De-Tethering of Metallic and Polymeric MEMS/NEMS Parts for the Direct Pick-and-Place Assembly of 3D Microsystem

We report our study on several de-tethering methods for various metallic and polymeric MEMS and NEMS parts including thick (30~100μm) metallic (nickel and its alloys) MEMS parts, sub-micron (350 nm) feature size 1 μm thick metallic NEMS parts, and thick polymer/metal bi-layer (polymer ~50μm, metal ~2μm) MEMS parts. The conventional stress-based de-tethering used in silicon would not be effective for all of these three types of devices. High current injection through narrow tethers was found to be effective and reproducible means of de-tethering thick metallic MEMS parts. But such a method could not be applied for metallic NEMS and polymer/metal bi-layer MEMS parts, as large areas near tethers were burned even with significantly reduced amount of currents. In order to de-tether these NEMS and polymer/metal bi-layer devices, we performed the milling of tethers using a focused ion beam. Very low current (20 pA) ion beam was found to be very effective means of de-tethering the metallic NEMS parts. Relatively larger current (0.3 nA) was found to be good for the polymer/metal bi-layer parts. We demonstrated 3D assembly and/or complete packaging of some of the de-tethered MEMS parts.