Application of femtosecond laser etching in the fabrication of bulk SiC accelerometer

Abstract

Silicon carbide (SiC) is a promising material to fabricate MEMS accelerometers used in extreme environments for vibration monitoring. However, with ultra-high hardness and corrosion resistance, it is difficult to etch bulk SiC by traditional MEMS processing methods. Here, we presented a bulk SiC accelerometer structure and its femtosecond laser deep etching method. Combined with the sensor design and femtosecond laser etching method, the sensitivity of the sensor could be improved and the processing difficulty could be reduced. The sensitive beams and mass block of the designed accelerometer were fabricated by femtosecond laser and high size accuracy with the maximum size error of about 3.1% was achieved. A fillet transition on the sensitive beam can eliminate crack propagation during laser etching and improve the quality of the etched gap. The cross-section of the etched sensitive beam can be regarded as an isosceles trapezoid with a steepness of 84.76°. The laser etching sidewall surface of the beam is smooth with a surface roughness (Sa) of 0.255 μm. The piezoresistors on the beam of the accelerometer remain stable before and after laser etching. Generally, the results show that femtosecond laser etching is a feasible method to fabricate bulk SiC accelerometers.