David Eugene Heim

Design, fabrication and testing of spin-valve read heads for high density recording

Spin-valve sensors of the type NiFe/Cu/Co have been designed for optimal biasing behavior and successfully incorporated into a gigabit-type shielded read head configuration with a read trackwidth of 2 /spl mu/m, a read gap of 0.25 /spl mu/m, and a MR sensor height of 1 /spl mu/m. The spin-valve sensor had a structure of 100 /spl Aring/ NiFe/25 /spl Aring/ Cu/22 /spl Aring/ Co/110 /spl Aring/ FeMn, and yielded a net spin-valve coefficient of /spl sim/3.5% at the completion of head processing. Uniform field testing of the read heads after wafer fabrication and lapping showed quiet and stable spin-valve response with near optimal bias performance. Recording tests of the read heads at a head-disk clearance of 1.5 /spl mu/m showed linear, non-saturated signal response on a media with an areal moment as high as 1.25 memu/cm/sup 2/, yielding reasonably symmetrical signals with peak-to-peak amplitudes ranging from /spl sim/750 /spl mu/V//spl mu/m to as high as /spl sim/1000 /spl mu/V//spl mu/m of read trackwidth. Linear density rolloffs and microtrack profiles have also been studied, and results showed behaviors closely agreeing with design targets for high density recording operations. >

Design and operation of spin valve sensors

Two types of patterned, unshielded Giant MagnetoResistance (GMR) spin valve sensors have been fabricated: nano-layered NiFe/Co/Cu/Co/NiFe and simpler NiFe/Cu/Co spin valves. GMR values of 7.6% for /spl Delta/H=10 Oe were measured for the nano-layered structures on coupons. Transfer curves in uniform fields were obtained and were in agreement with theoretical expectations. The sensors were highly linear and well biased. Optimum biasing of the free layer in the spin valve sensor has new features over that in AMR sensors. These were explored in shielded as well as unshielded spin valves using micromagnetic simulation. >

Design, fabrication and performance of spin-valve read heads for magnetic recording applications

Since the early 1990s, the introduction of dual-element recording heads with inductive write elements and magnetoresistive (MR) read elements has almost doubled the rate of areal density improvements for hard-disk-drive data storage products. In the past several years, prospects of even more rapid performance improvements have been made possible by the discovery and development of sensors based on the giant magnetoresistance (GMR) effect, also known as the spin-valve effect, for a particular class of sensor configurations. In this paper, we explore the potentials as well as challenges of spin-valve sensors as magnetic recording read heads. We first examine the data rate and areal density potentials of large read-back signals resulting from increases in the MR coefficient. We then discuss associated magnetic sensor performance, including linearity and noise suppression. Finally, we study in detail the magnetic and recording performance of a spin-valve read head designed for 1-Gbl/in. 2 density performance.

Thin-film inductive heads

The development of IBM thin-film inductive recording heads is traced from 1964, through their first introduction in 1979, to the present. We review a number of innovations in thin-film technology materials and processes associated with this type of head. Design and technology changes made since 1979 have led to the development and implementation of heads in several successful recording systems. We also describe efforts to predict the performance of thin-film inductive heads and to understand and control head instabilities and noise.

CAN SPIN VALVES BE RELIABLY DEPOSITED FOR MAGNETIC RECORDING APPLICATIONS?(INVITED)

The tolerance of the expected read-back signal of spin valve giant magnetoresistance based structures to varying deposition and process conditions are described. We determine if spin valves can be produced reliably, and evaluate which thicknesses and properties are most critical. First, the dependence of spin valve properties on layer thickness are experimentally determined. Next, the variation of read-back signal and transfer curve characteristics with spin valve properties is calculated from micromagnetic modeling. Finally, these are convolved with the expected reproducibility of layer thickness to obtain an effective “yield” of structures within 10% of the mean amplitude. We find that spin valves can be reliably deposited, with “yields” well in excess of 90% likely.

Dependence of magnetoresistive head readback characteristics on sensor height

The microtrack profile and bias point of a magnetoresistive (MR) head play a fundamental role in determining the full track response. In this paper the stripe height dependence of these properties is studied. The magnetic center of the MR head is found to approach the physical center, and microtrack side slopes become steeper and more equal as the stripe height is decreased. These experimentally observed trends can be understood using a simple model based on anisotropic flux propagation in the MR sensor.

Direct measurement of recording head fields using a high‐resolution inductive loop (invited)

A method is described for direct measurement of the magnetic microfield from a recording head. The method employs a thin film ‘‘microloop’’ as a transducer which by induction senses the recording head field. Measurements are presented on both a thin film and a ferrite head. Fits to the data allow the absolute efficiency to be determined. Data on the frequency dependence of head efficiency are also presented.

A new, horizontal MR head structure

A novel type of magnetoresistive (MR) head is described. It is based on the horizontal, inductive head and therefore offers a set of process options during fabrication not available with conventionally processed film heads. The authors describe the theory of operation of the head, give an estimate of the signal amplitude, and discuss the dependence of the performance on key parameters. >

On the track profile in magnetoresistive heads

The relationship of the track profile in MR heads to the magnetic state of the MR sensor is studied in two examples. The first, using an exchange bias film for transverse biasing, was chosen because it displays a range of track profile behavior. The second employs soft film biasing. Using a detailed micromagnetic model, the quiescent bias states and track profiles were computed, and the formation of the track profile analyzed in terms of the magnetic response of the MR sensor; The anisotropic propagation of signal flux in the magnetic films of the sensor was seen to have a strong affect. >

The sensitivity function for shielded magnetoresistive heads by conformal mapping

The sensitivity function for symmetric, shielded magnetoresistive heads is obtained using the Schwarz-Christoffel transformation. Various aspects of reading by these heads is then discussed including the previously reported dependance of pulsewidth on shield thickness.