M. Ho

Low-resistance IrMn and PtMn tunnel valves for recording head applications

We have investigated the use of ultrathin Al2O3 barriers to fabricate low-resistance tunnel-valve sensors suitable for recording heads. Tunnel valves of the type underlayer/(IrMn or PtMn)/CoFe/Al2O3/CoFe/NiFe/Cap layer have been fabricated by magnetron sputtering. Tunnel barriers are formed by Al metal deposition followed by in situ oxidation, and tunnel-junction test devices are built by photolithography with areas down to 1×1 μm2. Specific resistances as low as 13 Ω μm2 with 25% tunnel magnetoresistance have been obtained using Al thicknesses of 6–7 A.

IrMn spin-valves for high density recording

Simple IrMn spin-valves are investigated for use in high density recording head sensors. Top-IrMn spin-valves of the form NiFeCr(40 /spl Aring/)/NiFe(32 /spl Aring/)/CoFe(5)/Cu(25 /spl Aring/)/CoFe(30 /spl Aring/)/IrMn(80 /spl Aring/)/Ta(50 /spl Aring/) were deposited by magnetron sputtering. By tailoring the pinned layer composition at the CoFe/IrMn interface to Co/sub 60/Fe/sub 40/, the exchange bias can be increased above 400 Oe with a GMR amplitude of about 12%. Recording heads were fabricated with total gap thicknesses down to 900 /spl Aring/, magnetic trackwidth down to 0.2 /spl mu/m and stripe height down to 0.3 /spl mu/m. The transfer curve characteristics are found to agree reasonably well with micromagnetic modeling. The model is then used to predict head sensitivity loss from the combination of insufficient exchange bias and short sensor stripe heights.

Spin-valve and tunnel-valve structures with in situ in-stack bias

The use of in-stack longitudinal magnetic stabilization for spin-valve and tunnel-valve recording head sensors has been investigated. An in-stack ferromagnetic layer pinned with an IrMn antiferromagnet is used to magnetostatically stabilize the free layer by flux closure. The use of IrMn with lower blocking temperature than PtMn allows the bias layer to be set independently from the PtMn-pinned reference layer in the spin-valve or tunnel-valve. A Ta spacer 10-30 /spl Aring/ in thickness is used to separate the free layer from the bias layer resulting in low coupling fields. IrMn delivers up to 0.34 erg/cm/sup 2/ of pinning strength, resulting in stable unshielded sensor operation for device sizes below 0.2 /spl mu/m.

Study of magnetic tunnel junction read sensors

Unshielded magnetic tunnel junction (MTJ) sensors stabilized by insulating hard magnetic tails have been fabricated. Testing results showed that the control of oxidation condition was important for obtaining MTJ with low junction resistances and high TMR coefficients. The results also showed that the thickness of insulating spacer between hard magnet and MTJ stack had a significant influence on sensor stability. Finally, recording tests of stabilized MTJ read heads demonstrated linear densities of 420 Kbpi at 10/sup -9/ ontrack error.

Magnetic tunnel junctions with AlN and AlNxOy barriers

Nonoxide tunnel barriers such as AlN are of interest for magnetic tunnel junctions to avoid the oxidation of the magnetic electrodes. We have investigated the fabrication and properties of thin AlN-based barriers for use in low resistance magnetic tunnel junctions. Electronic, magnetic and structural data of tunnel valves of the form Ta (100 A)/PtMn (300 A)/CoFe20 (20 A–25 A)/barrier/CoFe20 (10–20 A)/NiFe16 (35–40 A)/Ta (100 A) are presented, where the barrier consists of AlN, AlNxOy or AlN/AlOx with total thicknesses between 8 and 15 A. The tunnel junctions were sputter deposited and then lithographically patterned down to 2×2 μm2 devices. AlN was deposited by reactive sputtering from an Al target with 20%–35% N2 in the Ar sputter gas at room temperature, resulting in stoichiometric growth of AlNx (x=0.50±0.05), as determined by RBS. TEM analysis shows that the as-deposited AlN barrier is crystalline. For AlN barriers and AlN followed by natural O2 oxidation, we obtain tunnel magnetoresistance >10% with ...

Magnetic tunnel-valve barriers with boron

The properties of magnetic tunnel junctions with aluminum oxide barriers alloyed with boron are presented. When aluminum is deposited by sputtering, 10 at. % B addition is sufficient to completely transform the deposited Al film from crystalline to amorphous. We have investigated if the deposition of amorphous AlB prior to oxidation results in a variation of tunnel-valve properties. It is found that ultrathin Al90B10 films can be readily oxidized using a procedure similar to that for Al films, resulting in tunnel valves with good magnetic properties. In the ultrathin regime (when the specific junction resistance is Rj<20 Ω μm2), the barriers with boron yield magnetoresistance values slightly above that of pure aluminum oxide, although the effect is not significant for Rj<5 Ω μm2.

Mg AlO/sub x/ barriers for low-resistance tunnel-valve sensors

In this work, to achieve practical tunnel-valve sensors for recording, the specific junction resistance of the tunnel barrier must be reduced.

Tunnel-valve and spin-valve structures with in situ in-stack bias

Summary form only given. As recording densities increase above 100 Gbit/in/sup 2/, read sensor trackwidth must be reduced below 0.2 /spl mu/m. To improve sensor operation, it is necessary to develop alternatives to traditional contiguous junction hard bias stabilization schemes. One such alternative consists of an in-stack magnetic bias layer deposited in close proximity to the sensor layer. Upon trackwidth definition, this results in a magnetostatic bias coupling at the sensor edges. For in-stack bias to be effective, several aspects must be optimized. (1) The bias layer must be as close as possible to the sensor free layer to increase the biasing effect. (2) Any direct ferromagnetic coupling between free and bias layer across a spacer layer must be minimized. (3) The bias layer must be well pinned and oriented perpendicular to the tunnel-valve pinned layer. To achieve these goals, we have studied bottom-PtMn spin-valve and tunnel valve structures of the type Ta/PtMn/CoFe/(Al/sub 2/O/sub 3/ or Cu)/CoFe/NiFe/Ta/CoFe/IrMn/Ta deposited in situ in a single process by magnetron sputtering. Ta thicknesses between 10 and 30 /spl Aring/ have been used to decouple the bias layer from the free layer, and IrMn is used to pin the bias layer magnetization.

Extendability of CIP spin-valve sensors to narrow dimensions

In this paper, we study the recording head, the parasitic lead resistance makes the spin-valve performance and its properties.

Areal density process advantages for CPP sensors

Summary form only given. This paper deals with a discussion of the process advantages of CPP geometry sensors for narrow trackwidth and narrow gap applications in thin film head read transducers. Simply stated, the CPP sensor geometry removes the CIP sensor processing requirement for thin insulating gaps and allows for precise confinement of current flow and hence magnetic trackwidth control.