Microscopic piezoelectric behavior of clamped and membrane (001) PMN-30PT thin films

TL;DR

This study investigates the microscopic piezoelectric behavior of (001) PMN-PT thin films under different boundary conditions, revealing how substrate clamping suppresses phase transitions and reduces piezoelectric response, with implications for device applications.

Contribution

It provides in-operando synchrotron XRD analysis of domain behavior in clamped and released PMN-PT thin films, highlighting the microscopic mechanisms affecting piezoelectricity.

Findings

Clamped films show inhibited R to T phase transition and lower d33 (<100 pm/V).

Released films recover R to T transition and exhibit higher d33 (>1000 pm/V).

Lateral constraints also inhibit phase transition, affecting piezoelectric response.

Abstract

Bulk single-crystal relaxor-ferroelectrics, like Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), are widely known for their large piezoelectricity. This is attributed to polarization rotation which is facilitated by the presence of various crystal symmetries for compositions near a morphotropic phase boundary (MPB). Relaxor-ferroelectric thin films, which are necessary for low-voltage applications, suffer a reduction in their piezoelectric response due to clamping by the passive substrate. To understand the microscopic behavior of this adverse phenomenon, we employ AC electric field driven in-operando synchrotron x-ray diffraction (XRD) on patterned device structures to investigate the piezoelectric domain behavior under an electric field for both a clamped (001) PMN-PT thin film on Si and a (001) PMN-PT membrane released from its substrate. In the clamped film, the substrate inhibits the field induced rhombohedral (R) to tetragonal (T) phase transition resulting in a reversible R to Monoclinic (M) transition with a reduced longitudinal piezoelectric coefficient d33 < 100 pm/V. Releasing the film from the substrate results in recovery of the R to T transition and results in a d33 > 1000 pm/V. Using diffraction with spatial mapping, we find that lateral constraints imposed by the boundary between active and inactive material also inhibits the R to T transition. Phase-field calculations on both clamped and released PMN-PT thin films simulate our experimental findings. Resolving the suppression of thin film piezoelectric response is critical to their application in piezo-driven technologies.