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 wit h commercial submicrometer CMOS wafers has been developed for low-cost real ization of smart accelerometers and improvement of device performance. The signal processing circuits for three-axis detection were formed using a com mercial 0.8-mum 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 pol ishing with chemical spin etching. Accelerometers with 3 x 3 mm(2) and 6 x 6 mm(2) die size were fabricated with the developed fabrication technology. As a result of device evaluation, 2.0 mg(rms) resolution of Z-axis acceler ation, and 10.8 mg(rms) resolution of X and Y-axis acceleration were obtain ed by the accelerometers with 6 x 6 mm(2) die size. Comparing for the same die area, the 6 x 6 mm(2) 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 fab ricated with 5.0-mum CMOS technology. Temperature dependence and reliabilit y for repetitive vibration loads were also evaluated. Through these evaluat ions, basic performance of the CMOS integrated three-axis accelerometer has been confirmed.