Thin film device and method for manufacturing thin film device

Abstract

Provided is a thin film device in which distortion is introduced into a thin film by a method different from conventional methods. This thin film device is provided with: a flexible base material (1); and a thin film (2) comprising a ferromagnetic body into which distortion different from that of the flexible base material is introduced.

Description

Thin film device and method for manufacturing the same

[0001] One aspect of the present invention relates to a thin film device and a method for manufacturing the thin film device.

[0002] The properties of solid materials change depending on the spacing between atoms that make up the material. For example, if the solid material is magnetic, the magnetization state (magnetization direction, etc.) of the magnetic material changes depending on the spacing between atoms.

[0003] The atomic spacing of a solid material is naturally determined by various interactions between atoms. In other words, the atomic spacing of a solid material depends on the elemental species that make up the solid material. On the other hand, when the solid material is a nanometer-thick thin film (hereinafter referred to as a nanothin film) formed on a substrate (or underlayer), the atomic spacing can change due to epitaxial strain. Here, epitaxial strain refers to the fact that when a thin film is formed on a substrate using epitaxial growth, the atomic spacing of the thin film becomes different from normal spacing because it attempts to match the lattice composed of atoms in the substrate or underlayer.

[0004] It is also possible to change the atomic spacing by applying an external stress. The magnitude of the external stress can be detected from the change in magnetism based on the change in atomic spacing in response to the external stress. Stress sensors (strain sensors) that detect external stress in this way are widely known, as disclosed in, for example, Patent Document 1.

[0005] Japanese Patent No. 7031023

[0006] The above-mentioned method of introducing epitaxial strain into nano-thin films has the following problems. In most cases, epitaxial strain is a phenomenon observed in single-crystal nano-thin films formed on single-crystal substrates. Therefore, there are problems in that a single-crystal substrate must be prepared, and only materials that can be epitaxially grown on the single-crystal substrate are applicable (i.e., there are limitations on the materials).

[0007] Furthermore, epitaxial strain often has the problem that only isotropic strain or strain dependent on the lattice of the substrate can be introduced (i.e., strain cannot be introduced in a desired direction or magnitude).

[0008] An object of one aspect of the present invention is to provide a thin film device in which strain is introduced into a thin film by a method different from conventional methods.

[0009] In order to solve the above problems, a thin film device includes a flexible substrate and a strain-introduced thin film made of a ferromagnetic material in which a strain different from that of the flexible substrate is introduced.

[0010] In order to solve the above problems, a method for manufacturing a thin film device comprising a flexible substrate and a thin film made of a ferromagnetic material includes a tensioning step of applying a tensile force to the flexible substrate to distort it, a deposition step of depositing the thin film while the tensile force is being applied to the flexible substrate, and a release step of releasing the tensile force applied to the flexible substrate.

[0011] In order to solve the above problems, a thin film device includes a flexible substrate and a strain-introduced thin film made of an inorganic semiconductor in which a strain different from that of the flexible substrate is introduced.

[0012] In order to solve the above problem, the thin film device comprises a flexible substrate and a plurality of strain-introducing thin films into which a strain different from that of the flexible substrate has been introduced, the plurality of strain-introducing thin films including a first strain-introducing thin film into which the strain has been introduced in a first direction, and a second strain-introducing thin film into which the strain has been introduced in a second direction that is not parallel to the first direction.

[0013] According to one aspect of the present invention, strain can be introduced into a thin film by a method different from the conventional method.

[0014] Fig. 1 is a process chart showing a method for manufacturing a thin film device according to embodiment 1. Fig. 2 is a process chart showing a method for manufacturing a thin film device according to embodiment 2. Fig. 3 is a schematic cross-sectional view showing an example of a thin film device according to embodiment 3, and a graph showing the magnetization curve of the thin film device. Fig. 4 is a schematic cross-sectional view showing another example of a thin film device according to embodiment 3, and a graph showing the magnetization curve of the thin film device. Fig. 5 is a schematic cross-sectional view showing yet another example of a thin film device according to embodiment 3, and a graph showing the magnetization curve of the thin film device. Fig. 6 is a graph showing the change in resistance value of the thin film device with respect to an external magnetic field.

[0015] [Embodiment 1] Figure 1 is a process diagram showing a method for manufacturing a thin film device 100 according to embodiment 1 of the present invention. Reference numerals 1001 to 1004 in Figure 1 are schematic cross-sectional views showing the longitudinal sections of each component of the thin film device 100 in each step. Note that Figure 1 shows each component of the thin film device 100 in a schematic manner and does not limit the actual dimensions of each component. The same applies to Figures 2 to 5.

[0016] (Schematic Configuration of Thin Film Device 100) As indicated by reference numeral 1004 in FIG. 1 , the thin film device 100 includes a flexible substrate 1 and a thin film 2 (strain-introducing thin film). The flexible substrate 1 is a substrate having stretchability. Specifically, the flexible substrate 1 is a substrate that can be stretched elastically. The flexible substrate 1 is sufficiently thick relative to the thin film 2, which will be described later. The flexible substrate 1 has a thickness, for example, on the order of μm to mm. The thin film 2 is formed on the flexible substrate 1. The thin film 2 has a thickness, for example, on the order of nm. The thin film 2 is, for example, about 1 / 1000 to 1 / 10,000 (preferably about 1 / 5,000) times thicker than the flexible substrate 1. The thin film 2 is, for example, a nano-thin film having a thickness of nanometers. The thin film 2 is, for example, a ferromagnetic material.

[0017] Here, compressive strain is introduced (built-in) into the thin film 2. More specifically, compressive strain in one axis direction is introduced into the thin film 2. That is, strain is introduced into the thin film 2 only in a predetermined direction. In other words, anisotropic strain in one axis direction is introduced into the thin film 2. Hereinafter, the predetermined direction is referred to as the X direction (first direction), the direction perpendicular to the predetermined direction on the surface of the thin film 2 is referred to as the Y direction (second direction), and the direction perpendicular to the X direction and the Y direction (i.e., the thickness direction of the thin film 2) is referred to as the Z direction.

[0018] The strain introduced into the flexible substrate 1 is typically about 0 to 2%. The amount of strain introduced into the flexible substrate 1 may be different from the amount of strain obtained by epitaxial strain.

[0019] (Method for Manufacturing Thin Film Device 100) A non-conventional method for manufacturing such a thin film device 100 will be described below with reference to the reference numerals 1001 to 1004 in FIG.

[0020] First, a flexible substrate 1 is prepared as shown by reference numeral 1001 in Fig. 1. The length of the flexible substrate 1 in the X direction is defined as L.

[0021] Next, as shown by reference numeral 1002 in Fig. 1 , a tensile force is applied to the flexible substrate 1 in the X direction to distort it (tensioning step). Due to this tensile force, the length of the flexible substrate 1 in the X direction becomes greater than L. The flexible substrate 1 is tensioned (or compressed) in a predetermined direction, for example, by sliding the fixing portion of the substrate holder that fixes the flexible substrate 1 in a predetermined direction. Note that when a tensile force is applied to the flexible substrate 1, the size of the thin film 2 in the Z direction (film thickness direction) actually becomes smaller.

[0022] 1, a thin film 2 is formed on the flexible substrate 1 while a tensile force is being applied to the flexible substrate 1 (film formation step). The thin film 2 may be formed by a known film formation method (for example, sputtering or vapor deposition).

[0023] 1, the tensile force applied to the flexible substrate 1 is released (release step), whereby a compressive strain in the X direction corresponding to the tensile force is introduced into the formed thin film 2.

[0024] (Effects) The above-described manufacturing method can realize a thin film device 100 including a thin film 2 into which strain different from that of the flexible substrate 1 has been introduced. The thin film 2 into which such strain has been introduced can have different properties compared to a state in which no strain has been introduced. For example, if the thin film 2 is a ferromagnetic material, the magnetization state or phase transition temperature of the thin film 2 can be changed by introducing strain into the thin film 2.

[0025] Furthermore, the combination of materials for the flexible substrate 1 and the thin film 2 may be any combination suitable for a known film formation method. For example, when forming the thin film 2 by sputtering, the flexible substrate 1 can be made of polyimide, polyethylene terephthalate, polyethylene naphthalate, polyurethane, polycarbonate, or the like, and the thin film 2 can be made of 3d transition metals such as iron, cobalt, nickel, or other metals, or alloys thereof, magnesium oxide, or the like. Therefore, the above-described manufacturing method can be applied to a wider range of material combinations than conventional strain-introducing methods (e.g., methods of introducing epitaxial strain into a thin film). The material for the thin film 2 is not limited to single crystal, but may also be polycrystalline or amorphous.

[0026] Furthermore, the above-described manufacturing method can introduce uniaxial compressive strain into the thin film 2 regardless of the material of the flexible substrate 1. Furthermore, by adjusting the magnitude and direction of the tensile force, it is possible to introduce strain of a desired direction and magnitude into the thin film 2. This is something that could not be achieved by methods that introduce epitaxial strain into a thin film. In particular, the above-described manufacturing method, unlike epitaxial strain, can introduce strain of, for example, 0.2% to 2% into the thin film.

[0027] (Modification) In reference numeral 1004 in Fig. 1 , a case has been described in which no strain has been introduced into the flexible substrate 1 in the thin film device 100. However, strain may remain in the flexible substrate 1 in the thin film device 100. In this case, too, it can be said that at least a strain different from that introduced into the flexible substrate 1 has been introduced into the thin film 2. In other words, it can be said that a strain of a different direction or magnitude than that introduced into the flexible substrate 1 has been introduced into the thin film 2.

[0028] The thin film device 100 may be manufactured by a roll-to-roll method. That is, the thin film 2 is formed on the flexible substrate 1 while a tensile force is applied to the flexible substrate 1 and the flexible substrate 1 is transported. Then, when (or after) the flexible substrate 1 on which the thin film 2 is formed is wound onto a roll, the tensile force is released. In this way, the thin film device 100 wound onto a roll can be provided.

[0029] Alternatively, the thin film 2 may be formed on the flexible substrate 1 by transfer. That is, the thin film 2 is transferred onto the flexible substrate 1 while a tensile force is applied to the flexible substrate 1, and then the tensile force is released. This allows compressive strain to be introduced into the thin film 2. In this case, the thin film 2 may be a layered material such as graphene, or may be an epitaxial nano-thin film peeled off from a single crystal substrate by a known method.

[0030] Furthermore, the flexible substrate 1 is not limited to a substrate that can be elastically stretched, but may also be a substrate that can at least be elastically bent. For example, the flexible substrate 1 may be a membrane-like substrate containing Si, SiN, SiO, or the like. In this case, bending the flexible substrate 1 applies a tensile force to the surface of the flexible substrate 1. By transferring the thin film 2 to the surface of the flexible substrate 1 while the flexible substrate 1 is bent and then releasing the bend, a thin film 2 into which compressive strain has been introduced can be formed.

[0031] Furthermore, tensile strain may be introduced into the thin film 2. That is, the thin film 2 may be formed on the flexible substrate 1 while a compressive force is being applied to the flexible substrate 1, and then the compressive force may be released.

[0032] Moreover, strain may be introduced in the same direction in the thin film 2. Alternatively, a predetermined amount of strain may be introduced in the X direction in the thin film 2, and a strain of a different amount from the predetermined amount may be introduced in the Y direction.

[0033] Furthermore, an underlayer may be formed between the flexible substrate 1 and the thin film 2. The underlayer is a layer for enhancing the adhesion between the flexible substrate 1 and the thin film 2.

[0034] [Embodiment 2] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0035] 2 is a process diagram showing a method for manufacturing the thin film device 100A according to the second embodiment of the present invention. Reference numerals 2001 to 2004 in Fig. 2 are schematic cross-sectional views showing the longitudinal sections of the components of the thin film device 100A in the respective steps.

[0036] (Schematic configuration of thin film device 100A) As indicated by reference numeral 2004 in Fig. 2, the thin film device 100A includes a flexible substrate 1 and a plurality of thin films 2A. The plurality of thin films 2A are stacked along the Z direction. The plurality of thin films 2A include, in order from the flexible substrate 1 side, a first thin film layer 21A (first strain-introducing thin film), a second thin film layer 22A, and a third thin film layer 23A (second strain-introducing thin film). The material, dimensions, etc. of each layer of the plurality of thin films 2A are the same as those of the thin film 2 according to the first embodiment.

[0037] Here, a strain of a corresponding amount is introduced into each layer of the multiple thin films 2A. In the example shown in Figure 2, a first compressive strain of a first amount in the X direction is introduced into the first thin film layer 21A, and a second compressive strain of a second amount in the X direction (a second strain smaller than the first strain) is introduced into the third thin film layer 23A. No strain is introduced into the second thin film layer 22A (i.e., the amount of strain introduced into the second thin film layer 22A is 0).

[0038] (Method for Manufacturing Thin-Film Device 100A) A method for manufacturing such a thin-film device 100A will be described below with reference to the reference numerals 2001 to 2004 in FIG.

[0039] First, as shown by reference numeral 2001 in Fig. 2 , a first tensile force T1 is applied in the X direction to the flexible substrate 1 to distort it. The first tensile force T1 causes the length of the flexible substrate 1 in the X direction to become L1 (L1 > L). Furthermore, with the first tensile force T1 being applied to the flexible substrate 1, a first thin film layer 21A is formed on the flexible substrate 1.

[0040] 2, the tensile force applied to the flexible substrate 1 is released. Furthermore, with no tensile force being applied to the flexible substrate 1, the second thin film layer 22A is formed on the first thin film layer 21A.

[0041] Next, as shown by reference numeral 2003 in Figure 2, a second tensile force T2 (T2 < T1) is applied to the flexible substrate 1 in the X direction to distort it. Due to the second tensile force T2, the length of the flexible substrate 1 in the X direction becomes L2 (L < L2 < L1). Furthermore, with the second tensile force T2 being applied to the flexible substrate 1, a third thin film layer 23A is formed on the second thin film layer 22A.

[0042] Next, as shown by reference numeral 2004 in Fig. 2, the tensile force applied to the flexible substrate 1 is released. As a result, a first compressive strain of a first strain amount corresponding to the first tensile force T1 is introduced into the first thin film layer 21A, and a second compressive strain of a second strain amount corresponding to the second tensile force T2 is introduced into the third thin film layer 23A. Furthermore, no strain is introduced into the second thin film layer 22A.

[0043] (Effects) The above-described manufacturing method allows for the introduction of a desired amount of compressive strain in a desired layer of the thin films 2 A. A configuration in which a desired amount of compressive strain is introduced in a desired layer is a configuration that could not be realized by conventional strain introduction methods.

[0044] (Modification) Note that strain may be introduced into each layer of the multiple thin films 2A in a direction corresponding to the layer. For example, strain in the X direction may be introduced into the first thin film layer 21A, and strain in a direction not parallel to the X direction (e.g., the Y direction) may be introduced into the third thin film layer 23A. This can be achieved by varying the direction of the tensile force applied to the flexible substrate 1 when forming each layer. Furthermore, the multiple thin films 2A do not have to be stacked in order along the Z direction.

[0045] [Embodiment 3] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0046] In the third embodiment, a magnetic sensor will be described as an application example of the thin film device described in the first and second embodiments. The plurality of thin films 2B, 2C, and 2D described in the third embodiment can be considered as specific examples of the plurality of thin films 2A described in the second embodiment. First, the magnetic characteristics of a part of the configuration of the magnetic sensor will be described with reference to FIGS. 3 and 4.

[0047] FIG. 3 is a schematic cross-sectional view (reference numeral 3001) showing an example of a thin-film device (thin-film device 100B) and a graph (reference numeral 3002) showing the magnetization curve of the thin-film device 100B. The thin-film device 100B is a thin-film laminate obtained by removing the pinned layer from a magnetic sensor. Note that reference numeral 3001 in FIG. 3 indicates the material and thickness (unit: nm) of each layer of the thin-film device 100B. The same applies to FIGS. 4 and 5. Furthermore, in reference numeral 3002 in FIG. 3, G31 and G32 are the magnetization curves of the thin-film device 100B when magnetic fields are generated in the Y and X directions, respectively.

[0048] 3, the thin-film device 100B includes a flexible substrate 1 and a plurality of thin films 2B. The plurality of thin films 2B include, in order from the flexible substrate 1 side, an underlayer 21B, an intermediate layer 22B, a first ferromagnetic layer 23B, an intermediate layer 24B, and a non-magnetic layer 25B.

[0049] The underlayer 21B is a layer for increasing the adhesion between the flexible substrate 1 and the plurality of thin films 2B. The underlayer 21B may also be a layer for improving surface flatness. The underlayer 21B is a non-magnetic material. In the example shown in FIG. 3, the underlayer 21B is a Ta layer.

[0050] The intermediate layers 22B and 24B are layers for improving the crystalline orientation of the first ferromagnetic layer 23B. The intermediate layers 22B and 24B may contain any material that exhibits crystallinity. The intermediate layers 22B and 24B are non-magnetic. In the example shown in FIG. 3, the intermediate layers 22B and 24B are Pt layers.

[0051] The first ferromagnetic layer 23B is a layer (free layer) whose magnetization direction changes depending on the direction of the magnetic field. In the example shown in Figure 3, the first ferromagnetic layer 23B includes, in order from the flexible substrate 1 side, a Co layer, a Pd layer, and a Co layer. Such a first ferromagnetic layer 23B (and the thin-film device 100B including the first ferromagnetic layer 23B) has a positive magnetoelastic coupling constant.

[0052] Here, compressive strain in the X direction is introduced into the first ferromagnetic layer 23B. This changes the magnetization state of the first ferromagnetic layer 23B. Specifically, because the first ferromagnetic layer 23B has a positive magnetoelastic coupling constant, it is easily magnetized in the Y direction, which is perpendicular to the direction in which the compressive strain is introduced (i.e., it has an easy axis of magnetization in the Y direction).

[0053] The non-magnetic layer 25B is a non-magnetic material, and in the example shown in FIG.

[0054] As shown by reference numeral 3002 in FIG. 3 , the magnetization of the first ferromagnetic layer 23B (and the thin-film device 100B including the first ferromagnetic layer 23B) is easily oriented in the Y direction. When a magnetic field is swept in the Y direction, the thin-film device 100B has spontaneous magnetization in the Y direction at zero magnetic field (see G31). That is, the magnetization curve of the thin-film device 100B exhibits hysteresis with respect to the sweep of the magnetic field in the Y direction. On the other hand, when a magnetic field is swept in the X direction, the magnetization curve of the thin-film device 100B exhibits a curve in which the magnetization rotates from the Y direction to the X direction and saturates (see G32). That is, the magnetization of the thin-film device 100B exhibits linearity over a predetermined range (approximately −300 Oe to approximately 300 Oe) centered on zero magnetic field.

[0055] 4 is a schematic cross-sectional view (reference numeral 4001) showing another example of a thin-film device (thin-film device 100C) and a graph (reference numeral 4002) showing the magnetization curve of the thin-film device 100C. Like the thin-film device 100B, the thin-film device 100C is a thin-film laminate in which the pinned layer is removed from the magnetic sensor. In the graph 4002 in FIG. 4, G41 and G42 are the magnetization curves of the thin-film device 100B when magnetic fields are generated in the Y and X directions, respectively.

[0056] 4, the thin-film device 100C includes a flexible substrate 1 and a plurality of thin films 2C. The plurality of thin films 2C include, in order from the flexible substrate 1 side, an underlayer 21C, an intermediate layer 22C, a first ferromagnetic layer 23C, and a non-magnetic layer 24C. The underlayer 21C, the intermediate layer 22C, and the non-magnetic layer 24C are members having the same functions as the underlayer 21B, the intermediate layer 22B, and the non-magnetic layer 25B, respectively.

[0057] The first ferromagnetic layer 23C is a layer (free layer) whose magnetization direction changes depending on the direction of the magnetic field. In the example shown in FIG. 4 , the first ferromagnetic layer 23C includes, in order from the flexible substrate 1 side, a Ni layer and a Co layer. Here, the Ni layer is thicker than the Co layer, and the magnetic properties of the Ni layer are dominant in the first ferromagnetic layer 23C. Such a first ferromagnetic layer 23C (and the thin-film device 100C including the first ferromagnetic layer 23C) has a negative magnetoelastic coupling constant.

[0058] Here, compressive strain in the X direction is introduced into the first ferromagnetic layer 23C, which has a negative magnetoelastic coupling constant and is therefore in a state where it is easily magnetized in the X direction where compressive strain is introduced (i.e., a state where it has an easy axis of magnetization in the X direction).

[0059] As shown by reference numeral 4002 in FIG. 4 , the magnetization of the first ferromagnetic layer 23C (and the thin-film device 100C including the first ferromagnetic layer 23C) is easily oriented in the X direction, and when a magnetic field is swept in the X direction, the thin-film device 100C has spontaneous magnetization in the X direction at zero magnetic field (see G42). On the other hand, when a magnetic field is swept in the Y direction, the magnetization curve of the thin-film device 100C becomes a curve in which the magnetization rotates from the X direction to the Y direction and becomes saturated. In other words, the magnetization of the thin-film device 100C exhibits linearity over a predetermined range (approximately −900 Oe to approximately 900 Oe) centered on zero magnetic field.

[0060] Next, the magnetic characteristics of a magnetic sensor utilizing GMR (giant magnetoresistance) will be described with reference to FIG.

[0061] 5 is a schematic cross-sectional view (reference numeral 5001) showing yet another example of a thin-film device (thin-film device 100D) and a graph (reference numeral 5002) showing the magnetization curve of the thin-film device 100D. The thin-film device 100D is a magnetic sensor that uses GMR. In reference numeral 5002 in FIG. 5, G51 and G52 are the magnetization curves of the thin-film device 100D when magnetic fields are generated in the Y and X directions, respectively.

[0062] 5 , the thin-film device 100D includes a flexible substrate 1 and a plurality of thin films 2D. The plurality of thin films 2D include, in order from the flexible substrate 1 side, an underlayer 21D, an intermediate layer 22D, a first ferromagnetic layer 23D, a non-magnetic layer 24D, a second ferromagnetic layer 25D, an antiferromagnetic layer 26D, and a protective layer 27D. The underlayer 21D, the intermediate layer 22D, the first ferromagnetic layer 23D, and the non-magnetic layer 24D are members having the same functions as the underlayer 21C, the intermediate layer 22C, the first ferromagnetic layer 23C, and the non-magnetic layer 24C, respectively.

[0063] The second ferromagnetic layer 25D and the antiferromagnetic layer 26D form a pinned layer with a fixed magnetization direction. That is, the antiferromagnetic layer 26D pins the magnetization direction of the second ferromagnetic layer 25D by an exchange bias generated by exchange coupling with the second ferromagnetic layer 25D. The magnetization of the exchange-biased pinned layer is pinned in the Y direction (positive direction of the Y axis). In the example shown in FIG. 5 , the second ferromagnetic layer 25D includes, in order from the flexible substrate 1 side, a Co layer and a NiFe layer. The antiferromagnetic layer 26D is an IrMn layer.

[0064] The first ferromagnetic layer 23D (free layer), the nonmagnetic layer 24D, and the second ferromagnetic layer 25D (pinned layer) constitute a GMR (giant magnetoresistance) element. Here, the first ferromagnetic layer 23D has an easy axis of magnetization in the X direction, and the second ferromagnetic layer 25D has a magnetization fixed in the Y direction. In other words, the easy axis of magnetization of the first ferromagnetic layer 23D is perpendicular to the fixed magnetization direction of the second ferromagnetic layer 25D. In other words, the first ferromagnetic layer 23D and the second ferromagnetic layer 25D form an orthogonal magnetization arrangement.

[0065] The protective layer 27D protects the GMR element. The protective layer 27D is made of a non-magnetic material. In the example shown in FIG. 5, the protective layer 27D is a Pt layer.

[0066] 5, the thin-film device 100D includes a first ferromagnetic layer 23D whose easy axis of magnetization is in the X direction, and therefore, like the thin-film device 100C, when a magnetic field is swept in the X direction, the thin-film device 100D has spontaneous magnetization in the X direction at zero magnetic field (see G52). On the other hand, the thin-film device 100D also includes a second ferromagnetic layer 25D whose magnetization is fixed in the Y direction, and therefore, when a magnetic field is swept in the Y direction, the magnetization curve shifts compared to the thin-film device 100C (see G51).

[0067] Fig. 6 is a graph showing the change in the resistance value of the thin-film device 100D with respect to an external magnetic field. In the example shown in Fig. 6, the external magnetic field is a magnetic field along the Y direction. In the example shown in Fig. 6, the resistance value of the thin-film device 100D is the resistance value of the non-magnetic layer 24D when electrodes are provided on both ends of the non-magnetic layer 24D in the surface direction and a current is passed through the non-magnetic layer 24D via the electrodes.

[0068] As shown in FIG. 6 , the resistance of the thin-film device 100D changes linearly within a predetermined range (approximately −300 Oe to approximately 300 Oe) centered on the zero magnetic field. Specifically, when a positive external magnetic field is applied, the magnetization of the first ferromagnetic layer 23D tilts toward the positive Y-axis direction, which is the fixed magnetization direction of the second ferromagnetic layer 25D, resulting in a relatively low resistance of the thin-film device 100D. When the external magnetic field is then swept toward zero, the magnetization of the first ferromagnetic layer 23D tends to orient toward the X-axis, and the magnetization, which was oriented in the positive Y-axis direction, gradually rotates toward the X-axis direction. This gradually increases the resistance of the thin-film device 100D. Furthermore, when the external magnetic field is swept toward the negative direction from zero, the magnetization of the first ferromagnetic layer 23D gradually rotates toward the negative Y-axis direction. This further increases the resistance of the thin-film device 100D. That is, by providing the first ferromagnetic layer 23D and the second ferromagnetic layer 25D with an orthogonal magnetization arrangement, the range in which the resistance value of the thin-film device 100D changes linearly with respect to the external magnetic field is increased.

[0069] The thin-film device 100D used as a magnetic sensor further includes a measuring device (not shown) that measures the resistance value of the nonmagnetic layer 24D. For example, the resistance value of the nonmagnetic layer 24D can be measured by applying a voltage to the nonmagnetic layer 24D and measuring the current.

[0070] The thin-film device 100D can also be used as a strain sensor. In this case, the thin-film device 100D further includes a measuring device (not shown) that measures the resistance of the nonmagnetic layer 24D. If the built-in strain of the first ferromagnetic layer 23D changes, the magnetization direction relative to the magnetization direction of the second ferromagnetic layer 25D changes in response to the change in the built-in strain, thereby changing the resistance value of the nonmagnetic layer 24D.

[0071] (Effects) The thin-film device 100D can provide a magnetic sensor with an increased range in which the resistance value of the thin-film device 100D changes linearly with respect to an external magnetic field, compared to conventional magnetic sensors. That is, the linearity of the output of the magnetic sensor with respect to the magnetic field can be improved. In other words, the range of the external magnetic field that the magnetic sensor can properly measure can be increased. This is an effect achieved by introducing compressive strain into the first ferromagnetic layer 23D and imparting an orthogonal magnetization arrangement to the first ferromagnetic layer 23D and the second ferromagnetic layer 25D, as described above. Similarly, when the thin-film device 100D is used as a strain sensor, the linearity of the output of the thin-film device 100D with respect to the amount of strain can be improved.

[0072] Furthermore, the thin-film device 100D can reduce the number of heat treatment processes required when using an exchange bias technique to achieve an orthogonal magnetization arrangement. Furthermore, since magnetic anisotropy in a desired direction can be easily imparted, fewer restrictions are imposed on the shape of the device structure.

[0073] (Variation) In the thin-film device 100D, the first ferromagnetic layer 23D may have a positive magnetoelastic coupling constant, and compressive strain in the Y direction may be introduced into the first ferromagnetic layer 23D. In this case, the first ferromagnetic layer 23D also has an easy axis of magnetization in the X direction. That is, an orthogonal magnetization arrangement can be imparted to the first ferromagnetic layer 23D and the second ferromagnetic layer 25D.

[0074] Furthermore, the easy axis of magnetization of the first ferromagnetic layer 23D may be at least not parallel to the fixed magnetization direction of the second ferromagnetic layer 25D. This improves the linearity of the output of the magnetic sensor relative to the magnetic field, at least compared to conventional magnetic sensors. For example, the easy axis of magnetization of the first ferromagnetic layer 23D may be approximately perpendicular to the fixed magnetization direction of the second ferromagnetic layer 25D.

[0075] Alternatively, a compressive strain may be introduced into the second ferromagnetic layer 25D so that the second ferromagnetic layer 25D has an easy axis of magnetization parallel to the fixed magnetization direction (the Y direction in the example shown in FIG. 5 ). In the example shown in FIG. 5 , the second ferromagnetic layer 25D has a positive magnetoelastic coupling constant, so that a compressive strain in the X direction may be introduced into the second ferromagnetic layer 25D.

[0076] This allows the first ferromagnetic layer 23D and the second ferromagnetic layer 25D to have an orthogonal magnetization arrangement, instead of the exchange bias technique described above, in which case the antiferromagnetic layer 26D is omitted.

[0077] The first ferromagnetic layer 23D may include a TMR (tunneling magnetoresistance) element instead of a GMR element, in which case the nonmagnetic layer 25B is a nonmagnetic insulator.

[0078] (Additional Notes) <Changing the Phase Transition Temperature by Introducing Strain> A thin-film device having a ferromagnetic layer with introduced strain can be utilized because the phase transition temperature indicating the magnetic state is different from that of a device without introduced strain. The ferromagnetic layer may be a single layer or a multilayer. The thin-film device may have a structure having an intermediate layer of a non-magnetic material between the ferromagnetic layers. The introduction of strain can either increase or decrease the phase transition temperature.

[0079] If a thin-film device with this configuration can be later strained to change the phase transition temperature near room temperature, it will be possible to impart or remove magnetic properties at room temperature. Furthermore, by releasing the tensile strain, the device can be returned to a non-magnetic state or a magnetic state. Therefore, it is possible to switch between magnetic and non-magnetic states by mechanical action without changing the temperature. This means that nanoelectromagnets can be created using mechanical energy rather than electrical energy.

[0080] Furthermore, by controlling the tensile strain, it is possible to turn on or off the GMR or TMR in the thin film device, thereby providing a sensor based on the resistance change caused by switching the onset of GMR or TMR.

[0081] Furthermore, by changing the material of each layer or the strain introduced, it is possible to control the strength of the magnetic properties due to the tensile strain applied later, which allows the sensitivity range of the magnetic sensor to be freely changed.

[0082] The term "magnetic state" refers to a ferromagnetic state, and the term "non-magnetic state" refers to a paramagnetic state.

[0083] <Superconductor> The thin-film device may also include a thin film of a superconductor into which strain has been introduced. The introduction of strain can change the phase transition temperature of the superconductor. Examples of superconductors whose phase transition temperature is improved by the introduction of strain include Nb, FeSe, MgB2, and copper oxide high-temperature superconductors.

[0084] <Semiconductor / Insulator> Alternatively, a semiconductor or insulator layer may be formed on the flexible substrate 1 by transfer while a tensile force is applied to the flexible substrate 1. This allows compressive strain to be introduced into the semiconductor or insulator. Introducing strain into a thin film of an insulator may improve the performance of a thin-film device. Examples of such insulators include MgO.

[0085] Furthermore, by introducing compressive strain into a thin film of a semiconductor (inorganic semiconductor, for example, an elemental semiconductor such as Si or Ge or an alloy thereof (SiGe), a III-V group compound semiconductor typified by GaAs or GaN, or a II-VI group compound semiconductor such as ZnO), the band gap of the semiconductor can be changed compared to when compressive strain is not introduced. By changing the band gap, the optical properties such as the emission wavelength and absorption wavelength of the semiconductor or the mobility can be changed. In other words, the emission wavelength of a semiconductor laser or semiconductor light-emitting element can be changed. Furthermore, as shown in FIG. 2, multiple semiconductor thin films (e.g., thin films made of semiconductors containing Si or GaN) into which different strains have been introduced may be stacked on a flexible substrate, and different strains may be introduced into each of the multiple semiconductor thin films. In other words, multiple semiconductor thin films may be formed, including a semiconductor thin film into which a first amount of strain has been introduced and a semiconductor thin film into which a second amount of strain different from the first amount of strain has been introduced. Therefore, a stack of semiconductor thin films with different band gaps can be formed. This leads to the realization of an artificial lattice with desired properties. Furthermore, after the thin film device is manufactured, the emission wavelength of the manufactured semiconductor laser or semiconductor light emitting element can be changed by applying or releasing a tensile force to the flexible substrate 1 .

[0086] <Others> Epitaxial strain is a strain that is introduced by a specific combination of materials. Therefore, if the amount of strain is known, it is possible to distinguish whether the strain present in the thin film is epitaxial strain or strain introduced by the method described in the above embodiment. The strain introduced into the thin film can be investigated by the following method. That is, depending on the size of the thin film device, the strain introduced into the thin film of the thin film device can be investigated by reverse engineering using, for example, transmission electron microscope measurement, X-ray diffraction method, or synchrotron radiation EXAFS (broadband X-ray absorption fine structure) measurement.

[0087] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. (Summary)

[0088] A thin film device according to a first aspect of the present invention includes a flexible substrate and a strain-introduced thin film made of a ferromagnetic material in which a strain different from that of the flexible substrate is introduced.

[0089] In the thin film device according to Aspect 2 of the present invention, in the above-mentioned Aspect 1, compressive strain may be introduced into the strain-introduced thin film.

[0090] In the thin film device according to Aspect 3 of the present invention, in Aspect 2, the compressive strain in one axial direction may be introduced into the strain-introduced thin film.

[0091] A thin film device according to aspect 4 of the present invention may be any of aspects 1 to 3 above, and may include a plurality of the strain-introducing thin films, and the plurality of strain-introducing thin films may include a first strain-introducing thin film into which the strain in a first direction is introduced, and a second strain-introducing thin film into which the strain in the first direction is introduced.

[0092] A thin film device according to aspect 5 of the present invention, in any of aspects 1 to 4 above, comprises a plurality of the strain-introducing thin films, and the plurality of strain-introducing thin films may include a first strain-introducing thin film into which a first amount of strain has been introduced, and a second strain-introducing thin film into which a second amount of strain different from the first amount of strain has been introduced.

[0093] In a thin-film device according to aspect 6 of the present invention, in any one of aspects 1 to 3 above, the strain-introducing thin film may be a first ferromagnetic layer, and may further include a second ferromagnetic layer that is a ferromagnetic material with a fixed magnetization direction, and a non-magnetic layer that is a non-magnetic material sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

[0094] In the thin film device according to Aspect 7 of the present invention, in the above-mentioned Aspect 6, the axis of easy magnetization of the first ferromagnetic layer may be substantially perpendicular to the fixed magnetization direction of the second ferromagnetic layer.

[0095] In a thin film device according to aspect 8 of the present invention, in the above-mentioned aspects 4 or 5, the first strain-introducing thin film may be a first ferromagnetic layer, the second strain-introducing thin film may be a second ferromagnetic layer, and the device may further include a non-magnetic layer that is a non-magnetic material sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

[0096] A method for manufacturing a thin film device comprising a flexible substrate and a thin film made of a ferromagnetic material according to aspect 9 of the present invention includes a tensioning step of applying a tensile force to the flexible substrate to distort it, a deposition step of depositing the thin film while the tensile force is being applied to the flexible substrate, and a release step of releasing the tensile force applied to the flexible substrate.

[0097] A thin film device according to a tenth aspect of the present invention includes a flexible substrate and a strain-introduced thin film made of an inorganic semiconductor in which a strain different from that of the flexible substrate is introduced.

[0098] A thin film device according to aspect 11 of the present invention comprises a flexible substrate and a plurality of strain-introducing thin films into which a strain different from that of the flexible substrate has been introduced, the plurality of strain-introducing thin films including a first strain-introducing thin film into which the strain has been introduced in a first direction, and a second strain-introducing thin film into which the strain has been introduced in a second direction that is not parallel to the first direction.

[0099] 100, 100A, 100B, 100C, 100D, 100E, 100F Thin film device 1 Flexible substrate 2 Thin film (strain-introducing thin film) 21A First thin film layer (first strain-introducing thin film) 22A Second thin film layer 23A Third thin film layer (second strain-introducing thin film) 23B, 23C, 23D First ferromagnetic layer 24C, 24D, 25B Non-magnetic layer 25D Second ferromagnetic layer

Claims

1. A thin film device comprising: a flexible substrate; and a strain-introduced thin film made of a ferromagnetic material in which a strain different from that of the flexible substrate has been introduced.

2. The thin film device according to claim 1, wherein compressive strain is introduced into the strain-introduced thin film.

3. The thin film device according to claim 2, wherein the compressive strain in one axis direction is introduced into the strain-introduced thin film.

4. A thin film device as described in claim 1, comprising a plurality of strain-introducing thin films, the plurality of strain-introducing thin films including a first strain-introducing thin film into which the strain in a first direction is introduced, and a second strain-introducing thin film into which the strain in the first direction is introduced.

5. A thin film device as described in claim 1, comprising a plurality of strain-introducing thin films, the plurality of strain-introducing thin films including a first strain-introducing thin film into which a first amount of strain has been introduced, and a second strain-introducing thin film into which a second amount of strain different from the first amount of strain has been introduced.

6. The thin film device according to claim 1, wherein the strain-introducing thin film is a first ferromagnetic layer, and further comprises: a second ferromagnetic layer that is a ferromagnetic material with a fixed magnetization direction; and a non-magnetic layer that is a non-magnetic material sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

7. The thin film device according to claim 6, wherein the easy axis of magnetization of said first ferromagnetic layer is substantially perpendicular to the fixed direction of magnetization of said second ferromagnetic layer.

8. A thin film device as described in claim 4 or 5, wherein the first strain-introducing thin film is a first ferromagnetic layer, the second strain-introducing thin film is a second ferromagnetic layer, and the device further comprises a non-magnetic layer that is a non-magnetic material sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

9. A method for manufacturing a thin film device comprising a flexible substrate and the thin film, the method comprising: a tensioning step of applying a tensile force to the flexible substrate to distort it; a deposition step of depositing a thin film made of a ferromagnetic material while the tensile force is being applied to the flexible substrate; and a release step of releasing the tensile force applied to the flexible substrate.

10. A thin film device comprising: a flexible substrate; and a strain-introduced thin film made of an inorganic semiconductor in which a strain different from that of the flexible substrate has been introduced.

11. A thin film device comprising: a flexible substrate; and a plurality of strain-introducing thin films into which a strain different from that of the flexible substrate has been introduced, wherein the plurality of strain-introducing thin films include a first strain-introducing thin film into which the strain has been introduced in a first direction, and a second strain-introducing thin film into which the strain has been introduced in a second direction that is not parallel to the first direction.

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