Amorphous layers in a magnetic tunnel junction device
View Patent ↗An improved TMR device is disclosed. The ferromagnetic layers of the device, particularly those that contact the dielectric tunneling layer have an amorphous structure as well as a minimum thickness (of about 15 Å). A preferred material for contacting the dielectric layer is CoFeB. Ways of overcoming problems relating to magnetostriction are disclosed and a description of a process for manufacturing the device is included.
1. A magnetic tunnel junction device, comprising:
a lower conductive electrode;
a seed layer on said lower conductive electrode;
an antiferromagnetic layer on said seed layer;
an AP2 layer on said antiferromagnetic layer;
an antiferromagnetic coupling layer on said AP2 layer;
an AP1 layer on said antiferromagnetic coupling layer;
a tunneling layer of aluminum oxide on said AP1 layer;
on said tunneling layer, a free layer comprising first and second free sub-layers;
said first free sub-layer further comprising a layer of CoFeB containing at least 10 atomic percent boron, having an amorphous structure, a thickness of at least 15 Angstroms, and a magnetostriction constant whose absolute value is no greater than about 1.5×10 −5 ;
said second free sub-layer further comprising a layer of material selected from the group consisting of CoB, CoNb, and CoNbHf, having an amorphous structure, a thickness of at least 15 Angstroms, and a magnetostriction constant whose absolute value and sign are negative such that it effectively cancels out magnetostriction due to said first free sub-layer, whereby said magnetic tunnel junction device has a magnetostriction constant whose absolute value is greater than 0.5×10 −5 ;
a capping layer on said free layer; and
an upper conductive electrode on said capping layer.
2. The magnetic tunnel junction device described in claim 1 wherein said antiferromagnetic layer is selected from the group consisting of PtMn, NiMn, OsMn, IrMn, and PtPdMn.
3. The magnetic tunnel junction device described in claim 1 wherein said seed layer is selected from the group consisting of Ta, NiCr, NiFeCr.
4. The magnetic tunnel junction device described in claim 1 wherein said capping layer is selected from the group consisting of Ru, Rh, Ta, TaO, Al 2 O 3 , Cu, and TaN.
5. The magnetic tunnel junction device described in claim 1 wherein said antiferromagnetic coupling layer is selected from the group consisting of Rh, Ru, Cr, Cu, and Ir.
6. The magnetic tunnel junction device described in claim 1 wherein said free layer has its anisotropy maximized along a direction of its long axis.
7. A magnetic tunnel junction device, comprising:
a lower conductive electrode;
a seed layer on said lower conductive electrode;
an antiferromagnetic layer on said seed layer;
an AP2 layer on said antiferromagnetic layer;
an antiferromagnetic coupling layer on said AP2 layer;
an AP1 layer on said antiferromagnetic coupling layer;
a tunneling layer of magnesium oxide on said AP1 layer;
free layer on said tunneling layer;
said free layer having an amorphous structure, a thickness of at least 15 Angstroms, and further comprising at least two layers whose magnetostriction constants are of opposite sign, including first and second free sub-layers, said first free sub-layer being CoFeB, having an amorphous structure and a thickness of at least 15 Angstroms whereby said first free sub-layer and said second free sub-layer together have a net magnetostriction constant whose absolute value is less than 0.5×10 −5 ;
a capping layer on said free layer; and
an upper conductive electrode on said capping layer.
8. The magnetic tunnel junction device described in claim 7 wherein said antiferromagnetic layer is selected from the group consisting of PtMn, NiMn, OsMn, IrMn, and PtPdMn.
9. The magnetic tunnel junction device described in claim 7 wherein said seed layer is selected from the group consisting of Ta, NiCr, NiFeCr.
10. The magnetic tunnel junction device described in claim 7 wherein said capping layer is selected from the group consisting of Ru, Rh, Ta, TaO, Al 2 O 3 , Cu, and TaN.
11. The magnetic tunnel junction device described in claim 7 wherein said antiferromagnetic coupling layer is selected from the group consisting of Ru, Rh, Ir, Cr, and Cu.
12. The magnetic tunnel junction device described in claim 7 wherein said free layer has its crystalline anisotropy maximized along a direction of its long axis.
13. A process, to form a magnetic tunnel junction device, comprising:
providing a lower conductive electrode and depositing thereon a seed layer;
depositing an antiferromagnetic layer on said seed layer;
depositing an AP2 layer on said antiferromagnetic layer;
depositing an antiferromagnetic coupling layer on said AP2 layer;
depositing, to a thickness of at least 15 Angstroms, an AP1 layer on said antiferromagnetic coupling layer;
depositing a dielectric tunneling layer of aluminum oxide on said AP1 layer;
by depositing a layer of amorphous material to a thickness of at least 15 Angstroms, forming, on said tunneling layer, a free layer comprising first and second free sub-layers, said second free sub-layer being selected from the group consisting of CoB, CoNb, and CoNbHf;
depositing a capping layer on said free layer; and
depositing an upper conductive electrode on said capping layer.
14. The process recited in claim 13 wherein said tunneling layer is aluminum oxide, said first free sub-layer is CoFeB containing at least 10 atomic percent boron, and said AP1 layer has a magnetostriction constant whose absolute value is no greater than 1.5×10 −5 .
15. A process to form a magnetic tunnel function device, comprising:
providing a lower conductive electrode and depositing thereon a seed layer;
depositing an antiferromagnetic layer on said seed layer;
depositing an AP2 layer on said antiferromagnetic layer;
depositing an antiferromagnetic coupling layer on said AP2 layer;
depositing, to a thickness of at least 15 Angstroms, an AP1 layer on said antiferromagnetic coupling layer;
depositing a dielectric tunneling layer of magnesium oxide on said AP1 layer;
forming said free layer by depositing at least two layers whose magnetostriction constants are of opposite sign to each other, thereby causing said free layer to have a net magnetostriction constant whose absolute value is less than 0.5×10 −5 ;
depositing a capping layer on said free layer; and
depositing an upper conductive electrode on said capping layer.