Solid-state thermal transistor demonstrated – ScienceDaily

An effective, stable, solid-state electrochemical transistor has been developed, ushering in a new era in thermal management technology.

In modern electronics, a large amount of heat is produced as waste during use – this is why devices such as laptops and mobile phones become warm during use and require cooling solutions. Over the past decade, the concept of managing this heat with electricity has been tested, leading to the development of electrochemical thermotransistors—devices that can be used to control the flow of heat with electrical signals. Currently, liquid-state thermal transistors are used, but they have critical limitations: mainly, any leak will cause the device to stop working.

A Hokkaido University research team led by Professor Hiromichi Ohta of the Research Institute for Electronic Science has developed the first solid-state electrochemical thermal transistor. Her invention, described in the magazine Advanced functional materialsis much more stable than and just as effective as current liquid state thermal transistors.

“Roughly speaking, a thermal transistor consists of two materials, the active material and the switching material,” explains Ohta. “The active material has variable thermal conductivity, and the switching material is used to control the thermal conductivity of the active material.”

The team constructed their thermal transistor on a yttria-stabilized zirconia base, which also acted as the switching material, and used strontium-cobalt oxide as the active material. Platinum electrodes were used to provide the power needed to drive the transistor.

The thermal conductivity of the active material in the “on” state was comparable to some liquid state thermal transistors. In general, the thermal conductivity of the active material in the “on” state was four times higher than in the “off” state. Also, the transistor was stable over 10 cycles of use, better than some current liquid-state thermal transistors. This behavior was tested on more than 20 separately manufactured thermal transistors to ensure that the results were reproducible. The only drawback was the operating temperature of around 300°C.

“Our results show that solid-state electrochemical thermal transistors have the potential to be as effective as liquid-state electrochemical thermal transistors without their limitations,” Ohta concludes. “The main hurdle for the development of practical thermal transistors is the high resistance of the switching material and thus a high operating temperature. This will be the focus of our future research.”

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