Josephson tunneling through locally thinned silicon wafers

We have made and tested Josephson junctions in which tunneling takes place through a locally thinned region in a single-crystal silicon wafer. An etching technique is used to produce a square uniform thinned layer, 87.5 μm on a side and ≈400 Å thick. After removal of the oxide layer, superconducting metals are deposited on both sides. Temperature and magnetic field dependences of the critical current, as well as the magnitude of the current, conform very closely to the theory for a Josephson tunnel junction. This is the first type of Josephson junction employing a barrier which is accessible for modification prior to deposition of the superconducting electrodes.