JP6299502B2 - Piezoelectric composition and piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric composition and a piezoelectric element widely used in the fields of a piezoelectric sounding body, a piezoelectric sensor, a piezoelectric actuator, a piezoelectric transformer, a piezoelectric ultrasonic motor, and the like.

Piezoelectric elements using piezoelectric compositions have the effect of generating distortion when an electric field is applied from the outside, and the effect of generating charges on the surface by receiving external stress. Is widely used. For example, a piezoelectric element using a piezoelectric composition such as lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT) generates a strain proportional to the applied voltage, and the displacement is 1 × 10 ⁻¹⁰ m. Since it is a level of / V order, it is excellent in fine position adjustment, and is used for fine adjustment of an optical system.

  In addition, the piezoelectric composition generates an electric charge having a magnitude proportional to the applied stress or the amount of deformation caused by the stress. Therefore, the piezoelectric composition is also used as a sensor for reading minute force and amount of deformation. Furthermore, since the piezoelectric composition has excellent responsiveness, it is possible to cause resonance by exciting the piezoelectric composition itself or an elastic body in a bonding relationship with the piezoelectric composition by applying an alternating electric field. It is also used as a piezoelectric transformer and an ultrasonic motor.

Currently, most piezoelectric compositions in practical use are solid solution systems (PZT system) composed of lead zirconate (PbZrO ₃ ; PZ) and lead titanate (PbTiO ₃ : PT). A wide variety of products have been developed to meet various needs by adding various subcomponents or additives to the PZT piezoelectric composition. For example, instead of a small mechanical quality factor (Q _m ), the piezoelectric constant (d) is large, and it is used for a position adjustment actuator that requires a large amount of displacement in a direct current usage. Q _m is large, up to what is suitable for application to the alternating-current use, such as ultrasonic wave generating element such as an ultrasonic motor, there are various.

In addition to the PZT system, there are piezoelectric compositions that have been put into practical use. However, the main component is a lead perovskite composition such as lead magnesium niobate (Pb (Mg, Nb) O ₃ : PMN). Most of them are solid solutions.

  However, the lead-based piezoelectric composition contains about 60 to 70% by mass of lead oxide having extremely high volatility even at a low temperature, and reduction of lead oxide used for environmental considerations is desired. Furthermore, as the application fields of piezoelectric ceramics and piezoelectric single crystals expand in the future, and the amount of use increases, lead-free piezoelectric compositions will become a very important issue.

Known piezoelectric compositions containing no lead include, for example, barium titanate (BaTiO ₃ : BT) or a bismuth layered ferroelectric. However, BT has a Curie point as low as 120 ° C., and the piezoelectricity disappears above that temperature, so it is not practical when considering applications such as soldering or in-vehicle use. On the other hand, bismuth layered ferroelectrics usually have a Curie point of 400 ° C. or higher and are excellent in thermal stability. However, since the crystal anisotropy is large, the shear applied by the hot forging method is used. It is necessary to orient spontaneous polarization by stress, which is problematic in terms of productivity.

  On the other hand, recently, as a new piezoelectric composition, research has been conducted on a sodium bismuth titanate composition. For example, Non-Patent Document 1 discloses a piezoelectric composition in which bismuth aluminate is added to sodium potassium potassium bismuth titanate.

D. S. Lee et al. , Jpn. J. et al. Appl. Phys. , 52 (2013) 021801.

  However, the piezoelectric composition disclosed in Non-Patent Document 1 does not provide sufficient piezoelectric characteristics as compared with the lead-based piezoelectric composition.

  Accordingly, the present invention provides an excellent piezoelectric composition and piezoelectric element from the standpoint of reducing the pollution, environmental friendliness, and ecology from the viewpoint of low piezoelectricity, particularly high spontaneous polarization, high resistivity, and no use of lead. The purpose is to provide.

  In order to solve the above-mentioned problems, the present inventors have found a piezoelectric composition exhibiting excellent piezoelectric characteristics with a sodium bismuth titanate composition.

That is, the present invention provides a piezoelectric composition containing as a main component an oxide of perovskite structure represented by the following formula _{(1) (Bi (x +} 0.5y + z) Na 0.5y) m (Al x Ti (y + 0.5z ₎ Ni _0.5z ) O ₃ (1)
In the above formula (1), x, y, z, and m are each 0.01 ≦ x ≦ 0.20.
0.60 ≦ y ≦ 0.95
0.01 ≦ z ≦ 0.35
0.75 ≦ m ≦ 1.00
x + y + z = 1
It is.

  By setting it as the composition of the said range, a piezoelectric characteristic, especially spontaneous polarization can be increased and a resistivity can be raised.

  Moreover, this invention provides the piezoelectric element provided with the said piezoelectric composition. According to the present invention, it is possible to provide a piezoelectric element having high actuator displacement and sensor sensitivity, for example, in an inkjet head, a piezoelectric actuator, a thin film sensor, and the like. Furthermore, since a high resistivity can be obtained, the power consumption of the drive circuit can be suppressed when operated as an actuator element.

  According to the present invention, it is possible to provide an excellent piezoelectric composition and piezoelectric element from the viewpoints of low pollution, environmental friendliness, and ecology, in particular, due to large spontaneous polarization, high resistivity, and no use of lead. .

1 is a schematic cross-sectional view of a piezoelectric element according to an embodiment of the present invention.

FIG. 1 is a schematic cross-sectional view of a piezoelectric element according to an embodiment of the present invention. A Ti adhesion layer 3, a lower electrode 4, a piezoelectric thin film 5 and an upper electrode 6 are sequentially deposited on a substrate 1 having a thermal oxide film 2 to obtain a piezoelectric element evaluation structure. Examples of the substrate 1 include a single crystal Si substrate or an oxide single crystal substrate such as MgO or SrTiO ₃ . The thermal oxide film 2 is formed, for example, by oxidizing the substrate 1, and is SiO ₂ when the substrate 1 is Si. However, when an oxide single crystal substrate is used, the thermal oxide film 2 may be omitted. Examples of the adhesion layer 3 include Ti. Examples of the upper electrode 4 and the lower electrode 6 include Pt or a conductive oxide such as SrRuO ₃ .

The piezoelectric composition according to this embodiment for forming the piezoelectric thin film 5 has an oxide (Bi _{(x + 0.5y + z)} Na _0.5y ) _m (Al _x ) represented by the following formula (1) whose main component is a perovskite structure. Ti _{(y + 0.5z)} Ni _0.5z ) O ₃ (1)
In the above formula (1), x, y, z and m are respectively
0.01 ≦ x ≦ 0.20
0.60 ≦ y ≦ 0.95
0.01 ≦ z ≦ 0.35
0.75 ≦ m ≦ 1.00
x + y + z = 1
It is.

  The range of x is 0.01 ≦ x ≦ 0.20, and more preferably 0.05 ≦ x ≦ 0.15. When x is smaller than 0.01, the resistivity is decreased, and when x is larger than 0.20, the spontaneous polarization is decreased due to the occurrence of heterogeneous phase. Furthermore, the range of y is 0.60 ≦ y ≦ 0.95, and more preferably 0.77 ≦ y ≦ 0.95. When y is smaller than 0.60, sufficient spontaneous polarization cannot be obtained. When y is larger than 0.95, the resistivity decreases. Furthermore, the range of z is 0.01 ≦ z ≦ 0.35, more preferably 0.01 ≦ z ≦ 0.18. When z is smaller than 0.01, sufficient spontaneous polarization cannot be obtained, and when z is larger than 0.35, the spontaneous polarization is reduced due to the occurrence of a different phase.

  M in the formula (1) is preferably in the range of 0.75 ≦ m ≦ 1.00. m represents the A / B ratio which is the composition ratio of the A site atom and the B site atom of the perovskite structure compound in the entire piezoelectric composition, and is 1.00 in the case of the stoichiometric composition. When m is 1.00 or more, the sintering temperature rises, grain growth is suppressed, and piezoelectric characteristics cannot be obtained. On the other hand, if m is 1.00 or less, the sinterability can be improved and higher piezoelectric characteristics can be obtained. However, if it is less than 0.75, the piezoelectric properties are reduced due to the generation of the perovskite phase other than the crystal phase, and the resistivity is also decreased due to the occurrence of the heterogeneous phase. Therefore, the range of 0.75 to 1.00 is preferable.

The piezoelectric composition according to the present embodiment is not limited in the mixing form of each component as long as it satisfies the composition formula of the above formula (1). For example, the first compound is bismuth aluminate, the second compound. The main component is bismuth sodium titanate and bismuth nickel titanate which is the third compound. That is, the first compound, the second compound, and the third compound are included and are in solid solution, but may not be completely dissolved. When the chemical formulas of the first compound, the second compound, and the third compound are used, it can be described by the following formula (2).
_{xBi s1 AlO 3 -y (Bi 0.5} Na 0.5) t1 TiO 3 -zBi u1 (Ni 0.5 Ti 0.5) O 3 (2)
In the above formula (2), x, y, z, s1, t1, and u1 are respectively
0.01 ≦ x ≦ 0.20
0.60 ≦ y ≦ 0.95
0.01 ≦ z ≦ 0.35
x + y + z = 1, and s1, t1, and u1 are 0.75 or more and 1.00 or less.

  Examples of the first compound of the above formula (2) include bismuth aluminate. The composition of bismuth aluminate is represented by the following formula (3), where Bi (bismuth) is located at the A site of the perovskite structure and Al (aluminum) is located at the B site of the perovskite structure.

Bi _s1 AlO ₃ (3)
In the above formula (3), which is the first compound, s1 represents the composition ratio (hereinafter referred to as A / B ratio) by the molar ratio of the element located at the A site to the element located at the B site, and stoichiometric. The composition is 1.00. If it is 1.00 or less, sinterability can be improved and higher piezoelectric properties can be obtained. Furthermore, if it is in the range of 0.75 or more and 1.00 or less, it is more preferable because higher piezoelectric characteristics can be obtained. The compositions of aluminum, bismuth, and O (oxygen) are determined from the stoichiometric composition, but may deviate from the stoichiometric composition.

  Examples of the second compound of the above formula (2) include sodium bismuth titanate. The composition of sodium bismuth titanate is represented by the following formula (4), where Na (sodium) and bismuth are located at the A site of the perovskite structure, and Ti (titanium) is located at the B site of the perovskite structure.

(Bi _0.5 Na _0.5 ) _t1 TiO ₃ (4)
In the above formula (4), which is the second compound, t1 represents an A / B ratio, and is 1.00 for a stoichiometric composition. If it is 1.00 or less, sinterability can be improved and higher piezoelectric properties can be obtained. Furthermore, if it is in the range of 0.75 or more and 1.00 or less, it is more preferable because higher piezoelectric characteristics can be obtained. The composition of bismuth, sodium, titanium, and oxygen is determined from the stoichiometric composition, but may deviate from the stoichiometric composition.

  Examples of the third compound of the above formula (2) include bismuth nickel titanate. The composition of bismuth nickel titanate is expressed by the following formula (5), where bismuth is located at the A site of the perovskite structure and Ni (nickel) and titanium are located at the B site of the perovskite structure.

Bi _u1 (Ni _0.5 Ti _0.5 ) O ₃ (5)
In the above formula (5), which is the third compound, u1 represents an A / B ratio, and is preferably 1.00 for a stoichiometric composition. However, if it is 1.00 or less, sinterability can be improved and higher piezoelectric characteristics can be obtained. Furthermore, if it is the range of 0.75 or more and 1.0 or less, since a higher piezoelectric characteristic can be acquired, it is more preferable. The composition of bismuth, nickel, titanium, and oxygen is determined from the stoichiometric composition, but may deviate from the stoichiometric composition.

  Since s1, t1, and u1 are xs1 + yt1 + zu1 = m, 0.75 ≦ m ≦ 1.00 can be satisfied.

In addition, the main component in the above shows 90 mol% or more of the whole component which comprises a material composition.

The reason why the piezoelectric composition according to the present embodiment has excellent piezoelectric characteristics is not necessarily clear, but is estimated as follows. (Bi _0.5 Na _0.5 ) TiO ₃ is a ferroelectric, and becomes a relaxor-type ferroelectric by being dissolved in Bi (Ni _0.5 Ti _0.5 ) O ₃ . However, in the case of a relaxor material, there is no domain structure, and only unstable polarization called Polar-Nano-Region exists. Therefore, stable and submicron-sized domains can be formed by solid solution with BiAlO ₃ which is a ferroelectric. Furthermore, since BiAlO ₃ has a feature that the ratio of the c-axis length to the a-axis length of the tetragonal perovskite structure compound is high, the amount of ion movement when an electric field is applied is increased by dissolving this material, As a result, a large piezoelectric displacement can be obtained. However, the mechanism is not necessarily limited to this.

  In this embodiment, in addition to the main component represented by the above formula (1), impurities or constituent elements of other compounds may be contained in the order of several tens to several hundred ppm. Examples of such elements include Mn (manganese), Fe (iron), Co (cobalt), Cu (copper), Ba (barium), Sr (strontium), Ca (calcium), K (potassium), Li (Lithium), Zr (zirconium), Hf (hafnium), Si (silicon), B (boron), and rare earth elements.

  In addition, although the piezoelectric composition of this embodiment may contain lead as an impurity, it is preferable that the content is 1 mass% or less, and it is more preferable that lead is not included at all. Volatilization of lead during firing and the release of lead into the environment after it has been distributed to the market as a piezoelectric component and discarded, it is possible to minimize pollution, environmental friendliness, and ecological aspects This is because it is preferable.

  The piezoelectric composition having such a configuration can be manufactured, for example, as follows. First, as starting materials, powders of bismuth oxide, sodium carbonate, titanium oxide, nickel oxide, aluminum oxide, etc. are prepared as needed, and after sufficient drying at 100 ° C. or higher, weighed according to the target composition To do. In addition, instead of the oxide, the starting material may be a carbonate or oxalate that becomes an oxide by firing,

  Next, the weighed starting materials are sufficiently mixed in an organic solvent or water in a ball mill or the like for 5 hours to 20 hours, then sufficiently dried, press-molded, and 700 ° C. to 800 ° C. for 1 hour to 3 hours. Calcinate to a degree. Subsequently, the calcined product is pulverized in an organic solvent or water for 5 to 30 hours with a ball mill or the like, dried again, and granulated by adding a binder solution. After granulation, this granulated powder is press-molded into a block shape.

  After forming into a block shape, this molded body is heat-treated at 400 ° C. to 800 ° C. for about 2 hours to 4 hours to volatilize the binder, and then subjected to main baking at 700 ° C. to 1200 ° C. for about 2 hours to 4 hours. The rate of temperature increase and the rate of temperature decrease during the main firing are, for example, about 50 ° C./hour to 300 ° C./hour. After the main firing, the obtained sintered body is polished as necessary to provide an electrode. After that, polarization treatment is performed by applying an electric field of 5 MV / m to 10 MV / m in silicon oil at 25 ° C. to 150 ° C. for about 5 minutes to 1 hour. Thereby, the piezoelectric composition mentioned above is obtained.

  The above production method is called a solid phase reaction method, but a typical production method other than this is a vapor phase growth method. The vapor phase growth method is a method in which a raw material (target material) is evaporated in a vacuum environment to form a thin film having a thickness of about several tens of nm to several μm on a smooth substrate.

  The vapor phase growth method is preferably a sputtering method, an electron beam evaporation method, a pulsed laser deposition (PLD) method, or the like. By using these methods, it is possible to form a dense film at the atomic level, and segregation is less likely to occur. In these vapor phase growth methods, the raw material (target material) is physically evaporated and deposited on the substrate, but the excitation source differs depending on the film forming method. In the case of the sputtering method, Ar ions, in the case of the electron beam evaporation method, an electron beam, and in the case of the PLD method, a laser beam serves as an excitation source and is irradiated to the target.

In the vapor phase growth method, there are various methods for forming a piezoelectric thin film as described above. As a typical example, details of the PLD method will be described. There is an effect of improving the cleanliness of the substrate surface by heating the substrate in a vacuum chamber in an ultrahigh vacuum with an ultimate pressure of 1 × 10 ⁻⁵ or less in a range of 500 to 1000 ° C. In the film forming process, when a focused laser beam is irradiated onto the target, a light emitting column called plume is generated from the target surface. A plume is composed of excited chemical species such as atoms, molecules, and ions, and these excited chemical species are deposited on a counter substrate to form a thin film. The deposition parameters other than the substrate temperature include oxygen partial pressure, laser power density, and substrate-target distance. A desired thin film can be obtained by controlling these parameters. In general, oxygen gas is introduced at the time of producing the oxide, but it is desirable that the oxygen partial pressure be in the range of about 10 to 10 ⁻⁴ Pa.

As a target material used as a raw material at the time of film formation, a sintered body produced by the above solid-phase reaction method can be used. When such a vapor phase growth method is used, the piezoelectric composition of the present invention is generally formed on a Si substrate, a MgO substrate, or a SrTiO ₃ substrate. When a piezoelectric material is deposited on a Si substrate, first, an adhesion layer such as Ti or Cr is formed, and then a Pt lower electrode is formed. As a method of obtaining a piezoelectric polycrystalline thin film, there are a method of crystal growth while heating a substrate, and a method of obtaining a polycrystalline film by forming a film at room temperature and then baking it at a desired temperature. In any method, a desired crystal phase can be obtained by adjusting the film formation parameter and the heat treatment parameter.

  The piezoelectric composition of the present invention can be used for, for example, a piezoelectric sounding body, a piezoelectric sensor, a piezoelectric actuator, a piezoelectric transformer, a thin film sensor, a thin film actuator, or a piezoelectric ultrasonic motor, but any other piezoelectric element that can use the piezoelectric composition. You may apply to

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

(Examples 1-12)
A piezoelectric element as shown in FIG. 1 was prepared. As the substrate 1, a Si substrate with a thermal oxide film was used. The substrate 1 is a circular substrate having a diameter of 3 inches, and includes a (100) plane orientation, a Si substrate having a thickness of 0.5 mm, and a thermal oxide film 2 having a thickness of 500 nm formed thereon. First, the Ti adhesion layer 3 and the lower electrode layer 4 were formed in this order on the substrate 1 by the RF magnetron sputtering method. The lower electrode layer 4 includes a Ti adhesion layer 3 having a thickness of 20 nm formed on the thermal oxide film 2 and a Pt lower electrode layer 4 having a thickness of 200 nm formed thereon and preferentially oriented on the (111) plane. Consists of. The thickness of the Ti adhesion layer 3 can be appropriately adjusted as long as it functions as an adhesion layer.

  The deposition conditions for the Ti adhesion layer 3 and the Pt lower electrode layer 4 were as follows: the substrate temperature was room temperature, the discharge power was 100 W, the introduced gas was Ar, and the deposition pressure was 0.3 Pa.

Next, a piezoelectric thin film 5 is formed on the Pt lower electrode layer 4. A PLD method was used as a film forming method. The thickness of the piezoelectric thin film 5 was 500 nm. As the PLD target, (Bi _0.5 Na _0.5 ) TiO ₃ , Bi (Ni _0.5 Ti _0.5 ) O ₃ , Bi ₂ O ₃ , and Al ₂ O ₃ were used as targets. The respective film formation rates are 0.04 nm / pulse, 0.03 nm / pulse, 0.13 nm / pulse, and 0.02 nm / pulse, and as shown in Table 1 by adjusting the number of laser pulses. The composition ratio was used. As film formation conditions, the substrate temperature was room temperature, the laser power was ˜2 J / cm ² , and the oxygen partial pressure was 1.33 × 10 ⁻³ Pa. After film formation, heat treatment was performed at 500 to 900 ° C. for 1 minute in an oxygen atmosphere. The piezoelectric thin film 5 which concerns on Examples 1-12 was obtained by these methods.

  In order to evaluate the electrical characteristics of the piezoelectric thin film 5, a Pt layer having a thickness of 100 nm was formed on the upper surface of the piezoelectric thin film 5 by RF magnetron sputtering as shown in FIG. The film forming conditions are the same as those for the lower electrode. After that, the upper electrode 6 was formed by patterning the Pt layer by photolithography, etching, etc., and a piezoelectric element capable of evaluating electrical characteristics as shown in FIG. 1 was produced.

As an evaluation of piezoelectric characteristics, measurement of spontaneous polarization P [μC / cm ² ] was performed. Since spontaneous polarization is determined by the product of piezoelectric constant [C / N] and stress [N / m ² ], it is necessary to maximize the spontaneous polarization in order to obtain a high piezoelectric constant. Spontaneous polarization was measured using a Soya tower circuit, the spontaneous polarization was measured while applying an AC electric field in a range of ± 50 kV / mm, and the maximum polarization value Pm was compared. The circuit input frequency at this time is 1 kHz. In addition, the resistance value of the piezoelectric element was evaluated. In the resistance measurement, the resistance value was calculated from the ratio between the current value and the voltage value obtained by the Soya Tower method, and the resistivity ρ [Ohm * cm] was calculated from the electrode area and the element thickness.

(Comparative Examples 1-6)
Regarding Comparative Examples 1 to 6, the composition of the Bi: Al element ratio of 1: 1, (Bi _0.5 Na _0.5 ) TiO ₃ , and Bi (Ni _0.5 Ti _0.5 ) O ₃ The ratio was changed as shown in Table 1, and a piezoelectric element was produced in the same manner as in the above example.

Table 1 shows the results of the maximum value Pm of spontaneous polarization and the resistivity ρ.

As shown in Table 1, the range of the composition ratio x of BiAlO ₃ is 0.01 ≦ x ≦ 0.20, and the range of the composition ratio y of (Bi _0.5 Na _0.5 ) TiO ₃ is 0.60 ≦ Spontaneous polarization when y ≦ 0.95 and the range of the composition ratio z of Bi (Ni _0.5 Ti _0.5 ) O ₃ satisfies 0.01 ≦ z ≦ 0.35 and x + y + z = 1. A maximum value Pm of 1.5 times or more that of Comparative Example 1 was obtained. That is, the first compound bismuth aluminate and the second compound sodium bismuth titanate and the third compound bismuth nickel titanate titanate are included, or a solid solution thereof is included. In this case, the piezoelectric characteristics can be improved.
For the resistivity ρ, the comparative example and the example were compared. The resistivity increased with increasing amount of bismuth aluminate.

(Examples 13 to 16 and Comparative Examples 7 to 8)
Furthermore, in examining the range of m, the composition in Table 2 was examined.
In Examples 13 to 16 and Comparative Examples 7 to 8, the A / B ratio (value of m) was changed (Bi _0.5 Na _0.5 ) _m TiO ₃ target, Bi (Ni _0.5 Ti _{0 .5) m} O ₃ target was prepared. Then, a target having an element ratio of Bi and Al of m: 1 was produced, and a pressure film element was produced in the same manner as in the example.

  As shown in Table 2, when m is smaller than 0.75, the maximum value Pm of spontaneous polarization is also decreased. In addition, when m is larger than 1.00, the maximum value Pm of spontaneous polarization becomes small.

  Although the PLD method has been described as the method for forming the piezoelectric thin film, any method such as a sputtering method, a solution method, or a chemical vapor deposition method can be used. In addition, it was confirmed that similar results were obtained even when a piezoelectric element using a piezoelectric composition was produced by using a solid phase reaction method.

  While the present invention has been described with reference to the embodiment and examples, the present invention is not limited to the above embodiment and example. In the above-described embodiments and examples, only the case where the first compound, the second compound, and the third compound are included has been described. However, in addition to these, other compounds may be included.

  The piezoelectric composition of the present invention can be widely used in fields such as actuators, sensors, and resonators.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Thermal oxide film 3 Ti adhesion layer 4 Lower electrode 5 Piezoelectric thin film 6 Upper electrode

Claims (2)

A piezoelectric composition containing an oxide having a perovskite structure represented by the following formula (1) as a main component.
_{(Bi (x + 0.5y + z} ) Na 0.5y) m (Al x Ti (y + 0.5z) Ni 0.5z) O 3 (1)
In the above formula (1), x, y, z, and m are each 0.01 ≦ x ≦ 0.20.
0.60 ≦ y ≦ 0.95
0.01 ≦ z ≦ 0.35
0.75 ≦ m ≦ 1.00
x + y + z = 1 A piezoelectric element comprising the piezoelectric composition according to claim 1.

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