Laminar to turbulent flow transition measurements using an array of SOI-CMOS MEMS wall shear stress sensors

The successful utilization of an array of silicon on insulator complementary metal oxide semiconductor (SOICMOS) micro thermal shear stress sensors for flow measurements at macro-scale is demonstrated. The sensors use CMOS aluminum metallization as the sensing material and are embedded in low thermal conductivity silicon oxide membranes. They have been fabricated using a commercial 1 mum SOI-CMOS process and a post-CMOS DRIE back etch. The sensors with two different sizes were evaluated. The small sensors (18.5 times 18.5 mum
²
sensing area on 266 times 266 mum
²
oxide membrane) have an ultra low power (100degC temperature rise at 6 mW) and a small time constant of only 5.46 mus which corresponds to a cut-off frequency of 122 kHz. The large sensors (130 times 130 mum
²
sensing area on 500 times 500 mum
²
membrane) have a time constant of 9.82 mus (cut-off frequency of 67.9 kHz). The sensorspsila performance has proven to be robust under transonic and supersonic flow conditions. Also, they have successfully identified laminar, separated, transitional and turbulent boundary layers in a low speed flow.