Abb. 1: MSA-400 Micro System Analyzer für Schwingungsanalyse (Zeitbereich, Frequenzbereich und Schwingungsmoden)
Abb. 2: Probecard für kontaktlose elektrostatische Schwingungsanregung von MEMS (bis 1 MHz)
Abb. 3: Software zur Berechnung von MEMS Kennwerten (Abmessungen und/oder mech. Spannung) aus Schwingungsmessdaten

A MEMS (micro electro mechanical system) combines the two domains of electrical and mechanical engineering in a miniaturized, complex device and extends microelectronics to the fascinating world of sensors and actuators. Today, acceleration sensors and gyroscopes as an example are very well known MEMS devices, which are successfully fabricated with quantities in the millions. But these tiny systems also present new challenges, especially to in production measurement techniques. The characterization of electrical parameters (resistance, capacitance and inductance) has to be extended with additional mechanical parameters. This includes in particular the geometric dimensions of structures, mass, spring stiffness, damping, resonant characteristics and material parameters, such as elastic modulus and mechanical stress. Not all of these parameters can currently be measured fast, non-destructive and accurate enough.

An interesting access to the parameters of a mechanical system provides the analysis of its dynamic properties, by measuring vibration mode shapes and frequency response functions. These parameters can be measured with a scanning laser Doppler interferometer (Fig. 1) very precise, fast and without physical contact. With the position of the resonance frequencies in the vibration spectrum, subsequent information on other parameters (e.g. mechanical stress) can be obtained. These calculations are precise enough to be used for monitoring and optimization of manufacturing processes and hence for increasing the fabrication yield.

Fraunhofer ENAS researches methods, algorithms, hardware (Fig. 2) and software (Fig. 3) for the time efficient characterization of MEMS using methods of vibration analysis. It provides analysis services for custom MEMS and consulting during the integrating of these methods into the customer’s fabrication process.