Fig. 2: Microscopic and electrical characterization of OFET.

a Schematic of the OFET in a bottom-gate bottom-contact structure fabricated on a polyethylene naphthalate (PEN) substrate combining low trap density-of-state (DOS) channel and high-k/low-k gate dielectric layer. b Cross-sectional scanning electron microscopy (SEM) image showing the material stack of the OFET. The scale bar is 200 nm. c Polarized optical micrograph showing contact-induced crystallization along the channel with the perfluorobenzenethiol-modified silver source/drain electrodes. The scale bar is 50 μm. d Measured typical transfer (I_D–V_GS) and output (I_D–V_DS) characteristics with well-behaved field-effect transistor behaviors and a steep subthreshold swing of about 80 mV·dec⁻¹ (W/L = 2000 µm/70 µm). e The extracted transconductance efficiency (g_m/I_D) as a function of the gate-to-source voltage (V_GS) with the maximum value of 28.8 V⁻¹ exceeding those of previously reported extended-gate OFET biosensors. f Left: the measured I_D–V_GS curves at each 10^th interval under continuously sweeping V_GS from OFF to ON for 120 times. Right: the measured I_D–V_GS curves under continuous bias stress (V_GS = V_DS = − 0.1 V) with the measured normalized drain current over the original value (I_D(t)/I_D(0)) for 4 h.