Polysilicon fatigue test-bed monitoring based on the 2nd harmonic of the device current measurement

As the micro technology field expands, the need of simple and standardized methodologies enabling to precisely evaluate device functionality and reliability increases. In particular, under operating conditions, polysilicon devices, e.g. accelerometers, gyroscopes and torsional micromirrors, are stressed by cyclic mechanical loading. Consequently, the characterization of long-term durability of polysilicon components becomes of primary importance to guarantee MEMS reliable functioning during the whole life. In this paper, the experimental set-up of a polysilicon fatigue test bed based on the 2/sup nd/ harmonic of the device current is proposed. The method focuses on the fact that the electrical output signal of electrostatically actuated microdevices is proportional to the driving velocity; thus an indirect system displacement monitoring is achievable and the sample breaking can be registered by electrical measurements. The technique takes advantage of on-chip test design combined with electrostatic actuation and provides with the development of inexpensive and stable test-systems.