Thermally Aided Nonvolatile Memory Using ReS₂ Transistors

Recently two-dimensional (2D) materials have attracted significant research interest for memory applications. Monolayer (MoL) as well as multilayer (ML) MoS₂ have been used for demonstrating thermally assisted non-volatile memories (NVM) [5, 6]. With increasing packing density of FETs on a single wafer, high performance ICs can reach an operating temperature closer to 370-530 K range [3] making it important to understand and exploit the behavioural changes in these materials at higher temperatures (HT). Thermally assisted NVM is one such application where locally generated heat is exploited to aid the switching between RESET (RST/STATE 0) and WRITE (WR/STATE 1) states [4]. In this study thermally varying hysteretic gate operation in ML MoS2 and for the first time in ML ReS₂ is studied and compared for NVM application. Due to lack of interlayer coupling ReS2 behaves as decoupled MoLs making it a direct band gap material (EG-1.5 eV) for both ML and MoL [2] and hence is of interest for optoelectronic applications in MoL as well as ML form. We demonstrate clockwise (CW) hysteresis at lower temperatures (LT) and anticlockwise (ACW) plus step like conductance crossover (STC) hysteresis at 373 K & 400 K for ML ReS₂ and MoS₂ respectively. Similar hysteresis behaviour has been previously reported for MoL MoS₂ only at a very high operating temperature of 500 K [5]. STC hysteresis provides an edge over CW hysteresis at HT in terms of lower operating voltages (Vp-p), larger RST to WR window defined here as ΔVth/Vp-p (where ΔVth is the hysteresis width) and larger READ (RD) window. These parameters for previous NVM reports are mentioned in Table 1 and compared with this work. ML ReS₂ operates at much lower temperatures, lower Vp-p and has larger WR to RST and RD windows as compared to MoS₂.