An implantable micro-miniature device is disclosed. The device comprises a thin hermetic insulating coating and at least one thin polymer or metal secondary coating over the hermetic insulating layer in order to protect the insulating layer from the erosive action of body fluids or the like. In one embodiment the insulating layer is ion beam assisted deposited (IBAD) alumina and the secondary coating is a parylene polymer. The device may be a small electronic device such as a silicon integrated circuit chip. The thickness of the insulating layer may be ten microns or less and the thickness of the secondary layer may be between about 0.1 and about 15 microns.