Liquid ejecting head, liquid ejecting apparatus and actuator device

A liquid ejecting head including a fluid channel forming substrate including a pressure generating chamber communicating with a nozzle opening that ejects a liquid droplet and a piezoelectric element. The piezoelectric element has a first electrode, a piezoelectric material layer that is provided on the first electrode and has a perovskite monoclinic structure, and a second electrode formed on the piezoelectric material layer opposite to the first electrode. An angle formed between a direction of an electric field generated between the first and second electrodes and an orientation of a polarization moment of the piezoelectric material layer is greater than an angle formed between the direction of the electric field at a time when the piezoelectric constant of the piezoelectric material layer reaches a maximum level and the orientation of the polarization moment.

The entire disclosure of Japanese Patent Application Nos. 2008-240389, filed Sep. 19, 2008 and 2009-159556, filed Jul. 6, 2009 are expressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a liquid ejecting head. More specifically, the present invention relates to a liquid ejecting head that ejects liquid through a nozzle opening, a liquid ejecting apparatus, and an actuator device.

2. Related Art

In some of piezoelectric elements currently used in liquid ejecting heads, a piezoelectric material layer made of a piezoelectric material exhibiting an electromechanical transducing function such as, for example, a crystalline dielectric material, is disposed between two electrodes. An example a liquid ejecting head which uses such an actuator is an ink jet recording head which has a pressure generating chamber communicating with a nozzle opening that ejects an ink droplet. A part of the pressure generating chamber is constituted by a diaphragm and the diaphragm is deformed by a piezoelectric element, so as to pressurize ink in the pressure generating chamber and to eject an ink droplet through the nozzle opening. The use of piezoelectric elements in ink jet recording heads is known in the art. In such a piezoelectric element, for example, a piezoelectric material layer is uniformly formed over an entire surface of a diaphragm by using a film forming technology. The piezoelectric material layer is cut to be divided into parts having a shape corresponding to a pressure generating chamber so as to form independent piezoelectric elements for the respective pressure generating chambers using a lithography method. One example of such a configuration is disclosed in JP-A-2003-127366 at pages 4 to 7 and in FIGS. 1 to 4.

One problem with this configuration, however, is that since the piezoelectric material forming the piezoelectric material layer repeatedly undergoes rotational expansion and contraction of polarization during its operation, a so-called wear phenomenon may occur where the orientation of the polarization becomes partially fixed so as to follow an electric field application direction as time passes, resulting in the decrease in the piezoelectric displacement amount. In a case where such a piezoelectric element is used, for example, in a liquid ejecting head, the piezoelectric displacement amount varies in accordance with the use of the liquid ejecting head so that it is difficult to perform stable ejecting of the liquid.

The above problem arises not only in an actuator device used in an ink jet recording head and other liquid ejecting heads but also in an actuator device mounted in other types of devices.

BRIEF SUMMARY OF THE INVENTION

An advantage of some aspects of the invention is that it provides a liquid ejecting head whose durability can be improved by reducing a degree of change of a displacement amount due to repeated operation, and it provides a liquid ejecting apparatus and an actuator device.

A first aspect of the invention comprises liquid ejecting head including a fluid channel forming substrate having a pressure generating chamber formed therein which communicates with a nozzle opening that ejects a liquid droplet and a piezoelectric element. The piezoelectric unit includes a first electrode, a piezoelectric material layer that is provided on the first electrode, the piezoelectric material layer having a perovskite structure indicated by a general formula: ABO3, and a second electrode formed on the piezoelectric material layer opposite to the first electrode. The piezoelectric material layer has a monoclinic structure, and an angle formed between the direction of an electric field generated between the first electrode and the second electrode and an orientation of a polarization moment of the piezoelectric material layer is greater than an angle formed between the direction of the electric field when the piezoelectric constant of the piezoelectric material layer reaches a maximum level and the orientation of the polarization moment of the piezoelectric material layer.

With this configuration, by regulating the orientation of the polarization moment, it is possible to reduce the rate of change of a displacement amount of the piezoelectric element at a time when a wear phenomenon in which the polarization of the piezoelectric material layer is partially fixed occurs due to application of the electric field.

A liquid ejecting apparatus according to a second aspect of the invention includes the liquid ejecting head according to the first aspect of the invention and a driving unit that applies a voltage across the first electrode and the second electrode so as to generate an electric field in a predetermined direction on the piezoelectric element. With this configuration, the rate of change of the displacement amount can be suppressed and the liquid ejecting apparatus having improved reliability can be realized.

A third aspect of the invention includes a piezoelectric element constituted by a first electrode, a piezoelectric material layer that is provided on the first electrode and has a perovskite structure indicated by a general formula: ABO3and a second electrode formed on the piezoelectric material layer at the side opposite to the first electrode. The piezoelectric material layer has a monoclinic structure, and an angle formed between a direction of an electric field generated between the first electrode and the second electrode and an orientation of a polarization moment of the piezoelectric material layer is greater than an angle formed between the direction of the electric field at a time when the piezoelectric constant of the piezoelectric material layer reaches the maximum level and the orientation of the polarization moment of the piezoelectric material layer.

With this configuration, by regulating the orientation of the polarization moment, it is possible to prevent enlarging of a rate of change of a displacement amount of the piezoelectric element when a wear phenomenon in which the polarization of the piezoelectric material layer is partially fixed, occurs due to application of the electric field.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention will be described in detail on the basis of preferable embodiments.

First Embodiment

FIG. 1is an exploded perspective view showing a schematic structure of an ink jet recording head, which is an example of a liquid ejecting head according to a first embodiment of the invention.FIG. 2Ais a plan view showing the structure of the ink jet recording head shown inFIG. 1andFIG. 2Bis a cross sectional view showing the structure of the ink jet recording head taken along line IIB to IIB inFIG. 2A.

The fluid channel forming substrate10shown inFIGS. 1 to 2Bis formed of a silicon monocrystalline substrate. An elastic film50formed of silicon oxide is provided on one face of the substrate10

A plurality of pressure generating chambers12are arranged in the fluid channel forming substrate10in the width direction thereof. A communicating portion13is formed in a region at the outside of the pressure generating chambers12in the long side direction thereof in the fluid forming substrate10. The communicating portion13communicates with each of the pressure generating chambers12via respective ink supply channels14and communication channels15which are provided so as to correspond to the pressure generating chambers12. The communicating portion13communicates with a reservoir portion31on a protection substrate (described later) so as to form a part of a reservoir as a common ink chamber for the pressure generating chambers12. Each of the ink supply channels14is constituted in such a manner that the width thereof is smaller than that of the pressure generating chamber12so that the resistance level is held constant for ink flowing into the pressure generating chamber12from the communicating portion13.

In the embodiment, while the width of the fluid channel is narrowed by modifying the width of one side so as to form the ink supply channel14, it is possible to narrow the fluid channel from both sides to form the ink supply channel14. In addition, the ink supply channel14can be formed by narrowing the fluid channel from the thickness direction not from the width direction.

In the embodiment, the fluid channel having the pressure generating chambers12, the communicating portion13, the ink supply channels14and the communication channels15are provided in the fluid channel forming substrate10

In addition, a nozzle plate20having nozzle openings21is attached to the fluid channel forming substrate10using an adhesive or a heat weldable film, so that each nozzle opening21communicates with a corresponding pressure generating chamber. The nozzle plate20is made of, for example, a glass ceramic, a silicon monocrystalline substrate or stainless steel.

On the other hand, as described above, the elastic film50is formed on the opposite side of the fluid channel forming substrate10, and an insulation material film55is formed on the elastic film50. The elastic film50is made of silicon oxide and has a thickness of 1000 nm. The insulation material film55is formed by a sputtering method and is formed of zirconium oxide including 2 mol % of yttrium. In addition, a first electrode60, a piezoelectric material layer70and a second electrode80are laminated on the insulation material film55to form a piezoelectric element300.

Here, the first electrode60, the piezoelectric material layer70and the second electrode80are referred to collectively as the piezoelectric element300. In general, the piezoelectric element300is constituted in such a manner that one of the electrodes of the piezoelectric element300is made to be a common electrode and the other electrode and the piezoelectric material layer70are formed for each pressure generating chamber12by a patterning process. In the embodiment, the first electrode60serves as the common electrode of the piezoelectric elements300and the second electrodes80serve as discrete electrodes of the respective piezoelectric elements300. However, the first electrode60and the second electrodes80can be switched with each other depending on the specific drive circuit or wiring used. Here, in addition, the piezoelectric element300and a diaphragm that generates a displacement by being driven by the piezoelectric element300are referred to collectively as the actuator device. Meanwhile, the elastic film50, the insulation material film55and the first electrode60function as the diaphragm in the above case. However, the structure is not limited thereto. For instance, it is possible to use only the first electrode60as the diaphragm without providing the elastic film50and the insulation material film55. Alternatively, the piezoelectric element300itself can substantially double as the diaphragm.

The piezoelectric material layer70is a crystalline film that is formed on the first electrode60and has a perovskite structure consisting of a piezoelectric material of oxide indicated by a general formula: ABO3having a polarization structure. A variety of materials may be used for the piezoelectric material layer70, for example, a ferroelectric material such as lead zirconate titanate (PZT) or a ferroelectric material including, added thereto, a metal oxide such as niobium oxide, nickel oxide or manganese oxide may be used. To be specific, it is possible to use lead titanate (PbTiO3), lead zirconate titanate (Pb(Zr, Ti)O3), lead zirconate (PbZrO3), lead titanate lanthanum ((Pb, La)TiO3), lead zirconate titanate lanthanum ((Pb, La)(Zr, Ti)O3), or lead magnesium niobate zirconium titanate (Pb(Zr, Ti)(Mg, Nb)O3). In the embodiment, PZT of Pb(ZrxTi1-x)O3, (x=0.5) is used as the piezoelectric material layer70.

The crystal of the piezoelectric material layer70is preferentially oriented to a (100) plane in a pseudo-cubic expression, and the crystal has a monoclinic structure. The structure of the crystal of the piezoelectric material layer70markedly depends on manufacturing conditions. However, in a case where the film thickness of the piezoelectric material layer70is not greater than 5 μm, when, for example, the value “x” is made to be in a range of approximately 0.45 to 0.55, the piezoelectric material layer70can have the monoclinic structure. In the invention, the description of “crystal is preferentially oriented to a (100) plane” includes a case where all of the crystals are oriented to the (100) plane and a case where most of the crystals (e.g., 90% or more) are oriented to the (100) plane. As a result of an X-ray diffraction examination performed on the piezoelectric material layer70in the embodiment, the orientation percentage of the (100) plane was 92%. In addition, the description of “the crystal has the monoclinic structure” includes a case where all of the crystals have the monoclinic structure and a case where most of the crystals (e.g., 90% or more) have the monoclinic structure and the remaining crystals which are not monoclinic have a tetragonal structure.

Moreover, the orientation of a polarization moment of the piezoelectric material layer70is inclined at a predetermined angle with respect to a direction perpendicular to the surface of the layer (a thickness direction of the piezoelectric material layer70). The angle formed between a direction of an electric field generated between the first electrode60and the second electrode80and the orientation of the polarization moment of the piezoelectric material layer70is greater than the angle formed between a direction of the electric field at a time when a piezoelectric constant (d31) reaches its maximum level and the orientation of the polarization moment of the piezoelectric material layer70

To be specific, as shown inFIG. 3, when a voltage is applied to the piezoelectric material layer70from the second electrode80toward the first electrode60, an electric field E directing to the first electrode60from the second electrode80is generated. Here, the application of the voltage toward the first electrode60from the second electrode80causes the first electrode60to have a negative polarity relative to the second electrode80. Driving of the piezoelectric element300by the above application of the voltage includes ejection driving for driving the piezoelectric element300so as to eject an ink droplet from the nozzle opening21and micro-vibration driving for driving the piezoelectric element300to the extent that an ink droplet is not ejected. The driving unit and a driving pulse for applying a voltage to the piezoelectric element300will be described more fully below.

The polarization moment is oriented in a (111) plane in the direction of the electric field E at a time when the piezoelectric constant (d31) of the piezoelectric material layer70reaches its maximum level, i.e., in an engineered domain arrangement. In this case, the angle formed between the direction of the electric field E at a time when the piezoelectric constant (d31) of the piezoelectric material layer70reaches its maximum level and the orientation of the polarization moment of the piezoelectric material layer70becomes θ0(seeFIGS. 4A and 5). When the crystal structure of the piezoelectric material layer70has, for example, the perovskite type structure represented by the pseudo-cubic expression, the angle θ0is approximately 57 degrees.

In this embodiment, an angle θa formed between the orientation of the polarization moment of the piezoelectric material layer70and the direction of the electric field E is made greater than the angle θ0formed between the electric field E at a time when the piezoelectric constant (d31) of the piezoelectric material layer70reaches its maximum level and the orientation of the polarization moment of the piezoelectric material layer70.

When the angle θa is greater than the angle θ0as shown inFIG. 4A, when the piezoelectric element300is repeatedly driven while generating the electric field E by applying the voltage to the first electrode60from the second electrode80, the wear phenomenon, wherein the orientation of the polarization is partially fixed along the electric field applying direction, occurs so that the orientation of the polarization moment (the angle θa) is moved in a direction A along a curve shown inFIG. 5, so as to be angle θb. At that time, since the piezoelectric constant (d31) passes through a point of a maximum value where increase and decrease of the piezoelectric constant is inverted in accordance with the change of the angle, the rate of change Δt of the piezoelectric constant (d31) becomes comparatively small.

In contrast, in a case where, for example, an angle θa′ formed between the orientation of the polarization moment and the direction of the electric field E is smaller than the angle θ0as shown inFIG. 4B, the orientation of the polarization moment (the angle θa′) is moved in a direction A′ along the curve shown inFIG. 5to be an angle θb′ due to the wear phenomenon. Since the piezoelectric constant is changed so as to be simply lowered in accordance with the change of the angle (change from θa′ to θb′), the rate of change Δt′ becomes greater than the rate of change Δt even when the same wear phenomenon occurs.

As described above, the fact that the rate of change Δt of the piezoelectric constant (d31) due to repeated driving of the piezoelectric material layer70is small, means that a rate of change of a displacement amount at a time when the piezoelectric element300is repeatedly driven is low. Namely, when the rate of change of the displacement amount of the piezoelectric element300due to repeated driving thereof is low, a difference between the displacement amount at the initial use and the displacement amount after the repeated driving becomes small. As a result, an ink ejection characteristic such as an ejection amount or an ejection speed of ink does not vary during the use of the piezoelectric element300so that it is possible to maintain stable printing conditions, thereby achieving a high quality print.

The above described orientation of the polarization moment of the piezoelectric material layer700can be acquired in such a manner that an inner electric field is measured by measuring the phase of an electron beam in accordance with an intensity transport equation and a measuring an electric field based on the result of the phase using a transmission electron microscope.

To be specific, a bright field image (a focused image of only a transmission wave) of the transmission electron microscope is utilized. Three images having the same focus including an image at a right focus position and images at under-focus and over-focus positions with respect to the image at the right focus position are prepared, and the deviation of intensity in a propagation direction is approximated by the difference of an observed intensity (the intensity transport equation) so as to measure a phase. The phase is deviated in order to obtain an electric field vector.

Since the electric field vector (a vector direction of the inner electric field formed by the polarization moment) is antiparallel to the vector direction of the polarization moment, it is possible to measure the orientation of the polarization moment (the angle with respect to the direction of the electric field) of the piezoelectric material layer70by measuring the electric field vector of the piezoelectric material layer70.

In addition, since an absolute value of the inner electric field is proportional to an absolute value of the polarization moment, it is possible to perform a relative comparison between absolute values of the polarization moment by performing a relative comparison between absolute values of the inner electric field.

Thus, by regulating the orientation of the polarization moment, the rate of change of the displacement amount due to repeated driving of the piezoelectric material layer70can be decreased. Namely, the durability can be improved. For example, in the case where, as described above, the angle θ0indicative of the direction by which the piezoelectric constant reaches its maximum level, is 55 degrees, it is possible to make the rate of change of the displacement amount of the piezoelectric material layer70can be not lower than 5% (a practical example) even when the piezoelectric material layer70is repeatedly driven 20 billion times as shown inFIG. 6under a condition that the angle θa indicative of the orientation of the polarization moment is 58 degrees, i.e., greater than the angle θ0by 3 degrees. In contrast, when the above described angle θa′ is formed between the orientation of the polarization moment and the direction of the electric field, so as to be smaller than the angle θ0, such as for example, 52 degrees, the rate of change of the displacement amount of the piezoelectric material layer70due to repeated driving is made to be greater by approximately 10% as shown inFIG. 6(a comparative example). Therefore, it is preferable that the angle θa indicative of the orientation of the polarization moment is greater than the angle θ0by 3 degrees or more. When the angle θa is greater than the angle θ0by 20 degrees or more, the piezoelectric constant continuously increases in an endurance test. However, a problem may arise that the displacement amount at the initial stage is lowered. Therefore, it is preferable that the difference between the angle θa and the angle θ0is made equal to or smaller than 20 degrees.

In addition, as shown inFIG. 6, the displacement amount of the piezoelectric material layer70of the practical example increases in accordance with the number of repetitions along with the repeated application of the electric field (preferably increases at the rate of change not greater than 5%), and then gradually decreases. As a result, it is possible to suppress the rate of change of the displacement amount as compared to a case that the displacement amount continuously decreases in accordance with the number of repetitions along with the repeated application of the electric field as in the comparative example shown inFIG. 6. Moreover, since the displacement amount of the piezoelectric material layer70of the practical example increases in accordance with increase of the number of repetitions with the repeated application of the electric field and then gradually decreases, the piezoelectric material layer70can be used immediately. Typically, when the rate of change of the displacement amount at the initial stage is great, such as in the comparative example shown inFIG. 6, it is necessary to perform a driving process so as to partially fix the polarization until the rate of change becomes stable beyond the rate of change of great displacement amount before the device may be used. However, using embodiments described herein, it is not necessary to perform the driving process for partially fixing the polarization, thereby reducing the cost. Note that,FIG. 6is a graph indicating the examination results of the practical example and the comparative example.

The orientation of the polarization moment can be adjusted to allow it to have a desired angle with respect to the direction of the electric field in such a manner that, for example, an oxygen deficient layer that is more deficient in oxygen than any other region is provided on the piezoelectric material layer70at the second electrode side, or a grounding material may be used for the first electrode60at the piezoelectric material layer70side when the piezoelectric material layer70is formed by performing an epitaxial growth process.

When an oxygen deficient layer exists on the piezoelectric material layer70at the second electrode80side, the oxygen deficient layer functions as a virtual plus bivalent ion so that the inner electric field from the second electrode28acts on the piezoelectric material layer70toward the first electrode60from the second electrode80. The generated inner electric field can be adjusted by a degree of deficiency of oxygen so that the orientation of the polarization moment can be adjusted as desired by an action of the inner electric field.

In addition, it is possible to adjust the orientation of the polarization moment of the piezoelectric material layer70as desired by choosing a material of a ground layer of the piezoelectric material layer70. When, for example, lanthanum nickel oxide (LNO) is used for the material of the ground layer of the piezoelectric material layer70, since a lattice constant in a plane of the LNO is smaller than a general lattice constant in a plane of the piezoelectric material layer70, the piezoelectric material layer70is formed on the LNO having a contracted lattice constant in the plane. Thus, the lattice constant in the plane of the piezoelectric material layer70is expanded or contracted depending on the material used for the ground layer so that the orientation of the polarization moment can be adjusted based on the expansion or contraction of the lattice constant.

In addition, while the voltage is applied toward the first electrode60from the second electrode80in the embodiment described above, the direction of application of the voltage is defined by a driving unit provided on an ink jet recording apparatus II, which will be described more fully below. As a result, the voltage can be applied toward the second electrode80from the first electrode60by the driving unit.

The thickness of the piezoelectric material layer70is not specifically limited. However, it is preferable to suppress the thickness so as to be at a level not generating a crack in a manufacturing process but exhibiting a sufficient displacement characteristic. When, for example, the piezoelectric material layer70is formed to have the thickness in the range of roughly 0.2 to 4 μm, a desired crystal structure can be readily obtained. In the embodiment, the piezoelectric material layer70is made to have the thickness of 1.2 μm in order to acquire an optimum piezoelectric characteristic.

The manufacturing method of the piezoelectric material layer70is not specifically limited. For example, the piezoelectric material layer70can be formed by using a so-called sol-gel method in which a sol having an organic metal compound dissolved and dispersed in a solvent is applied and dried to form a gel, and the gel is baked at a high temperature so as to obtain the piezoelectric material layer70made of metal oxide. Needless to say, the manufacturing method of the piezoelectric material layer70is not limited to the sol-gel method, and, for example, a MOD (Metal-Organic Decomposition) method or a sputtering method can also be used.

In addition, the second electrode80is, for example, formed of iridium (Ir) having a thickness of 200 nm. The second electrode80functions as a discrete electrode of the piezoelectric element300. A lead electrode90which is made of, for example, gold (Au) and is led from a portion in the vicinity of the end of the second electrode80at the ink supply channel14side so as to extend to the insulation material film55, is connected to the second electrode80.

A protective substrate30having a reservoir portion31constituting at least a part of a reservoir100is bonded to the fluid channel forming substrate10having the piezoelectric element300formed thereon with an adhesive35formed therebetween. That is, the protective substrate30is provided on the lower electrode film60, the insulation material film55and the lead electrodes90. The reservoir portion31, in the embodiment, is formed so as to pass through the protective substrate30in the thickness direction over the width direction of the pressure generating chambers12. The reservoir portion31communicates with the communicating portion13of the fluid channel forming substrate10so as to form the reservoir100which serves as the common ink chamber for the pressure generating chambers12.

Alternatively, the communicating portion13of the fluid channel forming substrate10may be preferably divided into a plurality of portions for each of the pressure generating chambers12, so that only the reservoir portion31may function as the reservoir100. Moreover, in a preferred example, only the pressure generating chambers12are provided in the fluid channel forming substrate10, and the ink supply channels14communicating with the reservoir100and the pressure generating chambers12are provided in a member, such as, for example, the elastic film50or the insulation material film55, interposed between the fluid channel forming substrate10and the protective substrate30.

A piezoelectric element holding portion32having a space which does not hinder the motion of the piezoelectric element300is provided in a region of the protective substrate30, the region facing the piezoelectric elements300. The piezoelectric element holding portion32may be sealed or may not be sealed as long as it has the space which does not hinder the motion of the piezoelectric element300.

As the protective substrate30, a material having roughly the same coefficient of thermal expansion as the fluid channel forming substrate10is preferably used, such as, for example, a glass material, ceramic material or the like. In this embodiment, a silicon monocrystalline substrate which is the same material as the fluid channel forming substrate10is used to form the protective substrate30.

A through-hole33passing through the protective substrate30in the thickness direction is provided in the protective substrate30. A portion in the vicinity of the end of the lead electrode90led from each piezoelectric elements300is provided so as to be exposed in the through-hole33.

A drive circuit110that drives the juxtaposed piezoelectric elements300is fixed to the protective substrate30. As the drive circuit110, for example, a circuit board or a semiconductor integrated circuit (IC) can be used. The drive circuit110and the lead electrodes90are electrically connected to each other via connection wires110aformed of conductive wires such as bonding wires.

A compliance substrate40constituted by a sealing film41and a fixing plate42is bonded on the protective substrate30. Here, the sealing film41is made of a material having a low rigidity and a flexibility and one face of the reservoir portion31is sealed by the sealing film41. The fixing plate42is made of a comparatively hard material. Since a region of the fixing plate42facing the reservoir100is made to be an open section43which is completely opened in the thickness direction, one face of the reservoir100is sealed only by the sealing film41having flexibility.

In the ink jet recording head I of the first embodiment, ink is taken from an ink flow-in hole connected to an outer ink supply unit (not shown), and inner portions from the reservoir100to the nozzle openings21are filled with the ink. After that, a voltage is applied across the first electrode60and the second electrode80corresponding to the pressure generating chamber12in accordance with a recording signal from the driving circuit110. As a result, the elastic film50, the insulation material film55, the first electrode60and the piezoelectric material layer70are deflectively deformed so as to increase the pressure in each of the pressure generating chambers12, thereby ejecting ink droplets from the nozzle openings21.

The above described ink jet recording head I constitutes a part of a recording head unit having an ink fluid channel communicating with an ink cartridge and is mounted on the ink jet recording apparatus II.FIG. 7is a schematic view showing an embodiment of the ink jet recording apparatus II.

In the ink jet recording apparatus II shown inFIG. 7, cartridges2A and2B forming the ink supply unit are detachably attached to recording head units1A and1B each having the ink jet recording head I. A carriage3having the recording head units1A and1B mounted thereon is attached to a carriage shaft5fixed to an apparatus frame4so as to be movable in the axial direction. The recording head units1A and1B are respectively adapted to eject, for example, a black ink composition and a color ink composition.

A driving force of a drive motor6is transmitted to the carriage3via a plurality of gears (not shown) and a timing belt7so that the carriage3having the recording head units1A and1B mounted thereon is moved along the carriage shaft5. A platen8is provided on the apparatus frame4along the carriage shaft5, and a recording sheet S as a recording medium such as paper fed from a paper feed roller (not shown) is wound around the platen8so as to be transported.

In addition, the ink jet recording apparatus II is provided with a driving unit (not shown). Here, a control structure of the ink jet recording apparatus II will be described below.FIG. 8is a block diagram showing the control structure of the ink jet recording apparatus II according to the embodiment.

The ink jet recording apparatus II according to the embodiment is mainly constituted by a printer controller111and a print engine112as shown inFIG. 8. The printer controller111includes an external interface113(hereinafter, referred to as external I/F113), a RAM114that temporarily stores various kinds of data, a ROM115that stores a control program, a control section116mainly constituted by a CPU, an oscillation circuit117that generates a clock signal, a drive signal generating circuit119that generates a drive signal to be supplied to the ink jet recording head I, and an internal interface120(hereinafter, referred to as an internal I/F120) that transmits dot pattern data (bitmap data) developed in accordance with a drive signal or print data to the print engine112.

The external I/F113receives print data formed of, for example, a character code, a graphic function and image data from a host computer (not shown). A busy signal (BUSY) or an acknowledge signal (ACK) is output to the host computer via the external I/F113. The RAM114functions as a reception buffer121, an intermediate buffer122, an output buffer123and a work memory (not shown). The reception buffer121temporarily stores print data received via the external I/F113, the intermediate buffer122stores intermediate code data converted by the control section116, and the output buffer123stores dot pattern data. The dot pattern data is formed of print data obtained by decoding (interpreting) gradation data.

The drive signal generating circuit119comprises a drive signal generating unit which generates a drive signal COM. The drive signal COM includes an ejection pulse for driving (driving for ejection) the piezoelectric element300so as to eject ink in one recording cycle and is repeatedly generated for each recording cycle T.

The ROM115stores a control program (a control routine) for allowing devices to perform various data processing operations, font data and a graphic function. The control section116reads print data in the reception buffer121and allows the intermediate buffer122to store intermediate code data obtained by converting the print data. In addition, the control section116analyzes the intermediate code data read from the intermediate buffer122and develops the intermediate code data into dot pattern data by referencing the font data and the graphic function stored in the ROM115. The control section116applies necessary decorative processing to the dot pattern data and allows the output buffer123to store the developed pattern data.

When the dot pattern data for one row of the ink jet recording head I is prepared, the one row of dot pattern data is output to the ink jet recording head I via the internal I/F120. After the one row of dot pattern data is output from the output buffer123, the developed intermediate code data is deleted from the intermediate buffer122, and then a process of developing next intermediate code data is performed.

The print engine112is mainly constituted by the ink jet recording head I, a paper transporting mechanism124and a carriage mechanism125. The paper transporting mechanism124is constituted by a paper transporting motor and the platen8, which sequentially feeds a recording sheet S such as recording paper in association with a recording operation of the ink jet recording head I. Namely, the paper transporting mechanism124relatively transports the recording sheet S in a sub-scanning direction.

The carriage mechanism125comprises by the carriage3to which the ink jet recording head I can be mounted, and a carriage driving section that moves the carriage3along a main scanning direction. By moving the carriage3, the ink jet recording head I is moved in the main scanning direction. As described above, the carriage driving section is constituted by the drive motor6and the timing belt7.

The ink jet recording head I has multiple nozzle openings21arranged in the sub-scanning direction and each of the nozzle openings21ejects a liquid droplet at a timing regulated by a dot pattern data. An electric signal such as the drive signal COM or print data (SI) is supplied to the piezoelectric element300on the ink jet recording head I via an external wire (not shown).

In the printer controller111and the print engine112constituted as the above, a drive unit that applies a predetermined drive signal to the piezoelectric elements300includes the printer controller111, and the drive circuit110that includes a shift register131, a latch132, a level shifter133and a switch134which are adapted to selectively input a drive signal to the piezoelectric elements300, the drive signal having a predetermined driving waveform output from the drive signal generating circuit119.

The shift register131, the latch132, the level shifter133, the switch134, and the piezoelectric element300are provided for each nozzle opening21, and these shift register131, the latch132, the level shifter133, and the switch134generate a drive pulse in accordance with the drive signal COM generated by the drive signal generating circuit119. The above described drive pulse is an application pulse to be actually applied to the piezoelectric elements300.

FIG. 9is a schematic view showing an example of the drive pulse according to the embodiment. A drive pulse200of the embodiment is applied to the second electrode80by making the first electrode60to be a reference electric potential V0as shown inFIG. 9. The drive pulse200is constituted by a contracting process period400for contracting a volume of the pressure generating chamber12by raising a drive electric potential V from a first electric potential V1higher than the reference electric potential V0to a second electric potential V2higher than the first electric potential V1, a first holding process period401for holding the second electric potential V2for a predetermined time period, an expanding process period402for expanding the volume of the pressure generating chamber12by lowering the drive electric potential V from the second electric potential V2to a third electric potential V3which is lower than the first electric potential V1and higher than the reference electric potential V0, a second holding process period403for holding the third electric potential V3for a predetermined time period, and a process period404for raising the drive electric potential V from the third electric potential V3to the first electric potential V1.

When the above drive pulse200is output to the piezoelectric element300, the piezoelectric element300is deformed so as to contract the volume of the pressure generating chamber12during the contracting process period400so that a meniscus of the nozzle opening21is pushed out, Next, the piezoelectric element300is deformed so as to expand the volume of the pressure generating chamber12by the expanding process period402so that the meniscus of the nozzle opening21is suddenly drawn toward the pressure generating chamber12. As a result, the ink pushed out the nozzle opening21is cut and the ink ejected from the nozzle opening21is allowed to fly as an ink droplet. Namely, the drive pulse200is for a so-called draw-and-eject method.

In terms of the piezoelectric material layer70of the embodiment, the description of the voltage being applied from the second electrode80toward the first electrode60indicates that since the reference electric potential V0is applied to the first electrode60, the first electric potential V1, the second electric potential V2and the third electric potential V3to be applied to the second electrode80are relatively higher than the reference electric potential V0. Even when the reference electric potential V0has a positive polarity, when each of the first electric potential V1, the second electric potential V2and the third electric potential V3have a positive polarity and are higher than the reference electric potential V0, the second electrode80to which the first electric potential V1, the second electric potential V2or the third electric potential V3are applied, is made to have a positive polarity and the first electrode60is made to have a negative polarity.

In this embodiment, while all of the electric potential V1, the second electric potential V2and the third electric potential V3are made to be positive and higher than the reference electric potential V0applied to the first electrode60, the invention is not so limited. For example, the second electric potential V2can be lower than the reference electric potential V0. That is, the second electrode80can have the negative potential. In the above case, when a factor defined by a voltage and an application time period indicated by integration of the drive pulse200based on the electric potential to be applied to the first electrode60, is configured such that the factor at the positive side is greater than that at the negative side with respect to the reference potential V0, the above described effect of the invention is enhanced.

Second Embodiment

In the above described first embodiment, the voltage is applied from the second electrode80toward the first electrode60. However, the voltage is applied from the first electrode60toward the second electrode80in the second embodiment of the invention.

Here, the orientation of the polarization moment of the piezoelectric material layer70will be described with reference toFIG. 10.FIG. 10is a graph showing the direction of the electric field and the orientation of the polarization moment. As shown inFIG. 10, an angle θc formed between the orientation of the polarization moment of the piezoelectric material layer70and the direction of the electric field is greater than the angle θ0formed between the direction of the electric field at a time when the piezoelectric constant (d31) reaches its maximum level and the orientation of the polarization moment of the piezoelectric material layer70. Here, the inner electric field was measured similarly to the first embodiment. As a result of the measurement, the angle θ0was 55 degrees and the angle θc was 60 degrees.

When the piezoelectric element300is repeatedly driven and the wear phenomenon occurs, an angle θd formed between the orientation of the polarization moment and the direction of the electric field is made smaller than the angle θ0. As a result, the rate of change of the piezoelectric constant (d31), i.e., the lowering rate of the displacement amount of the piezoelectric material layer70, can be decreased in a manner similar to the first embodiment. To be specific, when the driving process is repeated 20 billion time using the second embodiment of the invention, the displacement amount was initially increased by 2% with respect to the beginning of the displacement amount and it was finally decreased by 2% with respect to the beginning.

Regarding the above described piezoelectric element300, the drive pulse of the drive unit for driving the piezoelectric element300is made to be, for example, such as the drive pulse shown inFIG. 11.

Namely, a drive pulse201is applied to the second electrode80using the reference electric potential V0of the first electrode60. The drive pulse201includes an expanding process period410for expanding the volume of the pressure generating chamber12by lowering the drive electric potential V from a first electric potential V11lower than the reference electric potential V0(relatively having a negative polarity) to a second electric potential V12lower than the first electric potential V11, a first holding process period411for holding the second electric potential V12for a predetermined time period, a contracting process period412for contracting the volume of the pressure generating chamber12by raising the drive electric potential V from the second electric potential V12to a third electric potential V13, a second holding process period413for holding the third electric potential V13for a predetermined time period, and a process period414for returning the drive electric potential V from the third electric potential V13to the first electric potential V11.

When the above drive pulse201is output to the piezoelectric element300, the piezoelectric element300is deformed so as to expand the volume of the pressure generating chamber12by the expanding process period410so that a meniscus of the nozzle opening21is drawn toward the pressure generating chamber12. Next, the piezoelectric element300is deformed so as to contract the volume of the pressure generating chamber12in the contracting process period412so that the meniscus in the nozzle opening21is markedly pushed out from the pressure generating chamber12and an ink droplet is ejected from the nozzle opening21. Namely, the drive pulse201is for a so-called push-and-eject method.

Each of the first electric potential V11, the second electric potential V12and the third electric potential V13are lower than the reference electric potential V0. Therefore, using the above drive pulse201, an electric potential having a positive polarity is applied to the first electrode60and an electric potential having a negative polarity is applied to the second electrode80.

Third Embodiment

FIG. 12Ais a plan view of an ink jet recording head that is an example of a liquid jet head according to a third embodiment of the invention.FIG. 12Bis a cross sectional view taken along a line XIIB to XIIB in the FIG.12A.FIG. 13is a cross sectional exploded view showing a main part of a pressure generating chamber of the recording head in the juxtaposed direction of the pressure generating chambers. Note that, the elements or members the same as in the above described first embodiment are denoted by the same numerals, and their descriptions are omitted.

As shown inFIGS. 12A through 13, an elastic film50is formed on a fluid channel forming substrate10constituting the ink jet recording head of the embodiment and an insulation material film55is formed on the elastic film50. A piezoelectric element300A constituted by a first electrode60A, a piezoelectric material layer70A and a second electrode80A is provided on the insulation material film55.

The first electrode60A is provided on each of regions facing respective pressure generating chambers12. The first electrode60A is a discrete electrode of each piezoelectric element300A. To be specific, the first electrode60A is formed in such a manner that the width of the first electrode60A in a short side direction of the pressure generating chamber12(in the juxtaposed direction of the pressure generating chambers12) is smaller than the width of the pressure generating chamber12. In addition, one end of the first electrode60A in the lengthwise direction of the pressure generating chamber12(in a direction perpendicular to the juxtaposed direction of the pressure generating chambers12) is drawn to the outside of the pressure generating chamber12.

The piezoelectric material layer70A is provided on the first electrode60A corresponding to each pressure generating chamber12. To be specific, the piezoelectric material layer70A is provided on the first electrode60A in such as manner that the piezoelectric material layer70A covers both end faces in the width direction of the first electrode60A (in the width direction of the pressure generating chamber12) and the piezoelectric material layers70A are compartmentalized so as to be discontinuous at a portion on a partition wall11between adjacent piezoelectric elements300A. In addition, the piezoelectric material layer70A has a size so as to cover one end portion of the first electrode60A in the lengthwise direction (in the long side direction of the pressure generating chamber12) and to expose the other end portion thereof. The end portion of the first electrode60A exposed from the piezoelectric material layer70A serves as a terminal to be electrically connected to a drive circuit for driving each of the piezoelectric elements300A.

The second electrode80A is a common electrode and is provided on each piezoelectric material layer70A so as to be continuous over the plurality of piezoelectric material layers70A. More specifically, the second electrode80A is continuously provided over the piezoelectric material layers70A and the insulation material films55each being disposed between the adjacent piezoelectric elements300A.

In the piezoelectric elements300A having the above structure, each piezoelectric material layer70A is covered with the second electrode80A. In particular, since the side of the piezoelectric material layer70A is covered with the second electrode80A, the piezoelectric material layer70A can be protected from ambient moisture or the like by the second electrode80A even when a protection film having moisture resistance is not provided on the piezoelectric elements300A. With this configuration, it is possible to prevent lowering of the displacement amount of the piezoelectric element300A which may occur when a protection film is provided thereon. Namely, by obviating the need of a protection film, it is possible to suppress the cost and to realize the piezoelectric element300A with superior displacement characteristics.

In addition, since the first electrode60A is a discrete electrodes formed for each of the plurality of piezoelectric elements300A, it is possible to facilitate the application of a voltage from the first electrode60A to the second electrode80A similarly to the case of the above described second embodiment.

Fourth Embodiment

FIG. 14Ais a plan view of an ink jet recording head that is an example of a liquid jet head according to a Fourth Embodiment of the invention.FIG. 14Bis a cross sectional view taken along a line XIVB to XIVB in theFIG. 14A.FIG. 15is a cross sectional exploded view showing a main part of a pressure generating chamber of the recording head in the juxtaposed direction of pressure generating chambers. The elements or members the same as in the above described first embodiment are denoted by the same numerals, and their descriptions are omitted.

As shown inFIGS. 14A through 15, an elastic film50is formed on a fluid channel forming substrate10constituting the ink jet recording head of the embodiment and an insulation material film55is formed on the elastic film50. A piezoelectric element300B constituted by a first electrode60A, a piezoelectric material layer70B and a second electrode80B, is provided on the insulation material film55.

The first electrodes60A are provided independently corresponding to pressure generating chambers12, as described in the third embodiment of the invention.

The piezoelectric material layer70B is provided on each of the first electrodes60A so as to be continuous over the plurality of piezoelectric elements300B. To be specific, the piezoelectric material layer70B is formed over the first electrodes60A and the insulation material films55so as to be continues toward the juxtaposed direction of the first electrodes60A and to have a roughly uniform thickness. Here, the piezoelectric material layer70B is not provided on one end of the first electrode60A in the lengthwise direction thereof and no electrode is formed in the area where the piezoelectric material layer70B is not provided.

The second electrode80B is provided so as to be continuous over the plurality of piezoelectric material layers70B. Namely, the second electrode80B serves as a common electrode for the piezoelectric elements300B so as to be continuous over the piezoelectric elements300B.

Regarding the piezoelectric elements300B having the above structure, each piezoelectric material layer70B is covered with the second electrode80B. In particular, since the piezoelectric material layer70B between adjacent first electrodes60A is covered with the second electrode80B, the piezoelectric material layer70B can be protected from ambient moisture or the like by the second electrode80B even when a protection film having moisture resistance is not provided on the piezoelectric elements300B. With this configuration, it is possible to prevent lowering of the displacement amount of the piezoelectric element300B which may occur when a protection film is provided thereon. Namely, by obviating the need of a protection film, it is possible to suppress the cost and to realize the piezoelectric element300B superior in a displacement characteristic.

In addition, since the first electrode60A is made to be each of the discrete electrodes of the plurality of piezoelectric elements300B, it is possible to facilitate the application of a voltage from the first electrode60A toward the second electrode80B as described in the second embodiment of the invention described above.

Other Embodiments

While several embodiments of the invention are described above, the invention is not limited to the examples described herein. In the above first embodiment, while a silicon monocrystalline substrate is exemplarily used as the fluid channel forming substrate10, is the invention is not so limited. For example, a silicon monocrystalline substrate having a (100) crystal orientation or a (110) crystal orientation, an SOI substrate or a material such as glass can be used.

In the above described ink jet recorder II, while the ink jet head I (the head units1A and1B) that is mounted on the carriage3and is moved in the sub-scanning direction is exemplarily shown, the invention is not limited thereto. The invention can be applied to a so-called line type printer in which, for example, the ink jet recording head I is fixed and printing is performed by moving only a recording sheet S such as paper in the sub-scanning direction.

While the ink jet recording head is described as one example of the liquid ejecting head in the above first embodiment, the invention can be widely applied to a variety of liquid ejecting heads so that the invention can be applied to a liquid ejecting head that ejects liquid other than ink. As any other liquid ejecting heads, for example, various kinds of recording heads used in image recorders such as printers, a colorant ejecting head used for manufacturing a color filter of a liquid crystal display, an electrode material ejecting head used for forming an electrode of an organic EL display or an FED (field emission display), and a biological organic material ejecting for manufacturing a bio-chip may also be used.

The invention can be applied to not only the actuator device mounted on the liquid ejecting head, as a representative of the ink jet recording heads, but also an actuator device to be mounted on any other devices.