Analysis of current drift on p-channel pH-Sensitive SiNW ISFET by capacitance measurement

The mechanism of drift effect in pH-sensitive silicon nanowire (SiNW) ion sensitive field effect transistor (ISFET) is comprehensively studied by measuring the time-dependent drain current (ID) and the gate capacitance (CG) under different liquid-gate biases (VLGs) and pH levels. It was revealed that the origin of the current drift can be divided into three different mechanisms; the bulk ionic diffusion in sensing insulator, the chemical modification of insulator surface, and the oxide etch process induced by hydroxide (OH−) ion. Based on the VLG/pH dependency of current drift and the transient CG variation, it is clearly recognized that the drift of n-type SiNW (n-SiNW) ISFET results from H+ diffusion in the insulator, whereas that of p-type SiNW (p-SiNW) ISFET is caused by temporal chemical modification (hydration) of the insulator, along with the oxide thickness (tox) reduction by OH− ions.