In situ study of thermal deformation of metal resistive heater on silicon nitride membrane by digital holographic microscopy

Metal resistive heater on dielectric membrane structures are common in MEMS. In this paper, the evolution of the surface topography of this type of structure during operation is studied by in situ digital holographic microscopy with nanometer-scale resolution. Devices of a typical design with platinum resistive heater lying on 200 nm silicon nitride membrane were fabricated by standard MEMS processes. A permanent out-of-plane surface deformation up to 200 nm could be detected when applying heating cycles via real-time in situ images of the device surface profile. Such deformation bears the risk of failure in the thin membrane device.