June Key Lee

Characterization and elimination of dry etching damaged layer in Pt/Pb(Zr0.53Ti0.47)O3/Pt ferroelectric capacitor

The damage of Pb(Zr0.53Ti0.47)O3 thin film due to dry etching process was characterized in terms of the microstructure and electrical properties. The damaged layer seems to be amorphous and the thickness of the damaged layer is about 10 nm. The existence of such a layer in Pt/Pb(Zr0.53Ti0.47)O3/Pt ferroelectric capacitor tends to increase the coercive voltage and the leakage current. The damaged layer was not fully reverted to perovskite phase by the thermal annealing. With the wet cleaning treatment, however, the damaged layer was successfully removed thereby revealing significantly improved electrical properties.

Improvement of catastrophic optical damage (COD) level for high-power 0.98-μm GaInAs-GaInP laser

We investigate improvement of catastrophic optical damage (COD) level for Al-free 0.98-/spl mu/m ridge waveguide laser diodes (LDs) using the impurity induced layer disordering (IILD) process applied near the facets. The IILD is used for the purpose of forming transparent windows near both facets of the LDs utilizing its ability to increase bandgap energy of the GaInAs-GaInAsP strained quantum-well (QW) active layer. Improvement of the cod level by at least 1.65 times compared to the conventional LDs is obtained for the LDs with Si/sup +/ implantation followed by annealing at 900/spl deg/C for 10 min.

Liquid delivery metal-organic chemical vapor deposition of Pb(ZrxTi1-x)O3 thin films for high-density ferroelectric random access memory application

The growth characteristics of Pb(ZrxTi1-x)O3 (PZT) thin films were investigated for application to high-density ferroelectric random access memories (FeRAM) devices. Films were grown by the liquid source metal-organic chemical vapor deposition (LS-MOCVD) method with tmhd-family precursors, such as Pb(tmhd)2, Zr(tmhd)2(OiPr)2 and Ti(tmhd)2(OiPr)2, dissolved in octane. Film deposition was mainly performed at 560°C, because it is the highest temperature at which bottom electrode contact could be maintained against oxidation in our capacitor over bit-line (COB) structure. The control of Pb precursor supply plays the most critical role in realizing a reliable process for PZT thin film deposition. We have monitored the changes in the microstructure and electrical properties of films on increasing the Pb precursor supply into the reaction chamber. Under optimized conditions, Ir/IrO2/PZT(100 nm)/Ir capacitor shows well-saturated hysteresis loops with a remanent polarization (Pr) of ~ 28 µC/cm2 and coercive voltage of 0.8 V at 2.5 V.

Integration and electrical properties of diffusion barrier for high density ferroelectric memory

A reliable Ir diffusion barrier was prepared on polysilicon plugged substrate with a contact size of 0.6 μm. Using a Ti adhesion layer and stress-relief process, it was possible to integrate the Ir barrier into a high density 4 Mb ferroelectric random access memory device. After heat treating sol-gel derived Pb(Zr1−xTix)O3 (PZT) films at 700 °C, the Ir barrier contact displayed an ohmic behavior and showed a low resistance of 130 Ω per contact in 1k serial contact array. The PZT films on Pt/IrO2/Ir poly-plugged substrate exhibited excellent ferroelectric properties such as remnant polarization and coercive voltage of 25 μC/cm2 and 1.15 V, respectively. Auger depth profile and transmission electron microscopy analyses confirmed that no appreciable oxidation was formed between the Ir barrier and the polysilicon plug.

Evolution of residual stress in plasma-enhanced chemical-vapor-deposited silicon dioxide film exposed to room air

Considerable increase in compressive stress was observed in silicon dioxide films upon prolonged exposure to atmospheric moisture. The compressive stress change upon exposure to atmosphere consisted of a reversible change and an irreversible change. The irreversible component was found to be due to structural changes in the Si–O–Si network. The reversible change in stress is due to water molecules absorbed on walls of the pores.

InGaN/AlGaN Ultraviolet Light-Emitting Diode with a Ti3O5/Al2O3 Distributed Bragg Reflector

Here, we report InGaN/AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using distributed Bragg reflectors (DBRs). The DBRs consist of 11 layers of alternating quarter-wave thickness Ti3O5 and Al2O3 deposited onto the indium–tin-oxide ohmic contact layer of a 385 nm UV LED by ion-assisted electron beam evaporation. Numerical calculations showed that the angle averaged reflectivity of the GaN/DBR structure at 385 nm was 12% higher than that of a conventional GaN/Ag structure. The measured light output–current–voltage of the DBR UV LEDs at 20 mA current injection showed an increase of 15% in output power in comparison to a conventional Ag reflector with no degradation in electrical properties. We attributed this light output enhancement to the increased light extraction from the higher DBR reflectivity.

Enhanced Light Output Power of GaN-Based Vertical Light-Emitting Diodes by Using Highly Reflective ITO–Ag–Pt Reflectors

Highly reflective and thermally stable indium-tin-oxide (ITO)-Ag-Pt p-type reflectors for use in high-performance GaN-based light-emitting diodes (LEDs) have been investigated. The specific contact resistance of the ITO-Ag-Pt contacts was found to be 7.2 ×10-5Omegamiddotcm2. The ITO-Ag-Pt contacts showed a higher reflectance after thermal annealing (82% at 460 nm), while the reflectance of the ITO-Ag contacts was reduced from 81% to 65%. In addition, surface agglomeration was drastically decreased, indicating that the Pt layer efficiently prevents the surface agglomeration of the Ag layer. The vertical LEDs (VLEDs) fabricated with the ITO-Ag-Pt contacts had a 17% higher output power (at 20 mA) than the VLEDs fabricated with the ITO-Ag contacts.

Dopant effects on the grain structure and electrical property of PZT thin films prepared by sol-gel process

Abstract PZT ( Zr Ti = 53 47 ), PNZT (4% Nb doped PZT), PSZT (2% Sc doped PZT) and PSNZT (1% Sc and 1% Nb doped PZT) thin films were prepared by a sol-gel process. They were characterized by XRD, SEM, AFM and TEM. It was observed that the crystallographic orientation and the grain size of PZT film can be changed by doping. Pt/PZT/Pt capacitors were fabricated for the measurement of ferroelectric properties. By the doping of Sc and Nb together, the fatigue property of PZT was considerably improved and the coercive field was decreased, while the remanent polarization was not changed.

Ferroelectric behavior of orientation-controlled PbBi4Ti4O15 thin films

Ferroelectric lead bismuth titanate (PbBi4Ti4O15) thin films, selectively controlled in c-axis and off-c-axis orientation, were fabricated on a Pt layer by a chemical solution deposition method. The off-c-axis oriented PbBi4Ti4O15 films demonstrated much higher remanent polarization (8.7 μC/cm2) than those of c-axis oriented films (3.7 μC/cm2). Regardless of grain orientation, PbBi4Ti4O15 films were not fatigued up to 1010 cycles under 9-V application. It is deduced that the role of Bi2O22+ layer in inducing fatigue-free property for this Bi-layered perovskite structure is the self-regulation of space charge.

Investigation of hydrogen-induced degradation in Pb(ZrxTi1−x)O3 thin film capacitors for the application of memory devices

Hydrogen-induced degradation in Pb(ZrxTi1−x)O3 (PZT) thin film capacitors is investigated in terms of three process parameters, such as electrode structures (Pt/PZT/Pt and Ir/IrO2/PZT/Pt/IrO2), Zr/Ti compositional ratios (60/40, 53/47, 40/60, 30/70), and the domain poling states (±5 V). It was found that the hydrogen-induced degradation is enhanced when PZT films have high Ti portion, and can be suppressed by domain poling prior to the hydrogen anneal. From secondary ion mass spectroscopy analysis, it can be concluded that the hydrogen-induced degradation originates mainly from the interface of PZT and Pt electrodes. Hysteresis loop shifts in PZT capacitors indicate that negative charge develops at interfaces by the hydrogen anneal. Chemically, hydrogen-induced degradation can be elucidated as the formation of negatively charged hydroxyl group (OH−).