Internal Base Resistance Research Articles

Compact Layout and Bias-Dependent Base-Resistance Modeling for Advanced SiGe HBTs

In this paper, an improved and extended set of physics-based analytical equations for describing the external and internal base resistance of silicon-germanium HBTs as a function of geometry (layout) is presented. The investigated layouts include single- and double-base contacts not only in parallel but also perpendicular to the emitter finger. In addition, via and slot base contacts, a large range of link to internal-base-sheet-resistance ratio, and changes in external base layout dimensions are covered. The new equations are verified using quasi-3-D device simulation and are demonstrated to be applicable to all practically useful emitter aspect ratios.

A robust parameter extraction method for HBT small‐signal equivalent circuit

AbstractAn improved pad‐deembedding technique for InGaP/GaAs HBT reducing uncertainty in measurement and equivalent circuit is proposed. Intrinsic elements are obtained by iteratively determining the external and internal base resistance. The extracted equivalent circuits demonstrate good agreement with the measured S‐parameters obtained from 45 MHz to 40 GHz for different sizes of HBTs. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1845–1848, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22573

Transit frequency of fast Si self-aligned bipolar transistors

The small-signal current gain beta of fast Si self-aligned transistors is measured up to the transit frequency f/sub T/ using a 26.5-GHz microwave network analyzer system and special HF measuring probes. The influence of parasitic transistor elements such as the base-collector junction capacitance, the internal base resistance, and the peripheral transistor was confirmed in a real transistor at high frequencies by measurements on transistors with different emitter areas. The two-dimensional effects, which deviate from the expected one-pole frequency behavior of beta , can be described by the extended transistor model, namely the intrinsic model and the peripheral model. >

A compact physical large-signal model for high-speed bipolar transistors at high current densities—Part II: Two-dimensional model and experimental results

In this second part of the paper, the one-dimensional transistor model presented in Part I [1] is extended to the two-dimensional case, i.e., to real transistors. For this, well-known effects like emitter current crowding, emitter sidewall injection, and collector current spreading in the epitaxial collector were roughly taken into account, as well as the modulation of the internal base resistance. Furthermore, methods for determining the model parameters are given. For checking the model, high-speed transistors (f T ≈ 7 GHz) with small emitter stripes ( ≈2 µm) were fabricated. Experimental results agree well with the simulated ones for both the dc characteristics and the (more important) switching behavior even far within the region. Switching times, measured for single transistors, were in the range of 100 to 200 ps, typical of modern high-speed integrated circuits. The complete model, which is called HICUM (from high-current model), was already implemented in the circuit analysis program SPICE 2.

A simple method for separation of the internal and external (peripheral) currents of bipolar transistors

A simple method is described which enables the direct base and collector current of a bipolar transistor each to be separated into an internal and external (peripheral) part. Such a separation is, e.g. a necessary precondition for evaluating the reduction of current gain with decreasing emitter size and, furthermore, for estimating the effective internal base resistance as well as the emitter-current crowding due to the voltage drop across this resistance. The method described is based on very careful measurements of test transistors with different emitter geometries. The approach was experimentally verified with double-implanted high-speed transistors (transit frequency f T ⋍ 7 GHz ). For example, an emitter stripe width of about 2 μm leads to the following results: About 32% of the base current but only 9% of the collector current flow outside the emitter area defined by the implantation mask, resulting in a reduction of the common-emitter current gain to about 75% of its internal value.

Transistor Amplifier-Cutoff Frequency

The effect of positive feedback through the internal base resistance of a transistor on circuit cutoff frequency is considered.