High-Frequency Inductors by Co-Design Optimization of Self-Rolled-up Membrane Technology

Self-rolled-up membrane (S-RuM) 3D microtube inductors represent a significant advancement in miniaturization for radio frequency (RF) integrated circuit applications, particularly internet-of-things and 5G/6G communications. These inductors have excellent high-frequency performance due to better confinement of the magnetic field and weak dependence on substrate conductivity. However, previously reported S-RuM inductor frequencies are limited by the crosstalk capacitance between overlapping metal strips between rolled-up turns. This work advances S-RuM inductor design by co-optimizing inductance, frequency, and footprint, leading to significant reductions in crosstalk capacitance and enhancements in maximum operating frequencies. Design intricacies tailored to the unique structure of S-RuM inductors are thoroughly addressed, particularly by mapping the angle of the rolled-up inductor strips with respect to the number of turns. Self-resonance frequencies as high as 40–53 GHz (instrument testing limit) are reported for 2–5 rolled-up turns, demonstrating increases of over 15 GHz from previous S-RuM inductors. These designs, with footprints of 0.02–0.56 mm² and inductances of <1 nH to >5 nH at GHz frequencies, demonstrated the effectiveness of co-designing frequency, footprint, and inductance for RF inductors, openning a new paradigm for miniaturizing high-frequency on-chip passive electronic components.