Thermal Stability Of Electrical Properties Research Articles

Effect of ZnO cap layer deposition environment on thermal stability of the electrical properties of Al-doped ZnO films

Al-doped ZnO (AZO) is a promising candidate as a transparent conducting electrode. However, the electrical properties of AZO deteriorate greatly after exposing it to excessive heat. This limits the applications of AZO in devices that experience a demanding operation environment. It has been shown that a ZnO cap layer with proper morphology is capable to dramatically improve the thermal stability of AZO. However, the detailed mechanism is not yet clear. A comparison study of the electrical properties of AZO with a ZnO cap layer prepared by magnetron sputtering (MS) at low substrate temperature (70 °C) and chemical vapor deposition (CVD) at high substrate temperature (600 °C) indicates that MS-prepared ZnO is much less effective in protecting AZO from an oxidizing environment under elevated temperature than the CVD-prepared ZnO. The morphology and crystal structures of two types of ZnO/AZO, investigated by a scanning electron microscope and x-ray diffraction, are relatively similar, whereas the atomic structures (e.g., defects) revealed by Raman spectroscopy are rather different. The results suggest that it is difficult to improve the thermal stability of electrical properties of AZO without a proper restructuring process and a ZnO cap layer that could sacrifice its own structural order. The discoveries offer a novel approach to improve the performance of other transparent conducting oxides.

Effect of sintering temperature on the depolarization behavior of (Bi0.5Na0.5)TiO3‐based ceramics

Abstract(Bi0.5Na0.5)TiO3 (BNT)‐based ferroelectric ceramics have drawn extensive attention because of their excellent electrical properties and interesting depolarization behavior. However, the poor thermal stability of electrical properties limits their practical application. In this work, the effect of sintering temperature (Ts) on the depolarization behavior of BNT‐based ceramics was systematically investigated. It is found that the depolarization temperature Td determined from pyroelectric measurement tends to decrease with increasing Ts, which indicates that lower Ts defers the ferroelectric‐relaxor (FE‐RE) phase transition. However, for the samples sintered at higher Ts (such as 1180°C), although the Td is reduced, the thermal stability is better compared with the sample sintered at lower Ts (1100°C) because the diffuse behavior of the FE‐RE phase transition is suppressed. According to these results, we propose that the thermal stability of electrical properties for BNT‐based ceramics is not only related to high Td, but also to the diffuse degree of phase transition.

Magnetically tunable composite ferrite-dielectric microwave elements

Multiphase microwave dielectrics with high electrical quality and adjustable thermal stability of electrical properties have been investigated on the basis of barium polytitanates. The nature of high Q-factor and the opportunity to manage the thermal stability of multiphase systems is explained. Composite resonance elements based on high-quality multiphase dielectric materials and ferromagnetic film have been developed. It is shown that composite resonators are characterized by high Q-factor and the ability to control the resonant frequency by a magnetic field, which allows them to be used in various tunable microwave devices.

B-doping and annealing on the properties of B and Ga co-doped ZnO films

Transparent conducting boron (B) and gallium (Ga) co-doped ZnO (BGZO) films were deposited by radio frequency (RF) magnetron sputtering. The influence of B-doping and annealing treatment on properties of BGZO films was investigated. The results indicate that all samples have hexagonal wurtzite structure with (002) preferential orientation and the film crystallinity is improved with increasing annealing temperature. The hall mobility of films increases and the carrier concentration decreases with the increasing of annealing temperature. The films also show red shift of the optical bandgap with the increasing of annealing temperature. The incorporation of B increases the thermal stability of electrical properties of the BGZO film.

Temperature dependence of intrinsic and extrinsic dielectric contributions in 0.27Pb(In1/2Nb1/2)O3–0.46Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 single crystals

The temperature dependence of extrinsic and intrinsic dielectric contributions was quantitatively evaluated by Rayleigh analysis in [001]C‐oriented rhombohedral 0.27Pb(In1/2Nb1/2)O3–0.46Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 (PIN–PMN–0.27PT) single crystal. It is shown that both contributions increase with temperature and reach maximum values at around the rhombohedral–tetragonal phase‐transition temperature TR–T. However, the enhancement of the extrinsic part is more significant than the intrinsic one. The percentage of extrinsic contribution regarding the total dielectric response increases from 1% at room temperature to 34% at around TR–T. In addition, the influence of the polymorphic phase transition on intrinsic and extrinsic contributions is discussed. This work enables us to further understand the thermal stability of electrical properties and the influence of polymorphic phase transition in ferroelectrics.

Thermally stable yttrium–scandium oxide high-k dielectrics deposited by a solution process

We investigated the thermal stability of electrical properties in ternary alloy (YxSc1−x)2O3 high-k oxides as a function of yttrium fraction, x. The yttrium–scandium oxide dielectric films are deposited using a facile ink-based process. The oxides have a stoichiometry-dependent relative dielectric constant of 26.0 to 7.7 at 100 kHz, low leakage current density of 10−8 A·cm−2, high breakdown field of 4 MV⋅cm−1, and interface trap density of 1012 cm−2·eV−1 with silicon. Compared with binary oxides, ternary alloys exhibit less frequency dispersion of the dielectric constant and a higher crystallization temperature. After crystallization is induced through a 900 °C anneal, ternary (Y0.6Sc0.4)2O3 films maintain their low leakage current and high breakdown field. In contrast, the electrical performance of the binary oxides significantly degrades following the same treatment. The solution-processed ternary oxide dielectrics demonstrated here may be used as high-k gate insulators in complementary metal-oxide semiconductor (CMOS) technologies, in novel electronic material systems and devices, and in printed, flexible thin film electronics, and as passivation layers for high power devices. These oxides may also be used as insulators in fabrication process flows that require a high thermal budget.

Thermal Stability of Electrical Properties and Amine Vapour Sensitivity of In-Situ Prepared Polyaniline/Graphene Nanocomposites Assisted by Sodium Dodecyl Sulfate Micelles

Polyaniline (Pani)/graphene (GN) nanocomposites were prepared by in-situ oxidative polymerization of aniline with GN in presence of sodium dodecyl sulfate. The effects of polymerization and modification of the chemical structures in the nanocomposites were characterized by fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction techniques (XRD). Sodium dodecyl sulfate played the role of a surfactant, improving the dispersion of GN within the polymer matrix simultaneously. FTIR results revealed the presence of π-π interactions between Pani and GN leading to the formation of a charge-transfer complex. The thermal stabilities of the electric properties of the as-prepared nanocomposites were investigated as a function of GN content. As-prepared Pani/GN nanocomposites showed greater electrical conductivity as well as improved thermal stability in terms of DC electrical conductivity retention under isothermal and cyclic ageing conditions compared with pure Pani. They were also observed to possess better amine sensing properties in comparison to pure Pani when exposed to the vapour of methylamine.

A promising approach to enhanced thermal stability of DC conductivity of polyaniline - functionalised multi-walled carbon nanotube composites

Nanocomposites of polyaniline and 4-aminobenzoyl functionalised multiwalled carbon nanotubes (PANI-FMWCNT) were synthesised through interfacial polymerisation of aniline in presence of FMWCNT and protonating with various dopants. The composites were characterised by SEM, TEM and TGA. The high temperature DC conductivity stability was investigated through cyclic accelerated ageing and isothermal ageing studies. On thermal cyclic treatment up to 150°C, after the fifth cycle, electrical conductivity for various acid doped PANI samples rapidly dropped to 42–59% of their initial values, while PANI-FMWCNT samples showed only negligible decrease to 80–87%. Isothermal ageing studies showed that the PANI samples started reduction in conductivity at 110°C whereas nanocomposites retained conductivity stability even at 140°C. Both neat PANI and composites containing NSA and TSA had a higher thermal stability of electrical properties than polyaniline doped with HCl and H2SO4. The role of FMWCNTs in stabilising the DC conductivity of composites at elevated temperature is discussed.

Thermal stability of electrical properties of ZnO:Al films deposited by room temperature magnetron sputtering

In order to investigate the thermal stability of electrical properties for aluminum doped zinc oxide (ZnO:Al, AZO) films deposited by direct current reactive magnetron sputtering, AZO films deposited from an alloy target (0.8 wt.% Al) on soda-lime glasses were annealed in argon gas at different temperatures. A data capturer was applied to monitor and collect real-time sheet resistance ( R s) of the films throughout the annealing. Results revealed that R s of the film heated at 100 °C was reduced throughout the annealing, however, conductivity of the films annealed over 100 °C was improved at early stage but then deteriorated all along to the end. Some novel R s change points which need more penetrations were detected. The experimental results obtained from electron diffraction spectrum, X-ray diffraction pattern, X-ray photoelectron spectrum, and Hall measurement were analyzed to explore the effect of the annealing on the electrical properties of AZO films. It was found that the exotic element, which might influence the film properties, was not observed. It was also suggested that the transformation of the crystalline structure and surface chemical bonding states, which resulted in the decrease of carrier concentration and mobility could be the reason for the conductivity degeneration of the films annealed at higher temperature.

MgTiO3 Modified (Na0.53K0.41Li0.06)Nb0.91Sb0.09O3 Piezoelectric Ceramics with Improved Thermal Stability

MgTiO3-modified (Na0.53K0.41Li0.06)Nb0.91Sb0.09O3 ceramics were synthesized using solid-state reaction method. The addition of MgTiO3 makes the structure of the ceramics changes from the coexistence of orthorhombic and tetragonal phases to a single tetragonal phase. The orthorhombic-tetragonal phase transition temperature T O-T decreases to below room temperature, while the Curie temperature increases with the addition of MgTiO3. As a result, the tetragonal phase region is expanded, and good thermal stability of electrical properties is obtained in MgTiO3 modified ceramics. The 0.5mol% MgTiO3 modified ceramics exhibit outstanding properties of d 33∼258pC/N, ∼1431, k p∼0.435, and P r∼18.1 μC/cm2, with improved thermal stability.

Integration of HfxTayN Metal Gate Electrode with High-k Gate Dielectric in MOS Devices

In this work, the composition effects of hafnium (Hf) and tantalum (Ta) in HfxTayN metal gate on the thermal stability of metal-oxide-semiconductor (MOS) devices were investigated. The work function of the HfxTayN metal gate can reach a value of ~4.6 eV (midgap of silicon) by suitably adjusting the Hf and Ta compositions. In addition, with a small amount of Hf incorporated into a TaN metal gate, excellent thermal stability of electrical properties, including the work function, the equivalent oxide thickness (EOT), interface trap density and defect generation rate characteristics, can be achieved after a post-metal anneal up to 950 oC for 45 s. Experimental results indicate that Ta-rich HfxTayN is a promising metal gate for advanced MOS devices.

Thermal stability of Hf/sub x/Ta/sub y/N metal gate electrodes for advanced MOS devices

In this letter, the composition effects of hafnium (Hf) and tantalum (Ta) in Hf/sub x/Ta/sub y/N metal gate on the thermal stability of MOS devices were investigated. The work function of the Hf/sub x/Ta/sub y/N metal gate can reach a value of /spl sim/4.6 eV (midgap of silicon) by suitably adjusting the Hf and Ta compositions. In addition, with a small amount of Hf incorporated into a TaN metal gate, excellent thermal stability of electrical properties, including the work function, the equivalent oxide thickness, interface trap density and defect generation rate characteristics, can be achieved after a post-metal anneal up to 950/spl deg/C for 45 s. Experimental results indicate that Ta-rich Hf/sub x/Ta/sub y/N is a promising metal gate for advanced MOS devices.

Enhanced stability of polyaniline/inorganic salt composites during temperature cycling

The electrical conductivity of polyaniline sulfate was recorded during cycles between room temperature and 85, 105, 125 and 145°C. After each temperature cycle the conductivity decreased. The maxima of the conductivity–temperature heating curves are discussed. Composites of polyaniline sulfate with inorganic salts (ammonium sulfate or potassium bromide) were treated in the same manner. Experimental data and a simple model indicate that the temperature dependence of the composite conductivity changes its character at ca. 80 wt% PANI. Composites containing more than 20 wt% inorganic salt exhibit lower decrease in the conductivity after cycling; i.e. they have a higher thermal stability of electrical properties than polyaniline sulfate alone.

Effects of heat treatments on the electrical properties of Te-implanted laser-annealed GaAs

Results on the thermal stability of electrical properties of conducting layers formed in Te-implanted GaAs, pulsed laser-annealed and subsequently heat treated between 100 and 700 °C are reported. The extent of the observed reduction in electron concentration after heat treatment (200 to 500 °C) of pulsed laser-annealed samples depends on the GaAs substrate temperature during laser annealing. Implantation of tellurium into GaAs at elevated temperatures (e.g., 150 °C) is found to make the electron concentration in the laser-annealed layers thermally stable after subsequent heat treatment at temperatures up to 300 °C. Changes in the electrical properties of the heat-treated samples are observed to be reversible, as the electrical activity almost recovers to its original value after a further pulsed laser annealing. There are no observable structural changes after heat treatment of the samples up to 700 °C.