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

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