Vanadium oxide thin films growth by a chemical solution deposition method and its pH sensor toward bio-sensing devices

Abstract We report on the evaluation of the structure of VO x thin films under different fabrication conditions of the chemical solution deposition method and the pH response of an extended gate field effect transistor (EGFET)-type pH sensor. Polycrystalline V 2 O 5 thin films of 30 and 60 nm thick and amorphous VO x thin films of about 30 nm thick were successfully prepared under different precursor solution conditions. Using polycrystalline V 2 O 5 thin films and amorphous VO x thin films as extended gate (EG) electrodes, prototypes of EGFET-type pH sensors were fabricated and their pH response characteristics were investigated. The average pH responsibility of 64 mV pH −1 , which exceeded the theoretical Nernst limit, was observed over a wide pH range from 2.4 to 8.0 in the amorphous VO x extended gate sensor. It was also found that stable pH response measurements could be performed on amorphous VO x film samples.