Keywords: IGZO, In–Ga–Zn–O, indium gallium zinc oxide, EGFET, extended–gate FET, field effect transistors, sensitivity, RTA, rapid thermal annealing, nanotechnology, etch rate, drift coefficient, nanoelectronics, nanotechnology
Hydrogen ion sensing characteristics of IGZO/Si electrode in EGFET
In–Ga–Zn–O (IGZO) was widely applied in the substrate of TFT to replace α–Si in recent years. In this study, IGZO layer with thickness of 70 nm is firstly proposed as a pH–sensing membrane directly deposited on P–type Si substrate acting as an extended gate of conventional extended–gate field–effect transistor (EGFET). Post–deposition rapid thermal anneal (RTA) was performed to improve pH sensing performance of IGZO layer sputtered with Ar/O2 flow rate of 20/5 in sccm. Sensitivity could be increased from 41.5 mV/pH to 53.3 mV/pH by RTA in N2 ambience at 700°C in pH application range between pH 2 and 10. XRD analysis supports the orientation changes of IGZO layer after RTA at different temperature. Ar/O2 ratio was also modified in the RF sputtering. IGZO–EGFET prepared by Ar/O2 ambience of 24/1 in sputtering can have the highest sensitivity and linearity of 59.5 mV/pH and 99.7%, respectively. After 7 months, sensitivity and linearity are 51.4 mV/pH and 92%, respectively. Etch rate and drift coefficient in standard buffer solution are higher than in other sensing material for EGFET and ISFET. More studies on enlargement of pH application range and minimisation of non–ideal effect still need to be investigated before real applications.