Chemical Sensor Systems for Automotive Applications Udo Weimar - - PowerPoint PPT Presentation

University of Tübingen Institute of Physical Chemistry

Chemical Sensor Systems for Automotive Applications

Udo Weimar & Nicolae Barsan

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: why?

• For n-type MOX one needs porous sensing

layers for better performance

• The presence of noble metal dopants/sensitizers

is needed to decrease response time and

• peration temperature
• One can obtain such layers by using powders,

„dope“ them, make them into an ink and deposit them (screen-printing, drop coating, etc..)

• Micromachined substrates allow for decreasing

the power consumption and simplify packaging

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Microhotplate

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Microhotplate

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

Microsensor: drop coated microhotplate

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

1 10 100 1 10 100 300°C 250°C 200°C 350°C 400°C 30% r.h. 50% r.h. 70% r.h.

Sensor response G(CO)/G0 CO concentration (ppm)

Performance evaluation

University of Tübingen Institute of Physical Chemistry

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+

• Rgai n

Usenso r Uref measurement of the sensor signal

Au electrodes sensitive layer

Si N

3 4 membrane

membrane dimensions

U~ Iheat er

+12 V

heater and measurement of sensor temperature

silicon wafer Pt heater

Uheat er

a) b)

sensor type thickness area a 0.5 m 1x3 mm2 b 0.85 m 1x1 mm2

sensor type

Thick films/microhotplates: how?

Simultaneous chemoresistive and thermal effects

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1k 10k

200 400 600 1000 2000 2000 1000 500 200 100 200 100 60 30 15 10 7

C2H5OH [ppm] CH4 [ppm] CO [ppm]

time [min]

Pt doped / 50% r.h.

Rsensor []

120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

402 404 406

Tsensor [°C]

Simultaneous chemoresistive and thermal effects

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 1 10

Theater = 400°C / Pt doped / 50% r.h. CO CH4 C2H5OH sensor signal Rair / Rgas

•  T [°C]

Gas discrimination

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

Application exploration

CO, NO2 sensor system

a)

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

Test drive: prototype chemical sensor system

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: how?

• 500

500 1000150020002500300035004000 5 10 15 20 25 30 35 40

CO concentration (ppm)

Time (seconds)

Electrochemical Cell signal

5 10 15 20 25 30 35 40 Log (sensor conductance)

Microsensor signal

Test drive: comparison with EC

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: industrialization

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: industrialization

sensing layer Rsensing ~ 100Ω – 100MΩ Rheater = 100Ω

2 mm 1 mm 0.45 mm Si Si3N4 – membrane heater electrodes sensing layer

Commercial microsensor

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: industrialization

CO, NO2 sensor system

a)

Application solution

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: industrialization

From prototype to commercial chemical sensor system

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: applications

CO, NO2 smoke, flatulence fast food sensor system sensor system

a) b)

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: applications

• dor event

test panel sensor data AQL test panel AQL sensor module algorithm

similarity

citation

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Thick films/microhotplates: applications

50 100 150 200 250 300 350 400 450 500 10 20 30 40 50 60 time [min] concentration [ppm] CO NO2 Butanol 50 100 150 200 250 300 350 400 450 500 10

• 6

10

• 5

10

• 4

10

• 3

10

• 2

time [min] log conductivity [S] Pd3 Pt02 U

University of Tübingen Institute of Physical Chemistry

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Thick films/microhotplates: applications

500 1000 1500 2000 2500 3000 1 2 3 4 5 time [s] AQLD 500 1000 1500 2000 2500 3000 1 2 3 4 5 time[s] Marker AQL Fast Food Manure Flatulence Cigarette Smoke Exhaust Gas Stop and Go Order Hamburger Food in the car Fast Food Smell Parking Open bag Start Eating Eating finished Open/Close door Continue U-Turn Enter freeway Oil fogg Open/Close window Light Cigarette Extinguish Cigarette

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: why?

• Decrease of cost by using processes compatible

with large scale fabrication on foils (roll to roll, printed electronics)

• Possibility to integrate on the same substrate

additional functionalities (sensing and driving electronics, networking, etc)

• Possibility to integrate them into a wide range of

materials (textiles, packaging materials, etc )

• Possibility to address novel application fields
• Low-cost smart sensing systems

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: how?

By combining of different sensing principles

– Measurement of a wider range of gas concentrations – Higher selectivity – Differential measurements

At no additional processing steps for the transducers

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

University of Tübingen Institute of Physical Chemistry

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• Capacitive humidity and VOCs sensor [1]

– Area: 1.4 x 1.4 mm2 – Gap and finger width: 10 μm – Ultra-low power consumption

• Resistive metal oxide (MOX) gas sensor [2,3]

– 100 μm wide – Drop-coated – 10–28 mW (200-300°C)

• Pt temperature sensor: T   R 

– Area: 1.4 x 1.2 mm2

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

[1] A. Oprea, et al., Sensors and Actuators B, 140(2009)227-232. [2] D. Briand et al., Sensors and Actuators B, 130(2008)430-435. [3] J. Courbat et al., Proc. Transducers 2009, pp.584-587.

d A C

r 2 , 1 

 

Plastic sensors: how?

A d εr1 εr2

Substrate Heater Electrodes Gas sensitive layer Dielectric layer

100 µm

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: how?

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Technological platform: J. Courbat et al., Proc. of IEEE Sensors 2008 Conference, Lecce, Italy, pp.74-77.

• All processes on

polyimide foil

• Ti/Pt deposition (20/130

nm) and patterning

• MOX layers

– SnO2/Pd – WO3

• Polymer layers

– Cellulose acetate butyrate (CAB) – Polyetherurethane (PEUT)

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: how?

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Drop coated MOX Spray/drop coated polymers

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Example: environmental monitoring (CO, NO2, VOC, r.h.)

• Carrier gas:

– synthetic air, 200 sccm – 0% to 70 % r.h.

• Test gases:

– CO: 20 - 80 ppm – NO2: 0.1 – 1 ppm – Ethanol: 5 - 20 ppm and 300 - 3000 ppm

• Readout of the sensors

– Capacitive sensors: C to V converter (AD7746 from AD) – MOX gas sensors: power supply and multimeter – Temperature sensor: multimeter

2 cm

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Differential measurement of relative humidity

• Initial capacitance : ~10 pF
• Differential measurement: Subtraction of the reference channel

from the measurement channel  Removal of the parasitic influence of the substrate – Higher linearity – Faster response time

2 4 6 8 10 12 14 16 18 20 22 24 26 28 0.0 0.1 0.2 0.3 0.4 0.5 20 40 60 80

differential capacitance substrate

• nly

CAB + substrate

Capacitance shift [ pF ] Time [ h ]

CO [ ppm ] EtOH [ ppm ] r.h. [ % ]

Conc.

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

2 4 6 8 10 12 14 16 18 20 22 24 26 28 0.0 0.1 0.2 0.3 0.4 0.5 20 40 60 80

differential capacitance substrate

• nly

CAB + substrate

Capacitance shift [ pF ] Time [ h ]

CO [ ppm ] EtOH [ ppm ] r.h. [ % ]

Conc.

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Reproducibility of humidity measurement

• CAB coated, 40 cycles (20 days): 0% to 70% of relative humidity
• Good stability and reproducibility
• Slight decrease in sensitivity with time

10 20 30 40 20 40 60 80 100 120 140 160

Relative Humidity 0% r.h. 10% r.h. 20% r.h. 30% r.h. 40% r.h. 50% r.h. 60% r.h. 70% r.h.

Capacitance shift [ fF ] Exposure number

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

Combination of sensing principles

• PEUT: detection of EtOH at high

concentrations

• MOX sensors: 300°C (28 mW)

– WO3: more selective to NO2 – SnO2: more selective to EtOH

10

• 1

10 10

1

40 80

50% rh

NO2: 0.1 - 1 Et.: 2 - 20

Gas [ ppm ] Humidity [ % ] 1 2 3 4 5 6 7 8 9 10

Time [ h ]

10

4

10

5

10

6

10

7

10

8

SnO2 MOX WO3 MOX 10m WO3 10m SnO2: 0.2% Pd drop coating MOX 6 1 heating: 2.3V, 12mA

Resistance [  ]

• 100
• 50

50 100 150

Sensing capacitance Reference capacitance

Differential capacitance x 10

• Cap. shift

[ fF ]

Sensing capacitance: 10m PEUT drop coating

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

10

• 1

10 10

1

40 80

50% rh

NO2: 0.1 - 1 Et.: 2 - 20

Gas [ ppm ] Humidity [ % ] 1 2 3 4 5 6 7 8 9 10

Time [ h ]

10

4

10

5

10

6

10

7

10

8

SnO2 MOX WO3 MOX 10m WO3 10m SnO2: 0.2% Pd drop coating MOX 6 1 heating: 2.3V, 12mA

Resistance [  ]

• 100
• 50

50 100 150

Sensing capacitance Reference capacitance

Differential capacitance x 10

• Cap. shift

[ fF ]

Sensing capacitance: 10m PEUT drop coating

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

• Humidity (8 measurements)

– Capacitor: good linearity – MOX sensor:

• < 10%: reduced influence of r.h.
• > 10%: influence of r.h. lower than

a factor 1.2

• Gases (8 measurements)

– Good sensitivity – Logarithmic linearity

1 2 3 10 20 30 40 50 60 70 30 60 90 120 150 180

MOX 3 1 heated at 2.35 V x 7.7 mA = 18 mW

Response

CAP 3 1 : 20m CAB drop coating

Relative humidity [ % ] Capacitance [ fF ]

10 100 1 10

CO

MOX 3 1 heated at: 2.35 V x 7.7 mA = 18 mW

Response Concentration [ ppm ] 5

Ethanol

0% r.h. 50% r.h. 0% r.h. 50% r.h.

University of Tübingen Institute of Physical Chemistry

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Plastic sensors: current state of the art

Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

10 20 30 40 50 60 70 10

4

10

5

10

6

280 300

10 ppm Et-OH 200 ppm Et-OH 300 ppm Et-OH 400 ppb NO2 Et-OH bottle empty Temperature control 30°C

Sensor Resistance [  ] Time [ d ]

Baseline 24-26°C Heating interrupted 1d NO2 bottle changed SnO2 heater t [ °C ]

Stability MOX sensors

University of Tübingen Institute of Physical Chemistry

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Development partner: Institute of Microengineering (IMT), Samlab, Neuchâtel, Switzerland

10 20 30 40 50 60 70 10

6

10

7

10

8

280 300

Et-OH bottle empty Temperature control 30°C

Sensor Resistance [  ] Time [ d ]

Baseline 10 ppm Et-OH 200 ppm Et-OH 300 ppm Et-OH 400 ppb NO2 24-26°C Heating interrupted 1d NO2 bottle changed WO3 heater t [ °C ]

Stability MOX sensors

Plastic sensors: current state of the art

University of Tübingen Institute of Physical Chemistry

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Outline

• Thick films/microhotplates combination

– Why? – How? – Industrialization – Applications

• Plastic sensors

– Why? – How? – Current state of the art – Outlook

University of Tübingen Institute of Physical Chemistry

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Plastic sensors:outlook

120°C 500°C

Oxygen Methane Oxygen Oxygen Precursor liquid Syringe pump MFCs Exhaust vent Filter housing Spray flame Support flame Shield gas

PI PI

Water in Water out Deposition substrate

sensing area: 7 x 3.5 mm2

Development partner:Department of Production Engineering, University of Bremen, Germany

Novel direct synthesis and deposition technology; Flame Spray Pyrolysis

University of Tübingen Institute of Physical Chemistry

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Plastic sensors:outlook

Development partner:Department of Production Engineering, University of Bremen, Germany

Novel direct synthesis and deposition technology; Flame Spray Pyrolysis

high quality materials functional layers synthesis

University of Tübingen Institute of Physical Chemistry

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Plastic sensors:outlook

University of Tübingen Institute of Physical Chemistry

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Plastic sensors:outlook