Subcell misalignment in vertically cascaded metamaterial absorbers.

Metamaterial has demonstrated exotic electromagnetic (EM) properties and various applications, for example perfect absorbers. Cascaded perfect absorbers further extend the spectral engineering ability. Perfect alignment of subcells was usually presumed in previous studies. We numerically investigated the effect of lateral misalignments existing in the multiple lithography steps for vertically cascaded metamaterial absorbers and found that the position deviations of the subcells play an important role of the spectral response. As an example, near-unity absorbance reduces to only 30% for a λ/10 subcell misalignment. The detailed investigation of EM field and induced current distributions reveals that the relative position variations of strongly coupled subcells contribute to this phenomenon. The results give us an evaluation that how much registration accuracy is required in multi-step lithography for cascaded metamaterials and on the other side a hint of the potential application of this high position sensitivity.