Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Abstract

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 ...

Multiscale-structuring of polyvinylidene fluoride for energy harvesting: the impact of molecular-, micro- and macro-structure

“…Further details of ferroelectric polymer nanostructures under connement has been described 111 and recently nanostructured arrays of PVDF based polymers have been formed by nanoimprint lithography. 112 2.2.5 Surface charge and nucleation. The nucleation behaviour of a polymer depends on the properties of the nucleating agents, such as surface charge, surface area, lattice matching, concentration and dispersion, as well as the interfacial interactions between the nucleating agents with PVDF chains.…”

Fabrication of diisopropylammonium bromide aligned microcrystals with in-plane uniaxial polarization

“…The ferroelectric polymers, however, have not proven particularly amenable to synthetic modification for optimizing ferroelectric properties in the way the ferroelectric oxides have [28]. Polymers are also limited to polymorphous sample structures, and are therefore limited in terms of performance, due to the difficulty in obtaining long-range crystalline order [29,30]. Molecular ferroelectrics, on the other hand, readily grow into large single crystals and afford greater synthetic flexibility than polymers, while avoiding many of the difficulties presented by oxides.…”

Ferroelectricity and the phase transition in large area evaporated vinylidene fluoride oligomer thin films

“…Organic molecules can be selected, or designed, to suit specific needs, 1 leading to a rapid increase in both their use in fundamental physics and materials investigations, as well as in device applications. The latter includes organic light emitting diode (OLED) displays, [2][3][4] flexible electronics, [5][6][7] and even potential applications using voltage-controlled magnetic anisotropy. [8][9][10] Organic ferroelectric materials effectively combine the customizability afforded by organic synthesis with the useful electro-physical behaviors of ferroelectric materials, applications of which range from piezoelectric transducers 11 to data storage.…”