CMOS-Compatible scalable microfabrication of graphene polymeric strain gauge arrays

Official URL: https://risc01.sabanciuniv.edu/record=b2486619_(Table of contents)

Over the years, microelectromechanical systems (MEMS) have been utilized widely in sensing applications due to their characteristics such as small form-factor, ultra-high sensitivity, low-cost and scalability. Among the various sensing principles, piezoresistive effect has proved to be critical for strain sensing applications, owing to several advantages including compatibility with standard microelectronic fabrication techniques, ability for either monolithic or heterogeneous integration with readout circuitry which have rendered widespread use of piezoresistive sensors in various fields like structural and environmental monitoring. However, the sensitivity of strain gauges otherwise referred to as the gauge factor (GF) is limited to single digits (~ 2) for commercial metal-foil gauges on polymeric substrates. Single crystal silicon or polysilicon strain gauges achieve much higher GF values but at the expense of smaller ultimate strains and need for moderate to high levels of doping translating into additional process steps and higher device costs. On the other hand, graphene, a two-dimensional (2D) honeycomb structure of sp2 hybridized carbon atoms has vast potential for strain sensing applications due to its distinctive mechanical and electrical properties, provided that it can be integrated into standard semiconductor process flows. This thesis reports on the microfabrication of graphene strain gauges in arrayed format on flexible, polymeric structural layers where SU-8 was selected due its stable chemical and mechanical properties. Experimental characterization results show that, the fabricated graphene strain gauges achieve more than two orders of magnitude increase in GF values of up to 300, along with Raman results verifying successful integration of graphene layers into device format based on well-defined, scalable and IC-compatible processes