Graphene-Polyimide Nanocomposite Piezoresistive Thin Film Device for Strain and Pressure Measurement

In this thesis, piezoresistive thin film strain/pressure sensors made of graphene-polyimide (PI) nanocomposites with graphene concentration varies from 1.0wt% to 1.8wt% were fabricated, and their piezoresistive properties were characterized. The range of the graphene concentration is determined by percolation threshold theory, so the nanocomposites remain as semiconductors. The graphene-PI nanocomposites suspension were fabricated by blending method and was put into an ultrasonic water bath for a few hours to fully disperse the solution and avoid agglomeration of graphene nano-fillers. The graphene-PI nanocomposite thin film strain sensors were fabricated by depositing the suspensions on the polyimide substrate through a drop-on-demand piezoelectric inkjet printer, and electrodes were coated by sputter coater. The electrical impedance with respect to the strain that the nanocomposite thin films suffered under uniaxial tension and uniform pressure were monitored, and the gauge factor of these sensors under two experimental circumstances were calculated and compared. The respond of these strain sensor to pressure was also directly related. The temperature effect was evaluated, and the temperature coefficients of these graphene-PI nanocomposites devices were determined, and a feasible method to eliminate the temperature effect by temperature compensation was proposed. Finally, the most sensitive strain gauge represented by the largest gauge factor was found, proving that graphene-PI nanocomposites are superior materials than metals to fabricate high sensitive strain sensors, and inkjet printing technique is a desirable method to achieve this