of the pressure chamber <NUM>.

A method for manufacturing the inkjet printing head <NUM>, not forming part of the invention, shall now be described specifically.

<FIG> are sectional views of a manufacturing process of the inkjet printing head <NUM> and are sectional views corresponding to the section plane of <FIG>.

First, as shown in <FIG>, the silicon substrate <NUM> is prepared. Here, as the silicon substrate <NUM>, that which is thicker in thickness than the silicon substrate <NUM> at the final stage is prepared.

Next, as shown in <FIG>, the movable film formation layer <NUM> is formed on the front surface of the silicon substrate <NUM>. Specifically, a silicon film (for example, of <NUM> thickness) is formed on the front surface of the silicon substrate <NUM>. If the movable film formation layer <NUM> is constituted of a laminated film of a silicon film, a silicon oxide film, and a silicon nitride film, the silicon film (for example, of <NUM> thickness) is formed on the front surface of the silicon substrate <NUM>, the silicon oxide film (for example, of <NUM> thickness) is formed on the silicon film, and the silicon nitride film (for example, of <NUM> thickness) is formed on the silicon oxide film.

Next, as shown in <FIG>, a lower electrode film <NUM> that is a material layer of the lower electrodes <NUM> is formed on the movable film formation layer <NUM>. The lower electrode film <NUM> is constituted, for example, of a Pt film (for example, of <NUM> thickness). Such a lower electrode film <NUM> is formed, for example, by a sputtering method.

Next, as shown in <FIG>, a piezoelectric material film <NUM> that is a material of the piezoelectric films <NUM> is formed on an entire surface of the lower electrode film <NUM>. Specifically, the piezoelectric material film <NUM> of, for example, <NUM> thickness is formed by, for example, a sol-gel method. Such a piezoelectric material film <NUM> is constituted of a sintered body of metal oxide crystal grains.

Next, as shown in <FIG>, an upper electrode film <NUM> that is a material of the upper electrodes <NUM> is formed on an entire surface of the piezoelectric material film <NUM>. The upper electrode film <NUM> is constituted, for example, of an IrO<NUM>/Ir laminated film having an IrO<NUM> film (for example, of <NUM> thickness) as a lower layer and an Ir film (for example, of <NUM> thickness) as an upper layer. Such an upper electrode film <NUM> is formed by a sputtering method.

Next, as shown in <FIG>, a resist mask <NUM> with a pattern of the upper electrodes <NUM> is formed by photolithography. Each side surface 111a of the resist mask <NUM> is formed to an inclined surface that spreads outward toward a lower side.

Next, as shown in <FIG> and <FIG>, the upper electrode film <NUM> is etched using the resist mask <NUM> as a mask to form the upper electrodes <NUM> of a predetermined pattern. In the etching step, as shown in <FIG>, a front surface and the side surfaces 111a of inclined shapes of the resist mask <NUM> are etched gradually such that an etching amount increases toward outer sides at upper surface peripheral edge portions of the upper electrodes <NUM>. Consequently, the upper electrode <NUM> each constituted of the central portion (thick portion) <NUM> that is constant in film thickness and the peripheral edge portion (thin portion) <NUM> with which the film thickness decreases gradually toward the outside is obtained. The peripheral edge portion <NUM> has the tapered upper surface 92a with which the distance to the piezoelectric film <NUM> upper surface decreases gradually toward the outside. The outer edge portion 92b of the peripheral edge portion <NUM> is formed to the curved surface that is outwardly convex.

Next, as shown in <FIG>, the piezoelectric material film <NUM> is etched to form the piezoelectric films <NUM> of a predetermined pattern. Thereafter, the resist mask <NUM> is peeled off.

Next, as shown in <FIG>, a resist mask <NUM> with a pattern of the lower electrodes <NUM> is formed by photolithography.

Next, as shown in <FIG>, the lower electrode film <NUM> is etched using the resist mask <NUM> as a mask to form the lower electrodes <NUM> that are each constituted of the rectangular portion <NUM> including the main electrode portion 71A, the lead-out electrode portion <NUM>, and the common connection portion <NUM>. Thereafter, the resist mask <NUM> is peeled off.

Next, the hydrogen barrier film <NUM> covering the whole surface is formed. Thereafter, the insulating film <NUM> is formed on an entire surface of the hydrogen barrier film <NUM>. Subsequently, the insulating film <NUM> and the hydrogen barrier film <NUM> are etched successively to form the penetrating holes <NUM>. A wiring film that constitutes the wirings <NUM> is formed on the insulating film <NUM>, including interiors of the penetrating holes <NUM>, by a sputtering method. Thereafter, the wiring film is patterned by photolithography and etching to form the wirings <NUM>. Thereafter, as shown in <FIG>, the insulating film <NUM> and the hydrogen barrier film <NUM> are etched successively to form the cutout portions <NUM>.

Next, as shown in <FIG>, rear surface grinding for thinning the silicon substrate <NUM> is performed. The silicon substrate <NUM> is polished from the rear surface to make the silicon substrate <NUM> into a thin film. For example, the silicon substrate <NUM> of approximately <NUM> thickness in an initial state is thinned to approximately <NUM> thickness. Thereafter, the common ink passage <NUM>, the ink supply passages <NUM>, and the pressure chambers <NUM> are formed in the silicon substrate <NUM> by photolithography and etching.

Lastly, the nozzle substrate <NUM> is adhered to the rear surface of the silicon substrate <NUM> and the inkjet printing head <NUM> such as shown in <FIG> is thereby obtained.

With the preferred embodiment described above, each upper electrode <NUM> is constituted of the thick central portion <NUM> and the thin peripheral edge portion <NUM> at the outer sides of the central portion <NUM>. The film thickness of the central portion <NUM> is constant. The peripheral edge portion <NUM> is formed to the thin portion of tapered shape with which the film thickness decreases gradually towards the outside. In other words, the peripheral edge portion <NUM> has the tapered upper surface 92a with which the distance to the piezoelectric film <NUM> upper surface decreases gradually toward the outside.

The central portion (thick portion) <NUM> is low in electrical resistance value in comparison to the peripheral edge potion (thin portion) <NUM> and therefore, charges can be injected into the piezoelectric film <NUM> without causing a large voltage drop. On the other hand, in comparison to the central portion <NUM>, the peripheral edge portion <NUM> is high in electrical resistance value but is short in distance to the peripheral edge of the upper electrode <NUM> and short in distance through which charges pass and therefore, an amount of current flowing through the peripheral edge portion <NUM> is low. A large voltage drop thus does not occur in the peripheral edge portion <NUM> as well.

Consequently, in comparison to a case where an entirety of the upper electrode <NUM> is of the same thickness as the central portion <NUM>, a normal electric field can be applied to the piezoelectric film <NUM> even if an average thickness is decreased. Since the average thickness can be decreased in comparison to the case where the entirety of the upper electrode <NUM> is of the same thickness as the central portion <NUM>, a displacement amount of the movable film 10A can be increased.

Although with the preferred embodiment described above, an entirety of the peripheral edge portion of each upper electrode <NUM> is formed to the thin portion of tapered shape, just a portion of the peripheral edge portion of the upper electrode <NUM> may be formed to a thin portion of tapered shape instead. For example, of the both side portions and the both end portions of the upper electrode <NUM>, just the both side portions may be formed to thin portions of tapered shapes.

Also, although with the preferred embodiment described above, each upper electrode <NUM> has the rectangular shape in plan view, a planar shape of the upper electrode <NUM> may instead be a circular shape, an elliptical shape, or any other shape.

Also, although with the preferred embodiment described above, the peripheral edge portion <NUM> of the upper electrode <NUM> is formed to the thin portion of tapered shape, the peripheral edge portion <NUM> of the upper electrode <NUM>, in a non-claimed example, may instead be formed to a thin portion that is thinner than the central portion <NUM> and is of a constant thickness as in an inkjet printing head 1A shown in <FIG> is a sectional view corresponding to <FIG>. Even in this case, the length in the inside/outside direction of the peripheral edge portion <NUM> in plan view is preferably not less than <NUM>. With the example of <FIG>, the length in the inside/outside direction of the peripheral edge portion <NUM> is approximately <NUM>.

Also, although with the preferred embodiments described above, the insulating film <NUM> is formed on the hydrogen barrier film <NUM>, the insulating film <NUM> does not have to be formed on the hydrogen barrier film <NUM>.

Also, although with the preferred embodiments described above, cases where the present invention is applied to an inkjet printing head was described, the present invention can also be applied to a microphone, pressure sensor, acceleration sensor, angular velocity sensor, ultrasonic sensor, speaker, or IR sensor (heat sensor), etc., that uses a piezoelectric film.

Claim 1:
A piezoelectric film utilization device comprising:
a cavity (<NUM>);
a movable film formation layer (<NUM>) that includes a movable film (10A) disposed on the cavity (<NUM>) and defining a top surface portion of the cavity (<NUM>); and
a piezoelectric element (<NUM>) that is formed to contact a surface of the movable film (10A) at an opposite side from the cavity (<NUM>) and having a peripheral edge receded further toward an interior of the cavity (<NUM>) than the movable film (10A) in plan view; and
wherein the piezoelectric element (<NUM>) includes a lower electrode (<NUM>) formed on a surface of the movable film formation layer (<NUM>) at the opposite side from the cavity (<NUM>), an upper electrode (<NUM>) disposed at an opposite side from the movable film formation layer (<NUM>) with respect to the lower electrode (<NUM>), and a piezoelectric film (<NUM>) provided between the upper electrode (<NUM>) and the lower electrode (<NUM>),
the upper electrode (<NUM>) has a thin portion (<NUM>) at least at a portion of a peripheral edge portion,
the upper electrode (<NUM>) is composed of a lower layer (9A) formed on an upper surface of the piezoelectric element (<NUM>) and an upper layer (9B) formed on an upper surface of the lower layer (9A),
the upper layer (9B) has an upper layer thin portion (<NUM>) at least at a portion of a peripheral edge portion,
the upper layer thin portion has a tapered upper surface (92a) with which a distance to an upper surface of the piezoelectric film (<NUM>) decreases gradually toward the outside and characterized in that the film thickness of the lower layer (9A) is constant in all regions.