Abstract: Graphene, as an ultra-thin 2D membrane material, is very promising in applications of micro- and nanoelectromechanical system (MEMS and NEMS) due to its atomic thickness and unique mechanical, electrical and optical properties. Currently, studies have successfully shown the feasibility of using suspended graphene in resonators, pressure sensors, switches, loudspeakers, microphones and gas sensors, etc. Suspended graphene can be fabricated by transferring graphene from the original substrate to 1) a pre-fabricated substrate with trenches, cavities or membranes made of dielectric layers, or 2) a flat silicon dioxide (SiO2) or polymer substrate surface and then removing parts of the material underneath the graphene by sacrificial etching. However, fabrication of suspended graphene structures, especially suspended graphene with an attached proof mass is very challenging, such as collapse and rupture of the suspended graphene. We report a robust route for fabricating double-layer CVD graphene membranes and ribbons with attached SiO2/Si proof masses, which is compatible with wafer-scale MEMS and semiconductor manufacturing technologies. Graphene ribbons and membranes with attached SiO2/Si proof masses were demonstrated to be extremely robust and were able to withstand AFM tip indentation forces of up to ~7000 nN. Based on atomic force microscope (AFM) tip indentation experiments, the averaged Young’s modulus of stacked double-layer CVD graphene films in our devices was extracted to be 0.22 TPa. The built-in stress of hundreds of MPa exist in the graphene ribbons and thereby cannot be ignored. The measured resonance frequencies of graphene ribbons and membranes with attached SiO2/Si proof masses ranged from tens to hundreds of kHz, with Q between ~101 and ~102. We demonstrate that the suspended graphene ribbons and membranes with attached SiO2/Si proof masses can be used as combined spring-mass and piezoresistive transducers in NEMS accelerometer. The graphene NEMS accelerometers occupy at least two orders of magnitude smaller die area than conventional state-of-the-art silicon accelerometers while keeping competitive sensitivities. These findings pave the way for a new class of extremely small and highly sensitive graphene NEMS devices and are an important step toward bringing ultra-small piezoresistive graphene NEMS closer toward deployment in emerging applications such as internet of things (IoT) devices.

Biography: Dr. Xuge Fan is a researcher in the Division of Micro and Nanosystems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Sweden. He earned his PhD in 2018 from the Division of Micro and Nanosystems, KTH Royal Institute of Technology. His research interest mainly focuses on graphene-based 2D materials and NEMS, especially integration of graphene-based 2D materials into NEMS for exploration of properties and development of novel NEMS devices. As first author, he has published original research articles in top scientific journals including Nature Electronics, Science Advances, Nano Letters, Carbon, Microsystems & Nanoengineering (in print). Especially, he has pioneered the use of graphene for ultra-small NEMS accelerometer devices based on atomically thin electromechanical graphene transducers with attached silicon masses; he discovered an approach that allows fast visualization and evaluation of the large-area distribution of grain boundary-based line defects in chemical vapour deposited graphene by using vapour HF technology.