Kuo-Shung Liu

Improvement of (Pb1−xLax)(ZryTi1−y)1−x/4O3 ferroelectric thin films by use of SrRuO3/Ru/Pt/Ti bottom electrodes

This work deposits (Pb1−xLax)(ZryTi1−y)1−x/4O3 (PLZT) thin films, possessing good ferroelectric properties (Pr=14.4 μC/cm2), on Pt/Ti/SiO2/Si substrates, using SrRuO3 perovskite as bottom electrodes. Precoating a metallic Ru layer on Pt/Ti/SiO2/Si substrates prior to depositing SrRuO3 bottom electrode further improves the film electrical properties. The optimum ferroelectric properties achieved are Pr=25.6 μC/cm2, Ec=47.1 kV/cm, and er=1204. Analyzing the elemental depth profiles using secondary ions mass spectroscopy reveals that the presence of the metallic Ru layer effectively suppresses the outward diffusion of Ti and Si species. The interdiffusion between the SrRuO3 layer and the subsequently deposited PLZT is also substantially reduced, an effect that is presumed to be the primary factor in improving ferroelectric properties for PLZT thin films.

Two-step oxygen injection process for growing ZnO nanorods

Uniform hexagonal prismatic zinc oxide rods were grown over the entire alumina substrate at 550 °C using a two-step oxygen injection process, whether the substrates were coated with a catalyst or not. X-ray diffraction showed that all of the depositions exhibited a preferred orientation in the (002) plane. The influence of oxygen concentration was investigated by changing the oxygen flow rate. Oxygen concentration affected the size of ZnO nanorods, especially the diameter. The ZnO nanorods were further checked using high-resolution transmission electron microscopy, photoluminescence, Raman spectroscopy, and room-temperature ultraviolet lasing. The results showed that the rods were single crystals and had excellent optical properties. By observing the growth process, we found that the diameter increased slowly, but the longitudinal growth rate was very high. The growth of ZnO nanorods revealed that the uniform hexagonal prismatic ZnO nanorods were synthesized through vapor deposition growth and a self-catalyzed vapor-liquid-solid (VLS) process.

Electron field emission properties of pulsed laser deposited carbon films containing carbon nanotubes

Carbon nanotubes (CNTs) were successfully synthesized by using a modified pulsed laser deposition (PLD) process, in which the laser ejected carbon species were directly collected by silicon substrates. A catalyst layer is needed in this process. The morphology of catalyst clusters varies with the heat treatment process which, in turn, alters the morphology and field emission properties of the CNTs pronouncedly. Compared with the conventional laser ablation process, such a modified PLD process is simpler, has better collection efficiently, and has a higher production rate. The CNTs thus obtained exhibit superior field emission electron properties, viz. Je=160 μA/cm2 and E0=1.76 V/μm.

On the microwave sintering technology for improving the properties of semiconducting electronic ceramics

Abstract Microwave (millimeter wave) sintering technology used for enhancing the densification behavior and electrical properties of ZnO electronics ceramic materials was described. Successfulness in application of such a novel technique to sinter ceramics relies heavily on the microwave (millimeter-wave) absorption efficiency of the materials. Semiconducting oxides such as Bi2O3-doped ZnO materials perform satisfactorily in microwave (millimeter-wave) sintering. Using susceptors to facilitate absorption efficiency of the samples greatly improves the sinterability of the materials. The advantage of the microwave (millimeter-wave) sintering process over the conventional sintering technique is best demonstrated by fast firing of Bi2O3-based ZnO varistor materials, in which, the whole sintering process required only 18 min. The varistor characteristics obtainable are: α=38, JL=55.5×10−6 A/cm2 and Vbk=600 V/mm.

Effect of LaNiO3/Pt double layers on the characteristics of (PbxLa1 – x)(ZryTi1 – y)O3 thin films

Characteristics of LaNiO3 (LNO) thin films deposited by rf sputtering process were compared with that prepared by pulsed laser deposition (PLD) process. rf sputtered LNO films were [200] preferentially oriented with a low surface resistivity (ρs=0.55 mΩ cm) and the PLD deposited films were [110] predominated with a slightly larger surface resistivity (ρs=6.38 mΩ cm). Using Pt coating as underneath layer markedly reduced the surface resistivity (ρs=0.05 mΩ cm) without modifying the texture characteristics of the LNO layers. PLZT films subsequently deposited on LNO layers inherited the texture characteristics of the underlying LNO layers. Ferroelectric properties of PLZT films were optimized when using LNO–Pt double layers as bottom electrodes. The remanent polarization and coercive force obtained were Pr=14.9 μC/cm2 and Ec=3.5 kV/cm, respectively.

PYROELECTRIC PROPERTIES OF (PB1-XLAX)TIO3 THIN FILMS DEPOSITED USING SRRUO3 AS A BUFFER LAYER

In this study, we observed that the ferroelectric properties of (Pb1−xLax)TiO3, (PLT) thin films deposited on Pt/Ti/Si substrates using SrRuO3 as a buffer layer change markedly with the substrate temperature and the composition. All the films are perovskite with no secondary phases when deposited at 500–600 °C. However, only the films deposited below 520 °C possess a satisfactory small leakage current density, for example, JL⩽10−7 A/cm2, under a 50 kV/cm applied field. Both PLT10 (x=0.10) and PLT5 (x=0.05) thin films thus obtained possess large pyroelectric coefficient (p=0.009–0.018 °C−1). However, the PLT10 thin films show pyroelectric properties markedly superior to the PLT5 thin films, although the PLT5 thin films own much better ferroelectric properties. This phenomenon is explained by the lower Curie temperature (Tc) of the PLT10 materials.

Ferroelectric properties of (Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3 films deposited on Si3N4-coated Si substrates by pulsed laser deposition process

(Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3, PLZT, thin films deposited on either LaNiO3 (LNO) or LNO/Pt coated Si3N4/Si substrates, possessing good ferroelectric properties, were successfully obtained by the pulsed laser deposition process. Using LNO/Pt as double layer electrodes not only resulted in PLZT films with superior electric properties, but also of better handling endurance. The former is attributed to the low surface resistivity of electrode materials (i.e., ρLNO/Pt=0.5 mΩ cm) due to the bypassing effect of the Pt layer, whereas the latter is ascribed to the induction of compressive stress on PLZT and LNO layers due to a relatively larger thermal expansion coefficient (CTE) of the Pt layer. The ferroelectric properties of (PLZT )LNO/pt films were Pr=16.5 μC/cm2 and Ec=63.5 kV/cm, while the dielectric constant and leakage current were K=1.028 and Je⩽8×10−6 A/cm2 (under 150 kV/cm), respectively. Their fatigue life was longer than 2×109cycles under action of 300 kV/cm pulse.

Blue, Green and White InGaN Light-Emitting Diodes Grown on Si

High-brightness InGaN light-emitting diodes (LEDs) have been grown on Si substrates by metal-organic vapor phase epitaxy. Both blue and green LEDs with an output power exceeding 0.7 mW and a lifetime exceeding 500 h were achieved. Two factors were analyzed: the difference between identical LED structures grown on Si and sapphire substrates, and the effect of cracking on the performance of LEDs grown on Si. Using a Si substrate, the LED emission showed a shift toward longer wavelength compared with that from a LED grown on sapphire. The presence of cracking, unless serious, showed little effect on the brightness and performance of the LEDs grown on Si. The mechanisms involved are discussed.

Low-temperature growth of ZnO nanowires

ZnO nanowires with diameters of 40-200 nm were grown with a gold catalyst in bulk quantities on alumina substrates and sapphire substrates. This synthesis procedure was achieved by heating a 1: I mixture of ZnO and Zn powder to 500 °C with trace water vapor as an oxidizer. X-ray diffraction and transmission electron microscopy revealed that the nanowires were in the pure wurtzite phase. Photoluminescence spectroscopy showed two peaks: one was a strong ultraviolet emission at around 380 nm, which corresponds to the near-band-edge emission; the other was a weak near-infrared emission around 750 nm, which indicates a low concentration of oxygen vacancy. Moreover, we observed that the Zn/Au alloy droplets appeared on the tips of ZnO nanowires. As a consequence, we can select areas to grow ZnO nanowires by patterning the thin metal film on the substrates. These findings prove that the low-temperature growth mechanism is via vapor-liquid-solid rather than vapor transport deposition or vapor supersaturation (vapor-solid) mechanism. On the basis of the site-specific growth and the low-temperature requirement developed from this work, the synthesis of ZnO is compatible to microelectric machining system processing.

Effect of substrate materials on the electron field emission characteristics of chemical vapor deposited diamond films

Substrate materials used for growing diamond films were observed to modify thin films’ electron field emission properties significantly. Using heavily doped silicon (LR-Si) as a substrate lowered the turn-on field from (E0)Si=14.4 V/μm to (E0)LR-Si=9.7 V/μm and increased the emission current density from (Je)Si=4 μA/cm2 to (Je)LR-Si=40 μA/cm2 (at 16 V/μm). However, electron field emission properties can be further improved only by using Au precoatings to modify the characteristics of interfacial layer. The turn-on field was lowered further to (E0)Au–Si=8.7 V/μm and emission current density was increased further to (Je)Au–Si=400 μA/cm2 (at 16 V/μm). Secondary ion mass spectroscopic examination indicated that the main interaction is the outward diffusion of Au species into amorphous carbon layer, lowering the resistivity of this interfacial layer. The electrons can therefore be transported easily from Si substrate across the interfacial layer to the diamonds and subsequently field emitted.