Sub‑1 V Threshold\nSwitching in Microwave-Assisted\nSolvothermal Nickel Ferrite Films and Its Application for Steep Switching\nMoS<sub>2</sub>‑Phase FETs

Resistive switching elements have introduced a paradigm\nshift in\nemerging computation, offering energy- and space-efficient logic operations.\nA single-resistive threshold switch can enable applications that require\ntens of standard CMOS transistors. They can also be used to design\nhybrid-phase-FETs with a steep subthreshold slope. We report a back-end-of-line\n(BEOL)-compatible integration of nickel ferrite (NF) films by a microwave-assisted\nsolvothermal (MAS) process offering a very low energy barrier (<i>W</i><sub>0</sub> = 194 m eV) to electrochemical metallization\nof Ag without any doping. The Ag-contacted NF films display volatile\nthreshold switching with sub-1 V electroforming and threshold voltages\nof 0.8 and 0.16 V, respectively. Electroforming is achieved at electric\nfields as low as 107 kV/cm, among the lowest reported for spinel ferrites.\nThe NF film is also integrated into the top-gate stack of a MoS<sub>2</sub> FET to achieve a steep switching phase FET with a minimum\nsubthreshold slope of 8.5 mV/dec, surpassing the Boltzmann limit.\nElectrical measurements and cross-sectional high-resolution transmission\nelectron microscopy (HR-TEM) are used to investigate the filament\nformation in these films, providing crucial insights to enhance the\ndevice performance further. The results place the MAS process as a\npotential option for BEOL dielectric integration and offer pathways\nto sustainable, inexpensive, and low-power electronic devices for\nCMOS logic applications.