Temperature-dependence of noise figure of monolithic RF transformers on a thin (20 μm) silicon substrate

We demonstrate an analysis of the effect of temperature (from -45/spl deg/C to 175/spl deg/C) on the quality factor (Q-factor) and noise figure (NF) performances of monolithic RF transformers on both normal (700 μm) and thin (20 μm) silicon substrates. The results show a 36% reduction in minimum NF (NF_min) at 5 GHz and a 40.9% increase in maximum Q-factor (Q_max) if the silicon substrate is thinned down from 700 to 20 μm, which means the silicon substrate thinning is effective in improving the Q-factor and NF performances of transformers. The present analysis is helpful for RF engineers to design less temperature-sensitive low-voltage supply transformer-feedback low-noise amplifiers and voltage-controlled-oscillators, and other radio-frequency integrated circuits which include transformers.