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 a new class of materials for microwave applications: zirconium-doped hafnium oxide (HfZrO) ferroelectrics. Starting from atomistic simulations taking into account structural and spectroscopic data, the permittivity of the orthorhombic phase of HfZrO 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 HfZrO-based ferroelectrics have been explored: an interdigitated capacitor-like phase shifter and a two-element phased antenna array working at 2.55 GHz 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 the importance of a rigorous approach for their full chemical, physical and electromagnetic characterization.