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Polysilicon Strain Gauges

Cantilever Beam Strain Gauges

(by Ailbhe McCarthy (BEng.) and Uday Kiran Mannan (MSc.) Project Students, 2003)


Cantilever beams are a commonly used MEMS structure. They consist of long thin free standing beams anchored at one or both ends. Microfabricated cantilever beams have many applications including mechanical sensors and actuators, chemical sensing and sensing, AFM probes, etc. One simple use of cantilever beams is to quantify the level of strain in a thin film. With knowledge of Young? Modulus for the film, stress values can be obtained. Examples of strain gauges fabricated at NISRC are illustrated in Figure 1. These are polysilicon thin films, deposited on a sacrificial oxide. Etching the underlying oxide releases the cantilever beams. At this point, the stress in the film causes the beams to deflect to the right or to the left. The deflection distance is proportional to the stress; stress-free beams should remain in their original position after release.