Nb-AlOx-Nb SNAP Technology for 125 mm Wafers Developed in Partnership with Silicon Technology

Superconducting circuits based upon the Rapid Single Flux Quantum (RSFQ) Logic are an interesting approach for future digital electronics with clock frequencies in the range of 100 GHz. Our intention is to increase the integration density of such circuits. Therefore we have successfully fabricated and tested an RSFQ-circuit based on a new kind of stacked three terminal device, henceforth called a "Stacktron". A Stacktron consists of two vertically arranged all-niobium tunnel junctions, each separately shunted by a thin film resistor, and an access to the intermediate niobium layer. An RSFQ frequency divider (TFlip-Flop) including two Stacktrons has been tested up to 20GHz. As a shunt resistor we used Pd/Au, so that p, e 1 and the I-V-curve is nonhysteretic. The junctions showed a current density of approximately 250 A/cmz. The IcR,-product was 100 pV. These first steps toward a three dimensional (3D) RSFQ architecture will be discussed in the framework of highly integrated and complex RSFQ-circuits.

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Experimental realization of a 3D integrated RSFQ T-flip-flop using stacktrons

Ruck

Schmitz

Thyssen

et al. 1999

IEEE Trans. Appl. Supercond.

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Improved critical-current-density uniformity by using anodization

Nakada

Berggren

Macedo

et al. 2003

IEEE Trans. Appl. Supercond.

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We discuss an anodization technique for a Nb superconductive-electronics-fabrication process that results in an improvement in critical-current-density uniformity across a 150-mm-diameter wafer. We outline the anodization process and describe the metrology techniques used to determine the NbO thickness grown. In the work described, we performed critical current measurements on Josephson junctions distributed across a wafer. We then compared the uniformity of pairs of wafers, fabricated together, differing only in the presence or absence of the anodization step. The cross-wafer standard deviation of was typically 5% for anodized wafers but 15% for unanodized wafers. This difference in uniformity is suggestive of an in-process modification from an unknown cause that is blocked by the anodic oxide. It is interesting that small junctions do not see an improvement in uniformity-apparently the anodization improves only the uniformity and not the variation in junction size. Control of is important for all applications of superconductive electronics including quantum computation and rapid single-flux quantum (RSFQ) circuitry.

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Nb-AlOx-Nb SNAP Technology for 125 mm Wafers Developed in Partnership with Silicon Technology

Cited by 2 publications

References 5 publications

Experimental realization of a 3D integrated RSFQ T-flip-flop using stacktrons

Experimental realization of a 3D integrated RSFQ T-flip-flop using stacktrons

Improved critical-current-density uniformity by using anodization

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