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