Structural and Sensing Properties of High-$k$ $\hbox{PrTiO}_{3}$ Sensing Membranes for pH-ISFET Applications

We describe an electrolyte–insulator–semiconductor (EIS) device for biomedical engineering applications prepared from high-$k$ $\hbox{PrTiO}_3$ sensing membranes deposited on Si substrates by means of reactive radio-frequency sputtering. We used X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to investigate the structural and morphological features of these films after they had been subjected to annealing at various temperatures. The EIS device incorporating a high-$k$ $\hbox{PrTiO}_3$ sensing film that had been annealed at 800 $^\circ$C exhibited a higher sensitivity (56.8 mV/pH, in the solutions from pH 2 to 12), a smaller hysteresis voltage (2.84 mV in the pH loop 7 $\rightarrow$4$\rightarrow$7 $\rightarrow$10$\rightarrow$ 7), and a lower drift rate (1.77 mV/h in the pH 7 buffer solution) than did those prepared at the other annealing temperatures, presumably because of its thinner low-$k$ interfacial layer at the oxide–Si interface and its higher surface roughness.