Piezoresistive Accelerometer Based on Amorphous Carbon Films

Amorphous carbon film (a-C) has many outstanding characteristics, such as low friction, anti-wear properties and chemical stability. Its preparation is low cost, simple, and can well combined with microelectromechanical system (MEMS) process. Because it has remarkable piezoresistive effect, a-C piezoresistor was integrated in accelerometer to get a high-performance sensor. Using electron cyclotron resonance (ECR) plasma sputtering and ion evaporation deposition process, a-C was integrated on the quad-beam-mass structure as piezoresistor which had high gauge factor. By adjusting process parameters, the gauge factor could be controlled. In the ECR sputtering process, bias voltage +50 V and +100 V was applied to the substrate, respectively. And the gauge factor was within the range of 3.2-6.7 and 5.5-9.6; in the other process, a negative bias voltage 2 kV was applied to the substrate, then the hydrogenated amorphous carbon films (a-C: H) was deposited, which had a higher gauge factor 40.5-54.2. A MEMS piezoresistive accelerometer based on a-C piezoresistor was designed and fabricated. The piezoresistive accelerometer which used a-C: H had higher sensitivity 0.023 mV/V/g and natural frequency 18.1 kHz. This study provided a new method to further improvement of the comprehensive performance of MEMS piezoresistive accelerometer.