Packaging of two-dimensional microelectromechanical systems (MEMS) variable capacitors with liquid crystal polymer.

摘要

Packaging is a well-known barrier to the advancement of microelectromechanical systems (MEMS) for RF applications. To overcome this barrier, firstly, we have developed a flip-chip assembly technology to transfer foundry-fabricated MEMS devices from a host silicon substrate to a ceramic substrate. Our flip-chip process was specifically enhanced via the use of posts and tethers. The posts were designed to assure promising RF performance by achieving a precise gap between the device and the ceramic substrate. The tethers supported the MEMS structures during the release process before the flip-chip assembly. Such pre-assembly release was critical to the integration of electronic components and MEMS on the same substrate. By introducing necking in tethers and mechanical stops, we have achieved a high yield for the flip-chip assembly and device transfer.; Secondly, we have developed a liquid crystal polymer (LCP) encapsulation technology to protect the RF MEMS device. LCP is a good encapsulation material for polymer packaging because it significantly reduces packaging cost. We have demonstrated promising RF performance of a variable MEMS capacitor flip-chip assembled and LCP encapsulated. The quality (Q) factors of such capacitors were measured to be higher than 300 at 1.0 GHz. The LCP sealing was proven successful after evaluation using humidity and vacuum sensors. Finally, we have conducted basic studies on the LCP permeability. LCP permeabilities of Helium and Nitrogen were on the same order of magnitude as those of borosilicate glass. This thesis work demonstrated a cost-effective technology for integrating MEMS devices with other RF components on a substrate.