Accurate measurement of small currents using a CCC with DC SQUID readout


Rietveld, G. and Hiddink, M.G.H. and Bartolomé, E. and Flokstra, J. and Sesé, J. and Camón, A. and Rillo, C. (2000) Accurate measurement of small currents using a CCC with DC SQUID readout. Sensors and actuators A: Physical, 85 (1-3). pp. 54-59. ISSN 0924-4247

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Abstract:The continuous miniaturisation in the semiconductor industry increases the importance of accurate measurement and control of very small currents. In the field of precision electrical measurements, cryogenic current comparators (CCCs) are used as extremely sensitive and accurate instruments for scaling currents. In an international co-operation project, a special CCC system is being developed, optimised for the measurement of extremely small currents to less than 1 pA (10−12 A). DC superconducting quantum interference device (SQUID) readout is used for monitoring the ampere-turn unbalance of the CCC. In this paper, we report on the accurate determination of the CCC and SQUID input coil inductances. Matching of these inductances is required for obtaining ultimate current resolution with the CCC. We find very good agreement between measurements of the CCC inductance at room temperature and at 4.2 K, and results from numerical calculations. The measured values for the input and mutual inductance of the SQUID sensor are in good agreement with the design values when the effect of the slit in the SQUID washer is correctly taken into account. Final current resolution of our measurement system is expected to be better than 1×10−15 A/√Hz for a CCC with 20,000 primary windings.
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Copyright:© 2000 Elsevier
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