Infoscience

Thesis

Enabling High Frequency Reconfigurable Functions with Graphene

As the scaling of complementary metal-oxide-semiconductor (CMOS) technology is reaching fundamental limitations, novel device concepts and materials have started to be investigated to overcome the scaling challenges for integrated circuits. Graphene has been considered one of the most promising alternatives for the future due to its plethora of superlative properties that are not found in any other material or material system, and consequently, outstanding potential applications in various fields have arisen from this material. However, the high frequency applications of graphene have not seen much progress, with the notable exception of field effect transistors. The objective of this work is to experimentally investigate graphene’s potential for high frequency reconfigurable functions. We propose and demonstrate two novel types of variable capacitors based on graphene for digital and analog radio-frequency (RF) applications, and, finally, place the cornerstone for far and mid-infrared graphene-based technology through a framework that we have developed for applications such as isolators and reflect arrays. This thesis proposes technology approaches that enable the integration of graphene into high frequency reconfigurable functions and provides a design and optimisation pathway towards competitive performance relative to alternative technologies and unique functionality not matched by traditional counterparts. First, we demonstrated and fully characterise graphene nano-electromechanical (NEM) capacitive switches and varactors for digital and analog applications at RF frequencies. We empirically investigate several fabrication routes to find the most suitable to obtain a high yield of suspended graphene membranes. We then focus on opportunities for mass production of graphene-based RF NEM switches, examine and compare several approaches with potential for mass production, and further assess the potential for phase shifters working at 2.4 GHz, by calibrated simulations. The second type of variable capacitor, is a quantum capacitor exploiting graphene in a planar configuration and it is suitable for analog applications. We report the first investigations of graphene quantum capacitors at RF frequencies and demonstrate excellent performance. Moreover, we propose a novel design optimization strategy leading to a performance superior to alternative technologies at frequencies higher than 2.1 GHz and we showcase it in the development of a phase shifter RFID applications working at 5.8 GHz. The experimental results recommend this graphene-based technology as promising for reconfigurable RF analog functions, without the technological and reliability challenges of NEMS. Finally, we describe a graphene stacking technology on transparent and reflective substrates at mid and far-IR, with excellent performance in THz devices such as modulators and isolators, and make a systematic investigation of graphene properties at THz and IR.

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