Microfluidic devices for gas flow control

1
Flow and Gas Microsensors

• M.S. Roberto Jacobe Rodrigues (Ph.D. student)

• B.S. Douglas Melman (M.S. student)

• Dr. Rogerio Furlan

2
Microsensor structure
Sensor

• Gas and liquid applications

Heater

• Suitable for small flow values

Sensor

• Low power consumption

• Fast response

• Possibility of integration in microchannels

3
Analytical model
Based on T. S. J. Lammerink et al.,
Micro-Liquid Flow Sensor, Sensors and Actuators
A37-A38, 45-50, 1993
steady
incompressible
external
laminar
u
4
Analytical modeling results for air flow

• Compromise microsensor size x sensitivity x
  maximum flow range

5
2D Simulation with Ansis/Flotran
0 to 500 sccm
(tube with D 3 mm)

• Top polysilicon ( 0.6 µm)
• Bottom nitride ( 0.2 µm)
• 10 µm wide
• 200 µm long
• 0.7 µm above substrate

300 µm
3 mm
6
Simulation results for air flow

• Good agreement for

low flow velocities

• Heat dissipation by

radial convection
increases with flow
velocity
7
Simulation results for gas detection
Filaments distance 80 µm
?-DCT 300?m X 300?m
3 mm
40 mm

• Difference in thermal diffusivity D k/?.c
  (m2/s)

allows identification of gas contamination
8
Fabrication
9
Free-standing filaments

• Red light emission ? T 1000 C

10
Tests
11
Experimental results
Filaments distance 120 µm

• Qualitative validation of simulations

12
Conclusions

• Feasible microstructure for flow and gas
  microsensors

• Good qualitative agreement between analytical and
  numerical models and experimental results

• Possibility of integration in microchannels of
  fluidic devices

• Possibility of immediate application for
  identification of flow presence