Dong-Lak Kim

Influence of Pt heterostructure bottom electrodes on SrBi2Ta2O9 thin film properties

The properties of SrBi2Ta2O9 (SBT) films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films grown on stable Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibit high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films synthesized on Pt/Ti/SiO2/Si. It is shown that severe diffusion of Ti from the Ti interlayer onto the surface of the Pt bottom electrode and the increased surface roughness of this electrode stack play key roles in degradation of SBT properties.

Ferroelectric Properties of New Chemical Solution Derived SBT Thin Films for Non-Volatile Memory Devices

Ferroelectric SBT (Sr/Bi/Ta = 0.8/2.3/2) thin films on Pt/ZrO2/SiO2/Si were successfully prepared by using an alkanolamine modified chemical solution deposition method. Acetic acid as a solvent led to the formation of water in the solution, which might continuously induce the hydrolysis and condensation of the precursors, leading to reducing the stability of the solution with aging time. It was observed that alkanolamine provided the stability to the SBT solution by retarding the hydrolysis and condensation rates. This solution could be used as long as up to 30 days without any appreciable change of the solution properties. The typical hysteresis loop of SBT thin films was obtained at 2 V, and it was fully saturated even below an applied voltage of 3 V (2Pr ≈ 16 μC/cm2). The measured 2Pr value of the SBT thin film at 5 V was almost 20 μC/cm2. Fatigue and breakdown characteristics of the films, measured at 5 V, showed a stable behavior, and negligible degradation was observed up to 1010 cycles.

Narrow resonance profiling study of the oxidation of reactively sputtered Ti1−xAlxN thin films

Abstract The bottom electrode structure used with ferroelectric (FE) and high dielectric constant (HDC) materials requires a material to promote FE or HDC cristallisation (Pt or IrO2) and a material with diffusion barrier properties; this last material being between Pt (or IrO2) film and Si substrate. TiN, TiAlN and TaSiN have been proposed for diffusion applications. Ti1−xAlxN films have drawn much attention as alternatives to TiN diffusion barriers. In this paper we have investigated the effect of Al content on the oxidation resistance of Ti1−xAlxN films prepared by radio frequency reactive sputtering in a mixed Ar+N2 discharge. The concentration depth profiles of both 18O and 27Al were measured before and after the rapid thermal annealing of samples at 750°C for 30 s in 18O2, via the narrow resonances of 18O(p,α)15N at 151 keV (fwhm=100 eV) and 27Al(p,γ)28Si at 992 keV (fwhm=100 eV). It was found that Al incorporation in the films reduces oxide growth. The Al excitation curves indicate a uniform Al content for as deposited Ti1−xAlxN, and reveal Al diffusion to the surface during oxidation, which indicates the formation of an Al rich oxide layer at the Ti1−xAlxN surface. The results suggest that Ti1−xAlxN films with x>0.39 are promising candidates as electrically conductive diffusion barrier layers.

An optimized process for fabrication of SrBi2Ta2O9 thin films using a novel chemical solution deposition technique

Ferroelectric SrBi{sub 2}Ta{sub 2}O{sub 9} (SBT) thin films on Pt/ZrO{sub 2}/SiO{sub 2}/Si were successfully prepared by using an alkanolamine-modified chemical solution deposition method. It was observed that alkanolamine provided stability to the SBT solution by retarding the hydrolysis and condensation rates. The crystallinity and the microstructure of the SBT thin films improved with increasing annealing temperature and were strongly correlated with the ferroelectric properties of the SBT thin films. The films annealed at 800 degree sign C exhibited low leakage current density, low voltage saturation, high remanent polarization, and good fatigue characteristics at least up to 10{sup 10} switching cycles, indicating favorable behavior for memory applications. (c) 1999 Materials Research Society.

Thermally induced imprint properties of chemical solution derived PLZT thin films

Abstract We investigate the imprint phenomenon by poling ferroelectric PLZT capacitors into a known state and exposing the devices to elevated temperatures. It is found that the compensation of oxygen vacancies is a important process parameter in determining the tendency to imprint. In the case of PLZT thin films, the voltage shifts related to imprint failure are attributed to the trapping electrons at defect sites near film/electrode interface, the magnitude of polarization and concentration of defect-dipole complexes involving oxygen vacancies such as V″Pb - V″o. The thermally induced voltage shifts in PLZT thin films are dopant concentration dependent and decrease with increasing the La concentration of the films.

DESIGN OF THE OPTICAL SYSTEM FOR A PROTOMODEL OF SPACE INFRARED CRYOGENIC SYSTEM

Many technical challenges are being tried for a large space infrared telescope, which is one of the major objectives of the Strategic Technology Road Map (STRM) of KASI (Korea Astronomy and Space Science Institute), As one of these challenges, KASI and KBSI (Korea Basic Science Institute) have started a cooperation project for developing a space infrared cryogenic system with KIMM (Korea Institute of Machinery as Materials) and i3system co. In this paper, we generate optical requirements for the Protomodel of Space Infrared Cryogenic System (PSICS), and design a single lens optical system with a bandpass of , a field of view of , and an angular resolution of , to develop a further complex optical system.

Impact of changes in the Pt heterostructure bottom electrodes on the ferroelectric properties of SBT thin films

Abstract The crystallinity and the microstructure of Sr0.8Bi2.3Ta2O9 (SBT) thin films improved with increasing annealing temperature, and strongly influenced the ferroelectric properties. In addition, the properties of SBT films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films on Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibited high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films on Pt/Ti/SiO2/Si substrates. This is deduced to be related to differences in film orientation, electrode roughness, and out-diffusion of Ti onto the surface of the bottom electrode.

Measurement of the Effective Piezoelectric Constant of Nitride Thin Films and Heterostructures Using Scanning Force Microscopy

ABSTRACT Piezoelectric properties of wurtzite AlN and GaN/AlN are investigated using scanning force microscopy (SFM). The magnitude of the effective longitudinal piezoelectric constant d 33 of AlN and GaN/AlN thin films are measured and reported, and the d 33 coefficients of these films are verified using an interferometric technique. Simultaneous imaging of the topography, and of the phase and magnitude of the piezoelectric strain is performed. Using a GaN film with patterned polarities, we demonstrate that polarity can be inferred from the phase image of the piezoelectric strain. We report d 33 =3±1 pm/V for AlN/SiC and 2±1 pm/V for GaN/AlN/SiC. Films grown by organo-metallic vapor phase epitaxy (OMVPE) on SiC, sputtered AlN films and films grown by molecular beam epitaxy (MBE) are characterized and compared. INTRODUCTION The piezoelectric properties of III-V nitrides are important for new heterostructure devices. As such, measurement of the piezoelectric properties of nitride thin films and heterostructures with nanometer scale resolution is of considerable interest for determining how defects and patterned structures affect the piezoelectric response (piezoresponse). Spontaneous and piezoelectric polarization-induced electric fields have been used to achieve a two dimensional electron gas (2DEG) at the interface of AlGaN/GaN heterostructures with sheet concentrations as high as 2x10

Oxidation resistance of TaSiN diffusion barriers

Abstract Due to his resistance to oxidation, TaSiN is a promising candidate as an electric conductive barrier layer for integration of ferroelectrics and high permittivity oxides in advanced memory devices. Here we report on the properties and the resistance to oxidation of TaSiN thin films deposited by reactive sputtering using a TaSi2 target and then processed by rapid thermal annealing (RTA) in 18O2 at 650°C. We use RBS (Rutherford Backscattering Spectroscopy) and NRA (Nuclear Reaction Analysis) to determine film compositions and XRD (X-Ray Diffraction) to study their microstructure. The concentration depth profiles of 18O was measured after the RTA treatments via the narrow resonances 18O(p,α)15N at 151 keV (fwhm=100eV). The relationship between the depth profiles and the excitation curves were deduced with the aid of the SPACES simulation program.

Calculation of alternating current distribution on the current lead for HTS power cable

High temperature superconductor (HTS) power cable can obtain substantially lower transmission losses than conventional cables. Termination of HTS cable is a connecting part between copper electrical cable at room temperature and HTS cable at liquid nitrogen temperature. Alternating current (AC) has been considered as an important parameter for the design of current lead for the HTS cable termination. When AC were flowing on the current lead currents were mainly distributed on the edge of the current lead due to skin effect and resulted in the nonuniformity of the current density across the cross-section of the current lead. As area increased, the influence of skin effect became serious and therefore Joule heating, i.e., AC loss generated on the AC current lead increased. In order to reduce the nonuniformity of the current distribution, an AC current lead has divided into several current leads that have smaller cross-sections than the original current lead. In this case, however, the array of current leads was important because the inductance from each current lead was different depending on the position. Heat load calculations on the copper current lead have been performed by analytical and numerical method. Larger heat loads were generated on the AC current lead than on the direct current (DC) lead because of the skin effect. In addition, the effect of inductance on the current distribution was investigated. As the gap distance between current leads decreased the effect of mutual inductance was found to be important. For this case has increased current amount generated on the current lead as well as AC loss. Also, the current direction in each small area current lead varied depending on the gap distance.