fabrication of large area sub-wavelength structures for anti-reflection optical film

Fabrication of large area sub-wavelength structures for anti-reflection optical film

Reporter Wen-Yu Lee﹕Advisor ： Cheng-Hsin Chuang

Department of Mechanical Engineering, Southern Taiwan University of Science and Technology, Tainan, Taiwan

Date: 2013/03/05

製作具次波長結構之大面積抗反射光學元件

Outline

2

Introduction

Experimental setup and results

Anti-reflection film measurement

Conclusions & Future works

Porous Anodic Alumina Oxide (AAO) Template

Nano imprinting process

The transmittance and reflectance measurement results

Comparing the results of different experiment parameters

Motivation

Types of Anti-reflection film

Outline

3

Introduction








Motivation


4

Motivation

Reflection

Low contrast

Low contrastDecreased conversion efficiency

Low transmittance

Disadvantages of light reflection

n=1.5

Air n=1 Air n=1

n=1.5n=1.1~1.4

10%

5

Antireflective coating technology – Multilayer coatingAntireflective structure – Sub-wavelength structure

(SWSs)

Protective filmAntireflection

layerSubstrate with

hard coatingAdhesive layer

SeparatorThe refractive index of multilayer (Ladder)

High-cost facilities


6

Types of Anti-reflection filmAntireflective structure - Sub-wavelength structure (SWSs)

Moth eye structures

The reflective index of cylindrical SWSsThe reflective index of cone-shape SWSs

Information source : FINETECH JAPAN 2011

Multilayer coating

The lowest reflection and broadband

Sub-wavelength Structures(SWSs)

The best optical characteristicImprinting processLow-cost

How to achieve broadband and omnidirectional antireflection with low cost

process?

7

Types of Sub-wavelength structures (SWSs)Colloidal

lithography

RIE

Etching

Langmuir, 2009, 25 (13), pp 7375–7382

Interference lithography

Optics Communications 282 (2009) 434–438

Electron beam

lithography

BOE etching

KOH

etching

Solar Energy Materials & Solar Cells 94 (2010) 629–633

Electron beam lithography

Disadvantages• Complex• High-end facilities• Costly• Small size

Nano imprinting technique

Advantages Low-cost nano-scale mold Simple process The best optical characteristic Large area

Outline

8

Introduction








Motivation


9

Experimental – Fabrication of AAO template

ProceduresAcid cleaning pure Al

foil

1st anodization process

Removed anodic oxide layer by acid

2nd anodization process

Pure aluminum

Schematic of the cross section

Process condition• Constant voltage of 80V• Oxalic acid solution (0.3M)• Temperature at 4℃

Oxalic acid solution Platinum(Pt)Oxalic acid solution Phosphoric acid

etching Platinum(Pt)

Anodizing + etchig = 1 time (1st cycle)• Phosphoric acid solution (5wt%)• Temperature at 32℃

Anodizing + etchig = 1 time (2nd cycle)

10

Experimental result – Different 2nd anodization time Top view High purity aluminum foil

Cross section view

30sec 45sec 60sec

30sec 45sec 60sec

Aspect ratio 1:1 Aspect ratio 1:1.5 Aspect ratio 1:2

11

Experimental result – Different 2nd anodization time Top view Sputtering aluminum membrane with temper, widening time 10 min

Cross section view

30sec 45sec

30sec 45sec

Aspect ratio 1:1.2 Aspect ratio 1:2.5

12

Experimental result – Different Pore widening time Top view

15min

15min

Aspect ratio 1:1.5

Cross section view

10min

10min

Aspect ratio 1:2.5

Sputtering aluminum membrane with temper, widening time 10 min

13

Experimental result – Compare the results of temper

Anodizing time 45sec , widening time 15 min

5 ̊C / min

400 ̊C, 4hr

Rapid cooling

400

SEM images of AAO template

Tempering status Tempering champer

Without temper With temper

14

Experimental process – Nano imprinting process AAO template with cone structure

Schematic of nanoimprinting process by using UV exposure technique.

AAO template

Nano imprinting Process

UV curablePET substrate

Anti-reflection FilmPET substrate

Sub-wavelength structures

Roller UV light

Ontic photo

AAO template

Anti-reflection Film

0.5

15

Experimental result – Nano imprinting process byusing AAO template

AAO template SWSsAluminum substrate

45sec, 10min

Aspect ratio 1:1

Sputtering Al membrane(without temper)

45sec, 15min

Sputtering Al membrane

30sec, 10min


45sec, 15min


Aspect ratio 1:1

Aspect ratio 1:1

Aspect ratio 1:1.5

Aspect ratio 1:2

Outline

16

Introduction








Motivation


17

Optical measurements results – Transmittance (%) Transmittance and of the glass plate with/without

SWSs

89.7%

91.8%

92.9%

94.2%95.1%

Asp

ect r

atio

incr

ease

d

18

Optical measurements results – Reflectance (%) Reflectance and of the glass plate with/without the SWSs

60 ̊45 ̊30 ̊15 ̊5 ̊

Wavelength (nm)

Ref

lect

ance

(%)

Incident light angles

1%0.14%

0.16%

0.26%

0.64%

Aspect ratio increased

Outline

19

Introduction








Motivation


20

ConclusionsThis study successfully fabricated the large area AAO template by using homemade Circulate-coolded etching system.

In the fabrication of large area cone-shape AAO template, we could control the different depth characteristics of anodic alumina by phosphoric acid etching process and anodization parameters.

We have successfully produced sub-wavelength structures(SWSs) on glass plant by using hot embossing with AAO template

In the optical measurement results, the average transmittance of glass plate with SWSs was 96.5% and the reflection was reduced from 5.71% to 0.2%.

Due to the contact angle of high-aspect-ratio SWSs film exceeded 110°, the surface energy is much lower than bare glass whose contact angle is 25°. Consequently, a SWSs film could possess the self-cleaning effect.

21

Thanks for your attention!

fabrication of large area sub-wavelength structures for anti-reflection optical film

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