Graphene is the thinnest and strongest material known to man. It is electrically conductive, transparent, has a large surface area to volume ratio and a tiny areal mass. This combination of properties makes it appealing as a component in the next generation of Microelectromechanical systems (MEMS), unlocking capabilities such as a combined ultra-high sensitivity and high operable range. The most promising fabrication process for mass-producible graphene devices is chemical vapour deposition in which large graphene sheets are formed on transition metal. The transfer of graphene from the metal to the device structure leads to rips, tears and stiction issues in the graphene, which can be overcome by depositing an ultra-thin layer of polymer onto the graphene, forming a Graphene-Polymer Heterostructure (GPH) membrane. Depositing a polymer film that is ultra-thin maintains the superb qualities of graphene whilst improving the manufacturability of graphene devices. In this project, GPH membrane capacitive MEMS were fabricated, modelled and characterised. This involved techniques including Atomic Force Microscopy (AFM), optical microscopy, Raman spectroscopy and capacitance-pressure measurements. The first study compared GPH membrane deflection when a pressure differential is applied across the membrane. Inflated GPH membrane deflection was measured with AFM and compared to modelling of multi-layered thin membranes. The second study investigated the compatibility of GPH membranes with mass-producible standard process MEMS. A GPH membrane was laminated onto a PiezoMUMP (Multi-User MEMS Process) sensor base and tested as a capacitive pressure sensor and an ultrasonic resonator. In the final study, the benefits of using a parylene-C adhesion layer to aid in the fabrication of GPH-PiezoMUMP devices were examined.
Graphene-polymer heterostructure membranes for micro-electromechanical systems
Smith, K. (Author). 31 Dec 2023
Student thesis: Phd