Nanotube forests grown on silicon chips for future computers, electronics
October 02, 2007
Engineers have shown how to grow forests of tiny cylinders called carbon nanotubes onto the surfaces of computer chips to enhance the flow of heat at a critical point where the chips connect to cooling devices called heat sinks.
The carpetlike growth of nanotubes has been shown to outperform conventional "thermal interface materials." Like those materials, the nanotube layer does not require elaborate clean-room environments, representing a possible low-cost manufacturing approach to keep future chips from overheating and reduce the size of cooling systems, said Placidus B. Amama, a postdoctoral research associate at the Birck Nanotechnology Center in Purdue's Discovery Park.
Researchers are trying to develop new types of thermal interface materials that conduct heat more efficiently than conventional materials, improving overall performance and helping to meet cooling needs of future chips that will produce more heat than current microprocessors. The materials, which are sandwiched between silicon chips and the metal heat sinks, fill gaps and irregularities between the chip and metal surfaces to enhance heat flow between the two.
The method developed by the Purdue researchers enables them to create a nanotube interface that conforms to a heat sink's uneven surface, conducting heat with less resistance than comparable interface materials currently in use by industry, said doctoral student Baratunde A. Cola.
Findings were detailed in a research paper that appeared in September's issue of the journal Nanotechnology. The paper was written by Amama; Cola; Timothy D. Sands, director of the Birck Nanotechnology Center and the Basil S. Turner Professor of Materials Engineering and Electrical and Computer Engineering; and Xianfan Xu and Timothy S. Fisher, both professors of mechanical engineering.
Better thermal interface materials are needed either to test computer chips in manufacturing or to keep chips cooler during operation in commercial products.
"In a personal computer, laptop and portable electronics, the better your thermal interface material, the smaller the heat sink and overall chip-cooling systems have to be," Cola said.
Heat sinks are structures that usually contain an array of fins to increase surface contact with the air and improve heat dissipation, and a fan often also is used to blow air over the devices to cool chips.
Conventional thermal interface materials include greases, waxes and a foil made of a metal called indium. All of these materials, however, have drawbacks. The greases don't last many cycles of repeatedly testing chips on the assembly line. The indium foil doesn't make good enough contact for optimum heat transfer, Fisher said.
The Purdue researchers created templates from branching molecules called dendrimers, forming these templates on a silicon surface. Then, metal catalyst particles that are needed to grow the nanotubes were deposited inside cavities between the dendrimer branches. Heat was then applied to the silicon chip, burning away the polymer and leaving behind only the metal catalyst particles.
The engineers then placed the catalyst particle-laden silicon inside a chamber and exposed it to methane gas. Microwave energy was applied to break down the methane, which contains carbon. The catalyst particles prompted the nanotubes to assemble from carbon originating in the methane, and the tubes then grew vertically from the surface of the silicon chip.
"The dendrimer is a vehicle to deliver the cargo of catalyst particles, making it possible for us to seed the carbon nanotube growth right on the substrate," Amama said. "We are able to control the particle size - what ultimately determines the diameters of the tubes - and we also have control over the density, or the thickness of this forest of nanotubes. The density, quality and diameter are key parameters in controlling the heat-transfer properties."
The catalyst particles are made of "transition metals," such as iron, cobalt, nickel or palladium. Because the catalyst particles are about 10 nanometers in diameter, they allow the formation of tubes of similar diameter.
The branching dendrites are tipped with molecules called amines, which act as handles to stick to the silicon surface.
"This is important because for heat-transfer applications, you want the nanotubes to be well-anchored," Amama said.
Researchers usually produce carbon nanotubes separately and then attach them to the silicon chips or mix them with a polymer and then apply them as a paste.
"Our direct growth approach, however, addresses the critical heat-flow path, which is between the chip surface and the nanotubes themselves," Fisher said. "Without this direct connection, the thermal performance suffers greatly."
Because the dendrimers have a uniform composition and structure, the researchers were able to control the distribution and density of catalyst particles.
The research team also has been able to control the number of "defect sites" in the lattice of carbon atoms making up the tubes, creating tubes that are more flexible. This increased flexibility causes the nanotube forests to conform to the surface of the heat sink, making for better contact and improved heat conduction.
"The tubes bend like toothbrush bristles, and they stick into the gaps and make a lot of real contact," Cola said.
The carbon nanotubes were grown using a technique called microwave plasma chemical vapor deposition, a relatively inexpensive method for manufacturing a thermal-interface material made of carbon nanotubes, Fisher said.
"The plasma deposition approach allows us great flexibility in controlling the growth environment and has enabled us to grow carbon nanotube arrays over a broad range of substrate temperatures," Fisher said.
The research has been funded by NASA through the Institute for Nanoelectronics and Computing, based at Purdue's Discovery Park. Cola also received support through a fellowship from Intel Corp. and Purdue.
Related Carbon Nanotubes Current Events and Carbon Nanotubes News ArticlesNanotubes are beacons in cancer-imaging technique
Bathing a patient in LED light may someday offer a new way to locate tumors, according to Rice University researchers.New research shows how silver could be the key to gold-standard flexible gadgets
Research published in the journals Materials Today Communications and Scientific Reports has described how silver nanowires are proving to be the ideal material for flexible, touch-screen technologies while also exploring how the material can be manipulated to tune its performance for other applications. Effect of the Van-der-Waals and intramolecular forces
In modern microelectronics, nanobiotechnology, nanorobots increasingly have being used both organic biomacromolecules and fragments, as nucleotides, peptides, DNA, and inorganic elements, like as metallic nanoparticles, carbon nanotubes. Nature Photonics: Light source for quicker computer chips
Worldwide growing data volumes make conventional electronic processing reach its limits. Unraveling truly one-dimensional carbon solids
Even in its elemental form, the high bond versatility of carbon allows for many different well-known materials, including diamond and graphite.UTA researchers devise more efficient materials for solar fuel cells
University of Texas at Arlington chemists have developed new high-performing materials for cells that harness sunlight to split carbon dioxide and water into useable fuels like methanol and hydrogen gas. Nano-coating makes coaxial cables lighter
Common coaxial cables could be made 50 percent lighter with a new nanotube-based outer conductor developed by Rice University scientists.Cellulose nanogenerators could one day power implanted biomedical devices
Implantable electronics that can deliver drugs, monitor vital signs and perform other health-related roles are on the horizon.New process enables easier isolation of carbon nanotubes
Manufacture of longer, thinner, and uncontaminated carbon nanotubes, and successfully isolating them, have been ongoing challenges for researchers. A newly developed method has opened up new possibilities in carbon nanotube development.Fuel cell advance
"Planes, Trains and Automobiles" is a popular comedy from the 1980s, but there's nothing funny about the amount of energy consumed by our nation's transportation sector.
More Carbon Nanotubes Current Events and Carbon Nanotubes News Articles
Carbon Nanotube Science: Synthesis, Properties and Applications|
by Peter J. F. Harris (Author)
Carbon nanotubes represent one of the most exciting research areas in modern science. These molecular-scale carbon tubes are the stiffest and strongest fibres known, with remarkable electronic properties, and potential applications in a wide range of fields. Carbon Nanotube Science is the most concise, accessible book for the field, presenting the basic knowledge that graduates and researchers need to know. Based on the successful Carbon Nanotubes and Related Structures, this new book focuses solely on carbon nanotubes, covering the major advances made in recent years in this rapidly developing field. Chapters focus on electronic properties, chemical and bimolecular functionalisation, nanotube composites and nanotube-based probes and sensors. The book begins with a comprehensive...
Carbon Nanotube and Graphene Device Physics|
by H.-S. Philip Wong (Author), Deji Akinwande (Author)
Explaining the properties and performance of practical nanotube devices and related applications, this is the first introductory textbook on the subject. All the fundamental concepts are introduced, so that readers without an advanced scientific background can follow all the major ideas and results. Additional topics covered include nanotube transistors and interconnects, and the basic physics of graphene. Problem sets at the end of every chapter allow readers to test their knowledge of the material covered and gain a greater understanding of the analytical skill sets developed in the text. This is an ideal textbook for senior undergraduate and graduate students taking courses in semiconductor device physics and nanoelectronics. It is also a perfect self-study guide for professional...
Physical Properties of Carbon Nanotubes|
by G Dresselhaus (Author), M S Dresselhaus (Author), Riichiro Saito (Author)
This is an introductory textbook for graduate students and researchers from various fields of science who wish to learn about carbon nanotubes. The field is still at an early stage, and progress continues at a rapid rate. This book focuses on the basic principles behind the physical properties and gives the background necessary to understand the recent developments. Some useful computational source codes which generate coordinates for carbon nanotubes are also included in the appendix.
Carbon Nanotubes: Reinforced Metal Matrix Composites (Nanomaterials and their Applications)|
by Arvind Agarwal (Author), Srinivasa Rao Bakshi (Author), Debrupa Lahiri (Author)
From the Foreword, written by legendary nano pioneer M. Meyyappan, Chief Scientist for Exploration Technology NASA Ames Research Center, Moffett Field, California, USA: "…there is critical need for a book to summarize the status of the field but more importantly to lay out the principles behind the technology. This is what Professor Arvind Agarwal and his co-workers … have done here." Carbon Nanotubes: Reinforced Metal Matrix Composites reflects the authors’ desire to share the benefits of nanotechnology with the masses by developing metal matrix carbon nanotube (MM-CNT) composites for large-scale applications. Multiwall carbon nanotubes can now be produced on a large scale and at a significantly reduced cost. The book explores potential applications and applies the author’s own...
Carbon Nanotubes for Interconnects: Process, Design and Applications|
by Aida Todri-Sanial (Editor), Jean Dijon (Editor), Antonio Maffucci (Editor)
This book provides a single-source reference on the use of carbon nanotubes (CNTs) as interconnect material for horizontal, on-chip and 3D interconnects. The authors demonstrate the uses of bundles of CNTs, as innovative conducting material to fabricate interconnect through-silicon vias (TSVs), in order to improve the performance, reliability and integration of 3D integrated circuits (ICs). This book will be first to provide a coherent overview of exploiting carbon nanotubes for 3D interconnects covering aspects from processing, modeling, simulation, characterization and applications. Coverage also includes a thorough presentation of the application of CNTs as horizontal on-chip interconnects which can potentially revolutionize the nanoelectronics industry. This book is a must-read for...
Carbon Nanotubes: Synthesis, Structure, Properties and Applications|
by Mildred S. Dresselhaus (Editor), Gene Dresselhaus (Editor), Phaedon Avouris (Editor), R.E. Smalley (Editor)
After a short introduction and a brief review of the relation between carbon nanotubes, graphite and other forms of carbon, the synthesis techniques and growth mechanisms for carbon nanotubes are described. This is followed by reviews on nanotube electronic structure, electrical, optical, and mechanical properties, nanotube imaging and spectroscopy, and nanotube applications.
Helical Springs Made of Polymer Nanocomposite: Optimization for Design Variables of Carbon Fiber Reinforced Carbon Nanotube Additive Epoxy Composites|
by Yahya Kara (Author), Hamit Akbulut (Author)
In order to successfully reduce the weight of a machine or structural part it is possible to optimize the material parameters or to use alternative advanced materials instead of conventional engineering ones. Helical springs, important machine parts, are used for vibration damping in machines and are generally made of steel. As an alternative to helical steel springs in scope of the work, mechanical behaviors of helical springs made of carbon nanotube additive epoxy composite reinforced with carbon fiber have been investigated. First, mechanical properties for matrix resins with variable addition rates of CNT have been determined by using micromechanics approaches. In the study, mechanical behaviors of composite springs have been examined both analytically and numerically; numerical part...
Mechanical Behaviors of Carbon Nanotubes: Theoretical and Numerical Approaches (Micro and Nano Technologies)|
by K.M. Liew (Author), Yan Jianwei (Author), Lu-Wen Zhang (Author)
Mechanical Behaviors of Carbon Nanotubes: Theoretical and Numerical Approaches presents various theoretical and numerical studies on mechanical behaviors of carbon nanotubes. The main theoretical aspects included in the book contain classical molecular dynamics simulation, atomistic-continuum theory, atomic finite element method, continuum plate, nonlocal continuum plate, and shell models. Detailed coverage is also given to structural and elastic properties, trace of large deformation, buckling and post-buckling behaviors, fracture, vibration characteristics, wave propagation, and the most promising engineering applications. This book not only illustrates the theoretical and numerical methods for analyzing the mechanical behavior of carbon nanotubes, but also contains computational...
Modeling of Carbon Nanotubes, Graphene and their Composites (Springer Series in Materials Science)|
by Konstantinos I. Tserpes (Editor), Nuno Silvestre (Editor)
A large part of the research currently being conducted in the fields of materials science and engineering mechanics is devoted to carbon nanotubes and their applications. In this process, modeling is a very attractive investigation tool due to the difficulties in manufacturing and testing of nanomaterials. Continuum modeling offers significant advantages over atomistic modeling. Furthermore, the lack of accuracy in continuum methods can be overtaken by incorporating input data either from experiments or atomistic methods. This book reviews the recent progress in continuum modeling of carbon nanotubes and their composites. The advantages and disadvantages of continuum methods over atomistic methods are comprehensively discussed. Numerical models, mainly based on the finite element method,...
Functionalizing Graphene and Carbon Nanotubes: A Review (SpringerBriefs in Applied Sciences and Technology)|
by Filipe Vargas Ferreira (Author), Luciana Cividanes (Author), Felipe Sales Brito (Author), Beatriz Rossi Canuto de Menezes (Author), Wesley Franceschi (Author), Evelyn Alves Nunes Simonetti (Author), Gilmar Patrocínio Thim (Author)
This book compiles all current information on the different types of functionalization of carbon nanotubes (CNTs) and graphene, both covalent and non-covalent. The book starts with a general overview of the synthesis, characterization and application of functionalized CNTs and graphene. Special attention is dedicated to the characterization of functionalized materials, a topic rarely addressed on the literature. The authors provide a comparison between the functionalization of these two types of carbon materials.