A CMOS integrated three-axis accelerometer fabricated with commercial submicrometer CMOS technology and bulk-micromachining

In this paper, a bulk-micromachined three-axis accelerometer fabricated with commercial submicrometer CMOS wafers has been developed for low-cost realization of smart accelerometers and improvement of device performance. The signal processing circuits for three-axis detection were formed using a commercial 0.8-μm CMOS technology. After that, micromachining processes were performed to the complete CMOS wafers to form accelerometer structures. The important technologies to separate micromachining processes from the CMOS process are wafer thickness control after CMOS fabrication and backside polishing with chemical spin etching. Accelerometers with 3×3 mm² and 6×6 mm² die size were fabricated with the developed fabrication technology. As a result of device evaluation, 2.0 mg_rms resolution of Z-axis acceleration, and 10.8 mg_rms resolution of X and Y-axis acceleration were obtained by the accelerometers with 6×6 mm² die size. Comparing for the same die area, the 6×6 mm² size accelerometer showed about 21.3 times higher resolution of Z-axis acceleration and 37.8 times higher resolution of X, Y-axis acceleration as compared to our previous three-axis accelerometer fabricated with 5.0-μm CMOS technology. Temperature dependence and reliability for repetitive vibration loads were also evaluated. Through these evaluations, basic performance of the CMOS integrated three-axis accelerometer has been confirmed