Laminate structure and electronic device

Abstract

To provide a laminate structure having an improved electromechanical coupling coefficient and an electronic device including the laminate structure.SOLUTION: A laminate structure 10 includes a substrate 11 including a main surface 11p, a buffer film 12 formed on the main surface 11p, and a piezoelectric film 13 formed on the buffer film 12. The substrate 11 is made of an Si (100) substrate including the main surface 11p made of an Si (100) plane or an SOI substrate including an SOI layer including a main surface made of the Si (100) plane. The buffer film 12 is epitaxially grown on the main surface 11p, is (100) oriented in a pseudo-cubic crystal display, and is made of a metal oxide represented by the following composition formula (Chemical Formula 1), and x satisfies 0≤x<1. The piezoelectric film 13 is made of a metal nitride containing AlN, and AlN contained in the metal nitride is oriented so that a (0001) plane is inclined with respect to the main surface 11p. (Hf1-xZrx)O2...(Chemical Formula 1)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated structure and an electronic device. [Background technology]

[0002] A film structure having a substrate and a piezoelectric film containing aluminum nitride (AlN) formed on the substrate, and an electronic device including the film structure are known. Also, a surface acoustic wave (SAW) device such as a SAW filter is known as such an electronic device.

[0003] International Publication No. 2023 / 171108 (Patent Document 1) discloses a technology in which, in a film structure having a substrate, a buffer film containing ZrO2 formed on the substrate, and a piezoelectric film formed on the buffer film, the substrate is a Si substrate or an SOI substrate including a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer made of a Si film on the insulating layer, and the polarization direction of the piezoelectric film is preferentially oriented perpendicular to the substrate.

[0004] On the other hand, Non-Patent Document 1 discloses a technology in which an electronic device has a piezoelectric film made of AlN formed on a substrate, and is made up of a shear mode thin film resonator and an SH-SAW device, in which the AlN is oriented so that the c-axis of the AlN is parallel to the substrate.

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2023-106746 (Patent Document 2) discloses a technology for a frequency filter that includes a first laminate formed by alternately stacking multiple layers of a first layer made of a piezoelectric material whose polarization is oriented in a predetermined direction and a second layer made of a piezoelectric material whose polarization is oriented in a direction different from the polarization of the first layer or made of an insulating material that does not have piezoelectricity.

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 2006-036561 (Patent Document 3) discloses a method for growing a semiconductor crystal made of a Group III nitride compound semiconductor on a crystal growth substrate, the method comprising the steps of: forming a plurality of parallel stripe grooves, each having a flat inner wall surface, on a planar main surface of the crystal growth substrate; stacking a buffer layer on one of the main inner wall surfaces of the stripe groove; faceting or laterally growing the semiconductor crystal on the crystal growth surface provided by the buffer layer; and growing the semiconductor crystal in a direction perpendicular to the main surface. In the technique described in Patent Document 3, a first angle θ1 formed between the main inner wall surface of the stripe groove and the main surface satisfies θ0-10°≦θ1≦θ0+10° with respect to a second angle θ0 formed between the c-axis of the semiconductor crystal and the crystal orientation where the piezoelectric field of the semiconductor crystal is zero. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2023 / 171108 [Patent Document 2] Japanese Patent Application Publication No. 2023-106746 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-036561 [Non-patent literature]

[0008] [Non-Patent Document 1] M. Suzuki et al., “Polarization-inverted multilayered pure shear mode AlN film resonator”, 2011 IEEE International Ultrasonics Symposium Proceedings (2011) 312-315 [Non-patent document 2] Yukihiro Kanechika, "Technological Trends of High-Heat Dissipation AlN Substrates for Semiconductor Devices," Journal of the Japan Institute of Electronics Packaging, 2012, Vol. 15, No. 3, pp. 185-189 [Non-patent document 3] T. Yanagitani et al., “Electromechanical coupling and gigahertz elastic properties of ScAlN films near phase boundary”, Applied Physics Letters 105 (2014) 122907 [Non-patent document 4] Y. Kuroiwa et al., “Piezoelectricity in perovskite-type pseudo-cubic ferroelectrics by partial ordering of off-centered cations”, Communications Materials 71 (2020) 1 Summary of the Invention [Problem to be solved by the invention]

[0009] In the technology described in Patent Document 2, when the c-axis of AlN is tilted from the direction perpendicular to the substrate, the electromechanical coupling coefficient increases compared to when the c-axis of AlN is not tilted from the direction perpendicular to the substrate.

[0010] However, in practice, it has been difficult to control the angle at which the AlN c-axis is tilted from the direction perpendicular to the substrate to a fixed angle, making it even more difficult to form a piezoelectric film containing AlN on a general-purpose silicon substrate with the angle at which the AlN c-axis is tilted from the direction perpendicular to the substrate controlled to a fixed angle and thereby improve the electromechanical coupling coefficient.

[0011] The present invention aims to provide a laminated structure in which a piezoelectric film containing aluminum nitride is formed on a silicon substrate, and an electronic device equipped with the laminated structure, in which the electromechanical coupling coefficient is improved, and an electronic device equipped with the laminated structure. [Means for solving the problem]

[0012] As a result of extensive investigation, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] a substrate including a main surface; a buffer film formed on the main surface; a piezoelectric film formed on the buffer film; In a laminated structure having the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; The buffer film is epitaxially grown on the main surface, has a (100) orientation in pseudo cubic crystal notation, and is made of a metal oxide represented by the following composition formula (Chemical Formula 1): (Hf 1-x Zr x )O2...(Chemical 1) wherein x satisfies 0≦x<1; the piezoelectric film is made of a metal nitride containing AlN, The AlN contained in the metal nitride is oriented such that the (0001) plane of the AlN contained in the metal nitride is inclined with respect to the main surface. [2] The laminated structure according to [1], wherein the AlN contained in the metal nitride has a (10-12) orientation. [3] The laminate structure according to [1] or [2], wherein the laminate structure is positioned so that the first diffraction plane in the first X-ray diffraction measurement is inclined at 47° with respect to the main surface, and a diffraction peak showing four-fold symmetry is observed in a φ scan of the (0002) plane of AlN contained in the metal nitride measured by the first X-ray diffraction measurement. [4] In a state where the stacked structure is arranged so that a second diffraction plane in a second X-ray diffraction measurement using a θ-2θ method is parallel to the main surface, in a diffraction pattern of the stacked structure measured by the second X-ray diffraction measurement, the plane spacing of the (10-12) plane calculated from the diffraction peak angle of the (10-12) plane of AlN contained in the metal nitride is defined as the first plane spacing; The second interplanar spacing is the interplanar spacing of the (10-12) plane of AlN calculated assuming that AlN has a hexagonal crystal structure, the lattice constant in the a-axis direction is 0.311 nm, and the lattice constant in the c-axis direction is 0.498 nm. Assuming that AlN has a pseudo-tetragonal crystal structure, the lattice constant in the a-axis direction is 0.270 nm, and the lattice constant in the c-axis direction is 0.500 nm, the spacing of the (102) planes of AlN calculated based on this assumption is taken as the third plane spacing. The laminated structure according to any one of [1] to [3], wherein a first interplanar spacing difference between the first interplanar spacing and the second interplanar spacing is larger than a second interplanar spacing difference between the first interplanar spacing and the third interplanar spacing. [5] The stacked structure according to any one of [2] to [4], wherein the [10-12] direction of AlN contained in the metal nitride is aligned with the

[0100] direction of the metal oxide. [6] An electronic device comprising the laminate structure according to any one of [1] to [5]. [7] The electronic device according to [6], wherein the laminated structure has an interdigital transducer formed on an upper surface of the piezoelectric film. [Effects of the Invention]

[0013] The stacked structure of the present invention and an electronic device including the stacked structure can improve the electromechanical coupling coefficient in a stacked structure in which a piezoelectric film containing aluminum nitride (AlN) is formed on a buffer film formed on the main surface of a Si(100) substrate or an SOI substrate, and in an electronic device including the stacked structure. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing an example of a laminated structure according to a first embodiment. [Figure 2] FIG. 3 is a cross-sectional view showing another example of the laminated structure of the first embodiment. [Figure 3] FIG. 2 is a diagram showing the crystal structure of AlN having a hexagonal crystal structure and oriented in (10-12). [Figure 4] FIG. 1 shows a state in which AlN is distorted from a state having a hexagonal crystal structure to a state having a pseudo-tetragonal crystal structure. [Figure 5] FIG. 10 is a perspective view of an electronic device according to a second embodiment. [Figure 6] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 7] 1 is a graph showing a φ scan of the laminated structure of Example 1. [Figure 8] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 9] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 10] 1 is a graph showing a φ scan of the laminated structure of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0016] (Embodiment 1) First, the laminated structure of the first embodiment will be described. FIG. 1 is a cross-sectional view showing an example of the laminated structure of the first embodiment. FIG. 2 is a cross-sectional view showing another example of the laminated structure of the first embodiment. FIG. 3 is a diagram showing the crystal structure of AlN having a hexagonal crystal structure and oriented in (10-12). FIG. 4 is a diagram showing the state in which AlN is distorted from a state having a hexagonal crystal structure to a state having a pseudo-tetragonal crystal structure. In FIG. 4, the stress applied to the hexagonal crystal structure is indicated by arrows.

[0017] The laminated structure 10 shown in FIGS. 1 and 2 includes a substrate 11 including a principal surface 11p, a buffer film 12 formed on the principal surface 11p, and a piezoelectric film 13 formed on the buffer film 12.

[0018] 1, the substrate 11 is a Si(100) substrate including a main surface 11p of a Si(100) plane. In the example shown in Fig. 2, the substrate 11 is an SOI (Silicon On Insulator) substrate including a base 11a of a Si substrate, an insulating layer 11b on the base 11a, and an SOI (Silicon On Insulator) layer 11c made of a Si(100) film on the insulating layer 11b and including the main surface 11p of the Si(100) plane.

[0019] The buffer film 12 is epitaxially grown on the main surface 11p, has a (100) orientation in pseudo cubic crystal representation, and is made of a metal oxide represented by the following composition formula (Chemical Formula 1). (Hf 1-x Zr x )O2...(Chemical 1) In the above composition formula (Chemical Formula 1), x satisfies 0≦x<1.

[0020] In this specification, a metal oxide having a (100) orientation in pseudocubic notation means that the metal oxide has a cubic crystal structure and a (100) orientation, a tetragonal crystal structure and a (100) or (001) orientation, or a monoclinic crystal structure and a (100), (010) or (001) orientation. Hereinafter, the metal oxide represented by the above composition formula (Chemical Formula 1) may be referred to as HZO.

[0021] The piezoelectric film 13 is made of a metal nitride containing AlN, and the AlN contained in the metal nitride is oriented so that the (0001) plane of the AlN contained in the metal nitride is inclined with respect to the main surface 11p.

[0022] As described in the above Patent Document 2, the piezoelectric material of the first and second layers is aluminum nitride with scandium (Sc) added. 1-x Sc xWhen using N, it is said that the polarization direction is preferably inclined at an angle of 27° to 43° from the perpendicular to the first and second layers. That is, as described in Patent Document 2, when the c-axis of AlN is inclined from the direction perpendicular to the substrate, the electromechanical coupling coefficient increases compared to when the c-axis of AlN is not inclined from the direction perpendicular to the substrate. However, it has been difficult to control the angle at which the c-axis of AlN is inclined from the direction perpendicular to the substrate to a constant angle.

[0023] On the other hand, according to the laminated structure of the first embodiment, the angle at which the c-axis of AlN is inclined from the direction perpendicular to the substrate can be controlled to a constant angle. Therefore, according to the laminated structure of the first embodiment, it is possible to form a piezoelectric film containing AlN on a silicon substrate, which is a general-purpose substrate, while controlling the angle at which the c-axis of AlN is inclined from the direction perpendicular to the substrate to a constant angle, thereby improving the electromechanical coupling coefficient. Furthermore, according to the laminated structure of the first embodiment, when a SAW device such as a SAW filter is formed as an electronic device using the laminated structure, the electromechanical coupling coefficient can be improved and the intensity of surface acoustic waves such as shear waves generated in the laminated structure can be increased. That is, according to the laminated structure of the first embodiment, by inclining the (0001) plane of AlN at a constant angle with respect to the main surface, the electromechanical coupling coefficient can be improved compared to a laminated structure in which the (0001) plane of AlN is not inclined with respect to the main surface.

[0024] The technology described in Patent Document 3 is said to be able to obtain an r-plane, i.e., an r-plane orientation, on a substrate by forming a predetermined angle between the main inner wall surface of the stripe groove and the main surface, and by growing AlN c-planes on the main inner wall surfaces. However, it is extremely difficult to form a large number of fine stripe grooves, each parallel to the other and having flat inner wall surfaces, on the planar main surface of a crystal growth substrate, such that the angle between the main inner wall surface and the main surface satisfies the predetermined angle. On the other hand, the stacked structure of the first embodiment allows a piezoelectric film containing AlN to be formed on a general-purpose silicon substrate, particularly a Si(100) substrate or an SOI substrate including an SOI layer with a main surface made of a Si(100) plane, without forming a large number of fine stripe grooves such that the angle between the main inner wall surface and the main surface satisfies the predetermined angle, while controlling the tilt angle of the AlN c-axis from the direction perpendicular to the substrate to a constant angle.

[0025] As shown in FIG. 3, the AlN contained in the metal nitride preferably has a (10-12) orientation.

[0026] In this case, the angle of inclination of the c-axis of AlN, i.e., the polarization, from the direction perpendicular to the substrate is about 47°. At this angle of inclination, as shown in FIG. 2 of the above-mentioned Patent Document 2, the electromechanical coupling coefficient k' in the thickness shear direction 15 2 Although it is slightly smaller than the maximum value that can be achieved at an inclination angle of about 35°, it is still quite large. On the other hand, the longitudinal electromechanical coupling coefficient k 33 2is significantly smaller than the value that can be obtained when the tilt angle is approximately 35° or less. Therefore, when a SAW device such as a SAW filter is constructed as an electronic device using this laminate structure, the electromechanical coupling coefficient can be further improved, and the intensity of surface acoustic waves such as shear waves generated in the laminate structure can be further increased. Therefore, when the AlN contained in the metal nitride has a (10-12) orientation, the electromechanical coupling coefficient can be further improved compared to when the (0001) plane of the AlN is simply tilted with respect to the main surface.

[0027] It is preferable that a diffraction peak exhibiting four-fold symmetry is observed in a φ scan of the (0002) plane of AlN contained in the metal nitride measured by the first X-ray diffraction measurement, with the stacked structure positioned so that the first diffraction plane in the first X-ray diffraction measurement is inclined at 47° with respect to the main surface 11p. Note that in this specification, a φ scan of the (0002) plane of AlN means a case in which 2θ in the φ scan is equal to the diffraction peak angle of the (0002) plane of AlN in the diffraction pattern of the stacked structure measured by X-ray diffraction measurement using the θ-2θ method, with the stacked structure positioned so that the diffraction plane in the X-ray diffraction measurement is parallel to the main surface.

[0028] In this case, not only is the AlN simply (10-12) oriented, but the polarization direction of the AlN can also be aligned in the in-plane direction along the upper surface of the substrate, i.e., the AlN can be epitaxially grown. Therefore, when a SAW device such as a SAW filter is configured as an electronic device using the laminated structure, the electromechanical coupling coefficient can be further improved and the intensity of surface acoustic waves such as shear waves generated in the laminated structure can be further increased. That is, in the laminated structure of the first embodiment, the AlN contained in the metal nitride may be epitaxially grown so that the (0001) plane of the AlN is inclined with respect to the main surface 11p.

[0029] The stacked structure was positioned so that the second diffraction plane in the second X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p (see FIG. 1). In the diffraction pattern of the stacked structure measured by the second X-ray diffraction measurement, the interplanar spacing of the (10-12) plane calculated from the diffraction peak angle of the plane PL (see FIG. 3) consisting of the (10-12) plane of AlN contained in the metal nitride was defined as the first interplanar spacing. The interplanar spacing of the (10-12) plane of AlN calculated assuming that the AlN has a hexagonal crystal structure, the lattice constant in the a-axis direction is 0.311 nm, and the lattice constant in the c-axis direction is 0.498 nm was defined as the second interplanar spacing. The interplanar spacing of the (10-12) plane of AlN calculated assuming that the AlN has a pseudo-tetragonal crystal structure, the lattice constant in the a-axis direction is 0.270 nm, and the lattice constant in the c-axis direction is 0.500 nm was defined as the third interplanar spacing. In this case, it is preferable that the first interfacial distance difference between the first interfacial distance and the second interfacial distance is larger than the second interfacial distance difference between the first interfacial distance and the third interfacial distance.

[0030] Here, as the lattice constants of the a-axis and c-axis when AlN has a hexagonal crystal structure, the values ​​of the lattice constants of the a-axis and c-axis described in Non-Patent Document 2 can be used. Also, as the lattice constant of the a-axis when AlN has a pseudo-tetragonal crystal structure, the lattice constant value of the a-axis described in Non-Patent Document 2 can be used. 1 / 2 In addition, when the layered structure is arranged so that the second diffraction plane in the second X-ray diffraction measurement using the θ-2θ method is inclined at an angle of 47° with respect to the main surface, the lattice spacing of the (0001) plane calculated from the diffraction peak angle of the (0002) plane of AlN in the diffraction pattern of the layered structure measured by the second X-ray diffraction measurement can be used as the c-axis lattice constant when AlN has a pseudo-tetragonal crystal structure.

[0031] In such a case, it can be determined that the AlN has been distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure, as shown in Figure 4. It is believed that the piezoelectric properties of the AlN are further improved by distorting the AlN to a pseudo-tetragonal crystal structure. Therefore, the electromechanical coupling coefficient can be further improved compared to when the AlN is not distorted to have a pseudo-tetragonal crystal structure.

[0032] As will be explained using Table 1 in Example 1 below, even when focusing on the (10-11) and (10-13) planes instead of the (10-12) plane, and the plane spacing calculated from the diffraction peak angle is taken as the first plane spacing, the plane spacing calculated assuming that AlN has a hexagonal crystal structure is taken as the second plane spacing, and the plane spacing calculated assuming that AlN has a pseudo-tetragonal crystal structure is taken as the third plane spacing, it is preferable that the first plane spacing difference between the first plane spacing and the second plane spacing is larger than the second plane spacing difference between the first plane spacing and the third plane spacing.

[0033] The [10-12] direction of AlN contained in the metal nitride is preferably aligned with the

[0100] direction of the metal oxide.

[0034] As mentioned above, the metal oxide grows epitaxially on the primary surface and has a (100) orientation in the pseudocubic crystal representation. Therefore, the [10-12] direction of AlN is aligned with the

[0100] direction of the metal oxide, facilitating epitaxial growth of AlN. Furthermore, the

[0100] direction of the metal oxide is aligned with the

[0100] direction of the Si substrate, so the [10-12] direction of AlN can be aligned with the

[0100] direction of the Si substrate. Therefore, when fabricating a SAW device by forming an interdigital electrode on AlN (as described later with reference to FIG. 5 ), it is only necessary to control the relationship between the interdigital electrode and the orientation flat of the Si substrate, making it even easier to fabricate the SAW device.

[0035] (Embodiment 2) Next, an electronic device according to embodiment 2 will be described. The electronic device according to embodiment 2 is an electronic device including a SAW filter having the laminated structure according to embodiment 1. Fig. 5 is a perspective view of the electronic device according to embodiment 2.

[0036] The electronic device 20 shown in Figure 5 is an electronic device comprising a substrate 11 including a main surface 11p (see Figure 1), a buffer film 12 formed on the main surface 11p, a piezoelectric film 13 formed on the buffer film 12 and made of a metal nitride, and a laminated structure 10 having a comb electrode (interdigital electrode, interdigital transducer (IDT)) formed on the upper surface of the piezoelectric film 13, and is characterized in that the AlN contained in the metal nitride constituting the piezoelectric film 13 is oriented so that the (0001) plane of the AlN contained in the metal nitride is inclined with respect to the main surface 11p (see Figure 1).

[0037] The stacked structure 10 provided in the electronic device 20 of the second embodiment can also have a substrate 11, a buffer film 12, and a piezoelectric film 13, similar to the stacked structure 10 of the first embodiment. Therefore, among the substrate 11, buffer film 12, and piezoelectric film 13 of the stacked structure 10, descriptions of the same parts as the substrate 11, buffer film 12, and piezoelectric film 13 of the stacked structure 10 of the first embodiment may be omitted.

[0038] On the other hand, the electronic device 20 of the second embodiment is a SAW filter including the laminated structure 10 of the first embodiment, and therefore has electrodes 23 and 24 formed as comb electrodes on the upper surface of the piezoelectric film 13. That is, the electrodes 23 and 24 are comb-teeth electrodes formed on the upper surface of the piezoelectric film 13.

[0039] In this case, by applying an AC voltage between the electrodes 23 and 24, surface acoustic waves can be easily generated in the piezoelectric film 13. Furthermore, since it is possible to generate or pass surface acoustic waves having a resonance frequency determined depending on the elastic properties of the substrate 11, the piezoelectric film 13, and the electrodes 23 and 24, it is possible to make the laminate structure function as a resonator or a filter. Furthermore, since the c-axis of AlN is tilted from the direction perpendicular to the substrate, the electromechanical coupling coefficient can be improved and the strength of surface acoustic waves such as shear waves generated in the laminate structure can be increased compared to when the c-axis of AlN is not tilted from the direction perpendicular to the substrate.

[0040] For example, when the AlN contained in the metal nitride has a (10-12) orientation and the [10-12] direction of the AlN is aligned with the Si

[0100] direction of the substrate, the [10-12] direction of the AlN and the direction of the interdigital electrodes are preferably parallel or perpendicular to each other. In this case, the electromechanical coupling coefficient of the laminated structure can be further improved, and the strength of surface acoustic waves such as shear waves generated within the laminated structure can be further increased.

[0041] Here, the electrode 23 as a comb electrode, i.e., a comb-teeth electrode, includes a main body 23a extending in direction DR1 in a planar view, and a plurality of comb teeth 23b each protruding from the main body 23a in a direction DR2 that intersects or is preferably perpendicular to direction DR1 in a planar view, and extending in direction DR2 in a planar view and arranged at intervals in direction DR1. The electrode 24 as a comb electrode, i.e., a comb-teeth electrode, includes a main body 24a extending in direction DR1 in a planar view, and a plurality of comb teeth 24b each protruding from the main body 24a in a direction DR2 that intersects or is preferably perpendicular to direction DR1 in a planar view, and extending in direction DR2 in a planar view, and arranged at intervals in direction DR1. The comb teeth 23b and the comb teeth 24b are alternately arranged along direction DR1. In this case, the direction of the comb electrode is direction DR2, which is the direction in which the comb teeth 23b and the comb teeth 24b extend.

[0042] As mentioned above, the stacked structure 10 provided in the electronic device 20 of this embodiment 2 can also use an SOI substrate, which is a semiconductor substrate, as the substrate 11 instead of a Si substrate, as in the stacked structure 10 of embodiment 1. [Example]

[0043] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0044] (Example 1 and Comparative Example 1) [Formation of laminated structure] The stacked structure of Example 1 was fabricated. First, the crystal growth surface side of the Si substrate (100) was treated by reactive ion etching (RIE) and heated in the presence of oxygen to form a thermal oxide film. Then, without oxygen, molecular beam epitaxy (MBE) was performed to thermally react metals (Hf, Zr) from the deposition source with oxygen in the oxide film on the Si substrate, forming a metal oxide single crystal on the Si substrate as a buffer film 12 (see FIG. 1 ). Next, oxygen was introduced, the temperature was lowered, and the pressure was increased, and a metal oxide single crystal film was formed by MBE. The MBE conditions for this film formation were as follows: The target Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 1) was 0.75). Vapor deposition source: Hf, Zr Voltage: 3.5~4.75V Pressure: 3×10 -2 ~6×10 -2 Pa Substrate temperature: 450~700℃

[0045] Next, a piezoelectric film 13 (see FIG. 1) made of AlN was formed on the buffer film (see FIG. 1) by sputtering under the following conditions. Equipment: RF sputtering equipment Pressure: 1~2Pa Target: Al Gas: Ar / N2 Power: 2500~3500W(AC) Substrate temperature: 350~450℃ Thickness: 1.0~5.0μm Although the thickness of the piezoelectric film 13 described above is a thickness applicable to SAW devices, it can be changed depending on the application of various electronic devices such as SAW devices, and is not particularly limited.

[0046] On the other hand, a laminated structure of Comparative Example 1 was produced in exactly the same manner as in Example 1, except that only Zr was used as the vapor deposition source instead of Hf and Zr.

[0047] [X-ray diffraction measurement] After forming a buffer film 12 (see FIG. 1) on the main surface 11p of the substrate 11 (see FIG. 1), and before forming the piezoelectric film 13 (see FIG. 1), the layered structure was positioned so that the diffraction plane in the X-ray diffraction (XRD) measurement was parallel to the main surface 11p (see FIG. 1) using the θ-2θ method, and the diffraction pattern of the layered structure was measured by the X-ray diffraction measurement. The measured diffraction pattern of the layered structure of Example 1 is shown in FIG. 6. The XRD measurement was performed using an X-ray diffractometer SmartLab manufactured by Rigaku Corporation.

[0048] As shown in Figure 6, strong diffraction peaks of the (200) plane of tetragonal ZrO2 (T-ZrO2) and the (200) plane of monoclinic HfO2 (M-HfO2) were observed in the diffraction pattern. This revealed that the HZO contained in the metal oxide has a (100) orientation in the pseudocubic crystal representation.

[0049] Furthermore, a φ scan was performed on the obtained laminated structure with respect to the (110) plane (2θ=35.26°) of HZO contained in the metal oxide. The φ scan measured for the laminated structure of Example 1 is shown in FIG.

[0050] As shown in Figure 7, in the φ scan, four strong diffraction peaks of the (110) plane of HZO were observed at 90° intervals. That is, in the φ scan, diffraction peaks showing four-fold symmetry of HZO were observed. This revealed that the HZO contained in the metal oxide has its crystal axis aligned in the in-plane direction along the main surface 11p (see Figure 1) of the substrate 11 (see Figure 1), i.e., it has grown epitaxially.

[0051] After forming the piezoelectric film 13 (see FIG. 1), the resulting laminate structure was placed so that the diffraction plane in X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p (see FIG. 1), and the diffraction pattern of the laminate structure was measured by the X-ray diffraction measurement. The measured diffraction pattern of the laminate structure of Example 1 is shown in FIG.

[0052] As shown in FIG. 8, a strong diffraction peak of the (10-12) plane of AlN was observed in the diffraction pattern of Example 1. This revealed that the AlN contained in the metal nitride in Example 1 was (10-12) oriented. On the other hand, although not shown, the AlN contained in the metal nitride in Comparative Example 1 was (0001) oriented. Note that, since diffraction peaks of the (10-11) and (10-13) planes of AlN were observed in the diffraction pattern of Example 1, it is also possible to make the AlN contained in the metal nitride have a (10-11) or (10-13) orientation. That is, it was revealed that the AlN contained in the metal nitride in Example 1 was oriented so that the (0001) plane was inclined with respect to the main surface.

[0053] After forming the piezoelectric film 13 (see FIG. 1), the resulting multilayer structure was placed so that the diffraction plane in the X-ray diffraction measurement using the θ-2θ method was inclined at 47° with respect to the main surface 11p (see FIG. 1), and the diffraction pattern of the multilayer structure was measured by the X-ray diffraction measurement. The measured diffraction pattern of the multilayer structure of Example 1 is shown in FIG.

[0054] As shown in Figure 9, a strong diffraction peak of the (0002) plane of AlN was observed in the diffraction pattern. As explained with reference to Figure 3, the angle between the (10-12) plane of AlN and the c-axis is 47°. Therefore, the diffraction pattern in Figure 9 also reveals that the AlN contained in the metal nitride has a (10-12) orientation.

[0055] In addition, with the stacked structure positioned so that the first diffraction plane in the first X-ray diffraction measurement was inclined at 47° with respect to the main surface 11p (see FIG. 1), a φ scan was performed on the (0002) plane (2θ=36.03°) of AlN contained in the metal nitride. The measured φ scan is shown in FIG.

[0056] As shown in FIG. 10, in the φ scan, four strong diffraction peaks of the (0002) plane of AlN were observed at 90° intervals. That is, in the φ scan, diffraction peaks showing four-fold symmetry of AlN were observed. Therefore, it was revealed that the polarization direction of AlN contained in the metal nitride was aligned in the in-plane direction along the primary surface 11p of the substrate 11 (see FIG. 1), i.e., epitaxial growth occurred. Furthermore, as shown in FIGS. 7 and 10, it was revealed that the [10-12] direction of AlN contained in the metal nitride was aligned with the

[0100] direction of the metal oxide. That is, it was revealed that the AlN contained in the metal nitride includes, in a planar view, four regions (domains) in which the polarization direction of the AlN projected onto the main surface 11p is different from one another, and when one of the four regions is taken as a reference region, the directions in which the polarization direction of the AlN in the four regions is projected onto the main surface 11p are 0°, 90°, 180°, and 270° relative to the direction in which the polarization direction of the AlN in the reference region is projected onto the main surface 11p.

[0057] 9, the interplanar spacing of the (10-12) plane was calculated from the diffraction peak angle of the (10-12) plane of AlN contained in the metal nitride in the diffraction pattern, and the calculated interplanar spacing of the (10-12) plane is shown in Table 1 ((Actual) XRD Measurement) described later. Here, the calculated interplanar spacing of the (10-12) plane of AlN was defined as the first interplanar spacing.

[0058] Additionally, assuming that AlN has a hexagonal crystal structure, with a lattice constant in the a-axis direction of 0.311 nm and a lattice constant in the c-axis direction of 0.498 nm, the lattice spacing of the (hklm) planes of AlN was calculated. Here, the formula for calculating the hexagonal lattice spacing is expressed by the following formula (Equation 1).

[0059]

number

[0060] The interplanar spacings of the (0001), (10-11), (10-12), and (10-13) planes of AlN calculated using the above formula (Equation 1) are shown in Table 1 ((Calculated) Hexagonal Crystal) described below. Here, the calculated interplanar spacing of the (10-12) plane of AlN was defined as the second interplanar spacing.

[0061] Additionally, assuming that AlN has a pseudo-tetragonal crystal structure, with a lattice constant in the a-axis direction of 0.270 nm and a lattice constant in the c-axis direction of 0.500 nm, the lattice spacing of the (hkl) planes of AlN was calculated. Here, the formula for calculating the lattice spacing of a pseudo-tetragonal crystal is expressed by the following formula (Equation 2).

[0062]

number

[0063] The interplanar spacings of the (001), (101), (102), and (103) planes of AlN calculated using the formula (2) are shown in Table 1 ((calculated) tetragonal). Here, the calculated interplanar spacing of the (102) plane of AlN was taken as the third interplanar spacing.

[0064] [Table 1]

[0065] As shown in Table 1, the difference in first interplanar spacing between the first interplanar spacing ((actual) XRD measurement) and the second interplanar spacing ((calculated) hexagonal) is 0.012 nm, which is larger than the difference in second interplanar spacing (0.000 nm) between the first interplanar spacing ((actual) XRD measurement) and the third interplanar spacing ((calculated) tetragonal). Therefore, it became clear that AlN was distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure, as shown in Figure 4, for example.

[0066] Furthermore, as shown in Table 1, even when focusing on the (10-11) and (10-13) planes instead of the (10-12) plane, and assuming the first interplanar spacing to be the interplanar spacing calculated from the diffraction peak angle, the second interplanar spacing to be the interplanar spacing calculated assuming AlN has a hexagonal crystal structure, and the third interplanar spacing to be the interplanar spacing calculated assuming AlN has a pseudo-tetragonal crystal structure, the first interplanar spacing difference between the first and second interplanar spacings is larger than the second interplanar spacing difference between the first and third interplanar spacings. Therefore, even when focusing on the (10-11) and (10-13) planes, it was revealed that AlN is distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure, as shown in Figure 4, for example.

[0067] Although detailed explanation is omitted, when x in the above composition formula (Chemical Formula 1) satisfies 0≦x<1, the same results as in Example 1, in which the ratio of Hf:Zr is 25:75 (x in the above composition formula (Chemical Formula 1) is 0.75), were obtained.

[0068] Example 2 [Positive piezoelectric constant and electromechanical coupling coefficient] The laminated structure of Example 2 was fabricated in exactly the same manner as in Example 1, except that an upper electrode made of platinum (Pt) was formed on the piezoelectric film 13 .

[0069] As for the upper electrodes, a plurality of upper electrodes each having a pad shape and made of a metal film (not shown in FIG. 1) made of Pt were formed on a piezoelectric film 13 (see FIG. 1) made of a metal nitride.

[0070] The capacitance and piezoelectric constant d of the laminated structure of Example 2 thus fabricated were 33 and electromechanical coupling coefficient K 33 The capacitance and piezoelectric constant d shown in Tables 2 and 3 were measured. 33 and electromechanical coupling coefficient K 33 was measured using LPFS-01 manufactured by Lead Techno Corporation. 33 denotes the elastic compliance in the thickness direction.

[0071] [Table 2]

[0072] [Table 3]

[0073] As shown in Tables 2 and 3, the laminated structure of Example 2 has a high K 33 2 (average value), and a high K of about 42% 33 Furthermore, as described in Non-Patent Document 3, in AlN to which Sc is not added, the electromechanical coupling coefficient K t 2 is about 5%, and in ScAlN where Sc is added so that the amount of Sc added is 0.4, K t 2 is about 10 to 15%. Therefore, it was revealed that the stacked structure of Example 2, although the metal nitride contains AlN to which Sc is not added, can improve the electromechanical coupling coefficient to be almost the same as when the metal nitride contains ScAlN to which Sc is added so that the amount of Sc added is 0.4.

[0074] The reason why the electromechanical coupling coefficient can be improved by the layered structure of Example 2 can be considered as follows, for example, by referring to Non-Patent Document 4. Non-Patent Document 4 discloses a technology in which a ceramic material synthesized by dissolving barium titanate, magnesium bismuth titanate, and bismuth ferrite exhibits excellent ferroelectricity and piezoelectricity, even though the unit cell shaping the crystal appears to be cubic at first glance. In the technology described in Non-Patent Document 4, synchrotron X-ray diffraction experiments have revealed that the ferroelectricity and piezoelectricity are caused by bismuth ions with disordered atomic arrangements being biased in the direction of an applied electric field, significantly distorting the crystal lattice. Therefore, it is expected that the piezoelectricity of AlN can also be improved by shifting the atomic arrangement and significantly distorting the crystal lattice.

[0075] On the other hand, the stacked structure of Example 2 has a stacked structure similar to that of Example 1, and therefore the AlN is distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure. Here, the reason why the AlN is distorted to have a pseudo-tetragonal crystal structure has not been fully elucidated. However, it is thought that, for example, in the stacked structure of the present embodiment 1, the buffer film has a specific composition and orientation direction, and the piezoelectric film containing AlN has a specific orientation direction, which causes the AlN to have a large surface tension, and the AlN is distorted due to the influence of this large surface tension. Furthermore, it is thought that the distortion of the AlN to have a pseudo-tetragonal crystal structure causes the atomic arrangement to shift and the crystal lattice to become significantly distorted, resulting in improved piezoelectricity and an improved electromechanical coupling coefficient.

[0076] Although detailed explanation is omitted, when x in the above composition formula (Chemical Formula 1) satisfies 0≦x<1, the same results as in Example 2, in which the Hf:Zr ratio is 25:75 (x in the above composition formula (Chemical Formula 1) is 0.75), were obtained. [Explanation of symbols]

[0077] 10. Laminated structure 11 Circuit Board 11a Base 11b Insulating layer 11c SOI layer 11p main surface 12 Buffer film 13 Piezoelectric film 20 Electronic Devices 23, 24 electrodes 23a, 24a main body 23b, 24b comb teeth DR1, DR2 direction PL surface

Claims

1. a substrate including a major surface; a buffer film formed on the main surface; a piezoelectric film formed on the buffer film; In a laminated structure having the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including: a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; The buffer film is epitaxially grown on the main surface, has a (100) orientation in pseudo cubic crystal notation, and is made of a metal oxide represented by the following composition formula (Chemical Formula 1): (Hf ２ , ｘ Zr ｘ )O ２ ... (Formula 1) The x satisfies 0≦x<1, the piezoelectric film is made of a metal nitride containing AlN, The AlN contained in the metal nitride is oriented such that a (0001) plane of the AlN contained in the metal nitride is inclined with respect to the main surface.

2. 2. The laminated structure according to claim 1, wherein the AlN contained in the metal nitride has a (10-12) orientation.

3. 3. The stacked structure according to claim 2, wherein a diffraction peak exhibiting four-fold symmetry is observed in a φ scan of a (0002) plane of AlN contained in the metal nitride measured by the first X-ray diffraction measurement, when the stacked structure is positioned so that a first diffraction plane in the first X-ray diffraction measurement is inclined at 47° with respect to the main surface.

4. the stacked structure is arranged so that a second diffraction plane in a second X-ray diffraction measurement using a θ-2θ method is parallel to the main surface, and in a diffraction pattern of the stacked structure measured by the second X-ray diffraction measurement, the plane spacing of the (10-12) plane calculated from the diffraction peak angle of the (10-12) plane of AlN contained in the metal nitride is defined as a first plane spacing; The second interplanar spacing is the interplanar spacing of the (10-12) plane of AlN calculated when it is assumed that AlN has a hexagonal crystal structure, the lattice constant in the a-axis direction is 0.311 nm, and the lattice constant in the c-axis direction is 0.498 nm, Assuming that AlN has a pseudo-tetragonal crystal structure, the lattice constant in the a-axis direction is 0.270 nm, and the lattice constant in the c-axis direction is 0.500 nm, the spacing of the (102) planes of AlN calculated based on this assumption is taken as the third plane spacing. The laminated structure according to claim 3 , wherein a first interplanar distance difference between the first interplanar distance and the second interplanar distance is larger than a second interplanar distance difference between the first interplanar distance and the third interplanar distance.

5. 4. The laminated structure according to claim 3, wherein the [10-12] direction of AlN contained in said metal nitride is aligned with the [100] direction of said metal oxide.

6. An electronic device comprising the laminate structure according to any one of claims 1 to 5.

7. 7. The electronic device according to claim 6, wherein the laminated structure has an interdigital transducer formed on an upper surface of the piezoelectric film.

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