Detangling extrinsic and intrinsic hysteresis for detecting dynamic switch of electric dipoles using graphene field-effect transistors on ferroelectric gates

Abstract

A transition in source–drain current vs. back gate voltage (I_D–V_BG) characteristics from extrinsic polar molecule dominant hysteresis to anti-hysteresis induced by an oxygen deficient surface layer that is intrinsic to the ferroelectric thin films has been observed on graphene field-effect transistors on Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ gates (GFET/PLZT-Gate) during a vacuum annealing process developed to systematically remove the polar molecules adsorbed on the GFET channel surface. This allows the extrinsic and intrinsic hysteresis on GFET/PLZT-gate devices to detangle and the detection of the dynamic switch of electric dipoles using GFETs, taking advantage of their high gating efficiency on ferroelectric gate. A model of the charge trapping and pinning mechanism is proposed to successfully explain the transition. In response to pulsed V_BG trains of positive, negative, as well as alternating polarities, respectively, the source–drain current I_D variation is instantaneous with the response amplitude following the I_D–V_BG loops measured by DC V_BG with consideration of the remnant polarization after a given V_BG pulse when the gate electric field exceeds the coercive field of the PLZT. A detection sensitivity of around 212 dipole per μm² has been demonstrated at room temperature, suggesting the GFET/ferroelectric-gate devices provide a promising high-sensitivity scheme for uncooled detection of electrical dipole dynamic switch.