Nanostructured EGFET pH Sensors With Surface-Passivated ZnO Thin-Film and Nanorod Array

The sensing membrane of extended-gate field-effect-transistor (EGFET) pH sensors, intrinsic zinc oxide (i-ZnO) thin-film and nanorod array, was fabricated using the vapor cooling condensation method together with anodic alumina membrane (AAM) template. Furthermore, the photoelectrochemical (PEC) method was employed to passivate the ZnO thin-film and the sidewall surface of ZnO nanorod array in order to suppress the influence of Femi level pinning. The resulting EGFET pH sensors with passivated i-ZnO thin-film and i-ZnO nanorod array exhibited significantly improved sensing performances owing to the lower surface state density and the larger sensing surface-to-volume ratio. The measured sensitivities of the pH sensors with unpassivated i-ZnO thin-film and unpassivated i-ZnO nanorod array are 38.46 mV/pH and 44.01 mV/pH, respectively, at the pH value ranging from 4 to 12. The higher sensitivity of 42.37 mV/pH and 49.35 mV/pH, respectively, were measured with the pH sensors with passivated i-ZnO thin-film and passivated i-ZnO nanorod array.