A Novel Micro Thermal Shear Stress Sensor with a Cavity underneath

This paper describes a micro thermal shear stress sensor with a cavity underneath, based on novel micro bumps on the silicon substrate and sacrificial layer. The micro thermal shear stress sensor has been designed and fabricated by micromachining technology. A poly-silicon strip, 4 mum times 200 mum, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using micro bumps technique on the silicon substrate and sacrificial layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200 mum times 250 mum times 2 mum, is placed between the silicon nitride diaphragm and silicon substrate. Micro bumps formed by silicon isotropic etching in HNA (the system HF, HNO₃ and HC ₂H₃O₂) are arrayed in six lines on the silicon substrate, with distances of 32 mum and 26 mum alternately, which exactly support the silicon nitride diaphragm not to be adhered to the substrate