A cost-effective three axis CMOS accelerometer combining micromachining and digital technology

In this paper, a three axis accelerometer is successfully developed by a mixing-mode chip design using CMOS surface-micromachining technology. The chip consists of mass-spring, the analog core and the digital circuit. The vibration sensor is implemented with micro-spring to change the capacitance between two metals. The analog core detects the capacitance differential to the frequency shifting using an oscillator. The digital control is to compute the amount of acceleration to the form of digital bit. The chip can detect the acceleration to 140 g for x axis and y axis with 10-bit resolution, and from 110 g for z axis with 9 bits. The detected speed is about 4 k bits per second, for three-axis output in parallel. The chip size is about 1,400 × 1,400 um², when TSMC 0.18 um 1P6 M process is employed. This 3D accelerometer can directly connect to the digital interface with three serial-port output for the information of X, Y and Z axis.