Cyclic deformation and nano-contact adhesion of MEMS nano-bridges by in-situ TEM nanomechanical testing

MEMS nano-bridges fabricated by FIB have been deformed in-situ in the TEM. The polysilicon bridges show high levels of flexibility but also, at increased indentation depths, residual plastic deformation after fully unloading the bridges. Here, a significant number of cycles were applied to the centre of a bridge by a W-probe. This resulted in the formation of an adhesive contact with the W-probe. On unloading the nano-bridge regained its original shape and then deformed upwards, adhered to the W-probe. A significant high tensile force of -17μN was required to sever the nano-contact. Analysis of the W-probe and polysilicon nano-bridge indicate that carbon migration along the W-probe and local contact heating due to the associated fatigue cycles were responsible for the adhesive bond, with initial carbon contamination layer on the W-probe of 2nm, thickening during the loading cycles to 25nm.