**6. Conclusions**

138 Modern Metrology Concerns

AB

0,2 0,4 0,6 0,8 1,0 -2,0

Fig. 11. Normalized temperature derivative of the critical supercurrent calculated for conventional SIS (the AB curve) and SNS (the curve KO) junctions and the SNIS devices

Fig. 12. Voltage step at 1.25 V measured at T = 6.3 K on a binary-divided array of 8192 JJ.

Of course when using more complex circuits, as the programmable arrays described above, non-uniformities in the fabrication and in the distribution of the microwave signal reduce

The inset shows detail of the quantized step, 0.25 mA wide.

the maximum temperature, especially if the device is operated in gas.

with eff = 2, 10, and 20 (dashed, dashed-dotted, and dotted lines respectively).

*T*/*T* c KO


d(*I*

c(*T*)/*I*

c(0)/d*(T/T*c

*)*



0,0

The extension of DC Josephson Voltage standard to AC has led to the development of different type of circuits, according to the specific application, which have been analyzed in section 2.

In section 3 a comparison of different types of overdamped junctions developed for the large circuits needed by the AC extension of Josephson voltage standard has shown advantages and disadvantages of a certain electrode configuration or material. In order to achieve the desired noise immunity of the quantized voltage levels, the junctions must maximize both *J*c and *V*c this last issue being also useful for applications where the highest speed of the Josephson circuits is expected. And these issues must be attained using a tolerable degree of technological effort, also in terms of allowable integration. In fact, in order to have a widespread development in the world laboratories for these circuits, neither the number of junctions should be increased nor the size reduced beyond a certain limit. All together, these issues are not solved by any of the junctions reported in this analysis, even if some of the described technologies had achieved sound results.

In section 4 future developments of these circuits have been considered with attention to the problems to be solved.

Waiting for a further development of superconductive junction technology integration, and the use of high temperature materials, the employ of high characteristic voltage junctions is presented as a possible route for extending the performances and applications of Josephson voltage standard not only in fundamental metrology but also for laboratory instrumentation.

### **7. References**


[8] C.J. Burroughs, S.P. Benz, P.D. Dresselhaus, B.C. Waltrip, T.L. Nelson, Y. Chong, J.M.

[9] H. Yamamori, T. Yamada, H. Sasaki, and A. Shoji. A 10 V programmable Josephson

[10] J. Kohlmann, R. Behr, and T. Funck. Josephson voltage standards. *Measurement Science* 

[13] J-H. Kim A. Sosso. Phase lock of non-hysteretic Josephson junctions with pulse bias: analytical properties, *Phil. Mag. Part B*, 1463-6417, 80, 5, 973 – 977 (2000). [14] S.P. Benz and C.A. Hamilton. A pulse-driven programmable Josephson voltage

[15] S.P. Benz, C.A. Hamilton, C.J. Burroughs, and T.E. Harvey. AC and DC bipolar voltage standard using quantized pulses. *IEEE Trans. Instrum. Meas*, 48:266–269, 1999. [16] J. Kohlmann, O.F. Kieler, R. Iuzzolino, J. Lee, R. Behr, B. Egeling, and F. Muller.

[17] S.P. Benz. Synthesizing accurate voltages with superconducting quantum-based

[18] A.S. Katkov, A.M. Klushin, G.P. Telitchenko, R. Behr, and J. Niemeyer. Challenges of

standards, *IEEE Instrum. Magaz.*, vol.13, no.3, pp.8-13, June 2010.

modulation. *IEEE Trans. Appl. Supercond.*, 15(2 Part 1):352–355, 2005. [19] H.J.M. Ter Brake, F.I. Buchholz, G. Burnell, T. Claeson, D. Crété, P. Febvre, GJ Gerritsma, H.

*Superconductivity, IEEE Transactions on*, 1(1):3–28, Mar 1991.

97, page 012161. Institute of Physics Publishing, 2008.

25:1432–1435, March 1989.

*Technology*, 13(5):546–550, 2000.

*Applied Physics* , 57(3): 875-889, 1985.

*Phys.,* 78, 9, (1995).

Development and investigation of SNS Josephson arrays for the Josephson arbitrary waveform synthesizer. *IEEE Trans. Instr. Meas.*, 58(4):797–802, April 2009.

Josephson junction arrays for AC voltage generation by microwave pulse power

Hilgenkamp, R. Humphreys, Z. Ivanov, et al. SCENET roadmap for superconductor digital electronics. *Physica C: Superconductivity and its applications*, 439(1):1–41, 2006. [20] V.K. Semenov. Digital to analog conversion based on processing of the SFQ pulses. *IEEE Transactions on Applied Superconductivity*, 3(1 Part 4):2637–2640, 1993. [21] K.K. Likharev and V.K. Semenov. RSFQ logic/memory family: a new Josephson-

junction technology for sub-Teraherz-clock-frequency digital systems. *Applied* 

synchronization in Josephson junction arrays. *IEEE Transactions on Magnetics*,

converter for AC voltage standard. In *Journal of Physics: Conference Series*, volume

[22] V. K. Semenov and M. A. Voronova. DC voltage multipliers - A novel application of

[23] C.A. Hamilton. Josephson voltage standard based on single-flux-quantum voltage multipliers. *IEEE Transactions on Applied Superconductivity*, 2(3):139–142, 1992. [24] M. Maezawa and F. Hirayama. 10-bit rapid single flux quantum digital-to-analog

[25] J. Niemeyer. Josephson arrays for DC and AC metrology. *Superconductor Science &* 

[26] R.L. Kautz, Shapiro steps in large-area metallic-barrier Josephson junctions, *J. Appl.* 

[27] R.L. Kautz, R. Monaco, Survey of chaos in the rf‐biased Josephson junction, *Journal of* 

[11] R. Monaco. Enhanced AC Josephson effect. *Journal of Applied Physics*, 68:679, 1990. [12] J-H. Kim A. Sosso, A.F. Clark Dynamics of overdamped Josephson junctions driven by

*Instr. Meas.*, 56(2):289, 2007.

*Science and Technology*, 21(10):105007, 2008.

a square-wave pulse, *JAP,* 83,6, 3225-3232 (1998).

standard, *Applied Physics Letters*, 68:3171, 1996.

*and Technology*, 14(8):1216–1228, 2003.

Williams, D. Henderson, P. Patel, L. Palafox, et al. Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards. *IEEE Trans.* 

voltage standard circuit with a maximum output voltage of 20 V. *Superconductor* 

