News

August 2017

The next generation of feature-filled and energy-efficient electronics will require computer chips just a few atoms thick. For all its positive attributes, trusty silicon can't take us to these ultrathin extremes.

Now, electrical engineers at Stanford have identified two semiconductors – hafnium diselenide and zirconium diselenide – that share or even exceed some of silicon's desirable traits, starting with the fact that all three materials can "rust."

"It's a bit like rust, but a very desirable rust," said Eric Pop, an associate professor of electrical engineering, who co-authored with post-doctoral scholar Michal Mleczko a paper that appears in the journal Science Advances.

The new materials can also be shrunk to functional circuits just three atoms thick and they require less energy than silicon circuits. Although still experimental, the researchers said the materials could be a step toward the kinds of thinner, more energy-efficient chips demanded by devices of the future.

Silicon's strengths
Silicon has several qualities that have led it to become the bedrock of electronics, Pop explained. One is that it is blessed with a very good "native" insulator, silicon dioxide or, in plain English, silicon rust.

Exposing silicon to oxygen during manufacturing gives chip-makers an easy way to isolate their circuitry. Other semiconductors do not "rust" into good insulators when exposed to oxygen, so they must be layered with additional insulators, a step that introduces engineering challenges. Both of the diselenides the Stanford group tested formed this elusive, yet high-quality insulating rust layer when exposed to oxygen.

Not only do both ultrathin semiconductors rust, they do so in a way that is even more desirable than silicon. They form what are called "high-K" insulators, which enable lower power operation than is possible with silicon and its silicon oxide insulator.

As the Stanford researchers started shrinking the diselenides to atomic thinness, they realized that these ultrathin semiconductors share another of silicon's secret advantages: the energy needed to switch transistors on – a critical step in computing, called the band gap – is in a just-right range. Too low and the circuits leak and become unreliable. Too high and the chip takes too much energy to operate and becomes inefficient. Both materials were in the same optimal range as silicon.

All this and the diselenides can also be fashioned into circuits just three atoms thick, or about two-thirds of a nanometer, something silicon cannot do.

The combination of thinner circuits and desirable high-K insulation means that these ultrathin semiconductors could be made into transistors 10 times smaller than anything possible with silicon today.

"Silicon won't go away. But for consumers this could mean much longer battery life and much more complex functionality if these semiconductors can be integrated with silicon," Pop said.

More work to do
There is much work ahead. First, Mleczko and Pop must refine the electrical contacts between transistors on their ultrathin diselenide circuits. "These connections have always proved a challenge for any new semiconductor, and the difficulty becomes greater as we shrink circuits to the atomic scale," Mleczko said.

They are also working to better control the oxidized insulators to ensure they remain as thin and stable as possible. Last, but not least, only when these things are in order will they begin to integrate with other materials and then to scale up to working wafers, complex circuits and, eventually, complete systems.

"There's more research to do, but a new path to thinner, smaller circuits – and more energy-efficient electronics – is within reach," Pop said.


 

 

Reprinted from Stanford Magazine, "New semiconductor materials exceed some of silicon's 'secret' powers," August 14,2017

October 2017

It looks like a regular roof, but the top of the Packard Electrical Engineering Building at Stanford University has been the setting of many milestones in the development of an innovative cooling technology that could someday be part of our everyday lives.

Since 2013, Shanhui Fan, professor of electrical engineering, and his students and research associates have employed this roof as a testbed for a high-tech mirror-like optical surface that could be the future of lower-energy air conditioning and refrigeration.

Research published in 2014 first showed the cooling capabilities of the optical surface on its own. Now, Fan and former research associates Aaswath Raman and Eli Goldstein, have shown that a system involving these surfaces can cool flowing water to a temperature below that of the surrounding air. The entire cooling process is done without electricity.

"This research builds on our previous work with radiative sky cooling but takes it to the next level. It provides for the first time a high-fidelity technology demonstration of how you can use radiative sky cooling to passively cool a fluid and, in doing so, connect it with cooling systems to save electricity," said Raman, who is co-lead author of the paper detailing this research, published in Nature Energy Sept. 4, 2017.

Together, Fan, Goldstein and Raman have founded the company SkyCool Systems, which is working on further testing and commercializing this technology.

Radiative sky cooling is a natural process that everyone and everything does, resulting from the moments of molecules releasing heat. You can witness it for yourself in the heat that comes off a road as it cools after sunset. This phenomenon is particularly noticeable on a cloudless night because, without clouds, the heat we and everything around us radiates can more easily make it through Earth's atmosphere, all the way to the vast, cold reaches of space.

"If you have something that is very cold – like space – and you can dissipate heat into it, then you can do cooling without any electricity or work. The heat just flows," explained Fan, who is senior author of the paper. "For this reason, the amount of heat flow off the Earth that goes to the universe is enormous."

Although our own bodies release heat through radiative cooling to both the sky and our surroundings, we all know that on a hot, sunny day, radiative sky cooling isn't going to live up to its name. This is because the sunlight will warm you more than radiative sky cooling will cool you. To overcome this problem, the team's surface uses a multilayer optical film that reflects about 97 percent of the sunlight while simultaneously being able to emit the surface's thermal energy through the atmosphere. Without heat from sunlight, the radiative sky cooling effect can enable cooling below the air temperature even on a sunny day.

A fluid-cooling panel designed at Stanford being tested on the roof of the Packard Electrical Engineering Building
Photo credit: Aaswath Raman

The experiments published in 2014 were performed using small wafers of a multilayer optical surface, about 8 inches in diameter, and only showed how the surface itself cooled. Naturally, the next step was to scale up the technology and see how it works as part of a larger cooling system.

Putting radiative sky cooling to work
For their latest paper, the researchers created a system where panels covered in the specialized optical surfaces sat atop pipes of running water and tested it on the roof of the Packard Building in September 2015. These panels were slightly more than 2 feet in length on each side and the researchers ran as many as four at a time. With the water moving at a relatively fast rate, they found the panels were able to consistently reduce the temperature of the water 3 to 5 degrees Celsius below ambient air temperature over a period of three days.

The researchers also applied data from this experiment to a simulation where their panels covered the roof of a two-story commercial office building in Las Vegas – a hot, dry location where their panels would work best – and contributed to its cooling system. They calculated how much electricity they could save if, in place of a conventional air-cooled chiller, they used vapor-compression system with a condenser cooled by their panels. They found that, in the summer months, the panel-cooled system would save 14.3 megawatt-hours of electricity, a 21 percent reduction in the electricity used to cool the building. Over the entire period, the daily electricity savings fluctuated from 18 percent to 50 percent.

Broad applicability in the years to come
Right now, SkyCool Systems is measuring the energy saved when panels are integrated with traditional air conditioning and refrigeration systems at a test facility, and Fan, Goldstein and Raman are optimistic that this technology will find broad applicability in the years to come.

The researchers are focused on making their panels integrate easily with standard air conditioning and refrigeration systems and they are particularly excited at the prospect of applying their technology to the serious task of cooling data centers.

Fan has also carried out research on various other aspects of radiative cooling technology. He and Raman have applied the concept of radiative sky cooling to the creation of an efficiency-boosting coating for solar cells. With Yi Cui, a professor of materials science and engineering at Stanford and of photon science at SLAC National Accelerator Laboratory, Fan developed a cooling fabric.

"It's very intriguing to think about the universe as such an immense resource for cooling and all the many interesting, creative ideas that one could come up with to take advantage of this," he said. 


 

Reprinted from Stanford Engineering Magazine, "How a new cooling system works without using any electricity" September 8, 2017.

September 2017

Our phones and devices simply tell us where to go — and how long it will take to get there. But what are the risks? In the Future of Everything radio show, Professor Per Enge, Aeronautics and Astronautics, EE by Courtesy, discusses the accuracy of the system, how to keep the signals safe, and how systems will continue to improve.

 

In partnership with SiriusXM, Stanford University launched Stanford Radio, a new university-based pair of radio programs. The programs are produced in collaboration with the School of Engineering and the Graduate School of Education.

"The Future of Everything" is from the School of Engineering and "School's In" is from the Graduate School of Education.

September 2017


In the Future of Everything radio show, Kwabena Boahen discusses the evolution of computers and how the next big step forward will be to design chips that behave more like the human brain.

Boahen is a professor of bioengineering and electrical engineering, exploring in his lab how these chips can interface with drones or with the human brain. "It's really early days," he says.


In partnership with SiriusXM, Stanford University launched Stanford Radio, a new university-based pair of radio programs. The programs are produced in collaboration with the School of Engineering and the Graduate School of Education.

"The Future of Everything" is from the School of Engineering and "School's In" is from the Graduate School of Education.

 

Kai Zang (PhD '17)
October 2017

Kai Zang's (PhD '17) paper published in Nature Communications describes how nanotextured silicon can absorb more photons, furthering the effectiveness of solar cells. This research also resulted in a second discovery – improving the collision-avoidance technology in vehicles.

Professor Jim Harris said he always thought Zang's texturing technique was a good way to improve solar cells. "But the huge ramp up in autonomous vehicles and LIDAR suddenly made this 100 times more important," he says.

The researchers figured out how to create a very thin layer of silicon that could absorb as many photons as a much thicker layer of the costly material. Specifically, rather than laying the silicon flat, they nanotextured the surface of the silicon in a way that created more opportunities for light particles to be absorbed. Their technique increased photon absorption rates for the nanotextured solar cells compared to traditional thin silicon cells, making more cost-effective use of the material.

After the researchers shared these efficiency figures, engineers working on autonomous vehicles began asking whether this texturing technique could help them get more accurate results from a collision-avoidance technology called LIDAR, which is conceptually like sonar except that it uses light rather than sound waves to detect objects in the car's travel path.

In their Nature Communications paper, the team reports that their textured silicon can capture as many as three to six times more of the returning photons than today's LIDAR receivers. They believe this will enable self-driving car engineers to design high-performance, next-generation LIDAR systems that would continuously send out a single laser pulse in all directions. The reflected photons would be captured by an array of textured silicon detectors, creating moment-to-moment maps of pedestrian-filled city crosswalks.

Harris said the texturing technology could also help to solve two other LIDAR snags unique to self-driving cars – potential distortions caused by heat and the machine equivalent of peripheral vision. The Harris Group research website. 

 

 

Excerpted from "A new way to improve solar cells can also benefit self-driving cars," Stanford Engineering, October 2, 2017.

September 2017

During Spring quarter, lab64's expertise and tools were called into action for an unusual objective – Palo Alto Code:ART Festival 2017! Mateo Garcia, an undergraduate majoring in computer science and art practice utilized lab64 to help him realize his embedded systems art installation.

'Feng Shui : Flow of Energy' was created by Mateo Garcia (B.A.S.'18). His installation was on display at 455 Bryant Street, incorporating three levels of the parking garage stairway. Strands of LED lights were programmatically controlled, responding to various inputs and commands. Mateo's installation represented the flow of light energy from the sun to the earth. The Code:ART installations were on display for one weekend, throughout downtown Palo Alto. City of Palo Alto Code Art 

Maker lab64, housed in the Packard Building is available 24/7 for Stanford students. Embedded systems projects like Mateo's are encouraged and supported by lab64.

"This project would not have been possible without the dedicated time and energy of Steven Clark, who advised me on the design and engineering of this work," states Mateo. Steven Clark is the Instructional Labs Manager. Information about EE's lab64 can be found under EE's student resources, Maker lab64

 

David Hallac, EE PhD candidate
September 2017

David Hallac, EE PhD candidate, is the lead author of "Toeplitz Inverse Covariance-Based Clustering of Multivariate Time Series Data," which has been selected to receive the KDD 2017 Conference Best Paper Runner-Up Award and the Best Student Paper runner-up Award. Co-authors include research assistant Sagar Vare (CS), professor Stephen Boyd (EE) and professor Jure Leskovec (CS).

ACM SIGKDD is the Association for Computing Machinery Special Interest Group on Knowledge Discovery and Data Mining. The award recognizes papers presented at the annual SIGKDD conference, KDD2017, that advance the fundamental understanding of the field of knowledge discovery in data and data mining.

Their paper will received both the KDD 2017 Best Paper runner-up Award, as well as the Best Student Paper runner-up Award at the KDD 2017 ceremonies held in Halifax, Canada in August. The group will receive individual award plaques as well as a check.

 

Congratulations to David, Sagar, Stephen and Jure on this special recognition!

 

 

 

View "Toeplitz Inverse Covariance-Based Clustering of Multivariate Time Series Data" Abstract.

John Hennessy and Philip Knight. Image credit: L.A. Cicero
September 2017

The Knight-Hennessy Scholars program will be lead by EE professor and Stanford's former president John Hennessy. The program is funded by philanthropist Philip Knight (MBA '62).

The program aims to prepare a new generation of leaders with the deep academic foundation and broad skill set needed to develop creative solutions for the world's most complex challenges.

Fifty scholars will join the first cohort that enrolls in fall 2018, with up to 100 scholars admitted annually in subsequent years. Scholars will comprise an interdisciplinary graduate community representing a wide range of backgrounds and nationalities.

Building on his or her core Stanford graduate degree program, each scholar will participate in opportunities for leadership training, mentorship and experiential learning across multiple disciplines. Knight-Hennessy Scholars will receive financial support for the full cost of attendance to pursue a graduate education at Stanford.

"We recognize that an application cannot fully reflect who Knight-Hennessy Scholars are and how they live," said Derrick Bolton, dean of Knight-Hennessy Scholars admission. "We believe it's essential that we learn not only about what they have done, but also who they are: their influences, ideals, hopes and dreams."

The program's faculty advisory board and global advisory board, respectively comprising faculty from all seven schools and leaders from business, government, health care, law, technology and other fields, shaped the criteria to guide the selection of scholars. The Knight-Hennessy Scholars admission committee will consider three primary criteria when evaluating applications: independence of thought, purposeful leadership and a civic mindset.

Up to 100 application finalists will be invited to attend Immersion Weekend, which will take place at Stanford in January 2018.

"Immersion Weekend will be an experience that is fun, informal and informative for applicants," Bolton said. "Our aim is that the candidates will learn more about the graduate programs, the Knight-Hennessy Scholars program and themselves. It also gives a chance for the departments and us to get to know the applicants better."

In addition to submitting the Knight-Hennessy Scholars application, applicants must also apply to the Stanford graduate program of their choice.

 

Additional information available Knight-Hennessy.stanford.edu

 

Excerpted from "Knight-Hennessy Scholars launches inaugural application," May 2017.

Professor Lambertus 'Bert' Hesselink
August 2017

The paper, "Visualization of Second Order Tensor Fields and Matrix Data," was coauthored by professor Bert Hesselink and Thierry Delmarcelle in 1992. This paper describes some of their work on mathematical topology related to data analysis and lossless compression and visualization of tensor and vector data sets. The committee selected this paper for its importance and long term impact.

The IEEE VIS Test of Time Award is an accolade given to recognize articles published at previous conferences whose contents are still vibrant and useful today and have had a major impact and influence within and beyond the visualization community.

Papers are selected for each of the three conferences (VAST, InfoVis and SciVis) by Test of Time Awards panels appointed by the conference Steering Committees.

The decisions are based on objective measures such as the numbers of citations, and more subjective ones such as the quality and longevity and influence of ideas, outreach, uptake and effect not only in the research community, but also within application domains and visualization practice.

A full rationale will be provided for each paper at the conference opening, where we hope to encourage researchers to aim to produce work that is forward looking and has transformational potential. We're trying to build on our heritage to establish an ambitious future by making it clear at the outset of the conference opening that we want participants to aspire to be writing papers today that will be relevant in decades to come.

Professor Hesselink's research encompasses nano-photonics, ultra high density optical data storage, nonlinear optics, optical super-resolution, materials science, three-dimensional image processing and graphics, and Internet technologies.

 

Congratulations to Bert on this well-deserved recognition.

 

IEEE 2017 Test of Time Awards

Photo credit, The Marconi Society
August 2017

Engineering Professor emeritus Thomas Kailath will be given the Marconi Society's Lifetime Achievement Award in recognition of his many transformative contributions to information and system science, as well as his sustained mentoring and development of new generations of scientists.

Kailath is the sixth scientist to be honored with a Marconi Society Lifetime Achievement Award. The society is dedicated to furthering scientific achievements in communications and the internet.

"The award is being conferred on Kailath for mentoring a generation of research scholars and writing a classic textbook in linear systems that changed the way the subject is taught and his special purpose architecture to implement the signal processing algorithms on VLSI (Very Large-scale System Integration) chips," the society said.

Kailath's research and teaching at Stanford have ranged over several fields of engineering and mathematics, with a different focus roughly every decade.

 

Please join us in congratulating Tom for this very special recognition. Tom will receive his award at the annual Marconi Society Awards dinner in October.

 

Excerpted from Stanford News, "Stanford electrical engineering Professor Thomas Kailath honored for lifetime achievement by Marconi Society," August 16, 2017.

The Marconi Society press release, "Legendary Stanford Professor Thomas Kailath Will Receive The Marconi Society Lifetime Achievement Award," August 14, 2017. 

 

 

Related News

Professor Emeritus Thomas Kailath Awarded Honorary Degree, April 2017

Tom Kailath selected as Eminent Member, IEEE-HKN, February 2017

Professor Kailath Receives National Medal of Science from President Obama, October 2014

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February 2014

Three staff members each received a $50 Visa card in recognition of their extraordinary efforts as part of the department’s 2014 Staff Gift Card Bonus Program. The EE department received several nominations in January, and nominations from 2013 were also considered.

Following are January’s gift card recipients and some of the comments from their nominators:

Ann Guerra, Faculty Administrator

  • “She is very kind to students and always enthusiastic to help students… every time we need emergent help, she is willing to give us a hand.”
  • “Ann helps anyone who goes to her for help with anything, sometimes when it’s beyond her duty.” 

Teresa Nguyen, Student Accounting Associate

  • “She stays on top of our many, many student financial issues, is an extremely reliable source of information and is super friendly.”
  • “Teresa’s cheerful disposition, her determination, and her professionalism seem to go above and beyond what is simply required.”

Helen Niu, Faculty Administrator

  • “Helen is always a pleasure to work with.”
  • “She goes the extra mile in her dealings with me, which is very much appreciated.”

The School of Engineering once again gave the EE department several gift cards to distribute to staff members who are recognized for going above and beyond. More people will be recognized next month, and past nominations will still be eligible for future months. EE faculty, staff and students are welcome to nominate a deserving staff person by visitinghttps://gradapps.stanford.edu/NotableStaff/nomination/create.

Ann Guerra  Teresa Nguyen  Helen Niu

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