Organic Field-Effect Transistors and Unipolar Logic Gates on Charged Electrets from Spin-On Organosilsesquioxane Resins

Controllable shifting of threshold voltage and modulation of current in organic field-effect transistors (OFETs) is demonstrated, resulting in the formation of unipolar inverters by making use of space-charge electrets. Prior to the deposition of the organic semiconductor (OSC), negative corona charges are injected and trapped in the bulk of the organosilsesquioxane glass resin gate dielectrics. The effective surface potential is controlled by the corona-charging and subsequent annealing process. It is found that the shift of the transfer characteristics is governed by the electrostatic induction effects of the charged gate electrets, and this observed shift can be related to the surface potential of the layer next to the transistor channel. The process control, efficiency, and long-term stability of charge storage in spin-on organosilsesquioxane glass resins are sufficient to enable the construction of simple unipolar inverters and to allow for circuit tuning. New OFET unipolar inverters with an enhancement-mode driver and a depletion-mode load are presented, composed of only two simple OFETs with the same channel dimensions and the same p-type OSC on charged electrets. This design allows the implementation of full-swing organic logic circuits and illustrates a potential process simplification for organic electronics.