JP2006086368A - Piezoelectric element, piezoelectric actuator, piezoelectric pump, ink-jet type recording head, ink-jet printer, surface acoustic wave element, frequency filter, oscillator, electronic circuit, thin-film piezoelectric resonator, and electronic appliance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element having a good piezoelectric characteristic. <P>SOLUTION: The piezoelectric element 1 includes a substrate 2, a buffer layer 5 formed above the substrate 2, and a piezoelectric layer 6 formed on the buffer layer 5 and having a perovskite-type structure. The buffer layer 5 is conductive and made of a bismuth-based layered perovskite-structure compound oriented dominantly toward the c-axis (001). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric element, a piezoelectric actuator, a piezoelectric pump, an ink jet recording head, an ink jet printer, a surface acoustic wave element, a frequency filter, an oscillator, an electronic circuit, a thin film piezoelectric resonator, and an electronic apparatus.

Inkjet printers are known as printers that enable high image quality and high-speed printing. The ink jet printer has an ink jet recording head having a cavity whose internal volume changes, and performs printing by ejecting ink droplets from the nozzle while scanning the head. As a head actuator in an ink jet recording head for such an ink jet printer, a piezoelectric element using a piezoelectric layer represented by PZT (Pb (Zr, Ti) O ₃ ) has been conventionally used (for example, JP, 2001-223404, A).

  In addition, since surface acoustic wave elements, frequency filters, oscillators, electronic circuits, and the like are desired to have improved characteristics, it is desired to provide good products using new piezoelectric materials.

  As such a new piezoelectric material, a relaxor material has been researched and developed. The relaxor material has a sufficiently high piezoelectric constant compared to PZT or the like. In order to form a piezoelectric layer made of a relaxor material, for example, the following method is used (see, for example, JP-A-10-81016).

  First, a buffer layer is formed by using a laser ablation method and a complicated method such as an ion beam assist method. Next, a base is formed by forming a perovskite-type lower electrode on the buffer layer. Next, a piezoelectric layer is formed on the base. The reason for taking such a complicated method is as follows.

The manufacturing margin for forming a dense thin film of relaxor material on an electrode material such as platinum (Pt) or iridium (Ir) is small. On the other hand, a dense thin film can be obtained relatively easily on a perovskite electrode such as SrRuO ₃ . In order to control the orientation of a perovskite electrode such as SrRuO ₃ , a laser ablation method or an ion beam assist method is required. The result is a complex approach. In such a method, the process is complicated, the cost is high, and the piezoelectric characteristics of the obtained piezoelectric layer may not be sufficiently stable.
JP 2001-223404 A JP-A-10-81016

  An object of the present invention is to provide a piezoelectric element having good piezoelectric characteristics. Another object of the present invention is to provide a piezoelectric actuator, a piezoelectric pump, an ink jet recording head, an ink jet printer, a surface acoustic wave element, a frequency filter, an oscillator, an electronic circuit, a thin film piezoelectric resonator, and an electron using the above piezoelectric element. To provide equipment.

The piezoelectric element according to the present invention is
A substrate,
A buffer layer formed above the substrate;
A piezoelectric layer having a perovskite structure formed above the buffer layer,
The buffer layer is made of a bismuth-based layered perovskite structure compound having conductivity and preferentially oriented along the c-axis (001).

  In the present invention, other specific objects (hereinafter referred to as “B”) formed above a specific object (hereinafter referred to as “A”) are defined as B directly formed on A and A , B formed via the other on A. Further, in the present invention, forming B above A includes a case where B is formed directly on A and a case where B is formed on A via another on A.

  In the present invention, “preferential orientation” means that when 100% of crystals have the desired (001) orientation, most crystals (for example, 90% or more) are oriented to the desired (001) orientation. , And the case where the remaining crystals are in other orientations (for example, (111) orientation).

  According to this piezoelectric element, the buffer layer has conductivity. For example, when the buffer layer is made of a dielectric material, a sufficient voltage cannot be applied to the piezoelectric layer itself. On the other hand, according to this piezoelectric element, since the buffer layer has conductivity, a sufficient voltage can be applied to the piezoelectric layer itself.

In the piezoelectric element according to the present invention,
The bismuth-based layered perovskite structure compound is represented by SrBi ₂ X ₂ O ₉
X includes at least one of Ta and Nb, and can further include at least one of Ti, Zr, Hf, Fe, Co, Ni, W, Ru, and Rh.

In the piezoelectric element according to the present invention,
The bismuth-based layered perovskite structure compound is represented by (Bi _1-x La _x ) ₄ X ₃ O ₁₂
X includes Ti, and further includes at least one of Fe, Co, Ni, V, Nb, Ta, W, Ru, and Rh,
x can be in the range of 0 <x ≦ 0.4.

In the piezoelectric element according to the present invention,
The bismuth-based layered perovskite structure compound is represented by SrBi ₄ X ₄ O ₁₅ ,
X contains Ti, and can further contain at least one of Fe, Co, Ni, V, Nb, Ta, W, Ru, and Rh.

In the piezoelectric element according to the present invention,
The piezoelectric layer is made of Pb (Zr _1-x Ti _x ) O ₃ ,
x can be in the range of 0 ≦ x ≦ 1.

In the piezoelectric element according to the present invention,
The piezoelectric layer is made of a material represented by a general formula of A (B _1-b X _b ) O ₃ ,
A includes Pb,
B contains Zr and Ti, and the composition ratio of Zr and Ti is represented by (1-a): a,
X consists of at least one of V, Nb, and Ta,
a is in the range of 0.15 ≦ a ≦ 0.8,
b can be in the range of 0.05 ≦ b ≦ 0.4.

In the piezoelectric element according to the present invention,
The piezoelectric layer may include Si or Si and Ge.

In the piezoelectric element according to the present invention,
The piezoelectric layer may be made of a relaxor material.

In the piezoelectric element according to the present invention,
The relaxor material can be made of at least one of materials represented by the following formulas (1) to (9).

_{(1-x) Pb (Sc} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (1)
(Where x is 0.10 <x <0.42, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (In} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (2)
(Where x is 0.10 <x <0.37, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Ga} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (3)
(Where x is 0.10 <x <0.50, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Sc} 1/2 Ta 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (4)
(Where x is 0.10 <x <0.45, y is 0 ≦ y ≦ 1)
(1-x) Pb (Mg _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (5)
(Where x is 0.10 <x <0.35, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Fe} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (6)
(Where x is 0.01 <x <0.10, y is 0 ≦ y ≦ 1)
(1-x) Pb (Zn _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (7)
(Where x is 0.01 <x <0.10, y is 0 ≦ y ≦ 1)
(1-x) Pb (Ni _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (8)
(Where x is 0.10 <x <0.38, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Co} 1/2 W 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (9)
(Where x is 0.10 <x <0.42, y is 0 ≦ y ≦ 1)
In the piezoelectric element according to the present invention,
The piezoelectric layer may have a rhombohedral structure and be preferentially oriented to pseudo cubic (001).

  The piezoelectric actuator according to the present invention can have the above-described piezoelectric element.

  The piezoelectric pump according to the present invention can have the above-described piezoelectric element.

  The ink jet recording head according to the present invention can have the above-described piezoelectric element.

  The ink jet printer according to the present invention can have the ink jet recording head described above.

  The surface acoustic wave device according to the present invention can have the above-described piezoelectric device.

  The thin film piezoelectric resonator according to the present invention can have the above-described piezoelectric element.

  The frequency filter according to the present invention can include at least one of the above-described surface acoustic wave device and the above-described thin film piezoelectric resonator.

  The oscillator according to the present invention can include at least one of the above-described surface acoustic wave device and the above-described thin film piezoelectric resonator.

  The electronic circuit according to the present invention can include at least one of the above-described frequency filter and the above-described oscillator.

  The electronic device according to the present invention can include at least one of the above-described piezoelectric pump and the above-described electronic circuit.

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

1. 1. First embodiment 1-1. Piezoelectric Element FIG. 1 is a cross-sectional view showing a piezoelectric element 1 according to a first embodiment to which the present invention is applied. The piezoelectric element 1 includes a substrate 2, an elastic film 3 formed on the substrate 2, a lower electrode 4 formed on the elastic film 3, and a buffer layer 5 formed on the lower electrode 4. The piezoelectric layer 6 formed on the buffer layer 5 and the upper electrode 7 formed on the piezoelectric layer 6 are included.

  As the substrate 2, for example, a silicon substrate can be used. In the present embodiment, the substrate 2 is a (110) -oriented single crystal silicon substrate. As the substrate 2, a (100) -oriented single crystal silicon substrate or a (111) -oriented single crystal silicon substrate can also be used. Further, as the substrate 2, a substrate in which an amorphous silicon oxide film such as a thermal oxide film or a natural oxide film is formed on the surface of a silicon substrate can be used. The substrate 2 is processed to form ink cavities 521 in the ink jet recording head 50 as described later (see FIG. 9).

  As will be described later, the elastic film 3 functions as an elastic film 55 in the ink jet recording head 50. The thickness of the elastic film 3 is, for example, about 1 μm. When a plurality of piezoelectric elements 1 are formed in an ink jet recording head 50 described later, each piezoelectric element 1 can share the substrate 2 and the elastic film 3.

  The lower electrode 4 is one electrode for applying a voltage to the piezoelectric layer 6. For example, the lower electrode 4 can be formed in the same planar shape as the piezoelectric layer 6. When a plurality of piezoelectric elements 1 are formed in an ink jet recording head 50 described later, the lower electrode 4 is formed in the same planar shape as the common elastic film 3 so as to function as a common electrode for each piezoelectric element 1. Can also be done. The film thickness of the lower electrode 4 is, for example, about 100 nm to 200 nm.

  The buffer layer 5 is made of a bismuth-based layered perovskite structure compound (hereinafter also referred to as “Bi layered compound”) preferentially oriented in the c-axis (001). The Bi layered compound can be easily preferentially oriented in the c-axis (001) on the lower electrode 4 made of, for example, platinum (Pt) or iridium (Ir). Here, “preferential orientation” means that all crystals are oriented along the c-axis (001) of the desired orientation, and that most crystals are oriented along the c-axis (001) of the desired orientation. And the case where the remaining crystals not oriented to (001) are in other orientations. Thus, if most crystals are oriented in the c-axis (001) of the desired orientation, when the piezoelectric layer 6 is formed on the buffer layer 5 as described later, the piezoelectric layer 6 By taking over the crystal orientation of 5, it can be preferentially oriented to pseudo cubic (001).

The buffer layer 5 has conductivity. Specifically, the electric conductivity at room temperature of the buffer layer 5 can be set to 10 A / cm ² or more, for example. The Bi layered compound having conductivity can be represented by, for example, SrBi ₂ X ₂ O ₉ (hereinafter also referred to as “SBXO”). Here, X includes at least one of Ta and Nb. Furthermore, X can contain atoms having a valence different from that of Ta and Nb (+5 valence). Specifically, X is Ti (+4 valence), Zr (+4 valence), Hf (+4 valence), Fe (+3 valence), Co (+3 valence), Ni (+3 valence), W (+6 valence), At least one of Ru (+ trivalent) and Rh (+ trivalent) can be contained. Thereby, the whole crystal structure of the Bi layered compound is not electrically neutral, and the Bi layered compound can have conductivity. The proportion of atoms having a valence different from the valences of Ta and Nb in X is not particularly limited as long as the Bi layered compound has conductivity. For example, the ratio of atoms containing valences different from those of Ta and Nb in X is suitably 3 to 40 atomic% with respect to the total of transition metal atoms.

  X is an atom having a valence different from that of Ta and Nb described above, and preferably contains at least one of Fe, Co, Ni, Ru, and Rh. The reason for this is as follows.

  FIG. 2 shows the results of calculation of relative values of d-orbital energy levels of various transition metal atoms based on oxygen 2p-orbital energy levels. This calculation was performed by solving the Dirac equation in a scalar relativistic range for neutral atoms floating in a vacuum according to the density functional method in the range of local density approximation. The energy level of the oxygen 2p orbit is −0.68 eV when the vacuum level at infinity is used as a reference. As shown in FIG. 2, as the sum of the number of s electrons and the number of d electrons in the valence state increases, the energy level of the transition metal atom in the d orbital approaches the energy level of the oxygen 2p orbital. To go. The transition metal atoms (Fe, Co, Ni, Ru, Rh) described above have energy levels in the 2p orbit of oxygen as compared with the other transition metal atoms (Ti, Zr, Hf) described above. Close to the rank. The highest occupied state of the perovskite transition metal oxide is mainly composed of oxygen 2p orbitals. On the other hand, the lowest unoccupied orbit is mainly composed of d-orbitals of transition metals. Therefore, when the energy levels of both are close, it is difficult to form a band gap having a sufficient width. And the electrical resistance of a transition metal oxide falls and electroconductivity increases. That is, in a Bi layered compound having a perovskite type transition metal oxide structure, these transition metal atoms (Fe, Co, Ni, Ru, Rh) are preferable because the conductivity can be further increased.

Also, the bismuth layered compound having conductivity, for _example, it can be represented by _{(Bi 1-x La x)} 4 X 3 O 12. Here, X includes Ti. Furthermore, X can contain an atom having a valence different from that of Ti (+4 valence). Specifically, X is Fe (+ trivalent), Co (+ trivalent), Ni (+ trivalent), V (+ pentavalent), Nb (+ pentavalent), Ta (+ pentavalent), W (+ hexavalent), At least one of Ru (+ trivalent) and Rh (+ trivalent) can be contained. Thereby, like the SBXO described above, the entire crystal structure of the Bi layered compound is not electrically neutral, and the Bi layered compound can have conductivity. The proportion of atoms containing a valence atom different from the valence of Ti in X is not particularly limited as long as the Bi layered compound has conductivity. For example, the ratio of atoms having a valence different from the valence of Ti in X is suitably 3 to 40 atomic% with respect to the total of transition metal atoms.

X is an atom having a valence different from that of Ti described above, and preferably contains at least one of Fe, Co, Ni, Ru, and Rh. The reason is the same as in the case of SBXO described above. X is
0 <x ≦ 0.4
Range. If x is in this range, the crystal structure is stable. When x is larger than 0.4, the layered crystal structure cannot be maintained.

Also, the bismuth layered compound having conductivity, for example, it can be represented by SrBi ₄ X ₄ O _15. Here, X includes Ti. Furthermore, X can contain an atom having a valence different from that of Ti (+4 valence). Specifically, X is Fe (+ trivalent), Co (+ trivalent), Ni (+ trivalent), V (+ pentavalent), Nb (+ pentavalent), Ta (+ pentavalent), W (+ hexavalent), At least one of Ru (+ trivalent) and Rh (+ trivalent) can be contained. Thereby, like the SBXO described above, the entire crystal structure of the Bi layered compound is not electrically neutral, and the Bi layered compound can have conductivity. The proportion of atoms containing a valence atom different from the valence of Ti in X is not particularly limited as long as the Bi layered compound has conductivity. For example, the ratio of atoms having a valence different from the valence of Ti in X is suitably 3 to 40 atomic% with respect to the total of transition metal atoms.

  X is an atom having a valence different from that of Ti described above, and preferably contains at least one of Fe, Co, Ni, Ru, and Rh. The reason is the same as in the case of SBXO described above.

  The buffer layer 5 is not particularly limited as long as the buffer layer 5 has a film thickness that can provide an effect and effect as a buffer layer described later. Specifically, the thickness of the buffer layer 5 can be, for example, about 1 nm to 10 nm.

The piezoelectric layer 6 has a perovskite structure. The piezoelectric layer 6 preferably has a rhombohedral structure and is preferentially oriented to pseudo cubic (001). The piezoelectric layer 6 having a rhombohedral structure and preferentially oriented to pseudo cubic (001) can be obtained by adjusting film forming conditions such as temperature. Thus, the piezoelectric layer 6 has a perovskite type and a rhombohedral structure and is preferentially oriented to pseudo cubic (001), and is called an engineered domain arrangement. Therefore, the piezoelectric layer 6 has a high piezoelectric constant (d ₃₁ ). Here, as described above, the “preferential orientation” means that all crystals are oriented in the pseudo-cubic crystal (001) having a desired orientation and most crystals are in the pseudo-cubic crystal (001) having the desired orientation. It can include the case where the remaining crystals that are oriented and not oriented to pseudo cubic (001) have other orientations. The piezoelectric layer 6 is formed on the buffer layer 5 preferentially oriented with respect to the c-axis (001), and can take over the crystal orientation of the buffer layer 5 and preferentially be oriented to pseudo cubic (001). That is, since the buffer layer 5 is preferentially oriented along the c-axis (001), the buffer layer 5 is hardly mixed with crystals oriented in (111) or (110). Therefore, the piezoelectric layer 6 formed on the buffer layer 5 is hardly mixed with crystals oriented in (111) or (110).

  In the present embodiment, the piezoelectric layer 6 can be made of, for example, a relaxor material. As a relaxer material, the material shown by the following formula | equation (1)-(9) is mentioned, for example. One or a plurality of types selected from these are deposited by a liquid phase method or a gas phase method as described later, whereby the piezoelectric layer 6 is obtained.

_{(1-x) Pb (Sc} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (1)
(Where x is 0.10 <x <0.42, preferably 0.20 <x <0.42, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
_{(1-x) Pb (In} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (2)
(Where x is 0.10 <x <0.37, preferably 0.20 <x <0.37, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
_{(1-x) Pb (Ga} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (3)
(Where x is 0.10 <x <0.50, preferably 0.30 <x <0.50, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
_{(1-x) Pb (Sc} 1/2 Ta 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (4)
(Where x is 0.10 <x <0.45, preferably 0.20 <x <0.45, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
(1-x) Pb (Mg _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (5)
(Where x is 0.10 <x <0.35, preferably 0.20 <x <0.35, more preferably X = 0.3, y is 0 ≦ y ≦ 1, preferably 0 .7 ≦ y ≦ 1)
_{(1-x) Pb (Fe} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (6)
(Where x is 0.01 <x <0.10, preferably 0.03 <x <0.10, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
(1-x) Pb (Zn _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (7)
(Where x is 0.01 <x <0.10, preferably 0.03 <x <0.09, more preferably X = 0.09, and y is 0 ≦ y ≦ 1, preferably 0 .7 ≦ y ≦ 1)
(1-x) Pb (Ni _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (8)
(Where x is 0.10 <x <0.38, preferably 0.20 <x <0.38, more preferably X = 0.3, y is 0 ≦ y ≦ 1, preferably 0 .7 ≦ y ≦ 1)
_{(1-x) Pb (Co} 1/2 W 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (9)
(Where x is 0.10 <x <0.42, preferably 0.20 <x <0.42, y is 0 ≦ y ≦ 1, preferably 0.7 ≦ y ≦ 1)
As shown in FIG. 3, the relaxor material is a material that exhibits a broad (wide) peak in the temperature dependence of the dielectric constant in the bulk, and the peak shifts depending on the frequency. An arrow h shown in FIG. 3 indicates a peak shift direction when the frequency is increased. The relaxor material is a material that exhibits a broad (wide) peak in temperature dependence of the piezoelectric constant. On the other hand, a piezoelectric material that is a non-relaxer material such as Pb (Zr, Ti) O ₃ (hereinafter also referred to as “PZT”) has a very high temperature dependence of dielectric constant and piezoelectric constant as shown in FIG. Shows a sharp peak. Therefore, by using a relaxor material as the piezoelectric layer 6, the obtained piezoelectric element 1 exhibits good piezoelectric characteristics over a wide temperature range, which makes the characteristics highly reliable and stable. However, when the film thickness of the relaxor material is about 100 nm to 1 μm, the clear peak shown in FIG. 3 is not always shown. Some relaxor materials having a film thickness of about 100 nm to 1 μm exhibit a more gentle change in dielectric constant between room temperature and 100 ° C.

In the material for forming the piezoelectric layer 6 (relaxer material), as described above, the range of x representing the composition ratio on the Pb (Zr _1-y Ti _y ) O ₃ (hereinafter also referred to as “PZT”) side between the materials. In particular, the upper limit thereof is the value of x (hereinafter also referred to as “x _MPB ”) at the phase boundary (MPB: Morphotropic Phase Boundary) of the crystal structure of the piezoelectric layer 6. The value of x at the phase boundary (x _MPB ) is a value indicating the composition ratio on the PZT side when the rhombohedral structure and the tetragonal structure undergo phase transition. The range of x is smaller than the composition ratio at the time of phase transition, and is thus a range in which a rhombohedral structure is obtained. Here, the piezoelectric constant (d ₃₁ ) takes a local maximum near the phase boundary. Accordingly, a value close to the value of x (x _MPB ) at the phase boundary is selected as the lower limit value of x. Therefore, as a range of x, although a relatively small value can be allowed in constructing the present invention, in order to obtain a higher piezoelectric constant (d ₃₁ ), a preferable value of x, that is, a value of x at the phase boundary. A value closer to (x _MPB ) is selected. Accordingly, the lower limit value of the range of x is the value of x when the piezoelectric constant (d ₃₁ ) is allowed when the piezoelectric element 1 is operated. When the above content is expressed by an equation, for example, x is
(X _MPB −0.05) ≦ x ≦ x _MPB
Can range. If x is in the above-mentioned range, the piezoelectric layer 6 can be easily controlled to a rhombohedral structure, and high piezoelectric characteristics can be expressed. The piezoelectric layer 6 can also have x (x _MPB ) at the phase boundary of the crystal structure of the piezoelectric layer 6. Thereby, the piezoelectric constant (d ₃₁ ) can be set to the maximum value.

In the above-described example, the piezoelectric layer 6 is made of a relaxor material. However, the material of the piezoelectric layer 6 is not particularly limited as long as it has a perovskite structure. For example, the piezoelectric layer 6 is made of Pb (Zr _1-x Ti _x ) O ₃ , and x can be in a range of 0 ≦ x ≦ 1. The piezoelectric layer 6 can be made of a material represented by the general formula of perovskite type A (B _1-b X _b ) O ₃ . A includes Pb. B contains Zr and Ti, and the composition ratio of Zr and Ti is represented by (1-a): a. X may be composed of at least one of V, Nb, and Ta. For example, the piezoelectric layer 6 can be made of perovskite Pb ((Zr _1-a Ti _a ) _1-b X _b ) O ₃ (hereinafter also referred to as “PZTX”).

A in Pb ((Zr _1-a Ti _a ) _1-b X _b ) O ₃ has a certain range. The upper limit value of a is the value of a at the phase boundary (MPB) of the crystal structure of the piezoelectric layer 6 (hereinafter also referred to as “a _MPB ”). The value of a (a _MPB ) at the phase boundary is a value indicating the composition ratio of Ti when the rhombohedral structure and the tetragonal structure undergo phase transition. The range of “a” is smaller than the composition ratio at the time of phase transition, and thus the range becomes a rhombohedral structure. Here, the piezoelectric constant (d ₃₁ ) takes a local maximum near the phase boundary. Therefore, a value close to the value of a (a _MPB ) at the phase boundary is selected as the lower limit value of a. Therefore, as the range of a, although a relatively small value can be allowed in configuring the present invention, in order to obtain a higher piezoelectric constant (d ₃₁ ), a preferable value of a, that is, a value at the phase boundary. A value closer to (a _MPB ) is selected. Accordingly, the lower limit value of the range of a is the value of a when the lower limit value of the piezoelectric constant (d ₃₁ ) allowed when the piezoelectric element 1 is operated. When the above-mentioned content is expressed by a formula, for example, a is
(A _MPB −0.05) ≦ a ≦ a _MPB
Can range. a _MPB is about 0.5, for example. Note that a _MPB is not particularly limited because it can change depending on the film stress, etc.
0.2 ≦ a _MPB ≦ 0.8
Can range. Therefore, a is
0.15 ≦ a ≦ 0.8
Can range.

If a is in the above-mentioned range, the piezoelectric layer 6 made of PZTX can be easily controlled to a rhombohedral structure, and high piezoelectric characteristics can be expressed. The piezoelectric layer 6 can also have a (a _MPB ) at the phase boundary of the crystal structure of the piezoelectric layer 6. Thereby, the piezoelectric constant (d ₃₁ ) can be set to the maximum value.

A Pb-based perovskite structure, such as PZT, has a high vapor pressure of Pb, so that Pb located at the A site of the perovskite structure is likely to evaporate. In the above-described PZTX, the case where the composition formula is represented by Pb ((Zr _1−a Ti _a ) _1−b X _b ) O ₃ has been described. However, the composition formula of PZTX is Pb _{1− (b / 2)} (( Zr _1-a Ti _a) can also _1-b X _b) be represented by _{O 3.} In this case, X can be composed of at least one of V, Nb, and Ta. In the composition formula of PZTX, (b / 2) represents the amount of deficiency of Pb.

  When Pb escapes from the A site, oxygen is simultaneously lost due to the principle of charge neutrality. This phenomenon is called a Schottky defect. For example, when oxygen is lost in PZT, the band gap of PZT decreases. Due to the reduction of the band gap, the band offset at the electrode interface is reduced, and the insulating property of the piezoelectric layer made of PZT is lowered.

  However, in the case where the piezoelectric layer 6 is made of PZTX, by replacing X (+5 valence) higher than the valence (+4 valence) of Zr and Ti with the element (Zr, Ti) of the B site, Even if Pb deficiency occurs, the neutrality of the entire crystal structure can be maintained without oxygen deficiency. Thereby, the insulation property of the piezoelectric layer 6 becomes favorable, and current leakage can be prevented.

  For example, when X is made of Nb, Nb is almost the same size as Ti (the ionic radius is close and the atomic radius is the same) and the weight is twice, so collisions between atoms due to lattice vibrations. Makes it difficult for atoms to escape from the lattice. Furthermore, Nb has a very strong covalent bond with oxygen, and is expected to enhance the ferroelectric characteristics indicated by the Curie temperature and the polarization moment, and the piezoelectric characteristics indicated by the piezoelectric constant (H. Miyazawa). E. Natori, S. Miyashita; Jpn. J. Appl. Phys. 39 (2000) 5679). Although an example in which X is Nb has been described here, the case where X includes at least one of V and Ta has the same or similar effect.

The deficiency of Pb is preferably approximately half of the addition amount b of X. That is, the loss amount of Pb is indicated by b / 2. Thereby, PZTX can maintain neutrality electrically. And the addition amount b of X is:
0.05 ≦ b ≦ 0.4
It is preferable that it is the range of these. If the added amount b of X is less than 0.05, the current leakage preventing effect due to the addition of X is not good. On the other hand, even if the added amount b of X exceeds 0.4, the current leak preventing effect is not exceeded. I cannot expect much improvement.

  The piezoelectric layer 6 may contain 0.5 mol% or more and less than 5 mol% of silicon (Si), or silicon and germanium (Ge). Details will be described in the section of a method for manufacturing a piezoelectric element.

  The film thickness of the piezoelectric layer 6 is, for example, about 300 nm to 3000 nm, preferably about 500 nm to 1000 nm, and more preferably about 500 nm. With respect to the upper limit of the thickness, the thickness can be increased within a range that maintains the denseness and crystal orientation as a thin film, and can be allowed to be about 10 μm.

  The upper electrode 7 is the other electrode for applying a voltage to the piezoelectric layer 6. The thickness of the upper electrode 7 is, for example, about 50 to 150 nm.

  In the present embodiment, at least one of the ICP method, the XPS method, and the SIMS method can be used to determine the composition of the substance.

1-2. Next, a method for manufacturing the piezoelectric element 1 according to this embodiment will be described.

(1) First, a substrate 2 made of a silicon substrate having a (110) surface is prepared. Next, the elastic film 3 is formed on the substrate 2 as shown in FIG. As will be described later, the elastic film 3 is a material having a sufficient etching selectivity with the substrate 2 so that the elastic film 3 functions as an etching stopper layer when the substrate 2 is etched to form a cavity. It is preferable to form by. When silicon is used as the substrate 2, examples of such a material include SiO _{2 and} ZrO ₂ . The elastic film 3 can be formed by, for example, a CVD method, a sputtering method, or a vapor deposition method.

(2) Next, as shown in FIG. 6, the lower electrode 4 is formed on the elastic film 3. The lower electrode 4 can be formed by, for example, a sputtering method or a vacuum deposition method. The lower electrode 4 is made of, for example, Pt (platinum). Pt is preferentially oriented to (111) relatively easily. Therefore, for example, Pt can be easily oriented and grown on the elastic film 3 by employing a relatively simple method such as sputtering. The material of the lower electrode 4 is not limited to Pt, and for example, Ir (iridium), IrO _x (iridium oxide), Ti (titanium), or SrRuO ₃ can be used. By using a perovskite electrode such as SrRuO ₃ as the lower electrode 4, the buffer layer 5 formed on the lower electrode 4 can be more easily preferentially oriented to the c-axis (001) in the manufacturing process. . Furthermore, the piezoelectric layer 6 formed on the buffer layer 5 can be more easily preferentially oriented to pseudo cubic (001).

  (3) Next, as shown in FIG. 7, the buffer layer 5 made of the bismuth-based layered perovskite structure compound (hereinafter also referred to as “Bi layered compound”) is formed on the lower electrode 4. Specifically, first, a precursor solution of a Bi layered compound material is applied onto the lower electrode 4 by a known application method such as a spin coating method or a droplet discharge method. Next, the buffer layer 5 is obtained by performing a heat treatment such as baking.

  More specifically, first, a series of steps of the precursor solution coating step, the drying heat treatment step, and the degreasing heat treatment step is repeated as appropriate according to the desired film thickness. Next, the buffer layer 5 is formed by performing crystallization annealing.

  The precursor solution, which is a material for forming the buffer layer 5, is mixed with organic metals each containing a constituent metal of the Bi layered compound material to be the buffer layer 5 so that each constituent metal has a desired molar ratio, Furthermore, it is produced by dissolving or dispersing them using an organic solvent such as alcohol. An organic metal such as a metal alkoxide or an organic acid salt can be used as the organic metal containing the constituent metal of the Bi layered compound material. Specific examples include the following.

  Examples of the organic metal containing bismuth (Bi) include bismuth 2-ethylhexanoate. Examples of the organic metal containing strontium (Sr) include strontium 2-ethylhexanoate. Examples of the organic metal containing tantalum (Ta) include tantalum 2-ethylhexanoate. Examples of the organic metal containing niobium (Nb) include niobium 2-ethylhexanoate. Examples of the organic metal containing titanium (Ti) include titanium isopropoxide. Examples of the organic metal containing zirconium (Zr) include zirconium butoxide. Examples of the organic metal containing hafnium (Hf) include hafnium acetylacetonate and hafnium tert-butoxide. Examples of the organic metal containing iron (Fe) include iron acetate. Examples of the organic metal containing cobalt (Co) include cobalt (II) acetylacetonate or cobalt (II) acetate tetrahydrate. Examples of the organic metal containing nickel (Ni) include nickel acetylacetonate. Examples of the organic metal containing tungsten (W) include tungsten hexacarbonyl. Examples of the organic metal containing ruthenium (Ru) include ruthenium (III) acetylacetonate. Examples of the organic metal containing rhodium (Rh) include rhodium (III) acetylacetonate and rhodium acetate. Examples of the organic metal containing lanthanum (La) include lanthanum acetylacetonate dihydrate and lanthanum acetate hemihydrate. Examples of the organic metal containing vanadium (V) include vanadium acetylacetonate. In addition, as an organic metal containing the constituent metal of the material of a Bi layered compound, it is not necessarily limited to these.

  As an organic solvent for dissolving or dispersing the mixed organic metal, for example, octane, butoxyethanol, xylene, or the like can be used.

  Various additives such as a stabilizer can be added to the precursor solution as necessary. As the stabilizer, for example, diethanolamine or acetic acid can be used. 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.

  In the precursor solution coating step, the above-described precursor solution is coated on the lower electrode 4. For example, when the spin coating method is employed for this coating step, first, the precursor solution is dropped on the lower electrode 4. Then, spin is performed for the purpose of spreading the dropped solution over the entire surface of the lower electrode 4. The rotation speed of the spin is, for example, about 500 rpm in the initial stage, and then the rotation speed can be increased to about 2000 rpm so that coating unevenness does not occur. In this way, the application can be completed.

  In the drying heat treatment step, heat treatment (drying treatment) is performed at a temperature, for example, about 10 ° C. higher than the boiling point of the solvent used in the precursor solution, using a hot plate or the like in an air atmosphere.

  In the degreasing heat treatment step, heat treatment is performed at about 350 ° C. using a hot plate in an air atmosphere in order to decompose / remove the organometallic ligand used in the precursor solution.

  In the crystallization annealing, that is, the firing step for crystallization, heat treatment is performed in an oxygen atmosphere at, for example, about 600 ° C. This heat treatment can be performed by, for example, rapid thermal annealing (RTA).

  In this way, the buffer layer 5 made of a Bi layered compound having conductivity and preferentially oriented in the c-axis (001) can be formed on the lower electrode 4 made of (111) oriented Pt. In addition, about the formation method of the buffer layer 5, it is not limited to the method mentioned above, For example, a sputtering method or a laser ablation method etc. are employable. For example, when the sputtering method is employed, the power during sputtering can be set to 200 W, for example. When the buffer layer 5 is formed by sputtering, rapid thermal annealing (RTA) can be performed at 700 ° C. after the formation, for example.

  (4) Next, as shown in FIG. 8, the piezoelectric layer 6 is formed on the buffer layer 5. Specifically, first, a precursor solution of a relaxor material is applied onto the buffer layer 5 by a known application method such as a spin coating method or a droplet discharge method. Next, the piezoelectric layer 6 is obtained by performing a heat treatment such as firing.

  More specifically, first, a series of steps of the precursor solution coating step, the drying heat treatment step, and the degreasing heat treatment step is repeated as appropriate according to the desired film thickness. Next, the piezoelectric layer 6 is formed by performing crystallization annealing.

  The precursor solution, which is a material for forming the piezoelectric layer 6, is mixed with organic metals each containing a constituent metal of the relaxor material that becomes the piezoelectric layer 6 so that each constituent metal has a desired molar ratio, These are prepared by dissolving or dispersing them using an organic solvent such as alcohol. An organic metal such as a metal alkoxide or an organic acid salt can be used as the organic metal containing the constituent metals of the relaxor material. Specifically, examples of the carboxylate or acetylacetonate complex containing the constituent metal of the relaxor material include the following.

  Examples of the organic metal containing lead (Pb) include lead acetate. Examples of the organic metal containing zirconium (Zr) include zirconium butoxide. Examples of the organic metal containing titanium (Ti) include titanium isopropoxide. Examples of the organic metal containing magnesium (Mg) include magnesium acetate. Examples of the organic metal containing niobium (Nb) include niobium ethoxide. Examples of the organic metal containing nickel (Ni) include nickel acetylacetonate. Examples of the organic metal containing scandium (Sc) include scandium acetate. Examples of the organic metal containing indium (In) include indium acetylacetonate. Examples of the organic metal containing zinc (Zn) include zinc acetate. Examples of the organic metal containing iron (Fe) include iron acetate. Examples of the organic metal containing gallium (Ga) include gallium isopropoxide. Examples of the organic metal containing tantalum (Ta) include tantalum ethoxide. Examples of the organic metal containing tungsten (W) include tungsten hexacarbonyl. The organic metal containing the constituent metal of the relaxor material is not limited to these.

  Various additives such as a stabilizer can be added to the precursor solution as necessary. As the stabilizer, for example, diethanolamine or acetic acid can be used. 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.

  In the precursor solution coating step, the above-described precursor solution is coated on the buffer layer 5. For example, when this spin coating method is employed, the coating solution is first dropped onto the buffer layer 5. Then, spinning is performed for the purpose of spreading the dropped solution over the entire surface of the buffer layer 5. The rotation speed of the spin is, for example, about 500 rpm in the initial stage, and then the rotation speed can be increased to about 2000 rpm so that coating unevenness does not occur. In this way, the application can be completed.

  In the drying heat treatment step, heat treatment (drying treatment) is performed at a temperature, for example, about 10 ° C. higher than the boiling point of the solvent used in the precursor solution, using a hot plate or the like in an air atmosphere.

  In the degreasing heat treatment step, heat treatment is performed at about 350 ° C. using a hot plate in an air atmosphere in order to decompose / remove the organometallic ligand used in the precursor solution.

  In the crystallization annealing, that is, the firing step for crystallization, heat treatment is performed in an oxygen atmosphere at, for example, about 600 ° C. This heat treatment can be performed by, for example, rapid thermal annealing (RTA).

In the example described above, the manufacturing method in the case where the piezoelectric layer 6 is made of a relaxor material has been described. For example, the piezoelectric layer 6 has a general formula of perovskite type A (B _1-b X _b ) O ₃ . The manufacturing method in the case of the material shown below (hereinafter also referred to as “ABXO”) is as follows. A includes Pb, B includes Zr and Ti, and X can include at least one of V, Nb, and Ta. Here, representative as _{ABXO, Pb ((Zr 1-} a Ti a) 1-b X b) O 3 ( hereinafter, also referred to. As "PZTX") manufacturing method will be described. For example, regarding the manufacturing method in the case where the piezoelectric layer 6 is made of Pb _{1- (b / 2)} ((Zr _1-a Ti _a ) _1-b X _b ) O ₃ or the like, the following manufacturing of PZTX is performed. It is the same as the method.

  First, using the first to third raw material solutions containing at least one of Pb, Zr, Ti, and X, the first to third raw material solutions so that the piezoelectric layer 6 has a desired composition ratio. Are mixed in the desired ratio. This mixed solution (precursor solution) is disposed on the buffer layer 5 by a coating method such as a spin coating method or a droplet discharge method. Next, the piezoelectric layer 6 is obtained by performing a heat treatment such as firing.

  More specifically, first, a series of steps of the precursor solution coating step, the drying heat treatment step, and the degreasing heat treatment step is performed a desired number of times. Next, the piezoelectric layer 6 is formed by performing crystallization annealing.

  For the precursor solution, which is a material for forming the piezoelectric layer 6, organic metals each containing a constituent metal of PZTX are mixed so that each metal has a desired molar ratio, and further an organic solvent such as alcohol is used. These are prepared by dissolving or dispersing them. An organic metal such as a metal alkoxide or an organic acid salt can be used as the organic metal containing each constituent metal of PZTX. Specifically, examples of the carboxylate or acetylacetonate complex containing the constituent metal of PZTX include the following.

  Examples of the organic metal containing lead (Pb) include lead acetate. Examples of the organic metal containing zirconium (Zr) include zirconium butoxide. Examples of the organic metal containing titanium (Ti) include titanium isopropoxide. Examples of the organic metal containing vanadium (V) include vanadium oxide acetylacetonate. Examples of the organic metal containing niobium (Nb) include niobium ethoxide. Examples of the organic metal containing tantalum (Ta) include tantalum ethoxide. Note that the organic metal containing the constituent metal of PZTX is not limited to these.

For example, as the first raw material solution, a solution in which a polycondensation polymer for forming a PbZrO ₃ perovskite crystal composed of Pb and Zr among constituent metal elements of PZTX is dissolved in a solvent such as n-butanol in an anhydrous state is used. It can be illustrated.

For example, as the second raw material solution, a solution obtained by dissolving a polycondensation polymer for forming a PbTiO ₃ perovskite crystal of Pb and Ti among the constituent metal elements of PZTX in a solvent such as n-butanol in an anhydrous state. It can be illustrated.

For example, as the third raw material solution, a solution obtained by dissolving a polycondensation product for forming a PbXO ₃ perovskite crystal by Pb and X in a constituent metal element of PZTX in a solvent such as n-butanol in an anhydrous state. It can be illustrated. In addition, when X consists of 2 or more types of elements, the 3rd raw material solution can consist of a several raw material solution. For example, when X consists of three kinds of V, Nb, and Ta, the third raw material solution can consist of three kinds of raw material solutions. Specifically, for example, the third raw material solution includes a solution obtained by dissolving a polycondensation product for forming a PbVO ₃ perovskite crystal with Pb and V in a solvent such as n-butanol in an anhydrous state, and Pb and Nb. a polycondensation product for forming a PbNbO ₃ perovskite crystal containing a solution prepared by dissolving in an anhydrous state in a solvent such as n- butanol, the polycondensation product for forming a PbTaO ₃ perovskite crystal containing Pb and Ta, n- And a solution dissolved in an anhydrous state in a solvent such as butanol.

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

  In the precursor solution coating step, the mixed solution is coated by a coating method such as spin coating. First, the mixed solution is dropped on the buffer layer 5. Spin is performed for the purpose of spreading the dropped solution over the entire surface of the buffer layer 5. The rotation speed of the spin is, for example, about 500 rpm in the initial stage, and then the rotation speed can be increased to about 2000 rpm so that coating unevenness does not occur. In this way, the application can be completed.

  In the drying heat treatment step, a heat plate (drying treatment) is performed at a temperature, for example, about 10 ° C. higher than the boiling point of the solvent used in the precursor solution, using a hot plate or the like in an air atmosphere.

  In the degreasing heat treatment step, heat treatment is performed at about 350 ° C. to 400 ° C. using a hot plate in an air atmosphere in order to decompose / remove the organometallic ligand used in the precursor solution.

  In the crystallization annealing, that is, the firing step for crystallization, heat treatment is performed in an oxygen atmosphere at, for example, about 600 ° C. This heat treatment can be performed by, for example, rapid thermal annealing (RTA).

When forming the piezoelectric layer 6 made of ABXO, it is preferable to further add PbSiO ₃ silicate at a ratio of, for example, 1 mol% or more and 5 mol% or less. Thereby, the crystallization energy of ABXO can be reduced. That is, for example, when PZTX is used as the piezoelectric layer 6, it is possible to reduce the crystallization temperature of PZTX by adding PbSiO ₃ silicate together with the addition of X. Specifically, in addition to the first to third raw material solutions described above, a fourth raw material solution can be used. Examples of the fourth raw material solution include a solution obtained by dissolving a condensation polymer in a solvent such as n-butanol in an anhydrous state in order to form a PbSiO ₃ crystal. As an additive for promoting crystallization, germanate can also be used. When the piezoelectric layer 6 is formed, the piezoelectric layer 6 may contain Si or Si and Ge by using PbSiO ₃ silicate or germanate. Specifically, the piezoelectric layer 6 can contain 0.5 mol% or more and less than 5 mol% of Si, or Si and Ge.

  By forming the piezoelectric layer 6 on the buffer layer 5 preferentially oriented with respect to the c-axis (001), the piezoelectric layer 6 is easily oriented to pseudo cubic (001). As a result, the piezoelectric layer 6 can be a perovskite type, a rhombohedral structure, and can be preferentially oriented to pseudo cubic (001).

  In the example described above, an example in which the piezoelectric layer 6 is formed by the liquid phase method has been described. However, the piezoelectric layer 6 is formed by using a vapor phase method such as a sputtering method, a molecular beam epitaxy method, or a laser ablation method. It can also be formed.

(7) Next, as shown in FIG. 1, the upper electrode 7 is formed on the piezoelectric layer 6. The upper electrode 7 can be formed by, for example, a sputtering method or a vacuum evaporation method. The upper electrode 7 is made of, for example, Pt (platinum). The material of the upper electrode 7 is not limited to Pt, and for example, Ir (iridium), IrO _x (iridium oxide), Ti (titanium), SrRuO ₃ or the like can be used.

  Through the above steps, the piezoelectric element 1 according to this embodiment can be manufactured.

1-3. Action / Effect According to the piezoelectric element 1 according to this embodiment, the buffer layer 5 made of a bismuth-based layered perovskite structure compound formed on the substrate 2 and the relaxor material formed on the buffer layer 5 are used. The piezoelectric layer 6 can be included. The bismuth-based layered perovskite structure compound is a layered compound and can be easily preferentially oriented in the c-axis (001) on the lower electrode 4 made of platinum (Pt), iridium (Ir), or the like. According to the piezoelectric element 1 according to the present embodiment, since the piezoelectric layer 6 made of the relaxor material is formed on the buffer layer 5 preferentially oriented with respect to the c-axis (001), the piezoelectric layer 6 is also simulated. It is preferably preferentially oriented to cubic (001). Therefore, the piezoelectric element 1 according to the present embodiment can have the piezoelectric layer 6 having good piezoelectric characteristics. In other words, the piezoelectric element 1 according to the present embodiment has a high piezoelectric constant and undergoes greater deformation with respect to the applied voltage.

  Moreover, according to the piezoelectric element 1 according to the present embodiment, the relaxor material represented by the above-described formulas can be used as the piezoelectric layer 6. As a result, the piezoelectric element 1 according to the present embodiment has a sufficiently high piezoelectric constant. Therefore, the piezoelectric element 1 according to the present embodiment, more specifically, the piezoelectric layer 6 is more deformed.

  Moreover, according to the piezoelectric element 1 according to the present embodiment, the buffer layer 5 has conductivity. For example, when the buffer layer is made of a dielectric material, a sufficient voltage cannot be applied to the piezoelectric layer itself. On the other hand, according to the piezoelectric element 1 according to this embodiment, since the buffer layer 5 has conductivity, a sufficient voltage can be applied to the piezoelectric layer 6 itself.

The piezoelectric constant (d ₃₁ ) of the piezoelectric layer 6 according to this embodiment can be, for example, 400 pC / N or more in absolute value. For example, when the applied voltage is 100 kV / cm, the leakage current of the piezoelectric element 1 according to the present embodiment can be less than 10 ⁻⁵ A / cm ² . Repeated durability of the piezoelectric element 1 according to this embodiment, the applied voltage is at 300 kV / cm, it is possible to ensure 10 ⁹ times.

1-4. Experimental Example Based on the above-described method for manufacturing a piezoelectric element, the piezoelectric element 1 was manufactured as follows.

  First, the lower electrode 4 made of platinum (Pt) with (111) orientation was formed on the substrate 2 through the elastic film 3 by sputtering. The film thickness of the lower electrode 4 was 100 nm. The power during sputtering was 200 W.

Next, a buffer layer 5 made of Bi ₄ (Ti _0.90 Ni _0.10 ) ₃ O ₁₂ (hereinafter also referred to as “BTNO”) was formed on the lower electrode 4.

  First, metal reagents such as bismuth 2-ethylhexanoate, titanium isopropoxide, and nickel acetylacetonate were prepared. Next, these were mixed so as to have a molar ratio corresponding to BTNO to be formed, and dissolved (dispersed) in butoxyethanol. In this way, a precursor solution of BTNO was prepared.

  Next, the precursor solution was applied onto the lower electrode 4 by spin coating (precursor solution application step). Next, heat treatment (drying treatment) was performed at a temperature about 10 ° C. higher than the boiling point of the solvent (in the case of butoxyethanol, about 171 ° C.), and the solvent was removed and gelled (dry heat treatment step). Next, heat treatment was performed at about 350 ° C. to decompose / remove organic components other than the solvent remaining in the film (degreasing heat treatment step) to form an amorphous film. Next, rapid thermal annealing (RTA) was performed at about 600 ° C. in an oxygen atmosphere for crystallization. Thus, the buffer layer 5 was formed. The film thickness of the buffer layer 5 was 20 nm.

Next, a piezoelectric layer 6 made of 0.70 Pb (Mg _1/3 Nb _2/3 ) O ₃ -0.30 PbTiO ₃ (hereinafter also referred to as “PMN-PT”) was formed on the buffer layer 5. .

  First, metal reagents such as lead acetate, titanium isopropoxide, magnesium acetate, and niobium ethoxide were prepared. Next, while mixing these so that it might become a molar ratio corresponding to PMN-PT to form, these were melt | dissolved (dispersed) in the butyl cellosolve. Furthermore, diethanolamine was added as a stabilizer for this solution. Thus, the precursor solution of PMN-PT was produced.

  Next, the precursor solution was applied onto the buffer layer 5 by spin coating (precursor solution application step). Next, heat treatment (drying treatment) was performed at a temperature about 10 ° C. higher than the boiling point of the solvent (in the case of butyl cellosolve, about 170 ° C.), and the solvent was removed and gelled (dry heat treatment step). Next, heat treatment was performed at about 350 ° C. to decompose / remove organic components other than the solvent remaining in the film (degreasing heat treatment step) to form an amorphous film. Next, rapid thermal annealing (RTA) was performed at about 600 ° C. in an oxygen atmosphere for crystallization. In this way, the piezoelectric layer 6 was formed. The film thickness of the piezoelectric layer 6 was 500 nm.

  Next, the upper electrode 7 made of platinum (Pt) was formed on the piezoelectric layer 6 by sputtering, and the piezoelectric element 1 was obtained.

  The piezoelectric element 1 obtained in this way was analyzed especially by the X-ray diffraction (XRD) method of the piezoelectric layer 6. The piezoelectric layer 6 had a rhombohedral structure at room temperature, and had a pseudo cubic structure ( (001) was confirmed to be preferentially oriented.

Further, when the piezoelectric constant (d ₃₁ ) of the piezoelectric layer 6 was measured, it was 400 pC / N in absolute value. Moreover, the leakage current was less than 10 ⁻⁵ A / cm ² at 100 kV / cm. Furthermore, when the repeated durability of the piezoelectric element 1 when 300 kV / cm was applied was examined, the piezoelectric element 1 had a durability capable of guaranteeing 1 × 10 ⁹ times.

In addition, when the piezoelectric body layer 6 was produced using the material shown in the following Table 1 and the piezoelectric constant (d ₃₁ ) was examined, all showed high piezoelectric characteristics where d ₃₁ was 400 pC / N or more in absolute value. . As the buffer layer 5, SrBi ₂ (Ta _0.70 Ni _0.30 ) ₂ O ₉ was used. The Table 1 shows the absolute value of d _31. The piezoelectric constant (d ₃₁ ) was measured as follows.

First, the displacement S1 of the piezoelectric layer 6 at the time of voltage application in the actual ink jet recording head 50 (see FIG. 9) is measured using a laser displacement meter. By comparing this value S1 with the displacement amount S2 obtained by the piezoelectric displacement simulation by the finite element method, the actual piezoelectric constant (d ₃₁ ) of the piezoelectric layer 6 and the piezoelectric body assumed by the finite element method are used. The difference from the piezoelectric constant (d ′ ₃₁ ) of the layer 6 can be obtained. As a result, the piezoelectric constant (d ₃₁ ) of the piezoelectric layer 6 can be measured. The physical quantities required for the simulation of piezoelectric displacement by the finite element method are the Young's modulus of each film, the film stress, and the assumed piezoelectric constant (d ′ ₃₁ ) of the piezoelectric layer 6.

2. Second embodiment 2-1. Inkjet Recording Head Next, an embodiment of an inkjet recording head having the piezoelectric element 1 according to the first embodiment will be described. FIG. 9 is a side sectional view showing a schematic configuration of the ink jet recording head according to the present embodiment, and FIG. 10 is an exploded perspective view of the ink jet recording head. In addition, FIG. 10 is shown upside down from the state normally used.

  As shown in FIG. 9, the ink jet recording head (hereinafter also referred to as “head”) 50 includes a head main body 57 and a piezoelectric portion 54 provided on the head main body 57. 9 corresponds to the elastic film 3, the lower electrode 4, the buffer layer 5, the piezoelectric layer 6, and the upper electrode 7 in the piezoelectric element 1 shown in FIG. In the ink jet recording head according to the present embodiment, the piezoelectric element 1 can function as a piezoelectric actuator. A piezoelectric actuator is an element having a function of moving a certain substance.

  Further, the elastic film 3 in the piezoelectric element 1 shown in FIG. 1 corresponds to the elastic film 55 in FIG. The substrate 2 (see FIG. 1) constitutes a main part of the head main body 57.

  That is, the head 50 includes a nozzle plate 51, an ink chamber substrate 52, an elastic film 55, and a piezoelectric part (vibration source) 54 bonded to the elastic film 55, as shown in FIG. 56 is housed. The head 50 constitutes an on-demand piezo jet head.

  The nozzle plate 51 is composed of, for example, a stainless steel rolling plate or the like, and has a large number of nozzles 511 for ejecting ink droplets formed in a line. The pitch between these nozzles 511 is appropriately set according to the printing accuracy.

  An ink chamber substrate 52 is fixed (fixed) to the nozzle plate 51. The ink chamber substrate 52 is formed by the substrate 2 (see FIG. 1). The ink chamber substrate 52 has a plurality of cavities (ink cavities) 521, a reservoir 523, and a supply port 524 formed by a nozzle plate 51, side walls (partition walls) 522, and an elastic film 55. . The reservoir 523 temporarily stores ink supplied from the ink cartridge 631 (see FIG. 13). Ink is supplied from the reservoir 523 to each cavity 521 through the supply port 524.

  As shown in FIGS. 9 and 10, the cavity 521 is disposed corresponding to each nozzle 511. The cavities 521 each have a variable volume due to the vibration of the elastic film 55. The cavity 521 is configured to eject ink by this volume change.

  As a base material for obtaining the ink chamber substrate 52, that is, the substrate 2 (see FIG. 1), a (110) -oriented silicon single crystal substrate is used. Since this (110) -oriented silicon single crystal substrate is suitable for anisotropic etching, the ink chamber substrate 52 can be formed easily and reliably. Such a silicon single crystal substrate is used such that the formation surface of the elastic film 3 shown in FIG. 1, that is, the formation surface of the elastic film 55 is the (110) surface.

  An elastic film 55 is disposed on the side of the ink chamber substrate 52 opposite to the nozzle plate 51. Further, a plurality of piezoelectric portions 54 are provided on the side of the elastic film 55 opposite to the ink chamber substrate 52. The elastic film 55 is formed by the elastic film 3 in the piezoelectric element 1 shown in FIG. 1 as described above. As shown in FIG. 10, a communication hole 531 is formed at a predetermined position of the elastic film 55 so as to penetrate in the thickness direction of the elastic film 55. Ink is supplied from the ink cartridge 631 to the reservoir 523 through the communication hole 531.

  Each piezoelectric portion 54 is electrically connected to a piezoelectric element driving circuit described later, and is configured to operate (vibrate, deform) based on a signal from the piezoelectric element driving circuit. That is, each piezoelectric part 54 functions as a vibration source (head actuator). The elastic film 55 vibrates (deflection) due to vibration (deflection) of the piezoelectric portion 54 and functions to instantaneously increase the internal pressure of the cavity 521.

  The base 56 is made of, for example, various resin materials, various metal materials, or the like. As shown in FIG. 10, the ink chamber substrate 52 is fixed and supported on the base body 56.

2-2. Operation of Inkjet Recording Head Next, the operation of the inkjet recording head 50 in this embodiment will be described. In the head 50 in this embodiment, a predetermined ejection signal is not input via the piezoelectric element driving circuit, that is, a state where no voltage is applied between the lower electrode 4 and the upper electrode 7 of the piezoelectric portion 54. Then, as shown in FIG. 11, the piezoelectric layer 6 is not deformed. For this reason, the elastic film 55 is not deformed and the volume of the cavity 521 is not changed. Accordingly, no ink droplet is ejected from the nozzle 511.

  On the other hand, in a state where a predetermined ejection signal is input via the piezoelectric element driving circuit, that is, in a state where a voltage is applied between the lower electrode 4 and the upper electrode 7 of the piezoelectric portion 54, as shown in FIG. In the piezoelectric layer 6, bending deformation occurs in the minor axis direction (the direction of the arrow s shown in FIG. 12). As a result, the elastic film 55 bends and the volume of the cavity 521 changes. At this time, the pressure in the cavity 521 increases instantaneously, and the ink droplet 58 is ejected from the nozzle 511.

  That is, when a voltage is applied, the crystal lattice of the piezoelectric layer 6 is stretched in the direction perpendicular to the plane direction (the direction of the arrow d shown in FIG. 12), but is simultaneously compressed in the plane direction. In this state, the tensile stress f is in-plane for the piezoelectric layer 6. Therefore, the elastic film 55 is deflected and bent by the tensile stress f. The greater the amount of displacement (absolute value) of the piezoelectric layer 6 in the minor axis direction of the cavity 521, the greater the amount of deflection of the elastic film 55, making it possible to eject ink droplets more efficiently. .

  When the ejection of one ink is completed, the piezoelectric element driving circuit stops applying the voltage between the lower electrode 4 and the upper electrode 7. Thereby, the piezoelectric part 54 returns to the original shape shown in FIG. 11, and the volume of the cavity 521 increases. At this time, pressure (pressure in the positive direction) from the ink cartridge 631 toward the nozzle 511 acts on the ink. For this reason, air is prevented from entering the cavity 521 from the nozzle 511, and an amount of ink corresponding to the ink ejection amount is supplied from the ink cartridge 631 to the cavity 521 through the reservoir 523.

  In this way, arbitrary (desired) characters and figures are printed by sequentially inputting ejection signals via the piezoelectric element driving circuit to the piezoelectric unit 54 at the position where ink droplets are to be ejected. be able to.

2-3. Method for Manufacturing Inkjet Recording Head Next, an example of a method for manufacturing the inkjet recording head 50 in the present embodiment will be described.

  First, a base material to be an ink chamber substrate 52, that is, a substrate 2 made of a (110) oriented silicon single crystal substrate is prepared. Next, as shown in FIGS. 1 and 5 to 8, the elastic film 3, the lower electrode 4, the buffer layer 5, the piezoelectric layer 6, and the upper electrode 7 are sequentially formed on the substrate 2. The elastic film 3 formed here becomes the elastic film 55 as described above.

  Next, the upper electrode 7, the piezoelectric layer 6, the buffer layer 5, and the lower electrode 4 are patterned to correspond to the individual cavities 521, as shown in FIGS. 11 and 12, and as shown in FIG. The number of piezoelectric portions 54 corresponding to the number of cavities 521 is formed.

  Next, the base material (substrate 2) to be the ink chamber substrate 52 is patterned, and concave portions to be the cavities 521 are respectively provided at positions corresponding to the piezoelectric portions 54, and concave portions to be the reservoir 523 and the supply port 524 at predetermined positions. Form.

  In the present embodiment, since a (110) -oriented silicon substrate is used as the base material (substrate 2), wet etching (anisotropic etching) using a high-concentration alkaline aqueous solution is suitably employed. In wet etching with a high-concentration alkaline aqueous solution, the elastic film 3 can function as an etching stopper as described above. Therefore, the ink chamber substrate 52 can be formed more easily.

  In this manner, the ink chamber substrate 52 is formed by removing the base material (substrate 2) by etching until the elastic film 55 is exposed in the thickness direction. At this time, a portion left without being etched becomes the side wall 522. The exposed elastic film 55 is in a state where it can function as an elastic film.

  Next, the nozzle plate 51 on which the plurality of nozzles 511 are formed is aligned so that each nozzle 511 corresponds to a concave portion that becomes each cavity 521, and bonded in that state. Thereby, a plurality of cavities 521, a reservoir 523, and a plurality of supply ports 524 are formed. For the joining of the nozzle plate 51, for example, an adhesive method using an adhesive or a fusion method may be used. Next, the ink chamber substrate 52 is attached to the base 56.

  The ink jet recording head 50 according to this embodiment can be manufactured through the above steps.

2-4. Action / Effect According to the ink jet recording head 50 according to the present embodiment, as described above, the piezoelectric constant (d ₃₁ ) of the piezoelectric layer 6 of the piezoelectric portion 54 is high, and the deformation is larger than the applied voltage. It is what constitutes. That is, the piezoelectric portion 54 has good piezoelectric characteristics. Thereby, the amount of deflection of the elastic film 55 is increased, and ink droplets can be ejected more efficiently. Here, “efficient” means that the same amount of ink droplets can be ejected with a smaller voltage. That is, the driver circuit can be simplified and the power consumption can be reduced at the same time, so that the pitch of the nozzles 511 can be formed at a higher density. Therefore, high-density printing and high-speed printing are possible. Furthermore, since the length of the long axis of the cavity 521 can be shortened, the entire head can be reduced in size.

3. Third Embodiment 3-1. Inkjet Printer Next, an embodiment of an inkjet printer having the inkjet recording head 50 according to the second embodiment will be described. FIG. 13 is a schematic configuration diagram illustrating an inkjet printer 600 according to the present embodiment. The ink jet printer 600 can function as a printer that can print on paper or the like. In the following description, the upper side in FIG. 13 is referred to as “upper part” and the lower side is referred to as “lower part”.

  The ink jet printer 600 has an apparatus main body 620, a tray 621 for installing the recording paper P in the upper rear, a discharge port 622 for discharging the recording paper P in the lower front, and an operation panel 670 on the upper surface. Have.

  Inside the apparatus main body 620, there are mainly a printing apparatus 640 having a reciprocating head unit 630, a paper feeding apparatus 650 for feeding the recording paper P one by one to the printing apparatus 640, the printing apparatus 640 and the paper feeding apparatus 650. And a control unit 660 for controlling.

  The printing apparatus 640 includes a head unit 630, a carriage motor 641 serving as a driving source for the head unit 630, and a reciprocating mechanism 642 that receives the rotation of the carriage motor 641 to reciprocate the head unit 630.

  The head unit 630 includes an ink jet recording head 50 having a large number of the nozzles 511 described above, an ink cartridge 631 that supplies ink to the ink jet recording head 50, and the ink jet recording head 50 and the ink cartridge 631. And a carriage 632 mounted thereon.

  The reciprocating mechanism 642 includes a carriage guide shaft 643 whose both ends are supported by a frame (not shown), and a timing belt 644 extending in parallel with the carriage guide shaft 643. The carriage 632 is supported by the carriage guide shaft 643 so as to reciprocate and is fixed to a part of the timing belt 644. When the timing belt 644 travels forward and backward through a pulley by the operation of the carriage motor 641, the head unit 630 reciprocates while being guided by the carriage guide shaft 643. During this reciprocation, ink is appropriately discharged from the ink jet recording head 50 and printing on the recording paper P is performed.

  The sheet feeding device 650 includes a sheet feeding motor 651 serving as a driving source thereof, and a sheet feeding roller 652 that rotates by the operation of the sheet feeding motor 651. The paper feed roller 652 includes a driven roller 652 a and a drive roller 652 b that are opposed to each other across the feeding path (recording paper P) of the recording paper P, and the driving roller 652 b is connected to the paper feeding motor 651. Has been.

3-2. Action / Effect According to the ink jet printer 600 according to the present embodiment, as described above, since the ink jet recording head 50 having high performance and high nozzle density is provided, high density printing and high speed printing are possible. .

  The ink jet printer 600 of the present invention can also be used as a droplet discharge device used industrially. In that case, as the ink to be ejected (liquid material), various functional materials can be used by adjusting them to an appropriate viscosity with a solvent or a dispersion medium.

4). Fourth embodiment 4-1. Next, an embodiment of a piezoelectric pump having the piezoelectric element 1 according to the first embodiment will be described with reference to the drawings. 14 and 15 are schematic cross-sectional views of the piezoelectric pump 20 according to the present embodiment. In the piezoelectric pump 20 according to the present embodiment, the piezoelectric element can function as a piezoelectric actuator. 14 and 15 includes the lower electrode 4, the buffer layer 5, the piezoelectric layer 6, and the upper electrode 7 in the piezoelectric element 1 shown in FIG. 1, and is shown in FIG. The elastic film 3 in the piezoelectric element 1 is a diaphragm 24 in FIGS. 14 and 15. The substrate 2 (see FIG. 1) serves as a base 21 that constitutes a main part of the piezoelectric pump 20. The piezoelectric pump 20 includes a base 21, a piezoelectric unit 22, a pump chamber 23, a diaphragm 24, a suction side check valve 26a, a discharge side check valve 26b, a suction port 28a, and a discharge port 28b. Including.

4-2. Next, the operation of the above-described piezoelectric pump will be described. First, when a voltage is supplied to the piezoelectric portion 22, the voltage is applied in the film thickness direction of the piezoelectric layer 6 (see FIG. 1). And as shown in FIG. 14, the piezoelectric part 22 bends in the direction (direction of arrow a shown in FIG. 14) where the pump chamber 23 spreads. Further, the diaphragm 24 together with the piezoelectric portion 22 bends in the direction in which the pump chamber 23 expands. For this reason, the pressure in the pump chamber 23 changes, and the fluid flows from the suction port 28a into the pump chamber 23 by the action of the check valves 26a and 26b (in the direction of arrow b shown in FIG. 14).

  Next, when the supply of voltage to the piezoelectric portion 22 is stopped, the application of voltage in the film thickness direction of the piezoelectric layer 6 (see FIG. 1) is stopped. And as shown in FIG. 15, the piezoelectric part 22 bends in the direction (direction of arrow a shown in FIG. 15) where the pump chamber 23 narrows. Further, the diaphragm 24 together with the piezoelectric portion 22 bends in the direction in which the pump chamber 23 narrows. For this reason, the pressure in the pump chamber 23 changes, and the fluid is discharged from the discharge port 28b to the outside by the action of the check valves 26a and 26b (in the direction of arrow b shown in FIG. 15).

  The piezoelectric pump 20 can be used as a water cooling module for electronic equipment, for example, a personal computer, preferably a notebook personal computer. The water cooling module uses the above-described piezoelectric pump 20 for driving the coolant, and has a structure including the piezoelectric pump 20 and a circulating water channel.

4-3. Action / Effect According to the piezoelectric pump 20 according to the present embodiment, as described above, the piezoelectric layer 6 of the piezoelectric portion 22 has good piezoelectric characteristics, so that fluid can be sucked and discharged efficiently. it can. Therefore, the piezoelectric pump 20 according to this embodiment can have a large discharge pressure and discharge amount. In addition, the piezoelectric pump 20 can be operated at high speed. Furthermore, the overall size of the piezoelectric pump 20 can be reduced.

5. Fifth embodiment 5-1. Surface Acoustic Wave Element Next, an example of a surface acoustic wave element according to a fifth embodiment to which the present invention is applied will be described with reference to the drawings. As shown in FIG. 16, the surface acoustic wave device 30 as an example of this embodiment includes a substrate 11, a conductive layer 12, a buffer layer 13, a piezoelectric layer 14, a protective layer 15, an electrode 16, including. The substrate 11, the conductive layer 12, the buffer layer 13, the piezoelectric layer 14, and the protective layer 15 constitute a base 18.

As the substrate 11, for example, a (100) single crystal silicon substrate can be used. As the conductive layer 12, for example, a thin film such as IrO ₂ or TiO ₂ can be used. The buffer layer 13 can be composed of the buffer layer 5 in the piezoelectric element 1 shown in FIG. The piezoelectric layer 14 can be composed of the piezoelectric layer 6 in the piezoelectric element 1 shown in FIG. The protective layer 15 can be made of, for example, an oxide or a nitride. As the electrode 16, for example, a thin film such as aluminum can be used. The electrode 16 is an inter-digital type electrode (Inter-Digital Transducer: hereinafter referred to as “IDT electrode”). When viewed from the top, the electrode 16 has a shape such as interdigital electrodes 141, 142, 151, 152, and 153 shown in FIGS.

5-2. Action / Effect According to the surface acoustic wave element 30 according to the present embodiment, the piezoelectric layer 14 formed of the piezoelectric layer 6 in the piezoelectric element 1 shown in FIG. The wave element 30 itself has high performance.

6). Sixth Embodiment 6-1. Frequency Filter Next, an example of a frequency filter according to a sixth embodiment to which the present invention is applied will be described with reference to the drawings. FIG. 17 is a diagram schematically illustrating a frequency filter that is an example of the present embodiment.

  As shown in FIG. 17, the frequency filter has a base 140. As the substrate 140, the substrate 18 of the surface acoustic wave device 30 shown in FIG. 16 can be used.

  IDT electrodes 141 and 142 are formed on the upper surface of the substrate 140. Further, sound absorbing portions 143 and 144 are formed on the upper surface of the base 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 base 140. A high frequency signal source 145 is connected to the IDT electrode 141 formed on the base 140, and a signal line is connected to the IDT electrode 142.

6-2. Operation of Frequency Filter Next, the operation of the above frequency filter will be described. In the above configuration, when a high frequency signal is output from the high frequency signal source 145, the high frequency signal is applied to the IDT electrode 141, thereby generating a surface acoustic wave on the upper surface of the substrate 140. The surface acoustic wave propagated from the IDT electrode 141 to the sound absorbing portion 143 side is absorbed by the sound absorbing portion 143. Of the surface acoustic waves propagated to the IDT electrode 142 side, the specific surface acoustic wave is determined according to the pitch of the IDT electrode 142 or the like. A surface acoustic wave having a frequency or a frequency in a specific band is converted into an electric signal and taken out to terminals 146a and 146b through signal lines. Note that most of the frequency components other than the specific frequency or the frequency in the specific band pass through the IDT electrode 142 and are absorbed by the sound absorbing unit 144. In this way, it is possible to obtain (filter) only a surface acoustic wave having a specific frequency or a specific band of the electric signal supplied to the IDT electrode 141 included in the frequency filter of the present embodiment.

7). Seventh Embodiment 7-1. Oscillator Next, an example of an oscillator according to a seventh embodiment to which the present invention is applied will be described with reference to the drawings. FIG. 18 is a diagram schematically illustrating an oscillator which is an example of the present embodiment.

  As shown in FIG. 18, the oscillator has a base 150. As the base 150, the base 18 of the surface acoustic wave device 30 shown in FIG. 16 can be used as in the frequency filter described above.

  An IDT electrode 151 is formed on the upper surface of the substrate 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.

7-2. Next, the operation of the above-described oscillator will be described. In the above configuration, when a high-frequency signal is output from the high-frequency signal source 154, this high-frequency signal is applied to one comb-like electrode 151a of the IDT electrode 151, and thereby propagates to the IDT electrode 152 side on the upper surface of the base 150. The surface acoustic wave that propagates to the IDT electrode 153 side is generated. Among these surface acoustic waves, the surface acoustic wave having a specific frequency component is reflected by the IDT electrode 152 and the IDT electrode 153, and a standing wave is generated between the IDT electrode 152 and the IDT electrode 153. The surface acoustic wave having the specific frequency component is repeatedly reflected by the IDT electrodes 152 and 153, whereby the specific frequency component or the frequency component in the specific band resonates and the amplitude increases. A part of the surface acoustic wave of the specific frequency component or the frequency component of the specific band is extracted from the other comb-shaped electrode 151b of the IDT electrode 151, and corresponds to the resonance frequency of the IDT electrode 152 and the IDT electrode 153. An electric signal having a frequency (or a frequency having a certain band) can be taken out to the terminals 155a and 155b.

7-3. Voltage Control SAW Oscillator FIGS. 19 and 20 are diagrams schematically showing an example in which the above-described oscillator is applied to a VCSO (Voltage Controlled SAW Oscillator), and FIG. 19 is a side perspective view. FIG. 20 is a top perspective view.

  The VCSO is configured to be mounted inside a metal (Al or stainless steel) housing 60. On the substrate 61, an IC (Integrated Circuit) 62 and an oscillator 63 are mounted. In this case, the IC 62 is an oscillation circuit that controls the frequency applied to the oscillator 63 in accordance with a voltage value input from an external circuit (not shown).

  In the oscillator 63, IDT electrodes 65a to 65c are formed on a base 64, and the configuration thereof is substantially the same as that of the oscillator shown in FIG. As the base 64, the base 18 of the surface acoustic wave device 30 shown in FIG. 16 can be used, similarly to the oscillator shown in FIG. 18 described above.

  A wiring 66 for electrically connecting the IC 62 and the oscillator 63 is patterned on the substrate 61. The IC 62 and the wiring 66 are connected by a wire line 67 such as a gold wire, for example, and the oscillator 63 and the wiring 66 are connected by a wire line 68 such as a gold wire. As a result, the IC 62 and the oscillator 63 are electrically connected via the wiring 66.

  The VCSO can also be formed by integrating the IC 62 and the oscillator 63 on the same substrate. FIG. 21 shows a schematic diagram of a VCSO in which an IC 62 and an oscillator 63 are integrated on the same substrate 61. In FIG. 21, the oscillator 63 has a structure in which the formation of the conductive layer 12 is omitted in the surface acoustic wave device 30 shown in FIG.

  As shown in FIG. 21, the VCSO is formed by sharing the substrate 61 in the IC 62 and the oscillator 63. As the substrate 61, for example, the substrate 11 of the surface acoustic wave device 30 shown in FIG. 16 can be used. Although not shown, the IC 62 and the electrode 65a of the oscillator 63 are electrically connected. As the electrode 65a, for example, the electrode 16 of the surface acoustic wave element 30 shown in FIG. 16 can be used. As a transistor constituting the IC 62, a TFT (Thin Film Transistor) can be adopted.

  19 to 21 is used as, for example, a VCO (Voltage Controlled Oscillator) of the PLL circuit shown in FIG. Here, the PLL circuit will be briefly described.

  FIG. 22 is a block diagram showing a basic configuration of the PLL circuit. The PLL circuit includes a phase comparator 71, a low-pass filter 72, an amplifier 73, and a VCO 74. The phase comparator 71 compares the phase (or frequency) of the signal input from the input terminal 70 with the phase (or frequency) of the signal output from the VCO 74, and an error whose value is set according to the difference. A voltage signal is output. The low pass filter 72 passes only the low frequency component at the position of the error voltage signal output from the phase comparator 71. The amplifier 73 amplifies the signal output from the low-pass filter 72. The VCO 74 is an oscillation circuit in which the frequency that oscillates according to the input voltage value changes continuously within a certain range.

  Under such a configuration, the PLL circuit operates so that the difference between the phase (or frequency) input from the input terminal 70 and the phase (or frequency) of the signal output from the VCO 74 is reduced. Is synchronized with the frequency of the signal input from the input terminal 70. When the frequency of the signal output from the VCO 74 is synchronized with the frequency of the signal input from the input terminal 70, the frequency thereafter matches the signal input from the input terminal 70 except for a certain phase difference, and the input signal changes. A signal that follows the signal is output.

8). Eighth Embodiment Next, an example of an electronic circuit and an electronic apparatus according to an eighth embodiment to which the present invention is applied will be described with reference to the drawings. FIG. 23 is a block diagram illustrating an electrical configuration of an electronic device 300 that is an example of the present embodiment. The electronic device 300 is, for example, a mobile phone.

  An electronic device 300 illustrated in FIG. 23 includes an electronic circuit 310, a transmission unit 80, a reception unit 91, an input unit 94, a display unit 95, and an antenna unit 86. The electronic circuit 310 includes a transmission signal processing circuit 81, a transmission mixer 82, a transmission filter 83, a transmission power amplifier 84, a transmission / reception duplexer 85, a low noise amplifier 87, a reception filter 88, a reception mixer 89, a reception signal processing circuit 90, and a frequency. It has a synthesizer 92 and a control circuit 93.

  In the electronic circuit 310, the frequency filter shown in FIG. 17 can be used as the transmission filter 83 and the reception filter 88. The frequency to be filtered (frequency to be passed) is individually determined by the transmission filter 83 and the reception filter 88 according to the frequency required from the signal output from the transmission mixer 82 and the frequency required by the reception mixer 89. It is set. Further, as the VCO 74 of the PLL circuit (see FIG. 22) provided in the frequency synthesizer 92, the oscillator shown in FIG. 18 or the VCSO shown in FIGS. 19 to 21 can be used.

  The transmitter 80 is realized by, for example, a microphone that converts a sound wave signal into an electric signal. The transmission signal processing circuit 81 is a circuit that performs processing such as D / A conversion processing and modulation processing on the electrical signal output from the transmitter 80. The transmission mixer 82 mixes the signal output from the transmission signal processing circuit 81 using the signal output from the frequency synthesizer 92. The transmission filter 83 passes only a signal having a frequency that requires an intermediate frequency (hereinafter referred to as “IF”) and cuts a signal having an unnecessary frequency. A signal output from the transmission filter 83 is converted into an RF signal by a conversion circuit (not shown). The transmission power amplifier 84 amplifies the power of the RF signal output from the transmission filter 83 and outputs it to the transmission / reception duplexer 85.

  The transmitter / receiver demultiplexer 85 outputs the RF signal output from the transmission power amplifier 84 to the antenna unit 86 and transmits the RF signal from the antenna unit 86 in the form of a radio wave. The transmitter / receiver demultiplexer 85 demultiplexes the received signal received by the antenna unit 86 and outputs the demultiplexed signal to the low noise amplifier 87. The low noise amplifier 87 amplifies the received signal from the transmitter / receiver demultiplexer 85. The signal output from the low noise amplifier 87 is converted into IF by a conversion circuit (not shown).

  The reception filter 88 passes only a signal having a frequency necessary for IF converted by a conversion circuit (not shown), and cuts a signal having an unnecessary frequency. The reception mixer 89 uses the signal output from the frequency synthesizer 92 to mix the signal output from the reception filter 88. The reception signal processing circuit 90 is a circuit that performs processing such as A / D conversion processing and demodulation processing on the signal output from the reception mixer 89. The receiver 91 is realized by, for example, a small speaker that converts an electric signal into a sound wave.

  The frequency synthesizer 92 is a circuit that generates a signal to be supplied to the transmission mixer 82 and a signal to be supplied to the reception mixer 89. The frequency synthesizer 92 has a PLL circuit, and can divide a signal output from the PLL circuit to generate a new signal. The control circuit 93 controls the transmission signal processing circuit 81, the reception signal processing circuit 90, the frequency synthesizer 92, the input unit 94, and the display unit 95. For example, the display unit 95 displays the state of the device to the user of the mobile phone. The input unit 94 inputs an instruction from a user of a mobile phone, for example.

  In the above-described example, a mobile phone is used as the electronic device, and an electronic circuit provided in the mobile phone is used as the electronic circuit, and the present invention is not limited to the mobile phone. The present invention can be applied to a body communication device and an electronic circuit provided therein.

  Furthermore, the present invention can be applied not only to mobile communication devices but also to communication devices used in a stationary state such as tuners that receive BS and CS broadcasts, and electronic circuits provided therein. Furthermore, not only communication devices that use radio waves propagating in the air as communication carriers, but also electronic devices such as HUBs that use high-frequency signals propagating in coaxial cables or optical signals propagating in optical cables, and the electronics provided therein It can also be applied to circuits.

9. Ninth Embodiment Next, an example of a thin film piezoelectric resonator according to a ninth embodiment to which the present invention is applied will be described with reference to the drawings.

9-1. First Thin Film Piezoelectric Resonator FIG. 24 is a diagram schematically showing a first thin film piezoelectric resonator 700 which is an example of this embodiment. A thin film piezoelectric resonator 700 shown in FIG. 24 is a diaphragm type thin film piezoelectric resonator 700.

  The first thin film piezoelectric resonator 700 includes a substrate 701, an elastic film 703, a lower electrode 704, a buffer layer 705, a piezoelectric layer 706, and an upper electrode 707. The substrate 701, the elastic film 703, the lower electrode 704, the buffer layer 705, the piezoelectric layer 706, and the upper electrode 707 in the thin film piezoelectric resonator 700 are the substrate 2, the elastic film 3, and the lower part in the piezoelectric element 1 shown in FIG. This corresponds to the electrode 4, the buffer layer 5, the piezoelectric layer 6, and the upper electrode 7. That is, the first thin film piezoelectric resonator 700 has the piezoelectric element 1 shown in FIG.

  A via hole 702 that penetrates the substrate 701 is formed in the substrate 701. A wiring 708 is provided on the upper electrode 707. The wiring 708 is electrically connected to an electrode 709 formed on the elastic film 703 via a pad 710.

9-2. Action / Effect According to the first thin film piezoelectric resonator 700 according to this embodiment, the piezoelectric layer 706 has good piezoelectric characteristics, and thus has a high electromechanical coupling coefficient. Thereby, the thin film piezoelectric resonator 700 can be used in a high frequency region. Further, the thin film piezoelectric resonator 700 can be reduced in size (thinned) and can be operated satisfactorily.

9-3. Second Thin Film Piezoelectric Resonator FIG. 25 is a diagram schematically showing a second thin film piezoelectric resonator 800 which is an example of this embodiment. The second thin film piezoelectric resonator 800 is mainly different from the first thin film piezoelectric resonator 700 shown in FIG. 24 in that an air gap 802 is formed between the substrate 801 and the elastic film 803 without forming a via hole. In the point.

  The second thin film piezoelectric resonator 800 includes a substrate 801, an elastic film 803, a lower electrode 804, a buffer layer 805, a piezoelectric layer 806, and an upper electrode 807. The substrate 801, the elastic film 803, the lower electrode 804, the buffer layer 805, the piezoelectric layer 806, and the upper electrode 807 in the thin film piezoelectric resonator 800 are respectively the substrate 2, the elastic film 3, and the lower electrode in the piezoelectric element 1 shown in FIG. 4 corresponds to the buffer layer 5, the piezoelectric layer 6, and the upper electrode 7. That is, the second thin film piezoelectric resonator 800 has the piezoelectric element 1 shown in FIG. The air gap 802 is a space formed between the substrate 801 and the elastic film 803.

9-4. Action / Effect According to the second thin film piezoelectric resonator 800 according to the present embodiment, the piezoelectric layer 806 has good piezoelectric characteristics and thus has a high electromechanical coupling coefficient. Thereby, the thin film piezoelectric resonator 800 can be used in a high frequency region. Further, the thin film piezoelectric resonator 800 can be reduced in size (thinned) and can be operated satisfactorily.

9-5. Application Example The piezoelectric thin film 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. For example, in the electronic circuit 310 shown in FIG. 23, as the transmission filter 83 and the reception filter 88, the piezoelectric thin film resonator according to the present embodiment functioning as a frequency filter can be used. In addition, as the oscillator included in the frequency synthesizer 92, the piezoelectric thin film resonator according to the present embodiment functioning as an oscillator can be used.

  Although the embodiments of the present invention have been described in detail as described above, those skilled in the art will readily understand that many variations are possible without substantially departing from the novel matters and effects of the present invention. . Accordingly, all such modifications are intended to be included in the scope of the present invention. For example, the piezoelectric element according to the present invention is applicable not only to the above-described device but also to various devices.

Sectional drawing which shows the piezoelectric element which concerns on 1st Embodiment. The figure which shows the relative value of d orbital level of the transition metal atom with respect to 2p orbital level of oxygen. The graph for demonstrating a relaxor material. The graph for demonstrating a relaxor material. FIG. 5 is a manufacturing process diagram of the piezoelectric element according to the first embodiment. FIG. 5 is a manufacturing process diagram of the piezoelectric element according to the first embodiment. FIG. 5 is a manufacturing process diagram of the piezoelectric element according to the first embodiment. FIG. 5 is a manufacturing process diagram of the piezoelectric element according to the first embodiment. FIG. 5 is a schematic configuration diagram of an ink jet recording head according to a second embodiment. FIG. 6 is an exploded perspective view of an ink jet recording head according to a second embodiment. FIG. 4 is a diagram for explaining the operation of an ink jet recording head. FIG. 4 is a diagram for explaining the operation of an ink jet recording head. FIG. 9 is a schematic configuration diagram of an ink jet printer according to a third embodiment. The schematic sectional drawing of the piezoelectric pump which concerns on 4th Embodiment. The schematic sectional drawing of the piezoelectric pump which concerns on 4th Embodiment. FIG. 10 is a side sectional view showing a surface acoustic wave device according to a fifth embodiment. The perspective view which shows the frequency filter which concerns on 6th Embodiment. The perspective view which shows the oscillator which concerns on 7th Embodiment. Schematic which shows an example which applied the oscillator concerning 7th Embodiment to VCSO. Schematic which shows an example which applied the oscillator concerning 7th Embodiment to VCSO. Schematic which shows an example which applied the oscillator concerning 7th Embodiment to VCSO. The block diagram which shows the basic composition of a PLL circuit. The block diagram which shows the structure of the electronic circuit which concerns on 8th Embodiment. FIG. 10 is a side sectional view showing a thin film piezoelectric resonator according to a ninth embodiment. FIG. 10 is a side sectional view showing a thin film piezoelectric resonator according to a ninth embodiment.

Explanation of symbols

1 piezoelectric element, 2 substrate, 3 elastic film, 4 lower electrode, 5 buffer layer, 6 piezoelectric layer, 7 upper electrode, 11 substrate, 12 conductive layer, 13 buffer layer, 14 piezoelectric layer, 15 protective layer, 16 electrode , 18 substrate, 20 piezoelectric pump, 21 substrate, 22 piezoelectric section, 23 pump chamber, 24 diaphragm, 30 surface acoustic wave element, 50 inkjet recording head, 51 nozzle plate, 52 ink chamber substrate, 54 piezoelectric section, 55 elasticity Membrane, 56 substrate, 57 head body, 58 ink droplet, 60 housing, 61 substrate, 63 oscillator, 64 substrate, 66 wiring, 67 wire wire, 70 input terminal, 71 phase comparator, 72 low-pass filter, 73 amplifier, 80 transmitter, 81 transmission signal processing circuit, 82 transmission mixer, 83 transmission filter, 84 transmission power amplifier, 85 transmitter / receiver demultiplexer, 86 antenna unit, 87 low noise amplifier, 88 reception filter, 89 reception mixer, 90 reception signal processing circuit, 91 reception unit, 92 frequency synthesizer, 93 control circuit, 94 input unit, 95 display unit, 140 base, 141 electrode, 142 Electrode, 143 Sound absorbing part, 144 Sound absorbing part, 145 High frequency signal source, 150 Base, 151 Electrode, 152 Electrode, 153 Electrode, 154 High frequency signal source, 300 Electronic equipment, 310 Electronic circuit, 511 Nozzle, 521 Cavity, 522 Side wall, 523 reservoir, 524 supply port, 531 communication hole, 600 ink jet printer, 620 apparatus main body, 621 tray, 622 discharge port, 630 head unit, 631 ink cartridge, 632 carriage, 640 printing apparatus, 641 carriage mode 642 reciprocating mechanism 643 carriage guide shaft 644 timing belt 650 sheet feeding device 651 sheet feeding motor 652 sheet feeding roller 660 control unit 670 operation panel 700 first thin film piezoelectric resonator 701 substrate , 702 Via hole, 703 elastic film, 704 lower electrode, 705 buffer layer, 706 piezoelectric layer, 707 upper electrode, 708 wiring, 709 electrode, 710 pad, 800 second thin film piezoelectric resonator, 801 substrate, 802 air gap, 803 Elastic film, 804 Lower electrode, 805 Buffer layer, 806 Piezoelectric layer, 807 Upper electrode

Claims (20)

A substrate,
A buffer layer formed above the substrate;
A piezoelectric layer having a perovskite structure formed above the buffer layer,
The buffer layer is a piezoelectric element made of a bismuth-based layered perovskite structure compound having conductivity and preferentially oriented in the c-axis (001). In claim 1,
The bismuth-based layered perovskite structure compound is represented by SrBi ₂ X ₂ O ₉
X is a piezoelectric element that includes at least one of Ta and Nb and further includes at least one of Ti, Zr, Hf, Fe, Co, Ni, W, Ru, and Rh. In claim 1,
The bismuth-based layered perovskite structure compound is represented by (Bi _1-x La _x ) ₄ X ₃ O ₁₂
X includes Ti, and further includes at least one of Fe, Co, Ni, V, Nb, Ta, W, Ru, and Rh,
x is a piezoelectric element in a range of 0 <x ≦ 0.4. In claim 1,
The bismuth-based layered perovskite structure compound is represented by SrBi ₄ X ₄ O ₁₅ ,
X is a piezoelectric element including Ti and further including at least one of Fe, Co, Ni, V, Nb, Ta, W, Ru, and Rh. In any one of Claims 1-4,
The piezoelectric layer is made of Pb (Zr _1-x Ti _x ) O ₃ ,
x is a piezoelectric element in a range of 0 ≦ x ≦ 1. In any one of Claims 1-4,
The piezoelectric layer is made of a material represented by a general formula of A (B _1-b X _b ) O ₃ ,
A includes Pb,
B contains Zr and Ti, and the composition ratio of Zr and Ti is represented by (1-a): a,
X consists of at least one of V, Nb, and Ta,
a is in the range of 0.15 ≦ a ≦ 0.8,
b is a piezoelectric element in the range of 0.05 ≦ b ≦ 0.4. In claim 6,
The piezoelectric layer is a piezoelectric element containing Si or Si and Ge. In any one of Claims 1-4,
The piezoelectric layer is a piezoelectric element made of a relaxor material. In claim 8,
The relaxor material is a piezoelectric element made of at least one of materials represented by the following formulas (1) to (9).
_{(1-x) Pb (Sc} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (1)
(Where x is 0.10 <x <0.42, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (In} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (2)
(Where x is 0.10 <x <0.37, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Ga} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (3)
(Where x is 0.10 <x <0.50, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Sc} 1/2 Ta 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (4)
(Where x is 0.10 <x <0.45, y is 0 ≦ y ≦ 1)
(1-x) Pb (Mg _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (5)
(Where x is 0.10 <x <0.35, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Fe} 1/2 Nb 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (6)
(Where x is 0.01 <x <0.10, y is 0 ≦ y ≦ 1)
(1-x) Pb (Zn _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (7)
(Where x is 0.01 <x <0.10, y is 0 ≦ y ≦ 1)
(1-x) Pb (Ni _1/3 Nb _2/3 ) O ₃ -xPb (Zr _1-y Ti _y ) O ₃ Formula (8)
(Where x is 0.10 <x <0.38, y is 0 ≦ y ≦ 1)
_{(1-x) Pb (Co} 1/2 W 1/2) O 3 -xPb (Zr 1-y Ti y) O 3 ··· Equation (9)
(Where x is 0.10 <x <0.42, y is 0 ≦ y ≦ 1) In any one of Claims 1-9,
The piezoelectric layer has a rhombohedral structure and is preferentially oriented to pseudo cubic (001).   A piezoelectric actuator comprising the piezoelectric element according to claim 1.   A piezoelectric pump comprising the piezoelectric element according to claim 1.   An ink jet recording head comprising the piezoelectric element according to claim 1.   An ink jet printer comprising the ink jet recording head according to claim 13.   A surface acoustic wave device comprising the piezoelectric device according to claim 1.   A thin film piezoelectric resonator comprising the piezoelectric element according to claim 1.   A frequency filter comprising at least one of the surface acoustic wave device according to claim 15 and the thin film piezoelectric resonator according to claim 16.   An oscillator comprising at least one of the surface acoustic wave device according to claim 15 and the thin film piezoelectric resonator according to claim 16.   An electronic circuit comprising at least one of the frequency filter according to claim 17 and the oscillator according to claim 18.   An electronic apparatus comprising at least one of the piezoelectric pump according to claim 12 and the electronic circuit according to claim 19.

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