Fundamental criteria for the design of high-performance Josephson nondestructive readout random access memory cells and experimental confirmation

Fundamental design criteria for Josephson nondestructive readout random access memory (NDRO RAM) cells are presented, within the context of an LSI array environment. Emphasis is placed upon principles which are relevant to high performance. The criteria are elucidated via a specific design which is simulated and then experimentally evaluated in a technology with a smallest critical dimension of 5 μm. The specific cell differs from previously tested Josephson NDRO cells in several respects; namely, the cell stores only approx.8Phi0, employs interferometer gates and an external damping resistor, allows switching into device resonances, and eliminates the need for a special initialization cycle. The cell-selection scheme, employing triple coincidence, results in larger operating margins and smaller operating currents than have previously been achieved. The large operating margins and all basic cell design criteria were experimentally verified. The experimental interferometer gate characteristics were analyzed in detail and found to be describable by simple models. In addition, it was discovered that single flux quantum transitions in the interferometer gates could be exploited beneficially in order to enhance the insensitivity of operating margins to fabrication tolerances