Further considerations on the high-cycle fatigue of micron-scale polycrystalline silicon

Bulk silicon is not susceptible to high-cycle fatigue but micron-scale silicon films are. Using polysilicon resonators to determine stress-lifetime fatigue behavior in several environments, oxide layers are found to show up to four-fold thickening after cycling, which is not seen after monotonic loading or after cycling in vacuo. We believe that the mechanism of thin-film silicon fatigue is “reaction-layer fatigue”, involving cyclic stress-induced thickening of the oxide and moisture-assisted cracking within this layer.