Andreas Pawlak

An Improved Transfer Current Model for RF and mm-Wave SiGe(C) Heterojunction Bipolar Transistors

The carrier transport in advanced SiGe heterojunction bipolar transistor (HBT) process technologies exhibits bandgap-related transport effects that not only impact the transconductance and output conductance characteristics, but are also difficult to describe accurately by compact models. This paper addresses the modeling of bandgap-related effects in the collector current by formulating an improved version of a generalized integral charge-control relation (GICCR). As a result, the experimentally observed degradation of the transconductance at low and medium current injection, which is a strong function of the Ge grading, as well as the output conductance are described by simple bias- and temperature-dependent formulations of the GICCR weight factors. The derived formulations fit seamlessly into the compact model HICUM/L2. The extended model shows excellent agreement over a wide bias and temperature range with the experimental data of a large variety of SiGe HBTs from technologies of different manufacturers, including production and most advanced lab processes.

HICUM/2 v2.3 parameter extraction for advanced SiGe-heterojunction bipolar transistors

This paper presents extraction methodologies for advanced SiGe heterojunction bipolar transistors (HBTs). Demonstrated methods focus on extracting the transfer current related parameters over a large temperature range for the new version 2.3 of the compact HBT model HICUM Level 2. Also shown are the limitations of existing extraction methods. Results for DC and AC characteristics are shown for different temperatures.

Characterization of the Static Thermal Coupling Between Emitter Fingers of Bipolar Transistors

A strategy for compact modeling the static thermal coupling between the emitter fingers of SiGe heterojunction bipolar transistors (SiGe-HBTs) is described. An extraction methodology that includes the nonlinear temperature dependence of the thermal conductivity is introduced and applied to suitable test structures. The experimental results are used for calibrating a 3-D numerical solution of the equation for heat conduction based on a Greens function approach. The latter can then be employed for generating thermal coupling networks for arbitrary transistor configurations.

Scalable compact modeling for SiGe HBTs suitable for microwave radar applications

The suitability of the compact model HICUM for a state-of-the-art Silicon-Germanium (SiGe) heterojunction bipolar transistor (HBT) technology is evaluated with special emphasis on an efficient scalable modeling methodology. Multifinger HBTs particularly applicable to power applications are modeled. For modeling the critical self-heating effect a distributed thermal network is applied, yielding only a small impact on modeling results though. DC, AC, and large-signal distortion characteristics show good agreement between measurements and results from compact model simulation, demonstrating the capability of the modeling approach.

SiGe HBT modeling for mm-wave circuit design

An overview on the compact modeling activities within the DOTSEVEN project is given. Issues such as geometry scaling, substrate coupling and thermal effects as well as HICUM Level 2 features enabling the accurate modeling of the linear and non-linear characteristics of the latest generation of SiGe HBTs are discussed. Furthermore, experimental results for the most important DC and small-signal characteristics as well as selected examples for non-linear modeling of the most advanced SiGe HBTs from two different technologies are presented. Model verification issues related to limited on-wafer high-frequency measurement capability and the accurate calibration at multi-hundred GHz are briefly touched.

Geometry scalable model parameter extraction for mm-wave SiGe-heterojunction transistors

The observation of negative perimeter collector current in advanced SiGe HBT technologies is explained and a general geometry scaling approach is proposed. Application to mm-wave SiGe-HBTs shows excellent results of HICUM/L2 v2.31 for a wide range of emitter dimensions. Non-monotonic variation of peak fT with emitter dimensions demonstrates the relevance of a geometry scalable compact model for circuit optimization.

On the Feasibility of 500 GHz Silicon-Germanium HBTs

A procedure for rapid TCAD based evaluation of device design alternatives is presented. It employs 1D device simulation in combination with a physics-based compact model and a corre- sponding model generator. This enables to provide libraries with geometry scalable models for mm-wave circuit optimization. Based on an experimentally calibrated baseline the procedure is applied to demonstrate the feasibility of SiGe HBTs with (f T ,f max ) = (420, 520) GHz at realistic vertical and lateral dimen- sions. The proposed method is suitable for improving the existing ITRS 2007 SiGe HBT roadmap towards emerging mm-wave applications. Keywords-Device simulation, SiGe heterojunction bipolar tran- sistors, HICUM, Device scaling

Si/SiGe:C and InP/GaAsSb Heterojunction Bipolar Transistors for THz Applications

This paper presents Si/SiGe:C and InP/GaAsSb HBTs which feature specific assets to address submillimeter-wave and THz applications. Process and modeling status and challenges are reviewed. The specific topics of thermal and substrate effects, reliability, and HF measurements are also discussed.

A simple and accurate method for extracting the emitter and thermal resistance of BJTs and HBTs

A simple yet accurate extraction method for the emitter and thermal resistance of bipolar transistors is presented. Only DC measurements taken on a thermally controlled wafer prober are required. The knowledge of the collector resistance is preferable, but not mandatory. The method yields excellent results when applied to advanced HBT technologies.

Why is there no internal collector resistance in HICUM

The internal (or epi-) collector region in a bipolar (hetero-)junction transistor strongly determines the bias dependent terminal behavior. Most compact transistor model attempt to capture the current-voltage behavior of the epi-collector by a special equivalent circuit element (and associated analytical formulations) in addition to the usual transfer current source representing just the base region. This paper provides (i) theoretical proof that a separate representation of the epi-collector region in an equivalent circuit is neither required nor necessarily advantageous in terms of accuracy and (ii) a physics-based guide on how to model the epi-collector consistently if a separate description is still desired. The theoretical results are validated by numerical device simulation.