Fabrication and Characterization of Graphene based Biocompatible Ion-Sensitive Field Effect Transistor (ISFET)

Graphene, a two-dimensional material with a high surface to volume ratio, has drawn extensive research enthusiasm for applications in the field of electronic sensors. The special material properties that make graphene a highly promising material include its biocompatibility, very high mobility, low 1/f and thermal noise, modulation of carrier concentration and fermi level by electrical, optical, and chemical means. To exploit these properties for practical applications a large area high quality graphene, transferred on appropriate substrates, is required. In this work, high quality single monolayer graphene (determined from Raman spectroscopy) has been synthesized by chemical vapor deposition (CVD) technique for bio-sensing applications utilizing methane and hydrogen as precursor gases. In this work, small channel graphene field effect transistors (GFETs) were fabricated utilizing monolayer or few layer high quality transferred graphene, and electrical, voltage bias stressing and temperature dependent characterizations have been performed. The electrical characterization, carried out in a back-gated field effect transistor configuration, yielded mobility as high as 1000 cm2V-1s-1. Additionally, a novel bio-compatible device called Ion sensitive field effect transistor (ISFET) was fabricated using the CVD grown graphene. Graphene ISFET senses the ions efflux from solutions using graphene as the active layer (conducting channel). The graphene ISFETs were encapsulated using bio-compatible epoxy except the active layer (graphene) region to perform highly sensitivity solution based measurements. The ISFET devices were used to perform real-time Potassium (K+) efflux measurement from ion concentration change in electrolyte solution. The ion concentration change is transduced into an electrical (current) signal due to surface potential change in graphene. In this work, an extensive study of the I-V and C-V characteristics of the graphene ISFET in an electrolyte solution with different K+ concentration has been performed and superior performance of the graphene ISFET has been demonstrated. During development and testing of the graphene ISFET, we also discovered that the epoxy utilized for the sensor encapsulation has a significant impact on the electric transport properties of graphene including conductivity, carrier concentration and field-effect mobility. N-type doping impact of the epoxy on graphene has been demonstrated through systematic experiments, which is promising as a new method for surface doping of graphene