Bipolar transistors, Computer aided design, Heterojunctions, Microwave integrated circuits, Reliability (Engineering), Simulation methods


Recent years have shown real advances of microwave monolithic integrated circuits (MMICs) for millimeter-wave frequency systems, such as wireless communication, advanced imaging, remote sensing and automotive radar systems, as MMICs can provide the size, weight and performance required for these systems. Traditionally, GaAs pseudomorphic high electron mobility transistor (pHEMT) or InP based MMIC technology has dominated in millimeter-wave frequency applications because of their high fT and fmax as well as their superior noise performance. But these technologies are very expensive. Thus, for low cost and high performance applications, InGaP/GaAs heterojunction bipolar transistors (HBTs) are quickly becoming the preferred technology to be used due to their inherently excellent characteristics. These features, together with the need for only one power supply to bias the device, make InGaP/GaAs HBTs very attractive for the design of high performance fully integrated MMICs. With the smaller dimensions for improving speed and functionality of InGaP/GaAs HBTs, which dissipate large amount of power and result in heat flux accumulated in the device junction, technology reliability issues are the first concern for the commercialization. As the thermally triggered instabilities often seen in InGaP/GaAs HBTs, a carefully derived technique to define the stress conditions of accelerated life test has been employed in our study to acquire post-stress device characteristics for the projection of long-term device performance degradation pattern. To identify the possible origins of the post-stress device behaviors observed experimentally, a two iv dimensional (2-D) TCAD numerical device simulation has been carried out. Using this approach, it is suggested that the acceptor-type trapping states located in the emitter bulk are responsible for the commonly seen post-stress base current instability over the moderate base-emitter voltage region. HBT-based MMIC performance is very sensitive to the variation of core device characteristics and the reliability issues put the limit on its radio frequency (RF) behaviors. While many researchers have reported the observed stress-induced degradations of GaAs HBT characteristics, there has been little published data on the full understanding of stress impact on the GaAs HBTbased MMICs. If care is not taken to understand this issue, stress-induced degradation paths can lead to built-in circuit failure during regular operations. However, detection of this failure may be difficult due to the circuit complexity and lead to erroneous data or output conditions. Thus, a practical and analytical methodology has been developed to predict the stress impacts on HBTbased MMICs. It provides a quick way and guidance for the RF design engineer to evaluate the circuit performance with reliability considerations. Using the present existing EDA tools (Cadance SpectreRF and Agilent ADS) with the extracted pre- and post-stress transistor models, the electrothermal stress effects on InGaP/GaAs HBT-based RF building blocks including power amplifier (PA), low-noise amplifier (LNA) and oscillator have been systematically evaluated. This provides a potential way for the RF/microwave industry to save tens of millions of dollars annually in testing costs. v The world now stands at the threshold of the age of advanced GaAs HBT MMIC technology and researchers have been exploring here for years. The reliability of GaAs HBT technology is no longer the post-design evaluation, but the pre-design consideration. The successful and fruitful results of this dissertation provide methods and guidance for the RF designers to achieve more reliable RF circuits with advanced GaAs HBT technology in the future.


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Graduation Date





Liou, Juin J.


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Electrical Engineering and Computer Science








Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)


Dissertations, Academic -- Engineering and Computer Science, Engineering and Computer Science -- Dissertations, Academic