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dc.contributor.advisorCheung, Rebecca
dc.contributor.advisorMastropaolo, Enrico
dc.contributor.advisorEwen, Peter
dc.contributor.authorChen, Tao
dc.date.accessioned2015-09-02T15:31:21Z
dc.date.available2015-09-02T15:31:21Z
dc.date.issued2015-06-29
dc.identifier.urihttp://hdl.handle.net/1842/10538
dc.description.abstractIn this thesis, the design, fabrication and characterisation of graphene electromechanical resonators have been presented. Graphene features ultrahigh Young’s modulus and large surface to volume ratio that make it ideal for radio frequency (RF) components, sensors and other micro/nano-electromechanical systems (MEMS/NEMS). A novel batch fabrication process for graphene electromechanical resonators has been developed by using poly-Si film as sacrificial layer. Previously reported fabrication processes of graphene resonators use SiO2 as sacrificial layer only because graphene is visible on 300nm SiO2/Si substrate. However, the wet etching of SiO2 involves HF, which is not compatible with metal connections or SiO2 serving as dielectric or passivation layer in graphene NEMS devices. Moreover, the liquid surface tension during drying after wet etching could damage graphene bridges even critical point drying is used. Therefore, in this work, poly-Si is adopted as the sacrificial material. To facilitate the fabrication of graphene resonators, a poly-Si/SiO2/Si substrate has been designed and optimised to make graphene visible under optical microscope for the first time to the author’s knowledge. Chemical vapour deposition (CVD)-grown monolayer graphene sheet has been transferred onto the optimised poly-Si/SiO2/Si substrate and patterned into strips. Metal electrodes have been deposited by lift-off process to make electrical connections, which is prerequisite for integrating graphene resonator into practical devices. The graphene bridges have been released by etching the poly-Si layer with XeF2 in vapour phase, which completely avoids the capillary force induced damage to the graphene bridges. De-fluorination process has been performed by hydrazine reduction to recover graphene’s conductivity. This fabrication process is scalable for massive production of graphene electromechanical resonators, thus furthering their practical application. One-source current mixing characterisation setup has been constructed to test the graphene resonators. Besides the fundamental peak, the activation and enhancement of the second mode of doubly clamped resonator by electrostatic actuation have been observed for the first time. The second mode amplitude reaches 95% of the fundamental mode, whereas only odd higher modes of small intensity have been reported before in other MEMS/NEMS resonators actuated by electrostatic force or magnetomotive force. The findings in this thesis could lead to substantial increase of the sensitivity of sensors based on the graphene resonators. Modal analysis based on Euler-Bernoulli equation has been performed to understand the mechanism behind the activation and enhancement of the second mode. Finite element analysis agrees very well with experimental results and complies with the theoretical model. Finally, a set of novel alignment marks has been designed, which can be incorporated to process mechanically exfoliated 2D material flakes of micron size and irregular shape with conventional photolithography tools, as have been demonstrated by the successful fabrication of a graphene transistor. This optical alignment technique provides an alternative for prototype device development besides electron beam lithography to prevent electron-induced damage to fragile 2D materials.en
dc.language.isoenen
dc.publisherThe University of Edinburghen
dc.relation.hasversionEldad Grady, Enrico Mastropaolo, Tao Chen, Andrew Bunting, Rebecca Cheung, Low frequency graphene resonators for acoustic sensing, Microelectronics Engineering 119 (2014), pp105-108en
dc.relation.hasversionTao Chen, Enrico Mastropaolo, Andrew Bunting, Tom Stevenson, Rebecca Cheung, Optimization of the visibility of graphene on poly-Si film by thin-film optics engineering, J. Vac. Sci. Technol. B 30, 06FJ01 (2012)en
dc.relation.hasversionBoris Svilicic, Enrico Mastropaolo, Tao Chen, Rebecca Cheung, Piezoelectrically transduced silicon carbide MEMS double-clamped beam resonators, J. Vac. Sci. Technol. B 30, 06FD05 (2012)en
dc.relation.hasversionEnrico Mastropaolo, Boris Svilicic, Tao Chen, Brian Flynn, Rebecca Cheung, Piezoelectrically actuated and sensed silicon carbide ring MEMS resonators, Microelectronic Engineering, Vol 97, 2012, pp220-222en
dc.subjectgrapheneen
dc.subjectresonatorsen
dc.subjectMEMSen
dc.subjectNEMSen
dc.titleDesign, fabrication and characterisation of graphene electromechanical resonatorsen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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