Test instrumentation and procedures for PiezoMEMS

To determine the performance envelope of thin film piezoMEMS devices or verify their operation, electrical and mechanical components must be characterized individually then their combined electromechanical functionality tested. For this purpose, the authors have constructed a unique test system with supporting instrumentation, sensors, and software that allows automated testing of complex piezoMEMS over temperature (-195°C to 600°C). The system combines a laser doppler vibrometer (0.3 Ångstrom resolution) with an intelligent multiplexer circuit card to analyze the Device Under Test in a small temperature chamber or on a probe station. Integrated software captures the electrical response and mechanical motion from multiple devices on a single die while controlling temperature (if the optional temperature chamber is used). The authors will describe standardized tests that identify fundamental parameters of a piezoMEMS. The electrical properties of the capacitors are first evaluated for yield and uniformity. Those capacitors are then electrically poled to allow actuation of mechanical members to measure large signal, low frequency electromechanical displacements. The impulse response induces ring-down which reveals resonant frequencies of the mechanical members (Figure 1). Ring-up driven by a small continuous sinusoid (Figure 2) can establish the quality factor and displacement amplitudes at resonance.