Repositionable Liquid Micro-Lenses With Variable Focal Length (1’st presentation)

1. Repositionable Liquid Micro-Lenses With Variable Focal Length (1’st presentation) Institute : 奈微所 Name : 楊志誠 Student ID: d9635804

2. Outline • Introduction • Theory • Design and Fabrication • Experimental Results • Conclusion 同質量的液體以球形的表面積最小 因此水珠通常以球形式存在 這樣才符合自由能最小化的自然法則 [MIT John W. M. Bush (April 2004).]

3. Introduction • Surface Tension • Weight scales as L3 and surface tension scales as L1 • Hence weight decreases more rapidly than surface tension • Hence insects can walk on water and coins can float on water

4. Method of Microfludic Transfer Micro-fludic Transfer Centrifugal Force Pressure Gradient Capillary 毛細效應 Electric-Field Magnetic Electro-Osmosis 電 滲 Electro-Wetting 電 潤 濕 Dielectrophorsis 介電泳

5. Theory - No moving parts - 電 潤 濕 (Electro-wetting) 介 電 泳 Dielectrophoresis (DEP) 電 滲 Electro-osmosis

6. Theory (Electro-Wetting) :Lippmann-Young Equation(1875) ε 為真空中的介電係數 εr為介電材料的電介質 t 為介電材料的厚度 r 為 表面張力 低消耗功率及高速之微流體/液滴系統計與作分析 國家科學委員會補助專題研究計畫 NSC91－2218－E－007－043－

7. Paper Contribution : 1.None of old approaches have allowed lateral lens with high accuracy positioning 2.Lens diameter : 700μm Electrodes width : 100 μm Positioning accuracy : 100μm

8. Design and Fabrication Process Flow : a) Photo-resist structure starting 525μm thickness by HF etching b) The grooves are filled with ITO using lift-off c) The system covered with 800nm SiO2 layer d) The barrier grid is etched into SiO2 e) The droplet contact is sputtered onto the wafer using lift-off Note:透明導電電極技術（indium tin oxide，簡稱 IT O，氧化銦錫）

9. Experimental Results Movement & No movement: 1.Voltage Pulse amplitude 2.Voltage Pulse width Condition: Grid: 100μm mesh 300nm depth The electrodes are covered by a dielectric layer (800nm PECVD silicon dioxide)

10. Experimental Results (continue) Lippmann´s Equation & “Lens maker’s formula” D: diameter of the micro-lens n: refractive index U: Voltage Volume : 1.9 nl • The turning range is in focal length is roughly two times initial focal length • Increasing the voltage U therefore increases the focal length [2]

11. Conclusion • Precise positioning and focal tuning of liquid micro lens • Achieved 100 μm high-resolution positioning control with the need for large numbers of electrodes • Successfully using voltage pluses (pluses width & High) control liquid movement with the resolution of grid spacing

12. Thank you for your attention!

13. Reference [1] Modeling of Electrowetting Surface Tension for Addressable Microfludic System: Dominant Physical Effects,Material Dependences,and Limiting Phenomena, 2003,IEEE,Bennjamin Shapriri et. al.,UCAL,USA [2} OPTICAL CHARACTERIZATION OF REPOSITIONABLE LIQUID MICRO-LENSES, IEEE,2007,p2573-p2576 [3] Equilibrium and dynamic behavior of micro flows under electrically induced surface tension actuation forces Fortner, N.; Shapiro, B.;MEMS, NANO and Smart Systems, 2003. Proceedings. International Conference on20-23 July 2003 Page(s):197 - 202 [4]. B. Shapiro, H. Moon, R. Garrell, and C. J.Kim, "Equilibrium Behavior of Sessile Drops under Surface Tension, Applied External Fields, and Material Variations," Journal of Applied Physics (to appear), 2002. [5]. www-math.mit.edu/~bazant/talks/NU06.ppt [6]. www.physics.harvard.edu/~tomhunt/present/mrs_sf_apl04.ppt [7]. www.math.umd.edu/~dio/RIT/Biomem/Shapiro-RIT-15March07.pdf [8] Marc Madou, Fundamentals of Microfabrication, chapter 9, CRC Press, (1997). [9] Gregory T.A. Kovacs,Micromachined Transducers Sourcebook, chapter. 9, pp.845 McGraw- Hill,(2000).

14. Appendix Micro- & Nanofluidics Electrical Instrumentation Microelectronics Micromaterial Department of Microsystems Engineering 15 Professor University of Freiburg,Germany Process Technology Systems Theorie Simulation Design of Microsystems Micro-actuators Micro-optics http://www.imtek.de/

15. “Induced-Charge Electro-osmosis” = nonlinear electro-osmotic slip at a polarizable surface Bazant & Squires, Phys, Rev. Lett. 92, 0066101 (2004). Example: An uncharged metal cylinder in a suddenly applied DC field Same effect for metals & dielectrics , DC & AC fields… www-math.mit.edu/~bazant/talks/NU06.ppt

16. Scale Law Analysis

17. + - + + Review of Dielectrophoresis (DEP) conducting cover slip electric field lines microfluidic chamber suspended particle micropost to RF voltage source www.physics.harvard.edu/~tomhunt/present/mrs_sf_apl04.ppt

18. Review of electrowetting www.math.umd.edu/~dio/RIT/Biomem/Shapiro-RIT-15March07.pdf

19. 氣─固─液界面的三角關係 當液體潤濕固體表面時，原本氣─固的界面被液─固的界面所取代，而氣─固與液─固之界面張力的差，稱之為「濕潤張力」。當氣─固的界面張力大於液─固的界面張力時，也就是固體和液體間的吸引力大於固體和氣體間的吸引力時，固體和氣體間的界面張力會將液─固界面拉伸。換句話說，被濕潤的固體表面有較低的界面張力，因此液體會在固體表面擴張。 當液體滴在固體表面上時，固體表面和液滴切線的夾角，就是所謂的接觸角。假使接觸角小，如水滴在玻璃基板上的情形，表示液體易濕潤固體表面。但是，如果接觸角像水銀液滴在玻璃基板上那麼大，代表液體不易濕潤此表面。而濕潤張力和接觸角的關係，可以用楊格方程式（Young's equation）表示：氣─固與液─固界面張力的差等於氣─液界面張力乘上接觸角的餘弦函數。考慮兩種極端的情形，當接觸角為 0 度時，表示液體能完全的濕潤於固體表面；當接觸角為 180 度時，代表液體完全不能濕潤於固體表面。 從固─氣的界面張力觀點來看，當接觸角越小，餘弦函數（cosθ）會越大，固─氣的界面張力也會越大，此時表示固體表面較易被濕潤。而當接觸角越大，固─氣的界面張力越低（如鐵氟龍），代表越不易被濕潤。 液滴在表面的接觸角示意圖。上圖為疏水性的接觸；下圖為親水性的接觸。

20. Surface tension • Represented by the symbol σ, γ or T, is defined as the force along a line of unit length • Where the force is parallel to the surface but perpendicular to the line. A soap bubble balances surface tension forces against internal pneumaticpressure. a needle floating on the surface of water. Its weight, fw  , balanced by the surface tension forces on either side, fs  , Water striders using water surface tension when mating.

21. Surface and body force

22. SURFACE TENSION http://www.online-tensiometer.com/oberfl/frame_oberfl_values.html