Electronic Nose Development

for

Various Applications

by

Dr. Ravishankar Dudhe

Ph.D (IIT Bombay)

What is an Electronic Nose?

An Electronic Nose is a system that uses the

pattern of responses from an array of gas

sensors to examine and identify a gaseous

sample.

Motivation

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Limitations with Dogs To achieve optimal performance, each dog requires an assigned handler, which increases costs because the canine detector is really a dog–handler team. Dogs also show behavioral variations and changing moods, which are difficult to monitor in a quantifiable way. When performing a search task, dogs become tired after 30–120 min, which suggests the need for two or more dogs at each location

Emerging Interdisciplinary Challenges

Olfactory Physiology

Organic

Chemistry Signal Processing

Pattern Recognition Computational Learning

Electronic

Nose

Chemical Sensors /

Analytical Chemistry

.

.

.

.

.

Motivation for Enose

Electronic Nose Systems

Poly Coated Sensor

Sensor Processor

Signal Processor

Pattern Recognition Knowledge

Base

Odorant Molecules

Identification

Raw electrical signal

Processed Electrical signal

Denoised Electrical signal

Training &

Testing

Chemical Information

Feature Extractor

Relevant features

Various Electronic Noses

Amplifying chromophore quenching

Fiber optics and beads

Polymeric thin films

Gold nanoclusters

SAW

MEMS

Polymer amplification mechanism.

(a) Traditional chemosensor. (b) Receptors wired in series. Green is the

emissive polymer, blue the quenched, and red is the analyte; h is the light

at the excitation wavelength, h´ at the emission wavelength [20].

The light emitted by the LED passes through a lens and a filter, allowing only a narrow-wavelength band of light centered at 430 nm to impinge on the polymer film, which is coated on two thin glass sheets.

A pump pulls in air samples across the coated glass sheets. If the air sample contains explosive vapors, the photomultiplier detector will sense a decrease in light intensity and trigger an alarm.

Figure: Schematic of sensor design.

OC14H29

C14H29O

n

Pentiptycene Polymer

ADB

ADB

+ MNT

ADB

+ TNT

MEMS

microelectromechanical

systems It is the integration of mechanical elements, sensors,

actuators, and electronics on a common silicon

substrate by microfabrication.

It is based on microfabricated nanomechanical

cantilever sensors.

The cantilevers are silicon beams, a few hundred

micrometers long and 1 µm thick.

Each cantilever sensor in an array is coated with a

different sensor layer.

MEMS Contd…

When the sensor is exposed to an analyte, the analyte molecules adsorb on the cantilever’s surface, which leads to interfacial stress between the sensor and adsorbing layer that bends the cantilever.

Each cantilever bends in a characteristic way typical for each analyte.

From the magnitude of the cantilever’s bending response function of time, a fingerprint pattern for each analyte can be obtained.

It showed detection sensitivities in the parts-per-billion range

During the sampling, the molecules of explosive vapor adsorb on the cantilever surface, which is heated to a high temperature by a piezoresistive track implanted in the cantilever. As the cantilever is heated, the adsorbed explosive molecules undergo combustion, producing a large and sudden deflection of the cantilever.

Resonance curves of the cantilever before and after

loading with TNT. With TNT loading, the resonance

frequency shifted to a lower value due to the increased

mass. After deflagration, the resonance frequency

returned to the original value [7].

Organic Field Effect

Transistor Fabrication

18

Fabrication of OFETs

RCA

• RCA1(organic impurity removal) • DI H2O + NH4OH @ 348k for 5min

• Add H2O2 & wait for bubbles

• Place wafer in sol. & heat for 6-8 min

• RCA2 (ionic impurity removal) • DI H2O + HCl

• Add H2O2 & wait for bubbles

• Place wafer in sol. & heat for 3-6 min

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Oxidation

• Temperature of chamber set to 1323k (1050C)

• Oxygen passed in inner tube for 1hr 20min

• SiO2 layer of 100nm thickness grown

n+ Si

SiO2

Oxidized Si wafer

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Lithography

• Dehydration at 393k for 10 min

• Rinse with N2(g)

• Spin PPR at 1500 rpm for 30 sec (2µm)

• Bake at 343k for 15 min

• UV exposure for 90 sec

• Place in 0.01% NaOH sol. To remove developed

PPR

• Dry with N2(g)

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PPR UV Light

MASK

n+ Si

SiO2

n+ Si

n+ Si

PPR

PPR

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Fig 4. Structure of shadow mask

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RF Sputtering

• 60sec Ti deposition (5nm)

• 90sec Au deposition (80nm)

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n+ Si

Ti/Au

SiO2

PPR

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Liftoff

Sonicate wafer in acetone in order

to remove unwanted Au and PPR

Removal of Back Si02 Clean back side of wafer with buffered HF

Ti/Au SiO2

n+ Si

Ti/Au SiO2

n+ Si

n+ Si

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Spinning of polymer

N+ Si

N+ Si

P type polymer Au/Ti

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Length : 30µm to 70 µm

Width : 17,050µm to

24,850µm

OFET device OFET device after

spinning

For Sensor Application

Basic Key requirements for any Sensor

Selectivity

(To avoid false positive)

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• Sensitivity

(To avoid false negative)

Array based approach to improve selectivity

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Sensitivity to a wider range of analytes.

Better selectivity.

Multi component analysis and

Analyte recognition—rather than mere detection.

Sensor arrays are more analogous to olfaction systems containing multiple receptors.

The main advantage of array sensors resides in the fact that there is no need to design chemical specificity.

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System for OFET Array Characterization

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OFET Characterization for P3HT/SXFA

composite TNT Vapor

RDX Vapor

DNB Vapor

TNT

Vapor

RDX

Vapor

DNB

Vapor

Water

Vapor

OFET Characterization for P3HT/SXFA

composite

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TNT

Vapor

RDX

Vapor

DNB

Vapor

Water

Vapor

%ION , %IOFF , %gm and % ratio all

parameters

For Application works

To use analyses of

freshness of

product

e.g. Beverage,

food

product

-Environment

monitoring :

e.g Aqueous sensor

Network

-Movable robot,

Bomb detector,

rescue robot

,etc…

Mobile Robot Noses

QUESTIONS??????