Mark J. W. Rodwell - US grants

This Presidential Young investigator award will be used to support a research program in high speed circuits and devices for picosecond and millimeter-wave functions. Electronic circuits and devices performing time-domain (pulsed and other transient signals, logic) are an order of magnitude poorer in performance (speed) than comparable circuits and devices in narrowband millimeter wave systems. This discrepancy arises from both technological reasons (the bandwidth-efficiency limitations in matching to lumped-element devices) and historical/economic factors (strong research funding and large markets for narrowband microwave technologies used in radar). There is now strong demand for pulse and time-domain circuits operating on the 1- 100 ps time scale, in high-speed logic, multi-gagahertz fiber-optic digital transmission, real-time high-capacity signal processing, and instrumentation. We will address these areas by concurrent development of novel circuit designs and the required high-speed semiconductor devices. In the first year of the program, we will start development of devices and circuits for multi-gagahertz fiber- optic transmission. The bandwidth of semiconductor laser, photodetectors, and optical fibers has exceeded the capacity of digital decision, retiming, and multiplexing/demultiplexing circuits. The required digital functions can be performed with diode switching and pulse generation circuits similar to those previously demonstrated for picosecond pulse generation and sampling. A target goal for the NSF program will be the first demonstration of working diode multiplexing circuits at the end of the first year. The PYI funding will then be used to support initial investigation and process development for fabrication of high-speed 3-terminal devices (heterojunction bipolar transistors or modulation-doped field-effect transistors) to be used in novel high speed fiber-optic and millimeter-wave receivers and high-speed instrumentation.

With this award from Instrumentation for Materials Research Program the University of California, Santa Barbara, will develop a Laser Driven Terahertz System which will provide new research instrumentation for high-resolution linear terahertz spectroscopy of materials, material structures, and devices. The instrument will deliver microwatts of tunable radiation up to ~1 terahertz (THz). Above ~1 terahertz the power will be substantially less but more than adequate for linear, high-resolution spectroscopy of materials and material structures. Up to 1 terahertz, with suitable methods of excitation and sampling, the system will also be used to test the performance of state-of-the-art electronics at frequencies that exceed the capability of existing network analyzers. At the same time, the system will provide a test bed to explore new non-linear materials and devices for optical difference frequency generation of terahertz radiation by photoconductivity and non-linear susceptibility. The research and development of this new instrument will provide interdisciplinary education and training for postdoctoral researcher and to graduate and undergraduate students in physics, materials science and solid state electronics.
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With this award from Instrumentation for Materials Research program the University of California Santa Barbara will develop a Laser Driven Terahertz System which will provide new research instrumentation for high-resolution linear terahertz spectroscopy of materials, material structures, and devices. The terahertz part of electromagnetic spectrum, from 100 GHz to 10 THz, is science rich but relatively technology poor. The Laser Driven Terahertz System will provide new research instrumentation for high-resolution linear terahertz spectroscopy of materials, material structures, and devices. The research and development of this new instrument will provide interdisciplinary education and training for the post-doctoral researcher committed to the project and to graduate student and undergraduate researchers who will use the instrument in physics, materials science and solid state electronics. The instrument will deliver microwatts of tunable radiation up to ~1 terahertz (THz). Above ~1 terahertz the power will be substantially less but more than adequate for linear, high-resolution spectroscopy of materials and material structures.

Large scale wireless sensor networks with tens of thousands of nodes have a host of potential applications, including homeland security, environmental monitoring and planetary exploration. However, conventional multihop wireless networks do not scale to such large numbers of nodes, and node localization is difficult for random deployment of ultra low-cost sensors. This research provides a proof-of-concept for Imaging Sensor Nets, which address the problems of scale and localization simultaneously, employing ideas analogous to GPS, RFID and CDMA. A "smart" collector node sends an RF beacon, which is electronically reflected and data-modulated by "dumb" sensors illuminated by the beacon. The collector employs baseband and radar/imaging algorithms to process these reflected signals in order to simultaneously estimate the locations and data of the sensors. Millimeter wave carrier frequencies are employed in order to enhance resolution for localization of sensor nodes. The research activities
include the challenging task of low-cost CMOS IC implementation of sensor hardware at millimeter wave frequencies (which are an order of magnitude higher than commercial RF communication systems), hardware brassboarding of the collector transceiver, design and software implementation of innovative baseband signal processing algorithms for timing acquisition and demodulation at the collector, and design and software implementation of imaging algorithms at the collector. In addition to the dissemination of results via the standard avenues of publications and the Internet, both indoor and outdoor demos of the technology will be widely publicized to industry and funding agencies in order to establish a clear path to technology transfer.

The atomic force microscope acquired under this grant will be used by the national scientific research community from a wide range of disciplines. NNIN's technical staff will develop reliable protocols, training procedures, and extend the capabilities of the instrument by interacting with users and incorporating these new capabilities into user research projects. Potential results include the development of new reproducible techniques for nanoscale integration and characterization, the creation of complex three-dimensional heterogenous systems, and an enhanced understanding of molecular and biological phenomena.

Through its large research user population, the utilization of this technology will have wide geographic coverage involving researchers from academia, small and large companies and federal research laboratories. NNIN's educational efforts-including specific REU -focused projects using these instruments, the training of over 1000 new students every year, freely accessible web-based resources, and nanotechnology-focused workshops-will focus on outreach to the student and scientific community at large.

ECS-0636594
Chik Yue, Carnegie Mellon University
ECS-0636621
Upamanyu Madhow, University of Santa Barbara

Our objective is to develop the system architecture, signal processing algorithms and integrated circuit techniques for a robust, quick set-up, point-to-point wireless link which achieves speeds of 10-40 Gbps over a range of several kilometers, using millimeter (mm) wave spectrum. Since these speeds are comparable to those of optical fiber, the outcome of this project enables a fail-safe hybrid communication backbone infrastructure, which can be deployed or restored rapidly in the events of disaster and emergency. The system employs a novel hierarchical architecture which meshes beamforming (to provide link margins sufficient to overcome the limitations of mm-wave propagation in harsh weather) and spatial multiplexing (to provide large spectral efficiency, of the order of tens of bits per second per Hertz, required to realize optical link speeds using channel bandwidths of only several GHz). Beamforming gains are obtained by electronically steerable monolithic arrays. Each such array is a subarray in a larger array, forming a spatially multiplexed virtual multiple-input, multiple-output (MIMO) system: the transmit subarrays send separate data streams, which are separated out at the receiver using spatial interference suppression techniques. Key elements of this mm-wave MIMO system are CMOS IC design for monolithic steerable sub-arrays, signal processing/hardware co-design to obtain algorithms implementable at such high speeds, and hybrid analog/digital processing to enable low-power operation. Substantial effort will go into establishing a cell-based, reusable design/modeling framework to enable CMOS mm-wave VLSI design. The new findings will be incorporated into undergraduate and graduate classes through small design projects.

Intellectual Merit: This is an inherently interdisciplinary project whose success depends critically on intense interaction between the three PI's on this project, whose combined expertise spans CMOS IC design for communication applications (Yue), millimeter wave device and IC design (Rodwell) and signal processing for communication (Madhow). The proposed system is based on innovations at every level, including system concept, signal processing algorithms, and circuit design and packaging. Millimeter-wave MIMO provides spatial multiplexing in line of sight environments, and is therefore a completely new concept relative to MIMO at lower frequencies, which provides spatial multiplexing only in rich scattering environments. The electronically steerable sub-arrays are based on a unique row-column architecture amenable to monolithic realization. The innovation in the signal processing consists of drastic simplifications, including a hierarchical decomposition co-designed with the hardware. Circuit design at mm-wave frequencies push the limits of mixed signal design in low-cost CMOS processes, and our cell-based design framework has the potential of providing a systematic approach to such design. The baseband processing employs novel hybrid analog/digital processing techniques, in order to minimize the performance requirements on high-speed, high-cost, high-power analog-to-digital converters.

Broader Impact: Millimeter-wave MIMO provides the first feasible approach to bridging the capacity gap between wireless and optical systems, which has applications ranging from homeland security (e.g., disaster recovery) to last mile connectivity for enterprise and residential settings. An additional breakthrough is in terms of the ease of deployment of LOS outdoor links, which becomes a simple operation of roughly pointing the transmitter and receiver at each other, rather than precisely aligning the transmit and receive antennas as done in current practice. In addition, the breakthroughs in mm-wave CMOS circuit design and packaging required by this demanding application have the potential for impact well beyond the specific system considered here, and will open up a host of opportunities for harnessing mm-wave spectrum at reasonable cost. The PIs all have strong records of technology transfer, and intend to leverage their strong contacts with the communications industry to push for technology transfer by widely disseminating the results of this work not only through publications, but also using hardware demonstrations easily accessible to visitors. The proposed research will have a significant impact on the undergraduate and graduate curriculum at the PIs' institutions in terms of driving innovations and updates in a number of courses in circuit design and communication systems. Well-established outreach mechanisms in the nanotech area will be used to involve women and minorities, including high school students, in this effort. Due to the inherently interdisciplinary nature of this project, the students involved will receive a broad education cutting across several areas of Electrical and Computer Engineering.

This award provides funding for a three year standard award to support a Research Experiences for Teachers (RET) Site program at Georgia Institute of Technology, entitled, "RET Site: National Nanotechnology Infrastructure Network (NNIN) RET Program," under the direction of Dr. Nancy Healy. The objectives of this program are to assist a total of 45 in service and pre service science teachers in understanding and communicating the importance of using inquiry-based methods to solve problems by doing research in nanotechnology; establish a long-term mentorship support group of teachers who will become advocates for nanotechnology education and careers; nurture a mentorship community between professors, graduate student mentors, and science teachers in high-need school districts; and build a library of classroom modules, quicklabs, and activities for the classroom.

Technical Abstract

The University of California Santa Barbara will acquire a new molecular beam epitaxy (MBE) system for the growth of high-performance oxide thin films. Numerous research programs at UCSB require the growth of insulating or semiconducting oxide thin films. These include tunable dielectrics for microwave devices, oxide thin films for optoelectronics and sensing, gate dielectrics for the development of CMOS devices employing high-mobility semiconductor channels and for high-electron mobility transistors with reduced gate leakage and high charge densities. These applications require the deposition of structurally perfect oxide thin films with low impurity and point defect concentrations, control over interface atomic structures and compatibility with underlying active device layers. Oxide thin films grown by MBE will allow for the understanding of the basic physics and materials science of oxides that currently lags far behind that of other electronic materials. Experimental testing and realization of the theoretical predictions requires high-quality, pure materials and the atomic layer control afforded by MBE. We anticipate that the high-purity, structurally perfect oxide films synthesized by MBE will lead to new scientific insights that generate new device applications. Graduate students and post-doctoral researchers are the primary 'hands-on' users of MBE at UCSB. The proposed MBE system will be operated as a shared facility, impacting the education and training of a large number of students in a wide range of interdisciplinary research activities at UCSB and collaborating academic institutions - we will build on the strong culture for MBE of compound semiconductors at UCSB and house the tool in the same large shared facility. Formal training in MBE is offered in graduate courses and weekly MBE seminars in the Materials Department while hands-on-training is provided by two development engineers. The oxide MBE system will significantly extend the opportunities that have previously been offered to student and teacher research interns and education programs aimed at underrepresented groups.


Lay Abstract

Molecular beam epitaxy is unique among the techniques used for making new electronic materials that enable modern electronic and optical devices, such as transistors and lasers. The performance of these devices depends largely on the degree of materials perfection. In molecular beam epitaxy, layers that are a few atoms thick can be stacked and materials with different electronic properties can be combined. Molecular beam epitaxy allows for unprecedented purity of these layers - the impurity levels can be as low as a few ten parts per billion. The new molecular beam epitaxy system at the University of California Santa Barbara will be utilize these unique capabilities to develop new classes of electronic thin film materials, based on metal oxides. We anticipate that the high-purity, structurally perfect oxide films synthesized by molecular beam epitaxy will lead to new technologies, such as transistors with higher operating speeds and capacitors that enable new wireless communication devices. The oxide molecular beam epitaxy system will contribute greatly to the education and training of students at the University of California Santa Barbara, who will be the primary hands-on-users of the new system. The oxide MBE system will also significantly extend the opportunities that have previously been offered to student and science teacher interns and education programs aimed at underrepresented groups.

MRI Proposal: 0722812

The objective of this proposal is to advance nanotechnology research by providing state-of-the-art resources to the national user community in an open environment and technically supported by knowledgeable staff for hands-on use. This award provides for four new nanotechnology capabilities to be located at four of the NNIN facilities and available to all users across the nation: 1) for advanced materials deposition and novel device fabrication, a Carbon Nanotube Growth System (Cornell), 2) for processing of germanium semiconductors, an Automated Chemical Processor (Stanford), 3) for materials and biological systems characterization, a Mass Spectrometer (GaTech), 4) for processing of novel magnetic, optical and electronic devices, a multi-target reactive sputtering system (UCSB).

Intellectual Merit: These instruments will enable scientific research across nanotechnology by providing reproducible materials techniques for carbon nanotube, germanium and magnetic/optical/electronic structures; and for characterization of biological systems. NNIN's technical staff will extend the capabilities of these instruments by interacting with users and incorporating these new capabilities into user research projects. This interaction will foster strong inter-disciplinary and innovative uses across the breadth of nanotechnology.

Broader Impact: Through NNIN's large research user population, this technology will have wide geographic reach involving researchers from academia, small and large companies and federal research laboratories. NNIN's educational efforts?specific undergraduate research projects using these instruments, the training of over 1300 new students every year, freely accessible web-based resources, and nanotechnology-focused workshops?will focus on outreach to the student and scientific community at large.

The large amount of unlicensed and semi-unlicensed bandwidth available for millimeter (mm) wave communication enable multi-Gigabit wireless networking that can potentially transform the telecommunications landscape.

Intellectual Merit: This research investigates the use of the unlicensed 60 GHz ``oxygen absorption'' band for providing a quickly deployable broadband infrastructure based on multi-Gigabit outdoor mesh networking. Millimeter wave links are inherently directional: the directionality is required to overcome the increased path loss at higher frequencies, and is feasible for nodes with compact form factors using antenna arrays realized as patterns of metal on circuit board. This project addresses the cross-layer design of mesh networks with such highly directional links, in which implicit coordination using carrier sense mechanisms cannot be relied on, and there is no omni-directional mode for explicit coordination. In addition, the research will investigate new design principles for directional medium access control, with the challenge being to coordinate nodes despite the deafness induced by directionality, while taking advantage of the drastically reduced spatial interference. The project will also study methods for network discovery and topology updates, the interactions between scheduling and routing; and the impact of oxygen absorption on network capacity and protocol design/performance.

Broader Impact: The principal investigators will develop publicly available mm wave network simulation tool, intended to engage a larger research community in this emerging field. The investigators will also explore other mechanisms for broader impact including technology transfer, undergraduate research, and curriculum updates featuring mm wave communication.

Objective:
An entirely new type of semiconductor laser modulation process will be explored in this industry-university collaborative project. A novel Field-Induced Charge Separation Laser (FICSL) structure will provide direct modulation of the gain to enable much higher modulation speeds relative to conventional diode lasers in which current modulation is employed. Preliminary modeling suggests modulation speeds in the 100 GHz range. Collaborations with Ziva Corp., our GOALI partner, will help guide these activities.

Intellectual Merit:
The FICSL involves new physics, that of separating holes and electrons with an applied field via a gate structure placed above the active gain region in order to directly modulate the gain. An enhanced understanding of laser dynamics in multi-terminal configurations should result. The team brings high levels of expertise in MBE growth (Palmstrøm), high-speed transistors (Rodwell) and efficient, high-speed vertical-cavity lasers (Coldren) to uniquely address this new problem area. The UCSB labs in MBE growth, III-V nanofabrication, and materials and device characterization, are second to none for the VCSEL-like laser studies to be doneS. Complementary skills exist at Ziva.

Broader impact:
Such more-efficient, higher-speed devices may revolutionize optical interconnect approaches and enable more efficient computers and data centers. Interaction with Ziva greatly benefits the students involved. New processes developed within NSF-NNIN facility, will be available to future generations of students. Physics will be integrated into the ECE227 series, and it will be disseminated in journal and conference publications. The co-PIs and graduate students will continue to participate in one or more of the ten internship programs for under-represented minorities, high school, and undergrad students that are sponsored by NSF-MRL, NNIN, & COE.

Intellectual merit: This project is awarded under the Nanoelectronics for 2020 and Beyond competition, with support by multiple Directorates and Divisions at the National Science Foundation as well as by the Nanoelectronics Research Initiative of the Semiconductor Research Corporation. Progress in transistor and integrated circuit (IC) scaling has slowed, in part because of physical limits of transistor operation at small dimensions, but primarily because power consumption and power density are becoming excessive as complexity and density are further increased. IC power density results from opposing constraints in transistor and circuit design; the electron thermal distribution sets a minimum transistor control voltage for low off-state dissipation, while the dissipated energy on interconnects increases as the square of voltage. Addressing these limitations, radical changes in transistor design are proposed. To increase the on-current, designs are proposed that will overcome the so-called density of states (DOS) bottleneck in III-V semiconductors, adding additional valleys to those used in transport, therefore increasing the amount of charge that can be transported through the device at a high velocity. To increase drive current in N-channel field effect transistors (FETs) and the IC speed at reduced voltages III-V transistors will be develop using for the first time transport in the L (satellite) valleys, i.e. L-valley electronics. These will use the light electron part of their dispersion in the transport direction for fast carriers and will use the heavy electron characteristics to pack multiple bands into the ?same? energy space. Similar density of states engineering will be applied to P-channel FETs, achieved using light- and heavy-hole states mixed by strain and quantum confinement. To reduce supply voltages, steep transistors will be developed, having I-V characteristics varying much more rapidly than a thermal distribution. In addition to established tunnel injection devices having only moderate on-current, high-current steep-FETs will be developed. These use transport in energy bands of tightly constrained energy range, produced using 1-D semiconductor superlattices. Combining these two classes transisto rs, state-density-engineered transistors designed for high drive currents at low voltage, and steep transistors designed for very low off-state leakage, the program will explore new logic gate designs providing low power and high speed.

Broader Impacts: The proposed work seeks to increase the speed and complexity, and reduce the power consumption of ICs. The industry is of enormous worldwide value. The participants interact regularly with the VLSI industry, communicating ongoing work and seeking guidance, and will continue with this model in the NSF program. Development of high-speed yet low-power logic devices will circumvent present power-consumption limits now constraining VLSI speed and complexity. This program will enable further large increases in the speed and power-limited computational performance of ICs, benefiting applications in industry, commerce, and personal use. Ph.D. students will be trained in semiconductor materials, device physics, and IC design. Their training will emphasize the interaction of system and circuit design with device design. Simulation tools will be developed and distributed by nanoHub to a worldwide user community. The program will operate a summer internship program, affiliated with that of the NNIN, providing laboratory experience exposure to a research environment for 8 undergraduate students.

The goal of this Nanotechnology Undergraduate Education (NUE) in Engineering program at the University of California-Santa Barbara (UCSB) entitled "NUE: Using Peer-to-Peer Support to build NEMS and Consider SEE Implications of Nanotechnology", under the direction of Dr. Sumita Pennathur, is to prepare a new generation of well-rounded and educated engineers who are skilled in using cutting-edge nanofabrication tools and processes to build nanoscale systems (such as NEMS) and nanoscale devices. To do this a set of three new courses and a modification to an existing course will be developed. Two of the courses will increase a UCSB undergraduate's ability to build nanoscale devices and systems (NEMS), and the third, a new course will focus on their communication skills. Also proposed to be implemented is a high school education program that pairs high school students with undergraduate mentors who are enrolled in the NEMS class to enhance the communication skills of UCSB engineers.

The UCSB program will accelerate advances in nanotechnology via educational pathways across a broad range of sciences. Intensive, hands-on training in nanofabrication techniques building NEMS and through research experiences will prepare engineers for this exciting field.

Title: Integrated Synthesized Optical Sources


The successful pursuit of this research could lead to the first widely-tunable, integrated synthesized optical sources, which would be much more stable, and have smaller size, weight and power requirements than components currently available. The combination of photonic and electronic integration will produce a chip-scale tunable sources that do not require accurate temperature control or high input power to operate. The project's GOALI partner, Freedom Photonics LLC., intends to commercialize some version of the proposed device that may impact the optical components marketplace. The new technology will be developed within the NSF-NNIN facility and the new fabrication processes will be made to students and outside users. The PIs have a strong commitment to involving high school, and undergraduate students in research activities, including summer internships, and students of under-represented groups in STEM learning programs.

The proposed research aims to develop a highly-integrated widely-tunable optical frequency synthesizer (OFS) with sub-Hz-level accuracy. The integrated OFS is based on a monolithic, 4-section, widely-tunable laser offset-locked to any one of the lines of a frequency comb. By employing a combination of photonic and electronic integration, sub-Hz-level accuracy can be obtained with an integrated optical phase-locked loop (OPLL) technology. All of the photonics, except for the external reference laser, the photodiodes, and the comb generator, will be integrated on a single InP photonic IC . The tunable laser's output can be tuned across the entire comb by tuning the laser between the comb lines with the RF offset source, and alternately selecting different comb lines. With this approach sub-Hz-level relative frequency accuracy, as well as sub-kHz linewidth, should be possible. If successful, the proposed work would have a transformative impact on the design of optical systems for a series of new optical technologies.

Wireless communication technologies such as cellular and WiFi are indispensable for modern society. However, existing wireless networks are under severe stress due to the explosive demand caused by smart mobile devices capable of creating and consuming large amounts of multimedia content (especially images and video). Meeting these demands is estimated to require 1000-fold increases in wireless network capacity, which cannot be obtained by incremental advances using existing spectrum. A promising approach for delivering the required revolutionary advances in wireless by employ the so-called 'millimeter (mm) wave' band, which has huge amounts of available spectrum (e.g., 7 GHz in the unlicensed 60 GHz band alone). The wavelength in these bands is an order of magnitude smaller than that in today's wireless networks, drastically changing the physical and propagation characteristics: for example, mm waves are easily blocked by obstacles such as human bodies, but steerable antenna arrays with a very large number of elements (up to 1000) can fit in compact form factors, enabling us to potentially steer around obstacles using bounces from reflectors. As a consequence, realizing the potential for mm wave communication requires a comprehensive reexamination of existing wireless design principles, using an interdisciplinary approach that goes all the way from antenna design to network protocols. The goal of this project is to take such an approach for establishing fundamental principles for design of next generation mm wave communication networks, with a research agenda combining cross-layer modeling, design, and performance evaluation, firmly grounded in experiment. A key technical issue is to how to efficiently adapt electronically steerable arrays with a large number of elements, and to integrate them into network protocols.

The research is driven by the following cutting edge system concepts: (a) Cellular 1000X, aimed at relieving the cellular capacity bottleneck via 60 GHz cellular links delivering Gbps data rates to the mobile, together with a seamless extension to indoor networks; (b) 'Wireless fiber' backhaul at 140 GHz for enabling Cellular 1000X, based on easy to deploy outdoor wireless mesh networks with link speeds approaching 40-100 Gbps; (c) 40 Gbps indoor 60 GHz links, aimed at going beyond nascent industry efforts such as NG60 that aim to upgrade link speeds in the recently developed IEEE 802.11ad wireless local area network standard. The goal of this project is to design a system that will achieve the stated objectives, and prototype an advanced proof-of-concept that will help pave the way for eventual technology transfer leveraging the close ties of the project team to industry. A 60 GHz experimental platform developed to support the research will be made available to the research community, to stimulate a broader academic effort in this area.

Due to the small carrier wavelengths, beamforming at both ends is critical to make the link budget work, but it is essential to make the beams electronically steerable to steer around obstacles (which ``look bigger at smaller wavelengths''), and to allow automatic network configuration. Cross-layer frameworks for resilient pencil beam networking for both Cellular 1000X and indoor WLANs will be developed and demonstrated. These will incorporate compressive array adaptation techniques, a core innovation to be demonstrated in this project. Compressive adaptation enables 3D beamforming for robust link budgets, steering around blockage, and spatial reuse, and enables scaling of both the number of antenna elements and the nodes in the network, unlike existing scan-based IEEE 802.11ad medium access control (MAC) techniques. System concepts to be designed and tested include (a) `Picocloud' network architectures that employ tight coordination between base stations and APs (for outdoor and indoor environments, respectively) to provide seamless connectivity in the face of blockage; (b) Integration of beamforming with spatial multiplexing in LoS or near-LoS environments, demonstrating the scaling of available degrees of freedom with carrier frequency through prototypes at 60 GHz and 140 GHz.

A reconfigurable phased array at 60 GHz will be developed and integrated with the NSF/CRI-funded WiMi software defined radio platform, in order to enable the preceding system-level explorations (while beamsteering ICs developed by industry have been incorporated into products, external control of the beamsteering coefficients is not available). In addition, a hardware testbed for LoS spatial multiplexing at 140 GHz will be developed to demonstrate the potential for 'wireless fiber' backhaul links beyond 100 GHz.

Transistors are the key element in modern integrated circuits (ICs). Since a typical circuit has billions of transistors, heat generated during transistor operation limits how fast the chip can operate and how many transistors it can contain. Industry is seeking a transistor design with the lowest possible power-supply voltage and the smallest amount of leakage current when it is off. To switch quickly, it must provide large currents when it is on. The ratio of off-current to on current is determined by a factor called the sub-threshold swing (SS); in a normal transistor the SS is limited to 0.06 Volts per decade, i.e. each factor of 10:1 in the on-off ratio requires 0.06 Volts power supply voltage, and a typical 10 to the eighth on/off ratio requires 8*0.06V, or about 0.5 Volts. Tunnel transistors have been proposed to reduce the SS, but these have small on-currents because the probability of an electron tunneling, hence contributing to current, is very small. An electron which does not tunnel through the transistor is instead reflected. Exploiting the wave nature of electrons, we will suppress the reflection by using additional reflectors, in a structure much like the coatings which suppress the reflection from light from the surface of a camera lens. If the electron is not reflected, it instead passes through the transistor, and the on-current is increased. We will also develop another low-SS transistor, a superlattice transistor, which exploits electron wave properties to block transmission when the transistor is off but not when it is on. Success in the project would allow a ~5:1 reduction in IC power consumption, leading to faster, bigger, and more useful chips benefitting computers. This is a key broader impact. An intellectual broader impact is the use of fundamental physics, electron quantum interference in a device of vast public application. REU and summer internships are another broader impact.

The project seeks to replace the modern transistor in VLSI, a vast industry, with a new device, operating at lower voltage, for low switching power, yet giving low off-state current, for low standby power, and high on current, for high speed. One proposed transistor is a tunnel-FET, which has low operating voltage but low on-current, with added electron wave reflectors which cause destructive interference of the reflected electron wave. This suppresses electron reflection, hence increases transmission, hence on-current. The second transistor uses a superlattice in the electron source to suppress hot electrons, thereby producing on:off characteristics sharper than a Boltzmann distribution. This allows large on:off ration at low voltages. We will model (simulate) design, build and test these transistors. Modelling will use quantum transport simulators (NEMO) with the addition of scattering. Fabrication requires standard FET fabrication processes (well established at UCSB), but adds electron energy filters formed either during MBE channel growth or during MOCVD regrowth of the transistors. The intellectual significance is clear: coherent electron effects as the basis of a mass-market electron device.

Microprocessors containing billions of transistor switches are at the heart of PCs, cell phones, computer servers answering our internet searches, and supercomputers modeling the weather and designing new drugs and aircraft. Modern machinery is controlled by microprocessors; a typical car uses 50. After 50 years of rapid improvement, since 2000 progress has stalled, primarily because the transistors consume too much energy when they switch. As transistors are made smaller, more fit on a chip, and the energy consumed increases. The battery is drained quickly and chip becomes hot. Slowing the switching reduces heating, but then the software runs slowly. In this program, a new transistor design will be investigated. If successful, these transistors will consume 100 times less switching energy, allowing faster, more powerful chips.

The challenge is the power supply voltage; reducing the voltage by 2:1 reduces the switching energy 4:1. Between ~1990-2005, voltages were reduced from 5 to 1 Volt. Unfortunately, with normal (MOS) transistor switches, below ~0.7 Volts the transistor's switching becomes imperfect, with the transistor not turning completely off. This finite off-state leakage current increases energy consumption, hence it has not been possible to supplies much below 0.7 Volts. Ten years ago, tunnel transistors were proposed, as these can turn off nearly completely even at supplies as low as 0.3 Volts. Unfortunately, tunnel transistors do not turn on well, and microprocessors using them will therefore operate slowly. This limitation becomes much worse if the supply is dropped to 0.1 Volts. This program will research a new design, the triple-heterojunction tunnel transistor. This has added semiconductor junction layers which increased the on-current by as much as 100:1. If successful, rapidly-switching microprocessors will be feasible with even a 0.07V supply, and would consume as little as 1% of the energy of today's technology.

Advances in low-cost low-power silicon radio frequency (RF) integrated circuits (ICs) in the last two decades have opened up the commercial applications for millimeter wave (mmWave) frequencies which are an order of magnitude beyond those used in WiFi and cellular today. Large-scale deployment of mmWave communication networks, such as NextG cellular infrastructure outdoors and NextG WiFi infrastructure indoors, implies that these resources can be leveraged for RF imaging at scales that are not otherwise possible. The project develops foundational algorithms, architectures and protocols for such Joint Communication and Imaging (JCAI) systems. Each sensor in such a system provides 4D measurements (range, Doppler, azimuth angle and elevation angle) whose resolution improves by going to higher frequencies. The project establishes US leadership in a critical technology by developing large-scale RF imaging using frequencies beyond 100 GHz. Outdoor applications include pedestrian and vehicular tracking for global situational awareness supporting vehicular autonomy, and addressing security challenges such as timely detection of illegal drones or unauthorized personnel. In indoor settings, the technology enables fine-grained inference/prediction of human actions for eldercare and smart home applications. RF imaging technologies are especially useful in low-light or high-smoke/fog conditions when visible light or infrared technologies are not effective.<br/><br/>The project develops and demonstrates a framework for JCAI at mmWave frequencies. A core aspect of the technical plan is to drastically improve resolution by synthesizing large apertures (Thrust 1). This employs a combination of novel approaches to single sensor design which utilize large antenna arrays developed for communication, and networked collaboration between multiple sensors. A complementary aspect (Thrust 2) is the strategic utilization of unmanned vehicles to image difficult-to-reach areas, utilizing the fixed infrastructure to reduce the robot payload. In Thrust 3, hardware at 140 GHz previously developed by the PIs for communication will be adapted to support demonstration of networked RF imaging at 100+ GHz. Thrust 4 develops a control plane for networked imaging, including a resource management framework based on imaging demand and imaging capacity, and protocols supporting collaborative imaging. The concepts and methods to be developed have potential impact in a vast array of applications, including vehicular autonomy and road safety, manufacturing automation, indoor and outdoor security, eldercare, and healthcare. The PIs will work closely with industry partners, building on their strong track record in transitioning mmWave research, and plan to incorporate this research into the undergraduate curriculum through courses, capstone projects, and REU projects.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.