SiC for sensors in aggressive environment

Transcription

1 SiC for sensors in aggressive environment Anita Lloyd Spetz FunMat and Applied Physics Dep. Physics, Chemistry and Biology Linköping University

2 Outline Bio and Chemical Sensor Technology General Material properties, kiselkarbid (SiC( SiC) Applications SCR, selective catalytic reduction,, in diesel vehicles Control of boilers (pannor)

3 Definition of a sensor A Sensor is a device that recieves a stimulus and responds with an electrical signal J. Fraden, Handbook of Modern Sensors

4 Emissions of chemical species will have to be controlled by chemical sensors Chemical sensors sors are Non-specific History dependent Cross sensitive Temperature dependent Not long term stable Sensitive to 100s of parameters! Challinging to work with!!

5 Physicists in this area: Theoreticians,, for modelling and simulation Technical Physics (Teknisk Fysik) Measurement technology Electronics (elektronik) Biophysics

6 Bio and Gas sensor technologies conducting polymer film electrode Type Sensitive material Detection principle Semiconducting metal oxides (MOS) doped semiconducting metal oxides (SnO 2, WO 3, MoO3..) resistance change adsorbing layer Ion conducting metal oxides Ionic conductors, ZrO2, Ga2O3 Potential changes gold electrode substrate Quartz crystal microbalance, QCM, surface acoustic wave, SAW Field effect sensors, FET (Transistors, capacitors, Schottky diodes) AT-cut quartz crystal organic or inorganic layers catalytic materials frequency change due to mass change Potential changes of the gate Conducting polymers, CP Modified conducting polymer s resistance change Fibre optic sensors, FOS Organic dyes, etc. Changes in reflection, absorption, refraction index Surface Plasmon Resonance (SPR) sensors Organic films and thin metal films Changes in the angle of incidence of the light Pellistor/ thermistor/ thermopile Catalytic materials/ semiconductors/ metals temperature change Electrochemical cells solid or liquid electrolytes current or voltage change Infrared sensors, IR IR absorption

7 Sensor compared to an instrument Sensor device: An electric output signal to a stimilu Small Cheap Fast Reproducible (Mass production) Instrument: Quantitative Accurate Sensitive Expensive May have built in sample handling system

8 Flap Control Target Parameters Sensor element Flap OPEN green air slight pollution Air intake CO HC NOx electronics Flap CLOSED Ventilation system significant pollution strong pollution very strong pollution extreme, healthening pollution

9 Bio and Gas sensor technologies General definitions

10 Signal recording: feature extraction on integral off integral off derivative MOSFET 3 MOSFET 7 Figaro 3 sensor signal on derivative baseline response sample on off time [s]

11 Sensor response, S, can be measured as Difference between baseline and test line S = f (X 1 ) f (X 0 ) Ratio between baseline and test line S = f (X 1 ) / f (X 0 ) or S = f (X 1 )- f (X 0 ) / f (X 0 ) Eventually also useful: Derivative of initial change S = f (X)/dt The integral of the pulse S = f(x)dt The sensor signal is the output from the sensor, normally measured in mv

12 Sensor definitions, sensitivity The sensitivity is the change of the sensor (output) signal to a change of the concentration of the measurerand Sensitivity = S / x

13 Sensitivity of a QCM sensor to C 2 Cl 4 frequency shift [Hz] PDMS C 2 CL 4 [ppm] Linear response S = a + bx frequency [Hz] ppm 606 ppm 957 ppm 1808 ppm S / X =ds / dx = b time [sec]

14 Sensitivity of a Si-FET sensor to NH3 Langmuir response: Linear for small concentrations Saturated for larger concentrations V = V max ( kp H2 /P O2 ) 1/2 (1+ ( kp H2 /P O2 ) 1/2 )

15 Sensor definitions, selectivity The response to one stimuli in correlation to others Selectivity = S gas1 / S gas2 For large selectivity the response to gas 1 is large and gas 2 is small

16 A sensor is defined by The detection mechanism The gases or biomolecules it is sensitive for Sensitivity Concentration / Dynamic range Response time Reproducibility / repeatability Stability Working temperature Life time

17 Silicon carbide, SiC,, (aluminium( nitride, AlN, gallium nitride, GaN, zinkoxide, ZnO) material for high temperature and corrosive environments High band gaps: 4H SiC 3.2 ev for, GaN 3.4 ev, AlN 6.4eV, ZnO 3.4 ev For SiC: Break down electric field 2, V/ cm Thermal conductivity 5 W / cm K Melting point ~ 2700 C For all: Extremely good chemical inertness Processing, a challenge, but in progress

18 Field-effect effect sensors (MOSFET) I V Principle C 3 H 6 O O H 2 O H 2 O2 NH 3 CO2 H H H H H Si O Si O Si O Drain current (ma) I-V characteristics 400 o C V 500ppm H D 2 0.5% O 2 SiC/Si Drain voltage (V) Detection mechanism Charging of the gate material gives an electric field in the insulator and this influences the mobile charges in the semiconductor (the IV curve moves to higher / lower voltage) Voltage shift [mv] Sensor signal Time [min] Sensor signal, voltage at a constant current

19 MISiCFET sensors layout Design and processing, ACREO AB, Sweden Number of chips on 2 wafer: 356

20 MISiCFET sensors layout, chip Chip size: Design and processing, ACREO AB, Sweden 2.1 x 1.9 mm

21 Mounting of MISiC-FET gas sensor devices

22 Characterization of MISiC-FET sensors Pt Response versus temperature: Different selectivity patterns based on catalytic metal and temperature Ir The response to NO, CO, C 3 H 6, NH 3 and H 2, varies with metal, Pt or Ir. and temperature Drain current (ma) o C 500ppm H 2 V D 0.5% O 2 Mike Andersson Drain voltage (V)

23 Applications of MISiC-FET gas sensor devices In car exhausts and flue gases

24 Market: Legislations 0.15 US 2004 US EU3 (2000) PM g/kwh EU5 (2008) EU4 (2005) US NOx g/kwh

25 SCR, Selective Catalytic Reduction (NH 2 ) 2 CO + H 2 O 2NH 3 + CO 2 Engine Engine model Urea Tank Urea injection Catalyst Control Algorithms 4NO +4NH 3 + O 2 4N 2 + 6H 2 O 2NO 2 +4NH 3 + O 2 3N 2 + 6H 2 O NH3 NOx Catalyst model Requirements: Sensor operating > 300 C (short term 700 C) Stable operation > km Response time < 1 s Sensitivity < 10 ppm

26 Mounting of the SiC-FET sensor Sensor chip glued to the heater Pt 100 element for temperature control Mounting for the exhaust pipe

27 Montering av MISiCFET sensorer Helena Wingbrant Simulation for the new mounting showed a non-centred position of the sensor as optimal (Ilja Below, ACREO, Jönköping)

28 Characterization of MISiC-FET sensors Different selectivity patterns based on temperature Ir 300 C Ir 400 C Mike Andersson

29 The SiC-FET ammonia sensor H. Svenningstorp, H. Wingbrant Diesel engine measurement SCR system Two MISiCFET sensors and an optical reference instrument Detection limit< 10 ppm

30 MISiCFETs in a Volvo truck on a trip to Spain

31 Demonstration of filling station for A dispenser, modified for co-fueling, is mounted in a trailer. A HD nozzle and a LD nozzle are provided. A HD and a LD tank and fill pipe rig are provided. diesel and urea

32 Existing dispenser with vapor recovery, additive package addition, with materials upgrade Gasoline vapor recovery hose and nozzle housing New nozzle tube and fill pipe insert Design Concept for diesel and urea

33 SCR, Selective Catalytic Reduction, system Catalyst Engine Engine model Urea Tank Urea injection Control Algorithms NH 3 NOx To meet legislation both sensors may be required 4NO +4NH 3 + O 2 4N 2 + 6H 2 O 2NO 2 +4NH 3 + O 2 3N 2 + 6H 2 O Catalyst model

34 Flue gas measurements Control strategy: Control of primary and secondary air by 1-2 gas sensors 1 temperature sensor Increased efficiency and lower emissions Domestic boilers Gas sensors Mike Andersson Temperature sensor Commercialized by SenSiC AB

35 Measurements Domestic boilers Control strategy Controlled combustion Secondary air [a.u.] O 2 conc [%] o 325 o C C CO emissions HC emissions ,5 2,0 1,5 1,0 0,5 0,0 Sensor signals [V] Emissions [ppm] Uncontrolled combustion O 2 conc [%] CO emissions HC emissions Emissions [ppm]

36 Flue gas measurements Domestic boilers O 2 conc [%] CO emissions HC emissions Emissions [ppm]

37 Chemical sensor Sensors systems based on chemical sensors needed for environmental purpuses and lots of other applications Physicists are highly needed in this area