Microfabricated thermal conductivity detector for the micro-ChemLab™

Cruz, Dolores; Chang, Jane P.; Showalter, Steven K.; Gelbard, Fred; Manginell, Ronald P.; Blain, Matthew G.

doi:10.1016/j.snb.2006.04.107

Cited by 84 publications

(54 citation statements)

References 5 publications

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“…Therefore, the response speed can be more rapid, and the sensor can be operated in a continuous manner and be repeatedly used without memory effect. Miniature thermal conductivity sensors have been developed for gas chromatography systems 5,6 and demonstrated for methane determination in natural gas.7 Summaries of chemical sensor platforms based on thermal conductivity sensors are provided in references. 8,9 Other groups have investigated nanoscale bridge type gas sensors using chemically synthesized carbon nanotubes, 10 nanowires, 11 and nanobelts, 12 and a review by G. Di Francia et al 13 has been published.…”

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Simulation and Fabrication of an Ultra-Low Power Miniature Microbridge Thermal Conductivity Gas Sensor

Mahdavifar

Aguilar

Peng

et al. 2014

J. Electrochem. Soc.

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A miniature, ultra-low power, sensitive, microbridge-based thermal conductivity gas sensor has been developed. The batch fabrication of the sensors was realized by CMOS compatible processes and surface micromachining techniques. Doped polysilicon was used as the structural material of the bridge with critical dimension of 500 nm. A model of the microbridge was simulated in COMSOL that couples electrical and thermal physics together and includes minimal simplifications. Modeling results shows that the majority of heat is transferred via conduction through the gas gap under the bridge. Heat loss from constant voltage application was observed to be a function of the thermal conductivity of the gas ambient, resulting in different magnitude of resistance change. Maximum temperature occurs at the center of the bridge and could be as high as 800 K. Modeling results coincide with experimental data in predicting resistance changes. The sensor was tested with nitrogen, carbon dioxide, and helium. The response of the sensor to the mixtures of helium fractions in nitrogen was tested. We demonstrated that the sensitivity for helium in nitrogen was 0.34 m /ppm when operated at 3.6 V supplies (at power level of 4.3 mW). With a Wheatstone bridge with ac excitation and a lock-in amplifier the sensor limit of detection was ∼700 ppm helium in nitrogen. The stability of the sensor was excellent achieving over 30 billion measurements before failure. There is an increasing demand and variety of applications for miniaturized gas sensors. Applications range from environment safety sensing, transportation systems, medical and health to aid in diagnostics and even food safety and agriculture. Conventional gas detectors including the most widely used, relatively small pellistors 1 require large power consumption (hundreds of milli-Watts to Watts) with slow response time (tens of seconds). With MEMS technology, microhotplates have been built and are capable of reaching operating temperatures of 500• C in 20 ms at a power level of 100 mW. 2,3 Microfabricated thermal resistive bridges used for catalyst heater and resistance thermometer have been reported with 0.2 ms response time at even lower power level. 4 Compared with the calorimetric gas sensing principle used in the previous work, an electrothermal sensing mechanism based on the thermal conductivity of gases does not rely on gas adsorption and reaction with catalyst films. Therefore, the response speed can be more rapid, and the sensor can be operated in a continuous manner and be repeatedly used without memory effect. Miniature thermal conductivity sensors have been developed for gas chromatography systems 5,6 and demonstrated for methane determination in natural gas.7 Summaries of chemical sensor platforms based on thermal conductivity sensors are provided in references. 8,9 Other groups have investigated nanoscale bridge type gas sensors using chemically synthesized carbon nanotubes, 10 nanowires, 11 and nanobelts, 12 and a review by G. Di Francia et al. 13 has been published. Altho...

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confidence: 99%

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confidence: 99%

Simulation and Fabrication of an Ultra-Low Power Miniature Microbridge Thermal Conductivity Gas Sensor

Mahdavifar

Aguilar

Peng

et al. 2014

J. Electrochem. Soc.

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“…Cruz et al [7] reported a micro-TCD implemented by microfabrication techniques. Figure 13 shows schematic views and SEM images of the fabricated TCD.…”

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confidence: 99%

Miniaturized VOC Detectors for Monitoring Indoor Air Quality

Lee

Baek

Jung

et al. 2015

KAIST Research Series

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With the increased use of chemicals for laundry and cleaning, artificial adhesives, paints, and space heaters indoors, the concentration of volatile organic compounds (VOCs) increases, thus threatening human health. It is known that VOCs are the possible causes of atopic disease and asthma. Some of the VOC species such as formaldehyde and benzene are carcinogenic. The first step to avoid damage from VOCs is to determine their concentration in air. In typical approaches to detect VOCs, an adsorbent to capture the gas molecules of the VOCs is placed in the area of interest and taken to a laboratory, and subsequently, the VOCs are thermally desorbed and directed to large-sized detectors; the entire process is time-consuming and costly. With the increased public awareness of the hazards of VOCs, research on the cost-effective detection of VOCs using small personal devices has become more active. In this chapter, fundamental technologies to detect VOCs are introduced, and current research works are discussed on low-cost sensing of VOCs using miniaturized devices to evaluate indoor air quality.

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“…The primary device used for such a measurement is called a thermal conductivity sensor (TCS) or more commonly known as thermal conductivity detector (TCD). The main application of TCDs remains within the gas chromatography (GC) market primarily due to their detection universality, low manufacturing cost [1,2], simple construction [3,4], good sensitivity (up to 1 ppm) [5,6], ease of miniaturization for mass scale production [7] and non-destructive analytical characteristics [8].…”

Section: Introductionmentioning

confidence: 99%

“…In addition to this the micro thermal conductivity detector ( TCD) can be fabricated using existing micro fabrication techniques and the sensor cell can be designed for a streamlined structure with an extremely small dead volume [9]. This effectively improves the detection response and reduces the power consumption to the sub-watts level [3]. The primary application of TCD is in gas and liquid chromatography (GC) where the TCD is able to detect and identify the time separated chemical species as they elute from the column [8].…”

Section: Introductionmentioning

confidence: 99%