Bandgap Reference Design at the 14-Nanometer FinFET Node

As supply voltages continue to decrease, it becomes harder to ensure that the voltage drop across a diode-connected BJT is sufficient to conduct current without sacrificing die area. One such solution to this potential problem is the diode-connected MOSFET operating in weak inversion. In addition to conducting appreciable current at voltages significantly lower than the power supply, the diode-connected MOSFET reduces the total area for the bandgap implementation. Reference voltage variations across Monte Carlo perturbations are more pronounced as the variation of process parameters are exponentially affected in subthreshold conduction. In order for this proposed solution to be feasible, a design methodology was introduced to mitigate the effects of process variation. A 14 nm bandgap reference was created and simulated across Monte Carlo perturbations for 100 runs at nominal supply voltage and 10% variation of the power supply in either direction. The best case reference voltage was found and used to verify the proposed resistive network solution. The average temperature coefficient was measured to be 66.46 ppm/◦C and the voltage adjustment range was found to be 204.1 mV. The two FinFET subthreshold diodes consume approximately 2.8% of the area of the BJT diode equivalent. Utilizing an appropriate process control technique, subthreshold bandgap references have the potential to overtake traditional BJT-based bandgap architectures in low-power, limited-area applications

An accurate, trimless, high PSRR, low-voltage, CMOS bandgap reference IC

Bandgap reference circuits are used in a host of analog, digital, and mixed-signal systems to establish an accurate voltage standard for the entire IC. The accuracy of the bandgap reference voltage under steady-state (dc) and transient (ac) conditions is critical to obtain high system performance. In this work, the impact of process, power-supply, load, and temperature variations and package stresses on the dc and ac accuracy of bandgap reference circuits has been analyzed. Based on this analysis, the a bandgap reference that 1. has high dc accuracy despite process and temperature variations and package stresses, without resorting to expensive trimming or noisy switching schemes, 2. has high dc and ac accuracy despite power-supply variations, without using large off-chip capacitors that increase bill-of-material costs, 3. has high dc and ac accuracy despite load variations, without resorting to error-inducing buffers, 4. is capable of producing a sub-bandgap reference voltage with a low power-supply, to enable it to operate in modern, battery-operated portable applications, 5. utilizes a standard CMOS process, to lower manufacturing costs, and 6. is integrated, to consume less board space has been proposed. The functionality of critical components of the system has been verified through prototypes after which the performance of the complete system has been evaluated by integrating all the individual components on an IC. The proposed CMOS bandgap reference can withstand 5mA of load variations while generating a reference voltage of 890mV that is accurate with respect to temperature to the first order. It exhibits a trimless, dc 3-sigma accuracy performance of 0.84% over a temperature range of -40°C to 125°C and has a worst case ac power-supply ripple rejection (PSRR) performance of 30dB up to 50MHz using 60pF of on-chip capacitance. All the proposed techniques lead to the development of a CMOS bandgap reference that meets the low-cost, high-accuracy demands of state-of-the-art System-on-Chip environments.Ph.D.Committee Chair: Rincon-Mora, Gabriel; Committee Member: Ayazi, Farrokh; Committee Member: Bhatti, Pamela; Committee Member: Leach, W. Marshall; Committee Member: Morley, Thoma

Vapor phase growth system and its use in the preparation of several III-V compound semiconductors

Vapor phase growth and properties of semiconductor material

LOW POWER AND HIGH SIGNAL TO NOISE RATIO BIO-MEDICAL AFE DESIGN TECHNIQUES

The research work described in this thesis was focused on finding novel techniques to implement a low-power and noise Bio-Medical Analog Front End (BMEF) circuit technique to enable high-quality Electrocardiography (ECG) sensing. Usually, an ECG signal and several bio-medical signals are sensed from the human body through a pair of electrodes. The electrical characteristics of the very small amplitude (1u-10mV) signals are corrupted by random noise and have a significant dc offset. 50/60Hz power supply coupling noise is one of the biggest cross-talk signals compared to the thermally generated random noise. These signals are even AFE composed of an Instrumentation Amplifier (IA), which will have a better Common Mode rejection ratio (CMRR). The main function of the AFE is to convert the weak electrical Signal into large signals whose amplitude is large enough for an Analog Digital Converter (ADC) to detect without having any errors. A Variable Gain Amplifier (VGA) is sometimes required to adjust signal amplitude to maintain the dynamic range of the ADC. Also, the Bio-medical transceiver needs an accurate and temperature-independent reference voltage and current for the ADC, commonly known as Bandgap Reference Circuit (BGR). These circuits need to consume as low power as possible to enable these circuits to be powered from the battery. The work started with analysing the existing circuit techniques for the circuits mentioned above and finding the key important improvements required to reach the target specifications. Previously proposed IA is generated based on voltage mode signal processing. To improve the CMRR (119dB), we proposed a current mode-based IA with an embedded DC cancellation technique. State-of-the-art VGA circuits were built based on the degeneration principle of the differential pair, which will enable the variable gain purpose, but none of these techniques discussed linearity improvement, which is very important in modern CMOS technologies. This work enhances the total Harmonic distortion (THD) by 21dB in the worst case by exploiting the feedback techniques around the differential pair. Also, this work proposes a low power curvature compensated bandgap with 2ppm/0C temperature sensitivity while consuming 12.5uW power from a 1.2V dc power supply. All circuits were built in 45nm TSMC-CMOS technology and simulated with all the performance metrics with Cadence (spectre) simulator. The circuit layout was carried out to study post-layout parasitic effect sensitivity

Integrated reference circuits for low-power capacitive sensor interfaces

This thesis consists of nine publications and an overview of the research topic, which also summarizes the work. The research described in this thesis concentrates on the design of low-power sensor interfaces for capacitive 3-axis micro-accelerometers. The primary goal throughout the thesis is to optimize power dissipation. Because the author made the main contribution to the design of the reference and power management circuits required, the overview part is dominated by the following research topics: current, voltage, and temperature references, frequency references, and voltage regulators. After an introduction to capacitive micro-accelerometers, the work describes the typical integrated readout electronics of a capacitive sensor on the functional level. The readout electronics can be divided into four different functional parts, namely the sensor readout itself, signal post-processing, references, and power management. Before the focus is shifted to the references and further to power management, different ways to realize the sensor readout are briefly discussed. Both current and voltage references are required in most analog and mixed-signal systems. A bandgap voltage reference, which inherently uses at least one current reference, is practical for the generation of an accurate reference voltage. Very similar circuit techniques can be exploited when implementing a temperature reference, the need for which in the sensor readout may be justified by the temperature compensation, for example. The work introduces non-linear frequency references, namely ring and relaxation oscillators, which are very suitable for the generation of the relatively low-frequency clock signals typically needed in the sensor interfaces. Such oscillators suffer from poor jitter and phase noise performance, the quantities of which also deserve discussion in this thesis. Finally, the regulation of the supply voltage using linear regulators is considered. In addition to extending the battery life by providing a low quiescent current, the regulator must be able to supply very low load currents and operate without off-chip capacitors

Integrated Circuits for Programming Flash Memories in Portable Applications

Smart devices such as smart grids, smart home devices, etc. are infrastructure systems that connect the world around us more than before. These devices can communicate with each other and help us manage our environment. This concept is called the Internet of Things (IoT). Not many smart nodes exist that are both low-power and programmable. Floating-gate (FG) transistors could be used to create adaptive sensor nodes by providing programmable bias currents. FG transistors are mostly used in digital applications like Flash memories. However, FG transistors can be used in analog applications, too. Unfortunately, due to the expensive infrastructure required for programming these transistors, they have not been economical to be used in portable applications. In this work, we present low-power approaches to programming FG transistors which make them a good candidate to be employed in future wireless sensor nodes and portable systems. First, we focus on the design of low-power circuits which can be used in programming the FG transistors such as high-voltage charge pumps, low-drop-out regulators, and voltage reference cells. Then, to achieve the goal of reducing the power consumption in programmable sensor nodes and reducing the programming infrastructure, we present a method to program FG transistors using negative voltages. We also present charge-pump structures to generate the necessary negative voltages for programming in this new configuration

Correlating X-ray microanalysis and cathodoluminescence data from III-nitride semiconductors

Research in group III- nitride semiconductors has seen major developments during the last couple of decades. One of the materials that satisfy requirements for optoelectronic devices in the ultra-violet (UV) spectral range and high power, high frequency electronic devices is the AlGaN. Performance and reliability of these devices will strongly depend on the electronic properties of epitaxial layers which are critically affected by structural defects and unintentional and intentional doped impurities. This thesis presents research on III- nitride semiconductors, in particular AlGaN and GaN materials. It is focused on characterization of AlGaN materials and the effects of n- and p-type doping, AlN content, occurrence of defects and crystal orientation on its quality. Different electron microscopy techniques are used to investigate luminescence, composition and doping properties of semiconductor structures and their correlation with surface features. The main techniques used for the characterization consisted of cathodoluminescence spectroscopy (CL) for the probing of luminescence properties, secondary electron (SE) and backscattered electron (BSE) imaging for investigation of the sample morphology and wavelength dispersive X-ray (WDX) spectroscopy for compositional analysis. The type of growth method and choice of substrate have a great influence on the surface morphology and luminescence homogeneity of the AlGaN layer, with compositional inhomogeneity of the MBE samples confirmed only on sub μm level but having lower emission intensity compared to MOCVD samples. The thesis presents detailed steps of a procedure to quantify trace elements and investigates the associated challenges. The whole process of measurement optimization for Mg and Si dopants is described and final recipe on how to measure the concentration of major (alloy) and minor Si/Mg (dopant) elements is presented. A systematic study of polar and semipolar n-type doped AlGaN/AlN layers grown on sapphire by (MOCVD) with varied Si/group-III ratios in the gas phase was accomplished. The AlN incorporation was higher in the polar samples and the highest values of Si incorporations were observed for the polar samples with the highest Si/III ratios, while saturation of Si incorporation was seen for the semipolar samples at higher Si/III ratios. CL point spectra showed how changes in the relative intensity of the NBE peaks and impurity transitions depend strongly on the growth conditions and surface orientations. The semipolar samples showed better compositional homogeneity. A study was also performed on AlGaN:Mg samples to study the impurity transitions and luminescence properties of non LED epilayer samples grown on MOCVD AlN/sapphire templates and more complicated LED structures with different numbers of MBE-grown layers. MBE samples showed superior quality to other combinations of MBE and MOCVD structures, mainly due to problems associated with the transfer of sample between different reactors and the introduction of impurities that will form different defects within the material. Finally, some proposals for future work are presented.Research in group III- nitride semiconductors has seen major developments during the last couple of decades. One of the materials that satisfy requirements for optoelectronic devices in the ultra-violet (UV) spectral range and high power, high frequency electronic devices is the AlGaN. Performance and reliability of these devices will strongly depend on the electronic properties of epitaxial layers which are critically affected by structural defects and unintentional and intentional doped impurities. This thesis presents research on III- nitride semiconductors, in particular AlGaN and GaN materials. It is focused on characterization of AlGaN materials and the effects of n- and p-type doping, AlN content, occurrence of defects and crystal orientation on its quality. Different electron microscopy techniques are used to investigate luminescence, composition and doping properties of semiconductor structures and their correlation with surface features. The main techniques used for the characterization consisted of cathodoluminescence spectroscopy (CL) for the probing of luminescence properties, secondary electron (SE) and backscattered electron (BSE) imaging for investigation of the sample morphology and wavelength dispersive X-ray (WDX) spectroscopy for compositional analysis. The type of growth method and choice of substrate have a great influence on the surface morphology and luminescence homogeneity of the AlGaN layer, with compositional inhomogeneity of the MBE samples confirmed only on sub μm level but having lower emission intensity compared to MOCVD samples. The thesis presents detailed steps of a procedure to quantify trace elements and investigates the associated challenges. The whole process of measurement optimization for Mg and Si dopants is described and final recipe on how to measure the concentration of major (alloy) and minor Si/Mg (dopant) elements is presented. A systematic study of polar and semipolar n-type doped AlGaN/AlN layers grown on sapphire by (MOCVD) with varied Si/group-III ratios in the gas phase was accomplished. The AlN incorporation was higher in the polar samples and the highest values of Si incorporations were observed for the polar samples with the highest Si/III ratios, while saturation of Si incorporation was seen for the semipolar samples at higher Si/III ratios. CL point spectra showed how changes in the relative intensity of the NBE peaks and impurity transitions depend strongly on the growth conditions and surface orientations. The semipolar samples showed better compositional homogeneity. A study was also performed on AlGaN:Mg samples to study the impurity transitions and luminescence properties of non LED epilayer samples grown on MOCVD AlN/sapphire templates and more complicated LED structures with different numbers of MBE-grown layers. MBE samples showed superior quality to other combinations of MBE and MOCVD structures, mainly due to problems associated with the transfer of sample between different reactors and the introduction of impurities that will form different defects within the material. Finally, some proposals for future work are presented

Systems analysis on laser beamed power

The NASA SELENE power beaming program is intended to supply cost-effective power to space assets via Earth-based lasers and active optics systems. Key elements of the program are analyzed, the overall effort is reviewed, and recommendations are presented