No description available.

A full electro-thermal simulation of a three-phase space-vector-modulated (SVM) inverter is performed and validated with measurements. Electrical parameters are extracted over temperature for the insulated gate bipolar transistor (IGBT) and diode electro-thermal models. A thermal network methodology that includes thermal coupling between devices is applied to a six-pack module package containing multiple IGBT and diode chips. The electro-thermal device models and six-pack module thermal model are used to simulate SVM inverter operation at several power levels. Good agreement between model and measurement is obtained for steady state operation of the three-phase inverter. In addition, transient heating of a single IGBT in the six-pack module is modeled and validated, yielding good agreement. / Master of Science

The thermal design constraint of power electronic converters under the specific power loss and heat sink is mainly determined by the maximum permissible junction temperature of the power devices. As the power density and switching frequency increase, transient electro-thermal models become more and more important for the thermal management system design of the power electronic converters. In traction inverters, the junction temperature has huge variation because the fundamental frequency and phase currents vary significantly during the load cycles. Thus, the junction temperature estimation becomes extremely important for the reliability of traction inverters. In this thesis, the transient electro-thermal analysis of a traction inverter considering the inter-dependency of the power losses and junction temperature in an iterative process is implemented. Considering the impact of circuit stray parameters on the switching loss, the temperature dependent power loss model is built based on the datasheet values and the measured switching losses. A state-of-the-art thermal model of the entire inverter including the power modules and the heat sink is developed considering the thermal coupling effects of multiple power devices. By using transient thermal simulation, the linearity of the heat transfer process of the entire traction inverter is verified. The impact of the material thermal properties on the thermal impedance is also presented. In addition, the accuracy of the combination of the thermal subsystem models is verified with simulation. The developed transient electro-thermal model is then used to simulate the junction temperature profiles of the inverter under different operating conditions. Finally, the developed model is experimentally verified. By considering the thermal impedance of the thermal grease layer, the simulation results match with the experimental results very well. The proposed electro-thermal model can provide important information for the thermal management system design, package optimization, long-term reliability analysis, and maximum rating characterization of the traction inverters. / Thesis / Master of Applied Science (MASc)

The development of a fully automated tool that is used to optimize the design of a hybrid switch soft-switching inverter using a library of dynamic electro-thermal component models parameterized in terms of electrical, structural and material properties is presented. A multi-scale electro-thermal simulation approach is developed allowing for a large number of parametric studies involving multiple design variables to be considered, drastically reducing simulation time. Traditionally, electro-thermal simulation and analysis has been used to predict the behavior of pre-existing designs. While the traditional approach to electro-thermal analysis can help shape cooling requirements and heat sink designs to maintain certain junction temperatures, there is no guarantee that the design under study is the most optimal. This dissertation uses electro-thermal simulation to guarantee an optimal design and thus truly minimizing cooling requirements and improving device reliability. The proposed optimization tool is used to provide a step-by-step design optimization of a two-coupled magnetic hybrid soft-switching inverter. The soft-switching inverter uses a two-coupled magnetic approach for transformer reset condition [1], a variable timing control for achieving ZVS over the entire load range [2], and utilizes a hybrid switch approach for the main device [3]. Design parameters such as device chip area, gate drive timing control and external resonant capacitor and inductor are used to minimize device loss subject to design constraints such as converter minimum on-time, maximum device chip area, and transformer reset condition. Since the amount of heat that is dissipated has been minimized, the optimal cooling requirements can be determined by reducing the cooling convection coefficients until desired junction temperatures are achieved. The optimized design is then compared and contrasted with an already existing design from the Virginia Tech freedom car project using the generation II module. It will be shown that the proposed tool improves the baseline design by 16% in loss and reduces the cooling requirements by 42%. Validation of the device model against measured data along with the procedures for device parameter extraction is also provided. Validation of the thermal model against measured data is also provided. / Ph. D.

Microfluidic technology has been grown rapidly in the past decade. Microfluidics can find wide applications in multiple fields such as medicine, electronics, chemical and biology. Micro-pumping is an essential part of a microfluidic system. This thesis presents the optimization process of AC electro-thermal micropump with respect to the geometry of electrode array and channel height. The thesis first introduces the theories of AC electrokinetic including dielectrophoresis, AC electro-osmosis (ACEO) and AC electro-thermal (ACET). Also presented are the basic theory and governing equations of microfluidics, the continuity equation, the Navier-Stokes equation, and the conservation of energy equation. AC electro-thermal effect results from the interplays between electric field, temperature field and fluid mechanics. Since the governing equations are highly non-linear, numerical simulation is extensively used to understand the effects of factors such as the electrode dimensions and channel height. By interfacing finite element analysis software COMSOL Multiphysics with Matlab, to the simulation model is able to scan the geometry variables so as to find the optimal micropump design. The optimization has been performed with respect to flow rate and power efficiency of the micropump.

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially for night vision and remote sensing. Compared with cryogenically cooled IR sensors, uncooled infrared imaging devices have the advantages of being low cost, light weight, and superior reliability. The electro-thermal analysis of a microbolometer pixel is critical to determine both device performance and reliability. To date, most microbolometer analysis research has focused on performance optimization and computation of thermal conductance directly from the geometry. However, modeling of the thermal distribution across the microbolometer pixel is critical for the comprehensive analysis of system performance and reliability. Therefore, this thesis investigates the electro-thermo-mechanical characteristics of a microbolometer pixel considering the effects of joule heating and incoming IR energy. The contributions of the present research include the electro-thermal models for microbolometer and methods of validating thermal distribution using experimental results. The electro-thermal models explain the effect of microbolometer material properties and geometry on device performance and reliability. The research also contributes methods of estimating the thermal conductivity of microbolometer, which take into account different heat transfer mechanisms, including radiation and convection. Previous approaches for estimating the thermal conductance of uncooled microbolometer consider heat conduction via legs from the geometry of the pixel structure and material properties [2]. This approach assumes linear temperature distribution in the pixel legs structure. It also leaves out the various electro-thermal effects existing for multilayer structures. In the present research, a different approach is used to develop the thermal conductance of microbolometer pixel structure. The temperature distribution in the pixel is computed from an electro-thermal model. Then, the average temperature in the pixel microplate and the total heat energy generated by joule heating is utilized to compute the thermal conductance of the structure. The thesis discusses electro-thermal and thermo-mechanical modeling, simulation and testing of Polysilicon Multi-User MEMS Process (PolyMUMPs®) test devices as the groundwork for the investigation of microbolometer performance and reliability in space applications. An electro-thermal analytical and numerical model was developed to predict the temperature distribution across the microbolometer pixel by solving the second order differential heat equation. To provide a qualitative insight of the effect of different parameters in the thermal distribution, including material properties and device geometry, first an explicit formulation for the solution of the electro-thermal coupling is obtained using the analytical method. In addition, the electro-thermal model, which accounts for the effect of IR energy and radiation heat transfer, spreading resistance and transient conditions, was studied using numerical methods. In addition, an analytical model has been developed to compute the IR absorption coefficient of a Thin Single Stage (TSS) microbolometer pixel. The simulation result of this model was used to compute absorbed IR energy for the numerical model. Subsequently, the temperature distribution calculated from the analytical model is used to obtain the deflections that the structure undergoes, which will be fundamental for the reliability analysis of the device. Finite element analysis (FEA) has been simulated for the selected device using commercial software, ANSYS® multiphysics. Finite element simulation shows that the electro-thermal models predict the temperature distribution across a microbolometer pixel at steady-state conditions within 2.3% difference from the analytical model. The analytical and numerical models are also simulated and results for a temperature distribution within 1.6% difference. In addition, to validate the analytical and numerical electro-thermal and thermo-mechanical models, a PolyMUMPs® test device has been used. The test results showed a close agreement with the FEM simulation deflection of the test device.

Microfluidic technology has been grown rapidly in the past decade. Microfluidics can find wide applications in multiple fields such as medicine, electronics, chemical and biology. Micro-pumping is an essential part of a microfluidic system. This thesis presents the optimization process of AC electro-thermal micropump with respect to the geometry of electrode array and channel height.The thesis first introduces the theories of AC electrokinetic including dielectrophoresis, AC electro-osmosis (ACEO) and AC electro-thermal (ACET). Also presented are the basic theory and governing equations of microfluidics, the continuity equation, the Navier-Stokes equation, and the conservation of energy equation. AC electro-thermal effect results from the interplays between electric field, temperature field and fluid mechanics. Since the governing equations are highly non-linear, numerical simulation is extensively used to understand the effects of factors such as the electrode dimensions and channel height. By interfacing finite element analysis software COMSOL Multiphysics with Matlab, to the simulation model is able to scan the geometry variables so as to find the optimal micropump design. The optimization has been performed with respect to flow rate and power efficiency of the micropump.

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially for night vision and remote sensing. Compared with cryogenically cooled IR sensors, uncooled infrared imaging devices have the advantages of being low cost, light weight, and superior reliability. The electro-thermal analysis of a microbolometer pixel is critical to determine both device performance and reliability. To date, most microbolometer analysis research has focused on performance optimization and computation of thermal conductance directly from the geometry. However, modeling of the thermal distribution across the microbolometer pixel is critical for the comprehensive analysis of system performance and reliability. Therefore, this thesis investigates the electro-thermo-mechanical characteristics of a microbolometer pixel considering the effects of joule heating and incoming IR energy. The contributions of the present research include the electro-thermal models for microbolometer and methods of validating thermal distribution using experimental results. The electro-thermal models explain the effect of microbolometer material properties and geometry on device performance and reliability. The research also contributes methods of estimating the thermal conductivity of microbolometer, which take into account different heat transfer mechanisms, including radiation and convection. Previous approaches for estimating the thermal conductance of uncooled microbolometer consider heat conduction via legs from the geometry of the pixel structure and material properties [2]. This approach assumes linear temperature distribution in the pixel legs structure. It also leaves out the various electro-thermal effects existing for multilayer structures. In the present research, a different approach is used to develop the thermal conductance of microbolometer pixel structure. The temperature distribution in the pixel is computed from an electro-thermal model. Then, the average temperature in the pixel microplate and the total heat energy generated by joule heating is utilized to compute the thermal conductance of the structure. The thesis discusses electro-thermal and thermo-mechanical modeling, simulation and testing of Polysilicon Multi-User MEMS Process (PolyMUMPs®) test devices as the groundwork for the investigation of microbolometer performance and reliability in space applications. An electro-thermal analytical and numerical model was developed to predict the temperature distribution across the microbolometer pixel by solving the second order differential heat equation. To provide a qualitative insight of the effect of different parameters in the thermal distribution, including material properties and device geometry, first an explicit formulation for the solution of the electro-thermal coupling is obtained using the analytical method. In addition, the electro-thermal model, which accounts for the effect of IR energy and radiation heat transfer, spreading resistance and transient conditions, was studied using numerical methods. In addition, an analytical model has been developed to compute the IR absorption coefficient of a Thin Single Stage (TSS) microbolometer pixel. The simulation result of this model was used to compute absorbed IR energy for the numerical model. Subsequently, the temperature distribution calculated from the analytical model is used to obtain the deflections that the structure undergoes, which will be fundamental for the reliability analysis of the device. Finite element analysis (FEA) has been simulated for the selected device using commercial software, ANSYS® multiphysics. Finite element simulation shows that the electro-thermal models predict the temperature distribution across a microbolometer pixel at steady-state conditions within 2.3% difference from the analytical model. The analytical and numerical models are also simulated and results for a temperature distribution within 1.6% difference. In addition, to validate the analytical and numerical electro-thermal and thermo-mechanical models, a PolyMUMPs® test device has been used. The test results showed a close agreement with the FEM simulation deflection of the test device.

No description available.

abstract: In this work, an advanced simulation study of reliability in millimeter-wave (mm-wave) GaN Devices for power amplifier (PA) applications is performed by means of a particle-based full band Cellular Monte Carlo device simulator (CMC). The goal of the study is to obtain a systematic characterization of the performance of GaN devices operating in DC, small signal AC and large-signal radio-frequency (RF) conditions emphasizing on the microscopic properties that correlate to degradation of device performance such as generation of hot carriers, presence of material defects and self-heating effects. First, a review of concepts concerning GaN technology, devices, reliability mechanisms and PA design is presented in chapter 2. Then, in chapter 3 a study of non-idealities of AlGaN/GaN heterojunction diodes is performed, demonstrating that mole fraction variations and the presence of unintentional Schottky contacts are the main limiting factor for high current drive of the devices under study. Chapter 4 consists in a study of hot electron generation in GaN HEMTs, in terms of the accurate simulation of the electron energy distribution function (EDF) obtained under DC and RF operation, taking into account frequency and temperature variations. The calculated EDFs suggest that Class AB PAs operating at low frequency (10 GHz) are more robust to hot carrier effects than when operating under DC or high frequency RF (up to 40 GHz). Also, operation under Class A yields higher EDFs than Class AB indicating lower reliability. This study is followed in chapter 5 by the proposal of a novel π-Shaped gate contact for GaN HEMTs which effectively reduces the hot electron generation while preserving device performance. Finally, in chapter 6 the electro-thermal characterization of GaN-on-Si HEMTs is performed by means of an expanded CMC framework, where charge and heat transport are self-consistently coupled. After the electro-thermal model is validated to experimental data, the assessment of self-heating under lateral scaling is considered. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018