Smart micro-hotplate platform for high temperature gas sensor

There has been an increasing demand of hand held battery operated gas monitors because of their widespread applications. However, the existing gas sensors suffer from high power consumption (> 100 mW) and most of them are not CMOS compatible, thus expensive. The aim of this research is to develop a smart micro-hotplate platform for high temperature gas sensor application. The gas sensor devices should consume low power and be fully CMOS compatible. This will enable the monolithic integration of interfacing circuitry with the sensor device on the same chip and thus will make the device performance more reliable and reproducible. The work mainly focused on two aspects: (i) design and development of low power reliable micro-hotplates and (ii) design and integration of intelligent electronic interface for the amplification and read out of the gas sensing signal. The design and simulation were carried out in Cadence and ANSYS software. The devices were fabricated in two batches in XFAB, Germany. Both aluminium and tungsten metallization were used. Tungsten was used to avoid electro migration at high temperature. The first batch was a proof of concept batch, which contains mostly discrete micro-hotplates; whereas electronic integration was the main focus on the second batch. The micro-hotplate contains MOSFETs as the heating elements. The heaters are embedded in thin SOI membrane. The membranes were realized using DRIE technique in Silex, Sweden. The electro-thermal and optical characterisation of the micro-hotplates shows that the membranes are very stable. The devices measured on different positions and wafers show excellent reproducibility. The MOSFET micro-heaters survived temperatures above 500° C. The hotplates consumed low power, operating temperature up to 550° C was achieved at a power cost of only 16 mW, which is much lower than the present gas sensors. The sensing material in the form of a CNT layer was grown on the micro-hotplates (using local growth technique) and the preliminary gas testing results showed lots of promise.EThOS - Electronic Theses Online ServiceGBUnited Kingdo