High temperature reliability and failure of W-based microhotplates

The CMOS-compatible MHP with tungsten as the heater material shows excellent stability at 300 degrees Celsius, yet its thermal reliability at higher temperatures and failure mechanism have not been reported previously. In this paper, the fluctuation of the tungsten heaters of the MHPs were recorded when the MHPs were heating at temperatures higher than 400 degrees Celsius for 1 hour. For the MHP with Al electrodes for gas sensor application, failure occurs at around 650 degrees Celsius when the Al material begins to melt. Without Al, the W-based MHP worked stably with variation of heater resistance around 0.5% at 700 degrees Celsius before it broke down at 750 degrees Celsius. The microscope observations show that, unlike the electro-stress migration failure of Pt-based MHPs or the resistance drift problem of poly-Si-based MHPs, the W-based MHP breaks down because of the delamination of the membrane.