Prof. Jon Schuller “Pushing Photons” – Metasurface design methods can make LED light act more like lasers

June 3rd, 2020

image of an LED bulb
ECE researchers continue to push the boundaries of LED design a little further with a new method that could pave the way toward more efficient and versatile LED display and lighting technology

In the paper “Unidirectional luminescence from InGaN/GaN quantum-well metasurfaces” published in Nature Photonics, ECE  Prof. Jonathan Schuller and collaborators describe this new approach, which could allow a wide variety of LED devices — from virtual reality headsets to automotive lighting — to become more sophisticated and sleeker at the same time.

“What we showed is a new kind of photonic architecture that not only allows you to extract more photons, but also to direct them where you want,” said Schuller. This improved performance, he explained, is achieved without the external packaging components that are often used to manipulate the light emitted by LEDs.

Light in LEDs is generated in the semiconductor material when excited, negatively charged electrons traveling along the semiconductor’s crystal lattice meet positively-charged holes (an absence of electrons) and transition to a lower state of energy, releasing a photon along the way. Over the course of their measurements, the researchers found that a significant amount of these photons were being generated but were not making it out of the LED.

“We realized that if you looked at the angular distribution of the emitted photon before patterning, it tended to peak at a certain direction that would normally be trapped within the LED structure,” Schuller said. “And so we realized that you could design around that normally trapped light using traditional metasurface concepts.”

The design they settled upon consists of an array of 1.45-micrometer long gallium nitride (GaN) nanorods on a sapphire substrate. Quantum wells of indium gallium nitride (InGaN) are embedded in the nanorods to confine electrons and holes and thus emit light. In addition to allowing more light to leave the semiconductor structure, the design polarizes the light, which co-lead author Prasad Iyer said, “is critical for a lot of applications.”

Read more – Nanoscale Antennae and Right Place, Right Time

The UCSB Current – "Pushing Photons " (full article)

Schuller's COE Profile

Schuller's Nanophotonics Research Group

ECE Professor Kaustav Banerjee’s research featured in the UCSB Current article “Building An Ideal MOSFET”

May 28th, 2020

photo of a chip
Prof. Kaustav Banerjee and ECE researchers demystify the role of negative capacitance in modern MOSFETs after over a decade since its conception

As our electronics continue to proliferate and become more sophisticated, the race continues for more power efficient and scaleable semiconductor devices — components that use minimal power while being small enough to pack into increasingly dense integrated circuits.

MOSFETs (metal-oxide field-effect transistors) are an example of such a breakthrough. Developed in the 1960s, their low power consumption, scalability, compactness and ease of mass manufacture made them the go-to logic switch for a wide array of electronics. The rapid miniaturization and densification of these transistors (without a concurrent increase in power consumption) was what led Intel executive Gordon Moore to formulate his famous law: that the number of transistors in an integrated circuit would double every two years. The result has been a steady increase in the performance of our computers for several decades, from desktops and laptops to our smart devices and wearables. Today’s smartphones have billions of nanoscale MOSFETs.

However, the benefits of downward scaleability — at least in terms of conventional FETs — seems to be hitting a limit, according to UC Santa Barbara electrical and computer engineering professor Kaustav Banerjee, a renowned expert in nanoelectronics and one of the world’s most influential scientific minds, according to Clarivate Analytics. And though a certain type of transistor called a negative-capacitance FET (NC-FET) has been touted as a way to maintain performance, Banerjee thinks it’s time to reconsider its role.

“After over a decade of misconception and confusion in the scientific community, we have essentially blasted the myth that NC-FET is a steep-slope device,” Banerjee said of his paper, “Is negative capacitance FET a steep-slope logic switch?,” recently published in Nature Communications.

The UCSB Current – "Building An Ideal MOSFET" (full article)

Banerjee's COE Profile

Banerjee's Nanoelectronics Research Lab

ECE’s Dr. Chunfeng Cui and Professor Zheng Zhang receive a Best Paper from IEEE T-CPMT

May 12th, 2020

photo of chunfeng cui
ECE postdoc Chunfeng Cui and her supervisor Prof. Zheng Zhang receive a best paper award from IEEE Transactions Components, Packaging and Manufacturing Technology (IEEE T-CPMT)

The editors of the journal selected Cui’s paper “Stochastic Collocation with Non-Gaussian Correlated Process Variations: Theory, Algorithms and Applications” in the Electrical Performance of Integrated Systems category.

Today’s electronic and photonic integrated circuit chips are subject to increasing process variation due to the imprecise nanoscale fabrication. Due to these process variations, some chips have good performance, some have bad performance, and some fail to work. Therefore, how to quantify and control the impact of process variations in the design flow is a critical problem in both academia and industry. While numerous algorithms and tools have been developed in the design automation community, handling non-Gaussian correlated process variations is a long-standing challenge for both theorists and software designers. Their paper proposed a novel approach to solve this challenging problem with both high computational efficiency and rigorous theoretical performance guarantees.

Chunfeng Cui’s research is mainly focused in the areas of uncertainty quantification, tensor computations, and machine learning. She received her Ph.D. degree in 2016 from Chinese Academy of Sciences in Beijing, China and joined ECE department as a postdoc in November 2017. Dr. Cui received the Best Paper Award of the IEEE EPEPS 2018, the Zhongjiaqing mathematics award in China 2019, and was selected as one of the rising stars in Computational Data Sciences 2019 and rising stars in EECS 2019.

Since the June 2020 IEEE 70th Electronic Components and Technology Conference (ECTC) has been moved to a virtual platform, Cui will be recognized for the paper at next year’s ECTC event. The Electronic Components and Technology Conference is the premier international event that brings together the best in packaging, components and microelectronic systems science, technology and education in an environment of cooperation and technical exchange. ECTC is sponsored by the IEEE Electronics Packaging Society.

“Stochastic Collocation with Non-Gaussian Correlated Process Variations: Theory, Algorithms and Applications,” IEEE Transactions on Components, Packaging and Manufacturing Technology (Volume: 9 , Issue: 7 , July 2019)

Cui’s Google Scholar

Zheng Zhang Group

Doctoral student Christian Zollner, UCSB SSLEEC researchers and ECE Prof. Steve DenBaars contribute in the battle of the novel coronavirus

April 23rd, 2020

illustration of coronavirus
The UCSB Solid State Lighting & Energy Electronics Center (SSLEEC) and materials researcher Zollner’s work centers on advancing deep ultraviolet light LED technology for sanitation and purification purposes prove effective in eliminating coronavirus from surfaces and, potentially, air and water

As COVID-19 continues to ravage global populations, the world is singularly focused on finding ways to battle the novel coronavirus — that includes the SSLEEC and member companies. Researchers there are developing ultraviolet LEDs that have the ability to decontaminate surfaces — and potentially air and water — that have come in contact with the SARS-CoV-2 virus.

“One major application is in medical situations — the disinfection of personal protective equipment, surfaces, floors, within the HVAC systems, et cetera,” said Christian Zollner. He added that a small market already exists for UV-C disinfection products in medical contexts.

Indeed, much attention of late has turned to the power of ultraviolet light to inactivate the novel coronavirus. As a technology, ultraviolet light disinfection has been around for a while. And while practical, large-scale efficacy against the spread of SARS-CoV-2 has yet to be shown, UV light shows a lot of promise: SSLEEC member company Seoul Semiconductor in early April reported a “99.9% sterilization of coronavirus (COVID-19) in 30 seconds” with their UV LED products. Their technology currently is being adopted for automotive use, in UV LED lamps that sterilize the interior of unoccupied vehicles.

It’s worth noting that not all UV wavelengths are alike. UV-A and UV-B — the types we get a lot of here on Earth courtesy of the Sun — have important uses, but the rare UV-C is the ultraviolet light of choice for purifying air and water and for inactivating microbes. These can be generated here only via man-made processes.

“UV-C light in the 260 – 285 nm range most relevant for current disinfection technologies is also harmful to human skin, so for now it is mostly used in applications where no one is present at the time of disinfection,” Zollner said. In fact, the World Health Organization warns against using ultraviolet disinfection lamps to sanitize hands or other areas of the skin — even brief exposure to UV-C light can cause burns and eye damage.

Before the COVID-19 pandemic gained global momentum, materials scientists at SSLEEC were already at work advancing UV-C LED technology. This area of the electromagnetic spectrum is a relatively new frontier for solid-state lighting; UV-C light is more commonly generated via mercury vapor lamps and, according to Zollner, “many technological advances are needed for the UV LED to reach its potential in terms of efficiency, cost, reliability and lifetime.”

Other research contributors include Burhan K. SaifAddin (lead author), Shuji Nakamura, Steven P. DenBaars, James S. Speck, Abdullah S. Almogbel, Bastien Bonef, Michael Iza, and Feng Wu, all from SSLEEC and/or the Department of Materials at UC Santa Barbara.

The UCSB Current – "The Power of Light" (full article)

Solid State Lighting & Energy Electronics Center (SSLEEC)

DenBaar's COE Profile

ECE Associate Professor Yon Visell haptics research featured in The UCSB Current article “Skin That Computes”

April 20th, 2020

artist's illustration of skin
ECE Associate Professor Yon Visell and haptics researchers find that the biomechanics of the skin can perform useful tactile computations

As our body’s largest and most prominent organ, the skin also provides one of our most fundamental connections to the world around us. From the moment we’re born, it is intimately involved in every physical interaction we have.

Though scientists have studied the sense of touch, or haptics, for more than a century, many aspects of how it works remain a mystery.

“The sense of touch is not fully understood, even though it is at the heart of our ability to interact with the world,” said UC Santa Barbara haptics researcher Yon Visell. “Anything we do with our hands — picking up a glass, signing our name or finding keys in our bag — none of that is possible without the sense of touch. Yet we don’t fully understand the nature of the sensations captured by the skin or how they are processed in order to enable perception and action.”

We have better models for how our other senses, such as vision and hearing, work, but our understanding of how the sense of touch works is much less complete, he added.

To help fill that gap, Visell and his research team, including Yitian Shao and collaborator Vincent Hayward at the Sorbonne, have been studying the physics of touch sensation — how touching an object gives rise to signals in the skin that shape what we feel. In a study published in the journal Science Advances, the group reveals how the intrinsic elasticity of the skin aids tactile sensing. Remarkably, they show that far from being a simple sensing material, the skin can also aid the processing of tactile information.

To understand this significant but little-known aspect of touch, Visell thinks it is helpful to think about how the eye, our visual organ, processes optical information.

The UCSB Current – "Skin That Computes" (full article)

Visell's RE Touch Lab

Visell's COE Profile

B.S. Manjunath’s Vision Research Lab and graduate student Satish Kumar featured in The UCSB Current article “Show Me the Methane”

March 10th, 2020

photo of industry with smoke stacks
Hyperspectral imaging and artificial intelligence combine to augment detection of methane leaks

Though not as prevalent in the atmosphere as carbon dioxide, methane is a far more potent greenhouse gas. Occurring naturally as well as being manmade, methane is much shorter-lived than CO2, but it is fast acting and 20 to 80 times as effective at trapping heat. A little extra methane goes a long way.

In addition, methane is invisible, which makes detection by conventional means difficult. So when researcher Satish Kumar and colleagues noted the growing use of infrared sensing as a means of greenhouse gas detection, as was highlighted in a recent New York Times story, they were pleased. The interactive piece used infrared cameras to track emissions from oil and gas facilities in the Permian Basin, an oil field located in Texas and New Mexico.

It’s a topic close to his heart — as a member of ECE Professor B.S. Manjunath’s Vision Research Lab, Kumar does work involving multimedia signal processing and analysis.

“As a computer engineer interested in environmental management, I am incredibly glad methane leaks from previously unknown sources are being brought to light,” he said.

Now, to keep the conversation alive, Kumar and his colleagues have proposed a system that does the heat detection one better, by using hyperspectral imaging and machine learning to detect the specific wavelength of methane emissions. Their work was presented at the 2020 IEEE Winter Conference on the Applications of Computer Vision.

The UCSB Current – "Show Me the Methane" (full article)

Vision Research Lab

ECE Professors Yuan Xie and B.S. Manjunath Receive Prestigious Computer Society Technical Achievement Award

March 9th, 2020

photo of xie and manjunath
Manjunath and Xie selected to receive the Edward J. McCluskey Technical Achievement Award from the Institute of Electrical and Electronics Engineers (IEEE) Computer Society

The annual recognition is given for outstanding and innovative contributions to the fields of computer and information science and engineering or computer technology, usually within the past fifteen years. Contributions must have significantly promoted technical progress in the field.

“Congratulations to professors B.S. Manjunath and Yuan Xie for receiving this well-deserved, prestigious recognition and honor from their peers around the globe,” said Rod Alferness, dean of UCSB’s College of Engineering. “We are proud that they have taken international leadership roles in the areas of image search, computer vision, and technology-driven computer architecture.”

Xie, a fellow of IEEE, the Association for Computing Machinery (ACM), and the American Association for the Advancement of Science (AAAS), was selected “for contributions to technology-driven computer architecture and to [developing] tools for their implementation and evaluation.” Manjunath, a fellow of IEEE and ACM, received his award “for contributions to image search retrieval, and bio-image informatics.”

COE News – "ECE Professors Receive Prestigious Computer Society Technical Achievement Awards" (full article)

Xie's COE Profile

Manjunath's COE Profile

ECE Professor Dan Blumenthal receives The Optical Society of America (OSA) C.E.K. Mees Medal

February 20th, 2020

photo of dan blumenthal
Blumenthal honored with the 2020 medal for his “innovations in ultra-low-loss photonic integrated circuits and their applications”

ECE Prof. Daniel Blumenthal, who leads the Optical Communications and Photonic Integration (OCPI) Group and UCSB’s Terabit Optical Ethernet Center, was described by The Optical Society (OSA) President Stephen D. Fantone, founder and president of the Optikos Corporation, as “an excellent choice for the C.E.K. Mees Medal. He is an innovator who continues to push boundaries in the use of electronic and photonic materials.”

“This is a huge honor, not just for me but for my lab group, UCSB and the CoE, and our collaborators and colleagues,” said Blumenthal, who received the news on his birthday. “Charles Townes, who invented the laser, was a recipient.”

“We at the College of Engineering offer sincere congratulations to Dan Blumenthal upon receiving this extremely prestigious award,” said Rod Alferness, dean of the UCSB College of Engineering. “The C.E.K. Mees Medal recognizes a record of optics research that is marked not only pioneering innovation, but also by having widespread impact in diverse areas. We are deeply proud of Professor Blumenthal for his continuing contributions, and are delighted for him to receive this most-deserved recognition.”

Blumenthal’s research is focused in the areas of optical communications and optical packet switching, integrated ultra-narrow-linewidth (sub-Hz) Brillouin lasers, optical gyroscopes, highly integrated, ultra-low-loss indium photonic integrated circuits, integrated atom cooling, atomic clock photonics, nano-photonics, and microwave photonics. His UCSB lab develops new devices and system hardware to solve complex communications, transmission, switching, and signal-processing problems that are beyond the reach of current technologies. He and his colleagues have a particular focus on integrating new bench-scale functions on small chips, called photonic circuits, which are then used to build networks in ways that save energy and increase the scale of connectivity and bandwidth of data centers and the internet.

The group’s work in developing lasers characterized by having spectrally pure, ultra-stable light sources and ultra-low wave-guide losses is finding increasingly widespread application.

“The technology is becoming pervasive, which is validation of what we’ve thought for a long time and what has been one of my passions,” Blumenthal says, “that being able to put ultra-low-loss and ultra-narrow-linewidth lasers in photonic circuits on chips was the future for a wide variety of applications across a broad range of disciplines.”

The UCSB Current – “Laser Focus on the Prize” (full article)

OSA C.E.K. Mees Medal

Blumenthal's COE Profile

Blumenthal's Optical Communications and Photonic Integration (OCPI) Group

ECE graduate student Mohammed Mahmoodi’s research for better neural networks in UCSB Current article “Bring the Noise”

February 19th, 2020

illustration of connecting memristors in crossbar fashion
Mohammed “Reza” Mahmoodi, a fifth-year Ph.D. candidate in the lab of ECE Prof. Dmitri Strukov describes an approach to leverage noise, as the human brain does, for better neural networks

Those who design deep neural networks for artificial intelligence often find inspiration in the human brain. One of the brain’s more important characteristics is that it is a “noisy” system: not every neuron contains perfect information that gets carried across a synapse with perfect clarity. Sometimes partial or conflicting information is turned into action by the brain, and sometimes partial information is not acted upon until further information is accumulated over time.

“That is why, when you stimulate the brain with the same input at different times, you get different responses,” explained Mohammed “Reza” Mahmoodi, a fifth-year Ph.D. candidate in the lab of UC Santa Barbara electrical and computer engineering professor Dmitri Strukov. “Noisy, unreliable molecular mechanisms are the reason for getting substantially different neural responses to repeated presentations of identical stimuli, which, in turn, allow for complex stochastic, or unpredictable, behavior.”

The human brain is extremely good at filling in the blanks of missing information and sorting through noise to come up with an accurate result, so that “garbage in” does not necessarily yield “garbage out.” In fact, Mahmoodi said, the brain seems to work best with noisy information. In stochastic computing, noise is used to train neural networks, “regularizing” them to improve their robustness and performance.

It is not clear on what theoretical basis neuronal responses involved in perceptual processes can be separated into a “noise” versus a “signal,” Mahmoodi explained, but the noisy nature of computation in the brain has inspired the development of stochastic neural networks. And those have now become the state-of-the-art approach for solving problems in machine learning, information theory and statistics.

“If you want a stochastic system, you have to generate some noise,” Mahmoodi and his co-authors, Strukov and Mirko Prezioso, write in a paper that describes an approach to creating such a noisy system. “Versatile Stochastic Dot Product Circuits Based on Nonvolatile Memories for High Performance Neurocomputing and Neurooptimization” was published in a recent issue of the journal Nature Communications.

The UCSB Current – "Bring the Noise" (full article)

Mahmoodi on LinkedIn

Strukov Research Group

ECE Prof. Kaustav Banerjee’s research on 3D integration with 2D materials featured in The UCSB Current

January 6th, 2020

illustration of a city with chips
Banerjee and researchers propose 3D integration with 2D materials
It’s a well-known observation: The number of transistors on a microchip will double roughly every two years. And, thanks to advances in miniaturization and performance, this axiom, known as Moore’s Law, has held true since 1965, when Intel co-founder Gordon Moore first made that statement based on emerging trends in chip manufacturing at Intel.

However, integrated circuits are hitting hard physical limits that are rendering Moore’s Law obsolete — elements on a dense integrated circuit (IC) can get only so small and so tightly packed together before they begin to interfere with each other and otherwise lose their functionality.

“Apart from fundamental physical limits to the scaling of transistor feature sizes below a few nanometers, there are significant challenges in terms of reducing power dissipation, as well as justifying the incurred cost of IC fabrication,” said Kaustav Banerjee, a professor of electrical and computer engineering at UC Santa Barbara. As a result, the very devices that we rely on for their steadily improving performance and versatility — computers, smartphones, internet-enabled gadgets — would also hit a limit, he said.

The UCSB Current – "Saving Moore's Law" (full article)

Banerjee's COE Profile

Banerjee's Nanoelectronics Research Lab (NRL)