Large Area CVD MoS2 RF transistors with GHz performance

Molybdenum disulfide (MoS$_{\mathrm{2}})$ is a 2D semiconductor in the family of transition metal dichalcogenides (TMDs). Its single layer direct bandgap of \textasciitilde 1.8 eV allows for high I$_{\mathrm{ON}}$/I$_{\mathrm{OFF}}$ metal-oxide semiconducting field-effect transistors (FETs). More relevant for radio frequency (RF) wireless applications, theoretical studies predict MoS$_{\mathrm{2}}$ to have saturation velocities, $v_{\mathrm{sat}}$ \textgreater 3\texttimes 10$^{\mathrm{6}}$ cm/s. Facilitated by cm-scale CVD MoS$_{\mathrm{2}}$, here we design and fabricate both top-gated and embedded gate short channel MoS$_{\mathrm{2}}$ RF transistors, and provide a systematic comparison of channel length scaling, extrinsic doping from oxygen-deficient dielectrics, and a gate-first gate-last process flow. The intrinsic $f_{\mathrm{T}}$ ($f_{\mathrm{max}})$ obtained from the embedded gate transistors shows 3X (2X) improvement over top-gated CVD MoS$_{\mathrm{2}}$ RF FETs, and the largest high-field saturation velocity, $v_{\mathrm{sat}} \quad =$ 1.88 \texttimes 10$^{\mathrm{6}}$ cm/s, in MoS$_{\mathrm{2}}$ reported so far. The gate-first approach, offers enhancement mode operation, I$_{\mathrm{ON}}$/I$_{\mathrm{OFF}}$ ratio of 10$^{\mathrm{8}}_{\mathrm{,}}$ and the highest reported transconductance (g$_{\mathrm{m}})$ of 70 $\mu $S/$\mu $m. By manipulating the interfacial oxygen vacancies in atomic layer deposited (ALD) HfO$_{\mathrm{2-x}}$ we are able to achieve 2X current density over stoichiometric Al$_{\mathrm{2}}$O$_{\mathrm{3}}$. We demonstrate a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS$_{\mathrm{2}}$ may be suitable for industrial-scale electronic applications.