low-cost printed electronic nose gas sensors for ... printed electronic nose gas sensors for...
TRANSCRIPT
Low-cost Printed Electronic Nose Gas Sensors for
Distributed Environmental Monitoring
Vivek SubramanianDepartment of Electrical Engineering and Computer
SciencesUniversity of California, Berkeley
RD83089901
Distributed environmental monitoring
• Need for distributed monitoring- Identification of environmental hazards- Triggering of proactive action- Development of accurate environmental models
• Sensor Requirements- Ultra-low-cost- Ease of dispersal- Trainability / adaptability
• Our Approach: Arrayed organic FETs- Easily arrayed at low-cost via printing- Flexible for easy dispersal- Trainable via electronic nose architecture
Commercial E-noses
• ppbRAE Plus — $6215- For homeland security- Detects toxic agents,
mildew• Cyranose — $7995
- Can be trained to detect a wide range of odors: alcohols, chemicals, oil, food
Commercial Gas Sensors• Vernier O2 sensor — $186 • Minimax Pro H2 sensor— $199 • Gas Alert Micro 3 H2S sensor — $612
Arrayed Gas Sensors
Substrate
Molecule inambient
A B C D
GenerateChemical
Signatures
Map Responses
Pixel Array Index
Sens
or P
aram
eter
Responses to differentmolecules
Printing: a pathway to low-cost
No lithographyNo vacuum processing (CVD, PVD, Etch)
Reduced abatement costsCheap substrate handlingReduced packaging costs
Organic Gas SensorsGas sensing with OTFTs is a good match
- Good sensitivity- Synthetic richness- Easy array integration- Low performance
requirements- Short-term applications
available The New York Times, April 4, 2002, illustration by Mary Ann Smith
OTFT Gas Sensing
Gate
DrainSource
Odors
Active Material
Gate Dielectric
Absorbed through grain boundaries and reactive molecular sites
+ +++
Film expands Analyteintroduces traps and scattering
sitesAnalyte changes hopping barrier height
Analyte donates carriers or
activates existing donors
TTT
Low-cost Fabrication
• Inkjet deposition of organic material allows integration of sensor array
• Ultra-low cost requires integration of supporting circuitry
Printed Transistors
Substrate
Gate electrode is printed usinggold nanocrystals
Substrate
Low-temperature anneal forms gate stripeto edge of array (out of page)
Substrate
Polymer dielectric is depositedvia inkjet
Low-temperature anneal forms S/D stripesand connections (in plane of page)
Various active layers are deposited via inkjet
Substrate
Source / Drain contacts areprinted using gold nanocrystals
Substrate
Substrate
Baseline sensor screening process
S D
G
Materials are characterized using a
substrate-gated architecture (easy
fabrication for rapid screening)
A silicon substrate enables easy I/O via an edge connector
The channel is exposed to the analyte, resulting in performance changes
Sensor Characterization
Agilent 4156
To ensure accuracy, measurements are performed with a calibrated
precision semiconductor parameter analyzer.
Switching between individual sensors is performed via a
switch matrix PCB
Experimental Setup
N2
Mass FlowController
AnalyteDelivery
Valve
ValveSensor
Chamber
Bubbler
Exhaust
Exhaust
Agilent 4156
MassFlowMeter
Valve
Sensor RepeatabilityId-Vd (Zoomed)
-3.00E-08
-2.50E-08
-2.00E-08
-1.50E-08
-1.00E-08
-5.00E-09
-2.60E+01 -2.10E+01 -1.60E+01 -1.10E+01 -6.00E+00
Vd (Volts)
Id (A
mps
)
Baseline Toluene Regen
Multiple cycles can be performed with full regeneration
Multi-parameter sensingTransconductance
baseline 60 sccm regen 100 sccm regen0.00E+00
2.00E-09
4.00E-09
6.00E-09
8.00E-09
1.00E-08
gm (S
)Threshold Voltage
baseline 60 sccm regen 100 sccm regen-1.00E+01
-8.00E+00
-6.00E+00
-4.00E+00
-2.00E+00
0.00E+00
V (V
olts
)
Mobility
baseline 60 sccm regen 100 sccm regen0.00E+005.00E-051.00E-041.50E-042.00E-042.50E-043.00E-043.50E-044.00E-044.50E-04
u (c
m2/
Vs)
Drain Current
baseline 60 sccm regen 100 sccm regen-1.60E-07-1.40E-07-1.20E-07-1.00E-07-8.00E-08-6.00E-08-4.00E-08-2.00E-080.00E+00
Id (A
mps
)
Sensor dynamics – transient responseChange in Drain Current Under Toluene Exposure
-5.00E-09
-4.50E-09
-4.00E-09
-3.50E-09
-3.00E-09
-2.50E-09
-2.00E-09
-1.50E-09
-1.00E-09
-5.00E-10
0 30 60 90 120 150
Time (Minutes)
Id (A
mps
)
Sensor response can be very slow, due to slow analyte absorption. Speed can be increased by reducing film thickness
Interaction Mechanisms
Ion Change in P3HT due to Ethanol
0
20
40
60
80
100
120
-1 1 3 5 7 9Time (min)
Perc
ent o
f Bas
elin
e Va
lue
12 nm
75 nm
100nm
Ion Change in P3HT due to Acetic Acid
0
20
40
60
80
100
120
-1 4 9 14 19 24Time (min)
Perc
ent o
f Bas
elin
e va
lue
12 nm 40 nm 75nm
100 nm 12 nm 40 nm
75nm 100 nm
Baseline Baseline
- Sensors show a wide range of interactions, complicating analysis. Interactions include:
• Polar group interactions• Chain / bulk interactions• Swelling
Differential sensitivity – pathway to an electronic nose?
Nose Response to Water (Pentacene)
-2.20E-06
-2.00E-06
-1.80E-06
-1.60E-06
-1.40E-06
-1.20E-06
-1.00E-06
0 10 20 30 40
Time (Minutes)
Id (A
mps
)
Nose Response to Water (P3HT)
-1.50E-07-1.40E-07-1.30E-07-1.20E-07-1.10E-07-1.00E-07-9.00E-08-8.00E-08-7.00E-08
0 10 20 30 40
Time (Minutes)
Id (A
mps
)
Nose Response to Water (P3OT)
-4.50E-08
-4.00E-08
-3.50E-08
-3.00E-08
-2.50E-08
-2.00E-08
-1.50E-08
0 10 20 30 40
Time (Minutes)
Id (A
mps
)
Demonstration of basic electronic nose functionality
Nose Response to Water and Milk
30
40
50
60
70
80
90
100
110
0 10 20 30 40
Time (Minutes)
Perc
enta
ge o
f Bas
elin
e C
urre
nt
Pentacene P3OT P3HT
WaterMilk
Organic Transistor Stability
0
0.002
0.004
0.006
0.008
0.01
7/14 7/15 7/16 7/17Time (Date)
Mob
ility
(cm
2 /Vs)
-4.E-07
-3.E-07
-2.E-07
-1.E-07
0.E+00
Driv
e C
urre
nt (A
)mu (sat)mu (lin)Ion (sat)
Implication: We must either improve dielectric interface or use VT-insensitive differential sensing method
Sensing Circuits• Amplify sensor response• Desensitize against operational drift• Integration of encapsulated and
unencapsulated OTFTs• Integration of sensing OTFTs with
supporting OTFT or silicon CMOS circuitry
Sensing Circuits
Crone et al, J. Appl. Phys, vol 91, pp. 1014-10146, 2002
Conclusions & Future Work• Organic FET-based sensors show promising
responses, including transient behavior and cycle life
• Work remains to optimize structure and process flow, particularly in terms of stability and reliability
• Future Work:- Integration of latest sensing materials into printed device
architecture- Deployment in testing of environmentally-relevant analytes- Enhancement of specificity through functionalization / doping