Radio frequency magnetron sputtering of Au and low temperature plasma enhanced chemical vapor deposition of silicon nitride for ring ultramicroelectrodes fabrication

A procedure of fabricating ring ultramicroelectrodes (UMEs) is presented that employs radio frequency (RF) magnetron sputtering and low temperature plasma enhanced chemical vapor deposition (PECVD) technique. Specially, the fabrication of Au ring UMEs is described. The 125 μm diameter optical fibers are concentrically coated by RF magnetron sputtering with Au films of 300 nm thickness and then insulated by low temperature PECVD with silicon nitride films of 0.7 μm thickness. The silicon nitride films are found to be free of microcracks and characterized with excellent adhesion at the interfaces of Au films/silicon nitride films and silicon nitride films/optical fibers by scanning electron microscopy (SEM). In the electrochemical experiments the optical fiber scribe is used to produce tip surface. The electrochemical responses are sigmoidal in shape at different scan rates and indicate that the fabricated Au ring electrodes exhibit electrochemical response of UMEs. The diffusion-limited steady-state currents show that microgaps or microcracks of silicon nitride thin film at the electrode tip may be developed or that the quality of adhesion at the interfaces of silicon nitride thin film/Au thin film and Au thin film/optical fiber may be destroyed in the process of producing the electrode tip surfaces with the carbide fiber scribe, so a polishing fixture should be specifically developed to produce the electrode active surface for the quantitative analyses of ring UMEs with small overall size base on the RF magnetron sputtering and PECVD techniques.