MEMS above IC technology applied to a compact RF module (Keynote Paper)

Miniaturization, low cost and excellent performances at microwave and millimeterwave applications represent the main leitmotivs of the future mass market communication systems. Consequently, a novel "MEMS above IC" technology has developed in order to allow the elaboration of post-processed micro-machined passive components on top of SiGe circuits to realize a complete short-range communication receiver centered at 24 GHz. The developed technology is based on the use of : -a thick organic layer (BCB), which is employed as a dielectric membrane, -metallizations to realize the passive metal layer and also the vias to interconnect the active circuits with the post-processed passive components, -and a bulk silicon micromachining. This 'above IC' technology presents many advantages, as it uses conventional equipments of microelectronics and is in adequation with high frequency applications. A specific attention has been carried out in order to assure the compatibility of the post-process steps and the IC’s. This has been performed through the choice of the adequate technological steps, which had to present a low temperature budget. The compatibility of each step has been evaluated with a specific test protocol on SiGe transistors. It implies static and dynamic characterisation of these transistors as well as low frequency noise measurements. Each step has been validated, even the bulk silicon micromachining. Design rules have thus been defined in order to localize the silicon etching without any damage on the ICs.