On-chip gated graphene transistor arrays with engineered passivation for reliable liquid gate operation

Graphene field-effect transistors (GFETs) are attractive transducers for biosensing, but broader use is limited by fabrication complexity, device-to-device variability, stability concerns, and dependence on bulky external reference electrodes. Here, we report a wafer-scale, on-chip-gated GFET array platform that addresses these challenges through engineered passivation and array-level design. Across multiple fabrication runs, we benchmark monolayer-graphene arrays with three passivation schemes (Al 2 O 3 , SU-8, and Al 2 O 3 /SiN x ) and quantify the effects of lithographic resist exposure and aging on the liquid-gated response. Using phosphate-buffered saline (PBS) as a model electrolyte, we statistically evaluate Dirac-voltage spread, hysteresis, gate leakage, and stability, identifying Al 2 O 3 /SiN x as the most robust configuration. By varying the ionic strength from PBS 0.001 × to 1 ×, we map the response across relevant Debye lengths. The platform is integrated with PDMS microfluidics and a portable PCB readout, and its intrinsic ionic transduction capability is assessed through proof-of-concept NaCl measurements in deionized water, yielding sensitivities of ~ 70 mV/dec and LoDs down to ~ 3 mM without ion-selective membranes. These results establish a compact, scalable, and electrically stable graphene transducer platform for future integration with portable biofunctionalized sensing assays.