Membrane Structure and Electronic Device

Abstract

This film structure (10) comprises: a substrate which is an Si substrate or an SOI substrate; a buffer film which is formed on the substrate and contains ZrO2; and a piezoelectric film (11) which is formed on the buffer film. With respect to this film structure, the polarization direction of the piezoelectric film (11) is preferentially oriented in a direction that is parallel to the substrate.

Description

Technical Field

[0001] The present invention relates to a film structure and an electronic device.

Background Art

[0002] A film structure having a substrate and a piezoelectric film formed on the substrate, and an electronic device created from the film structure are known.

[0003] Japanese Patent Application Laid-Open No. 2003-198319 (Patent Document 1) discloses a thin-film piezoelectric resonator including a substrate made of a semiconductor or an insulator having a vibration space, and a laminated structure in which a lower electrode, a piezoelectric thin film, and an upper electrode are laminated in this order at a position facing the vibration space of the substrate. A technique is disclosed in which the piezoelectric thin film is an aluminum nitride thin film showing c-axis orientation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technology described in the above Patent Document 1, the aluminum nitride film, which is a piezoelectric film, is c-axis oriented, and the polarization direction of the piezoelectric film is oriented perpendicular to the substrate. Thus, it is easy to align the polarization direction of the piezoelectric film in a direction perpendicular to the substrate. On the other hand, in order to improve the dielectric constant characteristics and the breakdown voltage characteristics, there may be cases where it is preferable to align the polarization direction of the piezoelectric film in a direction other than the direction perpendicular to the substrate, but it is difficult to align the polarization direction of the piezoelectric film in a direction other than the direction perpendicular to the substrate. Depending on the device, it may be possible to create an advantageous device by aligning the polarization direction in a direction horizontal to the substrate.

[0007] The present invention has been made to solve the problems of the prior art as described above, and an object thereof is to provide a film structure having a piezoelectric film formed on a substrate, in which the polarization directions of the piezoelectric films are aligned in a direction horizontal to the substrate.

Means for Solving the Problems

[0008] Among the inventions disclosed in the present application, an outline of typical ones will be briefly described as follows.

[0009] A film structure as one aspect of the present invention has a substrate that is a Si substrate or an SOI substrate, a buffer film containing ZrO2 formed on the substrate, and a piezoelectric film formed on the buffer film, and the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate.

[0010] Also, as another aspect, the film structure may further include a metal film on the buffer film. Also, as another aspect, the metal film may be a Pt film, a Mo film, a W film, a Ru film, or a Cu film. Further, the film structure may further include an SRO film on the metal film.

[0011] Also, as another aspect, the piezoelectric film may be made of a nitride. Also, as another aspect, the nitride may be AlN. Also, as another aspect, the nitride may be doped with Sc.

[0012] An electronic device as one aspect of the present invention is an electronic device created from the film structure.

[0013] An electronic device as one aspect of the present invention is an electronic device created from the film structure, which includes comb electrodes on the upper or lower surface of the piezoelectric film in the film structure.

[0014] Also, as another aspect, the polarization direction of the piezoelectric film may be in the direction of the teeth of the comb electrodes. Also, as another aspect, the electronic device may have an alignment layer on the substrate.

[0015] Also, as another aspect, a hollow portion may be provided below the piezoelectric film.

[0016] Also, as another aspect, the electronic device may include an upper electrode and a lower electrode on the upper and lower portions of the piezoelectric film. Also, as another aspect, the area of the overlapping portion between the upper electrode and the lower electrode may be smaller than the area of the hollow portion. Also, as another aspect, the area of the overlapping portion between the upper electrode and the lower electrode may be 1 / 2 or less of the area of the hollow portion. Also, as another aspect, the electronic device may have an alignment layer on the substrate.

[0017] Also, as another aspect, the alignment layer may be a material whose hardness increases as the temperature rises. Also, as another aspect, the material may be a Si compound.

[0018] Also, as another aspect, either the upper or lower side of the piezoelectric film may be fixed.

[0019] Also, as another aspect, the piezoelectric film may be made of a nitride. Also, as another aspect, the nitride may be AlN.

Advantages of the Invention

[0020] By applying one aspect of the present invention, in a film structure having a piezoelectric film formed on a substrate, a film structure can be realized in which the polarization directions of the piezoelectric films are aligned in a direction horizontal to the substrate.

Brief Description of the Drawings

[0021]

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Mode for Carrying Out the Invention

[0022] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0023] Note that the disclosure is merely an example, and for those that can be easily conceived by those skilled in the art with appropriate modifications while maintaining the gist of the invention, they are naturally included in the scope of the present invention. Also, for the purpose of making the description clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the embodiments, but this is merely an example and does not limit the interpretation of the present invention.

[0024] Also, in this specification and each drawing, elements that are the same as those described above with respect to the previously shown drawings may be given the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0025] Furthermore, in the drawings used in the embodiments, hatching (cross - hatching) added to distinguish structures may be omitted according to the drawings.

[0026] In the following embodiments, when a range is indicated as A to B, unless otherwise specified, it means A or more and B or less.

[0027] (Embodiment 1) First, a film structure of Embodiment 1, which is an embodiment of the present invention, will be described. FIGS. 1 to 4 are cross - sectional views of the film structure of Embodiment 1.

[0028] As shown in FIG. 1, the film structure 10 of the present Embodiment 1 is a film structure having a piezoelectric film 11 and a substrate 12, and is characterized in that the polarization direction of the piezoelectric film 11, that is, the piezoelectric film portion, is preferentially oriented parallel to the substrate 12. In FIG. 1, the polarization direction is indicated by the polarization direction DP1 (the same applies in FIGS. 2 and 5 to 15). Since the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12, a film structure in which the polarization directions of the piezoelectric films are aligned in a direction horizontal to the substrate can be realized.

[0029] Alternatively, as shown in FIG. 2, the film structure 10 of the present Embodiment 1 is a film structure having a piezoelectric film 11, an electrode 13, and a substrate 12, and is characterized in that the polarization direction of the piezoelectric film 11, that is, the piezoelectric film portion, is preferentially oriented parallel to the substrate 12. As described above, since the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12, a film structure in which the polarization directions of the piezoelectric films are aligned in a direction horizontal to the substrate can be realized.

[0030] In the present specification, the term "the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12" means that, in the piezoelectric film 11, the portion whose polarization direction is oriented parallel to the substrate 12 exceeds, for example, 50% of the entire piezoelectric film 11 in terms of volume fraction. For example, when measuring the θ-2θ spectrum by the X-Ray Diffraction (XRD) method, in the measured θ-2θ spectrum, the peak intensity of the maximum peak indicating the portion whose polarization direction is oriented parallel to the substrate 12 is higher than the peak intensity of the maximum peak indicating the portion not oriented parallel to the substrate 12. Further, the case where the polarization direction is parallel to the substrate 12 includes not only the case where the polarization direction is completely parallel to the upper surface of the substrate 12, but also the case where the angle formed by the direction in which the polarization direction is projected onto the upper surface of the substrate 12 and the polarization direction is 20° or less.

[0031] Preferably, the material of the piezoelectric film 11 is a nitride. That is, the piezoelectric film 11 is made of a nitride. When the material of the piezoelectric film 11 is a nitride, aluminum nitride (AlN) or gallium nitride (GaN), which is a lead-free material and has excellent piezoelectric properties, can be used.

[0032] The material of the piezoelectric film 11 is preferably an a-axis oriented AlN-based piezoelectric material, that is, a piezoelectric material mainly composed of AlN. That is, the nitride is AlN. When the material of the piezoelectric film 11 is mainly composed of AlN, a lead-free material can be used, which contains elements with a high Clark number and is abundant on the earth, and has excellent piezoelectric properties. Further, by the a-axis orientation of AlN, AlN can be oriented so that the c-axis direction, which is the polarization direction of AlN, is parallel to the substrate 12. Note that AlN has a wurtzite structure with a hexagonal crystal structure and is polarized in the c-axis direction. GaN also has a wurtzite structure.

[0033] In the present specification, the term "a piezoelectric material mainly composed of AlN" means that the content of AlN in the piezoelectric material exceeds 50% by weight or the content of AlN in the piezoelectric material exceeds 50 mol%.

[0034] Preferably, scandium (Sc) is doped or added to the nitride. When, for example, AlN or GaN is used as the nitride material, the piezoelectric properties can be improved by adding Sc to the nitride.

[0035] Preferably, the polarization rate of the piezoelectric film 11 is 80% or more. Thereby, a film structure in which the polarization direction of the piezoelectric film is aligned in a direction horizontal to the substrate can be realized.

[0036] Preferably, as shown in FIG. 3, the substrate 12 has a structure in which an Si layer and a ZrO2 layer are laminated in this order. Si represents silicon, and ZrO2 represents zirconium oxide. ZrO2 serves as a buffer film and contributes to forming the piezoelectric material formed thereon with good crystallinity. Preferably, the substrate 12 includes a (100)-oriented Si layer 12a and a ZrO2 layer 12b formed on the Si layer 12a. The ZrO2 layer 12b preferably includes (200)-oriented ZrO2 and (002)-oriented ZrO2. As the Si layer 12a of the substrate 12, a (100)-oriented Si substrate can be used. In such a case, a piezoelectric film 11 having a polarization direction parallel to the substrate 12, such as a piezoelectric material mainly composed of an a-axis-oriented AlN-based piezoelectric material, can be easily formed on the substrate 12. Further, since a (100)-oriented Si substrate can be used as the Si layer 12a of the substrate 12, an electronic device in which the polarization direction of the piezoelectric film 11 is aligned in a direction horizontal to the substrate can be formed on an inexpensive semiconductor substrate.

[0037] As shown in FIG. 3, the electrode 13 has a structure in which a Pt(200) layer and a SrRuO3(100) layer are laminated in this order. Pt represents platinum, and SrRuO3 (SRO) represents strontium ruthenate. In other words, preferably, the electrode 13 includes a Pt layer 13a formed on the substrate 12 and having a (200) orientation, and an SRO layer 13b formed on the Pt layer 13a and having a (100) orientation. In such a case, a piezoelectric film 11 such as a piezoelectric material mainly composed of an a-axis-oriented AlN-based piezoelectric material, in which the polarization direction of the piezoelectric film 11 is oriented parallel to the substrate 12, can be easily formed on the substrate 12 via the electrode 13 as the lower electrode.

[0038] Note that it is not limited to the case where the Si layer 12a has a (100) orientation, nor is it limited to the case where the ZrO2 layer 12b has a (200) orientation or a (002) orientation, nor is it limited to the case where the Pt layer 13a has a (200) orientation, and it is not limited to the case where the electrode 13 includes an SRO layer 13b formed on the Pt layer 13a and having a (100) orientation. Also, the Si layer 12a of the substrate 12 can be regarded as the substrate. In such a case, the film structure 10 of the first embodiment has a substrate (Si layer 12a) that is a Si substrate, a buffer film (ZrO2 layer 12b) containing ZrO2 formed on the substrate (Si layer 12a), and a piezoelectric film 11 formed on the buffer film (ZrO2 layer 12b) via a metal film (Pt layer 13a), and the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the upper surface of the substrate 12, which is a film structure. Further, the piezoelectric film 11 is a piezoelectric film formed on Pt / ZrO2 / Si. Note that when the electrode 13 includes a Pt layer 13a and an SRO layer 13b, that is, when the film structure 10 further includes a metal film (Pt layer 13a) on the buffer film (ZrO2 layer 12b) and further includes an SRO film (SRO layer 13b) on the metal film (Pt layer 13a), the piezoelectric film 11 is a piezoelectric film formed on a substrate (Si layer 12a) that is a Si substrate via a ZrO2 film (ZrO2 layer 12b), a Pt film (Pt layer 13a), and an SRO film (SRO layer 13b) in this order from the bottom.

[0039] As shown in FIG. 4, as the Si layer 12a of the substrate 12, instead of the Si substrate, an SOI (Silicon On Insulator) substrate which is a semiconductor substrate can also be used. When an SOI substrate is used as the substrate 12, the substrate 12 includes a base 12c made of Si, a BOX (Buried Oxide) layer 12d which is a buried oxide film formed on the base 12c, and an Si layer 12a which is an SOI (Silicon On Insulator) layer formed on the BOX layer 12d. Thereby, a film structure excellent in the dielectric constant characteristics and breakdown voltage characteristics of the piezoelectric film can be formed on the SOI substrate, and an electronic device composed of a Micro Electro Mechanical Systems (MEMS) having a plurality of piezoelectric elements formed with good shape accuracy can be easily formed on the SOI substrate.

[0040] Note that the Si layer 12a of the substrate 12 can be regarded as the substrate. In such a case, the film structure 10 of the first embodiment includes a substrate (Si layer 12a) which is an SOI substrate, a buffer film (ZrO2 layer 12b) containing ZrO2 formed on the substrate (Si layer 12a), and a piezoelectric film 11 formed on the buffer film (ZrO2 layer 12b) via a metal film (Pt layer 13a). The film structure is such that the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the upper surface of the substrate 12. Further, the piezoelectric film 11 is a piezoelectric film formed on Pt / ZrO2 / Si on SOI. Note that when the electrode 13 includes a Pt layer 13a and an SRO layer 13b, that is, when the film structure 10 further includes a metal film (Pt layer 13a) on the buffer film (ZrO2 layer 12b) and further includes an SRO film (SRO layer 13b) on the metal film (Pt layer 13a), the piezoelectric film 11 is a piezoelectric film formed on the substrate (Si layer 12a) which is an SOI substrate via a ZrO2 film (ZrO2 layer 12b), a Pt film (Pt layer 13a), and an SRO film (SRO layer 13b) in this order from below.

[0041] Further, instead of the Pt layer 13a, the electrode 13 can also include a Mo layer 13c or a W layer 13d. In such a case, the electrode 13 will include the SRO layer 13b formed on the Mo layer 13c or the W layer 13d. Also, in such a case, the film structure 10 of the first embodiment has a piezoelectric film 11 formed on a substrate (Si layer 12a), which is a Si substrate or an SOI substrate, via a ZrO2 film (ZrO2 layer 12b) and a Mo film (Mo layer 13c) or a W film (W layer 13d) in this order from the bottom. Also, in such a case as well, similar to the case where the electrode 13 includes the Pt layer 13a, a piezoelectric film 11 having a polarization direction parallel to the substrate 12, such as a piezoelectric material mainly composed of an a-axis oriented AlN-based piezoelectric material, can be easily formed on the substrate 12 via the electrode 13 as the lower electrode. In addition to the materials described above for the electrodes 13a, 13c, or 13d, an Ru layer or a Cu layer may be used. These materials are common as electrode materials.

[0042] The film thickness of the piezoelectric film 11 is preferably 100 nm or more. When the film thickness of the piezoelectric film 11 is 100 nm or more, the film thickness of the piezoelectric film 11 can be made sufficiently large compared to the case where the film thickness of the piezoelectric film 11 is less than 100 nm. Therefore, an electronic device with the polarization direction of the piezoelectric film aligned horizontally with respect to the substrate can be formed on the substrate.

[0043] (Embodiment 2) Next, an electronic device according to Embodiment 2, which is one embodiment of the present invention, will be described. The electronic device of Embodiment 2 is a Bulk Acoustic Wave (BAW) filter or a Film Bulk Acoustic Resonator (FBAR) provided with the film structure of Embodiment 1. FIGS. 5 to 12 are cross-sectional views of the electronic device of Embodiment 2.

[0044] As shown in FIG. 5, the electronic device 20 of Embodiment 2 is an electronic device including a film structure 10 having a piezoelectric film 11, two electrodes, and a substrate 12, characterized in that the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12.

[0045] Regarding the film structure 10 provided in the electronic device 20 of the second embodiment as well, similar to the film structure 10 of the first embodiment, it can have a piezoelectric film 11, electrodes 13, and a substrate 12. That is, the electronic device 20 of the second embodiment has the electrodes 13 and the piezoelectric film 11 on the substrate 12. Therefore, for the parts of the piezoelectric film 11, the electrodes 13, and the substrate 12 of the film structure 10 that are the same as those of the film structure 10 of the first embodiment, the description thereof may be omitted.

[0046] On the other hand, since the electronic device 20 of the second embodiment is a BAW filter or an FBAR provided with the film structure 10 of the first embodiment, a hollow portion, that is, a hollow part 21, is provided in the substrate 12 below the piezoelectric film 11. In such a case, at least the central part of the part of the piezoelectric film 11 located above the hollow part 21 is not restricted by the substrate 12 and can vibrate freely. Therefore, bulk elastic waves can be easily generated in the central part.

[0047] In addition, in the film structure 10 provided in the electronic device 20 of the second embodiment, an electrode 22 as an upper electrode or a top electrode formed on the piezoelectric film 11 is provided. In such a case, the electrode 13 is an electrode as a lower electrode or a bottom electrode formed under the piezoelectric film 11. That is, the electrode 22 and the electrode 13 are an upper electrode and a lower electrode formed on the upper and lower portions of the piezoelectric film 11. In the example shown in FIG. 5, electrodes are formed above and below in contact with the piezoelectric film 11. The film structure 10 is a film structure having a piezoelectric film 11, two electrodes, i.e., the electrode 13 and the electrode 22, and a substrate 12, and is characterized in that the polarization direction of the piezoelectric film 11, i.e., the piezoelectric film portion, is preferentially oriented parallel to the substrate 12. In such a case, by applying a voltage such as an alternating voltage between the electrode 13 and the electrode 22, an electric field such as an alternating electric field in the thickness direction of the piezoelectric film 11 can be easily applied to the piezoelectric film 11, and a bulk acoustic wave can be easily generated in the piezoelectric film 11. Further, since a bulk acoustic wave having a resonance frequency determined according to the elastic characteristics and the like of the piezoelectric film 11 can be generated or passed through, it can function as a resonator or a filter.

[0048] Note that also in the second embodiment, as in the first embodiment, as the substrate 12, a substrate including a (100)-oriented Si layer 12a (see FIG. 3) and a ZrO2 layer 12b (see FIG. 3) formed on the Si layer 12a can be used. The ZrO2 layer 12b preferably includes (200)-oriented ZrO2 and (002)-oriented ZrO2. In such a case, the Si layer 12a of the substrate 12 can be regarded as the substrate, and the electronic device 20 of the second embodiment has the electrode 13 and the piezoelectric film 11 on a substrate (Si layer 12a) that is a Si substrate, the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12, and a hollow portion 21 is provided below the piezoelectric film 11.

[0049] Preferably, the area A of the overlapping portion of the upper and lower electrodes is smaller than the area B of the piezoelectric film 11 and the lower electrode exposed in the hollow portion. That is, the area of the overlapping portion between the electrode 22 as the upper electrode and the electrode 13 as the lower electrode is smaller than the area of the hollow portion 21. In such a case, by applying a voltage between the electrode 22 and the electrode 13, the portion of the piezoelectric film 11 where an electric field in the thickness direction is applied can be surely separated from the substrate 12. Therefore, the portion of the piezoelectric film 11 where an electric field in the thickness direction is applied is not restricted by the substrate 12 and can vibrate freely, and bulk elastic waves can be generated more easily.

[0050] Preferably, the area ratio of the area A of the overlapping portion of the upper and lower electrodes to the area B of the piezoelectric film 11 and the lower electrode exposed in the hollow portion, that is, A / B is smaller than 1 / 2 or 1 / 2 or less. That is, the area of the overlapping portion between the electrode 22 as the upper electrode and the electrode 13 as the lower electrode is 1 / 2 or less of the area of the hollow portion 21. In such a case, by applying a voltage between the electrode 22 and the electrode 13, the portion of the piezoelectric film 11 where an electric field in the thickness direction is applied can be more surely separated from the substrate 12. Therefore, the portion of the piezoelectric film 11 where an electric field in the thickness direction is applied is not more restricted by the substrate 12 and can vibrate more freely, and bulk elastic waves can be generated more easily.

[0051] As described above, the film structure 10 provided in the electronic device 20 of the second embodiment can also have a piezoelectric film 11, an electrode 13, and a substrate 12, similar to the film structure 10 of the first embodiment. Therefore, for the film structure 10 provided in the electronic device 20 of the second embodiment, similar to the film structure 10 of the first embodiment, as the Si layer 12a (see FIG. 4) of the substrate 12, an SOI substrate, which is a semiconductor substrate, can be used instead of the Si substrate, and the electrode 13 can include an Mo layer 13c (see FIG. 3) or a W layer 13d (see FIG. 3) instead of the Pt layer 13a (see FIG. 3). In addition to the materials described above for the electrodes 13a, 13c, or 13d, an Ru layer or a Cu layer may be used. These materials are common as electrode materials. Also, for the film structure 10 provided in the electronic device 20 of the second embodiment, similar to the film structure 10 of the first embodiment, the material of the piezoelectric film 11 is preferably a nitride, and the material of the piezoelectric film 11 is preferably an a-axis oriented AlN-based piezoelectric material, that is, the nitride is preferably AlN, and it is preferably doped with Sc, and the polarization rate of the piezoelectric film 11 is preferably 80% or more, and the film thickness of the piezoelectric film is preferably 100 nm or more.

[0052] As shown in FIG. 6, it is preferable to provide a dielectric layer 23 as a dielectric layer or an alignment layer between the substrate 12 and the piezoelectric film 11. That is, the electronic device 20 shown in FIG. 6 has, in addition to the parts that the electronic device 20 shown in FIG. 5 has, a dielectric layer 23 as an alignment layer on the substrate 12 and under the lower electrode, that is, under the electrode 13. For example, when the parts of the electronic device 20 other than the dielectric layer 23 are made of a material that becomes softer as the temperature rises, and the dielectric layer 23 is made of a material that becomes harder as the temperature rises, the temperature dependence of the dielectric constant characteristics or the piezoelectric characteristics of the electronic device 20, that is, the temperature characteristics, can be stabilized or adjusted.

[0053] Preferably, the dielectric layer 23 is a Si compound, for example, silicon dioxide (SiO2). In such a case, since the dielectric layer 23 is a dielectric layer made of a material with high affinity for the manufacturing process of the semiconductor device, the dielectric layer 23 can be easily formed.

[0054] As shown in FIG. 7, it is preferable to provide a dielectric layer 24 as an upper dielectric layer on the piezoelectric film 11. That is, the electronic device 20 shown in FIG. 7 has a dielectric layer 24 as an upper dielectric layer on the piezoelectric film 11 in addition to the portion that the electronic device 20 shown in FIG. 5 has. For example, when a portion other than the dielectric layer 24 of the electronic device 20 is made of a material having a property of becoming softer as the temperature rises, and the dielectric layer 24 is made of a material having a property of becoming harder as the temperature rises, the temperature dependence of the permittivity characteristics or piezoelectric characteristics of the electronic device 20, that is, the temperature characteristics can be stabilized or adjusted.

[0055] Preferably, the dielectric layer 24 is a Si compound, for example, SiO2. In such a case, since the dielectric layer 24 is a dielectric layer made of a material having high affinity with the manufacturing process of the semiconductor device, the dielectric layer 24 can be easily formed.

[0056] In addition, in the examples shown in FIGS. 5 to 7, for example, in the example shown in FIG. 5, either the upper or lower side of the piezoelectric film 11 can be made unfixed (the same applies to Embodiment 3 described with reference to FIGS. 13 to 15 to be described later). Thereby, an electronic device that utilizes the displacement in the sliding direction can be realized.

[0057] Further, in the examples shown in FIGS. 5 to 7, for example, in the examples shown in FIGS. 6 and 7, either one of the piezoelectric films 11 can be fixed, and the other side can be fixed weaker than the one side by a material whose hardness changes with temperature. That is, either the upper or lower side of the piezoelectric film 11 can be fixed, and the side opposite to one of the upper and lower sides of the piezoelectric film 11 can be fixed weakly by a material whose hardness changes with temperature (the same applies to Embodiment 3 described with reference to FIGS. 13 to 15 to be described later). Thereby, an electronic device that utilizes the displacement in the sliding direction and can compensate for temperature characteristics can be realized.

[0058] As shown in Fig. 8, it is preferable to provide a dielectric layer 23 as a lower dielectric layer between the substrate 12 and the piezoelectric film 11 and a dielectric layer 24 as an upper dielectric layer on the piezoelectric film 11. That is, the electronic device 20 shown in Fig. 8 has, in addition to the parts that the electronic device 20 shown in Fig. 5 has, a dielectric layer 23 as an alignment layer on the substrate 12 and under the lower electrode, that is, under the electrode 13, and a dielectric layer 24 as an upper dielectric layer on the piezoelectric film 11. Further, in the example shown in Fig. 8, the dielectric layer 24 is provided on the upper electrode, that is, the electrode 22. That is, also in the example shown in Fig. 8, electrodes are formed above and below in contact with the piezoelectric film 11. For example, when parts other than the dielectric layer 23 and the dielectric layer 24 of the electronic device 20 are made of a material having the property of becoming soft as the temperature rises, and the dielectric layer 23 and the dielectric layer 24 are made of a material having the property of becoming hard as the temperature rises, the temperature dependence of the dielectric constant characteristics or the piezoelectric characteristics of the electronic device 20, that is, the temperature characteristics can be stabilized or adjusted. As described above, the dielectric layer 23 and the dielectric layer 24 are Si compounds, for example, SiO2.

[0059] As shown in Fig. 9, it is preferable to provide a dielectric layer 23 as a lower dielectric layer between the substrate 12 and the piezoelectric film 11, a dielectric layer 24 as an upper dielectric layer on the piezoelectric film 11, and an electrode 22 as an upper electrode on the dielectric layer 24 as the upper dielectric layer. That is, the electronic device 20 shown in Fig. 9 is obtained by reversing the stacking order in the vertical direction of the electrode 22 and the dielectric layer 24 in the electronic device 20 shown in Fig. 8. Further, the structure shown in Fig. 9 is not a structure in which electrodes are formed above and below in contact with the piezoelectric film 11. Even in such a case, the same effect as that of the electronic device 20 shown in Fig. 8 can be obtained. Also, as described above, the dielectric layer 23 and the dielectric layer 24 are Si compounds, for example, SiO2.

[0060] As shown in Fig. 10, it is preferable that there are a plurality of either the upper or lower electrodes 13 or 22, so that there are two or more electric field directions in the plane. In the example shown in Fig. 10, the electronic device 20 has two electrodes 22 as upper electrodes. In Fig. 10, the two electrodes 22 are shown as electrode 22a and electrode 22b. Thereby, an electronic device that makes use of the displacement in the sliding direction can be realized more easily. Note that Fig. 10 schematically shows the case where the piezoelectric film 11 has displacements in two types of sliding directions.

[0061] As shown in Fig. 11, it is preferable that the polarization direction (polarization direction DP1) of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12 and in a plurality of directions, and electrodes 22 and 13 are provided on the upper and lower portions of the piezoelectric body. Also in such a case, an electronic device that makes use of the displacement in the sliding direction can be realized more easily.

[0062] As shown in Fig. 12, it is preferable that there are a plurality of electrodes on the upper or lower portion of the piezoelectric film 11. In the example shown in Fig. 12, the lower electrode is not provided, and two electrodes 22, that is, electrode 22a and electrode 22b are provided as the upper electrodes. Also in such a case, an electronic device that makes use of the displacement in the sliding direction can be realized more easily.

[0063] (Embodiment 3) Next, an electronic device according to Embodiment 3, which is an embodiment of the present invention, will be described. The electronic device according to Embodiment 3 is a surface acoustic wave (SAW) filter including the film structure of Embodiment 1. Figs. 13 to 15 are perspective views of the electronic device according to Embodiment 3.

[0064] As shown in Fig. 13, the electronic device 30 according to Embodiment 3 is an electronic device including a film structure 10 having a piezoelectric film 11, a comb-shaped electrode, and a substrate 12, and is characterized in that the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12.

[0065] Regarding the film structure 10 provided in the electronic device 30 of the third embodiment as well, similar to the film structure 10 of the first embodiment, it can have a piezoelectric film 11 and a substrate 12. Therefore, for the piezoelectric film 11 and the substrate 12 that the film structure 10 has, the description of the parts similar to the piezoelectric film 11 and the substrate 12 that the film structure 10 of the first embodiment has may be omitted.

[0066] On the other hand, since the electronic device 30 of the third embodiment is a SAW filter provided with the film structure 10 of the first embodiment, electrodes 31 and 32 as comb-shaped electrodes (comb-tooth electrodes) are formed on the upper surface or the lower surface of the piezoelectric film 11, that is, the piezoelectric part. That is, the electronic device 30 of the third embodiment has the electrodes 31 and 32 and the piezoelectric film 11 on the substrate 12. In such a case, by applying an alternating voltage between the electrodes 31 and 32, surface acoustic waves can be easily generated in the piezoelectric film 11. Further, since surface acoustic waves having a resonance frequency determined according to the elastic characteristics of the substrate 12, the piezoelectric film 11, and the electrodes 31 and 32 can be generated or passed through, it can function as a resonator or a filter.

[0067] Note that also in the third embodiment, similar to the first embodiment, as the substrate 12, a substrate including a (100)-oriented Si layer 12a (see FIG. 3) and a ZrO2 layer 12b (see FIG. 3) formed on the Si layer 12a can be used. The ZrO2 layer 12b preferably includes (200)-oriented ZrO2 and (002)-oriented ZrO2. In such a case, the Si layer 12a of the substrate 12 can be regarded as the substrate, and the electronic device 30 of the third embodiment has a piezoelectric film 11 on the substrate (Si layer 12a) which is a Si substrate, and the polarization direction of the piezoelectric film 11 is preferentially oriented parallel to the substrate 12.

[0068] In the example shown in FIG. 13, electrodes 31 and 32 as comb-shaped electrodes are formed on the upper surface of the piezoelectric film 11. That is, in the example shown in FIG. 13, electrodes 31 and 32 are comb-tooth electrodes formed on the upper surface of the piezoelectric film 11. On the other hand, although not shown, electrodes 31 and 32 as comb-shaped electrodes may be formed on the lower surface of the piezoelectric film 11. That is, electrodes 31 and 32 can also be comb-tooth electrodes formed on the lower surface of the piezoelectric film 11.

[0069] Preferably, the polarization direction of the piezoelectric film 11 and the direction of the comb-shaped electrode are parallel. That is, preferably, the polarization direction of the piezoelectric film 11 is the direction of the comb teeth of electrodes 31 and 32 which are comb-tooth electrodes.

[0070] Here, electrode 31 as a comb-shaped electrode, i.e., a comb-tooth electrode, includes a main body 31a extending in direction DR1 in a plan view, and a plurality of comb teeth 31b each protruding from the main body 31a in a direction DR2 intersecting, preferably orthogonal to, direction DR1 in a plan view, extending in direction DR2 in a plan view, and arranged in direction DR1. Also, electrode 32 as a comb-shaped electrode, i.e., a comb-tooth electrode, includes a main body 32a extending in direction DR1 in a plan view, and a plurality of comb teeth 32b each protruding from the main body 32a in a direction DR2 intersecting, preferably orthogonal to, direction DR1 in a plan view, extending in direction DR2 in a plan view, and arranged in direction DR1. Also, comb teeth 31b and comb teeth 32b are alternately arranged along direction DR1. In such a case, the direction of the comb-shaped electrode is direction DR2 in which comb teeth 31b and comb teeth 32b extend, and the polarization direction DP1 of the piezoelectric film 11 is the same direction as direction DR2 in which comb teeth 31b and comb teeth 32b extend.

[0071] Since the polarization direction of the piezoelectric film 11 and the direction of the comb-shaped electrode are parallel, it becomes possible to excite an SH wave having a higher electromechanical coupling coefficient than an SV wave, and the characteristics of the SAW filter can be improved.

[0072] As described above, the film structure 10 provided in the electronic device 30 of the third embodiment can also have a piezoelectric film 11 and a substrate 12, similar to the film structure 10 of the first embodiment. Therefore, for the film structure 10 provided in the electronic device 30 of the third embodiment as well, similar to the film structure 10 of the first embodiment, the substrate 12 can have a structure in which an Si layer and a ZrO2 layer are laminated in this order. As the Si layer 12a (see FIG. 4) of the substrate 12, instead of an Si substrate, an SOI substrate which is a semiconductor substrate can be used. The electrode 13 can also include an Mo layer 13c (see FIG. 3) or a W layer 13d (see FIG. 3) instead of the Pt layer 13a (see FIG. 3). In addition to the materials described above for the electrodes 13a, 13c, or 13d, an Ru layer or a Cu layer may be used. Also, for the film structure 10 provided in the electronic device 30 of the third embodiment as well, similar to the film structure 10 of the first embodiment, the material of the piezoelectric film 11 is preferably a nitride. The material of the piezoelectric film 11 is preferably an a-axis oriented AlN-based piezoelectric material, that is, the nitride is preferably AlN, and it is preferably doped with Sc. The polarization rate of the piezoelectric film 11 is preferably 80% or more, and the film thickness of the piezoelectric film 11 is preferably 100 nm or more.

[0073] As shown in FIG. 14, it is preferable to provide a dielectric layer 33 as a dielectric layer or an alignment layer between the substrate 12 and the piezoelectric film 11. That is, the electronic device 30 shown in FIG. 14 has, in addition to the parts that the electronic device 30 shown in FIG. 13 has, a dielectric layer 33 as an alignment layer on the substrate 12 and under the piezoelectric film 11. Thereby, acoustic matching between the substrate 12 and the piezoelectric film 11 can be achieved. Also, for example, when a part other than the dielectric layer 33 of the electronic device 30 is made of a material having a property of becoming softer as the temperature rises, and the dielectric layer 33 is made of a material having a property of becoming harder as the temperature rises, the temperature dependence of the dielectric constant characteristics or the piezoelectric characteristics of the electronic device 30, that is, the temperature characteristics can be stabilized or adjusted.

[0074] Preferably, the dielectric layer 33 is a Si compound, for example, SiO2. In such a case, since the dielectric layer 33 is made of a material having high affinity with the manufacturing process of the semiconductor device, the dielectric layer 33 can be easily formed.

[0075] As shown in FIG. 15, it is preferable to provide a dielectric layer 34 on the piezoelectric film 11. That is, the electronic device 30 shown in FIG. 15 has a dielectric layer 34 as an alignment layer on the piezoelectric film 11 in addition to the portion that the electronic device 30 shown in FIG. 13 has. Thereby, acoustic matching between the substrate 12 and the piezoelectric film 11 can be achieved. Further, for example, when a portion other than the dielectric layer 34 of the electronic device 30 is made of a material having a property of becoming soft as the temperature rises, and the dielectric layer 34 is made of a material having a property of becoming hard as the temperature rises, the temperature dependence of the dielectric constant characteristics or the piezoelectric characteristics of the electronic device 30, that is, the temperature characteristics can be stabilized or adjusted.

[0076] Preferably, the dielectric layer 34 is a Si compound, for example, SiO2. In such a case, since the dielectric layer 34 is made of a material having high affinity with the manufacturing process of the semiconductor device, the dielectric layer 34 can be easily formed.

Example

[0077] Hereinafter, this embodiment will be described in more detail based on examples. Note that the present invention is not limited by the following examples.

[0078] (Example 1 and Example 2) Hereinafter, a test was conducted to form the film structure 10 described with reference to FIGS. 2 and 3 in Embodiment 1 as the film structure of Example 1 and create an AlN film on a substrate including a-axis oriented SRO(100). Further, a film structure obtained by removing the Pt layer 13a and the SRO layer 13b from the film structure described with reference to FIG. 3 in Embodiment 1 was formed as the film structure of Example 2.

[0079] [Formation of substrate] The method for forming the substrate in the film structure of Example 1 will be described. First, as the Si layer 12a (see Fig. 3), a wafer made of a 6-inch silicon single crystal with an upper surface consisting of a (100) plane was prepared.

[0080] Next, a ZrO2 layer 12b (see Fig. 3) was formed on the wafer as the Si layer 12a by electron beam evaporation. The conditions at this time are shown below. Apparatus: Electron beam evaporation apparatus Pressure: 7.00×10 -5 Pa Evaporation source: Zr + O2 Acceleration voltage / Emission current: 7.5 kV / 1.80 mA Thickness: 60 nm Substrate temperature: 500 °C

[0081] Next, a Pt layer 13a (see Fig. 3) was formed on the ZrO2 layer 12b by sputtering. The conditions at this time are shown below. Apparatus: DC sputtering apparatus Pressure: 1.20×10 -1 Pa Evaporation source: Pt Power: 100 W Thickness: 150 nm Substrate temperature: 450 - 600 °C

[0082] Next, an SRO layer 13b (see Fig. 3) was formed on the Pt layer 13a by sputtering. The conditions at this time are shown below. Apparatus: RF magnetron sputtering apparatus Power: 300 W Gas: Ar Pressure: 1.8 Pa Substrate temperature: 600 °C Thickness: 40 nm

[0083] On one side, a substrate of the film structure of Example 2 was a substrate on which a Pt layer 13a (see FIG. 3) and an SRO layer 13b (see FIG. 3) were not formed on the ZrO2 layer 12b (see FIG. 3).

[0084] [Substrate θ-2θ spectrum] Regarding Example 1, the θ-2θ spectrum by the XRD method of the film structure in which up to the SRO layer 13b (see FIG. 3) was formed was measured. That is, for the film structure of Example 1 in which up to the SRO layer 13b was formed, X-ray diffraction measurement by the θ-2θ method was performed. The XRD data of this example was obtained using an X-ray diffractometer SmartLab manufactured by Rigaku Corporation.

[0085] FIG. 16 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure of Example 1 in which up to the SRO layer was formed. The horizontal axis of the graph in FIG. 16 indicates the angle 2θ, and the vertical axis of the graph in FIG. 16 indicates the intensity of the X-ray (the same applies to FIGS. 19, 20, and 22 described later). FIG. 16 shows the range of 20° ≤ 2θ ≤ 50°.

[0086] In the example shown in FIG. 16 (Example 1), peaks corresponding to the (002) plane and (200) plane of ZrO2, the (200) plane of Pt, and the (100) plane of SRO were observed in the θ-2θ spectrum.

[0087] [Formation of piezoelectric film] In Example 1, next, a piezoelectric film 11 (see FIG. 3) made of AlN was formed on the SRO layer 13b (see FIG. 3) by a sputtering method. The conditions at this time are shown below. Apparatus: DC sputtering apparatus Pressure: 2 Pa Evaporation source (target): Al Gas: Ar / N2 Power: 450 W Substrate temperature: 450 °C Thickness: 600 nm

[0088] On the other hand, in Example 2, a piezoelectric film 11 made of AlN was directly formed on the ZrO2 layer 12b (see FIG. 3) by sputtering. Other conditions were the same as those in Example 1.

[0089] [Out-of-plane measurement] Regarding Example 1, for the film structure in which up to the piezoelectric film 11 (see FIG. 3) was formed, that is, the sample in which AlN was deposited on the above film structure in which up to the SRO layer 13b (see FIG. 3) was formed, the crystallinity was evaluated by an X-ray diffractometer (XRD) (out-of-plane measurement and reciprocal lattice map measurement). Regarding Example 2 as well, the crystallinity was evaluated by out-of-plane measurement.

[0090] First, out-of-plane measurement was performed among out-of-plane measurement and reciprocal lattice map measurement. Out-of-plane measurement is to grasp the crystal structure by making X-rays incident from the surface, that is, incident substantially parallel to the surface. Thereby, the orientation direction of AlN is confirmed. For reference, FIGS. 17 and 18 show the definitions of the planes of a-axis orientation and c-axis orientation. FIG. 17 is a diagram showing the crystal structure of a-axis oriented AlN, and FIG. 18 is a diagram showing the crystal structure of c-axis oriented AlN. As described above, AlN has a wurtzite structure with a hexagonal crystal structure and is polarized in the c-axis direction. In FIG. 17, the hatched portion represents the a-plane, and the a-axis represents the a1(100) axis. In FIG. 18, the hatched portion represents the c-plane, and the c-axis represents the c(001) axis.

[0091] FIG. 19 is a graph showing the results of out-of-plane measurement of the film structure of Example 1. FIG. 20 is a graph showing the results of out-of-plane measurement of the film structure of Example 2. FIG. 19 shows the range of 20° ≤ 2θ ≤ 80°, and FIG. 20 shows the range of 20° ≤ 2θ ≤ 100°.

[0092] As shown in Fig. 19, in the film structure of Example 1, an AlN (200) peak was confirmed at around 2θ = 69.5°. The AlN (100) peak shown at around 2θ = 33.1° was not confirmed. It is considered that the AlN (100) peak is hidden in the tail of ZrO2 (002) because of its low intensity.

[0093] On the other hand, as shown in Fig. 20, in the case of the film structure of Example 2, that is, when AlN was deposited directly on ZrO2, although the peak intensity was one order of magnitude lower than that when deposited on SRO, an AlN (200) peak was confirmed at around 2θ = 69.5°. From this, it can be said that AlN is also a-axis oriented even directly on ZrO2.

[0094] [Reciprocal lattice map measurement] Next, for Example 1, a reciprocal lattice map measurement was performed. The reciprocal lattice map measurement is to three-dimensionally observe the film to be measured and confirm the fluctuation of the lattice constant and the inclination of the lattice plane.

[0095] Fig. 21 is a graph showing the results of the reciprocal lattice map measurement of the film structure of Example 1. As shown in Fig. 21, the peaks in the a-axis direction of AlN (010) were confirmed in a vertical row and the planes were aligned. Also, since the crystal vertices are clear, it can be said that there is little fluctuation. Note that AlN (010) has the same a-axis orientation as AlN (100).

[0096] From the above results, it was found that the AlN deposited on the film structure of Example 1 is a-axis oriented. Also, it was found that there is no crystal fluctuation in AlN and the lattice planes are aligned. From the above, it was found that AlN deposited on SRO / Pt / ZrO2 / Si, preferably on SRO (100) / Pt (100) / ZrO2 (200) and ZrO2 (002), is a-axis oriented and single-crystallized. Also, the same results were obtained for Example 2.

[0097] Generally, AlN (aluminum nitride) is considered to be c-axis oriented. In Example 1, a test was conducted to form an AlN film on a substrate including a-axis oriented SRO(100). As a result, an a-axis oriented AlN film was obtained, and it was found that there was no crystal fluctuation and the lattice planes were aligned. From these facts, it was found that when AlN is deposited on Pt / ZrO2 / Si in the above film structure, epitaxial growth occurs and AlN also becomes single-crystalline with a-axis orientation.

[0098] (Example 3) Next, the film structure 10 described with reference to FIGS. 2 and 3 in Embodiment 1 was formed as the film structure of Example 3, and a test was conducted to measure electrical characteristics.

[0099] [Formation of substrate] For the film structure of Example 3, a substrate was formed in the same manner as the film structure of Example 1.

[0100] [Formation of piezoelectric film] For the film structure of Example 3, a piezoelectric film was formed in the same manner as the film structure of Example 1. However, the pressure was 0.26 Pa and the power was 500 W.

[0101] [θ-2θ spectrum of film structure] For the film structure of Example 3, X-ray diffraction measurement was performed by the θ-2θ method. FIG. 22 is a graph showing an example of the θ-2θ spectrum of the film structure of Example 3 by the XRD method. FIG. 22 shows the range of 20° ≤ 2θ ≤ 80°.

[0102] As shown in FIG. 22, for the AlN film formed on the SRO(100) substrate, that is, on SRO(100) / Pt(100) / ZrO2(200) and ZrO2(002), AlN(200) can be confirmed, and it can be seen that AlN is a-axis oriented.

[0103] [Displacement amount] Regarding the film structure of Example 3, samples having a cantilever shape and a pad shape were fabricated, and the electrical characteristics of the film structure of Example 3 were measured by forming an upper electrode (Pt: 100 nm) on the AlN film. The structure is shown in FIGS. 23 to 26.

[0104] FIG. 23 is a plan view of a sample having a cantilever shape of the film structure of Example 3. FIG. 24 is a cross-sectional view of a sample having a cantilever shape of the film structure of Example 3. FIG. 25 is a plan view of a sample having a pad shape of the film structure of Example 3. FIG. 26 is a cross-sectional view of a sample having a pad shape of the film structure of Example 3.

[0105] As shown in FIGS. 24 and 26, both the sample having a cantilever shape and the sample having a pad shape are formed by sequentially laminating ZrO2 (60 nm) as the ZrO2 layer 12b, Pt (150 nm) as the Pt layer 13a, SRO (40 nm) as the SRO layer 13b, AlN (600 nm) as the piezoelectric film 11, and Pt (100 nm) as the electrode 22 on a Si substrate as the Si layer 12a. The numerical values in parentheses for each layer in FIGS. 24 and 26 indicate the film thickness. Also, as shown in FIGS. 24 and 26, Pt as the Pt layer 13a is formed on the side surface to make it conductive between the upper and lower Pt electrodes, and the Pt layer 13a as the lower electrode is drawn out on the upper surface of the piezoelectric film 11. Also, when eight pads were designated as pads PD1 to PD8, the diameters of pads PD1 to PD8 were 1 mm.

[0106] The displacement amount when a voltage was applied between the upper electrode and the lower electrode was measured using the sample having a cantilever shape shown in FIGS. 23 and 24. The measurement conditions and the dimensions of the sample at this time were as follows. Applied voltage: 20 V pp , offset = -10 V, F r = 700 Hz, Sin wave Sample: 20 × 2 × 0.725 mm

[0107] Table 1 shows the measurement results of the displacement when the voltage between the upper electrode and the lower electrode is 35V.

[0108]

Table 1

[0109] As shown in Table 1, in the first measurement, a displacement of 0.16 μm was obtained at 35V, and in the second measurement, a displacement of 0.14 μm was obtained at 35V. Although this displacement is about 1 / 3 compared to the displacement at 35V, which is about 0.51 μm, the value reported as a literature value in, for example, Non-Patent Document 1, it is considered that a higher displacement can be achieved by adjusting the film formation conditions in the future. Also, considering that when AlN is used for filter applications, the displacement is not such a highly required parameter, that is, the displacement of AlN itself is originally low, it is judged that there is no problem.

[0110] [Dielectric Constant] Using the cantilever shown in Fig. 23 and the pads PD7 and PD8 shown in Fig. 25, the dielectric constant was measured when a voltage was applied between the upper electrode and the lower electrode. The measurement conditions at this time were as follows. Measurement Conditions: C p -R p , F r = 1 kHz, V pp = 1V

[0111] The results are shown in Table 2.

[0112]

Table 2

[0113] As shown in Table 2, the relative dielectric constant is less than half of about 9, which is the value reported as a literature value in, for example, Non-Patent Document 1, indicating that a film with good characteristics has been formed.

[0114] [Breakdown Voltage] Using the pads PD1 to PD6 shown in Fig. 25, the breakdown voltage was measured when a voltage was applied between the upper electrode and the lower electrode. The measurement conditions at this time were as follows. The breakdown voltage of this example was measured using a source meter Model 2450 manufactured by Keithley Instruments, Inc. Condition: Voltage 0V → -200V, Step: 5V / step or 4V / step Considering each film thickness, a step voltage that could be equally incremented in terms of electric field strength was set. Holding time 5 sec Limit current 105 μA

[0115] Also, as the definition of breakdown, the measurement was stopped at the timing when the PZT film underwent dielectric breakdown. However, the limit current was set to 105 μA, and breakdown was determined when the current exceeded this value. Also, the voltage one step before the breakdown voltage was taken as the breakdown voltage.

[0116] The results are shown in Table 3.

[0117]

Table 3

[0118] As shown in Table 3, the breakdown voltage exceeded the maximum voltage of the device at 5 out of 6 locations. Also, it was confirmed that the breakdown voltage was more than 5 times better compared to, for example, about 60 V / μm reported as a literature value in Non-Patent Document 1. Therefore, it can be said that the breakdown voltage characteristics of AlN formed on the SRO(100) substrate, that is, on SRO(100) / Pt(100) / ZrO2(200) and ZrO2(002), are good.

[0119] Summarizing the above results, the following results were obtained as the characteristics of AlN (a-axis orientation) formed on the SRO(100) substrate. Note that V p-p represents the amplitude from the maximum to the minimum of the voltage waveform. Displacement: 0.14 - 0.16 μm @ 35V p-p Conversion (Literature value: 0.51 μm) Relative permittivity: < 3.93 (Literature value: about 9) Breakdown voltage: 350 V / μm or higher (literature value: 60 V / μm)

[0120] As shown for the film structure of Example 1, when an AlN film is formed on a substrate containing a-axis oriented SRO(100), it has been confirmed that it becomes a single crystal with a-axis orientation. In Example 3, tests were conducted on the electrical properties (displacement amount, dielectric constant, and breakdown voltage) of a-axis oriented single crystal AlN. As a result, although the displacement amount was inferior to the value reported as the literature value in Non-Patent Document 1 etc., the dielectric constant and breakdown voltage showed better characteristics than the values reported as the literature value in Non-Patent Document 1 etc.

[0121] As described above, the invention made by the present inventor has been specifically described based on its embodiments. However, it goes without saying that the present invention is not limited to the above embodiments and can be variously modified without departing from the gist thereof.

[0122] Those skilled in the art can conceive of various modification examples and correction examples within the scope of the idea of the present invention, and it is understood that those modification examples and correction examples also belong to the scope of the present invention.

[0123] For example, with respect to each of the above-described embodiments, those in which those skilled in the art have appropriately added, deleted, or changed the design of components, or added, omitted, or changed the conditions of the process also fall within the scope of the present invention as long as they have the gist of the present invention.

[0124] Also, a part of the content described in the above embodiments is described below.

[0125] [Appendix 1] Having a piezoelectric film formed on Pt / ZrO2 / Si, A film structure in which the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate.

[0126] [Appendix 2] The film structure according to Appendix 1, wherein the piezoelectric film is made of a nitride.

[0127] [Supplementary Note 3] The film structure according to Supplementary Note 2, wherein the nitride is AlN.

[0128] [Supplementary Note 4] Having a piezoelectric film formed on Pt / ZrO2 / Si on SOI, The film structure in which the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate.

[0129] [Supplementary Note 5] The film structure according to Supplementary Note 4, wherein the piezoelectric film is made of a nitride.

[0130] [Supplementary Note 6] The film structure according to Supplementary Note 5, wherein the nitride is AlN.

[0131] [Supplementary Note 7] The film structure according to any one of Supplementary Notes 1 to 6, having a polarization rate of 80% or more.

[0132] [Supplementary Note 8] The film structure according to Supplementary Note 3 or 6, wherein the film thickness of AlN is 100 nm or more.

[0133] [Supplementary Note 9] The film structure according to any one of Supplementary Notes 1 to 8, having a second electrode formed on the piezoelectric film.

[0134] [Supplementary Note 10] The film structure according to Supplementary Note 2 or 5, having the piezoelectric film doped with Sc in the nitride.

[0135] [Supplementary Note 11] The film structure according to any one of Supplementary Notes 1 to 10, having a structure in which SRO is on the underlying Pt.

[0136] [Supplementary Note 12] The film structure according to Supplementary Note 3 or 6, having AlN on an underlying film using Mo or W instead of Pt.

[0137] [Supplementary Note 13] The film structure according to any one of Appendices 1 to 12, wherein the piezoelectric film is a single crystal.

[0138] [Appendix 14] An electronic device including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate.

[0139] [Appendix 15] The electronic device according to Appendix 14, wherein a comb electrode is formed on the upper surface or the lower surface of the piezoelectric film.

[0140] [Appendix 16] The electronic device according to Appendix 14 or 15, wherein the piezoelectric film is made of a nitride.

[0141] [Appendix 17] The electronic device according to any one of Appendices 14 to 16, wherein the nitride is AlN.

[0142] [Appendix 18] The electronic device according to any one of Appendices 14 to 17, having a polarization rate of 80% or more.

[0143] [Appendix 19] An electronic device including an electrode, a piezoelectric film, and an alignment layer, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate.

[0144] [Appendix 20] The electronic device according to Appendix 19, wherein the alignment layer is a Si compound.

[0145] [Appendix 21] The electronic device according to any one of Appendices 14 to 20, wherein the polarization direction of the piezoelectric film is the direction of the teeth of the comb electrode.

[0146] [Appendix 22] An electronic device including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, and a hollow portion is provided below the piezoelectric film.

[0147] [Supplementary Note 23] An electronic device including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, electrodes are formed on the upper and lower portions of the piezoelectric film, and a hollow portion is provided in the lower portion of the piezoelectric film.

[0148] [Supplementary Note 24] An electronic device including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, electrodes are formed above and below in contact with the piezoelectric film, and a hollow portion is provided in the lower portion of the piezoelectric film.

[0149] [Supplementary Note 25] An electronic device including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, electrodes are formed above and below the piezoelectric film, a hollow portion is provided in the lower portion of the piezoelectric film, and the overlapping area of the upper and lower electrodes is smaller than the area of the hollow portion.

[0150] [Supplementary Note 26] The electronic device according to any one of Supplementary Notes 23 to 25, wherein the area of the overlapping portion of the upper and lower electrodes is 1 / 2 or less of the area of the hollow portion.

[0151] [Supplementary Note 27] The electronic device according to any one of Supplementary Notes 22 to 26, wherein the piezoelectric film is made of a nitride.

[0152] [Supplementary Note 28] The electronic device according to Supplementary Note 27, wherein the nitride is AlN.

[0153] [Supplementary Note 29] The electronic device according to any one of Supplementary Notes 22 to 28, wherein the polarization rate is 80% or more.

[0154] [Appendix 30] An electronic device according to any one of Appendices 23 to 26, wherein an alignment layer is provided under the lower electrode.

[0155] [Appendix 31] An electronic device according to Appendix 30, wherein the alignment layer is a Si compound.

[0156] [Appendix 32] An electronic device according to Appendix 28, wherein the film thickness of AlN is 100 nm or more.

[0157] [Appendix 33] Including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, An electronic device, wherein either the upper or lower side of the piezoelectric film is not fixed.

[0158] [Appendix 34] An electronic device according to Appendix 33, wherein the piezoelectric film is made of a nitride.

[0159] [Appendix 35] An electronic device according to Appendix 34, wherein the nitride is AlN.

[0160] [Appendix 36] An electronic device according to any one of Appendices 33 to 35, wherein the polarization rate is 80% or more.

[0161] [Appendix 37] Including an electrode and a piezoelectric film, wherein the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, wherein either one of the piezoelectric films is fixed, An electronic device, wherein the reverse side is weakly fixed with a material whose hardness changes with temperature.

[0162] [Appendix 38] Including an electrode and a piezoelectric film, The polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, there are electrodes on the upper and lower portions of the piezoelectric film, An electronic device having two or more electric field directions in the plane due to the presence of a plurality of either the upper or lower electrodes.

[0163] [Appendix 39] including an electrode and a piezoelectric film, the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate and in a plurality of directions, An electronic device having electrodes on the upper and lower portions of the piezoelectric film.

[0164] [Appendix 40] including an electrode and a piezoelectric film the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, An electronic device having a plurality of electrodes on the upper or lower portion of the piezoelectric film.

Explanation of Reference Numerals

[0165] 10 Film structure 11 Piezoelectric film 12 Substrate 12a Si layer 12b ZrO2 layer 12c Substrate 12d BOX layer 13 Electrode 13a Pt layer 13b SRO layer 13c Mo layer 13d W layer 20, 30 Electronic device 21 Hollow portion 22, 22a, 22b, 31, 32 Electrodes 23, 24, 33, 34 Dielectric layers 31a, 32a Body 31b, 32b Comb teeth DP1 Polarization direction DR1, DR2 Directions PD1~PD8 Pads

Claims

1. A substrate that is a Si substrate or an SOI substrate, A buffer film containing ZrO formed on the substrate ２ and and a piezoelectric film formed on the buffer film, having a film structure in which the polarization direction of the piezoelectric film is preferentially oriented parallel to the substrate, wherein the piezoelectric film is an a-axis oriented AlN film.

2. The film structure according to claim 1, further comprising a metal film on the buffer film.

3. The film structure according to claim 2, wherein the metal film is a Pt film, a Mo film, a W film, a Ru film, or a Cu film.

4. The film structure according to claim 2 or 3, further comprising an SRO film on the metal film.

5. The film structure according to any one of claims 1 to 4, wherein the AlN film is doped with Sc.

6. An electronic device made from the film structure according to any one of claims 1 to 5.

7. An electronic device made from the film structure according to claim 1, further comprising a comb electrode on the upper or lower surface of the piezoelectric film in the film structure.

8. The electronic device according to claim 7, wherein the polarization direction of the piezoelectric film is the direction of the teeth of the comb electrode.

9. The electronic device according to claim 7 or 8, having an alignment layer on the substrate.

10. The electronic device according to claim 6, wherein a hollow portion is provided below the piezoelectric film.

11. The electronic device according to claim 10, further comprising an upper electrode and a lower electrode on the upper and lower portions of the piezoelectric film.

12. The electronic device according to claim 11, wherein the area of the overlapping portion of the upper electrode and the lower electrode is smaller than the area of the hollow portion.

13. The electronic device according to claim 11, wherein the area of the overlapping portion of the upper electrode and the lower electrode is 1 / 2 or less of the area of the hollow portion.

14. The electronic device according to any one of claims 10 to 13, having an alignment layer on the substrate.

15. The electronic device according to claim 9 or 14, wherein the alignment layer is made of a material whose hardness increases as the temperature rises.

16. The electronic device according to claim 15, wherein the material is a Si compound.

17. The electronic device according to claim 6, wherein either the upper or lower side of the piezoelectric film is fixed. ​

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