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°C to 175°C) on the quality-factor (Q-factor) and noise figure (NF) performances of monolithic RF transformers on both normal (750 μm) and thin (20 μm) silicon substrates. The results show that silicon substrate thinning is effective in improving the Q-factor and NF performances of transformers. In addition, Q-factors of both primary and secondary coils decrease with increasing temperature but show a reverse behavior within a higher frequency range. The noise figure (NF) increases with increasing temperature. The present analysis enables RF engineers to understand more deeply the NF (i.e. power loss) behavior of RF monolithic transformers fabricated on a silicon substrate, and hence is helpful for them in designing less temperature-sensitive low-supply-voltage transformer-feedback low-noise-amplifiers (LNA) and voltage-controlled-oscillators (VCO), and other radio-frequency integrated circuits (RF-ICs) which include transformers.