MEMS-sensor with capabilities of measuring vacuum and flow_Cortes

1. MEMS-BASED
MEMS BASED FLUID FLOW
SENSOR
by Jean P. Cortes
P

2. Outline
Senior Design
S i D i #1
Objective
Applications
Design
Flow
Pressure/Vacuum
Senior Design #2
Fabrication
approaches
Testing
Pressure/Vacuum sensor
Micro gears.
gears
Summary

3. Senior design #1
Design and evaluate a MEMS sensor with
capabilities in measuring parameters, such as:
• Pressure/vacuum
• Fluid Flow rates
• Velocity/direction
based on thermal convection.

4. Applications
Aerospace,
Aerospace velocity measurements
Medical, respirators for pre-matured born, &
diagnostics of asthmatic attacks
Automotive industry,
Education,
Education related experiments
Semiconductor industry,
Control of home environment
environment,

5. Current technology: Bulky instruments
Flow meter that uses a mechanical principle. Bourdon Gage that uses a mechanical principle.

6. Hotwire principle: Low-power Micro-scale capability
B)
A)
Flow
HEATER
Rw= Rref [1 + TCR (Tw-Tref)]
A) Hotwire: flow rate depends on the loss of heat at the heater
B) H t i anemometry: fl
Hotwire t flow rates and di
t d direction can b measured.
ti be d
For flow measurement one or three elements can be used.

7. Example of MAF in a car
Rw= Rref [1 + TCR (Tw-Tref)]
Schematic representation of the Hotwire anemometry.

8. Pressure measurement
R= impingement Rate
P
Vacuum Chamber
Heater
Pumping
Gas Molecules
Schematic representation of the application to measure pressure.
For pressure measurement one element is needed.

9. Design - flow (1)
250 μm
3.5 mm
the three resistor for flow measurement.

10. Design – pressure (1)
Small heater
8mm
1.5 mm
Large heater
1.5 mm
Fast response
Miniture
Economical
Low power consumption
less thermal mass
More accurate 2 mm

11. Fabrication of Al-based sensor
Wafer
Wf Cleaning the processed samples
Piranha cleaning
Pi hl i
and Oxidation
Al-
deposition
Spin Coater used for PR
PR, UV-light,
developing
PR strip
Al-
Al etching

12. Fabrication of Ni/Cr based sensor
Glass
Ni/Cr
deposition
PR, UV-light,
UV light,
developing
Nichrome PR strip
etching

13. Fabrication summary
Hot Wire Principle
Flow Pressure
Magnitude Direction Vacuum
Nichrome Al Nichrome
RAl_large = 15 Ω RNiCr = 53 kΩ
RNiCr small heater = 7.8 kΩ large
NiCr_small_heater
RAl_small = 18 Ω
RNiCr_small_detectors = 80 Ω RNiCr_small = 7 kΩ
RAl_large_2 = 55 Ω
RNiCr_large_heater = 3 kΩ
RNiCr large detectors = 50 Ω
NiCr_large_detectors
t = 500 Å of thickness on glass
TCR = 120 ppm/oC
This t affects TCR!

14. Testing
Vacuum Chamber and probes.
“Special” probe station with sensor on it
Dr. Hashmi on the probe station Vacuum Chamber and probes.

15. Results
Resistance vs. Pressure
Resistance vs Pressure
0.135
80.0
0.134
75.0
70.0 0.133
Resistan (Ohm)
Resistance… Resistance…
Resistance (Ohm)
65.0 0.132
nce
60.0 0.131
(
55.0 0.130
50.0 0.129
45.0 0.128
R
40.0 0.127
20 70 120 170 220 0 0.02 0.04 0.06 0.08 0.1
Pressure (mTorr) Pressure (mTorr)
Al-small sensor:
P goes down R goes up

16. Cost
Total Cost for making HOT MEMS
HOT-MEMS
Total Tooling Total Labor Manufacturing
Operation Cost
cost Cost/Wafer
cost
Cleaning $21.00 $2.50 $23.50 $0.94
Oxidation $23.00 $2.50 $25.50 $0.51
Metal Deposition $260.00 $2.50 $262.50 $17.50
Mask creation $35.00 $50.00 $85.00 $3.74
Photolithography $25.80 $5.00 $30.80 $30.80
Metal Etch $4.20 $2.50 $6.70 $6.70
Dicing $10.50 $5.00 $15.60 $15.50
Total $369.50 $70.00 $439.60 *$75.69
1800 devices…….so the final price is ~ $ 0.045
• 6‘’ wafer

17. Conclusion
A hot wire based flow and pressure sensor was designed
hot-wire
and fabricated
A single element hotwire was used for pressure
measurement
A three component: hotwire + 2 sensors was used for
flow measurement
Two style of sensors were fabricated: Large and small
Two materials system were used: Al and NiCr
Testing showed considerable change in resistance with
change in pressure

18. Acknowledgements
D Mh
Dr. Mohamed-Ali H
d Ali Hasan ( d i )
(advisor)
Dr. Asghar Hashmi
Mr. John Hudak
Tanya Dias
y
Dr. Terry Xu

19. THAT’S ALL FOLKS!