Nearly arbitrary terahertz metamaterials by conformal metallization on multi-photon lithography

The advent of 5G/6G terahertz era brings an escalating demand for complexity-increasing function-integrated terahertz (THz) metamaterials beyond film-like in-plane ones. However, the high-complexity geometry-scalable THz architectures pose multiple challenges to current two-dimensional (2D) lithography. To radically unleash the potential of THz metamaterials at high dimensions, we propose a conformal metallization strategy templating on 3D multi-photon lithography with nanometric topologies and high conductivity by stepwise ion-sputtering metal or semimetal. The as-prepared THz metamaterials include chiral meta-atoms, hollow or arbitrary meta-structures, and metasensors of symmetric bound states in the continuum (BIC), showing programmable THz functions, unit-cell precision, and resonant nature, but without geometry limits. 3D THz metamaterials in out-of-plane nanostructures comprehensively extend the functional degrees to the third dimension and satisfy the complex requirements of next-generation THz metamaterials.