Collector Charge Research Articles

A low-loss variable-doped trench-insulated gate bipolar transistor with reduced on-state voltage

The performance of a superjunction trench-insulated gate bipolar transistor with variable vertical doping in the epitaxial region along with variation in the collector layer is investigated. The concept of vertical variation transfers the avalanche multiplication point from the epitaxial edges to the middle of the pillar. The proposed device offers increased effective doping in the drift region, which reduces the on-state voltage () without any degradation in the breakdown voltage. Furthermore, the horizontal doping variation in the collector layer supports the phenomenon in two ways: the left section of the collector layer reduces whereas the right portion enables an efficient discharging path, which allows improved switching performance. In addition to this, a reduction in the gate to collector charge () is observed because of the presence of a lightly doped n-region below the gate terminal. A two-dimensional numerical simulation revealed that the proposed device offers a 15.30% reduction in compared with the conventional device. The structural modification offers a 40% reduction in turn-off time, resulting in a reduction in turn-off energy loss ().

Lateral variation doped wide bottom trench gate IGBT for reduced on-resistance with improved gate charge

In this paper, novel concept of lateral variation doping profile in the drift region for IGBT is presented. The variation profile divides the drift region in four sections in such a way that highly doped p+ and n+ pillars are present at the center, while pillars with lesser concentration are situated at the drift region boundary. Higher concentration below the channel region, enables the presence of more free charges in the conduction path thereby reducing the specific resistance (Ron.A) in the conduction path. The p- and n- section reduces the critical electric field at the corner and maintains the similar breakdown voltage in comparison with the conventional design despite of higher concentration doping profile at the middle. Proposed structure offers 19% improvement in current density and 16% reduction in Ron.A. Lateral variation doped structure also able to reduce on-state voltage drop (Von) by 15.38%. Along with the lateral doping concept, Proposed structure utilizes the broad oxide at the gate region in order to improve the switching performance. The increment in the oxide thickness reduces the gate to collector capacitance (CGC) and leads to reduces the gate to collector charge (QGC) by 30%. Reduction in gate charge also improve the switching performance of the devices and reduces the energy losses during the turn-off period. The 20% improvement in turn-off losses at same on-state voltage drop is observed. Additionally, 5% improvement in the on-state voltage drop is also achieved. Additionally, various figure of merit (FOM) is also evaluated. The Baliga's FOM and industrial FOM is improved by 19% and 55% respectively as compared to conventional design.

Production of aligned electrospun polyvinyl alcohol nanofibers via parallel electrode method

Uniaxially alignment of electrospun nanofibers is one of the main concerns to produce nanofiber yarns. Parallel electrode collectors have been used for this purpose. In this study, the effect of gap distance between parallel electrodes, electrode plate’s width, tip to collector distance (TCD) and charge density (CD) on uniaxial alignment and average diameter of polyvinyl alcohol (PVA) nanofibers in parallel electrode electrospinning is investigated. Scanning electron microscopy analysis is used to measure alignment angles and average diameters of the nanofibers. The results indicate that plate width is an effective parameter on the nanofiber alignment and need be considered with gap distance together. Increasing of gap distance and plate width together, increases the alignment of the nanofibers. Also, decreasing of CD and TCD increases the alignment of the nanofibers. Gap distance and plate width affect the average nanofiber diameter, but there is no obvious relationship.

Research on SEE mitigation techniques using back junction and p+ buffer layer in domestic non-DTI SiGe HBTs by TCAD**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775167, 11575138, and 11835006).

In this paper we investigate two techniques for single event effect (SEE) mitigation by using back junction and p+ buffer layer in non-deep trench isolation (DTI) domestic silicon–germanium heterojunction bipolar transistors (SiGe HBTs) based on technology computer aided design (TCAD) simulation. The effectiveness of the two mitigation techniques and the influence of various structure parameters are investigated. Simulation results indicate that the two techniques are more effective in reducing collector charge collection induced by heavy ions striking at positions outside the collector–substrate (C–S) junction where charge collection is dominated by diffusion. By properly adjusting the parameters, charge collection of events outside the C–S junction can be reduced by more than an order of magnitude, while charge collection of events in the device center is halved without affecting the direct current (DC) and alternating current (AC) characteristics of the SiGe HBTs.

Experimental study of bias dependence of pulsed laser-induced single-event transient in SiGe HBT

This work presents a comprehensive investigation of single-event transient (SET) in SiGe HBT induced by pulsed laser irradiation at different bias conditions. The impacts of collector voltage VCC and base voltage VB on SET are compared and discussed. Experimental results show that SET in SiGe HBT highly depends on the applied bias conditions during irradiation. The underlying physical mechanisms are analyzed in detail. It is found that the variation of collector transient current approximately satisfies an ideal exponential discharge law. The additional discharge path plays a significant role in collector charge collection and discharge time constant once the transistors arrive at the reverse-active mode.

Capture of Soft Particles on Electrostatically Heterogeneous Collectors: Brushy Particles

This work investigated how particle softness can influence the initial adhesive capture of submicrometer colloidal particles from flow onto collecting surfaces. The study focused on the case dominated by potential attractions at the particle periphery (rather than, for instance, steric stabilization, requiring entropically costly deformations to access shorter-range van der Waals attractions.) The particles, "spherical polyelectrolyte brushes" with diameters in the range of 150-200 nm depending on the ionic strength, consisted of a polystyrene core and a corona of grafted poly(acrylic acid) chains, producing a relatively thick (20-40 nm) negative brushy layer. The adhesion of these particles was studied on electrostatically heterogeneous collecting surfaces: negatively charged substrates carrying flat polycationic patches made by irreversibly adsorbing the poly-l-lysine (PLL) polyelectrolyte. Variation in the amount of adsorbed PLL changed the net collector charge from completely negatively charged (repulsive) to positively charged (attractive). Adjustments in ionic strength varied the range of the electrostatic interactions. Comparing capture kinetics of soft brushy particles to those of similarly sized and similarly charged silica particles revealed nearly identical particle capture kinetics over the full range of collecting surface compositions at high ionic strengths. Even though the brushy particles contained an average of 5 vol % PAA in the brushy shell, with the rest being water under these conditions, their capture was indistinguishable from that of similarly charged rigid spheres. The brushy particles were, however, considerably less adherent at low ionic strengths where the brush was more extended, suggesting an influence of particle deformability or reduced interfacial charge. These findings, that the short time adhesion of brushy particles can resemble that of rigid particles, suggest that for bacteria and cell capture, modeling the cells as rigid particles can, in some instances, be a good approximation.

A Phenomenological Model for Particle Retention in Single, Saturated Fractures

Fractured aquifers are some of the most poorly characterized subsurface environments despite posing one of the highest risks to the protection of potable groundwater. This research was designed to improve the understanding of the factors affecting particle transport through fractures by developing a phenomenological model based on laboratory-scale transport data. The model presented in this research employed data from over 70 particle tracer tests conducted in single, saturated, variable-aperture fractures that were obtained from the natural environment and fractured in the laboratory or cast from epoxy in the laboratory. The particles employed were Escherichia coli RS2-GFP and microspheres. The tracer experiments were conducted in natural (dolomitic limestone and granite) as well as epoxy replicas of the natural fractures. The multiple linear regression analysis revealed that the most important factors influencing particle retention in fractures are the ratio of the ionic strength of solution to collector charge, the ratio of particle to collector charge, and the ratio of advective to diffusive forces as described by the Peclet number. The model was able to reasonably (R(2) = 0.64) predict the fraction of particles retained; however, it is evident that some factors not accounted for in the model also contributed to retention. This research presents a novel approach to understanding particle transport in fractures, and illustrates the relative importance of various factors affecting the transport mechanisms. The utility of this model lies in the increased understanding of particle transport in fractures, which is extremely useful for directing future research.

Double-Emitter HCBT Structure—A High-Voltage Bipolar Transistor for BiCMOS Integration

Fabrication of a novel high-voltage double-emitter horizontal current bipolar transistor (HCBT) structure integrated with the standard 0.18-μm CMOS and high-speed HCBT is presented. The device takes advantage of 3-D collector charge sharing to achieve full depletion of the intrinsic collector region and to limit the electric field at the base-collector junction. Transistors with BVCEO = 12.6 V, fT ·BVCEO = 160 GHz·V , and β·VA = 28 700 V are demonstrated. The device is fabricated in HCBT BiCMOS process flow without the use of additional lithography masks and represents a zero-cost solution for integration of a high-voltage bipolar device.

A Comprehensive Understanding of the Efficacy of N-Ring SEE Hardening Methodologies in SiGe HBTs

We investigate the efficacy of mitigating radiation-based single event effects (SEE) within circuits incorporating SiGe heterojunction bipolar transistors (HBTs) built with an N-Ring, a transistor-level layout-based radiation hardened by design (RHBD) technique. Previous work of single-device ion-beam induced charge collection (IBICC) studies has demonstrated significant reductions in peak collector charge collection and sensitive area for charge collection; however, few circuit studies using this technique have been performed. Transient studies performed with Sandia National Laboratory's (SNL) 36 MeV 16O microbeam on voltage references built with N-Ring SiGe HBTs have shown mixed results, with reductions in the number of large voltage disruptions in addition to new sensitive areas of low-level output voltage disturbances. Similar discrepancies between device-level IBICC results and circuit measurements are found for the case of digital shift registers implemented with N-Ring SiGe HBTs irradiated in a broadbeam environment at Texas A&M's Cyclotron Institute. The error cross-section curve of the N-Ring based register is found to be larger at larger ion LETs than the standard SiGe register, which is clearly counter-intuitive. We have worked to resolve the discrepancy between the measured circuit results and the device-level IBICC measurements, by re-measuring single-device N-Ring SiGe HBTs using a time-resolved ion beam induced charge (TRIBIC) set-up that allows direct capture of nodal transients. Coupling these measurements with full 3-D TCAD simulations provides complete insight into the origin of transient currents in an N-Ring SiGe HBT. The detailed structure of these transients and their bias dependencies are discussed, together with the ramifications for the design of space-borne analog and digital circuits using SiGe HBTs.

Design considerations for integration of Horizontal Current Bipolar Transistor (HCBT) with 0.18 μm bulk CMOS technology

Design issues associated with integration of Horizontal Current Bipolar Transistor (HCBT) with 0.18 μm bulk CMOS process are examined and the effects of fabrication parameters on transistor performance analyzed. HCBT is fabricated on a sidewall of a silicon hill defined by shallow trench isolation (STI). Height of the transistor is limited by the STI depth of 350 nm. Impact of vertical and horizontal dimensions on electrical performance of the transistor are analyzed by simulations with emphasis on extrinsic base design. Base current is reduced by high extrinsic base concentration and increased link-base length. Current gain is increased from 16 to 67 for transistor processed with the optimized extrinsic base profile. High-frequency performance is degraded by the collector charge sharing effect and can be improved by the larger separation between the extrinsic base and emitter, which is achieved with a small thickness of emitter polysilicon region. Misalignment tolerances of the extrinsic base implantation mask show no great impact on transistor’s AC performance.

Unified model for collector charge in heterojunction bipolar transistors

The base-collector capacitance and the collector transit-time in GaAs-based heterojunction bipolar transistors depend not only on base-collector voltage, but also on collector current. This has to be taken into account in a large-signal model. However, since collector transit-time and capacitance are both caused by the charge stored in the collector space-charge region, it is not possible to model them independently of each other. This paper investigates the interrelation between collector capacitance and transit-time due to transcapacitance effects, and presents an analytical unified description for both quantities, that is derived from measurement-extracted small-signal equivalent circuits. The model is verified by comparison of simulation and measurement data.

Analysis of Bacterial Deposition on Metal (Hydr)oxide-Coated Sand Filter Media

The aim of this study was to investigate the importance of surface potential in microbial deposition onto modified granular surfaces. Recent experimental and theoretical work has indicated that surfaces coated with metal oxides and hydroxide rich oxide/hydroxide mixtures ((hydr)oxides) have the potential to increase the capture efficiencies of commercial filtration systems. This study quantitatively compared different metal (hydr)oxide coatings in their abilities to enhance bacterial deposition. Specifically, the deposition rates of bacterial strainsStreptococcus faecalis, Staphylococcus aureus, Salmonella typhimurium,andEscherichia coliwere compared for Ottawa sand and surface coatings consisting of aluminum (hydr)oxide, iron (hydr)oxide, and mixed iron and aluminum (hydr)oxide. The metal-(hydr)oxide-modified granular media enhanced bacterial deposition relative to the noncoated Ottawa sand. The electropositive surfaces, the aluminum and the mixed (hydr)oxides, had similar average kinetic rate constants, five times larger than the rate constants observed for the untreated Ottawa sand. The measured kinetic rate constants for the positively charged systems of aluminum (hydr)oxide and mixed (hydr)oxide collectors suggested that the overall rate of deposition was limited by the transport of bacteria to the granular surface rather than the rate of attachment. For systems where the collector surfaces were negatively charged, as in the cases of Ottawa sand and the iron (hydr)oxide coating, large energy barriers to attachment were predicted from DLVO theory but these barriers did not totally inhibit bacterial deposition. The deposition results could not be fully explained by DLVO theory and suggested the importance of other factors such as collector charge heterogeneity, motility, and bacterial surface appendages in enhanced deposition.

Extension of the collector charge description for compact bipolar epilayer models

In this paper, an extension to the collector charge description for compact bipolar epilayer models is presented. With this extension, monotonic f/sub T/ and Early-voltage behavior is ensured when transistor operation extends into the quasi-saturation region. The modification leads to a major improvement in the modeling of nonlinear distortion at high current levels and high frequencies.

Collector model describing bipolar transistor distortion at low voltages and high currents

A model is presented for the stored collector charge in a bipolar transistor. Exponential functions are used to describe base and substrate doping. The model takes account of space charge regions as well as injection regions. Furthermore, it includes dissipation losses in the neutral collector, the Kirk effect and built-in electric fields in the neutral regions. Smooth transistions are made between the various space charge and injection modes. The model provides a direct relation between doping profiles, bias conditions and stored collector charge. The model is applied to the problem of signal distortion, to which stored collector charge is a major contributor, especially at low voltages and high currents. Distortion measurements are performed on a transistor in a test circuit. To describe the linear parts of the transistor crude estimates of relevant transistor parameters like e.g. Early voltage and saturation current are made. Therefore a simple neutral base model is used. Finally, circuit analysis has to be performed to calculate distortion. This is done using an almost periodic Fourier transform in order to calculate intermodulation products arising from two input signals to the circuit. Good agreement between model and experiment is shown. The large influence of the stored charge on distortion is demonstrated. The model is suited for predicting distortion properties of new designs as well as for assessing the effects of process spreading.

Measurements of collection efficiency of single, charged droplets suspended in a stream of submicron particles with an electrodynamic balance

An experimental system based on an electrodynamic balance has been developed and tested for measurements of collection efficiencies of single, stationary charged droplets in a stream of oppositely charged submicron droplets. A light scattering technique based on optical resonances has been used to obtain collector droplet size and size changes due to the deposition of droplets with high precision. The technique involves the application of Lorenz-Mie theory to high resolution experimental elastic scattering data obtained with a continuously tunable ring dye laser. The effects of collector size in the range 9–37 μm, aerosol particle size in the range 0.038–0.15 μm, collector charge varying from 3.2 × 10 −14 to 3.3 × 10 −13 C, and stream velocity ranging from 5.0 × 10 −3 to 6 × 10 −2 ms −1, on the collection efficiency have been studied. Results have been compared with a theoretical model for the collection efficiency in the presence of electrostatic forces. Experimental values of collection efficiency are found to be in good agreement with those predicted by the theory.

Collection of prolate spheroidal aerosol particles by charged spherical collectors

The effects of electrostatic forces and torques on the dynamics of prolate spheroidal particles are examined in relation to collision with a 30 μm radius collector droplet. When the non-spherical particles are uncharged the influence of the electrostatic torque can lead to either increases or decreases in collision efficiencies. Initial particle orientation is shown to be important for low collector charges but insignificant for high collector charges, when the electrostatic torque aligns the particle parallel to the electric field. For the charged particle case, where the Coulombic force is dominant, the collision efficiencies for particles having large aspect ratios are significantly lower than those for spherical particles. Depending on the particle and collector charge levels, both front and back capture modes are found. Image forces are shown to be insignificant for highly charged particles.

The saturation characteristics of n-p-ν-n power transistors

The transport equations and charge-control concepts are applied in an analysis of a static conductivity-modulation mechanism occurring in the collector region of n-p-ν-n power transistors. This results in an expression for collector-emitter saturation voltage as a function of terminal currents and device parameters. An expression is derived which describes the current gain characteristics of saturated epitaxial and triple-diffused devices. The analysis is also used to illustrate the relationship between the emitter metallization resistance, collector charge storage, and the turn-off crowding mechanism experienced by high-frequency saturating transistor switches. An analysis of a time-dependent collector conductivity modulation process is used to derive an expression which describes the repetition frequency dependence of the collector-emitter saturation voltage of an epitaxial (or triple-diffused) transistor switching a square wave of collector current. It is concluded that frequency-dependent edge-crowding mechanisms occur only at much higher frequencies than those considered in this study.