Superconducting Nb Nanobridges for Reduced Footprint and Efficient Next-Generation Electronics
Superconducting Nb Nanobridges for Reduced Footprint and Efficient Next-Generation Electronics
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DOI：
10.1109/tasc.2022.3218895
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发表时间：
2023-01-01
影响因子：
1.8
通讯作者：
Casaburi, Alessandro
中科院分区：
文献类型：
--
作者：
Collins, Jonathan A. A.;Rose, Calum S. S.;Casaburi, Alessandro
我们优化了一种工艺，可以可靠地制造薄Nb纳米桥弱链路，其物理尺寸与Nb相干长度xi(4.2K) & SIM相当；16 nm，相对于电极的可控退化超导性，以及优异的边缘粗糙度。然后，我们研究了将这些纳米桥用作约瑟夫森元件的可行性，以减少足迹和高效的下一代单通量量子（SFQ）逻辑电子器件。首先，我们证明了在这种薄的Nb纳米桥中，电流-电压特性（IVC）中没有热滞后，而在其他薄弱环节中通常会观察到这种滞后，从而阻止了它们在SFQ电子器件中的使用。我们将纳米桥的实验IVCs与分段线性电流相关系（CPR）实现的电阻分流结模型拟合，发现与数据吻合得很好。这使我们能够推断CPR参数并评估临界电流和正常电阻的乘积，IcRn和SIM；mV，在不同温度下。利用这些数据，我们模拟了在不同cpr下电压脉冲的产生，并验证了它们仍然具有等于磁通量量子phi(0)的量子化面积，并且产品IcRn允许运行速度为I-c R-N / phi(0) (sic)100 GHz。此外，它们的临界电流I-c渐近到100 μ A，与SFQ电子中使用的隧道约瑟夫森结（JJs）相当，比温度T = 4.2 k时渐近到0.2 μ A的热电流噪声I-TN = (2 pi / phi(0)) k(B) T大几个数量级，同时稳定且高效地运行，每个开关的能量仅为E-J渐近到I-c phi(0) (sic) 1aj。为了评估这些纳米桥在具有大量元件的SFQ逻辑电子器件中的潜在用途，我们使用开源仿真软件（JSim）来模拟标准dc -SFQ转换器电路的行为。从从实验数据推断的CPR的实现所做的模拟中，我们观察到电路的行为完全符合预期。我们的研究结果强烈表明，这些纳米桥可以用于开发大规模的SFQ电子器件，与隧道JJs相比具有几个优势。占地面积减少，仅为标准隧道jj的三分之一或更少，并简化了制造过程，仅涉及2个步骤。对于隧道jj来说，可以提供更好的制造公差，更好的操作参数控制，更高的电路密度，并且更容易与其他技术平台集成。这些特性也可能非常吸引人，以取代量子技术设备中的隧道jj，如transmon量子位和超导参数放大器。
We optimized a process to reliably fabricate thin Nb nanobridge weak links having a physical size comparable with Nb coherence length xi(4.2K) & SIM;16 nm, controlled degraded superconductivity with respect to the electrodes, and excellent edge roughness. We then investigated the feasibility to use these nanobridges as the Josephson element for reduced footprints and efficient next-generation single flux quantum (SFQ) logic electronics. First of all, we demonstrated that in such thin Nb nanobridges, there is no thermal hysteresis in the current-voltage characteristics (IVC) that instead is usually observed in other weak links and prevents their use in SFQ electronics. We fitted the experimental IVCs of nanobridges with the resistively shunted junction model implemented with piecewise linear current-phase relation (CPR) finding a very good agreement with data. This allowed us to infer the CPR parameters and evaluate the product of critical current and normal resistance, IcRn & SIM;mV, at varying temperatures. Using these data, we simulated the generation of voltage pulses at varying CPRs and verified that they still have a quantized area equal to the magnetic flux quantum phi(0) and the product IcRn allows for speed of operation I-c R-N / phi(0 )(sic)100 GHz. Moreover, their critical current I-c asymptotic to 100 mu A, comparable with that of tunnel Josephson junctions (JJs) used in SFQ electronics, is orders of magnitude larger than thermal current noise I-TN = (2 pi / phi(0)) k(B) T asymptotic to 0.2 mu A at temperature T = 4.2 K, for stable and, at the same time, efficient operation with energy per switch of only E-J asymptotic to I-C phi(0) (sic) 1 aJ. To assess the potential use of these nanobridges in SFQ logic electronics with a large number of elements, we used an open-source simulation software (JSim) to simulate the behavior of a standard DC-to-SFQ converter circuit. From the simulation made by implementing the CPR inferred from experimental data, we observed that the circuit behaves exactly as intended. Our results strongly suggest that these nanobridges can be used to develop large-scale SFQ electronics with several advantages over tunnel JJs. The reduced footprint, just one-third or less than standard tunnel JJs, and simplified fabrication process, with only 2 steps involved against typically & SIM;20 for tunnel JJs, could allow for a better fabrication tolerance, higher control on operation parameters, higher circuit density, and easier integration with other technology platforms. These characteristics could be very appealing also to replace tunnel JJs in quantum technology devices like transmon qubits and superconducting parametric amplifiers.