Direct optical control of a microwave phase shifter using GaAs fieldeffect transistors

The design and analysis of a novel optical-to-microwave transducer based upon direct optical control of microwave gallium arsenide (GaAs) field-effect transistor (FET) switches is the subject of this thesis. The switch is activated by illuminating the gate depletion region of the FET device with laser light having a photon energy and wavelength appropriate to the generation of free carriers (electron-hole pairs) within GaAs. The effects of light on the DC and microwave properties of the GaAs FET are explored and analyzed to permit the characterization of the switching performance and transient response of a reflective microwave switch. The switch is novel in that it utilizes direct optical control, whereby the optically controlled GaAs FET is directly in the path of the microwave signal and therefore relies on optically-induced variations in the microwave characteristics of the switch. This contrasts with previous forms of optically controlled switches which rely on indirect methods with the optical stimulus inducing variations in the DC characteristics of the GaAs FET, such that there is no direct interaction between the optically illuminated GaAs FET and the microwave signal. Measured and simulated results relating to the switching performance and transient response of the direct optically controlled microwave switch have been obtained and published as a result of this work. For the first time, good agreement is achieved between the measured and simulated results for the rise and fall times associated with the transient response of the gate photovoltaic effect in optically controlled GaAs FET switches. This confirms that the GaAs FET, when used as an optically controlled microwave switch, has a transient response of the order of several micro-seconds. An enhanced model of the GaAs FET switch has been developed, which represents a more versatile approach and leads to improved accuracy in predicting switching performance. This approach has been shown to be valid for both optical and electrical control of the GaAs FET. This approach can be used to model GaAs FET switches in discrete or packaged forms and predicts accurately the occurrence of resonances which may degrade the switch performance in both switching states. A novel method for tuning these resonances out of the switch operating band has been developed and published. This allows the switch to be configured to operate over the frequency range 1 to 20 GRz. The agreement between the models and measured data has been shown to hold for two very different GaAs FET structures. The results of the direct optically controlled microwave GaAs FET switch have been used as the basis for the design of a novel direct optically controlled microwave phase shifter circuit; Measured and simulated results are in good agreement and verify that the performance of the optically controlled phase shifter is comparable with previously published results for electrically controlled versions of the phase shifter. The 10 GRz phase shifter was optically controlled over a 1 GRz frequency range and exhibited a mid-band insertion loss of 0.15 dB. The outcome of the work provides the basis for directly controlling the phase of a microwave signal using the output of an optical sensor, with the GaAs FET acting as an optical-to-microwave transducer through a monolithic interface

Novel modelling methods for microwave GaAs MESFET device

Ph.DDOCTOR OF PHILOSOPH

4H-SiC Integrated circuits for high temperature and harsh environment applications

Silicon Carbide (SiC) has received a special attention in the last decades thanks to its superior electrical, mechanical and chemical proprieties. SiC is mostly used for applications where Silicon is limited, becoming a proper material for both unipolar and bipolar power device able to work under high power, high frequency and high temperature conditions. Aside from the outstanding theoretical and practical advantages still to be proved in SiC devices, the need for more accurate models for the design and optimization of these devices, along with the development of integrated circuits (ICs) on SiC is indispensable for the further success of modern power electronics. The design and development of SiC ICs has become a necessity since the high temperature operation of ICs is expected to enable important improvements in aerospace, automotive, energy production and other industrial systems. Due to the last impressive progresses in the manufacturing of high quality SiC substrates, the possibility of developing ICs applications is now feasible. SiC unipolar transistors, such as JFETs and MESFETs show a promising potential for digital ICs operating at high temperature and in harsh environments. The reported ICs on SiC have been realized so far with either a small number of elements, or with a low integration density. Therefore, this work demonstrates that by means of our SiC MESFET technology, multi-stage digital ICs fabrication containing a large number of 4H-SiC devices is feasible, accomplishing some of the most important ICs requirements. The ultimate objective is the development of SiC digital building blocks by transferring the Si CMOS topologies, hence demonstrating that the ICs SiC technology can be an important competitor of the Si ICs technology especially in application fields in which high temperature, high switching speed and harsh environment operations are required. The study starts with the current normally-on SiC MESFET CNM complete analysis of an already fabricated MESFET. It continues with the modeling and fabrication of a new planar-MESFET structure together with new epitaxial resistors specially suited for high temperature and high integration density. A novel device isolation technique never used on SiC before is approached. A fabrication process flow with three metal levels fully compatible with the CMOS technology is defined. An exhaustive experimental characterization at room and high temperature (300ºC) and Spice parameter extractions for both structures are performed. In order to design digital ICs on SiC with the previously developed devices, the current available topologies for normally-on transistors are discussed. The circuits design using Spice modeling, the process technology, the fabrication and the testing of the 4H-SiC MESFET elementary logic gates library at high temperature and high frequencies are performed. The MESFET logic gates behavior up to 300ºC is analyzed. Finally, this library has allowed us implementing complex multi-stage logic circuits with three metal levels and a process flow fully compatible with a CMOS technology. This study demonstrates that the development of important SiC digital blocks by transferring CMOS topologies (such as Master Slave Data Flip-Flop and Data-Reset Flip-Flop) is successfully achieved. Hence, demonstrating that our 4H-SiC MESFET technology enables the fabrication of mixed signal ICs capable to operate at high temperature (300ºC) and high frequencies (300kHz). We consider this study an important step ahead regarding the future ICs developments on SiC. Finally, experimental irradiations were performed on W-Schotthy diodes and mesa-MESFET devices (with the same Schottky gate than the planar SiC MESFET) in order to study their radiation hardness stability. The good radiation endurance of SiC Schottky-gate devices is proven. It is expected that the new developed devices with the same W-Schottky gate, to have a similar behavior in radiation rich environments.Postprint (published version

Advanced 3-V semiconductor technology assessment

Components required for extensions of currently planned space communications systems are discussed for large antennas, crosslink systems, single sideband systems, Aerostat systems, and digital signal processing. Systems using advanced modulation concepts and new concepts in communications satellites are included. The current status and trends in materials technology are examined with emphasis on bulk growth of semi-insulating GaAs and InP, epitaxial growth, and ion implantation. Microwave solid state discrete active devices, multigigabit rate GaAs digital integrated circuits, microwave integrated circuits, and the exploratory development of GaInAs devices, heterojunction devices, and quasi-ballistic devices is considered. Competing technologies such as RF power generation, filter structures, and microwave circuit fabrication are discussed. The fundamental limits of semiconductor devices and problems in implementation are explored

GaN heterojunction FET device Fabrication, Characterization and Modeling

This dissertation is focused on the research efforts to develop the growth, processing, and modeling technologies for GaN-based Heterojunction Field Effect Transistors (HFETs). The interest in investigating GaN HFETs is motivated by the advantageous material properties of nitride semiconductor such as large band gap, large breakdown voltage, and high saturation velocity, which make it very promising for the high power and microwave applications. Although enormous progress has been made on GaN transistors in the past decades, the technologies for nitride transistors are still not mature, especially concerning the reliability and stability of the device. In order to improve the device performance, we first optimized the growth and fabrication procedures for the conventional AlGaN barrier HFET, on which high carrier mobility and sheet density were achieved. Second, the AlInN barrier HFET was successfully processed, with which we obtained improved I-V characteristics compared with conventional structure. The lattice-matched AlInN barrier is beneficial in the removal of strain, which leads to better carrier transport characteristics. Furthermore, new device structures have been examined, including recess-gate HFET with n+ GaN cap layer and gate-on-insulator HFET, among which the insertion of gate dielectrics helps to leverage both DC and microwave performances. In order to depict the microwave behavior of the HFET, small signal modeling approaches were used to extract the extrinsic and intrinsic parameters of the device. An 18-element equivalent circuit model for GaN HFET has been proposed, from which various extraction methods have been tested. Combining the advantages from the cold-FET measurements and hot-FET optimizations, a hybrid extraction method has been developed, in which the parasitic capacitances were attained from the cold pinch-off measurements while the rest of the parameters from the optimization routine. Small simulation error can be achieved by this method over various bias conditions, demonstrating its capability for the circuit level design applications for GaN HFET. Device physics modeling, on the other hand, can help us to reveal the underlying physics for the device to operate. With the development of quantum drift-diffusion modeling, the self-consistent solution to the Schrödinger-Poisson equations and carrier transport equations were fulfilled. Lots of useful information such as band diagram, potential profile, and carrier distribution can be retrieved. The calculated results were validated with experiments, especially on the AlInN layer structures after considering the influence from the parasitic Ga-rich layer on top of the spacer. Two dimensional cross-section simulation shows that the peak of electrical field locates at the gate edge towards the drain, and of different kinds of structures the device with gate field-plate was found to efficiently reduce the possibility of breakdown failure

Design and characterization of GaAs multilayer CPW components and circuits for advanced MMICs

With the demand of modern wireless communications, monolithic microwave integrated circuit (MMIC) has become a very promising technique as it is mass-productive, low loss and highly integrated. Microstrip and Coplanar Waveguide (CPW) are both widely used in MMIC. Particularly, CPW has seen a rapid increase on research works recent years due to its unique capability including having less parasitic contribution to the circuit. In this thesis, a novel 3-D multilayer CPW technique is presented. Semi-insulating (S.I.) GaAs substrate, polyimide dielectric layers and Titanium/Gold metal layers are employed in this five-layer structure. The active devices are based on GaAs pHEMTs technology provided by Filtronic Compound Semiconductor Ltd. The fabricated components are simulated and characterized by Agilent Advanced Design System (ADS) and Momentum E.M simulator. A novel Open-short-through de-embedding technique is developed and applied to the passive circuits in order to reduce the impact of pads on probing. A new library of components and circuits are built in this work. Various structures of 3-D CPW transmission lines are designed and characterized to demonstrate the low-loss and highly compact characters. Meanwhile, the influence of various combinations of metal and dielectric layers is studied in order to provide designers with great flexibility for the realization of novel compact transmission lines for 3D MMICs. The effect of temperature on the performance of the transmission lines has also been investigated. Moreover, a set of compact capacitors are designed and proven to have high capacitance density with low parasitics. Finally, based on the extraction of pHEMT parameters from circuit characterization and analysis program (IC-CAP), RF switch and active filter MMICs have been designed and simulated to provide references for further development of 3-D multilayer CPW circuits.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Millimetre-wave optically injection-locked oscillators for radio-over-fibre systems

Theoretical analysis and experimental results for millimetre-wave optically injection-locked oscillators are presented in this thesis. Such oscillators can be employed to replace conventional photodiode plus amplifier receivers for local oscillator signal reception in millimetre-wave radio-over-fibre systems. The theories for electrical injection-locked oscillators are reviewed in detail. Three differences between Adler’s and Kurokawa’s equations for locking bandwidth are highlighted for the first time. These differences are the absence of l/cos# factor in Adler’s equation, larger bandwidth predicted by Kurokawa’s equation, and a difference in definition of Q factors. Locking bandwidth equations for optically injection-locked oscillators are developed based on the theories of electrical injection-locked oscillators and are then used to design optically injection-locked oscillators. A novel millimetre-wave indirect optically injection-locked oscillator is presented. An edge-coupled photodiode is used to detect the optical signal. Negative resistance and computer simulation techniques were used for predicting the free running oscillation frequency. The maximum output power of the oscillator is 5.3 dBm, and the maximum locking bandwidth is measured to be 2.6 MHz with an output power o f-12 dBm. Results from a comparison with conventional optical receivers show that the gain of the optically injection-locked oscillator is more than 10 dB higher than that of a photodiode plus amplifier receiver, that the oscillator output power remains constant with input signal power variations whereas the output power of the photodiode plus amplifier receiver changes (linearly) with the input signal power, and that, at high-offset frequencies, the phase noise of the optically injection-locked oscillator is much lower than that of the photodiode plus amplifier receiver. These advantages make the optically injection-locked oscillator an ideal replacement for the photodiode plus amplifier receiver in radio-over-fibre systems. An improved wide-band design for millimetre-wave optically injection-locked oscillators is presented for future work

An Analytic model for high electron mobility transistors.

Thesis (Ph.D.)-University of Natal, Durban, 1986.The last six years has seen the emergence and rapid development of a new type of field effect transistor, the High Electron Mobility Transistor (HEMT), which offers improved performance in both digital and analogue circuits compared with circuits incorporating either MEtal Semiconductor (MES) or Metal Oxide Semiconductor (MOS) FETs. A new physically-based analytic model for HEMTs, which predicts the DC and RF electrical performance from the material and structural parameters of the device, is presented. The efficacy of the model is demonstrated with comparisons between simulated and measured device characteristics, at DC and microwave frequencies. The good agreement with experiment obtained with the model indicates that velocity overshoot effects are considerably less important in HEMTs than has been widely assumed, and that the electron transit velocity in submicron devices is approximately 10 cm/s, rather than around 2x10 cm/s. The Inverted HEMT, one of the major HEMT structural variants, is emphasized throughout this work because of its potential advantages over other variants, and practical results from 0.5 micron gate length Inverted HEMTs are presented

Elevated temperature stability of gallium arsenide integrated circuits

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (p. 147-154).by Eric Braun.M.S