Evaluation of front flux guide-type magnetic tunnel junction heads

Abstract

Magnetic tunnel junction (MTJ) heads have been successfully fabricated using the free layer as flux guide to prevent electrical short during the definition of the air bearing surface (ABS). For a 6 Gbits/in 2 design, an output as high as 5740 Vpp was achieved for 3 mA sense current, and the output waveform was stable and noise free. Noise analysis confirmed that shot noise is prevailing in these MTJ heads, suggesting that the junction resistance has to be further reduced to challenge spin-valve heads in term of signal to noise ratio. Landau-Lifshitz-Gilbert simulations showed that for 20 Gbits/in 2 application, the flux guide height should not exceed 0.1 m.Index Terms-Magnetic recording/magnetic tunnel junction heads, front flux guide, shot noise, micromagnetic simulation.

Fabrication and electrical properties of lapped type of TMR heads for ∼50 Gb/in/sup 2/ and beyond

“…Two ways could be used to reduce the capacitance; one is the reduction of shield area and the other is to lengthen the shield to shield spacing. Combining these two ways, the capacitance of current design is successfully reduced down to around 0.5 pF, which is only of our first generation design [17] and increases the frequency limit in TMR head.…”

“…Three major changes have improved the design of current TMR head from that of our first generation one, 6 Gb/in [17]. The first of the changes is that MTJ has a bottom type of stack structure which helps to narrow the magnetic track width: buffer/PtMn/CoFe/Ru/CoFe/AlOx/CoFe/NiFe/cap.…”

“…For magnetic recording applications, there are two main items to make a good MTJ: a large TMR ratio and a low RA product. A low RA product translates to small shot noise [17]. The value of the RA product is mainly related to the oxidation method and the thickness of the insulating barrier.…”

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.…”

“…As a current perpendicular to the plane sensor, the tunnel junction can be inserted directly in between the shields, avoiding the insulating layers [1][2][3][4] and improving linear density. For proper signal to noise ratio, and for compatibility with head preamps, tunnel junctions must have very low resistance ͑few ⍀ϫ m 2 ͒ and maintain tunneling magnetoresonance ͑TMR͒ values near or excess than 20%.…”