Quantized voltage steps in arrays of stacked Josephson junctions demonstrated. (News Briefs).For these standards many junctions must be tightly packed into a size smaller than a quarter wavelength of the microwave drive frequency. This ensures that all the junctions see nearly the same microwave power. For ac and dc programmable voltage standards, lumped arrays will enable increased output voltage, increased bandwidth, increased operating margins Operating Margin A ratio used to measure a company's pricing strategy and operating efficiency. Calculated by: , and lower power operation. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researchers have measured the first constant voltage steps in stacked Ti-barrier Josephson junctions An ultra-fast switching technology that uses superconductor materials, originally conceived by Brian Josephson. Circuits are immersed in liquid helium to obtain near-absolute zero degrees required for operation. Switching takes place in a few picoseconds. . This is a significant milestone toward creating lumped arrays of Josephson junctions for ac voltage standards. One thousand double-junction stacks, for a total of 2000 series-connected junctions, were fabricated fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: . The 40 nm titanium barriers are separated by only 50 nm of niobium niobium (nīō`bēəm), metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.9064; m.p. about 2,468°C;; b.p. 4,742°C;; sp. gr. 8.57 at 20°C;; valence +2, +3, +4, or +5. . When a 16 GHz microwave bias was applied, a constant voltage step was measured at the expected quantized quan·tize tr.v. quan·tized, quan·tiz·ing, quan·tiz·es Physics 1. To limit the possible values of (a magnitude or quantity) to a discrete set of values by quantum mechanical rules. 2. value of 66.17 mV. The voltage of the step was constant over a 3.5 mA current range which is more than sufficient for operation as a programmable voltage standard array. This observation of constant voltage steps demonstrates that the stacked junctions are sufficiently uniform for application in voltage standard circuits. For each increase in the number of junctions per stack, an improvement in operating margins is expected. Adding a third and fourth junction to each stack will be the next step toward the goal of fabricating and observing steps in 50-junction stacks in order to create a 2 mm long lumped array with 50 [omega] impedance. CONTACT: Sam Benz, (303) 497-5258; benz@boulder.nist.gov. |
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