Irina Chircă | Searcharxiv

arXiv2024

Forming and Compliance-free Operation of Low-energy, Fast-switching HfO$_x$S$_y$/HfS$_2$ Memristors

We demonstrate low energy, 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 (HfS$_2$). Semiconductor - oxide heterostructures are achieved by low temperature ($<300^{o}$C) thermal oxidation of HfS$_2$ in dry conditions, carefully controlling process parameters. The resulting HfO$_x$S$_y$/HfS$_2$ heterostructures are integrated between metal contacts, forming vertical crossbar devices. Forming-free, compliance-free resistive switching between non-volatile states is demonstrated by applying voltage pulses and measuring the current response in time. We show non-volatile memory operation with an R$_{ON}$/ R$_{OFF}$ of 102, programmable by 80ns WRITE and ERASE operations. Multiple stable resistance states are achieved by modulating pulse width and amplitude, down to 60ns, $<$ 20pJ operation. This demonstrates the capability of these devices for low - energy, fast-switching and multi-state programming. Resistance states were retained without fail at 150$^o$C over 10$^4$s, showcasing the potential of these devices for long retention times and resilience to ageing. Low-energy resistive switching measurements were repeated in vacuum (8.6 mbar) showing unchanged characteristics and no dependence of the device on surrounding oxygen or water vapour. Using a technology computer-aided design (TCAD) tool, we explore the role of the semiconductor layer in tuning the device conductance and driving gradual resistive switching in 2D HfO$_x$ - based devices.

physics.app-ph↗

arXiv2024

Controlled Fabrication of Native Ultra-Thin Amorphous Gallium Oxide from 2D Gallium Sulfide for Emerging Electronic Applications

Oxidation of two-dimensional (2D) layered materials has proven advantageous in creating oxide/2D material heterostructures, opening the door for a new paradigm of low-power electronic devices. Gallium (II) sulfide ($β$-GaS), a hexagonal phase group III monochalcogenide, is a wide bandgap semiconductor with a bandgap exceeding 3 eV in single and few layer form. Its oxide, gallium oxide (Ga$_2$O$_3$), combines large bandgap (4.4-5.3 eV) with high dielectric constant (~10). Despite the technological potential of both materials, controlled oxidation of atomically-thin $β$-GaS remains under-explored. This study focuses into the controlled oxidation of $β$-GaS using oxygen plasma treatment, achieving ultrathin native oxide (GaS$_x$O$_y$, ~4 nm) and GaS$_x$O$_y$/GaS heterostructures where the GaS layer beneath remains intact. By integrating such structures between metal electrodes and applying electric stresses as voltage ramps or pulses, we investigate their use for resistive random-access memory (ReRAM). The ultrathin nature of the produced oxide enables low operation power with energy use as low as 0.22 nJ per operation while maintaining endurance and retention of 350 cycles and 10$^4$ s, respectively. These results show the significant potential of the oxidation-based GaS$_x$O$_y$/GaS heterostructure for electronic applications and, in particular, low-power memory devices.

physics.app-ph↗