Parylene-on-oil packaging for implantable pressure sensors

This paper reports the feasibility study of a parylene-on-oil encapsulation packaging method of pressure sensors targeted for long-term implantation. Commercial barometric digital-output pressure sensors are enclosed in silicone oil and then encapsulated in situ with parylene-C or -D (PA-C, PA-D). Experimentally, sensors encapsulated with 30,000cSt silicone oil and 24.92μm PA-D show good performance for 6 weeks in 77°C saline with >99% of original sensitivity, corresponding to a predicted lifetime of around 21 months in 37°C saline according to the Arrhenius equation with an activation energy of -0.6eV [1]. This work shows that, with proper designs, such a packaging method can preserve the original pressure sensor sensitivity without offset, validated throughout accelerated lifetime tests. A model to predict sensitivity retention after packaging is also presented.