60% magnetoresistance at room temperature in Co–Fe/Al–O/Co–Fe tunnel junctions oxidized with Kr–O2 plasma

Abstract

The influence of the mixed inert gas species for plasma oxidization process of a metallic Al layer on the tunnel magnetoresistance (TMR) was investigated for a magnetic tunnel junction (MTJ), Ta 50 Å/Cu 200 Å/Ta 200 Å/Ni–Fe 50 Å/Cu 50 Å/Mn75Ir25 100 Å/Co70Fe30 25 Å/Al–O/Co70Fe30 25 Å/Ni–Fe 100 Å/Cu 200 Å/Ta 50 Å. Using Kr–O2 plasma, a 58.8% of TMR ratio was obtained at room temperature after annealing the junction at 300 °C, while the achieved TMR ratio of the MTJ fabricated with usual Ar–O2 plasma remained 48.6%. A faster oxidization rate of the Al layer by using Kr–O2 plasma is a possible cause to prevent the over oxidization of the Al layer, which depolarizes the surface of the underlaid ferromagnetic electrode, and to realize a large magnetoresistance.

Magnetization process and domains in MTJ

“…The structure of investigated MTJs was composed of buffer layers Ta(5)/Cu(10)/Ta(5)/Ni 80 Fe 20 (2)/Cu(5), antiferromagnetic (AF) layer of Ir 25 Mn 75 (10), ferromagnetic "pinned" (FP) layer of Co 70 Fe 30 (2.5), insulator spacer Al-O x (1.5), "free" ferromagnetic (FF) layer of Co 70 Fe 30 (2.5)/Ni 80 Fe 20 (t) (where t = 10, 30 and 100 nm) and capping layer of Ta (5). The bilayer composition of CoFe(2.5) and NiFe (10) of soft electrodes allows to obtain high TMR ratio (>50%) and low coercivity [1]. The range of NiFe thickness t was chosen so as to observe the domain structure within the FF layer only.…”

“…2 Experiment MTJs were deposited in magnetic field 2.4 kA/m on thermally oxidized Si(100) wafers using DC magnetron sputtering with ultra clean Ar(9N) as the process gas, in a chamber with base pressure of 4 × 10 -9 hPa (for details see [1]). The 10 mm diameter samples were annealed in vacuum at 300 °C for 1 h in the external magnetic field of 80 kA/m, followed by field cooling.…”

Quantum theory of tunneling magnetoresistance in GaMnAs/GaAs/GaMnAs heterostructures

“…For such structures, much efforts have been made to increase the TMR ratio, which can be defined by the relative change in the current densities. Recently, a large TMR ratio as much as 60% has been reported in Co-Fe/Al-O/Co-Fe junctions [6] which opened a new era of technical applications of the tunnel junctions.…”

Tunnel barrier fabrication on Si and its impact on a spin transistor

“…Both of these tunnel barriers have been shown to spin inject with TMRs greater than 50% for Al 2 O 3 and 40% for ZrO 2 or Al 2 O 3 /ZrO 2 mixtures [6][7][8].…”