Sensory spin-out

Cambridge CMOS Sensors Limited (CCMOS) – a spin-out from Cambridge University’s Department of Engineering – has licensed technology from Warwick University that, it claims, will allow it to develop gas sensors that offer a significant improvement over those currently in use in portable instrumentation.

First off, the sensors under development will be able to operate at high temperatures of up to 500^oC, while consuming very low power – below 30mW. They will also have a fast thermal response time – this will be in the millisecond range as opposed to the seconds range that current state-of-the-art products offer.

The sensors themselves are fabricated in a foundry using a standard SOI CMOS process. A sensing layer of material sits on top of sensing electrodes made from the top high temperature metal layer of the device, which is exposed to allow it to contact to the sensitive layer on top of it.

But uniquely, buried beneath the sensory material and the sensor electrodes in the device sits a circular resistive microhotplate with a diode temperature sensor created from another metal layer.

In an exclusive interview with The Engineer Online, Prof Bill Milne from Cambridge University, and one of the founders of the new company, said that the  microhotplate allows the temperature of the actual sensing material in the sensor to be raised, a process, he said, that can enhance the sensitivity of the device.

Furthermore, the microhotplate buried in the sensor also allows the temperature applied to the sensory elements to be further increased after any sensing has occurred, essentially allowing the sensing material to be 'refreshed'.

In some cases, he added, the microhotplate will also allow the company to locally 'grow' a sensing material of its choice only on the heated area without affecting the surrounding CMOS circuitry should it choose to do so.

Milne said: ‘If we want to grow carbon nanotubes (as sensing elements) at an elevated temperature we cannot heat up the entire chip as it would destroy the CMOS devices. But by only heating up a small region we can grow the CNTs without adversely affecting the surrounding electronics.'

Prof Julian Gardner, another co-founder of the company, said that the company envisaged numerous applications ranging from chemical micro-sensors to physical sensors. He added: 'The technology is ideal for high volume and low unit cost products.'

Under special agreement, samples of the sensing devices are available from Cambridge CMOS Sensors.

Dave Wilson