Electronic sensors built on nanostructured cerium oxide films

Abstract

The influence of the technical parameters of nanostructured CeO x film production on electronic, structural, optical, and photoelectronic characteristics has been studied for their practical application as the active element of various microelectronic sensors—such as high-performance photoresistors, MOS-photodiodes for bioluminescence registration, ion-selective field-effect transistor (ISFETs), and MOS-varactors indicating pH changing as a result of biochemical processes. X-ray photoelectron spectroscopy analysis (XPS) has shown that the ratio of Ce3+ and Ce4+ ions in CeO x films has changed, depending on the technological regime and, first and foremost, on the temperature of the substrate, which results in an changing of the fundamental gap width. The correlation between these alterations and the optical and photoelectric characteristics has been determined. On the basis of highly sensitive photo photoreceivers and living organisms (daphnia and bioluminescence bacteria), a portative electron bioluminescent metric complex has been created to determine the overall water toxicity caused by mycotoxin patulin, biphentrin, and chlorpyrifos. The minimal sensitivity threshold for patulin is 0.1 mg/l after a 2 h experiment and 0.01 mg/l after 6 and 24 h experiments; for biphentrin, it is 0.01 mg/l after a 3 h experiment and 0.0001 mg/l after a 24 h experiment. It is shown that applying nanocrystalline films of cerium oxide CeO x as the dielectric of MOS structures increases the sensitivity and stability of these sensors due to the high density of the surface of sensitive centers of CeO x (to 1020 m−2), the high values of dielectric permeability (ɛ = 26) and the band-gap width (3.6 eV), and low values of leakage currents. The results of ISFET and MOS varactor application with nanocrystalline CeO x film for the creation of immune and enzymatic biosensors have been demonstrated. The sensitivity threshold of an enzymatic sensor based on choline esterase to organophosphorous pesticides is 10−9 M, and for ions of heavy metals it is 10−7 M. The pH sensitivity of ISFET is 58 mV/pH, which is close to the maximal possible sensitivity for the semiconductor-dielectric-solution structure (the so-called Nernst sensitivity is 59 mV/pH).