Thin-film encapsulation

Thin-film encapsulation is the conformal barrier that keeps water, ions, and biofluid away from the metal and electronics of a soft implant while adding as little thickness and stiffness as possible. Common materials include parylene-C deposited by vapour polymerisation, atomic-layer-deposited oxide nanolaminates (such as alternating aluminium oxide and hafnium or titanium oxide), silicon carbide, and thermally grown silicon dioxide. The relevant figure of merit is the water-vapour transmission rate, which must be extraordinarily low to protect a device for years.

Encapsulation is the dominant chronic failure mode of flexible and stretchable systems. Pinholes, cracks under repeated strain, and delamination at material interfaces let moisture in and cause corrosion and leakage current; strain tolerance and barrier quality are in tension, since the best inorganic barriers are brittle and the most stretchable polymers are permeable. Multilayer organic-inorganic stacks are the usual compromise.