Hong-Ki Kim

Effects of starting powder and thermal treatment on the aerosol deposited BaTiO3 thin films toward less leakage currents

To prepare high-density integrated capacitors with low leakage currents, 0.2-μm-thick BaTiO3 thin films were successfully deposited on integrated semiconductor substrates at room temperature by the aerosol deposition (AD) method. In this study, the effects of starting powder size were considered in an effort to remove macroscopic defects. A surface morphology of 25.3 nm and an interface roughness of less than 50 nm were obtained using BT-03B starting powder. The nano-crystalline thin films achieved after deposition were annealed at various temperatures to promote crystallization and densification. Moreover, the influence of rapid thermal annealing process on the surface morphology and crystal growth was evaluated. As the annealing temperature increased from room temperature to 650°C, the root mean square (RMS) roughness decreased from 25.3 to 14.3 nm. However, the surface was transformed into rough performance at 750°C, which agreed well with the surface microstructure trend. Moreover, the crystal growth also reveals the changes in surface morphology via surface energy analysis.

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.

Densification mechanism of BaTiO3 films on Cu substrates fabricated by aerosol deposition

In order to achieve the aerosol deposition (AD) process as a thin film deposition process, the densification mechanism of the AD process was investigated. BaTiO3 films with thicknesses of 0.2, 0.5, and 2 μm on Cu substrates were fabricated using the AD process at room temperature in order to investigate the densification mechanism according to the increased the film thickness; we also investigated the resulting properties, including the microstructure, the electrical properties, and the hardness. As a result, we confirmed that the enhanced hammering effect (which is a densification procedure that works by continuous impaction of ceramic particles onto pre-impacted particles), formed dense BaTiO3 films with greater hardness and decreased leakage current characteristics. Furthermore, we concluded that the BaTiO3 particles, which were sufficiently fractured due to the hammering effect, were important in fabricating the dense BaTiO3 thin films. Therefore, we suggested the two-step deposition method (deposition and etching).

Preparation of Ultrasensitive Humidity-Sensing Films by Aerosol Deposition

Aerosol deposition (AD) is a novel ceramic film preparation technique exhibiting the advantages of room-temperature operation and highly efficient film growth. Despite these advantages, AD has not been used for preparing humidity-sensing films. Herein, room-temperature AD was utilized to deposit BaTiO3 films on a glass substrate with a Pt interdigital capacitor, and their humidity-sensing performances were evaluated in detail, with further optimization performed by postannealing at temperatures of 100, 200, ..., 600 °C. Sensor responses (i.e., capacitance variations) were measured in a humidity chamber for relative humidities (RHs) of 20-90%, with the best sensitivity (461.02) and a balanced performance at both low and high RHs observed for the chip annealed at 500 °C. In addition, its response and recovery were extremely fast, respectively, at 3 and 6 s and it kept a stable recording with the maximum error rate of 0.1% over a 120 h aging test. Compared with other BaTiO3-based humidity sensors, the above chip required less thermal energy for its preparation but featured a more than 2-fold higher sensitivity and a superior detection balance at RHs of 20-90%. Cross-sectional transmission electron microscopy imaging revealed that the prepared film featured a transitional variable-density structure, with moisture absorption and desorption being promoted by a specific capillary structure. Finally, a bilayer physical model was developed to explain the mechanism of enhanced humidity sensitivity by the prepared BaTiO3 film.

Room Temperature Fabrication of MIMCAPs via Aerosol Deposition

We report the microwave dielectric properties of BaTiO3 thin films fabricated via aerosol deposition, which is capable of applying functional ceramic films to Si-based semiconductor fabrication at room temperature. As the starting powder, BaTiO3 powder with an average particle size of 300 nm afforded a dense thin film with a thickness of 500 nm as well as a smooth interface with the Pt/Ti/SiO2/Si substrate. In comparison, the interface roughness of BaTiO3 thin film was degraded (>100 nm) when BaTiO3 powder with an average particle size of 450 nm was used as the starting powder, owing to the excessive impact energy during film growth. Metal-insulator-metal capacitors were realized on a Si wafer via electron beam evaporation and inductively coupled plasma etching in order to determine the relative permittivity, loss tangent, and current-voltage characteristics. The average values of the relative dielectric permittivity and loss tangent of the BaTiO3 thin film were 78 and 0.03, respectively, in the frequency range of 1-6 GHz.

Development and Electrical Properties of (Ca 0.7 Sr 0.3 ) (Zr 0.8 Ti 0.2 )O 3 Thin Film Applied to Embedded Decoupling Capacitors

A formed device embedded-type 0402 sized (Ca_0.7Sr_0.3) (Zr_0.8Ti_0.2)O₃ (CSZT) embedded capacitor was fabricated for use in embedded printed circuit board. The capacitance and dielectric loss of the CSZT embedded capacitor were 406.1 pF and 0.015, respectively, at 1 MHz. The CSZT embedded capacitor exhibits stable capacitance with varying applied voltage and C Zero G (-55 °C-125 °C, delta C/C = ±30 ppm/°C) properties. The measured values of equivalent series resistance and equivalent series inductance were 6.1 Ω and 62.39 μH, respectively. The leakage current density was 0.78 μA/cm² at 3 V of applied voltage. These electrical properties indicate that the CSZT embedded capacitor holds promise for use as an embedded passive capacitor.

Effect of sintering temperatures on the piezoelectric and dielectric properties of 0.98(Na0.5K0.5)NbO3-0.02(Ba0.5Ca0.5)TiO3 ceramics

Lead-free 0.98(Na0.5K0.5)NbO3-0.02(Ba0.5Ca0.5)TiO3 (0.98NKN-0.02BCT) ceramics were produced by using a conventional mixed oxide method with sintering temperature from 1080°C to 1120°C and their piezoelectric properties were investigated. The results indicate that the sintering temperature influences the electrical and the piezoelectric properties of 0.98NKN-0.02BCT ceramics. For the 0.98NKN-0.02BCT ceramics sintered from 1080°C to 1120°C, the piezoelectric constant d33, electromechanical coupling factor kp, remnant polarization values Pr and curie temperature Tc increased with increase sintering temperature. However, for 0.98NKN-0.02BCT sintered above 1100°C, their values decreased. Piezoelectric properties of d33 = 210 ρC/N and kp=46%, ferroelectric properties of Pr = 16.2 µC/cm2 and dielectric constant ɛr = 5159 were obtained for specimen sintered at 1100°C for 4 h. Therefore, the 0.98NKN-0.02BCT ceramics are excellent candidate materials for lead-free piezoelectric ceramics.

Electrochemical Properties of (Li 0.5-x Na x La 0.5 )Ti 0.8 Zr 0.2 O 3 Ceramics as Improved Electrolyte Materials for Li-ion Batteries

We fabricated (Li0.5-xNaxLa0.5)Ti0.8Zr0.2O3(LNTLZ)ceramics (0≤x≤0.4) with a perovskite structure via standard solid state synthesis. The influence of Na content on the structural and electrical properties of LNTLZ ceramics was also investigated. During XRD patterns analysis, all of the samples showed orthorhombic structure. The resistance of LNTLZ ceramics decreased as Na content increased, and the maximum activation energy shows 0.56 eV at x=0.4 at room temperature. These results indicated that LNTLZ ceramics are a candidate for use Lithium ion batteries as electrolytes.

Post Annealing Effect on the Characteristics of Al2O3 Thin Films Deposited by Aerosol Deposition on 4H-SiC

thin films has been investigated by XRD (X-ray diffraction), AFM (atomic force microscope), SEM (scanning electron microscope), and AES (auger electron spectroscopy). Also electrical properties have been investigated by Keithley 4,200 semiconductor parameter analyzer to explain the interface trapped charge density (D