Thermal actuation based on bimetallic effect is often used in MEMS when large displacement or force output is required. Bimetallic effect created by joining two materials of different thermal expansion coefficients and subjecting it to a temperature variation which results in a net movement of the material. Often the base material is Silicon and a thin film of another material for example Aluminum is deposited on top. Structures like cantilevers are often used as it is easier to utilize the actuation force caused by bimetallic effect.
This design interface can be used to design a cantilever based bimetallic thermal actuator. The tip deflection for a given change in temperature and the resulting force at the tip of the cantilever can be calculated. A negative displacement output means that the film on top has a higher coefficient of thermal expansion that the base material, which would push the cantilever down. The beam is considered as a composite beam and the equivalent bending rigidity is used in the estimation of the force. A negative force means the force is acting down at the tip of the cantilever.
The plot shows the dependence of film thickness on the deflection of the cantilever. The film thickness is expressed as a percentage of the beam thickness. It can be seen that the deflection increases with the film thickness and reaches a maximum at a particular thickness and then it decreases. Using the cross hair tool, the film thickness and the corresponding deflection can be obtained from the graph.