Fabrication of polymer SAW sensor array to classify chemical warfare agents

An array with five SAW sensors using different kinds of polymers was fabricated to detect chemical agents and their gas response characteristics were extensively investigated. The SAW devices with different interdigital transducer (IDT) electrode line widths of 3, 4, 6, 8 and 20 μm, which corresponded to the central frequencies of 264, 198, 132, 99 and 39.6 MHz, respectively, were designed. The IDT electrodes consisted of 100 finger pairs of 200 nm thick aluminum films. The polymers used as the sensing materials were polyisobutylene (PIB), polyepichlorohydrin (PECH), polydimethylsiloxane (PDMS), polybutadiene (PBD) and polyisoprene (PIP). The thin films were coated on a quartz substrate by spin coating technique. Four simulant gases of chemical warfare agents of dimethylmethylphosphonate (DMMP), acetonitrile (CH₃CN), dichloromethane (CH₂Cl₂) and dichloropentane (DCP) were used as target gases, instead of the real nerve, blood, choking and vesicant agents. After spin coating of PIB and PECH, the substrate was heated at 65 °C in N₂ ambient for 1 h to remove the cyclohexane and ethylacetate, which were used as solvents. PDMS films were heated at 75 °C in a N₂ flow for 2 h to remove the ethylacetate used as a solvent. And PBD and PIP were heated at 60 °C in a N₂ flow for 1 h to remove the benzene used as a solvent. The sensing characteristics of the SAW sensors were measured by using E-5061A network analyzer. The polymer SAW sensor array showed good selectivity to simulant gases. Principal component analysis (PCA) was adapted to classify the chemical warfare agents.