Spiral inductors with projected floating shields: An alternative method for RF shielding

Higher values for quality factors (Q) in resonant tank circuits are desirable in RF/microwave applications because of reduced energy consumption and lower heating. This paper introduces spiral inductors with specially shaped shields that are floating capacitive plates, and are shown as a new and compact method to improve the efficiency of LC tank circuits without process modifications. The proposed shielding technique is intended to complement or improve existing Q enhancement methods. This improvement of Q is from electric field shielding, an effect that reduces energy dissipation caused by capacitive coupling to the surroundings. The effectiveness was demonstrated using microstrip spirals that were 3 cm across. The inductors were 70-270 nH and contributed to resonator frequencies ranging from 200-400 MHz. These test structures show 5-15% higher Qs when evaluated at resonance.