Thermal Transistors: Pioneering the Future of Electronic Cooling Systems

28-11-2023 | By Robin Mitchell

Recently, researchers from the University of California have developed a thermal transistor, a breakthrough in thermal management in electronics, that is said to be able to control the flow of heat and may provide advanced thermal management solutions for chips in the future. This innovation represents a significant leap in thermal management solutions in electronics, addressing a critical need in the industry. What challenges does heat introduce in semiconductors, what did the researchers develop, and how could it be used in future devices?

What challenges does heat introduce in semiconductors?

It is no secret that heat is the killer of electronic devices, causing computers to automatically turn off, batteries to spontaneously combust, and reduction in component capabilities such as maximum power rating, frequency, and operating voltage. For these reasons, ensuring that electronics keep their cool is an extremely important aspect of electronics. But what is it about heat that causes issues in semiconductors, and how do engineers get around these issues currently?

In passive components (such as resistors, capacitors, wires, and inductors), heat not only has the ability to physically damage structures, coatings, and contacts but also contributes to an increase in resistance. However, in semiconductor materials, an increase in heat actually decreases its resistance, and while this may sound like a benefit, it can lead to some rather nasty phenomena. 

In the case of transistors, an increase in temperature can result in an increase in conductance, and the resulting increase in current flow can generate more heat, which, in turn, heats up the transistor. This positive feedback loop, if left unchecked, can result in a transistor destroying itself rapidly, known as a thermal runaway. The use of negative feedback can help eliminate this issue, but it is not always an appropriate solution.

Another issue presented by heat in semiconductors is that, if left unchecked, it can degrade the quality of a semiconductor and, therefore, reduce its lifespan. This is especially true in delicate structures found in modern processors, where repeated heating cycles can induce stress and form cracks on a molecular level. 

Managing heat in semiconductors can be done via passive and active cooling. In the case of passive cooling, heat sinks can absorb large quantities of heat and re-emit it to the surrounding environment via convection (airflow) and radiation. However, for applications that need to rapidly remove large quantities of heat. advanced cooling systems such as fans and liquid cooling offer a better solution. These advanced cooling systems are crucial in maintaining optimal performance in high-tech electronic devices, ensuring they operate within safe thermal limits. These advanced cooling systems in high-tech devices are not just about removing heat but also about enhancing the overall efficiency and performance of the electronics. 

But for all the benefits that modern heat removal systems provide, they are generally expensive, large, and heavy, which makes integrating them into advanced devices extremely difficult, especially those that need to be portable (such as laptops and smartphones). 

Researchers develop thermal transistors

This breakthrough in thermal management in electronics signifies a major step forward in addressing the perennial challenge of heat dissipation in densely packed electronic circuits. Recognising the challenges faced by engineers when trying to remove heat from semiconductor systems, researchers from the University of California recently published a paper on a new device that they claim could be used for future thermal applications. The new device, dubbed a “thermal transistor”, is unique in that it is able to change its thermal conductivity based on an electric field.

The transistor is made up of a specialised molecular channel and an electric gate. Under normal conditions, heat flow across the channel is impeded by the weak bond between the molecules. However, when an electric field is applied to the gate, the bond between the molecules increases in strength. This increase in bond strength directly increases the thermal conductivity of the channel, thus resulting in an electrical field controlling thermal conductivity.

This development is among the latest innovations in semiconductor cooling, showcasing a novel approach to tackling heat dissipation challenges. 

The Role of Molecular Junctions in Thermal Transistors

A pivotal aspect of the thermal transistor's functionality, as highlighted in a detailed study on, is the use of molecular junctions. This approach is a prime example of molecular engineering in semiconductors, where a single molecule forms a bridge between two electrodes, key to manipulating thermal conductance.

The study's findings reveal that the application of an electric field strengthens the molecular bonds within the junction. This strengthening of bonds directly correlates with an increase in thermal conductivity, allowing for more efficient heat transfer. Such a mechanism is revolutionary, offering a new dimension to thermal management in semiconductor devices. It underscores the potential of molecular engineering in creating more effective and responsive cooling systems, especially in compact and densely packed electronic architectures. The role of molecular engineering in semiconductors is becoming increasingly vital, as it allows for the precise manipulation of thermal properties at the most fundamental level.

This integration of molecular junctions in thermal transistors could lead to significant advancements in semiconductor technology. By precisely controlling heat flow at such a granular level, it opens up possibilities for developing more efficient, smaller, and faster electronic devices. The implications of this technology extend beyond traditional applications, potentially revolutionising how we approach thermal management in various high-tech sectors.

The team behind the thermal transistor noted that the thermal conductivity increased 13-fold, which is higher than that of all other thermal switching devices. At the same time, the team also pointed out that the molecular channel was only one molecule thin, further demonstrating the capability of their switch. 

Furthermore, the researchers were able to demonstrate changes in conductivity at speeds of up to 1MHz, which allows for complete control of thermal characteristics in real time. Thus, it is possible for a PWM signal to control the degree of heat being removed from a system. The ability to achieve efficient heat transfer through such innovative means could revolutionise the design of future electronic devices.

How could such devices be used in the future?

If such transistors can be scaled and used in the same fabrication processes as current transistor technologies, it may be possible to use the new thermal transistors to help control heat across a semiconductor die. For example, an array of thermal transistors can be used to conduct heat away from hotspots and safely distribute it across the chip. This is a prime example of molecular engineering for thermal control, where intricate molecular interactions are harnessed for improved heat management. 

Such transistors could also be massively beneficial in removing heat in large 3D semiconductors. Unlike 2D semiconductors, the use of multiple active layers significantly increases the amount of heat generated while significantly impacting the thermal conductivity of the die as a whole. Thus, thermal transistors integrated into the design can help keep middle layers cool by moving heat towards the edge, topside, or underside of the die. 

While these devices are still in their infancy, if they can be scaled and adopted into mainstream processes, they could prove to be massively beneficial, especially in the field of mobile processors, where heat management significantly impacts performance. 

Real-World Applications of Thermal Transistors

The advent of thermal transistors opens up a plethora of practical applications, particularly in the realm of electronics. One of the most promising areas is in mobile processors. As smartphones and portable devices become increasingly powerful, managing the heat generated by their processors is a growing challenge. Thermal transistors could provide a more efficient way to dissipate heat, thereby enhancing the performance and longevity of these devices.

The advent of thermal transistors is set to play a crucial role in revolutionising thermal management in compact electronics, offering new solutions for heat dissipation in space-constrained environments. 

Another significant application lies in the field of 3D semiconductors. These multi-layered chips are becoming more common in advanced computing systems but face the challenge of heat accumulation in their densely packed structures. Thermal transistors, with their ability to precisely control heat flow, could be integral in managing thermal dynamics in these semiconductors. By effectively dispersing heat, they can prevent overheating and ensure the smooth functioning of the chips.

Furthermore, the integration of thermal transistors into various electronic components could revolutionise the design and efficiency of cooling systems. From laptops to data centres, the ability to manage heat at a molecular level could lead to smaller, more energy-efficient cooling solutions. This advancement is not just about improving existing technologies but also about enabling the development of new, more powerful electronic devices that were previously limited by thermal constraints.

Challenges and Future Research in Thermal Transistor Technology

Despite the groundbreaking potential of thermal transistors, there are challenges and areas for future research that need to be addressed. As highlighted in the article, one of the primary challenges lies in the scalability and integration of these devices into existing semiconductor manufacturing processes. The intricate nature of molecular junctions, while offering precise control over thermal conductance, also presents complexities in fabrication at a commercial scale.

Another challenge is the durability and reliability of these molecular structures under real-world operating conditions. The long-term stability of the molecular junctions, especially when subjected to repeated thermal cycling and varying electrical fields, is a critical area for future research. Ensuring that these devices can withstand the rigours of everyday use is essential for their practical application in electronics.

Future research will also need to focus on optimising the materials and design of thermal transistors to enhance their efficiency and effectiveness. Exploring different molecular compositions and configurations could lead to improvements in thermal conductivity and switching speeds. Additionally, integrating these devices with other semiconductor technologies, such as silicon-based chips or emerging materials like graphene, could open new avenues for advanced thermal management solutions.

The potential of thermal transistors to revolutionise thermal management in electronics is immense. However, overcoming these challenges through continued research and development will be key to unlocking their full potential. As the technology matures, it could pave the way for more efficient, compact, and powerful electronic devices, changing the landscape of electronics design and manufacturing.

The ongoing advancements in thermal transistor technology are not just about managing heat; they are about enhancing semiconductor performance through thermal regulation, opening up new frontiers in electronic device capabilities. 

In conclusion, the advancements in semiconductor technology, particularly through the development of thermal transistors, mark a significant milestone in the evolution of electronic devices.


By Robin Mitchell

Robin Mitchell is an electronic engineer who has been involved in electronics since the age of 13. After completing a BEng at the University of Warwick, Robin moved into the field of online content creation, developing articles, news pieces, and projects aimed at professionals and makers alike. Currently, Robin runs a small electronics business, MitchElectronics, which produces educational kits and resources.