Vertical silicon nanowires with atomic layer deposition with HfO ₂ membrane for pH sensing application

Vertical silicon nanowire (SiNW) platforms are candidates for use in ultrasensitive biosensors, with surface-to-volume ratio higher than one-dimensional SiNW. In this paper, a vertical SiNW electrolyteinsulatorsemiconductor (EIS) structure with an ALD-HfO ₂ sensing membrane is proposed for use in a hydrogen ion sensor. Hafnium dioxide is used as the sensing membrane, which was deposited on the surface of the vertical SiNW structure by atomic layer deposition. The sensing properties were examined using a HP4284A high-precision LCR analyzer. A linear relationship was found between the flatband voltage shift and the hydrogen ion concentration. Comparing with different diameters of SiNW, the sensitivity with diameter of 200 nm was slightly higher than 100 nm. A post-deposition rapid thermal annealing (RTA) was utilized to optimize the sensing properties, and the sensitivity was increased to 51.07 mV/pH.