Polydimethylsiloxane-based pattern transfer process for the post-IC integration of MEMS onto CMOS chips

Abstract

This paper presents a novel pattern transfer process of LIGA and UV-LIGA MEMS onto CMOS chips using polydimethylsiloxane (PDMS) replication and electroplating-based post-IC integration techniques. An array of cylindrical posts was fabricated by the standard LIGA process and an inverse replica was made using a PDMS replication technique. The replicated PDMS mold was used to transfer the LIGA MEMS onto a CMOS chip using electroplating. For the pattern transfer of UV-LIGA MEMS onto CMOS chips, double-layered circular spiral inductors were fabricated using the UV-LIGA technique as metallic master molds. Inverse replicas of the inductors were built in PDMS as double-layered PDMS electroplating mold (PEM). This PEM was aligned and attached onto the chips, and electroplating was performed to transfer the metallic UV-LIGA MEMS inductors onto the chips. The transferred inductors showed a self-resonant frequency of 7.5 GHz, an inductance of 2.11 nH, and a Q-factor of 78.9 at 0.6 GHz.