Sub-1 V Threshold Switching in Microwave-Assisted Solvothermal Nickel Ferrite Films and Its Application for Steep Switching MoS₂-Phase FETs

Resistive switching elements have introduced a paradigm shift in emerging computation, offering energy- and space-efficient logic operations. A single-resistive threshold switch can enable applications that require tens of standard CMOS transistors. They can also be used to design hybrid-phase-FETs with a steep subthreshold slope. We report a back-end-of-line (BEOL)-compatible integration of nickel ferrite (NF) films by a microwave-assisted solvothermal (MAS) process offering a very low energy barrier (W₀ = 194 m eV) to electrochemical metallization of Ag without any doping. The Ag-contacted NF films display volatile threshold switching with sub-1 V electroforming and threshold voltages of 0.8 and 0.16 V, respectively. Electroforming is achieved at electric fields as low as 107 kV/cm, among the lowest reported for spinel ferrites. The NF film is also integrated into the top-gate stack of a MoS₂ FET to achieve a steep switching phase FET with a minimum subthreshold slope of 8.5 mV/dec, surpassing the Boltzmann limit. Electrical measurements and cross-sectional high-resolution transmission electron microscopy (HR-TEM) are used to investigate the filament formation in these films, providing crucial insights to enhance the device performance further. The results place the MAS process as a potential option for BEOL dielectric integration and offer pathways to sustainable, inexpensive, and low-power electronic devices for CMOS logic applications.