MEMORY SYSTEM HAVING THERMALLY STABLE PERPENDICULAR MAGNETO TUNNEL JUNCTION (MTJ) AND A METHOD OF MANUFACTURING SAME
A spin-torque transfer magnetic random access memory (STTMRAM) element employed to store a state based on the magnetic orientation of a free layer, the STTMRAM element is made of a first perpendicular free layer (PFL) including a first perpendicular enhancement layer (PEL). The first PFL is formed on top of a seed layer. The STTMRAM element further includes a barrier layer formed on top of the first PFL and a second perpendicular reference layer (PRL) that has a second PEL, the second PRL is formed on top of the barrier layer. The STTMRAM element further includes a capping layer that is formed on top of the second PRL.
1 . A spin-torque transfer magnetic random access memory (STTMRAM) element employed to store a state based on the magnetic orientation of a free layer thereof comprising:
a first perpendicular free layer (PFL) including a first perpendicular enhancement layer (PEL), the first PFL formed on top of a seed layer;
a barrier layer formed on top of the first PFL;
a second perpendicular reference layer (PRL) including a second PEL, the second PRL formed on top of the barrier layer; and
a capping layer formed on top of the second PRL.
2 . The STTMRAM element, as recited in claim 1 , wherein the first PFL is made of perpendicular ferromagnetic layers.
3 . The STTMRAM element, as recited in claim 1 , wherein the first PEL is made of tantalum (Ta), titanium (Ti), hafnium (Hf), niobium (Nb), vanadium (V), yttrium (Y), rhenium (Re), tungsten (W), chromium (Cr), molybdenum (Mo), or ruthenium (Ru).
4 . The STTMRAM element, as recited in claim 1 , wherein the second PEL is made of tantalum (Ta), titanium (Ti), hafnium (Hf), niobium (Nb), vanadium (V), yttrium (Y), rhenium (Re), tungsten (W), chromium (Cr), molybdenum (Mo), or ruthenium (Ru).
5 . The STTMRAM element, as recited in claim 1 , wherein the barrier layer is made of magnesium oxide (MgO) or aluminum oxide (Al 2 O 3 ).
6 . The STTMRAM element, as recited in claim 1 , wherein the second PRL is a synthetic anti-ferromagnetic (SAF) pinned layer, composed of two antiferromagtically coupled perpendicular ferromagnetic layers separated by a non-magnetic exchange coupling layer.
7 . The STTMRAM element, as recited in claim 1 , wherein the capping layer is made of Ta, Ru, Hf, Ti, or MgO.
8 . The STTMRAM element, as recited in claim 1 , wherein the first PRL further includes a first free sub-layer formed on top of the seed layer and a second free sub-layer formed on top of the first PEL, the first PEL being formed on top of the first free sub-layer, the first PRL further including a first spin polarization enhanced (interface) layer (SPEL), formed on top of the second free sub-layer on top of which is formed the barrier layer.
9 . The STTMRAM element, as recited in claim 8 , wherein the second PRL further includes a second spin polarization enhanced (interface) layer (SPEL), formed on top of the barrier layer, a pinned sub-layer formed on top of the second SPEL and below the second PEL, a first synthetic antiferromagnetic (SAF) sub-layer formed on top of the second PEL, an exchange coupling layer formed on top of the second PEL, and a second SAF sub-layer formed on top of the exchange coupling layer and below the capping layer.
10 . The STTMRAM element, as recited in claim 1 , wherein the seed layer is made of Ta, Ti, Pt, Pd, TiCr, NiCr, Ru, or MgO.
11 . The STTMRAM element, as recited in claim 10 , further wherein where the seed layer is made of Ru, the seed layer has a thickness of 1 nm to 10 nm.
12 . The STTMRAM element, as recited in claim 10 , further wherein where the seed layer is made of MgO, the seed layer has a thickness of 0.3 nm to 0.7 nm.
13 . The STTMRAM element, as recited in claim 9 , the first free sub-layer is made of the alloy cobolt-iron-boron (CoFeB).
14 . The STTMRAM element, as recited in claim 13 , the atomic percentage of the iron in the CoFeB alloy of the first free sub-layer is greater than 20%.
15 . The STTMRAM element, as recited in claim 9 , wherein the second free sub-layer made of the alloy cobolt iron boron (CoFeB) with the atomic percentage of Fe being greater than 40% and boron being within a range of 20 to 30 atomic percent.
16 . The STTMRAM element, as recited in claim 1 , wherein the first PRL further includes a multilayer formed on top of the seed layer and a free sub-layer formed on top of the first PEL, the first PEL being formed on top of the multilayer, the first PRL further including a first spin polarization enhanced (interface) layer (SPEL), formed on top of the free sub-layer on top of which is formed the barrier layer.
17 . The STTMRAM element, as recited in claim 16 , wherein the second PRL further includes a second spin polarization enhanced (interface) layer (SPEL), formed on top of the barrier layer, a pinned sub-layer formed on top of the second SPEL and below the second PEL, a first synthetic antiferromagnetic (SAF) sub-layer formed on top of the second PEL, an exchange coupling layer formed on top of the second PEL, and a second SAF sub-layer formed on top of the exchange coupling layer and below the capping layer.
18 . The STTMRAM element, as recited in claim 16 , wherein the multilayer is made of at least one combination of a conducting ferromagnetic layer and a non-magnetic conducting layer.
19 . The STTMRAM element, as recited in claim 1 , wherein the first PRL further includes a first multilayer formed on top of the seed layer and a free sub-layer formed on top of the first PEL, the first PEL being formed on top of the multilayer, the first PRL further including a first spin polarization enhanced (interface) layer (SPEL), formed on top of the free sub-layer on top of which is formed the barrier layer and further wherein the second PRL further includes a second spin polarization enhanced (interface) layer (SPEL), formed on top of the barrier layer, a pinned sub-layer formed on top of the second SPEL and below the second PEL, a ferromagnetic (FM) layer formed on top of the second PEL, an exchange coupling layer formed on top of the FM layer, and a second multilayer formed on top of the exchange coupling layer and below the capping layer.
20 . The STTMRAM element, as recited in claim 19 , wherein each of the first and second multilayers is made of at least a combination of a first and second layer, the first layer being made of cobolt and the second layer being made of platinum or palladium.
21 . A method of manufacturing a spin toque transfer magnetic random access memory (STTMRAM) magnetic tunnel junction film stack comprising:
a) depositing a magnetic interface layer on top of a barrier layer to form a magnetic tunnel junction (MTJ), the magnetic interface layer being made partially of boron (B);
b) annealing the STTMRAM magnetic tunnel junction film stack at a first temperature after depositing the magnetic interface layer;
c) cooling down the STTMRAM MTJ film stack to a second temperature that is lower than the first temperature; and
d) continuing depositing a top layer on top of the magnetic interface layer, wherein the top layer is made of a single layer or has a multi-layer structure necessary to make the MTJ stack function in STTMRAM, wherein the top surface layer is made of magnetic material.
22 . A method of manufacturing, as recited in claim 21 , wherein the said interface layer has a top surface layer in direct contact with the said top layer
23 . A method of manufacturing, as recited in claim 22 , wherein the top surface layer is made of a material comprising any of: Co, Fe, B, Ni, Ta, Pd, Ru, Mg, O, Tb, Pt, Ti, Cu, Zr, Mn, Ir, or Hf.