Search

Various techniques have been developed to fabricate flexible sensors for applications in human-computer interaction and health monitoring. However, the accurate detection of 3D deformation using flexible sensors remains a challenge. In this study, a stretchable strain sensor with a hollow structure was developed for the dual-channel detection of 3D deformation. The sensor was fabricated using a molding technique and a mixture of graphene and Ecoflex and then coated with a layer of thermochromic material. The sensor was applied to detect the volume change of a sphere, and changes in the resistance and color of the sensor from Joule heating were simultaneously observed. The sensor has high detection accuracy and operational reliability and can be applied for the visual detection of 3D deformation.

In this work, we present a simple technique to prevent electromigration damage in printed Ag thin wires. The Ag thin wire can be protected by a silicone rubber layer during current supply. A comparison between protected Ag wires and unprotected Ag wires in the electromigration testing was made. Under same experimental conditions, electromigration induced damage including voids, hillocks and open circuit can be avoided by using the protection layer. It was found that the silicone rubber layer caused a resistance to prevent electromigration damage, the resistance increased with increasing the thickness of protection layer. This technique can provide great potential applications for improving reliability in electronic devices on both rigid and flexible substrate.

Recently, organic thermoelectric (TE) materials have attracted increasing attention in green energy conversion. However, researches on polymer nanostructured TE materials are still scarce, especially for the 1 D nanostructured polymer materials. In this work, 1D poly(3,4-ethylenedioxythiophene) (PEDOT) nanofiber was synthesized by a self-assembled micellar soft-template approach using anionic surfactant sodium dodecyl sulfate (SDS). Then, a flexible and free-standing PEDOT nanofiber film was prepared through a simple vacuum-assisted filtration method. FE-SEM and TEM characteristics real 1D configuration for all the PEDOT nanostructures. Through adjusting the molar ratio of SDS, oxidizing agent FeCl3 and EDOT monomer (nSDS: nFeCl3: nEDOT), nanofiber with different diameter (10–200 nm) and microtopography can be obtained. Electrical conductivity and Seebeck coefficient measurement indicates that the TE properties of PEDOT can be effectively tuned by adjusting its nanostructure, and a variation range as high as three orders of magnitude for the power factors (10-2–101 μW/mK2) can be realized. Due to a more ordered structure caused by the edge-on packing mode of PEDOT chain, the sample prepared with nSDS: nFeCl3: nEDOT = 30:15:7 shows the highest power factor of 7.2 μW/mK2. This value can be further enhanced to 14.4 μW/mK2 by constructing PEDOT nanofiber/SWCNTs composite.

A multilayered metallic structure, consisting of Cu foil and subsequently deposited Ag thin film covered with a passivation layer, was proposed to fabricate Ag micro/nanoparticles by stress migration. With employing a ductile Pt or brittle TiN thin film as passivation, Ag micro/nanoparticles were successfully fabricated by annealing the corresponding multilayered structure. The relationship between characteristics (average diameter, number and volume) of the formed Ag micro/nanoparticles and the annealing temperature was discussed. On this basis, the growth mechanism was developed, which indicates that the dimension of Ag particles was mainly dominated by the different pathways for the migration of diffused Ag atoms in the passivation layers of Pt and TiN and the annealing temperature.

Ag thin wires in the 1–2 µm diameter range with lengths of up to ~680 µm were fabricated in a metallic multilayer sample using stress migration. The sample, which was heated under atmospheric conditions, was a thin Ag film deposited on a Cu foil with an adhesion film of Ti and covered with a TiN passivation film. A compressive stress gradient, formed in the Ag film during the heating treatment, was the driving force for atomic diffusion. A tensile stress was produced in the TiN film, and brittle fracture occurred to cause cracks after the tensile stress exceeded the fracture strength of TiN. The cracks provided pathways for atomic discharge to generate long Ag thin wires. It was noted that a thick TiN passivation film was indispensable for wire formation. The long Ag thin wires may provide great potential applications as component materials in flexible transparent electrodes, integrated circuits and electromagnetic systems.

A comparison between stress migration (SM) and electromigration (EM) in the fabrication of thin Al wires was made. The samples used in each case had the same structure and were manufactured by depositing a thin Al film on a SiO2 layer, a native oxide layer covering the Al film. Al microwires were formed by SM by wide-area atomic migration, meanwhile, nanowires were formed by EM through local accumulation of atoms. It was found that the mechanisms of wire formation were same in both SM and EM tests except the ability of accumulating atoms. Al micro/nanowires with controlled geometry can be fabricated by SM or EM.

The effect of purity on the fabrication of Al micro/thin-materials (MTMs) by utilizing electromigration (EM) has been investigated. The samples that were used to fabricate the Al MTMs were passivated polycrystalline Al lines incorporating a slit and small holes at the anode end of each sample. Al materials of different purity, 99% (2 N) and 99.99% (4 N), were used, and it was found that the atomic flux of the 2 N sample was significantly larger than that of the 4 N sample, leading to the enhanced fabrication of Al MTMs due to EM under the same experimental conditions, which turned out to be related to a decrease in the activation energy for grain boundary diffusion.

The fabrication of electromigration induced micro-belts in passivated aluminum films was investigated. The experimental sample was a passivated polycrystalline Al line with a slit and a rectangular hole at the anode end. The micro-belts could be formed at predetermined positions, with their length dependent on the current stress time, and their widths and thicknesses controlled by the size of the hole. It was found that the growth of the micro-belt is affected by the purity of Al, the current density and the current stress time. The experimental results are explained in the discussion.