基于石墨烯/硅衬底的太赫兹超导热电子混频器中频带宽特性研究

The terahertz (THz) frequency region of the electromagnetic spectrum is very rich in scientific and technological applications, and many domestic and foreign research groups are exploring the detection techonolies for THz astronomy applications. Superconducting hot electron bolometer (HEB) mixing technology is a heterodyne mixing technology of high sensitivity and low local oscillator power requirement, based on the strong nonlinear resistance vs. temperature (R-T) response of superconducting ultrathin film of the order of micrometer or nanometer. It has become the preferred mixing technology at higher THz frequencies.Currently, most of superconducting HEB devices are fabricated on silicon substrates, and their intermideate frequency (IF) bandwidth is affected by many factors such as the heat transfer rate from phonons in the film to the phonons in the substrate and is only 3-4 GHz, which is not enough for the simultaneous observation of several spectral lines and for the observation of extragalactic objects with high redshift. Thus, this project aims to investigate the IF bandwidth characteristics of THz HEB mixers to understand the IF bandwidth mechanism of HEB mixers. We will characterize the Seebeck coefficient, thermal resistance and thermal conductivity of a graphene at 4 K to understand the effect of a graphene/silicon substrate on the IF bandwidth of HEB mixers, and develop a theorectical model for superconducting HEB mixers based on graphene/silicon substrates. We will develop a superconducting HEB mixer of large IF bandwidth and high sensitivity, based on a graphene/silicon substrate. This project will promote the development of a superconducting HEB mixer of large IF bandwidth and high sensitivity for astonomy applications at THz frequencies.

太赫兹频段在天文学领域具有重要科学意义和丰富应用前景，为此国内外正积极开展太赫兹天文探测技术研究。超导热电子混频技术是一种基于微纳尺寸超导薄膜强非线性电阻-温度效应的外差混频技术，其具有高灵敏度和低本振功率需求等优点，已成为太赫兹高频段首选相干探测技术。目前超导热电子混频器大多基于硅衬底制备，受超导薄膜与衬底间声子逃逸等影响,其中频带宽仅为3-4GHz，难以满足高红移河外天体和多谱线同时观测需求。为此，本申请项目拟针对超导热电子混频器中频带宽特性展开研究,研究制约超导热电子混频器中频带宽物理机制;研究石墨烯/硅衬底对超导热电子混频器中频带宽的影响，实测石墨烯4K低温环境下赛贝尔系数、热阻和热导等物理参量,建立基于石墨烯/硅衬底超导热电子混频器理论模型;完成基于石墨烯/硅衬底的宽中频和高灵敏度超导热电子混频器原理芯片研制。该项研究将为发展天文观测所需宽中频和高灵敏度超导热电子混频器打下基础。

本项目主要研究了太赫兹超导热电子混频器的探测机理及特性，实现了高灵敏度超导热电子混频器的研制，其性能达到了国际同类探测器水平，为研制我国的天文应用高灵敏度超导热电子混频器打下关键技术基础。本项目取得的主要研究进展包括：1）解明了超导热电子混频器的物理特性与临界温度相关性，研究发现超导热电子混频器的临界温度为7-9.5K时，超导热电子混频器存在最佳噪声温度，而超导热电子混频器中频带宽随临界温度升高而增加；2）解明了超导热电子混频器的物理特性与本振频率相关性，实验结果表明超导热电子混频器具有与频率无关的噪声特性，可实现超宽带信号检测；3）成功实现超导热电子混频器与量子级联激光器在同一金属腔内集成并实现太赫兹波高效输运，实现2.5THz频段灵敏度突破7倍量子极限的超导热电子混频器与量子级联激光器外差集成接收机研制。本项目除了成功研制了高灵敏度超导热电子混频器，还成功研制了基于热噪声读出的高灵敏度太赫兹石墨烯热电子探测器，3K温区实测太赫兹石墨烯热电子探测器噪声等效功率达10-12W/Hz1/2量级，达到国际同类探测器相当水平。