Space SOS technology adapted to expand sensor designs - Embedded.com

Space SOS technology adapted to expand sensor designs

Wrexham, UK — A Welsh electronics company is using space technology to enhance the safety features of aeroplanes, cars and trucks. By exploiting the silicon-on-sapphire (SOS) technology used in the development of integrated circuits for the NASA space programme, Ellison Sensors, the pressure transducer division of ESI Technology, has developed a high pressure sensor capable of accurately measuring vibration, torque, force or pressure in extreme temperatures and adverse conditions over a long duration.

Albert Ellison, managing director of Ellison Sensors, said “In the past it was very difficult to manufacture sensors which could be used over a wide temperature range. This resulted in expensive compensation methods, frequent replacements and a lot of downtime for maintenance work.”

To enhance the stability of the sensors ESI explored using the somewhat neglected SOS technology — recognised for its good insulation properties and ability to operate under high temperatures.

“Although SOS technology is quite mature in the UK, with wafers manufactured in the Midlands for the past 30 years, this technology has not been successfully adapted for use in sensor technology, said Ellison. “By growing single crystal silicon epitaxially onto a sapphire wafer and then selectively etching it to produce a four arm active resistive Wheatsone bridge, we have created a product which is highly stable and eliminates the need for costly maintenance or compensation.”

To create the pure single crystalline structure, silicon which is a desirable pressure sensing element is grown onto the sapphire wafer so that the growth becomes an atomic extension of the sapphire itself.

The sapphire is chemically inert, has good thermal and electrical properties and acts as a perfect insulator for the isolated silicon strain gauges.

Ellison explained “The homogenous single-crystalline structure of SOS offers a specification not previously available in pressure transducer technology. The structure has a modulus of elasticity exceeding that of stainless steel with virtually no hysteresis and provides excellent long-term stability and repeatability. The result: the creation of a very stable sensor with multiple applications and the ability to operate at high temperatures previously unattainable.

“SOS pressure transducers operate at temperatures of up to 450°C with optimal efficiency achieved at 350°C. The sapphire is five times harder than tungsten carbide and is highly abrasion resistant, making it ideal for use as a hot metal pressure transducer for plastic extrusion,” said Ellison.

By replacing the SOI technology with SOS the company were able to create a sensor which is stable, reliable and reduces drift by up to 95 per cent.

Ellison believes the technology needs to become consumer friendly by adapting it for the commercial mainstream.

Dr Chris Young, chief executive of the Welsh Electronics Forum (WEF) said, “While adapting military applications for the mainstream consumer markets might seem daunting at first, it still is far easier than developing the technology from scratch in the first place.”

Ellison added: “Over the past five years our sensors have undergone rigorous testing both by ourselves and our consumers and we feel confident that we are now in a position to supply the sensors — suitable for 99 per cent of industrial applications — to other market players.”

ESI recently constructed a purpose built factory in Wrexham to process the SOS wafers and increased its workforce by a third to cope with increasing demand.

Current applications include testing of jet engines, military vehicles and aircraft, and oil and gas exploration.

Earlier this year Ellison Sensors, the pressure transducer division of ESI Technology received a Gold Medal from United States Government for its performance on the US Top Supplier's list.

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