High Sensitivity of Dry-Type Nanowire Sensors With High-k Dielectrics for pH Detection via Capillary Atomic Force Microscope Tip Coating Technique

Abstract

Dry-type poly-Si nanowire pH sensors with high-k dielectrics have been demonstrated with the aid of novel focus ion beam engineered capillary atomic force microscopy (C-AFM) tip. By means of this C-AFM tip coating technique, the relatively few testing solutions can be transferred onto the surface of a nanowire, preventing the sensor device from the immersion in the liquid and therefore suppressing the possible leakage current from the testing solution. As compared with the TEOS SiO2, the pH sensors comprising Al2O3, TiO2, and HfO2 high-k materials exhibit the better sensitivities due to their enhanced capacitances. The best sensitivity (138.7 nA/pH) and linearity (99.69%) for a HfO2 dielectric can be ascribed to the higher k value and larger bandgap with respect to the Al2O3 and TiO2, accordingly. Consequently, the C-AFM tip coating technique incorporating with HfO2 dielectric suggests the potential for the detection of a minute quantity of biomedicines.