Structural properties and sensing performance of TaOx/Ta stacked sensing films for extended-gate field-effect transistor pH sensors

Abstract

In this article, the TaOx/Ta stacked sensing films as sensing membranes were deposited onto n+-type Si substrate by a radio-frequency (RF) magnetron sputtering technique for solid-state extended-gate field-effect transistor (EGFET) pH sensors. The effect of rapid thermal annealing (RTA) treatment (300–700 °C) on structural properties of the TaOx/Ta stacked sensing films was investigated in detail. The chemical compositions, element profiles, crystallographic structures, surface morphologies, and film microstructures of the TaOx/Ta stacked sensing films were characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy, respectively. The sensing performance of the TaOx/Ta stacked sensing films is most closely correlated with their relative structural features. Among these RTA temperatures, the best sensing performance including pH sensitivity, hysteresis and drift was achieved at the RTA temperature of 500 °C. The obtained experimental results showed that the TaOx/Ta stacked sensing film is considered a feasible alternative for pH sensor and biosensor applications.