Magnetic tunnel junctions on magnetic shield smoothed by gas cluster ion beam

In this work, a technique, gas cluster ion beam (GCIB), was introduced to smooth the bottom NiFe magnetic shield for magnetic tunnel junction (MTJ) read heads. The GCIB treatment can bring the surface roughness of the shield from 15 to 20 Angstrom to around 5 Angstrom, and the most of scratch marks can be removed. The efficiency of the GCIB process is dependent on the initial surface morphology. The MTJs grown on the magnetic shield smoothed by the GCIB show that the resistance area product RA is increased from 60 to similar to 100 Ohm mum(2) with the GCIB dose up to 1 x 10(16) ions/cm(2), arising from a smooth insulating layer, meanwhile, the tunneling magnetoresistance (TMR) is almost constant or slightly decreases. This GCIB process can also improve breakdown voltage (approximately 0.019 V per 10(15) ions/cm(2)) of the MTJs, and slightly increase the ferromagnetic coupling mainly due to the change of the surface morphology. Using this technology, an RA as low as 3.5-6.5 Ohm mum(2) together with a TMR of 14%-18% can be obtained for MTJs grown on the GCIB treated NiFe magnetic shield. (C) 2001 American Institute of Physics.