E-MRS SPRING MEETING 2006

1. E-MRS SPRING MEETING 2006 SnO2:Sb – A new material forhigh-temperature MEMS heater applications –performance and limitations A. Helwig, J. Spannhake, G. Müller Corporate Research Center – EADS Deutschland GmbH T.Wassner, M.Eickhoff Walter Schottky Institute, Technical University of Munich, Germany G.Sberveglieri, G.Faglia C.N.R. – INFM & Università di Brescia 29th of May 2006, Nice, France

2. Microsystems & Electronics CRC Germany SnO2:Sb – A new material forhigh-temperature MEMS heater applications –performance and limitations • Outline • IR emitter device – a high-temperature heater application • Employing SnO2:Sb as high-stability heater material • Performance & Limitations of SnO2:Sb metallisation • Liftetime estimation of SnO2:Sb based MEMS heater devices

3. T-Sensor Heater NearInfrared Design & concept of IR emitter device Hotplate design parameters: Chip surface 5 x 5 mm2 Suspended membrane 1.5 x 1.5 mm2 Membrane thickness 6 µm Length of suspensions 350 µm Width of suspensions 150 µm Emissivity 0.8 – 0.9 Operating temperatures 800 – 1200 °C Heating power 0.8 – 1.4 W operating emitter at ~T=1000 °C bonded emitter chip on TO8-carrier

4. Pt Pt Front side: Dry etching(STS) Backside: Wet etching (TMAH) SiO2 Fabrication of thermal IR emitter device • State of the art: SOI-based Hotplate Technology • Platinum is standard heater metallisation. Si • Pt heater lifetime at • T =600°C: ~10 years  What is the performance of Pt at higher T ?

5. Pt High-temperature test of emitter hotplates • Long-term stability at T ~ 850°C limited by Pt heater degradation • Thermal expansion mismatch • Electro-migration due to the high electric current + high temperature.  Alternative heater materials?

6. High-stability semiconductor heater material: SnO2:Sb Doped tin oxide SnO2:Sb Resistivity of SnO2:Sb as a function of Ta and Sb concentration. • good substrate adherence • an oxide cannotsuffer from oxidation • high-temperature stable • (Ta ~ 1050°C) • very little electro-migration • patterning by IBE and lift-off Advantages: • SnO2:Sb metallisation: • E beam evaporation ofSnO2powderwith an admixture of antimony • best conductivity at Ta~1050°C DepositedSnO2:Sb patterned by lift-off

7. SnO2:Sb • XRD measurements of deposited & annealed SnO2/Sb layers Thermal Activation of Dopant Sb SnO2  best resistivity at 1050°C • Optical absorption spectra of annealed SnO2 and SnO2/Sb layers

8. Pt heater SnO2:Sbheater Performance of SnO2:Sb as metallisation • Accelerated degradation tests of different metallisations • SnO2:Sb exhibits no degradation up to T ~1000 °C • Instability at lower T due to adsorption/desorption effects at the SnO2:Sb surface.  Long-term stability of SnO2:Sb heater ?

9. Degradation of Platinum and SnO2:Sb heaters Long-term stability of heater metallisation Pt heater after 32h at ~800°C SnO2:Sb after 18h at ~1000°C • Clear signs of degradation visible in hotspot areas. • Transmission microscopy reveals loss of Pt in these areas.

10. XPS Results: Loss of Sb dopants at T > 1050°C Thermal stability limitation of SnO2:Sb Loss of conductivitydue to high temperature annealing No current flow!

11. Thermaldegradation rate depending on T Activation energy for degradation EA ~ 9.45 eV EA ofthermal degradation Allows to compare performance and to estimate heater lifetime Activation energies for degradation of SnO2:Sb Ea could not be obtained with accelerated degradation testsdue to residual gas sensing effects

12. Si:B heater SnO2:Sb heater Pt heater Performance of heater metallisations • Activation energies for heater degradation • SnO2:Sb performs betterthan metals and silicides: • Little electro-migration! • No Oxidation problems!  EA allows estimating emitter life time

13. Estimated lifetime at T ~ 950°C: 10 years Life time estimation for heater materials • Emitters operated with DC voltage in ambient air Next Step  Verification of lifetime estimation!

14. Verification of lifetime estimation • Long-term durability test of heater metallisation inside a sealed tube with ambient air. Heater degradation test about 7 weeks  lifetime estimation has been approved!

15. Conclusion: • SOI-based micro heaters with standard metallisation long-term-stable up to T ~ 600°C • By introducing SnO2:Sb as heater material:Long-term stable operation can be extended up to T ~ 1000°C SnO2:Sb employed as heater metallisation- superior performance at high temperatures - reduced electromigration effect - no oxidisation problems - realized with standard technologies Wide Range of Potential Applications  - using SnO2:Sb as heater metallisation

16. Widerange of applications for high temperature MEMS WG n°C • Operating at T ~1000°C • Low Power supply • Long Lifetimes thermal infrared emitter Ionisation detector Leakage & Fire detection Detection ofdrugs & explosives Hydraulic Fluid Life Monitoring System NDIR & Light scattering Photo-Acoustic Gas Sensing Ion Mobility Spectroscopy Ion-Mobility-Spektrometer

17. Microsystems & Electronics CRC Germany THANK YOU FORYOUR ATTENTION! SnO2:Sb – A new material for high-temperature MEMS heater applications – performance and limitations A. Helwig, J. Spannhake, G. Müller Corporate Research Center – EADS Deutschland GmbH T.Wassner, M.Eickhoff Walter Schottky Institute, Technical University of Munich, Germany G.Sberveglieri, G.Faglia C.N.R. – INFM & Università di Brescia

18. SnO2:Sb Based Area Heater Elements • Previous design optimized for metallic heater materials. Disadvantage: High resistivity of SnO2:Sb (~4500µWcm) causes operating voltages of 100-120Vfor 1000°C operation. Solution: New Emitter designfeaturing a SnO2:Sb area heater contacted by Pt metallisations • New heater resistance: 130 W (Old: ~8kW) • Operating voltages < 24 V sufficient to obtain T > 1000 °C