Electroless Au Plating of CMOS Microelectrodes: Fabrication, Characterization, and Electrochemical Measurement

An essential step in developing amperometric sensors directly on CMOS integrated circuits (ICs) is to cover the exposed uppermost metal layer (aluminum pads) with a thin layer of noble metal to form the basis of the sensing electrode. A simple and scalable method to achieve the gold layer is through...

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Bibliographic Details
Published in:IEEE sensors letters 2024-06, Vol.8 (6), p.1-4
Main Authors: Li, Minghao, Naeem, Aishath N., Lancashire, Henry T., Vanhoestenberghe, Anne, Ghoreishizadeh, Sara S.
Format: Article
Language:English
Subjects:
Chemical and biological sensors
CMOS
CMOS chip
Deposition
Electrical measurement
Electrochemical analysis
electrode characterization
electroless gold plating
Electroless plating
Electrons
Gold
Gold coatings
Gold plating
Integrated circuits
Iron cyanides
Microelectrodes
Nickel
Noble metals
Oxygen plasma
Plating
Sensors
Surface morphology
Surface roughness
surface topography
Surface treatment
Voltammetry
Zinc
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Summary:An essential step in developing amperometric sensors directly on CMOS integrated circuits (ICs) is to cover the exposed uppermost metal layer (aluminum pads) with a thin layer of noble metal to form the basis of the sensing electrode. A simple and scalable method to achieve the gold layer is through electroless plating. Despite the popularity of electroless plating in, e.g., PCB manufacturing, there is a lack of information on how it can be applied to Al microelectrodes and what the electrochemical performances of Au-coated microelectrodes are. This letter presents a detailed process for electroless gold plating of CMOS microelectrodes, with a step-by-step characterization of the surface roughness, thickness, and elemental composition to optimize the deposition parameters (e.g., deposition time and temperature) for achieving a smooth and uniform gold coverage of the microelectrodes. A gold layer with an rms surface roughness of 53.6 \pm 7.9 nm is achieved on the microelectrodes and successfully characterized by cyclic voltammetry in a ferri/ferrocyanide solution. Sonication, oxygen plasma, and continuous cyclic voltammetry are applied to the Au-coated microelectrodes to determine their mechanical and electrochemical stability.
ISSN:2475-1472
2475-1472
DOI:10.1109/LSENS.2024.3404153