Modeling, control and characterization of highly coupled,
capacitively actuated micro-cantilever arrays
The starting point of this research is motivated by the potential uses
of microcantilever arrays for highly parallel scanning probe microscopy
and applications such as ultra high density data storage (e.g. the
IBM Millipede project).
There are two major issues confronting the designer of an arrayed MEMS device
- Dynamical coupling between neighboring devices, this is a particularly acute problem
in capacitively actuated devices due to fringe fields.
- Measurements of mechanical variables such as displacement. The most commonly used scheme
for AFM, optical levers, is not yet easily scalable to large arrays.
We have designed, built and tested arrays of capacitively actuated microcantilevers to directly address
these issues. The picture shown is representative of those arrays.
They are tightly packed movable plates
forming capacitors with the bottom, rigid, individually addressable plates. There's a large amount of
mechanical and electrostatic coupling between neighboring plates. We are using these devices for a "proof of
concept" of two new ideas that address the above two questions:
For details, see the Micro-cantilevers section of the publications page.
- Use feedback from displacement measurements of each cantilever to electronically compensate
for mechanical and electrostatic coupling. This means building an array of coupled feedback
controllers to achieve desired properties such as decoupling or perhaps other desired "global
behavior". This has the effect of simplifying the mechanical design of the MEMS device, with
the additional complexity in designing the feedback controllers.
- To estimate each cantilever displacement, we use the current through each capacitor as an
output (the input is the command voltage), and build a dynamical observer to estimate
displacement. In some sense, the common scheme of measuring capacitence using a parasitic
high frequency signal is a special case of this observer based scheme. We have been able to
demonstrate the ability to esitmate displacement without the use of parasitic high frequency
This project has been mostly the work of
and was done in collaboration with Professor
and funded in part by the National Science Foundation.
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