Simulation Threshold Voltage instability (Drift) in Ion selective Field Effect Transistor(ISFET) with Al2O3 Gate and Correct using Ion Implantation

In an ion-selective field effect transistors (ISFETs) Threshold-voltage instability or drift is manifested as a relatively slow, monotonic, temporal increase in the threshold voltage, and hence, in the drain current in absence of variations in the concentration of the given ion. In this work the ISFET device structure is modeled using Silvaco TCAD allowing simulation of the threshold voltage instability using the Silvaco’s ATLAS software based on a physical model for ISFET drift accounting for experimental drift data. In addition, ion implantation is introduced as a method for counteracting drift. This method is based on adjusting the threshold voltage by tuning the charge density at the insulator-semiconductor interface using ion implantation such that the net charge induced in the semiconductor at the operating point of the device is neutralized. The proposed method is analytically validated based on characterization and modeling of drift in an Al2O3-gate pH-sensitive ISFET. Counteraction of ISFET drift by ion implantation is also demonstrated using TCAD simulations.