Analog to Stochastic Bit Stream Converter Utilizing Voltage-Assisted Spin Hall Effect

Abstract

We introducea spintronic analog to stochastic bit stream (SBS) converter (ASC) based on a three terminal magnetic tunnel junction (MTJ) with a heavymetal layer. The critical current of the spin Hall effect (SHE) for switching the MTJ is efficiently modulated by applying a voltage across the MTJ via the voltage-controlled magnetic anisotropy effect. This effect results in the switching probability linearly depending on the amplitude of the analog input signal of the ASC. There are several advantages of using the voltage-assistedSHE for generating an SBS. The stochastic switching behavior of MTJ devices drastically reduces the area overhead by simplifying control circuits in the ASC. Moreover, the voltage-assisted SHE switching improves energy efficiency over traditional spin transfer torque (STT)-based MTJ switching by diminishing ohmic dissipation. Also, multiple MTJs on a single heavy metal layer increases the bandwidth by simultaneously converting analog input signals to SBSs. The performance of the spintronic ASC was evaluated by using the macrospin three terminal MTJ compactmodel integrated into a 45-nm CMOS technology. The proposed ASC can achieve 7x reduction in power consumption comparedto the previousSTT-basedwork and significant improvement in area-efficiency compared with the pure CMOS-based design.