Fabrication and measurement of low-stress membrane mirrors for adaptive optics

We have fabricated low-stress membranes from single-crystal silicon for use as deformable mirrors in adaptive optics. These membranes have lower stress than membranes made from silicon nitride or other materials and therefore are capable of greater deformation than previously used membrane mirrors. Membranes were assembled into devices by flip chip bonding to electrode chips with either 256 or 1024 electrodes. We have characterized devices with static and dynamic tests and compared their performance with an analytical model. We tracked the evolution of strain in the membrane during the device's fabrication and assembly and identified sources of stress and strain in this process. We identified boron dopant concentration as a critical determinant of intrinsic stress in the membrane.