A high-speed mass flow sensor with heated silicon carbide bridges

A novel type of micromachined thermal mass flow sensor has been developed which is characterised by enhanced mechanical and thermal stability. For its realisation β-SiC films were heteroepitaxially deposited onto pre-processed silicon wafers. After structuring the surface β-SiC films to form heater and temperature sensing elements, porous silicon was formed in predetermined parts of the silicon substrate to form flow channels. The so formed devices are able to detect bidirectional flows of air with a temporal resolution of 2-3 msec. Due to the excellent mechanical and thermal stability of the β-SiC heater and temperature sensing elements, the devices are able to sustain extremely harsh environmental and operating conditions: firstly, flows of pressurised air could be sustained without inflicting mechanical damage to the micromachined β-SiC bridges, secondly, several hours of thermal cleaning at white glow in ambient air could be endured before breakages due to thermal oxidation occurred