TMR Device with Low Magnetoresistive Free Layer

Abstract

A high performance TMR sensor is fabricated by employing a free layer with a trilayer configuration represented by FeCo/CoFeB/CoB, FeCo/CoB/CoFeB, FeCo/CoFe/CoB, or FeCo/FeB/CoB may also be employed. Alternatively, CoNiFeB or CoNiFeBM formed by co-sputtering CoB with CoNiFe or CoNiFeM, respectively, where M is V, Ti, Zr, Nb, Hf, Ta, or Mo may be included in a composite free layer or as a single free layer in the case of CoNiFeBM. A 15 to 30% in improvement in TMR ratio over a conventional CoFe/NiFe free layer is achieved while maintaining low Hc and RA<3 ohm-um 2 . In bilayer or trilayer embodiments, magnetostriction (λ) between −5×10 −6 and 5×10 −6 is achieved by combining CoB (−λ) and one or more layers having a positive λ.

We claim: 
     
         1 . A magnetoresistive element in a magnetic device, comprising:
 (a) a stack of layers comprised of a seed layer, anti-ferromagnetic (AFM) layer, and a pinned layer sequentially formed on a substrate;   (b) a tunnel barrier layer made of MgO on the pinned layer;   (c) a free layer comprised of CoNiFeBM formed on the tunnel barrier layer wherein M is one of V, Ti, Zr, Nb, Hf, Ta, or Mo; and   (d) a capping layer on the free layer.   
     
     
         2 . The magnetoresistive element of  claim 1  wherein said free layer is a single layer with a thickness from about 20 to 60 Angstroms, and M has a content greater than 0 atomic % and less than 10 atomic % in the CoNiFeBM alloy. 
     
     
         3 . The magnetoresistive element of  claim 1  wherein the free layer has a bilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer and an upper CoNiFeBM layer, the FeCo Y  layer has a thickness between about 2 and 10 Angstroms and the CoNiFeBM layer has a thickness between about 20 and 50 Angstroms. 
     
     
         4 . The magnetoresistive element of  claim 1  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle Co U Fe W B Z  layer having a thickness of about 5 to 20 Angstroms where u is from about 1 to 95 atomic %, w is from 0 to about 70 atomic %, and z is from about 1 to 30 atomic %, and an upper CoNiFeBM layer, the lower FeCo layer has a thickness between about 2 and 10 Angstroms and said upper CoNiFeBM layer has a thickness between about 20 and 40 Angstroms. 
     
     
         5 . The magnetoresistive element of  claim 1  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle CoNiFeBM layer, and an upper Co U Fe W B Z  layer where u is from about 1 to 95 atomic %, w is from 0 to about 70 atomic %, and z is from about 1 to 30 atomic %. 
     
     
         6 . The magnetoresistive element of  claim 1  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle CoFe V  layer where v is from 0 to 100 atomic % and is unequal to y, and an upper CoNiFeBM layer. 
     
     
         7 . The magnetoresistive element of  claim 1  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle FeB layer, and an upper CoNiFeBM layer. 
     
     
         8 . A magnetoresistive element in a magnetic device, comprising:
 (a) a stack of layers comprised of a seed layer, anti-ferromagnetic (AFM) layer, and a pinned layer sequentially formed on a substrate;   (b) a tunnel barrier layer made of MgO on the pinned layer;   (c) a free layer comprising at least two layers including a first layer which contacts the tunnel barrier layer and a Co P Ni R Fe S B T  layer that is separated from the tunnel barrier layer by the first layer, and wherein p is from about 5 to 90 atomic %, r is from about 5 to 20 atomic %, s is between about 5 and 90 atomic %, t is from about 1 to 30 atomic %, and p+r+s+t=100 atomic %; and   (d) a capping layer on the free layer.   
     
     
         9 . The magnetoresistive element of  claim 8  wherein the free layer has a bilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer and an upper Co P Ni R Fe S B T  layer, said FeCo Y  layer has a thickness between about 2 and 10 Angstroms and said Co P Ni R Fe S B T  layer has a thickness between about 20 and 50 Angstroms. 
     
     
         10 . The magnetoresistive element of  claim 8  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle Co U Fe W B Z  layer having a thickness of about 5 to 20 Angstroms where u is from about 1 to 95 atomic %, w is from 0 to about 70 atomic %, and z is from about 1 to 30 atomic %, and an upper Co P Ni R Fe S B T  layer, said lower FeCo layer has a thickness between about 2 and 10 Angstroms and said upper Co P Ni R Fe S B T  layer has a thickness between about 20 and 40 Angstroms. 
     
     
         11 . The magnetoresistive element of  claim 8  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle Co P Ni R Fe S B T  layer, and an upper Co U Fe W B Z  layer where u is from about 1 to 95 atomic %, w is from 0 to about 70 atomic %, and z is from about 1 to 30 atomic %. 
     
     
         12 . The magnetoresistive element of  claim 8  wherein the free layer has a trilayer configuration with a lower FeCo Y  layer where y is from 0 to 100 atomic % formed on the tunnel barrier layer, a middle FeB or CoFe V  layer where v is from 0 to 100 atomic % and v is unequal to y, and an upper Co P Ni R Fe S B T  layer.