Materials Science and Engineering - Electronic and Mechanical Properties of Materials Part 9 pps

3.225 15 Designer Wavelengths Variation of band-gap energy with composition x of In1-xGaxAs.. Tuller, 2001 Band-Gap Colors Mixed crystals of yellow cadmium sulfide CdS and black cadm

3.225 15

Designer Wavelengths

Variation of band-gap energy with composition x of In1-xGaxAs

© H.L Tuller, 2001

Band-Gap Colors

Mixed crystals of yellow cadmium sulfide CdS and black

cadmium selenide CdSe

3.225 17

Light Sources

• Photoluminescence

• Cathodoluminescence

• Electroluminescence

© H.L Tuller, 2001

♦ Energy

• onversion

• torage

• onservation

♦ Emissions

• Smoke stack

• Automotive

Challenges for New Millenium

Needed: dvances in sensors, actuators and energy conversion

C S C

a

3.225 19

Automotive

Emissions

Factory

Emissions

Process Control

Aerospace

Performance

Electroceramics

Ceramics:

• Traditionally admired for their stability

• Mechanical

• Chemical

• Thermal

• Exhibit other key functional properties

• Electrical, Electrochemical, Electromechanical

• Optical

• Magnetic

3.225 21

Electroceramics Versatility

Atmosphere dependent conductivity (I

Kosacki and H.L Tuller, Sensors &

Actuators B 24-25, 370 (1995).)

High Strain (Pb0.98La0.02(Zr0.7Hf0.3)1-xTixO3 AFE­

FE System (C Heremans and H.L Tuller, J Euro

Ceram Soc., 19, 1139 (1999).)

Semiconducting; Electrochemical; Piezoelectric; Electro-optic; Magnetic, …

Feedback Control System

System

Actuator

Sensor

Chemical Signal

Signal Electrical

Power

Chemical

Species

Micro-Processor Other Input

3.225 23

Sensors for Exhaust Gas Monitoring

Requirements

• clear dependence on pO2

• short response times < 100 ms

• 700<T<1000°C

• long term stability …

Sensor Materials

with Microprocessor System

Chemical

Environmental Stimulus

Requirements of Gas Sensor Materials

• High sensitivity

• High selectivity

• Reproducibility

• Fast response time

• Compatibility with Si microelectronics

• Long term stability

• Small size

• Low cost

3.225 25

3-Way Catalyst Conversion Efficiency

Potentiometric Gas Sensor

PO2(Ref)

PO2(Exhaust)

E Nernst Potential

3.225 27

Auto Exhaust Sensor

• Requirements

• Sensitivity

• Reproducibility

• Robust

• Low cost

•Miniaturization (e.g biological implants)

•Integration - logic, amplification, telemetry

•Portability - low power dissipation

•Rapid response

•Cost

Sensor Trends and Challenges

Neural recording/stimulation microprobe Probes 15µm thick 2-4mm long (Najafi and Hetke, IEEE

Trans Biomed Eng 37, 474 (1990).)

3.225 © H.L Tuller-2001 1

Measurement of Gas Sensor Performance

Si wafer ZnO film

H2

H2 H2 H2

Pt electrode SiO2 layer

Electrical Measurement

• Gas sensing materials:

1 Sputtered ZnO film (150 nm

(Massachusetts Institute of Technology)

2 Sputtered SnO2 film (60 nm)

(Fraunhofer Institute of Physical Measurement Techniques)

• Target gases:

H2, CO, NH3, NO2 , CH4

• Operating temperature:

320 - 460 ºC

Mechanisms in Semiconducting Gas Sensor

• Bulk:

O O = 2e ’ + V O + 1/2 O

2 (g)

n 2 [V O ] PO

2 1/2 = K R (T) ⇒ n = (2 K R (T)) 1/3 PO 2 -1/6

Bulk electronic conduction

modulate

Change in stoichiometry

3.225 © H.L Tuller-2001 3

Resistive Oxygen Sensors Based on SrTiO3

m

1

2

kT

E

pO

∝

σ

semiconducting oxide

Electrode

U I

2

O

p Exhaust

2-3

Acceptors: Al, Ni, Fe

Donors: Nb, Ta, Sb, Y, La , Ce, Pr, Nd, Pm, Sm, Gd

λ

log(pO2 / bar)

-5 -4 -3 -2 -1

0

1

donor acceptor

donor doped acceptor doped

3.225 © H.L Tuller-2001 5

Temperature Independence: High Acceptor Concentration in SrTiO3

10 -20 10 -15 10 -10 10 -5 10 0

0,1

1

750°C

800°C

900°C

850°C

950°C

pO2 / bar

m = 0,2

Sr(Ti0,65Fe0,35)O3

Response times

T / °C t90 / ms

900 6.5

800 26

750 83

700

[1] Menesklou et al, MRS fall meeting, Vol 604, p 305-10 (1999)

185

Oxygen Sensor in Thick Film Technology