Optimization of Hot-Wire Airflow Sensors on an Out-of-Plane Glass Bubble for 2-D Detection

This paper presents design, analysis, fabrication, and measurement of airflow sensors with three hot-wire resistors on an out-of-plane glass bubble. The fabrication process is based on etching cavities in silicon wafer, followed by anodic bonding of a thin Pyrex glass wafer to the etched silicon wafer. The bonded wafers are then heated inside a furnace at a temperature above the softening point of the glass, and because of the expansion of the trapped gas in the silicon cavities, the glass is blown into three-dimensional (3-D) spherical glass bubbles. Resistors patterned on the glass wafer above the cavities are elevated above the base during the glass bubble blowing process. An optimization analysis on the structure and geometry of the sensor, fabrication process, and properties of multilayer thin-film resistors on glass has been conducted in an attempt to improve the sensitivity.