Exchange bias effects along the out-of-plane direction have been investigated in arrays of 100 nm nanostructures prepared on top of prepatterned substrates, consisting of a ferromagnetic [PtCo] multilayer with out-of-plane anisotropy exchange coupled to an antiferromagnetic IrMn layer. A significant loop shift is observed in these nanostructures (dots and trenches). The relative evolutions of the bias fields with the IrMn thickness in the nanostructures and in the continuous film are ascribed to both the effects of the IrMn domain size and thermal activation. Lower coordinated spins in the trenches and at the dot edges are assumed to play a key role on the bias properties. A reduction of the blocking temperature is observed for both the dots and the trenches with respect to the continuous film. © 2006 American Institute of Physics.