Long Term Drift Observed in ISFET Due to the Penetration of H+ Ions into the Oxide Layer
Ion Sensitive Field Effect Transistor (ISFET) and related biosensors when undergo prolonged hours of operation, witnesses a temporal change in threshold voltage which is termed as drift. Drift is a secondary effect which leads to instability of the device resulting into inaccuracy in both in vivo and in vitro measurements. Various types of drift have been of great interest for researchers and long term drift is one of its kinds. Long term drift is observed in different sensing layer in ISFET devices of which silicon dioxide (SiO2) gate ISFET witnesses the maximum. This paper presents the modeling and analysis of long term drift observed in ISFET due to diffusion of H+ ions into the oxide layer and the field caused by this penetration. The additional hydrogen ions left after the protonation of dangling bonds penetrate through the sensing layer which results into an electric field that influences the threshold voltage. A physical model has been designed explaining the effect of this penetration of positive ions into sensing layer and simulations of this model has been carried out. This model has been further experimentally validated using a Schottky based ISFET device with SiO2 as the sensing layer. Both the theoretical and experimental data indicates toward the existence of this drift and its prominence can be observed in lower pH values.
KeywordsBiosensors Diffusion Ion Sensitive Field Effect Transistor Long term drift Threshold voltage
- 2.Hazarika, C., Sarma, D., Puzari, P., Medhi, T., Sharma, S.: Use of cytochrome P450 enzyme isolated from Bacillus Stratosphericus sp. as recognition element in designing schottky-based ISFET biosensor for hydrocarbon detection. IEEE Sens. J. 18(15), 6059–6069 (2018)Google Scholar
- 11.Wolf, S., Tauber, R.N.: Silicon Processing for the VLSI Era. Process Technology, vol. 1. Lattice Press, Sunset Beach (1986)Google Scholar
- 12.Hazarika, C., Sharma, S.: A mathematical model describing drift in SiO2 gate pH ISFET’s due to hydrogen ion diffusion. Int. J. Appl. Eng. Res. 9(23), 21099–21113 (2014)Google Scholar
- 13.May, G.S., Sze, S.M.: Fundamentals of Semiconductor Fabrication. Wiley, New York (2004)Google Scholar