Impact of CoFeB surface roughness on reliability of MgO films in CoFeB/MgO/CoFeB magnetic tunnel junction

Abstract

We investigated the impact of the interface roughness in W-CoFeB-MgO-CoFeB-W structures on MgO reliability using the atomic force microscopy images of a MgO underlayer surface and I-V measurements. As a result, the electric current in the MgO film increased as the MgO underlayer surface roughness increased. We assumed that this phenomenon is caused by the local electric field concentration, and verified it by comparing the two electric field concentration values simulated from the AFM images and calculated from the I-V measurements. These two electric field concentrations calculated from the different results have a strong correlation to each other. It is concluded that the current of the MgO film is increased by the large roughness between MgO and the electrodes. This causes the large current variation in memory cells in magnetic random access memory (MRAM), then it leads to a small margin in memory operation.

Interface imperfection effects on spin transfer torque switching: an atomistic approach

“…where Ĥ indicates the spin Hamiltonian [15]. Under the macrospin model in which a magnet is regarded as a macroscopic magnetic moment, the analytical solution of the LLG equation can be written as follows:…”

“…Note however that MRAM performance also depends on the physical properties and magnetization dynamics of the constituent magnetic materials [14]. Roughness at the CoFeB/MgO interface is a key parameter affecting electrical reliability [15]. Micromagnetic simulation is based on the Landau-Lifshitz-Gilbert (LLG) equation used in conjunction with the finite element method to simulate phenomena at the 'mesoscopic' scale [16].…”

“…In Park et al [15], they studied the effect of roughness on the electrical performance of MTJs; however, they did not account for magnetic properties. In Chureemart et al [21], they performed an atomistic investigation of the magnetic properties of MTJ (e.g.…”

High reliability CoFeB/MgO/CoFeB magnetic tunnel junction fabrication using low-damage ion beam etching

“…On the other hand, the electrical reliability of MgO film is also an important issue in practical STT-MRAM applications, as reported by previous studies. [14][15][16][17][18][19][20] The authors group has been investigating the impact of MTJ fabrication methods on electrical reliability of MgO films, including the relationship between the MgO reliability and MgO crystallization conditions, 20) micro-roughness of MgO/electrode interface 21) and so on. However, the previous studies considered the areal current when measuring and evaluating MgO reliability.…”