Heat seekers

A UK team aims to develop integrated circuits able to withstand the extreme temperatures inside turbines or oil wells.

Raytheon Systems Limited (RSL) — the UK division of defence and electronics giant Raytheon — and academic partner Strathclyde University are collaborating on a project to design silicon carbide integrated circuits that could operate in temperatures of up to 450ºC.

Conventional silicon devices can operate with insulating technology into the 200ºC range. Research into silicon carbide (SiC) integrated circuits, including work carried out by NASA, shows they have the potential to operate at much higher temperatures, and RSL hopes to make the first commercially-available products.

High-temperature SiC chips could be used directly alongside sensors monitoring very hot environments such as in deep oil and gas extraction, and inside internal combustion engines and turbines.

RSL process technology manager Dr Robin Thompson explained that the company had been following the development of SiC research alongside Strathclyde and was looking for a suitable application.

'We have a background in mixed-signal CMOS ASIC (complementary metal oxide semiconductor application-specific integrated circuit) control devices as opposed to power transistors or devices,' said Thompson. 'We realised that with silicon carbide we could address a new market area of high temperature ASICs and integrated circuits.'

The RSL/Strathclyde team realised that being able to operate devices at higher temperatures than is now possible would have a number of benefits in the energy arena. These include automotive sensors, power electronics and fuel-efficient aircraft.

There are two key potential application areas for SiC integrated circuits. One is where sensors already sit in higher temperature environments than current electronics can withstand — for example in aircraft or automotive engines. This is currently worked around by transmitting the raw signal out from the sensor to be processed in a lower-temperature environment.

'With SiC technology we should be able to design sensor interface electronics that can sit beside or much closer to the sensor in the higher temperature environment,' claimed Thompson. 'You want to have the sensor electronics as close to the sensor as possible as it may be producing a very small, weak signal which could degrade if transmitted down a long cable.'

The second area could be complementing SiC power devices as they become available with a control chip.

'One advantage of this technology is less cooling is needed as the device itself will still operate at much higher temperatures,' said Thompson. 'If the driver — the control chip that manages the power switch — could also go up to higher temperatures, it could be co-located with the power device.'

Silicon carbide electronics is still an embryonic field, so the team faces a number of challenges. Thompson said the quality and availability of silicon carbide wafers is currently an issue, but substrates are continually improving.

RSL aims to make a CMOS processor that follows the current silicon standard, which consists of two different types of transistors known as n-channel and p-channel transistors. 'No-one is currently making n-channels for silicon carbide, but people are doing it for power devices, so we have an approach to follow,' said Thompson. 'P-channel devices on SiC technology will be a challenge, but we have a possible workaround for that, using a different style of logic if we have to.'

Another challenge is that aluminium, which is used for connectors in standard semi- conductors, is unsuitable for such high temperatures, so other metals will have to be tested for this purpose.

The three-year project was launched this month, and by the end of it the researchers aim to have fabricated and evaluated two demonstrators — one control chip for high- temperature sensors and a power device driver.

Strathclyde is contributing power electronics expertise and will be responsible for producing the power device driver demonstrator circuit. It will also carry out semiconductor device modelling to do process and device simulation.

Thompson estimates that commercial versions of the SiC integrated circuits could be available one to two years after the end of the project, potentially bringing manufacturing work to its Glenrothes plant in Scotland. Alongside the technology development, the team will develop new manufacturing techniques based on RSL's experience in silicon-based electronics.

Berenice Baker