Seamless Fabrication and Threshold Engineering in Monolayer MoS ₂ Dual-Gated Transistors via Hydrogen Silsesquioxane

From its inception, extensive work on the characterization of field effect transistors (FETs) based on 2D-layered semiconductors has relied on a back-gated transistor architecture. This is useful for initial assessment but lacks ultimate compatibility with integrated circuit (IC) design since the threshold voltage of individual devices cannot be controlled independently in order to achieve specific ON-state and OFF-state performance. Note that threshold engineering via gate electrostatics is inevitable for 2D semiconductors owing to the absence of comprehensive, reliable, and universal doping schemes. In recent years, several strategies are adopted for the gating of individual 2D-FETs such as atomic layer deposition (ALD) of high-k dielectrics, drop casting of ionic liquids, and deterministic transfer of insulating 2D hexagonal boron nitride. These techniques have their respective strengths and weaknesses. A facile, low-temperature, scalable, and universally applicable fabrication scheme for dual-gated monolayer 2D-FETs is reported here, which is compatible with the back-end-of-the-line (BEOL) process flow of complementary metal oxide semiconductor (CMOS) technology, using hydrogen silsesquioxane (HSQ). HSQ is a negative tone resist that possesses dielectric properties similar to SiO ₂ when exposed to high electron beam irradiation and thermal curing and can produce features as small as 10 nm.