Design and fabrication of self-packaged, flexible MEMS accelerometer

This paper presents the design, fabrication process and characterization of a self-packaged MEMS accelerometer on a flexible substrate. The novelty lies in that the accelerometer is fabricated in between a polyimide substrate and a superstrate, thus allowing front-end encapsulation and bonding without the need for rigid packages. Modeling and optimization were done using Coventorware® software, where the designed structures were subjected to 6 cm-radius curvature, and the resulting stress was evaluated for each layer. Then, based on the simulated designs, a low-temperature fabrication process flow was developed using a double UV-LIGA fabrication technique in conjunction with surface micromachining. This novel technique allowed us to decouple the thicknesses of the proof-mass and the springs, thus attaining high sensitivity. Our experimental results indicate a sensitivity of about 125 fF/g at the resonant frequency for device size of 640 μm × 640 μm. The response from the device was two orders of magnitude higher than the noise. The resolution of the device was measured to be 150 millig in the range between -10g and +10g.