An Introduction to mems (Micro-electromechanical Systems)

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an-introduction-to-mems

4.3.2 Thermal Actuators

Thermal actuation in MEMS is usually as a direct result of incorporating tiny heaters, or

resistors. These resistors can be controlled to locally heat specific areas or layers as in the

case of a bilayer actuator. As already detailed, basic thermal actuation utilizes the difference

An Introduction to MEMS

Prime Faraday Technology Watch – January 2002

in thermal coefficients for expansion of two bonded materials and is referred to as thermal

bimorph actuation. A typical thermal bimorph actuator is shown in Figure 33.

Figure 33. Example of a MEMS thermal bimorph actuator [34].

This can be applied to a volume of fluid (liquid or gases) in sealed cavities with a thin

membrane as a wall. By incorporating a heater the liquid can be heated causing it to expand

and deform the membrane outwards. Large forces can be achieved using thermally actuated

devices but power consumption can be high and it can take time for material to cool to its

original activation state.

i) Shape memory alloy actuation

Shape memory alloys (SMAs) exhibit considerable changes in their length (contraction) when

heated. These include titanium/nickel alloys, of which some, once mechanically deformed,

would return to their original undeformed state when heated. Being conductive they can be

heated simply by passing a current through them.

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