Method for forming a perpendicular spin torque oscillator (PSTO) including forming a magneto resistive sensor (MR) over a spin torque oscillator (STO)

A method comprising:

• forming a spin torque oscillator (STO) having a first width, wherein the forming of the STO includes:
• forming a magnetic reference layer;
• forming a non-magnetic spacer layer over the magnetic reference layer;
• forming a perpendicular magnetic anisotropy (PMA) layer over the non-magnetic spacer layer;
• and
• forming a soft magnetic layer over the PMA layer, wherein the PMA layer and the soft magnetic layer together form a composite magnetic oscillation layer;
• forming a non-magnetic conductive layer having a second width over the STO;
• and
• forming a magneto resistive sensor having a third width over the non-magnetic conductive layer, the third and first widths being less than the second width, wherein the forming of the magneto resistive sensor includes:
• forming a magnetic sensing layer;
• forming a tunnel barrier layer over the magnetic sensing layer;
• and
• forming a reference layer over the tunnel barrier layer;
• wherein forming the tunnel barrier layer includes:
• forming a first magnesium layer over the magnetic sensing layer;
• performing a first oxidation process to oxidize an upper portion of the first magnesium layer;
• forming a second magnesium layer over the oxidized upper portion of the first magnesium layer;
• performing a second oxidation process to fully oxidize the second magnesium layer;
• performing a first annealing process during deposition of a third magnesium layer over the fully oxidized second magnesium layer;
• and
• after performing the first annealing process during deposition of the third magnesium layer, performing a second annealing process.