Electrothermally-Induced Spatial Inhomogeneities in Nonlinear Electronic Materials

Abstract

The success of implementing energy-efficient neuromorphic computing architectures requires the development of devices with intrinsically biomimetic responses. When coupled with passive circuit elements, devices with nonlinear electrical responses are able to produce action potentials and twenty-two other neurological functions. In certain materials, these nonlinear responses result from the formation of spatial inhomogeneities from metal-insulator transitions (MITs) or electro-thermal localizations that occur due to the interplay of Joule heating and temperature-dependent electrical conductivity. This work progresses the comprehension of electrothermally-induced inhomogeneous phenomena emerging in nonlinear electronic devices under a steady-state or quasi-steady electrical bias. In the first section of this work, a time-dependent relaxation effect is demonstrated in the MIT and electrical response characteristics of boron-alloyed VO2. The progression of the phase transition is indirectly observed in the step-by-step progression of its electrical response, which is attributed to the formation of domains or pinning sites in the material due to the inclusion of the interstitial diffusive dopant. The next study of this work focuses on the derivation of a criterion to predict the spontaneous occurrence of symmetry-breaking electro-thermal localizations in materials with nonlinear electrical transport. A parallel conductor-based model shows that these localizations occur due to the relationship between a material’s nonlinearly temperature-dependent electrical conductivity and its rate of change with respect to a temperature perturbation. This instability criterion relates symmetry breaking to nonequilibrium thermodynamics and dynamical instability through Local Activity theory. The parallel conductor model is next used to develop an equation to predict electrical hysteresis of threshold switching devices to estimate hysteretic energy dissipation. It is found that hysteretic energy dissipation is minimized as the device volume approaches the volume of the localization. Finally, the interplay between electro-thermal localizations and MITs emerging in different regimes of the electrical response of a modeled thin film device is explored with the goal of clarifying the role of localization on the onset of the MIT as device dimensions are decreased.