Significance StatementShow Affiliations
Metamaterials, which are artificially designed periodic subwavelength structures, have attracted great interests due to the exotic electromagnetic properties relying on the structures rather than the compositions. The effective electromagnetic parameters like the permittivity and permeability can be readily modulated by engineering the subwavelength structures. Novel functions including negative refraction, cloaking, ultra-resolution imaging and so on have been developed recently. These effects are always limited to the on-resonance wavelength and therefore cascaded metamaterials were proposed to extend the working bands. We can cascade metamaterial either horizontally or vertically. For horizontally cascading configuration, different subwavelength cell arrays can be fabricated in a same step. But for vertically cascading configuration, multiple-step lithography has to be conduct with an inevitable alignment error. However, almost all current research on vertically cascaded metamaterial ignores this serious issues. In this paper, we numerically investigate the absorption response of vertically cascaded metamaterial absorbers considering the misalignments of misalignments of subcells existing in multi-step photolithography by FDTD method. We found that the relative positions of the subcells play an important role of the absorption spectra. For a terahertz absorber, near-unity absortance reduces to only 30% for a tenth of wavelength misalignment. The detailed investigation of electromagnetic 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 andd on the other size a hint of the potential application of this high position sensitivity.
Optics Express, Vol. 21, Issue 13, pp. 15896-15903 (2013)
Qin Chen, Fuhe Sun, and Shichao Song
Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou 215123, China and
Peking University Shenzhen SOC Key Laboratory, PKU-HKUST Shenzhen-Hong Kong Institute, Hi-Tech Industrial Park South, Shenzhen 518057, China
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.
© 2013 OSA