Wake up and retention in zinc magnesium oxide ferroelectric films

Zn_0.64Mg_0.36O (ZMO) is a newly discovered ferroelectric oxide with the wurtzite structure. Epitaxial Zn_0.64Mg_0.36O films from 0.036 to 0.5 μm in thickness are grown on Pt/sapphire with the crystallographic c-axis out of plane. At room temperature, the remanent polarization is ∼80 μC/cm² and the coercive field is ∼3 MV/cm. The coercive field is strongly temperature dependent up to 240 °C with a pseudo-activation energy of 23 ± 0.3 meV, suggesting that polarization reversal occurs through an extrinsic process such as domain wall motion. ZMO films can be woken up in 20 electric field cycles on driving near the coercive field; they wake up in a single loop at fields in excess of 4 MV/cm. A thermally activated fluid imprint process, with a pseudo-activation energy of 67 ± 8 meV, enlarges the coercive field by several hundred kV cm⁻¹ after switching the polarization. Additionally, ZMO films exhibit excellent retention characteristics; no reduction in the polarization is observed up to 1000 h from room temperature to 200 °C bakes. This current early generation of ZMO films can survive several thousand switching cycles before dielectric breakdown occurs.