Dependence of critical current density on oxygen exposure in Nb-AlO/sub x/-Nb tunnel junctions

Kleinsasser, A. W.; Miller, Ronald E.; Mallison, W. H.

doi:10.1109/77.384565

Cited by 58 publications

(41 citation statements)

References 31 publications

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“…These pressure-times correspond to target critical current densities of 500 A/cm 2 and 50 A/cm 2 , respectively. 4 The surface morphology of these trilayers was studied with contact mode atomic force microscopy (AFM). The AFM characterizations show the surface roughness of the bottom Nb layer was not substantially increased by growing ALD-Al 2 O 3 on top of the Al wetting layers.…”

Section: Device Fabricationmentioning

confidence: 99%

“…3 A leak-free tunnel barrier with thickness much smaller than the superconducting coherence length is typically required for the superconductor electrodes to remain phase coherent. Further, because the critical current through the JJ decays exponentially with increasing tunnel barrier thickness, 4 in a) Authors to whom correspondence should be addressed. Electronic addresses: alane@ku.edu and jwu@ku.edu.…”

Section: Introductionmentioning

confidence: 99%

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Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions

Elliot

Malek

et al. 2014

Review of Scientific Instruments

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Articles you may be interested inResistive switching characteristics of integrated polycrystalline hafnium oxide based one transistor and one resistor devices fabricated by atomic vapor deposition methods J. Vac. Sci. Technol. B 33, 052204 (2015) Atomic Layer Deposition (ALD) is a promising technique for growing ultrathin, pristine dielectrics on metal substrates, which is essential to many electronic devices. Tunnel junctions are an excellent example which require a leak-free, ultrathin dielectric tunnel barrier of typical thickness around 1 nm between two metal electrodes. A challenge in the development of ultrathin dielectric tunnel barriers using ALD is controlling the nucleation of dielectrics on metals with minimal formation of native oxides at the metal surface for high-quality interfaces between the tunnel barrier and metal electrodes. This poses a critical need for integrating ALD with ultra-high vacuum (UHV) physical vapor deposition. In order to address these challenges, a viscous-flow ALD chamber was designed and interfaced to an UHV magnetron sputtering chamber via a load lock. A sample transportation system was implemented for in situ sample transfer between the ALD, load lock, and sputtering chambers. Using this integrated ALD-UHV sputtering system, superconductor-insulator-superconductor (SIS) Nb-Al/Al 2 O 2 /Nb Josephson tunnel junctions were fabricated with tunnel barriers of thickness varied from sub-nm to ∼1 nm. The suitability of using an Al wetting layer for initiation of the ALD Al 2 O 3 tunnel barrier was investigated with ellipsometry, atomic force microscopy, and electrical transport measurements. With optimized processing conditions, leak-free SIS tunnel junctions were obtained, demonstrating the viability of this integrated ALD-UHV sputtering system for the fabrication of tunnel junctions and devices comprised of metal-dielectric-metal multilayers. © 2014 AIP Publishing LLC. [http://dx

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Section: Device Fabricationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions

Elliot

Malek

et al. 2014

Review of Scientific Instruments

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“…This E b thickness dependence is reflected by the dramatic increase in critical current density, J c , observed in JJs with thermal AlO x tunnel barriers as the oxygen exposure drops below ~10 3 Pa-s, or ~0.4 nm in thickness [2,12]. Furthermore, a complete tunnel barrier is not even formed in this regime as the tunneling current is dominated by pinholes.…”

Section: Resultsmentioning

confidence: 94%

“…Considering native oxides can naturally form on the surface of most metals, producing an atomically-thin, uniform, and pinhole-free tunnel barrier represents a major challenge in the research of MIMTJs. In Nb/Al/AlO x /Nb JJs for example, an ultrathin (< 1 nm) tunnel barrier is the key to preserve phase coherence across the superconducting Nb electrodes, since the critical current (I c ) through the JJ exponentially decays with the barrier thickness [2]. Thermal oxidation has been the industry standard to produce AlO x tunnel barriers for JJs through in situ oxygen diffusion into an Al wetting layer ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Atomically Thin Al2O3 Films for Tunnel Junctions

Wilt

Gong

et al. 2017

Phys. Rev. Applied

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Metal-Insulator-Metal tunnel junctions (MIMTJ) are common throughout the microelectronics industry. The industry standard AlO x tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically-thin barriers demanded for enhanced quantum coherence. In this work, we employed in situ scanning tunneling spectroscopy along with molecular dynamics simulations to understand and control the growth of atomically thin Al 2 O 3 tunnel barriers using atomic layer deposition (ALD). We found that a carefully tuned initial H 2 O pulse hydroxylated the Al surface and enabled the creation of an atomically-thin Al 2 O 3 tunnel barrier with a high quality M-I interface and a significantly enhanced barrier height compared to thermal AlO x . These properties, corroborated by fabricated Josephson Junctions, show that ALD Al 2 O 3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next-generation of MIMTJs.

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“…The junctions are formed by growing Nb(200 nm)/Al(7 nm) stack, by oxidizing the surface. The oxygen exposure [7] used for the samples measured in this paper was 1000 Torr x h. After pumping the oxygen out, the Nb counter electrode is in situ grown on top. The junction geometry is then defined by anodizing the surroundings of the junction into Nb 2 O 5 .…”

Section: Fabrication Processmentioning

confidence: 99%

Characterization of a fabrication process for the integration of superconducting qubits and rapid-single-flux-quantum circuits

Castellano

Grönberg

Carelli

et al. 2006

Supercond. Sci. Technol.

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In order to integrate superconducting qubits with rapid-single-flux-quantum (RSFQ) control circuitry, it is necessary to develop a fabrication process that fulfills at the same time the requirements of both elements: low critical current density, very low operating temperature (tens of milliKelvin) and reduced dissipation on the qubit side; high operation frequency, large stability margins, low dissipated power on the RSFQ side. For this purpose, VTT has developed a fabrication process based on Nb trilayer technology, which allows the on-chip integration of superconducting qubits and RSFQ circuits even at very low temperature. Here we present the characterization (at 4.2 K) of the process from the point of view of the Josephson devices and show that they are suitable to build integrated superconducting qubits. Characterization of a fabrication process for the integration of qubits and RSFQ circuits 2 IntroductionOn the way towards a reliable and scalable quantum computer, superconducting qubits are promising candidates that are being developed worldwide [1]. To achieve the requested performance on-chip control and readout is of the utmost importance. A viable solution is rapidsingle-flux-quantum (RSFQ) logic, the most advanced superconducting digital technology, which is based on overdamped Josephson junctions [2].Ideally, the qubits must operate at very low temperature, in an environment with low dissipation to preserve the coherent behaviour, with control and readout circuit placed as close as possible, preferably integrated on-chip. These requirements are fulfilled by single-flux-quantum digital circuits, which are fast, scalable, require a very low power and share the same fabrication technology of at least some of the qubits (e.g. phase qubits, based on Josephson junctions, and flux qubits, based on Josephson interferometers).RSFQ logic has been investigated during many years, yielding to the development of complex circuits [3], optimized however for a range of temperatures and critical current densities different from those useful for qubits. Besides, at very low temperature the tolerable dissipated power is severely limited by the low refrigerating power of dilution refrigerators close to the base temperature. As a result, building an on-chip RSFQ circuit to control and read out qubits requires a new optimization procedure, a new design of the layout and a new fabrication process.Recently, a process satisfying these requirements has been developed by VTT. In the process, electron thermalization of the RSFQ part is improved by the use of copper cooling fins. To minimize dissipation, a target critical current density as low as 30 A/cm 2 is used. Here we characterize the process from the point of view of the Josephson junctions; measurements carried out at 4.2 K assess the good quality of unshunted junctions and their potential to build qubits.

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Dependence of critical current density on oxygen exposure in Nb-AlO/sub x/-Nb tunnel junctions

Cited by 58 publications

References 31 publications

Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions

Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions

Atomically Thin Al2O3 Films for Tunnel Junctions

Characterization of a fabrication process for the integration of superconducting qubits and rapid-single-flux-quantum circuits

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