research

March 2017

At the IEEE International Electron Devices Meeting, researchers presented work they say shows that molybdenum disulfide not only makes for superlative single transistors, but can be made into complex circuits using realistic manufacturing methods.

The researchers are part of Eric Pop's team. They showed transistors made from large sheets of MoS2 can be used to make transistors with 10-nanometer-long, gate having electronic properties that approach the material's theoretical limits. The devices displayed traits close to ballistic conduction, a state of very low electrical resistance that allows the unimpeded flow of charge over relatively long distances—a phenomenon that should lead to speedy circuits.

Most of the work on molybdenum disulfide so far has been what professor Eric Pop calls "Powerpoint devices." These one-off devices, made by hand in the lab, have terrific performance that looks great in a slide. This step is an important one, says Pop, but the 2D material is now maturing.

Pop Lab's transistors are not as small as the record-breaking ones demonstrated in October. What's significant is that these latest transistors maintained similar performance even though they were made using more industrial-type techniques. Instead of using Scotch tape to peel off a layer of molybdenum disulfide from a rock of the material, then carefully placing it down and crafting one transistor at a time, Pop's grad student started by growing a large sheet of the material on a wafer of silicon.

At these relatively small dimensions, the molybdenum disulfide transistors approach their ultimate electrical limit, a state called ballistic conduction. When a device is small enough (or at low enough temperature), electrons will travel through the conducting medium without scattering because of collisions with the atoms that make up the material. Transistors operating ballistically should switch very fast and enable high-performance processors. Pop estimates that about 1 in 5 electrons moves through the rusty transistors ballistically. By further improving the quality of the material (or making the transistors smaller), he expects that ratio to improve. The important thing, he says, is the way they achieved this: using methods that could translate to larger scales. "We have all the ingredients we need to scale this up," says Pop.

Eric Pop and graduate students talking during an informal lunchtime Q and A session in the Packard building.


 

Excerpted from IEEE Spectrum, "Molybdenum-Disulfide 2D Transistors Go Ballistic"

March 2017

Kristen Lurie (PhD '16) and Audrey Bowden authored a paper published in Biomedical Optics Express that presents a computational method to reconstruct and visualize a 3D model of organs from an endoscopic video that captures the shape and surface appearance of the organ.

Although the team developed the technique for the bladder, it could be applied to other hollow organs where doctors routinely perform endoscopy, including the stomach or colon.

"We were the first group to achieve complete 3D bladder models using standard clinical equipment, which makes this research ripe for rapid translation to clinical practice," states Kristen Lurie (EE PhD, '16), lead author on the paper.

"The beauty of this project is that we can take data that doctors are already collecting," states Audrey.

One of the technique's advantages is that doctors don't have to buy new hardware or modify their techniques significantly. Through the use of advanced computer vision algorithms, the team reconstructed the shape and internal appearance of a bladder using the video footage from a routine cystoscopy, which would ordinarily have been discarded or not recorded in the first place.

"In endoscopy, we generate a lot of data, but currently they're just tossed away," said Joseph Liao, professor of Urology and co-author. According to Liao, these three-dimensional images could help doctors prepare for surgery. Lesions, tumors and scars in the bladder are hard to find, both initially and during surgery.

This technique is the first of its kind and still has room for improvement, the researchers said. Primarily, the three-dimensional models tend to flatten out bumps on the bladder wall, including tumors. With the model alone, this may make tumors harder to spot. The team is now working to advance the realism, in shape and detail, of the models.

Future directions, according to the researchers, include using the algorithm for disease and cancer monitoring within the bladder over time to detect subtle changes, as well as combining it with other imaging technologies.

 

Read Paper

 

 

Excerpted from Stanford News, "Stanford scientists create three-dimensional bladder reconstruction"

 

March 2017

EE's Krishna Shenoy and neurosurgeon Jaimie Henderson are co-senior authors on a clinical research paper, which demonstrated that a brain-to-computer hookup can enable people with paralysis to type via direct brain control at the highest speeds and accuracy levels reported to date.

Their paper involved three study participants with severe limb weakness — two from amyotrophic lateral sclerosis, also called Lou Gehrig's disease, and one from a spinal cord injury. They each had one or two baby-aspirin-sized electrode arrays placed in their brains to record signals from the motor cortex, a region controlling muscle movement. These signals were transmitted to a computer via a cable and translated by algorithms into point-and-click commands guiding a cursor to characters on an onscreen keyboard.

Behind those results lie years of efforts by an interdisciplinary team of neurosurgeons, neuroscientists and engineers who brought different scientific vantages together to solve challenges that would have stumped any single discipline. Institutional support was another key ingredient in this long-term effort aimed at ultimately helping people with paralysis affect the world around them using only their minds.

Though more work lies ahead, this ongoing research shows that new engineering and neuroscience techniques can be directly applied to human patients. The milestone is heartening for Krishna Shenoy, who has led the effort to create brain-controlled prosthetic devices since he came to Stanford in 2001. Integral to that success has been his 12-year partnership with Jaimie Henderson, which he describes as a professional marriage of engineering, science and medicine.

"When you have a clear vision, you involve yourself in as many details as possible and you work with absolute mutual respect, as coequals, it's pretty interesting what you can do over a couple decades," Krishna said.

The study's results are the culmination of a long-running collaboration between Henderson and Shenoy and a multi-institutional consortium called BrainGate. Leigh Hochberg, MD, PhD, a neurologist and neuroscientist at Massachusetts General Hospital, Brown University and the VA Rehabilitation Research and Development Center for Neurorestoration and Neurotechnology in Providence, Rhode Island, directs the pilot clinical trial of the BrainGate system and is a study co-author.

 

Excerpted from Stanford Medicine News Centers "Brain-computer interface advance allows fast, accurate typing by people with paralysis" and "Listening in on the brain: A 15-year odyssey".

 

Related News:

Brain-Sensing Tech Developed by Krishna Shenoy and Team, September 2016.

Krishna Shenoy receives Inaugural Professorship, February 2017.


 

February 2017

In an article titled, "Graphene-Girded Interconnects Could Enable Next-Gen Chips," work by EE PhD candidate Ling Li, a Nanoelectronics Lab researcher, provides insight to the possible future of copper and graphene.

At the IEEE International Electron Devices Meeting in San Francisco in December, researchers described the coming problems for copper interconnects, and debated ways of getting around them. One approach studied by H.-S. Philip Wong's Nanoelectronics Lab, is to bolster copper with graphene. The research group found that the nanomaterial can alleviate a major problem facing copper, called electron migration.

Copper wires are getting so thin, and must carry so much current, that the atoms in the wire can literally get blown out of place. "The electron wind can physically move the copper atoms and create a void," says Wong. Growing graphene around copper wires prevents this, according to research Wong's group presented at the meeting. It also seems to bring down the resistance of the copper wires.

The Stanford group worked with Lam Research, which makes chip manufacturing tools, as well as researchers from Zhejiang University, in China, to make and test the composite interconnects. The materials are a good pair: graphene is often made by growing it on copper. Lam Research has developed a proprietary process for doing this at temperatures that won't damage the rest of the chip—below 400 °C. Compared to copper alone, the composite improved electromigration by a factor of 10. And the composite wires had half the electrical resistance.

Wong says the interconnect problem can no longer be dismissed. "Before, most of the time we were hearing about transistors," he says. "Now it's not just transistors but wires, memory—many other things that were previously not a problem are beginning to be a problem."

 

Excerpted from IEEE Spectrum, 6 January 2017.

January 2017

SPF is a place to use and share expertise; nurture innovation and learning; build efficient, specialized electronics; and reduce researchers' burden of developing electronics without expertise.

Located in the Allen Building, the newly renovated space sports glass-topped walls, surrounded by sleek workstations. Inside the SPF, workbenches and collaborative areas provide organized space for system design, building, and testing.

"The SPF's mission is to support electronic sub-system design for cutting-edge research across our campus," states Professor Boris Murmann, lead SPF faculty. "We are currently working on projects with Principal Investigators in the departments of Physics, Applied Physics, Electrical Engineering, Psychology, Psychiatry and Behavioral Sciences and Bioengineering, looking to enable new possibilities in a wide range of disciplines."

Professor Murmann is also pleased that SPF – together with ExFab (Experimental Fabrication lab) – provides a complete spectrum of device development from creation to software interfacing. Similar to ExFab, SPF usage will help inform the design of future system prototyping facilities on campus.

The SPF welcomes researchers from any department on campus, accommodating project needs with a tiered service and support structure. The tiered structure is based on how much expertise is needed – from independently using the tools to requesting a turnkey solution. Stanford researchers are able to design and build a system themselves, or collaborate with SPF's electrical engineers.

 

SPF is made possible by funding from SLAC and School of Engineering.

Interested in SPF? Please email lab director, Angelo Dragone: dragone@slac.stanford.edu

Pictured above: SPF faculty director, Professor Boris Murmann speaks with Professor Marty Breidenbach, Dr. Angelo Dragone,  Professor Chi-Chang Kao and Sawson Taheri.

January 2017

 "It's all in the name," state Professors Jonathan Fan and Roger Howe.

"Experimental fabrication. We want to change the way that people go from thinking about a device to making it in the lab. With ExFab, we will make that process faster and cheaper, with fewer restrictions on materials. It will allow the rapid prototyping of microscale and nanoscale devices in a time scale not typically associated with microelectronic fabrication, and it will bring together researchers from in engineering, medicine, and the basic sciences.

"With our investment in the tools and space, we can explore how it's used, and let that guide us in how to develop the space into the future."

ExFab emerged from a two-year process of faculty brainstorming about how best to address the need for new tools and processes for research in materials, electronics, and photonics. In addition, faculty also wanted to study how the new tools and space are used. The goal was to create an accessible space for faster, cheaper fabrication of a wider range of materials and processes.

Strategically located in the Allen Building near the engineering quad and the David Packard building, and across from the Medical School, ExFab is open to all: Stanford students and postdocs from all departments and schools, as well as researchers from other universities and industry.

Repurposing existing space, ExFab boasts several new tools, including those that can translate computer-generated images into physical microscale and nanoscale patterns within minutes. Many of these tools are housed in a reconfigured cleanroom. Complementing the System Prototyping Facility (SPF) – just a few steps away – students can easily utilize both areas to integrate fabricated devices into electronic systems.

In Spring, ExFab will be fully outfitted with equipment enabling researchers to define structures from the nanoscale (two-photon 3D printing) to the milli-scale (3D wax printing) and in between (direct-write lithography, aerosol jet printing) as well as to machine and meld disparate materials (laser cutting, CNC micromilling, grinding, bonding.) This toolset supports heterogeneous materials processing for emerging applications such as stretchable electronics, micro-batteries, photovoltaics, and microfluidics. With lower materials restrictions than a typical microelectronics fab, we anticipate the processing of a broad range of materials into devices and systems, including traditional semiconductors, soft materials, polymers, and bio-materials.

Nine months ago, excited for the potential of this proposed lab, over 30 faculty pledged they would use ExFab for their research, thus seeding this program. Now ExFab is a reality, and available to all. If you are an interested researcher or faculty, please email snf-access@stanford.edu or check out the website, snf.stanford.edu to learn more.

 

Pictured below (left to right) Jon Fan, Mary Tang, and Roger Howe in a nearly completed ExFab space.

November 2016

Clarivate Analytics, formerly the Intellectual Property & Science business of Thomson Reuters, announced the publication of its annual Highly Cited Researchers. The list is a citation analysis identifying scientists – as determined by their fellow researchers – whose research has had significant global impact within their respective fields of study.

More than 3,000 researchers, in 21 fields of the sciences and social sciences, were selected based on the number of highly cited papers they produced over an 11-year period from January 2004 to December 2014.

The Stanford EE faculty are

The 2016 Highly Cited Researchers list can be seen in its entirety by visiting: http://hcr.stateofinnovation.thomsonreuters.com

Excerpted from http://www.prnewswire.com/news-releases/clarivate-analytics-names-2016-highly-cited-researchers-300362643.html

November 2016

Sachin Katti and Pengyu Zhang, a postdoctoral researcher in Katti's lab, announced "HitchHike" this week at the ACM SenSys Conference. HitchHike is a tiny, ultra-low-energy wireless radio.

"HitchHike is the first self-sufficient WiFi system that enables data transmission using just micro-watts of energy – almost zero," Zhang said. "Better yet, it can be used as-is with existing WiFi without modification or additional equipment. You can use it right now with a cell phone and your off-the-shelf WiFi router."

HitchHike is so low-power that a small battery could drive it for a decade or more, the researchers say. It even has the potential to harvest energy from existing radio waves and use that electromagnetic energy, plucked from its surroundings, to power itself, perhaps indefinitely.

"HitchHike could lead to widespread adoption in the Internet of Things," Katti said. "Sensors could be deployed anywhere we can put a coin battery that has existing WiFi. The technology could potentially even operate without batteries. That would be a big development in this field."

The researchers say HitchHike could be available to be incorporated into wireless devices in the next three to five years.

The Hitchhike prototype is a processor and radio in one. It measures about the size of a postage stamp, but the engineers believe that they can make it smaller – perhaps even smaller than a grain of rice for use in implanted bio-devices like a wireless heart rate sensor (see video).

"HitchHike opens the doors for widespread deployment of low-power WiFi communication using widely available WiFi infrastructure and, for the first time, truly empower the Internet of Things," Zhang said.

 

 

Excerpted from Stanford Engineering News. Original article by Andrew Myers

 

Jon Fan's research on nanoscale optical devices
November 2016

A field of materials science known as metamaterials has recently captured the imagination of engineers hoping to create nanoscale optical devices. Jonathan Fan, an assistant professor of electrical engineering and director of the ExFab at the Stanford Nanofabrication Facility, is leading the way. He recently won the prestigious 2016 Packard Fellowship in Science and Engineering, which funds the most promising early-career professors in fields ranging from physics and chemistry to engineering. Fan is just the fourth Stanford electrical engineer to win the fellowship since 1988, and the financial support that comes with it will enable him to carry on work that is so innovative that it can otherwise prove difficult to fund through traditional means. We talked to Fan about his visions in metamaterial engineering and about his interdisciplinary collaborations with fellow Stanford professors Allison Okamura and Sean Follmer in projects such as integrating new types of electromagnetic systems with robots.

What are metamaterials?

At its most basic level, we are bringing the idea of an antenna down to the nanoscale. Back in the day before cable and satellite, TVs had metal antennas. If your picture wasn't very good, you would get up and physically reconfigure the antenna geometry to change its performance. Those antennas were designed for radio waves that were centimeters to meters in length. We are working to create nanoscale antennas that would be able to respond to visible light with wavelengths of 400 to 700 nanometers, or infrared light, where wavelengths are on the order of a micron. By configuring the geometry of these antennas individually and in collections, we can engineer systems that can interact with and manipulate light in entirely new ways.

These tiny antennas are many orders of magnitude smaller than a TV antenna. Fortunately, the development of the modern electronic integrated circuit platform over the last half-century has produced mature technological processes that can help us define nanoscale features. We use those same patterning technologies to make these nanoscale antennas. That's the very basic overview.

What is the derivation of the term "meta" in the name metamaterials?

When you think of a conventional lens, you think of glass – the material, right? The glass in your camera or your eyeglasses bends light in very predictable ways based on the intrinsic material response of glass. A lens made of a metamaterial will respond to light in ways that are no longer solely based on the properties of the material itself, but largely on the design and layout of these optical antennas. So the concept of "meta" comes from our ability to engineer artificial materials, consisting of a composite of nanoscale structures, which can respond to light in entirely new ways. It's kind of neat to see an example in the case of a metal like gold. We usually think of gold as a bulk material that is reflective, yellowish and shiny. Even when you go down to the nanoscale, gold is still gold. But by specifying the geometry of nanoscale gold, we can change the color of gold from yellow to green or red, and it can support many other types of optical properties that we don't associate with bulk gold. Those are properties engineers can use to make new devices.

What do metamaterials allow us to do that we couldn't before?

Metamaterials are promising for a couple reasons. First, they enable the extreme miniaturization of existing optical devices. For example, we can take an eyeglass lens and we can make it 100 times thinner than a strand of hair. This allows us to translate traditionally bulky optical systems to extremely small form factors. Second, they can be customized to support novel properties that currently are not accessible with existing optical hardware, leading to entirely new optical systems.

What's an example of a potential metamaterial device?

A major opportunity today arises from the fact that high-resolution cameras have miniaturized to sizes that can fit onto cellphones, making them accessible to audiences a million times larger than before. Part of my larger research question is: Is there something more we can do with imaging systems with form factors of a cellphone camera? There is so much information in the incoming light field that is not currently captured by a cellphone camera, but that could be captured with imaging systems that include metamaterials. Access to this additional information could change how we use the images we take. For example, if you have a skin condition, a great deal more optical information of the skin could be extracted from a simple cellphone image and used to better assess your condition.

What excites you about metamaterials?

Metamaterials lead us to a completely different set of questions – metaquestions, if you will. For instance, are these nanoantennas even the best way to go about doing what we want to do? At this point in time, even that's not clear. In addition, you get to the big questions of applications for these materials and devices. It's just wide open. That's why this is exciting to me.

Any early impressions to share as a new faculty member?

Stanford is a really special place. The people are top-notch and the environment is highly collaborative, not siloed. As an example, I have recently expanded into robotics, where I have been looking to apply concepts in radio frequency waves to create smarter soft robotic systems. In this effort, I've started a collaboration with Allison Okamura and Sean Follmer, who are mechanical engineers. It's been fantastic so far, and I've been learning so much. People here are very open-minded and are inspired to do exciting interdisciplinary research to identify and solve big problems. I'm thrilled to be a part of that.

By Andrew Myers
Source: Stanford School of Engineering News

 

 

Related News:

Fan awarded the Presidential Early Career Awards for Scientists and Engineers, January 2017

Jonathan Fan awarded 2016 Packard Fellowship for Science and Engineering, October 2016

Jonathan's EE Spotlight

November 2016

Professor Andrea Goldsmith and post-doc fellow Nariman Farsad are currently looking into how chemical communication could advance nanotechnology.

Goldsmith and Farsad's research aims to create a system that uses chemicals to transmit messages. Instead of zeros and ones, their system uses an acid-base combination. The complications of this type of system are largely due to the fact that it's completely new. Goldsmith has spent her entire career working in wireless communication. Chemical messaging offers a new twist on familiar problems.

One potential of chemical-based data exchange is that it could be self-powered, traveling throughout the body harmlessly – and undetectable by outside devices. "This is one of the most important potential applications for this type of project," Farsad said. "It could enable the emergence of these tiny devices that are working together, talking together and doing useful things."

While working to improve their current chemical texting system, Goldsmith and Farsad are also collaborating with two bioengineering groups at Stanford to make human body-friendly chemical messaging a reality.

 

Excerpted from Stanford News. Full article.

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