A fully operational 1-kbit variable threshold Josephson RAM

A 1-kb Josephson RAM chip in which all bits are operational has been demonstrated. The chip employs a new Josephson memory cell called the variable threshold memory cell. The cell has a simple structure and a wide operating margin. A directly coupled logic circuit has been introduced to drive a memory cell array instead of a superconducting loop circuit as used in previous Josephson RAM chips The directly coupled logic circuit using 4JL (four Josephson-junction logic) gates is superior because it applies a well-defined driving current to the memory cells. As a result, a fully operational Josephson RAM is realized. Experimental results on this RAM are presented