Intrinsic stress-induced self-assembly of multilayer thin films for fabrication of three-dimensional micro devices
Bajwa, Rayan (2018) Intrinsic stress-induced self-assembly of multilayer thin films for fabrication of three-dimensional micro devices. [Thesis]
This work reports on the process technology development for fabrication of three-dimensional (3D), on-chip micro devices based on self-assembly using intrinsic stresses otherwise referred to as residual or internal stresses in thin films. Stress-induced bending in different cantilever designs were modelled at various film thicknesses using finite element analysis (FEA) method and bending conditions were optimized. Intrinsic stress-induced bending mechanism is verified by fabrication of bi-layer metallic micro cantilever structures with varying stress conditions which reach bending angles of up to 137° and possibly more upon release. By modulating the loading mode (tensile or compressive) along the beam length, complex out-of-plane wavy cantilevers with multiple upward and/or downward bends were realized. The fabrication and modelling results display large overlap which further demonstrates the applicability of intrinsic stress-induced bending as a controllable technology towards fabrication of out-of-plane 3D micro components. Additionally, as a potential application to RF-MEMS inductors, stress-induced self-assembly of thin films into single and multiple-turn vertical inductors with ring and spiral geometry was investigated, and performance improvement was verified using coupled multi-physics simulation tools. Structures after transverse bending display higher Q factor and self-resonance frequency (fSR) as compared to inductor configurations in planar geometry with the same turn-density. Simulation results indicate that, performance increase of approximately 100% in both Q factor and resonance frequency can be achieved for ring and spiral inductors.
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