Development of Al based metallic glasses

(1)

Development of Al based metallic glasses

Current research issues

e-mail : [email protected] Seoul National University

ESPark Research Group.

W. Kim

Advanced Research of Structural Materials

Opening seminar

2016. 03. 21

(2)

Contents

Motivation : Al-based MG for Ag paste media

Al based Metallic glass & Alloy design

 High entropy effect

Statistical analysis of shear band by nano-indentation

EXTRA : Phase separation metallic glass (Al-Pb)

(3)

Motivation

Al-based metallic glass frit for Ag paste

(4)

1) Single crystal Si wafer 2) dopingPN junction

4) SiNx deposite with PECVD

anti reflection layer 증착

3) Plasma etching

5) metallization

대면적 실리콘 태양전지 공정

“Screen printing process” 적용해최대 효율20%의 태양전지 제조가능

Screen printing

Screen printing process

fine-mesh를 이용하여Ag paste를 미세 도포 하는 공정법

1) Screen Printing을 통한 Ag paste의 미세 도포

Ag paste

: silver + oxide + 유기물 1) Screen printing process

: Ag paste 미세 도포 2) 도포된Ag paste의 소결

: 은 전극-반도체간 전기적 접합

ESPark Research Group 2016-03-21

Screen printing Si solar cell

Ag

2) 소결을 통한 은 전극/Si 반도체 전기적 접합 가능

800 ℃ 급속 소결

은 (Silver) 전극 산화물 층

Si 반도체

(5)

Role of PbO

₂

계 Oxide glass

PbO₂계oxide 적용에 따른 장점 : Ag paste의 소결능 향상 전기전도성 증가

1) 소결능 향상접합면적 증가 통한 전도성↑ 2) SiN_x건식 에칭 가능실질적인 전극 접합 가능

pure Ag paste

8 ㎛

<Ag 분말 단독 소결:접합면적↓> <Oxide 첨가 소결:접합면적↑>

Bulk Ag Oxide glass layer

3㎛

PbO₂계 oxide 적용에 따른 단점 :전기저항의 증가 소자 효율 감소 1) Oxide 적용 따라 최대2% 효율 저하 발생

Bulk Ag

2) Ag crystal 석출 따른 전자 산란 발생

태양전지 효율 증가 위해 전기 저항성 높은

Oxide 대체 물질 개발 요구

<Oxide 의한silver 결성상의 석출>

Ag 결정상(최대 크기1㎛)

전자 산란 유발

전기전도도 감소

소자 효율 감소

<요소별 태양전지 효율 감소율>

<Oxide의 건식에칭 메커니즘>

(6)

Metallic glass 를 적용한 신개념 Ag paste 개발

back plane용 MG/Ag paste에Metallic glass 적용 통한 solar cell 효율0.1% 개선 가능

Al계 비정질 합금 적용한 front plane용 Ag paste 개발을 목표로 함

Oxide Glass Metallic Glass

스크린 프린팅 태양전지의 에너지 변환 효율을 획기적으로 개선 접촉면에 Ag 결정의 고른 분포

를 통한 접촉저항 감소 Ag 전극과 Si emitter 층의 두께 감소

Ag powder의 소결 능력 향상

ref: APL, 98 (2011) 222112

(7)

우수한 열적특성

(ΔT_x↑, T_m↓)

가진

Al

계 비정질 합금 개발 요구

Wetting layer

(1) (2)

Ref : Scientific reports, 3 2185 (2013)

과냉각액체영역 증가 통해 Cavity filling에 따른 SCLR의젖음성 증가(θ↓)

젖음성 증가 위해넓은 과냉각 액체영역 가진 합금 설계 요구

𝟐𝟒𝛈𝐝

𝟖𝛄𝐜𝐨𝐬𝛉

≤

^𝚫𝐓^𝐱

𝐑_{𝐡𝐞𝐚𝐭}

= 𝐭

_𝐒𝐂𝐋

우수한 열적 특성 가진 Al 계 비정질 합금 개발

급격한 점성 감소(super cooled liquid)

 Ag powder 내부로 모세관 확산

 Ag paste 소결능 및 전극접합성 향상

(8)

Metallic glasses

(9)

Metallic glasses

Glass forming ability

 Activation energy for nucleation ↑

 High initial viscosity of liquid

 High increase rate of viscosity

Crystallization

log η

Temperature

1^storder transition

2^ndorder transition

Reversible

Glass transition

 Reversible 2^nd order transition

T_m T_g

(10)

비정질 합금의 과냉각 액체 영역을 이용한

Thermoplastic forming (TPF)

Thermo-plastic deformation

T_x T_g

(11)

200 nm

수준의 리본 표면

roughness → TPF

공정을 통해 수

nm

수준으로 평탄화 구현 고온 환경 인장/압축 장치를 이용한

TPF 평탄화 공정 : Zr₅₀Cu₄₀Al₁₀ eutectic ribbon

0 20 40 60

-100 -50 0 50 100

Height (nm)

Distance (μm) Avg. roughness : 3.27 nm

200 1000

62.5

125 0

50

100

X axis (μm)

Y axis (μm) Z axis (nm)

0 20 40 60 80

-400 -200 0 200 400

Height (nm)

Distance (μm) Avg. roughness : 203nm

1000

0 500

62.5

125

0 50

100

X axis (μm) Y axis (μm)

Z axis (nm)

Before TPF

After TPF on flat glass

Thermo-plastic deformation

(12)

0 50 100 150 200 250 300 0

200 400 600 800 1000

Elastic modulus (GPa)

Glass transition Temperature (T g)

0 1 2 3 4 5 6

Fracture Strength (GPa)

W-based MG Fe-based BMG

Ni-based BMG Ti-based BMG

Zr-based BMG Cu-based BMG

Al-based MG Mg-based BMG Ca-based BMG

For the conventional application

→ relatively low cost elements (Al>80at%)

→ Good mechanical properties (Strength > 1GPa)

Metallic glasses

(13)

Al-based Metallic glasses

: Development of thermal properties

(14)

New Concept for Al-based MG design

Al

Ni RE

ΔH_mix< 0 kJ/mol ΔT_x < 20K

High entropy effect by multiple RE

1. complex RE complex bonding nature 2. liquid stability ↑

3. Dramatic increase of ΔT_x

ΔH_mix Al Ni Ce La Nd Y Gd Er

Al ^-- ^-22 ^-38 ^-38 ^-38 ^-38 ^-39 ^-39

Ni ^-- ^-- ^-28 ^-27 ^-30 ^-31 ^-31 ^-31

Addition of multi-component rare earth elements

TM RE

Al

TEM image of amorphous matrix

Bonding nature of Al-based MG

Ref: scripta, 65 (2011) 755

Coordination # Al-TM : 7~8 Al-RE : 16~18

(15)

→ ΔT

_x

has linear relationship with ψ of RE elements.

(Al

₈₄

Ni

₁₀

Y

₆

ΔT

_x

= 21.5K)

1.10 1.12 1.14 1.16 1.18 1.20 1.22 17

18 19 20 21 22

Supercooled Liquid Region Tx (K)

Electronegativity of RE (Pauling units)

La

Ce Gd

Y Nd

Al-Ni-RE ternary system

500 520 540 560 580 600 620

Heat Flow(arbitrary unit)

Temperature (K)

La Ce Nd Gd Y

T_g

Heating rate : 40K/min

T_x

Al₈₄Ni₁₀RE₆ amorphous alloy system

(16)

Multicomponent Al-based MG

520 540 560 580 600 620

Temperature (K)

Heat Flow (arbitrary unit) ^La¹⁰⁰

La₅₀Ce₅₀

La_33.3Ce_33.3Nd_33.3 La₂₅Ce₂₅Nd₂₅Gd₂₅ La₂₀Ce₂₀Nd₂₀Gd₂₀Y₂₀

Al₈₄Ni₁₀RE₆

T_g ΔT_x T_x

1.10 1.12 1.14 1.16 1.18 1.20 1.22

18 21 24 27

Tx (K)

Electronegativity (Pauling units)

Al₈₄Ni₁₀RE

6 La₁₀₀ Ce₁₀₀

Gd₁₀₀

Y₁₀₀ La₅₀Ce₅₀

La_33.3Ce_33.3Nd_33.3 La₂₅Ce₂₅Nd₂₅Gd₂₅ La₂₀Ce₂₀Nd₂₀Gd₂₀Y₂₀

Nd₁₀₀

High entropy effect

Al₈₄Ni₁₀RE₆ amorphous alloy system

→ ΔT

_x

increase with number of RE elements (Al

₈₄

Ni

₁₀

(LaCeNdGdY)

₆

ΔT

_x

= 25.5K)

Q : Increase of ΔT

_x

= Liquid stability & viscosity change?

(17)

Thermomechanical analyzer (TMA)

(18)

(19)

𝜌𝜕𝒗

𝜕𝑡+ 𝜌𝑣 ∙ 𝛻𝒗 = −𝛻𝑝 + 𝜂𝛻2𝒗 +1

3𝜂𝛻𝛻 ∙ 𝒗 The general vector eq. of motion of a Newtonian fluid

𝛿𝑣_𝑟/𝛿𝑡 = 0(Steady state flow)

𝐹 = −2𝜋𝑑ℎ 𝑑𝑡

3𝜂 ℎ³ ₀

𝑅

𝑅²− 𝑟² 𝑟 𝑑𝑟

𝐹𝑜𝑟 𝑐𝑎𝑠𝑒 𝑎 , 𝑅 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡

𝐹𝑜𝑟 𝑐𝑎𝑠𝑒 𝑏 , 𝑅 𝑐ℎ𝑎𝑛𝑔𝑒𝑠 𝑤𝑖𝑡ℎ 𝑡 𝑏𝑢𝑡 𝑉 = 𝑐𝑜𝑛𝑠𝑡𝑟𝑎𝑛𝑡 𝐹 = −3𝜋𝜂𝑅⁴

2ℎ³ 𝑑ℎ 𝑑𝑡

𝐹 = −3𝜂𝑉² 2𝜋ℎ⁵

𝑑ℎ 𝑑𝑡

𝑅 > 10 ℎ (Thin plate sample)

(𝑆𝑡𝑒𝑓𝑎𝑛 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛)

(𝐹𝑟𝑜𝑚 𝐷𝑖𝑒𝑛𝑒𝑠 𝑎𝑛𝑑 𝐾𝑙𝑒𝑚𝑚)

Case (a).

excess of material is squeezed out

Case (b).

Squeezing sample of constant volume

Viscosity in compression : Parallel plate rheometer (10

⁵

~10

⁹

pa∙s)

𝜼 = 𝝈/𝟑 𝜺

Applied Stefan equation

(20)

Viscous flow of Super cooled liquid

NEXT STEP

By applying of Stephan equation

 Calculation of viscosity

Case (b). Squeezing sample of constant volume

Strain rate

450 500 550

-0.10 -0.08 -0.06 -0.04 -0.02 0.00

Strain (%)

Temperature (K) Heating rate : 10K/min

TMA mode : expansion

Al₈₄Ni₁₀La₆

Al₈₄Ni₁₀(LaCeNd)₆ Al₈₄Ni₁₀(LaCeNdGdY)₆

T_x T_x T_x T_g T_g T_g

Heating rate 10K/min Tg. TMA Tx. TMA Al₈₄Ni₁₀La₆ 546.5 557.9K Al₈₄Ni₁₀(LaCeNd)₆ 539.9 552.1K Al₈₄Ni₁₀(LaCeNdGdY)₆ 538.3 549.3K

Strain of Super cooled liquid

(21)

Heating rate : 0.167K/sec TMA mode : expansion

Al₈₄Ni₁₀La₆ Al₈₄Ni₁₀LaCeNd₆ Al₈₄Ni₁₀LaCeNdGdY₆

510 520 530 540 550 560

1E9 1E10 1E11 1E12

Viscosity(Pa·s)

Temperature (K)

Increase of ΔT

_x

 Decrease of viscosity

 Good for TPF & precise fabrication

Viscous flow of Super cooled liquid

(22)

𝜂 = 𝜂₀exp(𝐷^∗ ∙ 𝑇₀ 𝑇 − 𝑇₀)

Kinetic fragility

0.90 0.95 1.00

1E9 1E10 1E11 1E12

Viscosity (Pa·s)

T_g*/T

La LaCeNd LaCeNdGdY

Strong

Fragility Strain of Super cooled liquid

Fragility

: liquids are classified as strong glass & fragile glass (by D. angell)

good glass forming alloy : strong liquid with a high viscosity

Fragile glass

1. Softening effect

2. Multiple shear band

(23)

Effect of free volume on mechanical properties

 Statistical analysis by complexity(SOC)

(24)

Plastic deformation of BMG

Shear bursting : Sum of free volume

Free volume

Interaction between matrix & Free volume & 2^nd phase

 Control the ductility of metallic glass

: multiple shear band or decrease the cut off size

<Serration by shear band deformation>

(25)

Self-organization

Self organization

자기조직화



무질서 복잡계속의 규칙성

Plan & Design  Organization

Ex) parts + parts + parts + = machine 조직화 하고 난 뒤 조립

Interactions of local parts  Organization Ex) Cells + Cells + Cells = Organics

만들어지고 나서 조직화

 각각의 개발적은 크고 작은 사건

ex)earthquake, Comet impact, car crash, 서로간에 영향은 주지 않으나, 큰 흐름에서 보았을때, 사건발생의 규칙성이 있다.

 complexity & SOC

(26)

Self-organized critical

𝑃 > 𝑆 = 𝐴𝑆

^−𝛽

exp(

^−𝑆_𝑆

𝑐

)

Grain size effect the dislocation avalanche size

Beta : scaling exponent Sc: cut off of strain

Single crystal (β=1), >> grain with 1.92(β=0.35)

 High beta value : close to self-organized state

Jamming state : statistically high level of interactions btw disl, matrix

 Low beta value : relatively chaotic state Unjamming state : low level of interactions

(27)

Pop-in of nano-indentation

Evaluation SOC in metallic glass

𝑃 > 𝑆 = 𝐴𝑆

^−𝛽

exp

^−𝑆

𝑆_𝑐 ²

0.01 1E-3

0.01 0.1 1

Cumulative probability distribution, P(>S)

Strain burst size S

β : scale exponent

 high β value = SOC state : Jamming state

 low β value = Chaotic state : Unjamming state

(28)

𝜂 = 𝜂₀exp(𝐷^∗ ∙ 𝑇₀ 𝑇 − 𝑇₀)

Kinetic fragility

0.90 0.95 1.00

1E9 1E10 1E11 1E12

Viscosity (Pa·s)

T_g*/T

La LaCeNd LaCeNdGdY

Strong

Fragility Strain of Super cooled liquid

Fragility

: liquids are classified as strong glass & fragile glass (by D. angell)

good glass forming alloy : strong liquid with a high viscosity

Fragile glass

1. Softening effect

2. Multiple shear band

(29)

0.01 10^-2

10^-1 10⁰

Cumulative probability distribution, P(>S)

Strain burst size S_c

La LaCeNd LaCeNdGdY

𝑃(> 𝑆) = 𝐴𝑆^−𝛽exp −_𝑆^𝑆

𝑐 2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

 (scaling exponent)

La LaCeNd LaCeNdGdY

0.000 0.005 0.010 0.015 0.020 0.025

Cut off, Sc

Statistical analysis depending on fragility

Fragility ↑ Free volume↑

Chaotic deformation Multicomponent High entropy effect

Al₈₄Ni₁₀La₆ Al₈₄Ni₁₀LaCeNdGdY₆

Effect of free volume on

(30)

Phase separated Al-based metallic glass

 Bending & fatigue test

(31)

ESPark Research Group

Al_82.87Ni_4.88Co_1.95Y_7.8Pb_2.5 상분리 합금 SEM 이미지

Al-Pb 상분리 합금을 이용한 Ag paste

Al-Pb phase diagram

 Al-Pb

이원계 시스템 전체 조성에서

miscibility gap

보유

: Al-Pb고용체의 부재로 인한 상분리 현상



상분리 된

Pb-rich phase : SiN_x

건식 에칭 메커니즘 보유 예상

Al – Pb

상분리 비정질 합금 개발



건식 에칭 가능

Al

계 비정질 신합금

2015-03-02

Ref: APL, 93 (2008) 131907

(32)

ESPark Research Group

(Al₈₄Ni₁₀MM₆)₉₇Pb₃DSC 열분석 결과 Al-Pb상분리 합금SEM 이미지

 AlNiMM 비정질 시스템에Pb 소량 첨가를 통해Pb-rich phase 상분리 가능 확인

 300 nm 수준의Pb-rich phase 다수 석출 : SiN_x 건식 에칭 가능여부 확인 요구

Al – Pb

상분리 비정질 합금 개발

추후 설계 방향

: Pb

절감 친환경

Ag paste 개발

Pb rich Al-Pb상분리 합금 개발

Pb rich phase의 용융 통한SiNx 건식에칭 가능

PbO₂ 완전 대체 가능Al-Pb상분리 합금 개발

최종Pb분율 감소 통한 친환경Ag paste 개발 가능

2015-03-02

200 300 400 500

Heat Flow (W/g)

Temperature (℃)

T_m: 314.73℃

↑

↓T_x: 267.35℃

Heating rate : 40K/min As-quenched

Annealed

1㎛

Pb-rich phase

Al-Pb 상분리 합금을 이용한 Ag paste

(33)

Ω ^{SUS 기판}

Ag paste

압착

Bending test

Ω ^{SUS 기판}

Ag paste

반복변형 반복변형

Fatigue test

(a) Oxide glass 적용

(b) 다성분계 Al계 MG Frit 적용 (c) Pb 상분리 Al계 MG Frit 적용

𝜀(%) =

_{(𝐷−𝑡)}^𝑡

× 100

^ ^{t : 시편 두께} / D : plate간 간격

Bending / Fatigue test for flexible

Al – Pb

상분리 비정질 합금

: Flexible Ag paste

로써의 가능성

(34)

3.0 2.5 2.0 1.5 1.0 0.5

0.010 0.015 0.020 0.06

Distance between plate (cm)

Resistance (Ω) / SUS bar with Ag paste

0.0 0.2 0.4 0.6 0.8 1.0

Strain (%)

(1)Oxide frit적용

(2)다성분계 Al계MG Frit 적용

(3) Pb상분리Al-계MG Frit 적용 Closed point : 전기저항

Opened point : strain

0.3Ω ↑

0 20000 40000 60000 80000

0.00 0.02 0.04 0.06 0.08

Electronic resistance (Ω)

Fatigue lifetime (Number of cycles) (1)Oxide frit적용

(2)다성분계 Al계MG Frit 적용 (3) Pb상분리Al-계MG Frit 적용

Bending / Fatigue test for flexible

Bending / fatigue

따른

Ag paste

의 전기저항 변화

 Oxide glass frit 적용

: brittle oxide로 인해 낮은 탄성한계 및 피로저항성

 Pb 상분리Al계 비정질 합금

: Pb상의 낮은 융점으로 인해 젖음성 항샹 : 금속개재물에 의한 유연성 증가

상분리

Pb Al-based MG

적용 통해

유연성 높은

Ag paste의 개발 가능

(35)

Thanks for your kind attention