Bringing flexibility to giant magnetoresistive sensors directly grown onto commercial polymeric foils

The emergence of augmented reality, robotics and point-of-care biosensors has pushed forward the frontiers of compliant sensors with mechanical resilience and capability of being arbitrarily shaped upon demand. Here, we report exchange-biased spin valve structures directly fabricated on 25 μm thick commercial polymeric substrates. Linear electrical response with low coercivity was demonstrated for sensors grown on polymers. Despite the higher roughness of polymers ≃0.75 nm, a Néel coupling field comparable to that of samples grown on conventional SiO₂ substrates was shown. Nevertheless, significant changes in the linear range of polymeric samples were observed, together with changes in the shift of the transfer curve. The measurements also indicate deviations from fully orthogonal magnetization orientation achieved in patterned linear sensors. Such results were ascribed to the presence of a non-negligible magnetostrictive component, most likely due to residual mechanical stress in the sensor's free- and pinned-layers. To support the study, a macrospin model was developed, considering the magnetoelastic anisotropy, to address in particular the impact of mechanical stress on final sensor output.