F. Anwar, R.A. Coutu, Jr.
Keywords: MEMS, Burst disks, Membrane, DRIE, SOI, 3D print
Summary:Microelectromechanical Systems (MEMS) membranes are widely used in applications ranging from stiffness tuning to gas pressure sensing. Superior device attributes, such as tunability and high sensitivity of MEMS membranes adapted for water-related applications. In aqueous environments, devices such as pressure sensors, microvalves, micropumps, and membranes can be subjected to immense water pressure that causes them to fail or burst. Once the device bursts, it will stop functioning. However, this event can be used to indicate the precise pressure level at which malfunction may occur. In this research, micromachined membrane burst disks were fabricated, using MEMS processes, to identify water leakage. Moreover, these devices can sense water pressure so that we can predict burst failure beforehand. The burst failure event will be used to detect leakages in household appliances, ranging from automatic sinks to dishwashers. Multiple membranes of the same thickness yet varying surface area were fabricated onto a single Silicon- on- Insulator (SOI) wafer/coupon to detect water leakage. Finite element analysis (FEA) is used to evaluate device designs and they were compared to the experimental data collected from actual devices. Besides, it helped us to investigate the mechanical and electrical responses of the Si membrane and the sensing material. The devices were characterized by applying thermal loads using both DC voltage (applied to the gold strain gauge) and a probe-station thermal heating stage. To observe device robustness, dry N2 flow was applied to the backside of the disks. Also, a micro-pump was used to provide water pressure ranging 0-30 psi to the disk. A 3D printed test fixture with glass bottom was used for these durability tests. While applying pressure, optical profilometer and Wheatstone bridge circuit were used to detect and characterize membrane deflection for different surface area and thickness. To detect water leakage optically, a laser beam is pointed on the membrane and its reflection is observed with the change of applied pressure. Laser beam is fired from the glass bottom of test fixture to pass water level. After hitting the membrane, it reflects back to the detector. Reflected beam will become unnoticeable if burst failure occurs. By calculating the elapsed time, water level within the test fixture can be found which will act as warning before failure.