A technique for force calibration MEMS traceable to NIST standards

Characterizing the mechanical properties of materials and biological systems at the nanoscale requires accurate measurement of forces on the order of 10's of μN and less. Many times custom fabricated MEMS actuators and load cells are employed to apply these forces. Force response of these devices may be very different from their anticipated response due to fabrication induced effects. This makes it necessary to develop a method for their calibration that can be traced back to the National Institute of Standards and Technology (NIST). Due to the scale of the measurements and size of the instrumentation, calibration of nanoscale devices presents a new challenge in metrology. We have developed a novel method to calibrate a MEMS actuator with force resolution on the order of 1 μN using the tried-and-true deadweight method, but on the microscale. Calibrations are performed by suspending weights (traceably weighed sapphire spheres) from the MEMS device using the surface tension of water. The displacement was measured by measuring changes in capacitance and verified using a co-fabricated vernier. Measurements have been made using this method. Comparisons between our traceably calibrated force-displacement curves to a non-linear theoretical prediction, errors as great as 29% are revealed.