Verbiest G J, Janssen H, Xu D, Ge X, Goldsche M, Sonntag J, Khodkov T, Banszerus L, von den Driesch N, Buca D, Watanabe K, Taniguchi T, Stampfer C
JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany, EU.
Peter Grünberg Institute (PGI-8/9), Forschungszentrum Jülich, 52425 Jülich, Germany, EU.
Rev Sci Instrum. 2019 Aug;90(8):084706. doi: 10.1063/1.5089207.
We developed an impedance bridge that operates at cryogenic temperatures (down to 60 mK) and in perpendicular magnetic fields up to at least 12 T. This is achieved by mounting a GaAs HEMT amplifier perpendicular to a printed circuit board containing the device under test and thereby parallel to the magnetic field. The measured amplitude and phase of the output signal allows for the separation of the total impedance into an absolute capacitance and a resistance. Through a detailed noise characterization, we find that the best resolution is obtained when operating the HEMT amplifier at the highest gain. We obtained a resolution in the absolute capacitance of 6.4 aF/Hz at 77 K on a comb-drive actuator while maintaining a small excitation amplitude of 15 kT/e. We show the magnetic field functionality of our impedance bridge by measuring the quantum Hall plateaus of a top-gated hBN/graphene/hBN heterostructure at 60 mK with a probe signal of 12.8 kT/e.
我们开发了一种能在低温温度（低至60 mK）下且在高达至少12 T的垂直磁场中工作的阻抗桥。这是通过将一个砷化镓高电子迁移率晶体管（GaAs HEMT）放大器垂直安装在包含被测器件的印刷电路板上，从而使其与磁场平行来实现的。所测量的输出信号的幅度和相位能够将总阻抗分离为绝对电容和电阻。通过详细的噪声特性分析，我们发现当以最高增益操作HEMT放大器时可获得最佳分辨率。在77 K下，我们在梳齿驱动致动器上实现了绝对电容分辨率为6.4 aF/Hz，同时保持15 kT/e的小激励幅度。我们通过在60 mK下用12.8 kT/e的探测信号测量顶部栅极hBN/石墨烯/hBN异质结构的量子霍尔平台，展示了我们阻抗桥的磁场功能。
