Engineered crystals could help computers run on less power

Date:
April 8, 2022
Source:
University of California - Berkeley
Summary:
In a new study, 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.



FULL STORY ========================================================================== 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 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." 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 Pennsylvania State University; Zhan Zhang and John W. Freeland
of Argonne National Laboratory; Christopher J. Tassone and Apurva Mehta of
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 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).


========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Kara Manke. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Engineered_crystal_structures ========================================================================== Journal Reference:
1. Suraj S. Cheema, Nirmaan Shanker, Li-Chen Wang, Cheng-Hsiang Hsu,
Shang-
Lin Hsu, Yu-Hung Liao, Matthew San Jose, Jorge Gomez, Wriddhi
Chakraborty, Wenshen Li, Jong-Ho Bae, Steve K. Volkman, Daewoong
Kwon, Yoonsoo Rho, Gianni Pinelli, Ravi Rastogi, Dominick Pipitone,
Corey Stull, Matthew Cook, Brian Tyrrell, Vladimir A. Stoica, Zhan
Zhang, John W. Freeland, Christopher J. Tassone, Apurva Mehta,
Ghazal Saheli, David Thompson, Dong Ik Suh, Won-Tae Koo, Kab-Jin
Nam, Dong Jin Jung, Woo-Bin Song, Chung-Hsun Lin, Seunggeol Nam,
Jinseong Heo, Narendra Parihar, Costas P. Grigoropoulos, Padraic
Shafer, Patrick Fay, Ramamoorthy Ramesh, Souvik Mahapatra,
Jim Ciston, Suman Datta, Mohamed Mohamed, Chenming Hu, Sayeef
Salahuddin. Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for
advanced transistors. Nature, 2022; 604 (7904): 65 DOI: 10.1038/
s41586-022-04425-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220408083839.htm

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