Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices

One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements that expose the technology's lack of high-density, high-speed and power-efficient memory. Here we demonstrate an array of cryogenic memory cells consisting of a non-volatile three-terminal magnetic tunnel junction element driven by the spin Hall effect, combined with a superconducting heater-cryotron bit-select element. The write energy of these memory elements is roughly 8 pJ with a bit-select element, designed to achieve a minimum overhead power consumption of about 30%. Individual magnetic memory cells measured at 4 K show reliable switching with write error rates below $10^{-6}$, and a 4x4 array can be fully addressed with bit select error rates of $10^{-6}$. This demonstration is a first step towards a full cryogenic memory architecture targeting energy and performance specifications appropriate for applications in superconducting high performance and quantum computing control systems, which require significant memory resources operating at 4 K.Comment: 10 pages, 6 figures, submitte

Electrothermal Bonding of Carbon Nanotubes to Glass

Applications that exploit the exceptional properties of carbon nanotubes CNTs[1] at practical length scales almost invariably involve the fundamental issues of nanotube-to-surface contacts; indeed, interface properties often dominate mechanical, electrical, and thermal performance in devices and materials based on CNTs. In this paper we present a method to attach CNTs to glass surfaces and investigate the mechanism of bonding at the interface. An electric field which induces migration of alkali ions from glass into CNTs, with a reversed polarity as compared to an analogous anodic bonding configuration, is employed to form a chemical bond between nanotubes and glass. We report a pull-off force of 4.35 N/cm2 averaged over the bonded area, with the possibility of localized areas of higher bonding strength

Correlating Structure, Conductance, and Mechanics of Silver Atomic-Scale Contacts

We measure simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature. We observe the formation of contacts with a conductance close to 1 G₀, the quantum of conductance, which can be attributed to a single-atom contact, similar to those formed by Au. We also find two additional conductance features at ∼0.4 G₀ and ∼1.3 G₀, which have been previously ascribed to contacts with oxygen contaminations. Here, using a conductance cross-correlation technique, we distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness. Our results allow us to assign the ∼0.4 G₀ conductance feature to an Ag–O–Ag contact and the ∼1.3 G₀ feature to an Ag–Ag single-atom contact with an oxygen atom in parallel. Utilizing complementary information from force and conductance, we thus demonstrate the correlation of conductance with the structural evolution at the atomic scale

Linker Dependent Bond Rupture Force Measurements in Single-Molecule Junctions

We use a modified conducting atomic force microscope to simultaneously probe the conductance of a single-molecule junction and the force required to rupture the junction formed by alkanes terminated with four different chemical link groups which vary in binding strength and mechanism to the gold electrodes. Molecular junctions with amine, methylsulfide, and diphenylphosphine terminated molecules show clear conductance signatures and rupture at a force that is significantly smaller than the measured 1.4 nN force required to rupture the single-atomic gold contact. In contrast, measurements with a thiol terminated alkane which can bind covalently to the gold electrode show conductance and force features unlike those of the other molecules studied. Specifically, the strong Au–S bond can cause structural rearrangements in the electrodes, which are accompanied by substantial conductance changes. Despite the strong Au–S bond and the evidence for disruption of the Au structure, the experiments show that on average these junctions also rupture at a smaller force than that measured for pristine single-atom gold contacts

Thoughts on an education

Research in nanoscience and nanotechnology has grown rapidly in recent years and has provided numerous scientific and technological breakthroughs. The field has also, in some sense, changed the way in which a research topic can be tackled, unconstrained by traditional scientific disciplines. However, what effect have the developments in research had on the curriculum being taught in universities? And what sort of education do the nanotechnologists of the future need to succeed? Nature Nanotechnology asked a range of current, or recently graduated, masters and PhD students about their own experiences, and what, if anything, they would change about the current education system.3 page(s

Importance of Direct Metal−π Coupling in Electronic Transport Through Conjugated Single-Molecule Junctions

We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono- and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S–Au donor–acceptor bond on one end and a relatively weak Au−π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the <i>meta</i> position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal−π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires