High-Q inductors and transmission lines on 20 Ω.cm Si using wafer-level packaging technology

High Q on-chip inductors and low loss on-chip interconnects and transmission lines are an important roadblock for the further development of Si-based technologies at RF and microwave frequencies. In this paper, inductors are realised on 20 Omega.cm Si wafers using thin-film Wafer-Level Packaging (WLP) technology: two low K benzo-cyclobutene (BCB, epsilon(r)=2.65) dielectric layers and a thick Cu interconnect layer are deposited on floating Si substrates. Inductors with 5 mum minimum lines and spaces are demonstrated for a 5 mum thick Cu layer, hereby leading to very compact and high performance inductors: maximum Q-factors of 25 have been obtained for inductances in the range of 1 to 5 nH. It is shown how Q-factor and resonance frequency vary as a function of the inductor layout parameters and the thickness of the BCB and Cu layers. The realised 50 Omega CPW lines (lateral dimension of 40 mum) have a measured loss of only 0.2 dB/mm@25 GHz. A good agreement between measured and simulated performance has been obtained.