Phase Separation in Organic Semiconducting/Ferroelectric Blend Films with Air-Stable Resistive Properties

Abstract

Organic semiconducting/ferroelectric blend films integrate both resistive and rectifying properties and thus well solve the cross-talk problem usually suffered in resistive memories. Till now several kinds of semiconducting/ferroelectric blend systems have been developed with good retention and ON/OFF properties. However, seldom work concerns air stability of their electrical properties. Here we report one kind of blend resistive films with air-stable Poly[(9,9-dioctylfluorenyl-2,7-diyl) -alt-co-(bithiophene)] (F8T2) as semiconducting material and the copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) as ferroelectric material. We introduce AFM based nanoscale electrical measurements into the observation of phase separation in F8T2/P(VDF-TrFE) blend films. Conductive AFM measurements present discrete high-conductivity circular domains embedded in continuous low-conductivity matrix. Surface Potential Microscopy results further indicate that these discrete circular domains show lower surface potential than those from their surrounding matrix, implying the difference in chemical structures. It is reasonable to attribute those continuous surrounding matrix to ferroelectric P(VDF-TrFE) phase and those discrete circular domains to semiconducting F8T2 phase who penetrates the whole film resulting in large electrical conductivity. F8T2/P(VDF-TrFE) resistive blend films present good restive performance with high ON/OFF ratio up to 3.5×103. Such blend films show excellent electrical stability in air even after aging of 200 days.