Read-Cycle Endurance of Magnetic Random Access Memory Elements

The read-cycle endurance of a magnetic tunneling junction (MTJ) has been investigated, focusing on the spin-dependent tunneling current at high temperatures. The MTJ structure used in this study consisted of Ta-NiFe-CoFe-AlOx-CoFe-IrMn-NiFe-Ta prepared on a thermally oxidized Si wafer. Both the tunneling current and tunneling magnetoresistance ratio showed no significant degradation during the 1E9 read-cycle test using unipolar voltage pulses of 0.5 V at room temperature. Temperature dependence of the MTJs resistance calculated from the measured tunneling current has also been examined in a temperature range from room temperature to 175/spl deg/C. Furthermore, in the case of read-cycle tests for thermally stressed MTJs, the variation of the tunneling current was less than 2% after 1E9 cycles at a stress temperature of 175/spl deg/C. This indicates that MTJs have sufficient read-cycle endurance under high-temperature operation.