Temperature dependence of Q in spiral inductors fabricated in a silicon-germanium/BiCMOS technology

The behavior of on-chip planar inductors fabricated over a conductive silicon substrate has been characterized over the temperature range from -55°C to 125°C for the first time. Q was observed to decrease with increasing temperature over the frequency range up to and including the frequency where Q peaks. Inductance was seen to vary little across the temperature and frequency range up to one-half the self-resonant frequency. The behavior of Q with temperature was explained in the context of the temperature coefficients of its resistive parasitics. An energy-based definition for Q that takes into account the distributed nature of the planar inductor was presented and shown to give higher numbers than the conventional impedance-based definition at frequencies above one-tenth of the self-resonant frequency