用于扫描隧道显微镜的低噪声前置电流放大器  

Low-noise preamplifier for scanning tunneling microscope

作　　者：唐海涛 米壮 王文宇 唐向前 叶霞 单欣岩[1,2] 陆兴华 Tang Hai-Tao;Mi Zhuang;Wang Wen-Yu;Tang Xiang-Qian;Ye Xia;Shan Xin-Yan;Lu Xing-Hua(Center for Applied Physics,Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China;School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 100190,China)

机构地区：[1]中国科学院物理研究所,应用物理中心,北京10019 [2]中国科学院大学物理学院,北京100190

出　　处：《物理学报》2024年第13期20-27,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11727902,21961142021);北京市自然科学基金(批准号:4181003)资助的课题。

摘　　要：前置电流放大器是扫描隧道显微镜的重要部件之一,其性能对于扫描隧道显微镜系统的基本操作及新功能开发至关重要.本文详细分析了影响前置电流放大器性能的因素,通过筛选噪声极低的运放芯片和电路结构优化,设计了一款针对扫描隧道显微镜系统的前置电流放大器.该放大器最灵敏档位(1 GΩ)的噪声低至4 fA/(Hz)1/2,带宽为2.3 kHz,具有10 MΩ,100 MΩ和1 GΩ三个测量量程并且可以通过控制信号实现自动切换,测量范围覆盖pA—μA量级的隧穿电流.利用该前置电流放大器展示了扫描隧道显微镜系统的主要功能,包括表面形貌表征、扫描隧道谱测量以及原子搬运,并探索了隧穿电流中散粒噪声的测量.通过散粒噪声随隧穿电流的变化关系,得到隧穿结中散粒噪声的法诺因子约等于1,验证了简单金属隧穿结中电子隧穿满足泊松过程,为表面电子关联体系的高精度表征提供了基础.The current preamplifier is one of the important components of the scanning tunneling microscope(STM),and its performance is crucial to the basic operations of the STM system,as well as for the development of demanding novel functionalities such as autonomous atomic fabrication.In this study,the factors that affect the performance of a current preamplifier,including its noise spectrum density and the bandwidth,are analyzed in depth,and a preamplifier is designed and fabricated specifically for the STM system.By using a carefully selected low-noise op amp chip,the optimized current preamplifier has a noise floor as low as 4 and a bandwidth of 2.3 kHz,at its most sensitive transimpedance gain of 1 GΩ.It has three transimpedance gains,10 MΩ,100 MΩ,and 1 GΩ,that can be switched through digital control signals.A two-switch configuration is adopted to minimize the noise floor while maintaining the optimal bandwidth.The current detectable by this three-level preamplifier ranges from pA toμA,satisfying the requirements of most STM operations.Using this preamplifier,the fundamental functions of the STM system are successfully demonstrated,including surface topographic characterization,scanning tunneling spectroscopy,and single atom/molecule manipulation.The measurement of shot noise in tunneling current is also explored,and a linear relationship between shot noise and tunneling current is obtained by carefully analyzing noise.It is illustrated that the Fano factor of the shot noise in a normal metallic tunneling junction is approximately equal to 1,revealing the expected Poisson process for electron tunneling in such a scenario.The results are valuable for the high-resolution characterization of correlation systems in the future.

关 键 词：扫描隧道显微镜 前置电流放大器 散粒噪声 

分 类 号：TN722[电子电信—电路与系统]