Magnetoresistive Heads Research Articles

Current-in-Plane GMR Trilayer Head Design for Hard-Disk Drives: Characterization and Extendibility

The current-in-plane giant magnetoresistive (GMR) trilayer readback sensor (CIP-3L), where only one permanent magnet at the back edge of the GMR stack is used to stabilize and bias a dual free layer system, is reviewed. Micromagnetic modeling is employed to show that the design has improved efficiency over abutted junction (ABJ) tunneling magnetoresistive (TMR) head designs. An experimental evaluation of how permanent magnet thickness (PM Th), interlayer exchange coupling (J), and stripe height impact the signal-to-noise ratio, symmetry, and stability of prototype CIP-3L heads is conducted. The study indicates that PM Th >400 nm, J<-0.8 erg/cm2, and a read width to SH aspect ratio of 1:1 to 0.75:1, gives optimal transfer curve performance. A head gimbal assembly spinstand comparison on perpendicular recording media with best-in-class TMR readers shows that although the amplitude of the CIP-3L heads is lower (believed to be process related), the symmetry, stability, and most important, bit-error rate normalized to electrical write width and read width, are comparable. In addition, the CIP-3L design shows better linearity and low-frequency noise performance than TMR heads. The areal density performance of the best CIP-3L heads shows 195 Gb/in2 recording capability and linear densities of 1100 kbpi

Tunneling Magnetoresistive Heads for Magnetic Data Storage

Spintronics is emerging to be a new form of nanotechnologies, which utilizes not only the charge but also spin degree of freedom of electrons. Spin-dependent tunneling transport is one of the many kinds of physical phenomena involving spintronics, which has already found industrial applications. In this paper, we first provide a brief review on the basic physics and materials for magnetic tunnel junctions, followed more importantly by a detailed coverage on the application of magnetic tunneling devices in magnetic data storage. The use of tunneling magnetoresistive reading heads has helped to maintain a fast growth of areal density, which is one of the key advantages of hard disk drives as compared to solid-state memories. This review is focused on the first commercial tunneling magnetoresistive heads in the industry at an areal density of 80 approximately 100 Gbit/in2 for both laptop and desktop Seagate hard disk drive products using longitudinal media. The first generation tunneling magnetoresistive products utilized a bottom stack of tunnel junctions and an abutted hard bias design. The output signal amplitude of these heads was 3 times larger than that of comparable giant magnetoresistive devices, resulting in a 0.6 decade bit error rate gain over the latter. This has enabled high component and drive yields. Due to the improved thermal dissipation of vertical geometry, the tunneling magnetoresistive head runs cooler with a better lifetime performance, and has demonstrated similar electrical-static-discharge robustness as the giant magnetoresistive devices. It has also demonstrated equivalent or better process and wafer yields compared to the latter. The tunneling magnetoresistive heads are proven to be a mature and capable reader technology. Using the same head design in conjunction with perpendicular recording media, an areal density of 274 Gbit/in2 has been demonstrated, and advanced tunneling magnetoresistive heads can reach 311 Gbit/in2. Today, the tunneling magnetoresistive heads have become a mainstream technology for the hard disk industry and will still be a technology of choice for future hard disk products.

Modeling Electrostatic Discharge Affecting GMR Heads

Electrostatic discharge (ESD) damage to giant magnetoresistive (GMR) heads is investigated using a charged device model tester. The sensor of a GMR head is easily affected by ESD during handling in production. Simulation of the picking procedure reveals that elevating such a small-capacitance device above the work surface increases the potential by up to ten times and the discharge current by up to five times. With 20-V initial potential, which could be applied by the picking tool, the elevation of a 5-pF capacitance by just 10 mm increases the potential to 200 V and the peak discharge current to 578 mA. In the case of a 1-pF capacitor, however, the potential and peak current remained low due to the effect of stray capacitance. In the case of a GMR head with 3.7-pF capacitance, a 5-mm lift reduced the initial potential causing ESD damage from 60 V to less than 40 V. Waveforms of discharge reveal that the GMR head can be designed to reduce the ESD risk.

Dilute Magnetic Materials for Spintronic Applications

AbstractThis issue of physica status solidi (a) contains papers submitted to the Symposium E: 'Dilute magnetic materials for spintronic applications' which took place during the 2006 European Materials Research Society (E‐MRS) Fall meeting held in Warsaw on 4–8 September 2006. It highlights the current high scientific interest in the development of dilute magnetic semiconductors (DMS) and other materials exhibiting ferromagnetism (FM) for e.g. spin‐enabled sensors, light emitters, and transistors. The magnetic behaviour of such materials is due to the introduction of transition metal (TM) ions, such as Mn and Cr, into appropriate semiconductor or oxide crystals. Ferromagnetic ordering in Mn‐doped narrow‐bandgap semiconductors, such as GaAs and InAs, has been studied for some time. However, these DMS materials have a relatively low Curie temperature (T C &lt; 180 K), which severely limits their usefulness.Recently, a number of research groups have reported achieving ferromagnetism at room temperature (RT) in TM‐doped wide‐bandgap materials, such as GaN and ZnO. Consequently, these DMS materials are very attractive for integration of photonic (light‐emitting diodes), electronic (field effect transistors), and magnetic (memory) devices on a single substrate. Indeed a new class of optoelectronic devices based on these materials may offer multipurpose functionality for sensing, information storage, and ultra‐low power switching elements.The symposium gathered some 70 contributions, which brought together physicists, chemists, materials scientists to discuss the status and future of spintronic materials in this fast evolving field. Indeed, the direct connection between fundamental developments in spintronics and applications to data storage (hard disk magnetoresistive read heads or magnetic random access memories), data processing (magnetic logic) is fuelling this research.The topics have included design of dilute magnetic materials, spin monitoring and investigation of FM in semiconductors, oxides, and organic materials doped with transition metals. One of the conclusions of this meeting has been that the origin of RT FM observed in wide bandgap DMS may be related to local disorder, and is probably not purely carrier mediated. And non‐uniform materials such as Konbu phases were theoretically as well as experimentally shown to be the origin of highly efficient RT FM.The issue is organized in three sections which reflect the sessions of the EMRS symposium. The first session deals with the theory of ferromagnetism in dilute magnetic materials, the second is basically concerned with ferromagnetism in various materials: oxides as well as semiconductors. The last section collects the contributions which have exploited advanced spectroscopic techniques to create, understand and manipulate spin polarization and coherence.The Organisers

Discharge Current From Coated Wire to GMR Head

The giant magnetoresistive (GMR) head used in magnetic recording is an extremely sensitive device that is sensitive to electrostatic discharge (ESD). A generally available coated wire that is electrified on its surface can increase the potential of the copper core. When the wire is touched to the GMR head terminal, the discharge current can damage the sensor of the GMR head. Four types of wires were measured for three lengths each. Resin-coated wires were electrified from 20 V to more than 1 kV. The peak current discharging to the GMR head ranged from 100 mA to more than 1000 mA. A resin-coated wire as short as 5 cm was found to damage the GMR head. Among the wires examined herein, only the enameled wire is recommended to connect the GMR head because no charge or discharge currents were observed for this wire. When an ionizer is used to neutralize the tribocharge on the surface of the wire, the remaining charge in the copper core depends on the effectiveness of the neutralization process. A wire with an antistatic coating is required in order to reduce the ESD threat to sensitive devices such as the GMR head

Thermal Transient Response of Electrical Self Heating in Current-in-Plane Magnetoresistive Heads

This paper presents an electrothermal model using dynamic resistance thermometry to determine the temperature rise of a current-in-plane GMR sensor in response to imperfect electrical bias (i.e., a DC bias with transients). Measurement and simulation results are given for two different GMR heads (width 500 and 150 nm, respectively). The smaller of the heads is shown to have a virtual instantaneous thermal response (0.2 ns) to transients. Such transients in the bias can, therefore, endanger the read stability and expected lifetime for today's small heads. It is also shown that the peak in the sensor temperature rise is much larger than the sum of the temperature rise due to the bias current and due to the transient current determined separately

Multichannel Write and GMR Heads for Over 1 TB Tape System

This paper reports on the structure and performance of multichannel write and giant magnetoresistive (GMR) heads for a helical-scan tape system. The four-channel write head was fabricated with four layers stacked and shifted by a track pitch. The eight-channel read head was also stacked four layers, each of which has two spin-valve elements. The write head and read head were assembled into a commercial drive. Four channels are written in one revolution without a guard band and each of the eight channels is read, in half of the track pitch. The feasibility of a recording density over 4.3 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was established, which would make possible a tape system of over 1 TB using an 8 mm cassette

Characteristics of Electrostatic Discharge Induced Damage on Magnetic Tunnel Junctions

We report on the investigation of electrostatic discharge (ESD) sensitivity of current perpendicular to plane (CPP) magnetic tunnel junction (MTJ) heads used in hard disk drives (HDD). Our results show that MTJs have different degradation characteristics and mechanisms from current in-plane (CIP) giant magnetoresistive (GMR) heads when exposed to cumulative ESD current transients. Both MTJ and GMR heads show gradual amplitude degradation as a result of increasing ESD levels, but MTJs are more robust than GMR heads in terms of sensor stack magnetic stability, such as polarity flip. Large ESD voltages could change stability state of the MTJ heads, which shows up as random telegraph noise associated with transfer curve magnetic distortions in low-frequency regime and noise spikes several times above baseline noise in high-frequency regime. This MTJ instability is likely a result of defects in the multilayer reader magnetics and disturbances, as well as degradation of tunnel oxide barrier.

Corrosion-Resistant GMR Head for Over 1-TB Tape System

We have developed a corrosion-resistant giant magnetoresistance (GMR) head using a spin-valve (Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) film for an over 1-TB helical tape system. The magnetic properties of the corrosion-resistant GMR head were preserved during a Battelle Class II test for 20 days. The sense current shunting in the spacer layer of the spin-valve film (SV) was less for CuAu than for Cu due to the higher resistivity of CuAu. The interlayer-coupling field in the corrosion-resistant SV film was about 25% that in conventional SV films. Therefore, each layer of the corrosion-resistant SV film was designed so as to optimize the bias point. For stripe-heights in the range from 0.7 to 0.4 mum, the asymmetry of the head output was maintained at plusmn20%. The recording characteristics had a signal-to-noise ratio (SNR) of 19.5 dB with a 0.7 mum track width at a 254 kFCI linear density. Using this head, a tape system of over 1 TB per cassette is possible

The Feasibility of$+15$Gb/in$^2$High-Density Recording With Barium-Ferrite Particulate Media and a GMR Head

The feasibility of a high-density magnetic particulate recording medium with a thin magnetic layer of evenly dispersed high-coercivity barium-ferrite particles was investigated. Thermal stability, writability, and an areal recording density of 17.5 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were confirmed for a flexible disk system using a giant magnetoresistive head

Field dependence of high-frequency magnetic noise in tunneling magnetoresistive heads

Thermal magnetization fluctuations in tunneling magnetoresistive heads with track width of ∼100nm have been studied through high-frequency magnetic noise measurement as a function of both transverse and longitudinal fields. The study suggests that in the dynamic region of the heads, the related power spectral density is determined by the magnetization fluctuations of the free layer. At high fields which drive the sensor to the magnetization saturation, an “abnormal” resonance with substantially high amplitude in comparison with that of the free layer is observed when the magnetization of the free layer is nearly antiparallel to that of the reference layer. This abnormal resonance is excluded from the spin torque effect. The detailed analysis suggests that this resonance is due to the magnetization fluctuations in the reference/pinned layers.

Magnetic actuators and sensors

Preface. PART I MAGNETICS. 1. Introduction. 1.1 Overview of Magnetic Actuators. 1.2 Overview of Magnetic Sensors. 1.3 Actuators and Sensors in Motion Control Systems. References. 2. Basic Electromagnetics. 2.1 Vectors. 2.1.1 Gradient. 2.1.2 Divergence. 2.1.3 Curl. 2.2 Ampere's Law. 2.3 Magnetic Materials. 2.4 Faraday's Law. 2.5 Potentials. 2.6 Maxwell's Equations. Problems. References. 3. Reluctance Method. 3.1 Simplifying Ampere's Law. 3.2 Applications. 3.3 Fringing Flux. 3.4 Complex Reluctance. 3.5 Limitations. Problems. References. 4. Finite-Element Method. 4.1 Energy Conservation and Functional Minimization. 4.2 Triangular Elements for Magnetostatics. 4.3 Matrix Equation. 4.4 Finite-Element Models. Problems. References. 5. Magnetic Force. 5.1 Magnetic Flux Line Plots. 5.2 Magnetic Energy. 5.3 Magnetic Force on Steel. 5.4 Magnetic Pressure on Steel. 5.5 Lorentz Force. 5.6 Permanent Magnets. 5.7 Magnetic Torque. Problems. References. 6. Other Magnetic Performance Parameters. 6.1 Magnetic Flux and Flux Linkage. 6.1.1 Definition and Evaluation. 6.1.2 Relation to Force and Other Parameters. 6.2 Inductance. 6.2.1 Definition and Evaluation. 6.2.2 Relation to Force and Other Parameters. 6.3 Capacitance. 6.3.1 Definition. 6.3.2 Relation to Energy and Force. 6.4 Impedance. Problems. References. PART II ACTUATORS. 7. Magnetic Actuators Operated by Direct Current. 7.1 Solenoid Actuators. 7.1.1 Clapper Armature. 7.1.2 Plunger Armature. 7.2 Voice Coil Actuators. 7.3 Other Actuators Using Coils and Permanent Magnets. 7.4 Proportional Actuators. 7.5 Rotary Actuators. Problems. References. 8. Magnetic Actuators Operated by Alternating Current. 8.1 Skin Depth. 8.2 Power Losses in Steel. 8.2.1 Laminated Steel. 8.2.2 Equivalent Circuit. 8.2.3 Solid Steel. 8.3 Force Pulsations. 8.3.1 Force with Single AC Coil. 8.3.2 Force with Added Shading Coil. 8.4 Cuts In Steel. 8.4.1 Special Finite-Element Formulation. 8.4.2 Loss and Reluctance Computations. Problems. References. 9. Magnetic Actuator Transient Operation. 9.1 Basic Timeline. 9.2 Size, Force, and Acceleration. 9.3 Linear Magnetic Diffusion Times. 9.3.1 Steel Slab Turnon and Turnoff. 9.3.2 Steel Cylinder. 9.4 Nonlinear Magnetic Diffusion Time. 9.4.1 Simple Equation for Steel Slab with B-H. 9.4.2 Transient Finite-Element Computations for Steel Slabs. 9.4.3 Simple Equation for Steel Cylinder with B-H. 9.4.4 Transient Finite-Element Computations for Steel Cylinders. Problems. References. PART III SENSORS. 10. Hall Effect and Magnetoresistive Sensors. 10.1 Simple Hall Voltage Equation. 10.2 Hall Effect Conductivity Tensor. 10.3 Finite-Element Computation of Hall Fields. 10.3.1 Unsymmetric Matrix Equation. 10.3.2 2D Results. 10.3.3 3D Results. 10.4 Toothed Wheel Hall Sensors for Position. 10.5 Magnetoresistance. 10.5.1 Classical Magnetoresistance. 10.5.2 Giant Magnetoresistance. 10.5.3 Newest Forms of Magnetoresistance. 10.6 Magnetoresistive Heads for Hard-Disk Drives. Problems. References. 11. Other Magnetic Sensors. 11.1 Speed Sensors Based on Faraday's Law. 11.2 Inductive Recording Heads. 11.3 Proximity Sensors Using Impedance. 11.3.1 Stationary Eddy Current Sensors. 11.3.2 Moving Eddy Current Sensors. 11.4 Linear Variable Differential Transformers. 11.5 Magnetostrictive Sensors. 11.6 Flux Gate Sensors. 11.7 Magnetometers and Motes. Problems. References. PART IV SYSTEMS. 12. Coil Design and Temperature Calculations. 12.1 Wire Size Determination for DC Currents. 12.2 Coil Time Constant and Impedance. 12.3 Skin Effects and Proximity Effects for AC Currents. 12.4 Finite-Element Computations of Temperatures. 12.4.1 Thermal Conduction. 12.4.2 Thermal Convection and Thermal Radiation. 12.4.3 AC Magnetic Device Cooled by Conduction, Convection, and Radiation. Problems. References. 13. Electromagnetic Compatibility. 13.1 Signal-to-Noise Ratio. 13.2 Shields and Apertures. 13.3 Test Chambers. 13.3.1 TEM Transmission Lines. 13.3.2 TEM Cells. 13.3.3 Triplate Cells. Problems. References. 14. Electromechanical Finite Elements. 14.1 Electromagnetic Finite-Element Matrix Equation. 14.2 0D and 1D Finite Elements for Coupling Electric Circuits. 14.3 Structural Finite-Element Matrix Equation. 14.4 Force and Motion Computation by Timestepping. 14.5 Typical Electromechanical Applications. 14.5.1 DC Solenoid with Slowly Rising Input Current. 14.5.2 DC Solenoid with Step Input Voltage. 14.5.3 AC Clapper Solenoid Motion and Stress. 14.5.4 Transformers with Switches or Sensors. Problems. References. 15. Electromechanical Analysis Using Systems Models. 15.1 Electric Circuit Models of Magnetic Devices. 15.1.1 Electric Circuit Software Including SPICE. 15.1.2 Simple LR Circuits. 15.1.3 Tables of Nonlinear Flux Linkage and Force. 15.1.4 Analogies for Rigid Armature Motion. 15.1.5 Maxwell SPICE Model of Bessho Actuator. 15.1.6 Simplorer Model of Bessho Actuator. 15.2 VHDL-AMS/Simplorer Models. 15.2.1 VHDL-AMS Standard IEEE Language. 15.2.2 Model of Solenoid Actuator. 15.3 MATLAB/Simulink Models. 15.3.1 Software. 15.3.2 MATLAB Model of Voice Coil Actuator. 15.4 Including Eddy Current Diffusion Using a Resistor. 15.4.1 Resistor for Planar Devices. 15.4.2 Resistor for Axisymmetric Devices. Problems. References. 16. Coupled Electrohydraulic Analysis Using Systems Models. 16.1 Comparing Hydraulics and Magnetics. 16.2 Hydraulic Basics and Electrical Analogies. 16.3 Modeling Hydraulic Circuits in SPICE. 16.4 Electrohydraulic Models in SPICE and Simplorer. 16.5 Hydraulic Valves and Cylinders in Systems Models. 16.5.1 Valves and Cylinders. 16.5.2 Use in SPICE Systems Models. 16.6 Magnetic Diffusion Resistor in Electrohydraulic Models. Problems. References. Appendix: Symbols, Dimensions, and Units. Index.

Analytic three-dimensional response function of a double-shielded magnetoresistive or giant magnetoresistive perpendicular head

Using the Fourier method, we have derived a three-dimensional, fully analytic model of a shielded magnetoresistive or giant magnetoresistive head for perpendicular replay. The head may include side shields. The field and the spectral response function are expressed in closed form. Here, we use the model to show the effect of varying the sensor-shield spacings and the air-bearing-surface-underlayer separation on the field and response of the sensor at high areal density.

Evaluation of gap length fluctuation with harmonic analysis method

Gap length (GL) of reading head is one of the most critical parameters for high-density magnetic recording systems. A novel method is proposed for quantitative evaluation of the GL fluctuation among a batch of magneto-resistive/giant magneto-resistive heads with same structure design. The method works at head-gimbal assembly level and the evaluation can be done with any read/write analysis equipment. The testing process is based on harmonic analysis of the readback signal. The testing system consists of a selected reference head and sample heads for evaluation. A GL variation function is introduced for the evaluation of GL deviation between the reference head and sample head. This method proved to be easy for implementation and results suggest that variation of GL is considerable and has obvious effect on recording performance in high recording density systems.

Current-induced magnetization switching in exchange-biased spin valves for current-perpendicular-to-plane giant magnetoresistance heads

In contrast to earlier studies performed on simple $\mathrm{Co}∕\mathrm{Cu}∕\mathrm{Co}$ sandwiches, we have investigated spin-transfer effects in complex spin-valve pillars with a diameter of 130 nm developed for current-perpendicular-to-plane magnetoresistive heads. The structure of the samples included an exchange-biased synthetic pinned layer and a free layer, both laminated by insertion of several ultrathin Cu layers. Despite the small thickness of the polarizing layer, our results show that the free layer can be switched between the parallel (P) and the antiparallel (AP) states by applying current densities of the order of ${10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{A}∕{\mathrm{cm}}^{2}$. A strong asymmetry is observed between the two critical currents ${I\phantom{\rule{0.1em}{0ex}}}_{c}^{\mathrm{AP}\text{\ensuremath{-}}\mathrm{P}}$ and ${I}_{c}^{\mathrm{P}\text{\ensuremath{-}}\mathrm{AP}}$, as predicted by the model of Slonczewski. Due to the use of exchange-biased structures, the stability phase diagrams could be obtained in the four quadrants of the $(H,I)$ plan. The critical lines derived from the magnetoresistance curves measured with different sense currents, and from the resistance versus current curves measured for different applied fields, match each other very well. The main features of the phase diagrams can be reproduced by investigating the stability of the solutions of the Landau-Lifshitz-Gilbert equation including a spin-torque term, within a macrospin model.

Commercial TMR heads for hard disk drives: characterization and extendibility at 300 gbit2

Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in/sup 2/ in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in/sup 2/ has been demonstrated. Advanced design can reach 311 Gbit/in/sup 2/.

A performance study of next generation's TMR heads beyond 200 gb/in/sup 2/

Practical level performance for /spl sim/200 Gb/in/sup 2/ has been verified by AlOx barrier tunneling magnetoresistive (TMR) heads, which resistance area product (RA) is more than 3 ohm/spl middot//spl mu/m/sup 2/, in perpendicular recording mode. In addition, improved AlOx barrier magnetic tunnel junctions (MTJs) formed on plated bottom shield with smoothed surface achieved TMR ratio of 25% and 16% with RA of 1.9 and 1.0 ohm/spl middot//spl mu/m/sup 2/, respectively, indicating over 200 Gb/in/sup 2/ is also possible by the AlOx barrier TMR heads with lower RA. Furthermore, TMR heads with crystalline MgO barrier were fabricated. The MgO barrier MTJs formed on plated bottom shield with smoothed surface achieved TMR ratio of 88% with RA of 2.0 ohm/spl middot//spl mu/m/sup 2/, which is 3.5 times higher than that of AlOx barrier MTJs under similar RA. Dynamic electrical test was also performed for TMR heads with the MgO barrier. As a result, good readback waveform with huge output was obtained. This is the first confirmation of readback waveform generated from TMR heads with crystalline MgO barrier. Our results indicate that the future of TMR heads technology is promising beyond 200 Gb/in/sup 2/ application.

Giant magnetoresistive electrostatic discharge damage by a surrounding trigger

Through an electrostatic discharge (ESD) damage case study of giant magnetoresistive (GMR) head in shunting process of head gimbal assemblies (HGA), this paper unveils that GMR heads would be damaged by a combination of field-induced voltage on HGA and surrounding trigger event. This investigation further demonstrates that the ESD protection technique, which derives from metal-to-metal contact to GMR terminals and thus focuses on eliminating metal-to-metal contact to GMR terminals, is not sufficient to prevent ESD. The electromagnetic interference caused by nearby trigger event needs to be noted also in the ESD control.

Simulation of noise, signal-to-noise and bandwidth of TMR and CIP/CPP GMR heads

In magnetic data storage the noise and signal-to-noise ratio (SNR) of the read heads is becoming more and more of a limiting factor given the smaller readout devices needed to follow the ever higher areal densities. For higher data rates this problem is aggravated by the needed wider signal bandwidths. This study presents the magnetic simulation of noise, SNR, and bandwidth for the most common types of head: tunneling magnetoresistive heads, CIP-GMR heads, and CPP-GMR heads. Such simulations allow the comparison of these different types of head. The sensitivity factors of the SNR for the most important head parameters are determined as well. The SNR of the total read path is also determined, including the head-amplifier interconnect and the electronics.

Magnetoresistive playback heads for bit-patterned medium recording applications

This work examines playback characteristics of common magnetoresistive heads applied in magnetic recording systems based on bit-patterned medium. Playback for different head designs is evaluated using the reciprocity principle. Analytical solution for a pointlike reader is used to elucidate the playback resolution limits for a given patterned medium morphology. Various recording system design parameters including recording layer design (thickness, bit geometry, and bit-to-bit spacing), exchange/buffer layer thickness, soft underlayers, and fly height are examined. Differential readers are shown to offer significantly higher spatial resolution, higher signal amplitude, and the weakest dependence on fly-height variations and bit geometry. For example, for a 1Tb∕in2 reader design considered, D50 is 1.46 and 2.64Tb∕in2 for shielded and differential readers, respectively; differential readers have more than 35% higher playback amplitude than equivalent shielded readers. The loss in playback amplitude can be as high 18% due to bit-corner rounding (lithography imperfections) for shielded readers; differential readers exhibit only a weak dependence on bit-corner rounding (±2%–3%). Pseudodifferential readers with a single-sensor element are shown to offer advantages similar to the advantages of conventional double-sensor differential readers while addressing manufacturability issues.