Dual-Bit Spin Dice Based on Spin–Orbit Torque in Perpendicular Magnetic Multilayers

In this letter, novel dual-bit spin dice based on spin–orbit torque are simulated. The design consists of two bistable magnetic tunnel junctions separated by a spacer layer of heavy metal. By utilizing the spin current at both sides of the heavy metal, the magnetization of free layers in the top and bottom magnetic tunnel junction can be pushed to a metastable state. Once the spin–orbit torque is removed, the magnetic moments of the two free layers relax to the stable state stochastically, which can be detected as two random numbers. A set of two random numbers is generated in a single device simultaneously, which leads to two-times improvement in the integration density and throughput over a conventional scenario. The simulation results indicate that the random bit streams can be produced steadily in the device against a wide range of process, voltage, and temperature variations. The designed system can generate random bits as fast as 200 MHz, while the energy consumption is only 18 fJ/bit, which has great potential in the fields of data/hardware security.