Opportunities and Challenges for Photonics in Next-Generation Data Centers

Data centers are driving the development of next-generation photonic technologies with the promise of higher performance at lower cost. Worldwide research encompasses multi and single-mode links, all-photonic switching and routing technologies, and hybrid networks combining electrical and optical switching.

This talk will provide background on the current role of optical interconnects in data centers and will highlight opportunities for photonics to dramatically improve the connectivity and performance of future installations. Integration of large-scale photonics with electronics in next generation multi-chip modules will be required, which raises a host of challenges and risks that provide fertile ground for research and innovation.

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UCSB is listed among the top national universities in Washington Monthly’s 2015 rankings

washington monthly logo and cover
UCSB is listed among the top national universities in Washington Monthly’s 2015 rankings; the campus also is lauded as an ‘Access Improver’ for low-income students

UC Santa Barbara has moved up a notch in Washington Monthly magazine’s annual National Universities Rankings. Continuing its upward trajectory, UCSB is ranked number 14 on the 2015 list, which appears in the magazine’s September/October issue.

In addition, UCSB is listed at number 17 in the magazine’s “Best Bang for the Buck” rankings in the Western Schools category. The university also is highlighted in the magazine’s College Guide as one of 10 “Access Improvers,” colleges and universities that have increased their enrollments of federally funded Pell Grant students while maintaining strong student outcomes.

“The University of California, Santa Barbara, for example, is in the top echelon of its state’s universities, serving students of variable income and ability,” wrote Mamie Voight, director of policy research at the Institute for Higher Education, and Colleen Campbell, a senior policy analyst at the Association of Community College Trustees. “Yet 38 percent of Santa Barbara students are low income, compared to only 15 percent at Penn State, and Santa Barbara charges low-income students about half as much.”

While U.S. News & World Report usually awards its highest ratings to private universities, the editors of Washington Monthly prefer to give public universities more credit, and higher rankings. Fifteen of the top 20 universities in the Washington Monthly rankings are taxpayer-funded.

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Nano to Micro Scale Coulter Counters

As biotechnology continues on advancing, one of the trends that has become prominent in recent years is personalized medicine. It is an endeavor that can be briefly described as an effort to provide preventative, diagnostic and treatment measures against health problems implemented on an individual basis. Resistive pulse technique is a measurement scheme that has found a wide range of applications in this field. In my doctoral defense, I will present my research on devices that are based on resistive pulse technique from nano to micro scale. I will briefly report my research on the use of synthetic nanopores for DNA sequencing research and biomolecule sorting. Then, I will talk about a micro scale application of this technique for cancer diagnosis. Particularly, Circulating Tumor Cells(CTCs) have recently emerged as indicators of cancer metastasis. Thus, efficient detection of CTCs can provide non-invasive biopsy, enable personalized medicine and help understand cancer biology. Currently used immunoassay based CTC detection techniques are inefficient and insufficient to classify extremely heterogeneous CTCs such as Circulating Melanoma Cells(CMCs). Cancer cells have markedly different physical attributes, such as size and stiffness, and can be used to distinguish tumor cells from normal cells. In this talk, I am going to report a micro-fluidic chip potentially meeting the urgent need to detect individual CTCs in a label-free, fast and inexpensive fashion while maintaining cell viability. The chip uses resistive pulse technique coupled with controlled pressure gradients to measure size and stiffness of cells without subjecting cells to large shearing forces. I am going to present the design, fabrication and modeling of microfluidic channels enabling the classification of CTCs based on their size and stiffness. Using coupled Nernst-Planck and Navier-Stokes models in COMSOL subtle features in the current profile are corroborated with the size, angle of entry and stiffness. The insight provided by careful modeling of these devices enables accurate classification and clustering, which would not otherwise be possible. Validity of the modeling was proven by sizing commercially available 10um polystyrene particles and matched results obtained by optical microscopy analysis. The device was used to classify melanoma (MNT1)and breast cancer (MCF-7) cells both with and without blood cells. Results show the interference due to the presence of blood cells is minimal demonstrating the reliability of the device in detecting CTCs from a blood sample.

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A Signal Processing Approach to Malware Analysis

There is an alarming increase in the amount of malware that is generated today. Several studies have shown that most of these new malware are just variants of existing ones. In this research we focus on developing orthogonal methods motivated by Signal and Image Processing. We exploit the fact that most malware variants are similar in structure. One could then treat malware as digital signals and apply Signal and Image Processing techniques to compute descriptions that facilitate detection and classification of malware.

First, we will present SARVAM: Search And RetrieVAl of Malware, an online malware search and retrieval system where one can upload a binary executable and search over a database of approximately 7 million malware samples using Image Similarity metrics.

Next, we generalize this approach by expanding malware as a sparse linear combination of other malware samples.

Finally, the methods can be generalized to data forensics, where given a block of data we can determine the data type (eg. a text file, a compressed zip file or an executable).

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III-V Ultra-Thin-Body InGaAs/InAs MOSFETs for Low Standby Power Logic Applications

As the device scaling beyond sub-10-nm regime, III-V InGaAs/InAs MOSFETs are promising candidates for replacing Si-based MOSFETs for future VLSI logic applications. III-V InGaAs materials have low electron effective mass and high electron velocity, allowing higher on-state current at lower Vdd and reducing the switching power consumption. However, III-V InGaAs materials have a narrower band gap and higher permittivity, leading to large band-to-band tunneling (BTBT) leakage at the drain end of the channel, and large subthreshold leakage due to worse electrostatic integrity. To utilize III-V MOSFETs in future logic circuits, III-V MOSFETs must have high on-state performance over Si MOSFETs as well as very low leakage current with low standby power consumption. In this talk, we will report three techniques for the reduction of leakage currents in InGaAs/InAs MOSFETs, as described below.

1) Wide band-gap barriers: We developed AlAs0.44Sb0.56 barriers lattice-matched to InP using molecular beam epitaxy, and studied the electron transport in In0.53Ga0.47As/AlAs0.44Sb0.56 heterostructures. We also demonstrated the reduction of barrier leakage on InGaAs MOSFETs using AlAs0.44Sb0.56 back barriers and p-doped In0.52Al0.48As barriers.

2) Ultra-thin channels: We investigated the electron transport in InGaAs and InAs ultra-thin quantum wells and ultra-thin body MOSFETs (tch~2-4 nm). For high performance logic, InAs channels enable higher on-state current, while for low power logic, InGaAs channels allow lower BTBT leakage current.

3) Source/Drain engineering: We developed raised InGaAs and recessed InP source/drain spacers. The source/drain spacers improve electrostatics, reducing subthreshold leakage, and smooth the electric field near drain, reducing BTBT leakage. With the further replacement of raised InGaAs spacers by the recessed, doping-graded InP spacers at high field regions, BTBT leakage can be reduced ~100:1.

Using the above-mentioned techniques, record high performance InAs MOSFETs were demonstrated with Ion = 500 μA/μm at Ioff = 100 nA/μm and Vds=0.5 V, showing comparable on-state performance to 22 nm Si FinFETs. Record low leakage InGaAs MOSFETs were also demonstrated with minimum Ioff = 60 pA/μm at 30 nm-Lg. This recessed InP source/drain spacer technique enables III-V MOSFETs for low standby power logic applications. Furthermore, InAs MOSFETs fabricated on Si substrates exhibit high yield, and high peak transconductance gm~2.0 mS/μm at 20 nm-Lg and Vds=0.5 V. With further scaling of gate length, a 12 nm-Lg III-V MOSFET has shown maximum Ion/Ioff>8.3·10^5, confirming that III-V MOSFETs can scale to sub-10-nm technology nodes.

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MaxLinear: Products and Technologies

This talk will briefly introduce Maxlinear’s history and current profile. We describe key products in both cable, satellite and infrastructure markets. We discuss how these products led to technology evolution within MaxLinear. We will briefly discuss future products and challenges that we attempt to solve. This talk will be concluded by summarizing career opportunities at MaxLinear.

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Wavelength Tunable Coherent Receivers and All Optical Switches on InP for Optical Transmission Systems

Internet traffic is projected to reach 2 zettabytes per year by 2019. To meet this demand, new methods must be developed to scale existing network infrastructure in a cost-effective manner. One approach to improving network bandwidth is to increase the spectral efficiency of the existing bandwidth by using more complex modulation formats to encode the data onto the polarization and phase of a carrier wave. However, these formats require more complex transmitters and receivers which increase system cost and complexity. One solution to this problem is to monolithically integrate all of the components necessary onto a single die; by fabricating all of the functions at once, transmitter and receiver costs can be greatly reduced.

To this end, we present results on novel photonic integrated circuits (PICs) on an InP substrate for next generation optical communication systems. These include the world’s first monolithically integrated DP-QPSK receiver with a widely tunable local oscillator capable of 100 Gbps as well as the first 16×40 Gbps all-optical switch based on wavelength conversion which integrates 81 optical functions on a single die. By using a widely tunable local oscillator in the receiver, existing network bandwidth can be more flexibly allocated, reducing the need for redundant receiver arrays. By using wavelength conversion and a tunable SG-DBR laser in the optical switch, switching times can be greatly reduced compared to existing MEMs solutions. In addition to the system demonstrations, we will also detail several improvements made to the existing offset quantum well development platform to enable these devices, including development of multiple quantum well waveguide photodetectors with a 30 GHz 3-dB bandwidth without the use of a butt-joint regrowth and a novel waveguide dry etch which reduces the series resistance of the diodes by more than 5x. Through this work, we show that larger-scale photonic integration is not only possible, but inevitable for the continued growth of optical networks.

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ECE and Materials Professor John Bowers leads West Coast hub of the American Institute for Manufacturing of Photonics (AIM Photonics)

photo from video interview with bowers
“AIM Photonics and UC Santa Barbara are leading a revolution that is integrating photonics and electronics for the benefits of both,” said John Bowers, Professor of ECE and Materials at UCSB, Director of UCSB’s Institute for Energy Efficiency (IEE) and lead of the West Coast hub of AIM”

In a bid to boost photonics manufacturing and bring more skilled, high-tech jobs to the country, as well as push the boundaries of energy efficiency and performance in computing and telecommunications, the Obama administration announced today that it has selected the American Institute for Manufacturing of Photonics (AIM Photonics) to lead research and manufacturing of integrated photonic technology and create jobs in this important area. UC Santa Barbara is leading the West Coast division of this public-private partnership, in collaboration with the State University of New York — the lead university in this institute.

In the age of the Internet and Big Data, conventional electronic technology — even with the advent of Moore’s Law, which predicts the doubling of transistors and processing power approximately every two years — will become overwhelmed by the demand for speed, performance and data capacity.

The solution to that impending demand lies in photonics, the use of light to transmit massive amounts of data at extremely high speeds. But to make the shift between electronic wires and photonic waveguides, the two technologies must be brought together.

“AIM and UC Santa Barbara are leading a revolution that is integrating photonics and electronics for the benefits of both,” said John Bowers, professor of electrical and computer engineering and of materials at UCSB, director of the campus’s Institute for Energy Efficiency (IEE) and lead of the West Coast hub of AIM. Just as photonics has enabled the fiber optic communications which led to the Internet revolution, he said, the increased data capacity, speed and energy efficiency promised by photonics integrated circuits will result in enormous gains for everything from handheld devices to personal computing to data centers. “Our goal is to use complementary metal-oxide semiconductor processing to move photonics onto silicon and accelerate the integration of photonics and eliminate the data bottleneck that advanced silicon chips are facing during the next decade,” said Bowers.

The UCSB Current (full article)

AIM Photonics in the News:

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Scalable High-rate Nanoscale Printing for Sensors, Energy and Materials Applications

Considerable investment and progress have been made in nanotechnology, but integration of nanomaterials and processes into products have been considerably slow. Printing offers an excellent approach to making structures and devices using nanomaterials. However, current electronics and 3D printing using inkjet technology, used for printing low-end electronics are slow and provide only micro-scale resolution (20,000 nm or larger). The NSF Center for High-rate Nanomanufacturing (CHN) has developed a new nanoscale printing process that can use a variety of nanomaterials and can print onto a variety of substrates with nanoscale resolution match the present state of the art silicon electronics circuit line width. The process can print metals, insulators and semiconductors, organic and inorganic materials into nanoscale structures and circuits (down to 20 nanometers). The process utilizes Damascene templates with nanofeatures to direct the assembly of nanomaterials (down to 2 nm) into nanoscale patterns in a short time and over a large area. Last year, the center has developed and built a fully-automated robotic cluster tool system that prints at the nanoscale to make products that fully take advantage of the superior properties of nanomaterials. The fully-automated robotic Nanoscale Offset Printing System (NanoOPS) is expected to eliminate some of the high cost entry barriers to the fabrication of nanoscale devices for sensors, electronics, energy, medical, and functional materials applications.

The center has many applications where the technology has been demonstrated. The center has developed many sensors, among them a biosensor chip (0.02 mm) capable of detecting multiple biomarkers simultaneously (in vitro and in vivo) with a detection limit that’s 200 times lower than current technology. In addition, the center made a printed Band-Aid sensor that could read glucose, urea and lactate levels using sweat. An inexpensive micro chemical sensor with a low detection limit that’s less than 1 mm has also been developed. The center has also made an energy harvesting rectenna (for infrared energy) that could be many times more efficient that thermoelectrics and a CNT battery that can be fully charged in a few minutes, retain more 90% capacity and last for many years with high capacity. The center develops the fundamental science and engineering necessary to manufacture a wide array of applications ranging from electronics, energy, sensors and materials to biotechnology.

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2D Steep Transistor Technology: Overcoming Fundamental Barriers in Low-Power Electronics and Ultra-Sensitive Biosensors

photo of deblina sarkar
Aggressive technology scaling as per Moore’s law has resulted in exponential increase in power dissipation levels due to the degradation of device electrostatics as well as the fundamental thermionic limitation in the steepness of turn-on characteristics or subthreshold swing of conventional Field-Effect Transistors (FETs). This dissertation, explores novel two-dimensional (2D) materials (MoS2, WSe2 etc) for obtaining improved electrostatic control and Tunneling-Field-Effect-Transistors (TFETs), employing a fundamentally different carrier transport mechanism in the form band-to-band tunneling (BTBT) for overcoming the fundamental limitations of conventional FETs. This tailoring of both material and device technology can lead to transistors with super steep turn-ON characteristics, which is crucial for obtaining high energy-efficiency and ultra-scalability.

The present dissertation, also establishes, for the first time, that the material and device technology which have evolved, mainly with an aim of power reduction in digital electronics, can revolutionize a completely diverse field of bio/gas-sensor technology. The unique advantages of 2D semiconductors for electrical sensors is demonstrated and it is shown that they lead to femtomolar sensitivity, and also provide an attractive pathway for single molecular detectability- the holy grail for all biosensing research. Moreover, it is theoretically illustrated that steep turn-ON, obtained through novel technology such as BTBT, can result in unprecedented performance improvement compared to that of conventional electrical biosensors, with around 4 orders of magnitude higher sensitivity and 10x lower detection time.

With the aim towards building ultra-scaled low power electronics as well as highly efficient sensors, this dissertation achieves a significant milestone, furnishing the first experimental demonstration of TFETs based on 2D channel material to beat the fundamental limitation in subthreshold swing (SS). This device is the first ever TFET, in a planar architecture to achieve sub-thermionic SS over 4 decades of drain current, a necessary characteristic prescribed by the International Technology Roadmap for Semiconductors and in fact, the only TFET to date, to achieve so, in any architecture and in any material platform, at a low power-supply voltage of 0.1 V. It also represents the world’s thinnest channel sub-thermionic transistor, thus, cracking the long-standing issue of simultaneous dimensional and power supply scalability and hence, can lead to a paradigm shift in information technology as well as healthcare.

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