Energy and Spatial Distribution of Traps in SiO2/Al2O3 nMOSFETs

The energy and spatial profiling of the interface and near-interface traps in n-channel MOSFETs with SiO₂/Al₂ O₃ gate dielectrics is investigated by charge-pumping (CP) measurements. By increasing the amplitude as well as lowering the frequency of the gate pulse, an increase of the charge recombined per cycle was observed, and it was explained by the contributions of additional traps located higher in energy and deeper in position at the SiO₂/Al₂O₃ interface. In addition, CP currents, acquired after different constant voltage stress, have been used to investigate the trap generation in this dielectric stack     

Luminescence Characteristics of YAG Glass–Ceramic Phosphor for White LED

Luminescence characteristics of Ce:Y₃Al₅O₁₂ (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO₂-Al₂ O₃-Y₂O₃ mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce³⁺ fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x, y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd₂O₃ substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd³⁺ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.     

Electrical and Reliability Studies of “Wet N2O” Tunnel Oxides Grown on Silicon for Flash Memory Applications

In this paper, we report the electrical characteristics and reliability studies on tunnel oxides fabricated by "wet N₂O" oxidation of silicon in an ambient of water vapor and N₂O at a furnace temperature of 800 degC. Tunnel oxides that have an equivalent oxide thickness of 67 A are subjected to a constant-current stress (CCS) amount of -100 mA/cm² using a MOS capacitor to obtain information on stress-induced leakage current (SILC), interface, and bulk trap generation. The obtained results clearly demonstrate the superior performance features of the present tunnel oxides with reduced SILC, lower trap generation, minimum change in gate voltage, and higher charge-to-breakdown during CCS studies. X-ray photoelectron spectroscopy depth profile studies of the tunnel oxide interfaces have shown that the improved performance characteristics and reliability can be attributed to the incorporation of about 8.5% nitrogen at the oxide-silicon interface of the samples formed by the "wet N₂O" process that involves low-temperature oxidation and annealing at 800 degC.     

Dry Etching of Anisotropic Microstructures for Distributed Bragg Reflectors in AlGaInP/GaAs Laser Structures

A process for anisotropically etching AlGalnP/GaAs laser structures in a high-temperature (180degC), single-step BCl₃/Cl₂/Ar plasma process is demonstrated. The etch rate is shown to be stable over the duration of the etch due to its in- sensitivity to temperature. However, this etch process is unsuitable for etching high-aspect-ratio features due to the strong aspect ratio dependence of the GaAs etch rate at 180degC. A two-step etch where the GaAs is etched at 25degC and the AlGalnP layers are etched at 180degC is demonstrated that etches both materials anisotropically. The relative amount of Ar in the plasma has a strong effect on both the sidewall quality and the aspect-ratio-dependent etch rate. Finally, a process to etch anisotropic microstructures with a weak etch rate dependence on aspect ratio is reported.     

Injection of a minimal space charge as mechanism for the initialphase of electrical polymer degradation

In this paper we present a model for polymer degradation during high-field stresses in analogy to the charge-to-breakdown concept in SiO ₂. The model is based on space charge injection under high fields which leads to a cumulative effect as in radiation damage. A critical total injected charge density Q_c is introduced, which is needed prior to any permanent damage. The assumption of a critical injection level explains the time and field dependence of the tree initiation time. The model is applied to electrical aging experiments in epoxy resins. It turns out that the critical charge for tree initiation is ~10 C/cm² similar to the value for trap creation in SiO₂ gate oxides     

Reliability and degradation of small molecule-based organiclight-emitting devices (OLEDs)

Studies of degradation mechanisms in small molecule-based organic light-emitting devices (OLEDs) are reviewed. A special emphasis is given to OLEDs based on tris (8-hydroxyquinoline) aluminum (AlQ₃), an emitter and electron transport material used in the majority of OLEDs emitting from the green to the red part of the spectrum. Different strategies used for increasing device stability are addressed and the models proposed to explain experimental observations related to OLED operational stability are discussed. Although none of the presently proposed models can explain all experimental observations, the largest body of experimental evidence appears to be consistent with a model based on the instability of cationic AlQ₃ species, produced by the injection of holes into the AlQ₃ electron transport and emitter layer. Other models may be of importance in explaining degradation behavior on different time scales. Models based on redistribution of space charge appear to be responsible for reversible short-term degradation, while a model based on indium migration may be important for degradation on very long time scales     

Postdeposition-Anneal Effect on Negative Bias Temperature Instability in HfSiON Gate Stacks

The effect of postdeposition anneals in various ambients on negative bias temperature instability (NBTI) in metal-organic chemical-vapor-deposited HfSiO(N) stacks is investigated. The nitrided stacks, either by anneal or decoupled plasma nitridation (DPN) followed by a postnitridation anneal in O₂ or N₂ (DPN + O₂ and DPN + N₂ ), are more degraded by NBTI than the nonnitrided ones (O₂, N₂ anneal, and as deposited stacks). Moreover, none of the nitrided stacks reaches the 10-year NBTI lifetime, while the lifetime for the nonnitrided ones is larger than 10 years. Nitrogen profiles measured by X-ray photoelectrons spectroscopy and charge-pumping-current data show a relation between nitrogen location and positively charged defects in the gate stack. The additional NBT degradation in nitrided stacks is due to filling or generation of nitrogen-related defects by holes that are injected from the channel.     

Effect of Nb doping on structural and electric properties of PZT (65/35) ceramic

The aim of this study is to determine the effect of Nb⁵⁺ doping on PZT (65/35) based bulk materials in their structure, micro structure and electrical properties. The Nb content was chosen 0-9 mole%. These materials were prepared by conventional mixed oxide method. X ray diffraction studies suggest the compound to be of rhombohedral perovskite phase. Excess addition of Nb result in pyrochlore and fluorite phase develops in PZT (65/35) sample. Detailed studies of dielectric constant as a function of temperature (40degC to 500degC) and frequency (100 Hz to 1 MHz) suggest that the compounds undergo diffuse type of phase transition. Maximum dielectric constant and resistivity were found to be strongly dependent on doping and measuring frequencies. Using complex impedance analysis micro structural parameters such as bulk and grain boundary resistance, bulk charge carrier concentration and relaxation time were determined     

Effect of the Interfacial $hbox{SiO}_{2}$ Layer in High-$k$ $ hbox{HfO}_{2}$ Gate Stacks on NBTI

A relative contribution of the interface and bulk dielectric defects to negative bias temperature instability (NBTI) in the metal/HfO₂/SiO₂ gate stacks was investigated. Interface trap generation was assessed by the direct-current current-voltage (DCIV) technique, which independently measures the interface defect density from bulk oxide charges and delineates the contribution of the interface defect generation to the overall NBTI measured by the threshold voltage shift (DeltaV_TH). The metal/high-fc induced traps in the interfacial SiO₂ layer were found to control the fast transient trap charging/generation processes, which affect the power-law exponents of DeltaV_TH and the stress-generated interface trap density DeltaD_IT stress time dependencies. Similar kinetics of the long-term DeltaV_TH(t) and DeltaD_IT(t) dependencies in the high-fe and SiO₂ gate stacks suggests that the degradation is governed by the same mechanism of trap charging/generation in the SiO₂ film. The investigation leads to a novel methodology for the time-to-failure (TTF) extrapolation, in which the measured DeltaV_TH and DeltaD_IT values are adjusted for the contributions from the fast transient defect charging/generation processes. It is shown that the conventional TTF analysis might greatly overestimate TTF. Post-NBTI stress recovery at zero relaxation voltage measured by the DCIV method showed that oxide charges and interface traps relax at the same rate indicating that the interface processes may dominate DeltaV_TH relaxation. At positive relaxation voltages, however, the oxide charge relaxation exhibits a fast transient component. Relaxation at positive bias also shows an as yet unexplained fast component in the interface trap recovery.     

Electromagnetic noise spectrum caused by partial discharge in airat high voltage substations

The authors investigated the characteristics of the electromagnetic spectrum caused by partial discharges (PDs) in air at three different types of high-voltage substations. From the measured results, they characterized the electromagnetic noise spectrum depending on the type of substation. They also measured the long-term change of the average gain of the noise spectrum and discussed the influence of atmospheric conditions on the results. Moreover, they introduced the “equivalent charge (q_e)” which was derived by converting the electric field strength estimated from the average gain into the charge magnitude of PD. They also proposed a “phase gate control method” for better understanding the electromagnetic noise spectrum characteristics and the mechanism causing electromagnetic waves from PDs     

Write/erase cycling endurance of memory cells with SiO/sub 2//HfO/sub 2/ tunnel dielectric

The write/erase cycling endurance of low voltage floating-gate memory cells programmed and erased by tunneling through a SiO/sub 2//HfO/sub 2/ dual layer tunnel dielectric stack is investigated. The use of fixed single pulse program and erase conditions leads to fast shifting (after /spl sim/1000 cycles) of the threshold voltage window, so that only a limited number of write/erase cycles can be achieved. Increasing the write and erase duration quickly leads to an excessive erase time so that a different erase method has to be used. Improvement of the erase behavior and cycling endurance has been obtained by a combination of two methods. Inclusion of soft write pulses between the erase pulses reduces the amount of charge trapped in the tunnel dielectric and therefore limits the increase in erase time. Also, the erase voltage can progressively be raised in order to further limit the erase time, leading to an endurance of 10 000 cycles on the considered cells. When combining the SiO/sub 2//HfO/sub 2/ stack with channel hot electron injection so that tunneling is only required in one direction, 100 000 write/erase cycles are demonstrated with minimal change of the memory window.     

Comparison of Quantum Well Interdiffusion on Group III, Group V, and Combined Groups III and V Sublattices in GaAs-Based Structures

An analytical electron microscope was used for direct measurement of the concentration profiles of In_1-xGa_xAs_yP_{1- y} quantum wells (QWs) and barriers grown by molecular beam epitaxy on GaAs substrates. The well and barrier layers had compositional differences on the group III (In/Ga) sublattice only, the group V (As/P) sublattice only, and on both sublattices. These were annealed over a range of temperatures (700-950degC), and the resultant changes in the QW widths and compositional profiles were determined along with the changes in the photoluminescence (PL) emission wavelength. The structures were annealed either uncapped or capped with either a 100-nm-thick layer of low temperature (250degC) grown InGaP (LT-InGaP) or with CVD-grown SiO₂. The LT-InGaP layer contains excess phosphorus expected to be present as P-antisite defects. This was used to enhance interdiffusion on the group V sublattice during annealing, producing a blue-shift in PL response. The SiO₂ capping leads to outdiffusion of Ga from the top GaAs layer producing additional group III defects that enhance interdiffusion of the group III sublattice. The interdiffusion activation energies and diffusivities were obtained from Arrhenius plots for each of groups III and V QWs profile changes. The compositional profiles of the QW after annealing are used to infer the defects involved in the interdiffusion process on each sublattice.     

Hot-carrier reliability comparison for pMOSFETs with ultrathinsilicon-nitride and silicon-oxide gate dielectrics

The degradation of 100-nm effective channel length pMOS transistors with 14 Å equivalent oxide thickness Jet Vapor Deposition (JVD) Si₃N₄ gate dielectric under hot-carrier stress is studied. Interface-state generation is identified as the dominant degradation mechanism. Hot-carrier-induced gate leakage may become a new reliability concern. Hot-carrier reliability of 14 Å Si₃N₄ transistors is compared to reliability of 16 Å SiO₂ transistors     

Electrical relaxation in iron-containing glasses

Glasses with composition 70 mol%(SiO₂, B₂O ₃, P₂O₅, TeO₂)-15 mol% Fe ₂O₃-15 mol%(BaO, CaO) were prepared by the conventional melt quenching technique. The electrical relaxation of these glasses has been studied in the frequency range 20 to 10⁵ Hz. The small polaron hopping between iron ions in a different valence state Fe²⁺ to Fe³⁺ is found to be the principal conduction mechanism. The ratio of Fe²⁺ ions to the total iron content, C=Fe²⁺/Fe_tot, is one of the factors determining the electrical conductivity. The glass former has a minor influence on dc conductivity, except of TeO₂ glass where conductivity is three order of magnitude higher than those of other glasses. The ac conductivity as a function frequency is divided into two domains, a dc plateau, followed by a power law in frequency. These two regions are well distinguished in the complex plot of electric modulus where all data points for different temperatures reside on the single plot. The results are discussed in the frame of the Hunt theory of dielectric relaxation in glasses containing mobile charge carriers     

Reliability of Low-Temperature-Processing Hafnium Oxide Gate Dielectrics Prepared by Cost-Effective Nitric Acid Oxidation Technique

In this paper, the physical and electrical characteristics of low-temperature-processing hafnium oxide (HfO₂) films are studied. A simple cost-effective room-temperature process was introduced to prepare high-k HfO₂ dielectrics. A novel technique of direct oxidation of an ultrathin Hf metal by nitric acid, followed by rapid thermal annealing in N₂ is demonstrated. The prepared HfO₂ gate dielectrics show good uniformity, low leakage currents, high breakdown field, and superior reliability under electrical stressing. The long-term ten-year lifetime was also evaluated by a time-dependent-dielectric-breakdown analysis to project the maximum operation voltage of -1.8 V for HfO₂ gate stacks. This low-temperature oxidation technology for preparing high-quality high-k HfO₂ dielectrics is promising for flat-panel-display applications.     

Reliability Challenges for CMOS Technology Qualifications With Hafnium Oxide/Titanium Nitride Gate Stacks

It has been demonstrated that the introduction of $hbox{HfO}_{2}/ hbox{TiN}$ gate stacks into CMOS technologies provides the means to continue with traditional device gate length scaling. However, the introduction of $hbox{HfO}_{2}$ as a new gate dielectric and TiN as a metallic gate electrode into the gate stack of FETs brings about new challenges for understanding reliability physics and qualification. This contribution summarizes recent advances in the understanding of charge trapping and defect generation in $hbox{HfO}_{2}/ hbox{TiN}$ gate stacks. This paper relates the electrical properties to the chemical/physical properties of the high-$varepsilon$ dielectric and discusses test procedures specifically tailored to quantify gate stack reliability of $ hbox{HfO}_{2}/hbox{TiN}$ gate stacks.      

Xerographic properties of a-Se:Te photoconductors

It is shown that the dark decay of the electrostatic surface potential on a corona-charged a-Se:Te alloy photoreceptor occurs via electric field-enhanced xerographic depletion discharge (FEXDD) in which Poole-Frenkel-assisted thermal emission of holes from deep mobility-gap states and their subsequent sweep out generates a negative bulk space charge. The theoretical model development is applied to explain the observed experimental dark discharge data over a wide range of charging (initial) voltages. It is shown that although the time required for the surface potential to decay to its half value t_1/2 initially increases with the charging voltage V₀ at the highest charging voltage, t_1/2 actually decreases with V₀. Results obtained from cycled-up xerographic experiments on single and double-layer photoreceptors are also reviewed and discussed in conjunction with transient photoconductivity experiments     

CO2活化氮掺杂炭气凝胶的制备及其性能研究

以间苯二酚、甲醛、氧化石墨烯和三聚氰胺为原料,通过溶胶-凝胶法制备氮掺杂炭气凝胶,再对其进行CO₂活化。用X射线衍射光谱法（XRD）、扫描电子显微镜法（SEM）、X射线光电子光谱法（XPS）和N₂吸附等进行物理性能分析,用交流阻抗谱、恒流充放电测试等进行电化学性能测试。随着活化温度的提高,材料表面形成了密集的具有大量孔的内部相互交联的网络结构。当活化温度为900℃时,所制备的样品比表面积最高,由NCAG-4的1 194 m²/g增大到CO₂-900-NCAG-4的1 849 m²/g。在经过活化以后,CO₂-900-NCAG-4表现出了最佳的电化学性能,将其组装成超级电容器,充放电循环2 000次后电容保持率达94.31%。     

Determination of charge mobility in He gas from current-voltagemeasurements in point-plane geometry

In order to clarify whether or not is it possible to extract reliable values of positive and negative mobility for ions and even for electrons in gas when using sharp point-plane geometry, the authors have undertaken a systematic study using He gas. Monitoring the purity level of the same gas filling two different cells (point-plane and plane-parallel), they have compared mobility values deduced from current-voltage curves (mobility K) with time of flight measurements (actual mobility μ) as a function of gas pressure (0.1-15 MPa) and purity. For negative charge carriers (ions or electrons), they have directly measured K^- and μ^- and then compared the results. They observed, as expected, that the measured negative charge carriers mobility was strongly dependent on gas purification. For commercial gas (O₂ of the order of 100 ppm), K^- was very close to the data obtained for negative O₂^- ions (i.e., K^- ≅ μ(O₂^-)) but, for better purification level, K^- increases quickly and can reach electronic values μ_e (K^- → μ _e). For positive ions, in all the range of studied pressure, it was shown that one can extract easily from I(V) measurements, mobility values K⁺ in accordance with the values of μ⁺ of He⁺ previously given in the literature     

Optical and Photoluminescence Properties of Erbium-Doped Chalcogenide Glasses (GeGaS:Er)

We have examined the optical and photoluminescence (PL) properties of Er³⁺-doped GeGaS glasses of near-stoichiometric composition Ge₂₈Ga_6.2S_65.3:Er_0.5. We have also used powdered samples of various mean sizes (L) to examine the dependence of the 1.54 -mum PL emission spectrum and the PL decay time on the average sample size. Optical absorption spectra of Er³⁺ ions arising from transitions between different energy manifolds, such as 4 I_{15 /2} -⁴ I_13/2,⁴ I_{15 /2} -⁴ I_{11 /2} , etc., have been used to extract Omega₂, Omega₄, and Omega₆ values using the Judd-Ofelt analysis and a Judd-Ofelt radiative lifetime T_JO = 2.6 ms for the ⁴ I_{13 / 2} -⁴ I_{15 / 2} transition. The PL emission spectra and the decay time have been found to depend on the mean sample size. The spectra are broader and the decay times are longer for larger sample sizes, due to photon trapping occurring in the sample. The extrapolated decay time to zero particle size yields a decay time that matches the Judd-Ofelt radiative lifetime almost perfectly, and confirms the argument that the true PL lifetime needs to be measured in fine powders to avoid reabsorption effects. We have estimated the maximum emission cross section as 15.5 X 10^-21 cm².