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Processing and low voltage switching of organic ferroelectric phase-separated bistable diodes

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Author: Li, M. · Stingelin, N. · Michels, J.J. · Spijkman, M.-J. · Asadi, K. · Beerends, R. · Biscarini, F. · Blom, P.W.M. · Leeuw, D.M. de
Type:article
Date:2012
Source:Advanced Functional Materials, 13, 22, 2750-2757
Identifier: 462986
Keywords: Electronics · bistable diodes · ferroelectric blends · ferroelectricity · non-volatile memory · self-affine surfaces · spinodal decomposition · Active components · Binary blends · Binary phase diagrams · Bistables · Blend components · Blend composition · Blend films · Blend ratios · De-mixing · Deposition temperatures · Inverted structure · Low voltages · Microstructure evolutions · Non-volatile memories · Poly(vinylidene fluoride-trifluoroethylene) · Processing parameters · Random copolymer · Self-affine · Self-affine surfaces · Small roughness · Systematic variation · Time-resolved · Microstructure · Phase diagrams · Phase separation · Plastic coatings · Polymers · Spinodal decomposition · Thermoanalysis · Ferroelectricity · Industrial Innovation · Mechatronics, Mechanics & Materials · HOL - Holst · TS - Technical Sciences

Abstract

The processing of solution-based binary blends of the ferroelectric random copolymer poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and the semiconducting polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) applied by spin-coating and wire-bar coating is investigated. By systematic variation of blend composition, solvent, and deposition temperature it is shown that much smoother blend films can be obtained than reported thus far. At a low PFO:P(VDF-TrFE) ratio the blend film consists of disk-shaped PFO domains embedded in a P(VDF-TrFE) matrix, while an inverted structure is obtained in case the P(VDF-TrFE) is the minority component. The microstructure of the phase separated blend films is self-affine. From this observation and from the domain size distribution it is concluded that the phase separation occurs via spinodal decomposition, irrespectively of blend ratio. This is explained by the strong incompatibility of the two polymers expressed by the binary phase diagram, as constructed from thermal analysis data. Time resolved numerical simulation of the microstructure evolution during de-mixing qualitatively shows how an elevated deposition temperature has a smoothening effect as a result of the reduction of the repulsion between the blend components. The small roughness allowed the realization of bistable rectifying diodes that switch at low voltages with a yield of 100%. This indicates that memory characteristics can be tailored from the outset while processing parameters can be adjusted according to the phase behavior of the active components. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.