Flexible Nanowiring of Metal on Nonplanar Substrates by Femtosecond‐Laser‐Induced Electroless Plating

Abstract

In recent years, metal nanowiring for circuitry and electronic interconnection has attracted much attention due to the growing requirements of highly integrated microcircuits, and is of benefit to the miniaturization of device features. [1] Generally, ultraviolet photolithography, which was considered a typical processing route for metal wiring, has already greatly contributed to integrated circuits. [2] However, the lithographic route shows strong demands on the surface flatness of each layer in the multilevel chip architectures. To meet the processing nature of lithography, a global planarization of interlayer metals by chemical-mechanical polishing is therefore needed to reduce the interval between the metal layer and the photomask, and to guarantee exposure resolution when wires reach the sub-300 nm scale. Two-photon absorption (TPA) has also been tried for the fabrication of metal microstructures by using suitable salt solutions as the metal source and photosensitive molecules as the photoinitiator. [3][4][5] However, these studies aimed at refined planar periodic gratings or dot arrays [6] for plasmonic wave coupling or three-dimensional (3D) mold making, which more or less ignore the conductivity of these precise metal structures. For example, by using surfactants as particle-growth inhibitor, delicate 3D structures with a smooth surface were achieved, [7] whereas the conductivity of these metal microstructures was significantly debased due to the residual organic components.To the best of our knowledge, both the photolithography and TPA micro/nanoprocessing conducted so far have focused on fabrication on flat substrates. [8][9][10] These methods cannot meet the increasing demands of circuitry and electronic connections on nonplanar substrates in microelectromechanical systems (MEMS), [1] lab on a chip (LoC), [11] and other intelligent microsystems. Taking LoC as an example, if an appropriate microheater could be embedded on the immediate base inside a microfluidic channel instead of sitting several hundreds of micrometers apart on the rear of the substrate, as is usually done with Peltier thermoelectric elements, [12] integrated resistive heaters, [13][14][15][16][17] and Joule heating of ionic liquids, [18] then local temperature regulation of fluids with higher precision, quicker response, and smarter switching at the exact point of care may be realized due to the effectively reduced thermal inertia. Such a capability is particularly desired for temperature regulation of miniaturized LoC systems that involve repeated thermal cycling, such as DNA amplification by the polymerase chain reaction (PCR), which comprises three sequential steps of denaturation (95 8C), annealing (55 8C), and extension (72 8C). [12] Nevertheless, convenient introduction of a local heating circuit inside a ready channel is almost inaccessible for lithography and other currently available micro/nanofabrication methods. Therefore, there is an urgent need for flexible micro/nanoprocessing technologies for metal nanowiring on nonplan...

Nanomanufacturing—Perspective and applications

“…Refined 3D silver structures have been successfully manufactured with the aid of suitable surfactants that inhibit the growth of metal particles. By controlling the laser power and the concentration of surfactants, minimum feature sizes as large as 180 nm for 3D structures and 120 nm for 2D patterns were obtained [222]. FsLDW has also been used to fabricate microrings, microdisks, and double microring lasers [121,231].…”

Noble Metal Nanomaterials

“…Sub-diffraction-limit fabrications of electrically conductive silver wire with a minimum width of 180 nm can be achieved [485]. Flexible silver nanowires have been fabricated on nonplanar substrates using femtosecond-laser-induced deposition from aqueous silver ion solutions in the presence of a reducing agent [486]. A double winding circuit was successfully produced for microheater uses.…”

Design and full-wave analysis of nonconformal Fermat-like spiral multi-port microantenna sensors

“…As it can be readily noticed, the n−turn spiral arm, having width w l = 500 nm, is printed on a dielectric hemisphere with diameter D s = 40 μm. To this end, the femtosecond-laser-induced silver electroless plating method detailed in [12] can be applied in combination with a suitable two-photon-absorption-induced photopolymerization of the substrate which, in the presented design, is assumed to be silicon with relative permittivity ε r = 11.9.…”