High-Q inductors on locally semi-insulated Si substrate by helium-3 bombardment for RF CMOS integrated circuits

A novel helium-3 ion bombardment technique is proposed for creating locally semi-insulating substrate areas. A helium-3 dose of only 1.5×10¹³cm^-2 increases a Si substrate resistivity from 6Ω-cm to 1.5kΩ-cm, which improves the quality factor of a 2-nH inductor with a 140μm-diameter by 38% (Q=16.3). An aluminum mask is used for covering active areas, and at most 15-μm 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 in the measured phase noise has been achieved.