ORCID Identifier(s)

0000-0002-1217-9023

Graduation Semester and Year

2016

Language

English

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering

Department

Electrical Engineering

First Advisor

Jung-Chih Chiao

Abstract

pH can be explained in general terms as a numerical scale used to state the acidity or basicity of an aqueous solution. Keeping track of pH is very useful in many applications like medicine, civil engineering, chemical engineering, biology, water purification etc. Most commonly used pH sensors employ glass electrodes but there are some disadvantages associated with these kinds of pH sensors. Glass is a rigid, chemically reactive and fragile material. Also, glass electrodes, owing to the size require significant quantity of solution to test for pH which makes it difficult to use in cases where we have very little quantities of the solution to be tested (say, milliliters). In addition, the sluggish response and requirement for a high input impedance pose a challenge for accurate pH measurements and thereby force us to look for a better alternative. Currently the research in this field points to a flexible micro pH sensor which employs Gold as one of the electrode with an Iridium Oxide (IrOx) sensing film and another Ag/AgCl reference electrode. The potential difference between these two electrodes can be used to calibrate the device and measure the pH of the solution. This method offers solution to many existing problems like flexibility, size of the sensor, fragile nature of the glass electrode etc. In this work, we have demonstrated the ability to use other metals as material of choice to replace Gold as an electrode in the existing flexible micro pH sensor. In addition, the effect of using different adhesion layers for these metal thin films is also tested and the pH sensing ability of all these materials are compared to the Gold electrode-IrOx thin film based pH sensor. We have used a commercial Ag/AgCl electrode as a reference. Nickel (Ni) and Aluminum (Al) in conjuncture with different adhesion layers like Chromium (Cr), Titanium (Ti) and Carbon (C) have been used as the alternative for Gold. Hence, we have significantly reduced the cost of pH sensor by replacing Gold with other metals to fabricate pH sensors which can be used in applications such as soil testing, water purity testing etc., which do not need a Gold electrode based pH sensor. The fabrication process includes metal deposition for electrodes, patterning, sol-gel coating and its thermal oxidation to form IrOx sensing film. This IrOx film has been characterized using scanning electron microscope (SEM) and electron dispersive analysis (EDAX). The sensors’ characterization and performance have been probed into, making note of many parameters like sensitivity, stability, reversibility and repeatability. The results are compared with Gold electrode based pH sensor. These sensors have shown encouraging sensing performance in the pH ranges of 2 to 12 in the case of Al based pH sensors and 4 to 10 in the case of Ni based sensors with a near-Nernstian response at 25o C. The sensors have been tested using standard buffer solutions with foreknown pH values. In conclusion, the flexible IrOx pH sensor mentioned in this thesis can be used for sensing applications where small spaces and curved surfaces pose problems to a traditional glass electrode based sensor. They also gives a significant cost reduction when compared to gold electrode based flexible pH sensor.

Keywords

pH sensor, Flexible, Micro pH sensor, Iridium oxide

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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