PH Sensitivity Improvement of Vertical Silicon-Nanowire Extended-Gate Ion-Sensitive Field Effect Transistor

Abstract

The extended-gate ion-sensitive field-effect transistor (EGISFET) is essential to the field of bio-chemical sensing. It has been reported that the nano-textured gate ISFET is suitable for high pH sensitivity. The small distance between each nano-structure results in the high sensitivity. However, due to the difficulties of manufacturing process, the distance between each nano-structure will no longer be shrunk, which means that it will be a challenge to keep improving sensitivity. To address this issue, we turn to make good use of the space above these nano-structures. Thus, a series of vertical silicon nanowire (SiNW) sensing membranes with different heights was developed in EGISFET pH sensors. The vertical SiNW sensing membranes were fabricated using the electroless etching technique called metal-assisted chemical etching (MACE). The ultra-thin Au nanomesh served as a catalyst in MACE process was replicated from a reusable porous anodic aluminium oxide (AAO) membrane. By photo-lithography the sensing area on the SiNW sensing membrane was defined. The transfer characteristics of such vertical SiNW EGISFET pH sensors exhibited a higher sensitivity (75.86 mV/pH) than that of the conventional planar EGISFET pH sensors (38.53 mV/pH) for the different pH solutions (pH 4, pH 7 and pH 10). The scanning electron microscopy images of SiNW with different heights are also presented.