As they strive to optimize the performance of increasingly powerful and higher temperature systems squeezed into ever smaller form factors, heat management looms as one of the biggest challenges facing designers today.
Temperature management is critical, since as transistor size shrinks more heat is generated within the same-size footprint. High heat also slows processor speeds, particularly at chip “hotspots” where heat concentrates and temperatures soar. It also requires a great deal of energy to keep processors cool and efficient. If CPUs didn’t get as hot, they could work faster, while requiring less energy to stay cool.
Addressing the growing need for better thermal management, researchers in laboratories worldwide are studying promising new materials and approaches that will help pave the way for smaller, more powerful computing and communication technologies.
A heat-absorbing semiconductor
As consumers demand smaller, faster and more powerful electronic devices that draw more current and generate more heat, the issue of heat management is reaching a bottleneck. With current technology, there's a limit to the amount of heat that can be dissipated from the inside out.
In July 2018, UCLA engineers announced that they had developed a semiconductor material — defect-free boron arsenide — that’s more effective at drawing and dissipating waste heat than any other known semiconductor or metal material. According to the researchers, defect-free boron arsenide offers record-high thermal conductivity and is more than three-times faster at conducting heat than currently used materials, such as silicon carbide and copper. This means that heat that would otherwise concentrate in hotspots is quickly swept away.
A potential downside is the fact that defect-free boron arsenide is not a naturally occurring material. This means that the substance must be synthesized in a lab, a potentially costly process. Defect-free boron arsenide also needs to have a very specific structure and low defect density for it to have peak thermal conductivity.
In a statement released by the university, Yongjie Hu, a UCLA assistant professor of mechanical and aerospace engineering, observed, “This material could help greatly improve performance and reduce energy demand in all kinds of electronics, from small devices to the most advanced computer data center equipment.” He also noted that the material has “excellent potential” to be integrated into current manufacturing processes due to its semiconductor properties and scale-up potential. “It could replace current state-of-the-art semiconductor materials for computers and revolutionize the electronics industry,” Hu predicted.
Back in 2013, researchers at Boston College and the U.S. Naval Research Laboratory reported that boron arsenide could potentially perform as well as diamonds when used as a heat spreader. Diamonds have the highest known thermal conductivity, around 2,200 watts per meter-kelvin, compared to about 150 watts per meter-kelvin for silicon.
Following up on that discovery, in July 2018, researchers at the University of Texas at Dallas, the University of Illinois at Urbana-Champaign, and the University of Houston announced they had created a potential heat conduction alternative that, while not as effective as diamonds, marks a significant improvement over silicon. “We have been working on this research for the last three years, and now have gotten the thermal conductivity up to about 1,000 watts per meter-kelvin, which is second only to diamond in bulk materials,” said Bing Lv, an assistant professor of physics in the School of Natural Sciences and Mathematics at the University of Texas at Dallas, in a statement released by the school.
Polymer thermal conduction
In March 2018, MIT engineers announced the creation of a new plastic material — a polymer thermal conductor — that functions as a heat conductor, dissipating heat rather than insulating it. The researchers claimed that the new material, which is lightweight and flexible, can conduct 10 times as much heat as most commercially used conventional polymers.
Traditional polymers are both electrically and thermally insulating. “The discovery and development of electrically conductive polymers has led to novel electronic applications such as flexible displays and wearable biosensors,” said Yanfei Xu, a researcher in MIT’s mechanical engineering department, in a statement released by MIT. Xu noted that the new polymer has the ability to thermally conduct and remove heat much more efficiently than existing techniques. “We believe polymers could be made into next-generation heat conductors for advanced thermal management applications, such as a self-cooling alternative to existing electronics casings.”
On average, test samples of the new polymer were able to conduct heat at about 2 W/m/K, approximately 10 times faster than what conventional polymers can achieve. In tests conducted at the Argonne National Laboratory, Xu and co-researcher Zhang Jiang, an Argonne physicist, discovered that the polymer samples appeared nearly isotropic, or uniform. Following this reasoning, the team predicted that the material should be able to conduct heat equally well in all directions, increasing its heat-dissipating potential.
Merging antennas and electronics
By integrating the design of antenna and electronics, Georgia Institute of Technology researchers claim to have found a way to increase the power and spectrum efficiency of a new class of millimeter wave transmitters, allowing improved modulation and reduced waste heat. The result promises to lead to longer talk time and higher data rates in millimeter wave wireless communication devices designed for upcoming 5G cellular applications.
The approach, announced in July 2018, opens the way for simultaneous optimization of the millimeter wave antennas and electronics. The hybrid devices rely on conventional materials and integrated circuit (IC) technology, so they should be relatively easy to manufacture and package. The new designs are implemented in 45-nm CMOS SOI IC devices and flip-chip packaged on high-frequency laminate boards, where testing has confirmed a minimum two-fold increase in energy efficiency, the researchers noted.
Fundamental to the new design is the ability to maintain a high-energy efficiency regardless whether the device is operating at its peak or average output power. The researchers stated that the efficiency of most conventional transmitters is high only at the peak power but drops substantially at low power levels, resulting in low efficiency when amplifying complex spectrally efficient modulations. Moreover, conventional transmitters often add the outputs from multiple electronics using lossy power combiner circuits, exacerbating the efficiency degradation.
“In this proof-of-example, our electronics and antenna were designed so that they can work together to achieve a unique on-antenna outphasing active load modulation capability that significantly enhances the efficiency of the entire transmitter,” said Hua Wang, an assistant professor in Georgia Tech’s School of Electrical and Computer Engineering, in a statement released by the school. “This system could replace many types of transmitters in wireless mobile devices, base stations and infrastructure links in data centers.”
