JP2021064733A - Stacked thin film and electronic device - Google Patents

Abstract

To provide a stacked thin film having both excellent piezoelectric properties and excellent magnetostrictive properties and an electronic device with high conversion efficiency.SOLUTION: A stacked thin film 2 having a piezoelectric thin film 10 composed of epitaxially grown films and a ferromagnetic thin film 20 formed on the piezoelectric thin film 10, and an electronic device are provided. The ferromagnetic thin film 20 includes one or more crystalline phases 24 and one or more amorphous phases 22.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electronic device having a laminated thin film having a piezoelectric portion and a ferromagnetic portion.

Electronic devices including a piezoelectric portion and a magnetostrictive material portion (ferromagnetic material) have been developed. It has been studied that this kind of electronic device is used as, for example, a magnetic electric sensor, a magnetic sensor, an electric sensor, an optoelectronic device, a microwave electronic device, a magnetic electric or an electromagnetic converter (for example, Patent Document 1).

However, for example, in the electronic device shown in Patent Document 1, the piezoelectric body portion and the magnetostrictive material portion are manufactured in bulk, and these are bonded with an adhesive. Therefore, conventionally, there is a problem that the magnetic and electrical coupling is small and the conversion efficiency (detection sensitivity in the case of a sensor) is low.

U.S. Pat. No. 9,276,192

The present invention has been made in view of such an actual situation, and an object of the present invention is to provide a laminated thin film having both excellent piezoelectric characteristics and excellent magnetostrictive characteristics, and an electronic device having high conversion efficiency.

In order to achieve the above object, the laminated thin film according to the present invention
Piezoelectric thin film made of epitaxial growth film and
It has a ferromagnetic thin film formed above the piezoelectric thin film and
The ferromagnetic thin film contains a crystalline phase and an amorphous phase.

In the laminated thin film of the present invention, since the piezoelectric thin film is made of an epitaxial growth film, it becomes a highly oriented piezoelectric film and has excellent piezoelectric characteristics. Further, the ferromagnetic thin film formed above the piezoelectric thin film has a _{small threshold magnetic field HTH} and holding force Hc for generating magnetostriction, and dλ / dH (unit magnetic field (unit magnetic field (unit magnetic field)) in a low magnetic field. Alternatively, it can function as a magnetostrictive thin film having a large amount of change in magnetostriction per unit magnetic field strength). Therefore, the device having the laminated thin film according to the present invention can be effectively used as an electronic device having high conversion efficiency.

Preferably, the crystal phase has a face-centered cubic structure. With such a configuration, the magnetostrictive characteristics of the laminated thin film are further improved, and the conversion efficiency of the electronic device is further increased.

Preferably, the ferromagnetic thin film contains at least Fe. With such a configuration, the characteristics of the laminated thin film are further improved, and the output of the electronic device is increased.

Preferably, the thickness (t2) of the ferromagnetic thin film is larger than the in-plane average particle size (D2) of the crystal phase contained in the ferromagnetic thin film. With such a configuration, the characteristics of the laminated thin film are further improved, and the conversion efficiency of the electronic device with respect to the input in a low magnetic field is further improved.

FIG. 1 is a cross-sectional view of a main part of a laminated thin film according to an embodiment of the present invention. FIG. 2 is a plan view showing an example of an electronic device having the laminated thin film shown in FIG. FIG. 3 is a cross-sectional view taken along the line III-III shown in FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV shown in FIG. FIG. 5 is a graph showing the magnetostrictive characteristics of the electronic device according to the embodiment of the present invention. FIG. 6 is a graph showing the X-ray diffraction result of the magnetostrictive thin film according to the embodiment of the present invention. FIG. 7A is a graph showing the X-ray diffraction results of the piezoelectric thin film. FIG. 7B is a graph showing the X-ray diffraction results of the piezoelectric thin film. FIG. 7C is a graph showing the X-ray diffraction results of the piezoelectric thin film.

Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

As shown in FIG. 1, the laminated thin film 2 according to the embodiment of the present invention directly or indirectly (electrode film or crystalline control layer) on the piezoelectric thin film 10 and the piezoelectric thin film 10. It has a ferromagnetic thin film 20 formed (via some layer such as). Hereinafter, the characteristics of the piezoelectric thin film 10 and the characteristics of the ferromagnetic thin film 20 will be described.

(Piezoelectric thin film 10)
The piezoelectric thin film 10 is made of a piezoelectric material and exhibits a piezoelectric effect or an inverse piezoelectric effect. The piezoelectric effect means the effect of generating an electric charge by applying an external force (stress), and the inverse piezoelectric effect means the effect of generating distortion by applying a voltage. Piezoelectric materials that exhibit such effects include crystals, lithium niobate, aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT: Pb (Zr, Ti) O ₃ ), and potassium niobate. Examples thereof include sodium (KNN: (K, Na) NbO ₃ ) and calcium titanate titanate (BCZT: (Ba, Ca) (Zr, Ti) O ₃ ).

In the present embodiment, among the above-mentioned piezoelectric materials, it is particularly preferable to use a piezoelectric material having a perovskite structure such as PZT, KNN, and BCZT. By using a piezoelectric material having a perovskite structure as the piezoelectric thin film 10, it is possible to obtain both excellent piezoelectric characteristics and high reliability. In addition, other elements may be appropriately added to the above-mentioned piezoelectric material constituting the piezoelectric thin film 10 in order to improve the characteristics.

The thickness t1 of the piezoelectric thin film 10 is preferably in the range of 0.5 to 10 μm. The thickness t1 can be obtained, for example, by performing an image analysis of a cross-sectional photograph as shown in FIG. In this case, it is preferable that the thickness t1 is measured at three or more points in the in-plane direction and calculated as an average value thereof. The variation in the thickness t1 is as small as ± 5% or less.

In the present embodiment, the piezoelectric thin film 10 is an epitaxially grown film, and the epitaxially grown film means an epitaxially grown film. Here, epitaxial growth means that during film formation, the crystals of the film match the crystal lattice of the underlying material in the film thickness direction (Z-axis direction) and in-plane direction (X-axis and Y-axis directions). It means to grow while being aligned. Therefore, the piezoelectric thin film 10 according to the present embodiment is a crystal in a state in which the crystals are aligned in all three axes of the X-axis direction, the Y-axis direction, and the Z-axis direction in a high temperature state during film formation. It has a structure (epitaxial film), and in a room temperature state after film formation, almost no crystal grain boundaries are formed and has a crystal structure close to a single crystal (not a perfect single crystal) (epitaxially grown film).

Whether or not it grows epitaxially can be confirmed by performing a reflection high-speed electron diffraction evaluation (RHEED evaluation) in the thin film forming process. When the crystal orientation is disturbed on the film surface during film formation, the RHEED image shows a ring-shaped elongated pattern. On the other hand, when epitaxially grown as described above, the RHEED image shows a sharp spot-like or streak-like pattern. The RHEED image as described above is observed in a high temperature state during film formation. The piezoelectric thin film 10 preferably has a crystal structure as shown below in a room temperature state (that is, an epitaxial growth film) after the film formation.

In the room temperature state after the film formation, the piezoelectric thin film 10 of the present embodiment preferably has a plurality of crystal phases, and preferably has a domain structure containing at least three types of domains (regions). When the piezoelectric thin film 10 has a domain structure, the piezoelectric characteristics are further improved and the piezoelectric response to external stress is enhanced.

The specific configuration of the domain structure depends on the piezoelectric material used. For example, when the piezoelectric thin film 10 is a PZT epitaxial growth film, it preferably has at least two types of crystal structures, a tetragonal crystal and a rhombohedral crystal. In this case, the tetragonal crystal preferably has a domain in which the c-axis (the longitudinal axis of the rectangular parallelepiped (crystal lattice)) faces the film thickness direction and a domain in which the c-axis faces the in-plane direction. .. That is, when the piezoelectric thin film 10 is a PZT epitaxial growth film, it preferably contains a total of three domains, that is, two domains of tetragonal crystals and a domain of rhombic crystals.

In the above, the domain in which the c-axis faces the film thickness direction means a domain oriented so that the (001) plane of the tetragonal crystal is substantially perpendicular (or orthogonal) to the film thickness direction. , C domain. On the other hand, the domain in which the c-axis faces the in-plane direction means a domain oriented so that the (001) plane of the tetragonal crystal is substantially parallel to the film thickness direction, and is hereinafter referred to as an a domain.

On the other hand, when the piezoelectric thin film 10 is a KNN epitaxial growth film, it preferably has two domains of orthorhombic crystals and one domain of monoclinic crystals (three domains in total). When the piezoelectric thin film 10 is a BCZT epitaxial growth film, it preferably has two tetragonal domains and two orthorhombic domains (a total of four domains). In the above case, the two types of orthorhombic domains are a domain in which the (001) plane of the orthorhombic crystal is oriented so as to be substantially parallel to the film thickness direction, and a (010) plane of the orthorhombic crystal. There may be domains oriented so as to be substantially parallel to the film thickness direction. In the case of a piezoelectric material having a perovskite structure, the crystal phase may include crystal structures such as tetragonal crystal, rhombohedral crystal, orthorhombic crystal, and monoclinic crystal as described above.

Since the plurality of domains as described above are in contact with each other with a common domain boundary in between, the direction of the crystal axis of each domain may be deviated by up to several degrees from the film thickness direction and the in-plane direction. Further, the plurality of domains as described above are equivalent domains oriented in the same orientation of the same crystal system, at least in a high temperature state at the time of film formation, and in the process of being cooled to room temperature or operating temperature after film formation, It is formed by transitioning to a more stable crystal phase or domain.

The state in which a plurality of domains as described above coexist can be confirmed by analyzing the piezoelectric thin film 10 by electron diffraction or X-ray diffraction (XRD) of a transmission electron microscope (TEM). .. For example, when θ-2θ measurement is performed using Cu-Kα rays using XRD, a reflection peak derived from the piezoelectric thin film 10 is confirmed in the range of 2θ = 42 ° to 46 °. 7A to 7C are schematic views schematically showing the reflection peaks derived from the piezoelectric thin film 10.

When the piezoelectric thin film 10 has only a single domain, a reflection peak as shown in FIG. 7C appears. In FIG. 7C, only a sharp single reflection peak is confirmed in the range of 2θ = 42 ° to 46 ° (particularly around 2θ = 44 °), and the half width of the reflection peak is about 0.1 ° or 0. . It will be 1 ° or less. On the other hand, when a plurality of domains are mixed in the piezoelectric thin film 10, the reflection peak shown in FIG. 7A or FIG. 7B appears.

In FIG. 7A, a plurality of reflection peaks derived from the piezoelectric thin film 10 are confirmed in the range of 2θ = 42 ° to 46 °. In FIG. 7A, the number of reflected peaks corresponds to the number of domains contained in the piezoelectric thin film 10. For example, when the PZT piezoelectric thin film 10 has three types of domains, a reflection peak (P1) indicating a tetragonal c domain appears at 2θ = 43 ° to 44 °, and a rhombohedral body appears at around 2θ = 44 °. A reflection peak (P2) indicating the domain of the crystal appears, and a reflection peak (P3) indicating the a domain of the tetragonal crystal appears at 2θ = 44 ° to 45 °.

Further, even when a plurality of reflection peaks are not confirmed, a broad reflection peak may be confirmed in the vicinity of 2θ = 44 ° as shown in FIG. 7B. In the case of FIG. 7B, a broad reflection peak is formed by overlapping a plurality of reflection peaks. Specifically, when the half width of the peak observed near 2θ = 44 ° is 0.2 ° or more, it is determined that at least three types of domains exist.

(Ferromagnetic thin film 20)
The ferromagnet thin film 20 of the present embodiment contains a ferromagnet. Examples of the ferromagnetic material include pure metals such as iron (Fe), cobalt (Co), and nickel (Ni), or alloys containing at least one of the above metal elements (for example, Fe-Co-based and Fe-Ni-based). , Fe-Si-based alloy, Fe-Si-Al-based alloy, etc.), or an oxide magnetic material containing an oxide of the above metal element can be used. Further, the ferromagnet thin film 20 may be a single film containing the above-mentioned ferromagnet, a multilayer film composed of a plurality of layers, or a laminated film of a ferromagnet and an antiferromagnet. Is also good.

In the present embodiment, the ferromagnetic thin film 20 preferably has an excellent magnetostrictive effect. The magnetostrictive effect means the property of generating strain by an external magnetic field. Most of the ferromagnetic materials exhibit a magnetostrictive effect, but as a material having a relatively large magnetostrictive effect, iron, gallium (Ga), boron (B), silicon (Si), or a rare earth element (samarium (Sm)), Examples of alloys to which dysprosium (Dy), terbium (Tb) formium (Ho), erbium (Er), etc. are added are exemplified, and Fe-Dy-Tb-based alloys and Fe-Ga-based alloys are generally known. ing. In the present embodiment, it is particularly preferable to use a Fe-Co alloy, a Fe-Co-Si-B alloy, a Fe-Ga-B alloy, or the like as the main component constituting the ferromagnetic thin film 20. ..

As shown in FIG. 1, the ferromagnetic thin film 20 has an amorphous phase 22 and a crystal phase 24 extending in the thickness direction of the amorphous phase 22. The crystal phase 24 extends from the thickness direction of the thin film 20 and extends so as to penetrate the thin film 20, the crystal phase 24 extending from the lower surface of the thin film 20 and not reaching the upper surface, and the upper surface of the thin film 20. There is a crystal phase 24 that extends and does not reach the lower surface.

The thickness t2 of the ferromagnetic thin film 20 is preferably in the range of 0.1 to 5 μm. By controlling the thickness t2 of the thin film 20 within this range, the piezoelectric thin film 10 can be sufficiently distorted, and a large electric output can be obtained from the piezoelectric thin film 10. Further, by making the thickness t2 of the thin film 20 not too thick, the productivity of the thin film 20 is also improved.

The thickness t2 is measured in the same manner as the thickness t1. The thickness t2 also has a small variation in the in-plane direction, and is about the same as the thickness t1. In the present embodiment, the ratio of the thickness t2 to the thickness t1 (t2 / t1) is preferably in the range of 1/10 to 10.

Further, in the present embodiment, the thickness t2 of the ferromagnetic thin film 20 is larger than the average particle size D2 of the crystal phase 24 contained in the thin film 20. Preferably, D2 / t2 is less than 1, more preferably 0.01 to 0.7. Here, the average particle size D2 of the crystal phase 24 is obtained by image analysis of a cross-sectional photograph (BF image). More specifically, the average particle size D2 is preferably calculated as an average value of at least three or more crystal phases 24 by measuring the particle size at three or more points in the thickness direction.

As described above, the ferromagnetic thin film 20 of the present embodiment has an amorphous phase 22 and a crystalline phase 24. In particular, in the ferromagnetic thin film 20, it is preferable that most of the contained crystal phases 24 have a face-centered cubic structure (fcc). However, at least a part of the crystal phase 24 may be mixed with the crystal phase 24 having a body-centered cubic structure (bcc).

The ferromagnetic thin film 20 is formed directly or indirectly on the piezoelectric thin film 10, but when the lower piezoelectric thin film 10 is an epitaxial growth film having excellent crystal orientation, the ferromagnetic thin film 20 is usually formed. Is also easy to crystallize. In particular, when the ferromagnetic thin film 20 contains iron, it is usually crystallized in a body-centered cubic structure. In the present embodiment, in the formation of the ferromagnetic thin film 20, the amorphous phase 22 and the crystal phase 24 having a face-centered cubic structure are appropriately selected by appropriately selecting the apparatus for forming the film and the film forming conditions. And can be mixed.

A polycrystalline electrode film made of a conductive material or an electrode film made of a polycrystalline phase and an amorphous phase may be formed between the ferromagnetic thin film 20 and the piezoelectric thin film 10. In that case, the electrode film is preferably a face-centered cubic polycrystalline film or a film composed of an amorphous phase and a face-centered cubic crystal phase. Such an electrode film can also function as a crystallinity control layer for controlling the crystallinity of the ferromagnetic film formed on the electrode film. That is, by forming the ferromagnetic thin film 20 on the epitaxial piezoelectric thin film 10 via the crystalline control layer, the ferromagnetic thin film 20 composed of the amorphous phase 22 and the crystal phase 24 having a face-to-face cubic structure is formed. And the laminated thin film 2 having the epitaxially grown piezoelectric thin film 10 can be easily obtained.

The state in which the amorphous phase 22 and the crystal phase 24 coexist in the ferromagnetic thin film 20 is that the crystal structure of the ferromagnetic thin film 20 is analyzed by electron diffraction or X-ray diffraction (XRD) of TEM. Can be confirmed by. For example, when θ-2θ measurement by Cu—Kα ray is performed using XRD, a reflection peak derived from the ferromagnetic thin film 20 as shown in FIG. 6 is confirmed. In FIG. 6, the reflection peak derived from the ferromagnetic thin film 20 of the present embodiment is shown by the solid line ex1. For comparison, the reflection peak when the ferromagnetic thin film 20 is composed of only the amorphous phase 22 is shown by the broken line ce1, and the reflection peak when the ferromagnetic thin film 20 is composed of only the crystal phase 24 is shown. It is indicated by the one-point chain line ce2.

As shown by the broken line ce1 in FIG. 6, when the ferromagnetic thin film 20 is composed of only the amorphous phase 22, sharp peaks due to the periodic array structure are not detected, and the halo is broad and wide. Only the pattern appears. Further, as shown by the alternate long and short dash line ce2 in FIG. 6, when the ferromagnetic thin film 20 is composed of only the crystal phase 24, only an extremely sharp reflection peak having a narrow full width at half maximum is detected.

On the other hand, in the case of the ferromagnetic thin film 20 of the present embodiment, the amorphous phase 22 and the crystal phase 24 are mixed and exist, so that the amorphous phase is as shown by the solid line ex1 in FIG. A reflected peak having both a broad raised (halo) portion indicating the presence of 22 and a sharp peak portion indicating the presence of the crystal phase 24 is detected. The crystal structure of the crystal phase 24 (whether or not it has a face-centered cubic structure) can be determined by analyzing the above diffraction pattern.

Further, the ratio of the amorphous phase 22 to the crystalline phase 24 can be confirmed by performing profile fitting on the reflected peak shown in FIG. 6 and calculating the crystallinity. Specifically, in the reflection peak shown in FIG. 6, the crystal phase portion (peak portion) and the amorphous phase portion (halo portion) are fitted, and the integrated intensity (area) of each portion is measured. The crystallinity (%) is the integrated strength (Ic) of the crystal phase portion with respect to the sum (that is, the total peak area) of the integrated strength (Ic) of the crystal phase portion and the integrated strength (Ia) of the amorphous phase portion. ) Is represented by the ratio (Ic / (Ic + Ia) × 100). In the present embodiment, the crystallinity of the ferromagnetic thin film 20 is preferably 1% to 50%, more preferably 5% to 20%.

In addition to the above calculation method, the ratio of the amorphous phase 22 to the crystal phase 24 is calculated as the area ratio of the crystal phase 24 to the predetermined area of the ferromagnetic thin film 20 in the cross section shown in FIG. You may. Even in this case, the area ratio of the crystal phase 24 is preferably 1% to 50%, more preferably 5% to 20%. As for the area ratio of the crystal phase 24 in the cross section, the cross-sectional photograph of the ferromagnetic thin film 20 is taken at three or more places, and in each cross-sectional photograph, the area of the crystal phase 24 existing in the range of 500 nm × 5000 nm is determined by image analysis. It is obtained by measuring and calculating the average value.

(Other functional membranes)
Although not shown in FIG. 1, the laminated thin film 2 may have other functional films formed in addition to the piezoelectric thin film 10 and the ferromagnetic thin film 20. For example, as described above, a conductive electrode film may be formed on the lower layer and the upper layer of the piezoelectric thin film 10 (that is, between the piezoelectric thin film 10 and the ferromagnetic thin film 20). Since the conductive electrode film is formed, the electric output can be efficiently extracted from the piezoelectric thin film 10. In this case, the electrode film includes a metal thin film having a face-centered cubic structure such as platinum (Pt), iridium (Ir), or gold (Au), or strontium ruthenate (SrRuO ₃ ) or lithium nickelate (LiNiO ₃ ). It is preferable to form an oxide conductor thin film having a perovskite structure.

Further, a buffer layer may be formed on the lowermost layer of the laminated thin film 2 in order to efficiently promote epitaxial growth. The buffer layer preferably contains zirconium oxide (ZrO ₂ ) or zirconium oxide (stabilized zirconia) stabilized by rare earth elements (including Sc and Y) as a main component. Further, an insulating protective layer or the like may be formed above the ferromagnetic thin film 20.

(Manufacturing method of laminated thin film 2)
Subsequently, an example of the method for manufacturing the laminated thin film 2 shown in FIG. 1 will be described below.

The laminated thin film 2 is formed on a substrate (not shown in FIG. 1). The substrate to be used can be selected from various single crystals such as Si, MgO, strontium titanate (SrTIO ₃ ), lithium niobate (LiNbO ₃ ), and in particular, a single crystal having a Si (100) -plane surface. It is preferable to use a silicon substrate that is made of. When a single crystal silicon substrate is used, it is preferable that the buffer layer and the electrode film are first epitaxially grown on the silicon substrate, and the piezoelectric thin film 10 is formed on the buffer layer. At this time, as a method for epitaxially growing the buffer layer and the electrode film, a known method may be adopted.

The piezoelectric thin film 10 is formed by various thin film manufacturing methods. As the thin film forming method, a physical or chemical method such as a vapor deposition method, a sputtering method, a sol-gel method, a CVD method, or a PLD method can be used. In the present embodiment, the method for producing the piezoelectric thin film 10 is not particularly limited, but it is particularly preferable to select the sputtering method. In the sputtering method, a film having high piezoelectric characteristics can be stably produced in a large area.

For example, when the piezoelectric thin film 10 is formed by the sputtering method, the composition of the sputtering target, the substrate temperature, the film formation rate, the gas composition, the degree of vacuum, the distance between the substrates and the target, etc. are appropriate for stable epitaxial growth. To control.

Further, in order for the piezoelectric thin film 10 to have a domain structure (including at least three domains), the composition of the sputtering target, the substrate temperature, the stress of the ferromagnetic thin films 20 to be laminated, and the like are controlled.

For example, the composition of the sputtering target is preferably selected so that a plurality of domains and crystal phases are easily formed depending on the material, and the element having a high vapor pressure is increased by 20 to 120% of the stoichiometric composition. .. Taking PZT as an example, it is preferable to control the Pb / (Zr + Ti) atomic ratio to be 1.2 to 2.2 and the Zr / (Zr + Ti) atomic ratio to be 1 to 1.5. Further, it is preferable to control the substrate temperature during sputtering so as to be 550 to 650 ° C. Further, the stress of the ferromagnetic thin film 20 is preferably a compressive stress. In addition, after epitaxially growing the piezoelectric thin film 10, annealing treatment at a temperature of 300 to 500 ° C. in an oxidizing atmosphere is also effective for obtaining the above-mentioned domain structure.

The ferromagnetic thin film 20 can also be formed by various thin film manufacturing methods like the piezoelectric thin film 10, but in the present embodiment, it is particularly preferable to adopt the sputtering method. In the case of the sputtering method, in order to mix the amorphous phase 22 and the crystalline phase 24, the film forming conditions such as the degree of vacuum, the substrate temperature, the gas composition, the gas pressure, the power, and the substrate distance may be appropriately controlled. .. For example, the degree of vacuum in the chamber is preferably 0.01 to 0.1 Pa, and the substrate temperature is preferably 20 ° C to 200 ° C. In particular, in order to form the crystal phase 24 in a face-centered cubic structure, the substrate temperature at the time of film formation should be maintained at 200 ° C. or lower by keeping the distance between the target and the substrate to 100 mm or more without heating the substrate. Is preferable.

By the above method, a substrate on which the laminated thin film 2 is formed can be obtained. The obtained substrate is appropriately subjected to patterning processing or the like and processed into a predetermined shape to obtain a magnetic-electric conversion element or a piezoelectric element having the laminated thin film 2.

An electrode film or the like may be appropriately formed between the piezoelectric thin film 10 and the ferromagnetic thin film 20 depending on the intended use. Further, the positional relationship between the piezoelectric thin film 10 and the ferromagnetic thin film 20 may be reversed. That is, the ferromagnetic thin film 20 may be on the upper side or the lower side of the piezoelectric thin film 10. Further, it is also possible to provide the ferromagnetic thin film 20 on both the upper and lower sides of the piezoelectric thin film 10. A ferromagnetic thin film 20 and a piezoelectric thin film 10 may be formed on different substrates by a thin film manufacturing method, and then the two may be joined to obtain a laminated structure. However, as described above, the piezoelectric material is preferable. It is preferable to form the ferromagnetic thin film 20 on the thin film 10 by the thin film method. If necessary, at least a part of the substrate on one side or both sides can be removed to form a structure having only a laminated film or a shape in which the laminated film is held by one substrate.

(Summary of the first embodiment)
In the laminated thin film 2 of the present embodiment, the piezoelectric thin film 10 is made of an epitaxial growth film, and there are almost no crystal grain boundaries inside the piezoelectric thin film 10. That is, the piezoelectric thin film 10 contained in the laminated thin film 2 has excellent crystal orientation. Therefore, in the piezoelectric thin film 10 of the present embodiment, the disturbance of the physical quantity due to the crystal grain boundaries is suppressed, and the piezoelectric thin film 10 exhibits excellent piezoelectric characteristics.

Further, the ferromagnetic thin film 20 formed above the piezoelectric thin film 10 has an amorphous phase 22 and a crystal phase 24, and has the characteristics of the amorphous phase 22 and the characteristics of the crystal phase 24. Combined. That is, in the ferromagnetic thin film 20 of the present embodiment, the responsiveness to the input magnetic field can be improved due to the characteristics of the amorphous phase 22. That is, the threshold magnetic field _HTH and the holding force Hc required to generate magnetostriction can be reduced. Moreover, in the ferromagnetic thin film 20 of the present embodiment, dλ / dH (amount of change in strain per unit magnetic field (or unit magnetic field strength)) at a low magnetic field can be increased due to the characteristics of the crystal phase 24. it can.

As described above, the laminated thin film 2 according to the present embodiment is configured by preferably combining the piezoelectric thin film 10 having high orientation and excellent piezoelectric characteristics and the ferromagnetic thin film 20 having excellent magnetostrictive characteristics. Therefore, the element (magnetic-electric conversion element or piezoelectric element) having the laminated thin film 2 according to the present embodiment has high conversion efficiency (for example, magnetic-electric conversion efficiency) and excellent detection sensitivity (high responsiveness and noise). It can be suitably used as an electronic device having both (small) and.

Further, in the present embodiment, the crystal phase 24 contained in the ferromagnetic thin film 20 has a face-centered cubic structure. With such a configuration, the magnetostrictive characteristics of the laminated thin film 2 are further improved, and the conversion efficiency of the electronic device is further increased.

Further, in this embodiment, the ferromagnetic thin film 20 contains at least Fe. With such a configuration, the characteristics of the laminated thin film 2 are further improved, and the output of the electronic device is further increased.

Further, in the present embodiment, the thickness (t2) of the ferromagnetic thin film 20 is larger than the in-plane average particle diameter (D2) of the crystal phase 24 contained in the ferromagnetic thin film 20. With such a configuration, the characteristics of the laminated thin film 2 are further improved, and the conversion efficiency of the electronic device with respect to the input in a low magnetic field is further improved.

(Industrial application field of laminated thin film 2)
The laminated thin film 2 of the present embodiment is formed on a predetermined substrate, and the substrate is incorporated into a magnetic-electric conversion element or a piezoelectric element for use. The magnetic-electric conversion element or piezoelectric element having the laminated thin film 2 is connected to a power source or an electric / electronic circuit, and constitutes an electronic device by being mounted on a circuit board or packaged.

For example, if an amplifier and a rectifier circuit are connected to a magnetic-electric conversion element having a laminated thin film 2 and packaged, a magnetic sensor can be obtained. Similarly, if a power storage element and a rectifying power management circuit are connected to a magnetic-electric conversion element, an energy conversion device (energy harvester) that generates electric power from an external magnetic field or vibration can be obtained. In addition, it can be used for various piezoelectric devices and magnetic electric devices such as inkjet printer heads, microactuators, gyroscopes, and motion sensors.

In particular, the above-mentioned energy conversion device is incorporated and used in a power supply system, a wearable terminal (earphone / hearable device, smart watch, smart glasses (glasses), smart contact lens, cochlear implant, cardiac pacemaker, etc.).

Second Embodiment In the second embodiment, the magnetic-electric conversion element 30 (hereinafter, also referred to as the element 30) will be described as an example of the electronic device according to the embodiment of the present invention. As shown in FIGS. 2 to 4, the magnetic-electric conversion element 30 has a laminated thin film 2 (including a piezoelectric thin film 10 and a ferromagnetic thin film 20) in the first embodiment. In FIGS. 2 to 4, the X-axis, the Y-axis, and the Z-axis are substantially perpendicular to each other, and the Z-axis coincides with the stacking direction.

The magnetic-electric conversion element 30 of the present embodiment receives energy such as a magnetic field, an electromagnetic wave, and an ultrasonic wave transmitted in a non-contact manner from a distance, and converts these energies (input signals) into an electric output. For example, when a magnetic field is applied from the outside, the ferromagnetic thin film 20 causes distortion due to the magnetostrictive effect. The strain generated here also distorts the piezoelectric thin film 10 located below the ferromagnetic thin film 20, and charges are generated on the surface of the piezoelectric thin film 10 due to the piezoelectric effect. The generated electric charge is taken out as an electric output through the first electrode film 50 and the second electrode film 52. In the present embodiment, a detailed configuration of 30 magnetic-electric conversion elements having the above-mentioned performance will be described as an example.

First, the form of the magnetic-electric conversion element 30 will be described with reference to the drawings. As shown in FIG. 2, the magnetic-electric conversion element 30 has a film laminated portion 32 on which functional films are laminated, and an outer peripheral portion 34 that surrounds the outside of the film laminated portion 32.

As shown in FIG. 3, the substrate 40 is present in the lowermost layer in the Z-axis direction. The substrate 40 has an opening 42 in a substantially central portion of the XY plane, that is, a portion of the film laminated portion 32. That is, the substrate 40 is substantially present only on the outer peripheral portion 34 of the magnetic-electric conversion element 30. The first electrode film 50, the laminated thin film 2, and the second electrode film 52 are laminated in this order on the film laminated portion 32 located above the Z axis of the opening 42. However, the second electrode film 52 may be formed between the piezoelectric thin film 10 and the ferromagnetic thin film 20 included in the laminated thin film 2.

The first electrode film 50 integrally has an end portion 50a and a central portion 50b. In the plan view shown in FIG. 2, the central portion 50b of the first electrode film 50 has a substantially rectangular shape smaller than the opening surface of the opening 42. Further, the end portions 50a of the first electrode film 50 are located at both ends of the central portion 50b in the X-axis direction, and have a substantially rectangular shape having a width smaller in the Y-axis direction than the central portion 50b in the plan view shown in FIG. Has. Since the first electrode film 50 has the above-mentioned shape, in the cross section shown in FIG. 3 (cross section along the line III-III), the upper opening surface of the opening 42 in the Z-axis direction is hung in the X-axis direction. Exists to pass. Then, only the end portion 50a of the first electrode film 50 exists on the surface of the substrate 40 located on the outer peripheral portion 34 of the element 30.

On the other hand, in the cross section shown in FIG. 4 (cross section along the IV-IV line in FIG. 2), only the cross section of the central portion 50b of the first electrode film 50 appears, and the end portion 50a does not exist. Therefore, in the cross section shown in FIG. 4, the first electrode film 50 appears to be floating above the opening 42. The film laminated portion 32, which appears to be floating above the opening 42, is likely to warp due to the imbalance of stress of each laminated film, but is at the center of the first electrode film 50 of the film laminated portion 32. It is preferable that the lower surface of the portion 50b and the lower surface of the end portion 50a of the first electrode film 50 in contact with the substrate 40 have substantially the same height (position) in the Z-axis direction and are flush with each other.

The laminated thin film 2 is located above the first electrode film 50 in the Z-axis direction and has a plan view shape similar to that of the first electrode film 50. However, in the plan view shown in FIG. 2, the size of the laminated thin film 2 is smaller than that of the first electrode film 50. Further, a second electrode film 52 exists above the laminated thin film 2 in the Z-axis direction, and the second electrode film 52 has a substantially rectangular plan view shape.

As described above, the second electrode film 52 may be located between the piezoelectric thin film 10 and the ferromagnetic thin film 20. In that case, only the piezoelectric thin film 10 has a laminated structure sandwiched between the first electrode film 50 and the second electrode film 52, and the ferromagnetic thin film 20 is located on the second electrode film 52. With such a configuration, the electric charge generated in the piezoelectric thin film 10 can be taken out more efficiently.

When the second electrode film 52 is located between the piezoelectric thin film 10 and the ferromagnetic thin film 20, the second electrode film 52 is a face-centered cubic polycrystalline film or an amorphous phase and face-to-face. It is preferably a film composed of a cubic crystal phase. By forming the ferromagnetic thin film 20 on this, the epitaxially grown piezoelectric thin film 10 and the ferromagnetic thin film 20 composed of the amorphous phase 22 and the crystal phase 24 having a face-to-face cubic structure are laminated. 2 is easy to obtain.

As shown in FIG. 3, the tip of the first extraction electrode film 51 is connected to one end 50a of the first electrode film 50. A first electrode pad 51a is formed on the surface of the substrate 40 at the rear end of the first extraction electrode film 51. An external circuit (not shown) can be connected to the first electrode pad 51a.

Further, the other end portion 50a of the first electrode film 50 is covered with an insulating film 54 together with a part of the surface of the laminated thin film 2. A second extraction electrode 53 is formed so as to hang over the insulating film 54 in the X-axis direction, and the tip of the second extraction electrode 53 is connected to the second electrode film 52. A second electrode pad 53a is formed on the surface of the substrate 40 at the rear end of the second extraction electrode film 53. An external circuit (not shown) can be connected to the second electrode pad portion 53a. Since there is an insulating film 54, the second extraction electrode 53 is insulated from the first electrode film 50.

In the present embodiment, the material of the substrate 40 _{can be selected from various single crystals such as Si, MgO, strontium titanate (SrTIO 3} ), lithium niobate (LiNbO ₃ ), and in particular, the surface is Si (100). ) It is preferable to use a silicon substrate that is a single crystal on the surface.

The material of the first electrode film 50 is preferably a metal thin film having a face-centered cubic structure such as Pt, Ir, Au, or an oxide conductor film having a perovskite structure such as _{SrRuO 3} or LaNiO _3. Further, the above metal thin film and the above oxide conductor film may be laminated (for example, Pt electrode / SrRuO ₃ or the like). In this case (in the case of a plurality of layers), it is preferable that the oxide conductor film is present on the piezoelectric thin film 10 side (that is, above the Z-axis direction) of the first electrode film 50. The thickness of the first electrode film 50 is preferably 30 nm to 200 nm.

The piezoelectric thin film 10 and the ferromagnetic thin film 20 included in the laminated thin film 2 may be the same as those in the first embodiment, and the description thereof will be omitted. Further, on the second electrode film 52, similarly to the first electrode film 50, a metal thin film having a face-centered cubic structure such as Pt, Ir, Au, or an oxide conductive film having a perovskite type structure such as _{SrRuO 3} or LaNiO ₃ It is preferable that a body membrane or the like is included. The thickness of the metal thin film or the oxide conductor film in the second electrode film is preferably 3 nm to 100 nm.

The first take-out electrode film 51 and the second take-out electrode film 53 need only have conductivity, and the material and thickness thereof are not particularly limited. For example, in addition to Pt, conductive metals such as Ag, Cu, Au, and Al can be included. Further, although not shown in FIGS. 2 to 4, a protective layer may be formed on the uppermost layer of the magnetic-electric conversion element 30. As the protective layer, an insulating film is preferable, but for example, _{an insulating film such as SiO 2} , Al2O3, or polyimide, or a metal film such as Ti or Ta can be used, and the thickness thereof is not particularly limited. It may be about 10 nm.

Further, a buffer layer may be formed below the first electrode film 50 in the Z-axis direction (that is, between the substrate 40 and the first electrode film). As described in the first embodiment, the buffer layer contains zirconium oxide (ZrO ₂ ) or zirconium oxide stabilized by rare earth elements (including Sc and Y) as a main component (stabilized zirconia). Is preferable. The formation of the buffer layer promotes epitaxial growth of the film located above the buffer layer (high quality). The buffer layer also functions as an etching stopper layer when forming the opening 42. When forming the buffer layer, the thickness thereof is preferably 5 nm to 100 nm.

In the present embodiment, since the element 30 has the above-described configuration, the central portion of the element 30 functions as an oscillator having a vibration mode of a specific frequency, particularly as an in-plane telescopic oscillator. Here, the in-plane expansion / contraction oscillator means an oscillator that utilizes the in-plane expansion / contraction vibration mode generated over the in-plane direction of the elastic body. Although FIGS. 2 to 4 show a rectangular shape as the vibrator, other shapes such as a disk type and a cantilever type can be taken. Preferably, it is a rectangular shape as shown in FIGS. 2 to 4.

When focusing on the function as a vibrator, the film laminated portion 32 in which the first electrode film 50, the laminated thin film 2 and the second electrode film 52 are laminated in the central portion of the element 30 becomes the vibrating portion 32, and the first electrode The portion (particularly, the portion that supports the vibrating portion 32 above the opening 42) where the end portion 50a of the film 50 and the end portion of the laminated thin film 2 are laminated becomes the support portion (or support arm) 36. The support portion 36 connects the vibrating portion 32 and the outer peripheral portion 34 of the element 30.

The support portion 36 is preferably in a form having low rigidity with respect to the vibrating portion 32 so as not to interfere with the movement of the vibrating portion 32 (in-plane expansion / contraction vibration). For example, the width in the Y-axis direction of the support portion 36 is narrower than the width in the Y-axis direction of the vibrating portion 32 (the length in the direction orthogonal to the X-axis direction in which the support portion 36 extends). Alternatively, the thickness of the support portion 36 in the Z-axis direction is made smaller than the thickness of the vibrating portion 32 in the Z-axis direction. The product of the thickness and width of the support portion 36 is preferably less than 90%, more preferably less than 75% of that of the vibrating portion 32. With this configuration, in-plane expansion and contraction vibration with a large amplitude can be induced, and the output of the magnetic-electric conversion element 30 is increased.

Further, the length of the support portion 36 is preferably about 1/4 of the wavelength of the vibration transmitted through the vibrating portion 32. By doing so, the energy can be efficiently confined in the vibrating portion, a large output can be obtained, and interference between the elements in the case of arraying can be suppressed.

Further, the surface of the vibrating portion 32 (that is, the surfaces of the first electrode film 50 and the second electrode film 52) is preferably flat. More specifically, the surface roughness is preferably an arithmetic average roughness (Ra) or an average length of elements (Rms) of less than 1 μm, and is 1/10 or less of the wavelength of vibration transmitted through the vibrating portion 32. Is more preferable.

The width of the element 30 in the vibration direction (Y-axis direction) is preferably extremely small compared to the wavelength of the electromagnetic wave having the same frequency because the vibrating portion 32 vibrates at the wavelength of the sound wave whose speed is slower than that of the electromagnetic wave. Specifically, the width of the element 30 in the vibration direction (Y-axis direction) is preferably smaller than 1/10 of the wavelength of the electromagnetic wave in vacuum. On the other hand, the size of the element is not limited in the direction orthogonal to the vibration direction (X-axis direction), and the vibrating portion 32 has a shape that extends linearly and a shape that is folded into a meander shape or a spiral shape. It can be taken.

Further, in the present embodiment, it is preferable that the ferromagnetic thin film 20 is configured to expand and contract in the in-plane direction (that is, in the XY plane direction). In this case, the vibration mode of the vibrator becomes the in-plane controller mode, and Q, which is a characteristic representing the sharpness of vibration, becomes large. By taking the vibration mode in which the Q is large in the magnetic-electric conversion element 30, a larger output can be obtained and energy can be efficiently converted into electric power.

In addition, Q can be expressed by the following equation.
Q = f0 / (f1-f2)
In the above equation, f0 is the intrinsic frequency of the oscillator, f1 is the higher frequency of the frequencies at which the output or amplitude is half the value at the intrinsic frequency, and f2 is also the lower frequency. The element 30 of the present embodiment has a Q greater than 100.

The natural frequency of the element 30 is determined by the vibration mode used, the shape, size, material, and the like of the element. By irradiating the element with energy having a frequency equal to the natural frequency of the element 30 or placing the element in an energy field, the element 30 is caused to cause natural vibration, which causes the piezoelectric thin film 10 to expand and contract to generate an electric output. Let me.

The element 30 may be a single element or an array element in which a plurality of single elements 30 are integrally formed on a common substrate 40.

Hereinafter, a method for manufacturing the magnetic-electric conversion element 30 shown in FIGS. 2 to 4 will be described.

In the manufacture of the magnetic-electric conversion element 30, first, the first electrode film 50, the laminated thin film 2, and the second electrode film 52 are formed on a substrate 40 such as a silicon wafer by various thin film manufacturing methods. As the thin film manufacturing method, a vapor deposition method, a sputtering method, a sol-gel method, a CDV method, a PLD method and the like can be applied, and a sputtering method is particularly preferable. The layers up to the piezoelectric thin film 10 are preferably formed by epitaxial growth. The specific method for forming the piezoelectric thin film 10 and the ferromagnetic thin film 20 may be the same as in the first embodiment.

The second electrode film 52 may be formed between the piezoelectric thin film 10 and the ferromagnetic thin film 20 of the laminated thin film. Further, when the ferromagnetic film 20 is made of a conductive material such as a metal or an alloy, the ferromagnetic film 20 can function as the second electrode film 52, so that the second electrode film 52 is separately provided. It is not necessary to provide.

The substrate on which the laminated film is formed as described above is subjected to patterning processing so as to have a pattern as shown in FIG. A known method can be adopted for the patterning process. However, at this time, the longitudinal direction (X-axis direction) or the lateral direction (Y-axis direction) of the element 30 is substantially in the <110> direction of the piezoelectric thin film 10 in the laminated thin film 2 and the <110> direction of the substrate 40. It is preferable to pattern them so that they match. That is, in the XY plane shown in FIG. 2, the <110> direction of the piezoelectric thin film 10 is substantially parallel to the X-axis direction or the Y-axis direction. Further, the <110> direction of the substrate 40 is also substantially parallel to the X-axis direction or the Y-axis direction. In addition, in the above, substantially parallel means that it is within a range of ± 3 degrees with respect to a direction that is completely parallel.

などが例示される。第１実施形態で述べたように、圧電体薄膜１０には、正方晶と菱面体晶など、複数の相が含まれるが、正方晶の［１１０］、［１０１］方向と、菱面体晶の［１１０］方向と、および、これらと等価な方向とが、それぞれ素子３０の長手方向または短手方向とほぼ平行となるようにする。こうすることによって、本実施形態の磁気電気変換素子３０は、外部からの応力や入力に対して破断しにくく、耐久性が高くなる。 Here, the <110> direction means a direction that comprehensively indicates equivalent directions such as [110] and [101]. The orientation equivalent to the above is, for example, in the case of cubic crystals.

Etc. are exemplified. As described in the first embodiment, the piezoelectric thin film 10 contains a plurality of phases such as a tetragonal crystal and a rhombic crystal, but the directions of the tetragonal crystals [110] and [101] and those of the rhombic crystal are The [110] direction and the direction equivalent thereto are made to be substantially parallel to the longitudinal direction or the lateral direction of the element 30, respectively. By doing so, the magnetic-electric conversion element 30 of the present embodiment is less likely to break due to external stress or input, and has high durability.

After the patterning process is performed, the first extraction electrode film 51, the second extraction electrode film 53, and the insulating film 54 are formed in a predetermined pattern as shown in FIG. Further, the opening 42 of the substrate 40 is formed by dry etching such as the Deep-RIE method or anisotropic wet etching. As a result, the magnetic-electric conversion element 30 shown in FIGS. 2 to 4 can be obtained.

As described in the first embodiment, the obtained magnetic-electric conversion element 30 can be mounted on a circuit board or packaged by connecting a power supply or an electric / electronic circuit to various sensors, piezoelectric actuators, or the like. Configure electronic devices. Since the electronic device composed of the magnetic-electric conversion element 30 has the laminated thin film 2 of the first embodiment, it is satisfied with both high conversion efficiency and excellent detection sensitivity.

The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

Experiment 1
(Example 1)
In Example 1, a substrate for an electronic device having the laminated thin film 2 of the present invention was produced by the procedure shown below. First, as a substrate, a silicon substrate having a single crystal whose surface is a Si (100) plane was prepared. The size of the prepared silicon substrate was 6 inches. The following laminated film is formed on this silicon substrate.

First, a base oxide thin film (functioning as a buffer layer) composed of _{ZrO 2} and Y ₂ O _{3 , a Pt lower electrode film, and a conductive oxide thin film composed of SrRuO 3} (hereinafter referred to as SRO) are formed of silicon. It was epitaxially grown on a substrate. At this time, a sputtering method was adopted as the thin film manufacturing method. The substrate temperature when forming the base oxide thin film was 700 ° C. to 900 ° C., and the substrate temperature at the end of film formation was adjusted to be lower than the substrate temperature at the start of film formation. Further, the substrate temperature at the time of forming the Pt lower electrode film was adjusted to 600 ° C. to 800 ° C. so as to be lower than the temperature at the end of the film formation of the underlying oxide thin film.

After forming the Pt lower electrode film, the substrate was once taken out into the atmosphere, and the Pt surface was exposed to oxygen in the air. Thereafter, the substrate was again placed in a deposition apparatus, by forming a conductive oxide thin film made of SrRuO _3. The film thickness of each layer was adjusted so that the base oxide thin film was 50 nm, the Pt lower electrode film was 100 nm, and the conductive oxide thin film was 30 nm.

In Example 1, the piezoelectric thin film 10 of PZT was epitaxially grown on the conductive oxide thin film. At this time, the composition of the sputtering target used was 1.3: 0.55: 0.45 in Pb: Zr: Ti in terms of atomic number ratio. The substrate temperature for forming the PZT film was 600 ° C., and the film formation rate was 0.1 nm / sec. In addition, the gas introduced during sputtering is a mixed gas of 10 mol% oxygen-90 mol% argon (Ar), the pressure of the introduced gas is 0.3 Pa, the distance between the substrate and the target is 200 mm, and the film thickness is 1 μm. A PZT film was formed.

Further, the substrate after the PZT film was formed was annealed. The conditions for the annealing treatment were that the treatment atmosphere was an oxygen atmosphere of 1 atm and the temperature was maintained at 350 ° C. for 1 hour.

At the time of film formation from the base oxide thin film to the PZT film, RHEED evaluation was performed to confirm whether or not each layer was epitaxially grown. As a result, it was confirmed that all the layers from the base oxide thin film to the PZT film were epitaxially grown in the film forming process.

Above the PZT film, an SRO conductive oxide thin film (referred to as an SRO adhesion layer) and a Pt upper electrode film were further formed. The thickness of the SRO adhesion layer was 50 nm, and the thickness of the Pt upper electrode film was 100 nm. At the time of forming the Pt upper electrode film, the substrate temperature was set to 200 ° C., and other film forming conditions were controlled so that the Pt upper electrode film had a polycrystalline structure.

After forming the Pt upper electrode film, a FeCoSiB ferromagnetic thin film 20 was formed on the Pt upper electrode film. In the formation of the ferromagnetic thin film 20, an ultra-high vacuum DC sputtering apparatus is used, and the film is formed after exhausting to a vacuum degree of ^{1 × 10 -4} Pa (more preferably 5 × 10 ^{-5 Pa) or less.} It was. The composition of the target used for film formation was Fe70% -Co8% -Si12% -B10% in terms of molar ratio. Further, at the time of film formation, the substrate was not heated, and the film was formed with a sufficient distance between the target and the substrate so that the substrate temperature did not rise. As for other film forming conditions, Ar gas was used as the introduction gas, the pressure of the introduction gas was 0.05 Pa, the output was 150 W (DC), and the ferromagnetic thin film 20 having a film thickness of 500 nm was formed.

After the film formation of the ferromagnetic thin film 20, an insulating protective film was further formed on the ferromagnetic thin film 20 with a thickness of 10 nm. By forming each layer in such a procedure, a substrate for an electronic device containing the laminated thin film 2 of the present invention was obtained.

The crystal structure of the ferromagnetic thin film 20 (FeCoSiB) contained in the produced substrate for an electronic device was confirmed by electron diffraction of XRD and TEM. As a result, in XRD, a reflection peak derived from the ferromagnetic thin film 20 as shown by the solid line ex1 in FIG. 6 was confirmed. In this reflection peak, a broad raised portion (halo portion) indicating the presence of the amorphous phase 22 and a sharp peak portion indicating the presence of the crystal phase 24 having a face-centered cubic structure were confirmed. Therefore, it was confirmed that the ferromagnetic thin film 20 included in the substrate for the electronic device of Example 1 contained both the amorphous phase 22 and the crystal phase 24 having a face-centered cubic structure.

In addition, the manufactured substrates for electronic devices were evaluated as shown below.

(Measurement of magnetostrictive characteristics)
The magnetostrictive characteristics were evaluated by applying an external magnetic field in the range of 0 to 80 Oe to the manufactured substrate for an electronic device and measuring the strain (unit: ppm) generated on the substrate. In the measurement of strain, a sample having a length of 4 cm and a width of 1 cm cut out from the produced substrate for an electronic device was used as a test piece. Then, the strain was obtained by measuring the warp when an external magnetic field was applied to the test piece with a laser displacement meter. The measurement results are shown in FIG.

(Characteristic evaluation as a magnetic sensor)
First, the produced substrate for an electronic device was subjected to patterning processing to produce a magnetic-electric conversion element 30 as shown in FIG. Then, a magnetic sensor (an example of an electronic device) is manufactured by connecting a circuit (a circuit including an amplifier and a rectifier circuit) for detecting the electric charge generated in the piezoelectric thin film 10 to the magnetic-electric conversion element 30 and packaging the circuit. did. With respect to the magnetic sensor produced in this way, the detection limit value (unit: nT) and the noise floor (unit: mV) were measured.

The detection limit value is an index showing the sensitivity of the magnetic sensor. In a magnetic sensor, when an alternating magnetic field (external magnetic field) is applied as an input, a voltage corresponding to the magnitude of the applied magnetic field is output. The detection limit means the minimum input value that the magnetic sensor responds to (that is, outputs a voltage), and the input value is expressed by the magnetic flux density. That is, the smaller the detection limit value, the better the characteristics as a magnetic sensor. In this embodiment, specifically, while applying a DC magnetic field of 1 mT as a bias magnetic field to the element 30, an alternating magnetic field near the intrinsic frequency (about 10 kHz) of the element 30 is applied, and the frequency of the alternating magnetic field is set near the intrinsic frequency. The lower limit of detection was obtained by decaying the size while scanning with. The measurement results are shown in Table 1.

The noise floor is an index showing the level of noise generated by the element 30 itself. In the magnetic sensor, some noise is output even when no signal is input (that is, when no external magnetic field is applied). If the value of this noise is large, the input signal will be buried in the noise. Therefore, noise affects the conversion efficiency and sensitivity of the magnetic sensor, and the smaller the noise floor value, the better the characteristics of the magnetic sensor. In this embodiment, specifically, the noise floor was measured by the following procedure. First, the magnetic sensor was covered with a magnetic field shield foil to completely eliminate the influence of the external magnetic field. Then, using a spectrum analyzer, the output (noise floor) generated by the magnetic sensor itself was measured. The measurement results are shown in Table 1.

(Comparative Example 1)
In Comparative Example 1, a substrate for an electronic device of Comparative Example 1 was produced in the same manner as in Example 1 except that the ferromagnetic thin film was an amorphous magnetostrictive film. However, in Comparative Example 1, the annealing treatment was not performed after the PZT film was formed.

Further, in Comparative Example 1, in order to obtain an amorphous magnetic strain film, unlike Example 1, a ferromagnetic thin film of FeCoSiB alloy was placed on the Pt upper electrode film via a SiO2 amorphous film having a thickness of 5 nm. , The film was formed by the DC sputtering method. As specific film forming conditions, Ar gas was used as the introduction gas, the pressure of the introduction gas was 1 Pa, and the output was 500 W (DC). In Comparative Example 1, the thickness of the ferromagnetic thin film was 500 nm.

Further, also in the substrate for the electronic device of Comparative Example 1, the crystal structure of the ferromagnetic thin film was analyzed by electron diffraction of XRD and TEM. As a result, in XRD, a reflection peak derived from the ferromagnetic thin film as shown by the broken line ce1 in FIG. 6 was confirmed. In the reflection peak of Comparative Example 1, only a broad raised portion (halo portion) indicating the presence of the amorphous phase 22 was confirmed.

In addition, Comparative Example 1 is also evaluated in the same manner as in Example 1, the evaluation result of the magnetostrictive characteristic is shown in FIG. 5, and the result of the characteristic evaluation as a magnetic sensor is shown in Table 1.

(Comparative Example 2)
In Comparative Example 2, the substrate for the electronic device of Comparative Example 2 was produced in the same manner as in Example 1 except that the ferromagnetic thin film was a polycrystalline magnetostrictive film. Even in Comparative Example 2, the annealing treatment was not performed after the PZT film was formed.

Further, in Comparative Example 2, in order to form a polycrystalline magnetostrictive film, unlike Example 1, a ferromagnetic thin film of FeCoSi alloy was formed by a vapor deposition method. Specifically, after exhausting the inside of the vapor deposition apparatus to 3 × 10 ^-4 Pa, a FeCoSiB alloy film was formed at a substrate temperature of 300 ° C. In Comparative Example 2, the thickness of the ferromagnetic thin film was 500 nm.

Further, also in the substrate for the electronic device of Comparative Example 2, the crystal structure of the ferromagnetic thin film was analyzed by electron diffraction of XRD and TEM. As a result, in XRD, a reflection peak derived from the ferromagnetic thin film as shown by the alternate long and short dash line ce2 in FIG. 6 was confirmed. In the reflection peak of Comparative Example 2, only a sharp peak indicating the presence of the crystal phase 24 having a body-centered cubic structure was confirmed.

In addition, Comparative Example 2 is also evaluated in the same manner as in Example 1, the evaluation result of the magnetostrictive characteristic is shown in FIG. 5, and the result of the characteristic evaluation as a magnetic sensor is shown in Table 1.

(Comparative Example 3)
In Comparative Example 3, the substrate for the electronic device of Comparative Example 3 was produced in the same manner as in Example 1 except that the piezoelectric thin film was a polycrystalline PZT film.

Specifically, in Comparative Example 3, first, the silicon substrate was subjected to a thermal oxidation treatment, and a base oxide thin film made of _{SiO 2 was formed on the surface of the silicon substrate.} Then, a Ti thin film, a Pt lower electrode film, and a PZT piezoelectric thin film were formed on the base oxide thin film. The method of forming the Pt lower electrode film and the PZT film is the same as that of the first embodiment. However, in Comparative Example 3, unlike Example 1, a piezoelectric thin film (PZT film) is formed via an amorphous SiO2 base oxide thin film and a polycrystalline Ti thin film. In Comparative Example 3, each layer above the PZT film (SRO adhesion layer, Pt upper electrode film, and ferromagnetic thin film) was formed under the same experimental conditions as in Example 1, and the electronic device of Comparative Example 3 was formed. Obtained a substrate for use.

In Comparative Example 3, when the RHEED evaluation was performed at the time of forming the piezoelectric thin film, it was confirmed that in Comparative Example 3, the RHEED image became a ring-shaped elongated pattern and the PZT formed was not epitaxially grown. It was. Further, when the electron device substrate obtained in Comparative Example 3 was subjected to electron diffraction of XRD and TEM, it was confirmed that the piezoelectric thin film of Comparative Example 3 was a polycrystalline film having no orientation. It was.

Further, also in Comparative Example 3, a magnetic sensor sample of Comparative Example 3 was prepared in the same manner as in Example 1, and the characteristics as a magnetic sensor were evaluated. The results are shown in Table 1.

Evaluation 1
FIG. 5 is a graph showing the magnetostrictive characteristics of Example 1 and Comparative Examples 1 and 2. The magnetostrictive characteristics of Example 1 are shown by solid lines, the magnetostrictive characteristics of Comparative Example 1 are shown by broken lines, and the magnetostrictive characteristics of Comparative Example 2 are shown by alternate long and short dash lines. In Comparative Example 1 in which the ferromagnetic thin film is an amorphous film, the occurrence of strain is confirmed even in a low magnetic field (near 1Oe), but the slope of the graph is small. That is, in Comparative Example 1, dλ / dH (the amount of change in magnetostriction per unit magnetic field) was small. In Comparative Example 2 in which the ferromagnetic thin film is a polycrystalline film, although the slope of the graph is large, strain does not occur unless an external magnetic field of about 40 Oe is applied.

On the other hand, in Example 1, strain is generated even when the external magnetic field is 1 Oe or less. Further, the slope of the graph is larger than that of Comparative Example 1, and dλ / dH (the amount of change in magnetostriction per unit magnetic field) is large. From this result, by making the crystal structure of the ferromagnetic thin film a mixed state of the amorphous phase 22 and the crystal phase 24, _{the values of the threshold magnetic field H TH} and the holding force H _C for generating magnetostriction are obtained. It was proved that the dλ / dH (the amount of change in magnetostriction per unit magnetic field) becomes large at a low magnetic field. That is, the substrate for an electronic device of Example 1 is particularly excellent in magnetostriction characteristics as compared with Comparative Examples 1 and 2. When the substrate for an electronic device (a substrate having excellent magnetic characteristics) of Example 1 is used for a magnetic sensor, high conversion efficiency can be obtained.

Actually, as shown in Table 1, the magnetic sensor of Example 1 has the smallest detection limit value and the smallest noise floor as compared with Comparative Examples 1 to 3, and both characteristics are excellent. I was able to confirm that it was there. From the results shown in FIGS. 5 and 1 above, it was confirmed that the electronic device having the laminated thin film 2 according to the present invention can satisfy both high conversion efficiency and excellent detection sensitivity at the same time.

Experiment 2
(Example 2)
In Example 2, a substrate for an electronic device was produced in the same manner as in Example 1 except that the relationship between the particle size D2 and the thickness t2 of the ferromagnetic thin film 20 was set to the relationship shown in Table 2. Then, using the substrate for the electronic device of Example 2, a magnetic sensor was manufactured in the same manner as in Example 1, and the detection sensitivity and the noise floor were measured. The results are shown in Table 2.

In Example 2, in order to make the relationship between the particle size D2 and the thickness t2 as shown in Table 2, unlike Example 1, the substrate temperature at the time of film formation is 180 ° C., and the ferromagnetic thin film is formed. 20 was formed.

(Example 4)
In Example 4, a substrate for an electronic device was produced in the same manner as in Example 1 except that the ratio of the crystal phases in the ferromagnetic thin film 20 was set to the numerical value shown in Table 2. The ratio of the crystal phases was calculated by measuring the crystallinity of the ferromagnetic thin film 20 with XRD. Further, using the substrate for the electronic device of Example 4, a magnetic sensor was manufactured in the same manner as in Example 1, and the detection sensitivity and the noise floor were measured. The results are shown in Table 2.

In Example 4, in order to set the numerical value of the ratio of the crystal phase to the numerical value shown in Table 2, unlike Example 1, the pressure of Ar gas (introduced gas) at the time of film formation was set to 0.02 Pa. The ferromagnetic thin film 20 was formed.

(Example 5)
In Example 5, the substrate for an electronic device is the same as in Example 1 except that the ferromagnetic thin film 20 is a FeCoSiB alloy film containing an amorphous phase 22 and a crystal phase 24 having a body-centered cubic structure. Was produced. Then, using the substrate for the electronic device of Example 5, a magnetic sensor was manufactured in the same manner as in Example 1, and the detection sensitivity and the noise floor were measured. The results are shown in Table 2.

In Example 5, in order to form the crystal lattice of the crystal phase 24 into a body-centered cubic structure, unlike Example 1, the epitaxially grown PZT film was placed on the epitaxially grown PZT film without passing through the SRO adhesion layer or the PT upper electrode film. , Directly formed the ferromagnetic thin film 20.

Evaluation 2
As shown in Table 2, it was confirmed that Example 1 was superior to Examples 2 to 5.

Experiment 3
In Experiment 2, a substrate for an electronic device was produced in the same manner as in Example 1 except that the piezoelectric thin film 10 was composed of KNN, BCZT, AlN, and ZnO instead of PZT, and the same evaluation was performed. .. As a result, it was confirmed that the same result as in Example 1 described above can be obtained even when the material of the piezoelectric thin film 10 is changed.

Experiment 4
In Experiment 3, the ferromagnetic thin film 20 was formed in the same manner as in Example 1 except that the ferromagnetic thin film 20 was composed of FeCo alloy, FeDyTb alloy (Terphenol-D), FeGa alloy (Galphenol), and FeGaB alloy instead of FeCoSiB alloy. , A substrate for an electronic device was prepared, and the same evaluation was performed. As a result, it was confirmed that the same result as in Example 1 described above can be obtained even when the material of the ferromagnetic thin film 20 is changed.

2 ... Laminated thin film 10 ... Piezoelectric thin film 20 ... Ferromagnetic thin film (magnetostrictive thin film)
22 ... Amorphous phase 24 ... Crystal phase 30 ... Magnetic-electric conversion element 32 ... Membrane laminated part (vibrating part)
34 ... Outer peripheral portion 36 ... Support portion 40 ... Substrate 42 ... Opening 50 ... First electrode film 50a ... End portion 50b ... Central portion 51 ... First extraction electrode film 52 ... Second electrode film 53 ... Second extraction electrode film 54 … Insulation film

Claims (5)

Piezoelectric thin film made of epitaxial growth film and
It has a ferromagnetic thin film formed above the piezoelectric thin film and
The ferromagnetic thin film is a laminated thin film containing a crystalline phase and an amorphous phase. The laminated thin film according to claim 1, wherein the crystal phase has a face-centered cubic structure. The laminated thin film according to claim 1 or 2, wherein the ferromagnetic thin film contains at least Fe. The laminated thin film according to any one of claims 1 to 3, wherein the thickness of the ferromagnetic thin film is larger than the average particle diameter of the crystal phase contained in the ferromagnetic thin film in the in-plane direction. An electronic device having the laminated thin film according to any one of claims 1 to 4.

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