Stretch-free, shape-induced 3D Island-Bridge Networks for flexible TFTs on Silicon Planar Technology verified through Bending and Scalability to 9x9 Matrix
This study presents a CMOS-compatible, fully integrated three-dimensional island-bridge concept for flexible electronics on silicon planar technology. By embedding metal bridges within trenches in a polyimide-passivated island matrix, the approach localizes mechanical stress to the bridges whereby active components on the islands are protected from mechanical stress, enabling high-performance thin-film transistors (TFTs) on flexible substrates. A concave, arc-shape forming fill in trenches between the islands and backside etching yield freestanding 3D bridges. Numerical simulations to determine the minimum bending radius reveal a characteristic stress distribution in the bridges during bending, with peak stresses at the bridge-island transitions. Variation of trench depth modulates von Mises stress, identifying design parameters for reliability. Experimental validation demonstrates TFT operation under bending, with stable threshold voltage, subthreshold swing, and saturation mobility across a range of bending radii; broader bridges exhibit enhanced mechanical robustness. A 9x9 island-bridge matrix with addressable integration of TFTs across islands demonstrates the scalability of the concept. Overall, the results verify the manufacturability of stretch-free 3D metal bridges where the three-dimensional shape is defined by the topography of the concave trench filling, with integrated active devices, and confirm the mechanical and electrical functionality of the produced flexible substrates.