3.225 15 Designer Wavelengths Variation of band-gap energy with composition x of In 1-x Ga x As. © H.L. Tuller, 2001 3.225 16 Band-Gap Colors Mixed crystals of yellow cadmium sulfide CdS and black cadmium selenide CdSe. © H.L. Tuller, 2001 8 3.225 17 Light Sources • Photoluminescence • Cathodoluminescence • Electroluminescence © H.L. Tuller, 2001 3.225 18 ♦ Energy • onversion • torage • onservation ♦ Emissions • Smoke stack • Automotive Challenges for New Millenium Needed: dvances in sensors, actuators and energy conversion devices. C S C a 9 3.225 19 Harsh Environments Ceramic Sensors Automotive Emissions Factory Emissions Process Control Aerospace Performance 3.225 20 Electroceramics Ceramics: • Traditionally admired for their stability •Mechanical •Chemical •Thermal • Exhibit other key functional properties • Electrical, Electrochemical, Electromechanical •Optical •Magnetic 10 3.225 21 Electroceramics Versatility Atmosphere dependent conductivity (I. Kosacki and H.L. Tuller, Sensors & Actuators B 24-25 , 370 (1995).) High Strain (Pb 0.98 La 0.02 (Zr 0.7 Hf 0.3 ) 1-x Ti x O 3 AFE- FE System (C. Heremans and H.L. Tuller, J. Euro. Ceram. Soc., 19 , 1139 (1999).) Semiconducting; Electrochemical; Piezoelectric; Electro-optic; Magnetic, … 3.225 22 Feedback Control System System Actuator Sensor Chemical Signal Signal Electrical Power Chemical Species Micro-Processor Other Input 11 3.225 23 Sensors for Exhaust Gas Monitoring Requirements • clear dependence on pO 2 • short response times < 100 ms • 700<T<1000°C • long term stability … 3.225 24 Sensor Materials Gas Sensor Electrical Signal compatible 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 12 3.225 25 3-Way Catalyst Conversion Efficiency 3.225 26 Potentiometric Gas Sensor PO 2 (Ref)PO 2 (Exhaust) E E = (kT/4q) ln {PO 2 / PO 2 (Ref)} Nernst Potential 13 3.225 27 Auto Exhaust Sensor • Requirements • Sensitivity •Reproducibility • Robust •Low cost 3.225 28 •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).) 14 3.225 1 © H.L. Tuller-2001 Measurement of Gas Sensor Performance Si wafer ZnO film H 2 H 2 H 2 H 2 Pt electrode SiO 2 layer Electrical Measurement • Gas sensing materials: 1. Sputtered ZnO film (150 nm (Massachusetts Institute of Technology) 2. Sputtered SnO 2 film (60 nm) (Fraunhofer Institute of Physical Measurement Techniques) • Target gases: H 2 , CO, NH 3 , NO 2 , CH 4 • Operating temperature: 320 - 460 ºC 3.225 2 © H.L. Tuller-2001 Mechanisms in Semiconducting Gas Sensor • Bulk: O O = 2e ’ + V O + 1/2 O 2 (g) Induce shallow donors: density related to PO 2 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 1 3.225 3 © H.L. Tuller-2001 Resistive Oxygen Sensors Based on SrTiO 3 m 1 2 kT E pOe A ± − ∝σ semiconducting oxide Electrode U I 2 O p Exhaust 3.225 4 © H.L. Tuller-2001 Influence of Dopants on Electrical Conductivity of SrTiO 3 Sr 2+ Ti 4+ O 2- 3 Acceptors: Al, Ni, Fe Donors: Nb, Ta, Sb, Y, La, Ce, Pr, Nd, Pm, Sm, Gd λ log(σ / (Ωcm) -1 ) T = 800 °C log(pO 2 / bar) 0.995 1,005 -16 -4 0 -5 -4 -3 -2 -1 0 1 donor acceptor -20 -12 -8 donor doped acceptor doped 2 3.225 5 © H.L. Tuller-2001 Temperature Independence: High Acceptor Concentration in SrTiO 3 10 -20 10 -15 10 -10 10 -5 10 0 0,1 1 750°C 800°C 900°C 850°C 950°C electrical conductivity / (Ω cm) -1 pO 2 / bar m = 0,2 Sr(Ti 0,65 Fe 0,35 )O 3 Response times T / °C t 90 / ms 900 6.5 800 26 750 83 700 [1] Menesklou et al, MRS fall meeting, Vol. 604, p. 305-10 (1999). 185 3.225 6 © H.L. Tuller-2001 Oxygen Sensor in Thick Film Technology 3 . T = 800 °C log(pO 2 / bar) 0 .99 5 1,005 -1 6 -4 0 -5 -4 -3 -2 -1 0 1 donor acceptor -2 0 -1 2 -8 donor doped acceptor doped 2 3.225 5 © H.L. Tuller-2001 Temperature Independence:. Wavelengths Variation of band-gap energy with composition x of In 1-x Ga x As. © H.L. Tuller, 2001 3.225 16 Band-Gap Colors Mixed crystals of yellow cadmium sulfide CdS and black cadmium selenide. conductivity (I. Kosacki and H.L. Tuller, Sensors & Actuators B 2 4-2 5 , 370 ( 199 5).) High Strain (Pb 0 .98 La 0.02 (Zr 0.7 Hf 0.3 ) 1-x Ti x O 3 AFE- FE System (C. Heremans and H.L. Tuller, J.