Silicon-Silicon Carbide (Si/SiC) Power Devices for high temperature, hostile environment applications

Several problems facing society in the 21st century share a common problem: that when electronic devices heat up, they become inefficient, wasting energy. It is therefore the case that in your laptop there is significant space, weight and significant design cost associated with implementing the right cooling system to efficiently extract the heat. The laptop is however, a relatively low-power system, operating on earth at a rather pleasant 20C room temperature. Engineers are regularly facing this problem on a much larger scale, in much ambient temperatures, and in a situation where it is often difficult, expensive and often highly impractical to implement active cooling.

Oil and gas engineers, attempting to harvest the fossil fuels we are still highly dependent on, face exactly this problem with the electronics that are driving the cutting tool motor. Power electronic devices delivering hundreds of Watts of power to the motor must do so in an ambient that can exceed 225C, operating miles under the ground with only slurry pumped from the surface to cool the devices. Similarly, electric cars are forced into restrictive design choices keeping the electronics as far from the engine as possible to minimise the cooling requirements. In space, near-sun planetary explorers are essentially floating refrigerators, the inner cabin cooled, at great cost to eventual mission length, down to earth-like temperatures when the temperature outside can exceed 300C around Venus or Mercury. The potential benefit for having electronics operating in these environments without cooling is huge, leading to greater efficiency, reliability and mission length, saving space, weight and importantly cost.

This project looks to redesign the silicon device and to push its thermal behaviour to the absolute limit, so minimising the need for cooling, or eliminating it entirely. This is to be done by combining it with another material, silicon carbide, that will act as a heat sink placed within fractions of a micro-meter of the active device itself. These new Silicon-on-Silicon Carbide (Si/SiC) devices are expected to offer gains in device efficiency over any existing silicon device operating at elevated temperature. Alternatively, the same level of performance could be retained as with existing solutions, except at temperatures as much as 100C higher, or at much higher power (as much as 4x).

The power transistor, implemented entirely with the silicon thin film, is a laterally-diffused metal-oxide-semiconductor field effect transistor (LD-MOS) or a lateral insulated gate bipolar transistor (L-IGBT), similar to those that have been developed for silicon on insulator (SOI) or silicon-on-sapphire. These devices shall be optimised for breakdown voltages rated from 50 to 600 V, making the devices ideal for applications such as downhole motor drives required by project partner Halliburton, and for solar array inverters destined for space.

The key deliverable from the proposed research project is a range of entirely new power electronic devices that can step silicon ever closer to the fundamental limits of its performance. The new devices will allow silicon-based converters to perform in much greater ambient temperatures, at higher power and/or with greater efficiency. As the project progresses, the appropriate exploitation of the results and the associated IP will lead to impact in a number of industrial sectors.

Engagement with industry during and after this project will be the key to delivering impact and eventually getting products to market that can generate profit within the UK. The downhole oil and gas industry is considered the primary target for this technology, given that the massive costs associated with subterranean exploration (off-shore drilling is often quoted as costing more than $1M per day [21]) mean that there is a constant drive for improved reliability to minimise downtime. Indeed, geopolitical events at the end of 2014 sent global oil prices tumbling, and as a result, the whole sector is seeking major efficiency savings. This has hit many UK based oil and gas companies and yet despite being directly affected by this, Halliburton have supported this research project, recognising the potential that can be delivered to their harsh environment electronics.

The space industry has the potential to be another major beneficiary from this technology. A report from NASA [17] outlined the need for electronics able to operate in temperatures up to 300C and beyond to 500C, which could lengthen the mission of near-sun planetary explorers (such as ESA's BepiColumbo or Venus Express), given the reduction in cooling requirements. Furthermore, a UK-based Space company have expressed an interest in this technology to transfer power between Earth and orbiting satellites.

UK company GE Aviation, who work very closely with the School of Engineering, have published details of their need for electronics at elevated temperatures, as they seek on-engine electronics capable of withstanding temperatures up to 250C. Furthermore, success in this project would undoubtedly lead to discussions with contacts in the automotive and power network companies, who could also benefit.

Impact will be delivered by the project for a number of people associated with this project also. The PI, Dr. Gammon, will benefit from the managerial experience as his research group expands to include a post-doctoral researcher. This post-doctoral researcher and the many students he supervises (3 PhD students, 1 MSc student by research, 1 MSC project student, 2 MEng project students and a summer undergraduate intern), will all benefit from increased exposure to the cutting-edge technologies and processes to be carried out on the project, from projects associated with the research, and from potential training opportunities at conferences or in-house.