JP7363556B2 - Laminates and electronic devices - Google Patents

Description

The present invention relates to a laminate having a piezoelectric layer and a magnetostrictive layer, and an electronic device including the laminate.

As shown in Patent Document 1 and Patent Document 2, a laminate having a piezoelectric layer and a magnetostrictive layer is known. This laminate has a magnetoelectric (ME) effect, which converts energy (input signals) such as magnetic fields, electromagnetic waves, and ultrasonic waves transmitted from a distance without contact into electrical output. be able to. In the above-mentioned laminate, when an external magnetic field or the like is applied, distortion occurs in the magnetostrictive layer due to the magnetostrictive effect. Then, the strain is transmitted to the piezoelectric layer, and the piezoelectric layer itself bends, thereby generating charges on the surface of the piezoelectric layer.

This laminate is expected to be applied to highly sensitive magnetic sensors capable of detecting biomagnetism, or energy conversion devices incorporated into wearable terminals and the like. However, in order to put it to practical use in the above applications, it is required to be able to output even to a minute input magnetic field, that is, to have excellent responsiveness.

Jitszen No. 58-040853 US Patent Application Publication No. 2013/0252030 (US, A1)

The present invention was made in view of the above circumstances, and an object thereof is to provide a laminate with excellent magnetoelectric effect responsiveness, and an electronic device including the magnetic laminate.

In order to achieve the above object, the laminate according to the present invention,
an epitaxially grown piezoelectric thin film,
A soft magnetic high magnetostriction thin film is formed directly or indirectly on the piezoelectric thin film by a vacuum deposition method.

In the above, the soft magnetic high magnetostrictive film is a film that is made of a soft magnetic material with low coercive force H _C and low threshold magnetic field H _TH , and has a saturation magnetostriction λ _MAX of 5 ppm or more, more preferably 10 ppm or more. .

Conventionally, in order to improve the magnetoelectric effect, it has been thought that it is important to increase the magnetic field sensitivity dλ/dH (hereinafter referred to as magnetic field sensitivity) of magnetostriction by increasing the saturation magnetostriction λ _MAX of the magnetostrictive layer. (See paragraphs 0010 to 0018 of Patent Document 2). As a result of intensive studies, the inventors of the present invention found that increasing the saturation magnetostriction λ _MAX of the magnetostrictive layer does not contribute much to improving the responsiveness to minute input signals. It has been found that the use of a soft magnetic material with a low coercive force H _C and a low threshold magnetic field H _TH improves responsiveness to minute input signals.

Furthermore, in the present invention, the soft magnetic high magnetostrictive film is not a thin plate obtained by mechanical processing such as rolling, but is a film formed directly or indirectly on a piezoelectric thin film by a vacuum deposition method. The thin plate obtained by machining must be laminated on the piezoelectric thin film via an adhesive layer or pressure laminated. When using an adhesive layer, the adhesive layer inhibits strain transmission and charge transfer between the magnetostrictive layer and the piezoelectric layer. Furthermore, in the case of lamination by pressure bonding, the surface oxide film on the surface of the thin plates inhibits the transmission of strain and the exchange of charge between the magnetostrictive layer and the piezoelectric layer. In the laminate of the present invention, since the soft magnetic high magnetostrictive film is formed by a vacuum deposition method, the above-mentioned inhibiting effect does not occur and the response is good. Further, it is also possible to make the laminate thinner.

Preferably, the soft magnetic high magnetostriction thin film has a coercive force H _C of less than 2500 A/m. According to experiments conducted by the present inventors, the smaller the coercive force H _C is than the above reference value, the greater the amount of charge generated in response to a minute external magnetic field.

Furthermore, in the laminate according to the present invention, a magnetic field in which 0.1 ppm of magnetostriction occurs is defined as a threshold magnetic field H _TH ,
Preferably, the threshold magnetic field H _TH of the soft magnetic high magnetostriction thin film is less than 500 A/m.
According to experiments conducted by the present inventors, the smaller the threshold magnetic field H _TH of the magnetostrictive layer is made than the above reference value, the greater the amount of charge generated in response to a minute external magnetic field.

Furthermore, in the laminate according to the present invention, the magnetic field sensitivity dλ/dH in an environment where a DC magnetic field of 500 A/m is applied as a bias magnetic field is as follows:
Preferably, the magnetic field sensitivity dλ/dH of the soft magnetic high magnetostriction thin film is 10 ppb·m·A ⁻¹ or more.
According to experiments conducted by the present inventors, it is possible to make the coercive force H _C and/or the threshold magnetic field H _TH smaller than a predetermined value, and then make the magnetic field sensitivity dλ/dH larger than the above reference value. This further improves the responsiveness of the magnetoelectric effect and further increases the amount of charge generated in response to a minute external magnetic field.

The laminate according to the present invention can be used in electronic devices such as magnetic sensors and energy conversion devices. When the laminate of the present invention is used in a magnetic sensor, the sensitivity characteristics of the magnetic sensor are improved, and a highly sensitive magnetic sensor capable of detecting biomagnetism can be obtained. On the other hand, when the laminate of the present invention is used in an energy conversion device, the device can obtain high electrical output even in the presence of a minute external magnetic field, and the conversion efficiency improves.

FIG. 1 is a sectional view of essential parts of a laminate according to an embodiment of the present invention. FIG. 2 is a plan view showing an example of the ME element having the stacked body shown in FIG. FIG. 3 is a sectional view taken along line III-III shown in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV shown in FIG. 2.

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

First Embodiment As shown in FIG. 1, a laminate 2 according to an embodiment of the present invention includes a piezoelectric thin film 10 and a piezoelectric thin film 10 directly or indirectly (an electrode film or a crystallinity control layer). It has a magnetostrictive layer 20 formed (via some layer, such as, etc.). The characteristics of the piezoelectric thin film 10 and the characteristics of the magnetostrictive layer 20 will be explained below.

(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 refers to the effect of generating electric charge when an external force (stress) is applied, and the inverse piezoelectric effect refers to the effect of generating strain when a voltage is applied. Piezoelectric materials that exhibit such effects include quartz, lithium niobate, aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT:Pb(Zr,Ti)O ₃ ), and potassium niobate. Examples include sodium (KNN: (K, Na) NbO ₃ ), barium calcium titanate zirconate (BCZT: (Ba, Ca) (Zr, Ti) O ₃ ), and the like.

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

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

In this embodiment, the piezoelectric thin film 10 is an epitaxially grown film, and the epitaxially grown film means a film epitaxially grown on a single crystal substrate. 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 growing together. Therefore, in the piezoelectric thin film 10 according to the present embodiment, in a high temperature state during film formation, the crystals are aligned in all the three axes of the X-axis direction, the Y-axis direction, and the Z-axis direction. (epitaxial film), and at room temperature after film formation, almost no crystal grain boundaries are formed and the crystal structure is close to single crystal (not completely single crystal) (epitaxially grown film).

Whether epitaxial growth has occurred can be confirmed by performing reflection high-energy electron diffraction evaluation (RHEED evaluation) during the thin film formation process. If the crystal orientation is disordered on the film surface during film formation, the RHEED image shows a ring-shaped pattern. On the other hand, in the case of epitaxial growth as described above, the RHEED image shows a sharp spot-like or streak-like pattern. The above RHEED image is observed only in a high temperature state during film formation. At room temperature after film formation (ie, epitaxially grown film), the piezoelectric thin film 10 preferably has a crystal structure as shown below.

At room temperature after film formation, the piezoelectric thin film 10 of this embodiment preferably has a plurality of crystal phases, and preferably has a domain structure including at least three types of domains. Since the piezoelectric thin film 10 has a domain structure, piezoelectric properties are further improved.

The specific configuration of the domain structure varies depending on the piezoelectric material used. For example, when the piezoelectric thin film 10 is an epitaxially grown film of PZT, it is preferable that it has at least two types of crystal structures: tetragonal and rhombohedral. In this case, it is preferable that the tetragonal crystal has a domain in which the c-axis (the axis in the longitudinal direction of the rectangular parallelepiped (crystal lattice)) is oriented in the film thickness direction, and a domain in which the c-axis is oriented in the in-plane direction. . That is, when the piezoelectric thin film 10 is an epitaxially grown film of PZT, it is preferable to include a total of three types of domains: two types of tetragonal domains and a rhombohedral domain.

In addition, in the above, a domain in which the c-axis faces the film thickness direction means a domain oriented such that the (001) plane of the tetragonal crystal is approximately perpendicular (or orthogonal) to the film thickness direction. , called the c domain. On the other hand, a domain in which the c-axis is oriented in the in-plane direction means a domain in which the (001) plane of the tetragonal crystal is oriented 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 an epitaxially grown KNN film, it is preferable to have two types of orthorhombic domains and one type of monoclinic domain (three types of domains in total). Further, when the piezoelectric thin film 10 is an epitaxially grown film of BCZT, it is preferable to have two types of tetragonal domains and two types of orthorhombic domains (four types of domains in total). In the above case, the two types of orthorhombic domains are a domain in which the (001) plane of the orthorhombic crystal is oriented approximately parallel to the film thickness direction, and a domain in which the (010) plane of the orthorhombic crystal is oriented so that it is approximately parallel to the film thickness direction. There may be domains oriented 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, rhombohedral, orthorhombic, and monoclinic as described above.

Since the plurality of domains as described above are in contact with each other across a common domain boundary, the direction of the crystal axis of each domain may deviate from the film thickness direction or the in-plane direction by a maximum of several degrees. In addition, the plurality of domains as described above are equivalent domains of the same crystal system and oriented in the same direction, at least in the high temperature state during film formation, and in the process of cooling to room temperature or usage temperature after film formation, It is formed by transitioning to a more stable crystalline phase or domain.

Note that the presence of a plurality of domains as described above can be confirmed by analyzing the piezoelectric thin film 10 using electron beam diffraction or X-ray diffraction (XRD) using a transmission electron microscope (TEM). . For example, when measuring θ-2θ using Cu-Kα rays using XRD, a reflection peak originating from the piezoelectric thin film 10 is observed in the range of 2θ=42° to 46°. When the piezoelectric thin film 10 has a domain structure, a plurality of reflection peaks may be observed depending on the number of domains. Alternatively, when multiple peaks corresponding to each domain overlap, a broad reflection peak with a half width of 0.2° or more may be observed.

(Magnetostrictive layer 20)
The magnetostrictive layer 20 of this embodiment is made of a soft magnetic high magnetostrictive film, and when a magnetic field, electromagnetic waves, ultrasonic waves, etc. are applied from the outside, distortion is generated due to the magnetostrictive effect. The soft magnetic high magnetostriction film is preferably a film that is made of a soft magnetic material with low coercive force H _C and low threshold magnetic field H _TH and has a saturation magnetostriction λ _MAX of 5 ppm or more. The saturation magnetostriction λ _MAX is more preferably 10 ppm or more. Note that the soft magnetic material is generally a low magnetostrictive material with a saturation magnetostriction λ _MAX of 1 ppm or less, but the magnetostrictive layer 20 of this embodiment is a soft magnetic material and has high magnetostrictive characteristics. This is very important.

Examples of soft magnetic materials having the above characteristics include iron (Fe)-cobalt (Co)-silicon (Si)-boron (B) alloy, Fe-Si-B alloy, Fe-Co-B alloy, Fe-chromium (Cr)-Si-B alloy, Fe-nickel (Ni)-molybdenum (Mo)-B alloy, Fe-Si-B-copper (Cu)-niobium (Nb) alloy, Co-Fe-Ni- Examples include Si-B-Mo alloy. The above-mentioned soft magnetic material has much smaller magnetocrystalline anisotropy than that of the hard magnetic material.

Further, in this embodiment, the coercive force H _C of the soft magnetic high magnetostrictive film is preferably less than 2500 A/m. The lower the coercive force _HC , the better the responsiveness of the magnetoelectric effect, as will be described later. However, it is difficult to set the coercive force H _C to 0 A/m, and the lower limit value of the coercive force H _C also depends on the specifications of the film forming apparatus used during manufacturing. The coercive force H _C of the soft magnetic high magnetostrictive film is more preferably 5 A/m or more and less than 2500 A/m, and even more preferably 5 A/m or more and 1500 A/m or less. Note that the coercive force H _C of the soft magnetic high magnetostrictive film can be measured using a vibrating sample magnetometer (VSM).

Furthermore, the threshold magnetic field H _TH of the soft magnetic high magnetostrictive film is preferably less than 500 A/m. In this embodiment, the threshold magnetic field H _TH means a magnetic field that generates 0.1 ppm magnetostriction in the magnetostrictive layer 20 . As for the threshold magnetic field H _TH , similarly to the coercive force H _C , the lower the value, the better the responsiveness of the magnetoelectric effect, but it is difficult to set it to 0 A/m. The threshold magnetic field H _TH of the soft magnetic high magnetostrictive film is more preferably 2 A/m or more and less than 500 A/m, and even more preferably 2 A/m or more and 350 A/m or less.

Note that the threshold magnetic field H _TH of the soft magnetic high magnetostrictive film can be measured, for example, by the method shown below. In the measurement of the threshold magnetic field _HTH , a rotating magnetic field (external magnetic field) of 0 to 6400 A/m was externally applied to the laminate 2 in an environment in which a DC magnetic field of 500 A/m was applied as a bias magnetic field, The strain generated in the laminate 2 is measured. At this time, the strain is obtained by measuring the warpage of the laminate 2 with a laser displacement meter when a rotating magnetic field is applied. The magnitude of the external magnetic field when a strain in the positive magnetostrictive direction corresponding to magnetostriction λ of 0.1 ppm is generated is defined as the threshold magnetic field H _TH of the soft magnetic high magnetostrictive film.

In addition, the magnetic field sensitivity dλ/dH of the soft magnetic high magnetostrictive film is preferably 10 ppb·m·A ⁻¹ or more, more preferably 15 ppm·m·A ⁻¹ or more. In this embodiment, the magnetic field sensitivity dλ/dH means the amount of change in magnetostriction in an environment where a DC magnetic field of 500 A/m is applied as a bias magnetic field. The larger the magnetic field sensitivity dλ/dH, the more responsive the magnetoelectric effect tends to be. However, if the magnetic field sensitivity dλ/dH is too large, the magnetostrictive layer 20 may peel off, and the durability of the laminate 2 may deteriorate. Therefore, the upper limit of the magnetic field sensitivity dλ/dH of the soft magnetic high magnetostrictive film is preferably 60 ppb·m·A ⁻¹ or less, more preferably 30 ppb·m·A ⁻¹ or less. By setting the upper limit value of the magnetic field sensitivity within the above range, the responsiveness of the magnetoelectric effect is improved and the durability of the laminate 2 can be sufficiently ensured.

Note that the magnetic field sensitivity dλ/dH can be measured in the same manner as the threshold magnetic field _HTH . Specifically, similarly to the above, a rotating magnetic field is applied to the laminate 2 under a bias magnetic field environment, and the warpage of the laminate 2 at that time is measured using a laser displacement meter to determine the amount of strain. get. The magnetic field sensitivity dλ/dH is obtained by calculating a magnetic field-magnetostriction curve from the amount of strain obtained by the above measurement, and calculating the slope of the obtained curve using a differential method or the like.

In this embodiment, the magnetostrictive layer 20 made of a soft magnetic high magnetostrictive film preferably has a crystal structure including an amorphous phase 22 and a crystalline phase 24 extending in the thickness direction of the amorphous phase 22. . As shown in FIG. 1, the crystal phase 24 extends in the thickness direction of the magnetostrictive layer 20, and includes a crystal phase 24 that extends through the magnetostrictive layer 20 and a crystal phase that extends from the bottom surface of the thin film 20 but does not reach the top surface. There may be a phase 24 and a crystalline phase 24 extending from the top surface of the thin film 20 but not reaching the bottom surface. In particular, when having the above crystal structure, it is more preferable that most of the included crystal phases 24 have a face-centered cubic structure (fcc). However, even in this case, at least a portion of the crystal phase 24 may include a body-centered cubic structure (BCC) crystal phase.

The magnetostrictive layer 20 is formed directly or indirectly on the piezoelectric thin film 10, but if the lower piezoelectric thin film 10 is an epitaxially grown film with excellent crystal orientation, the magnetostrictive layer 20 is usually also easily crystallized. Become. In particular, when the magnetostrictive layer 20 contains iron, it is usually crystallized in a body-centered cubic structure. In the present embodiment, in forming the magnetostrictive layer 20, the amorphous phase 22 and the crystalline phase 24 having a face-centered cubic structure are formed by appropriately selecting a film-forming device and film-forming conditions. Can be mixed.

The crystal structure of the magnetostrictive layer 20 can be confirmed by TEM electron beam diffraction or X-ray diffraction (XRD). For example, when the magnetostrictive layer 20 is composed of only the amorphous phase 22, when θ-2θ measurement using Cu-Kα rays is performed using XRD, only a broad halo pattern is detected. On the other hand, when the magnetostrictive layer 20 is composed of only the crystalline phase 24, only an extremely sharp reflection peak with a narrow half-width is detected. Further, when the magnetostrictive layer 20 has a mixture of the amorphous phase 22 and the crystalline phase 24, there is a broad bulge (halo) indicating the presence of the amorphous phase 22 and a sharp portion indicating the presence of the crystalline phase 24. A reflection peak having a peak portion is detected.

Further, the ratio of the amorphous phase 22 to the crystalline phase 24 can be confirmed by performing profile fitting on a reflection peak obtained by electron beam diffraction or XRD and calculating the degree of crystallinity. Specifically, a crystalline phase portion (peak portion) and an amorphous phase portion (halo portion) are fitted, and the integrated intensity (area) of each portion is measured. The degree of crystallinity (%) is the integrated intensity (Ic) of the crystalline phase portion relative to the sum of the integrated intensity (Ic) of the crystalline phase portion and the integrated intensity (Ia) of the amorphous phase portion (i.e., the total peak area). ) is expressed as the ratio (Ic/(Ic+Ia)×100). In this embodiment, when the magnetostrictive layer 20 has a mixture of the amorphous phase 22 and the crystalline phase 24, the degree of crystallinity is preferably 1% to 50%, more preferably 5% to 20%. be.

The thickness t2 of the magnetostrictive layer 20 is preferably within the range of 0.1 to 5 μm. Note that the thickness t2 is measured in the same manner as the thickness t1. This thickness t2 also has small variations in the in-plane direction, and the variations are about the same as the thickness t1. In this embodiment, the ratio of the thickness t2 to the thickness t1 (t2/t1) is preferably within the range of 1/10 to 10.

Further, when the magnetostrictive layer 20 has a mixture of the amorphous phase 22 and the crystalline phase 24, the thickness t2 of the magnetostrictive layer 20 is larger than the average grain size D2 of the crystalline phase 24. Preferably, D2/t2 is less than 1, more preferably from 0.01 to 0.7. Here, the average grain size D2 of the crystal phase 24 is determined by image analysis of a cross-sectional photograph (BF image). More specifically, the average grain size D2 is preferably calculated as the average value of the grain sizes measured at three or more points in the thickness direction for each of the at least three crystal phases 24.

(Other functional membranes)
Although not shown in FIG. 1, other functional films may be formed in the laminate 2 in addition to the piezoelectric thin film 10 and the magnetostrictive layer 20. For example, 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 magnetostrictive layer 20). By forming the conductive electrode film, electrical output can be efficiently extracted from the piezoelectric thin film 10. In this case, the electrode film may be a metal thin film with a face-centered cubic structure such as platinum (Pt), iridium (Ir), or gold (Au), or strontium ruthenate (SrRuO ₃ :SRO) or lithium nickel oxide (LiNiO ₃ ). It is preferable to form an oxide conductor thin film having a perovskite structure such as.

Further, when an electrode film is formed between the piezoelectric thin film 10 and the magnetostrictive layer 20, the electrode film is formed of a polycrystalline film with a face-centered cubic structure, or an amorphous phase and a crystalline phase with a face-centered cubic structure. It is preferable that the film is Such an electrode film can also function as a crystallinity control layer for controlling the crystallinity of the magnetostrictive layer 20. That is, by forming the magnetostrictive layer 20 on the piezoelectric thin film 10 via the crystallinity control layer, the magnetostrictive layer 20 having both the amorphous phase 22 and the crystalline phase 24 can be easily obtained.

Furthermore, a buffer layer may be formed at the bottom layer of the stacked body 2 in order to efficiently promote epitaxial growth. The buffer layer preferably contains zirconium oxide (ZrO2) or zirconium oxide (stabilized zirconia) stabilized with rare earth elements (including Sc and Y) as a main component. Furthermore, an insulating protective layer or the like may be formed above the magnetostrictive layer 20.

(Method for manufacturing laminate 2)
Next, an example of a method for manufacturing the laminate 2 shown in FIG. 1 will be described.

The laminate 2 is manufactured on a substrate not shown in FIG. The substrate to be used can be selected from various single crystals such as Si, MgO, strontium titanate (SrTiO3), and lithium niobate (LiNbO3). It is preferable to use a silicon substrate (wafer) that is By using the above single crystal substrate, the piezoelectric thin film 10 can be grown epitaxially. Note that when forming a buffer layer and an electrode film below the piezoelectric thin film 10 (on the opposite side of the magnetostrictive layer), it is preferable that these buffer layers and electrode films are also formed by epitaxial growth.

The piezoelectric thin film 10 is formed by various thin film manufacturing methods. As a thin film manufacturing 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 this embodiment, the thin film manufacturing method of the piezoelectric thin film 10 is not particularly limited, but it is particularly preferable to select a sputtering method. With the sputtering method, a film with high piezoelectric properties can be stably produced over a large area.

For example, when forming the piezoelectric thin film 10 by sputtering, in order to achieve stable epitaxial growth, the composition of the sputtering target, substrate temperature, film formation rate, gas composition, degree of vacuum, substrate-target distance, etc. must be adjusted appropriately. to control. Furthermore, in order for the piezoelectric thin film 10 to have a domain structure, the composition of the sputtering target, the substrate temperature, the stress of the stacked magnetostrictive layer 20, etc. are particularly controlled.

For example, depending on the material of the piezoelectric material, the composition of the sputtering target is selected such that multiple domains and crystal phases are likely to be formed, and the elements with high vapor pressure are added at a rate of 20 to 120% higher than the stoichiometric composition. It is preferable that Taking PZT as an example, the atomic ratio expressed by Pb/(Zr+Ti) is preferably 1.2 to 2.2, and the atomic ratio expressed by Zr/(Zr+Ti) is preferably 1 to 1.2. It is preferable to control it so that it becomes 5.

Further, the substrate temperature is preferably controlled to be 550 to 650° C., and the stress of the magnetostrictive layer 20 is preferably compressive stress. Note that when the crystal structure of the piezoelectric thin film 10 is a domain structure, it is also effective to perform annealing treatment at a temperature of 300° C. to 500° C. in an oxidizing atmosphere after film formation.

After forming the piezoelectric thin film 10, the magnetostrictive layer 20 is formed directly or indirectly on the piezoelectric thin film 10. The magnetostrictive layer 20 made of a soft magnetic high magnetostrictive film is formed by a vacuum deposition method such as a sputtering method, a vacuum evaporation method, a PLD method, or an ion beam evaporation method (IBD method). In particular, it is preferable to select a sputtering method.

As described above, the magnetostrictive layer 20 of this embodiment controls the coercive force H _C , the threshold magnetic field H _TH , and the magnetic field sensitivity dλ/dH within predetermined ranges. Although these characteristics can also be controlled by the composition of the soft magnetic material to be formed, it is preferable to control them by the degree of vacuum during film formation. Specifically, the degree of vacuum during film formation is preferably 1.0×10 ⁻⁴ Pa or less, more preferably 1.0×10 ⁻⁵ Pa or less. Note that the degree of vacuum during film formation means the maximum pressure reached within the film formation chamber during film formation, and the lower the value, the higher the degree of vacuum. Further, it is preferable that the pressure in the film forming chamber before film forming is set lower than the above numerical range. Furthermore, when forming a film by a sputtering method, it is preferable to carry out pre-sputtering for a sufficiently long time immediately before forming a film on a product to reduce residual gases such as oxygen and nitrogen remaining in the film forming chamber. Note that pre-sputtering means sputtering onto a dummy substrate immediately before film formation on a product.

Further, in order to mix the amorphous phase 22 and the crystalline phase 24, film forming conditions such as substrate temperature, gas composition, gas pressure, power, and distance from the supply source to the substrate may be appropriately controlled. For example, in the case of sputtering, the substrate temperature is preferably 20°C to 200°C. In particular, in order to make the crystal phase 24 have a face-centered cubic structure, the substrate temperature during film formation is kept below 200°C by separating the supply source and the substrate at a distance of 100 mm or more without heating the substrate. It is preferable. Furthermore, in order to control the crystallinity of the magnetostrictive layer 20, it is also effective to form a crystallinity control layer between the piezoelectric thin film 10 and the magnetostrictive layer 20, as described above.

By the method described above, a substrate on which the laminate 2 is formed is obtained. Note that the obtained substrate is subjected to appropriate patterning processing and processed into a predetermined shape, thereby becoming an ME element (Magnetoelectric (ME) element) including the laminate 2. In manufacturing this ME element, after the patterning process described above, part or all of the substrate may be removed by etching or the like. Note that the configuration of the ME element will be explained in detail in the second embodiment.

(Summary of the first embodiment)
In the laminate 2 of this embodiment, the piezoelectric thin film 10 is made of an epitaxially grown film, and there are almost no grain boundaries inside the piezoelectric thin film 10. That is, the piezoelectric thin film 10 included in the laminate 2 has excellent crystal orientation. Therefore, the piezoelectric thin film 10 of this embodiment suppresses disturbance of physical quantities due to grain boundaries and exhibits excellent piezoelectric properties.

Further, in this embodiment, the magnetostrictive layer 20 directly or indirectly formed on the piezoelectric thin film 10 is a soft magnetic high magnetostrictive film with a low coercive force H _C and a low threshold magnetic field H _TH .

Conventionally, in order to improve the magnetoelectric effect, it is important to increase the saturation magnetostriction λ _MAX of the magnetostrictive layer, and it is better to use a hard magnetic material with a larger saturation magnetostriction λ _MAX than a soft magnetic material as the magnetostrictive layer. It was thought that As a result of intensive studies, the inventors of the present invention found that even if the saturation magnetostriction λ _MAX of the magnetostrictive layer is increased, the responsiveness of the magnetoelectric effect does not improve _{much .} We have found that the responsiveness of the magnetoelectric effect can be improved by using a soft magnetic, high magnetostrictive film with low magnetic flux.

Here, "responsiveness of magnetoelectric effect" means that an output can be reliably obtained in response to an input signal transmitted from the outside. In other words, in this embodiment, "excellent responsiveness of the magnetoelectric effect" means that even if there is a minute external magnetic field (for example, an alternating current magnetic field of 1 kHz, 0.8 A/m or less), the piezoelectric thin film 10 will not be charged. occurs and an output (voltage) is obtained. Furthermore, it is determined that the larger the output obtained in response to a minute external magnetic field, the better the responsiveness.

Although the reason why the responsiveness of the magnetostrictive effect improves is not necessarily clear, the following reasons are considered. In the laminated body 2 which is a combination of an epitaxially grown piezoelectric thin film 10 and a soft magnetic high magnetostrictive film, the magnetic domain structure of the magnetostrictive layer 20 easily changes when subjected to an external magnetic field, and the magnetostriction in the same direction changes all at once due to the uniform film quality. Occur. Therefore, even if the magnitude of the external magnetic field is minute, it is thought that it is possible to generate a strain larger than the displacement noise generated in the piezoelectric thin film 10. That is, it is considered that in the laminate structure of the present invention, the piezoelectric thin film 10 can be sufficiently vibrated even with a minute external magnetic field (input signal).

Further, in this embodiment, the coercive force H _C of the soft magnetic high magnetostrictive film (magnetostrictive layer 20) is preferably less than 2500 A/m. According to experiments conducted by the present inventors, the lower the coercive force H _C , the better the responsiveness of the magnetoelectric effect, and the greater the amount of charge generated in response to a minute external magnetic field.

Furthermore, in this embodiment, the threshold magnetic field H _TH of the soft magnetic high magnetostrictive film (magnetostrictive layer 20) is preferably less than 500 A/m. According to experiments conducted by the present inventors, the lower the threshold magnetic field H _TH of the magnetostrictive layer, the better the responsiveness of the magnetoelectric effect, and the greater the amount of charge generated in response to a minute external magnetic field.

In addition, in this embodiment, the magnetic field sensitivity dλ/dH of the soft magnetic high magnetostrictive film (magnetostrictive layer 20) is preferably 10 ppb·m·A ⁻¹ or more, and preferably 15 ppb·m·A ⁻¹ or more. It is more preferable. According to experiments conducted by the present inventors, when the magnetic field sensitivity dλ/dH is larger than the above reference value, it is possible to respond to a smaller external magnetic field (for example, an alternating current magnetic field of 1 kHz, 800 μA/m or less). Become. Furthermore, as the magnetic field sensitivity dλ/dH increases, the amount of charge generated in response to a minute external magnetic field increases.

In this embodiment, the magnetostrictive layer 20 made of a soft magnetic high magnetostrictive film is not a thin plate obtained by mechanical processing such as rolling, but is formed directly or indirectly on a piezoelectric thin film by vacuum deposition. It has been formed. The thin plate obtained by machining must be laminated on the piezoelectric thin film via an adhesive layer or pressure laminated. However, when an adhesive layer is interposed, the adhesive layer inhibits strain transmission and charge transfer between the magnetostrictive layer and the piezoelectric layer. Furthermore, in the case of lamination by pressure bonding, a surface oxide film generated on the surface of the thin plate inhibits the transmission of strain and the exchange of charge between the magnetostrictive layer and the piezoelectric layer. In the laminate 2 of this embodiment, since the magnetostrictive layer 20 is formed by a vacuum deposition method, the above-mentioned inhibiting effect does not occur, and responsiveness is improved. Further, it is also possible to make the laminate 2 thinner.

Second Embodiment In a second embodiment, an ME element 30 including the laminate 2 of the first embodiment will be described with reference to FIGS. 2 to 4. The ME element 30 is connected to a power source and an electric/electronic circuit, and is mounted on a circuit board or packaged to constitute an electronic device such as an energy conversion device or a magnetic sensor.

As shown in FIG. 2, the ME element 30 according to the second embodiment has a generally rectangular shape in plan view. The dimensions of the ME element 30 are not particularly limited, and may be determined as appropriate depending on the use of the electronic device. The ME element 30 includes a film stacking section 32 in which functional films are stacked, and an outer peripheral section 34 surrounding the outside of the film stacking section 32 in plan view.

The film stack portion 32 is formed along a plane including the X axis and the Y axis, and has a substantially rectangular shape in plan view. The membrane laminated portion 32 has an edge parallel to the X-axis and an edge parallel to the Y-axis, and the longitudinal direction of the membrane laminated portion 32 coincides with the X-axis. Note that in FIGS. 2 to 4, the X-axis, Y-axis, and Z-axis are substantially perpendicular to each other, and the Z-axis coincides with the stacking direction of the films.

As shown in FIG. 3, the substrate 40 is present at the bottom layer in the Z-axis direction. This substrate 40 has an opening 42 approximately at the center of the XY plane, that is, at the film stack 32 portion. In other words, the substrate 40 exists substantially only on the outer peripheral portion 34 of the element 30. A lower electrode film 50, a piezoelectric thin film 10, and a magnetostrictive layer 20 are laminated in this order in the film lamination section 32 located above the Z-axis of the opening 42. That is, the film stack section 32 includes the stack 2 described in the first embodiment.

The lower 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 lower electrode film 50 has a substantially rectangular shape smaller than the opening surface of the opening 42. As shown in FIG. Furthermore, the end portions 50a of the lower electrode film 50 are located at both ends of the central portion 50b in the X-axis direction, and have a substantially rectangular shape with a smaller width in the Y-axis direction than the central portion 50b in plan view shown in FIG. have Since the lower electrode film 50 has the above shape, it exists so as to span the upper opening surface of the opening 42 in the Z-axis direction in the X-axis direction in the cross section shown in FIG. Only the end portion 50a of the lower electrode film 50 is present on the surface of the substrate 40 located at the outer peripheral portion 34 of the ME element 30.

On the other hand, in the cross section shown in FIG. 4 (the cross section along line III-III in FIG. 2), only the cross section of the central portion 50b of the lower electrode film 50 appears, and the end portion 50a does not exist. Therefore, in the cross section shown in FIG. 4, the film stack 32 including the lower electrode film 50 appears to be floating above the Z-axis of the opening 42. The film stack 32 floating above the opening 42 is likely to warp due to unbalanced stress among the stacked films, but the lower surface of the lower electrode film 50 of the film stack 32 and the substrate It is preferable that the heights in the Z-axis direction of the lower surface of the end portion 50a of the lower electrode film 50 that are in contact with the lower electrode film 40 are approximately the same.

The piezoelectric thin film 10 is located above the lower electrode film 50 in the Z-axis direction, and has the same shape in plan view as the lower electrode film 50. In FIG. 2, the planar dimension (area on the XY plane) of the piezoelectric thin film 10 is smaller than the planar dimension of the lower electrode film 50, but it is about the same size as the lower electrode film 50. Good too. Further, above the piezoelectric thin film 10 in the Z-axis direction, there is a magnetostrictive layer 20, and this magnetostrictive layer 20 also has a substantially rectangular shape in plan view. The planar dimension of the magnetostrictive layer 20 is smaller than the planar dimension of the piezoelectric thin film 10. By making the planar dimension of the magnetostrictive layer 20 smaller than that of the piezoelectric thin film 10, the durability of the ME element 30 tends to improve.

Further, as shown in FIG. 3, the tip of the first extraction electrode 51 is connected to one end 50a of the lower electrode film 50. At the rear end of the first extraction electrode film 51, a first electrode pad 51a is formed on the surface of the substrate 40, and an external circuit (not shown) can be connected via the first electrode pad 51a.

Furthermore, the other end 50a of the lower electrode film 50 is covered with an insulating layer 54 along with a portion of the surface of the piezoelectric thin film 10. A second lead-out electrode 53 is formed so as to span over the insulating film 54 in the X-axis direction, and the tip of the second lead-out electrode 53 is connected to the magnetostrictive layer 20 . At the rear end of the second extraction electrode film 53, a second electrode pad 53a is formed on the surface of the substrate 40, and an external circuit (not shown) can be connected via the second electrode pad portion 53a. . Note that because of the insulating film 54, the second extraction electrode 53 is insulated from the lower electrode film 50.

As described above, in the ME element 30 of the second embodiment, the piezoelectric thin film 10 is sandwiched and stacked between the lower electrode film 50 and the magnetostrictive layer 20 in the film stacking section 32 . Therefore, a voltage can be applied to the piezoelectric thin film 10 via the lower electrode film 50 and the magnetostrictive layer 20. Alternatively, charges generated in the piezoelectric thin film 10 can be taken out via the lower electrode film 50 and the magnetostrictive layer 20. Although not shown, an upper electrode film may be formed between the piezoelectric thin film 10 and the magnetostrictive layer 20.

In the second embodiment, the substrate 40 may be any insulator as long as it can support at least the film stack 32. However, the single crystal substrate used when epitaxially growing the piezoelectric thin film 10 may be used as the substrate 40. That is, the material of the substrate 40 can be selected from various single crystals such as Si, MgO, strontium titanate (SrTiO3), and lithium niobate (LiNbO3), and in particular, a single crystal with a Si (100) surface. It is preferable to use a silicon substrate that is

Further, the lower electrode film 50 is preferably a thin metal film with a face-centered cubic structure such as Pt, Ir, or Au, or an oxide conductor film with a perovskite structure such as SrRuO ₃ (SRO) or LaNiO ₃ . The metal thin film and oxide conductor thin film described above can be epitaxially grown on a single crystal substrate, and in the second embodiment, the lower electrode film 50 is also an epitaxially grown film. Further, the lower electrode film 50 may be formed by laminating the above metal thin film and the above oxide conductor film (for example, Pt electrode/SrRuO ₃ etc.). In this case (in the case of multiple lamination), it is preferable that an oxide conductor film exists on the piezoelectric thin film 10 side of the lower electrode film 50 (ie, above in the Z-axis direction). The average thickness of the lower electrode film 50 as a whole is preferably 3 nm to 200 nm.

Note that when an upper electrode film is formed between the piezoelectric thin film 10 and the magnetostrictive layer 20, this upper electrode film can have the same structure as the lower electrode film 50. However, the upper electrode film does not need to be an epitaxially grown film, and is preferably a polycrystalline film with a face-centered cubic structure or a film consisting of an amorphous phase and a crystalline phase with a face-centered cubic structure. These films can also function as a crystallinity control layer, as described in the first embodiment.

Note that the piezoelectric thin film 10 and the magnetostrictive layer 20 may have the same configuration as in the first embodiment, and a description thereof will be omitted.

Further, the first extraction electrode film 51 and the second extraction electrode film 53 only need to have conductivity, and their material and thickness are not particularly limited. For example, in addition to Pt, conductive metals such as Ag, Cu, Au, and Al can be included. Further, the insulating layer 54 only needs to have electrical insulation properties, and its material and thickness are not particularly limited. For example, the insulating film 54 can be made of SiO2, Al2O3, polyimide, or the like.

Although not shown, a buffer layer may be formed below the lower electrode film 50 in the Z-axis direction (that is, between the substrate 40 and the lower electrode film 50). As described in the first embodiment, the formation of the buffer layer promotes epitaxial growth of the film located above the buffer layer (results in high quality). Further, the buffer layer also functions as an etching stopper layer when forming the opening 42. When forming a buffer layer, its thickness is preferably 5 nm to 100 nm.

Further, a protective layer may be formed on the uppermost layer of the ME element 30 so as to cover at least the surface of the film stack 32. As the protective layer, an insulating film is preferable, but in addition to insulating films such as SiO ₂ , Al ₂ O ₃ , and polyimide, metal films such as Ti and Ta can also be used, and the thickness thereof may be determined depending on the There is no limitation, and the thickness may be at least about 10 nm.

Since the ME element 30 has the above-mentioned configuration, the membrane laminated portion 32 also functions as a vibrator having a vibration mode of a specific frequency. In the second embodiment, the membrane laminated portion 32 is capable of expanding and contracting vibrations, especially in the in-plane direction. Here, in-plane expansion and contraction means that the membrane stack 32 expands and contracts along the XY plane, and out-of-plane expansion and contraction means that the membrane stack 32 expands and contracts in the Z-axis direction. When in-plane expansion and contraction is possible as in this embodiment, the membrane laminated portion 32 is also capable of expansion and contraction vibration in the out-of-plane direction.

When focusing on the function as a vibrator, the portion where the end portion 50a of the lower electrode film 50 and the end portion of the piezoelectric thin film 10 are laminated (in particular, the portion where the end portion 50a of the lower electrode film 50 and the end portion of the piezoelectric thin film 10 are laminated) portion) becomes the support portion 36.

This support portion 36 is preferably of a form having lower rigidity than the membrane lamination portion 32 so as not to impede in-plane expansion and contraction of the membrane lamination portion 32 (vibrator). For example, the width of the support portion 36 in the Y-axis direction is made narrower than the width of the membrane stacked portion 32 in the Y-axis direction. Alternatively, the thickness of the support portion 36 in the Z-axis direction is made smaller than the thickness of the membrane stacked portion 32 in the Z-axis direction. The product of the thickness and width of the support portion 36 is preferably smaller than 90%, and more preferably smaller than 75%, of that of the membrane laminated portion 32. With this configuration, it is possible to induce large-amplitude in-plane stretching vibrations, and the output of the ME element 30 can be further increased.

Further, it is preferable that the length of the support portion 36 in the X-axis direction is approximately 1/4 of the vibration wavelength transmitted to the film laminated portion 32. By having such a length, energy is efficiently confined in the film stack 32, which allows the output to be larger than that of the ME element 30, and also reduces interference between elements when arrayed (combining a plurality of elements 30). can be suppressed.

Further, the surface of the film stack 32 (in the case of FIGS. 2 to 4, the lower surface of the lower electrode film 50 and the upper surface of the magnetostrictive layer 20) is preferably flat. More specifically, the surface roughness is preferably smaller than 1 μm in terms of arithmetic mean roughness (Ra) or average length of elements (Rms), and is 1/10 or less of the vibration wavelength transmitted through the membrane stack 32. It is more preferable that

In the ME element 30 of the second embodiment, since the membrane laminated portion 32 and the support portion 36 have the above configuration, Q, which is a characteristic representing the sharpness of vibration, becomes large. In the ME element 30 of the second embodiment, it is preferable that Q be larger than 100.

A method for manufacturing the ME element 30 shown in FIGS. 2 to 4 will be described below.

In manufacturing the ME element 30, first, the lower electrode film 50, the piezoelectric thin film 10, and the magnetostrictive layer 20 are formed on a film-forming substrate such as a silicon substrate. The method of forming the piezoelectric thin film 10 and the magnetostrictive layer 20 is as described in the first embodiment. The lower electrode film 50 is grown epitaxially, and known conditions may be applied to the film formation conditions.

The substrate on which the functional film is laminated is patterned to form a pattern as shown in FIG. The patterning process can be performed using various etching methods such as photo etching and laser dry etching, or a lift-off method.

After the patterning process, 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, a part of the film-forming substrate is removed by dry etching such as Deep-RIE or anisotropic wet etching to form a substrate 40 having an opening 42. Note that the entire film-forming substrate may be removed by the above-described etching. In this case, the film stacking section 32 (including the supporting section 36) that has been peeled off from the film-forming substrate may be fixed to a substrate 40 prepared as a separate member.

Through the above procedure, the ME element 30 including the laminate 2 is obtained.

(Summary of second embodiment)
The ME element of the second embodiment configures an electronic device such as an energy conversion device or a magnetic sensor by connecting a power source and an electric/electronic circuit and mounting it on a circuit board or packaging it.

For example, a magnetic sensor can be obtained by connecting and packaging an amplifier and a rectifier circuit to the ME element 30. The magnetic sensor exhibits excellent sensitivity characteristics because it includes the laminate 2 that has excellent responsiveness of the magnetoelectric effect. Specifically, the detection limit value of the magnetic sensor becomes smaller, and minute external magnetic fields such as biomagnetism can be detected.

Further, by connecting a power storage element and a rectifying power management circuit to the ME element 30, an energy conversion device that generates power from an external magnetic field or vibration can be obtained. Since the energy conversion device includes the laminate 2 with excellent magnetoelectric effect responsiveness, a high electrical output can be obtained even in response to a minute external magnetic field, and exhibits excellent conversion efficiency. The energy conversion device can be incorporated into wearable terminals such as earphones/hearable devices, smart watches, smart glasses, smart contact lenses, cochlear implants, and cardiac pacemakers, as well as power supply systems.

In addition to the above-mentioned uses, the ME element 30 can also be used as a piezoelectric device such as an inkjet printer head, a microactuator, and a gyroscope.

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and can be variously modified within the scope of the present invention.

For example, in the ME element 30 of the second embodiment, the film stacking section 32 has a substantially rectangular shape in plan view, but the shape of the film stacking section 32 is not limited to this, and may include an elliptical shape, a circular shape, It may have a meandering or spiral shape in plan view.

Further, the ME element 30 of the second embodiment has a structure in which both ends of the film stack 32 are supported by the substrate 40 and both ends are fixed, but in the ME element 30, one end of the film stack is It may be a cantilever type structure with a free end. Further, the ME element 30 may be a single element as shown in FIGS. 2 to 4, or may be an array element in which a plurality of single elements are integrally formed on a common substrate 40. .

Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Example 1)
In Example 1, a substrate sample having the laminate 2 of the present invention was produced using the procedure shown below. First, a silicon substrate having a single crystal surface with an Si (100) plane was prepared as a substrate for film formation. The size of the prepared silicon substrate was 6 inches, and the following laminated film was formed on this silicon substrate.

First, a base oxide thin film (buffer layer) made of ZrO ₂ and Y ₂ O ₃ , a Pt lower electrode film, and a conductive oxide film made of SRO are epitaxially grown on a silicon substrate in the above order. Ta. Note that each of the above films was formed by a sputtering method. Further, 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. Furthermore, the substrate temperature when forming the Pt lower electrode film was adjusted to 600° C. to 800° C., which was lower than the temperature at the end of forming the base oxide thin film.

After forming the Pt lower electrode film, the silicon substrate was once taken out into the atmosphere, and the Pt surface was exposed to oxygen in the air. Thereafter, the substrate was placed into the film forming apparatus again, and a conductive oxide thin film made of SrRuO3 was formed. The film forming conditions were adjusted so that the film thickness of each layer was 50 nm for the base oxide thin film, 100 nm for the Pt lower electrode film, and 30 nm for the conductive oxide thin film.

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

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

Note that during film formation from the base oxide thin film to the PZT film, RHEED evaluation was performed to confirm whether 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 during the film formation process.

Further, above the PZT film, as an upper electrode film, an RO conductive oxide thin film (referred to as an SRO adhesion layer) and a Pt upper electrode film were formed in this order. The thickness of the SRO adhesion layer was 50 nm, and the thickness of the Pt upper electrode film was 100 nm. Note that when forming the Pt upper electrode film, the substrate temperature was set at 200° C., and other film forming conditions were controlled so that the Pt upper electrode film had a polycrystalline structure.

After forming the upper electrode film, a FeCoSiB alloy film was formed thereon as the magnetostrictive layer 20. The FeCoSiB alloy film was formed using an ultra-high vacuum DC sputtering device (manufactured by Canon Anelva Co., Ltd.: C-7960UHV), and the degree of vacuum during film formation was set to 3×10 ⁻⁶ Pa. Furthermore, during film formation, the substrate was not heated, and the film was formed with a sufficient distance between the target and the substrate to prevent the substrate temperature from rising. Other film forming conditions were as follows: Ar gas was used as the introduced gas, the pressure of the introduced gas was 0.03 Pa, the output was 200 W (DC), and a FeCoSiB alloy film with a thickness of 500 nm was formed.

The crystal structure of the formed FeCoSiB alloy film was confirmed by XRD and TEM electron diffraction. As a result, it was confirmed that the amorphous phase 22 and the crystalline phase 24 coexisted in the FeCoSiB alloy film.

Note that after forming the FeCoSiB alloy film, an insulating protective layer was further formed thereon with a thickness of 10 nm. By forming each layer in such a procedure, a substrate sample including the laminate 2 of the present invention was obtained.

Next, a test piece of length 4 cm x width 1 cm is cut out from the fabricated substrate sample, and the test piece is used to determine the saturation magnetostriction λ _MAX , coercive force H _C , and threshold magnetic field H of the FeCoSiB alloy film contained in the substrate sample. _TH and magnetic field sensitivity dλ/dH were measured.

The coercive force H _C was calculated by measuring the magnetization curve of the FeCoSiB alloy film using a VSM (TM-VSM-211483-HGC type manufactured by Tamagawa Seisakusho). In addition, the saturation magnetostriction λ _MAX , the threshold magnetic field H _TH , and the magnetic field sensitivity dλ/dH are 0 to 6400 A/m externally applied to the test piece in an environment where a 500 A/m DC magnetic field is applied as a bias magnetic field. The amount of strain generated in the test piece was calculated by applying a rotating magnetic field of 1 and measuring the amount of strain generated in the specimen using a laser displacement meter. Specifically, a magnetic field-magnetostriction curve was obtained by the above measurement, and the saturation point of magnetostriction in the magnetic field-magnetostriction curve was defined as saturation magnetostriction λ _MAX . Further, the magnitude of the external magnetic field when a magnetostriction λ of 0.1 ppm was generated was defined as the threshold magnetic field H _TH . Furthermore, in the magnetic field-magnetostriction curve, the slope in the range of 500 A/m to 800 A/m was defined as the magnetic field sensitivity dλ/dH. The measurement results are shown in Table 1.

(Example 2)
In Example 2, a FeCoSiB alloy film was formed by changing the degree of vacuum during film formation from Example 1. More specifically, in Example 2, the degree of vacuum when forming the FeCoSiB alloy film was set to 1.5×10 ⁻⁵ Pa, which was set lower (=higher pressure) than in Example 1. The manufacturing conditions other than the above were the same as in Example 1, and a substrate sample according to Example 2 was obtained.

For the substrate sample of Example 2, the saturation magnetostriction λ _MAX , coercive force H _C , threshold magnetic field H _TH , and magnetic field sensitivity dλ/dH of the magnetostrictive layer 20 were measured in the same manner as in Example 1. As a result, as shown in Table 1, in Example 2, the coercive force H _C and the threshold magnetic field H _TH were higher than in Example 1. From this, it was found that the higher the degree of vacuum during film formation (=lower the pressure (Pa)), the lower the coercive force H _C and the threshold magnetic field H _TH . The reason why the coercive force H _C and the threshold magnetic field H _TH change depending on the degree of vacuum is not necessarily clear, but it is thought to be related to residual gases such as nitrogen, oxygen, and moisture remaining in the film forming apparatus. That is, when the degree of vacuum is low and there is a large amount of residual gas, locally nitrided or oxidized portions are generated in the formed film, and it is considered that the coercive force H _C and the threshold magnetic field H _TH become high.

(Examples 3 to 5)
In Examples 3 to 5, substrate samples were prepared by changing the degree of vacuum during film formation and the material of the magnetostrictive layer 20 from Example 1. Specifically, in Example 3, the FeSiB alloy film was formed with the degree of vacuum at the time of film formation set to 1.5×10 ⁻⁵ Pa. In Example 4, the FeCoB alloy film was formed with the degree of vacuum at the time of film formation set to 1.5×10 ⁻⁵ Pa. Furthermore, in Example 5, the FeCrSiB alloy film was formed with the degree of vacuum at the time of film formation set to 1.5×10 ⁻⁵ Pa.

In Examples 3 to 5, the manufacturing conditions other than the above were the same as in Example 1. Further, for the substrate samples of Examples 3 to 5, each characteristic of the magnetostrictive layer 20 was measured in the same manner as in Example 1.

(Example 6)
In Example 6, a substrate sample was prepared by changing the material of the magnetostrictive layer 20 and the film forming apparatus from Example 1. Specifically, in Example 6, a FeCoSiB alloy film was formed using a vacuum evaporation apparatus (C-7170C, manufactured by Canon Anelva Co., Ltd.). During the vacuum deposition, the degree of vacuum in the film forming chamber was set to 8.0×10 ⁻⁵ . The manufacturing conditions other than the above were the same as in Example 1. Further, regarding the substrate sample of Example 6 as well, each characteristic of the magnetostrictive layer 20 was measured in the same manner as in Example 1.

(Comparative example 1)
In Comparative Example 1, unlike Example 1, a hard magnetic high magnetostrictive film was formed as the magnetostrictive layer. Specifically, in Comparative Example 1, a FeCo alloy film was formed by a sputtering method. In addition, in Comparative Example 1, the manufacturing conditions other than the above were the same as in Example 1.

Furthermore, regarding Comparative Example 1, the characteristics of the magnetostrictive layer were also measured. However, in the case of a hard magnetic material like Comparative Example 1, the threshold magnetic field H _TH is higher than that of a soft magnetic material, so the analysis range of magnetic field sensitivity was changed from Example 1. Specifically, in Comparative Example 1, the slope of the magnetic field-magnetostriction curve in the range from H _TH to H _TH +300 A/m was defined as the magnetic field sensitivity dλ/dH. The FeCo alloy film of Comparative Example 1 is a high magnetostrictive film, but unlike each of Examples 1 to 6, it is made of a hard magnetic material. Therefore, as shown in Table 1, Comparative Example 1 has larger saturation magnetostriction λ _MAX , coercive force H _C , and threshold magnetic field H _TH than each of Examples 1 to 6. Examples of such a hard magnetic high magnetostrictive film include, in addition to the FeCo alloy film of Comparative Example 1, a FeNi alloy film, a SmFe alloy film, a TbFe alloy film, a GdFe alloy film, and the like.

(Comparative example 2)
In Comparative Example 2, unlike Example 1, a soft magnetic low magnetostrictive film was formed as the magnetostrictive layer. The soft magnetic low magnetostrictive film means a low magnetostrictive film that is made of a soft magnetic material but has a small saturation magnetostriction λ _MAX of less than 1 ppm. Specifically, in Comparative Example 2, a FeCoNiMoSiB alloy was formed by a sputtering method. Note that a substrate sample according to Comparative Example 2 was obtained under the same manufacturing conditions as in Example 1 except for the above.

(Comparative example 3)
In Comparative Example 3, unlike Example 1, a magnetostrictive layer was laminated on top of the upper electrode film. Specifically, in Comparative Example 3, a FeSiB alloy thin plate was produced by mechanical processing by rolling. Then, a thin plate of FeSiB alloy was attached onto the upper electrode film via an adhesive layer made of epoxy resin. Note that the average thickness of the FeSiB alloy was 25 μm.

Furthermore, when the FeSiB alloy thin plate was analyzed by XRD and TEM electron beam diffraction, it was confirmed that the FeSiB alloy was composed only of an amorphous phase. Note that manufacturing conditions other than those described above were the same as in Example 1, and a substrate sample according to Comparative Example 3 was obtained.

(Comparative example 4)
In Comparative Example 4, a piezoelectric thin film was formed under conditions different from those in Example 1. Specifically, in Comparative Example 4, the PZT film was formed at room temperature without heating the substrate. When analyzing the crystal structure of the PZT film obtained under these conditions, it was confirmed that although the predetermined crystal planes were unidirectionally oriented in the film thickness direction, the crystal orientation was random in the in-plane direction. Ta. In other words, the PZT film of Comparative Example 4 is not an epitaxially grown film but an oriented polycrystalline film.

In addition, in Comparative Example 4, a FeCoSiB alloy film was formed under the same conditions as in Example 2. Manufacturing conditions other than the above were the same as in Example 1, and a substrate sample according to Comparative Example 4 was obtained.

Rating 1
In each of the Examples and Comparative Examples, patterning was performed on the prepared substrate samples to produce at least 16 ME elements 30 as shown in FIG. 2, respectively. Then, the obtained ME element 30 was subjected to the following magnetoelectric effect responsiveness evaluation.

(Responsiveness evaluation)
In the response evaluation, a predetermined input signal is applied to the ME element 30 in an environment where a DC magnetic field of 500 A/m is applied as a bias magnetic field, and the voltage generated in the piezoelectric thin film is measured as a response output. In test condition 1, the predetermined input signal is an alternating magnetic field of 1 kHz, 0.8 A/m, and in test condition 2, it is an alternating magnetic field of 1 kHz, 800 μA/m, which is smaller than condition 1 (1/1000 of condition 1). ). In this responsiveness evaluation, it is determined that the larger the generated voltage, the better the responsiveness of the magnetoelectric effect. Further, in test condition 1, the reference value of the response output is set to 0.3 mV or more, and in test condition 2, the reference value of the response output is set to 1 μV or more.

The above response evaluation was performed on three samples for each example and each comparative example, and the response output was calculated as the average value. The evaluation results are shown in Table 1.

First, the evaluation results under test condition 1 will be considered. As shown in Table 1, in Comparative Example 1 in which the magnetostrictive layer is composed of a hard magnetic, high magnetostrictive film, no response output was obtained even though the saturation magnetostriction λ _MAX was larger than each of Examples 1 to 6. Ta. On the other hand, in Examples 1 to 6 in which the magnetostrictive layer was composed of a soft magnetic high magnetostrictive film, response outputs exceeding the reference value were obtained. From these results, it can be seen that increasing the saturation magnetostriction λ _MAX does not improve the responsiveness of the magnetoelectric effect, but that the responsiveness can be improved by using a soft magnetic high magnetostrictive film with a small coercive force _HC . I understand.

Further, in Comparative Example 2, although the magnetostrictive layer was made of a soft magnetic material, the saturation magnetostriction λ _MAX was only 0.5 ppm, so no response output could be obtained. From this result, it was found that the magnetostrictive layer is preferably a high magnetostrictive film having a saturation magnetostriction λ _MAX of at least 10 ppm or more, as shown in Example 4, rather than a low magnetostrictive film.

Furthermore, in Comparative Example 3, although the magnetostrictive layer was a soft magnetic high magnetostrictive film, no response output could be obtained because the magnetostrictive layer was laminated by bonding through an adhesive layer. From this result, it was found that the magnetostrictive layer needs to be laminated directly or indirectly on the piezoelectric thin film by a vacuum deposition method, rather than a thin plate obtained by mechanical processing such as rolling. In addition, in the case of a thin plate obtained by machining, the crystallinity can be easily controlled, and the surface can also be subjected to cutting processes. Therefore, it is possible to make the coercive force H _C and the threshold magnetic field H _TH lower than those of a film formed by a vacuum deposition method. However, as described above, a film formed by a vacuum deposition method has better responsiveness of the magnetoelectric effect than a thin plate.

Furthermore, in Comparative Example 4, although a small response output was obtained, it did not satisfy the standard value. From this result, it was found that in order to improve the responsiveness of the magnetoelectric effect, it is necessary to stack a soft magnetic high magnetostrictive film in combination with a piezoelectric thin film that is an epitaxially grown film.

By comparing the evaluation results under Test Condition 1 in Examples 1 to 6, it was confirmed that the lower the coercive force H _C , the higher the response output. From this result, it was found that the upper limit of the coercive force H _C is preferably less than 2500 A/m, more preferably 500 A/m or less, and even more preferably 400 A/m or less. According to experimental results, the lower limit of the coercive force H _C is preferably 20 A/m or more. Similarly, regarding the threshold magnetic field H _TH , the lower the threshold magnetic field H _TH , the higher the response output tended to be. From this result, it was found that the upper limit of the threshold magnetic field H _TH is preferably less than 500 A/m, more preferably 100 A/m or less, and even more preferably 50 A/m or less. Note that, according to experimental results, the lower limit of the threshold magnetic field H _TH is preferably 5 A/m or more.

Next, the evaluation results under test condition 2 will be considered. Regarding Comparative Examples 1 to 4, since none of them had the laminate 2 that satisfied the conditions of the present invention, it was not possible to obtain a response to an input signal smaller than Condition 1.

On the other hand, in Examples 1 and 2, response outputs greater than the reference value were obtained. These Examples 1 to 2 have a magnetic field sensitivity dλ/dH of 15 ppb·m·A ⁻¹ or more, which is higher than other Examples 3 to 6. From this result, when the coercive force H _C and the threshold magnetic field H _TH are kept below the predetermined reference values, the larger the magnetic field sensitivity dλ/dH, the more the responsiveness of the magnetoelectric effect improves, and the more minute the input signal becomes It was found that it was possible to respond to

In addition to the above-mentioned response evaluation, in order to evaluate the durability of the laminate 2, a huge alternating current magnetic field of 300 Hz and 800 kA/m was applied to the substrate samples of each example and each comparative example. An accelerated test was conducted in which the voltage was applied for minutes. In this test, a 1 cm square test piece was cut out from a substrate sample, and the above alternating current magnetic field was applied to the test piece. Then, in the test piece after the test, it was confirmed whether there was any peeling in the magnetostrictive layer.

As a result of the above durability test, in the sample of Comparative Example 1 having a high magnetic field sensitivity dλ/dH, severe peeling of the magnetostrictive layer was observed. From this result, from the viewpoint of responsiveness, it is preferable that the magnetic field sensitivity dλ/dH is larger, but when considering durability, it is preferable that the magnetic field sensitivity dλ/dH is 15 to 50 ppb・m・A ⁻¹ , and 15 It was found that it is more preferable to set it to 30 ppb·m·A ⁻¹ .

Evaluation 2
A circuit including an amplifier and a rectifier circuit was connected to the ME element sample and packaged to obtain a magnetic sensor corresponding to each Example and each Comparative Example. Similarly, a circuit including a power storage element and a rectifying power management circuit was connected to the ME element sample and packaged to obtain an energy conversion device corresponding to each Example and each Comparative Example. Then, the following performance evaluation was performed on the obtained magnetic sensor and energy conversion device.

(Performance evaluation as a magnetic sensor)
Regarding the magnetic sensor, in order to evaluate the detection sensitivity, the detection limit value (unit: nT) was measured. In a magnetic sensor, when an alternating current magnetic field (external magnetic field) is applied as an input, a voltage corresponding to the magnitude of the applied magnetic field is outputted. The detection limit value means the minimum input value to which the magnetic sensor responds (that is, outputs a voltage), and the input value is expressed in magnetic flux density. That is, the detection limit value means that the smaller the value, the better the characteristics as a magnetic sensor.

In this example, in an environment where a DC magnetic field of 1 mT is applied as a bias magnetic field, an AC magnetic field near the natural frequency (approximately 10 kHz) of the ME element 30 is applied to the magnetic sensor, and the frequency of the AC magnetic field is set near the natural frequency. The lower limit of detection was determined by attenuating the size while scanning. The detection limit value is determined to be good if it is 10 nT or less, and even better if it is 0.5 nT or less. Table 1 shows the results of measuring the detection limit values for the magnetic sensors of each example and each comparative example.

(Performance evaluation as an energy conversion device)
To evaluate the performance of the energy conversion device, the output power for a given input signal was measured. Specifically, in an environment where a DC magnetic field of 500 A/m was applied as a bias magnetic field, an AC magnetic field of 1 kHz and 5 A/m was applied to the device, and the output power obtained at that time was measured. The reference value of output power is 1.0 nW or more, and 5.0 nW or more is judged to be good. That is, it is determined that the greater the output power obtained, the better the conversion efficiency is.

First, we will discuss the evaluation results of the magnetic sensor. As shown in Table 1, in Comparative Example 1, it was confirmed that the detection limit value was very high and the sensitivity was on the order of millitesla. Biomagnetism cannot be detected with sensitivity on the order of millitesla. Furthermore, for Comparative Examples 2 to 4, the detection limit value could not be measured under the above evaluation conditions, and it was found that they could not function sufficiently as magnetic sensors in the first place. This is considered to be because the generated magnetostriction is too small or the generated magnetostriction is not sufficiently transmitted to the piezoelectric layer. On the other hand, since the magnetic sensors of Examples 1 to 6 included the laminate 2 of the present invention, the detection limit value was 10 nT or less, and results satisfying the standard value were obtained. In particular, it was confirmed that the magnetic sensors of Examples 1 to 3 had detection limit values of 0.5 nT or less, and exhibited superior sensitivity characteristics. As described above, since the magnetic sensor including the laminate 2 of the present invention has excellent sensitivity characteristics, it can be expected to be applied as a sensitivity sensor capable of detecting biomagnetism.

Next, we will discuss the evaluation results of the energy conversion device. As shown in Table 1, the devices of Comparative Examples 1 to 4 did not provide output power, but the devices of Examples 1 to 6 provided output power that satisfied the standard value. In particular, in the devices of Examples 1 to 3, the output power was 5.0 nW or more, and it was confirmed that the conversion efficiency was higher. As described above, since the energy conversion device including the laminate 2 of the present invention has high conversion efficiency, it can be expected to be incorporated into wearable terminals and the like.

2... Laminated body 10... Piezoelectric thin film 20... Magnetostrictive layer 22... Amorphous phase 24... Crystal phase 30... ME element 32... Film laminated part 34... Peripheral part 36... Support part 40... Substrate 50... Lower electrode film 50a... End portion 50b... Central portion 51... First extraction electrode film 53... Second extraction electrode film 54... Insulating film

Claims (4)

an epitaxially grown piezoelectric thin film,
a soft magnetic high magnetostrictive thin film formed directly or indirectly on the piezoelectric thin film by a vacuum deposition method ;
The soft magnetic high magnetostriction thin film has a coercive force H _C of less than 2500 A/m,
The magnetic field where 0.1 ppm of magnetostriction occurs is defined as the threshold magnetic field H _TH ,
A laminate wherein the soft magnetic high magnetostrictive thin film has a threshold magnetic field H _TH of less than 500 A/m . an epitaxially grown piezoelectric thin film,
a soft magnetic high magnetostrictive thin film formed directly or indirectly on the piezoelectric thin film by a vacuum deposition method;
The soft magnetic high magnetostriction thin film has a coercive force H _C of less than 2500 A/m,
A laminate wherein the magnetic field sensitivity dλ/dH of the soft magnetic high magnetostrictive thin film is 10 ppb·m·A ⁻¹ or more under an environment in which a DC magnetic field of 500 A/m is applied as a bias magnetic field. An energy conversion device comprising the laminate according to claim 1 or 2 . A magnetic sensor comprising the laminate according to claim 1 or 2 .

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