Out-of-plane microstructures using stress engineering of thin films

A new method is presented to fabricate out-of-plane microstructures using traditional planar micromachining technology. Composite LPCVD polysilicon/silicon nitride beams are fabricated to study this concept. Polysilicon films ranging from 0.5 micrometers to 1.3 micrometers , and silicon nitride films ranging from 150 to 450 nm, were used to fabricate various thickness ratios of composite out-of-plane microstructures. Upon release, these planar structures take on 3D shapes, due to the bending moment caused by inherit internal stresses in the thin films. These stress engineered 3D microstructures (SEMS) open the path to novel microstructures. This paper presents a design theory for SEMS, describes the fabrication process, and discusses the results of initial experiments.