Improvement of CMOS-MEMS accelerometer using post-CMOS selective electroplating technique

This study presents a simple approach to improve the performance of CMOS-MEMS capacitive accelerometer by means of the post-CMOS metal electroplating process. The metal layer can be selectively electroplated on the MEMS structures at low temperature; and the thickness of metal layer can be easily adjusted by process. Thus, the performance of capacitive accelerometer (i.e., structure deformation, sensitivity) can be improved significantly. In application, the designed accelerometers have been implemented using (1) standard TSMC CMOS 0.35μm 2P4M process, (2) Ti/Au seed-layer deposition/patterning by Asia Pacific Microsystems Inc. (apm), MEMS foundry, and (3) in-house post-CMOS electroplating and releasing processes. Measurements indicate the sensitivity is improved for 2.5-fold, and noise is decreased near 2.5-fold after Ni electroplating. Moreover, unwanted structure deformation due to the temperature variation is significantly suppressed by electroplated Ni.