Graphene field - effect transistors on ferroelectric substrates

Conference poster, 2016

The channel mobility in graphene field-effect transistors (G-FETs) is usually strongly degraded by Coulomb scattering caused by charged impurities. Additional issue is the zero-bandgap in monolayer graphene, which limits the power gain of the G-FETs. The both issues can be effectively addressed by using ferroelectric as a G-FET substrate [1,2]. We show that, at the same residual concentration of the charge carriers, the mobility in monolayer G-FETs on LiNbO3 substrate is higher than that on the SiO2/Si substrate (Fig. 1). The effect is associated with reduction of Coulomb scattering via screening the charged impurity field by the field induced in the ferroelectric substrate, but significant only for mobilities below 1000 cm2 /Vs. Raman spectra analysis [3] and correlations established between mobility and microwave loss tangent [4] of the Al2O3 gate dielectric indicate that the charged impurities are located predominantly in the gate dielectric and/or at the gate dielectric interface and likely associated with oxygen vacancies. The measured characteristic frequencies of the G-FETs on LiNbO3 substrates are approx. 2 GHz (Fig. 2) and limited mainly by parasitic capacitance at the source/drain electrode side walls. The corresponding intrinsic cutoff frequency is more than 10 GHz.