PEtra: A Flexible and Open-Source PE Loop Tracer for Polymer Thin-Film Transducers

Accurate characterization of ferroelectric properties in polymer piezoelectrics is critical for optimizing the performance of flexible and wearable ultrasound (US) transducers, such as screen-printed Poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TrFE)) devices. Standard charge measurement techniques, like the Sawyer-Tower circuit, often fall short when applied to ferroelectric polymers due to low-frequency leakage. In this work we present PEtra, an open-source and versatile polarization-electric field (PE) loop tracer. PEtra employs a transimpedance amplifier (TIA) (LMP7721, TI) to convert picoampere-level currents into well measurable voltages, covering a frequency range of 0.1 Hz to 5 Hz for a gain setting of 107 V/A, and 0.1 Hz to 200 Hz for gain settings between 103V/A to 106V/A (10-fold increments). We demonstrate through simulations and experimental validations that PEtra achieves a sensitivity down to 2 pA, effectively addressing the limitations of traditional charge measurement methods. Compared to the Sawyer-Tower circuit, PEtra directly amplifies currents without the need for a reference capacitor. As a result, it is less susceptible to leakage and can operate at lower frequencies, improving measurement accuracy and reliability. PEtra's design is fully open source, offering researchers and engineers a versatile tool to drive advancements in flexible P(VDF-TrFE) transducer technology.