Choon-Ho Lee

Preparation of BaTiO3 Thin Films by Metalorganic Chemical Vapor Deposition Using Ultrasonic Spraying

Ferroelectric BaTiO3 thin films were fabricated by metalorganic chemical vapor deposition (MOCVD) at atmospheric pressure. The ultrasonic spraying technique has been used to carry the source materials. The common solutions of barium-diethylhexanoate and diisopropoxy-titanium-bis-acetylacetonate in n-butanol were used as the starting materials. Since the concentration of sources can be controlled in the common solution, this method is more simple and precise than other CVD processes. The films had (110) preferred orientation with increasing temperature. The dielectric constant (e) and the loss factor (tan δ) of thin film deposited at 550° C were about 250 and 0.1, respectively. The leakage current density was 10-5 A/cm2 at 0.1 MV/cm.

Preparation of zirconia thin films by metalorganic chemical vapor deposition using ultrasonic nebulization

Zirconia (ZrO{sub 2}) thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using ultrasonic nebulization with new source materials, Zr(OBu){sub 4}, Zr(OBu){sub 3}(acac), Zr(OBu){sub 2}(acac){sub 2}, and Zr(OBu)(acac){sub 3}. This process is a simple and economic method to prepare oxide thin films. Zr(OBu){sub 4} was successfully reacted with acetylacetone at a molar ratio of 1:3. Polycrystalline thin films were deposited at a substrate temperature range from 300{degree}C to 550{degree}C. The substitution of alkoxy radicals by acetylacetone made the deposition rate higher and insensitive to substrate temperature. The films deposited below 450{degree}C mostly had a monoclinic structure, and those deposited above 450{degree}C had a tetragonal structure. The measured optical energy band gap of zirconia film was 5.32 eV. {copyright} {ital 1996 Materials Research Society.}

Effect of Zr/Ti Ratio on the Properties of PZT Thin Films Made by MOCVD Using Ultrasonic Nebulization

Pb(Zr,Ti)O3 (PZT) films with various Zr/Ti ratios were fabricated on Pt/MgTi2O5/Si substrates by MOCVD using the ultrasonic nebulization and their characteristics were investigated. PZT thin films with various composition deposited at 400°C were annealed in a RTA (Rapid Thermal Annealing) system at 800°C for 30 sec to minimize the loss of the lead and improve electrical properties. The composition ratio of PZT films affected the crystallographic and electrical properties. For the films crystallized by the RTA process, the remanent polarization of PZT film with near MPB (Morphotropic phase boundary) composition was about 15 μC/cm2 at ±5 Voltage in P-E hysteresis loops. Leakage-current density of PZT films was about 1.0 × 10−7 A/cm2 and 7.0 × 10−5 A/cm2 at +5 V and −5 V, respectively.

The Characteristics of Magnesium Titanate Thin Film as Buffer Layer by Electron Beam Evaporation

We have studied the application of magnesium titanate thin films as buffer layer for the improvement of adhesion of Pt films to Si substrate. Magnesium titanate films were successfully prepared on Si(100) substrate by electron beam evaporation. The crystal phase of MgTi2O5 and MgTiO3 films on Si substrate were observed. These films had a very smooth and densely packed surface morphology and showed a good characteristic as the adhesion layer for Pt. Also, AES analysis showed the excellent properties as the reaction barrier layer between Pt and Si.

Preparation of Pb(Mg1/3Nb2/3)O3 Thin Films by MOCVD Using Ultrasonic Nebulization

Lead magnesium niobate (PMN) films were fabricated on Si substrates by MOCVD using the ultrasonic nebulization and their characteristics were investigated. PMN thin films deposited at 400°C were annealed in a RTA(Rapid Thermal Annealing) system at 700°C for 30 sec to improve structural and electrical properties. The crystallinity of PMN films strongly depends on the composition ratio of Pb, Mg and Nb component. PbTiO3 seed layer have a good effect on the formation of perovskite PMN films. At −20°C, the PMN films with perovskite phase act as a ferroelectrics, which show a typical butterfly type curve in the Capacitance—Voltage characteristics.

Crystallization in Pb(Zr, Ti)O3/Pt Thin Films on Mg2TiO4 Buffer Layer

Pb(Zr, Ti)O3 (PZT)/Pt structures were fabricated on an Si substrate with a Mg2TiO4 buffer layer and their crystallographic and morphological properties were studied. PZT and Mg2TiO4 thin films were deposited by the ultrasonic spraying metal-organic chemical vapor deposition (MOCVD) at atmospheric pressure. Pt thin films were deposited by RF magnetron sputtering. The crystallographic properties of Pt films were affected by the structure of the Mg2TiO4 films on which they grow. (111)-oriented platinum films were deposited on (111) Mg2TiO4 independently of deposition conditions. However, the Pt films deposited on (100)-oriented Mg2TiO4 films show a mixed orientation of (111) and (100), and the degree of (100) orientation was a function of the deposition temperature and crystallinity of Mg2TiO4 films. The surface morphology of Pt films differs depending on their crystallographic properties. (111)-oriented Pt films have excellently flat and dense surface morphology. (111)- or (100)-oriented PZT thin films were deposited on (111)- or (100)-oriented Pt layers, respectively. The surface morphology of (111)-oriented PZT thin films was more dense and flat than that of (100)-oriented PZT films.

MOCVD of Pb(Zr x Ti1-x )O3 thin films on MgTiO3/Si substrates and their electrical properties

Abstract Pb(Zh x , Ti1-x )O3(PZT) thin films were deposited on Si substrates using MgTiO3 as the buffer layer and the electrical properties of those MFIS structures were investigated. PZT and MgTiO3 films were made by MOCVD using ultrasonic spraying technique. Perovskite PZT films have been succesfully made at the substrate temperature of 550 to 600°C only when using MgTiO3 buffer layer. AES depth profile analysis and RBS analysis revealed that there is no remarkable interdiffusion and no formation of reaction layer between PZT and MgTiO3 and/or between MgTiO3 and Si substrate. The capacitance-voltage (C-V) curves of the MFIS structure which were made with PZT and MgTiO3buffer layer have shown the hysteresis resulted from the ferroelectric switching of the PZT films.

A Study on the Characteristics of MgO Thin Films Prepared by Electron Beam

MgO 박막은 성장용 기판 또는 완충층으로 이용되고 있으며, 근래에는 AC PDP의 유전체 보호막으로써 그 활용도가 넓어지고 있다. 본 연구에서는 전자빔증착법에 의해 MgO 박막을 증착시켜 증착변수에 따른 MgO 박막의 성장특성을 연구 하였다. 실험은 증착기판, 증착속도, 기판온도 등의 변화에 따른 MgO 박막의 우선배향성, 표면형상을 통하여 MgO 박막의 물성을 알아보았다. 실험결과, Si 기판에서는 증착속도가 빠를수록 (111)우선배향된 박막을 얻을 수 있었고, 기판온도가 상온일때는 (200)에서 기판온도가 증가할수록 (220)의 peak이 관찰되었다. 비정질인 slide glass 기판일 경우에는 상온에서 MgO 박막의 (200)면의 우선배향을 얻을수 있었고, 온도에 의해 배향성이 (200)면에서 (111)면으로 바뀌는 것을 알 수 있었다. 또한 MgO 박막의 배향성과 특성에 대한 관계를 조사하였다.

Effect of rapid thermal annealing on the properties of Pb(zr, Ti)O3 thin films made by low-temperature metal-organic chemical vapor deposition

Pb(Zr, Ti)O3 (PZT) films with stoichiometric composition were prepared by the new method of the combination of low-temperature metal-organic chemical vapor depositon (MOCVD) and rapid thermal annealing (RTA) and the effect of RTA on the structural and electrical properties of PZT thin films was investigated. As the RTA time increased, the loss of Pb increased. However, after the RTA process, the PZT films had a condensed and fine-grain microstructure and a single perovskite phase at 800°C annealing temperature and annealing time of 30 s. For the film crystallized by the RTA process, the remanent polarization (2Pr) was about 15 µC/cm2 with an applied voltage of 5 V in P–E hysteresis loops and the films had a dielectric constant of 475 in the capacitance-voltage curve. Leakage-current densities of PZT films were about 9.6×10-5 A/cm2 and 5.0×10-5 A/cm2 at +5 V and -5 V, respectively.

Preparation of Ba6Ti2Nb8O30 Thin Films by MOCVD using Ultrasonic Nebulization

In this study, Ba6Ti2Nb8O30 thin films were deposited on Pt/Ti/SiO2/Si substrates by the MOCVD using ultrasonic nebulization and their deposition characteristics were investigated. Single phase Ba6Ti2Nb8O30 films could be obtained by varying the mixing ratios of the source solutions for BaTiO3 and BaNb2O6 films at the deposition temperature range of 350∼400°C. The crystallinity of Ba6Ti2Nb8O30 films was enhanced by the RTA treatment. The Ba6Ti2Nb8O30 thin films showed the dielectric constant of 53.5 (at 100 kHz). And the current density was 1.361 × 10−4 A/cm2 at +10 V, and 1.424 × 10−5 A/cm2 at −10 V. Also, the remanent polarization was 0.459 μC/cm2 and the coercive field was 36.865 kV/cm.