Josephson junctions coupled by an ion-implanted vertical semiconductor membrane

Superconducting devices with two niobium electrodes separated by a vertical silicon membrane have been fabricated. The silicon membrane typically of 100-300 nm thickness, is degenerately doped by arsenic ion implantation and capped by a thin layer of silicon dioxide. The small dimensions of the membrane are achieved by photolithography and controlled isotropic wet etching followed by CBrF
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reactive ion etching. The electrodes of 200 nm thickness are formed by sputter deposition and photolithographic patterning. The metal film on top of the membrane is removed using a photoresist planarization technique, followed by CF
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reactive ion etching. A typical device with a 300 nm-thick barrier and with 50 μm-wide electrodes displays Josephson junction characteristics with a critical current of about 8 μA at 4.2 K. The observed product of critical current and normal resistance is in the range of 0.4-0.8 mV at 4.2 K among the devices tested.