Abstract
In this study we developed ytterbium tantalum oxide (YbTaO4) sensing membranes for use in electrolyte–insulator–semiconductor (EIS) pH sensors. The influence of rapid thermal annealing (RTA) treatment on the sensing and impedance properties of the YbTaO4 sensing membranes deposited through reactive co-sputtering onto Si substrates was explored. X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy revealed the structural, morphological, and chemical features, respectively, of these YbTaO4 films annealed at 700, 800 and 900 °C. The YbTaO4 EIS device annealed at the 800 °C exhibited a super-Nernstian response of 71.17 mV/pH within the pH range of 2–12. It also showed the lowest hysteresis voltage ( < 1 mV) and the lowest drift rate (0.22 mV/h) among the tested systems. Presumably, the optimal annealing temperature improved the stoichiometry of YbTaO4 film and increased its (−131)-oriented nanograin size. Moreover, the impedance properties of YbTaO4 EIS sensors were investigated by using the capacitance–voltage method. The resistance and capacitance of YbTaO4 sensing films annealed at three various temperatures were evaluated by using different frequency ranges in accumulation, depletion, and inversion regions. The semicircle diameter of the YbTaO4 EIS sensor became smaller, due to a gradual decrease in the bulk resistance of the EIS device, as the RTA temperature was increased.
Highlights
An ion-sensitive field-effect-transistor (ISFET) device was first developed by Bergveld in 1970 as a replacement for a fragile glass electrode[1]
The aim of this paper is to explore the effect of post-annealing treatment on the structural, sensing, and impedance characteristics of ytterbium tantalum oxide (YbTaO4) sensing films deposited on Si substrates through reactive rf co-sputtering
X-ray diffraction (XRD), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS) were employed to examine the film structures, surface morphologies, and chemical compositions of YbTaO4 films annealed at three different temperatures (700, 800 and 900 °C), respectively
Summary
An ion-sensitive field-effect-transistor (ISFET) device was first developed by Bergveld in 1970 as a replacement for a fragile glass electrode[1]. In search of the low defect density and high thermal stability in high dielectric constant (κ) metal oxide films, rare-earth (RE) oxide thin films have been studied for use as a replacement MOSFET gate dielectric due to their high κ values, large bandgap energies, good thermodynamic properties, high resistivities, and high conduction-band offsets[15,16]. Of these RE oxides, ytterbium oxide (Yb2O3) thin film turns out to be a potential gate oxide because of its novel properties, including excellent thermal and chemical stability, large bandgap (~5 eV), and high κ (~15), in which the κ values depend on deposition processing[17,18]. The YbTiO4 membrane after RTA at 800 °C showed a higher pH sensitivity (71.17 mV/pH), a smaller hysteresis voltage (
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