Mask-less deposition of Au–SnO₂nanocomposites on CMOS MEMS platform for ethanol detection

Abstract

Here we report on the mask-less deposition of Au-SnO2 nanocomposites with a silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform through the use of dip pen nanolithography (DPN) to create a low-cost ethanol sensor. MEMS technology is used in order to achieve low power consumption, by the employment of a membrane structure formed using deep reactive ion etching technique. The device consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the SOI membrane. The tungsten micro-heater is used to raise the membrane temperature up to its operating temperature and the electrodes are used to measure the resistance of the nanocomposite sensing layer. The CMOS MEMS devices have high electro-thermal efficiency, with 8.2 °C temperature increase per mW power of consumption. The sensing material (Au-SnO2 nanocomposite) was synthesised starting from SnO nanoplates, then Au nanoparticles were attached chemically to the surface of SnO nanoplates, finally the mixture was heated at 700 °C in an oven in air for 4 h. This composite material was sonicated for 2 h in terpineol to make a viscous homogeneous slurry and then 'written' directly across the electrode area using the DPN technique without any mask. The devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100-1000 ppm. The sensitivity varied from 1.2 to 0.27 ppm(-1) for 100-1000 ppm of ethanol at 10% relative humid air. Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene.

Understanding the Potential of WO3 Based Sensors for Breath Analysis

“…Current research focuses on tailoring SMOX materials, in general, to better detect ethanol in breath [6,53,54]. Research exists on the suitability of WO 3 -based sensors for breath alcohol detection, see Table 4.…”

Sensitive Cross-Linked SnO2:NiO Networks for MEMS Compatible Ethanol Gas Sensors

“…In comparison with the various nanostructured SnO 2 prepared by other methods in Table 1, the crosslinked SnO 2 /NiO network exhibited comparable sensitivity [19,23,47,[49][50][51][52]. We also investigated the ethanol sensitivity of other MEMS compatible sensing materials in Table 1, such as DPN deposited Au/SnO 2 nanocomposites, ZnO nanowires grown on a MEMS microplate, and ZnO tetrapods deposited on a microheater [37,38,51]. Apart from the comparable or better sensitivity, there are several other advantages for the cross-linked SnO 2 /NiO networks including high yield, low device-to-device deviation, cheap and simple processing.…”

“…Second, some researchers have tried to integrate high-performance MOS nanomaterials onto microheaters, but it is difficult to control and cast the slurry-based MOS nanomaterials onto the suspending heating area of microheaters. Several groups have reported the fabrication of nanomaterialbased MEMS sensors via ink-jet printing, polymeric mask centrifugation, and dip pen nanolithography (DPN) methods [12,[36][37][38][39]. However, the low yield and large device-to-device deviation hampers the sensor fabrication in a large scale.…”

Electrospun Nanostructures for High Performance Chemiresistive and Optical Sensors

“…A new type of novel catalysts can further enhance sensitivity and selectivity to overcome current limitation. (iii)Power consumption is another issue to be addressed for application in portable devices because most of SMO sensing layers are activated at elevated temperatures. Either miniaturization of sensor platform or active sensing materials at room temperature can be solutions to realize portable chemical sensors.…”