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Atomic Layer Deposited Alumina for Micromachined Resonators

Atomic Layer Deposited Alumina for Micromachined Resonators. Y. J. Chang, K. Cobry, and V. M. Bright University of Colorado, Department of Mechanical Engineering, Boulder, USA Refer from: MEMS 2008, Tucson, AZ, USA. Team : Cheng-Yi Lin ( 林政毅 ) Yen-Po Lin ( 林諺伯 ) Date: November 11, 2008.

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Atomic Layer Deposited Alumina for Micromachined Resonators

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  1. Atomic Layer Deposited Alumina for Micromachined Resonators Y. J. Chang, K. Cobry, and V. M. Bright University of Colorado, Department of Mechanical Engineering, Boulder, USA Refer from: MEMS 2008, Tucson, AZ, USA Team:Cheng-Yi Lin (林政毅) Yen-Po Lin (林諺伯) Date: November 11, 2008

  2. Outline • Abstract • Introduction • Resonator • Atomic Layer Deposition • Fabrication • Measurement of Micor-resonators • Displacement • Frequency • Conclusion

  3. Abstract • Atomic layer deposited (ALD) aluminum (Al2O3) as the material for micro-resonator • A pinned-pinned beam model with axial stress of 250MPa is used • Higher modes of the resonator were observed

  4. Introduction (I) : Resonator • Device with a vibratory nature response • Application : Sensors of pressure, mass, or force with high resolution • Material : Silicon, Aluminum nitride… • Method : Chemical vapor deposition (CVD), Atomic layer deposition (ALD)…

  5. Atomic Layer Deposition Alumina • Used on structure with high ratio and irregular geometries • High quality • Pinhole free • Uniform • Deposited at low temperature Advantage

  6. Deposited Method (A) (B) 1. Precursor is introduced into the viscous flow reactor 2. A precursor (trimethyl aluminum) is purged form the chamber with nitrogen 3. B precursor (water) reacts with all of the available sites on the A layer that is introduced 4. B precursor is purged from the chamber with nitrogen 5. Again this step until the film is of the desired thickness

  7. AB binary surface reaction sequence for ALD

  8. Fabrication Process of ALD-based Resonator Cr 5nm Al2O3 85nm Deposit 5 nm Cr by e-beam evaporation Etch Al203 in 5％ HF (37s) Remove PR AZP 4210 Spin coat PR AZP 4210 Release Al2O3 structure by isotropic silicon etch with SF6 plasma Coat 85 nm Al2O3 on Silicon Etch Cr in CR-7(13s) Pattern and develop PR AZP 4210

  9. Fabrication Process 550 um 5nm 85nm Figure 4 SEM image of ALD Al2O3 micro-resonators

  10. Measurement (I): Displacement • Clamped-clamped model • Pinned-pinned model • Distributed transverse electrostatic force H Zo Z

  11. Experimental Results • Theoretical and experimental results of displacement vs. voltage of ALD Al2O3 micro-resonator • Measured and theoretical calculated profiles of the micro-resonator with different applied voltages

  12. Measurement (II): Frequency • Resonant frequency

  13. Experimental Results • Theoretical and experimental data of resonance modes

  14. Conclusion • Micromachined ALD Al2O3 resonators had been demonstrated • High quality thin film • Nano-scale resonator • Displacement and resonant frequencies have been calculated by pinned-pinned beam model • Axial stress in the resonators of 250MPa is determined by fitting the experiment data

  15. Reference • [1] G. Stemme, “Resonant silicon sensors”, J. Micromech.Microeng., vol. 1, pp.113-125, 1991. • [2] A.N. Cleland, M. Pophristic, and I. Ferguson, “Single-crystal aluminum nitride nanomechanical resonators”, Appl. Phys. Lett., vol. 79, pp.2070-2072 2001. • [3] N. D. Hoivik, J.W. Elam, R.J. Linderman, V.M. Bright,S.M. George, and Y.C. Lee, “Atomic layer deposited protective coatings for micro-electromechanical systems”, Sensors and Actuators A, vol. 103, pp. 100-108 2003. • [4] M. K. Tripp, C. Stampfer, D.C. Miller, T. Helbling, C.F. Herrmann, C. Hierold, K. Gall, S.M. George, and V.M. Bright, “The mechanical properties of atomic layer deposited alumina for use in micro- and nano-electromechanical systems”, Sensors and Actuators A, vol.130-131, pp. 419-429, 2006. • [5] M. K. Tripp, C.F. Herrmann, S.M. George, and V.M. Bright, “Ultra-thin multilayer nanomembranes for short wavelength deformable optics”, in Proc. of MEMS’04, Maastricht, The Netherlands, Jan. 25-29, 2004, pp. 77-80. • [6] B. Hälg, “On a nonvolatile memory cell based on micro-electro-mechanics”, in Proc. of MEMS’90, Napa Valley, California, Feb. 11-14, 1990, pp.172-176. • [7] S. D. Senturia, Microsystem Design, Kluwer Academic Publishers, Massachusetts, USA, 2001. • [8] R. D. Blevins, Formulas for Natural Frequency and Mode Shape, Van Nostrand Reinhold Co., New York, USA, 1979. 390

  16. Thank you for your attention

  17. Q & A Time

  18. Comparison of ALD and CVD ALD • Highly reactive precursors • Precursors react separately on the substrate • Precursors must not decompose at process temperature • Uniformity ensured by the saturation mechanism • Thickness control by counting the number of reaction cycles • Surplus precursor dosing acceptable • CVD • Less reactive precursors • Precursors react at the same time on the substrate • Precursors can decompose at process temperature • Uniformity requires uniform flux of reactant and temperature • Thickness control by precise process control and monitoring • Precursor dosing important

  19. Po • Need to compensate the bending when stress is present • The form of the polynomial

  20. Types of Loads Distributed Load F q Point Load • Types of Support Free Fixed Pinned Pinned on Rollers

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