High temperature ferromagnetic resonance study on pMTJ stacks with diffusion barrier layers

Abstract

We investigate the impact of Ru, Mo and W as an insertion layer between the second MgO and the top electrode in dual-MgO pMTJ stacks on the free layer magnetic properties from 25 °C to 260 °C. The insertion of Ru helps to improve the room temperature thermal stability by 97% in comparison to the control sample as its closely packed structure and large grain size suppresses interlayer diffusion. The effective anisotropy field (H eff) of these samples were found to decay linearly at an increased rate as compared to the areal moment (M s t) for the range of temperature measured through high temperature ferromagnetic resonance spectrometer and vibrating sample magnetometer. Furthermore, the extrapolated H eff values across all samples having the same free layer composition converge towards zero at T = 325 °C, independent of the initial H eff values measured at room temperature. Our measurement reveals that the free layer saturation magnetization plays a more significant role than H eff in achieving higher thermal stability at typical MRAM operating temperatures.

Thermal behavior of spin-current generation in PtxCu1-x devices characterized through spin-torque ferromagnetic resonance

“…Temperature studies using various characterization techniques including second harmonic measurement [16][17][18][19] , spin-pumping 20 and spin-transfer ferromagnetic resonance (ST-FMR) 21 have been explored but only within and below room temperature 22 . Although the effects of elevated temperature on SHE is crucial for device applications 23,24 , the quest for high temperature SHE characterization remains relatively uncharted. In a recent ST-FMR study by P. Phu, a joule heating technique was applied to momentarily raise the temperature of the sample during characterization 22 .…”

Enhancement of thermal robustness in magnetic tunnel junctions with perpendicular magnetic anisotropy

“…In addition, H eff is observed to degrade at a much faster rate in comparison to M s in the operating temperature range of STT-MRAM products [99]. A possible but inefficient strategy is to increase H eff instead of M s to increase Δ as H eff is proportional to H eff (T=0K).…”

“…While the thickness of the free layer can be increased for iMTJ to maintain a high thermal stability, the bulk anisotropy effect will start to dominate CoFeB-based free layer which relies on interfacial PMA in such pMTJ stack designs. Another potential concern to thermal stability would be the "magnetic dead layer" effect caused by energetic bombardment of atoms during sputtering or interlayer diffusion during annealing [76,[99][100][101][102][103].…”

“…Holmium (Ho) is theoretically able to achieve hcp-phase upon annealing at 400 °C [232,233]. Since Ho has a lower melting point of 1470 °C, the grain size should be larger as compared to Ru and Pt seed layers, which in turn leads to fewer grain boundaries for interlayer diffusion to occur [99,234]. To evaluate the native oxide formation and the ensuing change in resistivity, selected elements deposited on thermally oxidized Si substrates were sent for XRR measurements as presented in Figure 18.…”