News

March 2017

Kwabena Boahen's research on building brain-like computers, or neuromorphic computers, is moving toward creating physical devices that are more energy efficient and robust. Kwabena envisions this technology would be most useful in embedded systems that have extremely tight energy requirements, such as very low-power neural implants or on-board computers in autonomous drones.

While others have built brain-inspired computers, he and his collaborators have developed a five-point prospectus for how to build neuromorphic computers that directly mimic in silicon what the brain does in flesh and blood.

The first two points of the prospectus concern neurons themselves, which unlike computers operate in a mix of digital and analog mode. In their digital mode, neurons send discrete, all-or-nothing signals in the form of electrical spikes, akin to the ones and zeros of digital computers. But they process incoming signals by adding them all up and firing only once a threshold is reached – more akin to a dial than a switch.

That observation led Kwabena to try using transistors in a mixed digital-analog mode. Doing so, it turns out, makes chips both more energy efficient and more robust when the components do fail, as about 4 percent of the smallest transistors are expected to do.

From there, Kwabena builds on neurons' hierarchical organization, distributed computation and feedback loops to create a vision of an even more energy efficient, powerful and robust neuromorphic computer.

Over the last 30 years, Kwabena's lab has actually implemented most of their ideas in physical devices, including Neurogrid, one of the first truly neuromorphic computers. In another two or three years, Boahen said, he expects they will have designed and built computers implementing all of the prospectus's five points.

He states that neuromorphic computers will not replace current computers. The two are complementary.

An additional challenge is getting others, especially chip manufacturers, on board. Kwabena is not the only one thinking about what to do about the end of Moore's law or looking to the brain for ideas. IBM's TrueNorth, for example, takes cues from neural networks to produce a radically more efficient computer architecture. On the other hand, it remains fully digital, and, Kwabena said, 20 times less efficient than Neurogrid would be had it been built with TrueNorth's 28-nanometer transistors.

Professor Kwabena Boahen is also a member of Stanford SystemX and the Stanford Computer Forum. His work was supported by a Director's Pioneer Award and a Transformative Research Award from the U.S. National Institutes of Health and a Long Range Science and Technology Grant from the U.S. Office of Naval Research.

 

Below, Professor Kwabena Boahen shares his research with Electrical Engineering undergraduates who are in the REU program (Research Experience for Undergrads).

Boahen shares his research with EE undergrads who are in the REU program

 


 

Excerpted from Stanford News, "As Moore's law nears its physical limits, a new generation of brain-like computers comes of age in a Stanford lab"

Image credit (top): Linda A. Cicero / Stanford News Service

 

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 though 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"

February 2017

At the invitation of the Optical Society of America (OSA), Professor Jelena Vuckovic hosted a Reddit Science Ask Me Anything (AMA) session. The session was primarily directed to students, however anyone can post a question.

The Reddit Science community (known as /r/Science) has created an independent, science-focused AMA Series – the Science AMA Series. Their goal is to encourage discussion and facilitate outreach while helping to bridge the gap between practicing scientists and the general public. This series is open to any practicing research scientist, or group of scientists, that wants to have a candid conversation with the large and diverse Reddit Science community.

Reddit's AMA format introduced Jelena and her research in nanophotonics, quantum optics, nonlinear optics, quantum information technologies, and optoelectronics. She received about 25 questions and provided answers in the course of an afternoon.

The thread is available on Reddit, and can be viewed at www.reddit.com/r/science/comments/5ssbx2/science_ama_series_im_dr_jelena_vuckovic/

'AMA' is short for 'Ask Me Anything,' and was created by the Reddit community as an opportunity for interesting individuals to field questions about anything and everything. AMAs hosted on Reddit have become an exciting platform for people to have direct discussions and gain insight into the lives of unique individuals. Some of the historically most-popular AMAs include those from President Barack Obama, Sir David Attenborough, Bill Gates, Elon Musk and many others.

Related:

 

 

Additional Sources, Reddit.com

 

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

The goal of Eric Pop's team was to develop a manufacturing process to turn single-layer chips into practical realities.

The first atomically thin material was measured in 2004 when scientists observed that graphene – a material related to the "lead" in pencils – could be isolated in layers the thickness of a single carbon atom. The scientists who made this finding shared the 2010 Nobel Prize in Physics.

But the process used to make that discovery – the scientists lifted layers of graphene off a rock using sticky tape – was of no use in turning ultrathin crystals into next-generation electronics.

In the wake of the graphene discovery, engineers embarked on a quest to find similar materials and, more importantly, practical ways to fashion atomically thin switches into circuits.

It is on the issue of manufacturability where Pop's team made a big advance. They started with a single layer of material called molybdenum disulfide. The name describes its sandwich-like structure: a sheet of molybdenum atoms between two layers of sulfur. Previous research had shown that molybdenum disulfide made a good switch, controlling electricity to create digital ones and zeroes.

The question was whether the team could manufacture a molybdenum disulfide crystal big enough to form a chip. That requires building a crystal roughly the size of your thumbnail. This may not sound like a big deal until you consider the aspect ratio of the crystal required: a chip just three atoms thick but the size of your thumbnail is like a single sheet of paper big enough to cover the entire Stanford campus.

The Stanford team manufactured that sheet by depositing three layers of atoms into a crystalline structure 25 million times wider than it is thick. Smithe achieved this by making ingenious refinements to a manufacturing process called chemical vapor deposition. This approach essentially incinerates small amounts of sulfur and molybdenum until the atoms vaporize like soot. The atoms then deposit as an ultra-thin crystalline layer on a "handle" substrate, which can be glass or even silicon.

However, the researchers' job was not done. They still had to pattern the material into electrical switches and to understand their operation. For this, they made use of a recent advance led by English, who discovered that extremely clean deposition conditions are essential to form good metallic contacts with the molybdenum disulfide layers. The wealth of new experimental data available now in the lab has also enabled Suryavanshi to craft accurate computer models of the new materials and to begin predicting their collective behavior as circuit components.

"We have a lot of work ahead to scale this process into circuits with larger scales and better performance," Pop said. "But we now have all the building blocks."

 

 

Excerpted from Stanford School of Engineering news, "A team of engineers create a prototype chip a mere three atoms thick"

Lisa Sickorez receives 2016 SoE Leadership Award
March 2017

 

Lisa Sickorez received the School of Engineering's Leadership Award. Lisa's award underscores her dedication and enthusiasm for advancing the mission of the school and Stanford university.  

The Leadership Award recognizes mentoring and management contributions. Her citation reads, "Lisa is known as an individual who leads by example, finds solutions to difficult problems, and has the integrity to do the right thing. In addition to managing a demanding workload in the EE department, Lisa stepped up to assist the SoE Finance team with implementing a new budgeting system. Her business knowledge and expertise is a great resource to the EE department and to all departments in the school."

Lisa was presented with her award at an annual Staff Service Awards Ceremony in March.

 

Hearty congratulations to Lisa on receiving the 2016 School of Engineering Leadership Award.

March 2017

Congratulations to Isha Datye and Alexander Gabourie on their winning poster, "Reduction of hysteresis in MoS2 transistors using pulsed voltage measurements". 

 

The Device Research Conference (DRC) brings together leading scientists, researchers, and students to share their latest discoveries in device science, technology and modeling. 2016 marked the 75th anniversary of the DRC — the longest running device research meeting in the world.

 

Abstract

Transistors based on atomically thin two-dimensional (2D) materials like MoS2 have attractive properties for applications in low-power electronics. However, in practice their electrical measurements often exhibit hysteresis, masking their intrinsic behavior. In this study we used pulsed measurements to decrease hysteresis, examine charge trapping, and extract device parameters (like mobility) that represent the "true" behavior of 2D devices. Hysteresis is minimized even with modest ≤ 1 ms pulses, and the extracted mobility converges to a unique value, unlike the less reliable conventional methods which rely either on forward or reverse DC sweeps.

Link to paper

March 2017

Ning Wang, EE PhD candidate, received best paper and best poster awards at TECHCON 2016. The title of his paper is "GDOT: A Graphene-Based Nanofunction for Dot-Product Computation".

TECHCON is a technical conference and networking event for Semiconductor Research Corporation (SRC) members and students.

Ning Wang's research is in Physical Technology & Science and his advisor is Eric Pop.

 

Congratulations to Ning on his well-deserved recognition!

 

Abstract
Though much excitement surrounds two-dimensional (2D) beyond CMOS fabrics like graphene and MoS2, most efforts have focused on individual devices, with few high-level implementations. Here we present the first graphene-based dot-product nanofunction (GDOT) using a mixed-signal architecture. Dot product kernels are essential for emerging image processing and neuromorphic computing applications, where energy efficiency is prioritized. SPICE simulations of GDOT implementing a Gaussian blur show up to ~10(4) greater signal-to-noise ratio (SNR) over CMOS based implementations - a direct result of higher graphene mobility in a circuit tolerant to low on/off ratios. Energy consumption is nearly equivalent, implying the GDOT can operate faster at higher SNR than CMOS counterparts while preserving energy benefits over digital implementations. We implement a prototype 2-input GDOT on a waferscale 4" process, with measured results confirming dot-product operation and lower than expected computation error.

 

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".

March 2017

 

Jennifer Widom is the Fletcher Jones Professor in Computer Science and Electrical Engineering. She served as Computer Science Department chair from 2009 to 2014 and senior associate dean from 2014 to 2016.

Jennifer's interest in helping the world adopt knowledge of computer science led her to create one of the first three Stanford MOOCs in the fall of 2011, a course called Introduction to Databases that continues to attract thousands of students in an online self-study version. She chose to spend her sabbatical this academic year teaching short-form courses on big data and design-thinking workshops in 15 countries around the globe, including Peru, Tanzania and Bangladesh. Jennifer will curtail her spring travel plans to assume her new role as dean.

"This is an amazing time to be taking the reins of the School of Engineering, just as the university is embarking on its own long-range planning under a new administration," Widom said. "While Persis was dean, a number of exciting initiatives were launched as a result of the SOE-Future planning process, and I'm extremely excited to see them through: the Catalyst for Collaborative Solutions, new initiatives in improving diversity at all levels, and support for our non-tenure-line educators are a few examples that I feel very passionate about."

As dean, Widom will oversee a school that enrolls about 5,300 students and has more than 240 faculty members, including 130 national and international academy and society members. All nine of the school's departments are ranked in the top five nationally. Stanford Engineering has been at the forefront of innovation for nearly a century, creating pivotal technologies that have transformed the worlds of information technology, communications, health care, energy, business and more.

Widom said that one of her primary objectives will be to further integrate the school with the rest of the university.

"It has become evident to me that there are many opportunities for the School of Engineering to become better integrated across the university," Widom said. "I've set a long-term end goal: I'd like every faculty member in the university, regardless of field, to feel fortunate that they are in a university with a top engineering school, just as engineering faculty benefit tremendously from Stanford's strengths across the whole range of disciplines."

Widom will also seek to expand opportunities for engineering undergraduates to explore a wide curriculum.

Widom is an Association for Computer Machinery (ACM) Fellow and a member of the National Academy of Engineering and the American Academy of Arts & Sciences. She received the ACM-W Athena Lecturer Award in 2015, the ACM SIGMOD Edgar F. Codd Innovations Award in 2007 and a Guggenheim Fellowship in 2000.

 

Excerpted from the Stanford News. Read full article

 

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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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