Embedded-Electrode Boundary Control for Piezo-Suppressed Triboelectric Readout in Poled KNN–PDMS Ferroelectric Composites

Abstract Ferroelectric fillers are often used in triboelectric polymer composites to increase the dielectric response and output. However, in ferroelectric-containing devices, mechanical deformation can also generate piezoelectric signals, which complicates the interpretation of triboelectric output. Here, we use potassium sodium niobate–polydimethylsiloxane (KNN–PDMS) as a model ferroelectric composite and introduce a grounded middle electrode to reduce piezoelectric displacement current coupling in the external readout circuit. The grounded electrode acts as an internal equipotential boundary and attenuates the deformation-induced piezoelectric response to the measurement noise level. Under this piezo-suppressed condition, unpoled KNN–PDMS shows a composition-dependent triboelectric output, with maximum values of 119 V and 1.82 μA at 5.0 vol % KNN. After electrical poling, the output is modulated in opposite directions depending on the dipole orientation. Forward poling increases the output to 156 V and 2.46 μA, whereas backward poling decreases it to 84 V and 1.32 μA under the same measurement conditions. The normalized modulation increases with KNN content, and Kelvin probe force microscopy (KPFM) shows a poling-induced surface-potential shift from 222 to 809 mV. These results suggest that the poled KNN phase provides a directional electrostatic bias that modulates contact-electrification-governed output, while the grounded electrode suppresses piezoelectric artifacts in the measured signal.