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Fabrication of AlOx thin films by

photochemical deposition

Nagoya Institute of Technology

Ichimura, Kato Lab

Shunta Sato

・High dielectric constant: ~9 (Al2O3)

・Large band gap : 8.7 eV (Al2O3)

・High field strength : 6-8 MV/cm (Al2O3)

・Stability of chemical and thermal properties

About AlOx

Application to protection layer

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Back ground

・Chemical vapor deposition method [1]

・Plasma enhanced chemical vapor deposition method [2]

・Pulsed laser deposition [3]

・DC reactive magnetron sputtering [4]

・Atomic layer deposition [5]

・Solvothermal deposition [6]

・Electrochemical deposition [7]

→ Use aqueous solutions containing aluminum sulfate and sodium thiosulfate

[1] Chowdhuri AR, Takoudis CG, Klie RF, Browning ND. Appl Phys Lett 2002;80:4241.

[2] Tristant P, Ding Z, Trang Vinh QB, Hidalgo H, Jauberteau JL, Desmaison J, Dong C.. Thin Solid Films

2001;390:51.

[3] Cibert C, Hidalgo H, Champeaux C, Tristant P, Tixier C, Desmaison J, Catherinot A. Thin Solid Films

2008;516:1290-6.

[4] Koski K, Holsa J, Juliet P. Thin Solid Films 1998;326:189-93.

[5] Li X, Chen Q, Sang L, Yang L, Liu Z, Wang Z. Physics Procedia 2011;18:100-6.

[6] Duan XF, Tran NH, Roberts NK, Lamb RN. Thin Solid Films 2010;518:4290-3.

[7] A.M. Abdel Haleem, M. Ichimura., Materials Letters 130 (2014) 26-28.

Report of AlOx thin film fabrication

There are no reports of fabrication aluminum oxide by

photochemical deposition (PCD)

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Back ground

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・Simple technique and Economical

・No conductive substrate can be used

・Enables large-scale deposition

Photochemical deposition (PCD)

Spherical simple lens

Stirrer

Aqueous solution containing Al2(SO4)3 and Na2S2O3

Substrate

Substrate depth

Ultra high pressure mercury lamp

10mmFormation

region

10mm

10mm

5

PCD apparatus

Ultra high pressure mercury lamp

Stirrer

Deposition

solution

Mirror

Lens

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How to do AlOx PCD ?

Related thin film deposition

（1） AlOx deposition by Electrochemical deposition (ECD)

（2） Sulfide deposition by PCD

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ECD of AlOx

Al2(SO4)3 [mM] 10

Na2S2O3 [mM] 200

Purified water [mL] 50

・Na2S2O3 is necessary to get uniform films.

Aluminum sulfide is formed firstly and then oxidized

in water to form AlOx

Deposition solution

[7] A.M. Abdel Haleem, M. Ichimura., Materials Letters 130 (2014) 26-28.

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ZnSO4 [mM] 1

Na2S2O3 [mM] 600

Na2SO3 [mM] 3

Purified water [mL] 50

PCD of sulfide (ZnS)

Zinc from ZnSO4 reacts with sulfur from

Na2S2O3 and then ZnS is formed

[8] T.Miyawaki, M.Ichimura, Materials Letters 61(2007) 4683-4686

Deposition solution

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2S2O32- ＋ hν(UV) → S4O6

2- + 2e- (1)

S2O32- ＋ hν(UV) → S + SO3

2- (2)

2H+ + S2O32- → S + H2SO3 (3)

Zn2+ + S + 2e- → ZnS (4)

This time we use Al2(SO4)3 and Na2S2O3

Sulfide PCD reactions

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・Na2S2O3 acts as a reducing agent

2S2O32- + hν(UV) → S4O6

2- + 2e- (1)

Al3+ +x

2O2 + 3e- → AlOx (2)

Possible AlOx PCD reactions: (1)

Oxygen in water

S2O32- reduces Al ion, and AlOx is formed

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2S2O32- + hν(UV) → S4O6

2- + 2e- (1)

S2O32- + hν(UV) → S + SO3

2- (2)

Al3+ + xS + 3e- → AlSx (3)

AlSx + xH2O → xH2S + AlOx (4)

Possible AlOx PCD reactions: (2)

・Na2S2O3 acts as a reducing agent and sulfur source

AlSx is formed firstly and then oxidized in water to

form AlOx

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Al2(SO4)3 [mM] 5

Na2S2O3 [mM] 5 ~ 200

Purified water [mL] 50

Deposition time [min] 60

Substrate ITO

Substrate depth [mm] 2

Light intensity

[mW/cm2]

870 ~ 1400

Temperature [℃] RT(25℃)

pH 3.6~4.2

(Unadjusted)

Method of preparing solution

(1) The Al2(SO4)3 is added to a

hot water (80-90℃) with

stirring

(2) After the solution clear and

transparent, the solution is left

to cool down to about 25℃

(3) The Na2S2O3 is added

AlOx PCD conditions

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Na2S2O3 = 10 mM

Na2S2O3 = 200 mM

Na2S2O3 = 20 mM

Film thickness (870 mW/cm2)

・Not deposited

・Thin film is deposited

・Not deposited

Surface roughness meter result

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Al2(SO4)3 [mM] 5

Light intensity

[mW/cm2]

870

Na2S2O3 concentration dependence

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Al2(SO4)3 [mM] 5

Na2S2O3 [mM] 50

Light intensity dependence

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Thickness (Na2S2O3 = 50 mM)

Light

intensity

[mW/cm2]

1100

Light

intensity

[mW/cm2]

1400

Light

intensity

[mW/cm2]

870

Surface roughness meter result

Optical transmittance

Sample 17

Al2(SO4)3 [mM] 5

Na2S2O3 [mM] 50

Light intensity [mW/cm2] 1400

Time [min] 60

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B

A

In O AlS

O AlComposition ratio

O/Al = 1.139

Al2(SO4)3 [mM] 5

Na2S2O3 [mM] 50

Light intensity [mW/cm2] 1400

Time [min] 60

SEM image

Auger electron spectroscopy result

A

B

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AlOx thin film deposition by PCD

The AlOx film is deposited with x ≈ 1.1

Na2S2O3 is necessary to deposit films

Thicker films are fabricated by increasing light intensity

Too strong light intensity makes the films rough

Summary