TaFeB spacer for soft magnetic composite free layer in CoFeB/MgO/CoFeB-based magnetic tunnel junction

• Published in: Applied physics letters 2023-02, Vol.122 (7)
• Main Authors: Nakano, Takafumi, Fujiwara, Kosuke, Kumagai, Seiji, Ando, Yasuo, Oogane, Mikihiko
• Format: Article
• Language: English
• Subjects: Amorphous alloys; Applied physics; Energy value; Interlayers; Magnesium oxide; Magnetoresistivity; Sensors; Thickness; Tradeoffs; Tunnel junctions; Tunnel magnetoresistance
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0132866

CoFeB/MgO/CoFeB-based magnetic tunnel junctions (MTJs) with a soft magnetic composite free layer have been developed for magnetic sensor applications. Tunnel magnetoresistance (TMR) ratios in the sensor-type MTJs have reached a ceiling due to a trade-off between the TMR ratio and interlayer exchange coupling (IEC) depending on the spacer thickness of the composite free layer. In this study, we developed a paramagnetic amorphous TaFeB-alloy spacer to replace the conventional Ta spacer and solve this trade-off. The TaFeB film showed a wider thickness window for a sufficient IEC, resulting in IEC energy values of 0.18–0.19 erg/cm2 at a thickness of 1.0 nm. In addition, we confirmed that the TaFeB film had an ability to function as a boron sink comparable to that of pure Ta. These characteristics allowed us to thicken the TaFeB spacer up to 1.0 nm in the sensor-type MTJs and attain an enhanced TMR ratio of up to 234%, which is the highest compared with cases using the conventional Ta spacer reported to date. These findings demonstrate that TaFeB alloy is a promising material for breaking the ceiling of sensor-type MTJs and increasing sensitivity.