Low-Noise Large-Bandwidth High-Gain Transimpedance Amplifier for Cryogenic STM at 77 K

In this work, we design and fabricate the transimpedance amplifier (TIA) following the design mentioned in Liang (Ultramicroscopy, 267:114051, 2024). In the TIA, the pre-amplifier (Pre-Amp) is made of a junction field-effect transistor (JFET) that can work at 77 K. The post-amplifier (Post-Amp) is made of an operational amplifier. Cascade Pre-Amp and Post-Amp to form the inverting amplifier. With a 1.13 G\(\Omega \) feedback network, the gain of TIA is 1.13 G\(\Omega \) and its bandwidth is about 97 kHz. The equivalent input noise voltage power spectral density (PSD) of TIA is not more than 9 (nV)\(^2\)/Hz at 10 kHz and 4 (nV)\(^2\)/Hz at 50 kHz, and its equivalent input noise current PSD is about 26 (fA)\(^2\)/Hz at 10 kHz and 240 (fA)\(^2\)/Hz at 50 kHz. The measured electrical performances and noise performances of TIA are consistent with the simulations and calculations. As an example, the realization of TIA in this work verifies the design method and analytical calculations for the low-noise large-bandwidth high-gain TIA proposed in Liang (Ultramicroscopy, 267:114051, 2024), Liang (Ultramicroscopy, 234:13466, 2022). And, the TIA in this work is perfect for the cryogenic STM working at liquid nitrogen temperature. With this TIA, at 77 K, the scanning tunneling spectroscopy and scanning tunnel shot noise spectroscopy measurements can be performed at the frequency of tens of kHz, even in the case of high tip–sample resistance.