Workshop 1: Advanced Materials
Thu, 29 April 2004, 8:00 AM - 12:00 PM
1.1 SiC and GaN Wide Bandgap Device Technology Overview
1.3 RF MEMS for Radar and Phased-Array Applications
1.4 Artificial Magnetic Conductors
|1.1 SiC and GaN Wide Bandgap Device Technology Overview
By: Mr. Jim Milligan
This tutorial will review the current status of SiC MESFET and GaN HEMT wide bandgap device technology. These devices potentially offer significant advantages for next generation military systems. Operating at a drain voltage of 48 volts, the higher load-line impedance of these devices enables wider bandwidth power amplifiers than possible in conventional silicon or GaAs technologies. SiC MESFETs achieve a power density of approximately 4.0 W/mm and power added efficiencies of 50% on a repeatable basis and are commercially available in packaged or die formats. Reliability studies conducted on 10-watt parts demonstrate robust device characteristics. DC Accelerated Life tests on twelve 10-Watt SiC MESFETs operating at TJ = 240?C demonstrate an average reduction in saturated drain current of only 8.9% after being stressed for 2,100 hours. This is well within the 20% JEDEC guideline for defining a failure.
In June 2004, Cree announced that commercial SiC MMIC foundry services are now available. The MMIC process is similar to existing GaAs MMIC processes in that it offers thinned (100 mm) substrates, thin-film resistors, high voltage MIM capacitors, and through-wafer vias. The process has demonstrated good yield on large, high power MMIC amplifiers suitable for high power radar applications.
GaN also appears to be very promising as a next generation device technology. Power densities as high as 25 watts per mm of gate periphery have been reported. With ft?s > 40 GHz, GaN devices have the capability of satisfying system device requirements from UHF through millimeter-wave. Unlike SiC, which has demonstrated excellent reliability characteristics, GaN devices are not as mature. Problems with early device degradation have been observed and a status of this work will be presented during the tutorial.
By: Dr. Nader Engheta
Univ. of Pennsylvania
The concept of metamaterials has been the subject of research interest for many investigators worldwide. New concepts in synthesis and novel fabrication techniques may allow construction of new classes of composite materials with interesting electromagnetic properties. These metamaterials, which can in principle be synthesized by embedding various constituents/inclusions with novel geometrical shapes and forms in some host media, possess exciting features and response functions, not easily available in nature but physically realizable, with new potential applications in the design of devices and components. The electromagnetic properties of certain class of metamaterials in which both permittivity and permeability attain negative real parts in a given band of frequencies have attracted a great deal of interest in recent years. Various names, such as ?double-negative (DNG)? media, ?left-handed (LH) materials, ?backward-wave (BW) media?, ?negative index materials (NIM)?, have been coined for this type of metamaterials. These particulate composite media possess unconventional features such as negative refraction and backward wave propagation, in which the direction of the Poynting vector of a plane wave is antiparallel with the direction of its phase velocity. These can lead to some exciting wave characteristics with potential applications in various systems and subsystems involved in radiation, guidance and scattering of electromagnetic waves. In addition, the ?single-negative (SNG)? media, i.e., the materials in which only one of the material parameters of permittivity and permeability, but not both, can be negative, also exhibit certain interesting properties when they are paired in a conjugate manner. Another class of metamaterial structures in which the period arrangement of elements can provide interesting features is the electromagnetic bandgap (EBG) surfaces with high surface impedance. In such surfaces, by properly selecting the geometry, composition, arrangement and alignment of planar elements one can achieve high impedance surfaces, which can effectively behave as ?artificial magnetic conductors (AMC)? These can lead to useful applications in various problems involving low-profile, conformal antennas, miniaturized cavities, and thin absorbing low-observable surfaces.
In this tutorial, I will present a comprehensive overview of some of the selected topics in these areas. I will first give a brief background and history of this field, and will review some of the salient features of the metamaterials. I will then discuss in details some of the topics on metamaterials, including scattering and radar cross section properties of planar, cylindrical and spherical structures containing pairs of DNG-DPS and ENG-MNG metamaterial layers, waveguiding features of metamaterials, exciting properties of imaging systems containing layers of metamaterials, EBG surfaces acting as high-impedance surfaces and the role of space-filling and fractal geometries in forming such exotic ground planes for antenna applications, and several other related problems in the field of metamaterials with various potential applications in radar and antenna systems.
|1.3 RF MEMS for Radar and Phased-Array Applications
By: Dr. Gabriel M. Rebeiz
Univ. of Michigan, Ann Arbor
The development of RF MEMS switches has accelerated considerably over the past several years, and currently there are several switches which have been tested to 50-100 billion cycles with no failures. RF MEMS capacitive and metal-contact switches can now handle Watts of RF power at 10 GHz and this is ideal for most radar applications. RF MEMS phase shifters have also been demonstrated from 5 GHz to 110 GHz, with a loss of 0.25 dB/bit at 10 GHz and 0.7 dB/bit at 94 GHz. This results in 4-bit phase shifters with only 1.0 dB on-wafer loss at 10 GHz and 2.8 dB loss at 94 GHz, making them very attractive for phased-array applications and more specifically, reflect arrays. However, it is still hard to package these devices, and fundamental questions regarding the need of a hermetic package are not well understood. The talk will present the latest work in high isolation RF MEMS switches, switch networks, and phase shifters, and the use of these novel devices in radar systems.
This Tutorial has a recommended book:
?RF MEMS: Theory, Design and Technology?, Gabriel M. Rebeiz, Wiley, 2003.
You may order this book at a 15% discount and free shipping by contacting Dudley Kay at Scitech Publishing, 919-866-1501, or email firstname.lastname@example.org. Please order the book no later than April 15, 2004 in order to receive it before leaving for the conference (before April 23rd).
|1.4 Artificial Magnetic Conductors
By: Mr. Victor C. Sanchez
Artificial magnetic conductor (AMC) ground plane and antenna technology will be discussed. Topics will include theoretical treatment for the Sievenpiper "thumbtack" structure, enhanced bandwidth structures, reconfigurable geometries, practical antenna implementation issues and novel AMC/antenna concepts. The tutorial is based on research conducted under the DARPA RECAP (Reconfigurable Aperture) program as well as current work for the Office of Naval Research.