Scientists Uncover Secret of Material for Promising Thermal Imagers: Blow-Up Overheating Instability
While 100-nanometer thin films of vanadium dioxide (VO2) do not normally conduct electricity, their resistance drops up to 100,000 times when slightly heated. This may happen under applied voltage, for example. That property is used to create high-speed switchable devices and sensors for direct current or alternating signal in the terahertz, microwave, optical, or infrared range.
Materials scientists found VO2 films could become conductive in the mid-20th century. Until now, the precise mechanism behind the change in the material’s electrical properties was unknown. Being aware of that mechanism enables application-oriented materials design. That includes the synthesis of thin films with predefined properties, such as the temperature at which conductivity changes or the ratio between the resistances before and after heating.
“Among the most useful things these films could be valuable for are sensors for uncooled bolometers. Bolometers underlie thermal imaging systems. VO2 films can boost their sensitivity and reaction rate, extending their applicability to rapidly moving objects,” commented study co-author and MIPT doctoral student Viktor Polozov of the university’s Landau School of Physics and Research.
MIPT researchers proposed a scenario for a VO2 film transition between the insulating and the conductive state. First the film heats up and conductive areas sporadically emerge in it. Then those areas become linked, turning into a channel that makes the film conduct current. Further heating widens the channel, reducing the film’s resistance.
This process occurs via a so-called blow-up regime. Similar observations have already been made in other materials. For example, this regime is also characteristic for the superconducting transition in high-temperature superconductors.