Song-Min Nam

Relation between electrical properties of aerosol-deposited BaTiO3 thin films and their mechanical hardness measured by nano-indentation

To achieve a high capacitance density for embedded decoupling capacitor applications, the aerosol deposition (AD) process was applied as a thin film deposition process. BaTiO3 films were fabricated on Cu substrates by the AD process at room temperature, and the film thickness was reduced to confirm the limit of the critical minimum thickness for dielectric properties. As a result, the BaTiO3 thin films that were less than 1-μm thick showed unstable electric properties owing to their high leakage currents. Therefore, to overcome this problem, the causes of the high leakage currents were investigated. In this study, it was confirmed that by comparing BaTiO3 thin films on Cu substrates with those on stainless steels (SUS) substrates, macroscopic defects and rough interfaces between films and substrates influence the leakage currents. Moreover, based on the deposition mechanism of the AD process, it was considered that the BaTiO3 thin films on Cu substrates with thicknesses of less than 1 μm are formed with chinks and weak particle-to-particle bonding, giving rise to leakage currents. In order to confirm the relation between the above-mentioned surface morphologies and the dielectric behavior, the hardness of BaTiO3 films on Cu and SUS substrates was investigated by nano-indentation. Consequently, we proposed that the chinks and weak particle-to-particle bonding in the BaTiO3 thin films with thicknesses of less than 0.5 μm on Cu substrates could be the main cause of the high leakage currents.

High-performance laser mode-locker with glass-hosted SWNTs realized by room-temperature aerosol deposition.

We preserve optical nonlinear properties of single-walled carbon nanotubes (SWNTs) within SiO2-host employing aerosol deposition (AD) that guarantees the formation of dense ceramic thick films at room temperature without combustion and solubility limitation of the SWNTs. The intact nonlinearity is verified with transmittance check, Raman spectrometry and electron microscopes. As a saturable absorption device, the SiO2-SWNT composite film successfully mode-locks fiber lasers inducing high-quality output pulses with the measured pulse duration and repetition rate of 890 fs and 9.52 MHz, respectively. After experiencing the intracavity power higher than 20 dBm, the hosted SWNTs are survived to function as the pulse formers.

Effects of mechanical properties of polymer on ceramic-polymer composite thick films fabricated by aerosol deposition

Two types of ceramic-polymer composite thick films were deposited on Cu substrates by an aerosol deposition process, and their properties were investigated to fabricate optimized ceramic-based polymer composite thick films for application onto integrated substrates with the advantage of plasticity. When polymers with different mechanical properties, such as polyimide (PI) and poly(methyl methacrylate) (PMMA), are used as starting powders together with α-Al2O3 powder, two types of composite films are formed with different characteristics - surface morphologies, deposition rates, and crystallite size of α-Al2O3. Through the results of micro-Vickers hardness testing, it was confirmed that the mechanical properties of the polymer itself are associated with the performances of the ceramic-polymer composite films. To support and explain these results, the microstructures of the two types of polymer powders were observed after planetary milling and an additional modeling test was carried out. As a result, we could conclude that the PMMA powder is distorted by the impact of the Al2O3 powder, so that the resulting Al2O3-PMMA composite film had a very small amount of PMMA and a low deposition rate. In contrast, when using PI powder, the Al2O3-PI composite film had a high deposition rate due to the cracking of PI particles. Consequently, it was revealed that the mechanical properties of polymers have a considerable effect on the properties of the resulting ceramic-polymer composite thick films.

High loading of nanostructured ceramics in polymer composite thick films by aerosol deposition.

Low temperature fabrication of Al2O3-polyimide composite substrates was carried out by an aerosol deposition process using a mixture of Al2O3 and polyimide starting powders. The microstructures and dielectric properties of the composite thick films in relation to their Al2O3 contents were characterized by X-ray diffraction analysis. As a result, the crystallite size of α-Al2O3 calculated from Scherrers formula was increased from 26 to 52 nm as the polyimide ratio in the starting powders increased from 4 to 12 vol.% due to the crushing of the Al2O3 powder being reduced by the shock-absorbing effect of the polyimide powder. The Al2O3-polyimide composite thick films showed a high loss tangent with a large frequency dependence when a mixed powder of 12 vol.% polyimide was used due to the nonuniform microstructure with a rough surface. The Al2O3-polyimide composite thick films showed uniform composite structures with a low loss tangent of less than 0.01 at 1 MHz and a high Al2O3 content of more than 75 vol.% when a mixed powder of 8 vol.% polyimide was used. Moreover, the Al2O3-polyimide composite thick films had extremely high Al2O3 contents of 95 vol.% and showed a dense microstructure close to that of the Al2O3 thick films when a mixed powder of 4 vol.% polyimide was used.

Powder preparation in aerosol deposition for Al2O3-polyimide composite thick films

The influence of the pre-treatment of starting powders for Al2O3-polyimide composite thick films fabricated by an aerosol deposition (AD) process was investigated. The microstructures and the dielectric properties of the Al2O3-polyimide composite thick films in relation to their particle size of polyimide in the starting powder were characterized. As a result, polyimide starting powders larger than 1 μm in size were remained in the films after the deposition. Also, the Al2O3-polyimide composite thick films showed high loss tangents with large frequency dependences when the polyimide starting powders larger than 1 μm in size were used, due to the porous microstructure with cracks and rough surfaces. In comparison, the Al2O3-polyimide composite thick films had dense nanostructures, and the number of pores and cracks in the films were also noticeably decreased by using polyimide powders of less than 1 μm. Moreover, the frequency dependence of loss tangent was remarkably decreased, and the loss tangent was totally decreased below 0.01.

Room-temperature growth of Ni-Zn-Cu ferrite/PTFE composite thick films on PET via aerosol deposition

Ni-Zn-Cu ferrite and Ni-Zn-Cu ferrite/poly-tetra-fluoro-ethylene (PTFE) composite-thick-films were grown at room temperature on polyethylene terephthalate (PET) sheets via aerosol deposition (AD) as a magnetic shielding sheet for near-field communication. An 80 µm-thick Ni-Zn-Cu ferrite/PTFE composite-thick-film was grown on the PET sheet when 2.0 wt. % PTFE starting powder was used. The real relative permeability µr′ and the imaginary permeability µr″ of the Ni-Zn-Cu ferrite thick film were 10.1 and 2.1 at 13.56 MHz, respectively. In the case of the composite thick film, µr′ and µr″ decreased to 3.9 and 1.3, respectively, at 13.56 MHz; with the addition of the PTFE.

에어로졸 데포지션법으로 성막된 Al₂O₃ 후막의 유전특성

Aerosol Deposition Method (ADM) is a novel technique to grow ceramic thick films with high density and nano-crystal structure at room temperature. 1,2 ) For these unique advantages of ADM, it would be applied to the fabrication process of 3-D integration ceramic modules effectively. However, it is critical to control the properties of starting powders, because a film formation through ADM is achieved by impaction and consolidation of starting powders on the substrates. We fabricated alumina thick films by ADM for the application to integral substrates for RF modules. When the as-received alumina powders were used as a starting material without any treatments, it was observed that the dielectric properties of as-deposited alumina films, such as relative permittivity and loss tangent, showed high dependency on the frequency. In this study, some techniques of powder pre-treatments to improve the dielectric properties of alumina thick films will be shown and the effects of starting powders on the properties of AD films will be discussed.

Impedance Spectroscopy Analysis of the Screen Printed Thick Films

In this study, we fabricate 3 wt% doped thick films on the Ag/Pd bottom electrode printed substrates for the LTCCs (low temperature co-fired ceramics) applications. From the X-ray diffraction analysis, 3 wt% doped BST thick films on the Ag/Pd printed substrates, which sintered at , showed perovskite structure without any pyro phase. The dielectric properties of 3 wt% doped BST thick films are measured from 1 kHz to 1 MHz. To investigate the electrical properties of 3 wt% doped BST thick films, we employ the impedance spectroscopy. The complex impedance of 3 wt% doped BST thick films are measured from 20 Hz to 1 MHz at the various temperatures.