Measurements of tunneling barrier thicknesses for Nb/Al–AlO /Nb tunnel junctions

Kang, Xinjie; Ying, Liliang; Wang, Hai; Peng, Wei; Kong, Xiangyan; Xie, Xiaoming; Wang, Zhen

doi:10.1016/j.physc.2014.05.006

Cited by 20 publications

(31 citation statements)

References 21 publications

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“…Specifically, the influence of temperature [25] and oxygen pressure during static oxidation [26][27][28] and both combined [29][30][31] were studied. Variations of the critical current are usually attributed to the variation of the AlOx-layer thickness [32,33]. However, AlOx composition variations and changes of the Al-O coordination, i.e.…”

Section: Introductionmentioning

confidence: 99%

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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The structural and nanochemical properties of thin AlOx layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of AlOx layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated AlOx layers and correlate them with fabrication parameters. With respect to the application of AlOx as tunnel barrier in superconducting Josephson junctions, Al/AlOx/Al-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous AlOx layers is strongly dependent on the fabrication process and oxidation parameters.Dynamic and static oxidation of Al yields oxygen-deficient amorphous AlOx layers, where the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline -Al2O3 layers were grown by electron-beam evaporation of Al2O3 and reactive sputter deposition.

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Section: Introductionmentioning

confidence: 99%

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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“…This argument is supported by the dI/dV characteristics and E b observed for the thermal AlO x and the ALD Al 2 O 3 tunnel barriers. The dI/dV spectra for a thermal AlO x tunnel barrier of ~1.3 nm, in estimated thickness [12], is shown alongside a 10-cycle ALD Al 2 O 3 tunnel barrier with a comparable thickness of ~1.2 nm in Fig. 3(a).…”

Section: Resultsmentioning

confidence: 99%

“…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: 99%

“…ALD nucleation on inert metal surfaces, such as Pt and Au, can be completely frustrated for the first 30-50 cycles of alternating precursor pulses whereas for reactive metals, such as Al, even in situ deposited films can acquire an interfacial layer (IL) of AlO x up to ~2 nm thick [8][9][10]. In a previous work, fabricated Nb/Al/Al 2 O 3 /Nb JJs using in situ ALD of Al 2 O 3 had an IL >0.5 nm in thickness which was attributed to poor vacuum pressure (~500 mTorr) during sample transfer and pre-ALD sample heating [9,11,12]. This IL prevented the realization of truly atomically-thin tunnel barriers and led to poor quality JJs.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Kang et al. ( 2014 ), Shiota et al. ( 1992 ), Imamura and Hasuo ( 1991 , 1992 ), Kleinsasser et al ( 1995 , 1996 ).…”

Section: Introductionmentioning

confidence: 99%

Correlation between Al grain size, grain boundary grooves and local variations in oxide barrier thickness of Al/AlOx/Al tunnel junctions by transmission electron microscopy

et al. 2016

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A thickness variation of only one Ångström makes a significant difference in the current through a tunnel junction due to the exponential thickness dependence of the current. It is thus important to achieve a uniform thickness along the barrier to enhance, for example, the sensitivity and speed of single electron transistors based on the tunnel junctions. Here, we have observed that grooves at Al grain boundaries are associated with a local increase of tunnel barrier thickness. The uniformity of the barrier thickness along the tunnel junction thus increases with increasing Al grain size. We have studied the effect of oxidation time, partial oxygen pressure and also temperature during film growth on the grain size. The implications are that the uniformity improves with higher temperature during film growth.

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Measurements of tunneling barrier thicknesses for Nb/Al–AlO /Nb tunnel junctions

Cited by 20 publications

References 21 publications

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Atomically Thin Al2O3 Films for Tunnel Junctions

Correlation between Al grain size, grain boundary grooves and local variations in oxide barrier thickness of Al/AlOx/Al tunnel junctions by transmission electron microscopy

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