The realization and design considerations of a flip-chip integrated MEMS tunable capacitor

摘要

Microelectromechanical systems (MEMS)-based radio frequency (RF) components are being developed for various microwave and millimeter-wave applications. Using standard foundry processes, it is possible to create very complex MEMS devices. However, most RF MEMS need to be fabricated using GaAs, ceramics, high resistivity silicon or other RF-compatible materials. Such fabrication techniques are not commonly used by the mainstream silicon-based MEMS manufacturing infrastructure. As a result, the complexities of these MEMS devices are very limited. What is needed is a way to utilize the existing cost effective foundry processes, but not sacrifice RF performance. Utilizing a flip-chip transfer process, a complex, foundry fabricated, MEMS tunable capacitor has been demonstrated that yields high quality RF performance (Q ～ 100 at 10 GHz, 1050 at 1 GHz). The transfer process is described, and its performance (control, success rate, etc.) is presented. Several major design considerations for implementing the tunable capacitor using flip-chip technology are presented, including warpage, actuator design, and structural rigidity. Using the transfer process and design considerations, there is an opportunity to integrate complex MEMS onto any RF compatible substrate without the silicon semiconductor effects. Thus, it is possible to manufacture complex MEMS cost-effectively for a new generation of RF MEMS with superior functionality.