  We developed a cryogenic temperature deposition process for high-performance
CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on 300 mm thermally oxidized
silicon wafers. The effect of the deposition temperature of the CoFeB layers on
the nanostructure, magnetic and magneto-transport properties of the MTJs were
investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a
perpendicular magnetic anisotropy (PMA) of 214 uJ/m2 and a voltage-controlled
magnetic anisotropy (VCMA) coefficient of -45 fJ/Vm, corresponding to 1.4- and
1.7-fold enhancements in PMA and VCMA, respectively, compared to the case of
room-temperature deposition of CoFeB. The improvement in the MTJ properties was
not simply due to the morphology of the MTJ films. The interface-sensitive
magneto-transport properties indicated that interfacial qualities such as
intermixing and oxidation states at the MgO/CoFeB interfaces were improved by
the cryogenic temperature deposition. Cryogenic-temperature sputtering
deposition is expected to be a standard manufacturing process for
next-generation magnetoresistive random-access memory.
