CNT-BASED THERMAL CONVECTIVE ACCELEROMETER
Presented by Yu ZHANG. Supervised by Prof. Wen J. LI
OUTLINE
Introduction
Literature Review
Sensor Design
Test Setup
Test Results
Conclusion
2
INTRODUCTION
Literature Review
Sensor Design
Test Setup
3
INTRODUCTION
Background
The
method to align post grown Carbon-Nanotubes between
microelectrodes using dielectrophoretic (DEP) forces was developed in
CMNS. 2003
Experiments
showed CNT bundles can detect environmental temperature
change. 2004
When
heated within liquid, CNTs can generate thermal vapor bubble
around itself . 2007
4
INTRODUCTION
Idea
Acceleration/tilting will lead to deformation of the vapor bubble.
Temperature distribution around the bubble will change
If
other CNT bundles can be fabricated around the bubble, they can sense
the temperature change caused by acceleration.
5
INTRODUCTION
Aim of Research
Choose
applicable
principle, design
the structure
Review the
working principle
of thermal
motion sensor
Fabricate sensor
chips, build
prototypes
Purchase and set
up test
equipments
CNT-based
thermal
accelerometer
Test and
characterize
sensors’
response
6
Introduction
LITERATURE REVIEW
Sensor Design
Test Setup
Test Results
7
Motion Sensors
Thermal Motion Sensors
Carbon-Nanotube
Manipulation
Carbon-Nanotube
Sensors
LITERATURE REVIEW
Literature Review: Contents
8
Convert motion into electric
signal
LITERATURE REVIEW
Review of Motion Sensors
•Linear motion: accelerometer/inclinometer
•Angular motion: gyroscope
Application in industry, consumer electronics, input devices, instruments
•Inclination: automobile stability, platform stabilization
•Orientation: gesture recognition, inertial navigation, active control
•Vibration: active suspension system, machine noise detection
•Shock: air bag system, release systems, structure monitoring
9
Sensors
Piezoresistive
acceleration
Reference frame
y
deflection
piezoresistor
Damper
Spring
Proof mass
x
base (reference frame)
LITERATURE REVIEW
Conventional Motion
Piezoelectric
acceleration
Acceleration
deflection
piezoelectric
layer
Moving/bending
of solid structure
base (reference frame)
Capacitive
acceleration
Change of
detector output
Convert to
electric signal
C  r
A
d
d
deflection
base (reference frame)
10
Cons
Easy to design and model
Rely
Standard IC process *
Good cost/performance ration
Fast response
Acceleration
on solid moving parts: proof
mass
Better
sensitivity requires bigger
proof mass
LITERATURE REVIEW
Pros
Fragile,
cannot measure large
acceleration (<20g)
Low shock survival rate
Move/bending
of solid structure
Change of
detector output
replacement
for this step?
Convert to
electric signal
* for surface micromachined sensors only
11
sensor
Details
Acceleration
Acceleration
will lead to forced
convection of liquid within sealed
chamber
Use
Convection of
liquid
flow sensors to detect the
flow speed caused by convection
LITERATURE REVIEW
Thermal convective motion
Change of
detector output
Convert to
electric signal
Figure from [6]
12
Anemometer
Power
Based on thermal phenomenon:
•Add local heat to fluid, measure
the resulting temperature
•Very small Reynolds Number
•Laminar flow heat transfer
•Three sensing methods
Flow
Q
heater/detector
Temp.
LITERATURE REVIEW
Micro Flow Sensors
Calorimetric flow sensor
Power
Flow
Q
detector1 heater detector2
ΔTemp.
Time-of-flight flow sensor
Power
Flow
Q
heater
detector
ΔTime
13
First reported in 1997
Research
LITERATURE REVIEW
Research on Thermal Convective Accelerometer
groups in Canada, US, France, Germany,
China.
Acceleration
Commercial products by MEMSIC. Inc.
Based
Convection of liquid
on integrated thermal flow sensor, to sense
convection caused by acceleration.
Up to two sensing axis
Thermal detector
Convert to electric signal
14
LITERATURE REVIEW
Working Principle
Temperature
a=0
a≠0
ΔT≠0
ΔT=0
detector1
One-axis Structure
sealed
chamber
heater
detector2
Two-axis Structure
Heater
detector 1
detector 2
Substrate
Figure from….
15
What are they?
Allotropes of carbon with a cylindrical nanostructure
Single-walled and Multi-walled
Synthesis
method: arc discharge, laser ablation, chemical
vapor deposition
LITERATURE REVIEW
Carbon-Nanotubes
CNT Integration
How to integrate?
Selectively grow on desired position
In situ CVD
Manipulate post-grew CNTs
Use AFM tips to move
Fluid friction
Dielectrophoretic (DEP) force
16
Mechanical sensors, chemical sensors, thermal sensors, pressure
sensors
LITERATURE REVIEW
Review of CNT Sensors
Sensing method:
•Raman spectrum shift
•Performance change as circuit elements
•Resonators
•Transistors
•Resistance change
•Deformation
•Temperature
•Chemical reaction
Possible for micro sensors
Reported by CMNS and other research groups
17
Literature Review: Conclusion
Build the sensor upon thermal convection sensing principle
Follow and improve the DEP manipulation method
Deposited CNT bundles work as Temperature Detectors
18
Introduction
Literature Review
SENSOR DESIGN
Test Setup
Test Results
Conclusion
19
Sensor Design: Contents
Important Questions
Mask Design
Fabrication
Sensor Prototyping
20
SENSOR DESIGN
Important Design Questions
Power
Project requirement consideration
Flow
•The structure should be DEP compatible
•Sensing structure:
•Anemometer
•Calorimetric structure
•Time-of-flight structure
Q
heater/detector
Temp.
Power
selected structure
Flow
Q
detector1 heater detector2
•No conditioning and feedback circuit
ΔTemp.
Power
MEMS structure consideration
•Thermal insulation
Flow
Q
heater
detector
ΔTime
21
SENSOR DESIGN
Thermal Insulation
Where to insulate (minimize heat flux)
•Between heater and detectors
•Between the sensing block and the substrate
Better thermal insulation leads to
•Higher heater temperature
•Better sensitivity
22
SENSOR DESIGN
Benefits of Thermal Insulation
flow
Q
substrate
flow
brings away
heat
heat from substrate
Better thermal
insulation
Minimize heat
capacitance of
the substrate
Tdetector
Rdetector
Tsubstrate > Tdetector
Reduce heat
flux from
substrate
Improve
sensitivity
23
SENSOR DESIGN
Bridge Structure
Etched Cavity
sensor
sensor
heater
Top view
sensing block
sensor
heater
sensor
Side view
substrate
substrate
Insulation Layer
Membrane
sensing
block
sensing
block
thermal insulation layer
substrate
substrate
Side view
membrane
24
Use glass as substrate
Good thermal insulation result
Fabrication process available
Simple structure
Need Cr layer to improve adhesion
Cannot integrate with IC
sensing
block
metal
adhesion layer
Glass substrate
Material
Silicon
Porous Silicon
Glass
Air
κ (W•m-1•K-1)
125
1.1*
1.2
0.025
* From Reference [12]
SENSOR DESIGN
Thermal Insulation Design
25
One pair of electrodes -> anemometer structure
•One CNT bundle as heater/detector
Three pairs of electrodes -> calorimetric
One 1-axis
calorimetric
structure
structure (1-axis)
SENSOR DESIGN
Sensor Chip Mask Design
•One CNT bundle as heater, two as detectors
Five pairs of electrodes -> calorimetric
structure (2-axis)
•One CNT bundle as heater, four as detectors
Three
anemometer
structure
Mask Layout
Sensing Block
26
Au
Cr
Substrate
STEP 1
SENSOR DESIGN
Sensor Chip Fabrication
Substrate
STEP 2
CNT bundle
Substrate
STEP 3
Protection layer
STEP
STEP 44
Substrate
27
SENSOR DESIGN
CNT Manipulation
Improved DEP Circuits
Multi-walled CNTs are used
Signal
Generator
Disperse MWNT into ethanol
Resistors
Separate bundles using ultrasonic
Gaps
detector 1
Drop 2μL above the electrodes
heater
Apply
8V peak-peak, 1MHz AC,
from signal generator
detector 2
Captured Microscope
detector 1
Image
100μm
CNTs
heater
a
detector 2
28
Sensor
chip
PDMS-Glass
Bonding
Mask for sensor
chip
PDMS
chamber
Stick to
PCB board
SENSOR DESIGN
Sensor Building Processes
Mask for PDMS
Wire boding to
PCB board
29
SENSOR DESIGN
Prototypes
Air
Ethanol
Air
Ethanol
30
Introduction
Literature Review
Sensor Design
TEST SETUP
Test Results
Conclusion
31
TEST SETUP
Source and Measure
Test Circuit
Use
Source & Measure Units
(SMUs) to power up and measure.
Keithley 2400 Sourcemeter: 1 SMU
Keithley 2600 Sourcemeter: 2 SMUs
linked together to
computer via GPIB
HI
Im
I
Vm
CNT
Sourcemeters
synchronized by
collected time stamps
SMU
LO
Sourcemeter data
Source meters
Constant current configuration
32
TEST SETUP
Vibration Exciter
a
Tilting Plate
spring
LO
HI
N
S
coil
spring
Test Setup
Test Setup
PC with
LabTracer®
GPIB-USB
Adaptor
GPIB
USB
Sensor
signal
generator
power
amplifier
Computer
Single-channel
Sourcemeter
Vibration
Exciter
Tilting-rotary
plate
laser
vibrometer
sensor
SMU
Dual-channel
Sourcemeter
33
Introduction
Literature Review
Sensor Design
Test Setup
TEST RESULTS
Conclusion
34
Thermal Sensing Test
TEST RESULTS
Test Results: Contents
Tilting Test
Vibration Test
35
0
Sensor1: T CR=-0.12%
Resistance Change ( R/R)
-0.01
Sensor2: T CR=-0.11%
TEST RESULTS
Thermal Sensitivity
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
20
30
40
50
60
70
Temperature ( C)
R  R0 1   R TR  T0 
Tested in Climatic
Chamber. Fixed humidity.
Higher temperature -> Smaller resistance:
Negative TCR
36
TEST RESULTS
Self-heating Test
-3
3.5
Measure voltage
Ohm's Law prediction
15
x 10
3
failure point
Power (W)
Voltage (V)
2.5
10
2
1.5
safe bundary
1
5
0.5
0
0
0.5
1
1.5
Current (A)
2
2.5
3
-4
x 10
0
-8
10
-6
10
Current (A)
-4
10
37
TEST RESULTS
Temperature Change Caused by Heater
-3
2
x 10
Sensor 1
Sensor 2
Resistance Change (R/R)
0
Linear fit 1
Linear fit 2
-2
-4
-6
-8
-10
0
1
2
Heater Current (A)
3
-4
x 10
38
Proving Test
TEST RESULTS
Test Results: Contents
Tilting Test
Vibration Test
39
TEST RESULTS
Tilting Test
Tested on tilting plate
•Anemometer structure with air sealed: No response
•Anemometer structure with liquid sealed: No response
•Calorimetric structure with air sealed: No response
•Calorimetric structure with liquid sealed:
40
TEST RESULTS
Tilting Test
0.3
Detector1
Configuration
•Convection medium: ethanol
•Input power
•heater: 6μW
•detectors: 1nW each
Result
Change of Resistance (R/R)
0.2
•Two sensors give opposite
responses.
•Very good sensitivity.
•Very small power
consumption
•Liquid convection
medium
Conventional
thermal accelerometers:
Detector2
0.1
0
-0.1
-0.2
0
10
20
30
40
50
60
Tilting Degree (°)
70
80
90
0.2mW to 480mW*
*Table 2.2, Page 24, Thesis
41
Proving Test
TEST RESULTS
Test Results: Contents
Tilting Test
Vibration Test
42
TEST RESULTS
Vibration Exciter Calibration
Use laser vibrometer to measure velocity, then calculate acceleration
Fixed input power, varying input frequency.
Frequency limited by Sourcemeter sampling frequency
data
fit
Measured acceleration (m/s2)
1
0.1
0.01
y(x) = a x^n + c
a = 0.012068
c = -0.001069
n = 1.9357
1
2
3
4
Input frequency (Hz)
5
6
7
8 9 10
43
TEST RESULTS
Vibration Test Result
Test progress
•Anemometer structure with sealed air: yes
•Anemometer structure with sealed liquid: no
•Calorimetric structure: no
44
TEST RESULTS
Sensor Response to Vibration
Test mode: bias current 10nA
Power consumption:
P1  I 2 R1  10nA 106k  10.6 pW
2
P2  I 2 R2  10nA  39k  3.9 pW
2
45
1
0.9
Response (Percentage Amplitute)
0.8
Frequency fixed to 2Hz
Sourcemeter current lower range
0.7
0.6
Input current: 10pA to 0.1mA
0.5
Response defined by
0.4
0.3
Current used in test (10nA)
Rmax  Rmin
R
0.2
0.1
0
-11
10
TEST RESULTS
Sensor Response Under Different Heating Current
-10
10
-9
10
-8
-7
10
10
Input Current (A)
-6
10
-5
10
-4
10
1.8
In tests, driven current was set to
10nA
1.6
Response (Percentage Amplitute)
1.4
Sourcemeter current lower range
1.2
1
0.8
0.6
Current used in test (10nA)
0.4
0.2
0
-11
10
-10
10
-9
10
-8
-7
10
10
Input Current (A)
-6
10
-5
10
-4
10
46
TEST RESULTS
Acceleration Responsivity
13000
12000
Sensor R ( )
11000
10000
9000
8000
More
sensitive
acceleration
7000
to
small
6000
0
0.2
0.4
0.6
0.8
1
1.2
Acceleration peak (m/s 2)
Linear – log relationship
Saturation limit
7000
> 1.2m/s2
Sensor R ( )
6000
5000
4000
3000
2000
0
0.2
0.4
0.6
0.8
Acceleration peak (m/s 2)
1
1.2
47
4
x 10
2.85
1.5
1.25
1
2.74
velocity
0.5
2.63
0.25
0
-0.25
2.52
-0.5
Acceleration (mm/s2)
Sensor Resistace ( )
0.75
a=dv/dt
R=vi
Dual channel
Sourcemeter
voltage
output
-0.75
2.41
-1
-1.25
2.3
2
3
4
5
6
7
8
Time (second)
9
10
11
Laser
Vibrometer
TEST RESULTS
Phase Delay Test
Sensor
-1.5
12
4
x 10
1.5
1.25
11
0.75
10.5
0.5
10
0.25
0
9.5
-0.25
-0.5
9
Acceleration (mm/s2)
Sensor Resistance ( )
1
180°
phase delay
Response time not detectable
-0.75
-1
8.5
-1.25
8
2
3
4
5
6
7
8
Time (second)
9
10
11
-1.5
12
48
Introduction
Literature Review
Sensor Design
Test Setup
Test Results
CONCLUSION
49
CONCLUSION
Conclusion – Work Done
Working
principle, structures and performances of currently developed
thermal convective accelerometers were reviewed.
CNT-based
thermal convective accelerometers were designed and
prototyped.
Testing facilities
were purchased and set up.
Prototypes were tested under inclination and vibration.
50
Calorimetric
CONCLUSION
Conclusion - Results
structure with sealed ethanol can sense static inclination
Anemometer structure with sealed air can sense vibration
Contributions
•First CNT based motion sensor
•First CNT based thermal convective motion sensor
•Smallest power consumption *
•No solid proof mass, easy to fabricate
•More understanding about heating and sensing effect of CNTs
* Considering the sensing block only
51
52
SUPPORTING MATERIALS
53
SUPPLEMENTS
Improving Frequency Test Range
0.001Hz
sourcemeter
sampling limit
vibration exciter
working range
0.1Hz
10Hz
1Hz
crank-link mechanism
100Hz
1000Hz
vibration exciter
New circuit
sampling limit
0.001Hz
0.1Hz
1Hz
10Hz
100Hz
1000Hz
54
SUPPLEMENTS
Crank-link Mechanism
motor
controller
power
amplifier
Computer
sensor
SMU
55
SUPPLEMENTS
Sensor Read-out Circuit
+
-
I
Vm
CNT
Im
CNT
R3
+
Rg
+
SMU
R2
R1
R1
R2
Instrumentation amplifier
Rf
C
ADC
R3
Filter
56
SUPPLEMENTS
Future work – Sensor Charactorizaiton
Step response
Bandwidth (frequency response)
Saturation (requires higher acceleration peak)
57
Future Work – Sensor Design
Size of sealed chamber
Noise level
Optimized input current (sensitivity
Properties
and noise)
of convection medium (liquid, air, pressure)
Compensation of environmental temperature change
Feedback control
58