Power MEMS: Amazing devices and some interesting mechanics
Professor Mark Spearing
Associate Professor of Aeronautics and Astronautics, MIT, USA
Several programs are underway at MIT to develop the technology of high power density micro-systems.
Devices under development include, a micro-gas turbine engine, a micro-motor-compressor, a micro-rocket,
a micro-hydraulic transducer and various micro-chemical power devices. These devices are designed to
operate at high power densities in order to perform energy conversion tasks for applications such as
providing portable electrical power, small-scale propulsion or local actuation. Power densities are
projected to be in the rage of 10-100 W/cc, which is similar to that of large scale prime movers. The
design and fabrication of such devices offers many challenges and opportunities in the fields of
materials and structures. The major challenges arise from the very high stress levels (~ 1 GPa) required
to achieve the necessary performance and, for devices such as the micro-gas turbine and micro-rocket, the
high temperatures inherent to creating an efficient engine. The task is complicated by the need to
achieve a good structureal design within the constraints imposed by micro-facbrication processes. The
major opportunities arise from the use of silicon and ceramic materials at small lengthscales. In
particular, the use of micro-fabrication techniques offers the potential to control the processing
induced flaw size such that very high strengths can be obtained. In this presentation an overview of the
projects will be given and the role of materials, mechanics and the approach to strcutural desing for
this family of devices will be described. Key materials and mechanics issues will be presented, with
particular emphasis on th eramifications fo the devices' small size. Recent progress in the modelling of
the high temperature response of silicon and the development of mels for wager bonding will be
highlighted.
