Picoampere-Level Current Stability of High-Voltage Power Supplies for Electron Microscopes: Technical Core and Application Value

In the field of microcharacterization, electron microscopes (referred to as electron microscopes for short) have become core tools in materials science, life sciences, semiconductor industry, and other fields due to their nanoscale and even atomic-level resolution. The performance of an electron microscope depends not only on the precise design of its electron optical system but also on the stable output of the high-voltage power supply. Among these factors, picoampere-level current stability is a key indicator determining imaging quality and the reliability of data analysis. The current precision at the picoampere level (10⁻¹² amperes) requires the power supply to control fluctuations below the nanoampere level, which poses extremely high challenges to noise suppression, load adaptation, and environmental anti-interference capabilities.
From the perspective of technical principles, the current stability of the high-voltage power supply for electron microscopes is directly related to the intensity control of the electron beam. The electron beam formed by accelerating electrons via the power supply will convert slight fluctuations in its intensity into imaging signal noise: in a high-resolution transmission electron microscope (HRTEM), if the current fluctuation exceeds 0.1%, the details of the atomic arrangement in the lattice image will be blurred; in the secondary electron imaging of a scanning electron microscope (SEM), unstable current will cause uneven brightness of the sample surface morphology, affecting the dimensional measurement accuracy of nanoscale features. Such fluctuations mainly originate from three aspects: first, the inherent noise inside the power supply, including thermal noise generated by resistor thermal motion and 1/f low-frequency noise, which need to be suppressed through the selection of low-noise operational amplifiers and the design of multi-stage filter circuits; second, the impact of dynamic load changes. The load impedance of the electron optical system of the electron microscope changes with the movement of the sample stage and focus adjustment. Especially in in-situ experiments, changes in sample temperature or electric field will lead to fluctuations in load capacitance/resistance, and the power supply must have microsecond-level dynamic response to offset current drift; third, external environmental interference. A temperature change of 1°C may cause parameter drift of circuit components, thereby leading to picoampere-level current deviation. Therefore, the power supply needs to integrate a temperature compensation module and reduce the impact of electromagnetic interference (EMI) and ground loops through metal shielding and grounding design.
In practical applications, picoampere-level current stability is the guarantee for the accuracy of experimental results. When studying the particle size distribution of nano-catalysts in the field of materials science, current fluctuations will cause differences in imaging brightness of different particles, easily leading to misjudgment of particle size; when analyzing the three-dimensional structure of virus particles or protein complexes in life sciences, current stability directly affects the consistency of phase contrast, which is a prerequisite for obtaining high-resolution structures using single-particle reconstruction technology. More importantly, with the development of in-situ electron microscope technology, the power supply must maintain picoampere-level stability under external disturbances such as sample heating and energization. For example, when observing the charge-discharge process of lithium battery electrodes in-situ, if the power supply current drifts at the picoampere level, it will be impossible to distinguish between the structural changes of the electrode material and the signal interference caused by current noise, resulting in the failure of experimental data.
Currently, the optimization of picoampere-level current stability focuses on the combination of active control and passive anti-interference: on the one hand, real-time monitoring of current output is conducted through digital feedback algorithms, and millisecond-level deviation correction is achieved using FPGA (Field-Programmable Gate Array); on the other hand, an isolated power supply topology design is adopted to reduce the impact of input grid fluctuations on the output. At the same time, through a long-term stability calibration mechanism, the power supply output is regularly calibrated with a high-precision ammeter to ensure that the current drift is controlled within the picoampere range within several months.
In summary, the picoampere-level current stability of high-voltage power supplies for electron microscopes is not merely a technical indicator but an invisible cornerstone supporting cutting-edge research in the microcosmic field. As the resolution of electron microscopes breaks through to the sub-angstrom level, the requirements for power supply stability will be further enhanced. The continuous innovation of this technology will provide a reliable guarantee for the revelation of more unknown microscopic phenomena.