Packaged MEMS micromirrors for cryogenic environment

We are developing single-crystalline silicon micromirror arrays (MMA) for future generation infrared multiobject spectroscopy (IRMOS). Arrays of 5times5 gold-coated micromirrors were packaged and tested at below 100 K. The gold-coating and the cryogenic compatibility are crucial for the application in an IR MOS. The micromirrors could be actuated before, during and after cryogenic testing. The surface deformation of the uncoated 100 mum times 200 mum micromirrors is below 10 nm peak-to-valley (PTV), 35 nm for single-side gold coated mirrors and 17 nm for double-side gold coating. In cryogenic environment the PTV of the gold coated mirrors increased from 35 nm to 50 nm, thus still remaining in the requirements of < lambda/20 for lambda > 1 mum.