CMOS-integrated sige MEMS: Application to micro-mirrors

SiGe is a very interesting material for integrating MEMS and CMOS in a MEMS-last approach. SiGe layers are, due to their similar crystal structure, very comparable to Si layers: inherently very reliable, high elastic constants and high intrinsic quality factors and they can be processed using similar state-of-the-art tools. All these desired properties can be reached at a deposition temperature which is low enough to allow for post-processing the MEMS layers on top of the IC. As an application example, micro-crystalline SiGe has been used as structural layer for fabricating 10cm² 11 MPixel CMOS-integrated micromirror arrays. The array consists of 8 mum times 8 mum pixels which can be individually addressed by an analog voltage to enable accurate tilt angle modulation. A stable average cupping below 7 nm, an RMS roughness below 1 nm and a long lifetime (>10¹² cycles) are demonstrated.