Cryogenic Temperature Deposition of High-Performance CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on ϕ300 mm Wafers

Abstract

We developed a cryogenic temperature deposition process for high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on ϕ300 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 was investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a perpendicular magnetic anisotropy (PMA) of 214 μJ/m 2 and a voltage-controlled magnetic anisotropy (VCMA) coefficient of −45 fJ/V m, 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. A cryogenic temperature sputtering deposition is expected to be a standard manufacturing process for next-generation magnetoresistive randomaccess memory.

Large voltage-controlled magnetic anisotropy effect in magnetic tunnel junctions prepared by deposition at cryogenic temperatures

“…Making a comparison between different deposition temperatures, PMA for CoFeB deposited at RT exhibits a little higher PMA compared to that deposited at −173 ○ C. This tendency is opposite to that observed in the ultrathin CoFeB layer deposited on MgO reported in our previous work. 38…”

“…In our recent work, cryogenic temperature deposition was found to be effective for improving the PMA, TMR, VCMA, and magnetic damping properties of a top free ultrathin CoFeB layer deposited on a MgO tunneling barrier on account of the less-intermixed interface. 38,39 In this experiment, we adopted cryogenic temperature (−173 ○ C) deposition for the CoFeB bottom free layer, the CoFe termination layer, and the top CoFeB reference layer (see Fig. 1).…”

“…In our previous work, the low temperature deposition process was effective in reducing intermixing rather than improving the morphology when an ultrathin CoFeB layer was deposited on MgO. 38 Since the magnetic dead layer thickness of the RT-deposited CoFeB layer is a little larger (0.32 ± 0.03 nm) than that of the −173 ○ C-deposited one (0.28 ± 0.04 nm), we may obtain a lessintermixed interface even when growing CoFeB on a TaB buffer. To examine the effect of this on the VCMA properties, atomic scale chemical analysis, such as that provided by an atom probe method, 40 is required for future work.…”