Bipolar Transistor Model Research Articles

Charge storage in the quasineutral regions of Si homojunction, AlGaAs/GaAs heterojunction, and Si/SiGe heterojunction bipolar transistors

Charge storage in the quasineutral regions of a bipolar transistor often limits the switching speed of the device, particularly when the transistor is operated in saturation mode (both emitter-base and base-collector junctions are forward biased), a bias condition which occurs frequently in logic circuits. This paper studies and compares the free-carrier charges stored in the quasineutral regions of the conventional Si homojunction bipolar transistor (Si BJT) and the increasingly important AlGaAs/GaAs and Si/SiGe heterojunction bipolar transistors (HBTs). The diffusion capacitances associated with this stored charge, which are used in the Gummel–Poon bipolar transistor model, are also calculated and discussed. It is shown that the AlGaAs/GaAs HBT has the least carrier accumulation in the quasineutral regions among the three devices due primarily to the relatively large energy band gap of GaAs-related materials. Also, the Si/SiGe HBT is expected to operate at a higher switching speed compared to the Si BJT, because the valence band discontinuity at the Si/SiGe base-collector heteroface impedes the minority-carrier injection from the base into the collector.

Large signal modeling of HBT's including self-heating and transit time effects

A physically based, large signal heterojunction bipolar transistor (HBT) model is presented to account for the time dependence of the base, collector, and emitter charging currents, as well as self heating effects. The model tracks device performance over eight decades of current. The model can be used as the basis of SPICE modeling approximations, and to this end, examples are presented. A thesis for the divergence of high frequency large signal SPICE simulations from measured data is formulated, including a requisite empirical equation for the base-collector junction capacitance. >

A physically based base pushout model for submicrometer BJTs in the presence of velocity overshoot

By using a two-dimensional relaxation time approximation device simulator, base pushout phenomena for submicrometer bipolar junction transistors (BJTs) are analyzed. From the numerical analysis, it was clarified that, under the base pushout condition, the electron velocity exceeds the saturation velocity in most of the epi-collector region. Considering this velocity overshoot effect with two-dimensional carrier behavior, a base pushout model was developed. This model is applicable to the BJT equivalent circuit model. The model utility was verified for a 0.8 mu m emitter-width BIT, and excellent agreement with measured I-V characteristics was obtained over wide injection conditions. Scaling effects on the velocity overshoot are also calculated, based on the constant current scaling. It is shown that the base pushout is suppressed due to the increased velocity overshoot level as the device sizes are scaled down. >

High-power microwave bipolar transistor modeling

This article introduces a model for high-power microwave bipolar transistors and its associated parameter-measuring strategy, whose inclusion of thermal phenomena in the dc characterization allows a good estimate of the device's thermal resistance to be obtained. This type of model provides important capabilities for solid-state radar transmitter design.

Reply to ‘‘Comments on ‘Effects of using the more accurate intrinsic concentration on bipolar transistor modeling’ ’’ [J. Appl. Phys. 6 8, 5911 (1990)

This reply addresses the issues raised by Rode and Rosenbaum regarding the bipolar junction transistor model developed in the subject paper [J. Appl. Phys. 68, 5911(1990)]. The error associated with Eq. (4) in the subject paper is discussed and corrected, the value of the space-charge-region recombination time used is specified, and the results are recalculated. It is shown that the error in Eq. (4) does not alter notably the trends of the current gain calculated using the two different intrinsic concentrations.

Comments on ‘‘Effects of using the more accurate intrinsic concentration on bipolar transistor modeling’’ [J. Appl. Phys. 6 8, 5911 (1990)

Four points are raised concerning accuracy of results, correctness of approach, and significance of findings in the cited publication.

Two-dimensional lateral bipolar transistor model for circuit simulation

A lateral bipolar transistor circuit model including two-dimensional current characteristics has been developed. The model accounts for the physical effects of base width modulation, base conductivity modulation, hole-electron plasma-induced bandgap narrowing, and current-dependent base resistance. SPICE simulation employing the present model shows good agreement with computer experimental results.

Concise transient SPICE model for bipolar power transistor quasi-saturation simulation

A concise transient SPICE model is presented in this paper to predict both the static and the switching behaviour of power transistors, with emphasis placed on quasi-saturation effects. The model is proposed to simulate both ohmic and non-ohmic quasi-saturation phenomena by automatically adjusting the hole injection ratio term. The model incorporates the currently used Gummel-Poon (GP) model and an additional charge-control relation for the transistor's epitaxial collector. The turn-off charge removal phenomenon is not modelled specifically; however, the charge-control equation for the epitaxial collector region may partly simulate this effect where the quasi-saturation region is entered. The validity of the model is verified by comparison between the original SPICE bipolar junction transistor model and experimental data for both DC and turn-on conditions. Methods for determining the model parameters are described.

A transistor model for numerical computation of forward-bias second-breakdown boundary

A two-dimensional bipolar power transistor model for numerical computation of the forward-bias, second-breakdown boundary is proposed. The model takes into account high-current-density effects such as the base widening (Kirk's) effect and avalanche injection. The numerically determined forward-bias safe operating area is in good agreement with the experimentally obtained area, especially at high collector currents and lower collector voltages. The model is also used to analyze the dynamics of the forward-bias second breakdown. The model is verified experimentally, and is suitable for a parametric study of forward-bias second breakdown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave circuit design using linear and nonlinear techniques

Foreword by David Leeson. Preface. 1. RF/Microwave Systems. 2. Lumped and Distributed Elements. 3. Active Devices. 4. Two-Port Networks. 5. Impedance Matching. 6. Microwave Filters. 7. Noise in Linear Two-Ports. 8. Small- and Large-Signal Amplifier Design. 9. Power Amplifier Design. 10. Oscillator Design. 11. Microwave Mixer Design. 12. RF Switches and Attenuators. 13. Microwave Computer-Aided Workstations foor MMIC Requirements. Appendix A: BIP: Gummel-Poon Bipolar Transistor Model. Appendix B: Level 3 MOSFET. Appendix C: Noise Parameters of GaAs MESFETs. Appendix D: Derivations for Unilateral Gain Section. Appendix E: Vector Representation of Two-Tone Intermodulation Products. Appendix F: Passive Microwave Elements. Index.

Physics-based large-signal heterojunction bipolar transistor model for circuit simulation

A comprehensive single heterojunction bipolar transistor (HBT) model suited for circuit simulation is presented. The model is developed in the Gummel-Poon homojunction bipolar transistor model tradition, but adds important heterostructure device physics as well as physical properties of 3 or 4 compound materials such as AlGaAs and GaAs. In contrast to the existing HBT models, which use the Gummel-Poon model and fit HBT experimental data by optimising a large pool of parameters extracted from HBT measurements, the present physics-based model requires only the knowledge of the device make-up (such as the doping concentration and layer thickness) and the material parameters (such as the energy bandgap and electron affinity). Comparisons between the model and measured dependencies for AlGaAs/GaAs/GaAs HBTs on important device specifications such as the DC current/voltage characteristics, DC current gain, and cutoff frequency are included.

Gummel-Poon model for single and double heterojunction bipolar transistors

An analytical model for single and double heterojunction bipolar transistors has been developed by employing the concepts of the Gummel-Poon model. The equations for injected minority carrier concentrations are developed based on the thermionic diffusion theory. Linking current and total charges in the base are calculated. The Early voltages are treated as functions of the applied voltages rather than as constants. Tunnelling effect has been considered for abrupt heterojunctions. The resemblance of this model with the SPICE BJT model makes it easy to implement it in SPICE.

Simulating the current mirror with a self-heating BJT model

A Gummel-Poon (GP) BJT (bipolar junction transistor) model that includes self-heating is presented, and a current-mirror circuit is used to show its significance. Self-heating thermal effects are modeled by a simple electrical analog circuit, which also provides BJT junction temperature as part of the CAD solution. Both discrete-BJT and IC mirror circuits are tested. The self-heating model correctly simulates the temperature stability of the IC mirror circuit where the BJTs are in close thermal proximity. For the discrete-BJT circuit, a standard GP model produces errors up to 84% versus 6.1% for the self-heating model. >

Non-quasi-static models including all injection levels and DC, AC, and transient emitter crowding in bipolar transistors

Two-dimensional equivalent-circuit models for bipolar junction transistors are systematically derived by solving the continuity equations for DC, AC, and transient excitations. These models take into account carrier propagation delay, all injection levels, as well as exponential doping profiles. They include analytically DC, AC, and transient emitter crowding in a more detailed and accurate manner than previously available. Extensions of the models to accommodate arbitrarily doped and heavily doped quasi-neutral layers and to include energy-gap narrowing due to the electron-hole plasma present at high current density are described. The analysis leads to compact large- and small-signal equivalent-circuit lumped models, suitable for use in circuit simulators such as SPICE. The analytical solutions obtained reveal the two-dimensional distribution of the current and carrier densities in the intrinsic base layer and the onset of emitter crowding. They also provide information for the extraction of the intrinsic base resistance. Several assumptions made in the derivations are assessed by the computer program PISCES. The methods presented apply to both homojunction and heterojunction bipolar transistors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of recombination current on current gain of HBTs

In order to predict more accurately the current gain behaviour of HBTs at low collector current region, surface recombination and interface recombination have to be considered. Recombination current has been obtained by the combination of bulk recombination in the neutral base, interface recombination at the heterointerface, space charge recombination, and surface recombination components. Results from the present model have been compared with experimental results, and the most recent analytical models for abrupt and graded heterojunction bipolar transistors (HBTs). The study shows that this model can predict the device gain more accurately.

Unified minority-carrier transport equation for polysilicon or heteromaterial emitter contact bipolar transistors

An analytical minority-carrier transport equation is derived that unifies the various models for polysilicon-emitter contact bipolar transistors. The theory covers drift and diffusion in the arbitrary doped crystal-silicon-emitter region, recombination and tunneling at the polysilicon-silicon interface and the potential barrier associated with heteromaterial, and diffusion in the polysilicon emitter region. The ratio of recombination current at the interface and diffusion current in the polysilicon to the total hole current is formulated using this theory. The influence of the two-dimensional structure of the oxide at the polysilicon-silicon interface on current gain is also analyzed. The theory is applied to the heterojunction bipolar transistor (HBT), and it is found that the recombination velocity at the heteromaterial-silicon interface should be suppressed to less than 10/sup 4/ cm/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An improved Early voltage model for advanced bipolar transistors

An improved Early voltage model reflecting the effect of bias variation is developed. The bias dependencies of the Early voltage are more prominent as the base width of the bipolar transistor decreases. Thus, using the conventional constant Early voltage model can result in considerable errors in modeling the advanced bipolar transistors which possess very thin base region. Comparisons between the present model and the conventional model at different bias conditions support this assertion. SPICE simulations are performed to demonstrate the impact of this study on the small-signal performance of bipolar-transistor integrated circuits.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New nonlinear large-signal DC bipolar junction transistor model

A new DC nonlinear large-signal model for the bipolar junction transistor is described, together with the procedures for estimating its parameters. The main advantage of the new model over existing models is its very simple parameter estimation procedures. This produces high accuracy with very minor parameter optimisation effort. A further important feature of the model is that it is expandable so that its complexity can be altered to suit the required application.< >

The importance of the non-quasi-static bipolar transistor model for circuit applications

The need for non-quasi-static bipolar models is examined from a practical viewpoint in order to optimize compensation capacitor value, improve performance, and reduce chip area. This need depends on the circuit under study. The utility of non-quasi-static equivalent circuits in small-signal applications is investigated. The circuit example studied is a lateral p-n-p transistor used as a series pass transistor in a series voltage regulator. For the series voltage regulator, the non-quasi-static inductance model correctly predicts the rapid falloff of the magnitude of the current gain and thus reduces the required internal compensation and subsequent circuit area.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of using the more accurate intrinsic concentration on bipolar transistor modeling

A more accurate intrinsic concentration was suggested recently. Discrepancies between using the conventional and the more accurate intrinsic concentrations on bipolar transistor modeling are assessed in this study. Our calculations show that the conventional intrinsic concentration overestimates the collector and base currents by a factor of 1.5 to 2 but affects less severely the steady-state current gain.