Structure/method to fabricate a high performance magnetic tunneling junction MRAM
View Patent ↗An MTJ (magnetic tunneling junction) MRAM (magnetic random access memory) cell is formed on a conducting lead and magnetic keeper layer that is capped by a sputter-etched Ta layer. The Ta layer has a smooth surface as a result of the sputter-etching and that smooth surface promotes the subsequent formation of a lower electrode (pinning/pinned layer) with smooth, flat layers and a radical oxidized (ROX) Al tunneling barrier layer which is ultra-thin, smooth, and to has a high breakdown voltage. A seed layer of NiCr is formed on the sputter-etched layer of Ta. The resulting device has generally improved performance characteristics in terms of its switching characteristics, GMR ratio and junction resistance.
1. A magnetic tunneling junction (MTJ) device in an MRAM configuration comprising:
a substrate;
a bottom magnetic keeper and conducting lead layer formed on said substrate, said bottom keeper and lead layer formed of substantially planar layers and further comprising:
a first NiCr seed layer formed in said substrate;
a soft magnetic keeper layer formed on said seed layer;
a conducting lead layer formed on said keeper layer;
a Ta capping layer formed on said lead layer, the upper surface of said layer being rendered smooth and amorphous by being sputter-etched;
a bottom electrode, having smooth, flat layers, formed on said sputter-etched Ta layer, said bottom electrode further comprising:
a second NiCr seed layer formed on said sputter-etched second Ta layer;
a pinning layer of antiferromagnetic material formed on said seed layer;
a SyAP pinned layer formed on said pinning layer;
a smooth, uniform, ultra-thin layer of in-situ radical oxidized (ROX) Al formed as a barrier layer on said pinned layer;
a ferromagnetic free layer formed on said barrier layer;
a capping layer formed on said MTJ layer.
2. The device of claim 1 wherein said substrate includes a planar insulating layer on which said bottom magnetic keeper and conductor lead layer is formed.
3. The device of claim 1 wherein each of said first and second seed layers is a layer of NiCr with 35–45 atom % Cr formed to a thickness between approximately 40 and 60 angstroms.
4. The device of claim 1 wherein the soft magnetic keeper layer is a layer of NiFe formed to a thickness between approximately 50 and 200 angstroms.
5. The device of claim 1 wherein said conducting lead layer includes a third NiCr seed layer with 35–45 atom percent Cr formed to a thickness between approximately 40 and 60 angstroms on which is formed a Cu layer between approximately 50 and 100 angstroms in thickness.
6. The device of claim 1 wherein said conducting lead layer includes a layer of Ta approximately 50 angstroms in thickness on which is formed a layer of Cu between approximately 50 and 100 angstroms in thickness.
7. The device of claim 1 wherein the Ta capping layer is formed to an original thickness between approximately 50 and 100 angstroms and its surface is sputter-etched, removing between approximately 20 and 30 angstroms of original thickness and interrupting large grain formation and subsequent surface roughness.
8. The device of claim 1 wherein the antiferromagnetic pinning layer is a layer of MnPt formed to a thickness of between approximately 100 and 200 angstroms or a layer of IrMn formed to a thickness between approximately 50 and 100 angstroms.
9. The device of claim 1 wherein the SyAP layer comprises a first and second layer of CoFe separated by a coupling layer of Ru, wherein at least the second layer of CoFe, which is adjacent to the tunnel barrier layer, is CoFe(25%).
10. The device of claim 9 wherein the first layer of CoFe is approximately 15 to 25 angstroms thick, the second layer of CoFe is approximately 12 to 20 angstroms thick and the Ru layer is approximately 7 to 8 angstroms thick.
11. The device of claim 1 wherein the tunneling barrier layer is a layer of Al, formed to an initial thickness between approximately 7 and 12 angstroms and oxidized in-situ by a process of radical oxidation (ROX).
12. The device of claim 1 wherein the ferromagnetic free layer is a layer of NiFe(18%) formed to a thickness between approximately 30 and 60 angstroms.