Nonlinear Characterisation and Modelling of Microwave Semiconductor Devices
Doktorsavhandling, 2011

There is an increasing need for more accurate models taking into account the nonlinearities and memory effects of microwave transistors. The memory effects are especially important for transistor technologies suffering from relatively large low frequency dispersion, such as GaN baed HEMTs. Nonlinear measurement systems are today available off-the-shelf, but the use of them is still limited. It is therefore important to demonstrate the possibilities these new systems brings to the device characterisation and modelling community. This thesis deals with electrothermal characterisation and modelling of GaN based HEMTs, and also development and utilisation of new nonlinear measurement systems. The electrothermal properties of the AlGaN/GaN heterostructure were characterised, and it was shown that a thermal response is present up to 100 MHz. Moreover, a new characterisation method, making use of nonlinear measurements, allowed for isothermal measurements of the current transport through the access resistances of a GaN based HEMT. A new current transport model was proposed to correctly reproduce the isothermal IV characteristics. Furthermore, the temperature dependence of the high frequency noise was characterised, showing that the major limiting factors for the low noise performance were the access resistances. The combination of high power and low noise makes the GaN based HEMT suitable for monolithically integrated GaN based transceiver front-ends. The first steps toward a transceiver were taken by designing and manufacturing a GaN based receiver front-end consisting of an SPDT switch and an LNA. A new fast multi harmonic active load-pull system was developed, with waveform acquisition capabilities. The speed of the load-pull system was increased by the use of an improved optimisation routine for presenting the wanted load impedances. The load-pull system was capable of presenting dynamically varying load impedances to a transistor, enabling faster device characterisation without the need to build complete amplifiers. The system was also used to characterise the nonlinear distortion in SiC varactors. It was shown that the nonlinear distortion increases the losses, and hence a new general Q-factor description was proposed. Furthermore, a new characterisation method was proposed which enabled the study of memory effects in transistors driven by modulated signals.

noise modelling

nonlinear measurement

active load-pull

noise measurement

thermal characterisation


nonlinear modelling

Kollektorn, MC2, Chalmers University of Technology
Opponent: Prof. Larry Dunleavy, University of South Florida, Tampa, FL, USA


Mattias Thorsell


Chalmers, Mikroteknologi och nanovetenskap, Mikrovågselektronik

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Nonlinear Characterization of Varactors for Tunable Networks by Active Source-Pull and Load-Pull

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Thermal Study of the High-Frequency Noise in GaN HEMTs

IEEE Transactions on Microwave Theory and Techniques,; Vol. 57(2009)p. 19-26

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Characterization Setup for Device Level Dynamic Load Modulation Measurements

International Microwave Symposium Digest, 2009, Boston,; (2009)

Paper i proceeding

Electrothermal Access Resistance Model for GaN-Based HEMTs

IEEE Transactions on Electron Devices,; Vol. 58(2011)p. 466 - 472

Artikel i vetenskaplig tidskrift


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Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3260

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 200

Kollektorn, MC2, Chalmers University of Technology

Opponent: Prof. Larry Dunleavy, University of South Florida, Tampa, FL, USA

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