JP5716799B2 - Piezoelectric laminate, surface acoustic wave device, thin film piezoelectric resonator, and piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric laminate having a potassium sodium niobate layer, a surface acoustic wave device including the piezoelectric laminate, a thin film piezoelectric resonator, and a piezoelectric actuator.

For example, with the remarkable development of the communication field centered on mobile communications such as mobile phones, the demand for surface acoustic wave devices is rapidly expanding. The direction of development of surface acoustic wave devices is in the direction of miniaturization, high efficiency, and high frequency. For that purpose, a larger electromechanical coupling coefficient (k ² ), a more stable temperature characteristic, and a larger surface acoustic wave propagation velocity are required.

Conventionally, a structure in which an interdigital electrode is formed on a single crystal of a piezoelectric material has been used for a surface acoustic wave device. Typical examples of the piezoelectric single crystal include quartz crystal, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), and the like. For example, LiNbO ₃ having a large electromechanical coupling coefficient is used in the case of an RF filter that requires a wide band and a low loss in the pass band. On the other hand, in the case of an IF filter that requires stable temperature characteristics even in a narrow band, a crystal having a small center frequency temperature coefficient is used. Further, LiTaO ₃ having an electromechanical coupling coefficient and a center frequency temperature coefficient between LiNbO ₃ and quartz respectively plays an intermediate role. Recently, a cut angle showing a large electromechanical coupling coefficient value has been found in a potassium niobate (KNbO ₃ ) single crystal. The KNbO ₃ single crystal plate is described in JP-A-10-65488.

In a surface acoustic wave device using a piezoelectric single crystal substrate, characteristics such as an electromechanical coupling coefficient, a temperature coefficient, and a sound velocity are values specific to the material, and are determined by a cut angle and a propagation direction. For example, a 0 ° Y-XKNbO ₃ single crystal substrate has an excellent electromechanical coupling coefficient, but does not exhibit zero temperature characteristics near 45 ° C. from the 45 ° to 75 ° rotated Y-XKNbO ₃ single crystal substrate.

JP-A-10-65488

  An object of the present invention is to provide a piezoelectric laminate in which a potassium sodium niobate layer is formed on a substrate.

  Another object of the present invention is to provide a surface acoustic wave device and a thin film piezoelectric resonator having the piezoelectric laminate of the present invention.

  Still another object of the present invention is to provide a piezoelectric actuator having the piezoelectric laminate of the present invention.

The piezoelectric laminate according to the present invention is
A substrate;
A first piezoelectric layer made of potassium sodium niobate formed above the substrate.

  In the present invention, when a specific B member (hereinafter referred to as “B member”) provided above a specific A member (hereinafter referred to as “A member”), the B member directly on the A member. The meaning includes the case where it is provided and the case where the B member is provided on the A member via another member.

In the piezoelectric laminate according to the present invention, the first piezoelectric layer is represented by _a composition formula (K _a Na _1-a ) _x NbO ₃ , where 0.1 <a <1, ≦ x ≦ 1.2 may be satisfied.

  In the piezoelectric laminate of the present invention, the first piezoelectric layer may satisfy 1 <x ≦ 1.1 in the composition formula.

  In the piezoelectric laminate of the present invention, an orientation control layer can be formed below the first piezoelectric layer.

  In the piezoelectric laminate of the present invention, the orientation control layer can be made of nickel lanthanate. The nickel lanthanate may be polycrystalline.

  The piezoelectric laminate of the present invention has a second piezoelectric layer made of potassium sodium niobate that is continuous with the first piezoelectric layer, and the second piezoelectric layer is in contact with the second piezoelectric layer. And the element which comprises the layer located in the opposite side to the said 1st piezoelectric material layer can be included.

In the piezoelectric laminate of the present invention, the first piezoelectric layer is
A first phase portion made of a piezoelectric material represented by _a composition formula (K _a Na _1-a ) NbO ₃ ;
Compositional formula _{(K a Na 1-a)} x NbO 3 ( however, 1 <x) can include a portion of the second phase consisting of a piezoelectric material represented by the.

  The piezoelectric laminate of the present invention can have an electrode formed above the first piezoelectric layer.

  The piezoelectric laminate of the present invention includes a first electrode formed between the base and the first piezoelectric layer, and a second electrode formed above the first piezoelectric layer. Can do.

  The surface acoustic wave device according to the present invention includes the piezoelectric laminate of the present invention.

  The thin film piezoelectric resonator according to the present invention includes the piezoelectric laminate of the present invention.

  The piezoelectric actuator according to the present invention includes the piezoelectric laminate of the present invention.

Sectional drawing which shows typically the 1st piezoelectric material laminated body concerning embodiment of this invention. Sectional drawing which shows typically the piezoelectric material layer of the piezoelectric material laminated body concerning embodiment of this invention. Sectional drawing which shows typically the piezoelectric material layer of the piezoelectric material laminated body concerning embodiment of this invention. Sectional drawing which shows typically the modification of the 1st piezoelectric material laminated body concerning embodiment of this invention. Sectional drawing which shows typically the 2nd piezoelectric material laminated body concerning embodiment of this invention. Sectional drawing which shows typically the modification of the 2nd piezoelectric material laminated body concerning embodiment of this invention. The figure which shows the hysteresis characteristic of the piezoelectric material layer in the Example of this invention. (A), (B) is the figure by SEM of the surface of the piezoelectric material layer in the Example of this invention, (C) is the figure by SEM of the surface of the piezoelectric material layer in a comparative example. The figure of the XRD of the Example and comparative example of this invention. The figure which shows the relationship between the electric field of a piezoelectric material layer and distortion in the Example of this invention. The figure which shows the SAW oscillation waveform of the piezoelectric material layer in the Example of this invention. The figure which shows the result of the Raman emission analysis in the Example of this invention. The figure which shows the relationship between Na excess and the surface spacing in the Example of this invention. (A) shows the figure by SEM of the surface in the Example of this invention, (B) is the figure by SEM of the surface in a reference example. (A) shows the XRD figure in the Example of this invention, (B) is the XRD figure in a reference example. The figure which shows typically the surface acoustic wave element concerning embodiment of this invention. The figure which shows typically the frequency filter to which the surface acoustic wave element concerning embodiment of this invention is applied. The figure which shows typically the oscillator to which the surface acoustic wave element concerning embodiment of this invention is applied. The figure which shows typically the 1st thin film piezoelectric resonator concerning embodiment of this invention. The figure which shows typically the 2nd thin film piezoelectric resonator concerning embodiment of this invention. The figure which shows typically the ink jet type head to which the piezoelectric actuator concerning embodiment of this invention is applied. 1 is a perspective view schematically showing an ink jet head to which a piezoelectric actuator according to an embodiment of the present invention is applied.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

1. Piezoelectric laminate 1.1. First Piezoelectric Laminate FIG. 1 is a cross-sectional view schematically showing an example of a first piezoelectric laminate 100 according to the present embodiment.

  The piezoelectric laminate 100 includes a substrate 1, a piezoelectric layer 3 made of potassium sodium niobate formed on the substrate 1, and an electrode 4 formed on the piezoelectric layer 3.

  The substrate 1 is selected depending on the application of the piezoelectric laminate 100, and its material and configuration are not particularly limited. As the substrate 1, an insulating substrate, a semiconductor substrate, or the like can be used. As the insulating substrate, for example, a sapphire substrate, an STO substrate, a plastic substrate, a glass substrate, or the like can be used. As the semiconductor substrate, a silicon substrate or the like can be used. The substrate 1 may be a single substrate or a laminate in which other layers are laminated on the substrate.

On the substrate 1, as shown in FIG. 4, an orientation control layer 6 can be provided as required. The orientation control layer 6 is called a buffer layer or a seed layer and has a function of controlling the crystal orientation of the piezoelectric layer 3. That is, the piezoelectric layer 3 formed on the orientation control layer 6 has a crystal structure that inherits the crystal structure of the orientation control layer 6. As the orientation control layer 6, a complex oxide having the same crystal structure as that of the piezoelectric layer 3 can be used. As the orientation control layer 6, for example, a perovskite oxide such as nickel lanthanum (LaNiO ₃ ) can be used. The nickel lanthanate can be polycrystalline. The orientation control layer 6 only needs to be able to control the orientation of the piezoelectric layer 3 and can have a thickness of, for example, 50 to 100 nm.

The piezoelectric layer 3 is composed of a piezoelectric body represented by _a composition formula (K _a Na _1-a ) _x NbO ₃ . In the composition formula, preferably 0.1 <a <1, more preferably 0.2 ≦ a ≦ 0.7, preferably 1 ≦ x ≦ 1.2, more preferably 1 <x ≦ 1.1. It is. Piezoelectric of the compositional formula _{(K a Na 1-a)} x NbO 3 takes the structure of orthorhombic at room temperature. In the composition formula, when “a” is in the above range, phase change temperatures from orthorhombic to rhombohedral (a ≦ 0.55) and orthorhombic to monoclinic (0.55 ≦ a) are obtained. Is less than −40 ° C., which is preferable in that stable characteristics can be obtained in a low temperature region. When “a” is 0.1 or less, a heterogeneous phase is generated due to volatilization of potassium during the heat treatment for crystallization, which adversely affects physical properties such as piezoelectric characteristics and ferroelectric characteristics. When “x” is in the above range, crystals are formed at a low temperature, so that volatilization of potassium is suppressed and the layer density is improved.

  In the present embodiment, the piezoelectric layer 3 may be a homogeneous layer or a layer having an aspect as shown in FIGS. 2 and 3 are conceptual or schematic diagrams.

That is, as shown in FIG. 2, the piezoelectric layer 3 includes a first piezoelectric layer 32 made of potassium sodium niobate represented by _a composition formula (K _a Na _1-a ) NbO ₃ , and a first piezoelectric layer. And a second piezoelectric layer 34 formed of a piezoelectric body containing an element that forms at least a layer (in the illustrated case, the base body 1) that is in contact with the piezoelectric body layer 3. Compared to the first piezoelectric layer 32, the second piezoelectric layer 34 can contain an excess of potassium and sodium, which are A-site elements. In addition, the second piezoelectric layer 34 includes an element constituting the substrate 1 in the potassium sodium niobate of the first piezoelectric layer 32. For example, when an STO (SrTiO ₃ ) substrate is used as the substrate 1, the second piezoelectric layer 34 can contain strontium and titanium in potassium sodium niobate. When Nb: STO (Nb-doped SrTiO ₃ ) is used as the substrate 1, the second piezoelectric layer 34 can contain strontium, titanium, and niobium in potassium sodium niobate. As shown in FIG. 4, when the orientation control layer 6 is provided on the substrate 1, the second piezoelectric layer 34 can contain an element constituting the orientation control layer 6. For example, when nickel lanthanate is used as the orientation control layer 6, the second piezoelectric layer 34 includes lanthanum and nickel in potassium sodium niobate.

As shown in FIG. 3, the piezoelectric layer 3 includes a first phase portion 36 made of a piezoelectric material represented by _a composition formula (K _a Na _1-a ) NbO ₃ and a composition formula (K _a Na _{1 -a} ) _x NbO ₃ (where 1 <x) and a second phase portion 38 made of a piezoelectric material.

  The piezoelectric layer 3 of the present embodiment is preferably preferentially oriented to pseudo cubic (100).

  A typical layer thickness of the piezoelectric layer 3 is selected depending on the application of the piezoelectric laminate 100. A typical layer thickness of the piezoelectric layer 3 is 300 nm to 3.0 μm. However, with respect to the upper limit of the thickness, the thickness can be increased as long as the denseness and crystal orientation of the thin layer are maintained, and can be up to about 10 μm.

  The electrode 4 can be composed of a metal layer or a conductive complex oxide layer. The electrode 4 may be a laminate of a metal layer and a conductive complex oxide layer. As a material of the electrode 4, a metal layer such as platinum, iridium, and aluminum or a conductive complex oxide layer such as iridium oxide can be used.

  The first piezoelectric laminate 100 of this embodiment can be formed as follows, for example.

(1) First, the base body 1 is prepared. The substrate 1 is selected depending on the use of the piezoelectric laminate 100 as described above. As the substrate 1, for example, an STO (SrTiO ₃ ) substrate, an Nb: STO (Nb-doped SrTiO ₃ ) substrate, or a sapphire substrate can be used.

  (2) As shown in FIG. 1, a piezoelectric body 3 made of the piezoelectric body represented by the above-described composition formula is formed on a substrate 1.

  When the piezoelectric layer 3 is formed by the sol-gel method or the MOD method, it can be formed by forming a coating layer using a precursor solution having the composition of the above composition formula and crystallizing the coating layer.

  For the precursor solution that is a material for forming the piezoelectric layer 3, an organometallic compound that includes each of the constituent metals of the piezoelectric material that becomes the piezoelectric layer 3 is mixed so that each metal has a desired molar ratio. These can be prepared by dissolving or dispersing them using an organic solvent such as alcohol. As the organometallic compound containing the constituent metals of the piezoelectric material, organometallic compounds such as metal alkoxides, organic acid salts, and β-diketone complexes can be used. Specific examples of the piezoelectric material include the following.

  Examples of the organometallic compound containing sodium (Na) include sodium ethoxide. Examples of the organometallic compound containing potassium (K) include potassium ethoxide. Examples of the organometallic compound containing niobium (Nb) include niobium ethoxide. The organometallic compound containing the constituent metal of the piezoelectric material is not limited to these, and known ones can be used.

  Various additives such as a stabilizer can be added to the precursor solution as necessary. Furthermore, in the case where hydrolysis / polycondensation is caused in the precursor solution, an acid or a base can be added as a catalyst together with an appropriate amount of water to the precursor solution.

  A raw material solution is prepared so that the piezoelectric layer 3 has a desired composition ratio. After applying this raw material solution on the substrate 1, the piezoelectric layer 3 can be formed by applying heat treatment to crystallize the coating layer. Specifically, for example, a series of steps including a raw material solution coating step, a solvent removal step such as alcohol, a coating layer drying heat treatment step, and a degreasing heat treatment step are performed as many times as desired, and then fired by crystallization annealing. The piezoelectric layer 3 is formed. Further, the piezoelectric layer 3 can also be formed by performing a series of steps including the above-described coating step, solvent removal step, coating layer drying heat treatment step, degreasing heat treatment step, and crystallization annealing step a desired number of times. .

  (3) As shown in FIG. 1, the electrode 4 is formed on the piezoelectric layer 3. The metal layer or the conductive complex oxide layer constituting the electrode 4 is formed by, for example, known sputtering.

  (4) Next, post-annealing can be performed in an oxygen atmosphere using RTA (rapid thermal annealing) or the like, if necessary. Thereby, a good interface between the electrode 4 and the piezoelectric layer 3 can be formed, and the crystallinity of the piezoelectric layer 3 can be improved.

  As shown in FIG. 4, in the case of the piezoelectric laminate 100 having the orientation control layer 6 on the substrate 1, the orientation control layer 6 is formed on the substrate 1 after the step (1). When nickel lanthanate is used for the orientation control layer 6, a sputtering method can be used. By forming the orientation control layer 6, the piezoelectric layer 3 can have higher crystallinity and orientation reflecting the crystal structure of the orientation control layer 6.

  Through the above steps, the first piezoelectric laminate 100 according to the present embodiment can be manufactured.

By forming the piezoelectric layer 3 as described above, the piezoelectric layer 3 is composed of a piezoelectric body represented by the composition formula (K _a Na _1-a ) _x NbO ₃ . This piezoelectric material is a perovskite oxide having an orthorhombic structure at room temperature.

1.2. Second Piezoelectric Laminate FIG. 5 is a cross-sectional view schematically showing an example of the second piezoelectric laminate 200 according to the present embodiment.

  The piezoelectric laminate 200 is formed on the substrate 1, the first electrode (lower electrode) 2 formed on the substrate 1, the piezoelectric layer 3 formed on the lower electrode 2, and the piezoelectric layer 3. And a second electrode (upper electrode) 4.

  The substrate 1 is selected depending on the application of the piezoelectric laminate 200, and its material and configuration are not particularly limited. As the substrate 1, the same substrate as described in the first piezoelectric laminate 100 can be used.

  The lower electrode 2 can be a metal layer such as a platinum group or a conductive complex oxide layer. Moreover, as the lower electrode 2, a conductive layer having a multilayer structure in which a metal layer and a conductive complex oxide layer are stacked can be used. The uppermost layer of the lower electrode 2 may be a conductive layer that functions as a buffer layer. Such a buffer layer can have the same crystal structure as that of the piezoelectric layer 3, similarly to the first piezoelectric laminate 100. Since the buffer layer has such a structure, the piezoelectric layer 3 has a crystal structure that inherits the crystal structure of the buffer layer.

  As shown in FIG. 6, an orientation control layer 6 can be provided on the lower electrode 2 as required. The orientation control layer 6 is the same as that described in the first piezoelectric laminate 100 and is called a buffer layer or a seed layer and has a function of controlling the crystal orientation of the piezoelectric layer 3.

The piezoelectric layer 3 is the same as the piezoelectric layer 3 in the first piezoelectric laminate 100. That is, the piezoelectric layer 3 is composed of a piezoelectric body represented by the composition formula (K _a Na _1-a ) _x NbO ₃ . In the composition formula, preferably 0.1 <a <1, more preferably 0.2 ≦ a ≦ 0.7, preferably 1 ≦ x ≦ 1.2, more preferably 1 <x ≦ 1.1. It is. Piezoelectric of the compositional formula _{(K a Na 1-a)} x NbO 3 takes the structure of orthorhombic at room temperature. In the composition formula, when “a” is in the above range, phase change temperatures from orthorhombic to rhombohedral (a ≦ 0.55) and orthorhombic to monoclinic (0.55 ≦ a) Is less than −40 ° C., which is preferable in that stable characteristics can be obtained in a low temperature region. Since the matters relating to the numerical ranges of “a” and “x” in the composition formula and the characteristics of the piezoelectric layer 3 are the same as those described in the first piezoelectric laminate 100, detailed description thereof is omitted.

When the piezoelectric layer has a configuration corresponding to FIG. 2, the piezoelectric layer 3 includes a first piezoelectric layer 32 made of a piezoelectric material represented by _a composition formula (K _a Na _1-a ) NbO ₃ , and A piezoelectric body (excess potassium and / or sodium) formed between the first piezoelectric layer 32 and the substrate 1 and containing an element constituting at least a layer in contact with the piezoelectric layer 3 (in the illustrated case, the lower electrode 2). And a second piezoelectric layer 34 made of potassium sodium niobate).

When the piezoelectric layer has a configuration corresponding to FIG. 3, the piezoelectric layer 3 has a first phase portion 36 made of a piezoelectric material represented by the composition formula (K _a Na _1-a ) NbO _3. And a second phase portion 38 made of a piezoelectric material represented by _a composition formula (K _a Na _1-a ) _x NbO ₃ (where 1 <x).

  Similar to the lower electrode 2, the upper electrode 4 can be made of a metal layer, a conductive complex oxide layer, or a laminate thereof. That is, the upper electrode 4 can use a metal layer such as platinum or iridium or a conductive complex oxide layer such as iridium oxide.

  The second piezoelectric laminate 200 of this embodiment can be formed as follows, for example.

  (1) First, the base body 1 is prepared. As the substrate 1, the same substrate 1 as described in the first piezoelectric laminate 100 can be used. As the substrate 1, for example, a silicon substrate can be used.

  (2) As shown in FIG. 5, the lower electrode 2 is formed on the substrate 1. The metal layer or the conductive complex oxide layer constituting the lower electrode 2 is formed by, for example, known sputtering.

  (3) As shown in FIG. 5, the piezoelectric layer 3 represented by the above-described composition formula is formed on the lower electrode 2. Since the method for forming the piezoelectric layer 3 is the same as that of the first piezoelectric laminate 100, a detailed description thereof is omitted.

  (4) As shown in FIG. 5, the upper electrode 4 is formed on the piezoelectric layer 3. Since the configuration and formation method of the metal layer or the conductive complex oxide layer constituting the upper electrode 4 are the same as those of the electrode 4 of the first piezoelectric laminate 100, detailed description thereof is omitted.

  (5) Next, if necessary, post-annealing can be performed in an oxygen atmosphere using RTA or the like. Thereby, a good interface between the lower electrode 2 and the upper electrode 4 and the piezoelectric layer 3 can be formed, and the crystallinity of the piezoelectric layer 3 can be improved.

  As shown in FIG. 6, in the case of the piezoelectric laminate 200 having the orientation control layer 6 on the lower electrode 2, the orientation control layer 6 is formed on the lower electrode 2 after the step (2). When nickel lanthanate is used for the orientation control layer 6, a sputtering method can be used. By forming the orientation control layer 6, the piezoelectric layer 3 can have higher crystallinity and orientation reflecting the crystal structure of the orientation control layer 6.

  Through the above steps, the second piezoelectric laminate 200 according to this embodiment can be manufactured.

  The piezoelectric layer 3 can be formed not only by a liquid phase method such as a sol-gel method or a MOD (Metal Organic Decomposition) method but also by a vapor phase method such as a laser ablation method or a sputtering method.

  The first and second piezoelectric laminates 100 and 200 have the piezoelectric layer 3 having excellent piezoelectric characteristics, and can be suitably applied to various uses described later.

2. Examples Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

2.1. Example 1
Potassium ethoxide, sodium ethoxide and niobium ethoxide were mixed at a molar ratio of K: Na: Nb = 1.0: 0.2: 1.0, and the mixture was refluxed in butyl cellosolve to obtain a triple alkoxide solution. Adjusted. Furthermore, diethanolamine was added as a stabilizer for this solution. In this way, a precursor solution was prepared. Acetic acid can also be used in place of diethanolamine. This precursor solution is applied onto a substrate (platinum layer / silicon oxide layer / silicon substrate) on which a platinum layer is formed by spin coating, dried on a hot plate, pre-baked, and then subjected to rapid thermal annealing at 700 ° C. Was given. A polycrystalline sodium potassium niobate (KNN) layer having a thickness of about 1.5 μm obtained by repeating this process several times was obtained. A platinum electrode having a thickness of 100 nm and a diameter of 200 μm was formed on the KNN layer by sputtering. In this way, a capacitor sample was obtained.

  When the hysteresis characteristics were evaluated using the capacitor sample, the hysteresis shown in FIG. 7 was obtained. From FIG. 7, it was confirmed that the capacitor sample of this example had good hysteresis characteristics and the KNN layer had ferroelectricity.

2.2. Example 2, Comparative Example 1
A precursor solution for forming a KNN layer was prepared in the same manner as in Example 1 except that the molar ratio (mol%) of sodium to potassium in Example 1 was changed as shown in Table 1. That is, the sodium amount (excess Na amount) with respect to potassium in the precursor solution was adjusted to 10 mol%, 20 mol%, 40 mol%, and 50 mol%. These precursor solutions were applied on a Nb: STO (Nb-doped SrTiO ₃ ) single crystal substrate by spin coating, dried on a hot plate, pre-baked, and then subjected to rapid thermal annealing at 700 ° C. This process was repeated several times to obtain four types of polycrystalline KNN layers having a thickness of about 1 μm.

  Further, as Comparative Example 1, the precursor solution did not contain sodium, and potassium ethoxide and niobium ethoxide were mixed in the same molar ratio of K: Nb = 1.0: 1.0 as in Example 2. Thus, a potassium niobate layer (KN layer) was formed.

  The following evaluation was performed about the obtained KNN layer and KN layer.

(1) Composition analysis of KNN layer The composition analysis of the KNN layer concerning Example 2 was performed by the ICP (inductively coupled plasma) emission spectrometry. The results are shown in Table 1. According to Table 1, in the KNN layer of the example, _{x in} the formula (K _a Na _1-a ) _x NbO ₃ is larger than 1, and K and Na are excessively contained relative to Nb in comparison with the stoichiometric composition. It was confirmed. Further, even when the amount of Na in the precursor solution was increased, the value of “x” was about 1.1 at the maximum.

(2) Surface Observation of Layer by SEM The surfaces of the two types of KNN layers (x = 1.04, 1.09) according to Example 2 and the KN layer according to Comparative Example 1 were observed by SEM. The result is shown in FIG. 8A and 8B show the results of Example 2, and FIG. 8C shows the results of Comparative Example 1. 8 (A) and 8 (B), it was confirmed that the KNN layer according to Example 2 can obtain a uniform and good morphology. In contrast, from FIG. 8C, it was confirmed that a heterogeneous phase was formed in the KN layer of Comparative Example 1.

(3) Crystallinity by XRD Crystallinity of the same sample as used in (2) above was examined by XRD. The result is shown in FIG. In FIG. 9, the charts indicated by the symbols “a” and “b” are the results of the KNN layer according to Example 2, and the chart indicated by the symbol “c” indicates the results of the KN layer according to Comparative Example 1.

From FIG. 9, it was confirmed that the KNN layer according to Example 2 exhibited good crystallinity and was (100) oriented. In contrast, the KN layer of Comparative Example 1 was confirmed to have a different phase (K ₄ Nb ₆ O ₁₇ ) peak, and good crystallinity could not be obtained.

(4) Raman spectroscopic analysis KNN layer obtained in Example 2, that is, a precursor solution prepared by adjusting the sodium amount (excess Na amount) to 10 mol%, 20 mol%, 40 mol% and 50 mol% relative to potassium Raman spectroscopy was performed on the KNN layer obtained using the above and the KNN layer obtained in the same manner as in Example 2 using the precursor solution in which the excess Na amount was adjusted to 30 mol%. The result is shown in FIG. In FIG. 12, symbols a to e indicate spectra when the excess Na amount is 10 mol% to 50 mol%.

From the spectrum of FIG. 12, the excess amount of Na, and shift (peak located between 550 cm ^-1 to 500) a first peak derived from the A-site of the KNN, and, second peak around 600 cm ^-1 is broadened ing. From this, it was confirmed that potassium and sodium exist in the A site.

(5) Interplanar spacing determined from X-ray analysis For each sample in Example 2, the interplanar spacing of the (100) plane was determined from the peak of X-ray analysis (θ-2θ). The result is shown in FIG.

  From FIG. 13, it was confirmed that the value of the interplanar spacing (d (100)) decreases as the excess amount of Na increases. This is because the atomic radius of sodium is smaller than that of potassium, and the interplanar spacing decreases as the amount of sodium added increases. From this also, it was confirmed that potassium and sodium exist at the A site.

2.3. Example 3
A precursor solution for forming a KNN layer was prepared in the same manner as described in Example 1. This precursor solution was applied onto an Nb: STO (Nb-doped SrTiO ₃ ) single crystal substrate by spin coating, dried on a hot plate, pre-baked, and then subjected to rapid thermal annealing at 700 ° C. This process was repeated several times to obtain a polycrystalline KNN layer having a thickness of about 1 μm. A platinum electrode having a thickness of 100 nm and a diameter of about 30 μm was formed on the KNN layer by a lift-off method. Sputtering was used to deposit platinum. This substrate was bonded onto a platinum-coated silicon substrate via a silver paste.

  The sample thus prepared was subjected to electric field-strain measurement by AFM (Atomic Force Microscope). The result is shown in FIG. From the electric field-strain curve of FIG. 10, it was shown that the KNN layer of this example generates piezoelectric vibration by voltage. Further, from this result, it was confirmed that the hysteresis curve observed in Example 1 was caused by the piezoelectric characteristics of the KNN layer.

2.4. Example 4
A precursor solution for forming a KNN layer was prepared in the same manner as described in Example 1. This sol solution was applied onto an STO (SrTiO ₃ ) single crystal substrate by spin coating, dried on a hot plate, pre-baked, and then subjected to rapid thermal annealing at 700 ° C. This process was repeated several tens of times to obtain a polycrystalline KNN layer having a thickness of about 10 μm. After flattening this KNN layer by CMP, an aluminum layer having a thickness of 100 nm is deposited on the KNN layer, a 2-port comb electrode (L / S = 5 μm) is formed by photolithography, and a network analyzer is used. The S21 parameter representing the SAW propagation characteristics was measured.

  FIG. 11 shows the measurement result of the S21 parameter, and a resonance waveform (indicated by the symbol “a”) of the KNN / STO substrate having a relative bandwidth of about 15% was observed in the vicinity of 240 MHz. From FIG. 11, it was confirmed that the KNN / STO substrate of this example excites surface acoustic waves by stress.

2.5. Example 5, Reference Example 1
Potassium ethoxide, sodium ethoxide and niobium ethoxide were mixed at a molar ratio of K: Na: Nb = 1.0: 0.2: 1.0, and the mixture was refluxed in butyl cellosolve to obtain a triple alkoxide solution. Adjusted. Furthermore, diethanolamine was added as a stabilizer for this solution. In this way, a precursor solution was prepared. Acetic acid can also be used in place of diethanolamine. This precursor solution is applied by spin coating onto a substrate (nickel lanthanate layer / platinum layer / silicon oxide layer / silicon substrate) on which a polycrystalline nickel lanthanate (LNO) layer is formed as an orientation control layer, and a hot plate After drying and pre-baking above, rapid thermal annealing was performed at 700 ° C. This process was repeated 8 times to obtain a polycrystalline sodium potassium niobate (KNN) layer having a thickness of about 1 μm.

  Using this sample, the surface flatness was evaluated by SEM. The result is shown in FIG. From this result, it was confirmed that the KNN layer of this example has dense and good crystallinity reflecting the crystallinity of the LNO layer which is the orientation control layer. Further, when the crystallinity of this sample was examined by XRD, the result shown in FIG. 15A was obtained. From this result, in this example, it was confirmed that the KNN layer was (100) unidirectionally oriented even with a film thickness of 1 μm.

  Furthermore, when the S parameter representing the SAW propagation characteristics was observed for the KNN layer of Example 5, it was confirmed that the propagation loss was −1 db or less, which was a small value applicable to a SAW device or the like.

  As Reference Example 1, a KNN layer was formed in the same manner as in Example 5 except that the alignment control layer in Example 5 was not formed. The surface flatness of this KNN layer was evaluated by SEM. The result is shown in FIG. From this result, since the KNN layer of this example does not have the LNO layer which is the orientation control layer, the surface flatness was inferior to that of Example 5. Further, the crystallinity of this KNN layer was examined by XRD. The result is shown in FIG. From this result, it was confirmed that when the KNN layer was formed on the platinum layer, the KNN layer was randomly oriented.

3. Application example 3.1. Surface Acoustic Wave Element Next, an example of a surface acoustic wave element to which the first piezoelectric laminate 100 of the present invention is applied will be described with reference to the drawings.

  FIG. 16 is a cross-sectional view schematically showing a surface acoustic wave device 300 according to this embodiment.

  The surface acoustic wave element 300 is formed by applying the first piezoelectric laminate 100 shown in FIGS. 1 and 4. That is, the surface acoustic wave element 300 includes a substrate 1 in the piezoelectric laminate 100, a piezoelectric layer 3 formed on the substrate 1, and an electrode formed on the piezoelectric layer 3, that is, an interdigital electrode (hereinafter referred to as an interdigital electrode). 18 and 19) (referred to as “IDT electrodes”). The IDT electrodes 18 and 19 are formed by patterning the electrode 4 shown in FIG.

3.2. Frequency Filter Next, an example of a frequency filter to which the surface acoustic wave device of the present invention is applied will be described with reference to the drawings. FIG. 17 is a diagram schematically illustrating a frequency filter.

  As shown in FIG. 17, the frequency filter has a stacked body 140. As this laminated body 140, the laminated body (refer FIG. 16) similar to the surface acoustic wave element 300 mentioned above can be used. That is, the laminate 140 can include the base body 1 and the piezoelectric layer 3 shown in FIGS. 1 and 4.

  The laminated body 140 has IDT electrodes 141 and 142 formed by patterning the electrode 4 shown in FIGS. 1 and 4 on the upper surface thereof. In addition, sound absorbing portions 143 and 144 are formed on the upper surface of the laminate 140 so as to sandwich the IDT electrodes 141 and 142. The sound absorbing parts 143 and 144 absorb surface acoustic waves that propagate on the surface of the laminate 140. One IDT electrode 141 is connected to a high frequency signal source 145, and the other IDT electrode 142 is connected to a signal line.

3.3. Oscillator Next, an example of an oscillator to which the surface acoustic wave device of the present invention is applied will be described with reference to the drawings. FIG. 18 is a diagram schematically showing an oscillator.

  As shown in FIG. 18, the oscillator has a stacked body 150. As this laminated body 150, the laminated body (refer FIG. 16) similar to the surface acoustic wave element 300 mentioned above can be used. That is, the laminate 150 can include the base body 1 and the piezoelectric layer 3 shown in FIGS. 1 and 4.

  An IDT electrode 151 is formed on the upper surface of the multilayer body 150, and IDT electrodes 152 and 153 are formed so as to sandwich the IDT electrode 151. A high frequency signal source 154 is connected to one comb-like electrode 151a constituting the IDT electrode 151, and a signal line is connected to the other comb-like electrode 151b. The IDT electrode 151 corresponds to an electric signal applying electrode, and the IDT electrodes 152 and 153 are used for resonance to resonate a specific frequency component of a surface acoustic wave generated by the IDT electrode 151 or a frequency component of a specific band. It corresponds to an electrode.

  The above-described oscillator can also be applied to a VCSO (Voltage Controlled SAW Oscillator).

  As described above, the frequency filter and the oscillator can have the surface acoustic wave device according to the present invention.

3.4. Thin Film Piezoelectric Resonator Next, an example of a thin film piezoelectric resonator to which the piezoelectric laminate of the present invention is applied will be described with reference to the drawings.

3.4.1. First Thin Film Piezoelectric Resonator FIG. 19 is a diagram schematically showing a first thin film piezoelectric resonator 700 which is an example of this embodiment. The first thin film piezoelectric resonator 700 is a diaphragm type thin film piezoelectric resonator.

  The first thin film piezoelectric resonator 700 includes a substrate 701, an elastic layer 703, a lower electrode 704, a piezoelectric layer 705, and an upper electrode 706. The substrate 701, the lower electrode 704, the piezoelectric layer 705, and the upper electrode 706 in the thin film piezoelectric resonator 700 are the base 1, lower electrode 2, and piezoelectric layer 3 in the piezoelectric laminate 200 shown in FIGS. , And the upper electrode 4. As the elastic layer 703, a layer such as a buffer layer (an orientation control layer in FIG. 6) not shown in FIG. 5 can be used. That is, the first thin film piezoelectric resonator 700 has the piezoelectric laminate 200 shown in FIGS.

  A via hole 702 that penetrates the substrate 701 is formed in the substrate 701. A wiring 708 is provided on the upper electrode 706. The wiring 708 is electrically connected to an electrode 709 formed on the elastic layer 703 through a pad 710.

3.4.2. Second Thin Film Piezoelectric Resonator FIG. 20 is a diagram schematically showing a second thin film piezoelectric resonator 800 which is an example of the present embodiment. A difference between the second thin film piezoelectric resonator 800 and the first thin film piezoelectric resonator 700 shown in FIG. 19 is that a via hole is not formed and an air gap 802 is formed between the substrate 801 and the elastic layer 803. In the point.

  The second thin film piezoelectric resonator 800 includes a substrate 801, an elastic layer 803, a lower electrode 804, a piezoelectric layer 805, and an upper electrode 806. The substrate 801, the lower electrode 804, the piezoelectric layer 805, and the upper electrode 806 in the thin film piezoelectric resonator 800 are respectively the base 1, the lower electrode 2, the piezoelectric layer 3 in the piezoelectric laminate 200 shown in FIGS. And correspond to the upper electrode 4. Further, as the elastic layer 803, a layer such as a buffer layer (the orientation control layer 6 in FIG. 6) not shown in FIG. That is, the second thin film piezoelectric resonator 800 has the piezoelectric laminate 200 shown in FIGS. The air gap 802 is a space formed between the substrate 801 and the elastic layer 803.

  The piezoelectric thin layer resonator according to the present embodiment (for example, the first thin film piezoelectric resonator 700 and the second thin film piezoelectric resonator 800) can function as a resonator, a frequency filter, or an oscillator.

3.5. Piezoelectric Actuator An ink jet recording head will be described as an example in which the second piezoelectric laminate 200 of the present invention is applied to a piezoelectric actuator. FIG. 21 is a side sectional view showing a schematic configuration of an ink jet recording head to which the piezoelectric actuator according to the present embodiment is applied, and FIG. 22 is an exploded perspective view of the ink jet recording head, in a state in which it is normally used. Is shown upside down.

  As shown in FIGS. 21 and 22, the ink jet recording head 50 includes a head main body 57 and a piezoelectric portion 54 formed on the head main body 57. A piezoelectric laminate 200 shown in FIGS. 5 and 6 is applied to the piezoelectric portion 54, and the lower electrode 2, the piezoelectric layer 3, and the upper electrode 4 are sequentially laminated. In the ink jet recording head, the piezoelectric unit 54 functions as a piezoelectric actuator.

  The head main body 57 includes a nozzle plate 51, an ink chamber substrate 52, and an elastic layer 55. The base 1 in the piezoelectric laminate 200 shown in FIGS. 5 and 6 constitutes the elastic layer 55 in FIG. As the elastic layer 55, a layer such as a buffer layer (not shown in FIGS. 5 and 6) can be used. Further, the substrate 1 in the piezoelectric laminate 200 constitutes the ink chamber substrate 52 in FIG. A cavity 521 is formed in the ink chamber substrate 52. In addition, a nozzle 511 that is continuous with the cavity 521 is formed on the nozzle plate 51. Then, as shown in FIG. 22, these are housed in a housing 56 to constitute an ink jet recording head 50. The hole diameter of the nozzle 511 is 10 to 30 μm. The nozzles 511 are formed at a pitch of 90 to 300 nozzles per inch.

  Each piezoelectric unit is electrically connected to a piezoelectric element drive circuit (not shown) and is configured to operate (vibrate or deform) based on a signal from the piezoelectric element drive circuit. That is, each piezoelectric part 54 functions as a vibration source (head actuator). The elastic layer 55 vibrates due to the vibration (deflection) of the piezoelectric portion 54 and functions to instantaneously increase the internal pressure of the cavity 521. The maximum applied voltage to the piezoelectric body is 20V to 40V and is driven at 20 kHz to 50 kHz. A typical ink discharge amount is between 2 picoliters and 5 picoliters.

  In the above description, an ink jet recording head that discharges ink has been described as an example. However, the present embodiment is directed to a liquid ejecting head that uses a piezoelectric laminate as a piezoelectric actuator. Examples of the liquid ejecting head include a recording head used in an image recording apparatus such as a printer, a color material ejecting head used for manufacturing a color filter such as a liquid crystal display, an organic EL display, and an electrode formation such as an FED (surface emitting display). Examples thereof include an electrode material ejecting head used in manufacturing, a bioorganic matter ejecting head used in biochip manufacturing, and the like.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

  DESCRIPTION OF SYMBOLS 1 Base | substrate, 2 Lower electrode, 3 Piezoelectric layer, 4 Electrode (upper electrode), 6 Orientation control layer, 32 1st piezoelectric material layer, 34 2nd piezoelectric material layer, 36 1st phase part, 38 2nd phase Partial, 100,200 Piezoelectric laminate, 300 Surface acoustic wave device, 700,800 Thin film piezoelectric resonator.

Claims (10)

A substrate;
A piezoelectric layer made of potassium sodium niobate formed on the substrate;
A piezoelectric laminate having:
The piezoelectric layer is
Represented by _a composition formula (K _a Na _1-a ) _x NbO ₃ ;
In the composition formula, 0.1 <a <1, 1 ≦ x ≦ 1.2,
Takes an orthorhombic structure at room temperature,
A piezoelectric laminate, wherein the phase change temperature from orthorhombic to rhombohedral and orthorhombic to monoclinic is minus 40 degrees or less. In claim 1,
A second piezoelectric layer between the substrate and the piezoelectric layer;
The second piezoelectric layer is a piezoelectric laminate in which potassium and sodium are excessively contained as compared with the piezoelectric layer . In claim 1,
A second piezoelectric layer between the substrate and the piezoelectric layer;
The second piezoelectric layer is a piezoelectric laminate including an element constituting the substrate in addition to potassium sodium niobate . In claim 1,
A second piezoelectric layer between the substrate and the piezoelectric layer;
Having an orientation control layer between the substrate and the second piezoelectric layer;
The second piezoelectric layer is a piezoelectric laminate including an element constituting the orientation control layer in addition to potassium sodium niobate . In any of claims 1 to 4 ,
A piezoelectric laminate in which 1 <x ≦ 1.1 in the composition formula .   In any of claims 1 to 5,
  The piezoelectric layer is a piezoelectric laminate in which the pseudo-cubic crystal (100) is preferentially oriented.   In any one of Claims 1 thru | or 6.
  The piezoelectric layer is a piezoelectric laminate having a thickness of 300 nm to 10 μm.   A surface acoustic wave device comprising the piezoelectric laminate according to any one of claims 1 to 7.   A thin film piezoelectric resonator comprising the piezoelectric laminate according to any one of claims 1 to 7.   A piezoelectric actuator comprising the piezoelectric laminate according to any one of claims 1 to 7.