| Summary: | 博士 === 國立交通大學 === 電子研究所 === 106 === The purpose of this study is to demonstrate the new THz optical components using 3D-IC technologies. Because of THz wavelength between 10μm and 1000μm, the order of optical structure of THz components is in micro-meter. Therefore, semiconductor manufacture and 3D-integration technologies are very suitable for developing micron-level optical structure. In this thesis, THz optical components are developed by key technologies of 3D-integration, such as low temperature wafer bonding, micro-bumping, Si deep reactive etching (DRIE), to achieve low-cost THz components. The fabrication method can realize high-transmittance THz polarizers, and is further proposed to apply to THz filter and resonator.
Some of commercial THz optical components, such as free-standing or thin-film wire-grid polarizers, are fabricated without substrate or with thin-film to achieve high transmittance. However, the free-standing or thin-film structure are fragile. Wire-grid polarizer fabricated on thick-substrate is with high mechanical strength, but low transmittance. Also, wire-grid fabricated on substrate is hard to apply anti-reflection coating on both outward surfaces because of occupied surface by wire-grid. In this study, Cu-In/Sn asymmetric low temperature bonding with submicron thickness using Ni ultra-thin buffer layer (UBL) is demonstrated to seal Cu wire-grid into Si substrate. Therefore, this integration method provides both of outward surfaces of polarizer to fabricate anti-reflection layers. Besides, Cu-In/Sn interconnects can be further applied to integrate THz components and devices. In bonding results, Cu-In/Sn bonding structure with Ni UBL has excellent bonding yield and good specific contact resistance about 10-6 ohm-cm, and passes temperature cycling test (TCT) and highly accelerated stress test (HAST).
Next, the single-layer artificial layer were fabricated on outward surfaces of substrate for anti-reflection by Si DRIE. The THz polarizer with high transmittance at selected frequency can be accomplished by designed etching depth and pattern according to effective medium theory. The THz polarizers with designed parameter are verified by rigorous coupled wave analysis (RCWA) and measured by THz time-domain spectroscopy (TDS). The results show 100% transmittance at selected frequency and about 30dB extinction ratio of THz polarizer. Broad-band THz polarizer can be achieved by stacking two anti-reflection layers with different central frequency. Although the transmittance slightly degrade, the transmittance spectrum is much uniform, which means less distortion of propagated signal. Furthermore, ultra-high extinction ratio polarizer with high transmittance could be realized by stacking multi-layer of wire-grid and two anti-reflection layers. The same integration concept could be also applied to multiple anti-reflection layers to attain THz filter.
In conclusion, this thesis demonstrates a new fabrication method of THz polarizer with advantages such as robust structure, low cost and high performance. The wire-grid polarizer is successfully sealed into Si substrate through sub-micron Cu-In/Sn bonding. 100% transmittance at selected frequency of polarizer can be achieved by anti-reflection process through Si DRIE. By combining two different AR layers, the transmittance spectrum of polarizer is slightly degraded but much uniform. The transmission signal with efficient power could pass through without distortion. Finally, a new structure of linearly polarized Fabry-Pérot resonator is proposed for the future vertical-cavity surface-emitting linearly polarized THz laser according to results of this thesis.
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