Micromechanical voltage reference using the pull-in of a beam

TitleMicromechanical voltage reference using the pull-in of a beam
Publication TypeJournal Article
Year of Publication2001
AuthorsCretu, E., L. A. Rocha, and R. F. Wolffenbuttel
JournalInstrumentation and Measurement, IEEE Transactions on
Pagination1504 -1507
Date Publisheddec.
Keywords200 micron, 9.1 to 9.5 V, bifurcation, bifurcation diagrams, capacitive sensors, DC voltage reference, differential capacitor, electrostatic actuators, epi-poly process, feedback, finite element analysis, finite element modeling, hysteresis, lateral deflection, local continuation method, long-term stability, mechanical stability, micromachining, micromechanical voltage reference, microsensors, parallel-plate type electrostatic actuation, pull-in voltage, seesaw, semiconductor device models, single-end clamping, single-side anchored freestanding beam, stability border, static pull-in, surface micromachining, transfer standards, two-dimensional energy-based analytical model, voltage measurement

The pull-in voltage of a single-side anchored freestanding beam, under lateral deflection, has been investigated for application as a DC voltage reference. Two sets of electrodes, along side the tip, are used for parallel-plate type of electrostatic actuation of the 200 mu;m long beam in the plane of the wafer. Another set of buried electrodes is aligned with the plate electrode at the free-standing tip and is used as a differential capacitor for the simultaneous detection of the displacement, with the purpose to determine the stability border and thus the pull-in voltage. The single-end clamping ensures that the pull-in voltage is insensitive to technology-induced stresses. A 2D energy-based analytical model for the static pull-in is compared with measurements. Bifurcation diagrams are computed numerically, based on a local continuation method. Devices have been designed and fabricated in an epi-poly process. Measurements are in agreement with modeling and confirm a pull-in voltage in the 9.1-9.5 V range. Reproducibility is limited by hysteresis and charging of the dielectric layer in between the electrodes. The device can be operated in feedback or as a seesaw, by using the two sets of electrodes


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