A simple and versatile strategy is presented for the localized on-chip synthesis of an ordered metal oxide hollow sphere array directly on a low power microheater platform to form a closely integrated miniaturized gas sensor. Selective microheater surface modification through fluorinated monolayer self-assembly and its subsequent microheater-induced thermal decomposition enables the position-controlled deposition of an ordered two-dimensional colloidal sphere array, which serves as a sacrificial template for metal oxide growth via homogeneous chemical precipitation; this strategy ensures control in both the morphology and placement of the sensing material on only the active heated area of the microheater platform, providing a major advantage over other methods of presynthesized nanomaterial integration via suspension coating or printing. A fabricated tin oxide hollow sphere-based sensor shows high sensitivity (6.5 ppb detection limit) and selectivity toward formaldehyde, and extremely fast response (1.8 s) and recovery (5.4 s) times. This flexible and scalable method can be used to fabricate high performance miniaturized gas sensors with a variety of hollow nanostructured metal oxides for a range of applications, including combining multiple metal oxides for superior sensitivity and tunable selectivity.
Nanowire-assembled 3D hierarchical ZnCoO microstructure is synthesized by a facile hydrothermal route and a subsequent annealing process. In comparison to simple nanowires, the resulting dandelion-like structure yields more open spaces between nanowires, which allow for better gas diffusion and provide more active sites for gas adsorption while maintaining good electrical conductivity. The hierarchical ZnCoO microstructure is integrated on a low-power microheater platform without using binders or conductive additives. The hierarchical structure of the ZnCoO sensing material provides reliable electrical connection across the sensing electrodes. The resulting sensor exhibits an ultralow detection limit of 3 ppb toward formaldehyde with fast response and recovery as well as good selectivity to CO, H, and hydrocarbons such as n-pentane, propane, and CH. The sensor only consumes ∼5.7 mW for continuous operation at 300 °C with good long-term stability. The excellent sensing performance of this hierarchical structure based sensor suggests the advantages of combining such structures with microfabricated heaters for practical low-power sensing applications.
A robust silicon carbide (SiC) microheater is used for stable low-power catalytic gas sensing at high operating temperatures, where previously developed low-power polycrystalline silicon (polysilicon) microheaters are unstable. The silicon carbide microheater has low power consumption (20 mW to reach 500 °C) and exhibits an order of magnitude lower resistance drift than the polysilicon microheater after continuously heating at 500 °C for 100 h and during temperature increases up to 650 °C. With the deposition of platinum nanoparticleloaded boron nitride aerogel, the SiC microheater-based catalytic gas sensor detects propane with excellent long-term stability while exhibiting fast response and recovery time (~1 s). The sensitivity is not affected by humidity, nor during 10% duty cycling, which yields a power consumption of only 2 mW with frequent data collection (every 2 s). With a simple change of heater material from silicon to SiC, the microheater and resulting catalytic gas sensor element show significant performance improvement.
Now-a-days, there has been growing demand for the development of micro scale devices, due to its less cost, space requirements, high dimensional stability and especially manufacturing time. This paper reports the modeling of MEMS based Piezoelectric shear actuated beam by using COMSOL Multiphysics software of version 4.2a.The dimensions of the model beam is of 100-mm long, 30-mm width, 10-mm thickness. In this paper, we analysed the deflection of beam under different voltages. In the first step, deflection of beam is analysed by changing the material of sandwiched beam. In the second step deflection of beam is explored by changing material of electrodes. In the third step, deflection of beam is analysed by changing both materials of sandwiched beam and electrodes. In the final step defection of beam is explored by changing both thickness and material of electrodes. Finally, the results of analysis allowed to conclude us to design a piezo electric shear actuated beam with different ranges and resolutions, under the condition of changing both thickness and material of electrodes gives the optimum deflection of 216nm under 30v excited input voltage.
This paper reports the first use of a silicon carbide (SiC) microheater for stable low-power catalytic gas sensing. Catalytic combustion of hydrocarbon gases often requires high operating temperatures, which leads to instability in a previously developed low-power polycrystalline silicon (polysilicon) microheater. A silicon carbide microheater has been developed with low power consumption (20 mW to reach 500 °C) and improved stability, exhibiting an order of magnitude lower resistance drift than the polysilicon microheater after 100 hrs of continuous heating at 500 °C and during temperature increases up to 650 °C. When loaded with a high performance catalytic nanomaterial, the SiC microheater-based catalytic gas sensor exhibits fast response and recovery time (<1 s) and improved long-term stability for propane detection. The results show that a simple change of material from polysilicon to polySiC leads to a significant performance improvement of the microheater and the resulting sensor element.
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