**1. Introduction**

Power conversion systems are widely employed in the industry ranging from aircraft, automotive, deep oil/ gas extraction, and space exploration where high-temperature power electronics are required [1–3]. The aircraft field is moving towards more electric aircraft with the reduction or removal of the hydraulic, mechanical and pneumatic power systems [4]. This means more electrical actuators are needed to improve the efficiency, reliability, and maintainability. Power electronic devices, such as sensors and actuators should be placed close enough to the hot engine. Among them, some need to experience the ambient temperature varying from −55 to 225 ◦C due to the short distance to the jet engine, and the gas turbine must operate above 350 ◦C [5]. In electric automotive applications, operating ambient temperature ranges from −40 ◦C to a very high temperature differing with various locations. For example, the coolant temperature can reach up to 120 ◦C at 1.4 bar, the temperatures for wheel sensor and transmission are around 150 to 200 ◦C, and the exhaust sensor is up to 850 ◦C with an ambient temperature of 300 ◦C [6]. In the deep oil/gas extraction, the electrical downhole gas compressor is designed to improve the throughput of gas wells. The ambient temperature is expected to reach 150 ◦C since the compressor should be installed close to the gas reservoir, and the system is expected to work reliably under an ambient temperature of 225 ◦C with the lifetime of 5 years [7]. Regarding space exploration, it is obviously a "niche" market, but it is quite challenging to

develop power electronics used for this application. The surface temperature on Venus can reach up to ~460–480 ◦C, while on Jupiter the temperature increases with depth and pressure [8,9]. The ambient temperature reaches 400 ◦C at 100 bar and comes along with a very aggressive atmosphere with wind speed around 200 m/s and hydrogen-rich chemical composition. Moreover, thermal cycling can be another challenge in the space since the ambient temperature is −140 ◦C during the night. In these applications, it is common that electronic equipment works in a quite harsh environment, especially an extensive temperature range, and frequent deep thermal cycling [10]. Table 1 summarizes the applications requiring high-temperature power electronics in current/ future technologies.


**Table 1.** Applications of high-temperature power electronics.

Note: Bulk Si, SOI, WBG, and N/A stand for bulk silicon, silicon-on-insulator, wide band-gap, and currently no available, respectively.

To be able to withstand the high-temperature environment, power electronic equipment is always designed to have active or passive cooling systems [11]. These cooling solutions include forced convection air cooled heat sink, sided cooling with liquid cold plate, micro-channel liquid cooler built into the power module, in addition to jet impingement and direct contact liquid cooling. Although large numbers of thermal managemen<sup>t</sup> solutions have been designed to cool the power electronics and manipulate their operating temperature, these cooling solutions in oil/gas extraction applications are not efficient or effective. Besides, those applications have the typical issue associated with obviously undesired high cost, extra weight, and volume by introducing the cooling system. Moreover, due to the limited information about the actual operating environment and the actual load cycling, there is a lack of accurate thermal analysis and reliability assessment for each component [12]. Thus, failure of the cooling system can readily jeopardize and even destroy the whole electronic system. Considering these factors, it would be appealing to have electronic components capable of enduring elevated and fast varying temperatures. As a result, system reliability can be largely improved while both the upfront and operating costs can be reduced. Accordingly, the development of high-temperature power electronics is of grea<sup>t</sup> importance and has attracted considerable research efforts.

Currently, power electronic devices in conversion systems and micro-electromechanical systems (MEMS), such as DC/AC converters, AC/DC converters, DC/DC converters, control, ICs and sensors are mainly manufactured by silicon (Si) material [13]. The performance of Si-based power electronics has almost been driven to its logical boundary after about 60 years of tremendous development, but they still cannot o ffer satisfactory performance for many applications. For instance, the maximum permissible operating temperature for Si isolated gate bipolar transistor (IGBT) from Infineon is 125 ◦C, for Si MOSFET, the maximum obtainable junction temperature is 150 ◦C. Such a limited junction temperature together with switching frequency makes it unsuitable for individual application fields with required high-power, high-frequency, and high-voltage. To cater for the low-temperature tolerance, the Si IGBT is designed with complicated heat sink and maximum switching frequency at approximately 30 kHz. This structure results in cumbersome passive components, low power density, and poor dynamic performance. However, substantial improvement in power conversion systems is di fficult with simple employment of fabrication technologies or Si semiconductor devices. The demerits of power electronics manufactured by Si materials are evident and thus limit industrial applications of power electronic devices [14].

Fortunately, the third-generation semiconductor materials, represented by silicon carbide (SiC) and gallium nitride (GaN), have gradually shown superior characteristics compared to Si material. Due to the wide band-gap, high breakdown field strength, high thermal conductivity, and fast electron saturation drift velocity, SiC is one of the most promising alternative materials and it is very suited for high-temperature power electronic devices [15]. Compared with conventional Si power electronic devices, commercially available SiC devices have not only better thermal stability and higher temperature tolerance but also lower switching/conduction loss. Consequently, SiC devices are quite a promising solution to converters tailored for high-temperature applications. In theory, the permissible junction temperature of SiC power electronic devices can reach as large as 600 ◦C, thanks to the wide band-gap of the semiconductor material, which is about three times of that of Si material [16]. The integrated power modules operating in the full temperature range are expected to be widely applied in the foreseeable future.

Research on high-temperature power electronics is not new and has been going for 20 years ago. The first review paper on this research summarized many of the same challenges we are still su ffering in today's market [17]. The common conclusions have been drawn that the high-temperature power electronics cannot be developed by only one component. Although existing power converters equipped with SiC power electronic devices can operate at a top junction temperature above 150 ◦C [18,19], the heat-resistance attributions of high-temperature converters will disappear if gate drives cannot endure in a high-temperature environment. The associated issue for the gate drive is to be designed accordingly to match the requirement of high-temperature and high-speed capability. Furthermore, high-temperature passive components, such as capacitors, resistors, and magnetic materials, required to assemble high-temperature converters are equally as crucial as other components for reliable operation. The magnetic material can work in ambient temperatures up to 450 ◦C [20], but the issue comes for capacitors as most dielectric material cannot be used above 200 to 250 ◦C. Due to the performance of active and passive components which varies over the wide temperature range, the parameters matching should also be considered. Moreover, high-temperature packaging and integration technology are crucial for the design and development of high-temperature converters to give full play to high-temperature tolerance of SiC power electronic devices. Thereafter, there are some reviews on high-temperature power electronics, which are mainly focused on the process, packaging, ICs [21], MEMS sensors [22], and power converters [23,24], and the review on high-temperature applications is inclusive.

In view of the above aspects, a comprehensive overview of the development profiles of high-temperature power electronics based on SiC converters and MEMS devices is conducted, however, has not been presented in the available literature. This work starts with some of the most prominent applications for high-temperature power electronics, fills such a gap by discussing state-of-the-art high-temperature components technologies, including SiC material, power devices or modules, gate drives, and passive components. It is identified that advanced material techniques are essential for high-temperature power electronics. Meanwhile, several exemplary applications of high-temperature power electronics, such as motor drives, rectifier units, DC–DC converters, and MEMS devices are

analyzed, and the critical factors of performance promotion for converters are highlighted. Finally, the existing challenges in further advance of high-temperature power electronics are discussed.
