Uniform Electrical Properties Research Articles

Improvement in Characteristics of Thin Film Transistors upon High-Pressure Steam Annealing

Low-temperature (350 °C) and high-pressure (1 MPa) steam annealing is effective for improving the characteristics of low-temperature-processed polycrystalline silicon thin film transistors (LTPS-TFTs) and their uniformity. We developed high-pressure annealing systems for 600×720 and 400×500 mm2 glass substrates, and investigated the annealing effects on the electrical properties of n-channel TFTs. The TFTs fabricated without high-pressure annealing have a low saturation mobility caused by the large amount of fixed oxide charge in SiO2, and a high threshold voltage (Vth) caused by the high trap density at the SiO2/Si interface. High-pressure steam annealing effectively reduces the amount of fixed oxide charge and the number of interface traps, resulting in the improvement of TFT properties. The crystal orientation of poly-Si strongly affects the interface trap density, which causes the nonuniformity of the TFT characteristics. High-pressure annealing also decreases the deviation of the trap density caused by the crystal orientation, and uniform electrical properties are achieved.

Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties

Advanced applications for high k dielectric and ferroelectric materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. We report the synthesis, processing, and electrical characterization of thin (<100nm thick) nanostructured thin films of barium titanate (BaTiO3) built from uniform nanoparticles (<20nm in diameter). We introduce a form of processing as a step toward the ability to prepare textured films based on assembly of nanoparticles. Essential to this approach is an understanding of the nanoparticle as a building block, combined with an ability to integrate them into thin films that have uniform and characteristic electrical properties. Our method offers a versatile means of preparing BaTiO3 nanocrystals, which can be used as a basis for micropatterned or continuous BaTiO3 nanocrystal thin films. We observe the BaTiO3 nanocrystals crystallize with evidence of tetragonality. We investigated the preparation of well-isolated BaTiO3 nanocrystals smaller than 10nm with control over aggregation and crystal densities on various substrates such as Si, Si∕SiO2, Si3N4∕Si, and Pt-coated Si substrates. BaTiO3 nanocrystal thin films were then prepared, resulting in films with a uniform nanocrystalline grain texture. Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO3 nanocrystalline films with grain sizes in the range of 10–30nm. Dielectric measurements of the films show dielectic constants in the range of 85–90 over the 1KHz–100KHz, with low loss. We present nanocrystals as initial building blocks for the preparation of thin films which exhibit highly uniform nanostructured texture and grain sizes.

Textures of Ferroelectric BLT Films for Semiconductor Memories by Electron Backscatter Diffraction and Piezo-Response Force Microscope

Issues of ferroelectric high-density memories (>64Mb) indispensable for upcoming ubiquitous era have been on the cell integration less than 0.1um2 and reliabilities. Thus nanoscale control of microstructures of ferroelectric films with large switching polarization has been one of the issues to obtain the uniform electrical properties for realization of high-density memories. In this study the grain orientations and distributions of BT-based films by spin-on coatings were examined by EBSD (electron backscatter diffraction) technique. Ferroelectric domain characteristics by PFM (piezo-response force microscope) were also performed to study the dependence of reliabilities on the grain orientations and distributions. It is believed that understandings of the nucleation and growth mechanisms of the a- or b-axis oriented films during the thermal processes such as RTA and furnace annealing affecting on grain orientation and uniformity could be possible based on this experimental results.

Orientation Distributions of Ferroelectric BLT Films for High-Density Semiconductor Memories

Issues of ferroelectric high-density memories (>64Mb) indispensable for upcoming ubiquitous era have been on the cell integration less than 0.1um2 and reliabilities. Thus nanoscale control of microstructures of ferroelectric films with large switching polarization has been one of the issues to obtain the uniform electrical properties for realization of high-density memories. In this study the grain orientations and distributions of BT-based films by spin-on coatings were examined by an electron backscatter diffraction (EBSD) technique. Ferroelectric domain characteristics by a piezoresponse force microscope (PFM) were also performed to study the dependence of reliabilities on the grain orientations and distributions.

Extinction of spherulites and improvement of polyethylene properties by the use of lithium carbonate

AbstractPolyethylene (PE) consists of nonpolar molecular chains having simple structural units. Physically, this polymer is so stable and flexible that it is widely used for insulation of electric wires and power cables, as well as for fabrication of various molded products. The crystalline texture and the presence of spherulites are major factors determining the mechanical and electrical properties of polyethylene.For the purpose of improving these properties of PE, the spherulites are eliminated completely by heat mixing of PE with Li2CO3. PE processed in this manner is free of spherulites, has a uniform structure and excellent electrical, mechanical, and thermal properties, such as short treeing length, high dielectric breakdown strength, and high tearing impact strength. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 22–38, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10296

Texture Analyses for BLT Films by Electron Backscatter Diffraction and SPM Techniques

In this study the grain orientations and distributions of BT-based films by spin-on coatings were examined by Electron Backscatter Diffraction (EBSD) and Scanning Probe Microscope (SPM) Techniques. Issues of ferroelectric high-density memories (> 64Mb) indispensable for upcoming ubiquitous era have been on the cell integration less than 0.1 μ m2 and reliabilities. Thus, nanoscale control of microstructures of ferroelectric films with large switching polarization has been one of the issues to obtain the uniform electrical properties for realization of high-density memories. Ferroelectric domain characteristics by Piezoresponse Force Microscope (PFM) were also performed to study the dependence of reliabilities on the grain orientations and distributions. It is believed that understandings of the nucleation and growth mechanisms of the a- or b-axis oriented films during the thermal processes such as RTA and furnace annealing affecting on grain orientation and uniformity could be possible based on our experimental results.

The Effect of Temperature and Relative Humidity on Dimension, Volume Resistivity and Ionic Depletion Rate of Semi-Conductive Polyurethane

The effect of temperature and relative humidity on the physical and electrical properties of semi-conductive polyurethane used in EP process bias charge, developer and transfer rollers is investigated. Semi-conductive polyurethane materials are often specified and utilized in these applications due to the relative low cost, high endurance and uniform electrical and dimensional properties of this class of materials. As printing speeds and duty cycles increase, and registration requirements increase, the allowable tolerance to change in dimension and electrical properties of rollers utilized in these functions decreases. This puts added importance to defining and understanding the relative change in these properties across differing end user operating environments, across different environmental conditioning cycles during manufacture, and on the change in the mean expected life of these materials due to ionic depletion under these differing environmental conditions. It is known that polyurethane materials continue to cure and cross-link for as long as 30 to 90 days after initial curing. This continued curing along with absorption of moisture during the manufacturing operation, create a situation where final dimensional and electrical properties are different at each stage of manufacture and continue to change in the field. The magnitude of these changes are often much larger than most EP engineers realize. The time-dependence and relative order of magnitude of these changes is explored, as are predictive process control techniques during manufacture. A basic understanding of this dynamic phenomenon and these predictive techniques is required in order to properly specify both dimensional and electrical properties for these functions.

Fabrication of undoped semi-insulating InP by multiple-step wafer annealing

Recently, it was found that undoped semi-insulating InP can be reproducibly obtained by wafer annealing at 950°C for 40 h under phosphorus vapor pressure of 1 atm. Resistivity variation across the 50 mm diameter wafer after this annealing process, however, was in the range of 22.5–53.7%. In order to realize the fabrication of undoped semi-insulating (SI) InP with uniform electrical properties, multiple-step wafer annealing (MWA) procedure has been applied for the first time. It was found that two-step wafer annealing at 950°C for 40 h under phosphorus vapor pressure of 1 atm and at 807°C for 40 h under phosphorus vapor pressure ranging from 30 to 50 atm, was effective in improvement of the uniformity of the electrical properties of undoped SI InP. By the present MWA, the resistivity variation of 8–12% and the mobility variation of 2–4% could be obtained for 50 mm diameter wafers.

Deposition of Device Quality Amorphous Silicon by Hot-Wire CVD

ABSTRACTIn this paper we present the results of the optimization of hydrogenated amorphous silicon films deposited by the hot-wire method in a larger area system. Using a two-wire design, we succeeded in depositing films that exhibit uniform electrical properties over the whole 4” x 4” Corning 7059 glass substrate. At a substrate temperature of 430 °C. and a pressure of 20 μbar we obtained a growth rate of ∼2 nm/s. The temperature of the tungsten filaments was kept at 1850 °C. The values for the photoconductivity and dark conductivity were 8.9×10−6 S/cm and 1.6×10−10 S/cm respectively, whereas the ambipolar diffusion length, as measured with the Steady-State Photocarrier Grating technique (SSPG), amounted to 145 nm. This value is higher than for our device quality glow-discharge (GD) films, which yield devices with efficiencies higher than 10%. The hydrogen content was 9.5%.We report on the density-of-states (DOS) distribution in the films, which was measured with the techniques of Thermally Stimulated Conductivity (TSC) and Constant Photocurrent Method (CPM). Furthermore, we describe the behavior of the electrical properties on light-induced degradation. Finally, we incorporated these films in solar cells, using conventional GD doped layers. Preliminary SS/n-i-p/ITO devices yielded efficiencies in excess of 3% under 100 mW/cm2 AM 1.5 illumination. Further work concerning the optimization of the interfaces is in progress.

First nanotubes made of boron nitride

For the first time, scientists have synthesized nanotubes made of pure boron nitride. boron nitride nanotubes have electrical properties quite distinct from their carbon nanotube cousins, report Alex Zettl, Marvin L. Cohen, and colleagues at Lawrence Berkeley National Laboratory [ Science , 269 , 966 (1995)]. They have created a substance predicted to have highly uniform electrical properties that may be of great use in fabrication of new materials. As an offshoot of fullerene studies, scientists have been fabricating carbon nanotubes for several years. They use a plasma arc discharge, blasting carbon off a graphite anode into neat concentric nanotubes. The astonishing thing is that out of this violence one finds on a cathode just a millimeter away ... billions of nanotubes whose structure is incredibly ordered and perfect says Daniel T. Colbert, a postdoctoral fellow with buckyball codiscoverer Richard E. Smalley at Rice University in Houston. Scientists have speculated about the properties of boro...

Growth conditions for improving the quality of semiconductor single crystal material

Growth of crystalline semiconductor material with uniform electrical and optical properties requires a smooth growth face at which bunching of growth steps does not take place. Investigation of GaAs growth by liquid phase epitaxy shows that the two growth parameters, growth rate and growth face off-orientation, considerably influence the step bunching process. The appearance of the growth face suggests a distinction between four different growth regimes: facet growth, terrace growth, unstable terrace growth and terrace free growth. Small as well as large off-orientations suppress the formation of bunched steps at low growth rates. Small off-orientation additionally prevents bunching at high growth rate. Growth faces with an off-orientation exceeding 0.2° show enhanced step-bunching with increasing growth rate.

Improved uniformity of GaAs by carbon control

Gas analysis was used to monitor the atmosphere of a high-pressure crystal during the growth of semi-insulating gallium arsenide by the liquid-encapsulated Czochralski process. Apart from the background argon, the only gases detected were carbon monoxide and hydrogen. These were formed by reaction between the graphite components of the puller and residual water vapour. The quantities of CO and H2 increase with atmospheric humidity and this results in an increase in the electrical resistivity of the crystal. Diffusion through the boric oxide encapsulant appears to act as a rate-limiting step in the carbon transport. The CO concentration was increased by injection and decreased by gettering or by dilution, and by these means it was found possible to grow crystals with very uniform electrical properties and tightly controlled resistivities at selected values within the range 107-2*108 Omega cm.

Microwave sintering of Sb-doped SnO 2

The sintering behavior of coprecipitated Sb-doped SnO 2 was investigated using microwave power absorption. With microwave power, samples were sintered at 1450°C for 20 min and showed a density as high as 99.9% of theoretical. However, samples fired in conventional electric furnace at the same temperature for 4 h showed only 60% of theoretical density. Microwave sintering also led to improvement in terms of uniform structure and electrical properties.

Growth and properties of large-diameter indium lattice-hardened GaAs crystals

The liquid-encapsulated Czochralski (LEC) growth of In-doped GaAs from 3 kg melts in a Melbourn high-pressure puller has resulted in low-dislocation, large-diameter crystals. Post-growth boule annealing at 950°C for 18 h is found to be an effective stress-relief treatment. This allows high wafer yields, comparable to those from undoped GaAs crystals to be obtained from In-doped boules, with the added advantage of greatly improved uniformity in electrical properties. These substrates are semi-insulating, thermally stable ( ρ ≥ 10 7 ω cm and μ H ⩾ 5000 cm 2/V · s with a ± 10% or better radial uniformity), and contain low residual impurity concentrations ( ⩽ mid-10 15 cm -3) as determined by secondary ion mass spectroscopic (SIMS) analysis. In this study the effectiveness of various concentrations of indium in reducing the dislocation density in GaAs have been explored. A comparison of the thoretically calculated thermal stress experienced by a crystal during LEC growth, with observed reductions in dislocation etch pitch density, indicate an apparent 28-fold increase in the critically resolved shear stress (CRSS) of In-doped over undoped GaAs for 8 x 10 19 cm -3 In in the solid. Polished substrates obtained from these crystals show minimal subsurface damage, believed to be related to the increased hardness of this material, and are now approaching high-quality silicon wafers in this respect.

Effects of indium lattice hardening upon the growth and structural properties of large-diameter, semi-insulating GaAs crystals

The high-pressure liquid encapsulated Czochralski growth of indium lattice-hardened GaAs, from 3 kg melts, has resulted in low-dislocation, large-diameter crystals which exhibit thermally stable, semi-insulating properties. Post-growth boule annealing is found to be an effective stress-relief treatment, which assures high wafer yields and extremely uniform electrical properties. Observed reductions in dislocation density for mid 1019 cm−3 In-doped GaAs substrates indicate an apparent 28-fold increase in the critically resolved shear stress of this material over undoped GaAs near the melting point. Polished substrates obtained from these crystals exhibit very little subsurface damage, approaching high-quality silicon wafers in this respect.

Reconstruction of propagated electrical activity with a two-dimensional model of anisotropic heart muscle.

The propagated electrical activity in normal anisotropic cardiac muscle is characterized by directionally dependent variations in the rising phase of the action potential. An important question concerns the relation between such variations and the propagation velocity and extracellular potentials. This problem was studied here in a sheet of cells, under conditions of uniform intracellular anisotropic resistivity and constant electrical membrane properties, through a numerical solution of the two-dimensional propagation equation. The numerical solution implies a lumping of the cytoplasmic and intercellular resistances into an equivalent junctional resistance to form a distributed resistive network representing the intracellular domain. The interstitial space is assumed isotropic and unbounded, with a resistivity of 100 omega X cm. The electrical properties of the cell membrane are represented by a Beeler-Reuter model. The stimulus current is applied to a small area of the sheet, and attention is focussed on the stable propagated events occurring some 5 or 6 length constants away from the stimulation site. The numerical solution is a good approximation of a continuous uniform structure when the cell size is less than 10% of the length constant along both major axes. Conditions of non-uniform propagation, with directionally dependent variations in the maximum rate of rise and time constant of the foot of the action potential were simulated by increasing the cell size to 30% of the length constant in the transverse direction of the sheet. Our results indicate that the directional changes in the maximum rate of rise correspond to small modifications of the extracellular potentials, while the directional changes in time constant of the foot are associated with the propagation velocity. The maximum effects are observed along the transverse direction as follows: a 19% increase in maximum rate of rise corresponds to a decrease of about 6% in the peak-to-peak amplitude of the extracellular potential, and a 24% increase in time constant of the foot is associated with a decrease of about 7% in the propagation velocity. Under the conditions of the present study, however, the simulated directional changes in maximum rate of rise are smaller than those experimentally observed so the corresponding changes in the extracellular potentials are probably underestimated.

ＧａＡｓ ＩＣと結晶特性

Liquid-encapsulated Czochralski (LEC) grown, undoped GaAs exhibits high resistive, semiinsulating property and is very suitable for high performance GaAs IC's substrate with a direct ionimplantation technology. An FET threshold voltage, however, is strongly influenced by material properties. A close relationship between dislocations, native antisite defects AsGa and FET threshold voltage is briefly discussed, and it is demonstrated that dislocation-free GaAs exhibits a very uniform electrical properties desirable for GaAs ICs substrate.

Contour maps of EL2 deep level in liquid-encapsulated Czochralski GaAs

Contour maps of the EL2 deep level concentration across 3-in.-diam, semi-insulating 〈100〉 GaAs crystals grown by the liquid-encapsulated Czochralski technique were determined by optical profiling. The EL2 patterns at the seed end of the crystals are invariably fourfold symmetric, and correlate with the distribution of dislocations. EL2 distributions at the tail, on the other hand, are often less symmetrical. The contour maps are independent of the melt stoichiometry and relative direction of crystal and crucible rotation. The results indicate that whereas the average EL2 concentration along crystals is controlled by the melt stoichiometry, the 10%–20% concentration variations across crystals result from a second effect possibly related to dislocation climb or dislocation gettering. Implications of the observed EL2 distribution on the uniformity of electrical properties is also discussed.

Modelling electrical behaviour of nonuniform AlSi Schottky diodes

The heat-treated AlSi contacts show large nonuniformities and cannot be described by a one-dimensional theory. The authors partially succeed in describing circular Al/ n Si contacts by a crude model: two diodes in parallel (the first central and circular, the second peripheral and annular). It was shown that only a part of the contact area is effective for samples treated at lower temperatures, due to the interfacial oxide layer. However, the contacts treated at 550°C seem to have more or less uniform electrical properties, despite large nonuniformities in the contact geometry. Moreover, the effective energy barrier of these contacts is little influenced by the preparation conditions, including the amount of Al available for AlSi interaction and the rate of cooling. These results may modify the present conception of the formation of the Al-doped layer at the AlSi interface.

Electrohydrodynamics: A Review of the Role of Interfacial Shear Stresses

Electrohydrodynamics of fluids having uniform electrical properties, emphasizing shear effects for interfacially confined electromechanical coupling