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Title:Design and fabrication of high-performance indium gallium phosphide/gallium arsenide heterojunction bipolar transistors
Author(s):Fresina, Michael Thomas
Doctoral Committee Chair(s):Stillman, Gregory E.
Department / Program:Electrical and Computer Engineering
Discipline:Electrical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Physics, Condensed Matter
Engineering, Materials Science
Abstract:The heterojunction bipolar transistor (HBT) is a device whose time has come. The high gains, linearity, power efficiencies, current handling capabilities, and speeds available with HBT technology make this device attractive for a wide variety of applications from wireless communications to high-speed analog-to-digital converters. Companies across the United States are investing millions of dollars in developing HBT products and manufacturing capabilities.
A manufacturable fabrication process for state-of-the-art InGaP/GaAs HBTs has been established. The process features nonalloyed emitter metal, self-aligned emitter and collector etches, self-aligned base metal, mesa isolation, polyimide planarization, and an air bridge metallization. A citric acid-based, selective GaAs etch has been developed for use in the self-aligned emitter etch/base metallization process. The etch has demonstrated excellent control and the uniformity necessary for high-yield wafer processing. The citric acid etch has also been used to implement the selective collector etch which minimizes the base-collector parasitic capacitance. An evaporated gold air bridge process has been developed and replaces a plated gold process, thereby improving yield and quality.
State-of-the-art InGaP/GaAs HBTs have been developed. A baseline device structure and the standard fabrication process have consistently produced devices with a common-emitter current gain $\beta>50,$ a common-emitter breakdown voltage $BV\sb{\rm CEO}>10$ V, a current gain cutoff frequency $f\sb{\rm T}>50$ GHz, and a maximum frequency of oscillation $f\sb{\rm max}>100$ GHz. Advanced device structures have been investigated for improving device performance and $f\sb{\rm T}$'s as high as 93 GHz, and $f\sb{\rm max}$'s as high as 197 GHz have been achieved. For power applications, InGaP/GaAs double heterojunction bipolar transistors (DHBTs) were analyzed and a composite collector structure has been optimized to improve DHBT operating characteristics. Finally, a submicron, self-aligned emitter ledge structure has been demonstrated, which is formed using wet chemical selective etches and does not require additional masking layers as do present ledge fabrication technologies.
Presently, the leading HBT material technology is AlGaAs/GaAs. However, the InGaP/GaAs material system offers significant advantages in device performance and manufacturability. The band alignment of InGaP/GaAs improves device performance and the absence of aluminum in the emitter improves noise characteristics and long-term reliability. In addition, the availability of highly selective etch chemistries makes it easier to manufacture InGaP/GaAs HBTs. This work demonstrates the manufacturability and performance potential of InGaP/GaAs HBTs.
Issue Date:1996
Rights Information:Copyright 1996 Fresina, Michael Thomas
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9812828
OCLC Identifier:(UMI)AAI9812828

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