Iontronic Fringing‐Field Proximity Sensors via Edge‐Rich Stretchable Electrodes for High‐Sensitivity Noncontact Detection

Fringing‐field‐based capacitive proximity sensors offer noncontact detection but are limited by low sensitivity and poor stretchability, restricting their use in wearable systems. Here, we report a hybrid electrode iontronic proximity sensor integrating an iontronic dielectric with mold‐transfer‐printed, edge‐rich stretchable electrodes in a vertical architecture. Embedding ionic liquid ([EMIM][TFSI], IL) into a thermoplastic polyurethane matrix increases the effective permittivity 8.93–32.24 and lowers the elastic modulus, enabling ion‐mediated polarization to amplify the fringing field response while preserving mechanical compliance. Systematic comparison of six top–bottom electrode combinations reveals that an asymmetric line–planar configuration concentrates fringing fields and maximizes capacitance change. Optimizing line width to 100 µm and IL loading to 40 wt% yields a peak capacitance change of 5.12 pF at a separation of 0.01 mm, representing over fivefold enhancement compared to conventional polymer dielectrics while maintaining stable electrode conductance under 50% strain and ≥1 000 cycles. Tensile deformation narrows the line electrodes and thins the dielectric, further amplifying sensitivity (≈99% increase at 50% strain). On‐finger demonstrations enable simultaneous detection of joint‐bending posture and proximity, with material‐selective response of metallic, biological, and dielectric targets. These results establish a general design strategy combining iontronic dielectrics with edge‐dominated stretchable electrode for next‐generation wearable proximity and gesture‐sensing platforms.