Instructor: Dr. Cheng Hsien Liu Reported by: Student// Jiuun-Hwa (Tony) Horng

1. NOVEL SPATIAL LIGHT PHASE MODULATORWITH BI-DIRECTIONAL TILT-PISTON MICROMIRROR ARRAYAuthors: Fujitsu Laboratories Ltd.: S. Yamashita, T. Yamamoto, M. Kawai The Japan Aerospace Exploration Agency: M. Mita CIRMM, Institute of Industrial Science, The University of Tokyo: H. FujitaFujita Adamant Kogyo Company Ltd., JAPAN: M. Yano(Reference: Transducers & Eurosensors ’07/ 3B3.4) Class Presentation_I Instructor: Dr. Cheng Hsien Liu Reported by: Student// Jiuun-Hwa (Tony) Horng Date: April/ 16th/ 2008

2. Agenda • Introduction • State-of-the-Art of Proposed novel SLPM • Concept of Optical Wavefront Control • Operation Principle of SLPM • Schematic of SLPM • Device Design & Fabrication Process • Experimental Results & Conclusions • References

3. Introduction • Optical MEMS based on scanning mirrors are widely commercialized, spatial light phase modulator (SLPM) will play crucial roles in such applications as: • Scanning Display • Fiber Switch and Coupling • optical wavefront control • femto-second pulse shaping • tunable filters • Barcode Reader…etc. • MEMS-based SLPM shows good performance in terms ofcontrol flexibility • These devices reported so far, need relatively complicated fabrication process; This Report proposed a novel SLPM which realizes a simple fabrication process

4. Agenda • Introduction • State-of-the-Art of Proposed Novel SLPM • Concept of Optical Wavefront Control • Operation Principle of SLPM • Schematic of SLPM • Device Design & Fabrication Process • Experimental Results & Conclusions • References

5. Concept of Optical Wavefront Control <λ/2 Equilibrium conventional liquid crystal phase shifter MEMS-Based SLPM MEMS-based SLPM shows good performance in terms of control flexibility because the micromirror array can form smooth phase profile by bidirectional rotation and translation motion

6. Schematic of Proposed Novel SLPM • A novel structure of one dimensional SLPM that consists of: • 1) micromirror array on an SOI wafer • 2) ITO (Indium Tin Oxide) electrodeson a glass plate

7. Principle of Operation Each micromirror can exhibit bidirectional single-axis rotation, as well as up- and down translation motion

8. Silicone on Insulator (SOI) Wafer • 低耗能 • 低操作電壓 • 高運作效率

9. Silicone on Insulator (SOI) Technology:Most popular Produced Method The Smart Cut™ method developed by the French firm Soitec which uses ion implantation followed by controlled exfoliation to determine the thickness of the uppermost silicon layer. SIMOX - Separation by IMplantation of OXygen - uses an oxygen ion beam implantation process followed by high temperature (1100-1175 deg C) annealing to create a buried SiO2 layer 400-600C reaction SIMOX process Smart Cut process

10. Indium Tin Oxide (ITO) Electrode/Front ITO Process

11. Agenda • Introduction • State-of-the-Art of Proposed Novel SLPM • Concept of Optical Wavefront Control • Operation Principle of SLPM • Schematic of SLPM • Device Design & Fabrication Process • Experimental Results & Conclusions • References

12. Device Design: Math. Model • Torsion bar was designed so thatthe ratio of kt / kp had the optimized value • The ROC was 6.1 m in case of type A, whereas 0.4 m in case of type B. • The estimated driving voltages to rotate 0.1 degree were 55 V and 240 V • These results indicate that the thinned torsion bar is effective for decreasing the driving voltage and avoiding mirror warpage • The gap between the mirror and ITO electrode was set the gap 3 μm to match the wavelength of 1.55 μm widely used in optical communication (designed 3 times larger than the half of the wavelength of the input optical beam)

13. Device Design: Modal Analysis • The resonant frequencyof mode 1 is 122 kHz and that of mode 2 is 147 kHz; that means high speed • response below 10 μscan be realized. • It is estimated that the maximum rotation angle of 2.0 degree and displacement of 0.8 μm can be achieved with driving voltage up to 250 V. (the results of modal analysis using Intellisuite)

14. Fabrication Process: MicroMirror Array titanium tungsten • SOI wafer: 9.5-μm-Si / 4-μm-BOX/ 400-μm-substrate • The fabrication process of the micromirror array: • With Two step DRIE process, the torsion bar thickness was decreased from 9.5 μm to 2 μm. (The thinned suspension decreases driving voltage to avoid warpage of the mirror surface) • The micromirror array composed of 11 mirrors. The size of two types micromirror is 12 or 28μm (W) × 300 μm (L) and that of the torsion bar is 2 μm (W) × 30 μm (L).

15. Fabrication Process: DRIE Process • DRIE stands for Deep Reactive Ion Etching and is a dry etch micromachining method used to create deep, steep-sided holes and trenches in wafers • The use of ICP (inductively coupled plasma) allows for extremely high silicon etch rates using standard Cryo. and Bosch processes: • Cryogenic is a single step process done at cryogenic temperatures <-100 °C. • Bosch is a cycling two-step process altering between deposition and etch steps done at 10-20 °C • DRIE is currently the only etch method that can give a high etch rate, good mask selectivity, high aspect ratio, and vertical anisotropic etching required by many of today's MEMS processes. • Modern DRIE's have the following capabilities: - High aspect ratios (up to 50:1) - Deep etching (10μm-700μm) - High etch rate (4-20μm/min) - High selectivity (70-150:1 for resist,100-200:1 for oxide masks) • - Anisotropic and isotropic etches +/- 0.5deg sidewall angle control

16. Fabrication Process: ITO Wires

17. Agenda • Introduction • State-of-the-Art of Proposed Novel SLPM • Concept of Optical Wavefront Control • Operation Principle of SLPM • Schematic of SLPM • Device Design & Fabrication Process • Experimental Results & Conclusions • References

18. Experimental Results • Fig.10) Observed interference patterns, and calculated its rotation angle and displacement from the interval of these patterns. (wavelength of the light=408 nm) • Fig.11) Measured the temporal response • of the mirror to a triangular wave by laser Doppler vibrometer (LDV). Measured the displacement of the edge in width and the • middle in length of the mirror, and converted into angle

19. Conclusions • This Paper states a novel structure of SLPM that; • its mirror can exhibit bidirectional single-axis rotation, as well as • up- and down- translation motion. • 2) Investigated the optimum dimentions for realizing the device; Found that the structure having thinned torsion bars could avoid the warpage of the mirror surface. • 3) The device was fabricated by quite a simple process, and • 4) verified its motion experimentally. • The measured data for both tilt and piston motions were in good agreement with the simulated data. • What have learnt from this paper; • The State of the art of SLPM Technology • An typical MEMS development process -- Conceptual study -- Device Design and Simulation -- Fabrication Process settlement -- Experimental Design and data analysis • Some popular and emerging MEMS related technology learnt in the class has been reviewed, which are including; SOI, BOX, ITO electrode and DRIE…etc.

20. Reference • O. Solgaard and K. Yu, “Microoptical phased arrays for spatial and spectral switching”, Proc. of SPIE, vol. 4755, pp. 1-9, 2002 • 陳啟文∗ 陳韋旗 “絕緣層上矽分析及應用” Volume 32, pp.103-115, Minghsin Journal, August 2006, • 黃士豪助理教授, “微機電系統與製程簡介” 國立台灣海洋大學機械與機電工程學系 • “SPECIAL REPORT SOI Wafer Technology for CMOS ICs Robert Simonton, President, Simonton Associates • Wikipedia for: DRIE, SOI, BOX, ITO electrode, SLPM

21. ~ The End ~ Thanks for your Attention !!