aWith the increasing interest in deploying ferroelectric polymer in flexible electronics and electromechanics, high-throughput and low-cost fabrication of 3D ferroelectric polymer nanostructures on flexible substrates can be a significant basis for future research and applications. Here, we report that large arrays of ferroelectric polymer nanopillars can be prepared directly on soft, flexible substrates by using low-cost polydimethylsiloxane (PDMS) soft-mold reverse nanoimprint lithography at 135 1C and at pressures as low as 3 bar. The nanopillar arrays were highly uniform over large areas of at least 200  200 mm and had good crystallinity with nearly optimum (110) orientation. Furthermore, the method leaves little or no residual polymer layer, fully isolating the nanopillars to avoid cross-talk and, obviating the need for additional etching processes that arises with conventional low-contrast nanoimprinting. The ferroelectric properties of individual nanopillars were probed by piezoresponse force microscopy, which showed that they exhibited switchable and bi-stable polarization. In addition, the polarization hysteresis loops probed by pyroelectric measurements of the entire array showed that the nanopillar capacitor arrays had good ferroelectric switching characteristics, over areas of at least 1 mm  1 mm.
IntroductionFerroelectric polymer nanostructures are of great interest due to their potential use in a wide range of applications, such as organic electronics, 1,2 electro-mechanics, 3,4 nonvolatile memories, [5][6][7][8] and solid-state energy storage, harvesting and conversion. [9][10][11][12] With the increasing application of ferroelectric polymers in the area of flexible electronics, [13][14][15][16] high-throughput and low-cost fabrication of uniform ferroelectric polymer nanostructures with good ferroelectric properties over large areas on flexible substrates will be a significant basis for flexible electronics applications. Previous studies of ferroelectric polymers, like polyvinylidene-co-trifluoroethylene, P(VDF-TrFE), report results from conventional nanoimprint lithography (NIL) with highcost rigid molds at high pressures ranging from 20 bar to 120 bar and 130 to 150 1C to produce ferroelectric nanostructures on hard substrates. 5,7,[17][18][19][20][21] Application of conventional NIL to produce nanostructured films on flexible substrates has a number of drawbacks, such as mechanical and thermal deformation of the substrates, 22,23 poor adhesion, 24 and incompatibility with high temperatures. 25,26 These drawbacks lead to low throughput and poor pattern uniformity in large arrays. 27,28 In addition, the conventional nanoimprint procedure usually requires an additional etching process to remove a residual polymer layer left between the imprinted structures. 29,30 This extra etching process may also be incompatible with flexible substrates due to their poor etching resistance. 31 Previous research on reverse nanoimprinting, where the material is first coated onto rigid mold and then transferred ...