Analysis and application of bending deformation using flexible and soft substrates

Abstract

In recent years, as demand for flexible and wearable products in the electronics and bio industries has increased, products required a higher level of mechanical deformation. The systematic research about the deformation amount and deformation shape of the flexible and soft substrate depending on external factors becomes important to analyze, predict, and control the mechanical deformation. Mechanical deformations include bending, tension, compression, and twisting. Among them, bending deformation is the most typical deformation occurring in a flexible and wearable product. In this thesis, we observed bending deformation caused by environmental factors such as temperature and pH of dissimilar materials and investigate the deformation mechanism through theoretical approach and finite element method (FEM) simulation. A polymer packaging substrate that is thinned to obtain flexibility can be easily deformed due to residual stresses of deposited film and difference of the coefficient of thermal expansion between layers and substrate. During the manufacturing process, the initial room temperature warpage was rotated by the high temperature process. It was verified that the stress relaxation at the polymeric substrate due to the viscoelasticity was the main factor of the warpage orientation change by measuring the material properties and using the FEM simulation. The self-bending phenomenon of bilayed pH sensitive soft hydrogel with the different swelling ratio was verified through experiments and theories and FEM simulation. In order to observe the change of self-bending behavior, external geometric parameters such as thickness ratio and aspect ratio of double layer were controlled. The geometric parameters as well as intrinsic properties, including the elastic modulus and the swelling ratio, determine the final shape of the self-bending deformation of the hydrogel substrate. Soft and flexible substrate such as polymeric packaging substrate and hydrogel was systematically analyzed by measuring material properties and controlling parameters with experiment and FEM simulation.