Nb/Al-AlOx/Nb约瑟夫森结薄膜沉积研究

Nb/Al-AlO_x/Nb约瑟夫森结构成的低温超导器件有着广泛应用，高质量的S-I-S约瑟夫森结制备的关键之一在于制备高质量的三层膜。三层膜的质量可由许多属性参数影响，比如剩余电阻比R.R.R、超导转变温度T_c、表面粗糙度、应力、铝膜厚度等等。通过对薄膜的溅射沉积条件与上述参数进行分析研究，确定最佳的生长条件。调节不同的氧化工艺条件，可以获得约瑟夫森结的不同临界电流密度。     

10V约瑟夫森结阵电压基准

在 1V约瑟夫森结阵电压基准的基础上 ,10 V约瑟夫森结阵电压基准于 1999年底在中国计量科学研究院量子部电压实验室建立。其校准电压在 0 .1V～ 10 V范围内连续可调。校准固态电压标准 10 V输出值的合成不确定度为 5.4× 10 -9(1σ)     

10伏约瑟夫森结阵电压基准获国家科技进步奖

我院研制的“10伏约瑟夫森结阵电压基准”装置,荣获2 0 0 3年度国家科技进步奖二等奖。10伏约瑟夫森结阵电压基准是量子基准。1990年1月1日,国际计量委员会推荐用约瑟夫森效应复现电压单位量值,以保证国际范围内溯源的一致性。美、德、法、日等发达国家相继建立了1伏及10伏的约瑟夫森电压基准。我院1994年研制出1伏约瑟夫森结阵电压基准,1996年由世行贷款立项,建立10伏约瑟夫森结阵电压基准课题,于1999年研制成功,该装置系统的测量不确定度为5 4×10 - 9,达到了国际先进水平。10伏约瑟夫森结阵电压基准利用低温超导结电子跃迁效应复现电压…     

交流约瑟夫森电压合成装置的研究

设计制作了一套交流约瑟夫森电压合成装置(JAWS),能够驱动1 V SINIS型可编程约瑟夫森结阵合成峰值1.2 V、 200 Hz以下频率的交流量子电压。实验结果表明,该装置能够合成200 Hz以下频率的交流量子电压,且合成60 Hz交流电压的不确定度优于5×10^-6,为进一步开展我国首个交流量子电压基准的研究工作奠定了基础。     

10伏约瑟夫森结阵电压基准获国家科技进步奖

我院研制的“10伏约瑟夫森结阵电压基准”装置，荣获2003年度国家科技进步奖二等奖。     

计量院电压基准装置获国家科技进步奖

本刊讯中国计量科学研究院研制的“10伏约瑟夫森结阵电压基准”装置,荣获2003年度国家科技进步奖二等奖。10伏约瑟夫森结阵电压基准是量子基准,该基准利用低温超导结电子跃迁效应复现电压量值,可在很宽范围内复现高精度的电压量值。该装置的创新在于,硬件方面较好地解决了微波源,同时满足了结阵特性、输出功率、锁相环路三方面对微波频率的要求,在软件方面采用了数据处理技术,消除了10伏结阵电压阶数不稳定而对测量数据造成的影响,对提高测量效率及改善不确定度有着重要意义。计量院建立的10伏约瑟夫森电压基准,按照国际计量委员会的推荐用…     

中国计量科学研究院与国际计量局约瑟夫森电压基准之间的直接和间…

１９９５年１１月３－１０日，中国计量科学研究院的１Ｖ约瑟夫森结阵电压基准与国际计量局的１Ｖ约瑟夫森结阵电压基准之间进行了直接比对，比对在中国计量科学院研究进行，比对结果的综合不确定度为：实际测量标准电池的比对结果。     

新一代电压计量基准

新一代电压计量基准由中国测试技术研究院和中国计量科学研究院联合研制的“超导约瑟夫森结阵列１伏电压基准”采用了超导体的约瑟夫森效应和微波辐射感应阶梯技术，通过电子电荷等基本物理常数，把电压测量和国家原子频率基准联系起来。综合了超导、微波、电测量等多种学...     

约瑟夫森结Nb电极的实验研究

通过溅射Nb膜张力与氩（Ar）压强的关系，超导转变温度Tc，室温阻扰与液氮温度阻抗比RRT／RLN2，沉积中Ar浓度CAr与负偏压关系的测量和扫描电子显微镜的观察分析，对约瑟夫森结Nb电极作了研究。发现Ar压强在1．1Pa时，Nb膜呈现无应力状态；低负偏压下沉积的Nb膜晶粒结构是由致密膜到圆柱状。在偏压Ub＝－50V时，获得表面致密均匀、晶粒结构合适的Nb膜。对Nb膜用阳极氧化电压谱图（AVS）分析，证实沉积的Nb膜内不存在氧化物、寄生结和分层界面。     

1V及10V约瑟夫森结阵电压标准

为建立国家法定电压基准,中国计量科学研究院(NIM)对1-V和10-V约瑟夫森串联结阵电压标准进行了研究。其中结阵分别是由德国的PTB,日本的ETL,美国的NIST和韩国的KRISS提供的。采用的微波源是一个锁定到10MH_z频率标准上的高稳定高功率的85GH_z的G_aA_s耿氏管振荡器。所获得的1_v和10-V电压的总不确定度分别是9E-9和6E-9。     

A new 10-V array of Josephson junctions based on low-frequencydesigns scaled up to 94 GHz

A novel approach is described for the design of improved coupling of millimeter-waves in a 10-V array of Josephson junctions. In this approach, microwave structures were fabricated and tested in the range 2.8 GHz to 3.6 GHz, and a scaling calculation was then used to transform them to 94 GHz. By optimizing the trade-off between antenna size and efficiency, it was possible to make more space available on the device chip to increase the number of Josephson junctions. Simulation results showed that the optimal antenna is a short double-fin-line type. This antenna type allowed us to fabricate a Josephson junction array that had 25944 Nb/Al-AlO_x/Nb junctions. For this new array, zero-crossing steps were observed up to 18.5 V. The new array was then successfully used to calibrate a Zener voltage standard that had a 10-V output     

Y-Ba-Cu-O/Nb Josephson tunnel junctions

The authors fabricated Y-Ba-Cu-O/Au/AlO_x/Nb and Y-Ba-Cu-O/AlO_x/Nb Josephson tunnel junctions using electron-beam evaporation of Al and Nb films and natural oxidation. Sintered Y-Ba-Cu-O was used as the base electrode. Superconducting Josephson current and hysteresis of the current-voltage characteristics, which are typical features of Josephson tunnel junctions, have been observed at 4.2 K. RF-induced voltage steps at a voltage greater than 0.4 mV have been clearly observed, and RF-induced subharmonic steps have also appeared. The superconducting Josephson current was modulated by the magnetic field     

Direct comparison of two independent Josephson voltage standards at1 V and precision measurements up to 10 V

Two Josephson voltage standards have been compared using a room-temperature electronic nanovoltmeter with a peak-to-peak noise of about 2 nV at the 1-V level corresponding to a RMS uncertainty of 4×10^-10. The excellent stability in maintaining the desired voltage steps makes it possible to obtain recorder traces comparing Nb/Al₂O₃/Nb Josephson standards with Weston cells and Zener reference standards at 1 V and 10 V. At 10 V the best result shows a peak-to-peak noise of 250 nV corresponding to a RMS uncertainty of 5×10^-9 for a Zener reference and 50 nV corresponding to 1×10^-9 for a series connection of nine Weston cells. As an example for the application of the Josephson standard as a potentiometer the deviation in the linearity of a digital voltmeter is confirmed to be on the order of 0.1 p.p.m. in the range from -10 V to +10 V     

Upscaling DC resistance using a Josephson junction array

A ratio standard for DC resistance measurements in the range above about 10 kΩ using a three-terminal Josephson junction series array is described. Resistance ratios of two-terminal resistors from 1:1 to at least 1:10 are examined with a single device utilizing the voltage steps of the Josephson array as voltage sources of a potentiometer bridge configuration. Some features of the circuit are discussed. The system promises systematic ratio errors below 10^-8 and uncertainties which depend only on the quality of the resistors. Preliminary measurements with a prototype instrument show a relative reproducibility of 1×10^-7, limited by the noise of a commercial digital multimeter used as a detector     

Magnetic field effect on the escape rate in Nb/AlOx/Nb josephson junctions

We studied the escape rate of Nb/AlO_x/Nb Josephson junctions in zero and finite magnetic fields. The escape rate was determined from the distribution of the critical currents and the experimental data were fit to the theoretical model to determine effective temperatures, which govern the thermal activation over the energy barrier. The effective temperatures were found to depend strongly on the magnetic-field modulated critical current. We discuss a possible cause for the magnetic field dependence of the escape rate in terms of non-uniform current distribution in the junctions.     

First Direct Comparison of a Cryocooler-Based Josephson Voltage Standard System at 10 V

A commercially available and fully automated 10-V Josephson voltage standard system with a liquid helium free cooling has been developed as a result of the cooperation between the Institute of Photonic Technology and Supracon AG, both in Jena, Germany. The system operates with an array of 19 700 superconductor–insulator–superconductor Josephson tunnel junctions installed in a pulse tube cooler. A stable operation is achieved by the proper integration of the voltage standard circuit to the cold stage of the cryocooler. Different operation setups are discussed. A direct comparison of a cryocooler-based Josephson voltage standard system versus a liquid-helium-based system was performed at a voltage level of 10 V. We obtained a voltage difference of 1.3 nV with a total combined uncertainty of 2 nV. This corresponds to a relative uncertainty of $2 times 10^{-10}$.      

A Josephson-array calculable-waveform generator

This paper proposes a new method for using a Josephson array to create a voltage waveform with a root-mean-square value calculable to better than 2 in 10⁶ at frequencies below 50 Hz. A novel method of reliably switching the dc voltage from one known voltage step to another at precisely defined time intervals is investigated. In this method, transients in the microwave voltage driving the array are used to induce switching between steps. We consider two possible implementations of this concept. The first is for an array similar to that used in conventional dc voltage standards. The second uses the binary sequence of individually biased arrays introduced by Hamilton et al [1995]. Computer simulation and theoretical analysis are used to demonstrate that the uncertainties in switching times are potentially limited only by the speed of the available microwave attenuators, which is currently of the order of a nanosecond     

Josephson semiconductor interface circuit

This paper describes an output interface circuit which allows Josephson circuits to communicate with semiconductor circuits. The circuit combines Josephson and GaAs drivers to drive a 50 μ load at a signal level of semiconductor circuits. The output voltage of 2.8 mV (usual for Josephson gates using Nb/AlO_x/Nb junctions) was increased to 1.7 V. The interface circuit has been operated up to 800 MHz.