L.H. An

Low switching current flux-closed magnetoresistive random access memory

A spin valve magnetoresistive random access memory with a flux-closed structure is presented. The flux-closed structure prevents the disruption to magnetization of the recording layer and increases the thermal stability. Simulation results show that the switching field increases under the uniform external field, however, the switching field has no change under the bit current field. Only the bit current that flows mostly at the center is used to switch the cell. Experimental results show that the bit current of 10 mA is sufficient to switch the 1 μm×4 μm cell.

Spin-flop switching of the guided synthetic anti-ferromagnet MRAM

In this work, a new MRAM structure with guided SAF layers is presented. This new structure addresses the issues regarding additional read operation, reduction of saturation field, write operation margin, and unintentional switching.

Nanometer metal line fabrication using a ZEP520∕50K PMMA bilayer resist by e-beam lithography

In this work, we propose a bilayer resist system with 50K poly methylmethacrylate as the bottom layer and ZEP520 as the top layer for lift-off process. By making use of the different dissolution rates in the rinser for the top and bottom layers, it is possible to create an overhang resist pattern suitable for lift-off. In this specific study, a set of process parameters have been optimized to fabricate Cr metal lines with a width of about 70nm. The process has been used to fabricate nanometer scale magnetic sensors for data storage applications.

Sub-100-nm current-perpendicular-to-plane sensor fabrication

Two sets of processes for sub-100-nm current-perpendicular-to-plane (CPP) spin-valves (SVs) were developed. In the first method, a CPP SV was fabricated by using via-hole instead of small cell patterning. This method makes it easy to characterize the CPP spin valve films. The shunting effect has been analyzed in this method. In the second method, a resist layer for planarization, ion-milling, and wet etching for self-opening via-hole in a self-aligned fashion by making use of the height difference between the cell and surrounding regions was introduced. This method is suitable for the actual recording heads with small dimension even without an ion-beam-deposition system. CPP sensors with size from 0.05 /spl mu/m/spl middot/0.05 /spl mu/m to 0.4 /spl mu/m/spl middot/ 0.5 /spl mu/m with different free- layer structures have been investigated by means of the first method.

Exchange coupling between ferromagnetic and laminated antiferromagnetic layers and its application

Exchange bias (Hex) and coercivity (Hc) of the NiFe layer in the NiFe/IrMn system can be tuned by inserting either spacer layers such as Cu, Ru, and Ta or ferromagnetic layers such as CoFe into IrMn since the antiferromagnetic spin structure of IrMn is altered in consequence. Hex usually decreases while Hc increases when the thin discontinued spacer layers are inserted into IrMn. The crossover from the unidirectional exchange-biased coupling to the uniaxial exchange-spring coupling has been successfully observed in the NiFe/[IrMn/CoFe(t)]3/IrMn (here, 3 means the number of the repeated periods of IrMn/CoFe double layer) system when the thickness of CoFe layer t exceeds 1 nm. It indicates that much of the physics and reversal mechanisms in the exchanged-biased systems are similar to that observed in exchange-spring systems where the hard layer replaces the antiferromagnetic layer as the biasing layer. Uniaxial spin valves (both of current in the plane and current perpendicular to the plane modes) and uniax...

Development of current perpendicular to plane differential dual spin valve for ultrahigh resolution

Recently, a differential dual spin valve (DDSV) has been proposed to enhance the downtrack resolution for the application in the hard disk drive recording at 10 Tb/in2 and beyond. The following key issues for the implementation of a high-quality DDSV have been addressed. I. Formation of the antiparallel arrangement of the reference magnetization of two spin valves (SVs) with high pinning stability. II. Differential effect of a DDSV. To achieve perfect differential effect in a DDSV, not only should two SVs have the same giant magnetoresistance effect, but their free-layer (FL) magnetization should also respond to a field identically. Using 2.4 nm ruthenium as the gap layer to form a ferromagnetic interlayer coupling between FLs, a good differential effect is achieved. III. Quasistatic characterization of a DDSV. As there is no output from a DDSV under a uniform field, it would be difficult to evaluate performances of a DDSV. By varying the annealing field direction, field response of each SV as well as dif...

High thermal stable MRAM with a synthetic ferrimagnetic pinned layer

Magnetic random access memory (MRAM) with a synthetic ferrimagnetic (SF) pinned layer has been investigated experimentally and theoretically. The SF pinned layer offers the higher thermal stability due to its even higher anisotropy and larger total thickness. A smaller aspect ratio cell with single domain state, less switching field dependence on the cell size, and lower switching field can be achieved in the SF structure than that in the conventional structure because of the thinner effective thickness. The experimental results show that high heat tolerance can also be achieved in the SF MRAM structure.

The influence of oxygen on structure and magnetic properties of full Heusler Co2MnAl films and magnetic tunnel junctions

Two series of Co2MnAl (CMA) and Co2MnAlO (CMAO) thin films deposited on Si (100) coated with thermo-SiO2 by using two CoMnAl targets were studied. One target is oxygen-free and the other one contains 0.8% oxygen. The properties of the two series CMA (O) films strongly depend on deposition conditions and seed layers. The oxygen impurity is a key factor to influence the properties. It would obviously increase the thickness of magnetic dead layer, weaken the magnetic anisotropy, and significantly decrease the spin polarization in CMA film. The magnetoresistance ratios of IrMn pinned top-type magnetic tunnel junctions by utilizing CMAO/CMA as the bottom ferromagnetic electrode were 19% and 68%, respectively.

Scalable Toggle Read Sensor

A read sensor working in the toggle mode is presented. The free layer comprises a balanced synthetic-antiferromagnetic (SAF) multilayer. The magnetization of the free SAF layer is perpendicular to the air-bearing surface (ABS) when bias field is applied in the direction of the ABS. The magnetization of the reference layer is fixed to be parallel to the ABS instead of perpendicular as is the conventional case. The sensitivity of the toggle read sensor (for small track width) improves significantly compared to the conventional abutted junction bias type. For a toggle sensor with long height structure, performance in both the sensitivity and linearity has also been improved because increased sensor height can be used for the lower bias field. The lower bias field is also compatible with the small gap structure of an in-stack bias scheme. Simulation results also show that the thermal magnetic noise in the toggle sensor is much smaller than that in the conventional biased sensor. Experimental results for both the current-in-plane (CIP) and tunneling-magneto-resistive (TMR) sensors with toggle mode are consistent with our calculation results

High density Flash-like cross-point MRAM

A high density cross-point (CP) MRAM is presented. The CP MRAM comprises two guided synthetic-anti-ferromagnetic (SAF) tri-layers. The SAF tri-layer with higher stiffness serves as the recording layer, and another SAF tri-layer with lower stiffness serves as the reading layer. The easy axis of the recording layer is perpendicular to that of the reading layer. The two orthogonally oriented digital and word lines are aligned 45 degree with the easy axis of the SAF layer. At the un-selected or half-selected state, the resistance is half of the sum of the maximum. Similar to the flash memory, the cell can be selectively read without the selective transistor. These allow the CP MRAM to achieve higher integrated density and lower parasitic current. The SAF tri-layer increases the writing and reading reliability