Microwave Characterization of HfO₂/ZrO₂ superlattice MFM varactors integrated into BEoL

In this study, we present the low-frequency and mmWave performance of a thin-film metal-ferroelectric-metal (MFM) varactor, utilizing a 10 nm [HfO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/ZrO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>]<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> superlattice (SL) integrated into the Back-End-of-Line (BEoL) of 180 nm HV SOI technology. At low frequencies, the varactor achieves tunabilities of 29.6% and 21.96% before and after wake-up cycling, respectively. In the RF and microwave characterization between 1 GHz and 60 GHz, the device maintains stable tunability in the range of 17.4%–16.5% in its pristine state and 15.3%–14.1% after wake-up. Compared to thin-film varactors based on the standard Hf<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>Zr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (HZO) solid solution, integrated within a similar technology, the SL varactor shows superior performance, evidenced by a 22% increase in remanent polarization and an 11%–19% improvement in tunability across the mmWave range. The quality factor of the device also shows enhancement at higher frequencies. Moreover, the device demonstrates consistent performance in the varactor regime, achieving stable permittivity tuning during bias modulation over 12 cycles.