Tiny thermometers offer on-chip temperature monitoring for processors

(Press-News.org) UNIVERSITY PARK, Pa. — The semiconductor chips driving modern-day computer processors are covered in billions of individual transistors, each of which can overheat under stress, causing steep drops in performance. To address this, a team led by researchers at Penn State has developed a microscopic thermometer, smaller than an ant’s antenna, that can be integrated onto a chip to accurately track temperatures.

Using an advanced class of materials that are just a few atoms thick, known as two-dimensional (2D) materials, the team built sensors capable of differentiating subtle temperature changes in just 100 nanoseconds — millions of times faster than the blink of an eye. The sensors’ extremely compact structure allows many of them to be integrated directly onto a single computer chip, offering what the researchers called incredibly efficient temperature monitoring. The team detailed their work in a paper published today (March 6) in Nature Sensors.

According to Saptarshi Das, Ackley Professor of Engineering Science, professor of engineering science and mechanics at Penn State and corresponding author on the paper, accurately monitoring the temperature of transistors — tiny devices that control the flow of electricity in a circuit — is currently one of the most challenging aspects of developing computer chips or high-performance integrated circuits.

“These chips rapidly heat up during usage, but the sensors that monitor their temperatures are not embedded within the chip,” Das said. “One of the major questions researchers have had is whether it’s possible to integrate temperature sensing directly into the chips, which would offer faster, more accurate readings.”

A temperature sensor would have to be incredibly small to achieve this, as traditional sensors are too large and bulky to fit onto a chip directly, explained Das. To shrink their sensors into thermometers only one square micrometer across, or a tile several thousand times smaller than the width of a human hair, the team used a new class of 2D material – known as bimetallic thiophosphates — that had previously not been used in thermal sensors.

According to Das, this material’s distinctive properties, specifically how ions can continue effectively move even when exposed to electrical currents, enable the sensors to demonstrate strong temperature dependence, even at extremely small sizes. This means that the material’s physical properties can adjust dynamically as temperatures rise or fall.

“My research group works extensively with 2D materials, as Penn State is considered a leader in this research area,” Das said. “We found that using this class of material, we could develop thermal sensors that are very fast, low power and really miniaturized so that you can place many of them on a single chip.”

According to Dipanjan Sen, engineering science doctoral candidate and first author on the paper, this 2D material can “couple” together the transport of both ions and electrons — subatomic particles that both play different roles in energy transfer. Although improving the flow of electrons can lead to more powerful devices, better ion regulation in a system can lead to improved thermal management and monitoring, as these particles are notably sensitive to heat.

This coupling allows the tiny sensors to operate using the same electrical currents that power the overall chip, meaning they can provide extremely sensitive temperature readings, while not having a notable impact on chip performance. Das explained how recognizing this relationship was key to integrating the sensors directly on a chip.

“What is generally unwanted by industry in transistors actually is great for thermal sensing, so we really tried to exploit that in our design,” Das said. “Rather than try to remove these ions from this system, we use them to our advantage. Coupling these ions for temperature sensing and electrons for reading that thermal data allows us to have an extremely accurate but compact device.”

The team used advanced instruments in the Materials Research Institute's Nanofabrication Laboratory to manufacture the sensors and place thousands on a single computer chip. Not only is the sensor more than 100 times smaller than other leading sensor designs, it is also up to 80 times more power efficient than traditional silicon-based systems since it doesn’t need extra circuitry or signal converters.

Das said he believes that the team’s sensors could be integrated alongside existing technology to improve computer efficiency and stability. Going forward, the team plans to continue development and explore new opportunities to apply 2D materials in sensor design. According to Das, this research could be used as a framework to develop future sensors capable of measuring chemical, optical or physical information in an incredibly compact format.

“This is a proof of concept that shows this design can work — it can be miniaturized, it is low power and could be the next step in terms of integrating temperature monitoring directly into chips,” Das said.

Other co-authors affiliated with Penn State include Anirban Chowdhury, an engineering science and mechanics doctoral candidate; Adri van Duin, distinguished professor of mechanical engineering; Joan Redwing, professor of materials science and engineering and of electrical engineering; Anshul Rasyotra, a postdoctoral scholar in engineering science and mechanics; Chen Chen, an assistant research professor at the Materials Research Institute; and Alireza Sepehrinezhad and Arpan Ghosh, two engineering science and mechanics doctoral candidates.

Additional co-authors include Mercouri G. Kanatzidis, professor of chemistry at Northwestern University; Thomas S. Le, a chemistry doctoral candidate at Northwestern University; Safdar Imam, a postdoctoral fellow at Northwestern University; Zdenek Sofer, professor of inorganic chemistry at University of Chemistry and Technology Prague, Prague, Czech Republic; and Vlastimil Mazanek, assistant professor of inorganic chemistry at University of Chemistry and Technology Prague, Prague, Czech Republic.

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