Composite free layer within magnetic tunnel junction for MRAM applications

摘要

A magnetic tunneling junction (MTJ) in an MRAM array is disclosed with a composite free layer having a FL1/FL2/FL3 configuration where FL1 and FL2 are crystalline magnetic layers and FL3 is an amorphous NiFeX layer for improved bit switching performance. FL1 layer is CoFe which affords a high magnetoresistive (MR) ratio when forming an interface with a MgO tunnel barrier. FL2 is Fe to improve switching performance. NiFeX thickness where X is Hf is preferably between 20 to 40 Angstroms to substantially reduce bit line switching current and number of shorted bits. Annealing at 330° C. to 360° C. provides a high MR ratio of 190%. Furthermore, low Hc and Hk are simultaneously achieved with improved bit switching performance and fewer shorts without compromising other MTJ properties such as MR ratio. As a result of high MR ratio and lower bit-to-bit resistance variation, higher reading margin is realized.

主权项

1. A magnetic tunneling junction (MTJ) element in a magnetic device, comprising:
(a) a pinned layer formed on a substrate; (b) a tunnel barrier layer that forms a first interface with the pinned layer; and (c) a composite free layer consisting of a stack of three ferromagnetic layers in a FL1/FL2/FL3 configuration wherein FL1 is a first crystalline ferromagnetic layer with a first thickness that forms a second interface with the tunnel barrier layer along a surface that is opposite to the first interface, FL2 is a second crystalline ferromagnetic layer that is Fe with a second thickness substantially greater than the first thickness, and contacts a top surface of the FL1 layer, and FL3 is an amorphous NiFeX layer where X is one of Hf, Zr, Nb, Ta, or Mg and X has a content between 5 and 12 atomic % in the NiFeX layer, the amorphous NiFeX layer is the uppermost layer in the FL1/FL2/FL3 stack.