Film structure, piezoelectric film and superconducting film

Abstract

To form a film having a single crystal structure on a film structure for various piezoelectric and superconducting materials.SOLUTION: For various piezoelectric materials, a piezoelectric film having a single crystal structure can be formed on a film structure. The film structure 101 includes a substrate 11, a buffer film 12 having a tetragonal crystal structure containing zirconia, formed on the substrate, a conductive film 13 containing an epitaxially grown platinum group element, formed on the buffer film, and a film 16 containing epitaxially grown Sr(Ti1-x,Rux)O3 (0≤x≤1) formed on the conductive film.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a film structure provided with a buffer film that enables a single-crystal piezoelectric film or superconductor film to be formed on a substrate by epitaxial growth, the piezoelectric film, and the superconductor film. [Background technology]

[0002] In the IoT era, where everything is connected to the Internet, sensors play an important role, with the global market now worth $20 billion and growing at a rate of 7-8%, with 90 billion sensors produced annually worldwide. Among these, MEMS sensor technology using piezoelectric materials such as PZT is particularly active, and its use in a wide range of applications, including gyro sensors for autonomous driving, piezoelectric microphones, high-frequency filters for 5G communications, and vibration-powered energy harvesting elements, is expanding.

[0003] With the development of IoT technology, MEMS sensor technology using such piezoelectric materials is required to be smaller, thinner, and more sensitive with each passing year. However, to achieve high sensitivity, uniform polarization is required to ensure sufficient piezoelectricity. However, with piezoelectric materials, which are typically polycrystalline ceramic sintered bodies, uniform polarization does not occur. Furthermore, there are limits to how thin ceramic sintered bodies can be made. Therefore, in recent years, attempts have been made to obtain piezoelectric materials as thin-film single crystals by epitaxial growth (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-072428 Summary of the Invention [Problem to be solved by the invention]

[0005] In efforts to achieve single crystallization of such thin films, many piezoelectric materials are oxides. Therefore, when using a single-crystal Si substrate, for example, it is difficult to achieve single crystallization of the piezoelectric material by epitaxial growth. Therefore, oxide crystals such as YSZ (Yttria-stabilized zirconia) are sometimes used as buffer layers. However, because the crystal system of such oxide crystals differs from that of the piezoelectric material, the piezoelectric material is influenced by the crystal system of the buffer layer during crystal formation, making it difficult to achieve in-plane single crystallinity as a thin film. Furthermore, because the lattice constant varies for each piezoelectric material, the buffer layer configuration must be considered for each piezoelectric material, making the selection of the buffer layer difficult. [Means for solving the problem]

[0006] In order to solve the above problems, the film structure according to the present invention comprises a substrate, a buffer film having a tetragonal crystal structure containing zirconia formed on the substrate, an epitaxially grown metal film containing a platinum group element formed on the buffer film, and an epitaxially grown Sr(Ti 1-x ,Ru x )O3 and (0≦x≦1). [Effects of the Invention]

[0007] According to the present invention, films having a single crystal structure of various piezoelectric materials and superconducting materials can be formed on the film structure according to the present invention. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a substrate on which a buffer film according to the present invention is formed. [Figure 2] 1 is a cross-sectional view of a substrate having a lower electrode formed on a buffer film according to the present invention. [Figure 3] 1 is a cross-sectional view of a film structure including a buffer film according to the present invention. [Figure 4](a) is a STEM image of a cross section of a substrate 11 after a ZrO2 film was formed on the substrate 11 as a buffer film 12. The bottom image of (b) is an electron diffraction image of the substrate 11, and the top image is an electron diffraction image of the buffer film 12. [Figure 5] The buffer film 12 is a STEM image of a cross section observed when it is formed to a thickness of 1 nm (a), 12 nm (b), 15 nm (c), and 25 nm (d). [Figure 6] The results of measuring the θ-2θ spectrum of the film structure 101 by XRD are shown. [Figure 7] The conductive film 13 is a STEM image of a cross section observed when it is formed to a thickness of 10 nm (a), 20 nm (b), or 150 nm (c). [Figure 8] 1 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 1. [Figure 9] 1 shows a lattice image by STEM obtained by observing a cross section of PZT (30 / 70) as the piezoelectric film 14 according to Example 1. [Figure 10] Regarding the film structure 101 of Example 1, (a) is a pole figure of the Si(220) plane, (b) is a pole figure of the ZrO2(220) plane, (c) is a pole figure of Pt(220), and (d) is a pole figure of PZT(202). [Figure 11] 4 is a diagram showing the voltage dependence of polarization of the piezoelectric film 14 according to Example 1. FIG. [Figure 12] The results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 2 are shown. [Figure 13] 10A is a diagram showing an X-ray diffraction pattern by φ scanning of the substrate 11 and FIG. 10B is a diagram showing an X-ray diffraction pattern by φ scanning of the piezoelectric film 14 of the film structure 101 according to Example 2. FIG. [Figure 14] 10 shows a lattice image by STEM of a cross section of BTO as the piezoelectric film 14 according to Example 2. [Figure 15] FIG. 10 is a diagram showing the voltage dependence of polarization of the piezoelectric film 14 according to Example 2. [Figure 16]10 is a diagram showing the piezoelectricity of BTO as the piezoelectric film 14 according to Example 2. FIG. [Figure 17] 1 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 3. [Figure 18] 10A and 10B are diagrams showing X-ray diffraction patterns by φ scanning of the substrate 11 and the piezoelectric film 14, respectively, of the film structure 101 according to Example 3. FIG. [Figure 19] 10 shows a lattice image by STEM of a cross section of BFO as the piezoelectric film 14 according to Example 3. [Figure 20] FIG. 10 is a diagram showing the voltage dependence of polarization of the piezoelectric film 14 according to Example 3. [Figure 21] FIG. 10 is a diagram showing the piezoelectricity of BFO as the piezoelectric film 14 according to Example 3. [Figure 22] 10 shows the results of measuring the out-of-plane θ-2θ spectrum by the XRD method for the film structure 101 according to Example 4. [Figure 23] 10A and 10B are diagrams showing X-ray diffraction patterns by φ scanning of the substrate 11 and the piezoelectric film 14, respectively, of the film structure 101 according to Example 4. FIG. [Figure 24] 10 shows a lattice image by STEM of a cross section of BLT as the piezoelectric film 14 according to Example 4. [Figure 25] FIG. 10 is a diagram showing the voltage dependence of polarization of the piezoelectric film 14 according to Example 4. [Figure 26] FIG. 10 is a diagram showing the piezoelectricity of BLT as the piezoelectric film 14 according to Example 4. [Figure 27] The results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 5 are shown. [Figure 28] FIG. 10 is a diagram showing an X-ray diffraction pattern by φ scanning for the film structure 101 according to Example 5. [Figure 29] 10 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 6. [Figure 30]FIG. 10 is a diagram showing an X-ray diffraction pattern by φ scanning for the film structure 101 according to Example 6. [Figure 31] 1 shows the results of STEM observation of cross sections of the buffer film 12 and the conductive film 13 of a sample in which PZT (30 / 70) according to Example 1 was formed. [Figure 32] 10 shows the results of STEM observation of cross sections of the buffer film 12 and the conductive film 13 of the sample formed with BFO according to Example 3. [Figure 33] 1 shows the results of STEM observation of the cross section of the buffer film 12 and the conductive film 13 for the sample in which BLT was formed according to Example 4. [Figure 34] 1(a) is a lattice image showing a cross section of the interface between the conductive film 13 and the film 16 when the BFO film of Example 3 is formed, and FIG. 1(b) is a lattice image showing a cross section of the interface between the conductive film 13 and the film 16 when the BLT film of Example 4 is formed. [Figure 35] 10 shows the results of measuring the X-ray diffraction pattern of AlN by φ scanning using the XRD method for the film structure 101 according to Example 7. [Figure 36] 10 shows the results of measuring the X-ray diffraction pattern of LiNbO3 by φ scanning using the XRD method for the film structure 101 according to Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0010] The disclosure is merely an example, and any appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the invention are naturally included within the scope of the present invention. In addition, the drawings may be diagrammatic in width, thickness, shape, etc. of each part compared to the embodiment to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present invention.

[0011] In addition, in this specification and each drawing, elements similar to those previously described with respect to the previous drawings are given the same reference numerals, and detailed descriptions thereof may be omitted as appropriate.

[0012] Furthermore, in the drawings used in the embodiments, hatching (shading) used to distinguish structures may be omitted depending on the drawing.

[0013] (Embodiment) 1 is a cross-sectional view of a substrate on which a buffer film according to the present invention is formed. As shown in FIG. 1, a buffer film 12 is formed on a substrate 11.

[0014] The substrate 11 is, for example, a silicon (Si) substrate. In addition to Si, other substrates include, for example, SOI (Silicon on Insulator) substrates, substrates made of various semiconductor crystals other than Si, substrates made of various oxide single crystals such as sapphire, and substrates made of garnet (Al3Fe2Si3O 12 The substrate may be a 4-inch substrate, a glass substrate having a polysilicon film formed on its surface, or the like. These substrates may be not only 4-inch but also 6-inch or 8-inch substrates.

[0015] The substrate 11 may have any orientation, and in the case of a Si substrate, for example, Si(100), Si(110), Si(111), etc. may be used.

[0016] The buffer film 12 contains zirconia (ZrO2) epitaxially grown on the substrate 11 and is composed of a film portion 12a and a protruding portion 12b. It is known that ZrO2 undergoes a phase transition from monoclinic to tetragonal to cubic when energy is applied, but in the present invention, the buffer film 12 has a tetragonal crystal structure. The buffer film 12 is preferably grown epitaxially in accordance with the orientation of the substrate 11.

[0017] It has been reported that the performance of piezoelectric materials improves when they have a tetragonal crystal system, or even if they are not tetragonal, when they contain tetragonal crystals. Therefore, it is believed that providing tetragonal zirconium oxide as a buffer film has an advantageous effect on the formation of single crystals of piezoelectric materials.

[0018] Single-crystal ZrO2 contains up to 8% crystal defects, and it is believed that the presence of crystal defects causes the defect vacancies and adjacent atoms to exert elastic forces in a direction that reduces lattice distortion. The degree of this elastic force is believed to be proportional to the vacancy concentration. The buffer film 12 according to the present invention can utilize this elastic force to change its crystal structure.

[0019] 1, the buffer film 12 has protrusions 12b. The formation of the protrusions 12b is thought to be due to the fact that when the raw material concentration is supersaturated during the process of forming the buffer film 12, the crystals grow anisotropically along a certain axis or edge of the crystal, forming a pyramidal structure.

[0020] The buffer film 12 may contain not only ZrO2 but also rare earth elements and alkaline earth elements. In these, ZrO2 may contain oxygen defects. Furthermore, to improve characteristics, the buffer film 12 may contain transition metal elements such as Al, Sc, Mn, Fe, Co, and Ni.

[0021] Preferably, the film portion 12a is 10 nm or more, and the protrusion portion 12b is 3 to 8 nm.

[0022] 2 shows a cross-sectional view of a substrate in which a lower electrode is formed on the buffer film 12 shown in FIG. 1. The lower electrode includes a conductive film 13 and a film 16 epitaxially grown on the buffer film 12. The conductive film 13 can be formed using various metals, such as platinum group elements Ru, Rh, Pd, Os, Ir, and Pt. These materials are known to have similar physical and chemical properties.

[0023] The film 16 contains a composite oxide represented by the following general formula (Chemical Formula 1), such as strontium titanate (STO), strontium titanate ruthenate (STRO), or strontium ruthenate (SRO), where 0≦x≦1 is satisfied. Sr(Ti 1-x ,Ru x )O3… (Chem.1)

[0024] The lower electrode preferably has a flat surface, the conductive film 13 may be at least 20 nm thick, and the film 16 may be thinner than the conductive film 13 .

[0025] FIG. 3 shows a cross-sectional view of a film structure 101 according to the present invention, in which a piezoelectric film 14 and a conductive film 15 as an upper electrode are further formed on the substrate shown in FIG.

[0026] The material of the piezoelectric film 14 is, for example, a perovskite oxide such as lead zirconate titanate (PZT) or barium titanate (BaTiO3). Alternatively, for example, trigonal bismuth ferrite (BiFeO3) can be used. Similarly, trigonal lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) can be used. Alternatively, for example, hexagonal aluminum nitride (AlN) can be used.

[0027] Also, for example, a tungsten bronze type ferroelectric film or a bismuth layer structure ferroelectric film can be used as the piezoelectric film 14. Examples of materials having the crystal structure of a tungsten bronze type ferroelectric film include Ba2NaNb5O 15 is.

[0028] The crystal structure of the bismuth layer-structured ferroelectric film is represented by the general formula (Bi2O2) 2+ (A m-1 B m O 3m+1 ) 2- (m=1~5), or Bi2A m -1 B m O 3m+3 (m=1-5), (Bi2O2) 2+It has a plurality of suspected perovskite structures between the layers. The bismuth-layered structure ferroelectric, for example, is bismuth titanate (Bi4Ti3O 12 ). Or, for example, bismuth lanthanum titanate (Bi 4-x La x )Ti3O 12 (0 < x < 1) can be used.

[0029] Not limited to the above piezoelectric film 14, a superconducting film 14 may be formed using as a material a perovskite-structured yttrium-based superconductor such as YBa2Cu3O7 (YBCO) or a bismuth-based superconductor such as Bi2SrCa2Cu3O 10 (BSCCO).

[0030] When using a material for forming a piezoelectric film or a superconducting film as described above, a single-crystal piezoelectric film 14 or superconducting film 14 can be formed on the buffer film 12.

[0031] A conductive film 15 is formed on the piezoelectric film 14. The conductive film 15 can use the same material as the conductive film 13. Note that with the film 16, effects such as enhancing the adhesion between the conductive film 13 and the piezoelectric film 14 can be expected.

Examples

[0032] Hereinafter, this embodiment will be described in more detail based on examples. Note that the present invention is not limited by the following examples.

[0033] In Examples 1-4, a film structure 101 shown in FIG. 3 was created using a (100)-oriented Si substrate as the substrate 11. The piezoelectric film 14 was formed using, as the sputtering material, PZT (30 / 70) (Pb(Zr 0.3 ,Ti 0.7 )O3) in Example 1, BTO (BaTiO3) in Example 2, BFO (BiFeO3) in Example 3, and BLT ((Bi 3.25 ,La 0.75 )Ti3O 12 ) in Example 4.

[0034] First, a ZrO2 film was formed as a buffer film 12 on a substrate 11 by electron beam evaporation under the following conditions. Equipment: Electron beam evaporation equipment Pressure: 7.0×10 -3 Pa Vapor deposition source: Zr+O2 O2 flow rate: 10sccm Acceleration voltage / emission current: 7.5kV / 1.8mA Thickness: 25nm Substrate temperature: 600℃

[0035] Figure 4(a) is a STEM image of a cross section of a substrate 11 after a ZrO2 film was formed on the substrate 11 as a buffer film 12. The bottom image in Figure 4(b) is an electron diffraction image of the substrate 11, and the top image in Figure 4(b) is an electron diffraction image of the buffer film 12.

[0036] As shown in Figure 4(a), the surface of the buffer film 12 has pyramidal protrusions 12b, and it can be seen that the buffer film 12 is composed of a film portion 12a and protrusions 12b. As can be seen from the upper diagram of Figure 4(b), the buffer film 12 is an aggregate of fine ZrO2 single crystals, and is epitaxially grown on the upper surface of the substrate 11.

[0037] Figure 5 shows STEM cross-sectional views of the buffer film 12 at various film formation times. Figure 5(a) shows the buffer film 12 formed to a thickness of 1 nm, Figure 5(b) shows the buffer film 12 formed to a thickness of 12 nm, Figure 5(c) shows the buffer film 12 formed to a thickness of 15 nm, and Figure 5(d) shows the buffer film 12 formed to a thickness of 25 nm. In Figures 5(b) to 5(d), the shape of the protrusions 12b is highlighted by dotted lines so that it can be seen.

[0038] As shown in FIG. 5(a), it was found that no protrusions 12b were formed immediately after the buffer film 12 was formed. The film formation time was 3 seconds. Next, a sample was prepared by forming the buffer film 12 for 1 minute, and its cross section was observed (FIG. 5(b)). As shown in FIG. 5(b), it was found that the height of the protrusions 12b was non-uniform. Next, a sample was prepared by forming the buffer film 12 for 5 minutes, and its cross section was observed (FIG. 5(c)). As shown in FIG. 5(c), the protrusions 12b had a more uniform height than the protrusions 12b shown in FIG. 5(b). Next, a sample was prepared by forming the buffer film 12 for 8 minutes, and its cross section was observed (FIG. 5(d)). As shown in FIG. 5(d), the protrusions 12b had a more uniform height than the protrusions 12b shown in FIG. 5(b) or (c).

[0039] The average height of the protrusions 12b shown in Figures 5(b)-(d) was calculated based on the images, and was 2.2 nm in Figure 5(b), 3.33 nm in Figure 5(c), and 4.67 nm in Figure 5(d). The protrusions 12b had a square pyramid shape, and the diagonal length of the base was 3.3 nm in Figure 5(b), 5.0 nm in Figure 5(c), and 7.0 nm in Figure 5(d).

[0040] From the above results, the size of the quadrangular pyramids increased as the buffer film 12 was formed, and the height of the protrusions 12b increased with the film formation time. Furthermore, if the buffer film 12 formed for 0.05 minutes (3 seconds) (FIG. 5(a)) is considered to be flat and its surface area is set to 1.0, the surface areas of the buffer films 12 in FIGS. 5(b)-(d) were 1.30 to 1.60 times larger.

[0041] The film formation rate was calculated to be 3.33 [nm / sec] for Figure 5(a), 2.0 [nm / sec] for Figure 5(b), 0.50 [nm / sec] for Figure 5(c), 0.50 [nm / sec] for Figure 5(c), and 0.52 [nm / sec] for Figure 5(d). Thus, according to the film formation rate for each thickness of the buffer film 12, it was found that the film formation rate becomes constant when the film becomes thicker than 15 nm.

[0042] Figure 6 shows the results of measuring the θ-2θ spectrum by XRD after forming the conductive film 13 and the film 16 using a method described later. As shown in Figure 6, the peak positions indicate that the ZrO2 buffer film 12 has a tetragonal crystal structure oriented in the (200) plane.

[0043] Next, a platinum (Pt) film was formed as the conductive film 13 on the buffer film 12 by sputtering under the following conditions. Equipment: DC sputtering equipment Pressure: 1.2×10 -1 Pa Vapor deposition source: Pt Power: 100W Thickness: 150nm Substrate temperature: 450~600℃

[0044] 7A and 7B are STEM images of the cross section of a Pt conductive film 13 formed on a buffer film 12. Fig. 7A shows the conductive film 13 formed to a thickness of 10 nm, Fig. 7B shows the conductive film 13 formed to a thickness of 20 nm, and Fig. 7C shows the conductive film 13 formed to a thickness of 150 nm.

[0045] As shown in Figure 7(a), it was found that the surface of the conductive film 13 was almost flat even with a film thickness of 10 nm. Then, as shown in Figure 7(b), the surface of the conductive film 13 was made even flatter by increasing the film thickness to 20 nm, and even when the film was formed to a thickness of 150 nm, the flatness was maintained as shown in Figure 7(c).

[0046] Next, a SrRuO3 (SRO) film was formed as the film 16 on the conductive film 13 by sputtering under the following conditions. Equipment: RF magnetron sputtering equipment Power: 300W Gas: Ar Pressure: 1.8Pa Thickness: 20nm Substrate temperature: 600℃

[0047] Next, the piezoelectric film 14 was formed on the film 16. The formation conditions were the same in Examples 1 to 4, and only the sputtering materials were different. Equipment: RF magnetron sputtering equipment Material: [Example 1: PZT (30 / 70)] Pb(Zr 0.3 ,Ti 0.7 )O3, [Example 2: BTO] BaTiO3, [Example 3: BFO] BiFeO3, [Example 4: BLT] (Bi 3.25 ,La 0.75 )TiO 12 Power: 1500W Gas: Ar / O2 Pressure: 1.0Pa Substrate temperature: 450℃

[0048] Example 1 In Example 1, Si / ZrO2 / Pt / SRO / PZ / Pt were deposited as the film structure 101. Si(100) was used as the substrate 11. After PZT(30 / 70) was formed as the piezoelectric film 14, its film thickness was measured by XRF using a Rigaku X-ray fluorescence analyzer (AZX400) and found to be 1.0 μm.

[0049] Fig. 8 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 1. As shown in Fig. 8, it was found that PZT (30 / 70) was preferentially oriented along the c axis. Based on this X-ray diffraction pattern, the lattice constants a and c were determined, and the c / a axial ratio was calculated to be 1.046.

[0050] 9 is a cross-section of the film structure 101, showing a lattice image by STEM of PZT (30 / 70) as the piezoelectric film 14. As shown in FIG. 9, it was confirmed that the piezoelectric film 14 was single crystal, with no crystal lattice disturbance such as dislocation.

[0051] Fig. 10 shows the results of examining the in-plane orientation relationship of each layer of the film structure 101 according to Example 1 by measuring pole figures by the XRD method. Fig. 10(a) is a pole figure of the Si(220) plane, Fig. 10(b) is a pole figure of the ZrO2(220) plane, Fig. 10(c) is a pole figure of Pt(220), and Fig. 10(d) is a pole figure of PZT(202).

[0052] As shown in Figure 10(a)-(d), peaks with four-fold symmetry were observed, indicating that epitaxial growth had occurred with the in-plane orientation aligned with the substrate.

[0053] 11 is a graph showing the voltage dependence of polarization of the piezoelectric film 14 according to Example 1. As shown in FIG. 11, the piezoelectric film 14 according to Example 1 exhibits good characteristics, with a remanent polarization Pr of 50 μC / cm 2 The coercive electric field Ec was 180 kV / cm.

[0054] Example 2 In Example 2, the films were formed as follows: Si / ZrO2 / Pt / SRO / BTO. Si(100) was used as the substrate 11. After forming the BTO as the piezoelectric film 14, its film thickness was measured by XRF and found to be 1.0 μm.

[0055] Fig. 12 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 2. In Fig. 12, the upper curve shows the results of the out-of-plane measurement, and the lower curve shows the results of the in-plane measurement.

[0056] 12, the piezoelectric film 14 was preferentially oriented in the (001) plane. Furthermore, when the a-axis length and c-axis length of the piezoelectric film 14 were calculated from the measurement results, the a-axis length was 0.4012 nm and the c-axis length was 0.4262 nm. Therefore, the c / a ratio was 1.044, which indicated that the c-axis length was longer than the bulk value of 1.01.

[0057] 13 is a diagram showing an X-ray diffraction pattern by φ scanning for the film structure 101 according to Example 2. (a) is the pattern of the substrate 11, and (b) is the pattern of the piezoelectric film 14. As can be seen from FIG. 13, the piezoelectric film 14 has a four-fold axis of symmetry at the same angle as the substrate 11, and it was found that up to the piezoelectric film 14, the structure is formed in a cube-on-cube fashion.

[0058] 14 is a cross-section of the film structure 101 according to Example 2, showing a lattice image by STEM of BTO as the piezoelectric film 14. As shown in FIG. 14, it was confirmed that the piezoelectric film 14 was single crystal, with no crystal lattice disturbance such as dislocation.

[0059] Fig. 15 is a graph showing the voltage dependence of polarization of the piezoelectric film 14. As shown in Fig. 15, the piezoelectric film 14 according to Example 2 exhibited ferroelectric properties.

[0060] Figure 16 shows the piezoelectricity of the piezoelectric film 14 as confirmed by a d33 meter. The d33 meter is a d33 constant measurement device (model: LTFA-01) manufactured by Lead Techno Corporation, and is capable of measuring d33 even without a conductive film 15 as an upper electrode. Specifically, a force is applied to the film structure 101 and the change in the amount of charge is detected by an integrating circuit. If the film has piezoelectricity, a pulse-shaped waveform can be observed by applying or not applying force at regular time intervals, as shown in Figure 16. The d33 value at this time was 24.88 (pC / N).

[0061] Example 3 In Example 3, the films were formed as follows: Si / ZrO2 / Pt / SRO / BFO. Si(100) was used as the substrate 11. After forming BFO as the piezoelectric film 14, its film thickness was measured by XRF and found to be 2.1 μm.

[0062] Fig. 17 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 3. In Fig. 17, the upper curve shows the results of the out-of-plane measurement, and the lower curve shows the results of the in-plane measurement. As shown in Fig. 17, the piezoelectric film 14 was preferentially oriented in the (001) plane.

[0063] 18 shows X-ray diffraction patterns obtained by φ scanning. (a) shows the substrate 11, and (b) shows the pattern of the piezoelectric film 14. As can be seen from FIG. 18, after the piezoelectric film 14 was formed, it had a four-fold axis of symmetry at the same angle as the substrate 11, and it was found that up to the piezoelectric film 14, it was formed in a cube-on-cube fashion.

[0064] 19 is a cross-section of the film structure 101, showing a lattice image by STEM of BFO as the piezoelectric film 14. As shown in FIG. 19, it was confirmed that the piezoelectric film 14 was single crystal, with no crystal lattice disturbance such as dislocation.

[0065] 20 is a graph showing the voltage dependence of the polarization of the piezoelectric film 14. As shown in FIG. 20, the piezoelectric film 14 according to Example 3 exhibits good characteristics, with a remanent polarization Pr of 60 μC / cm 2 The coercive electric field Ec was 100 kV / cm.

[0066] Fig. 21 is a diagram showing the measurement results of the piezoelectric film 14 using a d33 meter. As shown in Fig. 21, it was found that the piezoelectric film 14 had piezoelectricity. The d33 value at this time was 16.69 (pC / N).

[0067] Example 4 In Example 4, the films were formed as follows: Si / ZrO2 / Pt / SRO / BLT. Si(100) was used as the substrate 11. After forming BLT as the piezoelectric film 14, its film thickness was measured by XRF and found to be 1.0 μm.

[0068] Fig. 22 shows the results of measuring the θ-2θ spectrum by the XRD method for the film structure 101 according to Example 4. Fig. 22 shows the results of the out-of-plane measurement. As shown in Fig. 22, the piezoelectric film 14 was preferentially oriented in the (001) plane.

[0069] Fig. 23 shows an X-ray diffraction pattern by φ scanning. (a) is the substrate 11, and (b) is the pattern formed up to the piezoelectric film 14. As can be seen from Fig. 24, after the formation of the piezoelectric film 14, it had a four-fold axis of symmetry at the same angle as the substrate 11, and was formed in a cube-on-cube manner.

[0070] Fig. 24 shows a cross section of the film structure 101, and a lattice image obtained by STEM observation of BLT as the piezoelectric film 14. As shown in Fig. 24, it was confirmed that the piezoelectric film 14 was single crystal, with no crystal lattice disturbance such as dislocation. In Fig. 25, W1 is the perovskite layer, and W2 is the bismuth oxide layer.

[0071] 25 is a graph showing the voltage dependence of the polarization of the piezoelectric film 14. As shown in FIG. 25, the piezoelectric film 14 according to Example 4 exhibits ferroelectricity, and the remanent polarization Pr is 4 μC / cm 2 The coercive electric field Ec was 4.5 kV / cm.

[0072] Fig. 26 is a diagram showing the measurement results of the piezoelectric film 14 using a d33 meter. As shown in Fig. 26, it was found that the piezoelectric film 14 had piezoelectricity. The d33 value at this time was 164.7 (pC / N).

[0073] Example 5 In Example 5, films were formed as follows: Si / ZrO2 / Pt / SRO / PZT. Si(111) was used as the substrate 11. After forming PZT as the piezoelectric film 14, its film thickness was measured by XRF and found to be 1.0 μm. A Pb / Zr / Ti(130 / 52 / 48) target was used as the PZT material.

[0074] Fig. 27 shows the results of measuring the θ-2θ spectrum by the XRD method for the sample prepared in Example 5. As shown in Fig. 27, the substrate 11, buffer film 12, conductive film 13, and piezoelectric film 14 were all oriented in the (111) plane.

[0075] Figure 28 shows the results of a φ scan performed by the XRD method on the sample prepared in Example 5, measured using the (111) plane as the diffraction plane. As shown in Figure 28, the substrate 11, conductive film 13, and piezoelectric film 14 exhibited three-fold symmetry. Note that although the peak of the conductive film 13 is shifted by 60°, it is an epitaxially grown single crystal film, and the piezoelectric film 14 is also an epitaxially grown single crystal film.

[0076] Example 6 In Example 6, films were formed as follows: Si / ZrO2 / Pt / SRO / PZT. Si (110) was used as the substrate 11. After forming PZT as the piezoelectric film 14, its film thickness was measured by XRF and found to be 1.0 μm. A Pb / Zr / Ti (130 / 52 / 48) target was used as the PZT material.

[0077] Fig. 29 shows the results of measuring the θ-2θ spectrum by the XRD method for the sample produced in Example 2. As shown in Fig. 29, the substrate 11 and the conductive film 13 were preferentially oriented in the (110) plane.

[0078] Figure 30 shows the results of a φ scan performed by the XRD method on the sample prepared in Example 6, measured using the (111) plane as the diffraction plane. As shown in Figure 30, the substrate 11, conductive film 13, and piezoelectric film 14 exhibited two-fold symmetry. This indicates that the piezoelectric film 14 is an epitaxially grown single crystal film.

[0079] As can be seen from the results of Examples 1-6, the buffer film 12 grows epitaxially in accordance with the orientation of the substrate 11, and the various piezoelectric films 14 formed thereon also grow epitaxially. This is thought to be because, as will be explained below, after the buffer film 12 is formed, the crystal structure of the buffer film 12 changes depending on the piezoelectric material formed thereon.

[0080] Fig. 31 shows the results of STEM observation of the cross section of the buffer film 12 and the conductive film 13 for the sample formed with PZT (30 / 70) according to Example 1. As shown in Fig. 31(a), the length between the protrusions 12b was 4.2 nm. Fig. 31(b) is an enlarged view of the protrusions 12b.

[0081] 32 shows the results of STEM observation of the cross section of the buffer film 12 and the conductive film 13 for the sample formed with BFO according to Example 3. As shown in Fig. 32(a), the distance between the protruding portions 12b was 3.9 nm. Fig. 32(b) is an enlarged view of the protruding portions 12b.

[0082] Fig. 33 shows the results of STEM observation of the cross section of the buffer film 12 and the conductive film 13 for the sample formed with BLT according to Example 4. As shown in Fig. 33(a), the distance between the protruding portions 12b was 5.5 nm. Fig. 33(b) is an enlarged view of the protruding portions 12b.

[0083] 31-33, the height of the protrusion 12b varies depending on the lattice constant of the piezoelectric film 14. For example, the lattice constant of the a-axis of BFO shown in FIG. 32 is 0.3971 nm, which is the shortest compared to PZT in FIG. 31 and BLT in FIG. 33. In this case, the height of the protrusion 12b is 6.3 nm as shown in FIG. 32(b), and it is thought that the protrusion 12b is stretched upward to match the BFO with its short lattice constant during the deposition process of BFO, which is the piezoelectric film 14.

[0084] On the other hand, the a-axis lattice constant of BLT shown in Fig. 33 is 0.5411 nm, which is the longest compared to PZT in Fig. 31 and BFO in Fig. 32. In this case, the height of protrusion 12b is 2.8 nm as shown in Fig. 33(b), and it is thought that protrusion 12b is crushed downward to fit the BLT with a long lattice spacing during the film formation process of BLT, which is the piezoelectric film 14.

[0085] In this way, the buffer film 12, particularly the protruding portion 12b, is deformed depending on the type of piezoelectric film 14, and the lattice spacing of the conductive film 13 and film 16 on the buffer film 12 also varies. Figure 34(a) is a lattice image showing a cross section of the interface between the conductive film 13 and film 16 when BFO is formed, and Figure 34(b) is a lattice image showing a cross section of the interface between the conductive film 13 and film 16 when BLT is formed.

[0086] As shown in Figure 34(b), the molecular spacing between the conductive film 13 and the film 16 when BLT is formed is longer than the molecular spacing between the conductive film 13 and the film 16 when BFO is formed, as shown in Figure 34(a).

[0087] Example 7 In Example 7, films were formed as follows: Si / ZrO2 / Pt / SRO / AlN. The substrate 11 was Si(100). The manufacturing conditions up to the SRO film were the same as in Examples 1-6. The AlN film was formed under the following conditions: Equipment: RF magnetron sputtering equipment Power: 200W Gas: Ar Pressure: 0.5Pa Film formation time: 60 minutes Substrate temperature: 200℃

[0088] Fig. 35 shows the results of measuring the X-ray diffraction pattern of AlN film structure 101 according to Example 7 by φ scanning using the XRD method. As shown in Fig. 35, it was found that the AlN film exhibited six-fold symmetry, was uniaxially oriented in (0001), and was single-crystallized. Note that the circled numbers 1 and 2 in Fig. 35 indicate a 90° rotation within the plane.

[0089] Example 8 In Example 8, films were formed as follows: Si / ZrO2 / Pt / SRO / LiNbO3 (LN). The substrate 11 was Si (100). The manufacturing conditions up to the SRO film were the same as in Examples 1-6. The LN film was formed under the following conditions: Equipment: RF magnetron sputtering equipment Power: 160W Gas: Ar / O2 ratio 2% Pressure: 0.8Pa Film formation time: 9 hours Substrate temperature: 400℃

[0090] Fig. 36 shows the results of measuring the X-ray diffraction pattern of the film structure 101 according to Example 8, in which LN was scanned along the φ axis by the XRD method. As shown in Fig. 35, it was found that the LN film exhibited four-fold symmetry, was uniaxially oriented in (001), and was single-crystallized.

[0091] As can be seen from the results of Examples 1 to 8 above, it was found that when an epitaxially grown Pt film and SRO film were formed on a buffer film containing zirconium, and a piezoelectric film was then formed thereon, a single-crystallized piezoelectric film could be formed. [Explanation of symbols]

[0092] 11 Circuit Board 12 Buffer film 12a Membrane part 12b Projection 13, 15 Conductive film 14 Piezoelectric film / Superconductor film 16 membrane 101 Membrane structure

Claims

1. A substrate; a buffer film having a tetragonal crystal structure containing zirconia and formed on the substrate and consisting of a film portion and a protrusion portion; an epitaxially grown metal film containing a platinum group element formed on the buffer film; An epitaxially grown Sr(Ti) １－ｘ , Ru ｘ ) O ３ (0≦x≦1), and A film structure for a single crystal piezoelectric film comprising:

2. The thickness of the metal film is 20 to 150 nm. The membrane structure according to claim 1 .

3. The film structure according to claim 1 or 2, wherein the buffer film further contains a rare earth element or an alkaline earth element.

4. The surface area of ​​the buffer film is 1.30 to 1.60 compared to a plane. The membrane structure according to any one of claims 1 to 3.

5. The substrate is oriented in the (100), (110), or (111) plane. The membrane structure according to any one of claims 1 to 4.

6. The buffer film is epitaxially grown according to the orientation of the substrate. The membrane structure according to any one of claims 1 to 5.

7. 7. The film structure according to claim 1, wherein the piezoelectric film has a trigonal crystal structure.

8. The material having a trigonal crystal structure is BiFeO ３ , LiNbO ３ , or LiTaO ３ The membrane structure according to claim 7, wherein

9. 7. The film structure according to claim 1, wherein the piezoelectric film has a hexagonal crystal structure.

10. The membrane structure according to claim 9, wherein the material having a hexagonal crystal structure is AlN.

11. 7. The film structure according to claim 1, wherein the piezoelectric film has a tungsten bronze type crystal structure.

12. 7. The film structure according to claim 1, wherein the piezoelectric film has a bismuth layer-type crystal structure.

13. The piezoelectric film is ABO ３ 7. The film structure according to claim 1, wherein the perovskite oxide is represented by the formula:

14. The ABO ３ 14. The film structure according to claim 13, wherein the perovskite oxide material represented by the formula (I) is lead zirconate titanate.

15. A substrate; a buffer film having a tetragonal crystal structure containing zirconia and formed on the substrate and consisting of a film portion and a protrusion portion; an epitaxially grown metal film containing a platinum group element formed on the buffer film; An epitaxially grown Sr(Ti) １－ｘ , Ru ｘ ) O ３ (0≦x≦1), and Use of the film structure as a single crystal piezoelectric film.

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