Distributed Circuit Analysis and Design for Ultra-wideband Communication and sub-mm Wave Applications

This thesis explores research into new distributed circuit design techniques and topologies, developed to extend the bandwidth of amplifiers operating in the mm and sub-mm wave regimes, and in optical and visible light communication systems. Theoretical, mathematical modelling and simulation-based studies are presented, with detailed designs of new circuits based on distributed amplifier (DA) principles, and constructed using a double heterojunction bipolar transistor (DHBT) indium phosphide (InP) process with fT =fmax of 350/600 GHz. A single stage DA (SSDA) with bandwidth of 345 GHz and 8 dB gain, based on novel techniques developed in this work, shows 140% bandwidth improvement over the conventional DA design. Furthermore, the matrix-single stage DA (M-SSDA) is proposed for higher gain than both the conventional DA and matrix amplifier. A two-tier M-SSDA with 14 dB gain at 300 GHz bandwidth, and a three-tier M-SSDA with a gain of 20 dB at 324 GHz bandwidth, based on a cascode gain cell and optimized for bandwidth and gain flatness, are presented based on full foundry simulation tests. Analytical and simulation-based studies of the noise performance peculiarities of the SSDA and its multiplicative derivatives are also presented. The newly proposed circuits are fabricated as monolithic microwave integrated circuits (MMICs), with measurements showing 7.1 dB gain and 200 GHz bandwidth for the SSDA and 12 dB gain at 170 GHz bandwidth for the three-tier M-SSDA. Details of layout, fabrication and testing; and discussion of performance limiting factors and layout optimization considerations are presented. Drawing on the concept of artificial transmission line synthesis in distributed amplification, a new technique to achieve up to three-fold improvement in the modulation bandwidth of light emitting diodes (LEDs) for visible light communication (VLC) is introduced. The thesis also describes the design and application of analogue pre-emphasis to improve signal-to-noise ratio in bandwidth limited optical transceivers

Reliability Study Of Ingap/gaas Heterojunction Bipolar Transistor Mmic Technology By Characterization, Modeling And Simulation

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

Millimeter and Sub-Millimeter Wave Integrated Active Frequency Down-Converters

In recent years, the increasing amount of data transmission, the need for automotive radars, and standoff imaging for security applications are the main factors that accelerate research in the millimeter and sub-millimeter wave frequency ranges. The semiconductor industries have continuously developed their processes, which have opened up opportunities for manufacturing monolithically integrated circuits up to a few hundred GHz, based on transistor technologies. In this thesis, a 100 nm GaAs mHEMT technology, a 250 nm InP DHBT technology, and a 130 nm SiGe BiCMOS technology, which show a typical ft / fmax of 200/300 GHz, 375/650 GHz, and 250/400 GHz, respectively, are verified for analog circuit design. In the above mentioned applications, the frequency mixer is one of the most important components. Consequently, a study of millimeter/submillimeter wave mixers is important for the choice of technology and topology. Aiming for either the next generation of high-speed communication or standoff imaging applications, different mixer topologies are studied, designed and fabricated as candidates for further integration in receivers. The presented mixer topologies include the self-oscillating mixer, the resistive FET mixer, the Gilbert mixer, and the transconductance mixer. All these topologies have been realized in given technologies, and cover the frequencies around ~145 GHz, ~220 GHz, and ~340 GHz. The designed 340 GHz Gilbert mixer with IF buffer amplifier and on-chip patch array antenna demonstrated the first fully integrated receiver in HBT technology at such high frequencies as well as a reasonable noise figure of 17 dB. A novel 110~170 GHz transconductance mixer is characterized in ×1, ×2, ×3, and ×4 harmonic mixing modes, which allows for flexibility in the overall system design. Apart from the mixer designs, a transceiver, which operates as an amplifier for transmitting and simultaneously as a down-converting mixer for receiving, is designed for the frequency range of 110~170 GHz, aiming for sub-cm resolution in multipixel standoff imaging systems. It is successfully demonstrated in a FMCW radar setup for distance measurements

Bismuth Surfactant Effects for GaAsN and Beryllium Doping of GaAsN Grown by Molecular Beam Epitaxy

Bi was investigated as a possible surfactant for growth of GaAs1-xNx layers on (100) GaAs substrates by molecular beam epitaxy using an RF plasma nitrogen source. Bi extends the useable growth conditions producing smoother surfaces to a significantly higher N content than without Bi. The conductivity of Be-doped GaAsN decreased significantly with increasing N concentration. Temperature dependent Hall measurement suggests possible compensation and increased activation energy. SIMS and Raman measurements indicate that the N composition increased by introducing Be, and for low [N], Bi. The addition of Bi during growth of Be-doped GaAsN only produced semi-insulating layers. GaAs1-xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 ºC a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples. The real substrate temperature preliminarily estimated by pyrometer measurement was further verified and determined by RHEED pattern transition. RHEED was also employed to observe the surface reconstruction. To optimize growth conditions, surface phase diagrams of As4/Ga BEP flux vs. the real substrate temperature under fixed As4 BEP ~4.5x10-6 Torr and fixed growth rate 0.46 μm/hr (0.45ML/s) were obtained. Different aperture plates of RF-plasma nitrogen discharge tube were used. Only the one with 10 x Ø0.2mm holes is able to produce streaky RHEED patterns under some growth circumstances, and was eventually selected to lead nitrogen species through for all growths in this work. Ga flux, N flow rate, and RF power were all found to be critical factors affecting the resultant N concentrations