Optimizing Sensitivity and Dimensions in CMOS Extended Gate FET Biosensors

Field-effect transistors (FETs) are widely considered as one of the most promising electronic devices for rapid, sensitive, and label-free biodetection. In many studies, floating gates are connected to extended electrodes to gather electrical charges of detected biomolecules. However, while the sensitivity typically increases with electrode size, this trend gradually diminishes beyond a certain threshold. This issue of overdesign is critical to address, particularly in the development of large-scale biosensing arrays. In this study, we investigated this phenomenon by varying transistor sizes, each accompanied by five extended electrodes with areas ranging from 5 to 50 times that of the transistors. We comprehensively tested these devices for the detection of DNA hybridization in both diluted and normal ionic solutions. The results indicated a decline in the rate of sensitivity increase beyond an area ratio of
$20{X}$
.