Out-of-plane high-Q inductors on low-resistance silicon

Integrated high-Q coils are much sought after because they enable high-quality radio-frequency circuits that do not rely on off-chip discretes. We present a novel surface micro-machined inductor with its coil axis parallel to the substrate plane. Coils fabricated on standard unaltered low-resistance silicon exhibit record-high-quality factors (Q) of over 70 at 1 GHz. The devices are made by three-dimensional (3-D) self-assembly of stress-engineered structures fabricated with standard semiconductor batch processing techniques. We also designed, fabricated, and characterized silicon Bi-CMOS L-C oscillators built around these coils. Compared side by side against state-of-the-art planar spirals, they produce a 12.3 dB lower phase noise at 100 kHz offset, and 14.6 dB after normalizing to frequency and power.