scholarly journals Sensitivity Enhancement of Silicon-on-Insulator CMOS MEMS Thermal Hot-Film Flow Sensors by Minimizing Membrane Conductive Heat Losses

Sensors ◽  
2019 ◽  
Vol 19 (8) ◽  
pp. 1860 ◽  
Author(s):  
Zahid Mehmood ◽  
Ibraheem Haneef ◽  
Syed Zeeshan Ali ◽  
Florin Udrea
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Film Flow ◽  
Heat Losses ◽  
Silicon On Insulator ◽  
Conductive Heat ◽  
Circular Membrane ◽  
Flow Sensors ◽  
Cmos Mems ◽  
Hot Film

Minimizing conductive heat losses in Micro-Electro-Mechanical-Systems (MEMS) thermal (hot-film) flow sensors is the key to minimize the sensors’ power consumption and maximize their sensitivity. Through a comprehensive review of literature on MEMS thermal (calorimetric, time of flight, hot-film/hot-film) flow sensors published during the last two decades, we establish that for curtailing conductive heat losses in the sensors, researchers have either used low thermal conductivity substrate materials or, as a more effective solution, created low thermal conductivity membranes under the heaters/hot-films. However, no systematic experimental study exists that investigates the effect of membrane shape, membrane size, heater/hot-film length and M e m b r a n e (size) to H e a t e r (hot-film length) Ratio (MHR) on sensors’ conductive heat losses. Therefore, in this paper we have provided experimental evidence of dependence of conductive heat losses in membrane based MEMS hot-film flow sensors on MHR by using eight MEMS hot-film flow sensors, fabricated in a 1 µm silicon-on-insulator (SOI) CMOS foundry, that are thermally isolated by square and circular membranes. Experimental results demonstrate that: (a) thermal resistance of both square and circular membrane hot-film sensors increases with increasing MHR, and (b) conduction losses in square membrane based hot-film flow sensors are lower than the sensors having circular membrane. The difference (or gain) in thermal resistance of square membrane hot-film flow sensors viz-a-viz the sensors on circular membrane, however, decreases with increasing MHR. At MHR = 2, this difference is 5.2%, which reduces to 3.0% and 2.6% at MHR = 3 and MHR = 4, respectively. The study establishes that for membrane based SOI CMOS MEMS hot-film sensors, the optimum MHR is 3.35 for square membranes and 3.30 for circular membranes, beyond which the gain in sensors’ thermal efficiency (thermal resistance) is not economical due to the associated sharp increase in the sensors’ (membrane) size, which makes sensors more expensive as well as fragile. This paper hence, provides a key guideline to MEMS researchers for designing the square and circular membranes-supported micro-machined thermal (hot-film) flow sensors that are thermally most-efficient, mechanically robust and economically viable.

Thermal Conductivity Measurement of CVD Diamond Films Using a Modified Thermal Comparator Method

2000 ◽  
Vol 122 (4) ◽  
pp. 808-816 ◽  
Author(s):  
K. R. Cheruparambil ◽  
B. Farouk ◽  
J. E. Yehoda ◽  
N. A. Macken
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Calibration Curve ◽  
Thermal Contact ◽  
Diamond Films ◽  
Conductivity Measurement ◽  
Cvd Diamond ◽  
Conductive Heat ◽  
Comparator Method

Results from an experimental study on the rapid measurement of thermal conductivity of chemical vapor deposited (CVD) diamond films are presented. The classical thermal comparator method has been used successfully in the past for the measurement of thermal conductivity of bulk materials having high values of thermal resistance. Using samples of known thermal conductivity, a calibration curve is prepared. With this calibration curve, the comparator can be used to determine thermal conductivity of unknown samples. We have significantly modified and extended this technique for the measurement of materials with very low thermal resistance, i.e., CVD diamond films with high thermal conductivity. In addition to the heated probe, the modified comparator employs a thermoelectric cooling element of increase conductive heat transfer through the film. The thermal conductivity measurements are sensitive to many other factors such as the thermal contact resistances, anisotropic material properties, surrounding air currents and temperature, and ambient humidity. A comprehensive numerical model was also developed to simulate the heat transfer process for the modified comparator. The simulations were used to develop a “numerical” calibration curve that agreed well with the calibration curve obtained from our measurements. The modified method has been found to successfully measure the thermal conductivity of CVD diamond films. [S0022-1481(00)00804-5]

Parametric Study of Zone-Melting-Recrystallization Processing of Silicon on Insulator Structures

1989 ◽  
Vol 157 ◽  
Author(s):  
Joseph Lipman ◽  
Ioannis N. Miaoulis ◽  
James S. Im
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Heat Source ◽  
Temperature Profile ◽  
Parametric Study ◽  
Zone Melting ◽  
Heat Losses ◽  
Silicon On Insulator ◽  
Graphical Form ◽  
The Relationship

ABSTRACTThe effects of four thermal parameters on the temperature distribution during Zone-Melting-Recrystalllzation processing of Slllcon-On-Insulator devices with graphite strip as the heat source were investigated numerically. Results indicate that the convective heat losses, the variability of the thermal conductivity of silicon as a function of temperature, and the multilayer nature of the structure do not affect the temperature distribution significantly. However, the velocity of the graphite strip can significantly affect the temperature distribution. The temperature profile remains the same for graphite strip velocities below 0.03 cm/sec. The relationship between required graphite strip temperature and velocity of the strip for film melting to occur is presented in graphical form.

scholarly journals Conductive Heat Transfer Prediction of Plain Socks in Wet State

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Tariq Mansoor ◽  
Lubos Hes ◽  
Amany Khalil ◽  
Jiri Militky ◽  
Maros Tunak ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Moisture Content ◽  
Thermal Resistance ◽  
Heat Loss ◽  
Algebraic Model ◽  
Conductive Heat ◽  
Testing Instrument ◽  
Filling Coefficient ◽  
Good Agreement

Abstract In this study, an algebraic model and its experimental verification was carried out to investigate the effect of moisture content on the heat loss that takes place due to conduction of sock fabrics. The results show that increasing moisture content in the studied socks caused a significant increase in their conductive heat loss. Plain knitted socks with different fiber composition were wetted to a saturated level, and then their moisture content was reduced stepwise. When achieving the required moisture content, the socks samples were characterized by the Alambeta testing instrument for heat transfer. Three different existing modified mathematical models for the thermal conductivity of wet fabrics were used for predicting thermal resistance of socks under wet conditions. The results from both ways are in very good agreement for all the socks at a 95% confidence level. In the above-mentioned models, the prediction of thermal resistance presents newly a combined effect of the real filling coefficient and thermal conductivity of the so-called “wet” polymers instead of dry polymers. With these modifications, the used models predicted the thermal resistance at different moisture levels. Predicted thermal resistance is converted into heat transfer (due to conduction) with a significantly high coefficient of correlation.

Thermal Conductivity Measurement of CVD Diamond Films Using a Modified Thermal Comparator Method

1999 ◽  
Author(s):  
Kumar R. Cheruparambil ◽  
Bakhtier Farouk ◽  
Joseph E. Yehoda ◽  
Nelson A. Macken
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Calibration Curve ◽  
Thermal Contact ◽  
Diamond Films ◽  
Conductivity Measurement ◽  
Cvd Diamond ◽  
Conductive Heat ◽  
Comparator Method

Abstract Results from an experimental study on the rapid measurement of thermal conductivity of chemical-vapor-deposited (CVD) diamond films are presented. The classical thermal comparator method has been used successfully for the measurement of thermal conductivity of bulk materials having high values of thermal resistance. Using samples of known thermal conductivity, a calibration curve is prepared. With this calibration curve, the comparator can be used to determine thermal conductivity of unknown samples. We have significantly modified and extended this technique for the measurement of materials with very low thermal resistance, i.e., CVD films with high thermal conductivity. In addition to the heated probe, the modified comparator employs a thermo-electric cooling element to increase conductive heat transfer through the film. The thermal conductivity measurements are sensitive to many other factors such as the thermal contact resistances, anisotropic material properties, surrounding air currents and temperature, and ambient humidity. A comprehensive numerical model was also developed to simulate the heat transfer process for the modified comparator. The simulations were used to develop a ‘numerical’ calibration curve that agreed well with the calibration curve obtained from our measurements. The modified method has been found to successfully measure the thermal conductivity of CVD diamond films.

Parametric Study of Salt Gradient Solar Ponds

1986 ◽  
Vol 108 (1) ◽  
pp. 75-77 ◽  
Author(s):  
R. S. Beniwal ◽  
N. S. Saxena ◽  
R. C. Bhandari
Keyword(s):  
Thermal Conductivity ◽  
Mathematical Model ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Parametric Study ◽  
Heat Losses ◽  
Insulating Materials ◽  
Solar Ponds ◽  
Solar Pond ◽  
Salt Gradient

A mathematical model for efficiency of a salt gradient solar pond is described. Heat losses from the bottom of the pond have been calculated, and the results for the effective thermal conductivity with the thicknesses of various insulating materials have been presented. The effect of the ground thermal resistance on the efficiency of the pond for different values of ΔT/So have also been shown.

Thermo-Mechanical Study of AlN Thin-Films As Heat Spreaders in III-V Photonic Devices

2017 ◽  
Author(s):  
Shenghui Lei ◽  
Ertugrul Kardemir ◽  
David McCloskey ◽  
John F. Donegan ◽  
Ryan Enright
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Residual Stress ◽  
Thermal Resistance ◽  
Semiconductor Lasers ◽  
Compressive Residual Stress ◽  
Silicon On Insulator ◽  
Tensile Failure ◽  
Processing Temperature ◽  
Residual Stress State

Ridge-type hybrid III-V active waveguides on silicon-on-insulator (SOI) substrates demonstrate poor thermal performance due to several factors. One aspect of their typical design that leads to large thermal resistance is the use of polymer-based optical cladding around the waveguide. To address this issue, we have been exploring the use of deposited aluminium nitride (AlN) as an alternative optical cladding material. AlN is an excellent dielectric with optical properties making it suitable as a cladding around III-V waveguides. Crucially, this material can demonstrate thermal conductivities ∼100 times larger than current polymer cladding materials such as benzocyclobutene (BCB). Electro-thermo simulation results suggest that replacing BCB with AlN could reduce device thermal resistance by ∼2 times. However, our previous linear elastic mechanical modelling indicates that mismatched thermal expansion has the potential to cause mechanical tensile failure in the III-V waveguide when cooled from the processing temperature to room temperature if AlN is deposited in a neutral residual stress state. Here, to facilitate the design of encapsulated reliable hybrid semiconductor lasers, we extend our finite element, electro-thermo-mechanical model to include a residual stress in the deposited AlN. Using the Christensen criterion to define the maximum allowable stress in the device, our simulations indicate that there is a window of residual compressive stress in the AlN where mechanical failure may be avoided. To assess the feasibility of accessing this region of compressive residual stress while maintaining suitable thermal properties in the deposited AlN, we measure the thermal conductivity of AlN thin films (∼1.6 μm thick) deposited on silicon using a time-domain thermo reflectance (TDTR) setup. Stress measurements demonstrate compressive residual stresses ranging from ∼0 to −0.5 GPa. The TDTR measurement results reveal a similar thermal conductivity of ∼155 Wm−1K−1 over the entire range of compressive residual stress. These results strengthen the promise of encapsulating III-V active waveguides with AlN that simultaneously satisfy both thermal and mechanical requirements.

An alternate to hot film flow sensors

1974 ◽  
Vol 45 (2) ◽  
pp. 300-301 ◽  
Author(s):  
F. Y. Sorrell ◽  
G. V. Sturm
Keyword(s):  
Film Flow ◽  
Flow Sensors ◽  
Hot Film
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