Structural Properties and Sensing Performance of CeYxOy Sensing Films for Electrolyte–Insulator–Semiconductor pH Sensors

Abstract

In this study we developed CeYxOy sensing membranes displaying super-Nernstian pH-sensitivity for use in electrolyte–insulator–semiconductor (EIS) pH sensors. We examined the effect of thermal annealing on the structural properties and sensing characteristics of the CeYxOy sensing membranes deposited through reactive co-sputtering onto Si substrates. X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy revealed the structural, morphological, and chemical features, respectively, of the CeYxOy films after their annealing at 600–900 °C. Among the tested systems, the CeYxOy EIS device prepared with annealing at 800 °C exhibited the highest sensitivity (78.15 mV/pH), the lowest hysteresis voltage (1.4 mV), and the lowest drift rate (0.85 mV/h). Presumably, these annealing conditions optimized the stoichiometry of (CeY)O2 in the film and its surface roughness while suppressing silicate formation at the CeYxOy–Si interface. We attribute the super-Nernstian pH-sensitivity to the incorporation of Y ions in the Ce framework, thereby decreasing the oxidation state Ce (Ce4+ → Ce3+) and resulting in less than one electron transferred per proton in the redox reaction.

Highly Sensitive Magnesium-Doped ZnO Nanorod pH Sensors Based on Electrolyte–Insulator–Semiconductor (EIS) Sensors

“…Drift is defined as the gradual change in the response of the sensors over time, while the pH value remains constant. The differences in the amount of surface sites over time are essentially due to the change in the chemical modification of the dielectric surface, consequently leading to an increase in the threshold voltage [ 73 ]. The difference in the reference voltage ( ) is given by: …”

“…The change in the reference voltage might occur from lattice defects, which co for example, vacancies or dangling bonds caused by capturing groups of ions. The fects might be eliminated by controlling the parameters of the preparation method for the sensing membranes, such as the annealing temperature [15,27,73] and the d process [33,67], which result in the improvement of the drift voltage over time. In to study the long-term stability (drift) of the sensing membranes, each sample wa merged in a solution of pH 7 for 12 h. Figure 10 presents the drift rates of the EIS d based on Mg-doped ZnO nanorod sensing membranes doped at different contents ( Figure 10 shows that, among the samples doped with Mg, the EIS device with the 3 ZnO membrane exhibited the highest stability (0.218 mV/h), whereas the 2% M membrane had the lowest stability of 0.659 mV/h.…”

Investigation of Sc2O3 Based All-Solid-State EIS Structure for AlGaN/GaN HEMT pH Sensor

“…Heterostructures and quantum structures including III-V and II-VI compounds semiconductors have also demonstrated interest in various types of chemicalsensing devices for biochemical processes [11][12][13][14]. For the gate functionalization, several metal oxides such as Si3N4, AFO3, ZrO2, HfO2, Ta2O5... [15][16][17][18] have been extensively studied, but most of them degrade when exposed to strong alkaline medium. In contrary, scandium oxide (Sc2O3), with a band gap of 6.3 eV and dielectric constant of 14, unlike other metal oxides, is compatible with strongly alkaline medium like cementitious materials.…”

“…In contrary, scandium oxide (Sc2O3), with a band gap of 6.3 eV and dielectric constant of 14, unlike other metal oxides, is compatible with strongly alkaline medium like cementitious materials. Furthermore, ISFET with glass reference electrode has been already demonstrated [13,15,18].…”

“…The operation principle of the EIS structure lies in the flatband voltage dependence on the surface potential at the insulator-electrolyte interface. This flat-band voltage for an ISFET or EIS device is [15]: VfB = Eref -^0 + Xsol -®s/q -(Qox + Qss)/Cox…”