Fabrication and characterization of high-speed and high-performance devices using emerging materials

Abstract

As the demand for radio-frequency (RF) devices rapidly grows and diversifies, traditional materials encounter limitations in meeting these evolving requirements. This dissertation focuses on the exploration of novel materials, ranging from two-dimensional (2D) materials to perovskite oxides, to improve the performance and capabilities of RF applications.The study begins with graphene, recognized for its extremely high mobility but limited by the absence of a bandgap. This feature restricts the RF performance of graphene-based transistors due to high output conductance. To leverage the high mobility of graphene while circumventing its inherent limitation, this research investigates graphene variable capacitors (varactors). Demonstrations of graphene varactors exhibit promising high-frequency performance. Different designs of graphene varactors have been explored, providing useful insights for further optimization. Additionally, a potential application of RF graphene varactors, the beam steering antennas, is simulated, with results supporting their feasibility. Moving beyond graphene, transition metal dichalcogenides (TMDCs) have emerged as a category of 2D materials with remarkable mobility and finite bandgaps. Among these TMDCs, tungsten disulfide (WS2) has been selected for this dissertation due to its superior electrical properties within the TMDCs. The yield and performance of RF WS2 were constrained by the unoptimized quality of contacts; therefore, a composite metal stack, Bi/Sb, has been proposed as contacts to WS2 and demonstrated good and reliable performance. Additionally, this dissertation extends beyond 2D materials and explores the potential of perovskite stannates, specifically SSO, for its wide bandgap, high room-temperature (RT) mobility among other perovskite oxides, and possible integration with other functional perovskites. In this work, the first-ever RF perovskite transistors with GHz operation have been demonstrated with SSO. Overall, this work aims to contribute to the field of RF electronics by exploring the potential of graphene, WS2, and SSO. The versatile properties of these materials make them promising alternatives to traditional semiconductors for specialized applications and can possibly enable the next generation of electronic devices.