Biomolecular Identification and Analyte Charge Measurement Using Drain-Current Readings from a Single Transistor: An Asymmetric Dual-Gate a-IGZO FET Biosensor

Abstract

Permittivity-based biomolecular identification becomes ambiguous when analyte charge also changes the measured electrical response: different combinations of charge and permittivity can produce similar currents, so a current change cannot be uniquely attributed to permittivity. Hence recovering permittivity when the analyte charge is unknown is a central sensing challenge. Our fundamental idea is to extract both charge and permittivity from a single transistor, enabling permittivity-based biomolecular identification under varied and initially unknown analyte charge conditions. This work demonstrates that strategy through a TCAD-based proof-of-concept study of an asymmetric dual-gate, dual-nanogap a-IGZO transistor. Gate-insulator dielectric engineering and nanogap design establish complementary responses: the bottom gate predominantly senses charge, while the top gate predominantly senses permittivity. The bottom-gate charge estimate and a top-gate pilot current select a charge-conditioned top-gate voltage, allowing permittivity recovery through one neutral-charge reference. After calibration, three sequential drain-current readings provide both properties while charge and permittivity vary simultaneously in both sensing regions. Mean charge and permittivity extraction errors remain below 1.8\% and 0.6\%, respectively, across the calibration and independent test datasets. The central contribution is a single-transistor device-and-readout strategy combining complementary gate responses with adaptive bias selection to support permittivity-based biomolecular identification across initially unknown analyte charge conditions in positive, negative, and neutral ranges.