Abstract
The threshold switch operated by a field-driven insulator-to-metal transition in VO(2) has attracted considerable interest for emerging devices due to its nonlinear and sensitive response to external voltage. However, the nucleation barrier intrinsic to the first-order phase transition causes a finite time delay before the abrupt rise in currents under voltage pulses, thereby hindering energy-efficient device operation. Here, we demonstrate that the strain-graded VO(2) epilayer on Pt nanoislands (NIs) enables percolation-limited threshold switching by promoting the nucleation process of metallic phases during voltage-triggered phase transitions. Unlike constantly strained VO(2), the Pt NIs locally disrupt lattice coherency at the VO(2)/TiO(2) interface, facilitating gradual relaxation of misfit strain energy; tailoring the spatial strain distribution in the strain-graded VO(2) films effectively lowers the activation barrier for the nucleation events of metallic domains, achieving one-twentieth lower incubation time (τ(inc)) compared to constantly strained VO(2) films. Moreover, this percolation-limited phase evolution stabilizes an intermediate metastable phase (i.e., negative differential resistance), enabling robust self-oscillatory behavior across a wide current range with enhanced tunability and dynamic controllability. These findings tailor the phase transition dynamics for ultrafast and energy-efficient switching applications.