Non-volatile magnetic memory with low switching current and high thermal stability
View Patent ↗A non-volatile current-switching magnetic memory element includes a bottom electrode, a pinning layer formed on top of the bottom electrode, and a fixed layer formed on top of the pinning layer. The memory element further includes a tunnel layer formed on top of the pinning layer, a first free layer formed on top of the tunnel layer, a granular film layer formed on top of the first free layer, a second free layer formed on top of the granular film layer, a cap layer formed on top of the second free layer, and a top electrode formed on top of the cap layer.
1. A magnetic memory element comprising:
a bottom electrode;
a pinning layer formed on top of and directly contacting the bottom electrode;
a fixed layer formed on top of and directly contacting the pinning layer;
a tunnel layer formed on top of and directly contacting the fixed layer;
a first free layer formed on top of and directly contacting the tunnel layer;
a granular film layer formed on top of and directly contacting the first free layer, the granular film layer being made of a base magnetic alloy having a compound and having a granular micro-structure with grains that, prior to the application of current to the magnetic memory element, have random magnetic moments associated therewith and are separated from each other by grain boundaries, the granular film layer being made of (CO x Fe (1-x) )(Z), wherein x is the atomic percent and is a value in the range of greater than 0 to 1 where 1 refers to 100 atomic percent and wherein Z is a compound chosen from any of the following list of compounds and can be a mixture of: Titatnium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), tungsten oxide (WO), tantalum nitride (TaN), or titanium nitride (TiN);
a second free layer formed on top of and directly contacting the granular film layer and having grains, the second free layer having a magnetic orientation associated therewith, the magnetic orientation of the second free layer switching when current is applied to the magnetic memory element, such that during the switching process, it is not until a substantial number of magnetic grains of the second free layer have switched that these grains couple together and build a critical volume to cause an avalanche type switching of the rest of the grains of the second free layer and once the grains of the second free layer have switched they are magnetostatically coupled together with the neighboring grains;
a cap layer formed on top of the second free layer; and
a top electrode formed on top of the cap layer, wherein the first free layer has grains, the grains of the first free layer being magnetically more exchange coupled than that of the second free layer.
2. A magnetic memory element, as recited in claim 1 , wherein the first and second free layers are made of different material.
3. A magnetic memory element, as recited in claim 1 , wherein the top electrode and the bottom electrode are each made of Tantalum (Ta).
4. A magnetic memory element, as recited in claim 1 , wherein the tunnel layer is made of material selected from a group consisting of: TiO 2 , Al 2 O 3 , MgO, Ta 2 O 5 , HfO 2 , ZrO 2 , TaN, SrO and RuO.
5. A magnetic memory element, as recited in claim 1 , wherein the cap layer is substantially made of a cubic crystal structure.
6. A magnetic memory element, as recited in claim 1 , wherein the cap layer is made substantially of one or more of the following layers: RuCr, NiAl, NiRu, NiAlRu, NiZr, Cu/Ru, or Au/Ru.
7. A magnetic memory element, as recited in claim 1 , wherein the fixed layer and the first layer are substantially amorphous.
8. A magnetic memory element, as recited in claim 1 , wherein the fixed layer, tunnel layer and the second free layer is substantially nano-crystalline following deposition.
9. A magnetic memory element, as recited in claim 1 , wherein the tunnel layer is made of magnesium oxide (MgO).
10. A magnetic memory element, as recited in claim 1 , wherein the tunnel layer has a thickness between the range of 0.8 to 3 nano meters (nm).
11. A non-volatile current-switching magnetic memory element, as recited in claim 1 , wherein the fixed layer is multi-layered.
12. A non-volatile current-switching magnetic memory element, as recited in claim 11 , wherein the muti-layers of the fixed layer are made of Cobalt-Iron(CoFe)/Ruthenium(Ru)/Cobalt-Iron-Boron(CoFeB) wherein the CoFe layer is formed adjacent to or on top of the pinning layer and the CoFeB layer is formed adjacent to or below the tunnel layer so that between the pinning layer and the tunnel layer are CoFe on top of which is formed Ru on top of which is formed CoFeB.
13. A method of manufacturing a non-volatile current-switching magnetic memory element comprising:
forming a bottom electrode;
forming a pinning layer on top of and directly contacting the bottom electrode;
forming a fixed layer on top of and directly contacting the pinning layer;
forming a tunnel layer on top of and directly contacting the fixed layer;
forming a first free layer on top of and directly contacting the tunnel layer;
forming a granular film layer formed on top of and directly contacting the first free layer, the granular film layer being a base magnetic alloy having a compound and having a granular micro-structure with grains that, during deposition, couple together to form the center of the grains which are isolated from each other by the compound, the granular film layer being made of (CO x Fe (1-x) ))(Z), wherein x is the atomic percent and is a value in the range of greater than 0 to 1 where 1 refers to 100 atomic percent and wherein Z is a compound chosen from any of the following list of compounds and can be a mixture of: Titatnium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), tungsten oxide (WO), tantalum nitride (TaN), or titanium nitride (TiN);
forming a second free layer formed on top of and directly contacting the granular film layer, the second free layer having grains, the second free layer having a magnetic orientation associated therewith, the magnetic orientation of the second free layer switching when current is applied to the magnetic memory element, such that during the switching process, it is not until a substantial number of magnetic grains of the second free layer have switched that these grains couple together and build a critical volume to cause an avalanche type switching of the rest of the grains of the second free layer and once the grains of the second free layer have switched they are magnetostatically coupled together with the neighboring grains;
forming a cap layer formed on top of and directly contacting the second free layer; and
forming a top electrode formed on top of and directly contacting the cap layer, wherein the first free layer has grains, the grains of the first free layer being magnetically more exchange coupled than that of the second free layer.
14. A magnetic memory element, as recited in claim 1 , wherein the cap layer is made substantially of one or more of the following layers: RuCr, NiAl, NiRu, NiAlRu, NiZr, or Cu/Ru.
15. A magnetic memory element, as recited in claim 1 , wherein the second free layer is made of magnetic material whose grains are weakly exchange coupled.
16. A magnetic memory element, as recited in claim 1 , wherein the second free layer is made of an alloy having one or more of the ferromagnetic elements: Co, Fe and Ni.
17. A magnetic memory element, as recited in claim 1 , wherein the second free layer contains less than 20 but greater than 0 atomic percent of platinum.
18. A magnetic memory element, as recited in claim 1 , wherein the second free layer contains greater than 0 and up to 20 atomic percent of one or more of the following elements: phosphorous (P), boron(B), chromium(Cr), tantalum(Ta), tungsten(W), or molybdenum(Mo).