Silica aerogel thick film, an alternative to micromachined air gap for thermal insulation

A uniform, smooth and crack-free multilayer silica aerogel film as thick as 5 μm is successfully coated on top of a silicon wafer. The multilayer spin-coated aerogel film was made possible by using the present authors´ recently developed novel state-of-the-art aerogel processing technique. The utilisation of the thick aerogel film for the thermal insulation of a microhotplate (μHP) is studied. The super heat insulator aerogel can replace the micromachined air cavity conventionally created under μHPs for the fabrication of metal oxide gas sensors. The thermal insulation capability of the unique aerogel film was investigated by measuring the temperature of the nichrome heaters built on the aerogel coated silicon wafers at different applied powers. The temperature coefficient of the resistivity of the heaters was measured by monitoring the change in the resistance of the heaters at different temperatures. Simulations were also performed using COMSOL multiphysics software for verification of the experimental results, showing good agreement.