Extended Gate Ion-Sensitive Field-Effect Transistors Using Al2O3/Hexagonal Boron Nitride Nanolayers for pH Sensing

A stack consisting of atomic layer deposited (ALD) Aluminium Oxide (Al2O3) and Hexagonal Boron Nitride (h-BN) is proposed and demonstrated as the sensing layer of Extended Gate Ion-Sensitive Field-Effect Transistors (EG ISFETs) in this work. The use of h-BN in the sensing stack is to suppress the voltage drift during pH measurement, owing to a low defect level inside the two-dimensional (2D) h-BN. The use of Al2O3 in the sensing stack is to improve the pH sensitivity due to the chemical inertness of h-BN and the resultant low sensitivity. A low power oxygen plasma treatment on the surface of the h-BN flake is employed to obtain a uniform and high-quality Al2O3 layer on top of h-BN. The influences of Al2O3 thickness in the Al2O3/h-BN sensing stack on the sensitivity and drift characteristics of 2D EG ISFETs are investigated. It is found that the EG ISFET with Molybdenum Disulfide (MoS2) Field-Effect Transistor (FET) and Al2O3/h-BN sensing stack with 5 nm thick Al2O3 provides a pH sensitivity of higher than...