MEMS piezo-resistive force sensor based on DC sputtering deposited amorphous carbon films

The rapid growing demand of micro-electromechanical system (MEMS) sensors brings an urgent need for high performance and low cost sensitive materials. In this work, amorphous carbon (a-C) film was in-situ deposited on silicon substrate as strain sensitive component using economical direct current (DC) magnetron sputtering process and the a-C sensor was systematically designed, fabricated and tested. By adjusting the negative bias voltage in the range of 0-400 V, the gauge factor (GF) of the a-C film was adjusted within the range of 3.3-6.9. What's more, the film's sp(2) cluster size played an important role in their piezo-resistive performance and conductivity, which illustrated the thick-film resistors (TFRs) theory. Additionally, CAFM results also supported the applying of TFRs theory in this work. Benefiting from the outstanding performance of a-C film, the MEMS force sensor, consisted a Wheatstone full-bridge with four a-C piezo-resistors, had a sensitivity of 9.8 mu V/V/mN and non-linearity about 2.0% FS in the testing range of 0-210 mN, while it also showed a good repeatability. These investigations provided deeper insight into the piezo-resistive behavior of a-C film and contributed to the development of high performance and more economical sensitive materials for MEMS sensors. (C) 2019 Elsevier B.V. All rights reserved.