Microwave applications of zirconium-doped hafnium oxide ferroelectrics: from nanoscale calculations up to experimental results

In this paper, a systematic approach is reported for the electrical properties investigation of an emerging new class of materials for microwave applications, namely zirconium-doped hafnium oxide (HfZrO) ferroelectrics. Starting from atomistic simulations that take into account both structural and spectroscopic data to determine the interatomic potentials, the dielectric constant for the orthorhombic phase of HfZrO ferroelectrics has been extracted. By employing well-established microwave characterization techniques, the tunability of both effective permittivity and loss tangent of HfZrO for a low DC bias voltage of ±5 V has been verified experimentally. Finally, two microwave applications of thin-film (~6-nm-thick) HfZrO-based ferroelectrics have been explored, namely an interdigitated capacitor-like phase shifter and a phased antenna array made of two patch elements working at 2.55 GHz, able to steer its beam of 25° for an applied bias of only ±1 V. These results demonstrate the potential impact that ferroelectric-based microwave circuits with tunable characteristics will have in the future telecommunications systems and, as well, the importance of a rigorous approach for their full chemical, physical and electromagnetic characterization.