Performance and stability improvement of CVD monolayer MoS2 transistors through HfO2 dielectrics engineering

Abstract

Monolayer molybdenum disulfide (MoS2) is a promising semiconductor channel material for future electronics due to its atomic thickness and high mobility. However, conventional back-gate MoS2 transistors suffer from substantial scattering caused by substrate and surface adsorbates, which impair carrier mobility and device reliability. In this work, we demonstrate an exemplary dielectric engineering approach that uses atomic-layer-deposited hafnium oxide (HfO2) as the gate dielectric and channel passivation layer to improve device performance and positive bias instability. The large-single-crystal monolayer MoS2 film was directly synthesized on SiO2/Si substrates by a low-pressure chemical vapor deposition method. MoS2 transistors with various dielectrics were fabricated and characterized for a fair comparison. The mobility increased from 4.2 to 19.9 cm2/V·s by suppressing charged impurities and phonon scattering when transferring the MoS2 channel from 100 nm SiO2 substrates to 20 nm HfO2 substrates. Passivation of another 10 nm HfO2 on the back-gate transistors further increased the mobility to 36.4 cm2/V·s with a high drive current of 107 μA/μm. Moreover, the threshold voltage shift of the passivated transistor was reduced by about 58% from 1.9 to 0.8 V under positive bias stress. This is due to the fact that channel passivation with HfO2 effectively eliminated charge trapping of adsorbed substances. These results reveal that HfO2 gate dielectric and passivation by atomic-layer deposition are effective methods to improve the performance and stability of MoS2 devices.