Shape engineering of the fillers in stretchable, electrically conductive adhesives: Its effect on percolation and conductivity change during stretching

Abstract

The effects of different shapes of silver; particles, flakes and dendrites on the electrical property of polydimethyl siloxane (PDMS)-based electrically conductive adhesives (ECA) under mechanical deformation are investigated. It is found that the high aspect ratio of silver dendrites helps to construct more conduction pathways in the ECAs compared with silver particles and flakes, therefore reducing the percolation threshold. Stretching made the bulk resistivity of spherical silver filled ECA increase exponentially, which is in good agreement with the classical piezoresistive models. On contrast, the resistivity of silver flakes filled ECAs did not change within 100% strain and up to 500 cycles of stretching/releasing tests. For silver dendrites, the resistivity decreased when stretching and increased slightly afterwards, resulting in an almost invariant value within 60% elongation. However, removing the external strain did not havethe resistance value recover back to the original level. IntroductionModern consumer electronics are striving for increased functionality and reduced form factor. Stretchable radiofrequency (RF) electronics are gaining popularity as a result of their increased functionality, impossible within the confines of rigid, planar substrates. However, the field of stretchable RF electronics is still in its infancy. Similarly to other emerging electronic technologies, new materials and new processing methods are the two driving forces for the development of stretchable RF electronics.There are currently two general approaches to the fabrication of stretchable RF electronics. The first one utilizes conventional rigid materials (such as silicon), but elegantly designed wavy or arc-shaped structures are capable of accommodating applied strains of 100% or more [1][2][3][4][5][6][7]. The second approach is to maintain the conventional layout, but embed stretchable or flowable conductive materials into a sheath, including conductive polymers [8,9], conductive polymer composites [10-12] and liquid metal alloys [13,14] as stretchable conduction lines.For RF electronics, the second approach is usually preferred because of the simplicity in circuit design and fabrication. However, this approach imposes stringent requirements for the conductive materials. These requirements include the following: 1) The material must have a very high electrical conductivity to achieve high-efficiency RF devices. 0[9]; 2) The material needs to be highly elastic for tunable resonant frequency [14] and still maintain a similar electrical conductivity. By stretching the antenna, the length is increased, leading to a decrease in resonant frequency. To gain a wide window of tunable resonant frequency, both the

Three-dimensional graphene-based composite for flexible electronic applications

“…To meet the requirements for stretchable electronic components, various materials have been explored to ensure excellent electrical conductivity and mechanical strength, such as single-wall carbon nanotubes (SWCNTs), silver nanoflakes, silver nanowires, eutectic metal alloys and graphene [4][5][6][7]. The SWCNTs and silver nanomaterials with elastomer matrices can deliver high electrical conductivity under mechanical deformations, which are of high cost.…”