Laminate

Abstract

To provide a laminate with a piezoelectric film and a metal film, which can maintain good characteristics even after being stored in a high temperature and high humidity environment.SOLUTION: A laminate is a laminate that is stacked on a substrate and has at least a lower metal film, a piezoelectric film located above the lower metal film, and an upper metal film located above the piezoelectric film, and the surface roughness P-V of the upper metal film, which is the opposite side of the lower surface, is smaller than the surface roughness P-V of the lower surface, which is the surface of the piezoelectric film side in the upper metal film.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a laminate having a piezoelectric film and a metal film, which is laminated on a substrate.

Background Art

[0002] Those that utilize the piezoelectric effect and inverse piezoelectric effect of a piezoelectric body are known. Also, there have been attempts to miniaturize by configuring a laminate in which a piezoelectric film and a metal film are laminated on a substrate (see Patent Document 1, etc.). In addition, development of a laminate having a metal film as a magnetic film and a piezoelectric film and a ferromagnetic film has also been underway. Such a laminate has a magnetoelectric (ME) effect and can convert energy (input signal) such as a magnetic field, electromagnetic wave, or ultrasonic wave transmitted non-contact from a distance into an electrical output (see Patent Document 2, etc.). That is, in a laminate having a piezoelectric film and a ferromagnetic film, when an external magnetic field or the like is applied, strain occurs in the ferromagnetic film due to the magnetostrictive effect. Then, the strain is transmitted to the piezoelectric film, and the piezoelectric film itself bends, generating charges on the surface of the piezoelectric layer.

[0003] On the other hand, in order to utilize the excellent characteristics of a laminate laminated on a substrate while being small, it is necessary to ensure storage reliability. Conventional laminates have been a problem because they may show a decrease in characteristics when stored in a high-temperature and high-humidity environment.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a laminate having a piezoelectric film and a metal film, which can maintain good characteristics even after being stored in a high-temperature and high-humidity environment.

Means for Solving the Problems

[0006] In order to achieve the above object, the laminate according to the present invention is a laminate laminated on a substrate, having at least a lower metal film, a piezoelectric film positioned on the lower metal film, and an upper metal film positioned on the piezoelectric film, characterized in that the surface roughness P-V of the upper surface, which is the surface opposite to the lower surface of the upper metal film, is smaller than the surface roughness P-V of the lower surface, which is the surface on the piezoelectric film side of the upper metal film.

[0007] The laminate according to the present invention can maintain good characteristics even after being stored in a high-temperature and high-humidity environment because the surface roughness of the upper surface of the upper metal film is smaller than that of the lower surface. One of the factors is considered to be that the corrosion of the upper metal film from the environment is suppressed because the surface roughness of the upper surface of the upper metal film, which is likely to be corroded by the environment near the upper surface of the laminate, is small.

[0008] Also, for example, the upper metal film may be a magnetic film.

[0009] Such a laminate has a magnetoelectric (ME) effect and can convert energy (input signal) such as a magnetic field transmitted non-contact from a distance, electromagnetic waves, and ultrasonic waves into an electrical output, and can be suitably used as a part of an ME element with good storage reliability.

[0010] Also, for example, the film thickness of the upper metal film may be larger than the surface roughness P-V of the lower surface of the upper metal film.

[0011] By making the film thickness larger than the surface roughness P-V of the lower surface, it is possible to secure the film thickness while suppressing the surface roughness of the upper surface, and to improve the characteristics after storage in a high-temperature and high-humidity environment.

[0012] The lower surface of the upper metal film may be in contact with the piezoelectric film and constitute the interface between the upper metal film and the piezoelectric film.

[0013] Such a laminate is advantageous for miniaturization because no other film is interposed between the upper metal film and the piezoelectric film, and is also advantageous in terms of characteristics because there are few elements that mechanically inhibit deformation. In addition, since the surface roughness of the interface between the upper metal film and the piezoelectric film is large, it becomes possible to employ a highly crystalline piezoelectric film, and the characteristics of the piezoelectric film can be improved.

[0014] Also, for example, the upper surface of the upper metal film may be covered with a protective film.

[0015] By covering the upper surface with a protective film, corrosion of the upper metal film from the environment can be more effectively prevented.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 10

[0017] Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

[0018] FIG. 1 is a plan view showing an example of an ME element 30 having a laminate 32 according to an embodiment of the present invention. The ME element 30 is connected to a power supply or 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.

[0019] As shown in FIG. 1, the ME element 30 has a substantially rectangular planar shape as a whole. The dimensions of the ME element 30 are not particularly limited and may be appropriately determined according to the use of the electronic device. The ME element 30 has a laminate 32 laminated on a substrate 40 and an outer peripheral portion 34 surrounding the outside of the laminate 32 in plan view.

[0020] The laminate 32 is formed along a plane including the X-axis and the Y-axis and has a substantially rectangular shape in plan view. The laminate 32 has an edge parallel to the X-axis and an edge parallel to the Y-axis, and the longitudinal direction of the laminate 32 coincides with the X-axis. In FIGS. 1 to 3, the X-axis, the Y-axis, and the Z-axis are substantially perpendicular to each other, and the Z-axis coincides with the film lamination direction. Further, in the description of the ME element 30 and the laminate 32, the Z-axis direction will be described as the vertical direction, but the arrangement of the ME element 30 and the laminate 32 is not limited to only the form arranged such that the Z-axis direction coincides with the gravitational direction. For example, the ME element 30 and the laminate 32 may be arranged such that the Z-axis direction coincides with the horizontal direction, or may be arranged such that the Z-axis direction is inclined with respect to the horizontal plane.

[0021] FIG. 2 is a cross-sectional view taken along line II-II shown in FIG. 1. As shown in FIG. 2, a substrate 40 exists in the lowermost layer in the Z-axis direction in the ME element 30. This substrate 40 has an opening 42 in a substantially central portion of the X-Y plane, that is, a portion overlapping the laminate 32 when viewed from the Z-axis direction. The substrate 40 exists substantially only in the outer peripheral portion 34 of the ME element 30. The laminate 32 located above the opening 42 in the Z-axis direction has a lower metal film 50, a piezoelectric film 10 located on the lower metal film 50, and an upper metal film 20 located on the piezoelectric film 10. Further, in the laminate 32 according to the present embodiment, no other film is interposed between the lower metal film 50 and the piezoelectric film 10 or between the piezoelectric film 10 and the upper metal film 20, and the lower metal film 50, the piezoelectric film 10, and the upper metal film 20 are laminated in this order from the substrate 40 side.

[0022] The lower metal film 50 integrally has an end portion 50a and a central portion 50b. In the plan view shown in FIG. 1, the central portion 50b of the lower metal film 50 has a substantially rectangular shape smaller than the opening surface of the opening 42. Also, the end portions 50a of the lower metal film 50 are located at both ends of the central portion 50b in the X-axis direction, and in the plan view shown in FIG. 1, they have a substantially rectangular shape with a smaller width in the Y-axis direction than the central portion 50b. Since the lower metal film 50 has the above-described shape, in the cross section shown in FIG. 2, it exists so as to span the upper opening surface of the opening 42 in the Z-axis direction in the X-axis direction. And only the end portions 50a of the lower metal film 50 exist on the surface of the substrate 40 located at the outer peripheral portion 34 of the ME element 30.

[0023] On the other hand, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. In FIG. 3, only the cross section of the central portion 50b of the lower metal film 50 appears, and the end portion 50a connected to the substrate 40 as shown in FIG. 2 does not appear. Therefore, in the cross section shown in FIG. 3, the laminate 32 including the lower metal film 50 appears to be floating above the opening 42 in the Z-axis direction. The laminate 32 disposed above the opening 42 may be warped due to the imbalance of the stresses of the respective films included in the laminate 32, and it is preferable that the warp is small from the viewpoint of reducing the energy transfer loss in the ME element 30.

[0024] The piezoelectric film 10 is located above the lower metal film 50 in the Z-axis direction and has a substantially rectangular plan view shape that is the same as or slightly smaller than the lower metal film 50. In FIG. 1, the planar dimensions (area on the X-Y plane) of the piezoelectric film 10 are smaller than those of the lower metal film 50, but the planar dimensions of the piezoelectric film 10 may be approximately the same as those of the lower metal film 50. Also, above the piezoelectric film 10 in the Z-axis direction, there is an upper metal film 20, and this upper metal film 20 also has a substantially rectangular plan view shape. And the planar dimensions of the upper metal film 20 are even slightly smaller than those of the piezoelectric film 10. By making the planar dimensions of the upper metal film 20 smaller than those of the piezoelectric film 10, the durability of the ME element 30 tends to be improved. However, the planar dimensions of the upper metal film 20 may be approximately the same as those of the piezoelectric film 10.

[0025] Also, as shown in FIG. 2, the tip of the first extraction electrode film 51 is connected to one end 50a of the lower metal 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, and an external circuit (not shown) can be connected via the first electrode pad 51a.

[0026] Furthermore, as shown in FIG. 2, the other end 50a of the lower metal film 50 is covered with an insulating film 54 together with a part of the surface of the piezoelectric film 10. Then, a second extraction electrode film 53 is formed so as to extend in the X-axis direction over the insulating film 54, and the tip of the second extraction electrode film 53 is connected to the upper metal film 20. 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, and an external circuit (not shown) can be connected via the second electrode pad 53a. Since there is the insulating film 54, the second extraction electrode film 53 is insulated from the lower metal film 50.

[0027] In the ME element 30, in the laminate 32, the piezoelectric film 10 is laminated in a state of being sandwiched between the lower metal film 50 and the upper metal film 20. Therefore, a voltage can be applied to the piezoelectric film 10 via the lower metal film 50 and the upper metal film 20. Or, the charges generated in the piezoelectric film 10 can be extracted via the lower metal film 50 and the upper metal film 20.

[0028] (Piezoelectric film 10) The piezoelectric film 10 in the laminate 32 is made of a piezoelectric material and exhibits a piezoelectric effect or a converse piezoelectric effect. The piezoelectric effect means an effect of generating charges when an external force (stress) is applied, and the converse piezoelectric effect means an effect of generating strain when a voltage is applied. Examples of such piezoelectric materials that exhibit such effects include quartz, lithium niobate, aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT: Pb(Zr,Ti)O3), potassium sodium niobate (KNN: (K,Na)NbO3), barium calcium zirconate titanate (BCZT: (Ba,Ca)(Zr,Ti)O3), and the like.

[0029] In this embodiment, among the above 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 with a perovskite structure as the piezoelectric film 10, excellent piezoelectric characteristics and high reliability can be achieved simultaneously. Note that other elements may be appropriately added to the above piezoelectric material constituting the piezoelectric film 10 to improve its properties.

[0030] The thickness of the piezoelectric film 10 can be, for example, 0.5 to 10 μm. The thickness of the piezoelectric film 10 can be obtained, for example, by image analysis of a cross-sectional photograph. That is, it is preferable to measure the thickness of the piezoelectric film 10 at three or more points in the in-plane direction and calculate the average value. Note that as the piezoelectric film 10, it is preferable to use one with a small thickness variation of ±5% or less.

[0031] The piezoelectric film 10 may be an epitaxial growth film. An epitaxial growth film means a film grown epitaxially on a single crystal substrate. Here, epitaxial growth means that during film formation, the crystals of the film grow while aligning in the film thickness direction (Z-axis direction) and in-plane direction (X-axis and Y-axis directions) in a form that matches the crystal lattice of the underlying material. Therefore, the piezoelectric film 10, which is an epitaxial growth film, has a crystal structure in which the crystals are aligned in all three directions of the X-axis, Y-axis, and Z-axis directions in the high-temperature state during film formation (epitaxial film), and in the room-temperature state after film formation, almost no crystal grain boundaries are formed, and it has a crystal structure close to a single crystal (not a perfect single crystal) (epitaxial growth (formed) film).

[0032] When the piezoelectric film 10 is an epitaxial growth film of PZT, it preferably contains a total of three types of domains: two types of tetragonal domains and one type of rhombohedral domain. On the other hand, when the piezoelectric film 10 is an epitaxial growth film of KNN, it preferably has two types of orthorhombic domains and one type of monoclinic domain (a total of three types of domains). Further, when the piezoelectric film 10 is an epitaxial growth film of BCZT, it preferably has two types of tetragonal domains and two types of orthorhombic domains (a total of four types of domains).

[0033] Note that the piezoelectric film 10 does not have to be an epitaxially grown film, and may be a piezoelectric thin film such as PZT, KNN, and BCZT formed by a thin film method other than epitaxial growth.

[0034] (Upper metal film) The upper metal film 20 in the laminate 32 is a magnetic film (ferromagnetic film). Since the upper metal film 20 is a ferromagnetic film, the elements shown in FIGS. 1 to 3 function as the ME element 30. However, when the upper metal film 20 functions only as an electrode of the piezoelectric film 10, a metal film that does not exhibit ferromagnetism may be used.

[0035] The upper metal film 20 that is a magnetic film is preferably composed of, for example, a soft magnetic high magnetostriction film, and generates strain due to the magnetostriction effect when a magnetic field, electromagnetic wave, ultrasonic wave, etc. are applied from the outside. A soft magnetic high magnetostriction film is composed of a soft magnetic material with a low coercive force H C and a threshold magnetic field H TH and is preferably a film with a saturation magnetostriction λ MAX of 5 ppm or more. The saturation magnetostriction λ MAX is more preferably 10 ppm or more. Note that a soft magnetic material is generally a low magnetostriction material with a saturation magnetostriction λ MAX of 1 ppm or less, but the upper metal film 20 of the present embodiment is a soft magnetic material and it is important to have high magnetostriction characteristics.

[0036] Examples of the soft magnetic material having the above characteristics include an iron (Fe)-cobalt (Co)-silicon (Si)-boron (B) alloy, an Fe-Si-B alloy, an Fe-Co-B alloy, an Fe-chromium (Cr)-Si-B alloy, an Fe-nickel (Ni)-molybdenum (Mo)-B alloy, an Fe-Si-B-copper (Cu)-niobium (Nb) alloy, a Co-Fe-Ni-Si-B-Mo alloy, and the like. The above soft magnetic material has a much smaller magnetocrystalline anisotropy than the hard magnetic material.

[0037] Also, in the present embodiment, the coercive force H of the soft magnetic high magnetostriction film C is preferably less than 2500 A / m. The lower the coercive force H C , the higher the responsiveness of the magnetoelectric effect in the ME element 30. 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 of the soft magnetic high magnetostriction film C 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.

[0038] Furthermore, the threshold magnetic field H of the soft magnetic high magnetostriction film TH 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. In the present embodiment, the threshold magnetic field H TH means the magnetic field at which a magnetostriction of 0.1 ppm occurs in the soft magnetic high magnetostriction film. In addition, the magnetic field sensitivity dλ / dH of the soft magnetic high magnetostriction film is preferably 10 ppb·m·A -1 or more, and more preferably 15 ppm·m·A -1 or more. In the present embodiment, the magnetic field sensitivity dλ / dH means the change amount of magnetostriction in an environment where a DC magnetic field of 500 A / m is applied as a bias magnetic field.

[0039] The upper metal film 20, which is a magnetic film, preferably contains an amorphous phase and a crystalline phase. Further, for the upper metal film 20 of the ferromagnetic film including an amorphous layer and a crystalline layer, it is more preferable that most of the contained crystalline phase has a face-centered cubic structure (fcc). However, even in this case, a body-centered cubic structure (bcc) crystalline phase may be mixed in at least a part of the crystalline phase.

[0040] The thickness of the upper metal film 20 is preferably in the range of 0.03 to 5 μm, more preferably 0.1 to 5 μm. Note that the thickness of the upper metal film 20 is measured in the same manner as the thickness of the piezoelectric film 10. As the thickness of the upper metal film 20, one having a small variation in the in-plane direction and having a variation similar to that of the thickness of the piezoelectric film 10 can be used. In the present embodiment, the ratio of the thickness of the upper metal film 20 to the thickness of the piezoelectric film 10 (thickness of the piezoelectric film 10 / thickness of the upper metal film 20) is preferably in the range of 1 / 10 to 10.

[0041] (Substrate 40) The substrate 40 in the ME element 30 is composed of at least an insulating member that supports the laminate 32. For example, as the substrate 40, a single crystal substrate used when epitaxially growing the piezoelectric film 10 of the laminate 32, or a substrate when laminating the portions constituting the laminate 32 by a thin film method or the like may be used. The material of the substrate 40 can be selected from various single crystals such as Si, MgO, strontium titanate (SrTiO3), and lithium niobate (LiNbO3). In particular, it is preferable to use a silicon substrate having a single crystal with a Si(100) surface.

[0042] The lower metal film 50 in the laminate 32 is composed of a conductive metal film such as Pt, Ag, Cu, Au, or Al. When the piezoelectric film 10 is an epitaxial growth film, it is preferable that the lower metal film 50 is also an epitaxial growth film. As the lower metal film 50 that is an epitaxial growth film, it is preferable to use a metal thin film with a face-centered cubic structure such as Pt, Ir, or Au, or an oxide conductor film with a perovskite structure such as SrRuO3 (SRO) or LaNiO3. Such a metal thin film and an oxide conductor thin film can be epitaxially grown on a single-crystalline substrate, whereby the lower metal film 50 can also be an epitaxial growth film. Further, the lower metal film 50 may be formed by laminating the above metal thin film and the above oxide conductor film (for example, Pt electrode / SrRuO3, etc.). In this case (when multiple layers are laminated), it is preferable that an oxide conductor film exists on the piezoelectric film 10 side (that is, above in the Z-axis direction) of the lower metal film 50. And the average thickness of the lower metal film 50 is preferably 3 nm to 200 nm as a whole.

[0043] Note that as an ME element according to a modified example, different from the laminate 32 shown in FIG. 2, it is also conceivable that an upper electrode film is formed between the upper metal film 20 as the ferromagnetic film shown in FIG. 2 and the piezoelectric film 10. When forming an upper electrode film between the piezoelectric film 10 and the ferromagnetic upper metal film 20, the upper electrode film can have, for example, the same material and thickness as the lower metal film 50.

[0044] The first extraction electrode film 51 and the second extraction electrode film 53 shown in FIGS. 1 to 3 are composed of a film having conductivity, and the material and thickness are not particularly limited. For example, the first extraction electrode film 51 and the second extraction electrode film 53 can contain conductive metals such as Ag, Cu, Au, and Al in addition to Pt. The insulating film 54 shown in FIGS. 1 to 3 is composed of a film having electrical insulation, and the material and thickness are not particularly limited. For example, regarding the material of the insulating film 54, SiO2, Al2O3, polyimide, etc. can be used.

[0045] Note that, as an ME element according to a modification example, unlike the ME element 30 shown in FIG. 2, a buffer layer may be formed below the lower metal film 50 in the Z-axis direction (that is, between the substrate 40 and the lower metal film 50). By forming a buffer layer between the substrate 40 and the lower metal film 50, it is possible to promote the epitaxial growth of the film located above the buffer layer. Further, the buffer layer also functions as an etching stopper layer when forming the opening 42. When forming the buffer layer, its thickness is preferably 5 nm to 100 nm.

[0046] Further, as an ME element according to a modification example, an ME element having a protective film 60 (refer to the virtual line (two-dot chain line) in FIG. 3) covering the upper surface 22 of the upper metal film 20 of the laminate 32 is conceivable. As the protective film 60, for example, in addition to insulating films such as SiO2, Al2O3, and polyimide, metal films such as Ti and Ta can also be used. The thickness of the protective film 60 is not particularly limited, but it may be at least about 10 nm. By having the protective film 60, attack from the environment can be effectively prevented. However, the laminate 32 in which the upper surface 22 of the upper metal film 20 is exposed without the protective film 60 is advantageous in that there are fewer layers that inhibit the deformation of the laminate 32.

[0047] In the ME element 30 shown in FIGS. 1 to 3, the laminate 32 also functions as a resonator having a vibration mode of a specific frequency. That is, the laminate 32 can cause in-plane expansion and contraction in which the film laminate 32 expands and contracts along the X-Y plane, and in-plane expansion and contraction vibration is possible. Note that the ME element 30 can also cause out-of-plane expansion and contraction in which the laminate 32 expands and contracts in the Z-axis direction in addition to in-plane expansion and contraction.

[0048] Focusing on the function of the laminate 32 as a resonator, a portion where the end 50a of the lower metal film 50 and the end of the piezoelectric film 10 are laminated but there is no upper metal film 20 (among them, particularly above the opening 42, the three-layer structure portion (vibration portion 38) in the laminate 32 that supports the laminate 32 from both sides in the X-axis direction) becomes the support portion 36.

[0049] The support portion 36 is preferably in a form with low rigidity with respect to the vibrating portion 38 (vibrator) of the laminate 32 so as not to prevent in-plane expansion and contraction occurring in the vibrating portion 38 of the laminate 32. For example, the width of the support portion 36 in the Y-axis direction is made narrower than the width of the vibrating portion 38 (or the upper metal film 20) of the laminate 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 vibrating portion 38 of the film laminate 32 in the Z-axis direction. The product of the thickness and width of the support portion 36 is preferably less than 90% of that of the vibrating portion 38, and more preferably less than 75%. By configuring in this way, in-plane expansion and contraction vibration with a large amplitude can be induced, and the output of the ME element 30 can be made larger.

[0050] Also, the length of the support portion 36 in the X-axis direction is preferably about 1 / 4 of the vibration wavelength transmitted to the laminate 32. By setting the length in this way, energy can be efficiently confined in the laminate 32, the output can be made larger than that of the ME element 30, and interference between elements when forming an array (combining a plurality of ME elements 30) can be suppressed.

[0051] FIG. 4 is an enlarged cross-sectional view showing an enlarged part of the end face of the laminate 32 shown in FIG. 2. As shown in FIG. 4, in the laminate 32, the surface roughness P-V of the upper surface 22, which is the opposite surface of the lower surface 24 of the upper metal film 20, is smaller than the surface roughness P-V of the lower surface 24 on the piezoelectric film 10 side of the upper metal film 20. Note that the surface roughness P-V means the surface roughness P-V value defined by the difference between the maximum height (peak value) and the minimum height (valley value V) in the reference length (JIS B 0633:2001).

[0052] Such a laminate 32 can maintain good characteristics even after being stored in a high-temperature and high-humidity environment because the surface roughness P-V of the upper surface 22 of the upper metal film 20 is smaller than the surface roughness P-V of the lower surface 24. One of the factors is that the upper surface 22, which is the upper surface of the laminate 32, is considered to be easily corroded by the environment. However, by reducing the surface roughness P-V of the upper surface 22 of the upper metal film 20, it is considered that corrosion of the upper metal film 20 from the environment is suppressed.

[0053] In particular, when the upper metal film 20 is a magnetic film and the laminate 32 is part of the ME element 30, the magnetic properties of the upper metal film 20 tend to deteriorate in a high-temperature and high-humidity environment, and this tendency is prominent when the upper metal film 20 is thin. However, by reducing the surface roughness P-V of the upper surface 22 of the upper metal film 20, the contact area between the upper surface of the upper metal film 20 and the storage environment of the laminate 32 is reduced. Therefore, it is considered that the laminate 32 can maintain good characteristics even after being stored in a high-temperature and high-humidity environment.

[0054] Also, the film thickness of the upper metal film 20 shown in FIG. 4 is preferably larger than the surface roughness P-V of the lower surface 24 of the upper metal film 20. When the upper metal film 20 is laminated and formed on the piezoelectric film 10 by a thin film method or the like, by making the film thickness of the upper metal film 20 larger than the surface roughness P-V of the lower surface 24 of the upper metal film 20, the surface roughness P-V of the upper surface 22 of the upper metal film 20 can be stably made smaller than the surface roughness P-V of the lower surface 24.

[0055] Also, when the upper metal film 20 is laminated and formed on the piezoelectric film 10 by a thin film method or the like, from the viewpoint of reducing the surface roughness P-V of the upper surface 22 of the upper metal film 20, the film thickness of the upper metal film 20 is preferably less than 1000 nm. The relationship between the film thickness of the upper metal film 20 and the surface roughness P-V of the lower surface 24 and the upper surface 22 of the upper metal film 20 will be described later while showing data in Example 2.

[0056] As shown in FIG. 4, in the laminate 32, the lower surface 24 of the upper metal film 20 is in contact with the piezoelectric film 10 and constitutes the interface between the upper metal film 20 and the piezoelectric film 10. Such a laminate 32 is advantageous for miniaturization because no other film is interposed between the upper metal film 20 and the piezoelectric film 10, and there are few elements that mechanically inhibit deformation, so it is also advantageous in terms of characteristics. Also, since the surface roughness of the interface between the upper metal film 20 and the piezoelectric film 10 is large, a film with good crystallinity can be adopted for the piezoelectric film 10, and the characteristics can be improved.

[0057] Note that it is preferable that the surface roughness P-V of the lower surface 24 of the upper metal film 20 is 30 nm or more from the viewpoint that the area of the interface between the upper metal film 20 and the piezoelectric film 10 is enlarged and the characteristics of the piezoelectric film 10 are improved, but the surface roughness P-V of the lower surface 24 of the upper metal film 20 may be less than 30 nm.

[0058] Hereinafter, a method for manufacturing the ME element 30 and the laminate 32 shown in FIGS. 1 to 4 will be described.

[0059] In the manufacture of the ME element 30 and the laminate 32, first, the lower metal film 50, the piezoelectric film 10, and the upper metal film 20 are formed on a film-forming substrate such as a silicon substrate. As a film-forming method for the lower metal film 50, the piezoelectric film 10, and the upper metal film 20, physical or chemical methods such as a vapor deposition method, a sputtering method, a sol-gel method, a CVD method, and a PLD method can be used. Further, when at least a part of the lower metal film 50, the piezoelectric film 10, and the upper metal film 20 is formed by epitaxial growth, it is preferable to use a sputtering method. Further, when the upper metal film 20 is a magnetic film composed of a soft magnetic high magnetostrictive film or the like, the upper metal film 20 can be formed by a vacuum deposition method such as a sputtering method, a vacuum evaporation method, a PLD method, or an ion beam deposition method (IBD method), and it is preferable to form it by a sputtering method.

[0060] Furthermore, the lower metal film 50, the piezoelectric film 10, and the upper metal film 20 formed on the film-forming substrate are subjected to patterning so as to have a pattern as shown in FIG. 1. The patterning can be performed by various etching methods such as photoetching and laser dry etching, or a lift-off method.

[0061] After performing 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. 1. Further, a part of the film-forming substrate is removed by a method such as dry etching using the Deep-RIE method or anisotropic wet etching to form a substrate 40 having an opening 42. Note that all of the film-forming substrate may be removed by the above etching. In this case, the laminate 32 (including the vibrating portion 38 and the supporting portion 36) peeled from the film-forming substrate may be fixed to a substrate 40 prepared as a separate member. By such a procedure, the ME element 30 including the laminate 32 is obtained.

[0062] As described above, the present invention has been described with reference to the embodiments. However, the laminate according to the present invention is not limited to only the above-described embodiments, and it goes without saying that other embodiments and modifications are included.

[0063] For example, although the laminate 32 included in the ME element 30 has a substantially rectangular shape in plan view, the form of the laminate 32 is not limited to this, and may be an elliptical shape, a circular shape, a meander shape, or a spiral shape in plan view.

[0064] Further, in the ME element 30, both ends of the laminate 32 are supported by the substrate 40 and have a structure fixed at both ends. However, the laminate may have a cantilever-type structure in which one end of the laminate is a free end. Further, the ME element 30 may be a single element as shown in FIG. 1, or may be an array element in which a plurality of single elements are integrally formed on a common substrate 40.

[0065] Further, in the embodiments shown in FIGS. 1 to 4, the description has been centered on a specific example in which the upper metal film 20 in the laminate 32 is a magnetic film (ferromagnetic film). However, the upper metal film 20 may be a metal film that does not exhibit ferromagnetism. Even when the upper metal film 20 is a metal film that does not exhibit ferromagnetism, deterioration of the upper metal film 20 after storage in a high-temperature and high-humidity environment can be prevented by making the surface roughness P-V of the upper surface 22 of the upper metal film 20 smaller than that of the lower surface 24.

Example

[0066] Hereinafter, the present invention will be described in more detail using examples. However, the present invention is not limited only to the examples.

[0067] (Example 1) In Example 1, a laminate 32 to be laminated on a substrate 40 was fabricated according to the procedure shown below. A lower metal film 50, a piezoelectric film 10, and an upper metal film 20 which is a ferromagnetic film were formed on a film-forming substrate of a silicon wafer (silicon substrate) whose surface is a single crystal of Si(100) plane as shown in FIGS. 2 and 3. At this time, the lower metal film 50 is a laminated film composed of a Pt electrode film with a thickness of (100 nm) and a conductive oxide thin film composed of SrRuO3 (hereinafter referred to as SRO) with a thickness of (100 nm), and these films were formed by epitaxial growth on the upper surface of the film-forming substrate. Further, as the piezoelectric film 10, an epitaxial growth film of PZT with a thickness of 1 μm was formed on the lower metal film 50.

[0068] Furthermore, as the upper metal film 20 which is a ferromagnetic film, an FeCoSiB alloy film with an adjusted thickness was formed on the piezoelectric film 10 by sputtering. In Example 1, samples of seven types of laminates 32 with different surface roughness P-V of the upper surface 22 of the upper metal film 20 were prepared. The surface roughness P-V of the upper surface 22 of the upper metal film 20 in each sample was adjusted by changing the thickness of the upper metal film 20 formed on the piezoelectric film 10 (see FIG. 7 in Example 2).

[0069] In Example 1, seven types of laminates 32 with different surface roughness P-V of the upper surface 22 of the upper metal film 20 were prepared as described above. The prepared laminates were stored in a high-temperature and high-humidity environment (80°C, 85%) for 50 hours. For each sample, the number of black dots observed on the upper surface 22 of the upper metal film 20 was counted before and after the high-temperature and high-humidity environment. The number of black dots observed on the upper surface 22 of the upper metal film 20 was defined as the number of black dots visually recognized in a 50-fold field of view (2×2 mm) of a stereomicroscope. Table 1 shows the surface roughness P-V of the upper surface 22 of each sample and the increase in the number of black dots before and after the high-temperature and high-humidity environment. Also, Fig. 5 plots the results of each sample shown in Table 1, with the surface roughness P-V of the upper surface 22 on the horizontal axis and the increase in the number of black dots on the vertical axis.

[0070]

Table 1

[0071] From Table 1 and Fig. 5, it can be understood that the larger the value of the surface roughness P-V of the upper surface 22 of the upper metal film 20, the larger the increase in the number of black dots. From Example 1, it is inferred that reducing the surface roughness P-V of the upper surface 22 of the upper metal film 20 is effective for improving the storage reliability. Note that the increased black dots on the upper surface 22 of the upper metal film 20 are considered to correspond to locations where various deteriorations of the upper metal film 20, such as metal oxidation, pinholes, and film peeling, have occurred, and the increase in the number of black dots comprehensively indicates the degree of film deterioration of the upper metal film 20.

[0072] (Example 2) In Example 2, the lower metal film 50 and the piezoelectric film 10 were formed on the substrate 40 in the same procedure as in Example 1. However, unlike Example 1, for the surface roughness P-V of the upper surface of the piezoelectric film 10 during film formation, three types of samples with different surface roughness P-V were fabricated. The surface roughness P-V of the upper surface of the fabricated piezoelectric film 10 was 25 nm, 30 nm, and 35 nm, respectively.

[0073] In Example 2, a laminate 32 was fabricated by forming an upper metal film 20, which is a ferromagnetic film, on the upper surface of a piezoelectric film 10 having a surface roughness P-V of 25 nm, 30 nm, or 35 nm in the same manner as in Example 1. However, six different samples with thicknesses of the upper metal film 20 of 20, 25, 30, 35, 40, and 50 nm were fabricated for each of the piezoelectric films 10 having surface roughnesses P-V of 25 nm, 30 nm, and 35 nm on their upper surfaces (a total of 18 levels). Furthermore, for the piezoelectric film 10 having a surface roughness P-V of 35 nm on its upper surface, five additional levels with thicknesses of the upper metal film 20 of 100 nm, 200 nm, 500 nm, 800 nm, and 1000 nm were fabricated.

[0074] For each of the fabricated samples, the surface roughness P-V of the upper surface 22 (see FIG. 4) of the upper metal film 20 was measured. As shown in FIG. 4, since the lower surface 24 of the upper metal film 20 is in contact with the upper surface of the piezoelectric film 10 and constitutes the interface between the upper metal film 20 and the piezoelectric film 10, the surface roughness P-V of the lower surface 24 (see FIG. 4) of the upper metal film 20 in each sample is the same as the surface roughness P-V of the upper surface of the piezoelectric film 10.

[0075] FIG. 6 is a graph plotting each sample of Example 2 with the vertical axis representing the surface roughness P-V of the upper surface 22 of the upper metal film 20 and the horizontal axis representing the thickness of the upper metal film 20 (excluding the additional levels). In FIG. 6, the solid line connects the plots of the samples with a surface roughness P-V of 25 nm for the lower surface 24 of the upper metal film 20, the dashed line connects the plots of the samples with a surface roughness P-V of 30 nm for the lower surface 24 of the upper metal film 20, and the dash-dotted line connects the plots of the samples with a surface roughness P-V of 35 nm for the lower surface 24 of the upper metal film 20.

[0076] Focusing on the dashed lines and the dash-dotted lines in FIG. 6, it can be understood that in a region where the thickness of the upper metal film 20 is very thin (for example, less than 25 nm), as the thickness of the upper metal film 20 increases, the value of the surface roughness P-V of the upper surface 22 of the upper metal film 20 increases. However, in a region where the thickness of the upper metal film 20 is equal to or greater than the surface roughness P-V of the lower surface 24 of the upper metal film 20 (that is, in the region to the lower right of the two-dot chain line 98 where the thickness of the upper metal film 20 is equal to the surface roughness P-V of the lower surface 24 of the upper metal film 20 in FIG. 6), as the thickness of the upper metal film 20 increases, the value of the surface roughness P-V of the upper surface 22 of the upper metal film 20 decreases. This tendency continues until the thickness of the upper metal film 20 reaches 200 nm (see FIG. 7).

[0077] FIG. 7 is a graph plotting samples (including additional levels) with a surface roughness P-V of the lower surface 24 of the upper metal film 20 of 35 nm, with the vertical axis being the surface roughness P-V of the upper surface 22 of the upper metal film 20 and the horizontal axis being the thickness of the upper metal film 20. As shown in FIG. 7, in a region where the thickness of the upper metal film 20 exceeds 200 nm, as the thickness of the upper metal film 20 increases, the value of the surface roughness P-V of the upper surface 22 of the upper metal film 20 tends to increase. However, it is recognized that in at least a region where the film thickness of the upper metal film 20 is less than 1000 nm and greater than the value of the surface roughness of the lower surface 24 of the upper metal film 20, the surface roughness P-V of the upper surface 22 of the upper metal film 20 is smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20.

[0078] As shown in FIGS. 6 and 7, in a region where the thickness of the upper metal film 20 is equal to or greater than the value of the surface roughness P-V of the lower surface 24 of the upper metal film 20, the surface roughness P-V of the upper surface 22 of the upper metal film 20 was smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20. This tendency was confirmed in at least a region where the film thickness of the upper metal film 20 is less than 1000 nm.

[0079] (Example 3) In Example 3, a laminate 32 to be laminated on the substrate 40 was fabricated in the same procedure as in Example 1 and Example 2. As shown in Table 2, in Example 3, surface roughness P-V of the lower surface 24 (FIG. 4) of the upper metal film 20, which is a ferromagnetic film (FeCoSiB alloy film), was fabricated at three levels of 25 nm, 30 nm, and 35 nm. Also, for the surface roughness P-V of the upper surface 22 (FIG. 4) of the upper metal film 20, those of 10 nm, 20 nm, 22 nm, 25 nm, 30 nm, and 35 nm were fabricated. The film thicknesses shown in Table 2 indicate the film thicknesses of the upper metal film 20 of each sample and were measured with a step gauge (a stylus profiler manufactured by KLA-Tenchore).

[0080]

Table 2

[0081] The left side of Table 2 shows the surface roughness of the upper metal film 20 in each sample fabricated in Example 3. As shown in Table 2, for Samples 1 to 6, the surface roughness difference ((A) - (B)) obtained by subtracting the surface roughness P-V of the upper surface 22 (Table 1 (B)) of the upper metal film 20 from the surface roughness P-V of the lower surface 24 (Table 1 (A)) of the upper metal film 20 is greater than 0 (Example). In contrast, for Samples 7 to 11, the surface roughness difference (Table 2 (A) - (B)) obtained by subtracting the surface roughness P-V of the upper surface 22 (Table 2 (B)) of the upper metal film 20 from the surface roughness P-V of the lower surface 24 (Table 2 (A)) of the upper metal film 20 is 0 or less (Comparative Example).

[0082] Furthermore, in Example 3, the prepared Samples 1 to 17 were stored in a high-temperature and high-humidity environment (80°C, 85%) for 50 hours, and the change in the output voltage from the laminate 32 before and after the high-temperature and high-humidity environment was measured. The right side of Table 2 shows the output voltage measured before the high-temperature and high-quality environment storage (initial output voltage (Table 2 (C))), the output voltage measured after the high-temperature and high-quality environment storage (output voltage after storage (Table 2 (D))), and the output voltage difference before and after storage (Table 2 (C) - (D)).

[0083] The measurement of the output voltage of the laminate 32 was performed by measuring the potential difference generated between the upper metal film 20 and the lower metal film 50 when an AC magnetic field of 1 kHz and 0.8 A / m was applied to the laminate 32 in an environment where a DC magnetic field of 500 A / m was applied as a bias magnetic field. Note that a sample with a large value of this output voltage can be judged to have excellent responsiveness due to the magnetoelectric effect of the laminate 32, and a sample with a small value of the output voltage difference ((C)-(D)) before and after storage can be judged to have little deterioration in responsiveness in a high-temperature and high-humidity environment. The rightmost column of Table 2 shows the thickness of the upper metal film 20 for each sample.

[0084] FIG. 8 is a plot of each of the samples 1 to 14 shown in Table 2 with the vertical axis being the output voltage after storage (Table 2 (D)) and the horizontal axis being the surface roughness P-V of the upper surface 22 of the upper metal film 20 (Table 2 (B)). As shown in FIG. 8, for Samples 7 to 11 of the comparative examples where the surface roughness P-V of the upper surface 22 of the upper metal film 20 is equal to or greater than the surface roughness P-V of the lower surface 24 of the upper metal film 20, the output voltage after storage is less than 0.7 V and is small. In contrast, for Samples 1 to 6 of the examples where the surface roughness P-V of the upper surface 22 of the upper metal film 20 is smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20, the output voltage after storage is 0.7 V or higher and is large. Thereby, it was confirmed that in Samples 1 to 14 where the surface roughness P-V of the upper surface 22 of the upper metal film 20 is smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20, the responsiveness due to the magnetoelectric effect after storage in a high-temperature and high-humidity environment is better than that of the comparative examples.

[0085] Figure 9 plots each of the samples 1 to 14 shown in Table 2, with the vertical axis being the output voltage after storage (Table 2(D)) and the horizontal axis being the difference in surface roughness P-V between the upper surface 22 and the lower surface 24 of the upper metal film 20 (surface roughness difference (Table 2(A)-(B))). As shown in Figure 9, as the surface roughness P-V of the upper surface 22 of the upper metal film 20 becomes smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20 and the surface roughness difference (horizontal axis) becomes larger, it can be seen that the value of the output voltage (vertical axis) after storage in a high-temperature and high-humidity environment becomes larger. In particular, it can be understood that in the region where the surface roughness P-V of the upper surface 22 of the upper metal film 20 is 5 nm or more smaller than the surface roughness P-V of the lower surface 24 of the upper metal film 20 (surface roughness difference 5.0 or more), the value of the output voltage after storage is particularly good.

[0086] Figure 10 is a graph plotting each of the samples shown in Table 2, with the vertical axis being the difference in output voltage before and after storage (Table 2(C)-(D)) and the horizontal axis being the difference in surface roughness P-V between the upper surface 22 and the lower surface 24 of the upper metal film 20 (surface roughness difference (Table 2(A)-(B))). However, in order to exclude the influence of the difference in the output voltage before storage, for the samples with the largest and smallest initial output voltages (Table 2(C)) in the examples (Sample 6 and Sample 3), and the samples with the largest and smallest initial output voltages (Table 2(C)) in the comparative examples (Sample 8 and Sample 10), they were excluded from the plot.

[0087] As shown in Figure 10, as the surface roughness P-V of the upper surface 22 of the upper metal film 20 becomes smaller relative to the surface roughness P-V of the lower surface 24 and the horizontal axis (surface roughness difference (Table 2(A)-(B))) becomes larger, there is a tendency for the difference in output voltage before and after storage (vertical axis) to become smaller. From Figure 10, it was confirmed that in samples where the surface roughness P-V of the upper surface 22 of the upper metal film 20 is smaller than the surface roughness P-V of the lower surface 24, the deterioration of responsiveness in a high-temperature and high-humidity environment is small. Also, regarding Samples 1 to 6, when paying attention to the relationship between the difference in output voltage before and after storage (Table 2(C)-(D)) and the film thickness, Samples 1, 2, 3, and 5 with a film thickness of 500 μm or less had a difference in output voltage before and after storage of 0.1 mV or less, and the difference in output voltage before and after storage was particularly small.

Explanation of Reference Numerals

[0088] 30…ME element 32…laminated body 10…piezoelectric film 20…upper metal film 22…upper surface 24…lower surface 50…lower metal film 50a…end portion 50b…central portion 36…support portion 38…vibration portion 40…substrate 51…first extraction electrode film 53…second extraction electrode film 54…insulating film 60…protective film 34…outer peripheral portion

Claims

1. A laminate to be laminated on a substrate, comprising: at least a lower metal film, a piezoelectric film located above the lower metal film, and an upper metal film located above the piezoelectric film; the surface roughness P-V of the upper surface, which is the surface opposite to the lower surface of the upper metal film, is smaller than the surface roughness P-V of the lower surface, which is the surface on the piezoelectric film side of the upper metal film; the upper metal film is a magnetic film with a thickness of 40 nm to 1000 nm; the lower metal film, the piezoelectric film, and the upper metal film each have a substantially rectangular shape in plan view, the planar dimensions of the piezoelectric film are smaller than the planar dimensions of the lower metal film, and the planar dimensions of the upper metal film are smaller than the planar dimensions of the piezoelectric film.

2. The laminate according to claim 1, wherein the film thickness of the upper metal film is larger than the surface roughness P-V of the lower surface of the upper metal film.

3. The laminate according to claim 1 or claim 2, wherein the lower surface of the upper metal film is in contact with the piezoelectric film and constitutes the interface between the upper metal film and the piezoelectric film.

Images