Tiny wrinkle in chip can trap heat and reduce conductivity by 5x, MIT study suggests

A wrinkle just a micrometer wide can become a major obstacle to heat inside an electronic device. In their new study, MIT researchers have shown that such a tiny defect can reduce local thermal conductivity by roughly four to fivefold, making it harder for heat to escape and potentially creating a dangerous hotspot, while also causing heat to spread differently in opposite directions. This finding reveals how microscopic imperfections can create hidden thermal bottlenecks inside increasingly powerful electronics and limit their performance. “I think overheating has become the real bottleneck in device performance,” Mingda Li, one of the study authors and an associate professor of nuclear science and engineering at MIT, said. More importantly, the study authors developed a way to directly map that disruption inside a layered material, something conventional thermal measurement techniques have struggled to do. Seeing heat through the layers As engineers pack more transistors into smaller spaces, controlling the heat they generate is becoming increasingly difficult. The problem is especially challenging in real devices, which can contain several layers through which heat must travel. Researchers already have techniques for measuring thermal transport, but they come with important limitations. Optical methods such as time-domain thermoreflectance can measure heat at small scales, but they mainly provide an overall optical signal and have difficulty resolving thermal transport in buried layers. “Because that technique uses optics, it doesn’t allow you to study different layers. Real devices have five or more layers. It also only provides an overall signal, and that makes it hard to see thermal transport happening in layers buried under the surface,” Jeehwan Kim, one of the study authors and a professor at MIT, added. Infrared cameras can also track temperature changes, but they lack the spatial and temporal resolution needed to follow extremely small and rapid changes. This means researchers can often determine how much heat a device is dissipating without being able to see exactly where that heat is getting held up. The MIT team approached the problem by combining laser pulses with ultrafast X-ray diffraction. They used a laser to rapidly heat the material and then used X-rays to track changes in its crystal lattice as the heat spread. The method works because heating a crystal causes its atoms to shift slightly, changing the spacing of its atomic lattice. That produces a measurable change in the way X-rays are diffracted by the crystal. By measuring those changes at different locations and at different times after the laser pulse, the researchers could reconstruct how heat was spreading through the material. The X-rays provided another crucial advantage: they could probe the layered structure rather than relying only on a surface measurement. This allowed the researchers to examine thermal transport within the GaN film and characterize heat transfer across the GaN-silicon interface. The wrinkle that stopped the heat The researchers tested the technique on a 500-nanometer-thick layer of gallium nitride, or GaN, on silicon. GaN is promising for high-power electronics because of its ability to handle high electrical fields and power. During processing, the thin film developed microscopic imperfections, including a wrinkle roughly 1 micrometer wide. When the researchers scanned across that defect, they found a surprisingly large change in thermal transport. Near the wrinkle, the researchers measured a local thermal conductivity of 21.2 ± 1.2 watts per meter-kelvin, roughly four to five times lower than in the surrounding GaN. The defect also reduced the thermal boundary conductance between GaN and silicon by about 25 percent, to approximately 2.12 × 10⁷ watts per square meter-kelvin. However, the wrinkle did more than simply slow heat down. The researchers found that heat spread asymmetrically around the defect. Heat approaching the wrinkle from one direction did not behave the same way as heat moving toward it from the opposite direction. The result shows that a localized defect can turn an otherwise uniform thermal pathway into a directional bottleneck. This matters because “when people model heat dissipation, they model perfect crystals without defects, but these types of large wrinkle defects are very common in 2D materials. People never even knew how much heat is blocked by these wrinkles. Those are things we can now directly observe with this technique,” Li said. The new technique provides a way to observe that effect rather than averaging it together with the behavior of the surrounding material. Such local reductions in thermal conductivity and interface conductance could contribute to hotspots, potentially affecting the reliability and lifetime of electronic devices. A new tool for thermal design The researchers believe the approach could eventually help engineers identify the microscopic features responsible for overheating in electronic devices. This could become highly valuable as more computing power is packed into smaller areas, including hardware designed for artificial intelligence, high-power electronics and flexible devices. The method is still a specialized laboratory technique that requires sophisticated X-ray facilities, so it is not yet a practical replacement for routine thermal testing in semiconductor manufacturing. The present demonstration also focused on a GaN-on-silicon structure rather than a complete commercial chip. However, the researchers believe the technique can be adapted to other materials and device architectures. A semiconductor industry consortium has already expressed interest in using it to study different types of chips. Ultimately, the work could shift thermal engineering away from treating materials as uniform blocks and toward understanding the tiny defects and interfaces that actually control where heat gets trapped. For increasingly compact electronics, finding those microscopic bottlenecks could be essential for preventing local hotspots from becoming a limit on performance. The study is published in the journal Nature Communications. Recommended ArticlesRupendra Brahambhatt is an experienced writer, researcher, journalist, and filmmaker. With a B.Sc (Hons.) in Science and PGJMC in Mass Communications, he has been actively working with some of the most innovative brands, news agencies, digital magazines, documentary filmmakers, and nonprofits from different parts of the globe. As an author, he works with a vision to bring forward the right information and encourage a constructive mindset among the masses.