Transcript midterm presentation..

NOVEL SPATIAL LIGHT PHASE MODULATOR
WITH BI-DIRECTIONAL TILT-PISTON MICROMIRROR ARRAY
Authors:
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. Fujita
Fujita 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
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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
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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 of control flexibility
 These devices reported so far, need relatively
complicated fabrication process; This Report
proposed a novel SLPM which realizes a
simple fabrication process
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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
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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
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Schematic of Proposed Novel SLPM
A novel structure of one dimensional SLPM that consists of:
1) micromirror array on an SOI wafer
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2) ITO (Indium Tin Oxide) electrodes on a glass plate
Principle of Operation
Each micromirror can exhibit bidirectional single-axis
rotation, as well as up- and down translation motion
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Silicone on Insulator (SOI) Wafer
•低耗能
•低操作電壓
•高運作效率
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Silicone on Insulator (SOI) Technology:
Most popular Produced Method
400-600C reaction
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.
Smart Cut process
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
SIMOX process
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Indium Tin Oxide (ITO) Electrode/
Front ITO Process
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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
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Device Design: Math. Model
Torsion bar was designed so that the 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
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larger than the half of the wavelength of the input optical beam)
Device Design: Modal Analysis
The resonant
frequency of mode 1 is
122 kHz and that of mode
2 is 147 kHz;
that means high speed
response below 10 μs
can 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)
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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:
1) 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
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2 μm (W) × 30 μm (L).
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
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Fabrication Process: ITO Wires
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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
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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
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into angle
Conclusions
 This Paper states a novel structure of SLPM that;
1) 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;
1) The State of the art of SLPM Technology
2) An typical MEMS development process
-- Conceptual study
-- Device Design and Simulation
-- Fabrication Process settlement
-- Experimental Design and data analysis
3) Some popular and emerging MEMS related technology learnt in the
class has been reviewed, which are including; SOI, BOX, ITO electrode
and DRIE…etc.
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Reference
(1) O. Solgaard and K. Yu, “Microoptical phased arrays for spatial
and spectral switching”, Proc. of SPIE, vol. 4755, pp. 1-9, 2002
(2) 陳啟文∗ 陳韋旗 “絕緣層上矽分析及應用” Volume 32, pp.103115, Minghsin Journal, August 2006,
(3) 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
(4) “SPECIAL REPORT SOI Wafer Technology for CMOS ICs
Robert Simonton, President, Simonton Associates
(5) Wikipedia for: DRIE, SOI, BOX, ITO electrode, SLPM
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