MIT LL SFQ5ee+ 工艺中绝热量子通量参变器的表征
Characterization of Adiabatic Quantum-Flux-Parametrons in the MIT LL SFQ5ee+ Process
AI总结：
本研究在MIT LL SFQ5ee+工艺中表征了面积减小25%、密度提高2倍的AQFP移位寄存器，发现密集设计磁通俘获概率高一个数量级，需优化沟槽设计以减少俘获效应。
摘要：
绝热量子通量参变器（AQFP）逻辑是一种已被验证的节能超导技术，适用于多种应用。为了解决可扩展性挑战，我们研究了AQFP移位寄存器，其AQFP占用面积相较于先前工作减少了25%，并且通过消除先前在AQFP之间使用的自由空间，整体设计密度提高了2倍以上。我们还研究了在超导地平面中采用不同磁通俘获沟槽设计的AQFP单元，以及利用麻省理工学院林肯实验室新制造工艺SFQ5ee+中更小特征尺寸的紧凑型AQFP单元。该新工艺具有九个平坦化铌层，最小线宽为0.25微米。\n\n制造出的电路在液氦探针和闭循环低温恒温器中进行了测试，测试时通过超导临界温度采用受控冷却速率。利用多次热循环，我们在约0.53微特斯拉和约1.2微特斯拉两个残余磁场水平下，研究了密集AQFP移位寄存器以及采用旧（稀疏）AQFP设计的寄存器中的磁通俘获。稀疏设计在冷却后表现出95%至接近100%的工作概率和非常宽的工作裕度，尽管磁通俘获概率随电路复杂度增加而上升。较新的密集设计中的裕度同样宽，但导致寄存器无法工作的磁通俘获概率在密集电路中显著更高，高出一个数量级，并且对沟槽的形状和位置非常敏感。\n\n我们的研究结果表明，AQFP电路适合扩大集成规模和进一步致密化，但需要仔细设计和优化沟槽，以减少密集AQFP电路中的磁通俘获效应。
英文摘要：
Adiabatic quantum-flux-parametron (AQFP) logic is a proven energy-efficient superconductor technology for various applications. To address the scalability challenges, we investigated AQFP shift registers with the AQFP footprint area reduced by 25% with respect to prior work and with more than 2x denser overall designs obtained by eliminating the previously used free space between the AQFPs. We also investigated AQFP cells with different designs of flux trapping moats in the superconducting ground plane as well as compact AQFP cells that took advantage of the smaller feature sizes available in the new fabrication process, SFQ5ee+, at MIT Lincoln Laboratory. This new process features nine planarized Nb layers with a 0.25 $μ$m minimum linewidth. The fabricated circuits were tested in a liquid He probe and in a closed-cycle cryocooler using a controlled cooling rate through the superconducting critical temperature. Using multiple thermal cycles, we investigated flux trapping in the dense AQFP shift registers as well as in the registers using the old (sparse) AQFP designs at two levels of the residual magnetic field, about 0.53 $μ$T and about 1.2 $μ$T. The sparse designs demonstrated 95% to almost 100% probability of operation after the cooldown and very wide operation margins, although the flux trapping probability was increasing with circuit complexities. The margins were similarly wide in the newer dense designs, but flux trapping probability that rendered the registers nonoperational was significantly, by an order of magnitude, higher in the denser circuits and was also very sensitive to the moats' shape and location. Our findings indicate that AQFP circuits are amendable to increasing the scale of integration and further densification, but a careful moat design and optimization are required to reduce flux trapping effects in the dense AQFP circuits.
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