Free-standing meta-surface on ultrathin Si substrate for high-transmission phase shifts in the 3.0-THz band

We present a free-standing meta-surface for a high-transmission phase shift in the 3.0-THz band. The structure consists of subwavelength Au patterns with 278,273 units of meta-atoms on both the front and back of an ultrathin (4 μm thick) silicon substrate. The meta-surface for the low terahertz range has been fabricated by etching on a flexible polymer substrate with metal layers. High-precision fabrication of the meta-surface on a silicon substrate by semiconductor processing techniques is powerful and essential for the integration with terahertz semiconductor sources. Measurements by terahertz time-domain spectroscopy (THz-TDS) demonstrate a high transmission of 0.91 and a phase modulation of -0.86π at 2.8 THz agreeing well with simulations. The meta-surface in the high terahertz range can be applied in an ultrathin meta-lens for terahertz quantum cascade laser sources.