There are a wide range of promising applications for RF MEMS switches, including use in tunable filters, antennas, tactile radio, and RF ID . Why it is so difficult to develop these devices?
There are several challenges that need to be overcome when designing an RF MEMS switch. Mechanically, the device needs to withstand billions of actuation cycles, opening and closing the actuator in a highly reliable manner. Contact blocks are often employed to avoid direct contact between the electrodes. It is also critical to understand the dynamic nonlinear behavior of the device. Pull-in, lift-off, and frequency hysteresis need to be optimized during device design to meet final product specifications. Moreover, the transient behavior of an RF MEMS switch is very sensitive to device dimensions and process variability, making these parameters critical to performance and yield. RF MEMS switches also often rely on complex composite materials, such as stacks of metals and dielectrics, that exhibit fabrication induced residual stress and stress gradients. Each of these factors has a substantial impact on achieving final device performance and maintaining design specifications.
The dynamic behavior of a RF MEMS switch must be understood to not only design the best switch, but also to design the system around it. The overall system includes the MEMS chip, the control electronics and integrated circuits, the RF components, and the packaging. Optimizing the overall system is key to success, and requires a realistic (and not an idealistic) device and system model.
Coventor’s MEMS+® is a transformational solution to solve these challenges. Three transformational capabilities in MEMS+ help overcome the challenges of RF MEMS switch design.
Transformation No 1 is the ability to capture transient switching behavior. MEMS+ enables high-fidelity models that predict detailed coupled physics performance, including the non-linear behavior caused by contact mechanics and hysteresis (see Figure 1). This provides an in depth understanding of pull-in and lift-off behavior, and a predictive, realistic understanding of how the switch will operate.Transformation No 2 is the exploration of the design-technology space. Compact models created in MEMS+ reduce simulation time from days to minutes. These fast simulation times enable a broad exploration of the design space and device manufacturability. Changes in geometry, process and material values can be quickly studied in design-of-experiments, improving the designer’s understanding of the trade-offs between device design (geometry) and technology (process, materials). Reliability failures caused by design-process interactions can be uncovered at an early stage, accelerating the yield optimization process (see Figure 2). Transformation No 3 is the ability to accurately simulate system-level behavior. MEMS+ models produce simulation results quickly and accurately, which is needed during system-level simulation. 3D multi-physics MEMS+ models can be brought directly into system-level modeling tools and electrical circuit simulators, enabling fast co-design of the RF MEMS switch with the surrounding circuitry and systems. These realistic MEMS+ device models can be used to optimize a complete product or system. For example, a designer can explore the optimal voltage modulation at the actuation electrodes within a control circuit. Idealistic, simplified MEMS behavioral models used during system design can risk product underperformance or even complete failure. With MEMS+, simulated results match measured values (see Figure 3).