SPEED AT BREAKDOWN TORQUE OF A SINGLE-PHASE INDUCTION MOTOR

ABSTRACT

The purpose of this paper is to present an “exact” analytical expression to calculate speed at breakdown torque and the breakdown torque of single-phase induction motors. From the theoretical expression for torque developed by a single-phase motor, a sixth order polynomial in speed at breakdown torque is obtained, and solved, using a well known method. A real root for per unit speed, i.e. the ratio of speed to the synchronous speed, that lies between 0 and 1 is selected and the actual breakdown torque is determined by substituting it in the torque equation. The breakdown torque, also termed as maximum torque, so obtained has been found to yield better correlation between the predicted and the tested results than the only existing empirical relation. Steps to calculate speed at maximum torque are also suggested. For an arbitrarily selected single-phase induction motor, a curve of speed at breakdown torque as a function of r₂/X is also included for the purposes of illustration and understanding.     

WO3/BTO heterostructures based NO2 sensor with enhanced response characteristics

Abstract

In the present work, an efficient NO₂ gas sensor has been realised using single phase Barium titanate, BaTiO₃, (BTO) thin film, grown by chemical solution deposition technique (CSD). The gas sensing characteristics of BTO thin film were enhanced by integrating WO₃ modifier in the form of uniformly distributed circular nano-clusters and continuous overlayer. The WO₃ nanoclusters/BTO sensing element exhibited enhanced sensor response (～156) with fast response speed (16?s) at a relatively low operating temperature (140?°C) towards 50?ppm NO₂ gas. An attempt has been made to explain the sensing mechanism involving the twin effect of “Fermi-level exchange mechanism” and “spill over mechanism” upon interaction with target NO₂ gas. The obtained results in the present work are encouraging for the realization of hand-held NO₂ gas sensor.     

An analytical model of threshold voltage for short-channel double-material-gate (DMG) strained-Si (s-Si) on Silicon-Germanium-on-Insulator (SGOI) MOSFETs

In this paper, an analytical short-channel threshold voltage model is presented for double-material-gate (DMG) strained-Si (s-Si) on Silicon-Germanium-on-Insulator (SGOI) MOSFETs. The threshold voltage model is based on the “virtual cathode” concept which is determined by the two-dimensional (2D) channel potential of the device. The channel potential has been determined by solving 2D Poisson’s equation with suitable boundary conditions in both the strained-Si layer and relaxed Si_1?x Ge _x layer. The effects of various device parameters like Ge mole fraction, Si film thickness, SiGe thickness and gate-length ratio have been considered on threshold voltage. Further, the drain induced barrier lowering (DIBL) has also been estimated. The validity of the present 2D analytical model is verified by using ATLAS?, a 2D device simulator from Silvaco.     

Magnetron sputter-deposited multilayer (BaxSr1x)Ti1+yO3+z thin films for passive and active devices

Abstract

High permittivity (Ba_xSr_1?x)Ti_1+yO_3+z(BST) thin films are being investigated for integration into charge storage dielectrics and electric-field tunable elements for high frequency devices. For the latter application, it is desirable to have BST capacitors with high tunability and low losses. Therefore, we investigated the use of multilayer BST thin films consisting of very low dielectric loss BST/electrode interfacial layers ((Ba+Sr)/Ti = 0.73) sandwiching a high tunability, high permittivity primary BST layer ((Ba+Sr)/Ti = 0.9). BST capacitors with multiple layers of controlled composition can be effectively produced insitu by magnetron sputter deposition, using a single stoichiometric target and controlling the layer composition by changing the total process gas (Ar+O<₂) pressure. The layered BST film capacitors exhibit simultaneous low loss (tan Δ = 0.005), high tunability (76%), high charge storage energy density (34 J/cm³), low leakage, and high dielectric breakdown (>2.8 MV/cm).     

Ferroelectric field effect in (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 heterostructures

Abstract

Epitaxial LaCoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃ (LSCO) heterostructures have been grown on LaAlO₃ by pulsed laser deposition for investigating ferroelectric field effect. In the heterostructure, semiconducting LaCoO₃ was used as a conducting channel layer, instead Si. The resistivity of the LaCoO₃ (LCO) channel layer was found to be dependent on an oxygen ambient, primarily the ambient oxygen pressure during deposition. The resistivity of the LCO layer varied in the range of 0.1 – 100 Ω cm. Ferroelectric field effect induced in LaCoO₃ layer was observed by measuring the resistance modulation of the LCO layer with respect to the polarized state of the PZT layer. The resistance modulation of 9% was obtained in the 680 Å thick LCO layer. Further the resistance modulation was improved up to 45% after applying dc bias. It is suggested that the LCO/PZT/LSCO heterostructure can be used as a ferroelectric field effect transistor.     

Ferroelectric La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O heterostructures on silicon

Abstract

Ferroelectric Pb_0.9La_0.1Zr_0.2Ti_0.8O₃ (PLZT) thin film capacitors with symmetrical La-Sr-Co-O top and bottom electrodes have been grown on [001] Si with a Yttria stabilized zirconia (YSZ) buffer layer and on SiO₂Si substrates. A layered perovskite “template” layer (300–500 Å thick), grown between the YSZ buffer layer or the SiO₂ layer and the bottom La-Sr-Co-O electrode, is critical for obtaining the required orientation of the subsequent layers. The fatigue, retention and aging characteristics of these new structures are quite desirable for nonvolatile memory operation. Preliminary studies show that this ferroelectric performance obtained in large (50–100 μm diameter) capacitors can be replicated in smaller capacitors (down to 4 μm diameter) processed by ion milling.     

Defect chemistry and transport properties of Pb(Zr1/2Ti1/2)O3

Abstract

In order to gain insight into the degradation mechanisms associated with ferroelectric thin films, such as fatigue and imprint, an understanding of the defect chemistry and transport properties of the material is needed. In this study several complimentary techniques have been used to either measure or calculate indirectly the various thermodynamic parameters governing defect formation and transport in Pb(Zr_1/2Ti_1/2)O₃, (PZT). By combining the results of DC equilibrium conductivity, thermoelectric power and the sealed cell techniques, “constant composition oxygen activity” and “constant composition conductivity,” values for the oxidation enthalpy (ΔH_ox), hole trapping energy (E _A) and the enthalpy of motion for holes (ΔE _A) have been determined to be ?0.49 eV, ≤0.9 eV and ≥0.1 eV, respectively. From these results, it is apparent that PZT is an oxygen excess p-type semiconductor in the experimental regime of 500°–700°C and P(O₂) ≥ 10^?4 atm. Furthermore, the results indicate that there is a significant concentration of trapped holes at high temperatures and hole conduction appears to be an activated process (i.e. small polaron conduction).     

Room temperature and 77K dielectric properties of acetate-derived PZT,PLZT, PSZT and PBZT thin films

Abstract

Ferroelectric thin films in the PZT, PLZT, PBZT (lead barium zirconate titanate) and PSZT (lead stannate zirconate titanate) compositional systems were prepared from as-received acetate precursors. Multiple-layer thin films were fabricated via a spin coating technique and sintered at 650 – 700°C for two to three minutes per layer, yielding an overall thickness of 0.45um. The dielectric and ferroelectric hysteresis loop properties of these films were measured at room temperature and 77K. The results show that the thin films experience a substantial loss (-80% avg.) in dielectric permittivity at 77K and a significant increase in P_R, E_c and electrical breakdown strength. The phase transformation trends on cooling from room temperature to 77K were from SFE (slim-loop FE)-to-FE and AFE-to-FE. Compositions in these systems show promise for potential low temperature applications.     

Fast and Superfast Motion of Ferroelectric Domain Boundaries

We present the review of our systematic investigation of the propagation of domain walls/boundaries in wide velocity range in uniaxial ferroelectrics with optically distinguished domains, such as lead germanate Pb₅Ge₃O₁₁, congruent and stoichiometric lithium tantalate LiTaO₃ and lithium niobate LiNbO₃. In situ optical observation of domain kinetics was widely used. Three different regimes of boundary propagation have been revealed and investigated in details. It was shown that except of conventional “slow” sideways domain wall motion “fast” and “superfast” domain growth regimes through formation of complicated self-maintained domain boundaries could be obtained. The crucial role of the retardation of screening/compensation of depolarization field has been pointed out. It was demonstrated that realization of proper regime is determined by the ratio of switching rate to bulk screening one. Computer simulation has been applied for verification of proposed approach.     

Life cycle CO2 emissions of a photovoltaic/wind/diesel generating system

A photovoltaic/wind/diesel generating system with a battery (PWD system) is discussed from the viewpoint of total CO₂ gas emissions during system lifetime. The total emissions are the sum of the emissions occurring at manufacturing and operating. First, the manufacturing CO₂ emissions of the photovoltaic generator and the wind turbine generator are calculated by “the process analysis method.” This method considers the material used in each generator, its weight and its CO₂ emission rate. On the other hand, the manufacturing CO₂ emissions of the diesel generator and the battery are calculated using “the interindustry (input‐output) table.” Second, the PWD system is operated on a computer so that the fuel consumption of the diesel generator is a minimum assuming that hourly series data of electric load, insolation intensity, wind speed, and air temperature are known during the year. And CO₂ emissions occurring at system operation are obtained from the annual fuel consumption of the diesel generator. The results show that CO₂ total emissions of the PWD system are lower than those of the conventional diesel generator system. The CO₂ total emissions reach a minimum when the photovoltaic/wind generating ratio is 50/50. The CO₂ emissions of manufacturing decrease with increasing of the wind generating ratio from 100/0 to 0/100. The CO₂ total emissions decrease as the natural energy ratio increases. It is, however, saturated to about 60% when the ratio is more than 60%. And the CO₂ total emissions increase with increasing of the battery capacity. It is concluded that the PWD system plays an important role in decreasing considerably the CO₂ total emissions while the total system cost is high under the present price circumstances. © 2001 Scripta Technica, Electr Eng Jpn, 138(2): 14–23, 2002     

Ferroelectric nonvolatile logic

Abstract

This paper describes the design of nonvolatile logic elements using ferroelectric materials. Two separate approaches are discussed. The first approach involves shadowing a CMOS latch or flip-flop with a single bit 2T/2C ferroelectric memory. The second approach offers improved density by integrating ferroelectric capacitors within the logic element. Both designs employ non-switching ferroelectric capacitors to establish the optimum bit line load in the absence of sufficient parasitic capacitance. The paper further describes low-voltage and wide-voltage design techniques used to realize 2.7 – 5.5V products on a “5-volt” ferroelectric process. These same techniques allow 1.8V ferroelectric memory products to be designed using the upcoming generation of production ready “3-volt” ferroelectric materials. Layout effects are discussed, as well as bit/cell ratio optimization.     

Insulation properties of a CO2/N2 50% SF6 gas mixture in a nonuniform field

This paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO₂/N₂/SF₆ gas mixture in a nonuniform field. These voltage characteristics were investigated with ac high voltage by changing the mixture rate of each gas of CO₂, N₂, and SF₆ gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO₂ gas into a N₂/SF₆ mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF₆ in N₂/SF₆ gas mixture is 50%, with the addition of 1% CO₂ the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N₂/50% SF₆ gas mixture and pure SF₆ gas, respectively. Moreover, those voltage characteristics of a CO₂/N₂/SF₆ gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to discuss the corona stabilization effect, which seems to be one reason for the drastic increase in the breakdown voltage. These results and breakdown mechanism of the CO₂/N₂/SF₆ gas mixture are discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter, and PD current waveforms. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 34–43, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10019     

Mechanisms of Pb(zr0.53Ti0.47)O3 thin film etching with ECR/RF reactor

Abstract

Ferroelectric capacitive devices for memory and MEMS applications require patterned ferroelectric thin films with high anisotropic etched features. In this paper, physical and chemical parameters during etching of Pb(Zr_0.53Ti_0.47)O₃ (PZT) by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask were investigated as a function of gas chemistry (Ar, halogen gases), substrate bias RF power and working pressure (from 5 × 10^?4 Pa to 1Pa). The etch processes were characterized in terms of etch rate, selectivity and mask stability. High etching rate processes (up to 70 nm/min with removable photoresist mask) were obtained and micron scale patterns were demonstrated. The impact of the etch process on the PZT surface layer modification was characterized by AFM, SEM, TEM and XPS. A strong influence of process chemistry and RF bias power on etching selectivity and surface topography (roughness, involatile residues) was observed. No surface damage layer was detected by Transmission Electron Microscopy. However, XPS revealed fluorine (up to 34%) and chlorine radicals (below 10%) in a 10nm thick surface layer.     

Numerical simulations of ultrathin CdTe solar cells with a ZnxCd1−xS window layer and a Cu2O hole transport layer

CdTe solar cells are investigated using a solar cell capacitance simulator software. First, a conventional fluorine-doped tin oxide (FTO)/i-SnO₂/CdS/CdTe structure is simulated using input experimental data to verify the simulation process. To make the cell more economical, the thickness of the CdTe layer is decreased, resulting in a degradation of the device performance. To decrease the minority-carrier recombination loss of the designed structure, a p-type Cu₂O layer is exploited at the back contact as a hole transport electron blocking layer (HT–EBL). To address the performance degradation, a ZnS/CdS bilayer is used as the window layer. The interdiffusion of Cd into the ZnS due to annealing treatment and the formation of Zn_xCd_1?xS compound are also studied. Cell parameters include the thickness, doping concentration, and carrier lifetime are then optimized to enhance the power conversion efficiency (PCE). The proposed FTO/i-SnO₂/Zn_0.5Cd_0.5S/CdTe/Cu₂O configuration shows the best PCE of 17.5%, short-circuit current density (J_sc) of 27.8 mA/cm², open-circuit voltage (V_oc) of 0.87 V, and fill factor of 72.34% under AM1.5G illumination.

     

Impulse partial discharge and breakdown characteristics of rod–plane gaps in air and N2 gases

In response to growing environmental concerns, we attempted to develop switchgear without using SF₆ gas. In our research, we used compressed air and pure N₂ as an electrical insulation gas, because of their low global warming potential. In this paper, we examined the impulse breakdown and impulse partial discharge characteristics under various conditions related to nonuniformity of the electric field. The experimental results show that the breakdown voltage (BDV) of air is higher than that of pure N₂ gas under highly nonuniform field conditions in the rod–plane gap. On the other hand, the discharge inception voltage of air and N₂ were almost the same. Furthermore, first partial discharge (PD), leader discharge, and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 36–43, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10277     

Surfaces structure of bulk and thin film ferroelectrics

Abstract

Based on the experimental results of thickness dependences of breakdown voltage and dielectric permittivity for BaTiO₃ family ceramics, (Pb, La)TiO₃ thin films and commercial multilayer capacitors, surface layer structures are discussed. Surface layers inside ferroelectric materials are consisting of non-ferroelectric Kanzig layer with low dielectric permittivity and with higher concentrations of impurities due to the inter diffusion between substrates and bulk, internal stresses induced by lattice mismatch, cubic-tetragonal phase transition, electric field induced anisotropies and internal bias field (space charge field). The Voltage - Current characteristics (V-I curve), D-E loops of ferroelectric materials show asymmetric behaviors. Saturation phenomena of V-I curves are observed only ferroelectric temperature region. The breakdown voltage almost depends on the non-ferroelectric Kanzig layer and the dielectric permittivity depends on the volume fraction of non-ferroelectric parts. Log-log plots of dielectric permittivity and breakdown voltage suggest that the thickness of non-ferroelectric Känzig layer should be at least more than 10～20 nm and in the grain boundary thickness of bulk ferroelectric materials should be more, especially in the liquid phase sintering, the thickness of grain boundary is a order of 0.1～0.2 μm.     

Characterization of hetero-epitaxial PZT capacitor

Abstract

A hetero-epitaxial Au/PbZr_0.48Ti_0.52O₃(PZT)/SrRuO₃(SRO) capacitor was fabricated on a single crystal SrTiO₃ (STO) substrate by pulsed laser deposition. An SRO buffer layer (a nucleation layer) was formed at the SRO/STO interface to ensure the highly epitaxial growth of the PZT and SRO films. An X-ray diffraction measurement revealed that the (00l) planes of the PZT and SRO grew parallel to the substrate surface. A transition layer of ～ 5 nm thickness was observed at the SRO/STO interface by high-resolution transmission electron microscopy (HR-TEM). This transition layer corresponds to the nucleation layer intentionally grown at the interface. Remanent polarization of the capacitor was 32.1 μC/cm² due to the good epitaxial growth of the films.     

DC conduction behavior of Bi3.15Nd0.85Ti3O12 thin films grown by RF-magnetron sputtering

The Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates by using RF-magnetron sputtering method and studied the ferroelectric and leakage current charateristics. The polarization – electric field (P-E) hysteresis loops of BNT film was well saturated with the remnant polarization (2P _r ) of 29.8 μC/cm² and a coercive field (2E _c ) of 121 kV/cm. The leakage current density – electric field (J-E) characteristics of the Pt/BNT/Pt capacitor reveals the presence of two conduction region, having Ohmic behavior at low electric field (below 50 kV/cm) and Schottky-emission or Poole-Frenkel emission at high electric field (above 60 kV/cm). The barrier height and trapped level of BNT films are estimated to be 1.11 eV and 0.90 eV, respectively.     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Effects of internal postoxidation on the oxygen deficiency and dielectric strength of buried oxide formed by the separation‐by‐implanted‐oxygen (SIMOX) process

Effects of internal postoxidation on buried silicon dioxide have been studied. The dioxide examined was the buried insulator in a silicon‐on‐insulator (SOI) structure fabricated by implantation of oxygen ions into Si, or the SIMOX process. Internal postoxidation is an oxidation process applied to the SOI structure after its fabrication. It was observed that the photoluminescence intensity due to neutral oxygen vacancies (O₃≡Si–Si≡O₃, “≡” denotes three separate bonds to oxygens) increased after the internal oxidation. The oxide thickness and the number of E centers (O₃≡Si·, “·” denotes an unpaired electron) were also found to increase similarly. The measurements repeatedly done by changing the oxide thickness revealed that the increased part of oxide by the internal oxidation contains the vacancies with a similar density to the original part. It is concluded that the internal oxidation scarcely affects the oxygen deficiency of the oxide. It was also observed that the number of breakdowns at low electric fields remarkably decreased after the internal oxidation, indicating that electrically weak spots such as silicon pipes were effectively reduced. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 15–20, 2000