Nanoscale Patterning and Electronics on Flexible Substrate by Direct Nanoimprinting of Metallic Nanoparticles

Abstract

Recent years have witnessed an expanding interest in the application of flexible polymer materials (e.g., polyimide, polyester, etc.) as the substrates for electronic and display devices. These applications include flexible organic light-emitting displays, [1,2] thin film transistors, [3][4][5] sensors, [6,7] and polymer MEMS. [8,9] The advantages of polymer-based materials are their mechanical flexibility, light weight, enhanced durability, and low cost compared with rigid materials (such as silicon and quartz). However, it can be difficult to integrate polymers into an integrated circuit (IC) microfabrication process due to their low thermal stability (low melting and low glass transition temperatures) and solvent susceptibility. In practice, conventional IC fabrication processes are subject to limitations, in that they are multi-step, involve high processing temperatures, caustic baths and strong solvents. In order to address the current problems of microfabrication on flexible substrate, many alternative approaches to conventional photolithography-based process have been introduced by a number of researchers. These include microcontact printing (lCP) combined with metal etching, [10] electroless plating, [11] electropolymerization, [12] and direct metal layer transfer [13] for the microscale metal patterning on flexible substrates. Stencil lithography [14] was mainly applied for dielectric layer patterning on polymer substrates for the formation of electrical capacitors [15,16] due to its limited resolution. Inkjet printing was used for a drop-on-demand patterning of conductive polymer PEDOT [17] and gold [18] layers for drain-source and gate electrodes. However, its best resolution is 20-50 lm [19,20] limited by the nozzle diameter, the statistical variation of the droplet flight, and spreading on the substrate. Organic semiconducting materials are being widely used as semiconducting layers in flexible electronics due to their costeffectiveness, mechanical flexibility, and ease of application via specific chemical modification. However, further channel size down-scaling is essential for better performance of organic field effect transistor due to the lower carrier mobility of the organic semiconducting materials. While the abovementioned methods cannot achieve ultrafine features (a few lm's down to ∼ 100 nm) in high aerial density and good reproducibility, nanoimprinting lithography (NIL) allows easy fabrication of precise nanoscale structures. NIL has been applied for nanopatterning in various fields such as biological nanostructures, [21] nanophotonic devices, [22,23] organic electronics, [24,25] and the patterning of magnetic materials. [26] Especially, metal nanopatterning via nanoimprinting is widely employed in nanoscale electronics and biosensing platforms. However, metal nanoimprinting has been typically an indirect process where a polymer (e.g., PMMA) pattern is first created by nanoimprinting, and then used as a mask for metal film etching or metal lift-off process. [27] This involves multiple and ...

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

“…33 The specific benefits of this process are as follows: it is based on the use of PDMS soft molds that are low-cost, easily replicable, and highly customizable. 28,[34][35][36] Furthermore, they often do not require surfactant pretreatment, as opposed to expensive pretreated rigid molds; the soft, non-sticking, PDMS mold enables conformal contact with the substrates even at very low pressures, 30,36 which makes Here, we report the results of a study of the application of low pressure, soft mold, reverse NIL to make regular arrays of ferroelectric nanopillars of P(VDF-TrFE) on substrates of polyethylene terephthalate (PET) coated with indium-tin-oxide (ITO) electrodes. Our results demonstrate that the P(VDF-TrFE) nanopillar arrays were faithful and uniform replicas of the PDMS mold over large areas of at least 200 mm  200 mm, with no detectable residual layer.…”

“…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.…”

“…33 The specific benefits of this process are as follows: it is based on the use of PDMS soft molds that are low-cost, easily replicable, and highly customizable. 28,[34][35][36] Furthermore, they often do not require surfactant pretreatment, as opposed to expensive pretreated rigid molds; the soft, non-sticking, PDMS mold enables conformal contact with the substrates even at very low pressures, 30,36 which makes it compatible with flexible substrates coated with conductive thin film bottom electrodes; it leaves little or no residual layer, fully isolating the nanopillars to avoid cross-talk and additional etching process that arise with conventional low-contrast nanoimprinting. Here, we report the results of a study of the application of low pressure, soft mold, reverse NIL to make regular arrays of ferroelectric nanopillars of P(VDF-TrFE) on substrates of polyethylene terephthalate (PET) coated with indium-tin-oxide (ITO) electrodes.…”

Direct stamping of silver nanoparticles toward residue-free thick electrode

“…Thus, variants of direct patterning methods have been developed to overcome the limitations. Some important techniques include nanotransfer printing (nTP) [1][2][3]7], direct imprinting [4,5], liquid-bridge transfer stamping (LB-nTM) [8], laser direct curing (LDC) [9] and direct ink writing [6].…”

“…Patterning of conductive media directly on a substrate has attracted much interest to overcome restrictions of indirect patterning techniques [1][2][3][4][5][6][7][8][9]. Patterning of metal on electronic devices is required for creating a conducting pass between active components or electrodes to apply potential and to receive signals [10].…”