Papers

AVS1997 Session MI+MR+AS-ThM: Magnetic Recording Technology: Advanced Media and Heads

Thursday, October 23, 1997 8:20 AM in Room J3

Thursday Morning

Start	Invited?	Item
8:20 AM		MI+MR+AS-ThM-1 Approaches to Hard Disk Media Storage Density Improvements D.N. Lambeth (Carnegie Mellon University) Today's typical hard disk drive for PC applications provides storage capacity of one to two giga-bytes in a small 2.5 or 3.5 inch format at a cost of around $300. This compares to the 5 to 10 mega-bytes in a full height 5.25 inch drive that sold for $600 with the PC's of 1984. To achieve the price and packaging of today's drives the areal storage densities have recently grown to over one giga-bit per square inch. This appears to be a phenomenal growth in areal densities and yet recent laboratory demonstrations are starting to approach the 10 giga-bits per square inch recording benchmark. A few years ago, following rather traditional scaling arguments, many of the system issues associated with the future disk recording media and heads were discussed by Murdock et. al.[1] The projections made at that time have been reasonably accurate. These scaling projections indicated that sub-micron trackwidths and sub-100 nm bit lengths would be required to achieve the benchmark. This places extreme demands on both the physical and magnetic properties of the recording medium. Some of these demands have recently raised the specter that recordings at densities just beyond the benchmark maybe thermodynamically unstable[2]. In this presentation the characteristics and performance required of the benchmark media-head combinations in light of the disk drive system and stability issues will be discussed. We will review various approaches to constructing current giga-bit per square inch media then discuss the role of the substrate, new multiple underlayer designs for epitaxial growth, new grain boundary diffussion materials and media alloy compositions on magnetic properties and film microstructure for future media. These results are taken in view of the limited techniques for evaluating media recording performance prior to the availability of the required record and playback heads. 1. E. Murdock, R. Simmons, and R. Davidson, "Roadmap for 10 Gbit/in2 media: challenges", IEEE Trans. Magn., MAG-28, 1992, pp. 3078. 2. S. H. Charap, Pu-Ling Lu, and Yanjun He, "Thermal Stability of Recorded Information at High Densities," IEEE Trans. Magn., MAG-33, 1997
9:00 AM		MI+MR+AS-ThM-3 Advanced Magnetoresistive (MR) Heads M. Re (IBM Storage Systems Division) Historically, IBM has lead the storage industry in delivering the highest areal density disk drive products to the market place. This has been again demonstrated with the recent announcement of a new 2.5" disk drive product with a storage capacity of 4Gb in a 12.5mm high format and 5Gb in a 17mm high format. This compounds to an areal density of 2.6Gb/in2. One element in achieving this areal density is the Advanced MR Head that is used. In this talk the advanced head technology will be discussed.
10:20 AM		MI+MR+AS-ThM-7 Spin Valves: Exploration of Magnetotransport in Layered Films Leads to a Better Recording Head B.A. Gurney, V.S. Speriosu, D.R. Wilhoit, R.E. Fontana (IBM Almaden Research Center); D.E. Heim (IBM Storage Division); C. Tsang (IBM Almaden Research Center) Spin valves and other giant magnetoresistance (GMR) materials are leading to a new generation of high density read-back sensors that may permit magnetic recording at tens of Gbit/in2 with data rates of tens of MB/s, resulting in data storage of unprecedented capacity and speed. GMR, is present in thin films of ferromagnetic (F) metal regions separated by as little as a few atomic spacings by a non-ferromagnetic (nF) metallic spacer material. A change of conductance results when the relative magnetization directions of nearby ferromagnetic regions changes in response to an external magnetic field: GMR values of multilayer structures can exceed 60% at room temperature, but require magnetic fields thousands of times the typical excitation of a recording head. Sandwich (i.e. F/nF/F layered) structures exhibit smaller GMR values (5-15%) than multilayers, but can do so in fields of a few Oe, suitable for recording. When one of the F layers of the sandwich is magnetically pinned by contact with an antiferromagnet the structure is called a spin valve. The underlying physical mechanism of GMR has challenged our understanding of transport in ferromagnetic metals and pushed the limits of characterization techniques. Spin Valves with signals more than three times that of a comparable AMR heads have been made, demonstrating the GMR advantage, and that GMR materials can be successfully processed.
11:00 AM		MI+MR+AS-ThM-9 Meeting the Process Challenges for Spin-Valve Fabrication on an Industrial Scale P. Schwartz, R. Bubber, A. Paranjpe, J.C.S. Kools (CVC) A decade after the discovery of the GMR effect, magnetic read heads based on GMR materials have been introduced to the market. By the turn of the century substantial amounts of GMR heads will be produced. A crucial issue in this industrialization process is the availability of a reliable deposition process capable of depositing spin-valves on a large scale. In this contribution, we will present such a process. We give an overview of the challenges that had to be overcome in its development and discuss the solutions which have been found. Deposition of GMR materials requires process control better than present state-of-the-art industrial PVD processes for two reasons: the nm-scale thickness of individual layers and the strict requirements on interface quality. We have developed a pulsed DC magnetron process which is shown to deposit Cu and NiFe films in the nm thickness range with controllability on a 0.1 nm scale , repeatability <1% 1σ and non-uniformity <1% 1σ over a 150 mm diameter wafer. When compared to an optimized RF process, the DC magnetron process is found to result in spin-valves with higher GMR-ratio's which can be attributed to the lack of self-bias of the substrate and thus of interface mixing by ion bombardment. Contamination by exposure to the residual background gas has various effects detrimental to the GMR response. Exposure of the seed layer decreases the degree of (111)-texture while exposure of the interfaces between the Cu layer and the ferromagnetic layers leads to lower mr-ratio's and smaller, less-oriented grains. However, the interface between the pinned layer and the antiferromagnet is found to be relatively robust. Deposition in a cluster tool equipped with a multitarget single wafer module minimizes the degree of interface contamination which leads to improved GMR response (5.5 % for simple Ta/NiFe/Cu/NiFe/IrMn/Ta structures and > 9 % for advanced structures (Ta/NiFe/CoFe/Cu/CoFe/IrMn) .
11:20 AM		MI+MR+AS-ThM-10 Optimization of NiO/X (X=Co, NiFe and CoFe) Exchange Bilayers for Spin-valve Sensors S.X. Li, T.S. Plaskett, P.P. Freitas (INESC, Portugal) In this work we report on three bilayer systems, NiO/X (where X is Co, Ni₈₁Fe₁₉ and Co₈₇Fe₁₃). The films were deposited on Si(100) substrate at 200 C ¹. It was found that the NiO/NiFe bilayers had the largest interfacial exchange coupling energy, J_k=0.059 erg/cm². This value of J_k is comparable with that found by Carey et al. ² and Michel et al. ³. We found the blocking temperature of NiO/NiFe to be 140 C, NiO/Co 117 C and NiO/CoFe 126 C. The NiO thickness in all structures was 500 Å, and the pinned layer was 20 Å. The value for NiO/NiFe was lower than that reported by Carey et al. and Michel et al.. This difference is attributed to a larger grain size of our NiO films (450 Å). Coupon spin-valves with the structure NiO(500)/X(10)/Co/(15)/Cu(22)/NiFe(45) (thickness in Å) where (a) X=Co, (b) X=NiFe and (c) X=CoFe were investigated. The NiO/X bilayers were deposited in a rf magnetron sputtering system, the remaining part of the spin-valve structure was deposited in another system preceded by a sputter etch. By changing the etch time, we could control the interlayer coupling between the free and pinned ferromagnetic layers from 0 to 50 Oe. The magnetoresistance ratio (MR) for the different pinned layers studied was between 5 and 8 %. We found that type (a) structures showed an uniaxial anisotropy, type (b) an unidirectional anisotropy with a blocking temperature of 110 C, and type (c) an unidirectional anisotropy similar to type (b). However, type (c) showed strong uniaxial anisotropy above the blocking temperature of 80 C. Unshielded spin-valve sensors with height of 2 µm and trackwidth of 4 µm and 6 µm were fabricated and characterized. Sensors with CoFe as the pinned layer showed well-linearized MR transfer curves, free of Barkhausen noise and good thermal stability. However the MR signal decreased 20 % at an operating temperature of 80 C. ¹P.T. Berge et al., IEEE Trans. Magn. 31, 2603 (1995). ²M.J. Carey et al., Appl. Phys. Lett. 60, 3060 (1992). ³R.P. Michel et al., IEEE Trans. Magn. 32, 4651 (1996).
11:40 AM		MI+MR+AS-ThM-11 Study of High Temperature Effect on Spin-Valve Sensor Transfer Curves. P.P. Freitas, O. Redon (INESC, Portugal) Unshielded exchange biased spin-valve sensors with 4 and 6µm trackwidths were fabricated and annealed to study the effect of high temperature processing on the transfer curves. A micromagnetic simulation program ¹ was developed to analyse the transfer curves upon annealings. Important parameters such as the exchange field, the pinned and free layer coercivities or the directions of the easy axis in the magnetic layers can be computed and compared to understand the transfer curve degradation. In the case of our TbCo based sensors, the comparison between the simulations and the experimental curves, shows a rotation of the pinned layer easy axis (which was initially set along the height of the sensor) toward the length of the sensor when the temperature of annealing exceeds the blocking temperature, namely 270 C. This rotation is responsible for the rapid decrease of the MR signal since a full antiparallel alignment can no longer be achieved. Moreover, an increase of the free layer anisotropy was also observed which seems to be linked to an additional anisotropy induced by stress during the annealing step. Treatment at high temperatures in magnetic fields slows the degradation of the MR signal, by pinning the pinned layer magnetization direction. An improvement of 2% in the MR signal was observed after cooling in 300 Oe field for annealings at 280 C and 300 C. ¹G.B.Albuquerque and P.P.Freitas, Physica B, May 1997, in press.