Title :
A 380 ps, 9.5 mW Josephson 4-Kbit RAM operated at a high bit yield
Author :
Nagasawa, S. ; Hashimoto, Y. ; Numata, H. ; Tahara, S.
Author_Institution :
NEC Corp., Tsukuba, Japan
fDate :
6/1/1995 12:00:00 AM
Abstract :
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.<>
Keywords :
random-access storage; superconducting device reliability; superconducting memory circuits; 20 muG; 380 ps; 4 Kbit; 9.5 mW; Mo; Mo resistors; Nb; Nb wirings; Nb-AlO-Nb; Nb/AlO/sub x//Nb Josephson junctions; RAM; SiO/sub 2/; SiO/sub 2/ insulators; access time; bias sputtering; bit yield; fabrication; fail bit map; magnetic field; memory cells; power dissipation; reliability; resistor coupled driver; sense circuit; trapped magnetic flux; Coupling circuits; Driver circuits; Fabrication; Josephson junctions; Magnetic field measurement; Niobium; Read-write memory; Resistors; Sputtering; Wiring;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
