High-temperature thermal stability driven by magnetization dilution in CoFeB free layers for spin-transfer-torque...

Area of Science:

• Materials Science
• Electrical Engineering
• Solid State Physics

Background:

• Spin-transfer-torque magnetic random access memory (STT-MRAM) is a leading non-volatile embedded memory technology.
• Operating temperature ranges, such as -40°C to +150°C for automotive use, challenge STT-MRAM data retention due to decreasing magnetic anisotropy.
• Increased anisotropy for high-temperature stability raises write currents at low temperatures, reducing energy efficiency.

Purpose of the Study:

• To investigate the physical mechanisms governing the temperature dependence of STT-MRAM anisotropy and thermal stability.
• To identify key parameters for optimizing high-temperature performance in STT-MRAM devices.
• To develop a predictive model for STT-MRAM thermal stability.

Main Methods:

• Fabrication of CoFeB free layers diluted with various non-magnetic metallic impurities.
• Systematic variation of impurity type and concentration to modulate material properties.
• Measurement of magnetic anisotropy and thermal stability in blanket films and patterned devices.

Main Results:

• Demonstrated that magnetization is the primary factor influencing the temperature dependence of anisotropy and thermal stability in diluted CoFeB layers.
• Showed that impurity concentration and material directly impact magnetization, thereby controlling thermal behavior.
• Developed a predictive model correlating blanket film properties with the thermal stability of patterned STT-MRAM devices.

Conclusions:

• Magnetization is the critical parameter for managing the temperature dependence of anisotropy and thermal stability in STT-MRAM.
• Diluting CoFeB layers with specific impurities offers a viable strategy to enhance high-temperature performance and energy efficiency.
• The developed model accurately predicts device thermal stability from fundamental material properties, aiding future STT-MRAM design.