Screen printing of silver nanowires: balancing conductivity with transparency while maintaining flexibility and stretchability

Printing metal nanowires are particularly attractive as compared to conventional coating methods due to the ease of processing,direct patterning,and large-scale fabrication capability.However,it is still challenging to print metal nanowire patterns that simultaneously have high conductivity,high transparency,flexibility,and stretchability.Three steps have been taken in this work to balance the transparency and conductivity of the screen-printed flexible and stretchable silver nanowire films,(1)selection of the ink formulation,(2)optimization of the printing parameters,and(3)posttreatment with a laser.The as-obtained silver nanowire patterns are large-area and demonstrate an ultralow sheet resistance of 1.9 ohm/sq,high transmittance(73%)at the wavelength of 550 nm,and an ultrahigh figure of merit(~136)as compared to the printed silver nanowire electrodes in the literature.The screenprinted transparent patterns exhibit excellent electrical stability and mechanical repeatability when subjected to 1000 bending cycles with a bending radius of 28 mm and 1000 stretch-release cycles with 10%strain,which makes the transparent patterns suitable for the fabrication of flexible,transparent microwave absorbers.The absorption performance of the prepared frequency selective surface absorbers indicates no obvious degradation after various manipulating configurations and multiple bending and stretching cycles.The results are promising enough to make this ink and screen-printing process suitable for many applications of flexible,stretchable,and transparent electronics.

Coat-and-print patterning of silver nanowires for flexible and transparent electronics

Silver nanowires(Ag NWs)possess excellent optoelectronic properties,which have led to many technology-focused applications of transparent and flexible electronics.Many of these applications require patterning of Ag NWs into desired shapes,for which maskbased and printing-based techniques have been developed and widely used.However,there are still several limitations associated to these techniques.These limitations,such as complicated patterning procedures,limited patterning area,and compromised optical transparency,hamper the efficient fabrication of high-performance Ag NW patterns.Here,we propose a coat-and-print approach for effectively patterning Ag NWs.We printed a polymer-based ink on the spin-coated Ag NW films.The ink acts as a protective layer to help remove excess Ag NWs from the substrate and then dissolves itself into an organic solvent.In this way,we can take advantage of both coating-based techniques(lead to Ag NWs with high transparency)and printing-based techniques(efficiently pattern diverse shapes).The resultant Ag NW patterns exhibit comparable conductivity(sheet resistance:7.1 to 30 Ohm/sq)and transparency(transmittance:84 to 95%atλ=550 nm)to those made by conventional coating methods.In addition,the patterned Ag NWs exhibit robust mechanical stability and reliability,surviving extensive bending and peeling tests.Due to higher conductivity,efficient patterning ability and inherent transparency,this material system and application method is highly suitable for transparent and flexible electronics.As a proof of concept,this research demonstrates a wide-band antenna,operating in the mm-wave range that includes the 5G communication band.The proposed antenna exhibits a wide bandwidth of 26 GHz(from 17.9 GHz to 44 GHz),robust return loss under 1000 cyclic bending(bending radius of 3.5 mm),and decent transparency over the entire visible wavelength(86.8%transmittance atλ=550 nm).This work’s promising results indicate that this method can be adapted for roll-to-roll manufacturing to efficiently produce patterned and optically transparent devices.

Fully inkjet-printed microwave passive electronics

Fully inkjet-printed three-dimensional(3D)objects with integrated metal provide exciting possibilities for on-demand fabrication of radio frequency electronics such as inductors,capacitors,and filters.To date,there have been several reports of printed radio frequency components metallized via the use of plating solutions,sputtering,and low-conductivity pastes.These metallization techniques require rather complex fabrication,and do not provide an easily integrated or versatile process.This work utilizes a novel silver ink cured with a low-cost infrared lamp at only 80℃,and achieves a high conductivity of 1×10^(7) S m^(−1).By inkjet printing the infrared-cured silver together with a commercial 3D inkjet ultraviolet-cured acrylic dielectric,a multilayer process is demonstrated.By using a smoothing technique,both the conductive ink and dielectric provide surface roughness values of <500 nm.A radio frequency inductor and capacitor exhibit state-of-the-art quality factors of 8 and 20,respectively,and match well with electromagnetic simulations.These components are implemented in a lumped element radio frequency filter with an impressive insertion loss of 0.8 dB at 1 GHz,proving the utility of the process for sensitive radio frequency applications.

Flexible and reconfigurable radio frequency electronics realized by high-throughput screen printing of vanadium dioxide switches

Smart materials that can change their properties based on an applied stimulus are in high demand due to their suitability for reconfigurable electronics,such as tunable filters or antennas.In particular,materials that undergo a metal–insulator transition(MIT),for example,vanadium dioxide(VO 2)(M),are highly attractive due to their tunable electrical and optical properties at a low transition temperature of 68°C.Although deposition of this material on a limited scale has been demonstrated through vacuum-based fabrication methods,its scalable application for large-area and high-volume processes is still challenging.Screen printing can be a viable option because of its high-throughput fabrication process on flexible substrates.In this work,we synthesize high-purity VO 2(M)microparticles and develop a screen-printable VO 2 ink,enabling the large-area and high-resolution printing of VO 2 switches on various substrates.The electrical properties of screen-printed VO 2 switches at the microscale are thoroughly investigated under both thermal and electrical stimuli,and the switches exhibit a low ON resistance of 1.8 ohms and an ON/OFF ratio of more than 300.The electrical performance of the printed switches does not degrade even after multiple bending cycles and for bending radii as small as 1mm.As a proof of concept,a fully printed and mechanically flexible band-pass filter is demonstrated that utilizes these printed switches as reconfigurable elements.Based on the ON and OFF conditions of the VO 2 switches,the filter can reconfigure its operating frequency from 3.95 to 3.77 GHz without any degradation in performance during bending.