Magnetic memory element and writing and reading method of information on magnetic memory element

Abstract

To provide a magnetic memory element capable of writing and reading information by a magnetic field at a room temperature.SOLUTION: A magnetic memory element comprises: a thin film composed of a chemical compound expressed by the following formula (1); a first electrode arranged at the thin film; and a second electrode arranged at the thin film. BiFe1-xAxO3...(1) [In the formula (1), A is Co or Mn, and x satisfies 0.05≤x<0.25.] The first electrode and the second electrode are arranged so that an electric field occurs in a direction parallel to the thin film by applying a voltage between the first electrode and the second electrode.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a magnetic memory element and a method for writing and reading information in a magnetic memory element. [Background technology]

[0002] BiFeO 3 BiFe in which some of the Fe is replaced by Co 0.9 Co 0.1 O 3 has both ferroelectricity and weak ferromagnetism at room temperature, and magnetization reversal accompanying 71° polarization reversal has been observed using a magnetic force microscope (MFM), so it is expected to be applied to ultra-low power magnetic memories that utilize this magnetization reversal phenomenon caused by the application of an electric field (Non-Patent Document 1). Magnetization reversal is also predicted for 109° polarization reversal (Non-Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] K. Shimizu, et al., Nano Lett. 19, 1767 (2019). [Non-Patent Document 2] JT Heron, et al., Nature 516, 370 (2014). Summary of the Invention [Problem to be solved by the invention]

[0004] However, although Non-Patent Document 2 predicts that magnetization reversal also occurs at 109° polarization reversal, the details are unclear. If the behavior can be clarified, it is believed that the application of magnetic memory elements can be greatly accelerated.

[0005] The present invention has been made in view of the above circumstances, and one of its exemplary objects is to provide a magnetic memory element in which information can be written and read by an electric field. [Means for solving the problem]

[0006] A magnetic memory element according to an embodiment of the present invention comprises a thin film composed of a compound represented by the following formula (1), a first electrode disposed on the thin film, and a second electrode disposed on the thin film. BiFe 1-x A x O 3 (1) [In formula (1), A is Co or Mn, and x satisfies 0.05≦x<0.25.] The first electrode and the second electrode are arranged such that application of a voltage between the first electrode and the second electrode generates an electric field in the thin film in a direction parallel to the thin film.

[0007] Another aspect of the present invention is a method for writing and reading information in the magnetic memory element, which includes the steps of: applying a voltage between a first electrode and a second electrode of the magnetic memory element to reverse the magnetization of the thin film to write information; and detecting the reversal of the magnetization of the thin film to read the written information.

[0008] Any combination of the above components and any conversion of the present invention into a method, device, system, etc. are also valid aspects of the present invention. Effect of the Invention

[0009] According to the present invention, it is possible to provide a magnetic memory element in which information can be written and read by an electric field at room temperature. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a magnetic memory element according to one embodiment of the present invention; [Diagram 2]Figure 2(a) shows the crystal structure and magnetic structure of BiFeO3, and Figure 2(b) shows the crystal structure and magnetic structure of BiFe1-xAxO3. [Diagram 3] 1 is a diagram for explaining the spontaneous polarization and polarization reversal that can be taken by BiFe1-xAxO3. [Figure 4] FIG. 4 is a diagram for explaining details of an electrode portion. [Diagram 5] 5(a) to 5(d) are diagrams for explaining an example of a method for manufacturing a magnetic memory element according to one embodiment of the present invention. [Figure 6] FIG. 2 is a top view of a sample according to an embodiment. [Figure 7] 7(a) shows the observation results of a ferroelectric domain when a voltage of +80 V is applied, FIG. 7(b) shows the observation results of a ferroelectric domain when a voltage of −80 V is applied, FIG. 7(c) shows the observation results of a ferromagnetic domain when a voltage of +80 V is applied, and FIG. 7(c) shows the observation results of a ferromagnetic domain when a voltage of −80 V is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (background) In magnetic memories such as HDDs (Hard Disk Drives) and MRAMs (Magnetoresistive Random Access Memory), the magnetization of ferromagnetic materials is controlled by a magnetic field generated by passing a current through a coil, and magnetic information is written. For this reason, as the amount of information increases, the problem of increased power consumption arises. In addition, in ferroelectric memories such as FeRAMs (Ferroelectric Random Access Memory), when reading information, the information must be destroyed once and then rewritten after reading. For this reason, there are hopes for electric field writing and magnetic reading by applying an electric field to magnetize reversal using ferromagnetic ferroelectrics (multiferroic materials), which can suppress the increase in power consumption that accompanies an increase in the amount of information and does not require the destruction of information when reading it.

[0012] (Embodiment) Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the configurations described below are examples, and do not limit the scope of the present invention in any way.

[0013] Fig. 1 is a schematic diagram of a magnetic memory element 1 according to one embodiment of the present invention. The magnetic memory element 1 includes a substrate 10, a thin film 12, a plurality of electrode units 14, a power source 16, and a reading unit 18. In Fig. 1, the power source 16 is for applying a voltage to each electrode unit 14. Although Fig. 1 shows eight electrode units 14, the number of electrode units may be seven or less, or nine or more.

[0014] The substrate 10 may be made of a compound having a perovskite structure and a lattice constant in pseudocubic notation of, for example, 3.90 to 3.97 Å. The substrate 10 may be made of, for example, SrTiO 3 Substrate, GdScO 3 Substrate, TbScO 3 Substrate and DyScO 3 The substrate 10 may be a SrTiO 3 In the case of the substrate, it may be a (110) oriented substrate, and GdScO 3 Substrate, TbScO 3 Substrate or DyScO 3 In the case of a substrate, the substrate may be oriented in (010). The thickness of the substrate 10 is not particularly limited, but from the viewpoints of thin film synthesis and ease of handling, it is preferably 300 μm to 1000 μm, and more preferably 400 μm to 600 μm.

[0015] The thin film 12 is made of a compound represented by the following formula (1). BiFe 1-x A x O 3 (1) In formula (1), A is Co or Mn, and x satisfies 0.05≦x<0.25. When x is 0.05 or more, the thin film 12 can exhibit ferromagnetism and ferroelectricity at room temperature. When x is less than 0.25, changes in the crystal structure of the thin film 12 can be suppressed. The magnitude of the spontaneous magnetization of the thin film 12 at room temperature is, for example, 1 emu / cm 3 ~10 emu / cm 3 The magnitude of the spontaneous polarization may be, for example, 50 to 150 μC / cm 2 It may be to some extent.

[0016] The thickness of the thin film 12 is preferably 10 nm to 1000 nm. With such a thickness of the thin film 12, an electric field can be reliably applied to the thin film 12, and the reliability of the device can be improved. From the viewpoint of lattice distortion, the thickness of the thin film 12 is more preferably 30 nm to 400 nm. By setting the thickness of the thin film 12 to 30 nm or more, the stripe domain of the thin film 12 can be stabilized.

[0017] Referring to Fig. 2(a) and Fig. 2(b), 1-x A x O 3 The spontaneous magnetization and spontaneous polarization of BiFeO are explained. 3 FIG. 2(b) shows the crystal structure and magnetic structure of BiFe 1-x A x O 3 FIG. 2 shows the crystal and magnetic structures of

[0018] BiFeO 3 BiFeO has a hexagonal crystal structure, and layers containing iron sites with spin magnetic moment (hereinafter simply referred to as "spin") indicated by the arrows are stacked in the c-axis direction. 3has electric polarization (spontaneous polarization) in the c-axis direction. As shown in FIG. 2(a), each iron site has a spin in the opposite direction to the nearest iron site in the adjacent layer in the c-axis direction. Moreover, iron sites on a straight line in the ab-plane (for example, five iron sites 201 shown in FIG. 2(a)) form a cycloid. In this cycloid, the spin rotates once in 620 Å. For this reason, BiFeO 3 has no spontaneous magnetization.

[0019] BiFe 1-x A x O 3 BiFeO 3 The Fe in BiFeO is partially replaced by A. 3 It has a hexagonal crystal structure, and layers containing spin-bearing iron or cobalt sites are stacked in the c-axis direction. 1-x A x O 3 has electric polarization (spontaneous polarization) in the c-axis direction. 1-x A x O 3 So, BiFeO 3 In contrast, the spins of the two layers adjacent to each other in the c-axis direction, which are arranged on the dashed line in Fig. 2(b), are tilted so that spontaneous magnetization occurs in the ab plane. As a result, BiFe 1-x A x O 3 Thus, BiFe exhibits weak ferromagnetism. 1-x A x O 3 has a spontaneous polarization along the c-axis and a spontaneous magnetization perpendicular to the spontaneous polarization.

[0020] Figure 3 shows the BiFe 1-x A x O 3 FIG. 3 is a diagram for explaining the spontaneous polarization and the polarization reversal that can occur in BiFe. 1-x A x O 3 The crystal structure of is shown in pseudocubic. The eight arrows in the cubic crystal represent BiFe 1-x A x O3 The diagram shows the possible directions of spontaneous polarization in BiFe 1-x A x O 3 By applying an electric field to the BiFe 1-x A x O 3 Specifically, the spontaneous polarization 200 can be inverted by 71°, 109°, or 180°.

[0021] For example, the spontaneous polarization 200 can be changed to spontaneous polarization 202 in a direction toward the other end of the shared side 220 (71° polarization reversal). The spontaneous polarization 200 can also be changed to spontaneous polarization 204 in a direction toward the other diagonal end of the shared surface 222 (109° polarization reversal). Furthermore, the spontaneous polarization 200 can be changed to spontaneous polarization 206 in the opposite direction (180° polarization reversal). When the spontaneous polarization 200 undergoes polarization reversal, the direction of the spontaneous magnetization is also reversed accordingly.

[0022] Fig. 4 is a diagram for explaining details of the electrode unit 14. As shown in Fig. 4, the electrode unit 14 has a first electrode 140 and a second electrode 142. The material constituting the first electrode 140 and the second electrode 142 is not particularly limited, but may be a metal such as platinum.

[0023] The

[0110] direction of the thin film 12 is the direction perpendicular to the surface of the thin film 12, the

[0001] direction and the [1-10] direction of the thin film 12 are in-plane directions of the thin film 12, and the

[0001] direction and the [1-10] direction are directions perpendicular to each other. Figure 4 shows the orientations of four spontaneous polarizations (first polarization 52, second polarization 54, third polarization 56, and fourth polarization 58) that the thin film 12 can have in the in-plane directions (directions parallel to the thin film 12).

[0024] In this embodiment, the first electrode 140 and the second electrode 142 are arranged so that an electric field is generated in the [1-10] direction of the thin film 12. More specifically, the first electrode 140 and the second electrode 142 are arranged so as to have a gap in the [1-10] direction. This makes it possible to more reliably change the spontaneous polarization of the thin film 12 by the electric field and write information in the magnetic memory element 1.

[0025] The first electrode 140 and the second electrode 142 may be formed by deposition on the upper surface of the thin film 12. An electric field region 120 is formed between the first electrode 140 and the second electrode 142 in the thin film 12. When a voltage is applied between the first electrode 140 and the second electrode 142 from the power source 16, an electric field is generated in the electric field region 120 in a direction parallel to the [1-10] direction. In response to this electric field, spontaneous polarization and spontaneous magnetization reversal occur in the electric field region 120, making it possible to write information in the electric field region 120.

[0026] The information written in the electric field region 120 is read by a reader 18 disposed above the electric field region 120, by detecting the reversal of magnetization in the electric field region 120. The reader 18 includes a sensor that is processed to a size equal to or smaller than the magnetic domain and can detect the reversal of magnetization. Examples of such sensors include a Hall element and a magnetoresistance effect element.

[0027] Thus, according to this embodiment, it is possible to provide a magnetic memory element capable of writing and reading information by an electric field. In addition, since the magnetic memory element 1 according to this embodiment has a configuration in which the electrodes (first electrode 140 and second electrode 142) are formed in the plane, it is possible to suppress short circuits between the electrodes more than when two electrodes are arranged at a distance in the direction perpendicular to the plane. In addition, since short circuits can be suppressed, it is also possible to make the thin film 12 thinner.

[0028] (Method of manufacturing magnetic memory element) An example of a method for manufacturing a magnetic memory element according to one embodiment of the present invention will be described with reference to FIGS. 5(a) to 5(d).

[0029] First, a thin film 12 is formed on a substrate 10 (FIG. 5(a)). The method for forming the thin film 12 is not particularly limited, and may be any of various known methods such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). Specific examples of PVD include pulsed laser deposition (PLD) and sputtering. Specific examples of CVD include metal organic (MO) CVD and mist CVD.

[0030] Next, an electrode having a desired pattern is formed on the thin film 12. In this embodiment, an example in which an electrode is formed on the thin film 12 by a lift-off method is described, but the method for forming the electrode is not limited to this, and various known methods may be used.

[0031] Specifically, patterned photoresists 20, 22 are attached onto the thin film 12 (FIG. 5(b)). Then, metal films 30, 32, 34, 36, 38 are formed onto the thin film 12 and the photoresists 20, 22 (FIG. 5(c)). The film formation method is not particularly limited and may be any of various known methods such as PVD and CVD. Next, the photoresists 20, 22 are peeled off to form electrodes made of the metal films 30, 34, 38 having a desired pattern (FIG. 5(d)). In this manner, a magnetic memory element in which electrodes having a desired pattern are formed on the thin film 12 can be manufactured. EXAMPLES

[0032] Examples of the present invention will be described below. These examples are for the purpose of conveniently explaining the present invention. These are merely examples and are not intended to limit the invention in any way.

[0033] In the embodiment, BiFe is deposited on the substrate. 0.9 Co 0.1 O 3 A thin film was prepared, and an electrode was formed thereon to prepare a sample according to the embodiment. 3One side of this substrate was polished, and a film was deposited on it by pulsed laser deposition (PLD) at an oxygen partial pressure of 15 Pa, a deposition temperature of 667-680°C, and a laser fluence of 1.0 J / cm. 2 Under the condition, BiFe 0.9 Co 0.1 O 3 A thin film (60 nm thick) was prepared. Platinum electrodes with a 1.5 μm gap were formed on the thin film by lift-off to prepare a sample.

[0034] FIG. 6 is a top view of the sample 40 according to this embodiment. The thin film 42 is (110) oriented. As shown in FIG. 6, in the sample 40 according to this embodiment, a first electrode 440 and a second electrode 442 are formed on the thin film 42 so as to have a gap of 1.5 μm in the [1-10] direction of the thin film 12. As a result, when a voltage is applied to the first electrode 440 and the second electrode 442, an electric field in the [1-10] direction is generated in the thin film 42 in the gap. In addition, the

[0001] direction of the thin film 12 is in-plane and is perpendicular to each of the

[0110] direction and the [1-10] direction. FIG. 6 shows the directions of four spontaneous polarizations (first polarization 52, second polarization 54, third polarization 56, and fourth polarization 58) that the thin film 42 can have in the in-plane direction (parallel to the thin film 12).

[0035] The crystallinity of the formed thin film was evaluated by reciprocal lattice mapping (RSM) using X-ray diffraction. 0.9 Co 0.1 O 3 It was confirmed that a thin film was obtained.

[0036] To investigate the correlation between ferroelectricity and ferromagnetism, ferroelectric and ferromagnetic domains were observed using a piezoelectric force microscope (PFM) and a magnetic force microscope (MFM) (Asylum, Cypher).

[0037] A voltage was applied between the first electrode 440 and the second electrode 442, and the ferroelectric domain and the ferromagnetic domain were observed. As described above, spontaneous polarization can occur in four directions in the plane, so in the PFM measurement, spontaneous polarization was measured in in-plane directions that differed by 90° from each other, and the measurement results of the spontaneous polarization in four directions were obtained by combining these measurement results.

[0038] When voltages of 30V, 60V, 80V, and 100V were applied between the first electrode 440 and the second electrode 442, polarization reversal was observed when a voltage of 80V (533kV / cm) or more was applied. FIGS. 7(a) to 7(d) show the results of observing the ferroelectric domain or ferromagnetic domain when a voltage of +80V and then a voltage of −80V were applied to a part (region B) of region A shown in FIG. 6. FIG. 7(a) shows the results of observing the ferroelectric domain when a voltage of +80V was applied, FIG. 7(b) shows the results of observing the ferroelectric domain when a voltage of −80V was applied thereafter, FIG. 7(c) shows the results of observing the ferromagnetic domain when a voltage of +80V was applied, and FIG. 7(c) shows the results of observing the ferromagnetic domain when a voltage of −80V was applied thereafter.

[0039] In Fig. 7(a) and Fig. 7(b), the direction of spontaneous polarization is indicated by an arrow in each domain. As shown in Fig. 7(a), when a voltage of +80V was applied, a domain 552 of the first polarization 52, a domain 554 of the second polarization 54, and a domain 558 of the fourth polarization 58 were observed in region B. When the applied voltage was inverted from +80V to -80V, a domain 658 of the fourth polarization 58 and a domain 656 of the third polarization 56 were observed in region B, as shown in Fig. 7(b). Comparing Fig. 7(a) and Fig. 7(b), it can be seen that the first polarization 52 was inverted by 109° to the third polarization 56 and the second polarization 54 was inverted by 109° to the fourth polarization 58 by inverting the applied voltage from +80V to -80V. In addition, a polarization inversion of 180° was also observed in some areas.

[0040] In Fig. 7(c) and Fig. 7(d), the direction of the out-of-plane component of spontaneous magnetization is shown in gray scale, and the direction of the out-of-plane component of spontaneous magnetization is opposite between the dark gray area and the light gray area. For example, the direction of the in-plane component of spontaneous magnetization is opposite between the area 700 in Fig. 7(c) and the adjacent area 702. Comparing Fig. 7(c) and Fig. 7(d), it can be seen that the spontaneous magnetization is also reversed by reversing the applied voltage from +80V to -80V. For example, the direction of the in-plane component of spontaneous magnetization is opposite between the area 700 in Fig. 7(c) and the corresponding area 704 in Fig. 7(d), and the direction of the in-plane component of spontaneous magnetization is opposite between the area 702 in Fig. 7(c) and the corresponding area 706 in Fig. 7(d). As described above, in this example, a sample was obtained in which the spontaneous polarization and spontaneous magnetization could be reversed by reversing the applied voltage.

[0041] The present invention has been described above based on the embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0042] 1 magnetic memory element, 10 substrate, 12 thin film, 14 electrode portion, 16 power supply, 18 reading portion, 20, 22 photoresist, 30, 32, 34, 36, 38 metal film, 52 first polarization, 54 second polarization, 56 third polarization, 58 fourth polarization, 140 first electrode, 142 second electrode, 200, 202, 204, 206, 208 spontaneous polarization, 440 first electrode, 442 second electrode, 552, 554, 558, 656, 658 domain.

Claims

1. A thin film composed of a compound represented by the following formula (1), A first electrode arranged in the thin film, The thin film comprises a second electrode arranged on the thin film, The first electrode and the second electrode are arranged such that when a voltage is applied between the first electrode and the second electrode, an electric field is generated in the thin film in a direction parallel to the thin film. Magnetic memory element. Bife １－ｘ A ｘ O ３ ・・・(1) [In equation (1), A is either Co or Mn, and x satisfies 0.05 ≤ x < 0.25.]

2. The thin film is (110) oriented, The magnetic memory element according to claim 1.

3. The first electrode and the second electrode are arranged such that an electric field is generated in the [1-10] direction of the thin film. The magnetic memory element according to claim 2.

4. The thickness of the thin film is 10 nm to 1000 nm. The magnetic memory element according to claim 1.

5. The substrate further comprises the thin film on which the aforementioned thin film is arranged. The substrate is (110) oriented SrTiO ３ Substrate, (010) oriented GdScO ３ Substrate, (010) oriented TbScO ３ Or (010) oriented DyScO ３ The substrate is The magnetic memory element according to claim 1.

6. A method for writing and reading information from a magnetic memory element according to claim 1, A step of writing information by applying a voltage between the first electrode and the second electrode of the magnetic memory element to reverse the magnetization of the thin film, The process includes detecting the reversal of the magnetization of the thin film and reading the written information. A method for writing and reading information from a magnetic memory element.

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