Research Highlights
Nonvolatile Electronic System (NES)
Due to the non-volatility and good scalability, magnetic random access memory (MRAM) has emerged as a competitive candidate for replacing the computer memory system. The main component in MRAM is a magnetic tunnel junction (MTJ). Traditional MTJ is switched by a magnetic field, which suffers from the problems of scaling down and high switching current. Recently, spin transfer torque (STT) based MTJ has been intensively studied because of better scalability. However, the inevitable large current still limits its development compared with the existing memories. Therefore, we intend to explore a MRAM cell which can realize low switching energy and fast access speed. We have developed a compact model describing the MTJ involving various spintronic effects like STT, spin orbit torque (SOT) and voltage control of magnetic anisotropy (VCMA). Based on the model, we have also designed and studied MRAM cells switched by VCMA and SOT. We hope that our research can advance the MRAM development.
Spintronic oscillators are compact microwave sources with low energy consumption. The steady oscillation in existing spintronic oscillators are achieved by balancing the Gilbert damping using spin torque. Based on different sources of spin current, they are categorized into spin torque nano-oscillator (STNO) and spin-Hall nano-oscillator (SHNO). However, both STNO and SHNO suffer low output power (PO) and poor linewidth. In one of our recent works, we propose a novel voltage-input spin torque oscillator (VI-STO) which relies on the back and forth switching of magnetization. The large oscillation window gives a maximum PO of 3.5 µW and tunable frequency from 1.7 to 8.7 GHz. Furthermore, the use of voltage source avoids the problem of accurate current control. We have also theoretically studied a switching based dual free layer spin torque oscillator (SW-STO) integrated with 130, 65, and 14 nm NMOS transistor, which gives PO = 2.5 µW and frequency in hundred MHz range.