JP6902783B2 - Magnetic memory element, and method of writing and reading information of magnetic memory element - Google Patents

Description

The present invention relates to a magnetic memory element and a method of writing and reading information on the magnetic memory element.

In recent years, the development of multiferroic materials having a plurality of properties such as ferromagnetism, ferroelectricity, and ferroelasticity has been progressing. Among such multiferroic materials, materials that have both ferroelectricity and ferromagnetism and whose magnetization can be controlled by an electric field are expected to be applied as low power consumption magnetic memory elements that utilize the response of magnetization by an electric field. ..

Conventionally, as an element using a multiferroic substance, a multiferroic element made of AFeO _{type 3} orthoferrite or the like is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2010-161272

Most of the multiferroic materials known so far show both ferromagnetism and ferroelectricity only at a low temperature of −200 ° C. or lower, or can reverse the magnetization by applying an electric field, so that they are magnetic memory devices. It was difficult to put it to practical use.

The present invention has been made in view of such a situation, and one of the objects thereof is to provide a magnetic memory element capable of writing and reading information by an electric field at room temperature.

In order to solve the above problems, the magnetic memory element of an embodiment of the present invention has a perovskite structure, and a substrate made of a compound having a lattice constant of 3.90 to 3.97 Å in pseudo-cube notation and a substrate on the substrate. An arranged lower electrode, a thin film having a thickness of 200 nm to 1000 nm, which is composed of a compound represented by the following formula (1) and arranged on the lower electrode, and an upper electrode arranged on the thin film. Including.
BiFe _1-x A _x O ₃ ... (1)
[In the formula (1), A is Co or Mn, and x satisfies 0.05 ≦ x <0.25. ]

The substrate, GdScO ₃ substrate 110 orientation, DyScO ₃ substrate 110 orientation, 110 SrTiO ₃ substrate of orientation may be selected from SrTiO ₃ group consisting of a substrate of SrTiO ₃ substrate and 001 the orientation of the 111 orientation.

A method of writing and reading a magnetic memory element according to an aspect of the present invention includes a step of writing information by applying a voltage to the lower electrode and the upper electrode of the magnetic memory element and reversing the magnetization of the thin film, and the magnetization of the thin film. Includes the step of reading the written information by detecting the inversion of.

The magnetic memory element of the present invention can write and read information by reversing the magnetization by applying an electric field at room temperature, and can significantly reduce power consumption.

It is the schematic which shows the structure of an example of the magnetic memory element which concerns on embodiment. 2 (A) and 2 (B) are process diagrams of a method of writing and reading information of a magnetic memory element according to an embodiment. FIG. 3A is a diagram showing the polarization and current of _{the BiFeO 3} thin film and the BiFe _0.9 Co _0.1 O _{3 thin film on the SrTiO 3} (111) substrate as a function with an electric field. Figure 3 (B) _is a piezoelectric response microscopy (PFM) images outside surface of BiFe _{0.85 Co 0.15} O ₃ thin film. Figure 4 (A) is a diagram showing temperature dependence of _{SrTiO 3 (111) BiFe x Co} 1-x O 3 -plane residual magnetization _{M r} of the thin film on the substrate. FIG. 4B is a diagram showing the external magnetic field dependence of the in-plane magnetization of these thin films at room temperature. Figure 4 (C) is a diagram showing temperature dependence of _BiFe 0.9 _Co 0.1 _{O 3-plane} residual magnetization _{M r} of a thin film of SrTiO ₃ (001) substrate. FIG. 4D is a diagram showing the external magnetic field dependence of the in-plane magnetization of the thin film at room temperature. Figure 4 (E) are diagrams showing the temperature dependence of _BiFe 0.9 _Mn 0.1 _{O 3-plane} residual magnetization _{M r} of a thin film of SrTiO ₃ (001) substrate. FIG. 4F is a diagram showing the external magnetic field dependence of the in-plane magnetization of the thin film at room temperature. FIG. 5A is a PFM image of a _{BiFe 0.9} Co _0.1 O _{3 thin film on a GdScO 3} (110) substrate before polling. FIG. 5B is an MFM image of the same thin film before polling. FIG. 5C is a PFM image of the thin film after polling. FIG. 5D is an MFM image of the thin film after polling.

Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The embodiments are not limited to the invention, but are exemplary, and all the features and combinations thereof described in the embodiments are not necessarily essential to the invention. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. In addition, the scale and shape of each part shown in each figure are set for convenience in order to facilitate explanation, and are not limitedly interpreted unless otherwise specified.

(Magnetic memory element)
FIG. 1 is a schematic view showing a configuration of an example of a magnetic memory element according to an embodiment. The magnetic memory element 10 has a perovskite structure, a substrate 11 made of a compound having a lattice constant of 3.90 to 3.97 Å in pseudocubic notation, a lower electrode 12 arranged on the substrate 11, and a lower electrode 12. The thin film 13 arranged on the thin film 13 and the upper electrode 14 arranged on the thin film 13 are included. In FIG. 1, the power supply 15 is a power supply for applying a voltage to the magnetic memory element 10.

The substrate 11 has a perovskite structure and is composed of a compound having a lattice constant of 3.90 to 3.97 Å in pseudocubic notation. By forming the thin film 13 on the substrate 11 made of such a compound, the essential magnetization of the thin film 13 itself can be expressed, and the magnetization of the thin film 13 can be reversed by applying an electric field at room temperature. Specific examples of the substrate 11, GdScO ₃ substrate 110 orientation, DyScO ₃ substrate 110 orientation, SrTiO ₃ substrate of 110 orientation, include SrTiO ₃ substrates of SrTiO ₃ substrate and 001 the orientation of the 111 orientation. The thickness of the substrate 11 is not particularly limited, but is preferably 300 μm to 1000 μm, more preferably 400 μm to 600 μm, from the viewpoint of easy thin film synthesis and handling.

The material constituting the lower electrode 12 is not particularly limited, and a known electrode material can be used. Examples of the material include SrRuO ₃ , LaNiO ₃ , La _0.5 Sr _0.5 CoO _{3, and the} like.

The thin film 13 is made of a compound represented by the following formula (1).
BiFe _1-x A _x O ₃ ... (1)
In the 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 13 can exhibit ferromagnetism and ferroelectricity at room temperature. When x is less than 0.25, the change in the crystal structure of the thin film 13 can be suppressed. The magnitude of spontaneous magnetization of the thin film 13 at room temperature is about 1 emu / cm ^{3 to} 10 emu / cm ³ , and the magnitude of spontaneous polarization is about 50 to 150 μC / cm ² . The magnetization direction of the thin film 13 can be reversed by an electric field generated by applying a voltage to the lower electrode 12 and the upper electrode 14. As a result, information can be written to the thin film 13, and the written information can be read by detecting the inverted magnetization.

The thickness of the thin film 13 is 200 nm to 1000 nm. With the thickness of the thin film 13, an electric field can be reliably applied to the thin film 13, and the reliability of the device can be improved. From the viewpoint of lattice strain, the thickness of the thin film 13 is preferably 200 nm to 400 nm.

The method for forming the lower electrode 12 and the thin film 13 is not particularly limited, and the lower electrode 12 and the thin film 13 can be formed by a method known to those skilled in the art, such as a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method). it can. Specific examples of the PVD method include a pulsed laser deposition (PLD) method and an electron beam deposition method. Specific examples of the CVD method include an organometallic (MO) CVD method and a mist CVD method.

The material constituting the upper electrode 14 is not particularly limited as in the lower electrode 12, and a known electrode material can be used. The materials constituting the lower electrode 12 and the upper electrode 14 may be the same or different. The upper electrode 14 may be formed by, for example, the above-mentioned vapor deposition method, similarly to the lower electrode 12. Alternatively, a known electrode pad may be attached on the thin film 13 as the upper electrode 14.

(Method of writing and reading information of magnetic memory element)
2 (A) and 2 (B) are process diagrams of a method of writing and reading a magnetic memory element according to an embodiment. The method of writing and reading the information of the magnetic memory element according to the present embodiment includes a step of applying a voltage to the lower electrode and the upper electrode of the magnetic memory element to invert the magnetization of the thin film and writing the information, and the magnetization of the thin film. Includes the step of detecting the inversion of and reading the written information. According to this method, since information is written to the magnetic memory element by applying an electric field, power consumption can be suppressed as compared with a conventional magnetic memory element that writes with a magnetic field generated by an electric current.

Specifically, FIG. 2A shows a magnetic memory element 10 before applying an electric field and a reading unit 20 arranged above the magnetic memory element. In FIG. 2A, the magnetization direction M of the thin film 13 before the application of the electric field is downward as shown by the black arrow.

Next, as shown in FIG. 2B, an electric field is applied to the thin film 13 by applying a voltage E to the lower electrode 12 and the upper electrode 14 of the magnetic memory element 10 in the direction indicated by the white arrow. As a result, the magnetization direction of the thin film 13 is inverted upward as indicated by the black arrow, and information is written to the thin film 13. In FIGS. 2 (A) and 2 (B), the direction M of the magnetization of the thin film is indicated by a black arrow for easy understanding, but in reality, the BiFe _1-x Co _x O constituting the thin film 13 is shown. _{Reference numeral 3} is formed on eight easy-to-magnetize planes oriented in 111 directions and perpendicular to the electric polarization. In the present embodiment, the magnetization of the planar component of the thin film 13 is reversed by applying a voltage to the lower electrode 12 and the upper electrode 14.

The information written in the thin film 13 is read by the reading unit 20 by detecting the reversal of the magnetization of the thin film 13. The reading unit 20 includes a sensor processed to a size smaller than the magnetic domain and capable of detecting the reversal of magnetization. Examples of such a sensor include a magnetoresistive sensor and the like.

Hereinafter, examples of the present invention will be described, but these examples are merely examples for suitably explaining the present invention, and do not limit the present invention in any way.

To generate BiFe _{1-x Co} x _{O 3} thin film, as the substrate, SrTiO ₃ (111) to stabilize the rhombohedral structure can be expected, and the lattice mismatch small GdScO ₃ (110) of the thin film was selected .. _{After forming a 15 nm SrRuO 3} thin film as a lower electrode on these substrates by a pulse laser deposition (PLD) method _{, a BiFe 1-x} Co _x O ₃ thin film (x) under the conditions of an oxygen partial pressure of 15 Pa and a substrate temperature of 700 ° C. = 0,0.05,0.10,0.15, film thickness 200 nm) was prepared. The crystallinity was evaluated using X-ray diffraction (XRD) (SmartLab manufactured by Rigaku Corporation). The electrical characteristics were evaluated using a ferroelectric evaluation system (FCE-1E manufactured by Toyo Technica Co., Ltd.) after depositing a Pt upper electrode having a diameter of 100 μm by electron beam deposition. Observation / writing of the ferroelectric domain and observation of the ferromagnetic domain were performed using a piezoelectric response microscope (PFM) and a magnetic force response microscope (MFM) (Agilent 5420). The magnetic properties were evaluated using a superconducting quantum interference device (SQUID) (MPMS manufactured by Quantum Design Co., Ltd.).

First shows a _{SrTiO 3 (111) BiFe 1-} x Co x O 3 results for the thin film on the substrate. In all compositions was confirmed by _{BiFe 1-x Co x O 3} XRD that thin film was obtained 2 [Theta]-theta scan and 121 peaks of φ scan with rhombohedral symmetry structure of a single phase. _{Subsequently,} to confirm the presence or absence of the ferroelectric at room temperature for _BiFe 1-x _Co x _{O 3} thin film. The PE hysteresis loop of the thin film having the composition of x = 0,0.10. Is shown in FIG. 3 (A). In the thin film (BiFeO ₃ ) having an x = 0 composition, a good prismatic hysteresis loop was obtained. On the other hand, in the thin film having x = 0.10 composition, the leakage increased, resulting in a rounded hysteresis loop. In the thin film having a composition of x = 0.15 in which the amount of Co substitution was further increased, a hysteresis loop could not be obtained due to the further increase in leakage. Therefore, writing was performed by PFM, which is not easily affected by the leak (FIG. 3 (B)). It can be seen that a clear ferroelectric domain can be written. From the above, it was confirmed that all the thin films were ferroelectrics at room temperature.

_{SrTiO 3 (111) BiFe 1-} x Co x O 3 Temperature dependence of the in-plane residual magnetization of the thin film on the substrate is shown in FIG. 4 (A). The magnetization of the thin film having x = 0 and 0.05 composition was almost zero in this temperature range. On the other hand, it can be seen that the magnetizations of the thin films having x = 0.10 and 0.15 compositions change significantly at approximately 220K and 130K, respectively. The external magnetic field dependence of the in-plane magnetization at 300K is shown in FIG. 4 (B). Thin films with x = 0.10 and 0.15 compositions showed a ferromagnetic hysteresis loop. The value of residual magnetization is 0.04 μB / f. u. Degree. From these results, it is considered that the thin films having the composition of x = 0.10 and 0.15 show weak ferromagnetism due to the tilt angle spin at room temperature. Similarly, it _{was confirmed that BiFe 0.9} Co _0.1 O ₃ and BiFe _0.9 Mn _0.1 O _{3 on the SrTiO 3} (001) substrate also showed weak ferromagneticness due to tilt angle spin at room temperature (FIG. 4). (C) to FIG. 4 (F)).

Finally, in order to investigate the presence or absence of the correlation between ferroelectricity and ferromagnetism, we attempted to observe the ferroelectric domain and the ferromagnetic domain using PFM and MFM. However, it was difficult to observe the magnetic domain using MFM because the spontaneous magnetization of _{the BiFe 1-x} Co _x O _{3 thin film on the SrTiO 3} substrate on which the change in magnetic structure could be observed exists in the thin film plane. Therefore, the same experiment was carried out for _BiFe 1-x _Co x _{O 3} thin film GdScO ₃ (110) substrate that can be expected to have a magnetization component in the thin film plane outward. _{Specifically,} the polarization of _BiFe 1-x _Co x _{O 3} is for facing the eight 111 direction, it is necessary to map the piezoelectric response of the plane of the out-of-plane, and the two orthogonal directions. Therefore, the polarization mapping image of total is obtained by measuring the out-of-plane and in-plane polarization of the film surface by PFM and synthesizing the obtained three images into one image by image processing. Was produced. FIG. 5 (A) shows a PFM image of a _{BiFe 0.9} Co _0.1 O _{3 thin film on a GdScO 3} (110) substrate. It can be seen that there is contrast on the stripes. Such domain structures are often reported in (001) oriented BiFeO ₃ thin films and are believed to be in the 71 ° domain. FIG. 5B shows an MFM image observed in the same region. It can be seen that there is a contrast similar to the PFM image. The direction of magnetization of the magnetic cantilever was reversed and observed, and it was confirmed that the contrasts were reversed, and it was confirmed that these contrasts corresponded to the magnetic domain. From the above results, it was clarified that there is a correlation between the ferroelectric domain and the ferromagnetic domain. Subsequently, an electric field was applied using PFM to invert the out-of-plane polarization, and then the same PFM and MFM were measured to verify whether or not the magnetization reversal due to the application of the electric field occurred.

The PFM image and the MFM image of the BiFe _0.9 Co _0.1 O ₃ thin film after polling are shown in FIGS. 5 (C) and 5 (D), respectively. From FIGS. 5 (C) and 5 (D), by applying an electric field, the polarization of the ferroelectric domain was reversed only in the plane-straight component while maintaining the domain shape, and the plane-direct magnetization was reversed accordingly. From this, it was confirmed that local magnetization reversal occurs by applying an electric field.

Although the present invention has been described above with reference to the above-described embodiment, the present invention is not limited to the above-described embodiment, and the present invention is not limited to the above-described embodiment, and the configuration of the embodiment may be appropriately combined or replaced. It is included in the present invention. Further, it is also possible to appropriately rearrange the combinations and the order of processes in the embodiment based on the knowledge of those skilled in the art, and to add modifications such as various design changes to the embodiments, and such modifications are added. The embodiments described may also be included in the scope of the present invention.

10 Magnetic memory element, 11 Substrate, 12 Lower electrode, 13 Thin film, 14 Upper electrode.

Claims (3)

A substrate composed of a compound having a perovskite structure and a lattice constant of 3.90 to 3.97 Å in pseudocubic notation.
With the lower electrode arranged on the substrate,
A thin film composed of a compound represented by the following formula (1) and having a thickness of 200 nm to 1000 nm arranged on the lower electrode, and a thin film having a thickness of 200 nm to 1000 nm.
With the upper electrode arranged on the thin film,
Unrealized, a magnetic memory device characterized by inverting the magnetization of the thin film by a voltage applied between the upper electrode and the lower electrode.
BiFe _1-x A _x O ₃ ... (1)
[In the formula (1), A is Co or Mn, and x satisfies 0.05 ≦ x <0.25. ] The substrate, 110 GdScO ₃ substrate orientation, 110 orientation DyScO ₃ substrate, 110 SrTiO ₃ substrate orientation, according to claim 1 selected from the group consisting of 111 SrTiO ₃ SrTiO ₃ substrate and 001 the orientation of the orientation Magnetic memory element. The method for writing and reading information on a magnetic memory element according to claim 1 or 2.
A step of applying a voltage to the lower electrode and the upper electrode of the magnetic memory element, inverting the magnetization of the thin film by the voltage, and writing information.
The step of detecting the reversal of the magnetization of the thin film and reading the written information,
A method of writing and reading information on a magnetic memory element, comprising:

Images