Chip-Scale Mass Spectrometers for Portable Gas Analyzers Luis Fernando Velásquez-García. A. I. Akinwande, K. Cheung, and L.-Y Chen.

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1 Chip-Scale Mass Spectrometers for Portable Gas Analyzers Luis Fernando Velásquez-García. A. I. Akinwande, K. Cheung, and L.-Y Chen. Microsystems Technology Laboratories (MTL) November 16 th 2010

2 Outline Introduction and Motivation Miniaturized Ionizers Double Gated Ionizer Array Gated Open Architecture Miniaturized QMFs µgripper MuSE Outline Conclusions, Current, and Future Work

3 Outline Introduction and Motivation Miniaturized Ionizers Double Gated Ionizer Array Gated Open Architecture Miniaturized QMFs µgripper MuSE Conclusions, Current, and Future Work

4 Introduction Research Main Theme Research focuses on the development of highperformance systems using micro/nano structures: Component scaling-down to achieve better performance (i.e., a specific metric in each case) Subsystems are large arrays (multiplexing) of scaled-down elements for larger total throughput Development of efficient individual flow control structures to optimize overall performance of multiplexed subsystems

5 Luis MEMS/NEMS Research K. Cheung et al, JMEMS L. F. Velasquez-Garcia et al, Nanotechnology L. F. Velasquez-Garcia et al, JMEMS Mass spectrometry L. F. Velasquez-Garcia et al, JMEMS High-Current Cathodes Chemical reactors L. F. Velasquez-Garcia et al, unpublished Hydraulics CNT Detail Accelerator Extractor Multiplexed Electrospray 4 um SiC Langmuir Probe Array 100 um Nanosatellite Systems 2 µm L-Y. Chen et al, IEDM CNT-enabled devices

6 Opportunity: Miniaturized Analytical Instruments 100X smaller 1000X less vacuum Mass Spectrometer Chip-Scale System Goal: Miniaturize analytical hardware to enable portability while conserving good performance (resolution, mass range, speed, low false-positive rate)

7 Miniaturized Rugged Analytical Instruments Many Exciting applications for low-cost miniaturized GC/MS/IMS: Wikipedia Threat Environmental Airport security Space Exploration Detection monitoring

8 Scaling-Down MS Scaling Down MS Size and power consumption dictated by working pressure: > Largest dimension of MS Scaling-down with MEMS technology enables: Higher-pressure operation (decreased mean free path) Lower-power (relaxed pumping requirements) Portability (reduced size and weight) Mass production for low-cost (batch-fabrication)

Current Field Portable MS KORE MS-200 Inficon HAPSITE

3 cm3 46 x 43 x 18 cm3 48.8 x 48.8 x 53.

9 Current Field Portable MS KORE MS-200 Inficon HAPSITE Griffin lb. 42 lb. 96 lb x 32.8 x 21.3 cm3 46 x 43 x 18 cm x 48.8 x 53.6 cm AMU (TOF) AMU (QUAD) AMU (CIT) 2.5 hours (30 W battery) 2-3 hours (30 W battery) Needs 600 W Power 5 minutes / analysis < 10 minutes / analysis few minutes / analysis

10 MIT s Micro Gas Analyzer Technical Approach Gas Molecules Ions Filtered Ion Inlet Ionizer Array Lens Mass Filter Lens Detector Array Vacuum Pump CNT-based Ionizers Quadrupole Mass Filter Electrometer/Microbalance Species Sensor Positive Displacement Pump

11 MIT s Micro Gas Analyzer MIT s Micro Gas Analyzer

12 Outline Introduction and Motivation Miniaturized Ionizers Double Gated Ionizer Array Gated Open Architecture Miniaturized QMFs µgripper MuSE Outline Conclusions, Current, and Future Work

CNT-based Ionizers Technical Approach We exploit two types of ionization: Field Electron Impact Ionization Field Ionization Two distinctive

13 CNT-based Ionizers Technical Approach We exploit two types of ionization: Field Electron Impact Ionization Field Ionization Two distinctive implementations: Arrays of Double-Gated isolated CNTs (closed architecture) Sparse CNT forests on porous substrate with a proximal gate (open Architecture)

14 CNT-based Ionizers Hardware

15 Double Gated Ionizer Array Fabrication Characterization CNTs PR Coating First oxide film Etch gate Aperture First Gate Etch Oxide

16 Double Gated Ionizer Array Fabrication Characterization Silicon Oxide Device L-Y. Chen et al, IEDM 2007 Schematic

(µfoam) and catalyst diffusion (no lithography required) 3D packaging

17 CNT-based Gated Open Architecture Ionizer PECVD CNTs (high field factor) Ionizer Schematic Sparse CNT growth using microstructures (µfoam) and catalyst diffusion (no lithography required) 3D packaging to provide a suspended global gate (increased flux of gas molecules and device yield)

18 Gated Open Architecture Fabrication Characterization Extractor Spring Extractor Insulation Main Body 1 cm µfoam Device Schematic L. F. Velasquez-Garcia et al, JMEMS 2010

19 High Voltage 3D MEMS Packaging Assembly Schematic Test Structure SEM of Assembly B. Gassend et al., JMEMS 2009 MEMS spring system allows robust and precise (micronlevel biaxial accuracy, submicron repeatability) High Voltage operation (5 kv) has been demonstrated

20 Gated Open Architecture Fabrication Characterization

21 CNT-based Ionizers Ionization Mode

22 Electron Impact Ionization E F - F Electron Tunneling Impact Ionization - - V D r G Flux of electrons to the surface E c φ F Transmission of electrons through the barrier (FN) r<<g, D E f e- Field emitter (FE) Field Emission Process

23 Electron Impact Ionization

24 CNT-Based Ionizers (EII) IV Characteristics (ions, electrons) I.-to-E. Current vs. Pressure Max. Ionization Efficiency ~ 5% Fabricated Devices 5 mtorr operation µa-level electron current

25 CNT-Based Ionizers (EII) CNT-Based Ionizers (EII) IV Characteristics (ions) Ionization Efficiency vs. Pressure Max. Ionization Efficiency ~20% Fabricated Devices 21 mtorr operation ma-level electron current

26 Field Ionization E F φ Isolated Vacuum Level I- φ I Molecule Near metal surface & Electrosta9c Field Electron Tunneling E F φ CNF Tip ~2 nm I Molecule Electric Field β eff ~r -1, F min ~1 x 10 8 V/cm Higher bias voltage than field emission Opposite polarity compared to field emission

27 CNT-Based Ionizers (FI) CNT-Based Ionizers (FI) IV Characteristics (ions) Ion Current vs. V -1 Fabricated Devices Same EII Device in Reverse Polarity works as Field Ionizer Less Fragmentation Products A-level Ion Current

28 CNT-Based Ionizers (FI) Velasquez-Garcia et al., MEMS 2008 Fabricated Devices Ion Current vs. V -1 Same EII Device in Reverse Polarity works as Field Ionizer Less Fragmentation Products 10-8 A-level Ion Current

29 Outline Introduction and Motivation Miniaturized Ionizers Double Gated Ionizer Array Gated Open Architecture Miniaturized QMFs µgripper MuSE Outline Conclusions, Current, and Future Work

30 MEMS Mass Filters Technical Approach MEMS based linear quadrupoles Two distinctive implementations: QMF with circular rods (µgripper) QMF with square rods (MuSE Round Electrode QMF Square Electrode QMF

31 QMFs Principle of Operation Mass Filtering The Mathieu Equation describes particle dynamics: Resonant (detected) ion Non-resonant (filtered out) ion

32 QMFs Stability Regions Trade-off between transmission and resolution between stability regions I and II

33 MIT s QMFs MEMS QMFs µgripper Velasquez-Garcia et al., JMEMS 1.44 MHz, First Stability Region QMF down to 250 µm rod diameter using a MEMS 3D packaging technology. L/D Dynamic range > 650 amu ΔM < 0.7 amu (FSR), 0.4 amu (SSR) Peaks are smoother! 2.0 MHz, Second Stability region, air

34 µgripper Structure Spacer Rods Spring Spring Spring Spring Ions Electrode Region Spacer Cross-section Top Wafer Lower Middle Wafer Upper Middle Wafer Bottom Wafer Top view focused at Top wafer Top view focused at Middle Top wafer Top view focused at Middle Top wafer -backlight

MEMS QMFs and Batch Fabrication S. Taylor et al. M.G.

(electrode rod length) 2 Long cylindrical rods can not

35 MEMS QMFs and Batch Fabrication S. Taylor et al. M.G. Geear et al. L.F. Velasquez-Garcia et al. Reported MEMS QMFs require serial downstream assembly Performance of a quadrupole is proportional to (electrode rod length) 2 Long cylindrical rods can not be microfabricated We are missing a key point in MEMS! (also some applied math)

36 Micro-Square Electrode (MuSE) QMF BOUNDARY VALUE PROBLEM! Ideal quadrupole term Higher-Order, non-ideal terms

37 MuSE QMF Highlights 3D Schematic Ion Trajectories Simulation Cross-Section Cheung et al., JMEMS 2010 Fabricated Device

38 MuSE QMF Mass Range NIST Library Spectra for FC-43

39 MuSE QMF Operation in Second Stability Region 4.0 MHz, SR1 3.0 ev, 50 amu V pp = 73 Volts, U pp = 14 Volts 2.0 MHz, SR2 5.0 ev, 50 amu V pp = 78 Volts, U pp = 40 Volts

40 MuSE QMF Lens Operation First Stability Region -3 Volts Second Stability Region -6 Volts Optimization of Inlet Lens voltage improves QMF resolution

41 Outline Introduction and Motivation Miniaturized Ionizers Double Gated Ionizer Array Gated Open Architecture Miniaturized QMFs µgripper MuSE Outline Conclusions, Current, and Future Work

42 Conclusions, Current, and Future Work Using micro- and nanotechnology, we have developed (with different degree of maturity) the subsystems of a portable MEMS/NEMS MS: CNT-based Ionizers QMFs Species sensors Pump Current research efforts are focused on the integration of the MS and the development of MEMS-enabled portable vacuum systems

43 MEMS Displacement Pumps

44 MIT s Chip Scale Vacuum Pump Mechanical rough pump followed by two stages of ion pumps Rough pump and ion pumps are separated by valves

CNT-based gas ionizers with integrated MEMS gate for portable mass spectrometry applications

CNT-based gas ionizers with integrated MEMS gate for portable mass spectrometry applications The MT Faculty has made this article openly available. Please share how this access benefits you. Your story