Microfabricated ultra-sensitive permeation sensors for real-time monitoring of compliant implantable bioelectronics

We propose and demonstrate a comprehensive method to quantify the ultra-low permeability of thin-film encapsulation coatings engineered for bioelectronic implantable micro-devices. The method relies on the monitoring of the corrosion of magnesium (Mg) thin-film integrated in resistive sensors, on rigid, flexible and stretchable substrates. Corrosion in the Mg film is induced by water diffusion through the coating and is analysed in terms of the evolving electrical resistance; the corrosion rate can next be correlated with the barrier properties, (i.e., the water vapour transmission rate, WVTR) of the encapsulation coating. The ultra-high sensitivity (3.3×10
^-8
g/m
²
/day at room temperature) that is achieved with this method is unmet and particularly suitable for ultrathin ultra-high barrier encapsulations of bioelectronic implants. The sensing method is next demonstrated in flexible and stretchable microsystems where the Mg monitoring sensor is integrated into an optimized and reliable microfabrication process.