Impact of rapid thermal annealing on structural and sensing properties of Ni-Ti sensitive films for extended-gate field-effect transistor pH sensors

In the present work, a facile Ni-Ti film deposited on n+-type Si substrate is introduced as a sensitive film for the development of a solid-state extended-gate field-effect transistor (EGFET) pH sensor. Influence of rapid thermal annealing (RTA) treatment (500-700 degrees C) on structural properties of the Ni-Ti sensitive films was extensively investigated. The film structures, surface morphologies, element profiles, film microstructures, and chemical compositions of the Ni-Ti sensitive films were characterized by a combination of X-ray diffraction, atomic force microscopy, secondary ion mass spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively. The structural features of the Ni-Ti sensitive films are most closely related to their sensing characteristics. The experimental results indicated that the Ni-Ti sensitive film annealed at the RTA temperature of 600 degrees C exhibited better sensing performances (a higher pH sensitivity of 71.01 mV/pH, a lower hysteresis voltage of 1 mV and a smaller drift rate of 0.15 mV/h) than other RTA temperatures. The proposed Ni-Ti sensitive film is expected to be effectively useful for various long-term pH sensor and biosensor applica-tions, since it satisfies the typically required sensing performances such as sensitivity and stability.