Nanosheet thickness-modulated MoS2 dielectric property evidenced by field-effect transistor performance

Abstract

We report on the nanosheet-thickness effects on the performance of top-gate MoS₂ field-effect transistors (FETs), which is directly related to the MoS₂ dielectric constant. Our top-gate nanosheet FETs with 40 nm thin Al₂O₃ displayed at least an order of magnitude higher mobility than those of bottom-gate nanosheet FETs with 285 nm thick SiO₂, benefiting from the dielectric screening by high-k Al₂O₃. Among the top-gate devices, the single-layered FET demonstrated the highest mobility of ∼170 cm² V⁻¹ s⁻¹ with 90 mV dec⁻¹ as the smallest subthreshold swing (SS) but the double- and triple-layered FETs showed only ∼25 and ∼15 cm² V⁻¹ s⁻¹ respectively with the large SS of 0.5 and 1.1 V dec⁻¹. Such property degradation with MoS₂ thickness is attributed to its dielectric constant increase, which could rather reduce the benefits from the top-gate high-k dielectric.