Electrical transport in magnetic tunnel junctions with low resistance-area product
Yen-Chi Lee1, Yong-Han Lin2, Jong-Ching Wu1*
1Department of Physics, National Changhua University of Education, Changhua, Taiwan
2Institute of Physics, National Chiao-Tung University, Hsinchu, Taiwan
* presenting author:Jong-Ching Wu, email:phjcwu@cc.ncue.edu.tw
The magnetic tunnel junction (MTJ) consisting of ultra-thin crystalline MgO sandwiched by two ferromagnetic layers, especially the CoFeB, is the best candidate to achieve high tunneling magnetoresistance (TMR) ratio and low resistance-area (RA) product for the potential applications. Therefore, many research regarding to the thickness, interfacial condition, quality and intrinsic property of the insulating oxide layer have been experimentally and theoretically investigated, in which most of the subjects are studied by analyzing and clarifying the electron transport mechanism. In this presentation, the electrical transport mechanism of CoFeB/ MgO/ CoFeB-based magnetic tunnel junctions (MTJs) with low resistance-area product will be reported by means of temperature-dependent, zero-bias resistance measurement. The tunneling magnetoresistance (TMR) ratio of each deep sub-micrometer scaled device with similar variation of 0.17 %/K indicates that spin-dependent tunneling dominates the electron transport. It is notable that a metal-insulator transition in specific devices is clearly observed in parallel states below 50K. Field-independent variations in resistance levels are observed, and the feature is associated with a three-dimensional electron-electron interaction (3-D EEI). 3-D EEI is introduced as a quantum correction term in the theoretical model, with the modified model consistently describing temperature-dependent conductance from 300K to 2K. Finally, in order to provide a complete illustration of the transport mechanism, it is argued that the narrow channels in the barriers should be taken into account as the TMR ratio is preserved even when the existence of extra conducting channels is confirmed.

Keywords: magnetic tunnel junctions, spin-dependent tunneling , metal-insulator transition, electron-electron interaction