fig3
Figure 3. Electrical characterization of crack-based devices. (A) Schematic illustration of the electromechanical characterization platform for simultaneous tensile and electrical measurements of U-shaped notch specimens under uniaxial loading. (Right) Top-view enlarged image of the sample fixation region (top) and cross-sectional schematic of the clamp configuration (bottom). The schematic depicts the polyimide double-sided adhesive layer between the specimen and the clamps, the two-point measurement configuration contacting the Pt electrode pads, and the screw-type clamping that maintains uniform contact pressure across all specimens. The active sensing region is rectangular (200 µm × 1.5 mm), with the U-shaped notch positioned at its geometric center; (B) SEM image of a Cond. 3 device at ~16% strain. The notch structure and crack formation are observed, with multiple cracks on the surface. These stripe-like features are not cracks but buckling-driven delamination morphologies; (C) Electrical response of Cond. 1 and Cond. 2 devices. The resistance increases gradually with applied strain, similar to conventional crack-based resistive sensors. The notched sample showed an earlier mechanical fracture; (D) Electrical response of the Cond. 3 device. A sharp resistance increase (up to ~10 MΩ) occurs at ~8% strain, corresponding to a crack-opening behavior prior to substrate fracture; (E) Cyclic tensile test of the Cond. 3 device, showing a mismatch between the strain at crack opening (εopen) and closing (εclose); (F) Evolution of εopen and εclose, characterized at R/R0 = 10 over 10 cycles. The values fluctuate and do not converge from cycle to cycle; (G) SEM image showing interfacial delamination of the HMDSO and metal films from the polymer substrate. SEM: Scanning electron microscopy; HMDSO: hexamethyldisiloxane.
