Expoxy cure monitoring with an interdigitated gate electrode field effect transistor (IGEFET)

摘要

An interdigitated gate electrode field-effect transistor (IGEFET) was designed, fabricated and used to monitor the cure of a common epoxy. The IGEFET sensor consists of an interdigitated gate electrode structure which is coupled to the gate contact of a conventional metal-oxide-semi-conductor field-efffect transistor (MOSFET). The epoxy was deposited on the interdigitated gate electrode, and the IGEFET's electrical performance was observed as the epoxy cured. The cross-linking chemical reaction during epoxy cure caused electrical impedance changes that were quantified when the IGEFET was operated with a periodic voltage pulse signal. Charge transferred through the chemically-active epoxy is manifested as a temporally-dependent potential applied to the MOSFET's gate contact. By operating the MOSFET as a linear amplifier, a potential corresponding to the temporally-dependent gate voltage was directly measured at the amplifier's 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 reproducible baseline spectrum, and an ensemble of difference spectra were computed to reveal the epoxy's chemical state at specific instances of time. The difference spectra features yield valuable information concerning the state of the epoxy's cure.