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

Abstract

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 Å to around 5 Å, 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 ∼100 Ω μm2 with the GCIB dose up to 1×1016 ions/cm2, 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 1015 ions/cm2) 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 Ω μm2 together with a TMR of 14%–18% can be obtained for MTJs grown on the GCIB treated NiFe magnetic shield.

Quantitative x-ray photoelectron spectroscopy study of Al/AlOx bilayers

“…Low-resistance MTJs are also potential candidates for replacement of spin-valve sensors in read heads, as recording densities move beyond 100 Gbit/inch 2 , provided RϫA is of the order of a few ⍀ m 2 and TMR ϳ20%. Two basic strategies are followed to meet these requirements: ͑i͒ thinner AlO x barriers ͑5 to 7 Å Al͒, 22 and ͑ii͒ lower band-gap oxides, ZrO x and HfO x among others, as barriers. 23 The performance of the junctions is strongly dependent on the oxidation of the FM electrodes at the FM/I interfaces.…”

Molecular dynamics simulations of sequential cluster ion impacts

“…Gas cluster ion beam technique is a promising tool for nano-scale surface modification process such as ultra smoothing, high-speed etching and thin film formation [1,2,3]. As the cluster ion beam technique spreads into industrial applications widely, the study about cluster impact process becomes more important in order to achieve precise design and higher performance.…”

Low-resistance spin-dependent tunnel junctions with ZrAlOx barriers

“…Results from various groups on low resistance junctions using naturally oxidized AlO x barriers ͑5-7 Å Al͒ report resistanceϫarea (RϫA) products ranging from 5 to 20 ⍀ϫ m 2 , but with TMR values scaled down to 10%-20%. [1][2][3][4][5][6] Better control of oxidation time and pressure can further optimize these values. 7 Another approach to produce low resistance junctions is to use lower band gap oxides ͑ZrO x , HfO x , among others͒ as barrier.…”