A flexible floating-gate organic thin-film transistor for detection of chemical species

A novel free-standing flexible OFET able to detect pH changes in chemical solutions thanks to a functionalized floating-gate has been realized and successfully tested. The structure includes a control gate on one side of a Mylar foil (on which gold drain/source contacts are photolithographically patterned and a pentacene active layer deposited) and a gold floating-gate on the opposite side of the foil. The floating-gate is functionalized with thio-aminic groups and represents the active area of the device as such groups protonize proportionally to the concentration of H3O+ ions in the solution. Consequently, the control-capacitor and the charge immobilized on the active area concurrently set the actual gate voltage drop on the transistor insulating layer, thus modulating the drain current. Such a structure does not require a counter-electrode and insulates the OFET from the solution, thus the working mechanism is independent of the choice of semiconductor, gate or dielectric material.