Using Residual Stresses to Develop CMOS-compatible RF MEMS Switches

Abstract

This research presents a novel MEMS-switches that fabricated with CMOS and post-process techniques of MEMS. This switch includes a controllable cantilever beam and static electrode. The switch is driven by using electrostatic force. So far, the pull-in voltage of MEMS switch is too large to combine with CMOS circuit chip. In addition, the residual stress produced from CMOS process will cause a large deflection of cantilever beam. Therefore, in this research, we use CoventorWare to inspect the feasibility about deflection of cantilever beam that caused by residual stress. Accordingly, we make use of deflection of cantilever beam as the principle of design. The cantilever beam is set in the reverse direction. And, a blocking layer can be used to constrain deflection of cantilever beam to diminish the pull-in voltage. Subsequently, the pull-in voltage can be reached below 3.3V. By defining the region of etching holes (RLS) preliminarily, silicon beneath could be excavated to reduce substrate loss and increase isolation. Only one etching process is needed in post-process to release the cantilever beam. Finally, we use thick photoresist to complete self-packaging to lower down the cost of chip fabrication. The advantages of this MEMS switch are as follows: small area, low pull-in voltage, uncomplicated fabrication, and compatible with CMOS process. We only use via layer, metal layer and poly layer of TSMC 0.35 mum 2P4M CMOS process to fabricate our design.