BEoL Varactors Based on HfO₂/ZrO₂ Superlattice for mmWave Applications

In this study, we demonstrate for the first time the mmWave performance of a thin-film metal-ferroelectric-metal (MFM) varactor utilizing $\left[\mathrm{HfO}_{2} / \mathrm{ZrO}_{2}\right]_{4}$ superlattice (SL), integrated into the Back-End-of-Line (BEoL) of 180 nm HV SOI technology. At low frequencies, the varactor exhibits tunability of $28.9 \%$ and $24 \%$ before and after wake-up cycling, respectively, using voltage sweeps ranging from -2.4 V to 1 V. During mmWave characterization spanning from 1 GHz to 60 GHz, the device demonstrates consistent tunability of $19.6 \%-18.8 \%$ and $17 \%$ - $15.7 \%$ before and after wake-up, respectively. Moreover, comparison with a standard $\mathrm{Hf}_{0.5} \mathbf{Z r}_{0.5} \mathrm{O}_{2}$ (HZO) varactor, integrated within a similar technology, reveals the superior performance of superlattice-based varactor, highlighting its immense potential for mmWave applications.