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

Abstract

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 °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 °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 applications, since it satisfies the typically required sensing performances such as sensitivity and stability.