Dependence of Natural Oxidation Spin-Dependent Tunneling Junction on Junction Area

Abstract

The top-type tunneling magnetoresistance (TMR) multilayer films with a structure of Ta5/NiFe10/ Ta5/NiFe10/FeMn10/NiFe2/CoFe2/Al 2 O 3 1/CoFe3/NiFe20 (thickness in nm) with in-situ natural AlO x oxidation were deposited by a sputtering system with a base pressure of 10 --9 Torr. Junctions with sizes from 4 to 80 mm 2 were fabricated by using a conventional photolithography process. The as-deposited junction showed TMR of 16% at room temperature with resistance of 14-15 W, dependent on junction area. IntroductionThe tremendous increase of magnetic recording areal density was partly possible because of this new generation of reading head. For applying TMR read head, to overcome several demerits of high junction resistance such as noise, impedance matching problem, and delay time, it needs to have its resistance time junction area product (R Â A) lowered below a few hundred W mm 2 [1, 2]. From in-situ natural oxidation of Al 2 O 3 , SDT devices can solve the problems of pinholes, barrier doping effect, and overoxidized ferromagnet surface [3,4].In this paper, we present the fabrication of ion beam deposited (IBD) exchanged bias SDT devices using in-situ natural oxidation of Al. The IBD method can produce higher quality thin films (less defects), making IBD devices a good candidate for the deposition of thin Al films in the junctions. Results from micron-sized junctions based on top TMR structure of FeMn/NiFe/CoFe/Al 2 O 3 /CoFe/NiFe are presented. TMR is 8-17% at room temperature, dependent on 80-500 W mm 2 . Annealing of these junctions at 185 C slightly increases the TMR signal, with a slight decrease in junction resistance.