From FPGA to ASIC: A RISC-V processor experience

This work document a correct design flow using these tools in the Lagarto RISC- V Processor and the RTL design considerations that must be taken into account, to move from a design for FPGA to design for ASIC

Bridging the gap between nanowires and Josephson junctions: a superconducting device based on controlled fluxon transfer across nanowires

The basis for superconducting electronics can broadly be divided between two technologies: the Josephson junction and the superconducting nanowire. While the Josephson junction (JJ) remains the dominant technology due to its high speed and low power dissipation, recently proposed nanowire devices offer improvements such as gain, high fanout, and compatibility with CMOS circuits. Despite these benefits, nanowire-based electronics have largely been limited to binary operations, with devices switching between the superconducting state and a high-impedance resistive state dominated by uncontrolled hotspot dynamics. Unlike the JJ, they cannot increment an output through successive switching, and their operation speeds are limited by their slow thermal reset times. Thus, there is a need for an intermediate device with the interfacing capabilities of a nanowire but a faster, moderated response allowing for modulation of the output. Here, we present a nanowire device based on controlled fluxon transport. We show that the device is capable of responding proportionally to the strength of its input, unlike other nanowire technologies. The device can be operated to produce a multilevel output with distinguishable states, which can be tuned by circuit parameters. Agreement between experimental results and electrothermal circuit simulations demonstrates that the device is classical and may be readily engineered for applications including use as a multilevel memory

Innovative teaching of IC design and manufacture using the Superchip platform

In this paper we describe how an intelligent chip architecture has allowed a large cohort of undergraduate students to be given effective practical insight into IC design by designing and manufacturing their own ICs. To achieve this, an efficient chip architecture, the “Superchip”, has been developed, which allows multiple student designs to be fabricated on a single IC, and encapsulated in a standard package without excessive cost in terms of time or resources. We demonstrate how the practical process has been tightly coupled with theoretical aspects of the degree course and how transferable skills are incorporated into the design exercise. Furthermore, the students are introduced at an early stage to the key concepts of team working, exposure to real deadlines and collaborative report writing. This paper provides details of the teaching rationale, design exercise overview, design process, chip architecture and test regime

Josephson junctions with centered step and local variation of critical current density

Superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel junctions based on Nb\Al2O3\Ni\Cu\Nb stacks with a thickness step in the metallic NiCu interlayer were fabricated. The step height of a few 0.1 nm was defined by optical lithography and controlled etching of both Nb and NiCu layers. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate a uniform NiCu thickness and similar interface transparencies for etched and non-etched parts. The critical current diffraction pattern was calculated and measured for stepped junctions having the same ground phase difference but different critical current densities in both halves. The measured data show a good agreement with simulations.Comment: slight modification

BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions

Josephson junctions with iron pnictides open the way for fundamental experiments on superconductivity in these materials and their application in superconducting devices. Here, we present hybrid Josephson junctions with a BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter electrode. The junctions show RSJ-like current-voltage characteristics up to the critical temperature of the counter electrode of about 7.2K. The temperature dependence of the critical current, IC, does not show an Ambegaokar-Baratoff behavior. Well-pronounced Shapiro steps are observed at microwave frequencies of 10-18GHz. Assuming an excess current, I_ex, of 200 {\mu}A at 4.2K we get an effective I_C R_N product of 6 {\mu}V.Comment: submitted to Appl. Phys. Let

Remediation of contaminated marine sediment using bentonite, kaolin and sand as capping materials

There is a growing public concern over the issue of sediment contamination resulting from industrial, municipal wastewater, mining activities, and improper use of chemical fertilizer or pesticides. The conventional treatment of contaminated sediment is dredging, but this treatment is expensive and requires a large area of land for disposal. In situ capping of contaminated sediment is considered as a cheaper technique compared to dredging and efficient treatment technology to immobilize pollutants in sediments on site. In this technique, sediments are capped by placing a layer of inert materials like sand, clean soil, or gravel or active materials like activated carbon, zeolite, or apatite over sediments in order to reduce the risk to the aquatic environment. The objective of this study is to determine the effectiveness of using active materials; bentonite (B), kaolin (K), mixture of bentonite with kaolin (1:1) (BK) as capping materials to block the release of five heavy metals (Pb, Cr, Cu, Cd and Zn) from artificially polluted sediments. The effectiveness of B, K, and BK for preventing the leachability of the trace metals was assessed on a bench-scale laboratory experiment in glass tanks for 90 days, where 1cm thick layer of capping material and sand was placed above the contaminated sediment. The results showed that B and BK reduced the leachability of Pb, Cr, and Cu from the sediments. The results also showed that B and BK could be used as potential capping materials for the remediation of contaminated sites due to their significant entrapping of Pb, Cu, and Cr. The pollutants were released into the overlying water from the contaminated sediment in the following decreasing order; Cd > Zn > Pb > Cu > Cr. The adsorption kinetics analysis also showed that the process of adsorption was by chemisorption. This study proved that bentonite and mixture of bentonite with kaolin clays covered with sand could be used as capping materials for in situ treatment of Pb, Cu, Cr, Zn, and Cd for contaminated marine sediment