Interface engineering enabled high breakdown strength in freestanding PZT thin films

High breakdown strength is crucial for ferroelectric thin films to achieve high energy storage density, field-induced strain as well as improved reliability. Interface engineering by heterostructure design can effectively enhance breakdown strength and dielectric response but often weaken ferroelectric properties, and most of them are confined to rigid substrates, failing to meet the requirements of flexible electronics. Here, we fabricated freestanding PbZr_0.4Ti_0.6O₃ (PZT) multilayer thin films with composition-gradient-induced interfaces by the intrinsic growth kinetics during chemical solution deposition, which could enhance the breakdown strength significantly. Firstly, the breakdown strength of as-grown PZT films strongly depends on the number of interfaces. Their DC breakdown strength increased from 1.1 MV/cm in the 2-layer films to 3.1 MV/cm in the 4-layer films with a fixed thickness of 260 nm. Furthermore, freestanding PZT thin films that were fabricated using a La_0.7Sr_0.3MnO₃ sacrificial layer have DC and AC breakdown strengths of 2.4 MV/cm and 2.9 MV/cm, respectively. Those freestanding films maintained stable ferroelectric properties during bending. Such highly flexible and high-breakdown-strength ferroelectric films show great promise for applications in flexible energy storage and smart actuation.