INTEGRATED-CIRCUIT MICROSENSOR FOR SELECTIVELY DETECTING NITROGEN-DIOXIDE AND DIISOPROPYL METHYLPHOSPHONATE

A novel gas-sensitive microsensor, known as the interdigitated gate electrode field effect transistor (IGEFET), was realized by selectively depositing a chemically-active, electron-beam evaporated copper phthalocyanine (CuPc) thin film onto an integrated circuit (IC). When isothermally operated at 150-degrees-C, the microsensor can selectively and reversibly detect parts-per-billion concentration levels of nitrogen dioxide (NO2) and diisopropyl methylpbosphonate (DIMP). The selectivity feature of the microsensor was established by operating it with a 5 V peak amplitude, 2 mus duration, 1000 Hz repetition frequency pulse, and then analyzing its time- and frequency-domain responses. The envelopes associated with the normalized-difference Fourier transform magnitude spectra, and their derivatives, reveal features which unambiguously distinguish the NO2 and DIMP challenge gas responses. Furthermore, the area beneath each response envelope may correspondingly be interpreted as the microsensor's sensitivity for a specific challenge gas concentration. Scanning electron microscopy (SEM) was used to characterize the morphology of the CuPc thin film. Additionally, infrared (IR) spectroscopy was employed to verify the alpha- and beta-phases of the sublimed CuPc thin films and to study the NO2- and DIMP-CuPc interactions.