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Microplasmas: Physics and Applications

Microplasmas: Physics and Applications. Presented at the MIT Plasma Science and Fusion Center February 18, 2005 Jeff Hopwood, Northeastern University. Outline. Motivation: Applications Plasma Display Panels Micro Propulsion Micro Chemical Analysis Systems “lab-on-a-chip” others

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Microplasmas: Physics and Applications

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  1. Microplasmas:Physics and Applications Presented at the MIT Plasma Science and Fusion Center February 18, 2005 Jeff Hopwood, Northeastern University

  2. Outline • Motivation: Applications • Plasma Display Panels • Micro Propulsion • Micro Chemical Analysis Systems • “lab-on-a-chip” • others • Microplasma Devices and Physics • DC (review) • RF (inductively coupled plasma on a chip) • microwave (split ring resonator) • Summary

  3. Plasma Display Panels

  4. blue red green Plasma Display Panels (PDPs) Structure From S.S. Yang, et al, IEEE Trans. Plasma Sci. 31, 596 (2003).

  5. initiate breakdown (~ 300 volts) sustain plasma (~ 180 volts) surface + + + + + + Plasma Display Panels (PDPs) Basic Operation Sustain Electrode + + + + 100 kHz Bus Electrode h ~ 200 m l ~ 400 m d ~ 60 m From S.S. Yang, et al, IEEE Trans. Plasma Sci. 31, 596 (2003).

  6. Some plasma details of PDPs • Ne + Xe (1-10%) • Ne is a buffer gas (Eiz-Ne>> Eiz-Xe) • but neon decreases diffusion losses of Xe+ • UV production from • Xe (1s4) • Xe (1s5) • Xe2* …optically thin, desired state for UV production • produced by three-body collision: e.g., Xe* + Xe* + M  Xe2* + M • Power  ions (large sheath voltage) • excitation is only ~15% of total system power } …optically thick, inefficient

  7. PDP Cell DiagnosticsK. Tachibana, et al., IEEE Trans. Plasma Sci. 31, 68 (2003)3-D temporally-resolved emission and diode laser absorption 150 um

  8. PDP Cell DiagnosticsK. Tachibana, et al., IEEE Trans. Plasma Sci. 31, 68 (2003)3-D temporally-resolved emission and diode laser absorption Address electrode Sustain electrode side view front view Plasma decays in ~1 ms near-IR emission from Xe(2p)

  9. Modelingexample from S.S. Yang, et al, IEEE Trans. Plasma Sci. 31, 596 (2003).

  10. Issues in PDP • Efficiency • currently < 2 lumens/watt • goal: 5 lumens/watt • incandescent lamp ~ 25 lm/w; fluorescent~100 lm/w) • gases, pressure, electrodes, geometry • something more creative? control of the eedf (Rauf-Kushner)? • Phosphor degradation/MgO degradation • due to energetic Xe+ bombardment • RF sustain voltages (LG Electronics) • electrons are trapped in cell; improves eff. (~2 lm/w) • but…complex microstructure, electronics, EMI

  11. Micro Propulsion

  12. Micro Propulsion for Nanosats(autonomous satellites with a mass <10 kg) from D.L. Hitt, et al, Smart Mater. Struct. 10 (2001) 1163–1175

  13. Field Emission Electric Propulsion Taylor cone; E~109 V/m (Cs) another microplasma opportunity? Source: http://www.centrospazio.cpr.it/FEEPPrinciple.html

  14. Micro Pulsed Plasma Thruster(micro-PPT) + from Keidar, et al., AIAA Joint Propulsion Conference, Huntsville, AL, 20-23July2003.

  15. Micro Chemical Analysis

  16. (95 references)

  17. power light process gas optical spectrometer mplasma J. Eijkel, Stoeri, Manz, Anal. Chem 71, 2600 (1999) Micro Chemical Analysis • Emission Spectrometry • possibly coupled with another separation technique (e.g., GC) • Issues • pumping • stability/repeatability • lifetime/contamination • power/heat

  18. Micro Chemical Analysis - differential ion mobility spectrometry - from R.A. Miller, et al, Sensors and Act. Workshop, Hilton Head, 2000) sionex.com

  19. Micro Chemical Analysis- Issues - • Very limited success in micropump development • must operate at or near atmospheric pressure • No practical method for storage of inert gases • must operate with air or other ambient • Long term stability of physical and chemical proc. • no erosion of the microstructure • no contamination/fouling • Low power (< 1W), to be portable • Low temperature (only ambient cooling)  will return to these topics later….

  20. Other Microplasma Applicationsmedical/surgicaldecontaminationchemical factory on a chip

  21. Medical Applications RF Plasma Needle • 1 atm, He (+ air, N2, Ar) • d ~ 0.1 – 1 mm • 13.56 MHz, < 1 W • 250-500 Vp-p • Trot < 100 C, non-equil. • Plasma surgery, dentistry • Apoptosis, not necrosis E. Stoffels, et al., Eindhoven University of Technology from Plasma Sources Science and Technology (2002)

  22. Materials Processing, Point of Use Micro Chemical Factories from R. M. Sankaran and K. P. Giapis, J. Appl. Phys. 92, 2406 (2002). Also, production of nanoparticles.

  23. Microplasmas • DC • RF capacitively coupled • RF inductively coupled • microwave

  24. DC microplasmas

  25. Sputtered material Review of DC Microplasma Sources DC helium plasma on a chip. Plasmas were created in volumes as small as 50 nL. Discharge voltage ~ 800V; Starting voltage ~ 6 kV; Lifetime ~ 2 hours. + Eijkel, Stoeri, and Manz, Dept. of Chemistry, Imperial College, UK “An atmospheric pressure dc glow discharge on a microchip and its application as a molecular emission detector,” J. Anal. At. Spectrom., pp.297-300, (2000). Higher pressure  Collisional sheathes  Reduced sputter erosion

  26. Anode Cathode Cathode - 250m DC Micro Hollow Cathode Discharges • Electron confinement within hollow cathode • thermionic emission? • Lower voltage than simple capillary: 300-400 V • Increased lifetime, but still has electrode erosion • Tgas~ 2000 K • Refs: K. Schoenbach, Old Dominion University • G. Eden, University of Illinois

  27. Exploiting Electrode Erosion:DC Micro Plasma with Liquid Electrodes Pb Liquid Electrode Spectral Emission Chip Wilson and Gianchandani, University of Michigan from IEEE Trans. on Electron Dev. 49, 2317 (2003).

  28. DC Microplasma Modeling Wilson, Kolobov, Wendt, Gianchandani. meas. model

  29. DC Microplasma Modeling Strong Spatial Potential Gradient: E = 300k-400 kV/m Electron Energy Distribution has a high energy tail

  30. RF capacitively coupled microplasmas

  31. RF Micro Plasma Sources 13.56 MHz Capacitively Coupled Plasma: M. Blades, U. British Columbia from Journal of Analytical Atomic Spectrometry (2002) • 1 atm, Helium only • 1 mm plasma channel • ~ 20 watts

  32. RF inductively-coupled microplasmas (mICP)

  33. Coil H ERF S Plasma ERF Capacitive vs. Inductive • ERF is perpendicular to boundary • High voltage sheaths • ~100’s V at 13 MHz • Sputter erosion by positive ions • Low ionization efficiency • Power  sputtering, heat • ERF is parallel to the boundary • Low voltage sheaths (~10’s V) • Little sputter erosion by ions • Higher ionization efficiency • Power  ionization, excitation

  34. Hybrid package Glass wafer Interdigitated capacitor 5 mm coil Microfabricated ICP

  35. Microfabrication Process SEM of Interdigitated Capacitor Structure with 10 micron thick Au

  36. ICP Frequency Scaling Choosing a frequency that maximizes the efficiency of ionization experiment parabolic least squares fit ~ w2

  37. Maximize frequency: Coil H Glass wafer Seal Plasma E Glass tube(Chamber) Vacuum Region Frequency Scaling Model Li ZS = RS + jwLeq Power efficiency= RS / (RS+RC) … RS = 2k2LPLCRP / (RP2 + 2LP2) RS 2k2LPLC/RP if RP2>> 2LP2 …mICP RS  k2LCRP /LP if RP2 << 2LP2 ...large ICP

  38. Frequency Scaling of Miniature ICPs Electron inertia limits further improvements as w>>ne-n. w>3ne-n

  39. 3nen< w mICP Efficiency vs. Pressure (nen)constant frequency, f = 493 MHz Efficiency, % Symmetric in freq. and pressure Can we reach 1 atm?

  40. Frequency Limitation Increasing coil resistance, RC Electron Density @ 690 and 818 MHz 690 MHz 818 MHz

  41. Coil’s cross section Coil Resistance (3D FEM model)- rf current crowds to the inner and outer radii of the coil (skin effect, RC ~ f 1/2) - the crowding is asymmetric toward the center (proximity effect, RC ~ f 2). LIMITS mICP OPERATION TO f < 1 GHz

  42. Miniature ICP Frequency Scaling Poor performance at 1 atm  requires 50 W (Horiike, U Tokyo)

  43. Application Example

  44. power light process gas optical spectrometer mplasma Low pressure application of an mICP: industrial process monitor Atomic layer deposition, Chemical vapor deposition, Gas purity… detection limit: 10 ppb < DL < 1 ppm

  45. spectrometer

  46. Microwave frequencymicroplasmas

  47. Why microwave microplasma? • Microwave breakdown • Sheath scaling • Vsheath ~ 1/f 2 • Low cost cellphone power amplifier chips • 3-4 W at ~900 MHz or 1800 MHz Meek J.M. and Craggs J.D., “Electrical Breakdown of Gases”, Wiley, New York, 1978 pp 697

  48. Glass tube Glass tube Glass tube Microstrip Microstrip Microstrip Split-Ring Resonator Microplasmain argon @ 1watt @ 900 MHz 9 torr 20 torr ~ 5 mm 760 torr 100x500 mm F. Iza and J. Hopwood, IEEE Trans. Plasma Sci., Aug 2003

  49. Line Dielectric Ground Plane Discharge gap Half-wave Split Ring Resonator Operation:Surface Current Simulation at 1.0 W GAP INPUT INPUT GAP

  50. Microwave Capacitive Coupling microplasma ~ 100 mm Eg ~ 1000kV/m Eg ~ 200kV/m -Vosinwt 500 um gap 100 um gap +Vosinwt er=10.8 Cross section view Rp Top view 1/wCS 1/wCS No sputter erosion: * DC gap voltage = 0 * Vsheath ~ 1/new2 * collisional sheaths

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