Impact of bulk conduction phenomena on the temporal stability of piezoelectric behavior of engineered PDMS ferroelectrets

Engineered ferroelectrets show great promise as high-performance piezoelectric materials; however, there is a limited range of materials compatible with microfabrication techniques and that possess suitable electrical properties. While polydimethylsiloxane (PDMS) has broad compatibility with microfabrication techniques, it compromises in electret potential and reported that PDMS ferroelectrets have inconsistent long term piezoelectric performance. Therefore, understanding the phenomena responsible for the loss of piezoelectric behavior is necessary to improve the temporal stability of engineered PDMS ferroelectrets. Engineered PDMS ferroelectrets were prepared by poling structured cellular films fabricated using 3D printed molds. The electric hysteresis of the PDMS ferroelectrets indicated that they were successfully polarized by dielectric barrier discharges (DBDs); however, quasi-static d33 measurements revealed that their piezoelectric behavior decayed rapidly indicating that the internal surface charges deposited by DBDs were unstable. The charge decay mechanism in PDMS ferroelectrets was investigated by direct resistivity measurements of PDMS films and isothermal surface charge decay (ISCD) experiments of PDMS films charged via corona and impulse charging techniques. ISCD experiments suggest that surface charge decay occurs predominantly due to bulk conduction phenomena. The PDMS films exhibited apparent bulk conduction behavior consistent with space-charge limited conduction. Therefore, it is hypothesized that the loss of piezoelectric behavior of PDMS ferroelectrets is due to charge injection from the electrodes. These results demonstrate that understanding bulk conduction phenomena at the electric fields encountered during poling is crucial to expanding the range of materials that can be used as engineered ferroelectrets.