Investigation of transition metal dichalcogenide monolayer channel ion sensitive fet as ph and biomolecule sensors

Abstract

Early and rapid detection of biomarkers indicative of various diseases has been an intensive field of research for past few decades. A wide variety of biosensing devices that employ nanoparticles or nanostructures have been investigated in a number of studies throughout the world. Potentiometric biosensors based on field-effect transistors have shown excellent performance due to several advantages like rapid electrical detection without the need for labeling the biomolecules, low power consumption, portability, inexpensive mass production, and the possibility of on-chip integration of both sensor and measurement systems. The 2D materials like graphene and transition metal dichalcogenides are highly promising, as they not only can provide excellent electrostatics due to their atomically thin structures but also possess planar nature, which is amenable to large-scale integrated device processing and fabrication. In this thesis, we develop a comprehensive theoretical framework to study 2D material based nanoscale sensors and correlate the geometry and physical properties of these sensors to their sensing performance of target molecules. The main objective of this work is to set some guidance for future design, implementation and optimization of these novel biosensors. A part of this work focuses on the scope of 2D material based FETs in sensing solution pH and detection of biomolecule in wet environment. TMDC monolayer materials show good sensitivity as pH sensor while operating above Nernst limit with back gate operation. With proper surface functionalization, monolayer TMDC FETs can be used for highly sensitive and selective detection of biomolecule in subthreshold regime. It is found that performance of the TMDC pH and Biosensors can be optimized through careful design of physical and operating parameters in Double-Gated Field Effect Transistor. In addition, this work also investigates the prospect of electrical biosensing in dry environment with state of the art devices structure like Junctionless Double Gate MOSFET and 2D material like MoS2 by developing analytical model for surface potential and current in such devices. The detection of both charged and neutral biomolecules have been analyzed under dry environment situation by investigating the electrical characteristics of n-type Junctionless Double Gate MOSFET. Bio-sensing application in dry environment using DMFET can be a viable alternative to overcome the screening limited sensitivity in electrolyte based systems and it can used to detect even charge neutral biomolecule. In addition, this work also offers a comparative study of sensor performance as a function of device physical parameters to maximize detection capability under dry environment condition.