IGZO nanoparticle-modified silicon nanowires as extended-gate field-effect transistor pH sensors

A high aspect ratio silicon nanowire (SiNW) sensing membrane modified with amorphous indium–gallium–zinc–oxide nanoparticles (IGZO NPs) was developed for use in extended-gate field-effect transistor (EGFET) pH sensors. The IGZO/SiNWs sensing membranes were first fabricated using the Ag-assisted electroless etching technique and were then decorated with IGZO NPs by sputtering in five separate batches for 3, 6, 9, 12 and 15 min to improve the pH sensing properties. SEM, TEM and FTIR spectroscopy were used to respectively analyze surface morphology, crystallinity and chemical binding. The IGZO NPs provided more oxygen-related binding sites than the pristine SiNWs to adsorb additional H+ ions, thus effectively improving pH sensitivity. The 9 min IGZO/SiNW sensor exhibited the best sensitivity of 50 mV/pH, an improvement of about 39% over that of the pristine SiNW sensor (36 mV/pH). The IGZO/SiNW sensor exhibited good pH sensing properties and stability that had potential for mass production in disposable biosensors.