Physical Origin and Theoretical Limit of the Phase Stability of a Spin-Torque Oscillator Stabilized by a Phase-Locked Loop

Abstract

Research on spin-torque oscillators (STOs) has been one of the hottest topics in spintronics for the past 20 years, yet STOs still have not actually seen use in microwave systems, because their phase noise is too great. Improving the phase stability of STOs is of paramount importance to their practical application. The authors build a phase-locked-loop circuit to dynamically stabilize an STO. Analysis of the residual phase error clarifies that the thermal stability of the STO under free-running oscillation sets the theoretical limit for phase error under phase-locked oscillation.