Long-term Adhesion Studies of Polyimide to Inorganic and Metallic Layers

Abstract

ABSTRACTDelamination between thin-film metal and substrate is a major cause of failure in polyimide based neural microelectrode arrays. Chemical adhesion is the only way to establish a long-term bond that will allow two materials to stick to each other even in a wet environment, given that the materials do not deteriorate in the presence of water. This study assesses, by means of peel and shear tests, a long-term quantitative and comparative study of the adhesion of polyimide to various metallic and other inorganic layers of interest. Polyimide (BPDA-PPD) was cured on the layers, which involve platinum, gold and tungsten-titanium as commonly used implant metals and diamond-like carbon (DLC), silicon carbide (SiC), silicon dioxide (SiO2) and silicone nitride (SiN) as potential adhesion promoters to be used later as intermediate layers between metal and polyimide. The adhesion was observed over one year under accelerated-aging conditions by storing the specimens in 60°C saline (corresponding to 40000 hrs at 37°C). Only silicon carbide and amorphous carbon showed almost unaffected adhesion to polyimide over the testing period. No water intrusion at the interface was observed and the strong bond is almost fully maintained.