Nano and micro stripe based metal oxide thin film gas sensor

Functional metal oxide micro and nanostructures for the detection of gas are a very promising candidate for future gas-sensors, Due to reduced size and thus an increased surface to volume ratio nanosized sensitive structures offer a high potential for increasing sensitivity. A top down sputtering approach for gas sensors with nano-sized gas sensitive metal oxide areas is presented. Oxidised silicon wafer were used as substrates. The silicon dioxide film of 1 um thickness was prepared by thermal oxidation in order to insulate the gas sensing elements from the substrate. At the sensor chips (1.5 x 1.5 mm 2) a Ta/Pt film (20/200 nm thickness) was deposited and patterned to act as interdigital electrodes, heater and temperature sensor. In a second step nano-scaled tin oxide layers (60nm thick, 5 um width) were deposited by sputtering techniques and photolithographical pattering between the platinum micro-electrodes (4 um gap). As the last step the width of the stripes was r educed by using Focused Ion Beam (FIB) technology to obtain the desired size and structure. This enables the control of the dimensions of the structures down to the resolution limit of the FIB-system which is a few tens of nm. The structural and electrical characterisation of the sensors and their responses during exposure to several test gases including O2, CO, NO 2 and H2O are presented as well.