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MEMS Flow Sensors Based on Self-Heated aGe-Thermistors in a Wheatstone Bridge.

Talic A, Cerimovic S, Beigelbeck R, Kohl F, Sauter T, Keplinger F - Sensors (Basel) (2015)

Bottom Line: The analyses include electrothermal feedback effects of current driven NTC thermistors.Combined with properly designed resistance values, a power demand in sub-1mW range enables efficient gas-flow transduction, as confirmed by measurements.The simulation results are in reasonable agreement with corresponding measurement data confirming the basic assumptions and modeling approach.

View Article: PubMed Central - PubMed

Affiliation: Center for Integrated Sensor Systems, Danube University Krems, Viktor-Kaplan Straße 2, A-2700 Wiener Neustadt, Austria. almir.talic@donau-uni.ac.at.

ABSTRACT
A thermal flow transduction method combining the advantages of calorimetric and hot-film transduction principles is developed and analyzed by Finite Element Method (FEM) simulations and confirmed experimentally. The analyses include electrothermal feedback effects of current driven NTC thermistors. Four thin-film germanium thermistors acting simultaneously as heat sources and as temperature sensors are embedded in a micromachined silicon-nitride membrane. These devices form a self-heated Wheatstone bridge that is unbalanced by convective cooling. The voltage across the bridge and the total dissipated power are exploited as output quantities. The used thin-film thermistors feature an extremely high temperature sensitivity. Combined with properly designed resistance values, a power demand in sub-1mW range enables efficient gas-flow transduction, as confirmed by measurements. Two sensor configurations with different arrangements of the membrane thermistors were examined experimentally. Moreover, we investigated the influence of different layouts on the rise time, the sensitivity, and the usable flow range by means of two-dimensional finite element simulations. The simulation results are in reasonable agreement with corresponding measurement data confirming the basic assumptions and modeling approach.

No MeSH data available.


Related in: MedlinePlus

Contour plot of the 10%–90% rise time tR (ms) as a function of the thermistor positions.
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sensors-15-10004-f014: Contour plot of the 10%–90% rise time tR (ms) as a function of the thermistor positions.

Mentions: Figure 14 depicts the design dependence of the simulated 10%–90% rise time tR in response to a step change of the flow velocity from 0 m/s to 1 m/s. For fast responses, all thermistors have to be positioned as close as possible to the membrane boundary, i.e., near the top corner of the design space. From Figure 12 and Figure 13 we see that this requirement excludes highly efficient flow conversion. However, from a comparison of Figure 11 and Figure 14 we see that fast response and a wide region of monotonous flow conversion can be combined easily. The region of fastest response is characterized by a lower thermal resistance between thermistors and the silicon frame acting as heat bath. Then the heat conduction along the membrane as well as via the fluid enables a rapid discharge of the heat capacity of the thermistors.


MEMS Flow Sensors Based on Self-Heated aGe-Thermistors in a Wheatstone Bridge.

Talic A, Cerimovic S, Beigelbeck R, Kohl F, Sauter T, Keplinger F - Sensors (Basel) (2015)

Contour plot of the 10%–90% rise time tR (ms) as a function of the thermistor positions.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481909&req=5

sensors-15-10004-f014: Contour plot of the 10%–90% rise time tR (ms) as a function of the thermistor positions.
Mentions: Figure 14 depicts the design dependence of the simulated 10%–90% rise time tR in response to a step change of the flow velocity from 0 m/s to 1 m/s. For fast responses, all thermistors have to be positioned as close as possible to the membrane boundary, i.e., near the top corner of the design space. From Figure 12 and Figure 13 we see that this requirement excludes highly efficient flow conversion. However, from a comparison of Figure 11 and Figure 14 we see that fast response and a wide region of monotonous flow conversion can be combined easily. The region of fastest response is characterized by a lower thermal resistance between thermistors and the silicon frame acting as heat bath. Then the heat conduction along the membrane as well as via the fluid enables a rapid discharge of the heat capacity of the thermistors.

Bottom Line: The analyses include electrothermal feedback effects of current driven NTC thermistors.Combined with properly designed resistance values, a power demand in sub-1mW range enables efficient gas-flow transduction, as confirmed by measurements.The simulation results are in reasonable agreement with corresponding measurement data confirming the basic assumptions and modeling approach.

View Article: PubMed Central - PubMed

Affiliation: Center for Integrated Sensor Systems, Danube University Krems, Viktor-Kaplan Straße 2, A-2700 Wiener Neustadt, Austria. almir.talic@donau-uni.ac.at.

ABSTRACT
A thermal flow transduction method combining the advantages of calorimetric and hot-film transduction principles is developed and analyzed by Finite Element Method (FEM) simulations and confirmed experimentally. The analyses include electrothermal feedback effects of current driven NTC thermistors. Four thin-film germanium thermistors acting simultaneously as heat sources and as temperature sensors are embedded in a micromachined silicon-nitride membrane. These devices form a self-heated Wheatstone bridge that is unbalanced by convective cooling. The voltage across the bridge and the total dissipated power are exploited as output quantities. The used thin-film thermistors feature an extremely high temperature sensitivity. Combined with properly designed resistance values, a power demand in sub-1mW range enables efficient gas-flow transduction, as confirmed by measurements. Two sensor configurations with different arrangements of the membrane thermistors were examined experimentally. Moreover, we investigated the influence of different layouts on the rise time, the sensitivity, and the usable flow range by means of two-dimensional finite element simulations. The simulation results are in reasonable agreement with corresponding measurement data confirming the basic assumptions and modeling approach.

No MeSH data available.


Related in: MedlinePlus