Raytheon UK's Integrated Power Solutions (IPS) business unit in Glenrothes, Scotland, has developed a high-temperature, small-form-factor bridge leg power module. Aimed at high-speed switching applications, the module has potential uses in the aerospace sector as it requires minimal external cooling and presents considerable weight-saving opportunities within the More Electric Aircraft power system. Also, by supporting applications in harsh environments and in meeting high operating temperature demands, the module can also be used in the geothermal power and oil and gas sectors.
A prototype module that includes two 1200V silicon carbide (SiC) bipolar junction transistors (BJTs) has currently amassed more than 1000 hours of stable operation at 300oC (a temperature at which traditional silicon-based semiconductors cannot operate). Tests on the module have been performed switching 500V at room temperature and switching 200V at 300oC. The BJTs are controlled by integrated base driver circuitry, fabricated using Raytheon's propriety High Temperature Silicon Carbide (HiTSiC) process.
"The co-location of BJT base driver circuitry and power transistors into a single high-temperature module is a major industry breakthrough," claims David Gordon, technical lead with Raytheon's IPS. "For example, in many instances it is necessary to switch power-stage transistors at tens of kHz, and that requires getting the base driver circuitry as close as possible to the power transistors. However, in a high-temperature environment, that presents a problem," he notes. "While silicon carbide transistors can switch high voltage and handle high temperatures, traditional silicon-based gate driver circuitry cannot cope with the heat. Silicon-on-insulator (SOI) raises the bar to about 220oC, but that's still not high enough for some existing and emerging applications for power electronics. Raytheon's HiTSiC CMOS circuitry on the other hand was designed to operate at 300oC, and has been tested at considerably higher temperatures."
The under-test switching speeds of Raytheon's prototype high-temperature bridge leg power module are exceeding expectations, says the firm. When switching 200V, the turn-on time at room temperature is 20ns. This increases linearly to 40ns at 300oC. "This performance has remained consistent throughout the 1000-plus hours of testing," notes Gordon.
The module is packaged in a 32-pin hermetic dual in-line (DIL) ceramic package measuring about 40mm x 23mm.
"Performance stability at extreme temperatures is one of the semiconductor industry's biggest challenges," says Gordon. "Our prototype and the hours it has amassed therefore represents an extremely encouraging demonstration of Raytheon's device capability," he claims. "Ageing tests continue, along with further testing at higher power levels."
Raytheon's development of this high-temperature module draws on experience gained during an Innovate UK project LAMPS (Lightweight, Affordable Motors and Power electronics Systems) in collaboration with other UK partners and led by UTC Aerospace Systems.
