Kroum S. Stoev

Return Field-Induced Partial Erasure in Perpendicular Recording Using Trailing-Edge Shielded Writers

Return field-induced partial erasure (RFPE) in trailing-edge shielded perpendicular writers has been studied, both by modeling and by experiments. For a given head-media combination, the return field underneath the trailing shield increases with increasing write current. Once exceeding a certain threshold, it will cause partial erasure of the bits that have just been written by the main pole. Recording performance, such as reverse overwrite, spectral signal-to-noise ratio, and bit-error rate are all found degraded at high write currents, due to RFPE. Design optimization of both head and media together is needed, in order to maximize the advantage of a trailing-edge shielded pole head and minimize the impact of RFPE

Magnetic recording at a data rate of one gigabit per second

Magnetic recording at a data rate of 1 Gb/s was studied in detail. Dynamic flux response of the inductive write head under the write current excitation of 40 mA/sub o-p/ at 500 MHz was simulated by Finite Element Model (FEM). Results show that, while severe eddy current damping was observed at the yoke region, an efficient design in the apex region can significantly reduce the eddy current damping at the pole tips, thus rendering sufficient magnetic flux at 1 Gb/s. The effects of magnetic yoke and interconnect on the current rise time were also simulated by SPICE model and were compared with empirical results. A reasonable agreement was obtained, Dynamic coercivities in the media were also characterized. Finally, magnetic recording at 1 Gb/s has been demonstrated on media as high as 4000 Oe of VSM coercivity and with better than 10/sup -7/ of bit error rate.

Writer pole tip remanence in perpendicular recording

We studied the remanent field from perpendicular writer pole tips by micromagnetic modeling. The pole tip remanence has two causes: 1) the residual flux from the yoke due to undesirable material properties and/or yoke design and 2) the geometry of the pole tip. An optimal yoke design for low remanence includes a wide and short yoke with relatively shallow yoke flare angle around 30/spl deg/ that favors transverse major domains. Horizontal anisotropy in the yoke and the pole tip also helps suppress the vertical magnetization, mainly in the yoke, which yields less residual flux into the pole tip, hence lower remanence. The remanent field is also a strong function of the throat height, i.e., the pole tip length, due to the shape anisotropy effect. Micromagnetic modeling shows that multilayer lamination, both in the yoke and in the pole tip, is an effective way to achieve low remanence. It also eliminates the sensitivity of remanence to the throat height. To improve the robustness of the remanence against the stray field, an antiferromagnetic coupling (AFC) between the lamination layers may also be necessary. Our results apply to both single pole heads and shielded pole heads.

Advanced heads for perpendicular recording at high areal densities and high data rates

Perpendicular magnetic recording at high areal densities and high data rates has been studied. Using ring heads and perpendicular media with soft underlayer, we have successfully demonstrated the areal density of 60 Gb/in/sup 2/ at the corresponding ultrahigh-linear density of 750 kbpi, a bit-aspect ratio (BAR) of 9.4, and a data rate of 300 Mb/s. Comparing the BAR of 5.7 in our recent 63.2 Gb/in/sup 2/ demonstration on longitudinal media, a larger BAR has been demonstrated with present perpendicular recording system. We have also demonstrated the data rate capability of 1 Gb/s by using both ring heads and modified-single-pole heads on perpendicular media with soft underlayer. Finally, a comparison of high-data-rate recording between ring heads and single pole heads has shown that neither magnetic viscosity nor gyromagnetic switching in perpendicular media is the limiting mechanism for magnetic recording at data rates as high as 1 Gb/s.

Finite Element Analysis of Alternating Write-Current-Induced Pole Tip Protrusion in Magnetic Recording Heads

This paper presents a finite element analysis of alternating write-current-induced pole tip protrusion (WPTP) generated in longitudinal magnetic recording (LMR) heads. An integrated magneto-thermal-mechanical model is developed for the simulations of the electromagnetic Joule heating generated in the LMR writer, the slider temperature distribution, and the slider deformation during writing. The computed results are compared with the experimental measurements in terms of writer resistance and inductance, the WPTP, and temperature rise at reader location. It is found that eddy currents are strongly induced near the surfaces of write poles, while the eddy currents induced in write coils are negligibly weak. The results show that the eddy current loss in the write poles dominates over the Joule heat generated in the write coils. It is also found that the maximum protrusion appears near the write pole in the overcoat and the protrusion profile is sharper than that induced by equivalent direct write current and coil resistance

Demonstration and characterization of 130 Gb/in2 magnetic recording systems

We have successfully demonstrated longitudinal recording at areal density of 130 Gb/in2 at a data rate as high as 170 Mbps (21 MB/s) and at a bit-aspect-ratio (BAR) of 2.9, using merged inductive-write/spin-valve-read heads on low noise thin film disks. The heads were fabricated with the standard photolithography and wafer pole trimming used in our currently available commercial products. The reader is a bottom synthetic spin valve (BSSV) with a 0.09 μm gap, and the writer has a conventionally trimmed pole with 0.09 μm gap. The reader magnetic read width (MRW) was measured at 0.10 μm. At read bias of ∼4 mA we measured reader sensitivity as high as 20 mV/μm. The write head was also optimized for tracks as narrow as 0.14 μm operating at overwrite (OW) of 36 dB and nonlinear transition shift (NLTS) better than −25 dB at 610 kBPI, without precomp. Using conventional media we measured total spectral SNR∼18 dB. The media to electronics noise ratio was 4.8, showing that we are still operating in a media noise li...

Advanced probe head for perpendicular recording

Basic design and recording performance of the advanced probe heads are described. Excellent writability of the advanced probe heads is demonstrated by a series of overwrite (OW) and nonlinear transition shift (NLTS) saturation measurements. Write currents as low as 5 mA/sub o-p/ are required for recording. Excellent OW can be obtained with both high and low OW ratios. Media with vibrating sample magnetometry coercivities as high as 7000 Oe can be recorded with OW of 30 dB. Better than -14 dB of NLTS was measured at a linear density of 600 kfci. Minimal side-writing has been observed using the advanced probe heads with square pole shape. External field sensitivity of the advanced probe heads has also been shown to be excellent as larger than 58 Oe of external field is required to erase a low density signal on a 3380-Oe disk. Modeling results also show that the basic architecture of advanced probe head is extendible to 0.1 /spl mu/m square pole.

Demonstration and characterization of greater than 60 Gb/in/sup 2/ recording systems

We have successfully demonstrated longitudinal recording at areal densities greater than 60 Gb/in/sup 2/ at data rates as high as 160 Mbps (20 MB/s) and at a Bit-Aspect-Ratio (BAR) of 5.7, using merged inductive-write/spin-valve-read heads with microactuators on low noise thin film disks. The heads were fabricated with standard photolithography and wafer pole trimming used in currently available commercial products. At track densities of 60 KTPI and higher, traditional servoing mechanisms are not adequate. With the use of a microactuator, we can further improve the track density by 15%, the linear density by 10% and the areal density by more than 20%. Thus, using a microactuator with the 50 Gb/in/sup 2/ head/media combination, we have increased our areal density achievement up to 63.2 Gb/in/sup 2/.

Demonstration and characterization of 36 Gb/in/sup 2/ recording systems

We have successfully demonstrated recording at areal densities as high as 36 Gb/in/sup 2/ at data rates as high as 173 Mbits/s (21.6 MB/s) and at a Bit-Aspect-Ratio (BAR) of 7.3, using merged inductive-write/spin-valve-read heads on low noise thin film disks. Recording at a data rate of 590 Mbits/s (73.8 MB/s) has also been achieved at the corresponding linear density of 231 KBPI. Comparisons with previous areal density demonstrations have also been summarized.

High Moment Materials and Fabrication Processes for Shielded Perpendicular Write Head Beyond 200 Gb/in

Commercial hard-drive products utilizing perpendicular magnetic recording technology have recently been announced and introduced. In this paper, we review key magnetic materials characteristics and wafer process attributes in fabricating perpendicular write heads. It becomes increasingly important for write-head materials to possess not only high magnetic moment, but also optimal coercivity, remanence, anisotropy Hk, magnetostriction, and stress in order to meet head performance and reliability requirements. Advanced materials and film architectures discussed in this paper resulted in a significantly improved performance margin, including reduced pole erasure; hence enabling higher recording densities. Novel wafer-processing techniques are required for fabrication of 3-D pole features with controlled shape, and with critical dimensions of less than 150 nm. The advance in wafer process has been driven by rapidly decreasing trackwidth, as well as by the evolving head architecture from unshielded rectangular pole to shielded trapezoidal pole