Fabrication of pseudo-spin-valves and 100 nm sized periodic elements for magnetic memory application

Abstract

Co–Cu–Co pseudo spin-valves (PSV’s) and Co–Cu multilayers have been fabricated and studied for the giant magnetoresistance (GMR) effect. Attention is focused on optimizing the low field response. They are deposited on Si (001) wafers without removing the natural silicon-dioxide layer, using S-research sputtering guns in high vacuum. A buffer layer of Cr–Cu was used before depositing the PSVs. Realization magnetic switching at low field for the soft layer and high field for the hard-layer makes the structure suited for MRAM application. The low and high switching fields are typically 100 and 2200 Oe, respectively. The magnetic measurement using SQUID magnetometry and VSM confirms the switching fields in the hysteresis loops of the magnetization. The GMR multilayers have a low switching field of 60 Oe at low temperatures. They are patterned into two-dimensional 100 nm sized periodic dot-array using ultraviolet interferometric lithography. The purpose is to develop processes of fabricating GMR structures over large areas with nanometer feature sizes for high-density memory devices. The coercive field for the patterned structures is enhanced by a factor of four at low temperatures and by a small fraction at higher temperatures. The magnetization remains to be in plane as in un-patterned case.