Integrated circuit microsensor for selectively detecting nitrogen dioxide and diisopropyl methylphosphonate

Abstract

A novel gas-sensitive microsensor, known as the interdiginatated gate electrode field effect transistor (IGEFET), was realized by selectively decositing a chemically-active, electron-beam evaporated copper phthalocyanine (CuPc) thin film onto an integrated circuit (IC). When isothermally operated at 150 °C, the microsensor can selectively and reversibly detect parts-per-billion concentration levels of nitrogen dioxide (NO 2) and diisopropyl methylphosphonate (DIMP). The selectivity feature of the microsensor was established by operating it with a 5 V peak amplitude, 2 μs 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 NO 2 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 α- and β-phases of the sublimed CuPc thin films and to study the NO 2- and DIMP-CuPc interactions.