An interdigitated gate electrode field effect transistor (IGEFET) for epoxy cure monitoring

An interdigitated gate electrode field effect transistor (IGEFET) has been fabricated and utilized to monitor the cure of a common epoxy. The IGEFET sensor consists of an interdigitated gate electrode structure coupled to the gate of a conventional MOSFET. The epoxy was deposited on the interdigitated gate electrode, and the IGEFET´s electrical performance was observed as the epoxy cured. The cross-linked chemical reaction during epoxy cure caused impedance perturbations that were quantified when the IGEFET was excited with a voltage pulse. Charge transferred through the chemically active epoxy is manifested as a time-dependent potential applied to the MOSFET gate contact. By operating the MOSFET as a linear amplifier, a potential corresponding to the time-dependent gate voltage was directly measured at the amplifier output. The Fourier transform of the IGEFET´s time-domain response at specific time increments was computed. The resulting epoxy cure spectra were compared to a common baseline formed by computing the difference spectra involving the IGEFET´s pulse excitation signal and the signal corresponding to the epoxy´s chemical state at a specific instant of time