<p>Silicon Carbide (SiC) is a wide band-gap semiconductor material with excel-lent material properties for high frequency, high power and high temperature elec-tronics. In this work different SiC field-effect transistors have been studied using theoretical methods, with the focus on both the devices and the methods used. The rapid miniaturization of commercial devices demands better physical models than the drift-diffusion and hydrodynamic models most commonly used at present.</p><p>The Monte Carlo method is the most accurate physical methods available and has been used in this work to study the performance in short-channel SiC field-effect devices. The drawback of the Monte-Carlo method is the computational power required and it is thus not well suited for device design where the layout requires to be optimized for best device performance. One approach to reduce the simulation time in the Monte Carlo method is to use a time-domain drift-diffusion model in contact and bulk regions of the device. In this work, a time-domain drift-diffusion model is implemented and verified against commercial tools and would be suitable for inclusion in the Monte-Carlo device simulator framework.</p><p>Device optimization is traditionally performed by hand, changing device pa-rameters until sufficient performance is achieved. This is very time consuming work without any guarantee of achieving an optimal layout. In this work a tool is developed, which automatically changes device layout until optimal device per-formance is achieved. Device optimization requires hundreds of device simulations and thus it is essential that computationally efficient methods are used. One impor-tant physical process for RF power devices is self heating. Self heating can be fairly accurately modeled in two dimensions but this will greatly reduce the computa-tional speed. For realistic influence self heating must be studied in three dimensions and a method is developed using a combination of 2D electrical and 3D thermal simulations. The accuracy is much improved by using the proposed method in comparison to a 2D coupled electro/thermal simulation and at the same time offers greater efficiency. Linearity is another very important issue for RF power devices for telecommunication applications. A method to predict the linearity is imple-mented using nonlinear circuit simulation of the active device and neighboring passive elements.</p>

There exist various models for Microwave MESFET equivalent circuit representations. These models use different mathematical models to describe the same MESFET and give similar results. However, there are some differences in the results when compared to the experimental measurements. In this thesis, various theoretical models are applied to the same MESFET and comparison made with measured data. It is shown that some models worked better on some parameters of the MESFET, while the others were more effective on other parameters. Altogether eight models were examined and data optimized to fit these theoretical models. In using optimization algorithms MATLAB FMINSEARCH and GENETIC ALGORITHM CODE were used alternatively to solve the initial value problem.

No description available.

The development of microwave Gallium Arsenide Metal Semiconductor Field Effect Transistor (MESFET) devices has enabled the miniaturization of pagers, cellular phones, and other electronic devices. With these MESFET devices comes the need to model them. This thesis extracts a small signal equivalent circuit model from a Gallium Arsenide MESFET device. The approach taken in this thesis is to use measured S- parameters to extract a small signal equivalent circuit model by optimization. Small signal models and S-parameters are explained. The Simplex Method is used to optimize the small signal equivalent circuit model. A thorough analysis of the strengths and weaknesses of the Simplex method is performed. / Master of Science

Ce mémoire de maîtrise traite des circuits actifs amplificateurs dont la conception est faite spécialement pour qu'ils soient intégrés aux métamatériaux électromagnétiques, en particulier à une antenne à ondes de fuite CRLH (Composite right/left-handed). Cette antenne a la particularité de pouvoir varier la direction de son rayonnement sur près de 180 degrés, en changeant simplement la fréquence du signal émis. Par conséquent, elle est une candidate de choix pour les applications radars. Toutefois, étant donné que son gain est relativement faible, des amplificateurs ont été ajoutés entre certaines de ses sections pour créer une antenne active CRLH [Casares-Miranda et al. , 2006]. Malheureusement, cette dernière n'est optimisée que pour une seule fréquence, donc pour un rayonnement dans une seule direction. Lobjectif de ce projet est donc la conception d'amplificateurs qui permettraient que cette antenne active ait un rayonnement optimal à toutes les fréquences. Dans ce texte, la théorie générale des métamatériaux est expliquée pour ensuite se concentrer sur les caractéristiques de l'antenne à ondes de fuite CRLH. Une étude de celle-ci est complétée de manière a déterminer les spécifications nécessaires des circuits amplificateurs qui y seront intégrés. Il est ainsi indiqué que pour fabriquer une antenne à ondes de fuite active idéale, les amplificateurs devraient avoir un gain constant sur toute la bande. Aussi, le déphasage introduit par ceux-ci doit être le plus constant possible sur toute cette bande, donc le délai de groupe de ces circuits doit être minimum. Cependant, un fait intéressant qui est amené par cette étude est qu'en intégrant des déphaseurs dans les circuits amplificateurs, il est possible de fabriquer une antenne à ondes de fuite CRLH active dont on peut obtenir une grande variété de diagrammes de rayonnement sur toute la plage de fréquences. Par conséquent, l'étude, la conception et la fabrication de circuits amplificateurs et déphaseurs sont discutées. Ces circuits sont faits avec des MESFET.

abstract: There is an ever-increasing demand for higher bandwidth and data rate ensuing from exploding number of radio frequency integrated systems and devices. As stated in the Shannon-Hartley theorem, the maximum achievable data rate of a communication channel is linearly proportional to the system bandwidth. This is the main driving force behind pushing wireless systems towards millimeter-wave frequency range, where larger bandwidth is available at a higher carrier frequency. Observing the Moor’s law, highly scaled complementary metal–oxide–semiconductor (CMOS) technologies provide fast transistors with a high unity power gain frequency which enables operating at millimeter-wave frequency range. CMOS is the compelling choice for digital and signal processing modules which concurrently offers high computation speed, low power consumption, and mass integration at a high manufacturing yield. One of the main shortcomings of the sub-micron CMOS technologies is the low breakdown voltage of the transistors that limits the dynamic range of the radio frequency (RF) power blocks, especially with the power amplifiers. Low voltage swing restricts the achievable output power which translates into low signal to noise ratio and degraded linearity. Extensive research has been done on proposing new design and IC fabrication techniques with the goal of generating higher output power in CMOS technology. The prominent drawbacks of these solutions are an increased die area, higher cost per design, and lower overall efficiency due to lossy passive components. In this dissertation, CMOS compatible metal–semiconductor field-effect transistor (MESFETs) are utilized to put forward a new solution to enhance the power amplifier’s breakdown voltage, gain and maximum output power. Requiring no change to the conventional CMOS process flow, this low cost approach allows direct incorporation of high voltage power MESFETs into silicon. High voltage MESFETs were employed in a cascode structure to push the amplifier’s cutoff frequency and unity power gain frequency to the 5G and K-band frequency range. This dissertation begins with CMOS compatible MESFET modeling and fabrication steps, and culminates in the discussion of amplifier design and optimization methodology, parasitic de-embedding steps, simulation and measurement results, and high resistivity RF substrate characterization. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

SiC MESFETs and GaN HEMTs have an enormous potential in high-power amplifiers at microwave frequencies due to their wide bandgap features of high electric breakdown field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. In this thesis, Class C switching response of SiC MESFET in TCAD and two different generations of broadband power amplifiers have been designed, fabricated and characterized. Input and output matching networks and shunt feedback topology based on microstrip and lumped components have been designed, to increase the bandwidth and to improve the stability. The first amplifier is a single stage 26-watt using a SiC MESFET covering the frequency from 200-500 MHz is designed and fabricated. Typical results at 50 V drain bias for the whole band are, 22 dB power gain, 43 dBm output power, minimum power added efficiency at P 1dB is 47 % at 200 MHz and maximum 60 % at 500 MHz and the IMD3 level at 10 dB back-off from P 1dB is below ‑45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66 % PAE. In the second phase, two power amplifiers at 0.7-1.8 GHz without feed back for SiC MESFET and with feedback for GaN HEMT are designed and fabricated (both these transistors were of 10 W). The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The SiC amplifier gives better results than for GaN amplifier for the same 10 W transistor. A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to large signal high frequency domain was developed in our group, is further extended to study the class-C switching response of the devices. By the extended technique the switching losses, power density and PAE in the dynamics of the SiC MESFET transistor at four different frequencies of 500 MHz, 1, 2 and 3 GHz during large signal operation and the source of switching losses in the device structure was investigated. The results obtained at 500 MHz are, PAE of 78.3%, a power density of 2.5 W/mm with a switching loss of 0.69 W/mm. Typical results at 3 GHz are, PAE of 53.4 %, a power density of 1.7 W/mm with a switching loss of 1.52 W/mm. / Report code: LIU-TEK-LIC-2008:32

<p>SiC MESFETs and GaN HEMTs have an enormous potential in high-power amplifiers at microwave frequencies due to their wide bandgap features of high electric breakdown field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. In this thesis, Class C switching response of SiC MESFET in TCAD and two different generations of broadband power amplifiers have been designed, fabricated and characterized. Input and output matching networks and shunt feedback topology based on microstrip and lumped components have been designed, to increase the bandwidth and to improve the stability. The first amplifier is a single stage 26-watt using a SiC MESFET covering the frequency from 200-500 MHz is designed and fabricated. Typical results at 50 V drain bias for the whole band are, 22 dB power gain, 43 dBm output power, minimum power added efficiency at P 1dB is 47 % at 200 MHz and maximum 60 % at 500 MHz and the IMD3 level at 10 dB back-off from P 1dB is below ‑45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66 % PAE.</p><p>In the second phase, two power amplifiers at 0.7-1.8 GHz without feed back for SiC MESFET and with feedback for GaN HEMT are designed and fabricated (both these transistors were of 10 W). The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The SiC amplifier gives better results than for GaN amplifier for the same 10 W transistor.</p><p>A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to large signal high frequency domain was developed in our group, is further extended to study the class-C switching response of the devices. By the extended technique the switching losses, power density and PAE in the dynamics of the SiC MESFET transistor at four different frequencies of 500 MHz, 1, 2 and 3 GHz during large signal operation and the source of switching losses in the device structure was investigated. The results obtained at 500 MHz are, PAE of 78.3%, a power density of 2.5 W/mm with a switching loss of 0.69 W/mm. Typical results at 3 GHz are, PAE of 53.4 %, a power density of 1.7 W/mm with a switching loss of 1.52 W/mm.</p> / Report code: LIU-TEK-LIC-2008:32

Indium-Gallium-Zinc-Oxide (a-IGZO) is an amorphous oxide semiconductor that has been attracting increasing attention for use in flat panel display and optoelectronic applications. This is largely due to IGZO’s high mobility at low processing temperatures. In this thesis, IGZO films were successfully grown on polyethylene naphthalate (PEN) substrates by RF magnetron sputtering at room temperature. These films were flexible, transparent and had a good Hall mobility (5-12 cm2/Vs). High quality metal oxide Schottky contacts were fabricated on these as-grown IGZO/PEN films with on-off rectification ratios of up to 108. These were then used as the gate contacts in transparent metal semiconductor field effect transistors (MESFETs). The performance and device stability of these IGZO/PEN MESFETs were investigated via a series of stress tests in both dark conditions and under illumination at different wavelengths in the visible spectrum. During constant voltage stress testing under illumination, the threshold voltage shifted by -0.54 V and 0.38 V for negative and positive gate biasing, respectively. These shifts proved reversible when devices were left in dark conditions for extended periods of time. The effect of persistent photoconductivity after exposure to different illumination sources was examined, with three potential passivation coatings to reduce this unwanted effect explored. Transparent IGZO/PEN MESFETs with an absolute transmission of up to 75% were achieved with the use of ITO ohmic contacts. These devices survived mechanical bending down to a radius of 7 mm with negligible variation in on-current and threshold voltage. This allows for the possibility of incorporating their use in future applications such as flexible transparent electronics.

abstract: There will always be a need for high current/voltage transistors. A transistor that has the ability to be both or either of these things is the silicon metal-silicon field effect transistor (MESFET). An additional perk that silicon MESFET transistors have is the ability to be integrated into the standard silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) process flow. This makes a silicon MESFET transistor a very valuable device for use in any standard CMOS circuit that may usually need a separate integrated circuit (IC) in order to switch power on or from a high current/voltage because it allows this function to be performed with a single chip thereby cutting costs. The ability for the MESFET to cost effectively satisfy the needs of this any many other high current/voltage device application markets is what drives the study of MESFET optimization. Silicon MESFETs that are integrated into standard SOI CMOS processes often receive dopings during fabrication that would not ideally be there in a process made exclusively for MESFETs. Since these remnants of SOI CMOS processing effect the operation of a MESFET device, their effect can be seen in the current-voltage characteristics of a measured MESFET device. Device simulations are done and compared to measured silicon MESFET data in order to deduce the cause and effect of many of these SOI CMOS remnants. MESFET devices can be made in both fully depleted (FD) and partially depleted (PD) SOI CMOS technologies. Device simulations are used to do a comparison of FD and PD MESFETs in order to show the advantages and disadvantages of MESFETs fabricated in different technologies. It is shown that PD MESFET have the highest current per area capability. Since the PD MESFET is shown to have the highest current capability, a layout optimization method to further increase the current per area capability of the PD silicon MESFET is presented, derived, and proven to a first order. / Dissertation/Thesis / M.S. Electrical Engineering 2011