Ma Yiming, Chang Yuhua, Dong Bowei, Wei Jingxuan, Liu Weixin, Lee Chengkuo
Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583.
Center for Intelligent Sensors and MEMS (CISM), National University of Singapore, Singapore 117608.
ACS Nano. 2021 Jun 22;15(6):10084-10094. doi: 10.1021/acsnano.1c01859. Epub 2021 Jun 1.
Mid-infrared absorption spectroscopy plays an important role in molecule identification and quantification for widespread applications. Integrated photonics provides opportunities to perform spectroscopic sensing on-chip for the minimization of device size, cost, and power consumption. The integration of waveguides and photodetectors is an indispensable step toward the realization of these on-chip sensing systems. It is desired to extend the operating wavelengths of these on-chip sensing systems to the long-wave infrared (LWIR) range to utilize more molecular absorption fingerprints. However, the development of LWIR waveguide-integrated photodetectors faces challenges from both waveguide platforms due to the bottom cladding material absorption and photodetection technologies due to the low LWIR photon energy. Here, we demonstrate LWIR waveguide-integrated photodetectors through heterogeneous integration of graphene photodetectors and Si waveguides on CaF substrates. A high-yield transfer printing method is developed for flexibly integrating the waveguide and substrate materials to solve the bottom cladding material absorption issue. The fabricated Si-on-CaF waveguides show low losses in the broad LWIR wavelength range of 6.3-7.1 μm. The graphene photodetector achieves a broadband responsivity of ∼8 mA/W in these low-photon-energy LWIR wavelengths under zero-bias operation with the help of waveguide integration and plasmonic enhancement. We further integrate the graphene photodetector with a Si-on-CaF folded waveguide and demonstrate on-chip absorption sensing using toluene as an example. These results reveal the potential of our technology for the realization of chip-scale, low-cost, and low-power-consumption LWIR spectroscopic sensing systems.
中红外吸收光谱在广泛的应用中的分子识别和定量分析方面发挥着重要作用。集成光子学为在芯片上进行光谱传感提供了机会，以最小化设备尺寸、成本和功耗。波导和光电探测器的集成是实现这些片上传感系统不可或缺的一步。期望将这些片上传感系统的工作波长扩展到长波红外（LWIR）范围，以利用更多的分子吸收指纹。然而，LWIR波导集成光电探测器的发展面临着来自波导平台的挑战，这是由于底部包层材料的吸收，以及来自光电探测技术的挑战，这是由于LWIR光子能量较低。在这里，我们通过在CaF衬底上异质集成石墨烯光电探测器和Si波导，展示了LWIR波导集成光电探测器。开发了一种高产率转移印刷方法，用于灵活集成波导和衬底材料，以解决底部包层材料吸收问题。所制备的CaF基Si波导在6.3 - 7.1μm的宽LWIR波长范围内显示出低损耗。在波导集成和等离子体增强的帮助下，石墨烯光电探测器在零偏置操作下，在这些低光子能量的LWIR波长下实现了约8 mA/W的宽带响应率。我们进一步将石墨烯光电探测器与CaF基Si折叠波导集成，并以甲苯为例展示了片上吸收传感。这些结果揭示了我们的技术在实现芯片级、低成本和低功耗LWIR光谱传感系统方面的潜力。
