TMR Device with Improved MgO Barrier

Abstract

A method of forming a high performance magnetic tunnel junction (MTJ) is disclosed wherein the tunnel barrier includes at least three metal oxide layers. The tunnel barrier stack is partially built by depositing a first metal layer, performing a natural oxidation (NOX) process, depositing a second metal layer, and performing a second NOX process to give a M OX1 /M OX2 configuration. An uppermost metal layer on the M OX2 layer is not oxidized until after the MTJ stack is completely formed and an annealing process is performed to drive unreacted oxygen in the M OX1 and M OX2 layers into the uppermost metal layer. In an alternative embodiment, a plurality of metal oxide layers is formed on the M OX1 layer before the uppermost metal layer is deposited. The resulting MTJ stack has an ultralow RA around 1 ohm-μm 2 and maintains a high magnetoresistive ratio characteristic of a single metal oxide tunnel barrier layer.

1 . A magnetic tunnel junction (MTJ), comprising:
 (a) a pinned layer;   (b) a free layer; and   (c) a tunnel barrier layer formed between the reference layer and free layer wherein the tunnel barrier is made of a stack of at least three metal oxide layers and wherein at least one of the metal oxide layers is comprised of a first metal, and at least one of the metal oxide layers is comprised of a second metal that is unequal to the first metal.   
     
     
         2 . The MTJ of  claim 1  wherein the metal in the at least three metal oxide layers is selected from Mg, MgZn, Zn, Al, Ti, AlTi, Hf, Zr or a combination thereof. 
     
     
         3 . The MTJ of  claim 1  wherein the pinned layer has a synthetic anti-parallel (SyAP) configuration having an AP2/Ru/AP1 structure wherein the AP1 layer contacts the tunnel barrier layer and is comprised of one or more of CoFe, CoFeB, CoNiFe, CoNiFeB, or alloys thereof with other elements selected from Ta, Ru, Mg, Hf, Zr, Zn, W, Cu, Ag, and Au. 
     
     
         4 . The MTJ of  claim 1  wherein the MTJ has a bottom spin valve configuration in which the pinned layer, tunnel barrier layer, and free layer are sequentially formed on a substrate, and the tunnel barrier layer has a configuration represented by M OX1 /M OX2 /M OX3  wherein a first metal oxide layer (M OX1 ) has a thickness greater than a second metal oxide layer (M OX2 ), and the uppermost metal oxide layer (M OX3 ) has a thickness less than that of the M OX1  and M OX2  layers. 
     
     
         5 . The MTJ of  claim 1  wherein the MTJ has a bottom spin valve configuration in which the pinned layer, tunnel barrier layer, and free layer are sequentially formed on a substrate, and the tunnel barrier layer has a configuration represented by M OX1 /M OX2 /M OX3 /M OX4  wherein a first metal oxide layer (M OX1 ) has a thickness greater than a second metal layer (M OX2 ), and third (M OX3 ) and fourth (MOX4) metal oxide layers have a thickness less than that of the M OX1  and M OX2  layers.