Abstract
With advancement of MEMS technology, the reliability of a microstructure has become a vital issue before a microdevice is widely accepted. Consequently, it is indispensable to understand the mechanical properties of a microstructure to meet the requirements of longer lifetime and reliable performance. This study investigates the fatigue characteristics of a microcantiliever beam (60-120μm long, 20μm wide, 2μm thick), one of the most common microstructures widely employed in sensors and actuators. Furthermore, a pad (500×500×2 and 560×560×2μm3 ), fabricated at the free end of the beam, is used for larger external electrostatic load generated between the specimen and the electrode with an air gap 525μm. In fatigue test, the specimen actuated by the applied voltage 150 and 200 V in the form of the digital wave at 100 Hz. The deflection of the beam is measured by the laser Doppler vibrometer. According to the experimental and ANSYS results, the displacement of the free end of the beam increases with the beam length, ranging from 61.3 to 597.8 nm; from S-N diagram, the maximum stress is inversely proportional to the corresponding fatigue life. The maximum stress occurs at the fixed end of the specimen between 14.3–32.0 MPa; the fatigue life lies between 6.1×10^6–1.4×10^8 cycles.