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Reliability evaluation of Nb 10 kA/cm2 fabrication process for large-scale SFQ circuits

Shuichi Nagasawa, K. Hinode, T. Satoh +3 more

Physica C SuperconductivityJul 20, 200523 citations

10 kA/cm^2 Nb Processを用いたSFQバタフライ演算回路の要素回路の動作評価

史滋宮岡, 泰浩島村, 世樹貝沼 +2 more

IEICE Technical Report; IEICE Tech. Rep.Oct 12, 20100 citations

50 GHz Demonstration of an Integer-Type Butterfly Processing Circuit for an FFT Processor Using the 10 kA/cm2 Nb Process

Y. Sakashita, Yuki Yamanashi, Nobuyuki Yoshikawa

We are developing a fast Fourier transform (FFT) processor using high-speed and low-power single-flux-quantum (SFQ) circuits. Our main concern is the development of an SFQ butterfly processing circuit, which is the core processing circuit in the FFT processor. In our previous study, we have confirmed the complete operation of an integer-type butterfly processing circuit using the AIST 2.5 kA/cm2 Nb standard process at the frequency of 25 GHz. In this study, we have designed an integer-type butterfly processing circuit using the AIST 10 kA/cm2 Nb advanced process and confirmed its high-speed operation at the maximum frequency of 50 GHz.We are developing a fast Fourier transform (FFT) processor using high-speed and low-power single-flux-quantum (SFQ) circuits. Our main concern is the development of an SFQ butterfly processing circuit, which is the core processing circuit in the FFT processor. In our previous study, we have confirmed the complete operation of an integer-type butterfly processing circuit using the AIST 2.5 kA/cm2 Nb standard process at the frequency of 25 GHz. In this study, we have designed an integer-type butterfly processing circuit using the AIST 10 kA/cm2 Nb advanced process and confirmed its high-speed operation at the maximum frequency of 50 GHz.

IEICE Transactions on ElectronicsJan 1, 20157 citations

Specific capacitance of Nb/AlOx/Nb Josephson junctions with critical current densities in the range of 0.1–18 kA/cm2

Masaaki Maezawa, Masahiro Aoyagi, Hiroshi Nakagawa +2 more

The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1–18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction.The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1–18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction.

Applied Physics LettersApr 17, 199566 citations

10kA/cm^2 Nb Processを用いたSFQバタフライ演算回路の要素回路の動作評価(超伝導エレクトロニクス基盤技術及び一般)

史滋宮岡, 泰浩島村, 世樹貝沼 +2 more

電子情報通信学会技術研究報告. SCE, 超伝導エレクトロニクスOct 12, 20100 citations

Uniformity and Reproducibility of Submicron 20kA/cm² Nb/AlOx/Nb Josephson Junction Process

Shuichi Nagasawa, T. Satoh, Mutsuo Hidaka

Submicron Nb/AlOx/Nb junctions having high critical current density of more than 20 kA/cm2are required for realizing single-flux-quantum (SFQ) circuits operating at a high speed of more than 100 GHz. We have developed a 20 kA/cm2process having submicron circular junctions. 1000-serially-connected circular shape junctions having six different diameters of 0.5 μm, 0.564 μm, 0.7 μm, 0.9 μm, 1.1 μm, and 1.3 μm have been designed. The 0.564 μm junction is designed to be 50 μA with critical current density of 20 kA/cm2, which is a minimum current value of a target SFQ circuit design. We totally fabricated 12 wafers with the 20 kA/cm2process. The 1σ spread of critical currents (Ic) depending on junction sizes and the run-to-run reproducibility of critical current densities are reported as a summary of these fabrications. We obtained Icscattering of 1σ≤ 2% even in the minimum circular junction of 0.25 μm2in several fabrication runs.Submicron Nb/AlOx/Nb junctions having high critical current density of more than 20 kA/cm2are required for realizing single-flux-quantum (SFQ) circuits operating at a high speed of more than 100 GHz. We have developed a 20 kA/cm2process having submicron circular junctions. 1000-serially-connected circular shape junctions having six different diameters of 0.5 μm, 0.564 μm, 0.7 μm, 0.9 μm, 1.1 μm, and 1.3 μm have been designed. The 0.564 μm junction is designed to be 50 μA with critical current density of 20 kA/cm2, which is a minimum current value of a target SFQ circuit design. We totally fabricated 12 wafers with the 20 kA/cm2process. The 1σ spread of critical currents (Ic) depending on junction sizes and the run-to-run reproducibility of critical current densities are reported as a summary of these fabrications. We obtained Icscattering of 1σ≤ 2% even in the minimum circular junction of 0.25 μm2in several fabrication runs.

IEEE International Superconductive Electronics Conference (ISEC)Jul 1, 201512 citations

10 kA/cm2 Nb Processを用いた SFQ浮動小数点乗算器の50 GHzでの動作評価

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10 kA/cm2 Nb Processを用いた SFQ浮動小数点乗算器の50 GHzでの動作評価

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