MAGNETIC TUNNEL JUNCTION ELEMENT WITH REDUCED TEMPERATURE SENSITIVITY

1 . A method of forming a device comprising:

providing a substrate comprising circuit component formed on a substrate surface;

performing back-end-of-line (BEOL) processing to form a BEOL dielectric layer over the substrate, wherein the BEOL dielectric layer comprises a plurality of interlevel dielectric (ILD) levels; and

forming a perpendicular magnetic tunnel junction (pMTJ) stack between adjacent ILD levels of the BEOL dielectric layer, the pMTJ stack is disposed between top and bottom electrodes, and wherein forming the pMTJ stack comprises

forming various layers of the pMTJ on the bottom electrode, wherein the various layers include,

a magnetic fixed layer, wherein the magnetic fixed layer includes a magnetic reference layer with a low temperature coefficient (TempCo) and good spin polarization, which results in good magnetoresistance ratio (MR),

a first tunnelling barrier layer, and

a magnetic free layer.

2 . The method of claim 1 wherein:

forming the magnetic reference layer comprises forming a composite reference layer comprising forming n magnetic reference layers separated by n−1 non-magnetic spacer layers;

an i th magnetic reference layer in which i=n is equal to the composite reference layer disposed closest to the first tunnel barrier layer and i=1 is the composite reference layer disposed farthest from the first tunnel barrier; and

the composite reference layer is configured with low TempCo and good MR by tuning the TempCo and MR of the magnetic reference layers.

3 . The method of claim 2 wherein tuning the TempCo and MR of the magnetic reference layers can be achieved by varying materials of the magnetic reference layers, compositional range of elements of the magnetic reference layers, thickness of the magnetic reference layers or a combination thereof.

4 . The method of claim 2 wherein:

the magnetic reference layer closest to the first tunnel barrier is tuned with the highest MR; and

the magnetic reference layers away from the first tunnel barrier are tuned with decreasing TempCo, with the magnetic reference layer farthest form the first tunnel barrier tuned with the lowest TempCo.

5 . The method of claim 2 wherein:

the composite reference layer comprises first and second magnetic reference layers (n=2) separated by a first spacer layer (n−1=1);

the first magnetic reference layer (i=1) is tuned for low TempCo; and

the second magnetic reference layer (i=2 or n) is tuned for high MR.

6 . The method of claim 2 wherein:

the composite reference layer comprises first and second magnetic reference layer (n=2); and

the first and second magnetic reference layer (i=1) are tuned for low TempCo.

7 . The method of claim 6 wherein the second magnetic reference layer is tuned with a higher MR than the first magnetic layer.

8 . The method of claim 2 wherein:

the composite reference layer comprises first, second and third magnetic reference layers (n=3) separated by first and second spacer layers (n−1=2);

the first magnetic reference layer (i=1) is tuned with the lowest TempCo;

the second magnetic reference layer (i=2 or n) is tuned with higher TempCo and higher MR than the first magnetic reference layer; and

the third magnetic reference layer (i=3) is tuned with the highest MR.

9 . The method of claim 2 wherein the n magnetic reference layers comprise magnetic layers which are cobalt-iron-based (CoFe-based), samarium-based magnetic layers or a combination thereof.

10 . The method of claim 2 wherein the n−1 non-magnetic comprise tantalum (Ta), molybdenum (Mo), tungsten (W), iridium (Ir) and zirconium (Zr) or a combination thereof.

11 . The method of claim 1 wherein the pMTJ stack comprises a single tunnelling barrier bottom pinned pMTJ stack in which sequentially forming the various layers comprises:

forming the magnetic fixed layer on the bottom electrode;

forming the first tunnelling barrier layer on the magnetic fixed layer;

forming the magnetic free layer on the first tunnelling barrier layer;

forming a cap layer on the magnetic free layer; and

forming the top electrode on the cap layer.

12 . The method of claim 1 wherein the pMTJ stack comprises a dual tunnelling barrier bottom pinned pMTJ stack in which sequentially forming the various layers comprises:

forming the magnetic fixed layer on the bottom electrode;

forming the first tunnelling barrier layer on the magnetic fixed layer;

forming the magnetic free layer on the first tunnelling barrier layer;

forming a second tunnelling barrier layer on the magnetic free layer; and

forming the top electrode over the second tunnelling barrier layer.

13 . The method of claim 1 wherein the pMTJ stack comprises a single tunnelling barrier top pinned pMTJ stack in which sequentially forming the various layers comprises:

forming the magnetic free layer on the bottom electrode;

forming the first tunnelling barrier layer on the magnetic free layer;

forming the magnetic fixed layer on the first tunnelling barrier layer; and

forming the top electrode on the magnetic fixed layer.

14 . The method of claim 1 wherein the pMTJ stack comprises a dual tunnelling barrier top pinned pMTJ stack in which sequentially forming the various layers comprises:

forming a second tunnelling barrier layer on the bottom electrode;

forming the magnetic free layer on the second tunnelling barrier layer;

forming the first tunnelling barrier layer on the magnetic free layer;

forming the magnetic fixed layer on the first tunnelling barrier layer; and

forming the top electrode on the magnetic fixed layer.

15 . A device comprising:

a substrate comprising circuit component on a substrate surface;

a back-end-of-line (BEOL) dielectric layer disposed over the substrate, wherein the BEOL dielectric layer comprises a plurality of interlevel dielectric (ILD) levels; and

a perpendicular magnetic tunnel junction (pMTJ) stack between adjacent ILD levels of the BEOL dielectric layer, the pMTJ stack is disposed between top and bottom electrodes, and wherein the pMTJ stack comprises various layers on the bottom electrode, wherein the various layers include,

a magnetic fixed layer, wherein the magnetic fixed layer includes a magnetic reference layer with a low temperature coefficient (TempCo) and good spin polarization, which results in good magnetic ratio (MR),

a first tunnelling barrier layer, and

a magnetic free layer.

16 . The device of claim 15 wherein:

the magnetic reference layer comprises a composite reference layer having n magnetic reference layers separated by n−1 non-magnetic spacer layers;

an i th magnetic reference layer in which i=n is equal to the composite reference layer disposed closest to the first tunnel barrier layer and i=1 is the composite reference layer disposed farthest from the first tunnel barrier; and

the composite reference layer is configured with low TempCo and good MR by tuning the TempCo and MR of the magnetic reference layers.

17 . The method of claim 16 wherein the TempCo and MR of the magnetic reference layers can be tuned by varying materials of the magnetic reference layers, compositional range of elements of the magnetic reference layers, thickness of the magnetic reference layers or a combination thereof.

18 . The method of claim 2 wherein:

the composite reference layer comprises first and second magnetic reference layer (n=2); and

the first and second magnetic reference layer (i=1) are tuned for low TempCo.

19 . The method of claim 16 wherein the n magnetic reference layers comprise magnetic layers which are cobalt-iron-based (CoFe-based), samarium-based magnetic layers or a combination thereof.

20 . A method of forming a device comprising:

providing a substrate comprising circuit component formed on a substrate surface;

performing back-end-of-line (BEOL) processing to form a BEOL dielectric layer over the substrate, wherein the BEOL dielectric layer comprises a plurality of interlevel dielectric (ILD) levels; and

forming a perpendicular magnetic tunnel junction (pMTJ) stack between adjacent ILD levels of the BEOL dielectric layer, the pMTJ stack is disposed between top and bottom electrodes, and wherein forming the pMTJ stack comprises

forming various layers of the pMTJ on the bottom electrode, wherein the various layers include,

a magnetic fixed layer, wherein the magnetic fixed layer includes a composite magnetic reference layer with n magnetic reference layers separated by n−1 spacer layers, the composite magnetic reference layer is tuned a low temperature coefficient (TempCo) and good spin polarization, which results in good magnetic ratio (MR),

a first tunnelling barrier layer, and

a magnetic free layer.