A Versatile Instrument for the Characterization of Capacitive Micro- and Nanoelectromechanical Systems

摘要

This paper presents a laboratory prototype of an instrument developed for electromechanical characterization of capacitive micro- and nanoelectromechanical systems (M/NEMS). The instrument aims at filling the gap between commercial electrical instrumentation (impedance meters) and optical instrumentation: For most M/NEMS devices, impedance meters allow only quasi-stationary measurements (i.e., capacitance–voltage $C$–$V$ curves) with a bandwidth limited to few hundreds of hertz; optical instrumentation allows dynamic characterization (Bode diagrams) but, besides being bulky and extremely costly, does not allow the measurement on packaged devices—and packaging is often an issue for the device performance and reliability. The proposed versatile characterization platform, controlled by LabVIEW libraries, monitors the capacitance variation, resulting from different kinds of electrical stimuli, via real-time capacitive sensing. The measurements are both stationary $C$–$V$ curves and dynamic responses to input steps in the time domain, which are convertible into Bode plots in the frequency domain. Measurements can be done on bare or packaged and on wafer-level or diced devices, in a differential or single-ended configuration, with a good immunity to parasitic capacitances, a sensing resolution on the order of $approx !1 hbox{aF}/sqrt{hbox{Hz}}$, and a maximum testable device mechanical bandwidth around 100 kHz. A characterization of two sample structures, a micromachined magnetometer and a clamped–clamped beam resonator, is given as an example, followed by a discussion on future improvements.