Investigation of AlGaN/GaN Ion-Sensitive Heterostructure Field-Effect Transistors-Based pH Sensors With Al2O3 Surface Passivation and Sensing Membrane

This paper demonstrates an AlGaN/GaN ion-sensitive heterostructure field-effect transistors (ISHFETs)-based pH sensors with an aluminum oxide (Al
₂
O
₃
) to serve as a passivation layer and a sensing membrane at the same time. Al
₂
O
₃
was deposited by the ultrasonic spray pyrolysis deposition (USPD) method. It was found that the ISHFET with Al
₂
O
₃
showed a higher pH sensitivity of 55.6 mV/pH, a faster response speed of 3 s (from pH 4 to pH 7) and 7 s (from pH 7 to pH 10), a lower hysteresis voltage of 4.3 mV, and a smaller drift rate of 1.25 mV/h (at pH 7) compared with the ISHFET without passivation. In addition, the ISHFET with an Al
₂
O
₃
passivation layer exhibited significant surface potential variation and low degradation rate. These results suggest that the performance of ISHFET improved using USPD-grown Al
₂
O
₃
.