Direct-write vapor sensors on FR4 plastic substrates

Functioning chemiresistor vapor sensing devices on plastic substrates were prepared using low-temperature direct-Xwrite techniques. Interdigitated Ag electrodes were first deposited onto printed circuit boards using a mesoscale maskless materials deposition system (M3D). These Ag lines were 20-50 mu m wide and 8-10 mu m thick with good adhesion to the substrate and electrical conductivity of 4-12 mu Omega.cm. Deposition of chemoselective polymer/C black composite transducer layers on such lines gave sensors that responded to nerve gas stimulant (dimethylmethyl phosphonate) thereby demonstrating the efficacy of direct write for this application. A new approach to localized direct-write deposition, termed Enhanced M3D, allows the formation of sharply defined line edges and enables printing of conductors that operate at radio frequency with low signal loss. The direct-write approaches described here are amenable to future deposition on more interesting substrates and development of more sensitive transducers, orthogonal sensor arrays and an integrated power source/communication platform that might constitute the basis for radio-frequency identification (RFID) sensor tags.