Silicon Membranes for Microbolometers: Simulation and Fabrication Using Frontend Bulk Micromachining

This paper presents a novel, simple, and cost-effective approach for fabricating monolithic silicon membranes through frontend bulk micromachining for microelectromechanical (MEMS) systems. Innovative mask designs with different geometries are proposed for use as pixels in microbolometer applications, aiming to achieve reliable and area-efficient microstructures. The design aligns rectangular openings at a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$45^{\circ}$</tex> angle to the primary flat of the wafer, exposing only the (100) planes for wet anisotropic etching. However, these rectangular openings result in significant silicon consumption, reducing the pixel fill factor. To address this, alternative geometries are introduced to minimize area consumption in undesired directions. Simulations using Intellisuite FABSIM show that wet etching alone (Method I) results in greater silicon consumption, while a combined dry and wet etching technique (Method II) achieves an 86% reduction in footprint. A single-pixel membrane was fabricated as a proof of concept using Method I, with simulation and experimental results showing strong agreement. The resulting robust, monolithic membrane is well-suited for various sensing applications.