A Three-Terminal Dual-Pillar STT-MRAM for High-Performance Robust Memory Applications

Abstract

The design of a three-terminal self-aligned dual-pillar (DP) magnetic tunnel junction (MTJ) utilizing both current-induced spin-transfer torque (STT) and magnetic domain-wall motion effects is proposed for high-speed nonvolatile robust memory applications. The choice of a thin tunneling oxide (~0.9 nm) in a write-in port, spatially and electrically separated from a read-out port incorporating a thicker (~1.8 nm) oxide on an extended thin-film multilayer stack, significantly improves the overall cell stability and parametric process yield of a memory array. A dual-bit-line memory architecture incorporating a single-ended voltage-sensing scheme for fast data readout with just one access transistor per cell is also proposed for the first time. The technology-circuit cooptimization of the proposed single-transistor (1T) DP STT magnetic random access memory (MRAM) cell is carried out using effective mass-based transport simulations in nonequilibrium Green's function formalism and accurate micromagnetic simulations involving the Landau-Lifshitz-Gilbert-Slonczewski equation. The proposed DP STT-MRAM bit cell outperforms a state-of-the-art 1T-1MTJ STT-MRAM cell in terms of higher cell tunneling magnetoresistance, simplified memory array architecture with a single supply for read/write, and significantly lower probability of disturb and access failures under parametric process variations with a marginal increase in critical switching current.