Test structures for developing packaging for implantable sensors

With their capacity for real time monitoring and spatial mapping, implantable sensors are becoming an increasingly important aspect of next generation precision healthcare. Microfabricated sensor systems are a popular choice, owing to their capacity for miniaturisation, repeatable mass manufacture, and numerous pre-existing sensor archetypes. Despite the drive for development, packaging these sensors for the environment within the body, as well as the implantation process itself, presents a significant challenge. This paper presents microelectronic test structures, which can be used to assess, compare, and optimise implantable packaging solutions in a standardised manner. The proposed structures are used to investigate: (i) the capacity of the material to be patterned, (ii) the permeability of the insulation material, (iii) adhesion of the encapsulant to the die, and (iv) the physical robustness of the package to implantation through a needle. They are used to characterise an example packaging strategy, using biocompatible epoxy-resin. In addition, a method of optimising the packaging performance using the test structures is presented.