Thermal behavior of freestanding microstructures fabricated by silicon frontside processing using porous silicon as sacrificial layer

Freestanding microstructures are essential elements in thermal and mechanical microsensors. In this paper, microbridges were fabricated by silicon surface micromachining using porous silicon as sacrificial layer. Two different approaches were considered. In first approach, n-Si was used as anodization masking material and n-Si/SiO₂ as microstructure material. In the second approach, silicon nitride and SiO ₂ /Si₃ N₄ bilayer has constituted masking and microstructure materials, respectively. In order to characterize their thermal behavior, platinum heating elements were defined on developed microbridges. Microstructures fabrication process was described, insisting specially on silicon anodization step. The process parameters (HF-electrolyte concentration, current density, and process duration) were established for both approaches. Thermal behavior of developed microbridges was studied in relation to anodization masking materials and freestanding microstructure materials. Microbridge temperature versus applied power to heating element was analyzed. Additionally, entire sample thermal behavior and microbridge dynamic thermal behavior was characterized. The obtained results suggest developing a third approach where n-Si will be used as masking material and SiO₂ / Si₃ N₄ bilayer as freestanding microstructure material