Abstract
It has been known for a long time that electrical resistance of a semiconductor is very sensitive to the presence of gas in its volume or at the surface. Measurement of breath NH3 is of interest in clinical applications as it can be used as a measure of liver functions. We have developed a III-V semiconductor conductivity InN sensor to measure NH3 in human breath. As mixture gas passes over the InN sensing layer, the film collects NH3 and the conductivity (measured by the multi-meter) increases accordingly. However, there are around 250 kinds of VOCs in our breath, so the issue of selectivity is very important. In this research, methods for selectivity improvement of semiconductor gas sensors are presented. Our groups define a reaction factor to compare the reaction rate of these VOCs gases and find out the noisy breath gas. In this step, two parameters, gas concentration and the activation energy took into consider. According to the result, acetone and isoprene are the noisy breath gas present in the breath of all individuals and are the major breath hydrocarbon in healthy people. Therefore, we set up a filter system to exclude the acetone by adding non-polar solvent which called polydimethylsiloxane (PDMS). PDMS is silicon oil, which can react with acetone, the result from Societe Generale de Surveillance (SGS) shows 10 c.c. PDMS silicon oil can decrease almost 40% acetone (from 0.778 ppm to 0.474 ppm) in the mixture. In addition, PDMS silicon oil will not react with target gas NH3 and shows a good way to exclude acetone from the mixture.