Forming and Compliance-free Operation of Low-power, Fast-switching HfOₓSy/HfS₂ Heterostructure Memristors

We demonstrate low power, forming and compliance-free operation of a resistive memory obtained by the partial oxidation of a two-dimensional layered van-der-Waals semiconductor: hafnium disulfide (HfS₂). Semiconductor - oxide heterostructures are achieved by low temperature (<300ᵒC) thermal oxidation of HfS₂ in dry conditions, carefully controlling process parameters such as pressure, temperature and oxygen flow. The resulting HfOₓSy/HfS₂ heterostructures are integrated between metal contacts, forming vertical crossbar devices. Forming-free, compliance-free resistive switching between two non-volatile states is demonstrated by applying voltage sweeps. By applying voltage pulses and measuring the current response in time, we show non-volatile memory operation programmable by 60ns, $<$ 20pJ WRITE and ERASE operations. Multiple stable resistance states are achievable by pulse width and amplitude modulation demonstrating the capability for multi-state programming. Resistance states were retained without fail at 85ᵒC and 150ᵒC, showcasing the potential of these devices for long retention times. Using a technology computer-aided design (TCAD) tool (Synopsys Sentaurus, 2022), we explore the role of the semiconductor layer in tuning the device conductance and driving gradual resistive switching in 2D HfOₓ - based devices.