41 research outputs found
Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions
This is the published version. Copyright 2014 American Institute of PhysicsAtomic 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/Al2O2/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 Al2O3 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
Integrating Atomic Layer Deposition and Ultra-High Vacuum Physical Vapor Deposition for In Situ Fabrication of Tunnel Junctions
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 barrier 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/Al2O3/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 Al2O3 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.Comment: 25 pages, 13 figures, 1 tabl
Doped graphene nanohole arrays for flexible transparent conductors
Graphene nanohole arrays (GNAs) were fabricated using nanoimprint lithography. The improved optical transmittance of GNAs is primarily due to the reduced surface coverage of graphene from the nanohole fabrication. Importantly, the exposed edges of the nanoholes provided effective sites for chemical doping using thionyl chloride was shown to enhance the conductance by a factor of 15–18 in contrast to only 2-4 for unpatterned graphene. GNAs can provide a unique scheme for improving both optical transmittance and electrical conductivity of graphene-based transparent conductors