The pioneering solid-state electrochemical thermal transistor developed in this study. (Image: Hiromichi Ohta)

In modern electronics, a lot of heat is produced as waste during usage — hence why in-use devices become excessively hot and require cooling solutions. Over the last decade, the concept of managing such heat via electricity has been tested, leading to the development of electrochemical thermal transistors.

Currently, liquid-state thermal transistors are in use, but have critical limitations — mainly, any leakage causes the device to stop working.

Now, a research team at Hokkaido University has developed the first solid-state electrochemical thermal transistor. The invention, described in the journal Advanced Functional Materials, is more stable than and just as effective as current liquid-state thermal transistors.

“A thermal transistor consists broadly of two materials: the active material and the switching material,” said Professor Hiromichi Ohta. “The active material has changeable thermal conductivity (k), and the switching material is used to control the thermal conductivity of the active material.”

The team constructed its thermal transistor on an yttrium oxide-stabilized zirconium oxide base — which also functioned as the switching material — and used strontium cobalt oxide as the active material. Platinum electrodes were used to supply the power necessary to control the transistor.

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

“Our findings show that solid-state electrochemical thermal transistors have the potential to be just as effective as liquid-state electrochemical thermal transistors, with none of their limitations,” said Ohta. “The main hurdle to developing practical thermal transistors is the high resistance of the switching material, and hence a high operating temperature. This will be the focus of our future research.”

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