58 November/December 2023 | E-Mobility Engineering Nick Flaherty reports on how semiconductor r&d is leading to more efficient and powerful electronic switching solutions for e-mobility Switch gear Power devices for e-mobility come in a range of technologies to boost performance and efficiency. Insulated gate bipolar transistors (IGBTs) made from silicon have been the first choice for decades; they are robust and low cost but can only switch at frequencies of around 10 to 20 kHz. Silicon carbide (SiC) increases that frequency to 200 kHz, with lower losses and higher robustness than IGBTs but at a higher cost. Gallium nitride (GaN) is now emerging as a potential highpower switching technology, with operating frequencies of up to 20 MHz, but their robustness and the maximum voltage, or withstand voltage, have previously been a challenge. SIC and GaN are both wide bandgap materials, where the higher bandgap compared to silicon gives higher electron mobility, leading to higher switching frequencies that in turn give higher efficiency and performance for power electronics designs. Of course, engineers have been working on all three technologies to boost the performance of each one in different ways. IGBT developments are working on ever higher voltages – 1200 to 2000 V – while SiC is looking to a trench structure to fit more devices onto an expensive SiC wafer to bring down the cost. GaN is intrinsically less expensive than SiC, using GaN layers on a lowcost silicon wafer. Designers are pushing up the withstand voltage of GaN, as the higher frequency is extremely appealing, although existing 650 V GaN devices are being used for 800 V inverters without having to go to 1000 or 1200 V. This higher frequency, up to 2 MHz or even 20 MHz, is highly attractive for power electronics designs, as it allows the magnetics of converters to be reduced in size, cutting the weight and footprint of onboard chargers and even inverters. The different technologies lead to different device structures and a range of implementations for power electronics. Bipolar IGBTs are the simplest, and share similar voltages with SiC MOSFETs. These are driven by voltages of about 5 V to switch them from off to on. In contrast, GaN high electron mobility transistors (HEMT) devices have a very different structure, and come in versions that are normally off, also known as depletion mode or d-mode, or normally on, with enhanced mode or e-mode. These have different drive requirements and implementations. However, these higher frequencies present challenges in designing the power electronics, so new techniques have been developed using machine learning to enable designers to exploit the advantages of GaN despite the design challenges. IGBTs Infineon Technologies has completed a €74 million project to build 1700 V IGBT power transistors on 300 mm silicon wafers. The Power2Power project brought together 43 partners from industry and research in eight A new design for a GaN device can boost the switching frequency of power electronics to over 20 MHz (Courtesy of QPT)
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