A MEMS-Based Electrolytic Tilt Sensor

A MEMS-based tilt sensor has been realized using electrolytic solution, which is filled in a micromachined 400 mum-deep cavity and responsed relative to tilt angle due to the gravity. The device consists of anisotropically etched deep cavity to contain electrolytic solution and Au/NiCr metal electrodes to detect the electrical signal formed on non-planar surfaces from the substrate surface to the bottom of the cavity. The tilting motion of the device changes the immersed area of the electrodes in the electrolytic solution and the unbalanced ratio of the electrical signal is monitored by the change in its resistance. Potassium hydroxide (KOH) solution is chosen as the electrolyte due to the relatively high ionic conductance and it is diluted with methanol for an optimized concentration considering the viscosity. The fabricated electrolytic tilt sensor is excited by an alternating current to prevent electrolysis in the electrolyte-filled cavity and measured by Wheatstone bridge circuit. Experiments reveal that the resistance of KOH electrolyte is smallest at 5 wt% in its concentration and 800 Hz in the driving frequency. The tested Micro Electro Mechanical Systems (MEMS)-based electrolytic tilt sensor with KOH solution shows a resolution of approximately 50 mV per one degree of inclination angle change and operating angle range of plusmn60deg. The measured output characteristic of the fabricated MEMS-based electrolytic tilt sensor sustains comparison with other conventional electrolytic tilt sensors.