fabrication of alox thin films by photochemical...
TRANSCRIPT
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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
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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