Researchers at the University of California, Los Angeles have created what can certainly be called the world’s smallest refrigerator today. And if you thought about some miniature copy of the familiar to all unit standing in your kitchen, you are deeply mistaken. What the Californian scientists have created is actually a tiny thermoelectric cooler, which is only 100 nanometers thick.
The cooler consists of two layers of different semiconductor materials sandwiched between metallized plates that act as electrodes. When one side of this “sandwich” is heated and the other remains cooler, the contact area between the semiconductor plates acts as a generator, generating electricity. Such thermoelectric converters have long been used in space technology. For example, in the Voyager spacecraft and the Curiosity and Perseverance Mars rovers, thermoelectric generators wrapped around a core of heat-producing plutonium provide energy to the systems of these vehicles and can do so continuously for several decades.
However, this thermoelectric effect begins to work in exactly the opposite way when an electric current is passed through the semiconductor structure. In this case, one side becomes hot and the other side cools, allowing this device to act as a refrigerator. Scientists believe that in the future, Peltier elements of the new type, which are more efficient and less expensive than the current ones, could replace the compressor and the gas system with freon in conventional household refrigerators.
Let’s return to the miniature refrigerator that was created. This device was created from two fairly common semiconductor materials – bismuth telluride and antimony-bismuth telluride. Thin films of these materials were obtained in the same way as the first samples of graphene. Scientists glued regular scotch tape to the surface of the crystals and after separating the tape from the crystal on its surface were found “flakes” of material of conditionally one-atom thickness. Later these flakes were given the appropriate shape and they were “stacked” in a package only 100 nanometers thick. Full active volume of thermoelectric cooler structure does not exceed one cubic micrometer and, of course, it cannot be seen with the naked eye.
Currently, California scientists are searching for alternative variants of semiconductor materials, the use of which will dramatically increase the efficiency of these microcoolers. The first experiments with such devices showed a very high speed of their reaction, which is a consequence of their small mass. When such a cell is turned on, it begins to cool immediately, with the minimum delay, a million times faster than a similar refrigerator with a volume of one cubic millimeter.
This property opens up quite great prospects for the application of such miniature cooling devices. In the future, it is likely that a large number of such devices can be placed directly on the crystals of semiconductor chips, dynamically changing the degree of cooling (the amount of cooling they produce) depending on the current value of the load on the logic circuits of that chip.