Design space exploration of typical STT MTJ stacks in memory arrays in the presence of variability and disturbances

Abstract

High leakage power in sub-100-nm memory technology nodes drives the need for nonvolatile memory devices to reduce power consumption and enhance battery life. Spin-transfer torque magnetic tunneling junction (STT-MTJ) is a promising nonvolatile memory device with comparable read and write performances as SRAM and eDRAM with almost zero standby power. In this paper, we present a simulation framework that can solve transport [using nonequilibrium Green's function (NEGF) formalism] and magnet dynamics [using Landau-Lifshitz-Gilbert (LLG) equation] self-consistently to study the read and write performances of STT-MTJ. Due to process variations, thermal disturbances, and stray fields, the performance of STT-MTJ degrades and results in one transistor-one STT-MTJ (1T-1STTMTJ) memory failures. A thorough memory design space investigation can help us to reduce such failures. Hence, we present a design space exploration framework for 1T-1STTMTJ memory, which consists of magnetic materials with different RAPA products, different genres of MTJ stacks, and a transistor. A comprehensive study based on critical memory performance metrics such as tunneling magnetoresistance, JC, and write cycle shows the relative merits and demerits of each MTJ stack for embedded memory applications. Finally, the benefits of synthetic antiferromagnet free layer in providing immunity against stray fields are shown illustrating the need for coupled free-layer stacks in scaled technology nodes. © 2011 IEEE.