When using single-stage thermoelectric coolers to control the temperature of equipment, we sometimes find that the cooling effect is less than ideal. This is especially true for applications with high cooling requirements, such as infrared detectors and deep-sea sensors (which require temperatures below -100°C to function properly). Single-stage coolers are no longer sufficient, and multi-stage coolers are needed for deep cooling. Let's first review the working principle of a single-stage semiconductor cooler: When the cooler is energized, current flows through the semiconductor material, creating a temperature differential at the contact point. One side absorbs heat (the cold end) and the other side releases heat (the hot end), achieving the desired cooling effect.

The multi-stage semiconductor refrigeration plate is composed of multiple single-stage refrigeration plates stacked in a "thermal series" manner - heat is transferred from the bottom layer to the upper layer step by step, and each level further cools down the temperature based on the next level, achieving a deep cooling effect through "relay cooling" to create an ultra-low temperature environment below -100°C.

Theoretically, the total temperature difference of a multi-stage refrigeration unit is n times that of a single-stage unit (n is the number of stages). For example, in an extreme environment with a hot-end temperature of 300°C, the cold-end temperature of a single-stage refrigeration unit can only reach a minimum of around 230°C. In a multi-stage refrigeration unit (taking a five-stage unit as an example), each stage can share a 40-50°C temperature difference, ultimately reducing the cold-end temperature to 80-100°C. However, in practical applications, we need to consider the thermal resistance loss between stages, so the actual total temperature difference will be slightly lower than the theoretical value.

*Hot spot power generally refers to the power consumed by a point or area in an electronic device or system where the temperature is significantly higher than the surrounding environment due to high current density or poor heat dissipation.

Another important point to note is that while the greater the number of cooling stages, the lower the temperature, the cooling capacity also decreases. This is like a small water pump: while it can pump water very high, the amount of water it can pump at a time is limited. As the figure above shows, as the heat input to the hot end (i.e., the hotspot power) increases, the cold end temperature rises significantly—what could have been reduced to -100°C might suddenly rise to -60°C or even higher, significantly compromising the temperature control effectiveness. Therefore, multi-stage semiconductor coolers are suitable for scenarios requiring "small amounts of heat, large cooling rates" and should not be used for high-power cooling. Once the cooling demand exceeds their capacity, not only will the target temperature not be reached, but cooling efficiency may also decrease due to overload.

Aerospace: In space, some equipment, such as infrared detectors and X-ray spectrometers, must operate at extremely low temperatures to maintain proper operation. For example, infrared imaging spectrometers on satellites are tasked with detecting extremely faint infrared signals from the universe. If the detector's own temperature is too high, it will generate interference noise, obscuring the target. Therefore, cooling to below 80K (approximately -193°C) is essential. However, at room temperature, a single-stage TEC can only lower the temperature to a maximum of 230K (approximately -43°C). This is where multi-stage refrigeration comes in: it cools the spectrometer down to below 80K through progressive cooling. Mineral analyzers on lunar or Martian rovers also face similar requirements. Their core sensors must operate below 100K. Since refrigerants like liquid nitrogen cannot be carried on long-term missions, multi-stage refrigeration is the only option for continuous temperature control.

From deep space exploration to deep-sea sensing, from high-end medical treatment to cutting-edge scientific research, multi-stage semiconductor refrigeration units are penetrating into a wide range of fields, including aerospace and healthcare, with their stable and precise temperature control capabilities. As TEC technology continues to evolve, it will demonstrate its unique value in even more challenging scenarios, becoming a key choice for future precision temperature control systems.