Temperature increase in STT-MRAM at writing: A fully three-dimensional finite element approach

• Published in: Solid-state electronics 2022-07, Vol.193, p.108269, Article 108269
• Main Authors: Hadámek, T., Fiorentini, S., Bendra, M., Ender, J., de Orio, R.L., Goes, W., Selberherr, S., Sverdlov, V.
• Format: Article
• Language: English
• Subjects: Current-induced heating; Magnetic tunnel junction; Non-uniform temperature; STT-MRAM; Temperature variations
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2022.108269

•Fully 3D heat transport during STT-MRAM switching is modelled using finite elements.•Heat transport is coupled to charge, spin and magnetization dynamics.•Strong temperature inhomogeneity in the free layer is observed during switching.•Passivation layer and broad contacts increase the temperature inhomogeneity.•Passivation layer and broad contacts decrease thermal time constant of STT-MRAM. The writing process in spin transfer torque magnetoresistive random access memories (STT-MRAM) is facilitated by elevated temperatures. In this work we investigate the temperature distribution and development in the free layer (FL) of an STT-MRAM during switching. With our fully three-dimensional (3D) finite element method simulation approach, we numerically solve the heat transport equation coupled to the electron, spin, and magnetization dynamics and demonstrate that the FL temperature is highly inhomogeneous due to the non-uniform magnetization of the FL during switching for an STT-MRAM with large magnetic tunnel junction (MTJ) diameter. While the average temperature in the FL can be obtained based on an average current density and an averaged potential drop across the tunnel barrier, a fully 3D model is required to evaluate the large local temperature variations. The temperature variations in the FL further increase, when realistic device structures with an MTJ coated by a passivation layer and contacted to broad electrodes are considered. Lowering the FL thermal conductivity increases the temperature variations even further. However, the variations are strongly reduced with the decrease of the MTJ diameter.