The stability of the subthreshold swing (SS) is quite important for switch and memory applications in logic circuits. The SS in our MoS₂ field effect transistor (FET) is enlarged when the gate voltage sweep range expands towards the negative direction. This is quite different from other reported MoS₂ FETs whose SS is almost constant while varying gate voltage sweep range. This anomalous SS enlargement can be attributed to interface states at the MoS₂–SiO₂ interface. Moreover, a deviation of SS from its linear relationship with temperature is found. We relate this deviation to two main reasons, the energetic distribution of interface states and Fermi level shift originated from the thermal activation. Our study may be helpful for the future modification of the MoS₂ FET that is applied in the low power consumption devices and circuits.

We investigated the influence of the flake thickness for molybdenum disulfide (MoS ₂ ) field effect transistors on the effect of a 150 keV high-energy proton beam applied on these devices. The electrical characteristics of the devices with channel thicknesses ranging from monolayer to bulk were measured before and after proton irradiation with a proton fluence of 5 × 10 ¹⁴ cm ⁻² . The subthreshold swing (SS), threshold voltage shift and electron mobility were extracted with the Y -function method after proton irradiation and significant degradation were observed. It is found that, with the increase of layer thickness, mobility degradation and threshold voltage shift both eased, but the SS degradation was insensitive to the MoS ₂ flake thickness increase. We also demonstrate that the threshold voltage shift is dominated by oxide charges; however, the mobility and SS degradations are mainly affected by the interface traps. Our study will enhance the understanding of the influence of high-energy particles on MoS ₂ -based nano-electronic devices. By increasing the MoS ₂ flake thickness to a certain extent, one can hopefully find a balance between effectively resisting V T H shift and achieving high mobility and small SS degradation.

Contact resistance ( R _C ) is of great importance for radio frequency (RF) applications of graphene, especially graphene field effect transistors (FETs) with short channel. FETs and transmission line model test structures based on chemical vapor deposition grown graphene are fabricated. The effects of employing traditional lithography solvent (Acetone) and strong solvents for photo resist, such as N, N-Dimethylacetamide (ZDMAC) and N-Methyl pyrrolidone (NMP), are systematically investigated. It was found that ZDMAC and NMP have more proficiency than acetone to remove the photo-resist residues and contaminations attached on graphene surface, enabling clean surface of graphene. However, strong solvents are found to destroy the lattice structure of graphene channel and induce defects in graphene lattice. Clean surface contributes to a significant reduction in the R _C between graphene channel and metal electrode, and the defects introduced on graphene surface underneath metal electrodes also contribute the reduction of R _C . But defects and deformation of lattice will increase the resistance in graphene channel and lead to the compromise of device performance. To address this problem, a mix wet-chemical approach employing both acetone and ZDMAC was developed in our study to realize a 19.07% reduction of R _C , without an unacceptable mass production of defects.

Recently, graphene has led to unprecedented progress in device performance at the atom limit. A high performance of field-effect transistors requires a low graphene–metal contact resistance. However, the chemical doping methods used to tailor or improve the properties of graphene are sensitive to ambient conditions. Here, we fabricate a single-layer perfluorinated polymeric sulfonic acid (PFSA), also known as Nafion, between the graphene and the substrate as a p-type dopant. The PFSA doping method, without inducing any additional structural defects, reduces the contact resistance of graphene by ∼28.8%, which has a significant impact on practical applications. This reduction can be maintained for at least 67 days due to the extreme stability of PFSA. Effective, uniform and stable, the PFSA doping method provides an efficient way to reduce the contact resistance of graphene applications.