Breakdown effects on MOS varactors and VCOs

The gate oxide breakdown effects of deep sub-micron devices, which degrade the performance of MOS varactors that in turn degrade the performance of LC voltage controlled oscillators (VCOs), are presented. On wafer 0.16 μm CMOS devices are stressed; experimental data are analyzed and used for analytical derivations and simulations to show that the breakdown has twofold effects on the performance of the VCOs. Firstly, the increased conductance of the varactor degrades its quality, which increases the phase noise of the VCOs. This also reduces the amplitude at the output of the oscillator. Secondly, the value of the capacitance of the MOS varactor reduces, which shifts the oscillation frequency of the VCOs.