Flip-chip assembly and liquid crystal polymer encapsulation for variable MEMS capacitors

Packaging is a well-known barrier to the advancement of microelectromechanical systems (MEMS) for RF applications. To pave the way for the removal of this barrier, we have developed a flip-chip assembly technology to transfer foundry-fabricated MEMS devices from the host silicon substrate to a ceramic substrate. Specifically, posts have been designed and fabricated to assure excellent RF performance by achieving a precise gap between the device and ceramic substrate. In addition, a novel liquid crystal polymer (LCP) encapsulation technology has been developed to protect the RF MEMS device. LCP is a good encapsulation material for nonhermetic packaging because it significantly reduces the packaging cost. We have demonstrated excellent RF performance of variable MEMS capacitors that have been flip-chip assembled and LCP encapsulated. The quality (Q) factors of such capacitors were measured to be higher than 300 at 1.0 GHz.