Magnetization Switching in Spin Torque Random Access Memory: Challenges and Opportunities
Dynamic thermal magnetization switching and magnetization switching variability determine nano-scale magnetic device performance. As a magnetic device scales down, achieving fast nanosecond time scale magnetization switching and maintaining thermal stability at second to years time scale become increasingly challenging. At the same time, the increased variability due to device dimension shrinking results device performance degradation. In the chapter, these challenges will be illustrated through spin torque random access memory device (SPRAM), which integrates magnetic tunneling junction (MTJ) and CMOS to achieve non-volatility, fast writing/reading speed, almost unlimited programming endurance and zero standby power. In order to fully characterize SPRAM performance, experiment and theoretical studies are pursued at widely separated time and spatial scales. Magnetization switching behaviors from nano-second to second region are measured and modeled. Microscopic quantum electronic spin transport model and macroscopic stochastic magnetization dynamics model are combined to study spin torque induced magnetization switching. Coupled micro-magnetic model and dynamic circuit model are used to simulate SPRAM device performance. Based upon these studies and future SPRAM scaling down requirements, research and development opportunities are identified to reduce switching current magnitude and control device variability.
