Research on graphene field effect transistor for high performance flexible electronics

Abstract

This dissertation focuses on the investigation of graphene field effect transistor (FET) for high performance flexible electronics. For that purpose, the enhancement of electrical characteristics has been accomplished by applying the various fabrication processes that improve each elements of flexible graphene FET. The graphene is emerging as promising candidates for flexible electronic devices due to its exciting electrical and mechanical properties. However, the properties of flexible substrate have limited the fabrication process for graphene FET, resulting in poor electrical characteristics of flexible graphene FET. In this work, we investigate the several unit fabrication processes for high performance flexible graphene FET. As a substrate engineering, aluminum nitride (AlN) interfacial layer has been introduced on the substrate. High surface phonon energy of AlN suppresses the surface phonon scattering from a substrate, resulting in superior electrical performance of graphene FET. In order to secure flexible dielectric, an initiated chemical vapor deposition (iCVD) process has been adapted. The iCVD process enable pin-hole free and conformal coating on any target surface even with inertness regardless of its chemistry The graphene FET with copolymer gate dielectric via iCVD has shown superior electric characteristics and mechanical stability. Also, optimization of overall fabrication process for flexible graphene FET has been done to minimize degradation of performance and maximize the yield. Finally, high-performance graphene RF transistor and RF mixer implemented on flexible substrate have been realized. Through the integration of above fabrication processes, flexible graphene RF transistor has exhibited 38.6 GHz cut-off frequency and flexible graphene RF mixer with passive element has shown the conversion loss of -29.8 GHz at $f_{LO}$ = 7 GHz. This is the first example of a flexible graphene RF application with passive element, exhibiting gigahertz-frequency power gain under strain condition.