Research On Fabrication Of Terahertz Metamaterial Devices By Laser Induced Andnon-electrolytic Plating

Metamaterials are artificial composite materials which are combined by a periodic arrays of subwavelength structural units, and could be flexibly changed the response of material to electromagnetic wave by changing the structure shape or size of the resonance unit to achieve a various of functional devices,such as absorbers, filters, sensors, and polarizers, etc. With the rapid development of micro-machining technology, to realize THz metamaterials has become possible and can usually be fabricated with the method of lithography. However, the process of this method is very complicated. Laser induced and non-electrolytic plating with copper, which is a novel processing technology and has advantages of simple, flexible and low cost, has gradually get the favored of researchers. In this paper, we mainly studied the technology of fabricating terahertz metamaterials with the method of laser induced and non-electrolytic plating with copper,and realized the metamaterial of double layers metal structure. Also an EIT-like resonator of single layer and a bilayer wire-grid polarizer was fabricated with this method and measured by terahertz time-domain spectroscopy system(THz-TDS) which proves that the method is simple and effective. The main research of our work are as follows:(1) A terahertz metamaterials fabrication technology based laser induced and non-electrolytic plating with copper was studied. This technology firstly use laser exposure in polymer which was coated with Ag NO3 so that the metallic silver will graphical sedimentary on the surface, then use non-electrolytic plating with copper to realize copper plating. The main work includes surface treatment, laser direct writing and chemical copper plating technology research, etc. Then we mainly introduces the effect of laser direct writing parameters on metal wire, realization of automatic focus and double layers metal structure metamaterial.(2) A planar double ring(DR) resonator composed of two different size concentric rings was analyzed by the finite-difference time-domain(FDTD) method and fabricated by the method of laser induced and non-electrolytic plating with copper on the polymer film with polymer thickness of 45 μm. The THz-TDS measurements show that the DR structure could be treated as a EIT-like resonator, the resonance peak is near 0.42 THz and Q≈12 which has raised an order of magnitude compared with the single ring.(3) A broadband terahertz polarizer consisting of two layers subwavelength metallic gratings on both sides of 45 μm polyimide film is studied theoretically, and realized by the method of laser induced and non-electrolytic plating with copper. The effect of film thickness, metal thickness, material loss and lateral shift between two metallic gratings on the performance of the THz polarizer was simulated by the FDTD method. The THz-TDS measurements show that the transmittance exceeds 67% and the extinction ratio is higher than 45 d B in 0.2~1.6 THz which is much better than conventional single wire-grid THz polarizer.