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Direction detection of a magnetic field by spin-valve-type magnetic tunnel junction (MTJ) has been investigated at temperatures ranging from room to 150/spl deg/C, concentrating on the magnetic property of the pinned layer. Angular dependencies of resistance curves show that detection errors from cosine curve increase with rising temperatures in MTJ with the IrMn/CoFe pinned layer. Measurements of the magnetization curves of the pinned layer found that detection errors are caused by rotation of the pinned layer magnetization. Direction detection of a magnetic field by MTJ with a IrMn/CoFe/Ru/CoFe of synthetic antiferromagnetic (SyAF) pinned layer, in which magnetizations of two CoFe layers nearly cancel each other, was also investigated. We confirmed that the pinned layer of SyAF structure in MTJ effectively reduces the dependence of detection errors on temperature.

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.

We have experimentally investigated a method of controlling the magnetization direction of a CoFe pinned layer in a spin-valve-type magnetic tunnel junction (MTJ) with an IrMn layer. Arbitrary control of the direction of the pinned layer magnetization was performed by a postannealing process in conditions above the blocking temperature of IrMn and in a magnetic field to saturate the magnetization of the pinned layer. The results show that it is possible to control and to uniformly rearrange the direction of the pinned layer magnetization in MTJs with a postannealing process in the magnetic random access memories manufacturing process.