Low-Voltage Permittivity Control of Coplanar Lines Based on Hafnium Oxide Ferroelectrics Grown on Silicon

This paper is dedicated to the study of the tunable electromagnetic properties of HfO2 doped with Zr (further referred to as HfZrO) grown on high-resistivity silicon using atomic layer deposition (ALD) techniques. Two metallic coplanar lines patterned on HfZrO having different lengths have been used to determine the effective permittivity and wave propagation constant in HfZrO in the frequency range 1-14 GHz, hence covering the L, S, C, X and (part of the) Ku bands. We have observed a significant modulation of the effective permittivity when a bias voltage is applied within the range 0-5 V, with an almost constant increase of 27% in a frequency range of 8 GHz. We have also extracted the attenuation constant, phase constant and loss tangent: the losses due to the thin HfZrO ferroelectric layer increase of maximum 21% at 5 V, which represents the saturation upper limit for ferroelectric's polarization. These results could have a significant impact on effective design of ferroelectric-based microwave circuits with tunable characteristics.