Avionics. The distributed control systems used in modern aircrafts require engine control systems to be closer to the engine, to reduce complexity of interconnections and increase reliability. Since the electronic components are closer to the engine, these now have to sustain much higher temperatures.
Automotive. The electromechanical or mechatronic systems in modern automobiles require sensors, signal conditioning and control electronics to be located close to engines and heat sources. Electric and hybrid vehicles also require power electronics with high-energy density for converters, motor controls and charging circuits that are also associated with high temperatures.
Space exploration. A space probe that goes to Neptune should be able to operate at –230°C. On Venus, the temperature would be close to 500°C. When orbiting the Earth, the temperature might drop to –230°C near the lunar poles. Beyond tolerating such temperatures, the electronics should also be able to handle sudden or gradual changes in temperature along the path to its destination. Further, this complex industry requires not just temperature resistance but also radiation-hardened components that can withstand particle radiation and high-energy electromagnetic radiation.
Astrophysical equipment. Astrophysical equipment, such as bolometers and infrared space telescopes, require electronics that can withstand very low temperatures.
Medical equipment. Medical equipment that handle liquid nitrogen and other such compounds often need to handle very cold temperatures.
Surveillance. Sensors and signal processors used in military surveillance equipment must withstand very harsh weather conditions as they may be deployed anywhere.
LED lighting. LED lighting, especially centrally-managed lighting systems, require control systems, signal processors, etc that can withstand high temperatures generated by the light.
Other applications including undersea cabling and industrial use.
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All this gives rise to the need for special electronics that can withstand extreme temperatures, especially on the higher end.
Modern technologies
New materials, testing, qualifiation and packaging techniques have helped silicon makers to come up with customised silicon chains that can work in extreme temperatures with high reliability.
“Integrated circuit (IC) technology from companies like ADI has produced devices that can operate reliably at elevated temperatures with guaranteed datasheet specifications. Advances hav been made in process technology, circuit design and layout techniques. Managing many key device characteristics is crucial for successful, high-performance operation at elevated temperatures. One of the most important and well-known challenges is posed by the increased substrate leakage current. Some others are decreased carrier mobility, variation in device parameters such as threshold voltage, beta and saturation voltage, increased electro-migration of metal interconnects, and decreased dielectric breakdown strength,” says Choudhury.
Let us look at how some of these problems are overcome in new technologies.
Handling substrate leakage. Although standard silicon can operate well beyond the military requirement of 125°C, leakage in standard silicon processes doubles for every 10°C increase in temperature, making it unacceptable for many precision applications. Trench isolation, silicon-on-insulator (SOI) and other variations to the standard silicon process help decrease leakage and enable high-performance operation at temperatures above 200°C. Use of wide-band-gap materials, such as silicon carbide (SiC), helps raise the limits even further, to as high as 600°C.
Testing and characterisation at high temperatures. Simulating extreme temperature environments in the lab to verify, qualify and characterise the components can be very challenging. Special materials, ovens and chambers are required to create the test platform, wherein the tests have to be done carefully without damaging the printed circuit board (PCB), by gradually increasing or decreasing the temperature. Specialised tools are available today, which can operate at such high temperatures to test and control electronic systems.
“Special industrial, aerospace and defence applications like monitoring oil and gas pipelines, and controlling heavy machinery and space vehicle test systems require control units and sensors that can function even at extreme conditions of temperature, pressure and vibration. These critical applications also demand extremely low failure rates. Testing the sensors and control systems thoroughly for all environmental conditions is necessary before they can be deployed in the field.Special test set-up with rugged control and measurement systems that can endure similar conditions are required to validate the functioning of these sensors and control units,” says Ravichandran Raghavan, technical marketing engineer, National Instruments, India (NI). NI has solutions for design and test of extreme temperature components.
Packaging the die. While plastic packaging would withstand temperatures up to 175°C, other technologies would be needed beyond that. TI, for example, offers three types of packages to support high-temperature applications: plastic package for 175°C, ceramic and known good die (KGD) packaging for higher temperatures. Ceramic and KGD parts are characterised to 210°C, operate in an extended temperature range of -55°C to +210°C, and have a high-temperature operating life of 1000 hours. Even the plastic package is ruggedised using special techniques to improve reliability at high temperatures.
