JP7415426B2 - Elements for electronic devices - Google Patents

Description

The present invention relates to an element for electronic devices used in electronic devices such as piezoelectric devices and magnetoelectric devices.

Various piezoelectric actuators, magnetoelectric sensors, magnetic sensors, electric sensors, optoelectronic devices, microwave electronic devices, energy conversion devices, memories, and the like are known as electronic devices having piezoelectric thin films.

The electronic devices mentioned above utilize the piezoelectric effect or inverse piezoelectric effect of the piezoelectric thin film to achieve various functions, but in order to improve the performance of the electronic device, it is necessary to It is necessary to improve the characteristics. In particular, in recent years, the miniaturization of electronic devices has progressed, and there has been a demand for the development of piezoelectric thin films and elements for electronic devices that have high piezoelectric properties even when the film thickness is as thin as several micrometers.

In response to the above problem, for example, Patent Document 1 discloses that piezoelectric properties can be improved by increasing the crystal orientation of a piezoelectric thin film. However, further improvements in piezoelectric properties are required in order to meet the ever-increasing demands of the market.

Japanese Patent Application Publication No. 2002-29894

The present invention has been made in view of the above circumstances, and an object thereof is to provide an element for an electronic device exhibiting excellent piezoelectric properties, and an electronic device having the element for an electronic device.

In order to achieve the above object, an element for an electronic device according to the present invention,
The piezoelectric thin film is epitaxially grown so as to be triaxially oriented, and has at least three types of domains.

In the electronic device element of the present invention, since the piezoelectric thin film has the above-described configuration, domain rotation and crystal phase transition occur smoothly when voltage or stress is applied from the outside, and external input The piezoelectric response to (voltage, stress, etc.) increases. That is, in the element for electronic devices of the present invention, a high piezoelectric constant (d31) can be obtained.

Therefore, in an electronic device having the electronic device element of the present invention, performances such as displacement characteristics and sensitivity characteristics are improved. For example, in the case of a piezoelectric actuator, piezoelectric distortion is more likely to occur when a voltage is applied, and a large displacement can be obtained. Furthermore, even in the case of memory, magnetization can be changed with a small drive voltage. Furthermore, in the case of various sensors, the piezoelectric thin film described above easily deforms in response to external mechanical input (stress, etc.), thereby improving characteristics such as sensitivity and detection limit.

In the element for an electronic device of the present invention, the piezoelectric thin film may include at least two types of crystal phases. For example, the at least three domains are:
a domain oriented such that the (001) plane of the tetragonal crystal is perpendicular to the film thickness direction;
a domain oriented such that a tetragonal (001) plane is parallel to the film thickness direction;
There can be three types of domains, including domains oriented such that the (100) plane of the rhombohedral crystal is parallel to the film thickness direction.

Further, in the element for an electronic device of the present invention, when the piezoelectric thin film is analyzed by θ-2θ method X-ray diffraction using Cu-Kα rays, at least three types of reflection peaks are present in the range of 2θ from 42° to 46°. It may have. Alternatively, the piezoelectric thin film may have a single reflection peak in a 2θ range of 42° to 46°, and in this case, the half width of the single reflection peak is 0.2° or more.

Further, in the element for an electronic device of the present invention, a base layer may be present below the piezoelectric thin film in the stacking direction, and the base layer has crystal axes aligned in all three directions. It is preferable that the film be epitaxially grown so that the film is epitaxially grown. Note that the base layer can be composed of a conductive electrode film and/or a buffer layer.

Furthermore, the element for an electronic device of the present invention preferably has a ferromagnetic thin film. Preferably, the ferromagnetic thin film is configured to expand and contract in an in-plane direction by an external magnetic field. By having a ferromagnetic thin film as described above, it can be usefully used as a magnetoelectric conversion element that converts an external magnetic field into electrical output.

FIG. 1 is a plan view showing an element for an electronic device according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line II-II shown in FIG. FIG. 3 is a sectional view taken along line III-III shown in FIG. FIG. 4A is a graph showing the X-ray diffraction results of the piezoelectric thin film. FIG. 4B is a graph showing the X-ray diffraction results of the piezoelectric thin film. FIG. 4C is a graph showing the X-ray diffraction results of the piezoelectric thin film. FIG. 5 is a graph showing the results of X-ray diffraction of a ferromagnetic thin film. FIG. 6 is a perspective view showing an electronic device according to an embodiment of the present invention.

The present invention will be described below based on embodiments shown in the drawings.

First Embodiment As shown in FIG. 1, an element 30 for an electronic device according to an embodiment of the present invention has a generally rectangular shape in plan view. The dimensions of the element 30 are not particularly limited, and may be appropriately determined depending on the use of the electronic device. The 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.

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. 1 to 3, 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. 2, 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 an upper electrode film 52 are laminated in this order in the film stacking section 32 located above the Z-axis of the opening 42.

The lower electrode 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 electrode film 50 has a substantially rectangular shape smaller than the opening surface of the opening 42. Further, 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-described 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 element 30.

On the other hand, in the cross section shown in FIG. 3 (the cross section taken along the line III--III in FIG. 1), 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. 3, 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 surface of the lower electrode film 50 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. 1, the stacked area (area on the XY plane) of the piezoelectric thin film 10 is smaller than the stacked area of the lower electrode film 50, but is about the same size as the lower electrode film 50. Also good. Further, an upper electrode film 52 exists above the piezoelectric thin film 10 in the Z-axis direction, and the upper electrode film 52 has a substantially rectangular shape in plan view.

As shown in FIG. 2, 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 upper electrode film 52. 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 first electrode film 50.

As described above, in the device 30 of this embodiment, the piezoelectric thin film 10 is sandwiched between the lower electrode film 50 and the upper electrode film 52 and stacked 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 upper electrode film 52, or charges generated in the piezoelectric thin film 10 can be transferred to the lower electrode film 50 and the upper electrode film 52. It can be taken out via the membrane 52.

Next, the characteristics of each layer (thin film) constituting the element 30 will be explained.

(Substrate 40)
In this embodiment, the material of the substrate 40 can be selected from various single crystals such as Si, MgO, strontium titanate (SrTiO ₃ ), and lithium niobate (LiNbO ₃ ). In particular, it is preferable to use a silicon substrate whose surface is a single crystal Si (100) plane. In other words, it is preferable to use a silicon substrate in which the cubic crystal (100) plane is oriented substantially parallel to the thickness direction. By using a single crystal substrate, each electrode film and the piezoelectric thin film 10 can be epitaxially grown on the substrate 40.

(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 can be determined by, for example, observing an X-Z cross section or a Y-Z cross section using a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM), and performing image analysis on the cross-sectional photograph obtained at that time. Desired. 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 grown epitaxially. 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, the crystals are aligned in all three axes of the X-axis direction, Y-axis direction, and Z-axis direction (triaxial orientation) at high temperatures during film formation. ) has a crystal structure (epitaxial film). More specifically, in the thickness direction of the piezoelectric thin film 10, it is preferable that the plane derived from the cubic crystal (100) plane of the substrate 40 is unidirectionally oriented substantially parallel to the thickness direction. At room temperature after film formation, the film is triaxially oriented, so almost no crystal grain boundaries are formed, and it has a crystal structure close to a single crystal (not a complete single crystal) (an epitaxially grown film). ).

Whether or not epitaxial growth has occurred with triaxial orientation 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 has a high orientation close to that of a single crystal, but it is particularly preferable to have a crystal structure as shown below.

At room temperature after film formation, the piezoelectric thin film 10 of this embodiment is triaxially oriented and has a domain structure including a plurality of types (at least two types) of crystal phases and at least three types of domains (regions). Take. For example, in the case of a piezoelectric material having a perovskite structure, the crystal phase may include at least two types of crystal phases selected from tetragonal, rhombohedral, orthorhombic, and monoclinic. Further, each of the at least three types of domains (regions) is composed of one of the above-mentioned crystal phases.

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 can have at least two types of crystal phases: tetragonal and rhombohedral. In this case, 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. Further, the rhombohedral crystal phase is oriented such that the (100) plane is parallel to the film thickness direction. That is, when the piezoelectric thin film 10 is an epitaxially grown film of PZT, it includes 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.

In addition, when the piezoelectric thin film 10 is an epitaxially grown film of PZT, the ratio of each domain is preferably such that the ratio of rhombohedral crystals is higher than the ratio of tetragonal crystals, and the ratio of rhombohedral crystals to the proportion of tetragonal crystals is higher. The ratio of abundance ratio (rhombohedral/tetragonal) is preferably greater than 1 and approximately 1 to 20. Further, the ratio of the abundance ratio of the tetragonal c domain to the abundance ratio of the tetragonal a domain (c domain/a domain) is preferably 0.5 to 2.

On the other hand, when the piezoelectric thin film 10 is an epitaxially grown KNN film, it can have two types of orthorhombic domains and one type of monoclinic domain (three types of domains in total). In the above case, the two types of orthorhombic domains are a domain (a domain) in which the (001) plane of the orthorhombic crystal is oriented approximately parallel to the film thickness direction, and a domain (a domain) of the orthorhombic crystal. 010) domains (c domains) whose planes are oriented substantially parallel to the film thickness direction may exist. Further, in the monoclinic domain, it is preferable that the (100) plane or the (010) plane be substantially parallel to the film thickness direction.

When the piezoelectric thin film 10 is KNN, the ratio of each domain is, for example, the ratio of the monoclinic crystal to the orthorhombic crystal (monoclinic/orthorhombic) from 0.1 to Preferably it is 10. Further, it is preferable that the abundance ratio of the orthorhombic c domain to the abundance ratio of the orthorhombic a domain is 0.1 to 10.

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 this case, the ratio of each domain is preferably such that the ratio of the orthorhombic crystal to the tetragonal crystal (orthorhombic/tetragonal) is 0.1 to 10. Further, it is preferable that the abundance ratio of the tetragonal c domain to the abundance ratio of the tetragonal a domain is 0.1 to 10. Furthermore, it is preferable that the abundance ratio of the orthorhombic c domain to the abundance ratio of the orthorhombic a domain is 0.1 to 10.

Furthermore, since the multiple domains mentioned above are in contact with each other across a common domain boundary, the orientation of the crystal axis of each domain is at most several degrees from the film thickness direction or in-plane direction (specifically, (approximately ±3 degrees) deviation is acceptable. 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 confirmed in the range of 2θ=42° to 46°. 4A to 4C are schematic diagrams schematically showing reflection peaks originating from the piezoelectric thin film 10.

When only a single domain exists in the piezoelectric thin film 10, a reflection peak as shown in FIG. 4C appears. In FIG. 4C, only a sharp single reflection peak is confirmed in the range of 2θ = 42° to 46° (especially around 2θ = 44°), and the half-width of the reflection peak is approximately 0.1° or 0. .1° or less. On the other hand, when a plurality of types of domains coexist in the piezoelectric thin film 10, a reflection peak shown in FIG. 4A or 4B appears.

In FIG. 4A, multiple (at least three) reflection peaks originating from the piezoelectric thin film 10 are confirmed in the range of 2θ=42° to 46°. In FIG. 4A, the number of reflection peaks corresponds to the number of domains included in the piezoelectric thin film 10. For example, when the PZT piezoelectric thin film 10 has three types of domains, a reflection peak (P1) indicating a tetragonal c domain appears at 2θ = 43° to 44°, and a rhombohedral c domain appears at 2θ = 44°. A reflection peak (P2) indicating a crystal domain appears, and a reflection peak (P3) indicating a tetragonal a domain appears at 2θ=44° to 45°.

Furthermore, even if multiple reflection peaks are not confirmed, as shown in FIG. 4B, a broad reflection peak may be observed in the 2θ range of 42° to 46°. In the case of FIG. 4B, a plurality of reflection peaks overlap, resulting in a broad reflection peak. Specifically, if the half width of the reflection peak is 0.2° or more, it is determined that at least three types of domains exist.

For example, when the piezoelectric thin film 10 is a PZT film, a broad reflection peak having a peak top near 2θ of 44°±1° may be observed. When the piezoelectric thin film 10 is a KNN film or a BCZT film, a broad reflection peak having a peak top near 2θ of 45.5°±1° may be observed. For any material, if the half width of the reflection peak is 0.2° or more, it is determined that at least three types of domains exist. In the case of FIG. 4B, the upper limit of the half-width is about 1.0° or less because the piezoelectric thin film 10 is an epitaxially grown film.

Furthermore, the abundance ratio of each domain can be determined by observing the domains using a transmission electron microscope. Specifically, using a transmission electron microscope, the domains are observed from the cross section or top surface of the membrane in an area equivalent to 1 um x 10 um, and the area ratio of each domain is determined, which is used as the abundance ratio of the domains. In addition, in TEM observation, when the observation range in one field of view is smaller than the above-mentioned area, observation may be performed in a plurality of fields of view, and the total area may be made equal to the above-mentioned area. In addition to the above, the proportion of each domain can also be determined by reciprocal lattice map measurement using XRD or electron beam diffraction, or crystal orientation distribution analysis (ODF analysis) based on pole point measurement.

(Lower electrode film 50)
The lower electrode film 50 is made of a conductive material, and is preferably a film epitaxially grown on the substrate 40. That is, the lower electrode film 50 is preferably an epitaxially grown film in which the crystal axes are aligned in all three directions. Specifically, the material of the lower electrode film 50 is, for example, a metal thin film with a face-centered cubic structure such as platinum (Pt), iridium (Ir), or gold (Au), or strontium ruthenate (SrRuO ₃ : hereinafter abbreviated as SRO). ) or lithium nickelate (LiNiO ₃ ). Such a metal thin film and an oxide conductor thin film can be epitaxially grown on the substrate 40, and become a film in which the (100) plane is oriented in the film thickness direction. Further, the overall thickness of the lower electrode film 50 is preferably 30 nm to 200 nm.

Note that the lower electrode film 50 may be constructed by laminating the above metal thin film and the above oxide conductor thin film. In that case, the metal thin film and the oxide conductor thin film in the lower electrode film 50 are both epitaxially grown films, and the oxide conductor thin film is on the upper side of the lower electrode film 50 (that is, on the piezoelectric thin film 10 side). Preferably present.

(Top electrode film 52)
The upper electrode film 52 only needs to be made of a conductive material, and may have the same structure as the lower electrode film 50, but does not necessarily need to be an epitaxially grown film. The upper electrode film 52 preferably includes a ferromagnetic thin film having magnetostrictive properties. The ferromagnetic thin film may constitute the upper electrode film 52 by itself, or may constitute a part of the upper electrode film 52 in combination with the above metal thin film or the above oxide conductor thin film. Also good.

When the upper electrode film 52 is composed of a combination of a metal thin film or an oxide conductor thin film and a ferromagnetic thin film, it is preferable to stack the layers so that the ferromagnetic thin film is located at the top layer. When the upper electrode film 52 includes a ferromagnetic thin film, the thickness of the ferromagnetic thin film is preferably 0.1 to 5 μm. In this case, the thickness of the metal thin film other than the ferromagnetic thin film in the upper electrode film 52 or the thickness of the oxide conductor thin film is preferably 3 nm to 100 nm.

The ferromagnetic thin film is made of a pure metal such as iron (Fe), cobalt (Co), or nickel (Ni), or an alloy containing at least one of the above metal elements (for example, Fe-Co series, Fe-Ni series). , Fe-Si system, Fe-Si-Al system alloy, etc.), or an oxide magnetic material containing an oxide of the above metal element. Further, the ferromagnetic thin film may be a single film containing the above-mentioned ferromagnetic material, a multilayer film consisting of multiple layers, or a laminated film of a ferromagnetic material and an antiferromagnetic material. good.

In this embodiment, the ferromagnetic thin film is preferably a magnetostrictive film. This film has magnetostrictive characteristics that cause large strain to occur even when a weak magnetic field is applied to the ferromagnetic thin film from the outside. More specifically, the ferromagnetic thin film is preferably a magnetostrictive film that generates a strain of 0.1 ppm or more in the in-plane direction of the film when a magnetic field smaller than 1 Oe is applied. Further, it is preferable that the magnetostrictive film exhibits a strain greater than 10 ppm when a magnetic field of 80 Oe is applied. Furthermore, it is preferable that the ferromagnetic thin film has compressive stress. This compressive stress is preferably 10 MPa or more, more preferably 30 MPa or more. By laminating such a ferromagnetic thin film with the piezoelectric thin film 10, three types of domains can be easily formed in the piezoelectric thin film 10. Note that the case where the element 30 includes a ferromagnetic thin film will be described in detail in the second embodiment.

(Extraction electrode film 51, 53)
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.

(Insulating film 54)
The insulating film 54 also 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 SiO ₂ , Al ₂ O ₃ , polyimide, or the like.

(Other functional membranes)
In addition to the electrode films 50 to 53 and the piezoelectric thin film 10 described above, the element 30 of this embodiment may include other functional films not shown in FIGS. 1 to 3.

For example, a buffer layer may be formed as a crystallinity control film below the lower electrode film 50 in the Z-axis direction (that is, between the substrate 40 and the lower electrode film 50). The buffer layer preferably contains zirconium oxide (ZrO ₂ ) or zirconium oxide (stabilized zirconia) stabilized with a rare earth element (including Sc and Y) as a main component. This buffer layer is also preferably an epitaxially grown film that is grown aligned 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 film-forming substrate. . By forming the buffer layer, the epitaxial growth of the film located above the buffer layer in the stacking direction is promoted (higher quality is achieved). 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 above the upper electrode film 52 in the Z-axis direction (or above the ferromagnetic thin film if it is included). The protective layer preferably has insulating properties, but for example, 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. The thickness is not particularly limited, and may be approximately 10 nm.

Next, an example of a method for manufacturing the element 30 shown in FIGS. 1 to 3 will be described below.

In manufacturing the element 30, first, a lower electrode film 50, a piezoelectric thin film 10, and an upper electrode film 52 are formed on a substrate 40 such as a silicon wafer using various thin film manufacturing methods. As a thin film manufacturing method, a vapor deposition method, a sputtering method, a sol-gel method, a CDV method, a PLD method, etc. can be applied, and a sputtering method is particularly preferable. Note that, as described above, at least the layers up to the piezoelectric thin film 10 are preferably formed by epitaxial growth. Any known method may be used to epitaxially grow the lower electrode film 50 (and the buffer layer).

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, distance between substrate targets, etc. must be appropriately controlled. .

Further, in order for the piezoelectric thin film 10 to have a domain structure (including at least three types of domains), the composition of the sputtering target, the substrate temperature, or the lamination when the upper electrode film 52 has a ferromagnetic thin film are particularly important. What is necessary is to control the stress of the ferromagnetic thin film, etc.

For example, depending on the material, the composition of the sputtering target should be selected so that multiple domains and crystal phases are likely to be formed, and the content of elements with high vapor pressure should be 20 to 120% higher than the stoichiometric composition. is preferred. Taking PZT as an example, the atomic ratio expressed by Pb/(Zr+Ti) is 1.2 to 2.2, and the atomic ratio expressed by Zr/(Zr+Ti) is 1 to 1.5. Preferably controlled. Further, the substrate temperature is preferably controlled to be 550 to 650°C. Further, in the case where the upper electrode film 52 includes a ferromagnetic thin film, it is preferable that the stress of the ferromagnetic thin film be compressive stress. In addition, it is also effective to perform an annealing treatment at a temperature of 300° C. to 500° C. in an oxidizing atmosphere after epitaxially growing the piezoelectric thin film 10 to obtain the above-described domain structure.

The substrate on which the laminated film is formed as described above is subjected to patterning so as to form a pattern as shown in FIG. A known method can be used for patterning. At this time, in the plane (XY plane) of the film stack 32, the longitudinal direction (X-axis direction) or the transverse direction (Y-axis direction) of the element 30 is the <110> direction of the piezoelectric thin film 10, and It is preferable to pattern the pattern so that it is substantially parallel to the <110> direction of the substrate 40. That is, in the XY plane shown in FIG. 1, the <110> direction of the piezoelectric thin film 10 is approximately parallel to the X-axis direction or the Y-axis direction. Further, the <110> direction of the substrate 40 is also approximately parallel to the X-axis direction or the Y-axis direction. Note that in the above, substantially parallel means within a range of ±3 degrees with respect to a completely parallel direction.

Here, the <110> direction means a direction that comprehensively indicates equivalent directions such as [110] and [101]. The orientation equivalent to the above is, for example, in the case of a cubic crystal,

Examples include. As mentioned above, when the piezoelectric thin film 10 is PZT, it contains multiple phases such as tetragonal and rhombohedral, but in this case, the [110] direction, [101] direction of the tetragonal crystal, It is preferable that the [110] direction of the rhombohedral crystal and a direction equivalent thereto are substantially parallel to the longitudinal direction or the lateral direction of the element 30, respectively. By controlling the longitudinal direction (patterning shape) of the element to match the predetermined crystal orientation of the piezoelectric thin film 10, the durability of the element 30 is improved. In this embodiment, round brackets represent Miller indices (planes), and triangular brackets and square brackets represent crystal orientations (directions).

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, the opening 42 of the substrate 40 is formed by dry etching such as the Deep-RIZ method, anisotropic wet etching, or the like. As a result, the element 30 shown in FIGS. 1 to 3 is obtained.

(Summary of the first embodiment)
As described above, in the element 30 of this embodiment, the piezoelectric thin film 10 is a film that is epitaxially grown so as to be aligned in all three axes, and has at least three types of domains.

When the piezoelectric thin film is a polycrystalline film, many grain boundaries exist within the film. In this case, diffusion of physical quantities occurs due to grain boundaries, resulting in a decrease in piezoelectric properties. Furthermore, even if the piezoelectric thin film has a single orientation in the film thickness direction, the crystal orientation is random within the plane (in this case, it is not called an epitaxially grown film in this embodiment). There are many grain boundaries in the plane. Therefore, even in this case, physical quantity diffusion occurs due to grain boundaries, and piezoelectric properties deteriorate.

Furthermore, if the piezoelectric thin film is a perfect single crystal, or even if the piezoelectric thin film is an epitaxially grown film, if there are only two or less types of domains, strain will be less likely to occur inside the film. Piezoelectric properties may deteriorate.

On the other hand, the piezoelectric thin film 10 of the present embodiment is triaxially oriented and has at least three types of domains, so there is no crystal mismatch that hinders wall movement at domain boundaries or crystal phase boundaries. not exist. As a result, in the element 30 of this embodiment, domain rotation and crystal phase transition occur smoothly when voltage, stress, etc. are applied from the outside, and piezoelectric responsiveness to external inputs (voltage, stress, etc.) is improved. It gets expensive. That is, in the element 30 of this embodiment, a high piezoelectric constant (d31) can be obtained. Furthermore, in the element 30 of this embodiment, the withstand voltage of the piezoelectric thin film 10 is increased, and the linearity of the piezoelectric characteristics is also improved.

The element 30 of this embodiment is connected to a power source and an electric/electronic circuit, and is mounted on a circuit board or packaged to constitute various electronic devices. For example, it can be used as various piezoelectric devices such as inkjet printer heads, microactuators, gyroscopes, and motion sensors. When used as various actuators, since the element 30 of this embodiment has excellent piezoelectric properties, piezoelectric distortion is more likely to occur when a voltage is applied. As a result, the displacement characteristics of the actuator are improved.

Further, the element 30 of this embodiment exhibits excellent performance as a magnetoelectric transducer because the film stack 32 further includes a ferromagnetic thin film. At this time, the ferromagnetic thin film preferably has magnetostrictive characteristics, and is preferably configured to expand and contract in the in-plane direction by an external magnetic field. Such magnetoelectric conversion elements can be used as various sensors such as magnetic sensors by connecting an amplifier and a rectifier circuit and packaging them. It can also be applied to constant voltage driven memories. Similarly, if a power storage element and a rectifying power management circuit are connected to the magnetoelectric conversion element, it becomes an energy conversion device (energy harvester) that generates electricity from external magnetic fields and vibrations.

When used as a memory, since the element 30 of this embodiment has excellent piezoelectric properties, the magnetization of the ferromagnetic thin film can be changed with a small driving voltage. Further, when used as various sensors as described above, the piezoelectric thin film 10 is easily deformed in response to external mechanical input (stress, etc.), so characteristics such as sensitivity and detection limit are improved.

The energy conversion devices described above are used by being incorporated into power supply systems and wearable devices (earphones/hearable devices, smart watches, smart glasses, smart contact lenses, cochlear implants, cardiac pacemakers, etc.). .

Second Embodiment In the second embodiment, a case in which a ferromagnetic thin film is particularly included in the film stack portion 32 of the element 30 shown in FIGS. 1 to 3 will be described. As described in the first embodiment, the ferromagnetic thin film becomes the upper electrode film 52 itself, or is formed above the metal thin film or the oxide conductor thin film and forms a part of the upper electrode film 52. Note that for the configurations in the second embodiment that are common to those in the first embodiment, explanations will be omitted and the same reference numerals will be used.

The device 30 of the second embodiment functions as a magnetoelectric transducer 30 because the film stack 32 includes a ferromagnetic thin film. The magnetoelectric conversion element 30 receives energy such as a magnetic field, electromagnetic waves, and ultrasonic waves that are transmitted from a distance without contact, and converts these energies (input signals) into electrical output. For example, when a magnetic field is applied from the outside, a ferromagnetic thin film generates strain due to the magnetostrictive effect. Due to the strain generated here, the piezoelectric thin film 10 located below the ferromagnetic thin film also bends, and charges are generated on the surface of the piezoelectric thin film 10 due to the piezoelectric effect. The generated charges are taken out as electrical output via the first electrode film 50 and the second electrode film 52.

When such a magnetoelectric conversion element 30 is manufactured in the form shown in FIGS. Functions as a stretching oscillator. Here, the term "in-plane expansion/contraction vibrator" means a vibrator that utilizes an in-plane expansion/contraction mode that occurs in the in-plane direction of an elastic body. In FIGS. 1 to 3, a rectangular shape is shown as the vibrator, but other shapes such as a disk shape, a cantilever shape, etc. can be taken. Preferably, the shape is rectangular as shown in FIGS. 1 to 3.

When focusing on the function as a vibrator, the membrane laminated part 32 in which the lower electrode film 50, the piezoelectric thin film 10, and the upper electrode film 52 are laminated becomes the vibrating part 32, and the end part 50a of the lower electrode film 50 and A portion where the end portions of the piezoelectric thin film 10 are laminated (particularly a portion supporting the vibrating portion 32 above the opening portion 42) serves as a support portion (or support arm) 36. The support portion 36 connects the vibrating portion 32 and the outer peripheral portion 34 of the element 30.

It is preferable that the support part 36 has a form with low rigidity relative to the vibrating part 32 so as not to hinder the movement (in-plane stretching vibration) of the vibrating part 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 32 in the Y-axis direction (the length in the direction perpendicular to the X-axis direction in which the support portion 36 extends). Alternatively, the thickness of the support portion 36 in the Z-axis direction is made smaller than the thickness of the vibrating portion 32 in the Z-axis direction. The product of the thickness and width of the support section 36 is preferably smaller than 90% of that of the vibrating section 32, and more preferably smaller than 75%. With this configuration, in-plane stretching vibration with large amplitude can be induced, and the output of the magnetoelectric transducer 30 can be increased.

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

Furthermore, it is preferable that the surface of the vibrating section 32 (that is, the surfaces of the upper electrode film 50 and the lower electrode film 52) be 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 wavelength of vibration transmitted through the vibrating section 32. It is more preferable that

The width of the element 30 in the vibration direction (in the case of in-plane stretching vibration, the Y-axis direction) is extremely small compared to the wavelength of electromagnetic waves of the same frequency because the vibrating part 32 vibrates at the wavelength of sound waves, which have a slower speed than electromagnetic waves. Preferably the size. Specifically, the width of the element 30 in the vibration direction is preferably smaller than 1/10 of the wavelength of electromagnetic waves in vacuum. On the other hand, the size of the element is not limited in the direction perpendicular to the vibration direction (that is, the It can also take a shape.

As described above, in the second embodiment, the ferromagnetic thin film has magnetostrictive characteristics and is configured to expand and contract in the in-plane direction (that is, in the XY plane direction). In this case, the vibration mode of the vibrator becomes an in-plane contour mode, and Q, which is a characteristic representing the sharpness of vibration, increases. By adopting a vibration mode with a large Q in the element 30, a larger output can be obtained and energy can be efficiently converted into electric power.

Note that Q can be expressed by the following formula.
Q=f0/(f1-f2)
In the above formula, f0 is the natural frequency of the vibrator, f1 is the higher frequency among the frequencies at which the output or amplitude becomes half of the value at the natural frequency, and f2 is the lower frequency. The element 30 of this embodiment has a Q larger than 100.

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

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

In the second embodiment, the ferromagnetic thin film included in the film lamination section 32 (vibrating section 32) preferably has particularly excellent magnetostrictive effects. The magnetostrictive effect refers to the property of generating distortion due to an external magnetic field. Many ferromagnetic materials exhibit a magnetostrictive effect, but materials that have a relatively large magnetostrictive effect include iron, gallium (Ga), boron (B), silicon (Si), or rare earth elements (samarium (Sm), Examples include alloys to which dysprosium (Dy), terbium (Tb), holmium (Ho), erbium (Er), etc. are added, and Fe-Dy-Tb alloys and Fe-Ga alloys are generally known. ing. In this embodiment, it is particularly preferable to use an Fe--Co alloy, a Fe--Co--Si--B-based alloy, a Fe--Ga--B-based alloy, or the like as the main component constituting the ferromagnetic thin film.

Furthermore, the thickness t2 of the ferromagnetic thin film is preferably within the range of 0.1 to 5 μm, as described in the first embodiment. By setting the film thickness as described above, it becomes possible to sufficiently distort the piezoelectric thin film 10, and a large electrical output can be obtained from the piezoelectric thin film 10. Further, by controlling the thickness t2 of the ferromagnetic thin film not to be too thick, the productivity of film formation is also improved.

Note that the thickness t2 of the ferromagnetic thin film is also measured in the same manner as the thickness t1 of the piezoelectric thin film 10. 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.

In the second embodiment, the ferromagnetic thin film may be amorphous or polycrystalline, but it is preferable to have a mixture of an amorphous phase and a crystalline phase. When the ferromagnetic thin film contains both an amorphous phase and a crystalline phase, the response to an input magnetic field can be improved due to the characteristics of the amorphous phase. In other words, the threshold magnetic field _HTH and coercive force Hc required to generate magnetostriction can be reduced. Moreover, due to the characteristics of the crystalline phase, dλ/dH (magnetostriction change per unit magnetic field) can be increased in a low magnetic field.

Further, when the ferromagnetic thin film has a crystalline phase, it is preferable that most of the included crystalline phases have a face-centered cubic structure (fcc). However, at least some of the crystal phases may include a body-centered cubic structure (BCC) crystal phase. By setting the crystal phase of the ferromagnetic thin film to have a face-centered cubic structure (fcc), the conversion efficiency from magnetism to electricity in the element 30 is further increased.

The ferromagnetic thin film is formed directly or indirectly on the piezoelectric thin film 10, but if the underlying piezoelectric thin film 10 is an epitaxially grown film with excellent crystal orientation, the ferromagnetic thin film is usually also crystalline. It becomes easier to become In particular, when a ferromagnetic thin film contains iron, it is usually crystallized in a body-centered cubic structure. In forming a ferromagnetic thin film, an amorphous phase and a crystalline phase having a face-centered cubic structure can coexist by appropriately selecting a film-forming device and film-forming conditions.

For example, it is preferable to laminate a polycrystalline electrode film made of a conductive material or an electrode film made of polycrystalline and amorphous phases between the ferromagnetic thin film and the piezoelectric thin film 10. That is, in the upper electrode film 52, the above electrode film is laminated below the ferromagnetic thin film. In particular, this electrode film 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. Such an electrode film also functions as a crystallinity control layer for controlling the crystallinity of the ferromagnetic film. Therefore, by forming a ferromagnetic thin film on the piezoelectric thin film 10, which is an epitaxially grown film, via a crystallinity control layer (electrode film), the amorphous phase and the face-centered cubic structure crystal phase can be separated. A ferromagnetic thin film can be formed.

The crystal structure of the ferromagnetic thin film can be confirmed by analysis using TEM electron beam diffraction or X-ray diffraction (XRD). For example, when measuring θ-2θ using Cu-Kα rays using XRD, a reflection peak derived from the ferromagnetic thin film as shown in FIG. 5 is confirmed. In FIG. 5, the reflection peak when the ferromagnetic thin film contains both an amorphous phase and a crystalline phase is indicated by a solid line ex1. Furthermore, the reflection peak when the ferromagnetic thin film is composed of only an amorphous phase is shown by a broken line ce1, and the reflection peak when the ferromagnetic thin film is composed of only a crystalline phase is shown by a dashed line ce2. .

As shown by the broken line ce1 in Figure 5, when the ferromagnetic thin film is composed of only an amorphous phase, no sharp peaks due to the periodic arrangement structure are detected, and only a broad halo pattern is detected. appears. Further, as shown by the dashed line ce2 in FIG. 5, when the ferromagnetic thin film is composed of only a crystalline phase, only an extremely sharp reflection peak with a narrow half-width is detected.

On the other hand, when the ferromagnetic thin film contains both an amorphous phase and a crystalline phase, as shown by the solid line ex1 in FIG. , a reflection peak having a sharp peak portion indicating the presence of a crystalline phase is detected. Note that the crystal structure of the crystal phase (whether it is a face-centered cubic structure or not) can be determined by analyzing the above-mentioned diffraction pattern.

In addition, when the ferromagnetic thin film contains both an amorphous phase and a crystalline phase, the ratio of the amorphous phase to the crystalline phase can be determined by profile fitting to the reflection peak shown in FIG. This can be confirmed by calculating . Specifically, in the reflection peak shown in FIG. 5, a crystal 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). When the ferromagnetic thin film contains both an amorphous phase and a crystalline phase, the crystallinity of the ferromagnetic thin film is preferably 1% to 50%, more preferably 5% to 20%.

The magnetoelectric conversion element 30 in the second embodiment can also be manufactured by the same method as in the first embodiment. In the second embodiment, a method for forming a ferromagnetic thin film will be particularly described.

Like the piezoelectric thin film 10, the ferromagnetic thin film can also be formed by various thin film manufacturing methods, but it is particularly preferable to employ the sputtering method. Further, the ferromagnetic thin film is formed by a thin film method directly above the piezoelectric thin film 10 or on a metal thin film or an oxide conductor thin film. However, as described above, when the ferromagnetic thin film is a layer containing both an amorphous phase and a crystalline phase, a metal thin film may be formed between the piezoelectric thin film 10 and the ferromagnetic thin film. is preferred. Furthermore, the amorphous phase and the crystalline phase can be mixed by appropriately controlling film forming conditions such as degree of vacuum, substrate temperature, gas composition, gas pressure, power, and substrate distance during sputtering. For example, the degree of vacuum is preferably 0.01 to 0.1 Pa, and the substrate temperature is preferably 20 to 200°C. Particularly, in order to make the crystal phase have a face-centered cubic structure, it is preferable to keep the distance between the target and the substrate at least 100 mm without heating the substrate, and to maintain the substrate temperature at 200° C. or less during film formation.

As described above, when the film stack 32 of the element 30 includes a ferromagnetic thin film, the element 30 can be effectively used as a magnetoelectric transducer that satisfies both high conversion efficiency and excellent detection sensitivity. be able to. In the magnetoelectric conversion element 30 of the second embodiment, the configuration other than the above is common to the element 30 of the first embodiment, and the same effects as those of the first embodiment are achieved. Note that the present invention is not limited to the embodiments described above, and can be variously modified within the scope of the present invention.

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

Experiment 1
(Example 1)
In Example 1, an electronic device substrate constituting the element 30 was manufactured using the procedure shown below. First, a silicon wafer (silicon substrate) having a single crystal surface with an Si (100) plane was prepared as a substrate. The size of the prepared silicon wafer was 6 inches. A laminated film shown below is formed on this silicon wafer.

First, a base oxide thin film made of ZrO ₂ and Y ₂ O ₃ (which functions as a buffer layer), a Pt lower electrode film, and a conductive oxide thin film made of SrRuO ₃ (hereinafter referred to as SRO) are deposited on silicon. Epitaxial growth was performed on the substrate. At this time, a sputtering method was adopted as the thin film manufacturing 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 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 SrRuO ₃ was formed. The film thicknesses of each layer were adjusted so that the base oxide thin film was 50 nm, the Pt lower electrode film was 50 nm, and the conductive oxide thin film was 50 nm. In Example 1, the lower electrode film 50 is composed of a Pt lower electrode film and a conductive oxide thin film (SRO).

In Example 1, a PZT piezoelectric thin film 10 was epitaxially grown on a conductive oxide thin film. At this time, the composition of the sputtering target used 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. In addition, the introduced gas 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, the distance between the substrate and target was 200 mm, and the film thickness was 1 μm. A PZT film was formed.

Further, the 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, a Pt upper electrode film with a thickness of 100 nm was formed by sputtering. At this time, the substrate temperature was set at 200° C., which is sufficiently lower than the epitaxial growth temperature, so that the Pt upper electrode film becomes a polycrystalline film. Further, when forming the Pt upper electrode film, argon (Ar) was used as the gas introduced for sputtering, and the pressure during film formation was 0.3 Pa.

After forming the Pt upper electrode film, the substrate was once taken out into the atmosphere, and the Pt surface was exposed to oxygen in the air. Then, the substrate is introduced into an ultra-high vacuum DC sputtering device, and after the inside of the device is evacuated to a degree of vacuum of 1×10 ⁻⁴ Pa or less (preferably 5×10 ⁻⁵ Pa or less), a ferromagnetic material made of FeCo alloy is A thin body membrane was formed. The composition of the target used for film formation was 50% Fe-50% Co in molar ratio. Furthermore, during film formation, the substrate was not heated, and the film was formed with a sufficient distance between the target and the substrate so as not to increase the substrate temperature. Other conditions were as follows: Ar gas was used as the introduced gas, the pressure during film formation was 0.02 Pa, the output was 150 W (DC), and a ferromagnetic thin film with a thickness of 500 nm was formed.

In Example 1, the ferromagnetic thin film and the Pt upper electrode film constitute the upper electrode film 52. After forming the ferromagnetic thin film, a polycrystalline titanium (Ti) film with a thickness of 10 nm was further formed thereon as a protective layer. The electronic device substrate according to Example 1 was obtained by forming each layer using such a procedure.

The crystal structure of the produced electronic device substrate was also confirmed after film formation by XRD and TEM electron diffraction. As a result, it was confirmed that each layer from the underlying oxide thin film to the PZT film was epitaxially grown with alignment in three axes. In particular, in the XRD analysis of the PZT film, a reflection peak due to the PZT film as shown in FIG. 4B was confirmed. Specifically, this reflection peak had a peak top at a 2θ of 44.05°, and a half width of 0.21°. No other peaks due to the PZT film were observed in the 2θ range of 42° to 46°.

Furthermore, when reciprocal lattice map measurements were performed using XRD, it was found that in the PZT film of Example 1, a domain (c domain) in which the tetragonal (100) plane was oriented in the film thickness direction, and a domain (c domain) in which the tetragonal (001 plane) was oriented in the film thickness direction. A domain in which the (100) plane of a rhombohedral crystal was oriented was confirmed. Further, the ratio of each domain expressed as "tetragonal c domain: tetragonal a domain: rhombohedral domain" was 1:1:8.

In addition, in the above crystal structure analysis, it was confirmed that the Pt upper electrode film is a polycrystalline film, and the FeCo alloy film is a film in which an amorphous phase and a face-centered cubic structure crystal phase coexist. I was able to confirm something.

(Example 2)
In Example 2, a base oxide thin film, a Pt lower electrode film, and a conductive oxide thin film made of SrRuO ₃ (hereinafter referred to as SRO) were formed on a silicon substrate in the same manner as in Example 1. It was filmed. However, in Example 2, the film forming conditions after the PZT film are different from Example 1. The manufacturing conditions in Example 2 will be explained below.

In Example 2, after forming a conductive oxide thin film (SRO), the substrate was once taken out into the atmosphere, and then a 1 μm thick PZT film was formed by a multi-dimensional vapor deposition method. Specifically, in film formation using the multi-component vapor deposition method, first, a substrate was placed into an apparatus, and then the inside of the apparatus was evacuated to 1×10 ⁻⁴ Pa to create a vacuum state. Thereafter, oxygen gas was introduced into the apparatus, the pressure inside the apparatus was set to 1×10 ⁻² Pa, and film formation was performed while maintaining this pressure. At this time, the substrate was kept heated to 600°C. Further, in forming the PZT film, the raw material gas was controlled so that the ratio of raw material components (Pb:Zr:Ti) supplied to the substrate surface was 2.2:0.52:0.48.

Further, the 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.

Thereafter, a 100 nm thick Pt upper electrode film was formed on the PZT film by sputtering. The conditions for forming the Pt upper electrode film were the same as in Example 1.

Furthermore, in Example 2, a ferromagnetic thin film made of FeCoSiB alloy was formed on the Pt upper electrode film. The FeCoSiB alloy film was also formed using an ultra-high vacuum DC sputtering device after evacuation to a degree of vacuum of 1×10 ⁻⁴ Pa (more preferably 5×10 ⁻⁵ Pa) or less. The composition of the target used for film formation was 70% Fe-8% Co-12% Si-10% B in terms of molar ratio. Furthermore, during film formation, the substrate was not heated, and the film was formed with a sufficient distance between the target and the substrate so as not to increase the substrate temperature. Other film forming conditions were as follows: Ar gas was used as the introduced gas, the pressure of the introduced gas was 0.05 Pa, the output was 150 W (DC), and a FeCoSiB alloy film with a thickness of 500 nm was formed. As a result of measuring the stress of the FeCoSiB alloy film from the change in the amount of warpage of the substrate before and after film formation, it was confirmed that this film had a compressive stress of 35 MPa.

An electronic device substrate according to Example 2 was obtained by the manufacturing method described above. When crystal structure analysis was performed on the electronic device substrate of Example 2 in the same manner as in Example 1, it was found that each layer from the base oxide thin film to the PZT film was epitaxially grown with uniform orientation in the three axes. It was confirmed that it was a membrane. In particular, in the XRD analysis of the PZT film of Example 2, a reflection peak due to the PZT film as shown in FIG. 4A was confirmed. Specifically, in Example 2, three reflection peaks originating from the PZT film were observed in the 2θ range of 42° to 46°. The peak top positions of these three reflection peaks were 43.75°, 44.10°, and 44.60°, respectively, and the half-value widths were all 0.12°.

Furthermore, when reciprocal lattice map measurements were performed using XRD, it was found that in the PZT film of Example 2, a domain (c domain) in which the tetragonal (100) plane was oriented in the film thickness direction, and a domain (c domain) in which the tetragonal (001 plane) was oriented in the film thickness direction. A domain in which the (100) plane of a rhombohedral crystal was oriented was confirmed. Further, in Example 2, the ratio of each domain expressed as "tetragonal c domain: tetragonal a domain: rhombohedral domain" was 2:1:7.

In addition, in Example 2, it can be confirmed that the Pt upper electrode film is a polycrystalline film, and the FeCo alloy film is a film in which an amorphous phase and a crystalline phase with a face-centered cubic structure coexist. was confirmed.

(Comparative example 1)
In Comparative Example 1, a FeCo alloy film was formed directly on the PZT film without forming a Pt upper electrode film, and an electronic device substrate according to Comparative Example 1 was manufactured. In forming the FeCo alloy film, the inside of the vapor deposition apparatus was evacuated to 3×10 ⁻⁴ Pa, and the substrate temperature was set to 300° C. to form the film. Similarly to Example 1, the FeCo alloy film of Comparative Example 1 also has a thickness of 500 nm. In Comparative Example 1, the films from the base oxide thin film to the PZT film were formed in the same manner as in Example 1. However, in Comparative Example 1, no annealing treatment was performed after forming the PZT film.

Crystal structure analysis was performed on the electronic device substrate of Comparative Example 1 in the same manner as in Example 1, and it was found that in Comparative Example 1, each layer from the base oxide thin film to the PZT film was an epitaxially grown film. was confirmed. However, in the PZT film of Comparative Example 1, no diffraction pattern as shown in FIGS. 4A and 4B could be confirmed. Specifically, in the PZT film of Comparative Example 1, two reflection peaks were confirmed at positions where 2θ is 44.02° and 44.88°, and the half-widths of these reflection peaks were respectively 0. They were 18° and 0.14°. Further detailed analysis revealed that in the PZT film of Comparative Example 1, only two types of tetragonal a domain and c domain were confirmed, and the ratio of each domain was ``tetragonal c domain: tetragonal a The ratio expressed by "domain" was 3:7.

Note that in Comparative Example 1, the FeCo alloy film was a polycrystalline film.

Rating 1
The piezoelectric constant (d31) of the electronic device substrates of Examples 1 and 2 and Comparative Example 1 was measured. The piezoelectric constant (d31) was measured by cutting out a cantilever test piece with a length of 15 mm and a width of 2 mm from each electronic device substrate, and using the test piece. Specifically, after fixing one end of the cantilever test piece, a voltage of 100 Hz and 0 to 10 V is applied to the piezoelectric thin film 10, and the amount of displacement of the end opposite to the fixed end is measured using a laser displacement meter. It was measured by Then, d31 was determined from the relationship between the applied voltage and the amount of displacement obtained. The measured results are shown in Table 1.

As shown in Table 1, it was confirmed that Examples 1 and 2 had higher piezoelectric constants (d31) than Comparative Example 1. From this result, it was proved that the piezoelectric properties of an electronic device element are improved when the piezoelectric thin film 10 has at least three types of domains.

Experiment 2
In Experiment 2, a predetermined patterning process was applied to the electronic device substrates of Examples 1 and 2 and Comparative Example 1, and a predetermined circuit was connected to the electronic device samples according to each Example and Comparative Example. Created. Specifically, as electronic device samples, a magnetic sensor having a substantially rectangular element 30 as shown in FIG. 1 and an actuator for minute position control having a cantilever-shaped element 300 as shown in FIG. 6 were fabricated. did.

Regarding the magnetic sensor sample, the dimensions of the film stack 32 of the element 30 are 5 mm (X-axis direction) x 1 mm (Y-axis direction), and the element 30 is equipped with a circuit (amplifier) for detecting the electric charge generated in the piezoelectric thin film 10. and a rectifier circuit) and packaged them. Then, the detection limit value of the magnetic sensor sample was measured according to the procedure shown below.

(Measurement of detection limit value)
The detection limit value (unit: nT) is measured by applying an alternating magnetic field near the natural frequency of the element 30 (approximately 10 kHz) while applying a DC magnetic field of 1 mT as a bias magnetic field to the magnetic sensor sample, and changing the frequency of the alternating magnetic field to It was found by attenuating the size while scanning around the natural frequency. Here, the detection limit value is an index representing the sensitivity of the magnetic sensor. 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. Table 1 shows the results of measuring the detection limit values for the magnetic sensor samples of Examples 1 and 2 and Comparative Example 1.

On the other hand, the actuator sample for minute position control has the following structure more specifically. The actuator element 300 in FIG. 6 includes a membrane stacking section 320 and a fixing section 400 that are substantially rectangular in plan view, and one end of the membrane stacking section 320 is fixed onto the fixing section 400. In the laminated portion 320, the lower electrode film 50, the piezoelectric thin film 10, and the upper electrode film 52 are laminated in this order. Furthermore, a first extraction electrode 510 and a second extraction electrode 530 for external circuit connection are formed in the laminated portion 320. The first extraction electrode 510 has a through-hole electrode portion 510a and is connected to the lower electrode film 50. On the other hand, the second extraction electrode 530 is formed so as to straddle the piezoelectric thin film 10 and the upper electrode film 52 above in the Z-axis direction.

In the actuator sample, the fixing part 400 in FIG. 6 is made of a silicon substrate, the lower electrode film 50 is made of a Pt lower electrode film and an SRO oxide conductor thin film, and the piezoelectric thin film 10 is made of PZT. The upper electrode film 52 is made of a ferromagnetic thin film of FeCoB alloy. Furthermore, in the actuator sample, the length of the membrane stack 320 in the longitudinal direction (X-axis direction) was 5 mm, and the length in the lateral direction (Y-axis direction) was 1 mm. Note that the fixing section 400 may be constructed of a silicon substrate during film formation as in the second embodiment, but it may also be constructed by pasting the film stack section 320 on another member. An external circuit for voltage application was connected to the element 300 shown in FIG. 6 to produce an actuator for minute position control.

In addition, regarding the manufactured actuator sample for minute position control, the amount of displacement with respect to the applied voltage in the longitudinal direction of the element was measured. Specifically, Table 1 shows the results of measuring the amount of displacement for the actuator samples of Examples 1 and 2 and Comparative Example 1.

Evaluation 2
As shown in Table 1, in the case of the magnetic sensor samples, it was confirmed that in Examples 1 and 2, the detection limit value was smaller than in Comparative Example 1, and the sensitivity characteristics were superior. Furthermore, even in the case of the actuator samples, it was confirmed that the displacement amount with respect to the applied voltage was larger in Examples 1 and 2 than in Comparative Example 1. From this result, it was proved that the electronic device having the electronic device element of the present invention has improved performance as a device.

Experiment 3
In Experiment 3, the piezoelectric thin film 10 was made of KNN or BCZT instead of PZT, and electronic device substrates according to Examples 3 and 4 were produced. The details of each example in Experiment 3 will be described below.

(Example 3)
In Example 3, an electronic device substrate was produced in the same manner as in Example 1, except that KNN was used as the piezoelectric thin film 10. Like the PZT film, the KNN film was formed by sputtering to a thickness of 1 μm. At this time, the composition of the target used (ie, the atomic ratio in the KNN film) was 1:1 (Ka:Na).

Crystal structure analysis was performed on the electronic device substrate of Example 3 in the same manner as in Example 1, and it was found that each layer from the underlying oxide thin film to the KNN film was epitaxially grown with alignment in the three axes. It was confirmed that there is. In particular, in the XRD analysis of the KNN film of Example 3, it was confirmed that there was a reflection peak derived from KNN with a half width of 0.30° at a 2θ of 45.52°. Note that no other peaks due to the KNN film were observed in the 2θ range of 42 to 46°.

Furthermore, when a reciprocal lattice map was measured by XRD, a total of three types of domains, two types of orthorhombic domains and one type of monoclinic domain, were confirmed in the KNN film of Example 3. In addition, in the KNN film of Example 3, the ratio of each domain expressed as "orthorhombic c domain: orthorhombic a domain: monoclinic domain" was 1:1:1. there were. In addition, even in the case of Example 3, it was confirmed that the FeCo alloy film was a film in which an amorphous phase and a crystal phase with a face-centered cubic structure coexisted.

(Example 4)
In Example 4, an electronic device substrate was produced in the same manner as in Example 1 except that the piezoelectric thin film 10 was made of BCZT. Like the PZT film, the BCZT film was formed by sputtering to a thickness of 1 μm. At this time, the composition of the target used (i.e., the atomic ratio in the BCZT film) was Ba:Ca:Zr:Ti in an atomic ratio of 0.85:0.15:0.1:0.9. there were.

Crystal structure analysis was performed on the electronic device substrate of Example 4 in the same manner as in Example 1, and it was found that each layer from the base oxide thin film to the BCZT film was epitaxially grown with alignment in the three axes. It was confirmed that there is. In particular, in the XRD analysis of the BCZT film of Example 4, it was confirmed that there was a reflection peak originating from BCZT with a half width of 0.28° at a 2θ of 45.4°. Note that no other peaks due to the BCZT film were observed in the 2θ range of 42 to 46°.

Furthermore, when reciprocal lattice map measurement was performed by XRD, a total of four types of domains, two types of tetragonal domains and two types of orthorhombic domains, were confirmed in the BCZT film of Example 4. In addition, in the BCZT film of Example 4, the ratio of each domain is expressed as "tetragonal c domain: tetragonal a domain: orthorhombic c domain: orthorhombic a domain". The ratio was 1:1:1:1. In addition, even in the case of Example 4, it was confirmed that the FeCo alloy film was a film in which an amorphous phase and a crystal phase with a face-centered cubic structure coexisted.

30... Element (magnetoelectric conversion element)
32... Membrane lamination part (vibrating part)
34...Outer peripheral part 36...Support part (support arm)
40... Substrate 42... Opening 10... Piezoelectric thin film 50... Lower electrode film 50a... End portion 50b... Center portion 51... First extraction electrode film 52... Upper electrode film 53... Second extraction electrode film 54... Insulating film

Claims (9)

An element for an electronic device having a piezoelectric thin film,
The piezoelectric thin film is a film epitaxially grown with triaxial orientation, and has at least three types of domains,
The at least three types of domains are
a domain oriented such that a tetragonal (001) plane is substantially perpendicular to the film thickness direction;
a domain oriented such that the (001) plane of the tetragonal crystal is substantially parallel to the film thickness direction;
a domain oriented such that the (100) plane of the rhombohedral crystal is substantially parallel to the film thickness direction,
The ratio of the abundance ratio of the rhombohedral crystal to the abundance ratio of the tetragonal crystal is greater than 1,
The (100) plane of the tetragonal crystal is substantially perpendicular to the film thickness direction relative to the abundance ratio of domains oriented such that the (001) plane of the tetragonal crystal is substantially parallel to the film thickness direction. The ratio of the proportion of domains oriented to is 0.5 to 2.
Elements for electronic devices . An element for an electronic device having a piezoelectric thin film,
The piezoelectric thin film is a film epitaxially grown with triaxial orientation, and has at least three types of domains,
The at least three types of domains are
a domain oriented such that the (001) plane of the orthorhombic crystal is substantially parallel to the film thickness direction;
a domain oriented such that the (010) plane of the orthorhombic crystal is substantially parallel to the film thickness direction;
a domain oriented such that a monoclinic (100) plane or (010) plane is substantially parallel to the film thickness direction,
The ratio of the monoclinic crystal to the orthorhombic crystal is from 0.1 to 10,
The (010) plane of the orthorhombic crystal is substantially parallel to the film thickness direction relative to the abundance ratio of domains oriented such that the (001) plane of the orthorhombic crystal is substantially parallel to the film thickness direction. The ratio of the proportion of domains oriented in such a manner is 0.1 to 10.
Elements for electronic devices . An element for an electronic device having a piezoelectric thin film,
The piezoelectric thin film is a film epitaxially grown with triaxial orientation, and has at least four types of domains,
The at least four types of domains are
a domain oriented such that the (001) plane of the tetragonal crystal is substantially parallel to the film thickness direction;
a domain oriented such that the (001) plane of the tetragonal crystal is substantially perpendicular to the film thickness direction;
a domain oriented such that the (001) plane of the orthorhombic crystal is substantially parallel to the film thickness direction;
a domain oriented such that the (010) plane of the orthorhombic crystal is substantially parallel to the film thickness direction,
The ratio of the abundance ratio of the orthorhombic crystal to the abundance ratio of the tetragonal crystal is 0.1 to 10,
The (001) plane of the tetragonal crystal is substantially perpendicular to the film thickness direction relative to the abundance ratio of domains oriented such that the (001) plane of the tetragonal crystal is substantially parallel to the film thickness direction. The ratio of the proportion of domains oriented to is 0.1 to 10,
The (010) plane of the orthorhombic crystal is substantially parallel to the film thickness direction relative to the abundance ratio of domains oriented such that the (001) plane of the orthorhombic crystal is substantially parallel to the film thickness direction. The ratio of the proportion of domains oriented in such a manner is 0.1 to 10.
Elements for electronic devices . The electronic device according to claim 1 , wherein the piezoelectric thin film has at least three reflection peaks in a 2θ range of 42° to 46° when θ-2θ X-ray diffraction measurement is performed using Cu-Kα rays. Element for use. The piezoelectric thin film has a single reflection peak in a 2θ range of 42° to 46° when subjected to θ-2θ X-ray diffraction measurement using Cu-Kα rays,
The element for an electronic device according to any one of claims 1 to 3 , wherein the half width of the single reflection peak is 0.2° or more and 1.0° or less . A base layer is formed below the piezoelectric thin film in the stacking direction,
6. The element for an electronic device according to claim 1, wherein the base layer is a film epitaxially grown with triaxial orientation. further comprising a ferromagnetic thin film,
7. The element for an electronic device according to claim 1, wherein the ferromagnetic thin film is configured to expand and contract in an in-plane direction by an external magnetic field. With respect to the longitudinal direction or the lateral direction of the piezoelectric thin film,
The element for an electronic device according to claim 1, wherein the [110] direction of the tetragonal crystal, the [110] direction of the rhombohedral crystal, and a direction equivalent to these of the tetragonal crystal of the piezoelectric thin film are substantially parallel. An electronic device comprising the electronic device element according to any one of claims 1 to 8 .