利用扩散几何结构和界面限域电导的可扩展全固态冰箱在1开尔文以下温度的演示
Demonstration of a scalable all-solid-state refrigerator exploiting diffusion geometries and limiting interfacial conductances at temperatures below 1 kelvin
AI总结：
该研究开发了采用NIS结、含1121个SINIS单元的可扩展全固态冰箱，首次实现了低于1开尔文下对整个硅芯片的冷却，将其声子温度降至70毫开尔文。
AI中文摘要：
采用正常金属/绝缘体/超导体（NIS）结的固态冰箱此前已展现出优异的电子冷却能力，但冷却声子的能力有限。超导体的能隙被用作能量过滤器，使能量高于平均值的电子优先从正常金属隧穿穿过绝缘体进入超导体，在超导体中它们以准粒子形式运动。通常，热量被转移，同时做功将热准粒子沉积到正常金属准粒子阱中，以排到下一个制冷级。研究人员发现：（1）准粒子在无电场的超导体中由浓度梯度驱动扩散流动；（2）通过设计超导体与阱之间界面的几何结构和材料，可减少热侧阱的不期望的反向热泄漏，从而实现增强的冷却。该冰箱的制备采用钨和钛钨合金作为冷侧正常金属，氧化铝作为绝缘体，铝作为超导体，金作为阱，冷侧NIS部分通过凸点键合连接到热侧金阱。该冰箱包含1121个结对，每个结对为SINIS单元，全部电串联连接。利用该装置，研究人员测量到一块3.9毫米×3.9毫米×0.65毫米硅芯片的有效声子温度从120毫开尔文的浴温降至70毫开尔文，从271毫开尔文的排热温度降至174毫开尔文（冷却幅度为-97毫开尔文）。这是首次演示利用NIS结对整个硅芯片进行低于1开尔文的冷却。
英文摘要：
Solid-state refrigerators using Normal-metal/Insulator/Superconductor (NIS) junctions have previously demonstrated excellent electron cooling but limited ability to cool phonons. The energy gap of the superconductor is used as an energy filter to allow higher than average energy electrons to preferentially tunnel from the normal-metal through the insulator into the superconductor where they travel as quasi-particles. Typically, the heat is moved and work is done to deposit hot quasi-particles into a normal-metal quasi-particle trap for rejection to the next refrigeration stage. Realizing that (1) the quasi-particles flow diffusively, driven by a concentration gradient in the electric field-free superconductor, and (2) that the undesirable backwards leaking of heat from the hot-side trap can be reduced by engineering the geometry and materials at the superconductor-to-trap interface, enhanced cooling can be achieved. Fabrication of the refrigerator was accomplished using a tungsten and titanium-tungsten alloy as the cold-side normal-metal, aluminum oxide as the insulator, aluminum as the superconductor, and gold as the trap, with the cold-side NIS portion being attached to the hot-side gold trap by bump bonding. The refrigerator consisted of 1121 junction pairs, each pair being an SINIS unit, all electrically connected in series. Using this we have measured the effective phonon temperature of a 3.9 mm x 3.9 mm x 0.65 mm silicon chip driven down to 70 mK from a bath temperature of 120 mK, and down to 174 mK from a 271 mK rejection temperature (a cooling of -97 mK). This is the first demonstration of the sub 1 K cooling of an entire silicon chip using NIS junctions.
