1. A Study on Aluminum Oxide (Al2O3) Insulator Deposited by Mist-Chemical Vapor Deposition based on atmospheric pressure
Dong-Hyun Kim1,Hyun-Jun Jung1 and Jin-Seong Park1*
1Division of Materials Science and Engineering, Hanyang University, Seoul , Korea
Corresponding author : hanyang.ac.kr
Introduction
Experiment
Why using Aluminum oxide(AlOx) as insulator?
Fabrication Method
Aluminum oxide(AlOx) - Typical high-k material with high dielectric constant (~9.3)
Excellent thermal stability, wide band gap energy of eV.
In vacuum system such as ALD, tri-methyl aluminum(TMA) has been used for precursor
→TMA properties; explosive and toxic
In this study, Aluminum acetylacetonate (Al(acac)3) → eco-friendly(non-toxic), low cost
material, soluble in aqueous solvent
Synthesis of precursor solutions
Precursor : Aluminum Acetylacetonate
(Al(acac)3), 0.04 M, Aldrich)
Solvent : DI Water + Acetone (ratio 9:1)
Substrate : p++ - Si wafer
Ultra sonicator Frequency : 1.6Mhz (Mist)
Deposition Temperature : 250, 300, 350oC
Al(acac)3 precursor
What is Mist-Chemical Vapor Deposition?
I-V Test Metal-Insulator-Metal Structure fabrication
Electrode ITO by using a sputter (100nm)
By-product
Mist-CVD Process Schematic
Solution
Droplet
(mist)
Analysis of Thin film; ( AlOx on Si Substrate )
XPS (X-ray Photoelectron Spectroscopy)
Chemical bonding state
Capacitance(C)-Frequency(F)
Dielectric property
Current(I)- Voltage(V)
Insulating property
Thin film
TGA (Thermogravimetric Analysis)
Thermal behavior
SE (Spectroscopic Ellipsometery)
Growth behavior
AFM (Atomic Force Microscopy)
Surface Roughness
Substrate
Heater
Rapid Deposition, Simple Process
Large-Area Benefit ; Uniform Thin Film Deposition, Deposition + Heating
Result & Discussion
Thermal behavior : TGA-DSC
Growth behavior: SE
Surface Morphology : AFM
(b)
(a)
250 oC, RMS: 4.169nm
300 oC, RMS: 2.592nm
350 oC, RMS: 2.275nm
(c)
AlOx Solution
TGA - Double step
■ ℃ : The evaporation of Solvent; Acetone, Water
■ ℃: Decomposition of Al(acac)3
DSC – Three endothermic peaks
■ 67℃ : The evaporation of solvents
■ 197oC : Melting point of Al(acac)3
■ 267oC : Total weight loss
3D Topographical images (5㎛ ×5㎛) of the film surfaces
■ As the substrate temperature increases from 250 to 350 ℃
→ the growth rate increases from 7.5 to 13.0 nm/min.
■ With the decrease of carbon, the refractive indices of the
films increased upon calcination; as high as 1.64 (at 350 °C)
■ RMS (root-mean-square) : 350 ℃ < 300℃ < 250℃
■ The surface roughness of film decrease with increasing
temperature.
■ The film has smooth surface at high temperature having
sufficient activation energy for diffusing of nuclei and clusters
Chemical bonding state : XPS
Dielectric Properties :Capacitance-Frequency
Insulating property: Current-Voltage
Mist Si
SiO2
SiO2 Si Si
SiO2
■ Capacitance measurements were conducted at 250 – 350oC
were measured to be 22.6, 41.3, 52.3 pF/cm2, respectively.
■ The dielectric constant (κ) of the AlOx film
→ From 2.64 (250oC) to 7.03 (350oC)
■ The more convert of hydroxyl groups to oxide lattices at high
temperature. → The decrease of M-OH states increase
the dielectric constant of AlOx films.
■ The peaks designated
O1 : Metal-oxygen bond (at eV)
O2 : Metal- hydroxide bond (at eV )
■ The Al precursor is not completely oxidized at low temperature
■ O1 peak →Enlarge, O2 peak → Reduce
As the higher temperature, leading to compose Al-O frameworks
■ The sufficient insulation characteristics of the AlOx films was
enhanced with increasing growth temperature
■ Due to the decomposition of metal precursor and the denser
formation of Al-O frameworks at high temperature
→ Insulating properties was enhanced
Conclusion
Contact
The AlOx (Mist-CVD) thin films were fabricated as gate insulator via facile, low cost, eco-friendly ‘aqueous solution’.
With the increase of the growth temperature, dielectric properties are enhanced due to decomposition of Al precursor and denser formation of Al-O.
The superior insulating property of AlOx deposited at 350 °C was measured to be 8.3×10−10 (A/cm2) at a 6 (MV/cm) and 9 (MV/cm).
These performance characteristics clearly exceed those reported for any other solution-processed Aluminum oxide dielectric.
Prof. Jin-Seong Park
Division of Materials Science and Engineering, Hanyang University, Seoul , Korea
This work supported by the Industry technology R&D program of MOTIE/KEIT [ , Development of mechanical UI device core technology for small and medium-sized flexible display] and the MOTIE (Ministry of Trade, Industry & Energy) (# ) and KDRC (Korea Display Research Corporation)