Alexander Zaslavsky, Ph.D. - US grants

9503708 Zaslavsky The addition of this processing extension equipment will enable new research in nansostructure fabrication by regrowth and in the transport, optical properties, and device physics of novel nanostructures. This processing extension will permit regrowth of modulation-doping, contacting and isolating layers on patterned heterostructures prepared with in-situ etched and clearned regrowth surfaces. The processing extension will have the following capabilities: low-damage electron-cyclotron resonance (ECR) plasma reactive ion etching of III-V semiconductors; ECR hydrogen plasma cleaning of etched substrates; surface cleanliness monitoring by Auger spectroscopy; and invacuum transfer of patterned substrates into the MBE growth chamber. The properties of strained and unstained uniform quantum wires fabricated by etching through quantum wells and regrowth with modulation-doping layers on the sidewalls will be studied. A heavily-doped gate electrode layer in the regrowth sequence will permit carrier density modulation in these wires independent of the confining potentials determined by the original heterostructure. Analogously, by pregrowing the appropriate barrier potentials, gated 2-dimensional tunneling structures and superlattices in III-V heterostructures will be fabricated and their transport and optical properties will be investigated down to the quantum dot limit. % This equipment will be used by a group of investigators having complimentary expertise ranging from semiconductor epitaxial growth to nanofabrication and fro transport and optical characterization to device physics and engineering. It represents fundamental materials research important for understanding processing of semiconductor materials, and is ultimately relevant for manufacturing.

9503701 Xiao A packaged commercial dilution refrigerator will be acquired and its usage will be divided among four research projects requiring experiments at millikelvin temperatures. One project studies quantum phase- coherent transport in normal-superconducting metal mesoscopic structures. The new quantum transport phenomenom reveals itself in the low temperature range. A second project investigates semiconductor devices exhibiting quantum transport effects such as resonant tunneling, ballistic transport over macroscopic distances, and Coulomb blockade. Low temperature transport measurements will be performed on semiconductor nanostructures of adjustable dimensionality and lateral extent. A third project will use the dilution refrigerator to test ultra-sensitive millimeter-wave detectors developed to study the background radiation of the universe. To achieve the required sensitivity, these detectors have to be operated at millikelvin temperatures. The fourth project studies phonon propagation in layered compounds and the effects of disorder on the scattering of phonons in crystalline solids at very low temperatures. %%% The acquisition of a single instrument for experiments impacting a wide range of fields is very cost effective. Quantum transport phenomena play an important role in small structures that are the result of the ever- decreasing dimensions of microelectronic devices. ***

9702725 Zaslavsky Technical CAREER Abstract The focus of the proposed research is the effect of strain on electronic properties of semiconductor nanostructures. Strain-induced effects in 1D wires and 0D dots are relatively unexplored, because the strain is strongly inhomogeneous and lacks the in-plane symmetry of the much studied 2D heterostructures. We will study two distinct classes of structures: silicon-germanium (SiGe) wires and dots, and strained III-V wires and rings fabricated by regrowth. The SiGe research will build on our recent measurements of strain relaxation and strain-induced quantization in submicron SiGe Quantum dots. The III-V structures will be fabricated by modulation-doping regrowth of in-situ patterned surfaces etched in strained heterostructures in a chamber attached directly to an MBE system. This research is relevant not only to strained nanostructure physics, but also to a number of proposed nanodevices that incorporate strained regions. In addition to graduate student training, this research will provide an ample number of semester and year-long projects for students interested in laboratory experience. %%% Nontechnical CAREER Abstract: As technology advances, semiconductor devices that underpin modern computers and lasers are becoming ever smaller. These ultrasmall structures are affected in complex ways by the mechanical strains that arise during their manufacture. We will experimentally investigate strain effects in two types of semiconductors: silicon, which is used for most electronic circuits, and gallium arsenide, which is crucial for applications that require very high speed operation or optical signals. In shedding light on strain in ultrasmall structures and gauging the promise of novel devices, this research will couple to the education of graduate and undergraduate students in semiconductor physics and technology at Brown. The education plan includes an update of semiconductor device courses and the revamping of a semester-long transistor fabrication laboratory, upon completing which students will have the background to take on semester and year-long supervised projects on sub- sections of the proposed research. ***

This proposal combines an experimental program intended to fabricate proof-of-concept solid-state THz sources and evaluate their technological promise (in terms of real-world benchmarks, such as power output over the attainable freqcuency range). together with a theoretical effort intended to clarity the high-frequency generation mechanisms and guide the experimental work among different device geometries. This proposal will complete the envisioned program fully with regard to fabricating and characterizing proof-or-concept devices and developing the theoretical framework.

This proposal was received in response to the Spin Electronics for the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on spin dependent transport and spintronics functionality in a unique nanostructured system - Y-junction Carbon Nanotubes.
The Y-junction nanotubes, first fabricated by one of the PIs (JMX)-combine the attractive properties of carbon nanotubes (effectively 1D electronic transport with long ballistic mean free paths and exceptionally high current densities)with a three-terminal geometry and a built-in heterojunction barrier at the Y-branching point. Spin transport in ordinary, straight ferromagnetically contacted multi-walled carbon nanotubes, first studied by another of the PIs, has yielded excellent spin-polarized injection efficiencies and long spin-scattering lengths on the order of 0.25 um, making ferromagnet-nanotube hybrids a promising spintronics platform. The spin transport in a Y-junction with the built-in heterobarrier is already interesting and unexplored. But what makes the proposed devices unique is the possibility applying both ferromagnetic and normal metal contacts to the three terminals of the Y-junction, as well as using different ferromagnetic materials (with separately switchable magnetizations)for contacts to the same device. This unprecedented flexibility will enable us, for example, to clearly distinguish spin-mediated injection and extraction of currents from ordinary injection, tune the transmission of spin up and spin down electrons by means of a control voltage on the third terminal, witch the spin-coherent current from one Y-junction arm to another by switching the magnetization with an external field, and more generally produce a true three-terminal spintronic transistor.
However great the potential of this new nanostructured system may be, a great amount of challenging work, from fabrication of the Y-junction nanotubes to fabrication of nano-scale contacts to cryogenic measurements of the contacted Y-junctions in the presence of magnetic fields externally modulated, will have to done first to prove the concepts. This NSF project is launched for these proof-of-concept explorations, and for paving the pathway to this new and exciting field of opportunities.

This Condensed Matter Physics project deals with nanoscale quantum conductors that have a circular, i. e., "ring" geometry. Ideal quantum rings have a number of fascinating properties: Ground-state persistent currents, strong Aharonov-Bohm interference effects, and an oscillatory dependence of the wavefunctions and all thermodynamic quantities on the enclosed magnetic flux, with period given by the flux quantum. This research will focus on the properties of individual and multiply-connected quantum rings in the few-electron and Coulomb blockade regime. The PI has recently discovered that inhomogeneous strain relaxation in sufficiently small Si/SiGe quantum dots leads to ring-like confinement. Additionally, tunneling measurements have confirmed the expected flux quantum periodicity. Given the control over device geometry, elliptical rings and coupled ring structures will be fabricated and few-carrier energy spectra, spin interactions, and Coulomb blockade effects will be measured as these rings are filled by carriers from zero carrier occupancy. The work will be coupled to state-of-the-art finite-element solid mechanics simulations. Experiment data will provide feedback on the interplay between electronic and mechanical properties in nanostructures. Graduate students involved in this research will acquire a full complement of skills, from deep-submicron fabrication, to low-temperature, low-signal measurements, to numerical simulation, which will prepare them for employment in academia, the semiconductor industry, or government. A teaching plan focusing on improved undergraduate teaching of core courses in the Electrical Engineering program is an integral part of this project.

Ideal quantum rings, in which carriers follow circular orbits without scattering, have fascinating properties: Currents that flow without resistance, phase-interference effects, and the oscillatory dependence of carrier energies and wavefunctions on the enclosed magnetic flux. Quantum rings have also been suggested as possible building blocks for quantum computation. This research will focus on the properties of individual and multiply-connected quantum rings in the few-electron and Coulomb blockade regime, where the one carrier circling the ring affects the probability of another tunneling into the ring. The rings in question arise from the strain relaxation at the sidewalls of etched structures, making it possible to control the geometry (circular or elliptical) and the topology (single-ring or multiply-connected ring) of the system. Tunneling current measurements will study the carrier and spin interactions as these rings are filled by carriers from zero; the results will be compared to state-of-the-art finite-element strain simulations and our data will provide experimental feedback on the interplay between electronic and mechanical properties of nanostructures. Graduate students involved in this research will acquire a full complement of skills, preparing them for research jobs in academia, the semiconductor industry, or government. A teaching plan focusing on improved undergraduate teaching of core courses in the Electrical Engineering program is an integral part of the project.

PROPOSAL NO: 0403958
INSTITUTION: Brown University
PRINCIPAL INVESTIGATOR: Zaslavsky , Alexander
TITLE: NER: Exploring Nanodevices for Probabilistic Computing Architectures

Abstract:
The progress of modern transistor-based digital technology has depended on shrinking silicon transistor to ever smaller sizes and integrating more of these transistors into logic circuits. At some point in the next decade, however, transistors will reach their ultimate physical size and circuits will contain so many transistors that some nonworking devices are inevitable. As a result, we may need both new types of devices to replace silicon transistors or new types of logic architectures that can tolerate some number of defective devices in a circuit, or both.

The proposed exploratory research targets both of these issues. We propose to map our previously developed probabilistic computer architectures onto real experimental devices, that will be fabricated from carbon nanotube material. Conversely, the nonlinear characteristics of the nanotube device prototypes will provide the experimental inputs to designing more advanced fault-tolerant logic circuits.

NIRT: Fault-tolerant, Probabilistic Computing with Markov Random Field Architectures and CMOS Nanodevices

Abstract



The project examines probabilistic design methodologies for computer architectures based on Markov random fields (MRF). The MRF approach can model arbitrary digital circuits with logic operation arising from the interaction of neighboring circuit nodes. The computation proceeds via probabilistic propagation of states through the circuit, with inputs and outputs treated on an equal footing. This approach may be particularly appropriate when dealing with the nanoscale since they are susceptible to high levels of noise. The MRF logic can be implemented in modified CMOS-based circuitry that uses output-input feedback to maximize the joint probability of correct logic states, trading off circuit area and speed for crucial fault tolerance and noise immunity. The research will map a probabilistic MRF design methodology onto CMOS, proceeding from individual devices and small combinational and sequential logic test circuits, through to higher-level architectural designs.

High-end computing architectures will increasingly have to deal with issues of reliability and robustness, in the face of reduced noise margins, process variability, and manufacturing tolerances. The probabilistic design methodology being followed in this project investigates one direction to extend silicon digital logic beyond the limits imposed on standard designs by fundamental physical constraints.

The objective of the proposed research is to investigate a new class of semiconductor devices compatible with dominant silicon technology -- tunneling transistors fabricated in epitaxial germanium-on-insulator channels. These devices are not constrained, in principle, by the subthreshold swing limit of standard field effect transistors, so there is the potential of obtaining large on/off current ratios at room temperature while reducing the power supply voltage and hence the power consumption of large integrated circuits. The enabling approach involves the use of ultrathin single-crystal germanium-on-insulator channels combined with lattice-matched epitaxial high- dielectrics, all grown on silicon substrates.

Intellectual merit: Although silicon-based tunneling transistors are a topic of current research in industry, germanium-on-insulator devices are both unexplored and promising, because the smaller Ge bandgap promises orders of magnitude higher tunneling current at the same power supply voltage and current drive is a key metric for downscaled transistors, tunneling or field-effect, that will determine how much device scaling will help in the future. Another interesting aspect of tunneling transistors is that they can dispense with the inversion channel altogether, greatly reducing the capacitance, which may prove of interest for high-speed analog amplifiers. Planar lateral tunneling transistors, with and without an inversion channel, fabricated in all-epitaxial Ge-on-insulator heterostructures will be studied by the combined IBM-Brown research team, which has complementary expertise and an existing close co-PI collaboration on Ge devices.

Broader Impact: The proposed research will gauge the technological potential of germanium-based tunneling transistors compared to standard field-effect devices. The insertion of alternative channel materials, such as Ge, is a key part of the silicon technology roadmap. The alternative tunneling devices to be studied maintain VLSI compatibility and room temperature operation, making them viable for hybrid electronic circuits. The proposed research will have an educational impact, with Brown graduate students interacting closely with IBM Research (including summer internships), and undergraduates gaining research experience, including undergraduates from minority institutions identified through the Brown MRSEC, which has a focused outreach program.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)"

Objective: The objective of this research is to enable development of nanopatterned conformal oxides for device applications. The approach is to acquire a processing module comprised of complementary inductively-coupled plasma (ICP) etch and atomic-layer deposition (ALD) tools for the Brown Microelectronics Central User Facility.

Intellectual Merit: This equipment cluster will enable the fabrication of nanopatterned conformal oxides for cutting-edge applications in electronic, fluidic, photonic, and implantable devices. Specifically, the proposed equipment will help researchers: (1) deposit high-?Û dielectrics for nanoelectronic devices; (2) control the dimensions and surface chemistry of nanofluidic channels; (3) pattern and protect optically active materials, including luminescent rare-earth oxides, for light emitters and detectors; and (4) encapsulate implants with bio-compatible coatings that prevent infection and promote tissue growth.




Broader impacts: Located in a central user facility with ongoing technical and administrative support, this equipment will constitute a linchpin of the Brown University infrastructure for research training in nanoscale science and engineering for years to come. Housed in a publicly accessible cleanroom, this equipment will be made available to researchers from many university departments, including Engineering, Physics, Chemistry, Biology and Medicine, as well as outside users from local industry and academic institutions via the Materials Research Facilities Network. Furthermore, this program will be enriched by established connections with outreach through the NSF sponsored GK-12 ¡§Physical Processes in the Environment¡¨ program in the Providence Public School system and the collaborative REU program offered by the Brown Materials Research Science and Engineering Center (MRSEC) and the Leadership Alliance.

INTELLECTUAL MERIT
We propose to study devices fabricated from sub-50 nm diameter nanowires with axial Si/Ge heterojunctions grown by the vapor-liquid-solid technique in collaboration with T. Picraux's epitaxy group at Los Alamos. Previous work has shown that sidewall strain relaxation greatly expands the available bandgap and strain engineering, allowing segments of essentially arbitrary SiGe composition to be incorporated into the axial nanowire. We plan to study the following classes of devices:
i) axial Si/Ge heteronanowire tunneling transistors, which promise a combination of sharper switching together with higher tunneling currents due to bandgap and strain engineering along the nanowire combined with the gate-all-around device geometry;
ii) Si/Ge double-barrier tunneling structures with high conduction and valence band barriers made possible by the relaxation of critical thickness limits in narrow heteronanowires;
iii) Si/Ge/Si pn heterojunctions with lateral size confinement that promise stronger optical transitions due to narrower and pseudo-direct bandgap in the Ge region.
Experimental results will be compared to numerical band structure simulations from both continuum elasticity and molecular dynamics (again, in collaboration with the Picraux group).

BROADER IMPACT
Heteronanowire tunneling transistors with gate-all-around geometry comprise one of the more realistic candidates for low-voltage switching compatible with silicon technology. Also, our work will provide experimental data for atomistic simulations of inhomogeneous strain at ~10 nm length scale.
The Los Alamos collaboration research will have added graduate education impact due to extended student visits to Los Alamos. Undergraduates will work on sub-sections, including REU students from minority institutions (identified through the Brown MRSEC).

This award supports the acquisition of a High Magnetic Field and Cryogen-Free Physical Property Measurement System (PPMS) at Brown University. It will enable experimental studies of the physical properties of materials including magnetism, electron transport, and thermodynamic properties. The instrument will provide fundamental information about new materials actively being studied by scientists from the disciplines of Physics, Chemistry, and Engineering. Proposed research using the PPMS includes: (1) spintronics based on half-metallic magnetic nanostructures, (2) magnetic nanoparticles for data storage, energy storage and biomedical applications, (3) low dimensional superconducting nanostructures, (4) type-II superconductors, (5) novel superconducting and spin liquid states, and (6) semiconductor hetero-nanowires. By studying physical properties over a wide range of temperatures and fields, scientists at Brown will uncover the quantum mechanical behavior and physical mechanisms underlying many novel and revolutionary materials. With this new instrument, they will have the ability to investigate the ground state properties of their materials directly, rather than rely on mere extrapolations of measurements conducted at room temperature or low magnetic fields. Since the PPMS provides a myriad of physical characterizations, they will be able to develop theoretical models that can then be almost immediately tested by multiple types of measurements and their correlations. The PPMS will open up new research opportunities for the materials research programs, and will help to reveal as yet unexplored physical phenomena while simultaneously producing devices of great practical significance. The proposed research not only will advance the development of material science, but also will lead to prototyping the next generations of spin-based electronics and semiconductor devices, thereby directly influencing the future development of the semiconductor industry.

This instrument will be used as an educational tool for graduate and undergraduate training. With this instrument, they will be able to teach students the fundamental properties of modern materials, develop a deeper understanding of physical mechanisms, and also provide invaluable practical experience in advanced characterization techniques. In particular, undergraduate students will use this sophisticated instrument for their research projects, thereby offering a unique opportunity for high-level investigations. These students will form the next generation of materials scientists in the United States, ensuring the development of the field and helping the US assume and maintain a preeminent role. The proposed research will also generate new basic knowledge and data on novel spintronic, superconducting, and semiconductor materials that can be leveraged to develop potentially revolutionary devices for widespread implementation in multiple arenas including information technology, medicine, and education.

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR) and the Energy, Power, and Adaptive Systems Program (EPAS) in the Division of Electrical, Communications and Cyber Systems (ECCS).

Technical Description: Efficient optoelectronic active materials, based on confined germanium quantum dots and germanium/silicon quantum wires, promise enhanced photoconversion mechanisms useful for chip-compatible photodetectors and solar cells with broadband absorption. This project focuses on two interrelated classes of optoelectronic materials and devices: (1) a close-packed array of Ge quantum dots for high-efficiency photodetectors and (2) Ge/Si heteronanowires for tandem solar cells. Materials properties of Ge quantum dots (such as concentration, crystallinity and surface passivation) are directly correlated to optoelectronic functionalities and optimized to improve the photodetection speed while retaining high responsivity. The response time and gain mechanisms are studied using time-resolved measurements as well as theoretical modeling of charging and inter-quantum-dot hopping. For the second class of materials and devices, the Ge/Si nanowires are grown using the vapor-liquid-solid technique to overcome lattice mismatch limitations. The transport and optical response of individual heteronanowires are correlated with nanowire diameter, length, doping and composition, and are used to predict the collective behavior of dense nanowire arrays with improved spectral coverage and reduced reflectivity. Simulations are performed to match the short-circuit currents in the Ge and Si sections in order to achieve enhanced photoconversion efficiency.

Non-technical Description: This research project is on light-matter interactions in germanium-based nanostructures, including quantum dots and quantum wires. These nanostructures combine attractive physical properties enabled by more efficient light-matter interaction at the nanoscale. Specifically, the project seeks to use these nanomaterials for higher-efficiency photodetectors and broadband solar cells. The research has educational impact in and out of the classroom at Brown University. It includes long-term collaboration between faculty and graduate students at Brown University and scientists at the Los Alamos National Laboratory, on nanowire growth. Undergraduates also work on parts of the research. In addition, solar energy-based K-12 outreach activities are expanded and local high-school students participate in laboratory summer research.

Objective:
The objective of the Advanced Research Workshop on Future Trends in Microelectronics, which is to be held in Corsica, France during June 25-29, 2012, is to discuss the future of the rapidly evolving microelectronics technology, in a small group, with leaders in the field.

Intellectual merit:
The Workshop will provide a forum for an exchange of views among leading research professionals in industry, academia, and government. The intent is to arrive at a far-reaching overview of the evolution of microelectronics in the coming decade or more, as perceived by leading practitioners in the field. The major goal of the workshop is to assess the current status, define future research directions in microelectronics and to establish collaborations between researchers. This will be achieved through presentations and open discussions of the key technical issues.

Broader impact:
It is expected that this Workshop will be instrumental in defining the research required by the growing demands of microelectronics in the coming decade. This workshop will also contribute to the training of participating students and the topics will be disseminated through the Conference Technical Digest.

Non-Technical Description: Semiconducting materials are an essential component of all modern electronics. In recent years, a new class of amorphous oxide based semiconducting materials has emerged. These materials are unique in that they can be deposited at room temperature on many solid surfaces while maintaining good electrical properties. The first application of such amorphous metal oxides has been in flat panel displays. The aim of this research project is to explore the fundamental materials science of miniaturized amorphous oxide devices integrated with new types of dielectric oxides. The structures can be made near room temperature and may enable an entirely new approach to design of electronic devices operating at radio frequencies for potential applications ranging from cell phones to satellites. Further, the combination of fundamental materials science and prototype device fabrication has educational impacts in and out of the classroom at Brown University. For instance, the low-cost, low-temperature amorphous oxide technology makes it ideal for a prototype fabrication lab in an undergraduate course on electronic materials and devices.

Technical Description: Indium zinc oxide (IZO) in the amorphous form can be deposited at room temperature and achieve a high charge carrier density. This control over charge carrier density during and after deposition, combined with high mobilities, arbitrary substrate compatibility, easy regrowth and low-temperature in-situ oxidation for doping control and dielectric formation, makes these materials a promising platform for integration-ready high-current radio-frequency transistors. In this project, researchers examine the kinetics, electronic properties, and interface structure of metal/IZO formed by an in-situ self-limiting interface reaction. The goal is to achieve localized controllable ultra-high doping and self-limiting dielectric formation. The fundamental materials science knowledge obtained on reacted metal (Ti, Al) oxide/IZO interface structures is applicable to the fabrication of prototype transistors, particularly IZO-based high-current radio-frequency devices. Several critical materials challenges are low-resistance metal/IZO contacts, high and stable carrier density channels, and integration of materials with high dielectric constants. To tackle these challenges, thermodynamic/kinetic modeling of interface stability is combined with analytical techniques ranging from high-resolution transmission electron microscopy, glancing incidence angle x-ray diffraction, to interface electronic characterization techniques.

With the recent advances in integrated circuit technology, devices and their operating voltages will continue to shrink. This aggressive scaling trend has the consequence of drastically reducing the total number of electrons on each circuit node, making the circuit much more susceptible to thermal noise making new approaches to estimating noise behavior in these circuits necessary. Also the need for error mitigation resulting from such noise is especially pressing for logic circuits operating using very low supply voltages, designed for ultra-low power applications, where higher error rates are expected due to the reduced noise margins. The project will involve graduate and undergraduate students, include members of underrepresented groups and will thus help enlarge the workforce in information and communication technologies.

This project will address the noise immunity of ultimately scaled silicon based logic through three interrelated thrusts. The first thrust will focus on the experimentally validated prediction of thermally induced and voltage-noise induced error rates in these circuits. The second thrust involves development of a new simulation framework for analyzing transient effects due to noise. This new framework will be capable of capturing rare failure-inducing events 1 to 3 orders of magnitude faster than conventional simulation techniques. Based on the findings obtained from these two initial thrusts, new noise-immune logic gate structures that confer additional noise margin will be developed. Moreover, these results will be used to design a new synthesis tool flow, that automatically determines where and how to optimally use these noise-immune logic gates to reach desired delay, power, and reliability requirements.

The aim of the triennial workshop on "Advanced Research Workshop on Future Trends in Microelectronics (FTM): Journey Into the Unknown" to be held June 21-26, 2015 in Mallorca, Spain, is to continue the tradition started in 1995 and now reaching the 8th iteration, to provide a forum for a free-spirited exchange of views among the leading professionals in Industry, Academia, and Government. Topics to be addressed include the evolution of microelectronics including not only computing and communications, but extending to sensors, displays, systems, bioelectronics, nanotechnology, and electronics-related material science for the coming decade or more, The speakers are asked to present their own uninhibited views, opinions and critiques of the present and future trends, rather than their own achievements. Debates and critical assessments are encouraged. The resulting free-spirited discussion, with varied and occasionally clashing viewpoints, will be available on the FTM workshop website as well as the conference volume (to be published by Wiley) providing a valuable educational tool for young researchers deciding on promising directions for microelectronics research in the next decade.

This award from the Major Research Instrumentation program supports Brown University with the acquisition of a modern maskless lithography system (Heidelberg Instruments MLA-150). Maskless lithography, where the pattern is transferred to the substrate by rapidly scanning a laser beam over the photoresist-covered substrate, under computer control overcomes many of the limitations of current photolithography techniques. The instrument will be located within the Nanofabrication Central Facility (NCF) and will support the research by some 25 research groups at Brown University including faculty from Engineering to Physics to Chemistry to Biomedical Engineering as well as local research community and industry. The MLA-150 will enable high-speed and flexible optical lithography down to micron-sized features at low cost and over large areas, without the constraints of pre-existing mask sets. In the immediate future, it will enable research in a range of funded or planned research projects in electronic and microfluidic devices. The flexibility of the system would help expand the range of laboratory courses currently supported by the NCF (three Engineering fabrication courses, currently focused on diode, transistor and solar cell fabrication) to encompass e.g. microfluidic devices. Postdoctoral scholars, graduate and undergraduate students will have an opportunity to be trained in this versatile fabrication technique.


This Major Research Instrumentation award supports the acquisition of a Heidelberg Instruments MLA-150 maskless lithography tool, with ~1 micrometer achievable feature size over a 150 mm field of exposure, with fast computer-controlled high-accuracy (0.5 micrometer) alignment and short (minutes-long) exposure times. The instrument includes two laser illumination modules and integrated cameras for high-accuracy alignment to pre-existing structures. The system will be integrated in a new Nanofabrication Central Facility (NCF) cleanroom at Brown University. This state-of-the-art instrument will foster interdisciplinary research at the intersection between diverse research fields in electronic and optoelectronic devices: fabrication of Ge quantum-dot based photodetectors; nitride vertical current flow transistors; piezoelectric energy harvesting devices; and magnetic tunnel junction-based memory elements and arrays. In the advanced materials area, it will contribute to: large-area surface patterning for THz emission spectroscopy; ultra-thin layered materials for structural coloration; templated surfaces for self-assembled nanoparticle arrays; 3D photocatalytic structures; and adaptive meta-surfaces based on phase-change materials. In the rapidly expanding bio-engineering area, the MLA-150 will permit large-area microfluidic structures to study spatially confined cell migration; DNA manipulation; and geometrically-constrained stem cell migration and differentiation. The instrument will be made available to other local academic institutions and local industry.

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.

Nontechnical description: Over the past decade, displays in electronic devices like laptops have been revolutionized in part by using transparent conducting amorphous oxides due to their processing versatility and higher carrier mobility combined with low-temperature, large-area deposition conditions. A team of investigators from Brown University and Technion (Israel) is investigating a new class of materials, amorphous metal iodides like CuSnI and CuPbI, that would add to the arsenal of transparent conducting materials for use in displays and other transparent circuit technologies. Compared to other amorphous materials, the amorphous metal iodides feature a different physical mechanism: under an applied voltage, the currents are carried by positively charged holes. This offers new low-power dissipation circuit possibilities, as long as the materials properties of these metal iodides, including impurity content, phase, and temperature behavior can be tuned using composition and processing parameters. The research program covers a number of topics, ranging from fundamental experimental materials science of material deposition and characterization to theoretical modeling of phase transformation and impurity incorporation to prototype transistor device fabrication, brings together transparent electronic material and device expertise at Brown University with cutting-edge materials characterization and modeling at the Technion. The research project has an educational impact in and out of the classroom, including graduate student support, Brown-Technion graduate student interaction and exchange visits, as well as outreach to underprivileged middle-school students in the Providence area.

Technical description: Two Brown experimentalists with complementary expertise in amorphous electronic materials and device physics, in collaboration with a Technion team experienced in atomic/nano/micro characterization and physical modeling, are focusing on the need for a high-mobility wide-bandgap low-temperature p-type material for thin film transistors (TFTs). The PIs have identified amorphous iodide-based materials as the most promising: they have a wide bandgap (3 eV), high hole mobility (up to 40 cm2/V.s), native vacancy doping, and are compatible with arbitrary substrates. They are also compatible with low-temperature-deposited amorphous n-type zinc oxide-based materials, opening the way for complementary TFT circuitry. The Brown PIs are leveraging their recent demonstration of high-performance indium-zinc-oxide materials by reconfiguring an oxide sputtering tool for in-situ iodide deposition. The Brown team is developing and optimizing the synthesis of a-Cu1-xMxI thin films (M = Sn, Pb, In, and others), studying the doping mechanism via Brouwer analysis, investigating phase stability, and fabricating prototype TFT demonstrator circuits. The experimental work is complemented by the detailed materials characterization and physical modeling performed by the Technion team, that has extensive experience in nanoscale amorphous and crystalline films. The final experimental goal is to develop the deposition of both n- and p-type transparent conducting materials in the same sputter-deposition process at low temperature on arbitrary substrates. The project provides training opportunities to the participating graduate and undergraduate students in cross-cutting electronic materials and devices fields, to the Brown-Technion visitor and student exchanges, as well as to the local underprivileged middle-school students.

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.