Mems stiction and anti stiction


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Mems stiction and anti stiction

  1. 1. Faculty of Electrical Engineering and Computer Science Master of Electronics Engineering (MScEE) MMM MEMS Stiction and Anti-StictionReferentKhalil Ahmed Rashid 6. July 2012333690 - Microsystems
  2. 2. Structure1. Introduction to MEMS2. MEMS Sensors and Actuators3. Failure Mechanisms in MEMS4. Stiction Effect on MEMS5. Creteria for Stiction in Microstructures6. Remedy or Anti-Stiction Procedures7. Stiction effect on Graphene8. Conclusion9. References Referent: Khalil Ahmed Rashid 2
  3. 3. MOTIVATION (SMART PHONE BOARD)MEMS sensors growth: from $ 3.55B in 2009 to $ 7.91B in 2015.Referent: Khalil Ahmed Rashid Reference: 3
  4. 4. Introduction to MEMS Micro Electro Mechanical Systems Size between 1 to 100 umMiniature devices formed bycombining mechanical parts andelectronic circuits, mostly on asemiconductor chip, withdimensions of millionths of a meter. Referent: Khalil Ahmed Rashid Reference: 4
  5. 5. MEMS Sensors & Actuators Sensors: Pressure Sensors Proximity Sensors Image Sensors Accelerometers Air bag crash sensors Active suspension systems Antilock brake systems Ride control systemsReferent: Khalil Ahmed Rashid 5
  6. 6. MEMS Sensors & Actuators Used for output or processing and produce some physicalActuators: changes. Microphones Fuel injection nozzles Inkjet print heads Gyroscopes Electrostatic Resonators Thermal actuators Magnetic actuators Reference: ,Referent: Khalil Ahmed Rashid 6
  7. 7. FAILURE MECHANISMS IN MEMS Stiction Effect Bonding between dissimilar materials Thermal cycle Shock & vibration Humidity  Radiation Moving parts at resonanceReferent: Khalil Ahmed Rashid 7
  8. 8. STICTION EFFECT The moving parts of micromechanical machines tend to seize up under the forces of Unintentional sticking and friction. Adhesion It is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. Reference: Khalil Ahmed Rashid Change/MIT-Harnesses-Void-to-Nix-Friction-in-MEMS-/ 8
  9. 9. STICTION TWO STAGES Release Related Stiction It occurs during the process of the sacrificial layer removal in fabrication of microstructures, and such Stiction is caused primarily by capillary forces. In Use Stiction Adhesive attractions exceed restoring forces. Surfaces permanently adhere to each other causing device failure. Accures due to high Humidity and Temperature. Reference: Khalil Ahmed Rashid tandard/2005/aug/a3/a3.html 9
  10. 10. STICTION CATEGORIESMechanical Collapse Induced by Capillary ForceDue to fabrication ofsuspended elements in MEMS.If etching is performed in aliquid environment, a liquidbridge will be formed betweenthe suspended member and thesubstrate, when the liquid isremoved during a dehydrationcycle, yielding an attractivecapillary force which may besufficiently strong to make itcollapse. Referent: Khalil Ahmed Rashid 10
  11. 11. STICTION CATEGORIESContact Stiction and Peel NumberStiction due to movable MEMS microstructures to thesubstrate.Peel number: proposed by Mastrangelo and HsuIt is the ratio of elastic strain energy stored in the deformedstrip to the adhesion between the strip and the substrate.If Np > 1, will not stick to substrateIf Np < 1, will stick to substrate Referent: Khalil Ahmed Rashid 11
  12. 12. STICTION CATEGORIESWhen the gap between contilever and sustrate is fewStiction by van der Waals and Casimir Forcesmicrometers then there is an adhesion force called CasimirForces. Casimir force has been associated with van derWaals forces.Van der Waals: a < lamda A = sepration Lamda= retardation lengthCasimir Force : a >~ lamda between ground to excited state Referent: Khalil Ahmed Rashid Reference: 12
  13. 13. ANTI-STICTION IN MEMSReducing Release Related StictionTexturing the surfaces to reducethe contact area like periodicarray of small supporting post,commonly known as "dimples"can be introduced. By effectively reversing the shape of the water meniscus which forms underneath microstructures during the drying process. This effect can be quantified by measuring the water contact angle on these surfaces. Referent: Khalil Ahmed Rashid Reference: 13
  14. 14. ANTI-STICTION IN MEMS Reducing In Use Stiction 1. Using surface roughening and surface coating with low surface-energy materials. 2. By reducing friction between microstructures.  Self-assembly mono-layers(SAMs) coatings.  Diamond-like carbon (DLC) coatings. Reference: Khalil Ahmed Rashid carbon-coatings-14476-871121.html 14
  15. 15. ANTI-STICTION IN MEMS Reducing In Use Stiction (conti…) 3. Eliminate the need for large input signals (or mechanical probing) in the start-up phase in micro- engines. 4. Better packaging for environments (thermally stable to 400~ in various, including oxygen containing)Referent: Khalil Ahmed Rashid 15
  16. 16. ANTI-STICTION IN MEMS Graphene and NANO-Technology (Future of MEMS) The lubrication effect is depends on the number of layers of graphene in the graphite. More layers means better lubrication. Reference:Referent: Khalil Ahmed Rashid promises-better-lube-for-nano-machines 16
  17. 17. Referent: Khalil Ahmed Rashid 17
  18. 18. CONCLUDING REMARKS The extremely high surface-to-volume ratio of MEMS makes interfacial Stiction, friction and wear significant factors in determining device reliability. MEMS proved to be a break through technology because of many possible applications in almost every field. These important problems must be solved in best way for production of reliable and long lasting MEMS.Referent: Khalil Ahmed Rashid 18
  19. 19. References1. Maboudian R, Ashurst WR, Carraro C. Tribological challenges in micromechanicM systems. Tribol Lett, 2002, 12(2): 95~1002. Ashurst WR, Yau C, Carraro C, et al. Alkene based monolayer films as anti-stiction coatings for polysilicon MEMS. Sensors Actuators, 2001, A91(3): 239~2483. Ashurst WR, Yau C, Carraro C, et al. Dichlorodimethylsilane as an anti-stiction monolayer for MEMS: A comparison to the octadecyltrichlosilane self-assembled monolayer. J Microelectromech Syst, 2001, 10(1): 41~494. Li QY, Yu SW. A model of computation of elastic and plastic contact considering adhesion effect. Int Y Nonlinear Sci Numerical Simulation, 2002, 3(3-4): 599~602 Zhao YP.5. Morphological stability of epitaxial thin elastic films by van der Waals force. Arch Appl Mech, 2002, 72(1): 77~846. Zhao YP, Li WJ. Surface stability of epitaxial elastic films by the Casimir force. Chin Phys Lett, 2002, 19(8): 1161~11637. Serry FM, Walliser D, Maclay GJ. The role of the casimir effect in the static deflection and stiction of membrane strips in micromechanical systems (MEMS). J Appl Phys, 1998, 84(5): 2501~25068. Johnstone RW, Parameswaran M. Theoretical limits on the freestanding length cantilevers produced by surface micromachining technology. J Micromech Microeng, 2002, 12(6): 855~861 19
  20. 20. Q&A Thanks for your attention !Khalil Ahmed Rashid 20