Track width definition of giant magnetoresistive sensors by ion irradiation

We describe the concept of using irradiation with light energetic ions in conjunction with a mask to define the edges of giant magnetoresistive sensors without milling. The irradiated material undergoes substantial interfacial mixing, and consequent loss of magnetoresistance (MR), accompanied by small changes in resistivity, and no significant change in magnetic moment. The ion species and energy may be chosen to minimize lateral scattering as they pass through the sensor film. Modeling of a perfect mask edge above a sensor film of thickness ~240 Å irradiated with a well-collimated ion beam indicates that sensor edge definition of ±20 Å is achievable-a vast improvement over sensor edges generated using ion milling, which may run to hundreds of Angstroms in width. Experimental data from irradiation of typical NiO, IrMn, NiMn and PtMn-based spin valves using 700 keV N⁺ ions indicate that doses between 10¹⁵ and 10¹⁷ ions/cm² are sufficient to diminish the MR of the films to below 5% of the as-grown value. Changes in MR caused by the irradiation are stable against annealing at temperatures typical for setting these sensors