MR/Inductive head for perpendicular magnetic recording

Contact-type magnetoresistive (MR) inductive head designs and recording characteristics have been discussed in perpendicular magnetic recording. The shielded-type MR head offered a high D50 of 100–135 kFRPI, and the unshielded MR head had the largest output in a low density region. However when the recorded bit length became shorter than the shield-to-shield spacing, the shield had little effect and the output of the shielded head was no longer almost equal to that of the unshielded MR head. In result, the shielded-type and even unshielded-type MR heads have good high density recording characteristics in the head-to-medium contact state.

Increased demands for higher storage capacity solution have driven the Hard Disk Drive (HDD) technological boundaries. As the Perpendicular Magnetic Recording (PMR) head shows promising increase in Areal Density away from the limit of Longitudinal Magnetic Recording, HDD companies have switch to 100% PMR drives. PMR heads requires tight physical specifications fabricating its Writer Element in order control the magnetic flux footprint of the writer on the disk. This magnetic footprint is also called the MCW (Magnetic Core Width). MCW variations in PMR head results to significant yield loss in DET (Dynamic Electrical Test). In addition to that, continuous tweaking in Wafer and Slider Fab process to improve yield contributes to changes in MCW performance during DET. A new method that will learn and predict the MCW model accurately is thus necessary to successfully control MCW variation. An Artificial Neural Network Multilayer Perceptron architecture was developed and used to derive the MCW model from Wafer & Slider process parameters. The Artificial Neural Network model was compared with conventional Multiple Linear Regression (MLR) method and has shown that ANN gives better accuracy in predicting the final MCW than MLR by 30%.

This paper presents a comparative study of alternating write-current-induced pole tip protrusions (WPTP) in perpendicular magnetic recording (PMR) and longitudinal magnetic recording (LMR) heads during writing operation. Both finite element modeling and experimental measurements were performed for this study. The results show that the writer resistance and inductance as well as the WPTP of PMR heads are all substantially lower than those of LMR heads within the write-current frequency range under consideration. It is found that the WPTP of a LMR head is mainly attributed to the eddy-current-induced Joule heating in yoke, whereas for a PMR head, the contribution to the WPTP from the Joule heating generated in write coils is comparable to that induced in yoke.

A thin film head of new probe type was fabricated, applicable to perpendicular recording on Co-Cr rigid disks. The head consists of a magnetic film for the main pole and multiturn spiral coils (2 layers, 10 turns) were fabricated on a ferrite substrate. The recording characteristics were measured on 14-in. sputtered Co-Cr disks having a high permeable Ni-Fe back layer. The magnetomotive force for saturation recording was 2 A-T and the output voltage was 0.65 mV at a pole thickness of 4 μm and pole width of 70 μm, at a head to medium spacing of 0.3 μm. The recording density was measured to be 17 kFRPI at a pole thickness of 0.7 μm.

A focused ion beam (FIB) has been used to trim write heads for perpendicular magnetic recording using untrimmed HGA-level longitudinal heads. The ion-beam imaging of the write head during FIB processing was minimized to limit exposure of the active magnetic material at the ABS to a 30 keV Ga+ ion dose of less than 1014 Ga+/cm2 (≈10−13 C/μm2) (the GMR reader was never exposed), which is significantly below levels where magnetic properties have been observed to degrade [W. M. Kaminsky et al., Appl. Phys. Lett. 78, 1589 (2001)]. The corresponding recording characteristics and spatial profiles of written tracks have been measured on a spin stand and a magnetic force microscope (MFM). Recording performance, such as SNR, and pulse shape of transitions, for example, as a function of head design and FIB processing is discussed, which compares very favorably to the performance of untrimmed heads. The MFM images reveal curvature in the magnetic transitions (transition smile) when writing with a single-pole writer with a straight trailing edge. Conversely, we demonstrate straight transitions using a single-pole writer with a curved trailing edge. Our results demonstrate the robustness of FIB-trimmed heads down to sub-100-nm length scales.

This paper presents a numerical analysis of adjacent track erasure (ATE) when operating wrapped-around shielded perpendicular magnetic recording (PMR) heads. Micromagnetic finite element modeling was used to investigate the magnetization dynamics in a PMR writer including a soft underlayer, and the resultant magnetic field in the recording layer. It is found that the ATE-field is an asymmetric and localized return field. Such an asymmetry is determined by the directions of both the magnetization in the pole tip and the initial magnetization in the WAS. The ATE-field is located near the corner and the inner edge of one side-shield. It is also found that the ATE-field remains strong for most of the time during write-field switching.

Basic design concepts for perpendicular magnetic recording—from viewpoints of high writing ability and resolution

Recording characteristics of low flying single pole head

The reproduction flux distributions of the dual track complementary (DTC) type of heads for perpendicular magnetic recording were calculated using a 3-D finite element method and compared with those of the single pole type (SPT) of heads. The calculated reproduction flux hardly changed along the head pole, which indicates that the flux sensitive detector can be placed far from the air bearing slider surface in the DTC head system. As a result, the DTC type of recording heads may be a candidate for heads for perpendicular magnetic recording systems.

Actual examples are given to show that low head impedance is extremely important in narrow track-width heads for high-density perpendicular magnetic video recording and reproduction, and that it strongly affects the wideband frequency characteristics and the noise level of the head. A main pole excitation probe-type head (MPD), with 7 μm track width, was fabricated to compare the dependence of frequency band and noise characteristics on head impedance. With high sensitivity and low impedance, the MPD head had a very favorable CN ratio of 54.5 dB, suggesting that in the future it will provide significant advantages for widebanddigital recording.

Principal complementarity between perpendicular and longitudinal magnetic recording

Effects of domain structures in main pole films on the reproduction sensitivity are investigated for single-pole-type perpendicular magnetic recording heads. The reproduction sensitivity of a single-pole head adopting a Co-Zr-Nb single-layer film becomes unstable and decreases with increases in closure domain sizes, when the track width is made narrow and the anisotropy field H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> is low. On the other hand, for a narrow-track main pole made of Co-Zr-Nb multilayer film with a 50 Å thick SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> intermediate layer, closure domains cannot be observed clearly. Consequently the reproduction sensitivity becomes larger than that of the single-layer main pole, and the reproduced voltage is very stable even for lower H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> and narrower track widths.

Summary form only given. Although, today, perpendicular magnetic recording receives substantial attention in the data storage industry, still conventional longitudinal readers (LR) are commonly used in perpendicular recording. Such a system cannot offer the optimal resolution because the LR is designed so that it is dominantly sensitive to the longitudinally written magnetization transitions. In this paper, the conformal mapping (CM) technique is used to develop a theory, which defines the guidelines on how to design an optimal perpendicular reader (PR), which is best suited for perpendicular recording. Schwartz-Christoffel transformation was used to find the requirements for optimal PR designs for providing the playback waveforms identical to the waveforms. provided by an equivalent LR in longitudinal recording. To support the theoretical conclusions, 3D boundary element modeling was developed to calculate the sensitivity field profiles for the yoke type PR and the conventional LR.

A quantitative calculation of the readback performance of shielded MR heads is performed for high density perpendicular magnetic recording, and compared with that from longitudinal recording. An analytical expression of the head field of the MR head with doule layer media is given to be used in a reciprocity calculation. Conditions to achieve a half-height pulse width, PW50' of 115 nm and 70 nm are presented. With these results and SNR estimations, issues of the read/write system to obtain areal densities of 20 Gbpsi and higher are discussed.

Micromagnetic recording field analysis of a fast-switching single-pole-type head