Parylene Capping Layer for Embedded Liquid Mass for MEMS Packaging

Abstract Microelectromechanical Systems (MEMS) packaging is over 80% of the cost of a typical MEMS device because there are no standard packaging methods, and each device requires unique packaging. Recently several MEMS devices have illustrated the desire to have a liquid filled cavity within the MEMS device for applications such as biomedical sensors, tunable energy harvesters, or liquid cooling microelectronics. However, embedded liquids in silicon pose a challenge when it comes to packaging. This paper illustrates a novel concept of using a conformal parylene coating to cap or encapsulate the liquid. The concept is validated using various liquids such as various viscosity silicone oils as well as Galinstan a Ga-based liquid metal. The study investigates the packaging reliability through a series of systematic accelerated life-time testing, elevated temperature testing, accelerated soak testing, and mechanical testing (shock and resonant frequency testing). Mass changes were monitored and compared to control (no capping), glass epoxy bonded packaging, and silicone spray coating encapsulation. The results demonstrate the superior mean-time-to-failure of the parylene capping method compared to the other methods. The results confirm that parylene can be used to package embedded liquids in silicon or 3D printed structures.