A Drain-side Gate-underlap I-MOS (DGI-MOS) transistor as a label-free biosensor for detection of charged biomolecules

Electronic devices are finding increasing application as biosensors for the label-free detection of biomolecules. These biosensors offer the advantage of fast detection and compatibility with existing CMOS processes that enable rapid commercialization, and achieve very low detection limits. A biosensor´s sensitivity is one of the main factors determining its performance. The application of emerging steep sub-threshold devices as biosensors is being actively explored due to their ability to provide very high sensitivities. In this paper, we propose the application of a Drain-side Gate-underlap Impact-ionization MOS (DGI-MOS) transistor as a sensor for label-free detection of charged biomolecules. The DGI-MOS biosensor is implemented by introducing an underlap in the gate electrode over the channel region at the drain side. The underlap serves as the location for the immobilization of biomolecules. With TCAD simulations, we demonstrate the proposed DGI-MOS biosensor to have a high sensitivity to the presence of charged biomolecules. In addition, the threshold voltage (V_T) shift observed due to the presence of biomolecules is observed to be significantly higher than the other reported steep sub-threshold device-based biosensors. We demonstrate that the DGI-MOS biosensor allows the underlap region length to be comparable with the gate electrode length, simplifying the manufacturing steps involved in creating the underlap region.