In today's rapidly advancing world of electronic devices, while chip performance continues to improve, the issue of heat dissipation has become an ever-present shadow, posing a critical bottleneck that hinders further breakthroughs. The common phenomenon of smartphones becoming hot after prolonged calls or computers' fans spinning wildly when running large software applications reflects the problem of accumulated heat within chip structures. Recently, a breakthrough study by the Peking University team led by Professor Peng Gao has brought new hope to solving this century-old challenge. For the first time, they achieved clear observation of the heat transfer process at the atomic scale, providing unprecedented insights into the microscopic mechanisms of chip cooling.
The Challenge of Atomic Heat Motion and Interfacial Thermal Resistance
To understand the challenges of chip heat dissipation, it is essential to comprehend how heat is transferred in solid materials. In solids, atoms do not remain stationary but vibrate around their equilibrium positions. These collective vibrations are abstracted as "phonons," quasi-particles in physics. Essentially, the transfer of heat in materials is the process where phonons carry energy through lattice jumps and propagation. It can be likened to a relay race in the micro-world, where phonons sequentially pass on energy, enabling heat transfer.
When heat transfer encounters different material interfaces, the situation becomes complex. Taking the interface between aluminum nitride (AlN) and silicon carbide (SiC), commonly found in chips, as an example, phonons face numerous obstacles when crossing this boundary, forming what is known as "interfacial thermal resistance." This thermal resistance is akin to toll booths suddenly appearing on a highway, slowing down vehicle (phonon) passage and causing heat transfer congestion. Within a fingernail-sized chip, countless such material interfaces are densely stacked, each acting like a tiny "blockage." The accumulation of these blockages ultimately leads to massive heat accumulation in the chip, severely affecting its performance and potentially causing device failure.
For a long time, despite scientists understanding interfacial thermal resistance as a key factor in chip heat dissipation, technical limitations have prevented them from clearly observing and comprehending the precise operation mechanism of this "toll booth" at the atomic scale. How heat is transmitted and why it is obstructed in this extremely small interface area remains shrouded in mystery, hindering the development of more effective heat dissipation technologies.
Innovative Technology: Microscopic Thermal World under Electron Microscopy
The key to the breakthrough achieved by Professor Gao's team lies in their innovative development of a cutting-edge technology based on electron microscopy. This technique cleverly utilizes the "inelastic scattering" phenomenon when electrons interact with materials. When high-speed electrons penetrate the material, they exchange energy with vibrating atoms (phonons). This exchange process leaves unique "footprints" in the microscopic world, carrying rich temperature information.
To precisely capture this information, the team meticulously customized a complex experimental setup. Among these, a specially designed miniature "heating stage" was particularly crucial. This "stage" could stably and controllably allow heat to flow across the AlN/SiC interface, simulating the actual heat transfer scenario within a chip. Simultaneously, the team used high-resolution electron microscopy to accurately measure the inelastic scattering caused by the interaction between electrons and phonons. Through a series of complex calculations and analyses, they achieved an astonishing sub-nanometer-level temperature resolution, which is less than one ten-thousandth of the diameter of a hair strand, providing an unprecedented "high-definition perspective" for observing microscopic thermal phenomena.
Observation Breakthrough: Revealing the Mysteries of Heat Transfer at the Atomic Scale
Leveraging this powerful technological tool, the research team successfully captured microscopic images of heat transfer at the material interface, yielding results that were shocking. Under an extreme temperature gradient of 180 Kelvin per micrometer (equivalent to a massive temperature difference of 180,000 degrees over a length of one meter), researchers clearly observed that when heat crossed the AlN/SiC interface, the temperature underwent a dramatic change of 10 to 20 Kelvin over just about 2 nanometers. In stark contrast, within the AlN or SiC materials themselves, achieving the same degree of temperature drop would require tens or even hundreds of nanometers. This observation clearly indicates that the thermal resistance at the interface is 30 to 70 times higher than within the material, vividly illustrating the immense obstacle heat encounters here, akin to being squeezed from a wide river into a narrow canyon.
Even more groundbreaking was the team's ability to capture phonons in a special "nonequilibrium" state within a narrow region of approximately 3 nanometers near the interface. Under normal conditions, phonons follow specific statistical rules, known as the "Bose-Einstein distribution." However, in this interface region, phonons seem to deviate from this conventional order, becoming somewhat "chaotic." To delve deeper into the underlying heat transfer mechanisms behind this phenomenon, the team ingeniously altered the heating direction, allowing heat to flow across the interface from the opposite direction. By comparing the differences in phonon mode distributions under the two scenarios, they successfully revealed the dynamic and complex inelastic microscopic processes during heat transfer. This is akin to not only clearly observing traffic congestion at the highway toll booth but also thoroughly understanding how vehicles (phonons) collide and exchange information within the station, greatly deepening our understanding of heat transfer at the atomic scale.
Scientific Value and Application Prospects: Reshaping the Future of Chip Heat Dissipation
The research findings of Professor Gao's team hold significance far beyond the realm of basic scientific research, offering revolutionary impetus to practical applications, especially in the development of chip heat dissipation technology. In the past, engineers designing chip cooling solutions often relied heavily on experience and trial-and-error methods due to a lack of precise understanding of microscopic heat transfer mechanisms, effectively groping in the dark with low efficiency and limited effectiveness. Now, armed with this atomic-level "thermal imaging" technology, they are like having a precise map, enabling them to clearly identify where and why heat is obstructed within the chip, thereby designing more efficient cooling structures and interface materials with precision.
This achievement holds significant importance for manufacturing high-performance, low-heat electronic devices. In power chips for electric vehicles, efficient heat dissipation ensures stable performance under high-load operations, enhancing both vehicle range and safety. In core components of 5G/6G communication base stations, good heat dissipation guarantees high-speed and stable signal processing, preventing data transmission interruptions caused by overheating. Stuart Thomas, a senior editor at Nature, highly praised the study: "Measuring temperature at the nanoscale is already an extremely challenging task, and this research goes further, revealing the flow of heat across interfaces and the key role of phonons." Moreover, the AlN/SiC materials involved in this study are popular candidates for high-power electronic devices, and their thermal management issues have long been focal points in the industry.
Original source: https://www.toutiao.com/article/7518289295657419275/
Disclaimer: This article solely represents the author's personal views. Please express your stance by clicking the "Like" or "Dislike" buttons below.