Abstract

Biosensing for nucleic acid sequences using graphene field-effect transistors (gFETs) allows for the detection of label-free target sequences with high sensitivity in multiplex arrangements. This particular type of DNA microarray combines the principles of low-dimensional physics and biophysics, using the unique charge transport properties of graphene to overcome the limitations of conventional fluorophore-based DNA microarrays. However, this technology has not yet matured enough to reach the level of reliability, reproducibility, and homogeneity required for clinical diagnostics or pathology. This thesis focuses on the fabrication and electrical characterization of gFETs designed for biosensing applications. More than 5000 gFETs were fabricated and characterized on more than 100 different chips, using backgate and electrolyte-gate configurations. A comprehensive analysis provides insight into the design choices, fabrication methods, and device processing of gFETs. The results suggest that the use of an alumina bottom passivation layer and an advanced graphene transfer method can improve the charge transport properties of gFETs. In addition, an electrochemical process is identified and experimentally studied, which is necessary for electrolyte-gating and biosensing with our devices. This thesis contributes significantly to the development of this technology by improving the reproducibility, reliability and homogeneity of gFET arrays fabricated with CVD-graphene, specifically tailored for multiplex biosensing. Furthermore, it also includes the development of adsorption isotherms and recommendations for probe-target design, which are useful for microarray technology in general.