High Temperature Electronic Technology Development
The temperature limitations of conventional silicon-based semiconductor devices remain one of the key bottlenecks in electronics. High temperatures often trigger two well-known phenomena: the "thermal carrier effect" and "junction temperature effect" in these devices. As temperatures rise, thermal generation creates more electron-hole pairs, escalating the intrinsic carrier concentration in silicon-based materials; and this rise suppresses the doping carriers crucial to the semiconductor's operation, leading to performance degradation (thermal carrier effect). Typically, this impact becomes significant at around 70°C and gets markedly profound at 150-200°C, to the point where silicon substrates can essentially become highly conductive, losing their semiconductive nature and resulting in significant leakage currents. Moreover, the elemental PN junction barrier of semiconductor devices, vital for diodes and MOSFETs, diminishes when temperatures reach 150-200°C, leading to a catastrophic collapse in semiconductor performance (junction temperature effect).
Nonetheless, the continuous advancements in electronic materials and manufacturing processes have given rise to the specialized field of high-temperature electronics. This technology essentially originated from commercial needs for applications like geological exploration and extraction of oil and natural gas, where the ambient temperatures increase with borehole depth, climbing on average by 3°C for every 100 meters. Depths exceeding 5000 meters can reach temperatures of 150°C or higher, and the demands of aerospace, with its environmental heat factors, fuel the need for highly reliable electronics that can operate without maintenance due to high costs and risks.
Notably, today's third-generation wide bandgap semiconductor devices have matured and commercialized, and their intrinsic high-temperature tolerance ushers in new heights in high-temperature electronics. Not only do they propel the development of traditional high-temperature applications in petroleum and aerospace, but they also pave the way for industrial uses like high-speed trains, electric vehicles, and mobile energy storage, indicating immense growth potential.
The key high-temperature scenarios for electronic systems typically involve two main aspects: first, applications that are inherently exposed to high ambient temperatures, such as satellites facing the Sun, spacecraft on extraterrestrial surfaces, or proximity to engines and motors in vehicular systems where temperatures often exceed 150°C. Secondly, the thermal rise caused by dissipation in power electronics: every power electronic component, including MOSFETs and IGBTs, emits some inherent power loss, which is especially crucial in high power density applications, making thermal management critical.
The development of high-temperature electronic devices and systems thus faces substantial technical challenges, including the design and manufacturing of high-temperature semiconductors, robust packaging and circuit assembly, high-temperature passive components, and thermal management from chip level to system level. Before delving into these challenges, let's revisit the history of the field.
The transition from vacuum tube technology to solid-state devices marked a transformative era in electronics, with semiconductor transistors revolutionizing the design landscape. Nevertheless, these semiconductors also had to confront thermal management issues, notably in high-power early devices that often overheated and damaged themselves. Subsequent innovations aimed at overcoming these shortcomings introduced techniques like forced air or liquid cooling systems that unfortunately increased system size, weight, and maintenance complexity.
For situations where cooling options are limited or absent, conventional semiconductors fail to meet the requirements. Various workarounds, such as operating in a derated mode to minimize heat generation, restrict design possibilities significantly.
Advancements in device physics, material science, and manufacturing have led to significant strides in high-temperature semiconductors, breaching the temperature restraints of conventional silicon-based materials. Current temperature standards are capped at 70°C for consumer and commercial electronics, 85°C for industrial use, 125°C for automotive electronics, and 150°C for military applications. High temperature typically refers to the 125-200°C range, with anything above considered extreme high temperature. For example, ultra-deep oil exploration wells can surpass 7000 meters deep, reaching beyond 200°C, while aircraft engine sensors frequently encounter temperatures around 300°C.
Despite substantial progress, pushing the limits within the 125-200°C range remains challenging for typical silicon devices. Modest design modifications, improved packaging, or some degree of derating can enhance their tolerance. However, for high-performance, high-reliability systems such as aerospace or defense, the reliability of standard silicon devices in high-temperature environments is inadmissible, prompting the need for novel semiconductor designs.
High-temperature electronics integrally rely on various factors, such as wide bandgap semiconductor materials capable of withstanding temperatures upwards of 500°C. With the continuous maturation and proliferation of silicon carbide (SiC) devices, their inherent high-temperature resilience, coupled with high-temperature SOI-based drivers, is poised to transform the design landscape of power electronics, opening new prospects for engineers.
The challenges in high-temperature electronics primarily revolve around semiconductor chips capable of tolerating high temperatures. For the common range of 125-200°C, and even above to 300°C, SOI semiconductor chips offer a promising solution. They effectively mitigate the increase in leakage currents due to intrinsic carriers and avert the junction temperature effect by using insulating layers and specialized device structures. Yet, the challenges extend to the chip manufacturing processes, where SOI technology differs significantly from conventional silicon processes and is limited by the relatively few international SOI production lines.
For applications over 300°C, wide bandgap semiconductors like GaAs, GaN, SiC, especially SiC with its optimal high-temperature properties, come into play. However, producing SiC devices is notably more complex due to the material's high melting point and hardness, requiring specialized techniques.
Recent developments have been pushed by the automotive sector's needs, particularly with Tesla's propulsion of SiC into the electric vehicle market. The evolutions in production technology and scale, driven by this demand, have led to reduced device prices and advances toward larger wafers, with industry leaders starting to invest in 8-inch SiC wafer production lines.
After manufacturing the high-temperature semiconductor bare chips, the subsequent challenges involve high-temperature packaging design, assembly processes, and soldering technics. High-thermal conductivity packaging is essential to prevent excessive temperature rises, and new materials and solder must withstand high temperatures without melting or delamination.
Finally, high-temperature passive components such as capacitors and resistors are also crucial. High-temperature resistors are more straightforward to implement, but finding suitable materials for high-temperature capacitors that maintain low variability with temperature fluctuations presents a more significant challenge.
In summary, high-temperature electronics technology, which encompasses advanced materials, semiconductor processes, and extreme packaging and assembly technics, are set to enter the power electronics field with widespread application thanks to the general adoption of SiC. This cross-disciplinary, cutting-edge science increasingly garners attention as it bridges fundamental research with industrial implementation.
