High performance MTJ element for conventional MRAM and for STT-RAM and a method for making the same
View Patent ↗A STT-RAM MTJ that minimizes spin-transfer magnetization switching current (Jc) is disclosed. The MTJ has a MgO tunnel barrier layer formed with a natural oxidation process to achieve a low RA (10 ohm-um 2 ) and a Fe or Fe/CoFeB/Fe free layer which provides a lower intrinsic damping constant than a CoFeB free layer. A Fe, FeB, or Fe/CoFeB/Fe free layer when formed with a MgO tunnel barrier (radical oxidation process) and a CoFeB AP 1 pinned layer in a MRAM MTJ stack annealed at 360° C. provides a high dR/R (TMR)>100% and a substantial improvement in read margin with a TMR/Rp_cov=20. High speed measurement of 100 nm×200 nm oval STT-RAM MTJs has shown a J c0 for switching a Fe free layer is one half that for switching an amorphous Co 40 Fe 40 B 20 free layer. A Fe/CoFeB/Fe free layer configuration allows the Hc value to be increased for STT-RAM applications.
1. A MTJ element comprised of a stack of layers formed on a substrate in a memory device, comprising:
(a) a synthetic anti-ferromagnetic (SyAF) pinned layer having an AP 2 /coupling layer/AP 1 configuration such that a magnetic moment of the AP 2 layer is anti-parallel to a magnetic moment in the AP 1 layer, the AP 2 layer is formed on an anti ferromagnetic (AFM) layer and the AP 1 layer contacts a bottom surface of a tunnel barrier layer;
(b) a crystalline MgO tunnel barrier layer that contacts the AP 1 pinned layer; and
(c) a free layer consisting of Fe/CoFeB/Fe formed on a top surface of the MgO tunnel barrier.
2. The MTJ element of claim 1 wherein the AFM layer is made of MnPt and said MTJ element is further comprised of a NiCr seed layer formed between the substrate and the AFM layer, and a Ta, Ta/Ru, or NiFeHf/Ta/Ru capping layer formed on the free layer.
3. The MTJ element of claim 1 wherein the free layer has the lower Fe layer on the MgO tunnel barrier with a thickness from about 3 to 5 Angstroms, the middle CoFeB layer has a thickness of about 10 to 12 Angstroms, and the upper Fe layer has a thickness from about 5 to 6 Angstroms.
4. The MTJ element of claim 2 wherein the memory device is a MRAM, the AP 2 layer is comprised of CoFe, and the AP 1 layer is made of CoFeB.
5. The MTJ element of claim 2 wherein the memory device is a STT-RAM, the AP 2 layer is comprised of CoFe, and the AP 1 layer is comprised of CoFeB.
6. The MTJ element of claim 1 wherein both of the lower Fe layer in the Fe/CoFeB/Fe configuration and MgO tunnel barrier layer have a (001) crystal orientation.
7. A MTJ element comprised of a stack of layers formed on a substrate in a memory device, comprising:
(a) a synthetic anti-ferromagnetic (SyAF) pinned layer having an AP 2 /coupling layer/AP 1 configuration such that a magnetic moment of the AP 2 layer is anti-parallel to a magnetic moment in the AP 1 layer, the AP 2 layer is formed on an anti-ferromagnetic (AFM) layer and the AP 1 layer contacts a bottom surface of a tunnel barrier layer;
(b) a crystalline MgO tunnel barrier layer that contacts the AP 1 pinned layer; and
(c) a free layer consisting of FeB with a boron content between 0 and 5 atomic% formed on a top surface of the MgO tunnel barrier.