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The Materials and Fabrication Techniques Used to Reduce Them

TRIBOLOGY CONCERNS IN MEMS DEVICES. Guide-PROF.S.CHAKKA presented by-SHAIKH JAWED. The Materials and Fabrication Techniques Used to Reduce Them. TRIBOLOGY ON THE MICROSCALE. Surface Contact Surface Roughness Interfacial Forces Adhesion Friction Wear Models

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The Materials and Fabrication Techniques Used to Reduce Them

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  1. TRIBOLOGY CONCERNS IN MEMS DEVICES Guide-PROF.S.CHAKKA presented by-SHAIKH JAWED The Materials and Fabrication Techniques Used to Reduce Them

  2. TRIBOLOGY ON THE MICROSCALE • Surface Contact • Surface Roughness • Interfacial Forces • Adhesion • Friction • Wear • Models • Environmental Effects

  3. Surfaces • Interfacial Forces • Capillary Forces • Electrostatic Forces • Van der Waals Forces asperities • Adhesion • Friction Surface Contact

  4. Wear Wear debris identified as amorphous oxidized silicon with no polysilicon.

  5. Adhesive • Low contact pressures • Augmented asperities • Abrasive • High contact pressures • Wear tracks Wear Mechanisms

  6. Environmental Effects on Wear • Humidity • Volume of wear debris • Morphology of wear debris

  7. Diamond has a variety of useful properties compared to Silicon • Low wear, low coefficient of friction, thermally stable, isotropic hardness • Diamond cannot be simply made into smaller and smaller flakes, then deposited on MEMS devices • Diamond (or diamond-like) film must be grown on surface. Diamond Coatings

  8. Methane (CH4) is introduced as a plasma in a PECVD process. • The disassociated carbon ions deposit on the MEMS device. • Under correct conditions, the carbon atoms form a diamond-like film. Conventional CVD

  9. Tribological properties better than silicon are achieved, but it’s not an ideal solution: • Low uniformity • Non-constant density • Amount of impurities and crystal growth suffers if dissociation is incomplete. If coating isn’t uniform, predicting failure is difficult and surface finish suffers. Results/Problems of Conventional PECVD Diamond Films

  10. A “better” method for producing diamond-like films. Grain size is 2-5nm. • Unlike conventional diamond film CVD, C60 is introduced into the reaction along with CH4. • C60 collides with itself, creating C2 (carbon “dimers”) • These C2 molecules enter the diamond lattice. • An abundance of C2 is the goal of the UNCD creation process. UNCDULTRANANOCRYSTALLINE DIAMOND

  11. Properties more like natural diamond • Method allows for uniform coating • Very little residual stress. Benefits of UNCD vs. Conventional CVD

  12. Coating Uniformity Lack of internal stress allows for free-standing structures. Demonstration Surface Finish Comparison

  13. Deposition O O O Si Si Si Si O O O O OH OH OH OH Si Si Si Si Si Si Si Si O O O O O O O O Self Assembled Monolayers (SAMs) • Two Types • Silane – deposits on silicon • Thiol – deposits on gold • Deposition Formations • Densely Packed • Amorphous Structure • Functional group determines: • applications • hydrophilicity/hydrophobicity • Used as: • binders for subsequent molecules • lubricants • Common hydrophobic SAMS: • OTS (long chain hydrocarbon) • FDTS (long chain fluorocarbon)

  14. Step 1: Deposit SAM layer of 3-mercaptopropyl trimethoxysilane (-SH terminus) • Step 2: • Oxidize SAM layer • Forms -SO3H terminus • Step 3: • Deposited Ceramic layer • ZrO2 in the presence of HCl • Y2O3 in the presence of urea Interstitial SAMs for Deposition

  15. Cantilever Beam Array Technique Beam Structures • Cantilever beams are fabricated of different lengths • Cantilevers are put into contact with surface • Longer beams adhere to surface • Longest beam that does not stick signifies adhesion force • SAM coated beams adhere after longer lengths than oxide surface Results

  16. Silicon Oxide Post Apparatus Proof Mass FDTS Covered Post Proof Mass Wear Results Proof Mass

  17. Electrostatic Lateral Output Motor Relative humidity can determine if failure occurs from Wear or Stiction

  18. Cantilevers in Contact Mode Friction Test Adhesion Test • Tests materials at the nanoscale • Cantilever tips are silicon nitride Results

  19. Friction and Wear are the biggest issues in blocking advances of MEMS technology • Once SAMS and Diamond Coatings are more fully developed, MEMS technology will be able to more completely realize its potential. Conclusion

  20. www.falexint.com • www.wikipedia.org • lqme.sjtu.edu.cn • www.tribology-abc.com • Design of machine elements- V.B BHANDARI • Fundamentals of Tribology-Basu, Sengupta, Ahuja Reference

  21. THANK YOU…

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