A Body-Voltage-Sensing-Based Short Pulse Reading Circuit for Spin-Torque Transfer RAMs (STT-RAMs)

Fengbo Ren,  Henry Park,  Richard Dorrance,  Yuta Toriyama,  C.-K. Ken Yang,  Dejan Marković
Department of Electrical Engineering, University of California, Los Angeles, CA, USA


With scaling of CMOS and Magnetic Tunnel Junction (MTJ) devices, conventional low-current reading techniques for STT-RAMs face challenges in achieving reliability and performance improvements that are expected from scaled devices. The challenges arise from the increasing variability of the CMOS sensing current and the reduction in MTJ switching current. This paper proposes a short-pulse reading circuit, based on a body-voltage sensing scheme to mitigate the scaling issues. Compared to existing sensing techniques, our technique shows substantially higher read margin (RM) despite a much shorter sensing time and current pulse. Such a narrow pulse of current applied to an MTJ significantly reduces the probability of read disturbance. The RM analysis is validated by Monte-Carlo simulations in a 65-nm CMOS technology with both CMOS and MTJ variations considered. Simulation results show that our technique can achieve over 550 mV RM (1V VDD) with a 1 ns sensing time, which is at least 1.5x higher than that of existing designs with a 5 ns sensing time.