1. A Chemocapacitive sensor array for the detection of complex odors
D. Goustouridis1,2, P. Oikonomou2, A. Botsialas1,2, K. Manoli2, M. Kitsara2, I. Raptis2
1. Department of Electronics
TEI Piraeus
2. Inst. Of Microelectronics
NCSR “Demokritos”

2. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Overview
Polymer based gas sensors
Principles of operation
Capacitive Polymer Based sensors
Methodology for the selection of the Polymers
Fabrication of the sensor array
Capacitance measurement set-up
Capacitance measurements
Read-out electronics
Applied Algorithms
Applications
Conclusions – Future Plans
2nd SENS-ERA Workshop, 5-6 Dec. 2012

3. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Chemical sensors
Piezoelectic (surface acoustic waves SAW, bulk acoustic waves BAW, cantilever resonator)
Optical (fluorescence, reflective, absorption)
Thermal (pellistor)
Electrical, Electrochemical ( chemoresistive, MOX, chemocapacitive)
2nd SENS-ERA Workshop, 5-6 Dec. 2012

4. InterDigitateElectrode (IDE) Capacitive Sensor
Top view
Side view + -
Electrode
Sensitive Layer
Substrate λ h W G
Simple and low cost fabrication
Suitable for parallel production
Low power consumption
Promising devices for sensing VOCs or humidity
Could be integrated with read-out electronics
2nd SENS-ERA Workshop, 5-6 Dec. 2012

5. IDE Chemocapacitor sensing principle
Change in permittivity of polymer (ΔCε ):
i) ΔCε >0, εA(analyte)>εpol(polymer)
ii) ΔCε <0, εA(analyte)<εpol(polymer)
Capacitance change (ΔC)
Sorption of
analyte
ΔC= f( ΔCε + ΔCh)
Swelling of polymer (ΔCh):
ΔCh>0
ΔCh~0 if i) h>0.5 λ, ii) εΑ>> εpol for any h
Sorbed molecules + -
Vapor phase
Electrode
Polymer
sensitive layer
Substrate λ h
2nd SENS-ERA Workshop, 5-6 Dec. 2012

6. IDE Chemocapacitor sensing principle
Useful Capacitance
Electric Field
ΔCh: Capacitance change due to swelling
ΔCε: Capacitance change due to permittivity change
Parasitic Capacitance
Requirements:
Substrate with low dielectric constant (Polymer or Quartz)
Small electrode distance (ideally <1μm)
2nd SENS-ERA Workshop, 5-6 Dec. 2012

7. IDE Chemocapacitor operating principle
Α) Response of chamocapacitor in neutral enviroment,
Β) Just before the first sorption
Γ) After the sorption, transiet response
Δ) Steady response in equilibrium
2nd SENS-ERA Workshop, 5-6 Dec. 2012

8. Development of an e-nose
Choosing of the polymers for gas sorption
Choosing of group of polymer (according to specific application) (Compatibility with the measuring gases, chemical affinity, technological issues, …)
Control of sorption – desorption, repeatability, selectivity
Transducer & Sensor Development
Deposition techniques
Implementation of Interdigitated Electrodes & characterization.
Read-Out electronics
Development of read-out electronics and data transmittion modules
Development of Data processing algorithms
Application of raw data processing algorithms for the identification of the gas composition.
2nd SENS-ERA Workshop, 5-6 Dec. 2012

9. Optical Characterization of the polymer swelling
Measurement
chamber
Symbolemtry principle of operation
White Light Reflectance Spectroscopy (WLRS)
The energy E at wavelength λ is (for the case of single layer film):
n : Refractive index, L: thickness, λ: wavelength.με 0: πολυμερές 1:.
0 indicates the polymer layer & 1 the SiO2 layer
Fitting (L0) of theoretical spectrum to the measurement one.
2nd SENS-ERA Workshop, 5-6 Dec. 2012

10. Optical Characterization of the polymer swelling
SiO2 Si
Nitrogen purging
Analyte Atmosphere (swelling)
Analyte atmosphere
(swelling more)
2nd SENS-ERA Workshop, 5-6 Dec. 2012

11. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Typical Results
Thickness (nm)
Time (min)
Polymer film: PHEMA
Analyte: Humidity
Concentrations: ppm
2nd SENS-ERA Workshop, 5-6 Dec. 2012

12. Fabrication process of IDC Array
Array of 8 chemopapacitors
2μm electrode – 2μm spacing
(die size 7x7mm2)
Plan view of IDC structure
2nd SENS-ERA Workshop, 5-6 Dec. 2012

13. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Measurement Set-up
Gas delivering unit
Sample’s chamber (volume ~4mm3)
Eight channel matrix switch board (Capacitance meter (HP 4278A)
The set-up is completely controlled by a LabView application
Capacitance change (pF)
Time(min)
2nd SENS-ERA Workshop, 5-6 Dec. 2012

14. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Measurement set-up
2nd SENS-ERA Workshop, 5-6 Dec. 2012

15. Response to concentrations of two analytes
Δcdouble.~(ΔCanalyte1+ ΔCanalyte2)
The sensors sense the present or the absent of each analyte.
2nd SENS-ERA Workshop, 5-6 Dec. 2012

16. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Aging through time
4 months later
Good reproducibility and reversibility
Time stability
2nd SENS-ERA Workshop, 5-6 Dec. 2012

17. Read out & Electronic Module
Electronic circuit for up to 8 Chemocapacitance reading
2nd SENS-ERA Workshop, 5-6 Dec. 2012

18. Typical results of Electronic Module
Mesurement of p-xylene(100ppm) with & without Humidity
2nd SENS-ERA Workshop, 5-6 Dec. 2012

19. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
PCA analysis
Processing of the raw data
2 or 3 axes representation
(the most important)
Principal Component Analysis (PCA)
2nd SENS-ERA Workshop, 5-6 Dec. 2012

20. Application I. Wine discrimination
Discrimination of white & red wine
1- Limnos white dry
2-Moschofilero-white
3- Agiorgitiko- red - boutari
4- Naousa-red - boutari
Απόκριση του αισθητήρα PBMA-IDC στα τέσσερα κρασιά για δυο ροές
Αποτέλεσμα PCA
2nd SENS-ERA Workshop, 5-6 Dec. 2012

21. Application II: Fragmentation monitoring
Response of 2 IDC vs time
Fragmentation vs time according to PCA analysis
2nd SENS-ERA Workshop, 5-6 Dec. 2012

22. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Conclusions
Methodology
Development of Methodology for the characterization of polymer based chemocapacitors
Polymeric Films
Characterization of polymers films for odors sensing
Chemocapacitors Array
Development of implementation techniques of chemocapacitos
Implementation & characterization of chemocapacitos Array
Read out electronics
Development of a hybrid system of chemocapacitors array with appropriate read-out electronics
Λογισμικό ανίχνευσης αερίων
Λογισμικό PCA
Εφαρμογές
Ζύμωση γλεύκους
2nd SENS-ERA Workshop, 5-6 Dec. 2012

23. 2nd SENS-ERA Workshop, 5-6 Dec. 2012
Future plans
Development of submicron IDCs.
Apply pattern recognition algorithms
Implementation of a wireless network
Measurements in real environment.
Δίκτυο
2nd SENS-ERA Workshop, 5-6 Dec. 2012

24. Thank you for your attention
2nd SENS-ERA Workshop, 5-6 Dec. 2012