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Takao Iwaki




Takao Iwaki


Sensors Research Laboratory

University of Warwick

Tel: 02476 574494







SOI-CMOS based gas sensors employing nanomaterials

The aim of this project is to develop novel low cost gas sensors with low power consumption and very high sensitivity. The project is divided into two parts: development of micro-hotplates and gas sensing characterisation of nanomaterials.


One of the main issues in commercial gas sensors is high power consumption for high temperature operation. Developments over the last 10 years in silicon microtechnology have made it possible to fabricate low power, low cost and small micro-hotplates that can be used for gas sensors. However, commercial exploitation of these micro-hotplates has not yet been fully realized. This is because these micro-hotplates employ either platinum or polysilicon as heater materials and both of them have drawbacks; platinum based micro-hotplates are not CMOS compatible and thus costly, and polysilicon ones are not thermally stable.


To settle the above issues, we are developing three types of micro-hotplates: tungsten based, highly doped single crystal silicon (SCS) based and FET based micro-hotplates. Tungsten and doped SCS are chosen as heater materials as they are more thermally stable than polysilicon and CMOS compatible unlike platinum. An example of our devices and a result of 3D electro-thermal simulation are shown in Figure 1 and 2. The fabricated micro-hotplates operate with a very low power consumption e.g. 10 mw at 300 oC as shown in Figure 3.


The second part of the project, which we are now concentrating on, is to deposit some nanomaterials onto the micro-hotplates and to characterise them aiming at high sensitivity. Nanomaterials such as metal oxide nanowires and carbon nanotubes are promising since their surface-to-volume ratio is extremely high.



Figure 1. A device comprised of 9 SCS micro-hotplates

Figure 2. 3D-electro-thermal simulation of a SCS micro-hotplate.

Figure 3. Power consumption of a SCS micro-hotplate.