A Study of Power Supply Stability in Ring Oscillator Structures

The stability of the supply rails while testing wafer-level ring oscillator structures has been studied. The power and ground supplies were observed to be disturbed by a switching output signal, a result of the tester hardware being unable to respond fast enough to maintain stable voltages. It was shown that using stronger test hardware to provide 0 V improved the stability of the ground voltage. It was further shown that the addition of discrete capacitors between the power supplies improved the stability of the supply voltage. The areas under curves in the supply voltage waveforms were used as quality metrics to quantify the charge involved in the disruption and to evaluate different solutions. Samples from six technologies built in three factories all showed the same issues and responded to the hardware changes, demonstrating that the issue was not sensitive to Si technology.