Injection-Locked Spin Hall-Induced Coupled-Oscillators for Energy Efficient Associative Computing

In this paper, we show that the dynamics of injection-locked Spin Hall Effect Spin-Torque Oscillator (SHE-STO) cluster can be exploited as a robust primitive computational operator for non-Boolean associative computing. A cluster of SHE-STOs can be locked to a common frequency and phase with an injected ac current signal. DC input to each STO from external stimuli can conditionally unlock some of them. Based on the input dc signal, the degree of synchronization of SHE-STO cluster is detected by CMOS interface circuitry. The degree of synchronization can be used for associative computing/matching. We present a numerical simulation model of SHE-STO devices based on Landau-Lifshitz-Gilbert equation with spin-transfer torque term and Spin Hall Effect. The model is then used to analyze the frequency and phase locking properties of injection-locked SHE-STO cluster. Results show that associative computing based on the injection locked SHE-STO cluster can be energy efficient and relatively immune to device parameter variations and thermal noise.