Gas Sensors and Sensor Systems for Air Quality Monitoring

Transcription

1 LAB FOR MEASUREMENT TECHNOLOGY Prof. Dr. rer. nat. A. Schütze MACPoll Workshop Gas Sensors and Sensor Systems for Air Quality Monitoring JRC Ispra, November 19, 2013, Ispra, IT Andreas Schütze Saarland University, Lab for Measurement Technology VOC-IDS

2 > Outline Background: indoor air air quality Gas sensors for air quality Electrochemical cells Semiconductor gas sensors Other technologies: mass sensitive devices, GasFETs Gas measurement systems more than just sensors The three S Gas measurement systems incl. signal processing and evaluation Calibration and field testing Performance example: ppb-level VOC identification Novel developments Novel sensor technologies: nanomaterials and integrated GasFETs System self monitoring Multifunctional multisensor systems Conclusions Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 2

3 > Background: Indoor Air Quality Why worry about indoor air? Safety Gas leak detection (combustible gases, e.g. CH 4 ) Fire detection (various gases) Hazardous gas detection (e.g. CO) Malodor detection (kitchen & bathroom ventilation) HVAC systems Reduced air circulation for greatly reduced energy consumption CO 2 monitoring for fresh air Increased levels of VOCs lead to sick building syndrome Selective (formaldehyde, benzene etc.) and sensitive (ppb level) detection Systems have to be adapted to the specific room use scenario Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 3

4 > Background: Indoor Air Quality Sensor requirements Low cost Networked systems (in major buildings, but also private homes) Long lifetime: >10 years without maintenance for private homes Which sensors are used today? Safety Gas leak detection: human nose, Japan: MOS; pellistors: only industr. Fire detection: various sensors, mostly optical; gas sensor systems under development (EC, MOS, GasFET) Hazardous gas detection: EC, MOS Malodor detection: MOS HVAC systems CO 2 monitoring: NDIR (in major rooms/buildings), EC, GasFET VOCs: MOS (total VOC), GasFET (emerging) Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 4

5 > Background: our research focus VOC-IDS: Volatile Organic Compound Indoor Discrimination Sensor Transnational project funded within MNT-ERA.net Selective VOC detection, primarily formaldehyde, benzene Novel ceramic nanomaterial metal-oxide semiconductor gas sensors Intelligent signal processing based on temperature cycling Networked systems connected to KNX bus SENSIndoor: Nanotechnology based intelligent multi-sensor System with selective pre-concentration for Indoor air quality control EU-FP7 project NMP : Nanotechnology-based sensors for environmental monitoring Microtechnology based approach for MOS and SiC-GasFET sensors Pre-concentration to boost sensitivity and selectivity Integrated multi-sensor approach Application specific priorities and field tests Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 5

6 > Outline Background: indoor air quality Gas sensors for air quality Electrochemical cells Semiconductor gas sensors Other technologies: mass sensitive devices, GasFETs Gas measurement systems more than just sensors The three S Gas measurement systems incl. signal processing and evaluation Signal Calibration processing and field and testing evaluation Calibration Performance and example: field testing ppb-level VOC identification Novel developments Novel sensor technologies: nanomaterials and integrated GasFETs System self monitoring Multifunctional multisensor systems Conclusions Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 6

7 > Gas sensors for air quality Electrochemical cells: amperometric gas sensors Gas molecules are ionized at sensing electrodes Ions are conducted through the electrolyte cell Current is proportional to gas concentration (diffusion limited) Sensitivity typically down to ppm, for some reactive gases sub-ppm Partial selectivity achieved, but still relevant cross-sensitivities Poor long term stability (especially at high temperature, low humidity) Plus: baseline drift, sensitivity change, poisoning Source: Alphasense Ltd. Quelle: Sixth Sense Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 7

8 > Gas sensors for air quality Metal Oxide Semiconductor (MOS), e.g. SnO2, Ga2O3, WO3 Oxygen adsorption leads to energy barrier at grain boundaries Gas adsorption or reaction with O- influences energy barrier Very high sensitivity (exponential effect of energy barrier on resistance) Very low cost: manufacturing based on MEMS and screen printing Source: Figaro Inc., Japan Source: UST Umweltsensortechnik GmbH Source: MicroChemical Systems S.A., Corcelles, CH Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 8

9 Source: Figaro Inc., Japan > Gas sensors for air quality Metal Oxide Semiconductor (MOS), e.g. SnO 2, Ga 2 O 3, WO 3 Great robustness (> 10 years lifetime in applications) Poor stability Sensor drift due to poisoning etc. Influence of background, esp. humidity quantitative meas. difficult Poor selectivity Response is mainly due to changing oxygen coverage Its surprising if the MOS sensor does not show a reaction! greatest challenge for R&D Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 9

10 Source: A. Schütze, Dissertation, JLU Gießen, 1994 > Gas sensors for air quality Organic semiconductor materials, i.e. Phthalocyanine p-type semiconductor esp. suitable for oxidizing gases, i.e. NO x, O 3 robust, low-cost, stability and selectivity similar to MOS Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 10

11 > Gas sensors for air quality Other sensor technologies? Mostly still under development Pellistors: detection of combustible gases at higher conc. Mass-sensitive devices Bulk or surface acoustic Mass change on surface leads to change of f res High sensitivity: SAW GHz: complex electronics high temp. stability req. GasFET Gas-sens. Field Eff. Transistor Classic Lundström FET: Hydrogen diffusing thru Pd Only H-containing gases Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 11

12 > Outline Background: indoor air quality Gas sensors for air quality Electrochemical cells Semiconductor gas sensors Other technologies: mass sensitive devices, GasFETs Gas measurement systems more than than just just sensors sensors The three S Gas measurement systems incl. signal processing and evaluation Signal Calibration processing and field and testing evaluation Calibration Performance and example: field testing ppb-level VOC identification Novel developments Novel sensor technologies: nanomaterials and integrated GasFETs System self monitoring Multifunctional multisensor systems Conclusions Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 12

13 > Gas measurement systems more than sensors The three S Sensitivity Broad spectrum from below ppb (for malodors, ozone, hazardous VOCs) up to 1000 ppm (gas leak, CO 2 ) Selectivity False alarms are primary concern for fire detection (ratio 10:1) VOC detection: hazardous (formaldehyde) vs. neutral (alcohol vapor, cleaning agents) vs. wanted (odorants) Stability Industrial applications: maintenance interval < 6 months Public buildings: annual or bi-annual tests (if that) Private homes: 10 years lifetime w/o regular maintenance? Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 13

14 > Gas measurement systems more than sensors Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 14

15 Conductance [a.u.] A. Schütze, A. Gramm, T. Rühl IEEE Sensors Journal, Vol. 4, No. 6, Gas measurement systems more than sensors Temperature Cycled Operation (TCO) Benzene Iso-Pentane 70% r.h. 30% r.h. Methyl Alcohol Diethyl Ether Methyl Tert-Butyl Ether Time in Temperature Cycle [sec] Signal evaluation: Propylene Oxide 1. Normalization of the response curves reduces sensor drift 2. Generation of secondary features, i.e. levels, slopes etc. 3. Suitable patterns are extracted for further evaluation Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 15

16 Gas measurement systems more than sensors Temperature Cycled Operation (TCO) Source: A. Schütze, A. Gramm, T. Rühl IEEE Sensors Journal, Vol. 4, No. 6, 2004 Evaluation of sensor data based on temperature cycling (example) Virtual multisensor Characteristic features of the curve shapes (i.e. slope at the end of the high temperature phase and curvature during the low temperature phase) are evaluated, to discriminate between different gases in several steps. Note: the decision tree reflects the chemical composition of the solvents starting with the alkane pentane and the aromatic benzene (both pure CH-compounds), then the alcohol (R-COH) and finally the three ether compounds (R1-O-R2). This indicates that an expansion might be possible to classify many different molecules. Synthetic air, Iso-Pentane, Benzene, Methyl Alcohol, Methyl Tert-Butyl Ether, Diethyl Ether, Prop. Oxide T-Cycle 1 Decision 1 Decision 2 T-Cycle 2 Decision 3 Decision 4 clean air & interferents Iso-Pentane Benzene Methyl Alcohol Methyl 4-Butyl Eth. Diethyl Ether Propylene Oxide Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 16

17 Gas measurement systems more than sensors Temperature Cycled Operation (TCO) hardware Hardware platform GasTON for exact temperature control and large dynamic range data acquisition Gas sensor T-cycle Operating unit Heater temperature control Heater resistor R H (T) controlled for exact temperature control of (micro-)hotplates Sensor read-out with large dynamic range for MOS, GasFET and pellistor type sensors ambient temperature +120 C U V R 1 R 2 R 3 R pot R 4 R adj R H now commercialized OdorChecker by 3S GmbH (spin-off of LMT) _ + R 5 R C C time [h] Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 17

18 Gas measurement systems more than sensors Electrical Impedance Spectroscopy (EIS) for MOS Hardware platform for Electrical Impedance Spectroscopy Hardware concept using ETFE (Empirical Transfer Function Estimate) Z ω = U ω I ω = U Sensor(ω) U Rref (ω) R ref Sensor excitation Sensor response M. Schüler, S. Darsch, P. Reimann, A. Schütze, Low-cost impedance spectroscopy for semiconductor gas sensors a hardware concept IWIS, Chemnitz, October 2010 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 18

19 Gas measurement systems more than sensors Gate Bias Cycled Operation (GBCO) for GasFETs TCO hardware platform extended to allow Gate Bias Variation Heater temperature control Heater resistor R H (T) controlled for exact temperature control of GasFET Sensor read-out: voltage drop V D measured at constant current I D Gate voltage VG varied to set temperature 280 actual temperature influence the operating point applied gate bias 3 temperature [ C] gate bias [V] time [s] C. Bur et al.: Combination of Temperature Cycled and Gate Bias Cycled Operation to enhance the Selectivity of SiC-FET Gas Sensors, Proc. Transducers 2013 & Eurosensors XXVII; Barcelona, Spain, June 16-20, 2013 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 19

20 Many possibilities for optimization: Sensor selection Operating mode TCO EIS GBCO Data acquisition Signal preprocessing Feature extraction Separation Classification and always testing under real application conditions (field testing)! Target appl. E. Leonhardt, Thesis project, UdS-LMT, Nov. 19, 20 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 20

21 > Gas measurement systems more than sensors Calibration: novel gas mixing system for VOC testing down to sub ppb-level Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 21

22 > Gas measurement systems more than sensors Novel gas mixing system: results of reference measurement (zero air) compound CAS no c [µg/m 3 ] c [ppb] benzene Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 22

23 > Gas measurement systems more than sensors Novel gas mixing system: results of first sensor tests 9,0x10 8,0x cond. UST 1000 conc. formaldehyde upper range value of ADC 4,2x Sensor reaction to 1 ppb formaldehyde conductance [A/V] 7,0x10-3 6,0x10-3 5,0x10-3 4,0x10-3 3,0x time [s] conductance [A/V] 4,1x time [s] ,1 0,01 1E-3 1E-4 concentration [ppm] Relevance? Legal limits in France: Formaldehyde 25 ppb in 2015; Benzene 0.6 ppb in 2016 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 23

24 > Indoor Air Quality monitoring MNT-ERA.net project VOC-IDS Volatile Organic Compound Indoor Discrimination Sensor Scenario specific detection of hazardous VOC Integration of sensor system into KNX building automation networks Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 24

25 > Indoor Air Quality monitoring MNT-ERA.net project VOC-IDS Example for selective detection of VOCs in interfering background Classification of Formaldehydye, Benzene, Naphthalene in presence of ethanol target gas Concentration (ppb) humidity Interferents (EtOH ppm) Air NA 40%, 60% none, 0.4, 2 Formaldehyde 10, %, 60% none, 0.4, 2 Benzene 0.5, %, 60% none, 0.4, 2 Naphthalene 2, 20 40%, 60% none, 0.4, 2 interferent concentrat. relative humidity number of LDA steps for charac. 0, 0.4, 2 40%, 60% 1 1 Estimated number of LDAs None 40%, 60% (?)*1 0, 0.4, 2 None 1 (2) (1+) 5*1 generalized classification classification w known EtOH classification w known r.h. Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 25

26 > Indoor Air Quality monitoring MNT-ERA.net project VOC-IDS Example for selective detection of VOCs in interfering background Classification of Formaldehydye, Benzene, Naphthalene in presence of ethanol General classification possible, but noisy Improved performance with known rel. humidity (from additional sensor) This proves VOC identification at levels below future thresholds! w/o additional information naphthalene air benzene formaldehyde naphthalene air with known rel. humidity formaldehyde benzene Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 26

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28 > Novel developments Novel sensor materials and transducer principles Nanotechnology for improved gas sensitive layers Novel transducer principles Gas ionization (can be electronically controlled!) GasFETs commercially available Source: Micronas Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 28

29 > Novel developments SiC Gas-sensitive Field Effect Sensors (Linköping U, SenSiC) high temperature operation allows temperature cycled operation as for MOS (nano-)pi0 usstnupimu,n ani iridium[( Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra

30 > Novel developments Highly sensitive VOC detection with SiC GasFETs (SenSiC AB) sensor signal V DS [mv] conc. [ppb] quasi static sensor response 220 C 4.5 ppb 3.5 ppb 2.5 ppb 1.5 ppb 0.5 ppb sensor response V DS smoothed signal 4 Benzene time [h] C. 866 Bur et al.: Detecting Volati Proc. IEEE Sensors 2013; Bal Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 30

31 > Novel developments System integration: Gate Bias Cycled Operation for SiC-GasFETs % O 2 in N 2 40 s ramp ppm CO 40 s ramp current i DS (µa) current i DS (µa) Nov. 19, C gate bias U G (V) 200 C gate bias U G (V) % O 2 in N 2 40 s ramp % O 2 in N s ramp current i DS [µa] C gate bias U G [V] current I DS [µa] gate bias U G [V] 200 C C. Bur et al.: Influence of a Changing Gate Bias on the Sensing Properties of SiC Field Effect Gas Sensors, IMCS 2012 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra

32 > Novel developments Electrical Impedance Spectroscopy achieves similar improvement in selectivity as Temperature Cycled Operation but time scale is completely different! shifts caused by 100 ppb ethene in 1% methane A. Schütze et al.: Improving MOS Virtual Multisensor Systems by Combining Temperature Cycled Operation with Impedance Spectroscopy, ISOEN 2011 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 32

33 A. Schütze et al.: Improving MOS Virtual Multisensor Systems by Combining Temperature Cycled Operation with Impedance Spectroscopy, ISOEN 2011 > Novel developments Sensor self-monitoring with combination of TCO and EIS T-cycle EIS feature extraction feature extraction d e c i s i o n p r o c e s s discrimination classification hardware for TCO operation available at reasonable cost diagnostic yes difference no output discrimination classification d e c i s i o n p r o c e s s hardware for EIS - poor mobility - high cost - long acquisition time Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 33

34 > Novel developments MOS-IR measurement system: Gas filled chamber (9 cm length) MOS gas sensor (MICS 5131, e2v) Transmission: Thermopile (HIS A21 F4.26, Heimann Sensors) Ambient condition monitoring (p, r.h./t) Electronics controlled by a microcontroller Configuration settings set by a GUI (LabVIEW) Data evaluation offline using Matlab K. Kühn et al.: Investigations on a MOX Gas Sensor as an Infrared Source for an IR-based Gas Sensing System, IMCS 2012 Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 34

35 > Novel developments Transmission signal, f A = 6 Hz square wave mod. of the MOS gas sensor (MICS 5131, SGX) DFT magnitude Y(f A ) ² (a.u.) K. Kühn et al.: Investigations on a MOX Gas Sensor as an Infrared Source for an IR-based Gas Sensing System, IMCS 2012 Carrier gas [ppm] 1.2M 1M 1M 800k 600k Transmission signal CO 2 (Thermopile detector) CO 2 C 2 H 4 NH 3 NO NO 2 CO 0 5,000 10,000 15,000 20,000 25,000 30,000 Time (s) 75 % r.h. RT 25k 20k 15k 10k 5k 0 CO 2 [ppm] Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 35

36 > Conclusions Gas sensor systems are more than just sensors Sensors are highly sensitive, but often lack selectivity and stability especially for quantitative measurements Intelligent multisensor/dynamically operated sensor systems address existing drawbacks to broaden application spectrum Application specific development still required Field testing is a must for chemical sensor systems Hardware for combined EIS-TCO currently in field test Field tests of VOC-IDS sensor systems are starting now Chemical sensor systems are complementary to analytical techniques for Air Quality Monitoring They can become ubiquitous due to low cost and portability Gas Sensors and Sensor Systems for Air Quality Monitoring MACPoll workshop JRC Ispra 36

37 LAB FOR MEASUREMENT TECHNOLOGY Prof. Dr. rer. nat. A. Schütze Thank you for your attention. VOC-IDS