The fabrication of MEMS with batch processing calls for a challenging characterization of the MEMS, especially in the case of a 100-percent testing. For the functional test of many of micromechanical structures it is necessary to measure the mechanical motion. A capacitance-change to voltage conversion is a cheap and commonly used method. To achieve an optimal signal to noise ratio, it is desired to have the conversion as close as possible to the MEMS.
The presented “MEMS Active Probe” has been developed and built for exactly this case of application. It allows the measurement of the motion of micromechanical elements. The “MEMS Active Probe” covers the frequency range up to 200 kHz (3 dB) with a sensitivity of 90 mV/nA. The output impedance is matched to 50 Ohm to be directly used with a spectrum analyzer. The bracket can be used with common positioners. The probe is used for dynamic measurement of very low currents (pA to nA).