Evaluation And Reliability Analysis Of Sic Bipolar Devices Under Pulsed Conditions
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Type of WorkText
DepartmentElectrical and Computer Engineering
ProgramDoctor of Engineering
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The demand for smaller volume, higher power density power electronics and pulsed power systems to operate at higher switching frequency and at higher temperatures for future combat systems requires advancement in the electrical and physical properties of current semiconductor switches. Because these new requirements are pushing the current limitation of silicon (Si) power semiconductor switches due to material properties limitation, wide bandgap materials such as silicon carbide (SiC) and gallium nitride (GaN) are being investigated for power devices. Silicon carbide is an extremely attractive material for semiconductor power devices because of its electrical and physical properties. Silicon carbide-based power devices offer several advantages over silicon-based power devices such as higher breakdown voltage, higher thermal conductivity, and higher temperature, frequency and radiation operation. Silicon carbide (SiC) is ideal for pulsed power applications that require high peak currents and action, fast recovery times, and fast voltage and current rise times, because the material is capable of tolerating very high localized temperatures generated during pulsed switching events due to its extremely low intrinsic carrier concentration. The following research will investigate the pulsed performance of SiC bipolar devices (particularly Super- gate turnoff thyristors (SGTOs)), evaluate the reliability and stability of SiC SGTOs under pulsed conditions, analyze failure mechanisms that occur in SiC bipolar devices under pulsed conditions, and determining a safe operating area for these devices when electrically and thermally overstressed. Various pulse measurements have been taken on several SiC SGTOs to assess pulse current sharing, dV/dt immunity, recovery time, dI/dt capabilities, maximum peak pulse current, forward voltage drop, peak power, and action rate. The pulse results obtained from individual SiC SGTOs were used to determine the projected pulse performance of two state-of-the-art pulsed power modules that consisted of 4 SiC SGTOs and 21 SiC SGTOs. These all-SiC pulsed power modules were fabricated, characterized, and integrated into pulsed power circuits. Critical parameters obtained from the modules included action rating (I^2*t), peak pulse current, and peak power. The modules utilized ThinPakTM technology which eliminated wire-bonds, enhanced mechanical support, and minimized electrical and thermal stresses on the switches when pulsed at very high current and voltage magnitudes. The 21 chip SiC pulsed power module demonstrated maximum peak current of 32 kA at 1 ms pulse-width, which equates to an action rate of 7.7 x 10^4 A^2*s. Repetitive pulsed switching evaluation has been accomplished to assess the reliability of SiC pulse power modules. These devices have been subjected to thousands of pulses without failure. This research will present reliability on the pulse performance of SiC SGTOs and PiN diodes. This research will also highlight the thermal performance of silicon carbide SGTOs based on experimental pulsed electrical data. The thermal simulations will provide further insight to areas where localized heating may occur in the devices. Furthermore, the development of a physics based model for SiC bipolar devices under pulsed conditions was implemented to investigate current crowding that occurs (non-uniform distribution of current in the device) during the forward conduction mode of SiC SGTOs. This dissertation will provide insight on the ability of SiC SGTOs and PiN diodes to operate at extremely high action and power density reliably for pulsed power systems suitable for Army applications.