基于亚微米尺寸约瑟夫森结的超高灵敏度SQUID研究
Towards ultra-sensitive SQUIDs based on sub-micrometer-sized Josephson Junctions
AI总结：
本研究通过将HfTi自分流结工艺拓展为带AlO_x绝缘层的SIS工艺，制备亚微米约瑟夫森结以降低结电容，显著提升了SQUID的能量灵敏度，在400 mK下非耦合器件可达0.65 h的白噪声能量灵敏度。
摘要：
我们近期演示了一款一阶轴向梯度计SQUID（超导量子干涉器件）系统，该系统在液氦杜瓦中运行，噪声贡献可忽略不计。测得的接近SQUID极限的耦合能量灵敏度ε_c约为30 h，对应的白场噪声低于180 aT Hz^-1/2。为进一步提升SQUID的噪声性能，我们将结的横向尺寸从2.5 μm减小至1 μm以下，以此降低结电容。这一目标通过将基于HfTi自分流结技术的亚微米尺寸Josephson Junctions（约瑟夫森结）制备工艺，拓展为以AlO_x为绝缘层的SIS工艺来实现。我们在4.2 K温度下，测得非耦合与耦合SQUID的能量灵敏度分别为4.7 h和20 h。我们还研究了非耦合SQUID噪声的温度依赖性，在400 mK的白噪声区间达到了0.65 h的能量灵敏度。
英文摘要：
We recently demonstrated a 1$^{\textrm{st}}$-order axial gradiometer SQUID system, which is operated in a liquid He dewar with negligible noise contribution. The achieved close to SQUID-limited measured coupled energy sensitivity $\varepsilon_{c}$ of $\sim 30\,h$ corresponds to a white field noise below 180~aT~Hz${^{-1/2}}$. In order to further improve the SQUID noise performance, the junction capacitance was reduced by decreasing its lateral size from $2.5~μ$m to below $1~μ$m. This was realized by extending the fabrication process for submicrometer-sized Josephson Junctions based on the HfTi self-shunted junction technology to an SIS process with AlO$_{\textrm{x}}$ as the insulating layer. We achieved energy sensitivities of 4.7$\,h$ and 20$\,h$ at 4.2~K for uncoupled and coupled SQUIDs, respectively. We also investigated the temperature dependence of the noise of the uncoupled SQUIDs and reached an energy sensitivity of 0.65$\,h$ in the white noise regime at 400~mK.
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