To improve the transmittance of THz component and overcome the difficulties of fragile structure as well as ensuring precise alignment of existing methods, a new method involving the mature 3DIC through-silicon via (TSV) technology has been proposed to make anti-reflection layer with suitable effective refractive index based on the robustness of Si wafer. Cu wire-grid polarizers were also fabricated on wafer. The THz polarizers were completed after wafer bonding with Cu sealing ring and In/Sn guard ring. Not only the new method is easier for production with better performance, but also the silicon substrate has several advantages. The novel method has proven that THz optical component could be constructed with a nearly 100% transmittance, or widened the transmittance spectrum range from 0.5 to 2 THz when transmittances is sacrificed to 70% instead of a near 100%. Furthermore, a robust structure could also be expected with broadband transmission and excellent extinction ratio. It is properly optimized for mass production because the fabrication method could be easily done and does not required high cost.
Due to the difficulties faced in fabricating robust Terahertz (THz) optical components with low Fresnel reflection loss, the need to increase the efficiency of THz system with reduced cost is still considered as one of the most essential tasks. In this report, a new low cost THz polarizer with robust structure is proposed and demonstrated. This new THz wire grid polarizer was based on an anti-reflection (AR) layer fabricated with low temperature metal bonding and deep reactive ion etching (DRIE). After patterning Cu wire gratings and the corresponding In/Sn solder ring on the individual silicon wafers, the inner gratings were sealed by wafer-level Cu to In/Sn guard ring bonding, providing the protection against humidity oxidation and corrosion. With the low eutectic melting point of In/Sn solder, wafers could be bonded face to face below 150°C. Two anti-reflection layers on both outward surfaces were fabricated by DRIE. With the mixing of empty holes and silicon, the effective refractive index was designed to be the square root of the silicon refractive index. The central frequency of the anti-reflection layers was designed between 0.5THz to 2THz with an approximate bandwidth of 0.5THz. The samples were measured with a commercial free-standing wire grid polarizer by a THz time domain spectroscopy (THz-TDS) from 0.2THz to 2.2THz. The power transmittance is close to 100% at central frequency. Extinction ratio of the polarizer is between 20dB to 40dB depending on the frequency. The advantages of this new polarizer include high transmittance, robust structure and low cost with no precision optical alignment required.