Advantages of superconducting Coulomb-blockade electrometers

We have measured the current-voltage gate charge characteristics and noise in superconducting Coulomb-blockade electrometers from 50 mK to 1.05 K. The Al-AlO/sub x/-Al junctions in our devices have capacitances which range from 0.3 fF to 1 fF and tunneling resistances from 20 k/spl Omega/ to 200 k/spl Omega/. We find that our normal and superconducting electrometers have comparable charge noise but that the latter have much larger modulation which persists to significantly higher temperatures. The maximum operating temperature in the superconducting state is close to T/sub c/. This behavior Is consistent with a simple model and makes the superconducting electrometer preferable for many applications.<
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