THz System on Chip Based on LT-GaAs Epitaxial Chip

Terahertz (THz) waves play an important role in material detection and is a potential biochemical sensor. However, the traditional terahertz time-domain spectroscopy (THz-TDS) system is complex in structure, low in integration and large in space. Therefore, guiding THz wave effectively, realising integrated transmission, and getting high-quality spectroscopy has become a research hotspot of the terahertz spectroscopy system. THz system on chip integrates the generation, transmission and detection of THz on the same chip, and then obtains THz time-domain spectroscopy by coherent detection. It can be used to detect many kinds of samples, especially in detecting trace samples thatare difficult to sample. It does notneed optical alignment, is easy to operate and has a high yield. The two research works in this paper are based on low-temperature GaAs (LT-GaAs) epitaxial wafers. Firstly, a 200 mu m diameter copper wire is fixed on the top of the LT-GaAs epitaxial wafer, and the antenna electrode is prepared by vacuum evaporation. At the same time, the antenna gap is obtained, and the THz antenna based on the LT-GaAs epitaxial wafer is developed. The high-quality THz signal is obtained by using the femtosecond laser with a wavelength of 800 nm, which verifies the practicability of the antenna. Then the transmission line and microelectrode are fabricated on another epitaxial wafer by lithography, and the integrated THz system on chip is obtained. A femtosecond laser with a wavelength of 1 550 nm is used to excite the terahertz generation antenna and the system's detection antenna on chip. The THz waves generated by the antenna propagate on the transmission line, and the high-quality THz time-domain signal is also obtained at the detection end, which proves the feasibility of the system achip. This method omits the steps of corrosion sacrificial layer, transfer and bonding of LT-GaAs film greatly improves the yield of the system a chip, and avoids the problems of fragility and toxicity of corrosive solutionthe process of film transfer. Finally, the influence of applied voltage on THz wave performance obtained from the system on chip is studied. The results show that the higher the voltage is, the stronger THz wave' ssignal strength is. Besides, the fact that THz waves propagate along the transmission line is verified by placing copper foil vertically above the transmission line. The system on chip based on LT-GaAs epitaxial wafer used in this study has the advantages of simple preparation method, short fabrication cycle, safe fabrication process and wide application field, which lays a foundation for detecting liquid samples by combining with microfluidic chips in the future.