Abstract:Through the use of silicon micromachining, we have developed a microhotplate structure capable of reaching temperatures in excess of 500 °C, onto which thin films have been selectively grown via metalorganic chemical vapor deposition. The microhotplate structure contains surface electrical contacts which permit conductance measurements to be made on films during and after deposition, and therefore presents some unique opportunities for the in situ characterization of growing films as well as for novel gas sens… Show more
“…The integration of SnO 2 sensing films on microsubstrates making gas sensors portable started only after surface micromachining of microhotplates became viable. The self-lithographic method of material deposition on the microhotplate surface became a good approach, as no lithographic steps were required to pattern the sensing films [3].…”
In this paper, the sensitivity, stability and selectivity of nanoparticle engineered tin oxide
(SnO2) are reported, for microhotplate chemical sensing applications. 16 Å of metals such as nickel,
cobalt, iron, copper and silver were selectively evaporated onto each column of the
microhotplate array. Following evaporation, the microhotplates were heated to
500 °C
and SnO2
was deposited on top of the microhotplates using a self-aligned chemical vapour
deposition process. Scanning electron microscopy characterization revealed control of
SnO2
nanostructures in the range of 20–121 nm. Gas sensing in seven different hydrocarbons
revealed that metal nanoparticles that helped in producing faster nucleation of
SnO2
resulted in smaller grain size and higher sensitivity. Sensitivity as a function of
concentration and grain size is addressed for tin oxide nanostructures. Smaller grain sizes
resulted in higher sensitivity of tin oxide nanostructures. Temperature programmed sensing
of the devices yielded shape differences in the response between air and methanol,
illustrating selectivity. Spiderweb plots were used to monitor the materials programmed
selectivity. The shape differences between different gases in spiderweb plots illustrate
materials selectivity as a powerful mapping approach for monitoring selectivity in various
gases. Continuous monitoring in 80 ppm methanol yielded stable sensor response for
more than 200 h. This comprehensive study illustrates the use of a nanoparticle
engineering approach for sensitive, selective and stable gas sensing applications.
“…The integration of SnO 2 sensing films on microsubstrates making gas sensors portable started only after surface micromachining of microhotplates became viable. The self-lithographic method of material deposition on the microhotplate surface became a good approach, as no lithographic steps were required to pattern the sensing films [3].…”
In this paper, the sensitivity, stability and selectivity of nanoparticle engineered tin oxide
(SnO2) are reported, for microhotplate chemical sensing applications. 16 Å of metals such as nickel,
cobalt, iron, copper and silver were selectively evaporated onto each column of the
microhotplate array. Following evaporation, the microhotplates were heated to
500 °C
and SnO2
was deposited on top of the microhotplates using a self-aligned chemical vapour
deposition process. Scanning electron microscopy characterization revealed control of
SnO2
nanostructures in the range of 20–121 nm. Gas sensing in seven different hydrocarbons
revealed that metal nanoparticles that helped in producing faster nucleation of
SnO2
resulted in smaller grain size and higher sensitivity. Sensitivity as a function of
concentration and grain size is addressed for tin oxide nanostructures. Smaller grain sizes
resulted in higher sensitivity of tin oxide nanostructures. Temperature programmed sensing
of the devices yielded shape differences in the response between air and methanol,
illustrating selectivity. Spiderweb plots were used to monitor the materials programmed
selectivity. The shape differences between different gases in spiderweb plots illustrate
materials selectivity as a powerful mapping approach for monitoring selectivity in various
gases. Continuous monitoring in 80 ppm methanol yielded stable sensor response for
more than 200 h. This comprehensive study illustrates the use of a nanoparticle
engineering approach for sensitive, selective and stable gas sensing applications.
“…The TiO 2 films deposited using TN discussed above are too resistive for such monitoring, given the contact geometry used in these experiments. Even with interdigitated comb contacts, limited success was attained for monitoring the growth of TN-deposited films. To demonstrate real-time conductance measurement on a growing film, TiO 2 was grown using TTIP as the CVD precursor.…”
Section: Resultsmentioning
confidence: 99%
“…The fact that the slope of the plots is considerably steeper in the early stages of film growth is not completely unexpected since measured resistance is related to both film thickness (which is increasing with time) and the chemoresistive nature of the film that allows changes in the ambient environment to change the film's electrical properties. In the early stages of film growth, the deposited material is similar in nature to a nanoparticle film in that the increased surface area-to-volume ratio of the growing film makes the device more sensitive to gases than a one with thicker film. , In the case of TiO 2 deposited using TTIP, this may be due to the increased sensitivity of the device toward the reaction products such as isopropyl alcohol, propylene, and water. 9 Conductance data obtained during the deposition of TiO 2 using titanium(IV) isopropoxide at 400 °C.…”
An approach for high-throughput rapid screening of chemical vapor deposition (CVD) materials using micromachined silicon microheater arrays is described. To illustrate this approach, titanium dioxide was deposited by CVD, using titanium(IV) nitrate and titanium-(IV) isopropoxide at temperatures between 130 and 815 °C. Deposition was confined to the microhotplate elements within 4-and 16-element arrays. Film microstructure was examined by scanning electron microscopy. In situ electrical measurements were made with integrated microcontacts during the deposition of TiO 2 using titanium(IV) isopropoxide. A novel approach using temperature-programmed deposition with temperature ramp rates up to 800 °C/s was also employed for microstructure modification during deposition. Additionally, the steep temperature gradients present on the microhotplate supports have been demonstrated to provide an excellent platform for investigating temperature-dependent microstructures.
“…1 The operating temperature of the sensing layer and power dissipation of gas sensor can be lowered by using the MEMS based silicon structures. [2][3][4] Micro heaters are implanted into gas sensors to warmth the sensing layer to a requisite temperature for getting improved sensitivity [5][6][7][8] and response time. Various semiconducting oxides such as Co 3 O 4 , SnO 2 have been reported on high operating temperature (350 C-450 C) with high power consumption.…”
The paper presents about employing two different algorithms (Genetic Algorithm or GA and Particle Swarm Optimization or PSO) to get optimized low power consumption of MEMS based micro-heater. The comparative performance study of GA algorithm and PSO algorithm is analyzed for getting superior parameter optimization of micro-heater. The optimum low value of power consumption of micro-heater is required to improve the efficiency of micro-heater. The input parameters of optimization techniques are the thickness of oxide layer, active area of membrane and temperature of micro-heater. The objective function of both optimization techniques is the power consumption. The simulation results are compared in terms of quality of results and computation time. The electrothermal characteristics of micro-heater are analyzed using the Intellisuite 8.2 software. Obtained results present that PSO based optimization technique offers better performance compare to GA based optimization technique in terms of no. of iterations and computation time.
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