Laminate structure and electronic device

Abstract

To provide a laminate structure having an improved electromechanical coupling coefficient, and an electronic device.SOLUTION: A laminate structure 10 includes a substrate 11 including a main surface 11p, and a first buffer film 12, a second buffer film 13, and a piezoelectric film 14 sequentially formed on the main surface 11p. The substrate 11 is made of an Si (100) substrate including the main surface 11p made of an Si (100) plane. The first buffer film 12 is epitaxially grown on the main surface 11p, is (100) oriented in a pseudo-cubic crystal display, is made of a metal oxide represented by the following composition formula (Chemical Formula 1), and x satisfies 0≤x<1. The second buffer film 13 includes AlN, and the AlN is oriented so that a (0001) plane is inclined with respect to the main surface 11p. The piezoelectric film 14 includes GaN. The GaN is oriented such that the (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) or gallium nitride (GaN) 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.

[0007] Furthermore, International Publication No. 2016 / 132746 (Patent Document 4) describes a technology in which a thin film substrate has a substrate and a buffer layer on the substrate, the substrate being a cubic crystal substrate, the buffer layer being a hexagonal crystal, the c-axis of the buffer layer being oriented in a first direction at a rate of 50% or more, and the first direction being inclined within a range of 10° or more and 60° or less with respect to a direction perpendicular to the surface of the substrate. [Prior art documents] [Patent documents]

[0008] [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 [Patent Document 4] International Publication No. 2016 / 132746 [Non-patent literature]

[0009] [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]

[0010] 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 is increased compared to when the c-axis of AlN is not tilted from the direction perpendicular to the substrate. Therefore, it is predicted that when the c-axis of GaN is tilted from the direction perpendicular to the substrate, the electromechanical coupling coefficient will also be increased compared to when the c-axis of GaN is not tilted from the direction perpendicular to the substrate.

[0011] However, it has been difficult to actually control the angle at which the GaN c-axis is tilted from the perpendicular to the substrate to a constant value, making it even more difficult to form a GaN-containing piezoelectric film on a general-purpose silicon substrate with the GaN c-axis tilted from the perpendicular to the substrate at a constant angle and thereby improve the electromechanical coupling coefficient.

[0012] The present invention aims to provide a laminated structure in which a piezoelectric film containing gallium 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]

[0013] 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 first buffer film formed on the main surface; a second buffer film formed on the first buffer film; a piezoelectric film formed on the second 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 first 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 second buffer film is made of a first metal nitride containing AlN; the piezoelectric film is made of a second metal nitride containing GaN, the AlN contained in the first metal nitride is oriented such that a (0001) plane of the AlN contained in the first metal nitride is inclined with respect to the main surface; The GaN contained in the second metal nitride is oriented such that a (0001) plane of the GaN contained in the second metal nitride is inclined with respect to the primary surface. [2] the second buffer film includes a first domain, a second domain, a third domain, and a fourth domain, in which (0001) planes of AlN contained in the first metal nitride are oriented so as to be inclined at a first angle with respect to the main surface, and in which

[0001] axes of AlN contained in the first metal nitride are oriented in directions different from one another; a

[0001] direction of AlN contained in the first metal nitride in the second domain is rotated by 90° counterclockwise from a

[0001] direction of AlN contained in the first metal nitride in the first domain when viewed from the normal direction of the main surface, a

[0001] direction of AlN contained in the first metal nitride in the third domain is a direction rotated by 180° counterclockwise from a

[0001] direction of AlN contained in the first metal nitride in the first domain when viewed from the normal direction of the main surface, The stacked structure described in [1], wherein the

[0001] direction of the AlN contained in the first metal nitride in the fourth domain is rotated 270° counterclockwise from the

[0001] direction of the AlN contained in the first metal nitride in the first domain when viewed from the normal direction of the main surface. [3] the piezoelectric film includes a fifth domain, a sixth domain, a seventh domain, and an eighth domain, in which the (0001) plane of GaN contained in the second metal nitride is oriented so as to be inclined at a second angle with respect to the primary surface, and the

[0001] axes of GaN contained in the second metal nitride are oriented in directions different from each other; a

[0001] direction of GaN contained in the second metal nitride in the sixth domain is rotated by 90° counterclockwise from a

[0001] direction of GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the primary surface, a

[0001] direction of GaN contained in the second metal nitride in the seventh domain is rotated by 180° counterclockwise from a

[0001] direction of GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the primary surface, The stacked structure according to [1] or [2], wherein the

[0001] direction of the GaN contained in the second metal nitride in the eighth domain is rotated 270° counterclockwise from the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the main surface. [4] The stacked structure according to any one of [1] to [3], wherein the AlN contained in the first metal nitride has a (10-12) orientation. [5] A laminate structure according to any one of [1] to [4], wherein the laminate structure is positioned so that the first diffraction plane in the first X-ray diffraction measurement is inclined at 47° relative 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 first metal nitride measured by the first X-ray diffraction measurement. [6] 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 first 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 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 interplanar spacing. The laminated structure according to [5], 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. [7] The stacked structure according to [2], wherein the [10-12] direction of AlN contained in the first metal nitride in the first domain is aligned with the

[0100] direction of the metal oxide. [8] The stacked structure according to [3], wherein, when viewed from the normal direction of the main surface, the [10-12] direction of GaN contained in the second metal nitride in the fifth domain is aligned with the [10-12] direction of AlN contained in the first metal nitride in the first domain. [9] The multilayer structure according to any one of [1] to [8], wherein the thickness of the piezoelectric film is greater than the thickness of the second buffer film.

[10] The thickness of the first buffer film is 35 to 75 nm; The second buffer film has a thickness of 40 to 80 nm, The laminated structure according to any one of [1] to [9], wherein the thickness of the piezoelectric film is 350 to 450 nm.

[11] An electronic device comprising the laminated structure according to any one of [1] to

[10] . [Effects of the Invention]

[0014] The laminated structure of the present invention and an electronic device including the laminated structure can improve the electromechanical coupling coefficient in a laminated structure in which a piezoelectric film containing gallium nitride is formed on a silicon substrate and in an electronic device including the laminated structure. [Brief explanation of the drawings]

[0015] [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] 1 is a plan view schematically showing the orientation state of the crystal lattice of AlN contained in a first metal nitride and the crystal lattice of GaN contained in a second metal nitride. [Figure 4] 3 is a side view schematically showing the orientation state of the crystal lattice of AlN contained in the first metal nitride and the crystal lattice of GaN contained in the second metal nitride. FIG. [Figure 5] FIG. 1 is a diagram showing the crystal structure of AlN having a hexagonal crystal structure and a (10-12) orientation. [Figure 6] 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 7] FIG. 10 is a perspective view of an electronic device according to a second embodiment. [Figure 8] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 9] 1 is a graph showing a φ scan of the laminated structure of Example 1. [Figure 10] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 11] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 12] 1 is a graph showing a φ scan of the laminated structure of Example 1. [Figure 13] 1 is a graph showing a diffraction pattern of the laminated structure of Example 2. [Figure 14] 1 is a graph showing a diffraction pattern of the laminated structure of Example 2. [Figure 15] FIG. 10 is a pole figure of the laminated structure of Example 2. [Figure 16] FIG. 10 is a pole figure of the laminated structure of Example 2. [Figure 17] 1 is a STEM image of the laminated structure of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0017] (Embodiment 1) First, a stacked structure according to a first embodiment will be described. FIG. 1 is a cross-sectional view illustrating an example of the stacked structure according to the first embodiment. FIG. 2 is a cross-sectional view illustrating another example of the stacked structure according to the first embodiment. FIG. 3 is a plan view schematically illustrating the orientation of the crystal lattice of AlN contained in the first metal nitride and the crystal lattice of GaN contained in the second metal nitride. FIG. 4 is a side view schematically illustrating the orientation of the crystal lattice of AlN contained in the first metal nitride and the crystal lattice of GaN contained in the second metal nitride. FIG. 5 is a diagram illustrating the crystal structure of AlN having a hexagonal crystal structure and a (10-12) orientation. FIG. 6 is a diagram illustrating a state in which AlN is distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure. Note that, for ease of understanding, in FIGS. 3 and 4, the hexagonal crystal lattices of AlN and GaN are represented by square pillars, and the (0001) plane is hatched. In FIG. 6, the stress acting on the hexagonal crystal structure is indicated by arrows.

[0018] The laminated structure 10 shown in Figures 1 and 2 has a substrate 11 including a main surface 11p, a first buffer film 12 formed on the main surface 11p, a second buffer film 13 formed on the first buffer film 12, and a piezoelectric film 14 formed on the second buffer film 13.

[0019] 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.

[0020] The first buffer film 12 is epitaxially grown on the main surface 11p, 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) In the above composition formula (Chemical Formula 1), x satisfies 0≦x<1.

[0021] 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.

[0022] The second buffer film 13 is made of a first metal nitride containing AlN, and the AlN contained in the first metal nitride is oriented so that the (0001) plane of the AlN contained in the first metal nitride is inclined with respect to the main surface 11p.

[0023] The piezoelectric film 14 is made of a second metal nitride containing GaN, and the GaN contained in the second metal nitride is oriented so that the (0001) plane of the GaN contained in the second metal nitride is inclined with respect to the primary surface 11p.

[0024] 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 x When using N, it is preferable that the polarization direction is tilted by 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 tilted from the direction perpendicular to the substrate, the electromechanical coupling coefficient is increased compared to when the c-axis of AlN is not tilted from the direction perpendicular to the substrate. Therefore, when the c-axis of GaN is tilted from the direction perpendicular to the substrate, the electromechanical coupling coefficient is expected to be increased compared to when the c-axis of GaN is not tilted from the direction perpendicular to the substrate. However, it has been difficult to control the angle at which the c-axis of GaN is tilted from the direction perpendicular to the substrate to a constant angle.

[0025] On the other hand, according to the stacked 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, and the angle at which the c-axis of GaN on AlN is inclined from the direction perpendicular to the substrate can be controlled to a constant angle. Therefore, according to the stacked structure of the first embodiment, it is possible to form a piezoelectric film including GaN on a silicon substrate, which is a general-purpose substrate, in a state in which the angle at which the c-axis of GaN is inclined from the direction perpendicular to the substrate is controlled to a constant angle, thereby improving the electromechanical coupling coefficient. Furthermore, according to the stacked structure of the first embodiment, when a SAW device such as a SAW filter is formed as an electronic device using the stacked structure, the electromechanical coupling coefficient can be improved and the intensity of surface acoustic waves such as shear waves generated in the stacked structure can be increased. That is, according to the stacked structure of the first embodiment, by inclining the (0001) plane of GaN at a constant angle with respect to the main surface, the electromechanical coupling coefficient can be improved compared to a stacked structure in which the (0001) plane of GaN is not inclined with respect to the main surface.

[0026] 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 second buffer 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. Furthermore, without forming such fine stripe grooves, a piezoelectric film containing GaN can be formed in a state in which the angle at which the c-axis of GaN is tilted from the direction perpendicular to the substrate is controlled to a constant angle.

[0027] Furthermore, in the technology described in Patent Document 4, when an AlN layer is formed on a Si(001) substrate by sputtering and a GaN layer is grown on the AlN layer using an MOCVD apparatus, the angle between the direction perpendicular to the Si(001) substrate surface and the direction in which the target is located is 36°, so the c-axis of the AlN is inclined in the sputtering direction, and the c-axis of the GaN layer is also inclined in the sputtering direction. However, when the sputtering direction is inclined with respect to the direction perpendicular to the substrate surface, unevenness occurs on the surface of the GaN layer, which tends to reduce flatness and reduce the uniformity of the film thickness distribution of the GaN layer within the Si substrate surface. On the other hand, according to the stacked structure of the first embodiment, the angle between the direction perpendicular to the surface of the Si(001) substrate and the direction in which the target is located can be set to 0°, and the second buffer film containing AlN can be formed under a controlled condition so that the angle at which the c-axis of AlN is tilted from the direction perpendicular to the substrate is a constant angle, and the piezoelectric film containing GaN can be formed under a controlled condition so that the angle at which the c-axis of GaN is tilted from the direction perpendicular to the substrate is a constant angle.

[0028] 3 and 4, the second buffer film 13 preferably includes a first domain DM1, a second domain DM2, a third domain DM3, and a fourth domain DM4 in which the (0001) plane of the AlN contained in the first metal nitride is oriented so as to be inclined at a first angle θ11 with respect to the main surface 11p, and the

[0001] axes of the AlN contained in the first metal nitride are oriented in different directions. The first angle θ11 can be, for example, 43 to 47°, and can be, for example, 47°.

[0029] Here, the

[0001] direction of the AlN contained in the first metal nitride in the second domain DM2 is rotated 90° counterclockwise from the

[0001] direction of the AlN contained in the first metal nitride in the first domain DM1 when viewed from the normal direction of the main surface 11p (around the axis perpendicular to the main surface 11p). Also, the

[0001] direction of the AlN contained in the first metal nitride in the third domain DM3 is rotated 180° counterclockwise from the

[0001] direction of the AlN contained in the first metal nitride in the first domain DM1 when viewed from the normal direction of the main surface 11p (around the axis perpendicular to the main surface 11p). Furthermore, the

[0001] direction of the AlN contained in the first metal nitride in the fourth domain DM4 is rotated 270° counterclockwise from the

[0001] direction of the AlN contained in the first metal nitride in the first domain DM1 when viewed from the normal direction of the main surface 11p (around an axis perpendicular to the main surface 11p).

[0030] In this case, as will be described later with reference to Fig. 5, the AlN contained in the first metal nitride has a (10-12) orientation, and the inclination angle of the (0001) plane of the AlN with respect to the main surface 11p can be easily controlled to be a constant angle. Furthermore, as will be described later with reference to Fig. 6, the AlN contained in the first metal nitride is distorted from a hexagonal crystal structure to a pseudo-tetragonal crystal structure, and the electromechanical coupling coefficient can be further improved compared to when the AlN is not distorted to have a pseudo-tetragonal crystal structure.

[0031] 3 and 4, the piezoelectric film 14 preferably includes a fifth domain DM5, a sixth domain DM6, a seventh domain DM7, and an eighth domain DM8 in which the (0001) planes of the GaN contained in the second metal nitride are oriented so as to be inclined at a second angle θ12 with respect to the primary surface 11p, and the

[0001] axes of the GaN contained in the second metal nitride are oriented in different directions. The second angle θ12 can be, for example, 54 to 58°, and can be, for example, 56°.

[0032] Here, the

[0001] direction of the GaN contained in the second metal nitride in the sixth domain DM6 is rotated 90° counterclockwise from the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain DM5 when viewed from the normal direction to the primary surface 11p (around the axis perpendicular to the primary surface 11p). Also, the

[0001] direction of the GaN contained in the second metal nitride in the seventh domain DM7 is rotated 180° counterclockwise from the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain DM5 when viewed from the normal direction to the primary surface 11p (around the axis perpendicular to the primary surface 11p). Furthermore, the

[0001] direction of the GaN contained in the second metal nitride in the eighth domain DM8 is rotated 270° counterclockwise from the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain DM5 when viewed from the normal direction of the primary surface 11p (around an axis perpendicular to the primary surface 11p).

[0033] In such a case, as will be described later with reference to FIG. 16, the inclination angle of the (0001) plane of GaN contained in the second metal nitride with respect to primary surface 11p can be easily controlled to be a constant angle.

[0034] The fifth domain DM5 is formed on the first domain DM1, and the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain DM5 preferably aligns with the

[0001] direction of the AlN contained in the first metal nitride in the first domain DM1 when viewed from the normal direction of the primary surface 11p. In this case, the polarization direction of the GaN contained in the second metal nitride approaches a direction parallel to the polarization direction of the AlN contained in the first metal nitride, thereby improving the piezoelectric characteristics of the piezoelectric film 14. That is, the

[0001] direction of the GaN contained in the second metal nitride in the fifth domain DM5 preferably aligns with the

[0001] direction of the AlN contained in the first metal nitride in the first domain DM1 in a three-dimensional manner.

[0035] Similarly, the sixth domain DM6 is formed on the second domain DM2, and the

[0001] direction of the GaN contained in the second metal nitride in the sixth domain DM6 preferably aligns with the

[0001] direction of the AlN contained in the first metal nitride in the second domain DM2 when viewed from the normal direction to the primary surface 11p. The seventh domain DM7 is formed on the third domain DM3, and the

[0001] direction of the GaN contained in the second metal nitride in the seventh domain DM7 preferably aligns with the

[0001] direction of the AlN contained in the first metal nitride in the third domain DM3 when viewed from the normal direction to the primary surface 11p. The eighth domain DM8 is formed on the fourth domain DM4, and the

[0001] direction of the GaN contained in the second metal nitride in the eighth domain DM8 preferably aligns with the

[0001] direction of the AlN contained in the first metal nitride in the fourth domain DM4 when viewed from the normal direction to the primary surface 11p.

[0036] Furthermore, the

[0001] direction of the GaN contained in the second metal nitride in the sixth domain DM6 preferably aligns three-dimensionally with the

[0001] direction of the AlN contained in the first metal nitride in the second domain DM2. Furthermore, the

[0001] direction of the GaN contained in the second metal nitride in the seventh domain DM7 preferably aligns three-dimensionally with the

[0001] direction of the AlN contained in the first metal nitride in the third domain DM3. Furthermore, the

[0001] direction of the GaN contained in the second metal nitride in the eighth domain DM8 preferably aligns three-dimensionally with the

[0001] direction of the AlN contained in the first metal nitride in the fourth domain DM4.

[0037] In this specification, the term "a first direction is aligned with a second direction" refers not only to the case where the first direction is parallel to the second direction, but also to the case where the angle between the first direction and the second direction is 20° or less.

[0038] As shown in FIG. 5, the AlN contained in the first metal nitride preferably has a (10-12) orientation.

[0039] 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 is 15 2 is slightly smaller than the maximum value that can be achieved at an inclination angle of about 35°, but is still quite large, while the longitudinal electromechanical coupling coefficient k 33 2 is 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 first 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.

[0040] 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 first 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.

[0041] 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 of the second buffer film 13 containing AlN 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 first metal nitride may be epitaxially grown so that the (0001) plane of the AlN is inclined with respect to the main surface 11p.

[0042] 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. 5) consisting of the (10-12) plane of AlN contained in the first 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.

[0043] 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 / 2In 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.

[0044] 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 FIG. 6. 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 of the second buffer film 13 containing AlN can be further improved compared to when the AlN is not distorted to a pseudo-tetragonal crystal structure.

[0045] 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.

[0046] In the first domain DM1, the [10-12] direction of AlN contained in the first metal nitride is preferably aligned with the

[0100] direction of the metal oxide.

[0047] 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 the epitaxial growth of AlN, and GaN can be easily grown epitaxially on 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 via GaN (as described later with reference to FIG. 7), 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.

[0048] In addition, when the [10-12] direction of the AlN contained in the first metal nitride in the first domain DM1 is along the

[0100] direction of the metal oxide, the [10-12] direction of the AlN in the second domain, the [10-12] direction of the AlN in the third domain, and the [10-12] direction of the AlN in the fourth domain will be along any of the

[0010] direction, the [-100] direction, and the [0-10] direction, which are directions equivalent to the

[0100] direction of the metal oxide.

[0049] When viewed from the normal direction of the primary surface 11p, the [10-12] direction of the GaN contained in the second metal nitride in the fifth domain DM5 preferably aligns with the [10-12] direction of the AlN contained in the first metal nitride in the first domain DM1. In this case, the polarization direction of the GaN contained in the second metal nitride in the fifth domain DM5 approaches a direction parallel to the polarization direction of the AlN contained in the first metal nitride in the first domain DM1, thereby improving the piezoelectric properties of the GaN-containing piezoelectric film 14.

[0050] Similarly, when viewed from the normal direction of the primary surface 11p, the [10-12] direction of the GaN contained in the second metal nitride in the sixth domain DM6 preferably aligns with the [10-12] direction of the AlN contained in the first metal nitride in the second domain DM2. When viewed from the normal direction of the primary surface 11p, the [10-12] direction of the GaN contained in the second metal nitride in the seventh domain DM7 preferably aligns with the [10-12] direction of the AlN contained in the first metal nitride in the third domain DM3. When viewed from the normal direction of the primary surface 11p, the [10-12] direction of the GaN contained in the second metal nitride in the eighth domain DM8 preferably aligns with the [10-12] direction of the AlN contained in the first metal nitride in the fourth domain DM4.

[0051] The thickness of the piezoelectric film 14 is preferably thicker than the thickness of the second buffer film 13. In such a case, even if the second buffer film 13 is made of a first metal nitride containing AlN as a piezoelectric material and the piezoelectric film 14 is made of a second metal nitride containing GaN as a piezoelectric material, the piezoelectric properties of the piezoelectric film 14 can be determined by the piezoelectric properties of the piezoelectric film 14 rather than the second buffer film 13.

[0052] Preferably, the thickness of the first buffer film 12 is 35 to 75 nm, the thickness of the second buffer film 13 is 40 to 80 nm, and the thickness of the piezoelectric film 14 is 350 to 450 nm. In this case, the thickness of the piezoelectric film 14 can be set to 4.375 times or more the thickness of the second buffer film 13, and can be made significantly thicker than the thickness of the second buffer film 13. Therefore, the second buffer film 13 can be used as an orientation control film for orienting the piezoelectric film 14 made of the second metal nitride containing GaN.

[0053] When the thickness of the first buffer film 12 is 35 nm or more, the first buffer film 12 can be epitaxially grown over the entire main surface 11p of the substrate 11, compared to when the thickness of the first buffer film 12 is less than 35 nm. On the other hand, when the thickness of the first buffer film 12 is 75 nm or less, the first buffer film 12 can be epitaxially grown more reliably while the deposition time for the first buffer film 12 can be shortened, compared to when the thickness of the first buffer film 12 exceeds 75 nm.

[0054] When the thickness of the second buffer film 13 is 40 nm or more, the second buffer film 13 can be epitaxially grown on the entire surface of the first buffer film 12, compared to when the thickness of the second buffer film 13 is less than 40 nm. On the other hand, when the thickness of the second buffer film 13 is 80 nm or less, the deposition time for the second buffer film 13 can be shortened while the second buffer film 13 is reliably epitaxially grown, compared to when the thickness of the second buffer film 13 exceeds 80 nm.

[0055] When the thickness of the piezoelectric film 14 is 350 nm or more, the piezoelectric film 14 can be epitaxially grown on the entire surface of the second buffer film 13, compared to when the thickness of the piezoelectric film 14 is less than 350 nm. On the other hand, when the thickness of the piezoelectric film 14 is 450 nm or less, the piezoelectric film 14 can be epitaxially grown more reliably and the deposition time for the piezoelectric film 14 can be shortened, compared to when the thickness of the piezoelectric film 14 exceeds 450 nm.

[0056] (Embodiment 2) Next, a description will be given of an electronic device according to embodiment 2. The electronic device according to embodiment 2 is an electronic device including a SAW filter having the laminated structure according to embodiment 1. Fig. 7 is a perspective view of the electronic device according to embodiment 2.

[0057] 7 is an electronic device including a stacked structure 10 having a substrate 11 including a primary surface 11p (see FIG. 1), a first buffer film 12 formed on the primary surface 11p, a second buffer film 13 formed on the first buffer film 12 and made of a first metal nitride, a piezoelectric film 14 formed on the second buffer film 13 and made of a second metal nitride, and a comb electrode (interdigital electrode, interdigital transducer (IDT)) formed on the upper surface of the piezoelectric film 14. The electronic device 20 is characterized in that the second buffer film 13 is oriented such that the (0001) plane of AlN contained in the first metal nitride is inclined with respect to the primary surface 11p (see FIG. 1), and the piezoelectric film 14 is oriented such that the (0001) plane of GaN contained in the second metal nitride is inclined with respect to the primary surface 11p.

[0058] The stacked structure 10 provided in the electronic device 20 of the second embodiment can also have a substrate 11, a first buffer film 12, a second buffer film 13, and a piezoelectric film 14, similar to the stacked structure 10 of the first embodiment. Therefore, among the substrate 11, the first buffer film 12, the second buffer film 13, and the piezoelectric film 14 of the stacked structure 10, descriptions of the same parts as the substrate 11, the first buffer film 12, the second buffer film 13, and the piezoelectric film 14 of the stacked structure 10 of the first embodiment may be omitted.

[0059] 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-shaped electrodes on the upper surface of the piezoelectric film 14. That is, the electrodes 23 and 24 are comb-teeth electrodes formed on the upper surface of the piezoelectric film 14.

[0060] In this case, by applying an AC voltage between electrodes 23 and 24, surface acoustic waves can be easily generated in piezoelectric film 14. Furthermore, since it is possible to generate or pass surface acoustic waves having a resonance frequency determined depending on the elastic properties of substrate 11, piezoelectric film 14, and 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 GaN 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 GaN is not tilted from the direction perpendicular to the substrate.

[0061] For example, when the GaN contained in the second metal nitride has a (10-12) orientation and the [10-12] direction of the GaN is aligned with the Si

[0100] direction of the substrate, the [10-12] direction of the GaN 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 intensity of surface acoustic waves such as shear waves generated within the laminated structure can be further increased.

[0062] 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 intersecting or preferably perpendicular to direction DR1 in a planar view, 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 intersecting or preferably perpendicular to direction DR1 in a planar view, extending in direction DR2 in a planar view, and arranged at intervals in direction DR1. The comb teeth 23b and 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 24b extend.

[0063] As described above, the stacked structure 10 provided in the electronic device 20 of the second embodiment can also use an SOI substrate, which is a semiconductor substrate, instead of a Si substrate as the substrate 11, similarly to the stacked structure 10 of the first embodiment. Furthermore, the electronic device provided with the stacked structure is not limited to a SAW device, and various electronic devices such as an FBAR (Film Bulk Acoustic Resonator) can be mentioned. [Example]

[0064] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0065] (Example 1, Example 2 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, molecular beam epitaxy (MBE) was performed without oxygen to thermally react metals (Hf, Zr) from the deposition source with oxygen in the oxide film on the Si substrate, forming a single crystal of metal oxide as the first buffer film 12 (see FIG. 1 ) on the Si substrate. Next, oxygen was introduced, the temperature was lowered, and the pressure was increased, and a single crystal film of metal oxide was formed as the first buffer film 12 (see FIG. 1 ) 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℃

[0066] Next, a second buffer film 13 (see FIG. 1) made of AlN was formed on the first buffer film (see FIG. 1) by sputtering, thereby producing the stacked structure of Example 1. The conditions for forming this second buffer film 13 are as follows: Equipment: RF sputtering equipment Pressure: 1~2Pa Target: Al Gas: Ar / N2 Power: 2500~3500W(AC) Substrate temperature: 350~450℃ Thickness: 60nm

[0067] In addition, a stacked structure of Example 2 was fabricated in exactly the same manner as Example 1, except that a piezoelectric film 14 (see FIG. 1) made of GaN was formed on a second buffer film 13 (see FIG. 1) by sputtering. The conditions for forming this piezoelectric film 14 are shown below. Equipment: RF sputtering equipment Pressure: 1~2Pa Target: Ga Gas: Ar / N2 Power: 2500~3500W(AC) Substrate temperature: 350~450℃ Thickness: 400nm

[0068] 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.

[0069] [X-ray diffraction measurement and SEM observation] After forming a first buffer film 12 (see FIG. 1) on the main surface 11p of the substrate 11 (see FIG. 1), and before forming a second buffer film 13 (see FIG. 1), the stacked 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 stacked structure was measured by the X-ray diffraction measurement. The measured diffraction pattern of the stacked structure of Example 1 is shown in FIG. 8. The XRD measurement was performed using an X-ray diffractometer SmartLab manufactured by Rigaku Corporation.

[0070] As shown in Figure 8, 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.

[0071] Furthermore, a φ scan was performed on the (110) plane (2θ=35.26°) of HZO contained in the metal oxide of the obtained laminated structure of Example 1. The φ scan measured for the laminated structure of Example 1 is shown in FIG.

[0072] As shown in Figure 9, 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.

[0073] After forming the second buffer film 13 (see FIG. 1), the obtained stacked structure of Example 1 was positioned 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 stacked structure of Example 1 was measured by the X-ray diffraction measurement. The measured diffraction pattern of the stacked structure of Example 1 is shown in FIG.

[0074] As shown in FIG. 10 , 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 first metal nitride in Example 1 was (10-12) oriented. On the other hand, although not shown, the AlN contained in the first 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 first metal nitride have a (10-11) or (10-13) orientation. That is, it was revealed that the AlN contained in the first metal nitride in Example 1 was oriented so that the (0001) plane was inclined with respect to the main surface.

[0075] After forming the second buffer film 13 (see FIG. 1), the obtained stacked structure of Example 1 was positioned so that the diffraction plane in 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 stacked structure of Example 1 was measured by the X-ray diffraction measurement. The measured diffraction pattern of the stacked structure of Example 1 is shown in FIG.

[0076] As shown in Fig. 11, a strong diffraction peak of the (0002) plane of AlN was observed in the diffraction pattern of Example 1. Furthermore, as described with reference to Fig. 5, the angle between the (10-12) plane of AlN and the c-axis was 47°. Therefore, the diffraction pattern in Fig. 11 also revealed that the AlN contained in the first metal nitride was (10-12) oriented.

[0077] In addition, with the stacked structure positioned so that the first diffraction plane in the first X-ray diffraction measurement was tilted at an angle of 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 first metal nitride. The measured φ scan is shown in FIG.

[0078] As shown in FIG. 12, 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. This revealed that the polarization direction of AlN contained in the first 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. Furthermore, as shown in FIGS. 9 and 12, it was revealed that the [10-12] direction of AlN contained in the first metal nitride was aligned with the

[0100] direction of the first metal oxide. That is, it was found that the AlN contained in the first 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, and when one of the four regions is taken as a reference region, the direction in which the polarization direction of the AlN in the four regions is projected onto the main surface 11p is 0°, 90°, 180°, or 270° relative to the direction in which the polarization direction of the AlN in the reference region is projected onto the main surface 11p.

[0079] 11, 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 first 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.

[0080] 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).

[0081]

number

[0082] 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.

[0083] 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).

[0084]

number

[0085] 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.

[0086] [Table 1]

[0087] 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 state having a hexagonal crystal structure to a pseudo-tetragonal crystal structure, as shown in Figure 6, for example.

[0088] 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 6, for example.

[0089] 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.

[0090] Furthermore, the stacked structure of Example 2 was positioned so that the diffraction plane in the 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 stacked structure of Example 2 was measured by the X-ray diffraction measurement. The measured diffraction pattern of the stacked structure of Example 2 is shown in FIG.

[0091] As shown in Figure 13, in the diffraction pattern of Example 2, in addition to the diffraction peak of the (10-12) plane of AlN, strong diffraction peaks of the (10-11) and (10-12) planes of GaN were observed. Therefore, it was revealed that in Example 2, the GaN contained in the second metal nitride was (10-11) oriented, (10-12) oriented, or oriented so that the (10-11) plane or the (10-12) plane was slightly tilted with respect to the primary surface 11p (see Figure 1). That is, the diffraction pattern shown in Figure 13 revealed that the GaN contained in the second metal nitride was also oriented so that the (0001) plane was tilted with respect to the primary surface 11p, similar to the AlN contained in the first metal nitride.

[0092] In the diffraction pattern shown in Fig. 13, the GaN contained in the second metal nitride includes a portion where the (0001) plane is not tilted with respect to the primary surface, i.e., a portion that is (0001) oriented. However, referring to the diffraction pattern of AlN shown in Fig. 11, it is expected that by further optimizing the film formation conditions, it will be possible to prevent the GaN contained in the second metal nitride from including a portion where the (0001) plane is not tilted with respect to the primary surface 11p (see Fig. 1).

[0093] Furthermore, after forming the piezoelectric film 14 (see FIG. 1), the resulting laminated structure was placed so that the diffraction plane in 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 laminated structure of Example 2 was measured by the X-ray diffraction measurement. The measured diffraction pattern of the laminated structure of Example 2 is shown in FIG.

[0094] 13 and 14 do not show the absolute values ​​of the peak intensities of the diffraction peaks, the peak intensities of the diffraction peaks of the GaN (10-11) and (10-12) planes observed in the diffraction pattern of Example 2 shown in Fig. 14 were smaller than the peak intensities of the diffraction peaks of the GaN (10-11) and (10-12) planes observed in the diffraction pattern of Example 2 shown in Fig. 13. Therefore, the diffraction pattern of Fig. 14 also reveals that in Example 2, the GaN contained in the second metal nitride is (10-11)-oriented, (10-12)-oriented, or oriented so that the (10-11) or (10-12) plane is slightly tilted with respect to the primary surface 11p (see Fig. 1).

[0095] Furthermore, for the stacked structure of Example 2, a pole figure corresponding to the lattice spacing d value (d value = 0.2490 nm, 2θ = 36.03° when CuKα radiation was used) corresponding to the lattice spacing of the (0002) plane of AlN contained in the first metal nitride was measured. The measured pole figure is shown in FIG.

[0096] Furthermore, for the stacked structure of Example 2, a pole figure corresponding to the d-value (d=0.2590 nm, 2θ=34.6° when CuKα radiation was used) corresponding to the lattice spacing of the (0002) plane of GaN contained in the second metal nitride was measured. The measured pole figure is shown in FIG.

[0097] As shown in Figure 15, in the pole figure of Example 2, four strong diffraction peaks of the (0002) plane of AlN were observed at 90° intervals. That is, in the pole figure, diffraction peaks showing four-fold symmetry of AlN were observed in an annular region (corresponding to a φ scan) where the diffraction plane was inclined 90°-43°=47° with respect to the main surface 11p. This revealed that the polarization direction of AlN contained in the first metal nitride was aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., epitaxial growth occurred.

[0098] 9, 12, and 15, it was revealed that the [10-12] direction of the AlN contained in the first metal nitride is aligned with the

[0100] direction of the metal oxide. That is, it was revealed that the AlN contained in the first 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 designated as a reference region, the polarization direction of the AlN projected onto the main surface 11p in the four regions is 0°, 90°, 180°, and 270° relative to the polarization direction of the AlN in the reference region projected onto the main surface 11p. In other words, it was revealed that the second buffer film 13 includes a first domain DM1, a second domain DM2, a third domain DM3, and a fourth domain DM4 (see FIGS. 3 and 4) in which the

[0001] axes of the AlN contained in the first metal nitride are oriented in different directions.

[0099] 16, in the pole figure of Example 2, four strong diffraction peaks of the (0002) plane of GaN were observed at 90° intervals. That is, in the pole figure, diffraction peaks showing four-fold symmetry of GaN were observed in an annular region (corresponding to a φ scan) where the diffraction plane was inclined by 90°-36°=54° with respect to the main surface 11p. This revealed that the polarization direction of GaN contained in the second metal nitride was aligned in the in-plane direction along the main surface 11p of the substrate 11 (see FIG. 1), i.e., epitaxial growth occurred.

[0100] 9, 12, 15, and 16, it was revealed that the [10-12] direction of the GaN contained in the second metal nitride is aligned with the

[0100] direction of the metal oxide. That is, the GaN contained in the second metal nitride includes, in a planar view, four regions (domains) in which the polarization direction of the GaN projected onto the main surface 11p is different from one another. When one of the four regions is defined as a reference region, the polarization directions of the GaN in the four regions projected onto the main surface 11p are 0°, 90°, 180°, and 270° relative to the polarization direction of the GaN in the reference region projected onto the main surface 11p. In other words, it was revealed that the piezoelectric film 14 includes a fifth domain DM5, a sixth domain DM6, a seventh domain DM7, and an eighth domain DM8 (see FIGS. 3 and 4) in which the

[0001] axes of the GaN contained in the second metal nitride are oriented in different directions.

[0101] Furthermore, FIG. 17 shows an image of a cross section formed by cleaving the substrate 11 included in the laminate structure of Example 2, which was processed by a focused ion beam (FIB) method, observed with a scanning transmission electron microscope (STEM).

[0102] 17, the crystal grains and grain boundaries of AlN contained in the first metal nitride were aligned along a direction forming an angle of 45° with the normal direction of the main surface 11p (see FIG. 1). Therefore, the results shown in FIGS. 15 and 17 revealed that the first angle θ11 was 43 to 47°.

[0103] Furthermore, as shown in region RG1 of AlN in Fig. 17, the crystal grains and grain boundaries of AlN contained in the first metal nitride were tilted in two directions, leftward and rightward, within the plane of the paper with respect to the normal direction to main surface 11p (see Fig. 1). That is, in the image shown in Fig. 17, it was observed that second buffer film 13 (see Fig. 1) included, in plan view, two of the four domains shown in the pole figure of Fig. 15, in which the polarization directions of AlN projected onto main surface 11p were different from each other.

[0104] Furthermore, as shown in FIG. 17, the crystal grains and crystal grain boundaries of GaN contained in the second metal nitride were aligned along a direction forming an angle of 56° with a direction parallel to primary surface 11p (see FIG. 1).

[0105] Example 3 [Positive piezoelectric constant and electromechanical coupling coefficient] A laminated structure of Example 3 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 14 .

[0106] 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 second buffer film 13 (see FIG. 1) made of a second metal nitride.

[0107] The capacitance and piezoelectric constant d of the laminated structure of Example 3 thus fabricated were 33 and electromechanical coupling coefficient K 33The 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.

[0108] [Table 2]

[0109] [Table 3]

[0110] As shown in Tables 2 and 3, the laminated structure of Example 3 has a high K 33 2 (average value), and a high K of about 42% 33 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 approximately 10 to 15%. Therefore, it was revealed that the stacked structure of Example 3, even though the first metal nitride contains AlN to which no Sc is added, can improve the electromechanical coupling coefficient to approximately the same extent as when the first metal nitride contains ScAlN to which Sc is added so that the Sc content is 0.4. Similarly, even when a piezoelectric film 14 containing GaN is formed on a second buffer film 13 containing AlN, the electromechanical coupling coefficient is expected to increase because the c-axis of GaN is tilted from the direction perpendicular to the substrate, compared to when the c-axis of GaN is not tilted from the direction perpendicular to the substrate.

[0111] The reason why the electromechanical coupling coefficient can be improved by the layered structure of Example 3 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.

[0112] On the other hand, the stacked structure of Example 3 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 first buffer film has a specific composition and orientation direction, and the second buffer 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 be significantly distorted, thereby improving the piezoelectricity and the electromechanical coupling coefficient.

[0113] Although detailed explanation is omitted, when x in the above composition formula (Chemical Formula 1) satisfies 0≦x<1, the same results as in Examples 1, 2, and 3, in which the ratio of Hf:Zr is 25:75 (x in the above composition formula (Chemical Formula 1) is 0.75), were obtained. [Explanation of symbols]

[0114] 10. Laminated structure 11 Circuit Board 11a Base 11b Insulating layer 11c SOI layer 11p main surface 12 First buffer film 13 Second buffer film 14 Piezoelectric film 20 Electronic Devices 23, 24 electrodes 23a, 24a main body 23b, 24b comb teeth DM1 First Domain DM2 Second Domain DM3 Third Domain DM4 Fourth Domain DM5 Fifth Domain DM6 6th domain DM7 Seventh Domain DM8 8th Domain DR1, DR2 direction PL surface RG1 area θ11 1st angle θ12 2nd angle

Claims

1. a substrate including a major surface; a first buffer film formed on the main surface; a second buffer film formed on the first buffer film; a piezoelectric film formed on the second 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 first 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 second buffer film is made of a first metal nitride including AlN; the piezoelectric film is made of a second metal nitride containing GaN, the AlN contained in the first metal nitride is oriented such that a (0001) plane of the AlN contained in the first metal nitride is inclined with respect to the main surface; a layered structure, wherein the GaN contained in the second metal nitride is oriented such that a (0001) plane of the GaN contained in the second metal nitride is inclined with respect to the primary surface;

2. the second buffer film includes a first domain, a second domain, a third domain, and a fourth domain, in which (0001) planes of AlN contained in the first metal nitride are oriented so as to be inclined at a first angle with respect to the main surface, and [0001] axes of AlN contained in the first metal nitride are oriented in directions different from one another; a [0001] direction of AlN contained in the first metal nitride in the second domain is a direction rotated by 90° counterclockwise from the [0001] direction of AlN contained in the first metal nitride in the first domain when viewed from the normal direction of the main surface, a [0001] direction of AlN contained in the first metal nitride in the third domain is a direction rotated by 180° counterclockwise from a [0001] direction of AlN contained in the first metal nitride in the first domain when viewed from a normal direction of the main surface, 2. The stacked structure of claim 1, wherein the [0001] direction of AlN contained in the first metal nitride in the fourth domain is rotated 270° counterclockwise from the [0001] direction of AlN contained in the first metal nitride in the first domain when viewed from the normal direction of the main surface.

3. the piezoelectric film includes a fifth domain, a sixth domain, a seventh domain, and an eighth domain, in which (0001) planes of GaN contained in the second metal nitride are oriented so as to be inclined at a second angle with respect to the primary surface, and [0001] axes of GaN contained in the second metal nitride are oriented in directions different from each other; a [0001] direction of GaN contained in the second metal nitride in the sixth domain is rotated by 90° counterclockwise from a [0001] direction of GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the main surface, a [0001] direction of GaN contained in the second metal nitride in the seventh domain is rotated by 180° counterclockwise from a [0001] direction of GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the main surface, 3. The stacked structure according to claim 2, wherein the [0001] direction of the GaN contained in the second metal nitride in the eighth domain is rotated 270° counterclockwise from the [0001] direction of the GaN contained in the second metal nitride in the fifth domain when viewed from the normal direction of the main surface.

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

5. 5. The stacked structure of claim 4, wherein a diffraction peak exhibiting four-fold symmetry is observed in a φ scan of the (0002) plane of AlN contained in the first metal nitride measured by the first X-ray diffraction measurement, when the stacked 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.

6. 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 a diffraction peak angle of the (10-12) plane of AlN contained in the first 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 5 , 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.

7. 3. The stacked structure according to claim 2, wherein the [10-12] direction of AlN contained in the first metal nitride in the first domain is aligned with the [100] direction of the metal oxide.

8. 4. The stacked structure according to claim 3, wherein, when viewed from the normal direction of the main surface, the [10-12] direction of GaN contained in the second metal nitride in the fifth domain is aligned with the [10-12] direction of AlN contained in the first metal nitride in the first domain.

9. The laminated structure according to claim 1 , wherein the thickness of the piezoelectric film is greater than the thickness of the second buffer film.

10. The first buffer film has a thickness of 35 to 75 nm, The second buffer film has a thickness of 40 to 80 nm, 10. The laminated structure according to claim 9, wherein the thickness of the piezoelectric film is 350 to 450 nm.

11. An electronic device comprising the laminate structure according to any one of claims 1 to 10.

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