Nano-structured micro-power smart gas sensors

Lead Research Organisation: University of Warwick
Department Name: Sch of Engineering

Abstract

The project aims to develop a new generation of smart silicon-based chemical sensors using advanced nano-materials as gas sensitive layers. Compared to current commercial solid-state gas sensors, these new sensors will offer ultra low power consumption (below 1 mW), a superior sensitivity to gases (by one order of magnitude), full CMOS compatibility and low unit cost for high-volume markets. We will study the properties of different nano-materials, such as doped CNTs, ZnO nanowires, and mesoporous WO3. We will increase their selectivity to pollutant gases and minimise the microhotplate area to enable ultra low power consumption by operating dynamically at temperatures of up to 750 degC. The project focuses upon a technology platform that combines novel nano-materials with SOI CMOS microelectronics and post-CMOS micromachining. The environmentally important gases of H2, NH3, O3, CO2, NO2, and will be targeted as well as volatile hydrocarbons (e.g. benzene in BTEX).
 
Description Gas sensors play an important role within our society. Though they receive little attention from the media, they are used within homes, factories and within the outside environment. Such sensors play a vital role in ensuring that the air around is of breathable quality, that there are no leaks within factories, to ensure the quality of manufacturing processes and even that the air in our cars is pleasant.

Currently, the UK is fourth largest producers of gas sensors in world and has a reputation for international leading research into new devices and materials for gas sensors. This project has helped to develop the next generation of gas sensors to support the UK gas sensor field. To achieve this, we have created highly novel micro-gas sensors deploying SOI CMOS technology combined with nanostructured materials.

By far the largest type of commercial gas sensors are those based on the use of metal-oxide semiconducting material whereby exposure to a gas modulates the resistance of a thin film. Such materials operate at significantly elevated temperatures (up to 600 C) thus power consumption of these sensors is a major issue. Furthermore, nearly all sensors employ a semi-manual manufacturing process which significantly increases the unit cost. The aim of this project was to produce an ultra-low cost, ultra-low power sensor, but with high sensitivity and value added electronic integration.

To reduce the power consumption micro-heater technology based on a standard manufacturing process has been deployed. This process, normally used for power devices, has been modified to create gas sensors. Here a tungsten metal layer, suspended in layers of glass and silicon nitride, is used to heat a sensing layer deposited above. This small size and low thermal mass has resulted in world leading power consumption of less than 50 mW for continuous operation at 600 C and 5 MW for pulsed mode. But, by being a standard process, these devices can be created for pence instead of 10's of pounds. Furthermore, by being a standard process we have been able to integrate value added electronic components without any additional cost to the sensor. On top of this, we have created custom integrated circuits to interface with our chips, adding additional functionality at minimum cost. Thus, we have formed almost a complete sensor system within one miniature, low cost package.

One major issue with taking our approach is that when the sensor is scaled down, the sensing material is also reduced in size. As the sensitivity of a sensor is usually associated with the surface area the, reducing the size of the sensing material results is lower sensitivity. Thus our approach has been to use nano-structured materials as either the sensing layer itself or as a scaffold for coating. These have employed the growing of forests of nano-materials (including carbon nano-tubes, zinc oxide nano-wires and tungsten oxide nano-rods). Due to their nano-structure such materials provide massive surface area for sensing and thus can provide the same sensitivity as macro-scale gas sensors. To achieve this many technical barriers, such as device material compatibility and material adhesion, have had to be solved, making the UK one of the world leaders in this area.

Our work has resulted in the commercialisation of these high temperature micro-hot plates based on a SOI CMOS platform. Furthermore, we have successfully shown these new sensors to be highly sensitivity to a range of gases and environmental pollutants. We hope that this will shortly lead to these materials being commercially available. This work has also been extensively report within both academic, commercial and media circles and we believe has been a major success.
Exploitation Route Yes by spin-out company.
Sectors Electronics,Environment,Healthcare
 
Description Yes. A spin out called Cambridge CMOS Sensors Ltd.
First Year Of Impact 2008
Sector Electronics
Impact Types Economic
 
Description European Union Framework 7
Amount £300,000 (GBP)
Funding ID 285275 GRAFOL CP-IP FP7-2011-NMP-ICT-FoF 
Organisation European Commission 
Department Seventh Framework Programme (FP7)
Sector Public
Country European Union (EU)
Start  
 
Description European Union Framework 7
Amount £300,000 (GBP)
Funding ID 285275 GRAFOL CP-IP FP7-2011-NMP-ICT-FoF 
Organisation European Commission 
Department Seventh Framework Programme (FP7)
Sector Public
Country European Union (EU)
Start  
 
Description Technology Strategy Board
Amount £170,000 (GBP)
Funding ID TSB CRD 027 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start  
 
Title Electromigration reduction in micro-hotplates 
Description N/A 
IP Reference US20110174799 
Protection Patent granted
Year Protection Granted
Licensed No