Mixed-Domain Simulation and Wafer-Level Packaging of RF-MEMS Devices

MEMS (Micro Electro-Mechanical System) technology for Radio Frequency (RF) applications has emerged in recent years as a valuable solution in order to fabricate passive components (e.g. inductors, varactors, switches etc.) with remarkable performances, like very high quality factor (Q-Factor) and wide capacitance tuning ranges. MEMS technology implies for its nature a deep interaction among different disciplines, like for instance structural mechanics and fluido-dynamics. Additionally, the process flow in fabricating RF-MEMS is not standardized like it happens for example when dealing with CMOS technology. Consequently, the need for mixed physical domain environments on one side, as well as the issue of dealing with several degrees of freedom (DoF’s) in defining the proper design of RF-MEMS devices on the other hand, urge for the availability of an on-purpose simulation tool. Once all the issues related to the RF performances optimization and fabrication of the MEMS devices are solved, another delicate key-factor must be faced to make the applicability of RF-MEMS successful within functional blocks. This is represented by the packaging of MEMS devices on one side and by their integration and interfacing to the CMOS active circuitry on the other hand. Indeed, RF-MEMS fabrication process is incompatible with standard CMOS technology. Despite the existence of few solutions for a unified MEMS/CMOS fabrication flow, the most valuable way to achieve the best performances for both parts is still represented by keeping the two processes separated and then integrating the MEMS to the CMOS part at last. Depending on the technological solutions selected for both of them the electrical interfacing on the two parts can be performed accommodating the CMOS chip directly onto the RF-MEMS devices area. Nonetheless, in other cases in happens that the electrical interconnection schemes of the two blocks are incompatible. In this case the redistribution of electrical signals is necessary. On this purpose, one of the possibilities is to exploit the package substrate itself, whose main task is to protect MEMS devices from harmful factors (e.g. moisture, dust particles, shocks etc.), to make available such a signals redistribution scheme. This solution in which the package plays an active role in realizing the interfacing of different parts is well known in literature as hybrid packaging