Large-signal modelling including low-frequency dispersion of n-channel SiGe MODFETs and MMIC applications Ingmar Kallfass a, * , Thomas J. Brazil b , Breandan OhAnnaidh b , Peter Abele a , Thomas Hackbarth c , Marco Zeuner c , Ulf K€ onig c , Hermann Schumacher a a Department of Electron Devices and Circuits, University of Ulm, 89069 Ulm, Germany b Department of Electronic and Electrical Engineering, University College Dublin, Dublin 4, Ireland c DaimlerChrysler Research Centre, Wilhelm-Runge-Straße 11, 89013 Ulm, Germany Received 30 October 2003; received in revised form 11 December 2003; accepted 30 January 2004 The review of this paper was arranged by Prof. C.K. Maiti Abstract This paper presents a circuit-design oriented, large-signal model for n-channel SiGe MODFET transistors, its application to the design of mixer and amplifier MMICs as well as measurement results. The model is based on an equivalent circuit approach and employs robust, globally continuous equations to describe the non-linear circuit ele- ments. All transistor operating regions are covered without the use of partially defined equations or smoothing functions. Significant low-frequency dispersion effects similar to those found in III–V HEMT devices are observed and incorporated in a large-signal dispersion model. The bias dependency of the gate–drain and gate–source capacitance is extracted and modelled, allowing for verification of the model for frequencies up to 50 GHz. Based on the presented transistor model, an active FET mixer MMIC and a travelling-wave amplifier using the SiGe MODFET technology are designed and good agreement between simulation and measurements is achieved. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Strained-Si/SiGe MODFET; Large-signal model; Low-frequency dispersion; Capacitance model; Active FET mixer; Travelling-wave amplifier 1. Introduction Modulation doped field-effect transistor (MOD- FET’s) based on SiGe offer a new concept for an ad- vanced high-frequency transistor, featuring similar performance advantages to the high electron mobility transistor (HEMT) in GaAs, but with the merits of low cost processing and compatibility with Si-based tech- nologies. Devices with cutoff frequencies as high as f T ¼ 90 GHz and f max ¼ 188 GHz have been reported [1,2]. In order to make this promising technology available for the design and realisation of high-speed circuits, an efficient non-linear simulation model is re- quired which reliably predicts device behaviour. In this paper, we present the development of such a new large- signal equivalent circuit model together with its use in the design and realisation of the first monolithic microwave IC (MMICs) based on the SiGe MODFET technology. Previous modelling work in conjunction with the new SiGe MODFET technology includes physical modelling and the extraction of small-signal equivalent circuit elements [3,4]. While physical modelling can provide valuable insight into the dependence of device RF properties on design parameters such as gate geome- try and operating conditions (temperature etc.), this approach cannot provide the computational efficiency * Corresponding author. Tel. +49-731-5031588; fax: +49- 731-5031599. E-mail address: ikall@ebs.e-technik.uni-ulm.de (I. Kallfass). 0038-1101/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.sse.2004.01.020 Solid-State Electronics 48 (2004) 1433–1441 www.elsevier.com/locate/sse