Enhanced Performance of IZO/ZnO Heterostructure Thin-Film Transistors and Its Biosensing Applications via Single-Precursor Solution Process

We report IZO/ZnO heterostructure thin film transistors (TFTs) fabricated by a single-precursor sol–gel process where a ZnO-rich surface region forms on an In-based oxide layer after annealing. The heterostructure improves the electrical response compared to a single-layer oxide TFT and provides a probe-free platform for biomolecule detection. As a demonstration, we detect pUC-18 plasmid DNA (2686 bp) over concentrations from 1 pg/mL to 10 ng/mL using transfer/output-curve changes as the sensing signal. The device exhibits a pronounced negative shift of threshold voltage and a strong increase in saturated current after exposure, enabling high sensitivity at low concentration; in particular, sensitivity exceeding 200% is obtained at 1 pg/mL, corresponding to a limit of detection of 1 pg/mL. These results suggest that the IZO/ZnO heterostructure TFT can serve as a simple and rapid probe-free biosensing platform produced via a low-cost solution process.