Thermally Aware Design Approaches for High Power Density Ultra-Wide Bandgap Power Electronics

Ultra-wide bandgap (UWBG) semiconductors like β-type gallium oxide (β-Ga2O3) show promise for the development of next-generation high power density electronics devices such as RF and power electronics. The large bandgap (4.8 eV), high breakdown fields (8 MV/cm), and excellent thermal stability of β-Ga2O3 give promise to the production of low-loss power switching devices with large breakdown voltage, and potentially allows for high-temperature and deep space operation. However, a major drawback of β-Ga2O3 arises from its poor thermal conductivity, which results in devices with unacceptably high junction-to-package thermal resistance. While there is considerable promise for future devices made from UWBG materials, their adoption as a technology will hinge upon novel approaches to address heat dissipation at the die level which will enable high power density operation. The aims of this thesis are i) to develop novel thermal management strategies to reduce the junction-to-package thermal resistance for devices made from low thermal conductivity UWBG materials for both lateral and vertical devices, ii) to conduct an analysis of architectures for homoepitaxial β-Ga2O3 metal-oxide semiconductor field effect transistors (MOSFETs) to optimize the device thermal performance and verify experimentally, and iii) to optimize thermal management design for both steady-state and transient-state of UWBG transistors. Overall, the optimal thermally-aware design for vertical and lateral structures for steady-state and transient applications will be provided by investigating the device layout such as substrate orientation, configuration of electrodes (number of fingers, channel width, location of metallization pads), dielectric heat spreader, and thermal boundary conductance between metal and β-Ga2O3.Ph.D

Materials Development for Gallium Nitride Power Devices

Gallium Nitride has gained prominence in the field of power electronics due to its high bandgap, high critical electric field, high mobility and high saturation-drift velocity. This means that GaN can be used to make devices that have a low on-resistance along with a high breakdown voltage. High frequency GaN HEMTs have been commercially available since 2006 and still being improved. The high power market is just starting to tap into GaN devices. Vertical transistors are especially attractive for high power applications, as they provide the possibility of a high breakdown voltage at a low chip size, thus, a low cost price. In addition to this, GaN devices can also use the two-dimensional electron gas formed at the GaN/AlGaN heterojunction to obtain a higher current.Several GaN based power devices are being investigated - both vertical and lateral. Our group has been focusing on the Oxide GaN-interlayer Field Effect Transistor (OGFET) and the Current Aperture Vertical Electron Transistor (CAVET). On the lateral side, power HEMTs are being developed. This work focuses on materials development for the various types of power devices. A primary motive for this thesis is for it to serve as a reference manual for researchers working on GaN power devices. Vertical power devices are united by a common feature – a thick drift region with a low n-type carrier concentration. Through simulations, it has been shown that the optimal carrier concentration to simultaneously achieve a low Ron and a high breakdown voltage is about 1 x 1016 cm-3. Through our experiments, it was demonstrated that it is also the carrier concentration range where the electron mobility peaks. Achieving such a low doping can be problematic as it is in the range of impurity dopants such as Carbon and Oxygen. A low doping and record mobility was achieved for vertical devices by MOCVD and applied to the OGFET and the CAVET. Devices were grown both, on sapphire and on bulk GaN and high breakdown voltages were achieved.Power devices require an elaborate growth and fabrication process, including regrowth on p-GaN doped by Magnesium and regrowth within trenches. Magnesium is known to diffuse into subsequent layers during regrowth, lowering device performance. A novel approach to circumvent this issue is presented, which can eliminate the need to remove the sample from the MOCVD chamber altogether. A low temperature GaN layer grown via flow modulation epitaxy successfully suppressed the Mg penetration at a rate of 5 nm/dec, the lowest ever by MOCVD, leading to the formation of an abrupt p-GaN:Mg/GaN junction.Regrowth within trenches was optimized for different applications. GaN was grown conformally within narrow trenches by exploring various growth conditions. A complete filling of trench was also achieved for a different set of applications. Finally, conformal regrowth of high composition, low temperature AlGaN was optimized for deep-recessed gate HEMTs to lower gate leakage. All of these were planar regrowths and no masks were used

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

Feature Papers in Electronic Materials Section

This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book