THz Thin Film Varactor Based on Integrated Ferroelectric HfZrO₂

Abstract

In this paper, we present a broadband microwave characterization of ferroelectric hafnium zirconium oxide (Hf 0.5 Zr 0.5 O 2 ) metal−ferroelectric−metal (MFM) thin film varactor from 1 kHz up to 0.11 THz. The varactor is integrated into the back-end-of-line (BEoL) of 180 nm CMOS technology as a shunting capacitor for the coplanar waveguide (CPW) transmission line. At low frequencies, the varactor shows a slight imprint behavior, with a maximum tunability of 15% after the wake-up. In the radio-and mmWave frequency range, the varactor's maximum tunability decreases slightly from 13% at 30 MHz to 10% at 110 GHz. Ferroelectric varactors were known for their frequency-independent, linear tunability as well as low loss. However, this potential was never fully realized due to limitations in integration. Here, we show that ferroelectric HfO 2 thin films with good back-end-of-line compatibility support very large scale integration. This opens up a broad range of possible applications in the mmWave and THz frequency range such as 6G communications, imaging radar, or THz imaging.

Optimization of ferroelectricity and endurance of hafnium zirconium oxide thin films by controlling element inhomogeneity

“…This phenomenon likely stems from the inhomogeneous distribution of Hf and Zr elements, indicating the crucial role of Hf/Zr elements distribution in the dielectric performance of Hf0.5Zr0.5O2 ferroelectric thin films. In addition, ferroelectric materials are widely utilized in tunable devices due to their dielectric nonlinearity [55][56][57]. To calculate the dielectric tunability (η) in this study, the following equation was employed [56].…”

“…In addition, ferroelectric materials are widely utilized in tunable devices due to their dielectric nonlinearity [55][56][57]. To calculate the dielectric tunability (η) in this study, the following equation was employed [56].…”