Coupled RF and Electromechanical Simulation of an RF-MEMS Ccomplex Network Based on Compact Models

MEMS technology for Radio Frequency and Microwave applications (i.e. RF-MEMS) has emerged, in the last decade, as a valuable solution to improve the performance and the reconfigurability of transceiver platforms for various applications, like mobile phones, satellites, surveillance and monitoring systems, and so on [1, 2]. The exploitation of RF-MEMS components (like lumped elements as well as complex networks) always urges for their hybridization with control and functional circuitry realized in standard technology, i.e. CMOS. This consideration poses several issues one has to cope with. On one side, there are several aspects concerning the integration and packaging of different technologies [3]. On the other hand, modeling and simulation of hybrid RF-MEMS/CMOS blocks has also to be properly addressed. However, given the different physical domains involved in their functioning, namely, electromagnetic, fluidic and coupled electromechanical [4], it would be desirable having a unique software environment in order to perform the performance optimization of the whole hybrid block at once. Having in mind this critical issue, the authors already presented an in-house developed MEMS compact model software library, implemented in a standard programming language, within a commercial framework for the simulation and development of ICs (Integrated Circuits) [5]. In this work, the mentioned tool is exploited in order to simulate the mixed RF/electromechanical behavior of a complex RF-MEMS network, namely a multi-state RF power attenuator, designed, fabricated and tested in the FBK RF-MEMS technology [6]. The power attenuator is based on 2 branches in parallel with 6 poly-silicon series resistors of different values. Each resistor can be selected or shorted depending on the state (actuated or not-actuated) of electrostatically controlled suspended gold membranes. Moreover, one or both the branches are selected by means of SPDTs (Single Pole Double Thru). Fig.1-left-top shows a microphotograph of the entire fabricated network together with a close-up (3D profilometer) of one branch and one single MEMS suspended membrane. We implemented the whole network with the compact models available within the above mentioned MEMS model library, and the schematic is reported in Fig. 1-left-bottom. The correspondence between the sub-sections of the physical network and the schematic are highlighted in figure, and the 6 resistive loads are labeled with letters from “a” to “f”. The schematic was then simulated (S-parameter simulation) from DC up to 40 GHz with an increasing number of electrostatically actuated MEMS membranes (from 0 to 6, corresponding to the maximum and minimum power attenuation levels, respectively). The simulation results are reported and compared in the plot shown in Fig. 1-right. In the full paper we will present more details concerning the RF-MEMS network and the simulations performed by means of the implemented MEMS compact models. Moreover, a validation of simulated outputs against experimental data will be also shown, defining the accuracy achievable by following such a modeling and simulation approach.