Chemical vapor sensing with novel coupled-channel field-effect transistors
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Chemical vapor sensing has numerous practical applications. Many small polar organic molecules, from alcohols to explosives, are tested for in ambient atmosphere every day as part of security and air quality monitoring. However, many of these tests require expensive monitoring equipment. This work explores organic and inorganic oxide semiconductors as room-temperature low-cost chemical vapor sensors. Organic semiconductors have well-known chemical vapor sensing capabilities that arise from the grain boundaries and charge transport in their non-crystalline structure. However, organic semiconductors suffer from the bias stress effect in atmosphere and low mobilities. Inorganic oxide semiconductors also display sensitivity to polar vapor molecules and are transparent at visible wavelengths, which makes them of interest to the display industry. Coupling disordered semiconductors with silicon channels can produce the detection range of organic and inorganic oxide semiconductors combined with the stability of electrical characteristics of silicon semiconductor devices. This work discusses three different device geometries designed to allow organic and inorganic oxide semiconductors to influence the current in a complementary silicon semiconductor channel. The four-terminal device is a novel device geometry developed to function in a chemical memory mode that produces a one hundred-fold increase in silicon drain current in response to polar analyte vapor exposure. Thin film transistor (TFT) geometry relies on a silicon substrate to function as a bottom gate and processing platform. The bilayer device geometry also uses a silicon substrate as a bottom gate and processing platform, but then relies on the interaction of an inorganic oxide semiconductor and organic semiconductor in a planar heterojunction to produce a sensing event. The sensing mechanisms and responses for these devices are discussed in this work.