Fabrication and Characterization of PDMS
Membranes for MEMS-based Micro Heat Engine
M. A. Brubaker, B. S. Preetham, R. F. Richards, M. J. Anderson, H. Bardaweel, C. D. Richards
Mechanical and Materials Engineering, Washington State University REU
FABRICATION
• Applicable for any situation where low grade waste heat exists.
•Small Military devices
Started with a silicon nitride wafer;
Photolithography and development of photo resist
(AZ5214)
•Portable Electronic Device
Expander
membrane
Semiconductor
tape
Wicks
Evaporator
membrane
Thermal
switch
•To decrease the resonant frequency of the engine compared to
a previous engine using Silicon Nitride, which had a resonant
frequency of 110 Hz 3.
•To fabricate PDMS membranes
•To investigate the material properties of the PDMS membranes.
Sputter Gold; photolithography and development
of photo resist
60
50
40
30
•As heat enters and leaves the
engine the working fluid evaporates
and condenses.
•Mechanical energy is created by the
oscillation of the expander
membrane.
•This creates mechanical energy that
can be converted into electrical
energy through the use of
piezoelectric material which can be
deposited on top of the expander
membrane. 1
•The engine’s performance is heavily
influenced by its resonant frequency,
the smaller the resonant frequency
the greater the performance.3
12
10
8
6
20
4
10
2
0
0
Gold Etch; remove photo resist
100
200
300
400
500
600
700
0
50
100
150
200
250
9
Deflection of Membrane
Reactive Ion Etch top layer of Silicon Nitride
Membranes were then diced and
assembled into the engine.
5
Voltage In
6
4
5
3
4
3
2
2
1
1
0
0
The membranes are 10mm by 10mm and
approximately 1 micrometer thick.
-1
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Time (s)
•The data shows the deflection of the PDMS membrane after
heat was added to the Engine. The resonant frequency was
estimated to be 58.3 Hz.
CONCLUSION
Function
generator
•The PDMS membranes were successfully fabricated and
characterized . A Pressure-Deflection curve was found and the
membranes showed to be very flexible. A modulus of elasticity of
6.89 N/m was measured for PDMS membranes.
Oscilloscope
PC
Laser head
Power supply
8
7
Voltage Out
0
Pulse circuit
300
Deflection (micrometers)
6
Vibrometer
DESIGN
14
•From the linear portion of the graph, the modulus of elasticity (k)
was estimated to be 6.89 N/m.
EXPERIMENTAL SET UP
Compression
70
y = 0.0689x
•The pressure-deflection curve reveals the flexibility of PDMS.
•To Investigate the effect of a PDMS expander membrane on the
engine
Heat rejection
16
Linear Portion
Deflection (micrometers)
Recipe based off of 2
Expansion
80
0
Chemical etching of Silicon using KOH
OBJECTIVES
Heat addition
18
Reactive Ion Etching of Silicon Nitride; remove
photo resist
Added mass
Polymer
90
Deflection (micrometers)
Working fluid
(3M PF-5060 L)
20
Voltage (V)
• Converts heat into mechanical energy then electrical power
The PDMS expander membrane was created using MEMS-based
fabrication techniques.
100
Pressure (pascals)
Micro Heat Engine
RESULTS
Pressure (pascals)
INTRODUCTION
•The membranes were incorporated into the micro heat engine
and an estimated resonant frequency of 58.3 Hz was measured.
This is a decrease by a factor of 2 from the previous
measurments3.
REFERENCES
Engine
(1) Whalen S, Thompson M, Bahr D, Richards C, Richards R 2003 Design,
fabrication, and testing of P3 micro heat engine Sensors Actuators A
104 290-8
•The thermal switch was not used to control heat addition to the
engine. However, a resistance heater enabled precise control of
the magnitude and duration of the heat addition process.
(2) Sang S, Witte H 2010 Fabrication of a surface stress-base PDMS micromembrane biosensor Microsystem Technologies 16 1001-8
•10 mJ of heat per cycle of energy was added into the engine at
10 Hz with a duty cycle of 1%.
(3) Bardaweel H, Anderson A, Richards R, Richards C 2008 Optimization of the
dynamic and thermal performance of a resonant micro heat engine
J. Micromech. Microeng. 18 104014
This work was supported by the National Science Foundation’s REU program under grant number EEC-0754370