Piezoresistive behavior of amorphous carbon films for high performance MEMS force sensors

In this study, microelectromechanical systems (MEMS) force sensors based on H-free amorphous carbon (a-C) films with controlled piezoresistive behavior were fabricated by a facile magnetron sputtering technique. By adjusting the substrate bias voltage from 0V (floating state) to -350V, the gauge factor (GF) of the a-C film was modulated in the range of 1.4-12.1. Interestingly, the GF showed a strong dependence on the sp(2) content and the sp(2) cluster size of the film, which was consistent with the theory of thick film resistors. In addition, the sensitivity of a-C based MEMS force sensors reached 80.7 mu V/V/N in the force range of 0-1.16N, with a nonlinearity of approximately 1.3% full scale and good repeatability in over 5000 test cycles.