Electrode roughness and interfacial mixing effects on the tunnel junction thermal stability
The thermal stability of magnetic tunnel junctions with ultrathin ({lt}8 Aa) Al{sub 2}O{sub 3} barriers was studied and compared with 15 Aa barriers. The tunnel magnetoresistance (TMR) decay cannot be explained only by Mn diffusion into the pinned CoFe layer since this diffusion starts above 300{degree}C independently of the barrier thickness, while the TMR degradation already occurs at 250{endash}270{degree}C for the thinner barriers. The thermal stability is probably controlled by changes at the CoFe/Al{sub 2}O{sub 3} interfaces and/or barrier structure. Structural analysis of 15 Aa barriers after annealing at 435{degree}C, shows the existence of an interface region (8{endash}12 Aa thick) where CoFe and Al{sub 2}O{sub 3} are found. This interfacial region can be explained by the increased roughness in the bottom electrode after annealing, as measured by atomic-force microscopy (from 1.5 to 4 Aa). Ultrathin barriers show a similar trend. The use of low-resistance junctions using thin barriers requires good control of the roughness of the low-resistance bottom electrodes. This is done by preannealing and low-angle ion-beam smoothing 500-Aa-thick Cu or Al films, which will then keep a roughness {lt}2 Aa during processing temperatures up to 400{degree}C. Low-resistance junctions (R{times}A{similar_to}40{endash}60 {Omega}{mu}m{sup 2}) with 7 Aa barriers grown on 600 Aa Al buffers after the surface treatment show 25% TMR after annealing at 270{degree}C. {copyright} 2001 American Institute of Physics.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40203827
- Journal Information:
- Journal of Applied Physics, Vol. 89, Issue 11; Other Information: DOI: 10.1063/1.1359216; Othernumber: JAPIAU000089000011006650000001; 379111MMM; PBD: 1 Jun 2001; ISSN 0021-8979
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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