JP7124445B2 - BNT-BT film and method for forming the same - Google Patents

Description

The present invention is a BNT-BT film that does not contain lead, has high crystallinity and film density, and has a high degree of orientation of the (110) plane or (100) plane, thereby having high piezoelectric properties or high capacitor properties. and a method of forming the same. As used herein, BNT-BT is an abbreviation for (Bi,Na)TiO ₃ -BaTiO ₃ . That is, BNT is an abbreviation for (Bi,Na)TiO ₃ and BT is an abbreviation for BaTiO ₃ . LNO film is an abbreviation for LaNiO ₃ film.

Conventionally, as this type of BNT-BT film, a first electrode 13 having only (110) orientation, a (Na _x Bi _0.5 )TiO _0.5x+2.75 -BaTiO ₃ layer 14 having only (110) orientation, (110 )-oriented (Bi, Na)TiO ₃ —BaTiO ₃ layer 15 and the second electrode 17 are laminated in this order, and the value of x is 0.29 or more and 0.40 or less. (See Patent Document 1, for example). The BNT-BT layer 14 is an interface layer between the first electrode 13 and the BNT-BT layer 15 .

The piezoelectric film disclosed in Patent Document 1 is formed, for example, on a Pt layer (first electrode 13) by a sputtering method to form 0.93(Na _x Bi _0.5 )TiO _0.5x+2.75 − having only (110) orientation. After forming a 0.07BaTiO ₃ layer 14 (x=0.350) with a thickness of 100 nm as an interface layer, a 0.93(Bi _0.5 Na _0.5 )TiO ₃ -0.07BaTiO ₃ layer 15 is formed to a thickness of 2.7 μm. Comparative Example 2 of Patent Document 1 shows a piezoelectric film using an interface layer made of (Na _0.5 Bi _0.5 )TiO ₃ .

As disclosed in Patent Document 1, when a piezoelectric film is formed by a sputtering method, the sputtering method involves bombarding an oxide target with, for example, ionized argon in a vacuum, so that the ejected elements are removed. Since the deposition is carried out on the substrate, there is a problem that the composition deviates from that of the oxide used as the target. In addition, since a high vacuum is required, an increase in the size and cost of the apparatus is inevitable.

In order to solve the problem of the sputtering method, a chemical solution deposition (CSD) method is known instead of the sputtering method. In this CSD method, a precursor solution containing a metal element with a target composition is used to form a film on a substrate by, for example, a spin coating method, a dip coating method, an inkjet method, etc., and then baked to form a piezoelectric film or a capacitor film. This method is preferable because it is possible to form the piezoelectric film or capacitor film at a lower temperature than the sputtering method, and because it does not require a high vacuum, it can be formed using a small and inexpensive apparatus.

Conventionally, as one method of forming a BNT-BT piezoelectric film by the CSD method, a piezoelectric film having a structural formula of 0.94(Bi _0.5 Na _0.5 )TiO ₃ -0.06BaTiO ₃ is deposited by metalorganic solution deposition (MOSD). (For example, see Non-Patent Document 1.). In the method of Non-Patent Document 1, first, a BNT solution and a BT solution are separately prepared in a stoichiometric ratio, then both solutions are mixed, and this mixed solution is applied to a Pt/Ti/SiO ₂ /Si substrate. Spin coat. The spin-coated liquid is dried on a hot plate at 170° C. for 10 minutes, calcined at 450° C. for 10 minutes, and finally baked by rapid heating at a temperature of 600° C. or higher and 700° C. or lower by RTA (Rapid Thermal Annealing). . In order to increase the film thickness, the spin coating, drying, calcining and baking are repeated several times to form a BNT-BT piezoelectric film.

Non-Patent Document 1 describes that the BNT-BT piezoelectric film obtained by the method of Non-Patent Document 1 has an average particle size of the order of 200 nm and is smooth and crack-free as observed with an atomic force microscope, and has a thickness of 356 nm. small-signal permittivity and dissipation factor at 1 kHz show 613 and 0.044, respectively, and ferroelectric hysteresis measurements show a remanent polarization value of 21.5 μC/cm ² at a holding field of 164.5 kV/cm. , and a leakage current density of 4.08×10 ⁻⁴ A/cm ² at an electric field of 200 kV/cm, and its effective piezoelectric constant (d ₃₃ ) is about 51.6 pm/V.

S. K. Acharya et al., "Ferroelectric and piezoeletric properties of lead-free BaTiO3 doped Bi0.5Na0.5TiO3 thin films from metal-organic solution deposition", J. All0ys Compd. 540 (2012) 204-209

WO2012/140811 (Claim 1, paragraphs [0067] to [0073], paragraphs [0085], paragraphs [0095], FIG. 1)

The method of Patent Document 1, in which a BNT-BT piezoelectric film is formed by a sputtering method, has the above-described problems. In addition, in the method of Non-Patent Document 1, in which a BNT-BT piezoelectric film is formed by the CSD method, a mixed solution obtained by mixing a BNT solution and a BT solution is applied to a substrate, dried, and calcined. , requires high energy because it contains a BT component with a high crystallization temperature. Therefore, it was difficult to obtain a film with good crystallinity by the CSD method represented by the method of Non-Patent Document 1. Since a film with poor crystallinity has poor electrical properties, it has been desired to improve the crystallinity.

An object of the present invention is a BNT-BT that does not contain lead, has high crystallinity and film density, and has a high degree of orientation of the (110) plane or (100) plane, thereby having high piezoelectric properties or high capacitor properties. An object of the present invention is to provide a system film and a method for forming the same.

The present inventors found that the BNT film crystallized at a temperature of about 500° C. in the CSD method, and by interposing the BNT film between the electrode of the substrate and the BNT-BT film, at the electrode interface during firing, The inventors have found that a BNT-BT film with high crystallinity and high density can be formed by increasing the generation density of crystal nuclei, and arrived at the present invention.

A first aspect of the present invention is a BNT-BT-based film comprising a (Bi, Na)TiO ₃ —BaTiO ₃ -based film formed on an electrode of a substrate, wherein the BNT-BT-based film is deposited by chemical solution deposition. (hereinafter referred to as the CSD method) and the diffraction angle 2θ = 32° to 33° obtained by the X-ray diffraction method using Cu—Kα rays. is 0.200° or less, and the degree of orientation of the (110) plane of the film represented by the following formula (1) is 90% or more.
(110) plane orientation = ΣIb(110)/{ΣIa(100) + ΣIb(110)} × 100 (1)
Here, ΣIa(100) and ΣIb(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively.

A second aspect of the present invention is an invention based on the _first aspect _, in which a _BNT-- A BT-based film, wherein the BNT-BT-based film is formed by a CSD method and has a diffraction angle 2θ of 22.5° to 23.5° obtained by an X-ray diffraction method using a Cu—Kα ray. The half width of the peak waveform of the (100) plane of is 0.200° or less, and the degree of orientation of the (100) plane of the film represented by the following formula (2) is 90% or more.
Orientation degree of (100) plane = ΣIc(100)/{ΣIc(100) + ΣId(110)} × 100 (2)
Here, ΣIc(100) and ΣId(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively.

A third aspect of the present invention is an invention based on either the first aspect or the second aspect, wherein the (Bi,Na)TiO ₃ —BaTiO ₃ -based film comprises (Bi,Na)TiO ₃ — BaTiO ₃ contains Mn and/or Nb.

A fourth aspect of the present invention is an invention based on any one of the first to third aspects, and is a BNT-BT film wherein the substrate is a silicon substrate or a sapphire substrate.

A fifth aspect of the present invention is an invention based on any one of the first to fourth aspects, wherein the electrode of the substrate is a BNT-BT film that is a Pt film oriented in the (111) plane. be.

A sixth aspect of the present invention is a method of forming a BNT-BT film consisting of a (Bi, Na)TiO ₃ —BaTiO ₃ film on an electrode of a substrate directly or via a LaNiO ₃ film by the CSD method. Then, the liquid composition for forming a (Bi, Na)TiO ₃ film is coated on the electrodes of the substrate directly or via the LaNiO ₃ film, dried, and calcined at a temperature of 350° C. or higher and 400° C. or lower to obtain a thickness of 4 nm. A first calcined film to be a seed layer having a thickness of 20 nm or less is formed, and a (Bi, Na) TiO ₃ —BaTiO ₃ -based film forming liquid composition is applied onto the first calcined film and dried to 350° C. or higher. After calcining at a temperature of 400° C. or less to form a second calcined film, the first calcined film and the second calcined film are heated at a rate of 25° C./second or more to 700° C. or more and 800° C. A crystallized (Bi, Na)TiO ₃ —BaTiO ₃ film system is formed by batch firing at the following temperature.

The BNT-BT film of the first aspect of the present invention has a high crystallinity and a (110 ) has a high degree of plane orientation. As a result, the BNT-BT film has high piezoelectric properties. In addition, the BNT-BT film of the present invention has a seed layer with a special composition such as the (Na _x Bi _0.5 )TiO _0.5x+2.75 -BaTiO ₃ layer (x=0.350) shown in Patent Document 1 at the interface. Since it is not provided as a layer, it can be formed by a small and inexpensive device by the CSD method without using a large and expensive sputtering device. In addition, this BNT-BT film has a degree of orientation of the (110) plane of 90% or more, and since the degree of orientation of the (110) plane is high, the dielectric constant is higher than that of a film having a high degree of orientation of the (100) plane. It is low and suitable for sensors such as gyro sensors.

A BNT-BT-based film according to the second aspect of the present invention is formed on a substrate electrode via a LaNiO ₃ film preferentially oriented in the (100) plane, and the LaNiO ₃ film controls the crystal orientation of the BNT-BT layer. Therefore, it has the degree of orientation of the (100) plane. Since the half width of the peak waveform of the (100) plane of this film is 0.200° or less, the crystallinity is high and the degree of orientation of the (100) plane is high. As a result, the BNT-BT film has high capacitor characteristics. In addition, the BNT-BT film of the present invention has a seed layer with a special composition such as the (Na _x Bi _0.5 )TiO _0.5x+2.75 -BaTiO ₃ layer (x=0.350) shown in Patent Document 1 at the interface. Since it is not provided as a layer, it can be formed by a small and inexpensive device by the CSD method without using a large and expensive sputtering device. In addition, the BNT-BT film preferentially oriented in the (100) plane has a higher dielectric constant than the film preferentially oriented in the (110) plane, and is suitable for a thin film capacitor.

The BNT-BT-based film of the third aspect of the present invention is a (Bi,Na)TiO ₃ -BaTiO ₃ -based film containing Mn and/or Nb in (Bi,Na)TiO ₃ -BaTiO ₃ , A piezoelectric film or capacitor film with a low current density can be obtained.

The BNT-BT-based film of the fourth aspect of the present invention is highly versatile because it is formed on a silicon substrate or a sapphire substrate that is used in ordinary piezoelectric devices or capacitors.

The BNT-BT film of the fifth aspect of the present invention is highly versatile because it is formed on a Pt layer oriented in the (111) plane used as the lower electrode of a normal piezoelectric device or capacitor.

In the method for forming a BNT-BT-based film according to the sixth aspect of the present invention, the BNT film-forming liquid composition is applied, dried, and calcined at a temperature of 350 ° C. or higher and 400 ° C. or lower to obtain a thickness of 4 nm or higher and 20 nm or lower. A first calcined film to be a certain seed layer is formed, a BNT-BT-based film forming liquid composition is applied to the first calcined film, dried, and calcined at a temperature of 350° C. or higher and 400° C. or lower. After forming the second calcined film, the temperature of the first calcined film and the second calcined film is raised at a rate of 25° C./second or more, and they are collectively baked at a temperature of 700° C. or more and 800° C. or less. In this method, the first calcined film made of BNT increases the crystal nucleus generation density at the interface between the electrode and the second calcined film when calcined at a predetermined temperature and fired at a predetermined heating rate. . That is, since there is no BT component (especially Ba component) at the interface as shown in Non-Patent Document 1, the occurrence of a composition different from the desired composition is suppressed during film formation, and high crystallinity and (110) A BNT-BT-based film having a high degree of plane or (100) plane orientation can be formed.

FIG. 4 is a schematic cross-sectional view showing a step of forming a BNT-BT film on the electrode of the first embodiment using BNT as a seed layer. FIG. 8 is a schematic cross-sectional view showing a step of forming a BNT-BT film on the LNO film of the second embodiment using BNT as a seed layer. FIG. 2 shows the X-ray diffraction profiles of the films of Example 1 (bold line) and Comparative Example 1 (thin line). FIG. 4 shows the X-ray diffraction profiles of the films of Example 9 (bold line) and Comparative Example 6 (thin line).

<First embodiment>
First, a method for forming a BNT-BT film according to the first embodiment of the present invention will be described with reference to FIG.

[Preparation of substrate with electrodes]
As shown in FIG. 1(d), the BNT-BT film 11 of the first embodiment is formed on a substrate 12. As shown in FIG. This substrate 12 has a heat-resistant substrate body 13 made of silicon or sapphire, as shown in FIG. 1(a). In the case of a substrate body made of silicon, a SiO ₂ film 14 is provided on this substrate body 13 and a lower electrode 15 is provided on this SiO ₂ film 14 . The lower electrode 15 is made of a conductive material such as Pt, TiO _x , Ir, Ru, etc., which does not react with the BNT-BT film 11 . For example, the lower electrode 15 can have a two-layer structure of a TiO _x film 15a and a Pt film 15b in order from the substrate body 12 side. A specific example of the TiO _x film 15a is a TiO ₂ film. Furthermore, the SiO ₂ film 14 is formed to improve adhesion. The Pt film 15b is formed oriented in the (111) plane by sputtering, for example.

[Formation of BNT film (first calcined film) as seed layer]
As shown in FIG. 1B, a BNT film 16 as a seed layer is formed on a substrate 12 by a CSD method (hereinafter also referred to as a sol-gel method). This BNT film 16 is produced as a first calcined film by applying a (Bi, Na)TiO ₃ film forming liquid composition onto the substrate 12, drying it, and calcining it. This liquid composition contains at least Bi, Na and Ti. Examples include bismuth acetate, sodium alkoxides and titanium alkoxides. The liquid composition is applied to a thickness of 4 nm or more and 20 nm or less, preferably 5 nm or more and 10 nm or less after calcination by spin coating, dip coating, LSMCD (Liquid Source Misted Chemical Deposition) method, electrostatic spray method, or the like. It is performed so as to become a coating film (gel film) having

Drying after applying the liquid composition is natural drying, or in order to remove low boiling point solvents and adsorbed water molecules, for example, using a hot plate at a temperature of 70 ° C. or higher and 90 ° C. or lower for 0.5 minutes. The low temperature heating is performed for 5 minutes as described above. The calcination after drying is performed at a temperature of 350° C. or higher and 400° C. or lower, preferably 360° C. or higher and 380° C. or lower, using a hot plate or RTA, for example. If the calcining temperature is less than 350° C., a phase different from the BNT phase is produced. If the temperature exceeds 400° C., the BNT film (first calcined film) becomes difficult to crystallize. If the thickness of the first calcined film after calcination is less than 4 nm, the density of crystal nuclei generated is low, and a BNT-BT film with high crystallinity and high density cannot be formed. If the thickness exceeds 20 nm, the BNT film (first calcined film) as the seed layer becomes too thick, and the dielectric properties (piezoelectric properties, capacitor properties, etc.) of the BNT-BT film formed on the BNT film deteriorate. to degrade.

[Formation of BNT-BT film (second calcined film)]
As shown in FIG. 1(c), a BNT-BT film (second calcined film) 17 is formed on a BNT film (first calcined film) 16 by a sol-gel method. This BNT-BT film 17 is produced as a second calcined film by applying a (Bi, Na)TiO ₃ —BaTiO ₃ film forming liquid composition onto the BNT film 16, drying it, and calcining it. be. This liquid composition contains at least Ba in addition to Bi, Na and Ti, and contains, for example, bismuth acetate, barium acetate, Na alkoxide and Ti alkoxide. This liquid composition may contain Mn and/or Nb. This liquid composition is applied once in the same manner as the BNT film-forming liquid composition, and is carried out so as to form a film having a thickness of preferably 50 nm or more and 100 nm or less after baking. If the film thickness after firing is less than 50 nm, productivity is poor, and if it exceeds 100 nm, cracks are likely to occur in the BNT-BT film after firing.

The calcination after coating and drying the above liquid composition is, for example, by a hot plate or RTA, the same as the calcination of the BNT film forming liquid composition, 350 ° C. or higher and 400 ° C. or lower, preferably 360 ° C. or higher and 380 ° C. or lower. at a temperature of If the calcining temperature is less than 350° C., a phase different from the BNT-BT phase is generated. If the temperature exceeds 400° C., the BNT-BT film (second calcined film) becomes difficult to crystallize.

[Batch firing of the first calcined film and the second calcined film]
After the BNT-BT film (second calcined film) 17 is produced, the BNT-BT film (second calcined film) 17 and the BNT film (first calcined film) 16 are baked together. By this batch firing, the first calcined film becomes an easily crystallizable film at the interface between the electrode and the second calcined film and increases the density of crystal nuclei generation, and is integrated with the second calcined film during firing. Then, as shown in FIG. 1(d), a BNT-BT film 11 is formed. In the state of the BNT-BT film 11, the first calcined film, which was the seed layer, disappears. This BNT _- BT film ₁₁ is formed with a perovskite structure. Mn and/or Nb are included in the site and/or the B site. This batch firing is carried out by heating the first calcined film and the second calcined film in an oxygen (O ₂ ) atmosphere, in a gas atmosphere of N ₂ , Ar, N ₂ O or H ₂ , or in a mixed gas atmosphere of these. For example, the temperature is raised to 600° C. or higher and 700° C. or lower by RTA at a rate of 25° C./second or higher, and the temperature is maintained for 0.5 minutes or longer and 5 minutes or shorter. A preferable heating rate is 25° C./second or more and 200° C./second or less, and a preferable firing temperature is 50° C. or more and 100° C. or less. If the heating rate is less than 25° C./sec, the firing temperature is less than 600° C., or the firing time is less than 0.5 minutes, the resulting BNT-BT film 11 has insufficient crystallinity and low density. . If the firing temperature exceeds 700° C. or the firing time exceeds 5 minutes, the productivity will deteriorate.

[Formation of BNT-BT film as thickness adjustment layer]
As shown in FIG. 1(e), a BNT-BT film 18 may be further formed on the BNT-BT film 11 as a thickness adjusting layer according to a desired film thickness. The BNT-BT-based film 18 is formed by coating the BNT-BT-based film 11 with the same liquid composition as the liquid composition forming the second calcined film, drying, and calcining. One layer or two or more calcined films are laminated according to the desired film thickness. The coating, drying and calcining conditions at this time are the same as the coating, drying and calcining conditions for forming the second calcined film. After laminating one or more layers of calcined films, these calcined films are collectively sintered. FIG. 1(e) shows an example in which four calcined films for forming a thickness adjusting layer are stacked and then fired. The thickness of a single BNT-BT-based film, that is, the thickness of a BNT-BT-based film formed by one firing is preferably 250 nm or more and 400 nm or less, and more preferably 270 nm or more and 380 nm or less. preferable. Here, the reason why the thickness of the BNT-BT-based film formed by one firing is limited to the range of 250 nm or more and 400 nm or less is that if it is less than 250 nm, the productivity decreases, and if it exceeds 400 nm, the BNT-BT film is formed during the film formation. This is because cracks are likely to occur in the -BT film.

[Characteristics of BNT-BT film of the first embodiment]
The BNT-BT films 11 and 18 of the first embodiment are formed by the sol-gel method described above, and the diffraction angle 2θ obtained by the X-ray diffraction method using Cu—Kα rays is 32° to 33°. The half width of the peak waveform of the (110) plane of is 0.200° or less. Therefore, the BNT-BT films 11 and 18 have high crystallinity and a high degree of orientation of the (110) plane. As a result, the BNT-BT films 11 and 18 have high piezoelectric properties. If the half width exceeds 0.200°, the crystallinity of the film is poor.

In the BNT-BT films 11 and 18 of the first embodiment, the degree of orientation of the (110) plane represented by the following formula (1) is 90% or more.
(110) plane orientation=ΣIb(110)/{ΣIa(100)+ΣIb(110)} (1)
Here, ΣIa(100) and ΣIb(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively.
Therefore, the dielectric constant is lower than that of a film having a high degree of orientation of the (110) plane and a high degree of orientation of the (100) plane, and is suitable for a sensor such as a gyro sensor.

<Second embodiment>
Next, a method for forming a BNT-BT film according to the second embodiment of the present invention will be described with reference to FIG. A feature of the second embodiment is that a LaNiO ₃ film (LNO film) 20 is formed on the lower electrode 15 of the substrate 12 as shown in FIGS. A BNT film (first calcined film) 26 and a BNT-BT film (second calcined film) 27 are laminated in this order on the film, and the first calcined film 26 and the second calcined film 27 are collectively baked. Then, the BNT-BT film 21 is formed. Reference numeral 28 denotes a BNT-BT film for forming a thickness adjusting layer laminated on the baked BNT-BT film 21 . It is the same as the first embodiment except that the LNO film 20 is formed. Therefore, repeated explanations are omitted except for the explanation of the formation of the LNO film.

[Formation of LNO film]
As shown in FIG. 2B, the LNO film 20 is formed on the electrode 15. As shown in FIG. Since the LNO film 20 has self-orientation in the (100) plane, it is used as a crystal orientation control layer for controlling the crystal orientation of the BNT-BT films 21 and 28 to the (100) plane. The LNO film 20 is formed by applying an LNO film forming liquid composition onto the electrode 15, drying it, calcining it, and then baking it. The LNO film forming liquid composition contains at least La and Ni. La sources include metal carboxylates such as lanthanum acetate, lanthanum octylate, and lanthanum 2-ethylhexanoate; metal nitrates such as lanthanum nitrate; metal alkoxides such as lanthanum isopropoxide; A diketonate complex or the like is selected, and the Ni source includes metal carboxylates such as nickel acetate, nickel octylate, and nickel 2-ethylhexanoate, metal nitrates such as nickel nitrate, and metal β-diketonate complexes such as nickel acetylacetonate. etc. are selected.

The coating, drying, calcining, and firing of the LNO film-forming liquid composition on the electrode 15 are performed under the same conditions as those for forming the BNT film or BNT-BT film.

[Characteristics of BNT-BT film of the second embodiment]
The BNT-BT films 21 and 28 of the second embodiment are formed by the sol-gel method described above and have the LNO layer 20 on the substrate electrode, so the diffraction obtained by the X-ray diffraction method using Cu-Kα rays The half width of the peak waveform of the (100) plane of the film near the angle 2θ=22.5° to 23.5° is 0.200° or less. Therefore, the BNT-BT films 21 and 28 have high crystallinity and a high degree of orientation of the (100) plane. As a result, the BNT-BT films 21 and 28 have high capacitor characteristics. If the half width exceeds 0.200°, the crystallinity of the film is poor.

In the BNT-BT films 21 and 28 of the second embodiment, the degree of orientation of the (100) plane represented by the following formula (2) is 90% or more.
Orientation degree of (100) plane = ΣIc(100)/{ΣIc(100) + ΣId(110)} × 100 (2)
Here, ΣIc(100) and ΣId(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively.
Since the dielectric constant of the film in which the degree of preferential orientation of the (100) plane is enhanced is higher than that of the film in which the degree of preferential orientation of the (110) plane is enhanced, it is suitable for a thin film capacitor.

Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
[Synthesis of 0.94Bi _0.55 Na _0.58 TiO ₃ -0.06BaTiO ₃ liquid composition]
In a flask, tetratitanium isopropoxide (Ti source) and acetylacetone with respect to the Ti source were added so that the molar ratio (Ti: acetylacetone) was 1:2 and stirred, and the mixture was heated to 150°C. of oil bath for 30 minutes. Next, bismuth acetate (Bi source) and barium acetate (Ba source) were added to the resulting solution in the flask so that the molar ratio (Ti:Bi:Ba) was 1:0.517:0.06. Furthermore, acetic acid was added at a rate of 20 mol per 1 mol of Ti, stirred, and refluxed in an oil bath at 150° C. for 30 minutes to obtain a homogeneous liquid. Next, sodium ethoxide (Na source) was added to this solution in the flask so that the molar ratio (Ti:Na) was 1:0.545, and 20 mol of ethanol was added to 1 mol of Ti and stirred. and refluxed for 30 minutes to obtain a homogeneous liquid. By reducing the pressure in the flask, the by-products and excess solution in the liquid were removed. The oxide concentration of the solution after removal was 20 mass %. Furthermore, 2-dimethylaminoethanol as a stabilizer was added so that the molar ratio (Ti: stabilizer) was 1:1, followed by dilution with acetic acid to 8% by mass in terms of oxide. The resulting liquid was filtered with a filter to remove dust, thereby obtaining a sol-gel liquid 0.94Bi _0.55 Na _0.58 TiO ₃ -0.06BaTiO ₃ liquid composition (hereinafter referred to as BNT-BT liquid composition). .

[Synthesis of Bi _0.60 Na _0.60 TiO ₃ -liquid composition]
A 1 mass% Bi _0.60 Na _0.60 TiO ₃ liquid composition (hereinafter referred to as BNT liquid composition I got a thing.).

[Formation of BNT-BT film]
First, a silicon substrate with a diameter of 100 mm was thermally oxidized to form an SiO ₂ film with a thickness of 500 nm on its surface. Ti was formed on the SiO ₂ film to a thickness of 20 nm by a sputtering method, followed by baking at 700° C. for 1 minute in an oxygen atmosphere by RTA to form a titanium oxide film. A lower electrode made of a (111) oriented Pt film with a thickness of 100 nm was formed on the titanium oxide film by a sputtering method. A BNT liquid composition of 1% by mass in terms of oxide was directly dropped onto the Pt film and spin-coated at 3000 rpm for 15 seconds. Further, calcination was performed on a hot plate at 350° C. for 5 minutes to form a first calcination film as a seed layer with a thickness of 10 nm on the Pt film. A BNT-BT liquid composition of 8% by mass in terms of oxide was applied onto the first calcined film and spin-coated at 3000 rpm for 15 seconds. Further, calcination was performed on a hot plate at 350° C. for 5 minutes to form a second calcined film as a BNT-BT dielectric layer with a thickness of 10 nm on the first calcined film. In an oxygen atmosphere, the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) were heated to 700° C. at a rate of 50° C./sec by RTA and held for 3 minutes. By collectively firing, the first calcined film and the second calcined film were integrated and crystallized. Each thickness of the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) was measured by a spectroscopic ellipsometer (JA Woollam Model M2000-DI).

Subsequently, the 8 mass% BNT-BT liquid composition was applied again on the collectively baked film, spin-coated at 3000 rpm for 15 seconds, and calcined on a hot plate at 350 ° C. for 5 minutes to perform the second calcination. A baked film (BNT-BT dielectric layer) was laminated. This formation of the second calcined film was repeated four times. The four layers of the second calcined film were heated up to 700° C. at a rate of 50° C./second by RTA, held for 3 minutes, and baked all at once. A BNT-BT film with a thickness of 320 nm was formed on the Pt film by firing the four-layer second calcined film (BNT-BT dielectric layer).

<Example 2>
BNT with a thickness of 320 nm was prepared in the same manner as in Example 1, except that the calcining temperature of each of the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) was changed to 375 ° C. - A BT film was formed.

<Example 3>
A BNT-BT film was formed in the same manner as in Example 1, except that the calcining temperature of each of the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) was changed to 400 ° C. formed.

<Example 4>
In the same manner as in Example 1, A BNT-BT film was formed.

<Example 5>
A BNT-BT film was formed in the same manner as in Example 1, except that the BNT-BT liquid composition was changed to a 0.90Bi _0.55 Na _0.58 TiO ₃ -0.10BaTiO ₃ liquid composition.

<Examples 6 to 8>
BNT-BT film was prepared in the same manner as in Example 1 except that the thickness of the first calcined film (seed layer) was changed to 4 nm (Example 6), 15 nm (Example 7) and 20 nm (Example 8). formed.

<Comparative Example 1>
A BNT-BT film was formed in the same manner as in Example 1, except that the calcining temperature of each of the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) was changed to 325 ° C. formed.

<Comparative Example 2>
A BNT-BT film was formed in the same manner as in Example 1, except that the calcining temperature of each of the first calcined film (seed layer) and the second calcined film (BNT-BT dielectric layer) was changed to 425 ° C. formed.

<Comparative Example 3>
In the same manner as in Example 1, A BNT-BT film was formed.

<Comparative Examples 4-5>
A BNT-BT film was formed in the same manner as in Example 1, except that the thickness of the first calcined film (seed layer) was changed to 3 nm (Comparative Example 4) and 25 nm (Comparative Example 5).
The following Tables 1 and 2 show the manufacturing conditions for forming BNT-BT films according to Examples 1 to 8 and Comparative Examples 1 to 5.

<Comparative evaluation test 1>
For the 13 types of BNT-BT films obtained in Examples 1 to 8 and Comparative Examples 1 to 5, the orientation plane, the half width of the peak waveform of the (110) plane, the degree of orientation of the (110) plane, the density and the relative dielectric ratio was measured or calculated. These results are shown in Table 2 above.

(1) Orientation Planes The preferential orientation planes of 13 types of BNT-BT films were measured by X-ray diffraction profiles. Specifically, the Cu-Kα ray of the BNT-BT films of Example 1 and Comparative Example 1 was used by a concentration method using an X-ray diffraction (XRD) apparatus (manufactured by PANalytical, model name: Empyrean). XRD analysis was performed. The results (only Example 1 and Comparative Example 1) are shown in FIG. As is clear from FIG. 3, the preferential orientation planes of the BNT-BT films of Example 1 and Comparative Example 1 were the (110) planes. In FIG. 3, the orientation plane having the diffraction angle 2θ within the range of 32° to 33° and having the highest intensity excluding the diffraction peak derived from the substrate was taken as the preferential orientation plane. Further, the BNT-BT films of Examples 2 to 8 and Comparative Examples 2 to 5 were also subjected to XRD analysis in the same manner as described above, and the preferential orientation planes were all (110) planes.

(2) Half width of peak waveform of (110) plane Half width of peak waveform of (110) plane of 13 types of BNT-BT films with diffraction angles 2θ = 32° to 33° obtained by the above XRD device (°) were asked for respectively.

(3) Peak intensity In the X-ray diffraction profiles of 13 types of BNT-BT films, the peak intensity of the (110) plane at diffraction angles 2θ = 32° to 33° was measured.

(4) Orientation degree of (110) plane In the X-ray diffraction profiles of 13 types of BNT-BT films, the diffraction angle 2θ is in the range of 22.5 ° to 23.5 ° (100) plane and (110) plane The integrated intensity (ΣIa(100) and ΣIb(110)) of each peak intensity was obtained, and the degree of orientation of the (110) plane was obtained by the following equation (1).
(110) plane orientation = ΣIb(110)/{ΣIa(100) + ΣIb(110)} × 100 (1)

(5) Density The film density (%) of 13 types of BNT-BT films was measured by SEM. The cross-section of the film is observed with an SEM, and the cross-sectional image is image-analyzed to calculate the area of the film and the area of voids in the film, [(area of film-area of voids)/area of film]. The film density (%) was calculated by performing the calculation of ×100.

(6) Relative dielectric constant First, after forming a pair of electrodes of 200 μmφ on the upper surface of the BNT-BT film by sputtering, they were held at 700° C. for 1 minute in an oxygen atmosphere using RTA to recover the damage. Annealing was performed to obtain a capacitor structure, which was used as a sample for relative permittivity measurement. After measuring the dielectric constant of this sample with a ferroelectric evaluation device (manufactured by aix ACCT: TF-analyzer 2000), in order to make it dimensionless, the measured dielectric constant is divided by the vacuum dielectric constant to obtain the specific dielectric rate was calculated.

<Evaluation result 1>
As is clear from Table 2, when Examples 1, 2, and 3 are compared with Comparative Examples 1 and 2, the preferential orientation of the (110) plane increases at a calcining temperature of 350°C to 400°C, and half of the peak It was confirmed that the price range has become smaller. A film with a small half-value width is excellent in crystallinity and can be expected to have high piezoelectric properties.

Comparing Examples 1 and 4 with Comparative Example 3, the film is sufficiently densified when the heating rate is 25° C./sec or more, but when it is less than 25° C./sec, the densification does not proceed sufficiently and the electrical properties are deteriorated. Deterioration was confirmed.

Comparing Examples 6, 7, and 8 with Comparative Examples 4 and 5, when the thickness of the BNT layer is less than 4 nm, the degree of orientation does not increase sufficiently, resulting in poor electrical properties. electrical characteristics are inferior. From these results, in order to obtain a BNT-BT film with good electrical properties, the calcination temperature is 350 ° C. or higher and 400 ° C. or lower, the temperature increase rate during firing is 25 ° C./sec or more, and the thickness of the BNT layer is 4 nm or more. It became clear that it is necessary to be 20 nm or less.

<Example 9>
[Formation of LaNiO ₃ film]
As LaNiO ₃ precursors, nickel acetate tetrahydrate (Ni source) and lanthanum nitrate hexahydrate (La source) were prepared, and these were mixed so that the metal atomic ratio of La and Ni was 1:1. weighed. As a stabilizer, N-methylformamide was prepared in an amount of 5 moles per 1 mole of the total amount of the above precursors. Next, after putting the nickel acetate tetrahydrate (Ni source) and the lanthanum nitrate hexahydrate (La source) into a flask, ethylene glycol monopropyl ether was added to prepare a mixed solution. .

After the mixed solution was dehydrated by distillation, N-methylformamide was added as a stabilizer. Further, this mixed solution was heated in an argon gas atmosphere at a temperature of 150° C. for 20 minutes for reaction, and then mass-adjusted with ethylene glycol monopropyl ether. As a result, a LaNiO ₃ film-forming liquid composition (hereinafter referred to as LNO liquid composition) having a metal atomic ratio of La and Ni of 1:1 and a LaNiO ₃ precursor concentration of 4% by mass in terms of oxide was obtained. Obtained.

The resulting LNO liquid composition was dropped onto a Si/SiO ₂ /TiO _x /Pt substrate having the same structure as in Example 1 and spin-coated at 3000 rpm for 15 seconds to form a coating film on the Pt film of the substrate. did. Next, after calcining the coating film on the substrate with a hot plate at 450° C. for 5 minutes, the temperature is raised to 800° C. at a rate of 10° C./sec in an oxygen atmosphere by RTA, and held at this temperature for 5 minutes. Firing was performed to form a LaNiO ₃ film (LNO film) on the substrate.

[Formation of BNT-BT film]
Using a BNT liquid composition having the same composition as in Example 1 and a BNT-BT liquid composition having the same composition as in Example 1, a first calcined film (seed layer) was formed on this LNO film in the same manner as in Example 1. was formed, a second calcined film (BNT-BT dielectric layer) was formed, and these were collectively sintered to form a BNT-BT film with a thickness of 300 nm. That is, in Example 9, a BNT-BT film was formed in the same manner as in Example 1, except that an LNO film was used as a base.

<Example 10>
In Example 10, a BNT-BT film was formed in the same manner as in Example 9, except that the calcination temperature was changed to 375°C.

<Example 11>
In Example 11, a BNT-BT film was formed in the same manner as in Example 9, except that the calcination temperature was changed to 400.degree.

<Example 12>
In Example 12, a BNT-BT film was formed in the same manner as in Example 10, except that the heating rate during firing was set to 25° C./sec).

<Example 13>
In Example 13, a BNT-BT film was formed in the same manner as in Example 10, except that the heating rate during firing was 100° C./sec).

<Example 14>
In Example 14, a BNT-BT film was formed in the same manner as in Example 10, except that the firing temperature was 750.degree.

<Example 15>
In Example 15, a BNT-BT film was formed in the same manner as in Example 10, except that the firing temperature was 800.degree.

<Comparative Example 6>
In Comparative Example 6, a BNT-BT film was formed in the same manner as in Example 10, except that no BNT layer was used.

<Comparative Example 7>
In Comparative Example 7, a BNT-BT film was formed in the same manner as in Example 10, except that the calcination temperature was set to 325.degree.

<Comparative Example 8>
In Comparative Example 8, a BNT-BT film was formed in the same manner as in Example 10, except that the calcination temperature was set to 425.degree.

<Comparative Example 9>
In Comparative Example 9, a BNT-BT film was formed in the same manner as in Example 10, except that the heating rate was 10° C./sec.
The manufacturing conditions for forming the BNT-BT films according to Examples 9-15 and Comparative Examples 6-9 are shown in Tables 3 and 4 below.

<Comparative evaluation test 2>
For the 11 types of BNT-BT films obtained in Examples 9 to 15 and Comparative Examples 6 to 9, in the same manner as in Comparative Evaluation Test 1, the half width and peak in the peak waveform of the oriented plane and (100) plane The strength, the degree of orientation of the (100) plane, the density and the dielectric constant were measured or calculated. These results are shown in Table 4 above.

(1) Orientation Planes The preferential orientation planes of 11 types of BNT-BT films were measured by X-ray diffraction profiles. Specifically, the XRD analysis of the BNT-BT films of Example 9 and Comparative Example 6 was performed in the same manner using the same X-ray diffraction (XRD) apparatus as in Comparative Evaluation Test 1. The results (only Example 9 and Comparative Example 6) are shown in FIG. As is clear from FIG. 4, the preferential orientation planes of the BNT-BT films of Example 9 and Comparative Example 6 were (100) planes. In FIG. 4, the orientation plane having the diffraction angle 2θ within the range of 22.5° to 23.5° and having the highest intensity excluding the diffraction peak derived from the substrate was taken as the preferential orientation plane. Also, the BNT-BT films of Examples 10 to 15 and Comparative Examples 7 to 9 were subjected to XRD analysis in the same manner as described above, and the preferential orientation planes were all (100) planes.

(2) Half width of the peak waveform of the (100) plane of the peak waveform of the (100) plane of 11 types of BNT-BT films with diffraction angles 2θ = 22.5° to 23.5° obtained by the XRD device The price range (°) was obtained for each.

(3) Peak intensity In the X-ray diffraction profiles of 11 types of BNT-BT films, the peak intensity of the (100) plane at diffraction angles 2θ = 22.5 to 23.5° was obtained.

(4) Orientation degree of (100) plane In the X-ray diffraction profiles of 11 types of BNT-BT films, the diffraction angle 2θ is in the range of 22.5 ° to 23.5 ° (100) plane and (110) plane The integrated intensity of each peak intensity (.SIGMA.Ic(100) and .SIGMA.Id(110)) was determined, and the degree of orientation of the (100) plane was determined by the following equation (2).
Orientation degree of (100) plane = ΣIc(100)/{ΣIc(100) + ΣId(110)} × 100 (2)

(5) Density The film densities (%) of 11 types of BNT-BT films were calculated by the same method as in Comparative Evaluation Test 1.

(6) Relative permittivity The relative permittivity of 11 types of BNT-BT films was calculated by the same method as in Comparative Evaluation Test No. 1.

<Evaluation result 2>
As is clear from Table 4, when Examples 9, 10, and 11 are compared with Comparative Examples 7 and 8, the half-value width of the peak waveform by XRD evaluation becomes smaller at a calcining temperature of 350 ° C. or more and 400 ° C. or less, and the peak intensity was also found to be improved. Generally, a film with a higher peak strength has better properties, so the calcining temperature above was favorable. Comparing Examples 10, 12, and 13 with Comparative Example 9, it was found that if the heating rate during firing was less than 25° C./sec, the film would not be sufficiently densified and high characteristics would not be obtained.

The BNT-BT film of the present invention is a piezoelectric film for MEMS applications such as vibration power generation elements, pyroelectric sensors, actuators, inkjet heads, and autofocus, or thin film capacitors, capacitors, IPDs, DRAM memory capacitors, multilayer capacitors, It can be used for capacitor films such as ferroelectric memory capacitors.

11, 21 BNT-BT film 12 substrate 15 electrode 16, 26 first calcined film (seed layer)
17, 27 Second calcined film 18, 28 BNT-BT film 20 LNO film

Claims (6)

A BNT-BT film composed of a (Bi, Na)TiO ₃ —BaTiO ₃ film formed on an electrode of a substrate,
The BNT-BT-based film is formed by a chemical solution deposition method (CSD method),
The half width of the peak waveform of the (110) plane of the film having a diffraction angle 2θ of 32° to 33° obtained by an X-ray diffraction method using Cu—Kα rays is 0.200° or less, and the following formula ( A BNT-BT film represented by 1), in which the degree of orientation of the (110) plane of the film is 90% or more.
(110) plane orientation = ΣIb(110)/{ΣIa(100) + ΣIb(110)} × 100 (1)
Here, ΣIa(100) and ΣIb(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively. A BNT-BT-based film composed of a (Bi, Na)TiO ₃ -BaTiO ₃ -based film formed on an electrode of a substrate via a LaNiO ₃ film,
The BNT-BT-based film is formed by a chemical solution deposition method (CSD method),
The half width of the peak waveform of the (100) plane of the film having a diffraction angle 2θ of 22.5° to 23.5° obtained by an X-ray diffraction method using Cu—Kα rays is 0.200° or less, A BNT-BT film represented by the following formula (2) and having a degree of orientation of the (100) plane of the film of 90% or more.
Orientation degree of (100) plane = ΣIc(100)/{ΣIc(100) + ΣId(110)} × 100 (2)
Here, ΣIc(100) and ΣId(110) denote the integrated intensities of the peak intensities of the (100) plane and the (110) plane, respectively.

3. The BNT-BT film according to claim 1, wherein said (Bi,Na)TiO ₃ --BaTiO ₃ film contains Mn and/or Nb in (Bi,Na)TiO ₃ --BaTiO ₃ . The BNT-BT film according to any one of claims 1 to 3, wherein said substrate is a silicon substrate or a sapphire substrate. The BNT-BT film according to any one of claims 1 to 4, wherein the electrode of the substrate is a Pt film oriented in the (111) plane. A method for forming a BNT-BT film composed of a (Bi, Na)TiO ₃ —BaTiO ₃ film on an electrode of a substrate directly or via a LaNiO ₃ film by a chemical solution deposition method (CSD method), comprising:
The liquid composition for forming a (Bi, Na)TiO ₃ film is applied directly or through the LaNiO ₃ film on the electrode of the substrate, dried, and calcined at a temperature of 350° C. or higher and 400° C. or lower to give a thickness of 4 nm or more and 20 nm. A first calcined film to be a seed layer is formed as follows, and a (Bi, Na) TiO ₃ —BaTiO ₃ -based film forming liquid composition is applied on the first calcined film and dried at 350° C. to 400° C. After calcining at a temperature below to form a second calcined film, the first calcined film and the second calcined film were heated at a rate of 25° C./second or more to 700° C. or more and 800° C. or less. A method for forming a BNT-BT film that forms a crystallized (Bi, Na)TiO ₃ —BaTiO ₃ film system by collectively sintering at a high temperature.

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