Atomic Layer Deposition Al$_{2}$O $_{3}$ Films for Permanent Magnet Isolation in TMR Read Heads

Al
₂
O
₃
films made with atomic layer deposition (ALD) have been developed for use as isolation layers in CPP tunneling magnetoresistive readers. A low-temperature deposition process was developed to permit integration with a self-aligned patterning scheme. The resulting films show excellent thickness uniformity (<2% within-wafer), leakage current density (J
_leak
<1times10
^-18
A/cm
²
) and breakdown properties (F
_bd
>9 MV/cm). TEMs of sub-100 nm TMR readers fabricated using these processes show>95% conformality on junction sidewalls, indicating nonselective growth of ALD Al
₂
O
₃
on the various stack and bottom shield surfaces. Permanent magnets with well-controlled junction grain structure and coercivities in excess of 2500 Oe have been deposited with existing processes. FEM modeling shows the effective stabilizing field from the magnets at the junction edge scales inversely with ALD layer thickness, in agreement with device-level free layer stability metrics showing improvements at lower ALD thicknesses. As the conformal ALD layer thickness is easily tuned, this technology provides flexibility in trading off reader amplitude and stability that should support scaling of the abutted TMR design out to 1 Tb/in
²
and beyond.