Reliability Analysis of Several Conductors at High Current Densities for use in Bubble Memories

Abstract

Magnetic bubble memories have recently. emerged as production products and are being considered for various applications where non-volatility, modularity and ruggedness are desirable. In order to reduce manufacturing costs, densities have been pushed to the 106 bit/cm2 level with further increases being paced mainly by lithography constraints. Bubble memories require magnetic fields generated by current pulses for various functions such as bubble generation, transfer-in, transfer-out and replication. Among the above-mentioned functions, bubble generation and replication require current amplitudes in the. range of 80mA to 200mA for conductors on the order of 4000 Å in thickness with widths of 2-3¿m. These conditions correspond to current densities of 5 × 106 to 2 × 107A/cm2. As the density of bubble devices increases, the current carrying capacity requirements of the conductors will also increase. Among the prominent causes of failure in conductors carrying high current densities are electromigration and melting due to Joule heating. An associated large temperature rise, due to localized Joule heating, may also give rise to metallurgical reactions in a multimetal metallization,. or chemical reactions with the passivation layer or atmosphere. The major constraint in selecting a conductor system is dictated by the desirability of operating device functions with industrial standards of 5 and 12-volt power supplies. This constraint limits potential metallizations to systems with conductivities better than the Al-4% oCu alloy system. Therefore, conductor choices are limited to Cu, Ag, Au and Al based systems.