a protective , biocompatible coating or encapsulation material protects and insulates a component or device intended to be implanted in living tissue . the coating or encapsulation material comprises a thin layer or layers of alumina , zerconia , or other ceramic , less than 25 microns thick , e . g ., 5 - 10 microns thick . the alumina layer may be applied at relatively low temperature . once applied , the layer provides excellent hermeticity , and prevents electrical leakage . even though very thin , the alumina layer retains excellent insulating characteristics . in one embodiment , an alumina layer less than about 6 microns thick provides an insulative coating that exhibits less than 10 pa of leakage current over an area 75 mils by 25 mils area while soaking in a saline solution at temperatures up to 80 ° c . over a three month period .