Encapsulated Micromachined Silver Devices for RF MEMS

Silicon micro-electromechanical devices such as capacitively- and piezoelectrically- transduced resonators and inertial sensors have found way into low-frequency consumer applications by offering small size, low cost, and low power consumption. Metallic MEMS, on the other hand, are more suitable candidates for RF applications as they can offer the added advantage of easy integration with CMOS, and the possibility of ultimately replacing several off-chip passives to reduce the cost and enhance the overall performance of the RF systems. However, the performance of this type of MEMS devices is not yet sufficiently high to achieve mass market adoption, and requires further research and development.
Metallic MEMS tunable filters in particular can find applications in several RF systems including multi-standard radios, once they meet the desired system specifications. These specifications are directly dependent on the quality factor of the individual filter components, which should be in excess of 100 for most applications. Such high-Q passives and specially inductors are not available in commercial CMOS processes. In this talk, I will present novel post-CMOS-compatible thick silver micromachining techniques that we used for implementation of record high-Q tunable capacitors as well as fixed and switchable inductors on silicon substrate. These high-Q integrated passives offer the possibility of achieving high-performance tunable filters on CMOS-grade silicon, which have not been available through conventional silicon technology. Moreover, they can be used in integrated matching networks, voltage-controlled oscillators, low-noise amplifiers, and power amplifiers.
I will also present preliminary results on low insertion-loss fixed and tunable lumped filters that are fabricated using these low-temperature fabrication techniques. The results of wafer-level encapsulation of the fabricated devices will be demonstrated, showing great promise for increasing the reliability of the RF MEMS devices. I will then discuss the integration of arrays of piezoelectrically-transduced acoustic filters and lumped filters to implement high-performance analog spectral processors for anti-jam and cognitive radio applications.
I will discuss our contribution to address some of the challenges involved with the integration of such high-performance tunable filters on silicon substrate, and describe the challenges that are yet to be overcome before tunable MEMS filters can become viable solutions to RF microsystems. Last but not least, I will describe the latest result on application of this silver micromachining technique to implement other high-performance RF devices, such as resonators and switches to achieve the ultimate goal of single-chip low-power RF integrated circuit and system.

Mina Rais-Zadeh received her B.S degree in Electrical Engineering from Sharif University of Technology, Tehran, Iran in 2002 and the M.S degree in Electrical and Computer Engineering from Georgia Institute of Technology, Atlanta, GA in 2005. She is currently a Ph.D. Candidate in the Department of Electrical and Computer Engineering at Georgia Institute of Technology and plans to complete her doctorate by August, 2008. Her research interests include integrated RF MEMS filters, MEMS-enabled ICs, and micro-fabrication techniques. Her research is currently focused on the design, implementation, and characterization of reconfigurable filters and high-performance passive components for realization of ultra low-power RF transceivers.