Presentation Information
[7p-P03-39]A Comparison of Electrical 1/f Noise in Magnetic Tunnel Junctions with MgO and Mg-Al-O Barriers
Shintarou Nii1, 〇Chaoliang Zhang1, Haoxiang He1, Yupeng Wang1, Takayuki Hojo1, Takafumi Nakano1,2, Mikihiko Oogane1,3 (1.Department of Applied Physics, Tohoku Univ., 2.Green X-tech, Tohoku Univ., 3.CSIS, Tohoku Univ.)
Keywords:
TMR sensor
The biomedical applications of Magnetic tunnel junction (MTJ)-based tunnel magnetoresistance (TMR) sensors involve sensing magnetic fields in the sub-100 Hz frequency range, where electrical 1/f noise becomes a limiting factor. This noise originates from charge trapping/detrapping at the tunnel barrier or its interfaces. Although MgO is widely used, its lattice mismatch with Fe-based electrodes often introduces interfacial defects. In contrast, magnesium aluminum oxide (MAO) offers a better lattice match to Fe, making it a potential alternative. Although previous studies have focused on the TMR properties, detailed comparison of their 1/f noise is still required. Here we perform a direct comparison of the electrical 1/f noise characteristics of MgO- and MAO-based MTJs.
The MTJ stacks are MgO(001) substrate/Cr(60)/Fe(50)/Mg(0.2)/MgO or MAO(2)/Fe(5)/IrMn(10)/Cr(5) (thickness in nm). MgO or MAO are deposited via electron beam evaporation, while the remaining layers are formed using sputtering. Devices with MgO barriers (MgO-MTJs) exhibited TMR ratios ranging from 140-180%, whereas those with MAO barriers (MAO-MTJs) showed TMR ratios between 60-100%. The power spectra density of MgO and MAO-MTJs is measured to assess their noise electrical 1/f noise, which is quantified with the Hooge parameter. MgO-MTJs shows a value of 5.74×10-8 μm2, while MAO-MTJs showed a substantially lower value of 5.69×10-9 μm2, confirming the noise suppression capability of MAO. To further investigate the underlying cause, scanning transmission electron microscopy is utilized to examine interfacial defect densities. The analysis reveals that the MAO/Fe interface had approximately 1% defect density, significantly lower than the 4% observed at the MgO/Fe interface, pointing to the superior lattice compatibility and structural quality of MAO, which is considered to contribute to the noise suppression.
The MTJ stacks are MgO(001) substrate/Cr(60)/Fe(50)/Mg(0.2)/MgO or MAO(2)/Fe(5)/IrMn(10)/Cr(5) (thickness in nm). MgO or MAO are deposited via electron beam evaporation, while the remaining layers are formed using sputtering. Devices with MgO barriers (MgO-MTJs) exhibited TMR ratios ranging from 140-180%, whereas those with MAO barriers (MAO-MTJs) showed TMR ratios between 60-100%. The power spectra density of MgO and MAO-MTJs is measured to assess their noise electrical 1/f noise, which is quantified with the Hooge parameter. MgO-MTJs shows a value of 5.74×10-8 μm2, while MAO-MTJs showed a substantially lower value of 5.69×10-9 μm2, confirming the noise suppression capability of MAO. To further investigate the underlying cause, scanning transmission electron microscopy is utilized to examine interfacial defect densities. The analysis reveals that the MAO/Fe interface had approximately 1% defect density, significantly lower than the 4% observed at the MgO/Fe interface, pointing to the superior lattice compatibility and structural quality of MAO, which is considered to contribute to the noise suppression.