Magnetic read head with magnetoresistive (MR) enhancements toward low resistance X area (RA) product
A method of forming a magnetoresistive (MR) sensor with a composite tunnel barrier comprised primarily of magnesium oxynitride and having a MR ratio of at least 70%, resistance x area (RA) product <1 ohm-μm 2 , and fewer pinholes than a conventional MgO layer is disclosed. The method involves forming a Mg/MgON/Mg, Mg/MgON/MgN, MgN/MgON/MgN, or MgN/MgON/Mg intermediate tunnel barrier stack and then annealing to drive loosely bound oxygen into adjacent layers thereby forming MgO/MgON/Mg, MgO/MgON/MgON, MgON/MgON/MgON, and MgON/MgON/MgO composite tunnel barriers, respectively, wherein oxygen content in the middle MgON layer is greater than in upper and lower MgON layers. The MgON layer in the intermediate tunnel barrier may be formed by a sputtering process followed by a natural oxidation step and has a thickness greater than the Mg and MgN layers.
1. A composite tunnel barrier formed between a first ferromagnetic layer and a second ferromagnetic layer in a magnetic tunnel junction (MTJ), the composite tunnel barrier has a metal oxide/metal oxynitride/metal oxide configuration wherein a thickness of each metal oxide layer is less than a thickness of the metal oxynitride layer such that the composite tunnel barrier layer is primarily metal oxynitride, and each metal oxide layer has an oxygen content less than that of the metal oxynitride layer.
2. The composite tunnel barrier layer of claim 1 wherein the metal is selected from Al, Ta, Zn, Ti, AlZn, AlTi, CoMg, ZnMg, Mg, and Sn.
3. The composite tunnel barrier of claim 1 wherein the MTJ has a bottom spin valve configuration wherein the first ferromagnetic layer is a pinned layer and the second ferromagnetic layer is a free layer.
4. The composite tunnel barrier of claim 1 wherein the MTJ has a top spin valve configuration wherein the first ferromagnetic layer is a free layer and the second ferromagnetic layer is a pinned layer.
5. A composite tunnel barrier formed between a first ferromagnetic layer and a second ferromagnetic layer in a magnetic tunnel junction (MTJ), the composite tunnel barrier has a metal oxide/first metal oxynitride/second metal oxynitride, third metal oxynitride/first metal oxynitride/second metal oxynitride, or third metal oxynitride/first metal oxynitride/metal oxide configuration wherein a thickness of the metal oxide, second metal oxynitride, and third metal oxynitride layers is less than a thickness of the first metal oxynitride layer such that the composite tunnel barrier layer is primarily metal oxynitride, and each of the metal oxide, second metal oxynitride, and third metal oxynitride layers has an oxygen content less than that of the first metal oxynitride layer.
6. The composite tunnel barrier layer of claim 5 wherein the metal is selected from Al, Ta, Zn, Ti, AlZn, AlTi, CoMg, ZnMg, Mg, and Sn.
7. The composite tunnel barrier of claim 5 wherein the MTJ has a bottom spin valve configuration wherein the first ferromagnetic layer is a pinned layer and the second ferromagnetic layer is a free layer.
8. The composite tunnel barrier of claim 5 wherein the MTJ has a top spin valve configuration wherein the first ferromagnetic layer is a free layer and the second ferromagnetic layer is a pinned layer.
9. A magnetoresistive (MR) sensor, comprising:
(a) a first ferromagnetic (FM 1 ) layer formed on a substrate;
(b) a composite tunnel barrier layer having a MgO/MgO y1 N z1 /MgO, MgO/MgO y1 N z1 /MgO y2 N 22 , MgO y3 N z3 /MgO y1 N z1 /MgO or MgO y3 N z3 /MgO y1 N z1 /MgO y2 N z2 configuration comprised primarily of magnesium oxynitride wherein a bottom MgO or MgO y3 N z3 layer contacts the first ferromagnetic layer and an uppermost MgO or MgO y2 N z2 layer contacts an overlying second ferromagnetic (FM 2 ) layer, y 1 , y 2 , y 3 are an oxygen content and z 1 , z 2 , z 3 are a nitrogen content in the magnesium oxynitride layers, y 2 and y 3 are each less than y 1 , and z 1 is from 1 to at least 50 atomic %; and
(c) the FM 2 layer.
10. The MR sensor of claim 9 wherein the MgO y1 N z1 layer has a thickness from about 4 to 8 Angstroms.
11. The MR sensor of claim 9 wherein the MR sensor further comprises a seed layer, AFM layer, and a capping layer as the uppermost layer, the FM 1 layer is a pinned layer, and the FM 2 layer is a free layer to give a bottom spin valve configuration with a stack of layers represented by seed layer/AFM layer/pinned layer/composite tunnel barrier/free layer/capping layer.
12. The MR sensor of claim 9 wherein the MR sensor further comprises a seed layer, AFM layer, and a capping layer as the uppermost layer, the FM 1 layer is a free layer, and the FM 2 layer is a pinned layer to give a top spin valve configuration with a stack of layers represented by seed layer/free layer/composite tunnel barrier/pinned layer/AFM layer/capping layer.
13. The MR sensor of claim 9 wherein the oxygen content in the MgO y3 N z3 layer and in the MgO y2 N z2 layer decreases with increasing distance from the MgO y1 N z1 layer.
14. The MR sensor of claim 9 wherein an oxygen content in the MgO layers decreases with increasing distance from the MgO y1 N z1 layer.
15. The MR sensor of claim 9 wherein each of the MgO, MgO y3 N z3 , and MgO y2 N z2 layers has a thickness less than that of the MgO y1 N z1 layer.