Simultaneous Dual-Mode Vital Signal Detection (PPG-Like and ECG) Utilizing a Piezotronic Bipolar Junction Transistor

The The integration of physiological signal detection into compact, multifunctional platforms is critical for advancing next-generation biomedical devices. We present a Piezotronic Bipolar Junction Transistor (PBJT) capable of simultaneous electrocardiogram (ECG) and photoplethysmogram-like (PPG-like) signal detection without external amplification or circuitry. Built from a ZnO/NiO/ZnO npn heterojunction on a flexible PET substrate, the device leverages the piezotronic effect to transduce mechanical signals and uses capacitive coupling through the thin PET layer to detect bioelectrical signals. Positioned on the neck over the jugular and carotid regions, and tested across multiple human subjects, the device captures biopotentials and pressure-induced deformations in real time. Band modulation analysis reveals distinct responses corresponding to ECG and PPG-like signals, while frequency-domain characterization confirms signal fidelity and strong ECG–PPG-like separation. This dual-mode functionality highlights the PBJT’s potential for compact, low-power, and integrated biosensing platforms for wearable health monitoring.