Stacked Josephson Junction Arrays for the Pulse-Driven AC Josephson Voltage Standard

Abstract

We developed a fabrication process to establish large arrays of up to 5-stacked Josephson junctions for the Josephson Arbitrary Waveform Synthesizer (JAWS). SNS-type Josephson junctions with NbxSi1-x barriers are used for this application. By modifying our standard window process, e.g. to add a CMP (chemical mechanical polishing) and an ALD (atomic layer deposition) step, the yield of this process was increased. An output voltage of 1 V RMS could be achieved by using 4 JAWS arrays in series with a total number of 60,000 5-stacked junctions. The investigation of the current-voltage characteristics (IVC) showed an interesting and potentially useful feature. The required pulse amplitude per junction for getting the maximum Shapiro step width reduces for higher junction stacks. We found that the pulse power linearly reduces with the square of the junction number in the array. The origin of this effect might be a strong neighbour-neighbour interaction of the junctions, which are closely arranged within the stacked configuration. This might generate a strong self-synchronization of the junctions.

Coherent amplification of radiation from two phase-locked Josephson junction arrays

“…The samples were fabricated by Oliver Kieler (Braunschweig, Germany) and were measured in AlbaNova University Center (Stockholm, Sweden). The fabrication is a self-aligning process using e-beam lithography and reactive ion etching [16,17]. Similar arrays were studied earlier in [9,12,13], where additional information about sample characterization can be found.…”

Josephson voltage standards as toolkit for precision metrological applications at PTB

“…In this way the CPW can be shorter for the same number of JJs improving pulse dispersion and, in addition, coupling between the junctions is stronger. A sophisticated 'window type' process for the fabrication of up to 5-stacked JJ arrays was developed at PTB (Kieler et al 2021). The thicknesses of resist as well as of the Nb and SiO 2 layers were increased.…”

Влияние контактного сопротивления интерфейса YBCO|Au на транспортные и СВЧ-свойства массивов джозефсоновских контактов из высокотемпературных сверхпроводников

“…Для реализации эталона переменного напряжения Бенцем и Гамильтоном в 1996 г. был предложен синтезатор сигналов произвольной формы на основе ниобиевых джозефсоновских контактов [3,4]. В синтезаторе цепочка джозефсоновских контактов управляется импульсами тока, которые позволяют генерировать переменный сигнал произвольной формы с квантовой точностью [5][6][7]. В настоящее время квантовые синтезаторы сигналов произвольной формы на основе низкотемпературных сверхпроводников используются в джонсовской термометрии, эталонах переменного напряжения, калибровке термопреобразователей и т. д.…”