Influence of 0-level packaging on the microwave performance of RF-MEMS devices

RF-MEMS devices (Radio Frequency-MicroElectroMechanical Systems) are made of moveable and fragile structures (membranes, beams, cantilevers,...) that must be encapsulated for protection and for stable performance characteristics. Zero-level or wafer-level packaging developed so far has been limited to dc-components. This paper elaborates on the design and fabrication of a 0-level package for housing RF-MEMS devices. The fabrication process is described and packages are characterized in terms of mechanical strength, hermeticity and microwave performance in the range 1-50 GHz. Simulations and experiments show minimal impact of the package on the RF losses if the cap has a minimal height of 50 μm, if low-loss materials (e.g., glass) are used, and if matched RF feedthroughs are implemented. Finally, in a multi-switch design, we recommend to minimize the number of feedthroughs, i.e. to use a single cap for the entire design.