Vertical Bipolar Inter-company Model Research Articles

SiC BJT Compact DC Model With Continuous- Temperature Scalability From 300 to 773 K

The first vertical bipolar intercompany (VBIC)-based compact dc model has been developed and verified for a low-voltage 4H-SiC bipolar junction transistor to continuously map a wide temperature range from 300 to 773 K. Temperature and doping dependent physical models for bandgap, incomplete ionization, carrier mobility, and lifetime have been taken into account to give physically meaningful fitting parameters for the compact model. Isothermal simulations using the default VBIC model are performed to extract key parameter sets from measured data at seven different temperature points. Then new temperature dependent equations for the key parameters are proposed and embedded in the default VBIC model. Consequently, a single set of model parameters at 300 K is used to achieve fitting over a wide temperature range from 300 to 773 K. This new model can be used for simulating circuits that require continuous description of device dc performance over a wide temperature range.

An Improved VBIC Large-Signal Equivalent-Circuit Model for SiGe HBT With an Inductive Breakdown Network by <formula formulatype="inline"><tex Notation="TeX">$X$</tex> </formula>-Parameters

In this paper, the $X$ -parameter measurements are applied first to establish an improved vertical bipolar inter-company (VBIC) large-signal equivalent-circuit model for silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs), which can accurately describe novel and unusual characteristics of inductive behavior at breakdown that can occur in the active region under large-signal drive. This improved VBIC model presented here for SiGe HBTs is modified by incorporating a nonlinear base–collector junction breakdown network to account for the RF avalanche delay effect in the breakdown region. Good agreement between simulated and measured $X$ -parameters, which contain small-signal $S$ -parameters, large-signal spectrum, and hot $S$ -parameters, is achieved, validating the presented large-signal VBIC model in the breakdown region. The determined breakdown inductance and resistance agree well with the theoretical results. This modified model can be used to describe and predict RF large-signal performance accurately when transistors are operated in the breakdown and active regions.

Improved VBIC model for SiGe HBTs with an unified model of heterojunction barrier effects

An improved bipolar transistor model considering heterojunction barrier effect (HBE) in SiGe double heterojunction bipolar transistors is developed. The effect of barrier formation due to high level injection, which is related to the rapid degradations of the dc current gain (/spl beta/) and cutoff frequency (f/sub T/), is carefully investigated and analyzed. As the collector current becomes high, the conduction band barrier is induced and increased. It causes the saturation of collector current (J/sub C/) due to the blocking of carrier transport, the sharp increase of base transit time (/spl tau//sub B/) due to the additional charge storage, the increase of base current (J/sub B/) due to the increased recombination, and the decrease of intrinsic base resistance (R/sub bi/) due to the increased charge and base pushout. Those phenomena are included into a vertical bipolar intercompany model (VBIC) compact model by employing a unified model of the HBE on J/sub C/, J/sub B/, /spl tau//sub B/, and R/sub bi/. Furthermore, portions of /spl tau//sub B/ and R/sub bi/ from the Kirk effect itself are modeled according to the high current model description and the new formulation of widened base, respectively. A full extraction of parameters has been performed and the modified VBIC model is applied. The modeling accuracy is significantly improved at the high current region for the dc and RF characteristics.

Implementation of a scalable VBIC model for SiGe:C HBTs

This work examines the utility of semi-physical vertical bipolar inter-company (VBIC) model for the first time to develop for an accurate, easy and fast scaling methodology for high-frequency SiGe:C heterojunction bipolar transistors (HBTs) with a peak f T of 75 GHz fabricated in a low-cost BiCMOS technology. The methodology allows one to find transistor models from single-finger transistor to multi-finger and variable length emitter devices with a minimal parameter extraction procedure. The devices modeled include several base–emitter structures in parallel, on top of a single collector to obtain different transistor area. The scaling rules are given in detail. Using this methodology, scalable VBIC model parameters were generated to describe the DC and RF behavior of SiGe:C HBTs up to peak f T and f max within ±10% accuracy. The key advantage of this methodology is that one does not need any special test structure while keeping the extraction procedure simple and fast.

Enhanced high-current VBIC model

The widely used vertical bipolar inter-company (VBIC) model for bipolar junction transistor-heterojunction bipolar transistors (HBTs) was modified to incorporate high-current effects. The modified VBIC model keeps all features of the original model and adds new features such as mobile carrier modulation of the base-collector capacitance, high-current Kirk effects, high-current reverse emitter-base injection, and current dependence of the reverse transit time in HBTs. The new model accurately fits the dc I-V characteristics, the bias-dependent transit-time, and S-parameters at active and quasi-saturation region biases. It is shown that the new formulation accurately models the strong current dependence of f/sub t/ and G/sub max/ over a wide range of biases. It also predicts very well the power performance in class-AB operation and at the loading for maximum power-added efficiency and maximum output power. The model also shows good fitting of two-tone linearity characteristics when simulated with the same fundamental and harmonic load conditions as in the measurements.

Advanced SPICE modelling of SiGe HBTs using VBIC model

The vertical bipolar intercompany (VBIC) model has been applied to silicon-germanium heterojunction bipolar transistors (SiGe HBTs). The model includes the improved Early effect, quasi-saturation, substrate parasitic, avalanche multiplication, and self-heating. Several device parameters have been extracted from SiGe HBTs and implemented in the VBIC model. A comparison is made with the SPICE Gummel-Poon model. The usefulness and accuracy of the VBIC model for SiGe HBTs are demonstrated by way of comparison of simulated and measured room temperature device data.