“We are the first in the world to present a logic circuit, in this case a transistor, that is controlled by a heat signal instead of an electrical signal,” said Professor Xavier Crispin.
The heat-driven transistor builds on research into supercapacitors in which heat is converted to electricity. From this work, the researchers produced a liquid electrolyte whose ability to convert a temperature gradient to a voltage was 100 times that of previous electrolytes. The liquid electrolyte consists of positively charged ions, which are small and move rapidly, and negatively charged polymer molecules, which are large and heavy. When one side is heated, the ions move rapidly towards the cold side, producing a voltage difference.
According to the team, a heat driven transistor could enable a range of new applications, including detecting small temperature differences and monitoring the healing process when used in medical dressings. The researchers also believe it might be possible to produce circuits controlled by the heat present in infrared light.
Because of the electrolyte’s high sensitivity to heat – 100 times that of traditional thermoelectric materials – a connector from the electrolyte, which acts as sensor, to the transistor circuit is sufficient. One sensor can be combined with one transistor to create a ‘smart pixel’.