Stability of a micromechanical pull-in voltage reference

The reproducibility over temperature and time of the pull-in voltage of micromechanicat structures has been analyzed and verified using fabricated devices in silicon. The pull-in structures are intended for use as an on-chip voltage reference. Microbeams of 100-mum length, 3-mum width, and 11-mum thickness are electrostatically actuated with a very reproducible pull-in voltage at 9.1 V. Devices demonstrated an initial drift of - 12 mV over 10 days and stabilized within the 500-muV measurement uncertainty. The measured temperature coefficient of -1 mV/K is in good agreement with the analysis and is due to the combined effect of thermal expansion and the temperature dependence of the Young's modulus in silicon.