High- $Q$ Inductors on Locally Semi-Insulated Si Substrate by Helium-3 Bombardment for RF CMOS Integrated Circuits

A helium-3 ion bombardment technique is proposed to realize high- $Q$ inductors by creating locally semi-insulating substrate areas. A dose of $1.0\times 10^{13}$ cm $^{-2}$ helium-3 increases a Si substrate resistivity from 4 $\Omega \cdot $ cm to above 1 $\text{k}\Omega \cdot $ cm, which improves the quality factor of a 2-nH inductor with a 140- $\mu \text{m}$ diameter by 38% ( $Q=16.3$ ). An aluminum mask is used for covering active areas, and at least 15- $\mu \text{m}$ distance from the mask edge is required to avoid the p-n junction leakage. The proposed technique is applied to an 8-GHz oscillator, and an 8.5 dB improvement of the measured phase noise has been achieved.