Organic Field-effect Transistor Channel Perturbation at Two Surfaces through Analyte Binding and Dielectric Charging

Field-effect transistors, including those based on organic semiconductors, are typically gated via an electrical potential applied from a gate contact across a dielectric to the "buried" interface between the dielectric and the semiconductor. We are presently investigating and utilizing additional gate potentials arising from interactions at both the buried and "free" semiconductor interfaces. Charging of the gate dielectric can occur by multiple mechanisms. Experiments that separate bulk and interface effects include the formation of self-assembled monolayers at the interface and measurements of surface potential and capacitance on both the semiconductor-dielectric bilayer and the dielectric itself. Charging can occur at both buried and free interfaces, and can be in electret and ferroelectric polymers. Chemisorption of polar analytes leads to changes in channel current that can be rationalized by an electrostatic model, including dipole fields and binding constants that agrees with results reported from electron spectroscopy. Analyte binding constants >1000 can be projected for suitably functionalized semiconductor films. Order-of-magnitude current changes result from both chemisorption and dielectric charging. Use of these effects for sensing of analytes relevant to national security and for approaches to plastic electronic logic elements are discussed