John Melngailis - US grants

Recent results have demonstrated that metal-insulator-Si-field-effect transistors (MOSFET's) can be made narrow enough that the electronic conduction process in them changes in a fundamental way. At low temperature, large, nonmonotomic variations of the conductance are observed when the voltage on the gate is varied. Recent results on devices with 70nm wide inversion layers indicate that the current is limited by electron tunneling through localized states in the inversion layer of the MOSFET. These are apparently caused by the random potential resulting from ions on the surface of the oxide or variations in the width of the gate wire. This represents an unusual situation in which the current is limited by electronic transitions through just one electronic state. New fabrication methods are being developed with the goals of reducing the disorder caused by impurities on the oxide surface and localized electronic states in the oxide, and making the gate wires narrower and more uniform. Devices are being fabricated in the MIT Submicron Structures Laboratory, and they are being characterized at temperatures above 2;soK at MIT.

The proposed research, a collaboration between MIT and Raytheon Research Laboratories, is aimed at applying focused ion beam implantation to high performance GaAs integrated circuits. Since microwave and millimeter wave monolithic circuits (MMIC's) often have a variety of high performance devices on each chip, we will particularly focus on this class of circuits. The research will have three main components: a) integration of the focused ion beam into MMIC fabrication including verification of registration and of equivalence with conventional implantation; b) demonstration of the focused ion beam for prototyping of MMIC's by the implantion of a large variety of doses and energies in one step and; c) fabrication of high performance FET's by special implanted structures, i.e. variation also of the implant geometry within a device; d) implantation of complete MMIC.

This proposal request funds to support the attendance by graduate students of the 1990 Gordon Research Conference on the Chemistry and Physics of Microstructure Fabrication which will be held on July 9-12, 1990 at Colby-Sawyer College in New London, NH.

The goal of this research is to understnd the fundamental features of ion induced surface reactions in focused ion beam microfabrication, and of the materials and surfaces that are produced by the resulting deposition or etching. This will be accomplished by bringing to bear expertise from chemical engineering, materials science, and microfabrication technology. In the case of the deposition, understanding of the basic process is expected to point to ways of eliminating unwanted carbon impurities, for example, by the addition of a second, appropriately reactive, precursor gas or an atomic beam. Eliminating or significantly reducing the impurities in the deposited material would be a major breakthrough. The reduced resistivity and increased density would immediately make focused ion beam device and circuit repair processes more effective and open the door to new applications of maskless, resistless, patterned conductor deposition by projection ion techniques and to in situ processing. %%% Ion induced deposition and ion assisted etching are new processes for material addition and removal. Since ion beams can be focused to extremely small dimensions (0.05 microns and below), this permits material manipulation with unprecedented resolution and flexibility and has spawned commercial applications in micro- repair of integrated circuits and in microsectioning for fault diagnosis. By developing a better understanding of the mechanisms of these new processes, and by extending them to new materials, the proposed research work aims to broaden the applications to the deposition of the original wiring of future ultrafast integrated circuits.

This Major Research Instrumentation (MRI) program award provides funding to acquire a combined precision alignment system and wafer bonder. The aligner part of the instrument precisely lines up multiple wafers and substrates and puts them into contact. The bonder portion of the instrument permanently bonds the aligned substrates together. This instrument will be used at the University of Maryland for research and education in micro-electro-mechanical systems, integrated optics, chip-scale and wafer-level packaging, 3D interconnections, and hot embossing. Researchers will produce micro-turbine engines, biomedical drug delivery systems, microsurgical tools, micro-pumps for cooling high-density circuitry, and radio frequency devices. The wafer-to-wafer alignment system will be permanently located in a new 11,000 sq. ft. multi-user class 1000 clean room facility, the Engineering and Applied Sciences Building, dedicated to micro- and nano-systems research at the University of Maryland.

The availability of a wafer-to-wafer alignment system at the University of Maryland will benefit the following research projects: micro-turbomachinery, micro-combustion, safety and arming micro-systems, micromachined cooling structures, 3-dimensional micro-mechanisms, conjugated polymer films for microfluidics, and actively positioned neural probes. This equipment will also enhance education by making available to undergraduate and graduate students hands-on training on state-of-the-art equipment in a modern clean room environment. Newly developed undergraduate and graduate courses in microsystems in both the Electrical and Mechanical Engineering departments will also utilize this instrument for class projects. The instrument will also assist research and interdisciplinary collaboration between the University of Maryland and surrounding universities and national laboratories.

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 01-157, category NER. Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained recently in our measurements of light tunneling through individual subwavelength pinholes in a thick gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousands photons per second. This result has been explained theoretically in terms of "photon blockade", similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. The single-photon tunneling effect may find many applications in the emerging fields of quantum communication and information processing. The experiments reported so far have been performed for random pinholes that are naturally present in thin metal films. There is no detailed knowledge on the shape and size of the pinholes necessary to produce this effect under controlled conditions, which severely limits advancement of the theoretical description of the effect and its possible applications. We propose to expand these experiments to study single-photon tunneling effect in well-controlled geometries, by making use of ion-beam milling fabrication techniques. Based on this research we are going to explore a number of novel device ideas in the areas of optical communications and quantum optics.

A new and important phenomenon involving single photon tunneling has been discovered recently by a multidisciplinary team of researchers at the University of Maryland. Transmission of light through nanometer-scale pinholes in a gold film covered by a nonlinear dielectric saturates at a few thousand photons per second. The transmittance of such a nanometer-scale hole is nonlinear with light intensity, and at the single photon level corresponds to each photon in the process of being transmitted through the hole controlling the transmittance of successive photons. This result is analogous to the Coulomb blockade observed in single electron tunneling experiments. The phenomenon was initially observed only for random nanoscale pinholes that occur naturally in thin evaporated gold films. Further work has shown that the transmittance of both individual nanofabricated holes (nanopores), and arrays of nanopores, both made by focused ion-beam nanaofabrication techniques, has shown not only the simple iiphoton-blockadel effects, but also controlled photon transmission. For example, the transmittance of a nanopore or nanopore array at one wavelength can be controlled by illumination with a second, different, wavelength.

In this project a multidisciplinary team of optical scientists, theorists and nanofabricators
will study of this new phenomenon and explore potential applications based on fabricated nanopores or arrays of nanopores in metal films. They expect that a detailed study of optical properties of such well-controlled nanopore and other nanostructures will reveal novel quantum phenomena in nonlinear optical transmission. For example, electrons in a Coulomb blockade tunnel one at a time, at more or less fixed time intervals. If photons tunneling through nonlinear optical nanopores show similar behavior (as an initial experiments suggest), the fabricated nanopores will become very unusual and useful light sources emitting individual photon periodically, one at a time. Such controlled light sources are being actively pursued by researchers in the areas of quantum communication and quantum cryptography.

In addition, novel and potentially important applications of nonlinear nanopore materials may also be expected in the areas of optical communications and all-optical signal processing. Optical signal processing relies on nonlinear interactions of light, which usually happen at very high optical intensities. Preliminary results indicate that the local optical field in a nanopore is enhanced by at least six or eight orders of magnitude, enabling nonlinear optical interactions to occur at much lower illuminating light intensities. This opens the door to devices where light is used to gate light, which they have already demonstrated at a fundamental level. Thus, a great number of optical communication and optical signal processing devices, such as all-optical switches, and signal and image processing devices, may be realized on a microscopic scale, and at much smaller operating optical powers than macro-devices.

Proposal ID: 0508213
Title: NER: Far-Field Optical Microscopy Based on In-Plane Image Magnification by Surface Plasmon-Polaritons
Inst: U of Maryland
PI: Igor Smolyaninov


ABSTRACT

This NER proposal is based on the recently introduced new design of an optical microscope, which theoretically could reach resolution down to a scale of a few nanometers. In this new design a regular optical microscope is supplemented by a two-dimensional optical arrangement, which utilizes surface electromagnetic waves called surface plasmon-polaritons. These two-dimensional light waves have an unusual combination of nanometer scale wavelengths and visible-range frequencies, which means that the theoretical diffraction limit on resolution of an optical microscope may be pushed down to nanometer-scale values defined by the short wavelengths of plasmon-polaritons. Such a microscope has the potential to become a valuable tool in medical and biological imaging, where far-field optical imaging of individual viruses and DNA molecules may become reality. In addition, used in reverse such a microscope may be utilized in nanometer-scale optical lithography. The development of the proposed novel microscopy and nanolithography tools may have profound impacts on technology and society on many levels. We can envision building new inexpensive optical microscopes, which would look and cost very much like regular optical microscopes in a high school biology class, while allowing direct visualization of biomaterials (such as viruses and DNA molecules) on the 30-50 nm scale. Such a development would open the "nano-universe" to very broad layers of our society.

Intellectual Merit: This project will address the two important aspects of NW FETs - device designs and characterization techniques, with a goal to demonstrate the operation of SiNW FETs in the 1 ? 4 GHz range. Nanowire based HF transistors operating in this range could have transformative impacts in the fields of flexible/wearable/implantable electronics, medical diagnostics/imaging, remote sensing, micro-RFID, etc. The adopted research methodology is general enough to be relevant for different nanowire material systems. This study for the first time would address the fundamental question ? can we get high-speed devices using SiNWs grown by bottom-up methods? Similarly, this study will investigate the effect of various novel NW device designs on their HF performances.

Broader Impact: Successful completion of this project will advance our understanding of the fundamental high-frequency operating limits of SiNW transistors. The nature of the proposed research is such that the knowledge gained from it can be readily incorporated into graduate level curriculum. The PIs have planned to introduce two small course modules: 1) Fabrication of Nanowire Transistors for the course ENEE 719A -Advanced Topics in Microelectronics: Nanostructure Fabrication Technology and 2) Device Physics of Nanowire Transistors for the course ENEE 601 -Semiconductor Devices & Technology. These two modules will expose the students to the latest research results in nanoscale semiconductor devices while broadly disseminating the knowledge gained from the research.