Effects of layer thickness and annealing process on low-frequency noise and detectivity in tunnel magnetoresistive sensors with CoFeSiB soft magnetic layers

We investigated the effects of CoFeSiB soft magnetic layer thickness and annealing process on the magnetic field sensing and low-frequency 1/f noise characteristics of tunnel magnetoresistive (TMR) sensors. A thicker CoFeSiB layer improved the soft magnetic properties of the free layer, and the process order of device fabrication and annealing significantly influenced the 1/f noise characteristics of the TMR sensors. A magnetic field detectivity of 0.8 nT/Hz0.5 at 10 Hz was achieved in a single device TMR sensor annealed after device fabrication, which suppressed both electrical and magnetic 1/f noises compared to the annealing performed before device fabrication. The spectral density of the 1/f noise voltage scaled linearly with the sensitivity of the sensor; thus, detectivity showed an approximately constant value regardless of the change in sensitivity.