Patent Description:
A piezoelectric element generally includes a substrate, a piezoelectric layer having an electromechanical conversion characteristic, and two electrodes sandwiching the piezoelectric layer. In recent years, devices (piezoelectric element application devices) using such a piezoelectric element as a drive source have been actively developed. One of the piezoelectric element application devices is a liquid ejection head represented by an ink jet recording head, a MEMS element represented by a piezoelectric MEMS element, an ultrasonic measurement device represented by an ultrasonic sensor, and further, a piezoelectric actuator device.

Lead zirconate titanate (PZT) is known as a material (piezoelectric material) for the piezoelectric layer of the piezoelectric element. In recent years, non-lead-based piezoelectric materials having a reduced lead content have been developed from the viewpoint of environmental load reduction.

Further, in recent years, there is a strong demand for further size reduction and higher performance of various electronic devices, electronic components, and the like, and accordingly, size reduction and higher performance of piezoelectric elements are also demanded.

As one of the non-lead-based piezoelectric materials, for example, as disclosed in <CIT>, potassium sodium niobate, KNN (K,Na)NbO<NUM> has been proposed.

Generally, when a KNN-based material is used as a piezoelectric material, a problem that a leakage current is likely to be generated is known. In this regard, <CIT> discloses that generation of a leakage current can be prevented by containing at least one of iron and manganese.

However, according to the studies of the inventors, it has been found that a leakage current density is increased due to an organic component remaining in the piezoelectric layer. That is, the leakage current density may not be sufficiently reduced only by improving a crystal orientation by adding an additive into the KNN-based piezoelectric layer.

Under such circumstances, a piezoelectric layer capable of sufficiently reducing a leakage current is demanded in a piezoelectric substrate or a piezoelectric element including a KNN-based piezoelectric layer.

Such a problem is not limited to a piezoelectric element used in a piezoelectric actuator mounted on a liquid ejection head represented by an ink jet recording head, but also exist similarly in a piezoelectric element used in another piezoelectric element application device.

<CIT> discloses a method of preparing a lead-free piezoelectric thin film comprising the steps of: providing a precursor solution comprising at least one alkali metal ion, a polyamine carboxylic acid, and an amine; depositing the precursor solution on a substrate to form a film; and annealing the film. The document also describes a lead-free piezoelectric thin film prepared according to the method, a precursor solution for use in the method and a method of preparing the precursor solution.

<CIT> discloses a piezoelectric element that includes a piezoelectric layer composed of a perovskite structure complex oxide containing potassium, sodium, niobium and manganese, disposed between first and second electrodes on a substrate. The manganese includes divalent manganese, trivalent manganese and tetravalent manganese. A molar ratio Mn2+/((Mn3+) + (Mn4+)) ranges from <NUM> to <NUM>, and a molar ratio K/Na is less than or equal to <NUM>.

<CIT> discloses a piezoelectric element comprising a piezoelectric film containing potassium, sodium, niobium, lithium and copper.

In order to solve the above problem, according to the invention, there is provided a piezoelectric substrate as defined in claim <NUM>.

According to a second aspect of the invention, there is provided a piezoelectric element as defined in claim <NUM>.

According to a third aspect of the invention, there is provided a piezoelectric element application device as defined in claim <NUM>.

In the drawings, the same reference signs denote the same members, and the description thereof is omitted as appropriate. The number after a letter which makes up the reference sign is referenced by a reference sign which includes the same letter and is used to distinguish between elements which have similar configurations. When it is not necessary to distinguish elements indicated by the reference signs which include the same letter from each other, each of the elements is referenced by a reference sign containing only a letter.

In each drawing, X, Y, and Z represent three spatial axes orthogonal to one another. In the present description, directions along these axes are referred to as a first direction X (X-direction), a second direction Y (Y-direction), and a third direction Z (Z-direction), a direction of an arrow in each drawing is referred to as a positive (+) direction, and a direction opposite from the arrow is referred to as a negative (-) direction. The X-direction and the Y-direction represent in-plane directions of a plate, a layer, and a film, and the Z-direction represents a thickness direction or a stacking direction of a plate, a layer, and a film.

Components shown in each drawing, that is, a shape and size of each part, a thickness of a plate, a layer, and a film, a relative positional relation, a repeating unit, and the like may be exaggerated for describing the present disclosure. Furthermore, the term "above" in the present description does not limit that a positional relation between the components is "directly above". For example, expressions such as "a first electrode on a base body" and "a piezoelectric layer on the first electrode", which will be described later, do not exclude those including other components between the base body and the first electrode or between the first electrode and the piezoelectric layer.

First, a configuration of a piezoelectric substrate <NUM> according to the embodiment will be described with reference to the drawings. <FIG> is a cross-sectional view schematically showing the piezoelectric substrate <NUM>.

As shown, the piezoelectric substrate <NUM> includes a base body <NUM>, an electrode 60A, and a piezoelectric layer <NUM>. The piezoelectric substrate <NUM> is provided above the base body <NUM>. In the shown example, the piezoelectric substrate <NUM> is provided at the base body <NUM>. Thicknesses of the elements shown in the drawings are merely examples, and can be changed without departing from the scope of the present invention.

The base body <NUM> is a flat plate formed of, for example, a semiconductor or an insulator. The base body <NUM> may be a single layer or a structure in which a plurality of layers is stacked. An internal structure of the base body <NUM> is not limited as long as an upper surface thereof has a planar shape, and the base body <NUM> may have a structure in which a space and the like is formed therein.

The base body <NUM> includes, for example, a vibration plate <NUM> that can be deformed by an operation of the piezoelectric layer <NUM>. In the shown example, the vibration plate <NUM> includes a silicon oxide layer <NUM> and an oxide layer <NUM> provided at the silicon oxide layer <NUM>. In the shown example, the base body <NUM> includes a silicon substrate <NUM>, and the vibration plate <NUM> is provided at the silicon substrate <NUM>.

The silicon oxide layer <NUM> is a layer containing silicon and oxygen, and is, for example, a silica (SiO<NUM>) layer. The silicon oxide layer <NUM> may function as an elastic film. The vibration plate <NUM> may not include the silicon oxide layer <NUM>.

The oxide layer <NUM> is, for example, a zirconium oxide layer. When the oxide layer <NUM> is a zirconium oxide layer, the oxide layer <NUM> is a layer containing zirconium and oxygen, and is, for example, a ZrO<NUM> layer.

The electrode 60A is formed at the base body <NUM> (the vibration plate <NUM> in <FIG>). A shape of the electrode 60A is, for example, a layer shape or a thin film shape. A thickness (a length in a Z-axis direction) of the electrode 60A is, for example, <NUM> or more and <NUM> or less.

Examples of a material of the electrode 60A include various metals such as nickel, iridium, and platinum, conductive oxides thereof (for example, iridium oxide), composite oxides of strontium and ruthenium (SrRuOx: SRO), and composite oxides of lanthanum and nickel (LaNiOx: LNO). The electrode 60A may have a single-layer structure of the materials shown above, or may have a structure in which a plurality of materials is stacked.

The material of the electrode 60A is suitably a noble metal such as platinum (Pt) or iridium (Ir), or an oxide thereof. The material of the electrode 60A may be any material having conductivity.

An adhesion layer (not shown) may be provided between the electrode 60A and the oxide layer <NUM>. The adhesion layer is made of, for example, titanium oxide (TiOx), titanium (Ti), and SiN, and has a function of improving adhesion between the piezoelectric layer <NUM> and the vibration plate <NUM>. In a case where a titanium oxide (TiOx) layer, a titanium (Ti) layer, or a silicon nitride (SiN) layer is used as the adhesion layer, when the piezoelectric layer <NUM> is formed, the adhesion layer also functions as a stopper that prevents potassium and sodium, which are constituent elements of the piezoelectric layer <NUM>, from passing through a first electrode <NUM> and reaching the silicon substrate <NUM>. The adhesion layer may be omitted.

It is preferable that an orientation control layer (seed layer) <NUM> is provided between the electrode 60A and the piezoelectric layer <NUM>. The orientation control layer <NUM> functions as an orientation control layer that controls an orientation of a crystal of a piezoelectric body constituting the piezoelectric layer <NUM>. That is, by providing the orientation control layer <NUM> at the electrode 60A, the crystal of the piezoelectric body constituting the piezoelectric layer <NUM> can be preferentially oriented in a predetermined plane orientation (for example, (<NUM>) plane). By improving the crystal orientation of the piezoelectric layer, it is possible to efficiently utilize domain rotation and improve displacement characteristics. Examples of a material of the orientation control layer <NUM> include various metals such as titanium, nickel, iridium, and platinum, oxides thereof, and compounds containing bismuth, iron, titanium, and lead.

The piezoelectric layer <NUM> is formed at the electrode 60A and covers the electrode 60A. The piezoelectric layer <NUM> contains a composite oxide having a perovskite structure represented by a general formula ABO<NUM> as a main component. In the embodiment, the piezoelectric layer <NUM> contains a piezoelectric material made of a KNN-based composite oxide represented by Formula (<NUM>).

The composite oxide represented by Formula (<NUM>) is a so-called KNN-based composite oxide. Since the KNN-based composite oxide is a non-lead-based piezoelectric material having a reduced content of lead (Pb) and the like, the KNN-based composite oxide is excellent in biocompatibility and has low environmental load. In addition, since the KNN-based composite oxide is excellent in piezoelectric characteristics among non-lead-based piezoelectric materials, it is advantageous for improving various characteristics.

A relationship between an organic component remaining in the piezoelectric layer <NUM> (hereinafter referred to as the remaining organic component) and a leakage current will be described below together with new findings obtained by the inventors.

Generally, in the case of a piezoelectric substrate (or a piezoelectric element to be described later) using a KNN-based material as a piezoelectric material as represented by Formula (<NUM>), there is known a problem that a leakage current is likely to be generated. For factors of the generation of the leakage current, according to the intensive studies of the inventors, it has been found that a leakage current density increases due to the remaining organic component in the piezoelectric layer, that is, there is a correlation between the remaining organic component and the leakage current density. Further, it has been found that the leakage current density may not be sufficiently reduced only by improving the crystal orientation by adding an additive to the piezoelectric layer, which is known in the related art as one of the methods for reducing a leakage current.

Therefore, in the embodiment, attention is paid to the remaining organic component contained in the piezoelectric layer <NUM>, and a correlation of peaks during measurement by Fourier transform infrared (FT-IR) spectroscopy is defined. Specifically, a value of IR2/IR1 obtained by dividing an integrated intensity IR2 of a peak <NUM> by an integrated intensity IR1 of a peak <NUM>, when a surface of the piezoelectric layer <NUM> is measured by FT-IR spectroscopy, is less than <NUM>. Here, the peak <NUM> has a strongest area intensity among peaks detected at wavenumbers of <NUM>-<NUM> to <NUM>-<NUM>, and the peak <NUM> has an area intensity that is a sum of area intensities of peaks detected at wavenumbers of <NUM>-<NUM> to <NUM>-<NUM>. More specifically, in the piezoelectric layer <NUM> according to the embodiment, the peak <NUM> corresponds to a peak related to niobium oxide (NbO), and the remaining organic component contained in the piezoelectric layer <NUM> can be quantitatively evaluated by correlating a peak related to the remaining organic component with the peak <NUM>. When the IR2/IR1 is less than <NUM>, the organic component remaining in the piezoelectric layer <NUM> can be reduced, the leakage current can be sufficiently reduced, and the domain rotation can be added, and thus a displacement amount can be increased. The IR2/IR1 is preferably <NUM> or less.

Since the IR2/IR1 is preferably as small as possible, a lower limit value thereof is not particularly limited. However, when a preferable method of manufacturing the piezoelectric substrate according to the embodiment and the piezoelectric element to be described later is a liquid phase method and the liquid phase method using a precursor solution is used, since the organic component is more likely to remain in the piezoelectric layer <NUM> than in a gas phase method, for example, the IR2/IR1 may be <NUM> or more.

The piezoelectric layer <NUM> contains lithium. Lithium has an effect of improving leakage characteristics. Therefore, in order to reduce the leakage current more efficiently, it is effective to contain lithium as the material constituting the piezoelectric layer <NUM>. A content of lithium is preferably <NUM> mol% or less. When the content of lithium is more than <NUM> mol%, a different phase may be generated in the piezoelectric layer <NUM>, and a crystal orientation of the piezoelectric body may deteriorate. More preferably, the content of lithium is <NUM> mol% or less.

The piezoelectric layer <NUM> also contains copper. Similar to lithium, copper has an effect of improving leakage characteristics. Therefore, in order to reduce the leakage current more efficiently, it is effective to contain copper as the material constituting the piezoelectric layer <NUM>. Among transition metals, elements having a higher effect of improving leakage characteristics are manganese and copper. Both manganese and copper may be contained in the piezoelectric layer <NUM>.

When a content of copper in the piezoelectric layer <NUM> is more than <NUM> mol%, a different phase may be generated in the piezoelectric layer <NUM>, and the crystal orientation of the piezoelectric body may deteriorate. Therefore, a total content of copper is preferably <NUM> mol% or less.

In order to further improve the leakage characteristics, lithium and copper are contained in the piezoelectric layer <NUM>.

An average crystal grain size of the KNN-based composite oxide constituting the piezoelectric layer <NUM> is preferably <NUM> or less. When the average crystal grain size of the KNN-based composite oxide is coarse, a residual stress accumulated in the piezoelectric layer <NUM> is concentrated on an existence region of coarse crystal grains, and cracks may be generated in the piezoelectric layer <NUM>. Therefore, the average crystal grain size of the KNN-based composite oxide is preferably <NUM> or less, more preferably <NUM> or less. Since the average crystal grain size of the KNN-based composite oxide is preferably small from the viewpoint of preventing the generation of cracks, a lower limit value thereof is not particularly limited, but is, for example, <NUM> or more.

Although the piezoelectric substrate <NUM> is described above, the piezoelectric material constituting the piezoelectric layer <NUM> is not limited to a composition represented by Formula (<NUM>) as long as the piezoelectric material is the KNN-based composite oxide with Li and Cu. For example, another metal element (additive) may be contained in an A site or a B site of potassium sodium niobate. Examples of such additives include manganese (Mn), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), and zinc (Zn). One or more of these additives may be contained. By using the additive, it is easy to improve various characteristics to diversify the configuration and function. In the case of a composite oxide containing other elements, the composite oxide also preferably has an ABO<NUM> type perovskite structure.

In the present specification, the "perovskite type composite oxide containing K, Na, and Nb" is "a composite oxide having an ABO<NUM> type perovskite structure containing K, Na, and Nb", and is not limited to only the composite oxide having the ABO<NUM> type perovskite structure containing K, Na, and Nb. That is, in the present specification, the "perovskite type composite oxide containing K, Na, and Nb" contains a piezoelectric material represented as a mixed crystal containing a composite oxide having the ABO<NUM> type perovskite structure containing K, Na, and Nb (for example, the KNN-based composite oxide shown above) and another composite oxide having the ABO<NUM> type perovskite structure.

The other composite oxide is not limited within the scope of the embodiment, and is preferably a non-lead-based piezoelectric material that does not contain lead (Pb). Accordingly, the piezoelectric substrate <NUM> is excellent in biocompatibility and has low environmental load.

According to the piezoelectric substrate <NUM> of the embodiment described above, the remaining organic component in the piezoelectric layer <NUM> can be reduced, and the leakage current can be reduced.

Next, a configuration of a piezoelectric element <NUM> according to the embodiment will be described with reference to the drawings. <FIG> is a cross-sectional view schematically showing the piezoelectric element <NUM>, and is an enlarged cross-sectional view taken along a line B-B' in <FIG>. In <FIG> and <FIG>, the same reference signs denote the same members, and the description thereof may be omitted as appropriate.

As shown, the piezoelectric element <NUM> includes the base body <NUM>, the first electrode <NUM>, the piezoelectric layer <NUM>, and a second electrode <NUM>. The piezoelectric element <NUM> is provided above the base body <NUM>. In the shown example, the piezoelectric element <NUM> is provided at the base body <NUM>. Thicknesses of the elements shown in the drawings are merely examples, and can be changed without departing from the scope of the present invention.

The configurations, materials, and the like of the base body <NUM> and the vibration plate <NUM> may be the same as those of the piezoelectric substrate <NUM> (see <FIG>) according to the embodiment. Therefore, the description thereof is omitted.

The first electrode <NUM> is formed at the base body <NUM> (the vibration plate <NUM> in <FIG>). A shape of the first electrode <NUM> is, for example, a layer shape or a thin film shape. A thickness (a length in the Z-axis direction) of the first electrode <NUM> is, for example, <NUM> or more and <NUM> or less. A planar shape (a shape viewed from the Z-axis direction) of the first electrode <NUM> is not particularly limited as long as the piezoelectric layer <NUM> can be disposed between the second electrode <NUM> and the first electrode <NUM> when the second electrode <NUM> faces the first electrode <NUM>.

Examples of a material of the first electrode <NUM> include various metals such as nickel, iridium, and platinum, conductive oxides thereof (for example, iridium oxide), composite oxides of strontium and ruthenium (SrRuOx: SRO), and composite oxides of lanthanum and nickel (LaNiOx: LNO). The first electrode <NUM> may have a single-layer structure of the materials shown above, or may have a structure in which a plurality of materials is stacked.

The first electrode <NUM> can be paired with the second electrode <NUM> to serve as one electrode (for example, a lower electrode formed below the piezoelectric layer <NUM>) for applying a voltage to the piezoelectric layer <NUM>.

The second electrode <NUM> is formed at the piezoelectric layer <NUM>. The second electrode <NUM> faces the first electrode <NUM> with the piezoelectric layer <NUM> interposed therebetween. A shape of the second electrode <NUM> is, for example, a layer shape or a thin film shape. A thickness of the second electrode <NUM> is, for example, <NUM> or more and <NUM> or less. A planar shape of the second electrode <NUM> is not particularly limited as long as the piezoelectric layer <NUM> can be disposed between the first electrode <NUM> and the second electrode <NUM> when the second electrode <NUM> faces the first electrode <NUM>.

As a material of the second electrode <NUM>, for example, the materials listed above as the material of the first electrode <NUM> can be applied. However, in order to make a ratio of a Young's modulus of the piezoelectric layer <NUM> to a Young's modulus of the second electrode <NUM> satisfy the above range, platinum (Pt) or iridium (Ir) is preferably used as the material of the second electrode <NUM>.

As one of the functions of the second electrode <NUM>, the paired second electrode <NUM> and first electrode <NUM> serve as another electrode (for example, an upper electrode formed above the piezoelectric layer <NUM>) for applying a voltage to the piezoelectric layer <NUM>.

The materials of the first electrode <NUM> and the second electrode <NUM> both are suitably a noble metal such as platinum (Pt) or iridium (Ir), or an oxide thereof. The material of the first electrode <NUM> and the material of the second electrode <NUM> may be materials having conductivity. The material of the first electrode <NUM> and the material of the second electrode <NUM> may be the same or different.

An adhesion layer (not shown) may be provided between the first electrode <NUM> and the oxide layer <NUM>. The adhesion layer is made of, for example, titanium oxide (TiOX), titanium (Ti), and SiN, and has a function of improving adhesion between the piezoelectric layer <NUM> and the vibration plate <NUM>. In a case where a titanium oxide (TiOX) layer, a titanium (Ti) layer, or a silicon nitride (SiN) layer is used as the adhesion layer, when the piezoelectric layer <NUM> is formed, the adhesion layer also functions as a stopper that prevents potassium and sodium, which are constituent elements of the piezoelectric layer <NUM>, from passing through the first electrode <NUM> and reaching the silicon substrate <NUM>. The adhesion layer may be omitted.

The orientation control layer (seed layer) <NUM> is preferably provided between the first electrode <NUM> and the piezoelectric layer <NUM>. The orientation control layer <NUM> functions as an orientation control layer that controls the orientation of the crystal of the piezoelectric body constituting the piezoelectric layer <NUM>. That is, by providing the orientation control layer <NUM> at the first electrode <NUM>, the crystal of the piezoelectric body constituting the piezoelectric layer <NUM> can be preferentially oriented in a predetermined plane orientation (for example, (<NUM>) plane). By improving the crystal orientation of the piezoelectric layer, it is possible to efficiently utilize the domain rotation and improve the displacement characteristics. Examples of the material of the orientation control layer <NUM> include various metals such as titanium, nickel, iridium, and platinum, oxides thereof, and compounds containing bismuth, iron, titanium, and lead.

The piezoelectric layer <NUM> is formed at the first electrode <NUM> and covers the first electrode <NUM>. The piezoelectric layer <NUM> contains a composite oxide having a perovskite structure represented by a general formula ABO<NUM> as a main component. In the embodiment, the piezoelectric layer <NUM> contains a piezoelectric material made of the KNN-based composite oxide represented by Formula (<NUM>).

Definitions of the configuration, the material, the IR2/IR1, the lithium, and the copper of the piezoelectric layer <NUM> can be adopted as those of the piezoelectric substrate <NUM> according to the embodiment.

According to the piezoelectric element <NUM> of the embodiment described above, the remaining organic component in the piezoelectric layer <NUM> can be reduced, and the leakage current can be reduced.

Next, an example of a method of manufacturing the piezoelectric element <NUM> will be described. Hereinafter, a case where the piezoelectric layer <NUM> is manufactured by a chemical solution method (also referred to as a wet method or a liquid phase method) will be described as an example.

First, the silicon substrate <NUM> is prepared, and the silicon substrate <NUM> is thermally oxidized to form the silicon oxide layer <NUM> made of silicon dioxide (SiO<NUM>) on a surface of the silicon substrate <NUM>.

Next, the oxide layer <NUM> made of zirconium oxide (ZrO<NUM>) is formed at the silicon oxide layer <NUM> by atomic layer deposition (ALD). A film formation temperature is, for example, from <NUM> to <NUM>. The oxide layer <NUM> can be formed by a sputtering method, a vapor deposition method, and the like in addition to ALD. First, a zirconium film is formed at the silicon oxide layer <NUM> by, for example, the sputtering method or the vapor deposition method, and the zirconium film is thermally oxidized to obtain the oxide layer <NUM> made of zirconium oxide (ZrO<NUM>). In this manner, the vibration plate <NUM> including the silicon oxide layer <NUM> and the oxide layer <NUM> is formed at the silicon substrate <NUM>.

Next, an adhesion layer made of metal titanium (Ti) is formed at the oxide layer <NUM>. The adhesion layer can be formed by the sputtering method and the like. Next, the first electrode <NUM> made of platinum (Pt) is formed at the adhesion layer. The first electrode <NUM> can be appropriately selected according to an electrode material, and can be formed by, for example, vapor phase film formation such as a sputtering method, a physical vapor deposition method (PVD method), or a laser ablation method, or liquid phase film formation such as a spin coating method.

Next, the orientation control layer (seed layer) <NUM> is formed at the first electrode <NUM>. The orientation control layer <NUM> can be formed by, for example, a chemical solution method (wet method) in which a solution (precursor solution) containing a metal complex is applied, then is dried and degreased, and then fired at a high temperature to obtain a metal oxide. Examples of the material of the orientation control layer <NUM> include various metals such as bismuth, iron, titanium, lead, nickel, iridium, and platinum, and oxides thereof.

Next, a resist having a predetermined shape is formed at the first electrode <NUM> as a mask, and the adhesion layer, the first electrode <NUM>, and the orientation control layer <NUM> are simultaneously patterned. The adhesion layer, the first electrode <NUM>, and the orientation control layer <NUM> can be patterned by, for example, reactive ion etching (RIE), dry etching such as ion milling, or wet etching using an etchant. Shapes of the adhesion layer, the first electrode <NUM>, and the orientation control layer <NUM> in the patterning are not particularly limited.

Next, a plurality of piezoelectric films is formed at the first electrode <NUM>.

The piezoelectric layer <NUM> includes the plurality of piezoelectric films. The piezoelectric layer <NUM> can be formed by, for example, a chemical solution method (wet method) in which a solution (precursor solution) containing a metal complex is applied and dried, and then fired at a high temperature to obtain a metal oxide. In addition, the piezoelectric layer <NUM> can be formed by a laser ablation method, a sputtering method, a pulse laser deposition method (PLD method), a chemical vapor deposition (CVD) method, an aerosol deposition method, and the like.

For example, the piezoelectric layer <NUM> formed by the wet method (liquid phase method) includes a plurality of piezoelectric films formed by a series of steps including a step (applying step) of applying a precursor solution and forming a precursor film, a step (drying step) of drying the precursor film, a step (degreasing step) of heating and degreasing the dried precursor film, and a step (firing step) of firing the degreased precursor film. That is, the piezoelectric layer <NUM> is formed by repeating the series of steps from the applying step to the firing step a plurality of times. In the series of steps described above, the firing step may be performed after repeating the steps from the applying step to the degreasing step a plurality of times.

A specific procedure for forming the piezoelectric layer <NUM> by the wet method (liquid phase method) is, for example, as follows.

First, a precursor solution containing a predetermined metal complex is prepared. The precursor solution is obtained by, in an organic solvent, dissolving or dispersing a metal complex capable of forming a composite oxide containing K, Na, and Nb by firing. At this time, a metal complex containing an additive such as Mn, Li, or Cu may be further mixed. By mixing the metal complex containing Mn, Li, or Cu with the precursor solution, it is possible to further increase insulation of the obtained piezoelectric layer <NUM>.

Examples of a metal complex containing potassium (K) include potassium <NUM>-ethylhexanoate and potassium acetate. Examples of a metal complex containing sodium (Na) include sodium <NUM>-ethylhexanoate and sodium acetate. Examples of a metal complex containing niobium (Nb) include niobium <NUM>-ethylhexanoate and pentaethoxyniobium. When Mn is added as the additive, examples of a metal complex containing Mn include manganese <NUM>-ethylhexanoate. When Li is added as the additive, examples of a metal complex containing Li include lithium <NUM>-ethylhexanoate. When Cu is added as the additive, examples of a metal complex containing Cu include copper <NUM>-ethylhexanoate. At this time, two or more kinds of metal complexes may be used in combination. For example, potassium <NUM>-ethylhexanoate and potassium acetate may be used in combination as the metal complex containing potassium (K). Examples of a solvent include <NUM>-n-butoxyethanol, n-octane, and mixed solvents thereof. The precursor solution may contain an additive which stabilizes dispersion of the metal complex containing K, Na, and Nb. Examples of such an additive include <NUM>-ethylhexanoate.

The precursor solution is applied onto the silicon substrate <NUM> on which the silicon oxide layer <NUM>, the oxide layer <NUM>, and the first electrode <NUM> are formed to form the precursor film (applying step).

Next, the precursor film is heated to a predetermined temperature, for example, about <NUM> to <NUM> and dried for a certain period of time (drying step).

Next, the dried precursor film is heated to a predetermined temperature, for example, <NUM> to <NUM>, and is held at this temperature for a certain period of time to perform degreasing, thereby removing an organic component in the precursor film (degreasing step).

Next, the precursor film after degreasing is heated to <NUM> to <NUM> and is fired by being held at this temperature for <NUM> minute to <NUM> minutes (firing step). When the held temperature is too high, the crystal orientation may deteriorate. On the other hand, when the held temperature is too low, firing may be insufficient. Therefore, in the embodiment, the held temperature is preferably <NUM> to <NUM>. An average heating rate in the firing step is preferably <NUM>°/s or less. When the average heating rate is too fast, a time until crystallization is completed is short, and the organic component tends to remain in the precursor film. Therefore, the average heating rate is preferably <NUM>/s or less.

Examples of a heating device used in the drying step, the degreasing step, and the firing step include a rapid thermal annealing (RTA) device which performs heating by irradiation with an infrared lamp, and a hot plate. The above steps are repeated a plurality of times to form the piezoelectric layer <NUM> including the plurality of piezoelectric films. In the series of steps from the applying step to the firing step, the firing step may be performed after repeating the steps from the applying step to the degreasing step a plurality of times.

Before and after the second electrode <NUM> is formed at the piezoelectric layer <NUM>, a reheat treatment (post-annealing) may be performed in a temperature range of <NUM> to <NUM> as necessary. By performing the post-annealing in this way, a good interface between the piezoelectric layer <NUM> and the first electrode and a good interface between the piezoelectric layer <NUM> and the second electrode <NUM> can be formed. Crystallinity of the piezoelectric layer <NUM> can be improved, and the insulation of the piezoelectric layer <NUM> can be further increased.

After the firing step, the piezoelectric layer <NUM> including the plurality of piezoelectric films is patterned into a desired shape. Patterning can be performed by dry etching such as reactive ion etching or ion milling, or wet etching using an etchant.

Thereafter, the second electrode <NUM> is formed at the piezoelectric layer <NUM>. The second electrode <NUM> can be formed by the same method as the first electrode <NUM>.

By the above steps, the piezoelectric element <NUM> including the first electrode <NUM>, the piezoelectric layer <NUM>, and the second electrode <NUM> is manufactured.

Next, an ink jet recording device, which is an example of a liquid ejection device including a recording head which is an example of a piezoelectric element application device according to the embodiment, will be described with reference to the drawings. <FIG> is a perspective view showing a schematic configuration of the ink jet recording device.

As shown in <FIG>, in an ink jet recording device (recording device) I, an ink jet recording head unit (head unit) II is detachably provided in cartridges 2A and 2B. The cartridges 2A and 2B constitute an ink supply unit. The head unit II includes a plurality of ink jet recording heads (recording heads) <NUM> (see <FIG> and the like), and is mounted on a carriage <NUM>. The carriage <NUM> is movable in an axial direction on a carriage shaft <NUM> attached to a device main body <NUM>. The head unit II and the carriage <NUM> can dispense, for example, a black ink composition and a color ink composition, respectively.

A driving force of a drive motor <NUM> is transmitted to the carriage <NUM> via a plurality of gears (not shown) and a timing belt <NUM>, such that the carriage <NUM> on which the head unit II is mounted is moved along the carriage shaft <NUM>. On the other hand, the device main body <NUM> is provided with a conveyance roller <NUM> as a conveyance unit, and a recording sheet S which is a recording medium such as paper is conveyed by the conveyance roller <NUM>. The conveyance unit which conveys the recording sheet S is not limited to the conveyance roller, and may be a belt, a drum, and the like.

In the recording head (head chip) <NUM>, the piezoelectric element <NUM> (see <FIG>) is used as a piezoelectric actuator device. By using the piezoelectric element <NUM>, it is possible to avoid deterioration of various characteristics (piezoelectric characteristics, durability, ink ejection characteristics, and the like) in the recording device I. The piezoelectric element application device according to the embodiment can improve, in particular, the piezoelectric characteristics (in particular, leakage characteristics) by applying the piezoelectric element <NUM>.

Next, the recording head (head chip) <NUM> as an example of the head chip mounted on the liquid ejection device will be described with reference to the drawings. <FIG> is an exploded perspective view showing the schematic configuration of the ink jet recording head. <FIG> is a plan view showing the schematic configuration of the inkjet recording head. <FIG> is a cross-sectional view taken along a line A-A' in <FIG>. <FIG> each show a part of a configuration of the recording head <NUM>, and are omitted as appropriate.

As shown in the drawings, the recording head (head chip) <NUM> includes a nozzle plate <NUM> having nozzle openings <NUM> for dispensing liquid droplets, pressure generation chambers <NUM> communicating with the nozzle openings <NUM>, partition walls <NUM> provided at the nozzle plate <NUM> and forming the pressure generation chambers <NUM>, the flow path forming substrate (silicon substrate) <NUM> forming a part of wall surfaces of the pressure generation chambers <NUM>, the piezoelectric element <NUM> provided at the silicon substrate <NUM>, and lead electrodes (voltage application units) <NUM> applying a voltage to the piezoelectric element <NUM>.

A plurality of partition walls <NUM> are formed in the silicon substrate <NUM>. A plurality of pressure generation chambers <NUM> are partitioned by the partition walls <NUM>. That is, in the substrate <NUM>, the pressure generation chambers <NUM> are arranged side by side along the X-direction (the direction in which the nozzle openings <NUM> that dispense ink of the same color are arranged side by side). With such a configuration, a movable portion of the piezoelectric element <NUM> is formed. As the silicon substrate <NUM>, for example, a silicon single crystal substrate can be used.

In the silicon substrate <NUM>, ink supply paths <NUM> and communication paths <NUM> are formed at one end portion side (+Y-direction side) of each of the pressure generation chambers <NUM>. Each of the ink supply paths <NUM> is formed such that an area of an opening on the one end portion side of the pressure generation chamber <NUM> is reduced. Each of the communication paths <NUM> has substantially the same width as the pressure generation chamber <NUM> in the +X-direction. A communication portion <NUM> is formed at an outer side (+Y-direction side) of the communication paths <NUM>. The communication portion <NUM> constitutes a part of a manifold <NUM>. The manifold <NUM> serves as a common ink chamber for each pressure generation chamber <NUM>. Therefore, liquid flow paths each including the pressure generation chamber <NUM>, the ink supply path <NUM>, the communication path <NUM>, and the communication portion <NUM> are formed in the silicon substrate <NUM>.

The nozzle plate <NUM> made of, for example, SUS is bonded to one surface (a surface on a -Z-direction side) of the silicon substrate <NUM>. In the nozzle plate <NUM>, the nozzle openings <NUM> are arranged side by side along the +X-direction. The nozzle openings <NUM> communicate with the pressure generation chambers <NUM>. The nozzle plate <NUM> can be bonded to the silicon substrate <NUM> by an adhesive, a thermal welding film, and the like.

The vibration plate <NUM> is formed at the other surface (surface on a +Z-direction side) of the silicon substrate <NUM>. The vibration plate <NUM> includes, for example, the silicon oxide layer <NUM> formed at the silicon substrate <NUM> and the oxide layer <NUM> formed at the silicon oxide layer <NUM>. The silicon oxide layer <NUM> is made of, for example, silicon dioxide (SiO<NUM>), and the oxide layer <NUM> is made of, for example, zirconium oxide (ZrO<NUM>). The silicon oxide layer <NUM> may not be a member separated from the silicon substrate <NUM>. A part of the silicon substrate <NUM> may be thinned and used as the silicon oxide layer <NUM>. The oxide layer <NUM> functions as a stopper that prevents potassium and sodium, which are constituent elements of the piezoelectric layer <NUM>, from passing through the first electrode <NUM> and reaching the substrate <NUM> when the piezoelectric layer <NUM> described later is formed.

The first electrode <NUM> is provided for each pressure generation chamber <NUM>. That is, the first electrode <NUM> is provided as an individual electrode that is independent for each pressure generation chamber <NUM>. The first electrode <NUM> has a width smaller than a width of the pressure generation chamber <NUM> in ±X-directions. The first electrode <NUM> has a width larger than the width of the pressure generation chamber <NUM> in ±Y-directions. That is, in the ±Y-directions, both end portions of the first electrode <NUM> are formed up to an outer side of a region on the vibration plate <NUM> facing the pressure generation chamber <NUM>. The lead electrode (voltage application units) <NUM> that apply a voltage to the piezoelectric element <NUM> are coupled to one end portion side (opposite side from the communication paths <NUM>) of the first electrodes <NUM>.

The piezoelectric layer <NUM> is provided between the first electrode <NUM> and the second electrode <NUM>. The piezoelectric layer <NUM> is a thin-film piezoelectric body. The piezoelectric layer <NUM> has a width larger than the width of the first electrode <NUM> in the ±X-directions. In the ±Y-directions, the piezoelectric layer <NUM> has a width larger than a length of the pressure generation chamber <NUM> in the ±Y-directions. An end portion of the piezoelectric layer <NUM> on the ink supply path <NUM> side (the +Y-direction side) is formed up to an outer side of an end portion of the first electrode <NUM> on the +Y-direction side. That is, the end portion of the first electrode <NUM> on the +Y-direction side is covered with the piezoelectric layer <NUM>. On the other hand, an end portion of the piezoelectric layer <NUM> on the lead electrode <NUM> side (the -Y-direction side) is on an inner side (the +Y-direction side) of an end portion of the first electrode <NUM> on the -Y-direction side. That is, the end portion of the first electrode <NUM> on the -Y-direction side is not covered with the piezoelectric layer <NUM>.

The second electrode <NUM> is continuously provided at the piezoelectric layer <NUM> and the vibration plate <NUM> over the +X-direction. That is, the second electrode <NUM> is implemented as a common electrode common to the plurality of piezoelectric layers <NUM>. In the embodiment, the first electrode <NUM> constitutes an individual electrode independently provided corresponding to the pressure generation chamber <NUM>, and the second electrode <NUM> constitutes a common electrode continuously provided in a direction in which the pressure generation chambers <NUM> are arranged side by side. Alternatively, the first electrode <NUM> may constitute the common electrode, and the second electrode <NUM> may constitute the individual electrode.

In the piezoelectric element <NUM> according to the embodiment, the vibration plate <NUM> and the first electrode <NUM> are displaced by the displacement of the piezoelectric layer <NUM> having electromechanical conversion characteristics. That is, the vibration plate <NUM> and the first electrode <NUM> substantially function as vibration plates. However, in practice, since the second electrode <NUM> is also displaced due to the displacement of the piezoelectric layer <NUM>, a region in which the vibration plate <NUM>, the first electrode <NUM>, the piezoelectric layer <NUM>, and the second electrode <NUM> are sequentially stacked functions as the movable portion (also referred to as a vibration portion) of the piezoelectric element <NUM>.

On the substrate <NUM> (the vibration plate <NUM>) at which the piezoelectric element <NUM> is formed, a protective substrate <NUM> is bonded by an adhesive <NUM>. The protective substrate <NUM> has a manifold portion <NUM>. At least a part of the manifold <NUM> is implemented by the manifold portion <NUM>. The manifold portion <NUM> according to the embodiment penetrates the protective substrate <NUM> in the thickness direction (the Z-direction), and is further formed over a width direction (+X-direction) of the pressure generation chamber <NUM>. The manifold portion <NUM> communicates with the communication portion <NUM> on the substrate <NUM>. With this configuration, the manifold <NUM> which is an ink chamber common to the pressure generation chambers <NUM> is formed.

The protective substrate <NUM> has a piezoelectric element holding portion <NUM> formed in a region including the piezoelectric element <NUM>. The piezoelectric element holding portion <NUM> has enough space not to interfere with a movement of the piezoelectric element <NUM>. This space may or may not be sealed. The protective substrate <NUM> is provided with a through hole <NUM> penetrating the protective substrate <NUM> in the thickness direction (the Z-direction). An end portion of each of the lead electrodes <NUM> is exposed in the through hole <NUM>.

Examples of a material of the protective substrate <NUM> include Si, SOI, glass, a ceramic material, a metal, and a resin, and the protective substrate <NUM> is more preferably formed of a material having substantially the same thermal expansion coefficient as that of the substrate <NUM>.

A drive circuit <NUM> functioning as a signal processing unit is fixed at the protective substrate <NUM>. As the drive circuit <NUM>, for example, a circuit board or a semiconductor integrated circuit (IC) can be used. The drive circuit <NUM> and the lead electrodes <NUM> are electrically coupled to each other via coupling interconnects <NUM> each of which is made of a conductive wire such as a bonding wire and which are inserted through the through hole <NUM>. The drive circuit <NUM> can be electrically coupled to a printer controller <NUM> (see <FIG>). Such a drive circuit <NUM> functions as a control unit for the piezoelectric actuator device (the piezoelectric element <NUM>).

On the protective substrate <NUM>, a compliance substrate <NUM> including a sealing film <NUM> and a fixing plate <NUM> is bonded. The sealing film <NUM> is made of a material having low rigidity, and the fixing plate <NUM> can be made of a hard material such as a metal. A region of the fixing plate <NUM> facing the manifold <NUM> is an opening portion <NUM> with a part completely removed in the thickness direction (the Z-direction). One surface (a surface on the +Z-direction side) of the manifold <NUM> is sealed only with the sealing film <NUM> having flexibility.

Such a recording head <NUM> dispenses ink droplets by the following operation.

First, ink is taken in from an ink introduction port coupled to an external ink supply unit (not shown), and an inside of the recording head <NUM> is filled with the ink from the manifold <NUM> to the nozzle openings <NUM>. Thereafter, according to a recording signal from the drive circuit <NUM>, a voltage is applied between the first electrode <NUM> and the second electrode <NUM> corresponding to each pressure generation chamber <NUM>, and the piezoelectric element <NUM> is deflected and deformed. Accordingly, a pressure in each pressure generation chamber <NUM> is increased, and ink droplets are dispensed from the nozzle openings <NUM>.

In the above embodiment, the ink jet recording head is described as an example of a liquid ejection head. However, the present invention is applicable to liquid ejection heads in general, and is also applicable to a liquid ejection head for ejecting liquid other than ink. Examples of other liquid ejection heads include various recording heads used in image recording devices such as printers, color material ejection heads used for manufacturing color filters for liquid crystal displays, electrode material ejection heads used for forming electrodes for organic EL displays and field emission displays (FEDs), and bioorganic material ejection heads used for manufacturing biochips.

The present invention is not limited to the piezoelectric element mounted on the liquid ejection head, and can also be applied to a piezoelectric element mounted on another piezoelectric element application device. Examples of the piezoelectric element application device include an ultrasonic device, a motor, a pressure sensor, a pyroelectric element, and a ferroelectric element. Completed bodies using these piezoelectric element application devices, for example, an ejection device of the liquid and the like using an ejection head for the liquid and the like, an ultrasonic sensor using the ultrasonic device, a robot using the motor as a drive source, an IR sensor using the pyroelectric element, and a ferroelectric memory using the ferroelectric element are also in the piezoelectric element application device.

In particular, the piezoelectric element according to the present invention is suitable as a piezoelectric element mounted on a sensor. Examples of the sensor include a gyro sensor, an ultrasonic sensor, a pressure sensor, and a speed and acceleration sensor. When the piezoelectric element according to the present invention is applied to a sensor, for example, a voltage detection unit which detects a voltage output from the piezoelectric element <NUM> can be provided between the first electrode <NUM> and the second electrode <NUM> to form the sensor. In a case of such a sensor, when the piezoelectric element <NUM> is deformed due to some external change (change in physical quantity), a voltage is generated according to the deformation. Various physical quantities can be detected by detecting the voltage with the voltage detection unit.

Hereinafter, the present invention will be described in more detail with reference to Examples, and the present invention is not limited to these Examples.

First, a surface of a silicon substrate (<NUM> inches (= <NUM>); (<NUM>) plane orientation) as a substrate was thermally oxidized to form a silicon oxide layer (<NUM>) made of silicon dioxide at the substrate. Further, a ZrO<NUM> film was formed at the silicon oxide layer by an ALD method to form an oxide layer (<NUM>) made of zirconium oxide. A film formation temperature was <NUM>. In this manner, a vibration plate including the silicon oxide layer and the oxide layer was formed at the silicon substrate.

Next, an adhesion layer (<NUM>) made of titanium (Ti) was formed at the vibration plate by a sputtering method, and a first electrode containing platinum (Pt) and iridium was formed at the adhesion layer by the sputtering method. The first electrode is formed by sequentially stacking a layer (<NUM>) containing platinum (Pt) and a layer (<NUM>) containing iridium (Ir) at the adhesion layer.

Next, an orientation control layer (seed layer) was formed at the first electrode by the following procedure.

First, a propionic acid solution of bismuth, iron, titanium, and lead was prepared such that Bi : Pb : Fe : Ti = <NUM> : <NUM> : <NUM> : <NUM>. The solution was applied onto the first electrode by a spin coating method. Thereafter, the applied solution was dried/degreased using a hot plate, and subjected to a heat treatment using rapid thermal annealing (RTA) to form the orientation control layer. Film formation conditions of the orientation control layer are as shown in Table <NUM>.

Next, a piezoelectric layer was formed at the vibration plate by the following procedure.

First, a precursor solution containing potassium <NUM>-ethylhexanoate, sodium <NUM>-ethylhexanoate, lithium <NUM>-ethylhexanoate, niobium <NUM>-ethylhexanoate, manganese <NUM>-ethylhexanoate, and copper <NUM>-ethylhexanoate was used to prepare K<NUM>Na<NUM>Li<NUM>Nb<NUM>Mn<NUM>Cu<NUM>Ox, and the precursor solution was applied onto the orientation control layer by the spin coating method to form a precursor film (applying step). Thereafter, the precursor film was dried (drying step), and then degreased (degreasing step). Next, the degreased precursor film was subjected to a heat treatment using the rapid thermal annealing (RTA) to form a piezoelectric film (firing step). Upper limits of the applying step, the drying step, the degreasing step, and the firing step are as shown in Table <NUM>.

The steps from the applying step to the firing step were repeated five times to produce a piezoelectric layer made of five piezoelectric films and having a total film thickness of <NUM>.

A second electrode (<NUM>) made of platinum (Pt) was formed at the obtained piezoelectric layer by a sputtering method in the same manner as the first electrode, thereby obtaining a piezoelectric element.

Example <NUM> was the same as Example <NUM> except that a composition of the piezoelectric layer was K<NUM>Na<NUM>Li<NUM>Nb<NUM>Cu<NUM>Ox.

Comparative Example <NUM> was the same as Example <NUM> except that the composition of the piezoelectric layer was K<NUM>Na<NUM>Li<NUM>Nb<NUM>Mn<NUM>Ox.

Comparative Example <NUM> was the same as Example <NUM> except that the composition of the piezoelectric layer was K<NUM>Na<NUM>Nb<NUM>Mn<NUM>Ox, and manufacturing conditions were as shown in Table <NUM>.

In each of Examples and Comparative Examples described above, the obtained piezoelectric layer was subjected to FT-IR spectroscopy.

Measurement was performed by the ATR method using FT/IR-<NUM> (detector: TGS) manufactured by JASCO Corporation. Diamond was used as an ATR crystal, and the ATR crystal was pressed in close contact with a sample. A measurement region was set to <NUM>-<NUM> to <NUM>-<NUM>, a resolution was set to <NUM>-<NUM>, and the number of times of integration was set to <NUM>. <FIG> shows FT-IR spectroscopy results of Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM>. In <FIG>, analysis results of Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM> are shown side by side along a vertical axis direction in order to facilitate comparison of the analysis results.

A leakage current of the obtained piezoelectric element was measured using a pA meter (4140B, manufactured by Hewlett-Packard Company). As measurement conditions, a delay time was set to <NUM> seconds, a first electrode side was used as a drive for measurement, and a leakage current at an electric field intensity of <NUM> kV/cm was measured.

Table <NUM> shows leakage current measurement results at an electric field intensity of <NUM> kV/cm in Examples <NUM> and <NUM> and Comparative Example <NUM>. In Comparative Examples, after the piezoelectric layer is formed, the surface of the piezoelectric layer was observed by a scanning electron microscope (SEM). Since occurrence of cracks was confirmed, a leakage current density was not measured.

The measurement results are shown in Tables <NUM> and <NUM>. In Table <NUM>, "BE" means the first electrode, and "TE" means the second electrode. In Table <NUM>, "E-0x" in a "leakage current amount" represents "× <NUM>-x". For example, "<NUM>. 71E-<NUM>" means "<NUM> × <NUM>-<NUM>".

Claim 1:
A piezoelectric substrate (<NUM>) comprising:
a base body (<NUM>);
an electrode (60A) formed at the base body; and
a piezoelectric layer (<NUM>) formed at the electrode and containing potassium, sodium, niobium, lithium and copper, characterized in that
a value of IR2/IR1 obtained by dividing an integrated intensity IR2 of a peak <NUM> by an integrated intensity IR1 of a peak <NUM>, when a surface of the piezoelectric layer is measured by Fourier transform infrared spectroscopy, is less than <NUM>,
the peak <NUM> has a strongest area intensity among peaks detected at wavenumbers of <NUM>-<NUM> to <NUM>-<NUM>, and the peak <NUM> has an area intensity that is a sum of area intensities of peaks detected at wavenumbers of <NUM>-<NUM> to <NUM>-<NUM>.