High‐Sensitivity pH Sensors Based on W-doped VOx Thin Films Prepared by Chemical Solution Deposition toward Biosensing Applications

We report the fabrication and evaluation of VOx and W-doped VOx thin films via the chemical solution deposition method, with a focus on their pH response characteristics. VOx and W-doped VOx thin films were prepared from precursor solutions under different conditions. The deposited films were employed as extended electrodes in extended-gate field-effect transistor (EGFET)-type pH sensors. Their pH response and sensitivity were evaluated over a range of neutral to basic conditions. Although the single-phase VOx film exhibited instability under alkaline conditions, the W-doped VOx film demonstrated significantly enhanced stability and achieved highly sensitive pH responses that exceeded the Nernst limit.