Stress effects of water sorption in cure baked photoresist underlayers on the magnetic easy axis of Permalloy film overlayers

Variations in the uniaxial mechanical stress of Permalloy films can change the magnetic easy axis of the Permalloy films through the magnetostrictive effect. Conventional inductive film heads are fabricated with the use of cure baked photoresist (CBP). We show that water absorption in the CBP can produce significant changes in the magnetic properties of Permalloy films similar to those used in recording head yokes. The diffusion coefficient of water in 3 μm thick CBP films was measured with a quartz crystal microbalance and found to be 2.2×10^-9 cm²/s at 25 degrees C. A large and reversible change in the magnetic easy axis is observed in 1 μm thick Permalloy films that overlay a mound of CBP when it is exposed to water vapor. We infer from the observed magnetic easy axis changes that uniaxial stresses of greater than 5×10⁸ dynes/cm² are produced due to the swelling and contraction of the underlaying CBP