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Thickness and Interface-Dependent Crystallization of CoFeB Alloy Thin Films | IEEE Journals & Magazine | IEEE Xplore

Thickness and Interface-Dependent Crystallization of CoFeB Alloy Thin Films


Abstract:

We have analyzed the crystallization processes of sputtered thin films of Co20Fe60B20 and Co20Fe60B20−X alloys (X = Ta, Hf) using the increase in saturation magnetization...Show More

Abstract:

We have analyzed the crystallization processes of sputtered thin films of Co20Fe60B20 and Co20Fe60B20−X alloys (X = Ta, Hf) using the increase in saturation magnetization that accompanies the formation of α-FeCo. Constant heating rate analysis shows a decrease in crystallization temperature for MgO/CoFeB/Ta multilayers with decreasing CoFeB thickness (from 350 °C for a 20 nm film to 275 °C for a 2 nm film) that we attribute to interface effects on critical nucleus formation. Alloying CoFeB with Ta or Hf is found to decrease Curie temperature and inhibit crystallization. For very thin (<2 nm) CoFeB films, such as those found in modern perpendicular devices, interdiffusion of adjacent Ta layers in the absence of a low-energy nucleation surface, such as MgO, can prevent crystallization altogether. CoFeB films with adjacent TaN layers are found to crystallize regardless of film thickness, and we suggest that these alternate capping layers have lower interdiffusivity.
Published in: IEEE Transactions on Magnetics ( Volume: 51, Issue: 11, November 2015)
Article Sequence Number: 3400903
Date of Publication: 21 May 2015

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