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Researchers Submit Patent Application, "Voltage-Controlled Magnetic Memory Element with Canted Magnetization", for Approval

July 8, 2014

By a News Reporter-Staff News Editor at Physics Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Wang, Kang L. (Santa Monica, CA); Khalili Amiri, Pedram (Los Angeles, CA); Alzate, Juan G. (Los Angeles, CA), filed on December 9, 2013, was made available online on June 26, 2014.

The patent's assignee is The Regents Of The University Of California.

News editors obtained the following quote from the background information supplied by the inventors: "This invention pertains generally to magnetic tunnel junctions, and more particularly to electrical switching of magneto-electric tunnel junctions (MEJ's).

"Spin-polarized currents have been widely used to manipulate and switch the magnetization in nanomagnets via the spin-transfer-torque (STT) effect, giving rise, for example, to STT-MRAM as an emerging memory technology. The use of currents, however, limits the energy efficiency of spintronic memory and logic devices. Thus, the use of electric fields to control magnetic properties may enable devices with significantly lower power consumption, thereby potentially resulting in a paradigm shift in spintronics expanding the range of applications of nonvolatile spintronic devices beyond memory, and enabling a new generation of ultralow-power nonvolatile systems."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "An aspect of the present invention is a magneto-electric tunnel junction that is electrically switchable via voltage-controlled magnetic anisotropy (VCMA) at a CoFeB--MgO interface, where the free layer has canted equilibrium states. The device allows for VCMA-induced switching between two canted states, without the influence of spin-polarized currents, with pulses down to the sub-1 ns regime. The device may also include a partially out-of-plane configuration that allows for selective precessional switching, or combining thermally-activated and precessional switching regimes, resulting in control of the switching direction at a fixed bias magnetic field or even without a bias magnetic field.

"In one aspect, the perpendicular magnetic anisotropy at the interface of MgO and metallic magnetic films is modulated by a voltage applied across the MgO layer. This interfacial voltage-controlled magnetic anisotropy (VCMA) effect is of considerable practical value, given that it uses materials which offer high tunneling magnetoresistance (TMR) ratios, and are compatible with the fabrication processes used for conventional semiconductor electronics.

"In another aspect, VCMA-driven manipulation and switching of voltage-controlled nanoscale MEJ devices is achieved via the competition between easy-plane shape anisotropy and interfacial perpendicular anisotropy (including higher order contributions) that results in canting of the equilibrium states of the free layer. This configuration, which enhances the tunability of the magnetization state of the free layer by the applied voltage, shows VCMA-induced, thermally-activated switching of the free layer with voltage pulses down to 10 ns, assisted by a small (few 10 Oe) in-plane external magnetic field applied to the device. Finally, by reducing the pulse duration to the sub-nanosecond regime, the presence of canted states allows for the elimination of the symmetry of VCMA-induced precessional switching, allowing for control of precessional switching direction by timing the write pulse.

"In one aspect, a memory cell comprises information that is stored in the state of a magnetic bit (i.e. in a free layer, FL), wherein the FL magnetization has two stable states that may be canted (form an angle) with respect to the horizontal and vertical directions of the device. In one embodiment, the FL magnetization may be switched between the two canted states by the application of a voltage (i.e. electric field), which modifies the perpendicular magnetic anisotropy of the free layer.

"In a preferred embodiment, the direction of switching is determined by either one or the combination of: (a) the magnitude of the applied voltage, and/or (b) the width of the voltage pulse applied to the device. I.e., switching between canted states is achieved by either one or a combination of: (a) setting the magnetization into a precessional motion upon application of a voltage pulse, with the pulse width timed such as to ensure switching to the opposite stable state (typical switching time5 ns).

"In one embodiment, the device has at least one additional dielectric layer DE in close proximity with the FL, and an additional pinned (fixed) magnetic layer PL separated from the FL by the DE layer.

"In another embodiment, the PL may have a magnetization orientation that is in-plane or out-of-plane with respect to the sample plane.

"In another embodiment, the relative orientation of the canted FL states with respect to the PL state results in two stable high and low resistance states HR and LR.

"Another aspect is a Magneto-Electric (i.e. voltage-controlled) magnetic Random Access Memory (MERAM) bit as a device exhibiting tunneling magnetoresistance (TMR). This magnetic bit may be integrated with CMOS circuits to perform the write operation (applied voltage) and read operation (readout of the bit resistance). Controlling of the switching direction in MEJ devices is a key requirement for practical MERAM products. In the present invention, canted magnetization states along with differently timed voltage pulses are used to achieve switching in opposite directions (HR to LR and LR to HR).

"Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.


"The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:

"FIG. 1A and FIG. 1B show basic schematic diagrams (cross-sectional views) of memory bits in accordance with the present invention having tilted magnetization in the free layer, representing low and high-resistance states (LR and HR).

"FIG. 2A and FIG. 2B show the memory bits of FIG. 1A and FIG. 1B respectively with additional fixed layers comprising in-plane and/or perpendicular magnetization directions used to realize an overall canted magnetic field acting on the free layer.

"FIG. 3A shows a schematic cross section view of an exemplary device configuration having an in-plane fixed layer in accordance with the present invention.

"FIG. 3B shows a schematic cross section view of an exemplary device configuration having a perpendicular fixed layer in accordance with the present invention.

"FIG. 4 shows a schematic diagram of an exemplary voltage tunable MERAM device in accordance with the present invention.

"FIG. 5A and FIG. 5B show plots of the out-of-plane (FIG. 5A) and in-plane (FIG. 5B) hysteresis loops for an exemplary memory device in accordance with the present invention.

"FIG. 6 shows a plot of measurements of the electric resistance versus in-plane magnetic field (R-H) loops for various free layer thicknesses, where the field H.sub.x is applied along the major axis of the elliptical nanomagnets.

"FIG. 7 shows magnetoresistance versus effective in-plane magnetic field curves for different bias voltage levels.

"FIG. 8 is a plot of the magnetic hysteresis curves at equilibrium (0 V) and at a positive voltage to illustrate the switching process in accordance with the present invention.

"FIG. 9A and FIG. 9B illustrate schematic diagrams of the magnetization of the tested structure along various points on the curve of FIG. 8.

"FIG. 10A and FIG. 10B are plots illustrating dependence of pulse width and magnetic field dependence.

"FIG. 11 shows a plot of switching probability measurement results for the tested device as a function of the applied voltage pulse width."

For additional information on this patent application, see: Wang, Kang L.; Khalili Amiri, Pedram; Alzate, Juan G. Voltage-Controlled Magnetic Memory Element with Canted Magnetization. Filed December 9, 2013 and posted June 26, 2014. Patent URL:

Keywords for this news article include: Physics, Magnetoresistance, The Regents Of The University Of California.

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Source: Physics Week

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