From The University of California-Berkeley: “Engineered crystals could help computers run on less power”

From The University of California-Berkeley

April 7, 2022
Kara Manke
kjmanke@berkeley.edu

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Researchers at the University of California, Berkeley, have created engineered crystal structures that display an unusual physical phenomenon known as negative capacitance. Incorporating this material into advanced silicon transistors could make computers more energy efficient. UC Berkeley image credit Ella Maru Studio.

Computers may be growing smaller and more powerful, but they require a great deal of energy to operate. The total amount of energy the U.S. dedicates to computing has risen dramatically over the last decade and is quickly approaching that of other major sectors, like transportation.

In a study published online this week in the journal Nature, University of California, Berkeley, engineers describe a major breakthrough in the design of a component of transistors — the tiny electrical switches that form the building blocks of computers — that could significantly reduce their energy consumption without sacrificing speed, size or performance. The component, called the gate oxide, plays a key role in switching the transistor on and off.

“We have been able to show that our gate-oxide technology is better than commercially available transistors: What the trillion-dollar semiconductor industry can do today — we can essentially beat them,” said study senior author Sayeef Salahuddin, the TSMC Distinguished professor of Electrical Engineering and Computer Sciences at UC Berkeley.

This boost in efficiency is made possible by an effect called negative capacitance, which helps reduce the amount of voltage that is needed to store charge in a material. Salahuddin theoretically predicted the existence of negative capacitance in 2008 and first demonstrated the effect in a ferroelectric crystal in 2011.

The new study shows how negative capacitance can be achieved in an engineered crystal composed of a layered stack of hafnium oxide and zirconium oxide, which is readily compatible with advanced silicon transistors. By incorporating the material into model transistors, the study demonstrates how the negative capacitance effect can significantly lower the amount of voltage required to control transistors, and as a result, the amount of energy consumed by a computer.

“In the last 10 years, the energy used for computing has increased exponentially, already accounting for single digit percentages of the world’s energy production, which grows only linearly, without an end in sight,” Salahuddin said. “Usually, when we are using our computers and our cell phones, we don’t think about how much energy we are using. But it is a huge amount, and it is only going to go up. Our goal is to reduce the energy needs of this basic building block of computing, because that brings down the energy needs for the entire system.”
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Bringing negative capacitance to real technology

State-of-the-art laptops and smart phones contain tens of billions of tiny silicon transistors, and each of which must be controlled by applying a voltage. The gate oxide is a thin layer of material that converts the applied voltage into an electric charge, which then switches the transistor.

Negative capacitance can boost the performance of the gate oxide by reducing the amount of voltage required to achieve a given electrical charge. But the effect can’t be achieved in just any material. Creating negative capacitance requires careful manipulation of a material property called ferroelectricity, which occurs when a material exhibits a spontaneous electrical field. Previously, the effect has only been achieved in ferroelectric materials called perovskites, whose crystal structure is not compatible with silicon.

In the study, the team showed that negative capacitance can also be achieved by combining hafnium oxide and zirconium oxide in an engineered crystal structure called a superlattice, which leads to simultaneous ferroelectricity and antiferroelectricity.

“We found that this combination actually gives us an even better negative capacitance effect, which shows that this negative capacitance phenomena is a lot broader than originally thought,” said study co-first author Suraj Cheema, a postdoctoral researcher at UC Berkeley. “Negative capacitance doesn’t just occur in the conventional picture of a ferroelectric with a dielectric, which is what’s been studied over the past decade. You can actually make the effect even stronger by engineering these crystal structures to exploit antiferroelectricity in tandem with ferroelectricity.”

The researchers found that a superlattice structure composed of three atomic layers of zirconium oxide sandwiched between two single atomic layers of hafnium oxide, totaling less than two nanometers in thickness, provided the best negative capacitance effect. Because most state-of-the-art silicon transistors already use a 2-nanometer gate oxide composed of hafnium oxide on top of silicon dioxide, and since zirconium oxide is also used in silicon technologies, these superlattice structures can easily be integrated into advanced transistors.

To test how well the superlattice structure would perform as a gate oxide, the team fabricated short channel transistors and tested their capabilities. These transistors would require approximately 30% less voltage while maintaining semiconductor industry benchmarks and with no loss of reliability, compared to existing transistors.

“One of the issues that we often see in this type of research is that we can we can demonstrate various phenomena in materials, but those materials are not compatible with advanced computing materials, and so we cannot bring the benefit to real technology,” Salahuddin said. “This work transforms negative capacitance from an academic topic to something that could actually be used in an advanced transistor.”

Nirmaan Shanker of UC Berkeley is also a co-first author of this study. Additional co-authors include Li-Chen Wang, Cheng-Hsiang Hsu, Shang-Lin Hsu, Yu-Hung Liao, Wenshen Li, Jong-Ho Bae, Steve K. Volkman, Daewoong Kwon, Yoonsoo Rho, Costas P. Grigoropoulos, Ramamoorthy Ramesh and Chenming Hu of UC Berkeley; Matthew San Jose, Jorge Gomez, Wriddhi Chakraborty, Patrick Fay and Suman Datta of The University of Notre Dame; Gianni Pinelli, Ravi Rastogi, Dominick Pipitone, Corey Stull, Matthew Cook, Brian Tyrrell and Mohamed Mohamed of The Massachusetts Institute of Technology’s Lincoln Laboratory; Vladimir A. Stoica of The Pennsylvania State University; Zhan Zhang and John W. Freeland of The DOE’s Argonne National Laboratory; Christopher J. Tassone and Apurva Mehta of The DOE’s SLAC National Accelerator Laboratory ; Ghazal Saheli and David Thompson of Applied Materials; Dong Ik Suh and Won-Tae Koo of SK Hynix; Kab-Jin Nam, Dong Jin Jung, Woo-Bin Song, Seunggeol Nam and Jinseong Heo of Samsung Electronics; Chung-Hsun Lin of Intel Corporation; Narendra Pariha and Souvik Mahapatra of the Indian Institute of Technology; and Padraic Shafer and Jim Ciston of The DOE’s Lawrence Berkeley National Laboratory.

This research was supported in part by the Berkeley Center for Negative Capacitance Transistors (BCNCT), the DARPA Technologies for Mixed-mode Ultra Scaled Integrated Circuits (T-MUSIC) program, the University of California Multicampus Research Programs and Initiatives (UC MRPI) project and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract No. DE-AC02-05-CH11231 (Microelectronics Co-Design program).

See the full article here .

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The The University of California-Berkeley is a public land-grant research university in Berkeley, California. Established in 1868 as the state’s first land-grant university, it was the first campus of the University of California system and a founding member of the Association of American Universities . Its 14 colleges and schools offer over 350 degree programs and enroll some 31,000 undergraduate and 12,000 graduate students. Berkeley is ranked among the world’s top universities by major educational publications.

Berkeley hosts many leading research institutes, including the Mathematical Sciences Research Institute and the Space Sciences Laboratory. It founded and maintains close relationships with three national laboratories at DOE’s Lawrence Berkeley National Laboratory, DOE’s Lawrence Livermore National Laboratory and DOE’s Los Alamos National Lab, and has played a prominent role in many scientific advances, from the Manhattan Project and the discovery of 16 chemical elements to breakthroughs in computer science and genomics. Berkeley is also known for student activism and the Free Speech Movement of the 1960s.

Berkeley alumni and faculty count among their ranks 110 Nobel laureates (34 alumni), 25 Turing Award winners (11 alumni), 14 Fields Medalists, 28 Wolf Prize winners, 103 MacArthur “Genius Grant” recipients, 30 Pulitzer Prize winners, and 19 Academy Award winners. The university has produced seven heads of state or government; five chief justices, including Chief Justice of the United States Earl Warren; 21 cabinet-level officials; 11 governors; and 25 living billionaires. It is also a leading producer of Fulbright Scholars, MacArthur Fellows, and Marshall Scholars. Berkeley alumni, widely recognized for their entrepreneurship, have founded many notable companies.

Berkeley’s athletic teams compete in Division I of the NCAA, primarily in the Pac-12 Conference, and are collectively known as the California Golden Bears. The university’s teams have won 107 national championships, and its students and alumni have won 207 Olympic medals.

Made possible by President Lincoln’s signing of the Morrill Act in 1862, the University of California was founded in 1868 as the state’s first land-grant university by inheriting certain assets and objectives of the private College of California and the public Agricultural, Mining, and Mechanical Arts College. Although this process is often incorrectly mistaken for a merger, the Organic Act created a “completely new institution” and did not actually merge the two precursor entities into the new university. The Organic Act states that the “University shall have for its design, to provide instruction and thorough and complete education in all departments of science, literature and art, industrial and professional pursuits, and general education, and also special courses of instruction in preparation for the professions”.

Ten faculty members and 40 students made up the fledgling university when it opened in Oakland in 1869. Frederick H. Billings, a trustee of the College of California, suggested that a new campus site north of Oakland be named in honor of Anglo-Irish philosopher George Berkeley. The university began admitting women the following year. In 1870, Henry Durant, founder of the College of California, became its first president. With the completion of North and South Halls in 1873, the university relocated to its Berkeley location with 167 male and 22 female students.

Beginning in 1891, Phoebe Apperson Hearst made several large gifts to Berkeley, funding a number of programs and new buildings and sponsoring, in 1898, an international competition in Antwerp, Belgium, where French architect Émile Bénard submitted the winning design for a campus master plan.

20th century

In 1905, the University Farm was established near Sacramento, ultimately becoming the University of California-Davis. In 1919, Los Angeles State Normal School became the southern branch of the University, which ultimately became the University of California-Los Angeles. By 1920s, the number of campus buildings had grown substantially and included twenty structures designed by architect John Galen Howard.

In 1917, one of the nation’s first ROTC programs was established at Berkeley and its School of Military Aeronautics began training pilots, including Gen. Jimmy Doolittle. Berkeley ROTC alumni include former Secretary of Defense Robert McNamara and Army Chief of Staff Frederick C. Weyand as well as 16 other generals. In 1926, future fleet admiral Chester W. Nimitz established the first Naval ROTC unit at Berkeley.

In the 1930s, Ernest Lawrence helped establish the Radiation Laboratory (now DOE’s Lawrence Berkeley National Laboratory (US)) and invented the cyclotron, which won him the Nobel physics prize in 1939. Using the cyclotron, Berkeley professors and Berkeley Lab researchers went on to discover 16 chemical elements—more than any other university in the world. In particular, during World War II and following Glenn Seaborg’s then-secret discovery of plutonium, Ernest Orlando Lawrence’s Radiation Laboratory began to contract with the U.S. Army to develop the atomic bomb. Physics professor J. Robert Oppenheimer was named scientific head of the Manhattan Project in 1942. Along with the Lawrence Berkeley National Laboratory, Berkeley founded and was then a partner in managing two other labs, Los Alamos National Laboratory (1943) and Lawrence Livermore National Laboratory (1952).

By 1942, the American Council on Education ranked Berkeley second only to Harvard University in the number of distinguished departments.

In 1952, the University of California reorganized itself into a system of semi-autonomous campuses, with each campus given its own chancellor, and Clark Kerr became Berkeley’s first Chancellor, while Sproul remained in place as the President of the University of California.

Berkeley gained a worldwide reputation for political activism in the 1960s. In 1964, the Free Speech Movement organized student resistance to the university’s restrictions on political activities on campus—most conspicuously, student activities related to the Civil Rights Movement. The arrest in Sproul Plaza of Jack Weinberg, a recent Berkeley alumnus and chair of Campus CORE, in October 1964, prompted a series of student-led acts of formal remonstrance and civil disobedience that ultimately gave rise to the Free Speech Movement, which movement would prevail and serve as precedent for student opposition to America’s involvement in the Vietnam War.

In 1982, the Mathematical Sciences Research Institute (MSRI) was established on campus with support from the National Science Foundation and at the request of three Berkeley mathematicians — Shiing-Shen Chern, Calvin Moore and Isadore M. Singer. The institute is now widely regarded as a leading center for collaborative mathematical research, drawing thousands of visiting researchers from around the world each year.

21st century

In the current century, Berkeley has become less politically active and more focused on entrepreneurship and fundraising, especially for STEM disciplines.

Modern Berkeley students are less politically radical, with a greater percentage of moderates and conservatives than in the 1960s and 70s. Democrats outnumber Republicans on the faculty by a ratio of 9:1. On the whole, Democrats outnumber Republicans on American university campuses by a ratio of 10:1.

In 2007, the Energy Biosciences Institute was established with funding from BP and Stanley Hall, a research facility and headquarters for the California Institute for Quantitative Biosciences, opened. The next few years saw the dedication of the Center for Biomedical and Health Sciences, funded by a lead gift from billionaire Li Ka-shing; the opening of Sutardja Dai Hall, home of the Center for Information Technology Research in the Interest of Society; and the unveiling of Blum Hall, housing the Blum Center for Developing Economies. Supported by a grant from alumnus James Simons, the Simons Institute for the Theory of Computing was established in 2012. In 2014, Berkeley and its sister campus, University of California-San Fransisco, established the Innovative Genomics Institute, and, in 2020, an anonymous donor pledged $252 million to help fund a new center for computing and data science.

Since 2000, Berkeley alumni and faculty have received 40 Nobel Prizes, behind only Harvard and Massachusetts Institute of Technology among US universities; five Turing Awards, behind only MIT and Stanford University; and five Fields Medals, second only to Princeton University (US). According to PitchBook, Berkeley ranks second, Stanford University, in producing VC-backed entrepreneurs.

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