Heterogeneous 3D integration of hidden hinge micromirror arrays consisting of two layers of monocrystalline silicon

We present a complementary metal-oxide-semiconductor (CMOS) compatible heterogeneous 3D integration process that allows the integration of two monocrystalline silicon layers on top of CMOS control electronics. With this process we demonstrate the fabrication of hidden hinge micromirror arrays from monocrystalline silicon for adaptive optics applications. The piston-type micromirror arrays have the flexures underneath the mirror plates on separate silicon layers. Arrays of 48 × 48 mirror elements with an air-gap between mirror and address electrode of 10 µm were fabricated. The mirrors were found to be drift free and showed no imprinting. A maximum electrostatic mirror displacement of 3 µm is demonstrated.