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

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 SiO ₂, benefiting from the dielectric screening by high-k Al ₂O₃. 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.