복합 재료의 전도 경로 설계와 신축성 전자 소자의 개발

Abstract

Stretchable conductors have been actively investigated for reliable operation of stretchable electronic devices, such as real-time monitoring wearable sensors and deformable circuits. In order to obtain practical stretchable conductors in near future, composite materials comprising metallic fillers and polymer matrix are most proper candidates due to their high conductivity and stretchability. On the basis of percolation theory, they are able to have conductive micro-paths, which are accurate and controllable. Especially, conductive particles (0-dimensional) can be individually arranged by diverse technologies which have been continuously developed such as colloidal (e.g., convection, liquid interface-mediated approaches) and dry rubbing assembly. On the other hands, metal nanowire (1-dimensional) and nanosheets (2-dimensional) still have many difficulties to be arrayed without the agglomerates. The well-programmed particle assembly guarantees constant performance as a reliable stretchable conductor. When electrical networks of the conductive fillers are confined to two dimensions, conduction path variation of the stretched composite materials can be tracked by conductive atomic force microscopy (C-AFM) measurement. Here, novel stretchable electronic system is proposed based on understanding the response of the designed composite materials against physical deformation. On the basis of the information, unique performance of the system is demonstrated: 1) High sensitivity in low strain and pressure; 2) Scalability and Reliability; 3) Anisotropic conductivity with high resolution in micro level. First, functional microparticles are positioned within well structure (line, dots, squares, hexagons and so on) of the rubber template. The diverse geometric patterns of the template can be micro-controlled, providing periodicity of conductive area. High degree of freedom allows the particle assembly to be an ideal model eliminating the complicated and randomized electrical conduction paths in general composite materials (3-dimensional). In this work, a lot of conductive microparticle assemblies in 2D are designed and characterized. A conductive composite with close-packed particle assembly in rubber has continuous electrical networks in-plane direction across the composite, so high strain-sensitivity occurs as soon as it is stretched. Dot pattern of conductive microparticles in the rubber template is inserted between two electrodes and is designed to have only out-of-plane direction conduction path. One Particle per One Pixel structure is adjust to pressure sensors. Since instable point contact between microparticles and electrodes induces high electrical resistance, the pressure-sensitivity gets higher than other pressure sensor structures such as film, pyramid, and dome. Also, the lateral conduction path between the particles is all disconnected in One Particle per One Pixel structure. Thus, the stretchability and anisotropic conductivity are guaranteed by the polymer wall in the structure. Finally, this non-closely packed particle assembly system is used as an anisotropic conductive film (ACF) which physically and electrically interconnects different kinds of conductive circuits. Thermoplastic block-copolymer rubber is proposed as template materials because of their solubility and thermo-softening properties. This microparticle and polymer composites can be a new platform nearest to the practical stretchable electronic system containing sensors and electrodes.