Temperature and substrate thickness dependence of Q and NF in broadband spiral inductors for CMOS RF MEMSOC applications

In this paper, we demonstrate a comprehensive analysis of the effects of temperature (-50 ∼ 200°C) and silicon substrate thickness (750 μm, 50 μm, 20 μm, and 0 μm (fully etched away)) on the quality factor (Q-factor) and noise figure (NF) performances of high-Q broadband spiral inductors with 6 μm thick top metal for CMOS radio-frequency micro-electro-mechanical system-on-chip (RF MEMSOC) applications for the first time. We found that Q-factor and power gain (G_A) decreased with increasing temperature but showed a reverse behavior at a higher frequency range. In addition, stability factor (K-factor) and NF increased with increasing temperature but showed a reverse behavior at a higher frequency range. The reverse frequency f_R, corresponding to zero temperature coefficient of Q-factor, increased with increasing substrate impedance or decreasing substrate thickness. Moreover, the f_R´s of Q-factor, G_A, K-factor, and NF were almost the same. In addition, the silicon substrate thinning was effective in reducing the NF of the inductors, loss of the transmission lines, and coupling loss between devices due to the reduction of substrate loss. This means this post process was very promising for high performance RF MEMSOC applications.