Microstructural observation on effect of oxidation method of AlO[sub x] in magnetic tunnel junction by high resolution transmission electron microscopy.

The formation of the insulating A1O[sub x] tunnel barrier is a critical and sensitive process in magnetic tunnel junctions. Both the natural oxidation and the plasma oxidation methods were employed to fabricate the A1O[sub x] insulating layer in this study. In the natural oxidation, the A1 layer was exposed to pure oxygen gas at 20 Torr for up to 50 min to produce the A10[sub x] tunnel barrier. It was revealed by high resolution transmission electron microscopy that the oxidation occurred preferentially through the grain boundary of A1 grains. Also, the A10[sub x] grains expanded isotropically when fully oxidized, thereby making the surface of the A1O[sub x] layer modulated. In plasma oxidation, the oxygen plasma was used at 20 mTorr of pure oxygen gas for up to 30 s and the flat A10[sub x] layer formed uniformly on the A1 layer. It had sharp interfaces with the underlying metallic A1 and the rate of oxide layer growth decreased as the oxidation proceeded. [ABSTRACT FROM AUTHOR]