基于LT-GaAs外延片的THz片上系统

太赫兹（THz）波在物质检测方面发挥着巨大的作用，是一种非常有潜力的生化传感工具。但是传统的太赫兹时域光谱系统（TDS）结构复杂，系统的集成度低，占用空间较大。所以，如何对THz波进行有效引导、实现集成化传输并得到高质量光谱就成为太赫兹光谱系统的研究热点。太赫兹片上系统是将THz的产生、传输以及探测都集成到同一芯片上，然后通过相干探测的方法获得THz时域光谱。它可以实现对多种样品的检测，尤其在对难于取样的微量样品探测方面具有广泛的应用价值。它无需光路准直，操作简便，成品率高。两个研究工作都是基于低温砷化镓(LT-GaAs)外延片开展的。首先将一根直径为200 μm的铜线固定在LT-GaAs外延片的上方，通过真空蒸镀的方法制备出天线电极，同时得到天线间隙，研制出基于LT-GaAs外延片的THz天线。利用波长为800 nm的飞秒激光对其进行测试，得到了质量较高的THz信号，验证了天线的实用性。然后在另一外延片上利用光刻微加工工艺制作出传输线和微电极，得到了集成的THz片上系统。使用波长为1 550 nm的飞秒激光分别激发片上系统的太赫兹产生天线和探测天线，天线产生的太赫兹波在传输线上传播，在探测端同样得到了质量较高的THz时域信号，证实了THz片上系统的可行性。该方法省去了腐蚀牺牲层以及LT-GaAs薄膜的转移、键合等步骤，极大地提高了片上系统的成品率，避免了薄膜转移过程中易破碎及腐蚀液存在毒性的问题。最后，研究了外加电压对从片上系统中获得的THz波性能的影响，结果为电压越高，THz波的信号强度越强；另外，通过在传输线上方垂直放置铜箔的方法验证了THz波沿着传输线传播的事实。该研究中采用的基于LT-GaAs外延片的片上系统的制备方法简单，制作周期短，制作过程安全，应用领域广泛，这为将来与微流控芯片相结合实现对液体样品的探测打下了基础。

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 200μm 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 1550 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.