High Voltage Power Supply: The Key Component for High Resolution SEM Imaging

Scanning electron microscope (SEM) is an advanced high resolution imaging tool that is widely used in material science, biology and other research fields. Its ultra-high imaging resolution relies on the powerful electron beam. The key component that generates and controls such powerful electron beam is the high voltage power supply system of SEM.

The electron beam in SEM is emitted from the electron gun under high voltage. The working voltage of a typical SEM is in the range of 0.5-30 kV. Only when the acceleration voltage reaches a certain level, can the electron beam attain adequate kinetic energy to scan the sample surface and excite various signals that carry the sample information. As the acceleration voltage increases, the penetration power of the electron beam enhances, which excites more signals and significantly improves the resolution of SEM. The state-of-the-art field emission SEM can achieve sub-1nm super high resolution imaging, largely thanks to the working voltage at tens of kV or even higher.

However, employing higher working voltage also brings certain challenges. The high voltage power supply system needs to provide extremely stable and precisely controlled high voltage. Even minimal voltage fluctuation may lead to increased image noise and reduced resolution. Moreover, as the voltage increases, the current and loading of the power supply also rise, posing higher requirements for stability. Finally, safety issues need to be addressed to avoid electric shock hazards of high voltage.

Currently, SEM high voltage power supply systems mainly adopt multi-stage regulated power supply topology. Each stage consists of precision controlled switch mode power supply and filtering circuits, providing maximally flat and clean high voltage output through multi-stage regulation. Some top-level systems also utilize full digital control to achieve voltage regulation precision up to 0.01%. Insulating materials with better dielectric strength are also under development to reduce leakage current and ensure stable high voltage delivery.

With the continuous advancement of SEM technology, building more powerful and stable high voltage power supply systems remains a key research direction. We look forward to further improvements in power supply technology that will enhance the imaging capability of SEM and allow its indispensible applications in more fields.