Lawrence Berkeley Laboratory
09/12/2024 | Press release | Distributed by Public on 09/12/2024 09:29
New Computer Simulations Help Scientists Advance Energy-Efficient Microelectronics
Uncovering the atomistic origins of negative capacitance
In 2008, co-author Sayeef Salahuddin, a professor of electrical engineering and computer sciences at UC Berkeley and senior faculty scientist in Berkeley Lab's Materials Sciences Division, first proposed the concept of negative capacitance to demonstrate a new approach to designing energy-efficient computers. Negative capacitance typically appears in materials with ferroelectric properties. Ferroelectric materials have promise as energy-efficient computer memories because their built-in electrical polarization can be used to store data, for example, that can be written and erased using a low-power electric field.
In the years following Salahuddin's pioneering proposal, researchers have learned that the negative capacitance effect in thin films of ferroelectric hafnium oxide and zirconium oxide (HfO2-ZrO2) occurs when the films are composed of a mixture of phases. That means that small regions or "grains" of the film have slightly different arrangements of atoms or "phases." The size of these phase grains are tiny - just a few nanometers across - but the different phases have distinct electronic properties that can interact with each other and give rise to macroscopic phenomena such as negative capacitance.
The Salahuddin group has already made use of this phenomenon to produce record-breaking microcapacitors, but in order to unlock the full potential of negative capacitance, the researchers needed a deeper understanding of its atomistic origins.
To do this, a multidisciplinary team co-led by Yao and Kumar developed FerroX. The open-source framework allowed them to develop 3D phase-field simulations of a ferroelectric thin film, in which they could vary the phase composition at will and study the impacts on the film's electronic properties.
"Our goal was to understand the origin of negative capacitance in these films, which is not well understood," Kumar said. "Our simulations are the first to help researchers tailor a material's properties for further improvements in negative capacitance observed in the lab."
As a result, the Berkeley Lab researchers found that the negative capacitance effect can be enhanced by optimizing the domain structure - reducing the size of the ferroelectric grains and arranging them to have a particular direction of ferroelectric polarization.
"This approach to enhancing negative capacitance was unknown before our study because previous models lacked the scalability to easily explore the design space and lacked physics customization," Yao said.
Yao attributes this new modeling capability to working firsthand with materials scientists like Salahuddin, who helped the FerroX development team understand how to shape their models around the physics of ferroelectrics, and to the unique multidisciplinary strengths of Berkeley Lab, where researchers across the scientific disciplines are in close proximity to the Perlmutter supercomputer at the Department of Energy's National Energy Research Scientific Computing Center (NERSC). Perlmutter supports complex simulation, data analytics, and artificial intelligence experiments requiring multiple graphics processing units (GPUs) at a time. Yao, Kumar, and team relied significantly on Perlmutter to develop FerroX, which is now available to other researchers as an open-source framework that is portable from laptops to supercomputers.
"It's exciting that FerroX will be able to help such a vast community of researchers in academia, industry, and the national labs," Yao said.
While FerroX models in the current study simulate the origin of negative capacitance as it evolves at the transistor gate, the Berkeley Lab team plans to use the open-source framework to simulate the entire transistor in future studies.
"Over the years, we have made significant progress in both the physics of negative capacitance and integrating that physics into real microelectronics devices," said Salahuddin. "With FerroX, we can now model these devices starting from atoms, and that will allow us to design microelectronics devices with optimal negative capacitance performance. That would not have been possible without the strength of this co-design group of researchers spanning computing sciences and materials sciences."
NERSC is a DOE Office of Science user facility at Berkeley Lab.
Other authors on the study include Andy Nonaka (Berkeley Lab) and Michael Hoffman (UC Berkeley).
Berkeley Lab's Alison Hatt contributed to this article.
From Atoms to Architectures: How Berkeley Lab's Microelectronics Co-design Researchers Are Building Energy-Efficient Microchips From the Inside Out
Berkeley Lab is bringing a co-design approach to the quest for higher-performing and more energy-efficient microelectronics.
Co-design means that experts focusing on different parts of the problem inform and guide each other in a synergistic way to drive innovation faster than the traditional linear approach.
These Berkeley Lab scientists are working closely together to develop materials that exploit atomic-scale phenomena, build new tools for semiconductor device fabrication, and design new computer simulations to test systems and materials virtually.
Described as spanning "atoms to architectures," Berkeley Lab's microelectronics co-design approach draws on the Lab's unique facilities and capabilities to deliver transformative science solutions.
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Lawrence Berkeley National Laboratory (Berkeley Lab) is committed to delivering solutions for humankind through research in clean energy, a healthy planet, and discovery science. Founded in 1931 on the belief that the biggest problems are best addressed by teams, Berkeley Lab and its scientists have been recognized with 16 Nobel Prizes. Researchers from around the world rely on the lab's world-class scientific facilities for their own pioneering research. Berkeley Lab is a multiprogram national laboratory managed by the University of California for the U.S. Department of Energy's Office of Science.
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