Ultrathin Hafnium Oxide Integration for Two-Dimensional Functional Electronic Devices.

Two-dimensional (2D) materials are considered promising candidates for next-generation electronic devices, especially field-effect transistors (FETs). However, deposition of a uniform dielectric layer on 2D materials with an inert surface is challenging. Herein, the integration of HfOx on graphene is demonstrated through simple thermal oxidation of HfS2 precursor to form a high-quality HfOx/graphene stack. The thermal treatment enables complete conversion from HfS2 into ultrathin HfOx with an atomically smooth surface and sharp interface with graphene. The transformed thin HfOx shows decent dielectric properties, including a high dielectric constant of 18 and a robust breakdown field of 10 MV/cm. High-performance MoS2 FETs based on HfOx/graphene gate stack demonstrate a high ON/OFF ratio of 106, a low subthreshold swing of 75 mV/dec, and a low leakage current. Resistive switching devices were also fabricated showing coexistence of volatile and nonvolatile switching, and a steep switching slope. This nondestructive integration of high-quality high-κ dielectrics on 2D materials opens up possibilities for developing multifunctional 2D electronics.