Toward a GHz-Frequency BEOL Ferroelectric Negative-Capacitance Oscillator With a Wide Tuning Range

The potential to utilize negative-capacitance dynamics in a ferroelectric capacitor as a back-end-of-line (BEOL) element to construct a tuned oscillator operating in the GHz range is proposed and investigated. Using tools established in the field of non-linear dynamics, the operating principles of the circuit are rigorously explored, a criterion for oscillation is developed, and amplitude and frequency control are investigated. Furthermore, this novel architecture is compared with a traditional LC oscillator. Through the comparison, we find that the FE oscillator can provide a substantially larger tuning range (149%, between 1.29 GHz–8.75 GHz, vs. 50% achieved by the traditional LC oscillator) and requires a vastly lower on-chip area $(\sim\!\! 50\,{\bm{\mu}}{{\mathbf{m}}^2}\,\text{vs}{\rm{.}}\,\sim 40000\,{\bm{\mu}}{{\mathbf{m}}^2})$ , while achieving a similar figure of merit $\mathbf{FO}{{\mathbf{M}}_2}$ (reduced by only 6 dB). Such improvements motivate the continued exploration and development of negative-capacitance ferroelectrics as BEOL elements that can significantly improve integrated-circuit performance.