Ultra Low Power Gas Sensing for Health and Environmental Tracker (HET) TestbedStudents: Steven Mills, Daniel Schulman, Alexander Tellado, Michael Lim
Post-docs: Dr. Oren Z. Gall, Dr. Xiahua Zhong
PIs: Veena Misra, Bongmook Lee, Theresa Mayer and Thomas Jackson
Institutions: North Carolina State University and Penn State University
1
Testbeds: HET Block Diagram
Smart Phone
IOIO
Signal Processing
User Interface
Radio
ASSIST CustomTechnologies
Antenna
Power Management
SPI
RADIO
Battery
Sensors
SPIMSP SOC
Breakout Board
Antenna
Power Management
SPI
RADIO
Battery
Sensors
SPIMSP SOC
Breakout Board
CHEST PATCH w/ breakout sensor boards
WRISTBAND w/ breakout sensor boards
Aggregator
Hydration
ECG
Pulse Ox
Accelerometer
Ozone Sensor
Humidity/ Temp Sensor
Pulse Ox
Accelerometer
Microphone
Cloud Storage
Signal Processing
CustomizedOff the Shelf Technologies
Ozone sensor for HET 1.0 2
Metal oxide sensors have good response to gases but suffer from high power and poor specificity
Ozone gas sensors based on metal oxides are commercially used in industrial and automotive
applications
Gas sensor typically operate at temperatures >200 C with the use of microheaters. Power
consumption can reach well over 10 mW
*Spa
nnha
keJ.
Sen
sors
200
6 6,
405
-419
Thin-film based ozone sensor with integrated micro heater
Miniaturization of gas sensors for ubiquitous applications
Most thin film sensors require significant heating
Sensaris
Futurlec
3
Research Goals driven by HET Specifications for Gas Sensing Ultra Low Power ~ 100microwatts
ALD Nanowires ALD nanofilms with room temperature operation Self heating or UV erase
Specificity towards targeted gases (Ozone vs. NO2 vs. CO) Temperature enhanced specificity Filters against ozone E-nose pattern matching
Sensitivity down to 25ppb Nanofilms and nanowires FET approaches
Reversibility at low power levels UV erase Self heating
4
ASSIST Gas Sensing Strategy
Materials
Low Power Sensitivity
Specificity Multi-gas VOCResponse
Time
Sensing Mechanism Systems
Repeatability
Resonant based CMUTs
Field Effect Transistors
Resistance BasedHeterogeneous Field Assisted assembly
Multichannel CMUT
Metal Oxides Nanofilms and
Nanowires
Polymer Coatings
Top Down Arrays
5
5-20nm ALD (tetrakis dimethylamino tin) + H2O + ozone= SnO2
400C 30 min crystallization anneal
10 nm Ti/150 nm Au
Testing Teledyne T700U Ozone generator
Keithley 4200
Characterization and Analysis Sensitivity based on slope of response
Selectivity against NO2 and CO
(top left) Optical image of electrodes and 3D model of sensor (top right) XDS analysis of film (bottom) low and high resolution STEM images showing device structure and film crystallinity
Nanofilms: ALD SnO2 can enable thicknesses down to the Debye length resulting in increased sensitivity
66
Nanofilms: Post processing leads to crystallization of ultrathin SnO2 films 200C deposition temperature Linear deposition rate Rutile crystal phase after 400C anneal
7
Sensing Power consumption
Slope of R correlated with O3 Concentration Response magnitude linearly correlated with ozone concentration
0 1000 2000
20200
20400
20600
20800
21000
21200 O3 Concentration24% RH
Res
ista
nce
()
Time (s)
Room Temperature Response to O3
0
50
100
O3 C
once
ntra
tion
(ppb
)40 50 60 70 80 90 100 110
0.7
0.8
0.9
1.0
1.1
1.2
Sen
sitiv
ity, d
R/d
T (
/s)
O3 Concentration (ppb)
Rate of Change for Room Temperature O3 Exposure
24% RH
Nanofilms: Quantification of R with ozone concentration has been achieved
9
Year 2 SWOT related to Gas Sensing
Attention to sufficient selectivity is lacking in metal oxide gas sensors
Response: we have used two routes to address selectivity
10
Selectivity @ Room temperature
100ppb NO2
Selectivity Towards Gases Using Organic Filters
Improvement in real time detection and selectivity of phthalocyanine gas sensors dedicated to oxidizing pollutants evaluation. Brunet J. et al Thin Solid Films (490) 1 2005 pp.28
Glass or SiO2
GateAl2O3
ZnO
Al2O3
75 nm of a thin film of Indigo dye is deposited over the entire device.
Exposed open active area: no filter
Ozone is expected to be filtered by the indigo film before reaching the ZnO interface
Indigo dye molecule
12
Indigo films prevent ozone from diffusing to sensor surface
Stable ZnO TFT ozone sensor with low power UV sensor reset with
Nanowire Metal-Oxide Sensors
High performance, low-power metal-oxide nanowire sensors Optimal sensitivity when
operated between 100 C to 250C
High surface-to-volume ratio gives enhanced sensitivity
Joule heating for low power dissipation of 10s W per sensor
O2(g)+ 2e- 2O-(s) CO(g)+O-(s) CO2(g)+ e-
Depleted Conducting (n-type)
Power Dissipation
Sensing Mechanism
14
Cross-Reactive Nanosensor Array
Monolithic integration of multiple nanosensor types on CMOS readout and processing circuitry Discrimination through classification of sensor array response On-chip response amplification and signal conditioning
http://lnbd.technion.ac.il/NanoChemistry 15
Metal-Oxide/Si Core-Shell Nanowires
Batch fabrication of metal-oxide nanosensors Optimize process for each
type of metal oxide Uniform and highly
reproducible dimensions High-quality metal-oxide
shell with low impurities and defects
Mechanically robust with intrinsic Si wire core
600nm
Si core ALD MOX shell
1. Deep reactive ion etching of Si wires2. Atomic layer deposition of MOX shell3. Thermal crystallization of MOX shell
under optimized conditions16
Optimized Metal-Oxide Synthesis
Different high-temperature annealing conditions are required to crystallize amorphous metal-oxide shell to optimize sensitivity to target environmental pollutants
30 nm TiO2 shell Anneal: N2 600C, 10 min
30 nm SnO2 shell Anneal: N2 600C, 10 min
30nm SnO2Anneal: O2 650C, 1 hour
anatase rutile rutile
International collaboration with Osaka U (2014) 17
Field-Assisted Directed Assembly
Localized regions of highest field intensity within patterned depressions provide high-yield nanowire assembly with registration to predefined features on the CMOS chip
Dielectrophoretic Force: FDEP E2
log(E2)Top view
Cross section through well
18
Field-Assisted Directed Assembly
Localized regions of highest field intensity within patterned depressions provide high-yield nanowire assembly with registration to predefined features on the CMOS chip
Top view
Cross section through well
Video
19
15 nm SnO2 Shell Sensor Response
Sensitivity to CO of
Uniformity of SnO2 and TiO2 NanosensorsDevices Diameter Variation in Resistance Reference
50 In2O3 nanowire
chemiresistors10nm 45% Zhang, et al.
55 Si nanowire FET 20nm 106% Jin, et al.
40 ITO nanowire resistors 20nm 108% Wan, et al.
30 TiO2 coated nanowires30nm TiO2 coated,
260nm dia.18% this work
30 SnO2 coated nanowires 30nm SnO2 coated,
260nm dia.15% this work
[i]. Zhang, D., Liu, Z., Li, C., Tang, T., Liu, X., Han, S., Lie, B., Zhou, C. Detection of NO2 down to ppb levels using individual and multiple In2O3 nanowire devices. Nano Lett. 4, 1919-1924 (2004)[ii]. Jin, S., Whang, D., McAlpine, M., Friedman, R., Wu, Y., Lieber, M. Scalable interconnection and integration of nanowire devices without registration. Nano Lett. 4, 915-919 (2004)[iii]. Wan, Q., Dattoli, E., Fung, W., Guo, W., Chen, Y., Pan, X., Lu, W. High-performance transparent conducting oxide nanowires. Nano Lett. 5, 2909-2915 (2006) 21
Highlight Organic EDLC Powered SnO2 Nanosensor Measurement of supercapacitor
discharge current in response to 400 ppm CO exposure
Low power regulator supplies stable operating voltage and demonstrates system level integration with wearable platforms
Supercapacitor energy density = 4J/cc ~40 wires can run for 10min Leakage current
GEN I - Monolithic Integration on CMOS
Prototype CMOS 32 x 32 multiplexer with three metal interconnect layers fabricated by Lincoln Labs foundry for back-end nanosensor assembly and integration
CMOS design Calhoun group, UVA
FESEM image
23
Back-End Nanosensor Integration
Process compatible with single-wire sensor test structures and back-end integration on CMOS
Assemble nanowires
Pattern contacts
Deposit contact metal
Vias to CMOS access
transistor
On-Chip Assembly
24
Integration of 15 nm SnO2 Sensors on CMOS
Comparing the I-V characteristics of an 15 nm SnO2 nanowire sensor when the access transistor is open and closed confirm circuit operation
0 0.5 1-5
0
5
10
15
20
25
Vin (V)
Iin (
A)
OpenWire PresentWire Present90 nm PDK Simulation
Linear Saturation
Circuit used to electrically address individual metal-oxide nanowire sensors N2 at 25C
25
Integration into HET 1.0: SnO2 Nanofilm Sensors
ASSIST Ozone sensor with HET26
Benchmarking ASSIST Low Power ozone sensors
Gas MaterialTem
pSensing range Method
Response time
structure Type
humidity selectivity Ref
O3 CoPc RT20-200
ppb conductometric 5min100 nm
film organic SC N/A O3 over NH3 [30]
O3 SnO2-CNT RT 20 ppb conductometric 4 min compositeMOx
hybrid N/A N/A [33]
O3 In2O3 RT20-2400
ppb conductometric 16/75 min5 m
porous film MOx 20~40% N/A [35]
O3 SnO2-CNT RT 20 ppb conductometric 3/20 min200 nm
filmMOx
hybrid Zero Air N/A [37]
O3 ZnO-InOx RT16-2300
ppb conductometric 10 min 1 m film MOx Zero Air N/A [40]
O3 SnO2 RT 58 ppb conductometric 1/20 min100 nm
film MOx Zero Air N/A [41]
O3 ZnO RT30-600
ppb conductometric 2 min100 nm
NW MOx Zero Air N/A [42]
O3Poly-
butadiene RT 28-50 ppb frequency shift 4 min tuning fork Polymer N/A N/A [43]
O3ALD SnO2
RT 20-300 ppb conductometric 1 min 7 nm film MOx Zero AirOnly Sensitive
to O3
NCSU ALD based ozone sensors provide highly sensitive (20 ppb) with very fast response time and only sensitive to ozone.
27
Summary Nanofilms of ALD SnO2 provide room temperature ozone
sensing with power levels of 100nWatts and recovery via UV erase
Selectivity of sensors has been achieved by i) room temperature operation of SnO2 nanofilms and ii) use of organic filters
Nanowires were integrated with CMOS for cross-reactive nanosensor arrays
ALD nanofilm SnO2 sensors have been packaged and delivered to HET Testbed team
Future work: Reducing nanowire diameter and UV free recovery of gas sensors
28
Preliminary results towards UV free recovery using SnOx nanotiles
Thermal CVD process: Graphite/SnO2nanoparticle mixture heated to 900C
Substrate located downstream of furnace
0 1000 2000 3000 4000 5000 6000 7000 8000 900011500
12000
12500
13000
13500
14000
14500
15000
15500
16000
16500
AirAirAirAirAirAirAirAirAirAirAir
10 ppb O3
10 ppb O3
20 ppb O3
30 ppb O3
40 ppb O3
50 ppb O3
60 ppb O3
70 ppb O3
80 ppb O3
90 ppb O3
Air
Res
ista
nce
()
Time (s)
100 ppb O3
UV free recovery at RT Reducing response to ozone Very high sensitivity to O3 at RT Possibility: p-type SnOx films
29
Thank you
30
Scaling to Smaller Nanosensors
=1E-8W/nmK-1,L=300nm, S=(RNW2-RSi2)=2E4nm2 , S*=2RNWL=8E5nm2,T=T-T0 =100K
Pmetal 4S T/L~280W
Pgas 0
S*T~20W
Prad~S*(T4+T3T0+T2T02+TT03-4T04)
References
[1] Appl. Phys. Lett. 93, 123110 (2008)
[2] Sensors and Actuators B 77 (2001) 496-502
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[7] IEEE SENSORS JOURNAL, VOL. 12, NO. 5, MAY 2012
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[20] Sensors and Actuators B 54 (1999) 202 209
[21] Sensors and Actuators B 124 (2007) 111117
[22] Sensors and Actuators B: Chemical(2012)[23] Nanotechnology 2008, 19, 175502
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[28] Sensors and Actuators B 110 (2005) 5465
[29] Sensors and Actuators B 130 (2008) 589593
[30] Sensors and Actuators B 159 (2011) 163 170
[31] Sensors and Actuators B 146 (2010) 2834
[32]IEEE Transactions on Nanotechnology, VOL. 10, NO. 5, SEPTEMBER 2011
[33] Journal of Physics: Conference Series 307 (2011) 012054[34] Thin Solid Films 520 (2011) 966970[35] Thin Solid Films 520 (2011) 918921[36] J. Mater. Chem., 2012, 22, 6716
[37] Sensors and Actuators B 170 (2012) 67 74
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[39] Sensors and Actuators B 168 (2012) 8 13[40] Vacuum 86 (2012) 495e506
[41] Sensors and Actuators B 176 (2013) 811 817[42] small 2012, 8, No. 21, 33073314[43] Sensors 2009, 9, 5655-5663
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[45] Sensors and Actuators B 181 (2013) 77 84
[46] Sensors and Actuators B 183 (2013) 20 2432
Uniformity of SnO2 and TiO2 NanosensorsDevices Diameter Variation in Resistance Reference
50 In2O3 nanowire
chemiresistors10nm 45% Zhang, et al.
55 Si nanowire FET 20nm 106% Jin, et al.
40 ITO nanowire resistors 20nm 108% Wan, et al.
30 TiO2 coated nanowires30nm TiO2 coated,
260nm dia.18% this work
30 SnO2 coated nanowires 30nm SnO2 coated,
260nm dia.15% this work
[i]. Zhang, D., Liu, Z., Li, C., Tang, T., Liu, X., Han, S., Lie, B., Zhou, C. Detection of NO2 down to ppb levels using individual and multiple In2O3 nanowire devices. Nano Lett. 4, 1919-1924 (2004)[ii]. Jin, S., Whang, D., McAlpine, M., Friedman, R., Wu, Y., Lieber, M. Scalable interconnection and integration of nanowire devices without registration. Nano Lett. 4, 915-919 (2004)[iii]. Wan, Q., Dattoli, E., Fung, W., Guo, W., Chen, Y., Pan, X., Lu, W. High-performance transparent conducting oxide nanowires. Nano Lett. 5, 2909-2915 (2006) 33
TiO2 Nanosensor Response Benchmark
Type Sensitivity tresponse
(minutes)
trecovery
(minutes)
Temp.
(C)
[H2] (ppm) Reference
Nanotube 3 20 16 180 1000 Varghese, et al.
Thin film 2.5 1.5 NA 250 1000Ren, et al.
Thin film 19 0.3 NA 370 5000Tang, et al.
Nanotube 26 30 30 150 1000Sennik, et al.
Nanowire 25 29 15 175 1000 This work[i]. Varghese, et al. Adv. Mater. 15, 624-627 (2003)
Ren et al. Sens. Actua. B 148, 195-199 (2010)[ii]. Tang et al. Sens. Actuat. B 26, 71-75 (1995)[iii]. Sennik, et al. International Journal of Hydrogen Energy 35, 4420-4427 (2010)
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Ultra Low Power Gas Sensing for Health and Environmental Tracker (HET) TestbedTestbeds: HET Block DiagramMetal oxide sensors have good response to gases but suffer from high power and poor specificityResearch Goals driven by HET Specifications for Gas SensingASSIST Gas Sensing StrategyNanofilms: ALD SnO2 can enable thicknesses down to the Debye length resulting in increased sensitivityNanofilms: Post processing leads to crystallization of ultrathin SnO2 filmsALD nanofilms of SnO2 can sense ozone at room temperature resulting in significant savings in power consumptionNanofilms: Quantification of R with ozone concentration has been achievedYear 2 SWOT related to Gas SensingNanofilm sensors exhibit intrinsic selectivity towards Ozone at room temperatureSelectivity Towards Gases Using Organic FiltersIndigo films prevent ozone from diffusing to sensor surfaceNanowire Metal-Oxide SensorsCross-Reactive Nanosensor ArrayMetal-Oxide/Si Core-Shell NanowiresOptimized Metal-Oxide SynthesisField-Assisted Directed AssemblyField-Assisted Directed Assembly15 nm SnO2 Shell Sensor ResponseUniformity of SnO2 and TiO2 Nanosensors Highlight Organic EDLC Powered SnO2 Nanosensor GEN I - Monolithic Integration on CMOSBack-End Nanosensor IntegrationIntegration of 15 nm SnO2 Sensors on CMOSIntegration into HET 1.0: SnO2 Nanofilm SensorsBenchmarking ASSIST Low Power ozone sensorsSummaryPreliminary results towards UV free recovery using SnOx nanotiles Thank youScaling to Smaller NanosensorsReferencesUniformity of SnO2 and TiO2 Nanosensors TiO2 Nanosensor Response Benchmark
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