A Reliable 2T2MTJ Nonvolatile Static Gain Cell STT-MRAM With Self-Referencing Sensing Circuits for Embedded Memory Application

This paper presents a reliable nonvolatile static gain cell made of two transistors and two magneto-tunneling junctions (MTJs) for cache memory application. The wide distribution in the resistance of MTJs in parallel and anti-parallel states and the variations in the threshold voltage of gain cells are overcome by connecting two complementary MTJs and self-reference sensing circuits, respectively. An enhanced sensing margin and immunity to read disturbance are achieved by applying high voltage across the stacked complementary MTJs. The sensing margin of $8\sigma $ is assured after the Monte Carlo simulation using the measured parameters of the MTJ, including a tunneling magneto-resistance of 200%, a 5% distribution of resistance, and a 5% distribution of threshold voltage in the 65 nm standard CMOS process.