Three-Terminal Spintronics Devices for CMOS Integration

Abstract

I report our effort on realizing three-terminal spintronics devices that can be used for integration with CMOS VLSI; three-terminal devices, in principle, allow higher speed and more reliable operation compared to their two-terminal counterpart [1]. Of particular interest are devices that utilize spin-orbit torque (SOT) switching, which does not require an antiferromagnetically aligned pair of magnetic electrodes like in current-induced domain wall motion devices [2]. The first topic I discuss is a high speed operation of an SOT switching device with a target ferromagnetic pillar having an in-plane magnetic easy axis collinear with the current flow direction in the underneath heavy-metal [3]. We show that one can switch magnetization as fast as 500 ps in this structure; a switching speed not readily available in two-terminal devices utilizing spin-transfer torque (STT) switching because STT requires switching current inversely proportional to the switching speed in this speed range. Another advantage of this scheme is that one can fabricate from exactly the same stack two different SOT devices; another being pillars having in-plane easy-axis but its direction perpendicular to the current direction, where conventional STT switching takes place. Using the two, we discuss the torques operating in the switching events. The second topic to be discussed is the use of an antiferromagnetic material as a source of spin flow as well as the exchange field: The former is for the switching and the latter is for the switching in the absence of external magnetic field. A small external magnetic field was required to induce SOT switching in structures other than ordinary STT switching took place, which was clearly an obstacle for future integration. It has been shown in a (Co/Ni)-multilayer/PtMn structure one can switch magnetization in the absence of external magnetic field [4].