One-step selective laser patterning of copper/graphene flexible electrodes

Copper-Graphene Composite (CGC) Conductors: Synthesis, Microstructure, and Electrical Performance

Improving the electrical performance of copper, the most widely used electrical conductor in the world is of vital importance to the progress of key technologies, including electric vehicles, portable devices, renewable energy, and power grids. Copper-graphene composite (CGC) stands out as the most promising candidate for high-performance electrical conductor applications. This can be attributed to the superior properties of graphene fillers embedded in CGC, including excellent electrical and thermal conductivity, corrosion resistance, and high mechanical strength. This review highlights the recent progress of CGC conductors, including their fabrication processes, electrical performances, mechanisms of copper-graphene interplay, and potential applications.

Flexible Copper-Based Thermistors Fabricated by Laser Direct Writing for Low-Temperature Sensing

With the flexibilization tendency of traditional electronics, developing sensing devices for the low-temperature field is demanding. Here, we fabricated a flexible copper-based thermistor by a laser direct writing process with Cu ion precursors. The copper-based thermistor performs with excellent temperature sensing ability and high stability under different environments. We discussed the effect of laser power on the temperature sensitivity of the copper-based thermistor, explained the sensing mechanism of the as-written copper-based films, and fabricated a temperature sensor array for realizing temperature management in a specific zone. All of the investigations have demonstrated that such copper-based thermistors can be used as candidate devices for low-temperature sensing fields.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Flexible Heater Fabrication Using Amino Acid-Based Ink and Laser-Direct Writing

Nature's systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials used in this study requires low laser power for sintering compared to conventional nanoparticle ink sintering. This suggests applicability in various and sophisticated pattern fabrication applications without incurring substrate damage. An efficient electron transfer mechanism between amino acids (e.g., tryptophan) enables silver patterning on flexible polymer substrates (e.g., PET) by laser-direct writing. The reduction of silver ions to nanoparticles was induced and sintered by simultaneous photo/thermalchemical reactions on substrates. Furthermore, it was possible to fabricate a stable, transparent, and flexible heater that operates under mechanical deformation.

Cu Nanowires Passivated with Hexagonal Boron Nitride: An Ultrastable, Selectively Transparent Conductor

The copper nanowire (Cu NW) network is considered a promising alternative to indium tin oxide as transparent conductors for advanced optoelectronic devices. However, the fast degradation of copper in ambient conditions largely overshadows its practical applications. Here we demonstrate a facile method for epitaxial growth of hexagonal boron nitride (h-BN) of a few atomic layers on interlaced Cu NWs by low-pressure chemical vapor deposition, which exhibit excellent thermal and chemical stability under high temperature (900 °C in vacuum), high humidity (95% RH), and strong base/oxidizer solution (NaOH/H₂O₂). Meanwhile, their optical and electrical performances remain similar to those of the original Cu NWs (e.g., high optical transmittance (∼93%) and high conductivity (60.9 Ω/□)). A smart privacy glass is successfully fabricated based on a Cu@h-BN NW network and liquid crytal, which could rapidly control the visibility from transparent to opaque (0.26 s) and, at the same time, strongly block the mid-infrared light for energy saving by screening radiative heat. This precise engineering of epitaxial Cu@h-BN core-shell nanostructure offers broad applications in high-performance electronic and optoelectronic devices.

Remarkable Effects of an Electrodeposited Copper Skin on the Strength and the Electrical and Thermal Conductivities of Reduced Graphene Oxide-Printed Scaffolds

Architected Cu/reduced graphene oxide (rGO) heterostructures are achieved by electrodepositing copper on filament-printed rGO scaffolds. The Cu coating perfectly contours the printed rGO structure, but isolated Cu particles also permeate inside the filaments. Although the Cu deposition conveys a certain mass augment, the three-dimensional (3D) structures remain reasonably light (bulk density ≅ 0.42 g·cm^-3). The electrical conductivity (σ_e) of the Cu/rGO structure (∼8 × 10⁴ S·m^-1) shows a notable increment compared to σ_e of the rGO structure (∼2 × 10² S·m^-1). The effect on the scaffold robustness is also notable with an increase of the compressive strength by nearly 10 times (from 20 kPa of the rGO scaffold to 150 kPa of the Cu/rGO structure) and cyclability as well. The improved thermal conductivity of the Cu-coated scaffolds (∼4 times higher), in addition to the σ_e and strength improvements, suggests that 3D Cu/rGO structures could be suitable assemblies for integration into thermal dissipation systems, particularly as thermal interface materials, for compact electronic devices.

Micro-Pattern of Graphene Oxide Films Using Metal Bonding

Recently, graphene has been explored in several research areas according to its outstanding combination of mechanical and electrical features. The ability to fabricate micro-patterns of graphene facilitates its integration in emerging technologies such as flexible electronics. This work reports a novel micro-pattern approach of graphene oxide (GO) film on a polymer substrate using metal bonding. It is shown that adding ethanol to the GO aqueous dispersion enhances substantially the uniformity of GO thin film deposition, which is a great asset for mass production. On the other hand, the presence of ethanol in the GO solution hinders the fabrication of patterned GO films using the standard lift-off process. To overcome this, the fabrication process provided in this work takes advantage of the chemical adhesion between the GO or reduced GO (rGO) and metal films. It is proved that the adhesion between the metal layer and GO or rGO is stronger than the adhesion between the latter and the polymer substrate (i.e., cyclic olefin copolymer used in this work). This causes the removal of the GO layer underneath the metal film during the lift-off process, leaving behind the desired GO or rGO micro-patterns. The feasibility and suitability of the proposed pattern technique is confirmed by fabricating the patterned electrodes inside a microfluidic device to manipulate living cells using dielectrophoresis. This work adds great value to micro-pattern GO and rGO thin films and has immense potential to achieve high yield production in emerging applications.

The laser writing of highly conductive and anti-oxidative copper structures in liquid

Flexible conductive structures are essential for the fabrication of commercial integrated electronic devices. Developing efficient processes for manufacturing these structures with high conductivity and stability is significant. Based on a modifiable cost-effective Cu-based ionic liquid precursor, here we present an in situ laser patterning technique to manufacture flexible electrodes. The fabricated Cu structure has excellent conductivity, approximately comparable to bulk Cu, while its oxidation resistance could be further enhanced through introducing an additional carbon source to form a Cu@C microstructure. The chemical and electrical stabilities are evaluated. This method provides a possible bottom-up route for manufacturing microelectronic devices in one step, as we demonstrated through a flexible heater.