High- $Q$ On-Chip $C$ -Band Inductor With a Nanocrystalline MnZn-Ferrite Film Core

The miniaturized on-chip inductor was developed for the C-band (4-8 GHz) and beyond, to meet the requirements of upcoming 5G technology devices. This paper presents the deposition of nanocrystalline manganese-zinc ferrite (Mn_xZn_1-xFe₂O₄; x = 0.5) thin films in a CMOS-compatible way on top of an on-chip inductor structure. A 200 nm-thick film was conformally deposited directly on a foundry-fabricated inductor after removing the top passivation layer by dry etching. The Q-factor is found to be enhanced by 10% at the upper end (8 GHz) of the C-band, while the self-resonance frequency of the inductor is up-shifted to 21 from 16 GHz. The film on a dummy Si (100) substrate exhibits saturation magnetization (4πMS = 160 mT) and coercivity (H_C = 3.5 mT) much lower than for the bulk material. The film was deposited by a rapid (c5 min) and low-temperature (c200 °C) solution-based process under microwave irradiation (2.45 GHz) of 300 W. This is the first report of an on-chip C-band inductor with a manganese-zinc ferrite film core.