1 / 17

Friction Reduction in Micro-motors using Self-Assembled Monolayers

Friction Reduction in Micro-motors using Self-Assembled Monolayers. ME 395 Project Y. Zhu, J. Gregie & P. Prabhumirashi 5 th June, 2000. SAM used in Micro-motors.

avonaco-williams
Download Presentation

Friction Reduction in Micro-motors using Self-Assembled Monolayers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Friction Reduction in Micro-motors usingSelf-Assembled Monolayers ME 395 Project Y. Zhu, J. Gregie & P. Prabhumirashi 5th June, 2000

  2. SAM used in Micro-motors Micro-motor is operating based on the electrostatic-drive principles. It’s composed of three main components: Stator, Rotor and Hub(bearing). Friction becomes a serious problem compared with the usual macroscopic situation. So, contacting parts would have a limited lifetime due to wear.

  3. SAM used in Micro-motors excitation bearing stator Micro-motor operation is based on the electrostatic-drive principles. It’s composed of three main components: Stator, Rotor and Hub (bearing). EnergyE= rotor Rotor rotation Torque

  4. Self-Assembled Monolayers (SAMs) • Surface Engineering - One of the major issues of concern. • Stiction - peeling • Friction - vertical pull-off force • Modification of Surface • Topographic Modification • Chemical Modification • Hydrogen Terminated Surfaces • fluorocarbon films • Diamond-like Carbon Coatings • SAMs

  5. Self-Assembled Monolayers (SAMs) • Introduced in 1946 by Zisman • Ordered molecular structures formed by adsorption on an active surface • Original application as building blocks for super-molecular structures • Dense and Stable structures • Applications in corrosion prevention, wear protection • Biocompatible nature • Applications in chemical and biochemical sensors • Used in semiconductor patterning • Used in transducer technology • Molecular level understanding of surface phenomena

  6. Types of SAMs • Monolayers of Fatty acids • CnH2n+1COOH type acids • Driving force is the formation of a surface salt between anion and cation • Organosilicon Derivatives • alkyloxysilanes, alkylaminosilanes • Driving force is in situ formation of polysiloxane • Organosulfur Adsorbates on Metal Surfaces • alkanethiolets on Au (111) • Multilayers of Diphosphates • Alkyl monolayers on Si

  7. Stator Rotor Ground Plane Hub Synchronous Micro-motor Schematic -Top View After Fan, et. al. (1988)

  8. Micro-motor Fabrication Silicon/Poly-Si SiO2 Si3N4 • Insulate the Si substrate • Thermal Oxide • CVD Silicon Nitride - will also act as an etch stop • Deposit polysilicon and pattern grounding plate with Mask #1 Mask #1

  9. PSG Micro-motor Fabrication Mask #2 • Deposit and pattern phosphosilicate glass (PSG) using Mask #2 • Deposit polysilicon and pattern rotors and stators using Mask #3 Mask #3

  10. Micro-motor Fabrication Mask #4 Mask #5 • Deposit an additional layer of PSG using Mask #4, to act as a spacer between the rotor and the hub. • Use PR and Mask #5 to etch PSG to form cavity for hub • RIE etch, followed by isotropic etch

  11. SAM Micro-motor Fabrication Mask #6 • Deposit polysilicon to form hub, using Mask #6 • Use BHF to remove PSG, and deposit SAMs from solution

  12. CH3 CH3 CH3 CH3 [ [ [ [ [ [ [ [ n n n n OH Si Si Si Si OH Cl O OH Cl O OH Cl O OH O O SAM deposition of alkyl-siloxanes Oxide Silicon • Oxidize surface • Native, thermal • Hydrate Surface, Hydrolysis of trichloro-silane • H2SO4:H2O2 • Covalent bonding to the surface • Cross-linking After Deng, et. al. (1995)

  13. SAM used in Micro-motors Gear ratio is defined as the ratio of the electrical excitation frequency to the rotor rotational frequency. Under ideal conditions From the figure, we can see how much the OTS monolayer reduces the friction.

  14. y U Y Fluid mechanics model SAM used in Micro-motors The torque due to the frictional forces Shear stress on the bottom of rotor The torque due to the viscous forces

  15. R1 Rc R2 SAM used in Micro-motors Governing Equation Moment of Inertia I= 0.5 M (R22-R12) Theoretical solution Geometric description Comparing this result with the experimental curve, we can get an estimate of Cd

  16. SAM used in Micro-motors Normal Load Microscratch Test: 1) approaching the surface 2) indent into sample surface by loading the tip to 0.2mN 3) translating the sample at a constant load of 0.2mN 4) translating the sample in the opposite direction at ramping loads 5) unloading of the tip to 0.2mN 6) translating the sample at constant load of 0.2mN 7) final unloading of the tip Normal Load

  17. Conclusions • SAMs provide a means of reducing stiction and friction in micro-motors. • The size and chemistry of SAMs can be controlled and optimized from friction reduction • Deposition of SAMs on wear surfaces is an inexpensive and simple process.

More Related