Investigation of the Influence of Sublayer Thickness on Pairing of Metallic MEMS Shutter Blades

Abstract

For the 3D self-assembly of microstructures, the net intrinsic stress within a hybrid metal layer stack is utilised to study the dynamics of the pairing of metallic MEMS shutter blades with dimensions of 150 × 400 µm2, representing a highly nonlinear Casimir system. The study focuses on two main geometries: (i) unpaired (freestanding) and (ii) paired metallic Micro-Electro-Mechanical Systems (MEMS) shutter blades. The hybrid metal stack comprises three metal layers that are under intrinsic stress, which enables the curling of the freestanding shutter blades. The top aluminum layer thickness is varied systematically, creating tailored stress in the shutter blades, resulting in the freestanding blades curling differently, as well as geometrical changes in the paired shutter blades. Concerning the thickness variations, a large technological processing window has been identified, during which the pairing of the neighbouring shutter blades occurs (the top aluminum layer thickness ranges between 70 and 88 nm). Circles and ellipses have been fitted to micrographs obtained by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). We observed a trend of the reduction of the radius of curvature RoC (ranging between 17 and 79 µm) for the unpaired shutters, and eccentricity (0.36 < ε < 0.67) occurs throughout the system for the paired shutters. Concerning the specific shape of the overlapping region of the two blades of the paired shutters, three pairing scenarios (I, II, and III) have been identified, classified, evaluated, and reported. The overlapping length lo between the paired shutter blades ranges between 31 and 8 µm. These scenarios also reveal nonlinearities in the pairing process.