Low-noise high-gain large-bandwidth transimpedance ampli?er with cascode-type preamplifier for cryogenic STM

Abstract: A low-noise high-gain large-bandwidth transimpedance amplifier (TIA) for cryogenic scanning tunneling microscope (CryoSTM) is proposed. The TIA connected with the tip-sample component in CryoSTM is called as CryoSTM-TIA. The CryoSTM-TIA has a transimpedance gain of 10 Gohm, a bandwidth of over 100 kHz, and an equivalent input noise current power spectral density less than 4 (fA)²/Hz at 100 kHz. The low inherent noise of the CryoSTM-TIA is due to its special design: (1) its pre-amplifier (Pre-Amp) is made of the low-noise cryogenic high electron mobility transistors; (2) the cascode-type configuration for the Pre-Amp is used to avoid Miller effect to reduce its input capacitance C_A; (3) the capacitance of the cable connected the Pre-Amp input to the tip, i.e. C_I, is minimized; (4) thermal noise sources, such as the feedback resistor, are placed in the cryogenic zone. Its high gain and large-bandwidth are realized together, due to the application of the frequency compensation in the feedback loop, the reduced C_A, and the minimized C_I. This apparatus can be used for fast high-energy-resolution measurements of scanning tunneling spectra for low conductivity materials, especially for measuring their scanning tunneling shot noise spectra.