High-temperature operations of rotation angle sensors with spin-valve-type magnetic tunnel junctions

Direction detection of a magnetic field by spin-valve-type magnetic tunnel junction (MTJ) has been investigated at temperatures ranging from room to 150°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.