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A 380 ps, 9.5 mW Josephson 4-Kbit RAM operated at a high bit yield

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4 Author(s)
Nagasawa, S. ; NEC Corp., Tsukuba, Japan ; Hashimoto, Y. ; Numata, H. ; Tahara, S.

We have developed a Josephson 4-Kbit RAM with improved component circuits and a device structure having two Nb wiring layers. A resistor coupled driver and sense circuit are improved to have wide operating margins. The fabrication process is simplified using bias sputtering, as a result, its reliability is increased. The RAM is composed of approximately 21000 Nb/AlO/sub x//Nb Josephson junctions, Mo resistors, Nb wirings, and SiO/sub 2/ insulators. Experimental results show a minimum access time of 380 ps and power dissipation of 9.5 mW. Maximum bit yield of 84% is obtained in minimum magnetic field of about 20 /spl mu/G. We confirm that most of fail bits are caused by trapped magnetic flux, and the RAM functions properly for 98% of the memory cells after measuring fail bit map several times.<>

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Applied Superconductivity, IEEE Transactions on  (Volume:5 ,  Issue: 2 )