Design and fabrication of a micro electro mechanical systems-based electrolytic tilt sensor

An electrolytic tilt sensor has been designed and fabricated using micro electro mechanical systems (MEMS) technique. The anisotropic KOH etching is used to form a deep Si cavity where conductive electrolyte solution is filled in. Au/NiCr electrodes are simultaneously deposited and patterned using e-beam evaporator with an aligned shadow mask, which is fabricated by through-wafer via etching on a 400-μm-thick Si wafer. A composite electrolyte of 4.8 μL in the volume is filled in the anisotropically-etched cavity that has a volume of 7.3 μL. The electrolyte solution is comprised of variable amount of KCl and a mixture of deionized (DI) water, ethanol and methanol (50, 25, and 25 vol %, respectively). When the electrolyte is injected into the cavity, a cover glass is bonded to seal the electrolyte solution. The fabricated electrolytic tilt sensor is excited by an alternating current to prevent electrolysis in the electrolyte-filled cavity and measured by Wheatstone bridge setup that reads the variation of resistance with respect to an incoming inclination. The measured output characteristic of the MEMS-based electrolytic tilt sensor is as good as that of a conventional electrolytic tilt sensor. Moreover, MEMS-based sensor prevails in its small size, low cost and possible mass production.