Fabrication of NbN/Al-AlNx/NbN tunnel junctions on several kinds of substrates

H. Akaike, T. Funai, Shunya Sakamoto, A. Fujimaki
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引用次数: 4

Abstract

We have evaluated the electrical characteristics of NbN/Al-AlNx/NbN tunnel junctions fabricated on sapphire-C or fused-silica substrates. NbN/Al-AlNx/NbN multilayers were prepared by reactive dc-magnetron sputtering deposition of lower and upper NbN layers, and rf-magnetron sputtering deposition of the Al layer, followed by radical-nitridation. The junctions showed low sub-gap leakage currents in the current-voltage characteristics at 4.2 K. The quality parameter, Rsg/Rn, where respective Rsg and Rn are the sub-gap resistance at 2 mV and junction resistance at 5 mV, was above 15. The gap voltage (Vg) was around 3.3 mV, which was reduced in comparison with Vg values of ~4.3 mV for junctions on MgO substrates. The reduced Vg was caused by superconducting properties of lower NbN layers deposited on the sapphire or fused-silica substrates. Uniformity in critical current (Ic) was relatively good, and the maximum-to-minimum spread in Ic was ±1.7% for 200 junctions on a sapphire substrate and ±2.0% for the junctions on a fused-silica substrate.
几种衬底上NbN/Al-AlNx/NbN隧道结的制备
我们评估了在蓝宝石- c或熔融二氧化硅衬底上制造的NbN/Al-AlNx/NbN隧道结的电学特性。通过反应性直流磁控溅射沉积下层和上层NbN层,rf磁控溅射沉积Al层,再进行自由基氮化,制备了NbN/Al- alnx /NbN多层膜。在4.2 K的电流-电压特性中,结显示出较低的亚隙漏电流。质量参数Rsg/Rn大于15,其中Rsg和Rn分别为2mv的子隙电阻和5mv的结电阻。间隙电压(Vg)约为3.3 mV,与MgO衬底上结的~4.3 mV的间隙电压相比有所降低。降低的Vg是由沉积在蓝宝石或熔融二氧化硅衬底上的低NbN层的超导特性引起的。临界电流(Ic)的均匀性相对较好,蓝宝石衬底上200个结的Ic最大到最小扩展为±1.7%,熔融硅衬底上的结为±2.0%。
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