Atomic nitrogen source for the formation of aluminum nitride tunnel barrier SIS junctions

Endo, Akira; Noguchi, Takashi; Kroug, M.; Tamura, Takuya; Inoue, H.

doi:10.1016/j.physc.2009.05.256

Cited by 6 publications

(10 citation statements)

References 11 publications

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“…F While the oxidation of Al films is well researched and the room temperature growth is solely a function of oxygen pressure and exposure time, plasma nitridation is an inherently more complex process, with multiple nitrogen species available for AlN growth. Correlation between plasma conditions and the quality of Nb/Al-AlN/Nb junctions produced with an ECR plasma have been reported, and most recently a similar trend has been observed by our research group for AlN junctions grown via ICP [2][3][4]. As new ICP nitridation conditions are investigated during optimization of growth processes, we note the AlN growth rate is heavily dependent upon process parameters.…”

Section: Introductionsupporting

confidence: 80%

In situ spectroscopic ellipsometry of SIS barrier formation

Cyberey

Lichtenberger

2014

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

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First reported by our research group in 2007, AlN tunnel barriers grown by ICP nitridation of thin Al overlayers offer a promising alternative to Al oxide barriers for high current density SIS junctions used in quantum limited THz heterodyne receivers [1]. However, the growth rate of AlN is heavily dependent on ICP operating conditions and as new uncharacterized nitridation processes are investigated, knowledge of the barrier thickness is integral to realizing SIS junctions of desired current density, which is exponentially dependent upon barrier thickness. An in situ method for real time monitoring of ICP AlN growth on thin Al overlayers through the use of spectroscopic ellipsometry and a correlation of the determined AlN thickness to the normal resistance area product (RNA) of the resulting trilayer is reported.

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Section: Introductionsupporting

confidence: 80%

In situ spectroscopic ellipsometry of SIS barrier formation

Cyberey

Lichtenberger

2014

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

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“…A correlation between junction quality and plasma dissociation has been reported for Nb/Al-AlN/Nb junctions produced with an ECR plasma, but at the time of writing, nothing is reported for ICP [2]. In this work, we investigate the effects of various process parameters of a nitrogen ICP on the RD and report an observed correlation of RD with both the AlN growth rate and the quality of the resulting Nb/Al-AlN/Nb junctions.…”

Section: Introductionmentioning

confidence: 86%

“…I N/N 2 are the measured intensities of the spectral emissions from excited N and N 2 respectively, and n N/N 2 are their corresponding densities [2], [6], [7]. Our trilayer deposition system, discussed in detail elsewhere [1], [8], was equipped with an Ocean Optics USB4000 Spectrometer and a 1 inch diameter collimating lens to record optical emissions from a nitrogen ICP.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…For the spectrum of atomic nitrogen, we focus on the 3p 4 S 0 → 3s 4 P nitrogen atomic triplet, as it lies within the range of optical emission captured by our spectrometer, overlapping spectra from the B 3 Π g − A 3 Σ u system, and is one of brightest emissions from atomic N in plasmas [7]. To extract the separate N and N 2 spectra, a similar approach to the one used by Endo [2] is implemented and described below.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Optical Spectroscopic Analysis of ICP Nitridation for SIS Junctions With AlN Barriers

Cyberey

Oakland

Zhang

et al. 2015

IEEE Trans. Appl. Supercond.

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High quality, low-leakage superconductorinsulatorsuperconductor (SIS) junctions with Nb electrodes and aluminum oxide barriers are widely reported in the literature, and have become integral in the design and fabrication of various superconducting circuits. However, as current densities are increased, aluminum oxide based tunnel barriers show excess leakage currents due to defects and pinholes in the barrier layer. First reported by our group in 2007, AlN tunnel barriers grown via inductively coupled plasma (ICP) nitridation of Al overlayers are a promising alternative, producing low-leakage Nb/Al-AlN/Nb SIS junctions, with current densities in excess of 30 kA/cm 2 . A correlation between junction quality and plasma dissociation has been reported for Nb/Al-AlN/Nb junctions produced via an electron cyclotron resonance (ECR) plasma. In this work, a quantitative measure of the relative dissociation (RD) of an ICP is determined through the use of a commercially available Ocean Optics USB4000 Optical Spectrometer. The effects of various ICP parameters on the RD, and a correlation between the RD and quality of the resulting Nb/Al-AlN/Nb junctions are reported.Index Terms-Aluminum nitride, inductively coupled plasma, superconductorinsulatorsuperconductor (SIS), spectroscopy. 1051-8223

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“…15 -20 , are integrated. A technology based on trilayers, proven to be reliable for all Nb circuits [9], is the most promising choice and currently being developed in our laboratory [18]. Other changes in the fabrication are minor.…”

Section: Resultsmentioning

confidence: 99%

SIS Mixer Fabrication for ALMA Band10

Kroug¹,

Endo²,

Tamura³

et al. 2009

IEEE Trans. Appl. Supercond.

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Band10 of the Atacama Large Millimeter Array (ALMA) is a planned heterodyne receiver covering the frequency range 790 GHz-950 GHz. The waveguide mixers are superconductor insulator superconductor (SIS) Nb Al AlO Nb junctions integrated with NbTiN SiO 2 Al tuning circuits. Our junction definition process has been greatly simplified by introducing an inductively-coupled-plasma (ICP) etcher to the fabrication. The etching process, which employs a low-pressure CF 4 O 2 plasma, allows to remove the entire Nb Al AlO Nb tri-layer in a single step. SIS mixers with current densities up to 10 kA cm 2 and quality factor above 15 have been fabricated with good reproducibility. Minimum receiver noise temperature, corrected for optical losses, is 210 K at 860 GHz. With the goal to further improve the performance, optimization of circuit design and fabrication technology are discussed.Index Terms-ICP etching, SIS mixer, submillimeter wave receiver.

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Atomic nitrogen source for the formation of aluminum nitride tunnel barrier SIS junctions

Cited by 6 publications

References 11 publications

In situ spectroscopic ellipsometry of SIS barrier formation

In situ spectroscopic ellipsometry of SIS barrier formation

Optical Spectroscopic Analysis of ICP Nitridation for SIS Junctions With AlN Barriers

SIS Mixer Fabrication for ALMA Band10

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