Giant Magnetoresistance Elements Research Articles

Off-Track and Azimuth Angle Effects in Perpendicular Replay

We investigated the effects of transition curvature on T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50 </sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</sub> for a shielded giant magnetoresistive (GMR) element reading a single, isolated transition recorded on a perpendicular medium in the presence of a soft magnetic underlayer. We considered displacement and rotation of the read head relative to the recorded track and a range of read head geometries. The curvature of the transition adversely affects T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> , which also increases with azimuth angle. Both T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</sub> decrease as either the GMR element or the element-side shield spacing is reduced

Half-metallic ferromagnets for magnetic tunnel junctions byab initiocalculations

Using theoretical arguments, we show that, in order to exploit half-metallic ferromagnets in tunneling magnetoresistance (TMR) junctions, it is crucial to eliminate interface states at the Fermi level within the half-metallic gap; contrary to this, no such problem arises in giant magnetoresistance elements. Moreover, based on an a priori understanding of the electronic structure, we propose an antiferromagnetically coupled TMR element, in which interface states are eliminated, as a paradigm of materials design from first principles. Our conclusions are supported by ab-initio calculations.

Effects of Ga+ ion implantation on the magnetoresistive properties of spin valves

The effects of Ga + ion implantation in SiO 2 /Ta(5 nm)/NiFe(3.5 nm)/CoFe(1.5 nm)/Cu(2.9 nm) /CoFe(2.5 nm)/IrMn(10 nm)/Ta(5 nm) spin valve stacks were investigated. As-deposited films show a giant magnetoresistance (GMR) of 7.3% and an exchange bias field ( H ex ) of 42 mT. After implantation with 30 keV Ga + ions at doses ranging from 10 12 to 10 16 ions/cm 2 , we observe a dramatic decrease in GMR and exchange bias field together with an increase in film resistance. The effects of Ga + ion implantation during FIB milling of small GMR elements was investigated by reducing 10 μm spin valve lines to line widths ranging from 7 to 0.5 μm. The GMR and exchange bias field were found to rapidly decrease with decrease in spin valve width. Magnetic field annealing after Ga + ion implantation does not restore the spin valve properties.

Detailed modeling of temperature rise in giant magnetoresistive sensor during an electrostatic discharge event

With further miniaturization of the giant magnetoresistive (GMR) heads, the electrostatic discharge (ESD) failure has become the primary reliability issue in manufacturing of these sensors. In this article, the thermal response of the GMR read head to excessive current/voltage during an ESD event is investigated numerically, using a three-dimensional (3D) finite element analysis. Unlike the previous studies, the thermal properties of the GMR, Al2O3 gap, and shield layers used in the simulation are the experimentally measured values, which are different from the bulk values. The simulation results show that temperature in the GMR element sharply increases as the GMR dimensions are reduced, indicating the future GMR heads will be more susceptible to the ESD damages. In addition, thermal properties of the GMR elements and the gap materials play key roles in the accurate prediction of the temperature field in a GMR head during ESD events. The simulations are performed for both the current-in-plane (CIP) and perpendicular-to-plane configurations, indicating that latter can sustain much higher ESD voltage (∼160 V) than the CIP-GMR head (∼48 V) for 100 Gbits/in.2 recording density.

Effect of Stress on Magnetic Performance of GMR Head Used for Hard-Disk Drive

The effect of stress on the magnetic performance of a giant magneto-resistive (GMR) head was investigated. The stress in the GMR head consists of residual stress caused by thin-film processing and thermal stress due to heat dissipation in the GMR element. When the difference between the in-plane stresses in the GMR element is large, the output voltage of the head changes; thus, the read characteristic of the hard-disk drive is deteriorated. The stress in the GMR head was analyzed by a three-step finite-element analysis, called zooming FEA, and the magnetic performance of the head under the effect of the stress was calculated. Accordingly, it was found that to reduce the effect of the stress on magnetic performance, the intrinsic stress in the protective layer on the head must be optimized and the temperature rise of the GMR element must be decreased during operation.

Vertical GMR recording heads for 100 Gb/in/sup 2/

Vertical giant magnetoresistive (GMR) recording head designs have been proposed to achieve the optimum bias point and magnetic stability. Using a micromagnetic model, several design options were simulated and a test feature was built to validate the model prediction. The vertical GMR head uses a front lead to connect the GMR element to shield at the air-bearing surface (ABS) and the sense current passes vertically from ABS to the back lead through the active elements. Canted stabilization fields are needed for proper bias for vertical GMR (VGMR) heads. A design proposal for 100 Gb/in/sup 2/ is presented.

Dry etching of AlTiC with CF/sub 4/ and H/sub 2/ for slider fabrication

AlTiC etching in CF/sub 4/ and H/sub 2/ high-density plasma is investigated. Its etching rate is relatively high and it is not corrosive to the giant magnetoresistive elements. The effects of etching parameters such as pressure, gas flow rate, radio-frequency power, and inductively coupled plasma power on the etching rate, selectivity and surface roughness are studied. The etching parameters are optimized to balance the etching rates of Al/sub 2/O/sub 3/ and TiC in order to obtain a smooth etched surface. The etching wall profile and a fabricated 6-nm flying height femto slider are also presented.

Flux-enhanced giant magnetoresistive head design and simulation

The possibility of introducing a back flux-guide to increase the efficiency of a shielded giant magnetoresistive (GMR) head was studied. The flux-guide instead of the air effectively increases flux at the top of the GMR element, which leads to an increase of GMR head's sensitivity. The flux distribution was calculated by a two-dimensional (2-D) finite element method. In the simulation, the shield to shield spacing, free layer thickness, and GMR element height are assumed to be 90 nm, 4 nm, and 100 nm, respectively. Parameters such as permeability, thickness and height of flux-guides and spacing between the GMR element and flux-guides have been taken into account. The detailed magnetization distribution is simulated using a three-dimensional (3-D) micromagnetic modeling. A back flux-guide with permeability of more than 100, thickness of more than 10 nm, as well as short spacing between the element and flux-guide enhances the sensor's sensitivity. After optimization, the sensitivity of flux-enhanced magnetic tunnel junctions (MTJ) GMR head can be 40% higher than that of the conventional MTJ GMR head.

Magnetoresistive sensors for string instruments

Pickup elements for string instruments, in particular for electric guitars, represent a new application area for magnetoresistive sensors. Recently we developed a sensor configuration with permanent magnets for this purpose. For the first experiments we used commercial anisotropic magnetoresistance sensors (Philips KMZ10) mounted on small ferrite bias magnets. Recently we equipped an electric guitar with prototypes comprising giant magnetoresistance (GMR) sensors. These prototype MR pickup elements showed several clear advantages compared to the presently commonly used inductive pickup units. They are much less sensitive to disturbing electromagnetic fields (&amp;gt;1000×at 5 kHz), mainly because their active sensor area is several orders of magnitude smaller (a few mm2 instead of cm2). Also the larger freedom in the choice of the permanent magnets (due to the larger sensitivity of the GMR elements) is advantageous: employing smaller magnets reduces the damping and thus significantly improves the sustain, the magnets can be less expensive and more stable magnet materials can be chosen so that aging effects are eliminated.

Effect of Stresses on Magnetic Performance of GMR Heads used for Hard-Disk Drives.

In giant magneto-resistive (GMR) heads used for hard disk-drives, residual stress is caused by thin film processing, and thermal stress due to heat dissipation of the GMR elements. When the difference in in-plane principal stresses in the GMR elements is large, the output voltage of the GMR heads changes and thus the read/write characteristic of hard disk-drives may be deteriorated. We have analyzed the stress in a GMR head by a finite element method with three-step zooming models. Then, we calculated the effect of this stress on magnetic performance of the GMR head. It was found that an intrinsic stress in the protective layer must be optimized and temperature increase of a GMR element must be decreased during operation to decrease the effect of the stress on magnetic performance.

Directional sensitivity of GMR element and its industrial applications

Giant magneto-resistive (GMR) elements are applied to several industrial magnetic sensors. This paper deals with the directional sensitivity of GMR elements, and their industrial applications. The use of GMR element has several advantages for other sensors. In the area of data storage, GMR elements are generally used to detect the magnetic field impressed in the direction of the stripe width. However, the GMR element has high sensitivity in the direction of the length as well as the width, even if it is a stripe shape. In addition, we obtain an omnidirectional sensitivity of GMR elements. Using the GMR element, we developed a GMR line sensor. This sensor visualized a magnetic field by only a single scan.

Nonvolatile reprogrammable logic elements using hybrid resonant tunneling diode–giant magnetoresistance circuits

We have combined resonant interband tunneling diodes (RITDs) with giant magnetoresistance (GMR) elements so that the GMR element controls the switching current and stable operating voltage points of the hybrid circuit. Parallel and series combinations demonstrate continuous or two-state tunability of the subsequent RITD-like current–voltage characteristic via the magnetic field response of the GMR element. Monostable–bistable transition logic element operation is demonstrated with a GMR/RITD circuit in both the dc limit and clocked operation. The output of such hybrid circuits is nonvolatile, reprogrammable, and multivalued.

Integrated giant magnetoresistance bridge sensors with transverse permanent magnet biasing

Two types of giant magnetoresistance (GMR) multilayer bridge sensors with integrated permanent magnet biasing are demonstrated. These sensors differ from previous designs where external permanent magnets were used. The bridges consist of four active GMR multilayer elements at the first antiferromagnetic coupling peak of a NiFe/[NiFe/CoFe/Cu]10 structure (GMR=18%). Bridge linearization is obtained by creating opposite biasing fields of equal amplitude (±200 Oe) in contiguous GMR elements of the bridge structure. This is achieved either by using pairs of permanent magnets with the same Mrt value (14 memu/cm2) but different coercivities (type I bridge, Hc1=1400 Oe, Hc2=800 Oe), or by using a single type of permanent magnet and placing the GMR sensor either under the magnet, or on its side (type II bridge). Linear ranges of ±200 Oe with field sensitivities of 0.3 mV/(V×Oe) were obtained in these bridges.

GMR Revolution Sensors for Automobiles

In order to apply Giant Magneto-Resistive (GMR) elements to revolution sensors for automobiles, we studied an annealing effect upon GMR elements. After the GMR elements were annealed with the optimized condition, they showed sufficient temperature stability for automobile applications, as well as large MR ratio. The GMR elements were integrated with a sensing processing IC without any damage during the GMR wafer process. Sensitive sensor properties were obtained, especially the repeatability was three times better than that of a semiconductor Hall revolution sensor, which was due to that the integration of the GMR element with IC prevented noise and the signal output of the GMR element was one order higher than that of the semiconductor Hall revolution sensor.

The electrical and magnetic response of yoke-type read heads based on a magnetic tunnel junction

Based on model calculations a comparison is made between yoke-type read heads containing a tunnel junction magnetoresistive element (TMRE) and containing a giant magnetoresistive element (GMRE). For typical head design parameters, TMR-based heads are 3-5 times more flux-efficient than GMR-based heads. However, for approximately 1/spl times/1 /spl mu/m/sup 2/ elements, the SNR of TMRE-based heads is not advantageous as long as the junction's tunnel resistance is not drastically reduced below R=1 k/spl Omega/.

Planar, contact, yoke GMR head vs. conventional, flying, shielded GMR head: a comparative study

A comparative study was conducted between planar, contact, yoke GMR (Giant Magneto-resistive) heads and conventional, flying, shielded GMR heads by modeling. Magnetic flux efficiencies to the GMR element of the various planar yoke GMR heads were estimated using the reluctance network method and FEM(Finite Element Method). Results showed that it would be necessary to separate the reading magnetic circuit from the writing magnetic circuit in order to obtain higher efficiencies which could be up to 37%, 5 and 10 Gbits/in/sup 2/ recording simulation shows that the shielded GMR are expected to be superior to the yoke GMR even at 10 Gbits/in/sup 2/ but yoke GMR will start to show its advantages in the higher capability of writing and ease of processing at higher densities.

Experimental study of the validity of simple design rules for the biasing of spin-valve-type GMR heads

From an analytical description of magnetic interactions combined with finite-element modelling, design rules for a giant magnetoresistance (GMR) element can be derived. For some practical designs we arrive at the conditions tPMSP < tfMSf and tpMSP ≈ γhHF. Here tp, tf, MSP and MSf are the layer thicknesses and the saturation magnetizations of the pinned and the free layer, respectively; h is the element height, HF is the ferromagnetic interlayer coupling and γ accounts for the soft magnetic environment of the sensor. We have fabricated yoke-type GMR heads in an adapted design conforming to these rules. The GMR elements were Ta/8 nm Ni80Fe20/2.8 nm Cu/6 nm Ni80Fe20/10 nm FeMn/Ta. From finite-element calculations we find that for our heads γ ≈ 2, which together with HF = 6 Oe and h = 5 μm obeys the design rules. Measurements of these heads show that indeed the optimum bias state is obtained without using the integrated bias conductor to apply a d.c. bias current. Measurements also show that the limiting factor for the head output in this case may no longer be the head efficiency (geometry), but the maximum driving amplitude (saturation) of the GMR element. This sheds new light on the current discussion whether for application of spin-valve materials in thin-film heads, a yoke-type or a shielded-type design would be advantageous.

Anisotropic and giant magnetoresistive elements

The technology of magnetoresistive element (MRE) fabrication and integration as well as some experimental results on the performance of anisotropic and giant magnetoresistive elements are discussed. Most emphasis is put on isolated MREs in specially designed test structures, although results on completed heads will also be discussed. Aspects such as output signal level, noise level, distortion and magnetic stability are the performance indicators considered.

1/f noise in anisotropic and giant magnetoresistive elements

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction.

Chemical-mechanical polishing as an enabling technology for giant magnetoresistance devices

Abstract Giant magnetoresistance (GMR) devices, integrated with conventional Si interconnects (ICs), are promising candidates for future data-storage applications. Chemical-mechanical polishing (CMP), a surface smoothing and planarization process, is anticipated to be a key technology in the demonstration of full functionality of such GMR components. In this work, we report on the fabrication of GMR device elements through chemical-mechanical polishing of silicon nitride interlevel dielectrics (ILD). Our results show that the silicon nitride polishing process using commercially available slurries and pads is compatible with copper interconnects and copper metallized GMR elements. Contact resistivity between Cu and Cu as low as 5×10 −10 Ω -cm 2 has been achieved with the CMP process and related processing techniques, as obtained by de-embedding the contact resistance from GMR device measurements.