Organic vapor sensing and discrimination using enhanced sensitivity thickness shear mode devices

Thin film coatings of poly-isobutylene (PIB) on 96 MHz TSM resonators were utilized as high sensitivity organic vapor sensors. Commercially available AT-quartz TSM devices were milled to 17 µm, leading to a thin quartz membrane surrounded by a 50 µm thick outer ring. The organic vapors studied were benzene, toluene, hexane, cyclohexane, heptane, dichloroethane, dichloromethane, and chloroform at levels ranging from 0.2 to over 13.7 volume percentage in the vapor phase. The Butterworth-VanDyke (BVD) equivalent circuit model was used to model both the perturbed and unperturbed TSM resonators. Monitoring the sensor response through the equivalent circuit model allowed for discriminating between the organic vapors. Detailed results for various sensor parameters such as sensitivity, baseline noise and drift, limit of detection, response and recovery times, dynamic range, and repeatability for the 96 MHz device were compared with those for 10 and 20 MHz devices.