MoS$_{2}$ Transistors Operating at Gigahertz Frequencies

The presence of a direct band gap and an ultrathin form factor has caused a considerable interest in 2D semiconductors from TMD family with MoS$_{2}$ being the most studied representative of this family of materials. While diverse electronic elements, integrated circuits and optoelectronic devices have been demonstrated using ultrathin MoS$_{2}$ and related materials, very little is known about their performance at high frequencies. We fabricated top-gated MoS$_{2}$ transistors operating in the gigahertz range of frequencies. The presence of a band gap also gives rise to current saturation, allowing voltage gain higher than 1. The RF transistors are fabricated from exfoliated MoS$_{2}$ with different layer thickness. All our devices presented transconductance typical of n-type materials with on-state current reaching 300 $\mu$A/$\mu$m for $V_{\mathrm{ds}} = $ 2 V and gate voltage $V_{\mathrm{tg}} = $ 10 V in the case of monolayer MoS$_{2}$. The current gain of the MoS$_{2}$ FETs decreases with increasing frequency and shows the typical 1/$f $dependence. In conclusion, we studied top-gated MoS$_{2}$ transistors with a 240 nm gate length. Our MoS$_{2}$ RF-FETs show an intrinsic transconductance higher than 50 uS/um and a drain-source current saturation with a voltage gain higher than 1. Our devices show cut-off frequencies in the GHz range and are able not only to amplify current in this frequency range but also power and voltage, with the maximum operating frequency $f_{\mathrm{max}}= $ 8.2 GHz.