Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model - Part II: Verilog-A Model Implementation

TL;DR

This paper presents a Verilog-A implementation of a macrospin-based analytical model for MTJ spin torque oscillators, enabling accurate circuit and system-level simulations including phase noise effects.

Contribution

The paper introduces a comprehensive Verilog-A model of MTJ STO that reproduces key device characteristics and phase noise, validated against analytical models and system simulations.

Findings

Model accurately reproduces frequency, linewidth, and amplitude.

Verilog-A implementation validated against analytical model.

System simulation demonstrates applicability in circuit design.

Abstract

The rapid development of the magnetic tunnel junction (MTJ) spin torque oscillator (STO) technology demands an analytical model to enable building MTJ STO-based circuits and systems so as to evaluate and utilize MTJ STOs in various applications. In Part I of this paper, an analytical model based on the macrospin approximation, has been introduced and verified by comparing it with the measurements of three different MTJ STOs. In Part II, the full Verilog-A implementation of the proposed model is presented. To achieve a reliable model, an approach to reproduce the phase noise generated by the MTJ STO has been proposed and successfully employed. The implemented model yields a time domain signal, which retains the characteristics of operating frequency, linewidth, oscillation amplitude and DC operating point, with respect to the magnetic field and applied DC current. The Verilog-A implementation is verified against the analytical model, providing equivalent device characteristics for the full range of biasing conditions. Furthermore, a system that includes an MTJ STO and CMOS RF circuits is simulated to validate the proposed model for system- and circuit-level designs. The simulation results demonstrate that the proposed model opens the possibility to explore STO technology in a wide range of applications.