An electron holography study of perpendicular magnetic tunnel junctions nanostructured by deposition on pre-patterned conducting pillars
Résumé
The fabrication of muti-gigabit magnetic random access memory (MRAM) chips requires the patterning of magnetic tunnel junctions at very small dimensions (sub-30 nm) and very dense pitch. This remains a challenge due to the difficulty in etching magnetic tunnel junction stacks. We earlier proposed a strategy to circumvent this problem by depositing the magnetic tunnel junction material on prepatterned metallic pillars, the junction being then naturally shaped during deposition. Once electrically contacted, the deposit on top of the pillars constitutes the magnetic storage element of the memory cell. However, in this process, magnetic material is also deposited in the trenches between the pillars that might affect the memory cell behaviour. Here we study the magnetic interactions between the deposit on top of the pillars and in the trenches by electron holography, at room temperature and up to 325 °C. Supplied by models, we show that the additional material in the trenches is not perturbing the working principle of the memory and even plays a role of flux absorber which reduces the crosstalk between neighboring dots. Besides, in the studied sample, the magnetization of the 1.4 nm thick storage layer of the dots is found to switch from out-of-plane to an in-plane configuration above 125 °C, while gradually decreasing with temperature. Electron holography is shown to constitute a very efficient tool for characterizing the micromagnetic configuration of the storage layer in MRAM cells.
Domaines
Physique [physics]
Fichier principal
holography on MTJ deposited on prepatterned pillars_revised version_vb.pdf (825.66 Ko)
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