In order to efficiently design complex microelectromechanical systems (MEMS) having large numbers of multi-domain components, a hierarchically structured design approach that is compatible with standard IC design is needed. A graphical-based schematic, or structural, view is presented as a geometrically intuitive way to represent MEMS as a set of interconnected lumpedparameter elements. An initial library focuses on suspended-MEMS technology from which inertial sensors and other mechanical mechanisms can be designed. The schematic representation has a simulation interface enabling the designer to simulate the design at the component level. Synthesis of MEMS cells for common topologies provides the system designer with rapid, optimized component layout and associated macro-models. A synthesis module is developed for the popular folded-flexure micromechanical resonator topology. The algorithm minimizes a combination of total layout area and voltage applied to the electromechanical actuators. Synthesis results clearly show the design limits of behavioral parameters such as resonant frequency for a fixed process technology.

We are developing physical design tools for surfacemicromachined MEMS, such as polysilicon microstructures built using MCNC’s Multi-User MEMS Process service. Our initial efforts include automation of layout synthesis and behavioral simulation from a MEMS schematic representation. As an example, layout synthesis of a folded-flexure electrostatic combdrive microresonator is demonstrated. Lumpedparameter electromechanical models with two mechanical degrees-of-freedom link the physical and behavioral parameters of the microresonator. Simulated annealing is used to generate global optimized layouts of five different resonators from 3 kHz to 300 kHz starting with mixed-domain behavioral specifications and constraints. Development of the synthesis tool enforces codification of all relevant MEMS design variables and constraints. The synthesis approach allows a rapid exploration of MEMS design issues. 1.

Microresonator layouts are synthesized such that their preferred mode of oscillation is well-separated from the higher order in-plane and out-of-plane modes. Building on our previous work, we have incorporated models for four out-of-plane modes. All these modes are modeled as springmass systems. The spring constants and the effective masses of these modes are analytically derived. Synthesis is accomplished by encoding a design quality metric as the design objective while simultaneously constraining the design to meet user specifications. These constraints require that the resonant frequency in the preferred direction is sufficiently lower than (and, hence, dominates over) the resonant frequency of other modes of vibration of the structure. The models are verified by comparison with 3D FEM simulations and also with experimental measurements on fabricated resonators. The usefulness of these models is illustrated by comparing the oscillation modes of layouts synthesized with and without these models. This exercise also shows that such mode-separation can be achieved only if the microresonators have a structural thickness larger than flexure width.

Efficient built-in and external test strategies are becoming essential in MicroElectroMechanical Systems (MEMS), especially for high reliability and safety critical applications. To be realistic however, internal and external test must be properly validated in terms of fault coverage. Fault simulation is hence likely to become a critical utility within the design flow.