Title: Capacitive Carbon Dioxide Gas Sensor
Dr. Oliver Brand, ECE, Chair , Advisor
Dr. Muhannad Bakir, ECE
Dr. Levent Degertekin, ECE
Dr. Omer Inan, ECE
Dr. Peter Hesketh, ME
Dr. William Taylor, Allegro
Abstract: This thesis investigates CO2 sensors based on microfabricated interdigitated capacitors coated with amine-based sensing films in dry and humid environment at different sensor temperature. Finite element modeling was used to optimize the sensor structure and investigate sensor heating with an embedded heater. The optimized sensor structures were fabricated in the cleanroom facilities of Georgia Tech’s Institute for Electronics and Nanotechnology as well as a commercial foundry. After sensing packaging, the sensors were first characterized thermally and electrically to establish heating efficiencies and baseline electrical behavior, respectively. A mixture of 3-aminopropyltrimethoxysilane and propyltrimethoxysilane sensing film was used as initial sensing film and CO2 sensing behavior was investigated as a function of the sensor temperature and sensing film thickness in a dry environment. The chemical measurements demonstrate a good sensor sensitivity to CO2 around 80-90˚C, with good repeatability, linearity, and response time. Amine-functionalized silica nanoparticle films were explored as alternative sensing film in order to increase the CO2 capacity using a functionalized large surface area material. In addition to investigating the sensor response as a function of the sensor temperature, measurements were performed in different relative humidity conditions. Moreover, the quality factor of the capacitive sensor was analyzed as an additional sensor output for CO2 detection. Lastly, room temperature CO2 detection was demonstrated using a heating pulse to periodically refresh the sensing film.