Life Expectancy of Plated Wire Memories

Abstract

The life expectancy of DRO-plated wires was studied from various aspects by using an accelerated aging technique. Theoretical predictions regarding annealing processes were made by considering a structural defect model which assumes fixed and rotatable components of anisotropy with different activation energies. The predictions were verified experimentally under various annealing conditions. An extrapolation method to estimate the lifetime at operating temperature was established by adopting the Arrhenius equation. Activation energies were determined by using the rate of decay of output voltage under a worst-case DRO memory test as a criterion. Three activation energies were evaluated: (1) 1.3 eV for the zero applied field case, (2) 2.4 eV for a 36 Oe hard-axis field applied, and (3) 0.8 eV for fringing fields off the ends of a solenoid applying the 36-Oe hard-axis fields. The shelf life was extrapolated to be 2×106 years at 40°C. The dynamic test evaluated the lifetime under environmental conditions using a 256-bit experimental plane which was exercised, sensed, and data recorded at 150°C and the memory lifetime at operating temperature was determined by extrapolating the above results using the lowest activation energy projection. Therefore, memory working lifetime in DRO mode is estimated to be >100 years at 50°C with no dropouts, and >350 years at 50°C with a 5% dropout occurrence.