Date of Award
Doctor of Philosophy (PhD)
Stanley A. Napper
The methods for production of recessed oxygen microelectrodes developed by Whalen, et al. (1967) and improved upon by Linsenmeier, et al. (1987) are dated production methods by the standards of sensor production of the current time. The production process for this type of polarographic oxygen sensing electrode has remained unchanged for over 10 years, and is a time consuming, extremely low-yield process. The goal of this project has been to use the techniques of micromanufacturing available at the Institute for Micromanufacturing at Louisiana Tech University to construct a recessed oxygen microelectrode with a batch process that has higher yield than the methods used to make the Whalen/Nair microelectrode, and to prove functionality at least equivalent to the Whalen/Nair electrode.
The thin-film micromanufacturing process takes advantage of batch processing techniques and uses DC vacuum sputter deposition to apply a 0.5 micrometer catalytic platinum layer and RF vacuum sputter deposition to deposit a 2.0 micrometer outer insulation coating of silicon dioxide over a pulled glass core to construct the electrode. It uses a spin-on-glass coating over the silicon dioxide layer to insure complete sealing of the outer insulation coating. Focused ion beam machining is used to machine the tip of the electrode to expose the catalytic sensing surface and give an overall tip diameter of 7–8 micrometers.
These electrodes have been tested for response to oxygen by comparing responses in air-equilibrated 0.1M sodium chloride solutions with responses in 100% nitrogen-equilibrated 0.1M sodium chloride solutions. Electrodes have been tested for stir sensitivity by comparing response in moving and stagnant air-equilibrated 0.1M sodium chloride solutions.
Using the thin-film micromanufacturing process and focused ion beam machining, a process has been developed to produce recessed oxygen microelectrodes with a tip diameter of less than 10 micrometers that have a 3.0% stir sensitivity and a zero oxygen equilibrated 0.1M sodium chloride solution response that is less than 0.5% of an air equilibrated response. The process can produce a batch of electrodes with a 60% yield, which is at least a 50% improvement over the yield reported by Ober, et, al. (1996).
McGuyer, James Clay Jr., "" (1999). Dissertation. 178.