Ferroelectric Controlled Nanoscale MoS$_{2}$ Transistor

We report the study of the device characteristics of MoS$_{2}$ field effect transistors with a SiO$_{2}$ backgate and a ferroelectric polymer top gate. We mechanically exfoliated MoS$_{2}$ flakes on 300 nm SiO$_{2}$ substrates. The thinner MoS$_{2}$ pieces were identified by Raman spectroscopy and atomic force microscopy (AFM), and flakes of 1 - 5 nm thick were fabricated into two point devices via e-beam lithography with Ti/Au (5nm/50nm) as the contact electrodes. We then deposited on the top of the device a ferroelectric polymer layer, 20-40 nm polycrystalline poly(vinylidene-fluoride-trifluorethylene) (PVDF-TrFE), using the Langmuir-Blodgett approach. At room temperature, we achieved a current modulation of a factor of 10$^{3}$ using the SiO$_{2}$ back gate. The field effect mobility of the devices is $\sim$ 20 cm$^{2}$V$^{-1}$s$^{-1}$. We then used conducting AFM to control the polarization of the top ferroelectric gate, and examined the SiO2-gated I-Vg characteristics in different polarization states of PVDF-TrFE. By switching the ferroelectric polarization, we induced a 30 V shift in $I$-$V_{\mathrm{g}}$. At fixed backgate voltage, we achieved a maximum switching ratio in the drain current of $\sim$ 15.