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 8s 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.