Passivation and corrosion of microelectrode arrays

Application of silicon based microsensors in electrolyte solutions is hampe red by insufficient barrier properties and poor corrosion resistance of com mon passivation layers used to protect the underlying conducting tracks and microelectronic structures. Therefore, the protectivity of various types o f compatible passivation layers (organic polyimide and photoresist films, i norganic mono, duplex and tripler layers based on PECVD silicon oxide and s ilicon nitride) was investigated and improved on microelectrode arrays expo sed to 1 M NaCl (pH 2 to 10) at 25 degrees C. Duplex SiO2/Si3N4 and oxide/n itride/oxide (ONO) triplex layers with optimised nitride PECVD process yiel ded the best barrier properties. Burying the conducting tracks in the therm al silicon oxide layer improves the performance significantly Failures of t he passivation layers, detected by leak current and layer resistance measur ements with subsequent SEM investigation, result from cracking due to intri nsic and extrinsic (less important) mechanical stress, film defects (pinhol es, particle inclusions), from chemical, physicochemical and electrochemica l reactions (external, internal, sublayer corrosion) and from the combined action of mechanical stress and chemical interaction (stress corrosion crac king). (C) 1999 Elsevier Science Ltd. All rights reserved.