This thesis investigates the possibility of realizing bandgap reference crcuits for processes having sub-1V supply voltage. With the scaling of gate oxide thickness supply voltage is getting reduced. But the threshold voltage of transistors is not getting scaled at the same rate as that of the supply voltage. This makes it difficult to incorporate conventional designs of bandgap reference circuits to processeshaving near to 1V supply voltage. In the first part of the thesis a comprehensive study on existing low voltage bandgap reference circuits is done. Using these ideas a low-power, low-voltage bandgap reference circuit is designed in the second part of the thesis work. The proposed bandgap reference circuit is capable of generating a reference voltage of 0.730V. The circuit is implemented in 0.18µm standard CMOS technology and operates with 0.9V supply voltage, consuming 5µA current. The circuit achieves 7 ppm/K of temperature coefficient with supply voltage range from 0.9 to 1.5V and temperature range from 0 to 60C.

With the evolution of technologies, mixed-signal system integration is becoming necessary for combining heterogeneous functions such as high-speed processors, radio frequency (RF) circuits, memory, microelectromechanical systems (MEMS), sensors, and optoelectronic devices. This kind of integration is required for convergent microsystems that support communication and computing capabilities in a tightly integrated module. A major bottleneck with such heterogeneous integration is the noise coupling between the dissimilar blocks constituting the system. The noise generated by the high-speed digital circuits can couple through the power distribution network (PDN) and this noise can transfer to sensitive RF circuits, completely destroying the functionality of noise-sensitive RF circuits. One common method used for mixed-signal integration in the package is splitting the power and/or ground planes. The gap in the power and ground planes can partially block the propagation of electromagnetic waves. However, electromagnetic energy can still couple through the split, especially at frequencies greater than 1 GHz. The AI-EBG structure in this dissertation has been developed to suppress unwanted noise coupling in mixed-signal systems and this AI- EBG structure shows excellent isolation (-80 dB ~ -140 dB), which results in a noise coupling-free environment in mixed-signal systems. The AI-EBG structure would be part of the power distribution network (PDN) in systems and is expected to have a significant impact on noise suppression and isolation in mixed-signal systems in future.

With electronic devices trending toward higher clock rates, lower voltage levels, and smaller form factors, the simultaneously switching noise (SSN), which is induced in package and printed circuit board, is one of the major factors affecting the performance and design of the high speed digital circuits. This noise will lead to false switching and malfunctioning in digital and/or analog circuits, and causes serious signal integrity (SI) and electromagnetic interference (EMI) problems for the high speed digital systems. Therefore, mitigating the SSN becomes a major challenge for the high speed circuits design. In this thesis, first of all, we introduce and discuss previously proposed solutions to suppress the SSN. These solutions include the use of decoupling capacitors, isolation moats, and electromagnetic bnadgap (EBG) structures. We analyzed the EBG structures and generated some EBG design rules. As the speed of digital circuits moving toward higher frequencies, the Double L-bridge EBG structure can be used to improve the performance of Hybrid EBG structure by employing the EBG design rules that were generated. The Double L-bridge EBG structure design improved the behavior at the high frequencies, which also maintained the low frequency performance. It is demonstrated numerically and experimentally. For fast estimating the stopband, we use one-dimensional lump circuit model. Then, we propose another structure, named Double Cross EBG structure. This design, compared to the Double L-bridge EBG structure, not only maintained the high frequency performance, but also improved the low frequency behavior. It is also both experimentally and numerically validated.

In this thesis, we propose a new structure of GaP/a-Si:H/BulkSi solar cell in which the additional a-Si:H layer due to the concept of energy bandgap is used to improve the open-circuit voltage. As the a-Si:H doping concentration is increased, the upward bandgap bending is expected to be observed; hence, a high open-circuit voltage is obtained. But in this situation, the upward bandgap bending also hinders the carrier transport, leading a low short-circuit current density. It is worth noting that the proposed solar cell can have a high open-circuit voltage of 0.758 V. In addition, we carefully investigate the characteristics of wide-bandgap gallium phosphide (GaP) material used for silicon-based solar cells. According to the simulated results, the absorption of GaP is better than silicon with a wavelength below 450 nm. Also, the GaP/BulkSi solar cell is shown to have a lower reflectivity value than the conventional PN_BulkSi solar cell. Hence we can prove that the internal quantum efficiency and external quantum efficiency are improved accordingly. As a result, the short-circuit current density is increased about 10 %. In addition, the optimized parameters of a GaP/BulkSi solar cell are as follows: the short-circuit current density is 21.264 mA/cm2, the open-circuit voltage is 0.624 V, the fill factor is 82.4 %, the conversion efficiency is 11.236 %, respectively.

Transient current surges resulted from the simultaneous switching of output buffers in the high-speed digital circuits can induce significant ground bounce noise (GBN) on the chip, package, and printed circuit board (PCB). The GBN not only causes the signal integrity (SI) problems, such as glitches or timing push-out of signal traces, but also increases the electromagnetic interference (EMI) in the high-speed digital circuits. With the design trends of digital circuits toward higher speed, low voltage level, smaller volume, the impact of GBN has become one of the most important issues that determine the performance of electronic products. Adding decoupling capacitors between the power and ground planes is a typical way to suppress the GBN. However, they are not effective at the frequencies higher than 600MHz due to their inherent lead inductance. Recently, a new idea for eliminating the GBN is proposed by designing electromagnetic bandgap (EBG) structure with high impedance surface (HIS) on the ground or power plane. Several new EBG power/ground plane designs have been proposed to broaden the stopband bandwidth for suppressing the GBN. However there are some drawbacks, such as high cost, large area occupation and complicated fabrication process. In this paper, we propose a novel Hybrid EBG power planes for PCB or package to suppress the GBN. Its extinctive behavior of broadband suppression of GBN (over 10GHz) is demonstrated experientially and numerically. Finally, we combine the periodic high-low dielectric material with the EBG power plane to control the position and bandwidth of stopband.

The power/ground plane structure within an electronic system not only delivers power, but also provides return path for the currents associated with the propagating signals. The cavity resonances within the power/ground plane structure affect the signal integrity of the system at high frequencies. The chip complexity and clock speed continue to increase and new structures, such as meshed planes and electromagnetic bandgap structures, are used in plane pair structure design. The signal integrity analysis of the power/ground plane structure becomes exceedingly important and challenging.The primary goal of this research is an in-depth investigation of the impact of the cavity resonances associated with the plane pair structure on the signal integrity. This includes development of modeling, simulation, and measurement methodologies for accurate and efficient characterization or prediction of the time/frequency domain electrical characteristics of power/ground plane pair structures. This research is divided into three parts. First, new SPICE compatible models are proposed for the new structures, such as the meshed plane and EBG embedded plane pair designs, so that the power/ground plane designs with these new structures can be simulated efficiently. Second, the accuracy of the simulation results is vital. The behavior of the benchmark structures is simulated and simulation results are verified either experimentally or by comparing with those from tools that are proven to be accurate. Third, high frequency measurement data is vulnerable to all parasitic parameters. The factors that affect the accuracy of measured data are investigated and methods to improve the accuracy of the measured data are proposed and verified.

GaN RF switches are widely used in today’s communication systems. With digital communications getting more and more popular nowadays, the need for improving the performance of involved RF switches is inevitable. Designing low ON-state resistance GaN switches are exceedingly important to improve the switch insertion loss, isolation and power loss. Moreover, considerations need to be taken into account to improve the switching speed of the involved GaN HEMTs. In this dissertation, a new GaN HEMT structure called “Tunnel MOS Heterostructure FET (TMOSHFET)” is introduced which has lower ON-state resistance and faster switching speed compared to conventional AlGaN/GaN HEMTs. In the switch ON process, the channel of this device is charged up by electron tunneling from a layer underneath the channel as opposed to typical AlGaN/GaN HEMTs in which electron injection from the source is charging up the channel. The tunneling nature of this process together with the shorter travel distance of electrons in TMOSHFET provide for a faster switching speed. In order to understand the tunneling mechanisms in TMOSHFET, the fabrication of AlGaN/GaN Schottky Barrier Diodes (SBDs) with various AlGaN thicknesses is demonstrated on Si (111) substrate. The impacts of SF6 dry etching on the trap density and trap state energy of AlGaN surface are investigated using the GP/w- w method. Various tunneling mechanisms at different biases are then characterized in samples and compared with each other. To improve the source and drain resistances in TMOSHFET, a model is generated to optimize the 2DEG density and electric field in AlGaN/GaN heterostructure based on Al mole fraction, AlGaN thickness and the thickness of SiN passivation layer and it is experimentally verified by non-contact Hall 2DEG density measurements. The spontaneous and piezoelectric polarizations together with strain relaxation have been implemented into the model, taking into account the annealing effects. From the experimental data on obtained parameters, the operation and device parameterization of the TMOSHFET is outlined and design considerations to improve the device R_(ON)-V_(BR) figure of merit are discussed.

Photonic bandgap materials are periodic structures that exclude electromagnetic field propagation over frequency intervals known as bandgaps. These materials exhibit remarkable wave dispersion and have found use in many applications that require control over dynamic electromagnetic fields, as their properties can be tailored by design. The two principal objectives of this thesis are the development of a liquid crystal-based microwave photonic bandgap device whose bandgap could be tuned during operation and the design and implementation of a spectral transmission-line modeling method for band structure calculations. The description of computational methods comprises an overview of the implemented numerical routines, a derivation of the spectral properties of the transmission-line modeling method in periodic domains, and the development of an efficient sparse matrix eigenvalue algorithm that formed the basis of the spectral transmission-line modeling method. The discussion of experimental methods considers the use of liquid crystals in microwave applications and details the design and fabrication of several devices. These include a series of modified twisted nematic cells that were used to evaluate liquid crystal alignment and switching, a patch resonator that was used to measure liquid crystal permittivity, and the liquid crystal photonic bandgap device itself. Numerical experiments showed that the spectral transmission-line modeling method is accurate and substantially faster and less memory intensive than the reference plane wave method for problems of high dielectric contrast or rapidly varying spatial detail. Physical experiments successfully realized a microwave photonic bandgap structure whose bandgap could be continuously tuned with a bias voltage. The very good agreement between simulated and measured results validate the computational and experimental methods used, particularly the resonance-based technique for permittivity measurement. This work's results may be applied to many applications, including microwave filters, negative group velocity/negative refraction materials, and microwave permittivity measurement of liquid crystals.

Photonic bandgap materials are periodic structures that exclude electromagnetic field propagation over frequency intervals known as bandgaps. These materials exhibit remarkable wave dispersion and have found use in many applications that require control over dynamic electromagnetic fields, as their properties can be tailored by design. The two principal objectives of this thesis are the development of a liquid crystal-based microwave photonic bandgap device whose bandgap could be tuned during operation and the design and implementation of a spectral transmission-line modeling method for band structure calculations. The description of computational methods comprises an overview of the implemented numerical routines, a derivation of the spectral properties of the transmission-line modeling method in periodic domains, and the development of an efficient sparse matrix eigenvalue algorithm that formed the basis of the spectral transmission-line modeling method. The discussion of experimental methods considers the use of liquid crystals in microwave applications and details the design and fabrication of several devices. These include a series of modified twisted nematic cells that were used to evaluate liquid crystal alignment and switching, a patch resonator that was used to measure liquid crystal permittivity, and the liquid crystal photonic bandgap device itself. Numerical experiments showed that the spectral transmission-line modeling method is accurate and substantially faster and less memory intensive than the reference plane wave method for problems of high dielectric contrast or rapidly varying spatial detail. Physical experiments successfully realized a microwave photonic bandgap structure whose bandgap could be continuously tuned with a bias voltage. The very good agreement between simulated and measured results validate the computational and experimental methods used, particularly the resonance-based technique for permittivity measurement. This work's results may be applied to many applications, including microwave filters, negative group velocity/negative refraction materials, and microwave permittivity measurement of liquid crystals.

Referências de tensão são blocos fundamentais em uma série de aplicações de sinais mistos e de rádio frequência, como por exemplo, conversores de dados, PLL's e conversores de potência. A implementação CMOS mais usada para referências de tensão é o circuito Bandgap devido sua alta previbilidade, e baixa dependência em relação à temperatura e tensão de alimentação. Este trabalho estuda aplicação de Referência de Tensão Bandgap. O princípio, as topologias tradicionalmente usadas para implementar este método e as limitações que essas arquiteturas sofrem são investigadas. Será também apresentada uma pesquisa das questões recentes envolvendo alta precisão, operação com baixa tensão de alimentação e baixa potência, e ruído de saída para as referências Bandgap fabricadas em tecnologias submicrométricas. Além disso, uma investigação abrangente do impacto causado pelo o processo da fabricação e do ruído no desempenho da referência é apresentada. Será mostrado que o ruído de saída pode limitar a precisão dos circuitos Bandgap e seus circuitos de ajuste. Para desenvolver nosso trabalho, três Referências Bandgap foram projetadas utilizando o processo IBM 7RF 0.18 micra com uma tensão de alimentação de 1.8V. Também foram projetados os leiautes desses circuitos para prover informações pósleiaute extraídos e resultados de simulação elétrica. Este trabalho provê uma discussão de algumas topologias e das práticas de projeto para referências Bandgap. / A Voltage Reference is a pivotal block in several mixed-signal and radio-frequency applications, for instance, data converters, PLL's and power converters. The most used CMOS implementation for voltage references is the Bandgap circuit due to its highpredictability, and low dependence of the supply voltage and temperature of operation. This work studies the Bandgap Voltage References (BGR). The most relevant and the traditional topologies usually employed to implement Bandgap Voltage References are investigated, and the limitations of these architectures are discussed. A survey is also presented, discussing the most relevant issues and performance metrics for BGR, including, high-accuracy, low-voltage and low-power operation, as well as the output noise of Bandgap References fabricated in submicrometer technologies. Moreover, a comprehensive investigation on the impact of fabrication process effects and noise on the reference voltage is presented. It is shown that output noise can limit the accuracy of the BGR and trim circuits. To support and develop our work, three BGR´s were designed using the IBM 0.18 Micron 7RF process with a supply voltage of 1.8 V. The layouts of these circuits were also designed to provide post-extracted layout information and electrical simulation results. This work provides a comprehensive discussion on the structure and design practices for Bandgap References.