Fast low-noise transimpedance amplifier for scanning tunneling microscopy and beyond

TL;DR

This paper presents a low-noise, high-bandwidth transimpedance amplifier designed for scanning tunneling microscopy, with applications in electron microscopy and low-temperature measurements, emphasizing noise reduction and dynamic range.

Contribution

The paper introduces a transimpedance amplifier with optimized low noise, wide bandwidth, and large dynamic range suitable for STM and other microscopy techniques, including cryogenic applications.

Findings

Achieved low noise limited by Johnson noise of 1 GΩ resistor

Bandwidth of 50 kHz at 35 pF input capacitance

Dynamic range from 0.1 pA to 50 nA

Abstract

A transimpedance amplifier has been designed for scanning tunneling microscopy (STM). The amplifier features low noise (limited by the Johnson noise of the 1 G{\Omega} feedback resistor at low input current and low frequencies), sufficient bandwidth for most STM applications (50 kHz at 35 pF input capacitance), a large dynamic range (0.1 pA--50 nA without range switching), and a low input voltage offset. The amplifier is also suited for placing its first stage into the cryostat of a low-temperature STM, minimizing the input capacitance and reducing the Johnson noise of the feedback resistor. The amplifier may also find applications for specimen current imaging and electron-beam-induced current measurements in scanning electron microscopy and as a photodiode amplifier with a large dynamic range. This paper also discusses the sources of noise including the often neglected effect of non-balanced input impedance of operational amplifiers and describes how to accurately measure and adjust the frequency response of low-current transimpedance amplifiers.