12月8日(水)10:50-11:30

MEMSミラーと集積化

東北大学 工学研究科
羽根 一博

内容

１．集積型MEMSミラーについて
２．LSIと集積した波長選択スイッチ用MEMSミラー積
波長選択３．Si連続メンブレン デフォ マブルミラ の開発状況
３．Si連続メンブレン-デフォーマブルミラーの開発状況

ホームシアター
ホムシアタ
データプロジェクター

マイクロミラー（ＤMD）ディスプレイの光学系
ボード
プロセッサーメモリー

投影レンズ

マイクロミラー
レンズ
色フィルタ

スクリーン

レンズ
白色光源

https://youtu.be/qOsibeDX8jM

マイクロミラー（ＤMD）ディスプレイの構造

マイクロミラーとありの足マイクロミラー（ＤMD）ディスプレイの内部構造

マイクロミラーの構造と動作
ミラー

ミラー支持柱 ねじれバネ

電極
ヨーク

ねじれバネ支持柱

電極柱

金属：アドレスパッド

20μm

接触
サイト
バイアス
リセットバス

マイクロミラーの構造

SRAMへマイクロミラーの動作原理
入射光+帯電とクーロン力+力のモーメント： L=F・ r

マイクロミラーの機械構造

ねじれねじれフックの法則

F=kx

ねじれのフックの法則

L = kθ θ（L 力のモ メント θ：回転角）（L:力のモーメントθ 回転角）

集積回路の微細加工技術

One-Megapixel Monocrystalline-Silicon Micromirror Array on CMOS Driving
Electronics Manufactured With Very Large-Scale Heterogeneous Integration
F. Zimmer, M. Lapisa, T. Bakke, M. Bring, J. MEMS 20(3)(2011)564-572 Fraunhofer InstitutePACKAGING OF 11 MPIXEL CMOS-INTEGRATEDSIGE MICRO-MIRROR ARRAYS A Witvrouw et.al. IMEC, Philips Applied Technologies, ASML
MEMS 2009 136
136-139
139

CMOS-INTEGRABLE PISTON-TYPE MICRO-MIRROR ARRAY FOR ADAPTIVEOPTICS MADE OF MONO-CRYSTALLINE SILICON USING 3-D INTEGRATIONM Lapisa, F Zimmer, F Niklaus, A Gehner, G Stemme Royal Institute of Technology, Fraunhofer Institut MEMS (2009) 1007-1010

Transducers 13 pp. 2505-2508

波長選択スイッチ（MEMSグレーティング)
MEMS gratings

Movable ribbons

250
0 ribbons

MEMS gratings

Lens
L
24 channels

MEMS chip
LSI chip

Ribbon MEMS

Output fiber

MEMS grating:
9μm wide, 1μm space
Input fiber
400μm long, 250 ribbons
1μm‐3μm gap
Outputp fiber

GratingAnamorphicprism

Optical network
in town

光ビーム走査の原理
Incidentlight

MEMS gratings250 ribbbons

MiMirror

Reflectedlightnπ

24 channels

Si gratings

DividedmirrorsnπMEMS chip
Movable grating
LSI chipπ
DividedDi
id d mirrors
iwithithequivalent phase

制御用LSIの設計

Date inputt and conD
ntrol term
minalsAddress register

Address selector

Serial-parallel
Si lll lconverter

MemoryDAconverter

Parallel-serial
converter
DA convertertregisterElectrodes for
MEMS gratings

製作プロセス
Si

SiO2

SixNy

AlSpacer(c) SOI wafer bonding(f) Si patterning

Polymer BOXSiO2
LSI wafer
SiO2

AlVi

(g) Polymer etching

GND(d) Polymer filling

Pad for bonding(a) Photolithography ,SiN etching(h) Wire bonding(b) PPolymerl& spacer ddeposition
iti ,Patterning

Channel grating

Au wire直径 2.6µm (e) Si etching , SiO2 etchingVi
Pad for bonding

GND

製作したLSI
25 mm

122.5 mmElectrodes ffor signal control

Alignment marks

Electrodes for movable grating
24 channels

Memory and DAC

Supporting partfor MEMS
grating mirrors

Voltage output by program

100μmElectrodes for grating

Memory and DAC

8 inch wafer

LSI上に製作したSiグレーティング

Memory and DAC
Grating

1cm
100μm
Silicon grating on LSI circuit

LSI上に製作したMEMSグレーティング

Z [μm]

Y [μm]

LSI上に集積したグレーティング

グレーティングの光学顕微鏡写真＊一部にポリマー接合が不十分であるが、グレーティングは精度よく製作できた＊ガラス上に製作したグレーティングで見られた凹凸も解消された

200400200

400

600 X [μm]

グレーティングの高さ分布電圧印加時のグレーティング変位測定
グレーティング形状測定： 下部電極に５Vを印加し800nmの変位が得られた
電圧未印加

５V印加時

0.5zz[μm]0-0.5-1

グレーティングを交互の2レベルに動作させた場合の形状測定：
グ
グを交ベ動作さ た場合
状 定 おおよそ目標の断おお
標 断面形状へと変化させることができた
200z[nm]0-200-400

矢印部のグレーティングに5Vの電圧を印加（マイコンの不具合により印加できていない部分がある）

応答速度測定
グレーティングの動的特性をレーザードップラー振動計を用いて測定した
測定

Trigger voltage

Grating• ピークの時間
ピ時 ：30μs• 収束時間：70μs

LSIによるSiグレーティングの動作

OperationOti off addressed
ddd ribbons
ibbof grating

Switching
Sit hi iin
diffraction pattern

Experimental demonstration by T. Suzuki and T. Sasaki

MEMS-DM – Main design We p
proposepa new structure membrane MEMS-DM by
y combining
g wafer bonding
gprocess and Si/HfO2 Bimorph spring array

1. HfO2 crystallization-induced stress is used to introduce large air gap.
2. Relatively soft spring structure (small spring constant) instead of fixed posts is used
to increase the stroke
stroke.
3. High optical quality mirror surface is guaranteed by single-crystal-silicon membrane.
25

MEMS-DM – Inter-actuator coupling
pto chose the inter-actuator couplingp g of the mirror actuator at adjacentj
It is importantactuator.
We considered an approximated model for analytic calculation of the influencefunction. As the inter-actuator coupling is defined as the ratio of the deflection of thepixel adjacent to the actuated pixel to that of the actuated pixel, thus, in the coordinate
shown in Fig. 1, the inter-actuator coupling IC is given byy x l /2552 EIkl 3  1152 E 2 I 2  6k 2l 6IC y x 3l /2 1260 EIkl 3  1152 E 2 I 2  13k 2l 6

(EI is the flexure rigidity)

Calculation model of the continuous membrane DM

The calculated inter-actuator coupling for the previous bimorph spring structure:
59%. The measured inter-actuator coupling is 51%.

26

MEMS-DM – Si/HfO2 Bimorph spring
The out-of-planeout of plane deflection needed to be checked to determined the length of thebimorph spring using in DM.

27

MEMS-DM – Si/HfO2 Bimorph spring
Fabricated bimorphp spring
p g
HfO2Sit1=0.2μm
t2=1.0μm

200μm

Microscope image

密着性がよい28

MEMS-DM – Si/HfO2 Bimorph spring: out-of-plane deflection
Before Crystallization

After Crystallization
Measured by Confocal laser scanningmicroscope

Ｎｏ

Length(μm)

Deflection(μm)

Curvatureradius(mm)

1100

9 29
9.29

0 538
0.538

2100

10.06

0.497

3100

8.65

0.578

4100

8.78

0.56

Averange
Curvatureradius(mm)

0.545

ＮＮｏ

Length(μm))

D fl ti ( )Deflection(μm)

Curvatureradius(mm)
di ()

1100

34.44

0.145

2100

33.13

0.150

3100

33.70

0.148

4100

33.59

0.148

5200

130.46

0.153

6200

133.80

0.149

7200

132.64

0.150

8200

130 54130.54

0 153
0.153

Averange
C
Curvatureradius(mm)

0.150
29

MEMS-DM – Design

Dimensions of thebimorph spring

300μm

Design of the2×2 Pixels DM

0.86mm30

MEMS-DM – Fabrication results(3)2×22 2 pixel
i l DM

4×4 pixel DM

31

MEMS-DM – Design

1.80mmDesign of the 4×4 Pixels DM32

MEMS-DM –Process flow(a) Actuator chip(b) Mirror chip33

MEMS-DM –Fabrication flow：Bonding and Release(c) Bonding and release34

MEMS-DM – Fabrication results(1)ElectrodeBimorphspring

AubondingpadFabricated actuator chip35

MEMS-DM – Fabrication results(2)Au Si eutectic bonding: 400℃,
Au-Si
400℃ 1.67MPa,
1 67MPa 30min,
30min 44.5×105×10-22Pa

35μm

300μm
5mm

The irregular bonding edge(in yellow line) suggests that Au was melted
during bonding.
36

MEMS-DM – Fabrication results(2)4×4 pixel mirror
37

MEMS-DM – Fabrication results(4) –10μm
The optical micrograph of the mirror membrane with the square Au-Si
reaction area

SEM image of the bonding point after peeling the mirror membrane

The SEM image and the surface profileof the bonding reaction area

38

MEMS-DM – Fabrication results(5) –(a)(b)

120y(μμm)

100
80
60
40
2000204060x(μm)80

100

The surface around the bonding point is flat and smooth
except theh ~5μm
5reaction
i area. By
B removing
i theh area off
reaction point, the fill factor of the fabricated mirror iscalculated to be 99.9%.
99 9%

MEMS-DM – Device initial deflection
2×2 pixel mirror

Electrode gap: 20μm

ElecttrodeGap

Peak valley value: <2μm
Peak-valley

4×4 pixel
i l mirror
iPeak-valley value: <4μm
Electrode gap: 18μm

40MEMS-DM – device driving experiment(2×2 pixel mirror)

Actuated pixel
Sine wave drivingg test: Frequency:1Hz→20Hz→1Hzqy
A ppull-in voltage(~120V)
g () is applied.
pp41

MEMS-DM – device driving experiment(4×4 pixel mirror)
Sine wave driving test: Frequency:1Hz→20Hz→1Hz 80V(peak-peak)

Actuated pixel

42

MEMS-DM – static deflection measurement
2×2 pixels mirror
(a)

(b)

(a)deflection profile of the 2×2 pixels DM with a single pixel
actuated at different voltage(b)deflection profile of the 2×2 pixels DM with a single pixel
actuated at different voltage with zero-voltage profile
subtracted;
43

MEMS-DM – static deflection measurement
4×4 pixel mirror
(a)

(b)

(a)deflection profile of the 4×4 pixel DM with a single pixel
actuated at different voltage with zero-voltage profile
subtracted;((b)color-coded)
surface pprofile of the 4×4 ppixel DM at 80V withzero-voltage profile subtracted.
44

MEMS-DM – response time measurement
Ri time:Riseti
1.3ms
13F ll time:
Fallti
0.9ms
09

Dynamic response of the fabricate 4×4 DM with a single pixel actuated45

MEMS-DM – frequency response

frequency response of the fabricated 4×4 pixel DM
46

8×8 pixel MEMS-DM -Design

Design of the 8×8 Pixels DM
47

8×8 pixel MEMS-DM –Process flow(a) Actuator chip(b) Mirror chip48

8×8 pixel MEMS-DM –Process flow(c) Bonding and release49

8×8 pixel MEMS-DM –Fabrication result (1)Al wire1cmBimorph springs with bonding pad

Al electrode pad for wire bonding50

8×8 pixel MEMS-DM –Fabrication result (2)(a)

200m5mm(c)200200m
Infra red micrographs of the DM after bonding process518×8 pixel MEMS-DM –Fabrication result (3)Mirror membrane

2mm5mm52

Conclusions
An improved membrane transfer process for large-stroke
continuous membrane DM is proposed and demonstrated• A 2μm-thick membrane is transferred to a flexible bimorph
arrayy by
y combining
g bulk micromachining
g and Au-Si eutectic
bonding technology;• Au-Si
Au Si eutectic bonding shown a reliable bonding quality fortransferring large scale mirror membrane;• The stroke of the DMs are 4.0μm
4 0μm at 125V(2×2 Pixel DM) and3.5μm at 115V(4×4 Pixel DM), respectively. The fill factor ofthe fabricated mirror is ~99.9%.
• A freestanding 4mm×4mm×2μm mirror membrane issuccessfully fabricated.
53

New design

MEMS-DM – Influence function(IF) at adjacent actuatorPrevious calculation modle(design(g 1))：y x l /2552 EIkl 3  1152 E 2 I 2  6k 2l 6IF y x 3l /2 1260 EIkl 3  1152 E 2 I 2  13k 2l 6
(EI is the flexure rigidity)

Current calculation model(design 2)：

yaqlklksubstratex
k3ka 3  16kla 3  384 EIIF y x l 39ka 3  96kla 3  384 EI
y x  2l55

MEMS-DM – Spring design
Design a400μm

40μm

Design b350μm

250μm
Cantilever spring
B i spring
Brigei1.0

Design d0.8

Design c
Design c

0.6120120μm

Design a

0.5

Design d0.440μm

IF0.740μm

0.9

Design b

0.3240μm
μ0.2
1.0x10-4

1.5x10-4

2.0x10-4

2.5x10-4

3.0x10-4

3.5x10-4

Spring Length (m)56MEMS-DM – 3×3 DM layout
Mirror membrane

金属配線 電極を採用
金属配線、電極を採用

Groundd Electrrode

DrivingElectrode

初期変位を低減させるため、周辺支持を設ける
57

MEMS-DM – fabrication

58

MEMS-DM – Bonding(design 2)
Bonding experiment@Kyoto tou, Suss Bonder SB-6e
Au-Si eutectic bonding condition :400℃, 12KPa(30min)

59MEMS-DM – SEM(design 2)

60

MEMS-DM – SEM(design 2)

61

MEMS-DM – initial deflection(design 2)00.5-100.4

Height(m)Height(m)

0.3

20-20-30

0.2
0.1
0.0

40-40-0.1-0.2-50400

600

800

1000

1200

1400

1600

1800

Position(m)( )60-60-200

0200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

Position(m)62MEMS-DM – membrane initial deformation

60
050-10H
Height(m)Height (m)

40
30
20-20-30-40

10-500-200

0200400

600

800

1000 1200 1400 1600 1800

-60-2000200 400 600 800 1000 1200 1400 1600 1800 2000 2200 24Position (m)Position(m)Without edge support

With edge support

Mirror size: 1.5mm×1.5mm

Mirror size: 1.7mm×1.7mm

Mirror initial deformation: PV value=3900nm

Mirror initial deformation: PV value=350nm

63MEMS-DM – initial deflection mirror：bonding point

Height(m)0.0-0.1-0.2

400

600

800

1000

1200

Position(m)

14001600

1800

MEMS-DM – Au/Cr coating
Cr: ~10nm, Au: ~60nm is coated on the mirror by sputtering

2520Heigght(m)

151050-5200

400600800 1000 1200 1400 1600 1800 2000

Position(m)

65

まとめ

１．集積型MEMSミラーについて
２．LSIと集積した波長選択スイッチ用MEMSミラー

３．Si連続メンブレン-デフォーマブルミラーの開発状況