Researchers at Tohoku University have used a new scheme of spin-orbit-torque-induced (SOT-induced) magnetization switching to develop a unique magnetic memory device that can store data without power supply. The study was headed by Professor Hideo Ohno and Associate Professor Shunsuke Fukami of Tohoku University.
Over the past two decades, significant efforts have been made to develop magnetic random access memories or MRAMs that are capable of storing data as the magnetization direction of a magnet. This magnetization can be reversed at high speed indefinitely. As a result, MRAMs are considered as a potential substitute for semiconductor-based working memories, like dynamic random access memories (DRAMs) and static random access memories (SRAMs), which are presently being used, but now facing serious problems.
A major challenge faced in the development of MRAMs is to obtain magnetization reversal in an efficient way. In SOT-induced magnetization switching, torques induced by an in-plane current via the spin-orbit interactions are used. This scheme of SOT-induced magnetization switching has been recently explored and demonstrated. Theoretically, an ultrafast magnetization reversal occurs in a nanosecond timescale through the SOT-induced switching.
Tohoku University researchers demonstrated a novel scheme of SOT-induced magnetization switching. Generally, there had been two types of switching schemes, where the magnetization is orthogonally directed to the applied write current. In the case of the current structure, the magnetization is collinearly directed with the current. Using the new structure, the research team developed three-terminal devices, where a magnetic tunnel junction based on Ta/CoFeB/MgO was employed, and effectively demonstrated the operation of magnetization switching.
The current density needed to promote the magnetization switching was reasonably small, and the resistance variation between 0 and 1 states was found to be resonably large. This suggested that the new-structure magnetic memory device is a potential candidate for MRAM applications.
The researchers also demonstrated that the new-structure magnetic memory device can serve as a handy tool to analyze the physics of SOT-induced switching further, where hidden issues still exist. The structure can store the data without using power, and will allow integrated circuits to consume less power. This advantage is especially critical for applications that experience long standby times, like sensor nodes that could carry out key roles in future Internet of Things (IoT) societies.
The current study, in this regard, has the potential in the development of high-performance, ultralow-power IoT societies and integrated circuits.
The study is financed by JSPS KAKENHI Grant numbers 15K13964 and 15J04691 and the ImPACT Program of CSTI, R&D Project for ICT Key Technology to Realize Future Society of MEXT.
Schematics of structures for three kinds of spin-orbit-torque-induced magnetization scheme. (a) The first previous structure where the magnetization is perpendicular to the film plane. (b) The second previous structure where the magnetization is in-plane and orthogonal to channel current. (c) The new structure where the magnetization is in-plane and collinear with the current.