Mechanics of conformable electronics achieved through water-assisted transfer

Bio-surfaces are curvilinear and rough. Electronics that can conform to complex three-dimensional (3D) bio-surfaces hold the key to the next generation bio-integrated electronics. Although advances in flexible and stretchable electronics enabled conformable devices on curved surfaces, challenges still exist when integrating electronics to surfaces of large areas and/or with non-zero Gaussian curvatures. On the one hand, existing transfer printing methods induce excessive strain that ruptures or distorts stretchable electronics designed into filamentary serpentines. On the other hand, devices with high-density arrays have no space for serpentine designs, so how to conform non-stretchable electronics to spherical surfaces poses even greater challenges. The objective of this dissertation is to develop water-assisted transfer procedures and suitable structural designs to enable large-area or high-density body-conformable electronics through numerical and analytical mechanics modeling. For large-area electronics with filamentary serpentine design, I propose water-assisted Cartan transfer printing (CTP) to enable strain-free, pattern preserving transfer from a donor substrate to complex bio-surfaces. However, this method does not apply to high-density electronic sheets. Therefore, next, I focus on how to conform non-stretchable electronic sheets to spherical bio-surfaces, motivated by the example of a high-density ultrathin image sensor array (1935 pixels in 3 cm²) as a retinal prosthesis. Initially, a truncated icosahedron design inspired by soccer balls was adopted to minimize buckling after conforming to a spherical dome. A more systematic approach to designing the cuts demands a fundamental understanding of the buckling-controlled conformability of both intact and slit sheets. Hence, I perform the experimental measurement and my collaborator carries out coarse-grained molecular dynamics to quantify water-assisted conformability between a thin circular sheet and a spherical surface. Through consistent experimental and numerical findings, I discover a mechanics-guided scaling law that can capture the shape of buckle delaminations, which can ultimately offer a prediction for conformability. The effect of radial cuts on improving conformability is also quantitatively investigated. Eventually, I am able to offer a guideline that can enhance the conformability of an electronic sheet to a spherical surface from 40% to more than 90%.Engineering Mechanic